Research ArticleEffect of Annealing on Microstructure and MechanicalProperties of Magnetron Sputtered Cu Thin Films

Shiwen Du and Yongtang Li

School of Materials Science and Engineering Shanxi Key Laboratory of Metallic Materials Forming Theory and TechnologyTaiyuan University of Science and Technology Taiyuan 030024 China

Correspondence should be addressed to Shiwen Du tykddsw126com

Received 11 December 2014 Revised 26 February 2015 Accepted 26 February 2015

Academic Editor Filippo Giannazzo

Copyright copy 2015 S Du and Y Li This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Cu thin films were deposited on Si substrates using direct current (DC) magnetron sputtering Microstructure evolution andmechanical properties of Cu thin films with different annealing temperatures were investigated by atomic force microscopy(AFM) X-ray diffraction (XRD) and nanoindentation The surface morphology roughness and grain size of the Cu films werecharacterized by AFM The minimization of energy including surface energy interface energy and strain energy (elastic strainenergy and plastic strain energy) controlled themicrostructural evolutionA classicalHall-Petch relationshipwas exhibited betweenthe yield stress and grain size The residual stress depended on crystal orientation The residual stress as-deposited was of tensionand decreased with decreasing of (111) orientation The ratio of texture coefficient of (111)(220) can be used as a merit for the stateof residual stress

1 Introduction

With the rapid change of materials systems and decreasedfeature size thin film microstructure and mechanical prop-erties have become critical parameters for microelectronicsreliability [1] Copper is an attractive interconnectingmaterialfor current Si ultralarge scale integrated (ULSI) device due toits low resistivity and superior resistance to electromigration[2ndash4] Cu film has attracted great attention worldwide due toits potential applications in replacing Al-based interconnectson silicon chips

According to research object film structure can bedivided into crystalline form crystallographic structure andsurface structure Microstructure of materials here mainlyrefers to crystal orientation and grain sizeThe electrical resis-tivity and mechanical properties of Cu films are importantfactors for its use as interconnecting material Magnetronsputtering has become one of commonly used techniquesfor industrial deposition of thin films and coatings dueto its simplicity and reliability [5] Generally structure andelectrical qualities of films strongly depend on the depositionprocess [6] On the other hand the postprocessing such as

annealing can also change themicrostructure andmechanicalproperties of the films [7 8]

In sputter deposition the nature of the substrate thedeposition temperature the deposition pressure and thevacuum quality are some of the parameters that influencethe film properties Properties such as stress texture andmorphology are of key importance for predicting the relia-bility of thin film systems The influence of the magnetronsource operation mode (standard or self-sustained) as wellas the type of power (DC medium frequency or pulsedDC) on the microstructure and surface morphology of thecopper thin films have been reported [5] Sputtering DCpower affected the structural features electrical propertiesand the nucleation and growth of Cu films during the initialstage of sputtering [6] A comparative study of structuralelectrical and thermoelectric properties of nanocrystallinecopper thin films deposited using anodic vacuum arc plasmadeposition technique and DCmagnetron sputtering was alsoconducted [9] The effects of barrier layer and annealingtemperature on texture variation grain growth and voidformation of nanocrystalline Cu films were investigated [10]The deposition pressure and the type and cleaning condition

Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2015 Article ID 969580 8 pageshttpdxdoiorg1011552015969580

2 Advances in Materials Science and Engineering

of substrate had important role on the film propertiesThe substrate type and the substrate surface condition hadmarked influences on the texture of as-deposited Cu films[11] Cu films were deposited on Si(001) substrates undervarious Ar deposition pressure by radio frequency (RF)magnetron sputtering The intensities of Cu peaks changedwith the Ar pressure systematically Strong correlations wereobserved between optical emission electron temperatureand the microstructure of Cu films [12]

For Cu nanocrystalline films to be widely used it is neces-sary to explore its microstructure andmechanical propertiesThe physical properties and microstructure of Cu films suchas mechanical properties grain boundary and crystallo-graphic texture can significantly influence the work reliabilityinmicroelectronic devices [10]Mechanical properties of thinfilms often differ from those of the bulk materials [13ndash16]The physical dimensions of thin film materials are generallycomparable to the characteristicmicrostructural length scalesthat strongly influence their mechanical properties [17]In general two different size dependencies determine theproperties of a material One is the dimension character-istic of the physical phenomenon involved The other issome microstructural dimension Microstructural evolutionduring elevated temperature annealing of sputter depositedcopper (Cu) films was investigated by electron backscatterdiffraction (EBSD) Not only are the Cu film texture andgrain size a function of film thickness but also the fraction oftwin boundaries present in thematerial is strongly dependentupon film thickness [18]

Generally microstructure and mechanical properties offilms depend on the deposition process and postproductionprocess such as annealing However most previous workshave focused on the deposition process As we know phys-ical properties of the sputtered films are controlled by itsmicrostructure In this paper we report the microstructuralevolution and mechanical properties of the magnetron sput-tered Cu thin films with different thicknesses after annealingat several temperatures Surface topographyroughness andgrain size are measured by AFM Residual stress (stressesthat remain in the films after annealing) and textures of theCu films are evaluated with X-ray diffraction Furthermorenanoindentation is also performed to study the mechanicalproperties of the Cu films which include the hardnessyield stress (the stress at which a material begins to deformplastically) and elastic modulus Discussions are made interms of the mechanical properties with film microstructure

2 Experimental Details

Three series of copper films were produced by magnetronsputtering deposition on commercial Si(100) single-crystalwafer whose thickness was 525 plusmn 25 120583m Size of the coppertarget isΦ60mm 3mm thicknessThe substrate temperature119879119904is 473 K and the substrate bias 119880

119904is grounded Before

sputtering wafer was ultrasonically cleaned in high purityacetone After vacuum drying wafer was reserved in a drycylinder for use Copper thin films were deposited by amagnetron sputter coater (FJL560II) Copper target materialpurity was 9999wt Base vacuum pressure of the sputter

coater was 2 times 10minus4 Pa and 999 argon was used as aworking gas whose pressure was 15 PaThe distance betweenthe sputter target and the Si wafer was 60mm Sputteringvoltage was 470V and power was 36W Thickness of thefilms is tested by SEM Deposition rate is calculated by filmsthickness and deposition time Different thickness films aredeposited by controlling the deposition time The depositiontime was 60 90 and 170min respectively and these sampleswere labeled as A B and C accordingly The film thicknesswas measured by S-4800 field emission scanning electronmicroscope (SEM) For samples A B and C thickness was10 120583m 16 120583m and 30 120583m accordingly Some samples wereannealed in vacuum at 300 400 and 500∘C respectivelyThebase pressure during annealing is 4 times 10minus4 Pa

Agilent 5420 atomic force microscope (AFM) was usedto observe the sample surface morphology Each samplewas scanned at three different regions and then the typicalregion was utilized for analysis Grazing incidence X-raydiffraction (GIXRD) was performed to study the texture inthe annealed Cu films Experiment was performed using thePhilips XrsquoPert Pro XRD system with 05∘ grazing incidenceThe stresses of film specimens have been studied by the sin2120595The mechanical properties of the annealed copper films wereevaluated using a nanoindenter with a Berkovich tip [19]Thecontinuous stiffness modulation (CSM) technique was usedwherein the contact stiffness was measured continuously as afunction of displacement under the load

3 Results and Discussion

31 Surface Characterization by AFM The representativeAFM images of the coating samples with different thicknessand after annealing at 300∘C are shown in Figure 1 All thesamples have a columnar surface morphology The imagesof the Cu films were acquired in a 1 120583m times 1 120583m area It isclear that as the annealing temperature increased the surfacemorphology evolved and the grains grew larger in the Cufilms119878119902is the root mean square (RMS) height of the surface

which is a statistical amplitude parameter representing theroot mean square of surface roughness deviation from ref-erence datum It can be seen from Table 1 that the lowest119878119902value is observed for the samples annealed at 400∘C The

roughness decreases when continuous and compact filmswith crystal structure are formed during the films depositedWhen the annealing temperature exceeds 400∘C recrystal-lization occurs Due to agglomeration and coalescence of thegrains the roughness of Cu film surface increases

The grain growth in the Cu films can be correlated tothe annealing temperature as shown in Table 2 using thegrain size data determined by AFM The driving force forgrain growth in thin films materials is the reduction of grainboundary energy that results from the reduction of the totalgrain boundary area In grain growth some grains alreadypresent in the matrix grow at the expense of the other grainsA few grains which consume the surrounding (stagnant)fine-grained matrix will grow until the large grains meetand the fine-grained matrix is completely consumed [19ndash22]

Advances in Materials Science and Engineering 3

425

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(a)

55

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(b)

174

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(c)

27

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(d)

27

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(e)

24

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(f)

Figure 1 3D surface topographies of the Cu films (a) 10 120583m thick as-deposited (b) 10 120583m thick annealed at 300∘C (c) 16120583m thick as-deposited (d) 16 120583m thick annealed at 300∘C (e) 30 120583m thick as-deposited and (f) 30 120583m thick annealed at 300∘C

The higher the annealing temperature is the larger thegrain growth driving force is If the annealing temperatureexceeds 400∘C grains grow quickly and coalescence happenswhich will cause grain boundary groove deepening and filmagglomeration to occur

32 Texture and Microstructure Texture in materials hasa large influence on many properties of thin films XRDhas been the primary method for the characterization offilm texture for many years The texture coefficient (TC)represents the texture of a particular plane whose deviation

4 Advances in Materials Science and Engineering

Table 1 Surface roughness Sq (nm) for the Cu films with differentthicknesses annealing temperatures

Annealing temperature (∘C) Thickness (120583m)10 16 30

As-deposited 388 34 298300 366 309 261400 163 291 216500 288 408 948

Table 2Grain size119889 (nm) for theCufilmswith different thicknessesand annealing temperatures

Annealing temperature (∘C) Thickness (120583m)10 16 30

As-deposited 66 88 91300 100 124 143400 120 165 170500 375 405 550

from the ideal value implies the preferred growth Quan-titative information concerning the preferential crystalliteorientation was obtained from the texture coefficient TC

ℎ119896119897

defined as [23]

TCℎ119896119897=119868(ℎ119896119897)1198680(ℎ119896119897)

sum119899

119894=1119868(ℎ119896119897)1198680(ℎ119896119897)

times 100 (1)

where 119868(ℎ119896119897)

is the measured relative intensity of a plane (ℎ119896119897)and 1198680(ℎ119896119897)

is the standard intensity of the plane (ℎ119896119897) takenfrom the JCPDS data The value TC

ℎ119896119897= 1119899 = 025 (ie

119899 = 4 for our case as four planes are included in our XRDstudy) represents films with randomly oriented crystalliteswhile higher values indicate the abundance of grains orientedin a given (ℎ119896119897) direction [23]

321 Effect of Thickness on Texture From Figures 2 and 3we can see that the preferred orientation and texture in thethin films change with the thickness The strongest X-rayreflections are visible from Cu(111) planes This indicates thatthe crystallization occurs preferentially in the (111) planesWhile the polycrystalline films are thin growth of grainwith (111) texture is favored by surface and interface energyminimization especially in very thin films [24 25] Withthe increase of the thickness the (111) orientation decreaseswhereas the (220) orientation increases Strain energy (theenergy stored by a system undergoing deformation includingelastic strain energy and plastic strain energy) controls thegrain growth gradually as the thickness increases Elasticstrain energy is the potential mechanical energy stored in theconfiguration of a material as work is performed to distort itsvolume or shape Plastic strain energy is the energy stored bya system undergoing plastic deformation

322 Effect of Annealing Temperatures on Texture Figure 4shows the XRD patterns of the Cu films with a thick-ness of 10 120583m under different annealing temperatures All

(311)(220)(200)

(111)

40 50 60 70 80 90 100

Inte

nsity

I(a

u)

10 120583m

16 120583m

30 120583m

2120579 (∘)

Figure 2 XRD patterns of the Cu films with different thicknesses

010

015

020

025

030

035

040

045

050

Text

ure c

oeffi

cien

t TC

(111)(200)

(220)(311)

Thickness h (120583m)10 15 20 25 30

Figure 3 Texture coefficients of the Cu films with different thick-nesses

(311)(200)As-deposited

(220)

(111)

2120579 (∘)

Inte

nsity

I(a

u)

40 50 60 70 80 90

Annealing temperature 500∘CAnnealing temperature 400∘C

Annealing temperature 300∘C

Figure 4 XRD patterns of the 10 120583m Cu film annealed at differenttemperatures

the films exhibit X-ray reflections from Cu (111) (200) (220)and (311) To investigate the evolution of crystallite orien-tations with different annealing temperatures the texturecoefficient under different annealing temperatures is shownin Figures 5ndash7 for the films with thickness of 10 16 and30 120583m respectively

Advances in Materials Science and Engineering 5

0001020304050607080910

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 5 Texture coefficients of the 10 120583m Cu film annealed atdifferent temperatures

01

02

03

04

05

06

07

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 6 Texture coefficients of the 16 120583m Cu film annealed atdifferent temperatures

The main driving force for subsequent grain growth isminimum total free energy (surface energy grain interfaceenergy and film strain energy) [21] For thinner films graingrowth is under the control of surface energy minimizationOnly a few grains can grow whose surface energy is relativelylower than the others Grains whose surface energy is higherwill be merged into adjacent grains Grain growth eliminatesfree surface and thus the total surface energy decreasesaccordingly However for thicker films grain growth is underthe control of strain energy minimization For face-centeredcubic (fcc) metals grain orientation which has the lowestplastic strain energy is the (220) plane [24] Development ofstrain energy minimizing textures does not minimize surfaceand interface energies [25 26] Therefore surface struc-ture of the copper films with different thicknesses reflects

016

020

024

028

032

036

040

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 7 Texture coefficients of the 30 120583m Cu film annealed atdifferent temperatures

a dynamic equilibrium between surface energy and strainenergy Surface energy is very important for the structure ofthinner films whereas strain energy is very important for thestructure of thicker films

During the annealing processes the intensity of the(220) grain increases but that of the (111) grain decreases Apreferred grain orientation (220) after annealing is observedwhile (111) is the preferred orientation before annealing Theeffect of yield in grain is proposed to explain the (220)preferred orientation during annealing When the annealingtemperatures increase thin films will start to yield Also theminimum strain energy will control the grain growth In-plane stress in a grain is a function of grain orientation factor119862119894119895119896 and the yield stress of the grain also varies depending

on its orientationThe orientation factor 119862119894119895119896

of (220) has thesmallest one of 142 while that of (111) has the largest one of346 [27] When the thin films start to yield for grains ofequal initial sizes the (220) grains will yield before the (111)grains thus the (220) grains have an energetic advantage forfurther growth [28] This yielding process also leads to strainenergy minimization This may explain why the (220) grainsgrow faster than other grains and become the final preferredorientation

In addition initial grain size also has an effect on thetexture evolution With a certain volume the smaller andthe more uniform the grain is the more evenly the strainenergy will disperse to all the grain So the distribution ofinternal stress (the stress due to difference in the thermalexpansion coefficients and thickness between films and sub-strates during annealing) will be more even which will makethe grain with minimization strain energy grow easily andquickly Grain size in thin films is smaller than thick filmsWe can see from Figures 5ndash7 that the finial texture coefficientafter annealing at 500∘C in thick films is less than thin films

33 Mechanical Properties Nanoindentation was performedon all the Cu films annealed at different temperatures

6 Advances in Materials Science and Engineering

The typical load-indentation depth curves for the 30 120583mfilmannealed at different annealing temperatures are shown inFigure 8 It can be seen from Figure 8 that the loadunloadcurves for all the samples are nearly similar which maybe attributed to the similar crystalline nature of Cu filmsFigure 9 shows the hardness as a function of the annealingtemperature for the Cu films with various thicknesses Morerecent and systematic experiments indicate that both thegrain size and the film thickness have a marked influence onthe strength of thin films [29ndash32] Relationship between thehardness and the yield stress can be expressed as119867 = 3120590

119910 120590119910

is the yield stress and119867 is the hardnessEffect of different parts of microstructure on the yield

stress can be expressed as [29]

120590119910= 1205900+ 119896119889minus119899

+ 1198961015840

119905minus119898

(2)

where 1205900is the bulk yield stress (large-grained polycrystal)

119896119889minus119899 is the contribution from the grain boundaries (119889 grain

size) 1198961015840119905minus119898 is the contribution from the film surface orinterface (119905 film thickness) The first two terms togetherform the well-known Hall-Petch relation where 119899 = 05commonly Combining the data in Table 2 and Figure 9Figure 10 can be obtained which shows that the grain sizedependence of strength in Cu thin films on Si substratesfollowed a Hall-Petch type relation This is the describedHall-Petch effect that establishes a linear dependency ofthe hardness with the reciprocal square root of grain sizeClearly the strengthening of the sputtered copper films wasmainly attained by grain refinement The Hall-Petch effect isexplained in terms of a restriction in the movement of grainsthat is strengthening due to the formation of pileups in thelarger grain boundaries associated with low grain size FromFigure 8 we can see that the indentation depth increases withthe annealing temperatures under the same load which maybe a factor affecting the Hall-Petch type relation In additiongrain size changes with the films thickness which may beanother reason for the yield stress variation

Different load-indentation depth curves for the Cu filmsannealed at different temperatures imply different indenta-tion plastic characteristics for these films These curves canbe separated into the following three stages pure elasticdeformation stage at the beginning of the load elastic-plastic deformation stage after displacement jump and elasticresponse during unload It agrees with the Hertz contacttheory well during the elastic deformation stage The lowerthe annealing is the less the elastic displacement is Displace-ment jump caused by the dislocation pileup and incrementon the plastic deformation region increase with the increaseof the grain size With the decrease of the grain size thedensity of the grain boundaries increases It cannot only actas the source of dislocation but also decrease the dislocationactivation energy

The values of elastic modulus can also be obtainedby nanoindentation The Young modulus decreased 20compared to that of the traditional coarse-grained Cu Theelastic modulus is one of the intrinsic properties of a material[33] Elastic modulus is an important indicator to reflect thebond strength between the atoms Many factors can affect

0

5

10

15

20

25

30

35

40

As-deposited

0 100 200 300 400 500 600 700 800 900

Annealing temperature 500∘C

Annealing temperature 400∘C

Annealing temperature 300∘C

Load

P(m

N)

Indentation depth h (nm)

Figure 8 Load-indentation depth curves for the 30 120583m Cu filmsannealed at different temperatures

20

21

22

23

24

25

26

27

28

29

10 120583m16 120583m30 120583m

100 200 300 400 500

Annealing temperature T (∘C)

Har

dnes

sH(G

Pa)

Figure 9 Hardness versus annealing temperature for the Cu filmswith different thicknesses

the elastic modulus such as texture [33] grain coalescenceandmicrocrack [34] Elasticmodulus of the Cu thin filmswilldecrease 20when 13 of grain boundaries is destroyed basedon the microcrack mechanism

XRD diffraction technique was carried out to investi-gate the residual stress by the well-know sin2Ψ methodFigure 11 shows the relationship between residual stressand TC(111)TC(220) ratio in Cu films The film with (111)-orientated grains had the highest tensile one and that with(220)-orientated grains had the lowest tensile one Theresidual stress in as-deposited copper films reached a highvalue but decreased down to a minimum value after samplesannealing This was obviously due to the thermal relaxationof residual stresses and the annealing effect onmicrostructuredefects This may be due to the preferred growth of grainswhich leads to a change of residual stress

Advances in Materials Science and Engineering 7

05

06

07

08

09

10

004 005 006 007 008 009 010 011 012 013

Yield

stre

ss120590y

(GPa

)

dminus05 (nmminus05)

10 120583m16 120583m30 120583m

Figure 10 Trend of yield stress dependency on grain size for the Cufilms

03

06

09

12

15

18

21

0

20

40

60

80

100

Resid

ual s

tress

(MPa

)

TC(1

11)

TC(2

20)

Annealing temperature T (∘C)0 50 100 150 200 250 300 350 400 450

minus20

TC(111)TC(220) of 10 120583mTC(111)TC(220) of 16 120583mTC(111)TC(220) of 30 120583m

Residual stress of 10 120583mResidual stress of 16 120583mResidual stress of 30 120583m

Figure 11 TC(111)TC(220) ratio and residual stress versus anneal-ing temperatures of 10 120583m 16 120583m and 30 120583m

4 Conclusions

The effect of annealing treatment on magnetron sputteredCu films is investigated using AFM XRD and nanoinden-tation techniques Surface topography and microstructuralevolution after annealing is studied in detail Relationshipbetween themicrostructure and themechanical properties ofthe thin films is also proposed The higher the texture of (111)is the lower the resistivity isWith the increase of (111) texturetensile stress increases For microelectronic application largeresidual stress will cause cavity crack and peeling of Cu filmswhich will cause circuit deformation and even produce shortcircuit or open circuit Annealing is usually taken during ICAlthough the resistivity of Cu films decreased a little thereliability of the system is greatly increased

The following are our main conclusions

(1) Annealing treatment can provide enough energy forthe grain to growWhen the annealing temperature isless than 400∘C the higher the annealing temperatureis the more the energy for the grain growth will beWith the grain growth surface void is filled and thesurface RMS decreases However when the annealingtemperature is gt400∘C grain grows abnormally andcoalescence occurs Surface void defects and microc-racks increase and the surface RMS increases

(2) Films thickness grain size and annealing tempera-tures are the main factors that affect the microstruc-ture of the annealed Cu films The minimization ofenergy including surface energy interface energy andstrain energy (elastic strain energy and plastic strainenergy) controls the microstructural evolution

(3) The grain size dependence of strength in the Cuthin films on the Si substrates followed a Hall-Petchtype relation In addition grain size changes with thefilms thickness which may be another reason for theyield stress variationThe as-deposited Cu films are intensile state and have strong (111) orientation Duringthe annealing with the decreasing of (111) orientationtensile stress decreased The ratio of TC(111)TC(220)can be used as a merit for the state of residual stress

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project is supported by National Basic Research Devel-opment Program of China (973 Program Grant no 2009CB724200) Research Fund for the Doctoral Program ofHigher Education of China (Grant no 20111415120002) andShanxi Provincial Science Foundation for Youths of China(Grant no 2010021023-4)

References

[1] A A Volinsky J Vella I S Adhihetty et al ldquoMicrostructureand mechanical properties of electroplated Cu thin filmsrdquo inProceedings of the Materials Research Society Symposium vol649 pp Q 531ndashQ 536 Boston Mass USA November 2001

[2] S P Murarka ldquoMultilevel interconnections for ULSI and GSIerardquo Materials Science and Engineering R Reports vol 19 no3-4 pp 87ndash151 1997

[3] S P Murarka R J Gutmann A E Kaloyeros and W ALanford ldquoAdvanced multilayer metallization schemes withcopper as interconnection metalrdquoThin Solid Films vol 236 no1-2 pp 257ndash266 1993

[4] R W Vook ldquoElectrical control of surface electromigrationdamagerdquoThin Solid Films vol 305 no 1-2 pp 286ndash291 1997

[5] A Wiatrowski W M Posadowski G Jozwiak J SerafinczukR Szeloch and T Gotszalk ldquoStandard and self-sustainedmagnetron sputtering deposited Cu films investigated bymeans

8 Advances in Materials Science and Engineering

of AFM and XRDrdquoMicroelectronics Reliability vol 51 no 7 pp1203ndash1206 2011

[6] M-T Le Y-U Sohn J-W Lim and G-S Choi ldquoEffect ofsputtering power on the nucleation and growth of Cu filmsdeposited by magnetron sputteringrdquo Materials Transactionsvol 51 no 1 pp 116ndash120 2010

[7] AK Siker AKumar P Shukla P B Zantye andM SanganarialdquoEffect of multistep annealing on mechanical and surfaceproperties of electroplated Cu thin filmsrdquo Journal of ElectronicMaterials vol 32 no 10 pp 1028ndash1033 2003

[8] P Shukla A K Sikder P B Zantye A Kumar and MSanganaria ldquoEffect of annealing on the structural mechanicaland tribological properties of electroplated Cu thin filmsrdquoMaterials Research Society Symposium Proceedings vol 182 ppF3161ndashF3167 2004

[9] S KMukherjee L Joshi and P K Barhai ldquoA comparative studyof nanocrystalline Cu film deposited using anodic vacuum arcand dc magnetron sputteringrdquo Surface amp Coatings Technologyvol 205 no 19 pp 4582ndash4595 2011

[10] Z H Cao H M Lu and X K Meng ldquoBarrier layer andannealing temperature dependent microstructure evolution ofnanocrystalline Cu filmsrdquoMaterials Chemistry and Physics vol117 no 1 pp 321ndash325 2009

[11] B Okolo P Lamparter UWelzel TWagner and E JMittemei-jer ldquoThe effect of deposition parameters and substrate surfacecondition on texture morphology and stress in magnetron-sputter-deposited Cu thin filmsrdquo Thin Solid Films vol 474 no1-2 pp 50ndash63 2005

[12] Q X Zhao F Bian Y Zhou et al ldquoOptical emission electrontemperature and microstructure of Cu film prepared by mag-netron sputteringrdquo Materials Letters vol 62 no 25 pp 4140ndash4142 2008

[13] W D Nix J R Greer G Feng and E T Lilleodden ldquoDefor-mation at the nanometer and micrometer length scales effectsof strain gradients and dislocation starvationrdquoThin Solid Filmsvol 515 no 6 pp 3152ndash3157 2007

[14] Z P Bazant Z Guo H D Espinosa Y Zhu and B PengldquoEpitaxially influenced boundary layer model for size effect inthin metallic filmsrdquo Journal of Applied Physics vol 97 no 7Article ID 073506 2005

[15] H D Espinosa M Panico S Berbenni and K W SchwarzldquoDiscrete dislocation dynamics simulations to interpret plas-ticity size and surface effects in freestanding FCC thin filmsrdquoInternational Journal of Plasticity vol 22 no 11 pp 2091ndash21172006

[16] D S Gianola S van PetegemM Legros S Brandstetter H vanSwygenhoven and K J Hemker ldquoStress-assisted discontinuousgrain growth and its effect on the deformation behavior ofnanocrystalline aluminum thin filmsrdquo Acta Materialia vol 54no 8 pp 2253ndash2263 2006

[17] E Arzt ldquoSize effects in materials due to microstructural anddimensional constraints a comparative reviewrdquo Acta Materi-alia vol 46 no 16 pp 5611ndash5626 1998

[18] N-J Park D P Field M M Nowell and P R Besser ldquoEffect offilm thickness on the evolution of annealing texture in sputteredcopper filmsrdquo Journal of Electronic Materials vol 34 no 12 pp1500ndash1508 2005

[19] G M Pharr ldquoMeasurement of mechanical properties by ultra-low load indentationrdquoMaterials Science and Engineering A vol253 no 1-2 pp 151ndash159 1998

[20] J-M Zhang K-W Xu and V Ji ldquoCompetition between surfaceand strain energy during grain growth in free-standing and

attached Ag and Cu films on Si substratesrdquo Applied SurfaceScience vol 187 no 1-2 pp 60ndash67 2002

[21] V Weihnacht and W Bruckner ldquoAbnormal grain growth in 111textured Cu thin filmsrdquoThin Solid Films vol 418 no 2 pp 136ndash144 2002

[22] C V Thompson and R Carel ldquoTexture development in poly-crystalline thin filmsrdquoMaterials Science and Engineering B vol32 no 3 pp 211ndash219 1995

[23] C S Barret and T B Massalski Structure of Metals PergamonPress Oxford UK 1980

[24] J-M Zhang K-W Xu and M-R Zhang ldquoTheory of abnormalgrain growth in thin films and analysis of energy anisotropyrdquoActa Physica Sinica vol 52 no 5 pp 1207ndash1211 2003

[25] H LWei HHuang CHWoo R K Zheng GHWen andXX Zhang ldquoDevelopment of ⟨110⟩ texture in copper thin filmsrdquoApplied Physics Letters vol 80 no 13 pp 2290ndash2292 2002

[26] RCarel CVThompson andH J Frost ldquoComputer simulationof strain energy effects vs surface and interface energy effects ongrain growth in thin filmsrdquo Acta Materialia vol 44 no 6 pp2479ndash2494 1996

[27] J E Sanchez Jr and E Arzt ldquoEffects of grain orientation onhillock formation and grain growth in aluminum films onsilicon substratesrdquo Scripta Metallurgica et Materiala vol 27 no3 pp 285ndash290 1992

[28] F Spaepen ldquoSubstrate curvature resulting from the capillaryforces of a liquid droprdquo Journal of the Mechanics and Physics ofSolids vol 44 no 5 pp 675ndash681 1996

[29] Y-J Choi and S Suresh ldquoSize effects on the mechanicalproperties of thin polycrystalline metal films on substratesrdquoActa Materialia vol 50 no 7 pp 1881ndash1893 2002

[30] M A Meyers A Mishra and D J Benson ldquoMechanicalproperties of nanocrystalline materialsrdquo Progress in MaterialsScience vol 51 no 4 pp 427ndash556 2006

[31] D Y W Yu and F Spaepen ldquoThe yield strength of thin copperfilms on Kaptonrdquo Journal of Applied Physics vol 95 no 6 pp2991ndash2997 2004

[32] W D Nix and H Gao ldquoIndentation size effects in crystallinematerials a law for strain gradient plasticityrdquo Journal of theMechanics and Physics of Solids vol 46 no 3 pp 411ndash425 1998

[33] S H Hong K S Kim Y-M Kim J-H Hahn C-S Leeand J-H Park ldquoCharacterization of elastic moduli of Cu thinfilms using nanoindentation techniquerdquoComposites Science andTechnology vol 65 no 9 pp 1401ndash1408 2005

[34] N R Shamsutdinov A J Bottger and B J Thijsse ldquoGrain coa-lescence and its effect on stress and elasticity in nanocrystallinemetal filmsrdquo Acta Materialia vol 55 no 3 pp 777ndash784 2007

Submit your manuscripts athttpwwwhindawicom

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Nano

materials

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Journal ofNanomaterials

2 Advances in Materials Science and Engineering

of substrate had important role on the film propertiesThe substrate type and the substrate surface condition hadmarked influences on the texture of as-deposited Cu films[11] Cu films were deposited on Si(001) substrates undervarious Ar deposition pressure by radio frequency (RF)magnetron sputtering The intensities of Cu peaks changedwith the Ar pressure systematically Strong correlations wereobserved between optical emission electron temperatureand the microstructure of Cu films [12]

For Cu nanocrystalline films to be widely used it is neces-sary to explore its microstructure andmechanical propertiesThe physical properties and microstructure of Cu films suchas mechanical properties grain boundary and crystallo-graphic texture can significantly influence the work reliabilityinmicroelectronic devices [10]Mechanical properties of thinfilms often differ from those of the bulk materials [13ndash16]The physical dimensions of thin film materials are generallycomparable to the characteristicmicrostructural length scalesthat strongly influence their mechanical properties [17]In general two different size dependencies determine theproperties of a material One is the dimension character-istic of the physical phenomenon involved The other issome microstructural dimension Microstructural evolutionduring elevated temperature annealing of sputter depositedcopper (Cu) films was investigated by electron backscatterdiffraction (EBSD) Not only are the Cu film texture andgrain size a function of film thickness but also the fraction oftwin boundaries present in thematerial is strongly dependentupon film thickness [18]

Generally microstructure and mechanical properties offilms depend on the deposition process and postproductionprocess such as annealing However most previous workshave focused on the deposition process As we know phys-ical properties of the sputtered films are controlled by itsmicrostructure In this paper we report the microstructuralevolution and mechanical properties of the magnetron sput-tered Cu thin films with different thicknesses after annealingat several temperatures Surface topographyroughness andgrain size are measured by AFM Residual stress (stressesthat remain in the films after annealing) and textures of theCu films are evaluated with X-ray diffraction Furthermorenanoindentation is also performed to study the mechanicalproperties of the Cu films which include the hardnessyield stress (the stress at which a material begins to deformplastically) and elastic modulus Discussions are made interms of the mechanical properties with film microstructure

2 Experimental Details

Three series of copper films were produced by magnetronsputtering deposition on commercial Si(100) single-crystalwafer whose thickness was 525 plusmn 25 120583m Size of the coppertarget isΦ60mm 3mm thicknessThe substrate temperature119879119904is 473 K and the substrate bias 119880

119904is grounded Before

sputtering wafer was ultrasonically cleaned in high purityacetone After vacuum drying wafer was reserved in a drycylinder for use Copper thin films were deposited by amagnetron sputter coater (FJL560II) Copper target materialpurity was 9999wt Base vacuum pressure of the sputter

coater was 2 times 10minus4 Pa and 999 argon was used as aworking gas whose pressure was 15 PaThe distance betweenthe sputter target and the Si wafer was 60mm Sputteringvoltage was 470V and power was 36W Thickness of thefilms is tested by SEM Deposition rate is calculated by filmsthickness and deposition time Different thickness films aredeposited by controlling the deposition time The depositiontime was 60 90 and 170min respectively and these sampleswere labeled as A B and C accordingly The film thicknesswas measured by S-4800 field emission scanning electronmicroscope (SEM) For samples A B and C thickness was10 120583m 16 120583m and 30 120583m accordingly Some samples wereannealed in vacuum at 300 400 and 500∘C respectivelyThebase pressure during annealing is 4 times 10minus4 Pa

Agilent 5420 atomic force microscope (AFM) was usedto observe the sample surface morphology Each samplewas scanned at three different regions and then the typicalregion was utilized for analysis Grazing incidence X-raydiffraction (GIXRD) was performed to study the texture inthe annealed Cu films Experiment was performed using thePhilips XrsquoPert Pro XRD system with 05∘ grazing incidenceThe stresses of film specimens have been studied by the sin2120595The mechanical properties of the annealed copper films wereevaluated using a nanoindenter with a Berkovich tip [19]Thecontinuous stiffness modulation (CSM) technique was usedwherein the contact stiffness was measured continuously as afunction of displacement under the load

3 Results and Discussion

31 Surface Characterization by AFM The representativeAFM images of the coating samples with different thicknessand after annealing at 300∘C are shown in Figure 1 All thesamples have a columnar surface morphology The imagesof the Cu films were acquired in a 1 120583m times 1 120583m area It isclear that as the annealing temperature increased the surfacemorphology evolved and the grains grew larger in the Cufilms119878119902is the root mean square (RMS) height of the surface

which is a statistical amplitude parameter representing theroot mean square of surface roughness deviation from ref-erence datum It can be seen from Table 1 that the lowest119878119902value is observed for the samples annealed at 400∘C The

roughness decreases when continuous and compact filmswith crystal structure are formed during the films depositedWhen the annealing temperature exceeds 400∘C recrystal-lization occurs Due to agglomeration and coalescence of thegrains the roughness of Cu film surface increases

The grain growth in the Cu films can be correlated tothe annealing temperature as shown in Table 2 using thegrain size data determined by AFM The driving force forgrain growth in thin films materials is the reduction of grainboundary energy that results from the reduction of the totalgrain boundary area In grain growth some grains alreadypresent in the matrix grow at the expense of the other grainsA few grains which consume the surrounding (stagnant)fine-grained matrix will grow until the large grains meetand the fine-grained matrix is completely consumed [19ndash22]

Advances in Materials Science and Engineering 3

425

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(a)

55

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(b)

174

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(c)

27

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(d)

27

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(e)

24

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(f)

Figure 1 3D surface topographies of the Cu films (a) 10 120583m thick as-deposited (b) 10 120583m thick annealed at 300∘C (c) 16120583m thick as-deposited (d) 16 120583m thick annealed at 300∘C (e) 30 120583m thick as-deposited and (f) 30 120583m thick annealed at 300∘C

The higher the annealing temperature is the larger thegrain growth driving force is If the annealing temperatureexceeds 400∘C grains grow quickly and coalescence happenswhich will cause grain boundary groove deepening and filmagglomeration to occur

32 Texture and Microstructure Texture in materials hasa large influence on many properties of thin films XRDhas been the primary method for the characterization offilm texture for many years The texture coefficient (TC)represents the texture of a particular plane whose deviation

4 Advances in Materials Science and Engineering

Table 1 Surface roughness Sq (nm) for the Cu films with differentthicknesses annealing temperatures

Annealing temperature (∘C) Thickness (120583m)10 16 30

As-deposited 388 34 298300 366 309 261400 163 291 216500 288 408 948

Table 2Grain size119889 (nm) for theCufilmswith different thicknessesand annealing temperatures

Annealing temperature (∘C) Thickness (120583m)10 16 30

As-deposited 66 88 91300 100 124 143400 120 165 170500 375 405 550

from the ideal value implies the preferred growth Quan-titative information concerning the preferential crystalliteorientation was obtained from the texture coefficient TC

ℎ119896119897

defined as [23]

TCℎ119896119897=119868(ℎ119896119897)1198680(ℎ119896119897)

sum119899

119894=1119868(ℎ119896119897)1198680(ℎ119896119897)

times 100 (1)

where 119868(ℎ119896119897)

is the measured relative intensity of a plane (ℎ119896119897)and 1198680(ℎ119896119897)

is the standard intensity of the plane (ℎ119896119897) takenfrom the JCPDS data The value TC

ℎ119896119897= 1119899 = 025 (ie

119899 = 4 for our case as four planes are included in our XRDstudy) represents films with randomly oriented crystalliteswhile higher values indicate the abundance of grains orientedin a given (ℎ119896119897) direction [23]

321 Effect of Thickness on Texture From Figures 2 and 3we can see that the preferred orientation and texture in thethin films change with the thickness The strongest X-rayreflections are visible from Cu(111) planes This indicates thatthe crystallization occurs preferentially in the (111) planesWhile the polycrystalline films are thin growth of grainwith (111) texture is favored by surface and interface energyminimization especially in very thin films [24 25] Withthe increase of the thickness the (111) orientation decreaseswhereas the (220) orientation increases Strain energy (theenergy stored by a system undergoing deformation includingelastic strain energy and plastic strain energy) controls thegrain growth gradually as the thickness increases Elasticstrain energy is the potential mechanical energy stored in theconfiguration of a material as work is performed to distort itsvolume or shape Plastic strain energy is the energy stored bya system undergoing plastic deformation

322 Effect of Annealing Temperatures on Texture Figure 4shows the XRD patterns of the Cu films with a thick-ness of 10 120583m under different annealing temperatures All

(311)(220)(200)

(111)

40 50 60 70 80 90 100

Inte

nsity

I(a

u)

10 120583m

16 120583m

30 120583m

2120579 (∘)

Figure 2 XRD patterns of the Cu films with different thicknesses

010

015

020

025

030

035

040

045

050

Text

ure c

oeffi

cien

t TC

(111)(200)

(220)(311)

Thickness h (120583m)10 15 20 25 30

Figure 3 Texture coefficients of the Cu films with different thick-nesses

(311)(200)As-deposited

(220)

(111)

2120579 (∘)

Inte

nsity

I(a

u)

40 50 60 70 80 90

Annealing temperature 500∘CAnnealing temperature 400∘C

Annealing temperature 300∘C

Figure 4 XRD patterns of the 10 120583m Cu film annealed at differenttemperatures

the films exhibit X-ray reflections from Cu (111) (200) (220)and (311) To investigate the evolution of crystallite orien-tations with different annealing temperatures the texturecoefficient under different annealing temperatures is shownin Figures 5ndash7 for the films with thickness of 10 16 and30 120583m respectively

Advances in Materials Science and Engineering 5

0001020304050607080910

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 5 Texture coefficients of the 10 120583m Cu film annealed atdifferent temperatures

01

02

03

04

05

06

07

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 6 Texture coefficients of the 16 120583m Cu film annealed atdifferent temperatures

The main driving force for subsequent grain growth isminimum total free energy (surface energy grain interfaceenergy and film strain energy) [21] For thinner films graingrowth is under the control of surface energy minimizationOnly a few grains can grow whose surface energy is relativelylower than the others Grains whose surface energy is higherwill be merged into adjacent grains Grain growth eliminatesfree surface and thus the total surface energy decreasesaccordingly However for thicker films grain growth is underthe control of strain energy minimization For face-centeredcubic (fcc) metals grain orientation which has the lowestplastic strain energy is the (220) plane [24] Development ofstrain energy minimizing textures does not minimize surfaceand interface energies [25 26] Therefore surface struc-ture of the copper films with different thicknesses reflects

016

020

024

028

032

036

040

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 7 Texture coefficients of the 30 120583m Cu film annealed atdifferent temperatures

a dynamic equilibrium between surface energy and strainenergy Surface energy is very important for the structure ofthinner films whereas strain energy is very important for thestructure of thicker films

During the annealing processes the intensity of the(220) grain increases but that of the (111) grain decreases Apreferred grain orientation (220) after annealing is observedwhile (111) is the preferred orientation before annealing Theeffect of yield in grain is proposed to explain the (220)preferred orientation during annealing When the annealingtemperatures increase thin films will start to yield Also theminimum strain energy will control the grain growth In-plane stress in a grain is a function of grain orientation factor119862119894119895119896 and the yield stress of the grain also varies depending

on its orientationThe orientation factor 119862119894119895119896

of (220) has thesmallest one of 142 while that of (111) has the largest one of346 [27] When the thin films start to yield for grains ofequal initial sizes the (220) grains will yield before the (111)grains thus the (220) grains have an energetic advantage forfurther growth [28] This yielding process also leads to strainenergy minimization This may explain why the (220) grainsgrow faster than other grains and become the final preferredorientation

In addition initial grain size also has an effect on thetexture evolution With a certain volume the smaller andthe more uniform the grain is the more evenly the strainenergy will disperse to all the grain So the distribution ofinternal stress (the stress due to difference in the thermalexpansion coefficients and thickness between films and sub-strates during annealing) will be more even which will makethe grain with minimization strain energy grow easily andquickly Grain size in thin films is smaller than thick filmsWe can see from Figures 5ndash7 that the finial texture coefficientafter annealing at 500∘C in thick films is less than thin films

33 Mechanical Properties Nanoindentation was performedon all the Cu films annealed at different temperatures

6 Advances in Materials Science and Engineering

The typical load-indentation depth curves for the 30 120583mfilmannealed at different annealing temperatures are shown inFigure 8 It can be seen from Figure 8 that the loadunloadcurves for all the samples are nearly similar which maybe attributed to the similar crystalline nature of Cu filmsFigure 9 shows the hardness as a function of the annealingtemperature for the Cu films with various thicknesses Morerecent and systematic experiments indicate that both thegrain size and the film thickness have a marked influence onthe strength of thin films [29ndash32] Relationship between thehardness and the yield stress can be expressed as119867 = 3120590

119910 120590119910

is the yield stress and119867 is the hardnessEffect of different parts of microstructure on the yield

stress can be expressed as [29]

120590119910= 1205900+ 119896119889minus119899

+ 1198961015840

119905minus119898

(2)

where 1205900is the bulk yield stress (large-grained polycrystal)

119896119889minus119899 is the contribution from the grain boundaries (119889 grain

size) 1198961015840119905minus119898 is the contribution from the film surface orinterface (119905 film thickness) The first two terms togetherform the well-known Hall-Petch relation where 119899 = 05commonly Combining the data in Table 2 and Figure 9Figure 10 can be obtained which shows that the grain sizedependence of strength in Cu thin films on Si substratesfollowed a Hall-Petch type relation This is the describedHall-Petch effect that establishes a linear dependency ofthe hardness with the reciprocal square root of grain sizeClearly the strengthening of the sputtered copper films wasmainly attained by grain refinement The Hall-Petch effect isexplained in terms of a restriction in the movement of grainsthat is strengthening due to the formation of pileups in thelarger grain boundaries associated with low grain size FromFigure 8 we can see that the indentation depth increases withthe annealing temperatures under the same load which maybe a factor affecting the Hall-Petch type relation In additiongrain size changes with the films thickness which may beanother reason for the yield stress variation

Different load-indentation depth curves for the Cu filmsannealed at different temperatures imply different indenta-tion plastic characteristics for these films These curves canbe separated into the following three stages pure elasticdeformation stage at the beginning of the load elastic-plastic deformation stage after displacement jump and elasticresponse during unload It agrees with the Hertz contacttheory well during the elastic deformation stage The lowerthe annealing is the less the elastic displacement is Displace-ment jump caused by the dislocation pileup and incrementon the plastic deformation region increase with the increaseof the grain size With the decrease of the grain size thedensity of the grain boundaries increases It cannot only actas the source of dislocation but also decrease the dislocationactivation energy

The values of elastic modulus can also be obtainedby nanoindentation The Young modulus decreased 20compared to that of the traditional coarse-grained Cu Theelastic modulus is one of the intrinsic properties of a material[33] Elastic modulus is an important indicator to reflect thebond strength between the atoms Many factors can affect

0

5

10

15

20

25

30

35

40

As-deposited

0 100 200 300 400 500 600 700 800 900

Annealing temperature 500∘C

Annealing temperature 400∘C

Annealing temperature 300∘C

Load

P(m

N)

Indentation depth h (nm)

Figure 8 Load-indentation depth curves for the 30 120583m Cu filmsannealed at different temperatures

20

21

22

23

24

25

26

27

28

29

10 120583m16 120583m30 120583m

100 200 300 400 500

Annealing temperature T (∘C)

Har

dnes

sH(G

Pa)

Figure 9 Hardness versus annealing temperature for the Cu filmswith different thicknesses

the elastic modulus such as texture [33] grain coalescenceandmicrocrack [34] Elasticmodulus of the Cu thin filmswilldecrease 20when 13 of grain boundaries is destroyed basedon the microcrack mechanism

XRD diffraction technique was carried out to investi-gate the residual stress by the well-know sin2Ψ methodFigure 11 shows the relationship between residual stressand TC(111)TC(220) ratio in Cu films The film with (111)-orientated grains had the highest tensile one and that with(220)-orientated grains had the lowest tensile one Theresidual stress in as-deposited copper films reached a highvalue but decreased down to a minimum value after samplesannealing This was obviously due to the thermal relaxationof residual stresses and the annealing effect onmicrostructuredefects This may be due to the preferred growth of grainswhich leads to a change of residual stress

Advances in Materials Science and Engineering 7

05

06

07

08

09

10

004 005 006 007 008 009 010 011 012 013

Yield

stre

ss120590y

(GPa

)

dminus05 (nmminus05)

10 120583m16 120583m30 120583m

Figure 10 Trend of yield stress dependency on grain size for the Cufilms

03

06

09

12

15

18

21

0

20

40

60

80

100

Resid

ual s

tress

(MPa

)

TC(1

11)

TC(2

20)

Annealing temperature T (∘C)0 50 100 150 200 250 300 350 400 450

minus20

TC(111)TC(220) of 10 120583mTC(111)TC(220) of 16 120583mTC(111)TC(220) of 30 120583m

Residual stress of 10 120583mResidual stress of 16 120583mResidual stress of 30 120583m

Figure 11 TC(111)TC(220) ratio and residual stress versus anneal-ing temperatures of 10 120583m 16 120583m and 30 120583m

4 Conclusions

The effect of annealing treatment on magnetron sputteredCu films is investigated using AFM XRD and nanoinden-tation techniques Surface topography and microstructuralevolution after annealing is studied in detail Relationshipbetween themicrostructure and themechanical properties ofthe thin films is also proposed The higher the texture of (111)is the lower the resistivity isWith the increase of (111) texturetensile stress increases For microelectronic application largeresidual stress will cause cavity crack and peeling of Cu filmswhich will cause circuit deformation and even produce shortcircuit or open circuit Annealing is usually taken during ICAlthough the resistivity of Cu films decreased a little thereliability of the system is greatly increased

The following are our main conclusions

(1) Annealing treatment can provide enough energy forthe grain to growWhen the annealing temperature isless than 400∘C the higher the annealing temperatureis the more the energy for the grain growth will beWith the grain growth surface void is filled and thesurface RMS decreases However when the annealingtemperature is gt400∘C grain grows abnormally andcoalescence occurs Surface void defects and microc-racks increase and the surface RMS increases

(2) Films thickness grain size and annealing tempera-tures are the main factors that affect the microstruc-ture of the annealed Cu films The minimization ofenergy including surface energy interface energy andstrain energy (elastic strain energy and plastic strainenergy) controls the microstructural evolution

(3) The grain size dependence of strength in the Cuthin films on the Si substrates followed a Hall-Petchtype relation In addition grain size changes with thefilms thickness which may be another reason for theyield stress variationThe as-deposited Cu films are intensile state and have strong (111) orientation Duringthe annealing with the decreasing of (111) orientationtensile stress decreased The ratio of TC(111)TC(220)can be used as a merit for the state of residual stress

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project is supported by National Basic Research Devel-opment Program of China (973 Program Grant no 2009CB724200) Research Fund for the Doctoral Program ofHigher Education of China (Grant no 20111415120002) andShanxi Provincial Science Foundation for Youths of China(Grant no 2010021023-4)

References

[1] A A Volinsky J Vella I S Adhihetty et al ldquoMicrostructureand mechanical properties of electroplated Cu thin filmsrdquo inProceedings of the Materials Research Society Symposium vol649 pp Q 531ndashQ 536 Boston Mass USA November 2001

[2] S P Murarka ldquoMultilevel interconnections for ULSI and GSIerardquo Materials Science and Engineering R Reports vol 19 no3-4 pp 87ndash151 1997

[3] S P Murarka R J Gutmann A E Kaloyeros and W ALanford ldquoAdvanced multilayer metallization schemes withcopper as interconnection metalrdquoThin Solid Films vol 236 no1-2 pp 257ndash266 1993

[4] R W Vook ldquoElectrical control of surface electromigrationdamagerdquoThin Solid Films vol 305 no 1-2 pp 286ndash291 1997

[5] A Wiatrowski W M Posadowski G Jozwiak J SerafinczukR Szeloch and T Gotszalk ldquoStandard and self-sustainedmagnetron sputtering deposited Cu films investigated bymeans

8 Advances in Materials Science and Engineering

of AFM and XRDrdquoMicroelectronics Reliability vol 51 no 7 pp1203ndash1206 2011

[6] M-T Le Y-U Sohn J-W Lim and G-S Choi ldquoEffect ofsputtering power on the nucleation and growth of Cu filmsdeposited by magnetron sputteringrdquo Materials Transactionsvol 51 no 1 pp 116ndash120 2010

[7] AK Siker AKumar P Shukla P B Zantye andM SanganarialdquoEffect of multistep annealing on mechanical and surfaceproperties of electroplated Cu thin filmsrdquo Journal of ElectronicMaterials vol 32 no 10 pp 1028ndash1033 2003

[8] P Shukla A K Sikder P B Zantye A Kumar and MSanganaria ldquoEffect of annealing on the structural mechanicaland tribological properties of electroplated Cu thin filmsrdquoMaterials Research Society Symposium Proceedings vol 182 ppF3161ndashF3167 2004

[9] S KMukherjee L Joshi and P K Barhai ldquoA comparative studyof nanocrystalline Cu film deposited using anodic vacuum arcand dc magnetron sputteringrdquo Surface amp Coatings Technologyvol 205 no 19 pp 4582ndash4595 2011

[10] Z H Cao H M Lu and X K Meng ldquoBarrier layer andannealing temperature dependent microstructure evolution ofnanocrystalline Cu filmsrdquoMaterials Chemistry and Physics vol117 no 1 pp 321ndash325 2009

[11] B Okolo P Lamparter UWelzel TWagner and E JMittemei-jer ldquoThe effect of deposition parameters and substrate surfacecondition on texture morphology and stress in magnetron-sputter-deposited Cu thin filmsrdquo Thin Solid Films vol 474 no1-2 pp 50ndash63 2005

[12] Q X Zhao F Bian Y Zhou et al ldquoOptical emission electrontemperature and microstructure of Cu film prepared by mag-netron sputteringrdquo Materials Letters vol 62 no 25 pp 4140ndash4142 2008

[13] W D Nix J R Greer G Feng and E T Lilleodden ldquoDefor-mation at the nanometer and micrometer length scales effectsof strain gradients and dislocation starvationrdquoThin Solid Filmsvol 515 no 6 pp 3152ndash3157 2007

[14] Z P Bazant Z Guo H D Espinosa Y Zhu and B PengldquoEpitaxially influenced boundary layer model for size effect inthin metallic filmsrdquo Journal of Applied Physics vol 97 no 7Article ID 073506 2005

[15] H D Espinosa M Panico S Berbenni and K W SchwarzldquoDiscrete dislocation dynamics simulations to interpret plas-ticity size and surface effects in freestanding FCC thin filmsrdquoInternational Journal of Plasticity vol 22 no 11 pp 2091ndash21172006

[16] D S Gianola S van PetegemM Legros S Brandstetter H vanSwygenhoven and K J Hemker ldquoStress-assisted discontinuousgrain growth and its effect on the deformation behavior ofnanocrystalline aluminum thin filmsrdquo Acta Materialia vol 54no 8 pp 2253ndash2263 2006

[17] E Arzt ldquoSize effects in materials due to microstructural anddimensional constraints a comparative reviewrdquo Acta Materi-alia vol 46 no 16 pp 5611ndash5626 1998

[18] N-J Park D P Field M M Nowell and P R Besser ldquoEffect offilm thickness on the evolution of annealing texture in sputteredcopper filmsrdquo Journal of Electronic Materials vol 34 no 12 pp1500ndash1508 2005

[19] G M Pharr ldquoMeasurement of mechanical properties by ultra-low load indentationrdquoMaterials Science and Engineering A vol253 no 1-2 pp 151ndash159 1998

[20] J-M Zhang K-W Xu and V Ji ldquoCompetition between surfaceand strain energy during grain growth in free-standing and

attached Ag and Cu films on Si substratesrdquo Applied SurfaceScience vol 187 no 1-2 pp 60ndash67 2002

[21] V Weihnacht and W Bruckner ldquoAbnormal grain growth in 111textured Cu thin filmsrdquoThin Solid Films vol 418 no 2 pp 136ndash144 2002

[22] C V Thompson and R Carel ldquoTexture development in poly-crystalline thin filmsrdquoMaterials Science and Engineering B vol32 no 3 pp 211ndash219 1995

[23] C S Barret and T B Massalski Structure of Metals PergamonPress Oxford UK 1980

[24] J-M Zhang K-W Xu and M-R Zhang ldquoTheory of abnormalgrain growth in thin films and analysis of energy anisotropyrdquoActa Physica Sinica vol 52 no 5 pp 1207ndash1211 2003

[25] H LWei HHuang CHWoo R K Zheng GHWen andXX Zhang ldquoDevelopment of ⟨110⟩ texture in copper thin filmsrdquoApplied Physics Letters vol 80 no 13 pp 2290ndash2292 2002

[26] RCarel CVThompson andH J Frost ldquoComputer simulationof strain energy effects vs surface and interface energy effects ongrain growth in thin filmsrdquo Acta Materialia vol 44 no 6 pp2479ndash2494 1996

[27] J E Sanchez Jr and E Arzt ldquoEffects of grain orientation onhillock formation and grain growth in aluminum films onsilicon substratesrdquo Scripta Metallurgica et Materiala vol 27 no3 pp 285ndash290 1992

[28] F Spaepen ldquoSubstrate curvature resulting from the capillaryforces of a liquid droprdquo Journal of the Mechanics and Physics ofSolids vol 44 no 5 pp 675ndash681 1996

[29] Y-J Choi and S Suresh ldquoSize effects on the mechanicalproperties of thin polycrystalline metal films on substratesrdquoActa Materialia vol 50 no 7 pp 1881ndash1893 2002

[30] M A Meyers A Mishra and D J Benson ldquoMechanicalproperties of nanocrystalline materialsrdquo Progress in MaterialsScience vol 51 no 4 pp 427ndash556 2006

[31] D Y W Yu and F Spaepen ldquoThe yield strength of thin copperfilms on Kaptonrdquo Journal of Applied Physics vol 95 no 6 pp2991ndash2997 2004

[32] W D Nix and H Gao ldquoIndentation size effects in crystallinematerials a law for strain gradient plasticityrdquo Journal of theMechanics and Physics of Solids vol 46 no 3 pp 411ndash425 1998

[33] S H Hong K S Kim Y-M Kim J-H Hahn C-S Leeand J-H Park ldquoCharacterization of elastic moduli of Cu thinfilms using nanoindentation techniquerdquoComposites Science andTechnology vol 65 no 9 pp 1401ndash1408 2005

[34] N R Shamsutdinov A J Bottger and B J Thijsse ldquoGrain coa-lescence and its effect on stress and elasticity in nanocrystallinemetal filmsrdquo Acta Materialia vol 55 no 3 pp 777ndash784 2007

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Advances in Materials Science and Engineering 3

425

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(a)

55

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(b)

174

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(c)

27

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(d)

27

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(e)

24

0

02

04

06

08

1

0

02

04

06

08

1

y (120583m) x(120583m

)

(f)

Figure 1 3D surface topographies of the Cu films (a) 10 120583m thick as-deposited (b) 10 120583m thick annealed at 300∘C (c) 16120583m thick as-deposited (d) 16 120583m thick annealed at 300∘C (e) 30 120583m thick as-deposited and (f) 30 120583m thick annealed at 300∘C

The higher the annealing temperature is the larger thegrain growth driving force is If the annealing temperatureexceeds 400∘C grains grow quickly and coalescence happenswhich will cause grain boundary groove deepening and filmagglomeration to occur

32 Texture and Microstructure Texture in materials hasa large influence on many properties of thin films XRDhas been the primary method for the characterization offilm texture for many years The texture coefficient (TC)represents the texture of a particular plane whose deviation

4 Advances in Materials Science and Engineering

Table 1 Surface roughness Sq (nm) for the Cu films with differentthicknesses annealing temperatures

Annealing temperature (∘C) Thickness (120583m)10 16 30

As-deposited 388 34 298300 366 309 261400 163 291 216500 288 408 948

Table 2Grain size119889 (nm) for theCufilmswith different thicknessesand annealing temperatures

Annealing temperature (∘C) Thickness (120583m)10 16 30

As-deposited 66 88 91300 100 124 143400 120 165 170500 375 405 550

from the ideal value implies the preferred growth Quan-titative information concerning the preferential crystalliteorientation was obtained from the texture coefficient TC

ℎ119896119897

defined as [23]

TCℎ119896119897=119868(ℎ119896119897)1198680(ℎ119896119897)

sum119899

119894=1119868(ℎ119896119897)1198680(ℎ119896119897)

times 100 (1)

where 119868(ℎ119896119897)

is the measured relative intensity of a plane (ℎ119896119897)and 1198680(ℎ119896119897)

is the standard intensity of the plane (ℎ119896119897) takenfrom the JCPDS data The value TC

ℎ119896119897= 1119899 = 025 (ie

119899 = 4 for our case as four planes are included in our XRDstudy) represents films with randomly oriented crystalliteswhile higher values indicate the abundance of grains orientedin a given (ℎ119896119897) direction [23]

321 Effect of Thickness on Texture From Figures 2 and 3we can see that the preferred orientation and texture in thethin films change with the thickness The strongest X-rayreflections are visible from Cu(111) planes This indicates thatthe crystallization occurs preferentially in the (111) planesWhile the polycrystalline films are thin growth of grainwith (111) texture is favored by surface and interface energyminimization especially in very thin films [24 25] Withthe increase of the thickness the (111) orientation decreaseswhereas the (220) orientation increases Strain energy (theenergy stored by a system undergoing deformation includingelastic strain energy and plastic strain energy) controls thegrain growth gradually as the thickness increases Elasticstrain energy is the potential mechanical energy stored in theconfiguration of a material as work is performed to distort itsvolume or shape Plastic strain energy is the energy stored bya system undergoing plastic deformation

322 Effect of Annealing Temperatures on Texture Figure 4shows the XRD patterns of the Cu films with a thick-ness of 10 120583m under different annealing temperatures All

(311)(220)(200)

(111)

40 50 60 70 80 90 100

Inte

nsity

I(a

u)

10 120583m

16 120583m

30 120583m

2120579 (∘)

Figure 2 XRD patterns of the Cu films with different thicknesses

010

015

020

025

030

035

040

045

050

Text

ure c

oeffi

cien

t TC

(111)(200)

(220)(311)

Thickness h (120583m)10 15 20 25 30

Figure 3 Texture coefficients of the Cu films with different thick-nesses

(311)(200)As-deposited

(220)

(111)

2120579 (∘)

Inte

nsity

I(a

u)

40 50 60 70 80 90

Annealing temperature 500∘CAnnealing temperature 400∘C

Annealing temperature 300∘C

Figure 4 XRD patterns of the 10 120583m Cu film annealed at differenttemperatures

the films exhibit X-ray reflections from Cu (111) (200) (220)and (311) To investigate the evolution of crystallite orien-tations with different annealing temperatures the texturecoefficient under different annealing temperatures is shownin Figures 5ndash7 for the films with thickness of 10 16 and30 120583m respectively

Advances in Materials Science and Engineering 5

0001020304050607080910

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 5 Texture coefficients of the 10 120583m Cu film annealed atdifferent temperatures

01

02

03

04

05

06

07

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 6 Texture coefficients of the 16 120583m Cu film annealed atdifferent temperatures

The main driving force for subsequent grain growth isminimum total free energy (surface energy grain interfaceenergy and film strain energy) [21] For thinner films graingrowth is under the control of surface energy minimizationOnly a few grains can grow whose surface energy is relativelylower than the others Grains whose surface energy is higherwill be merged into adjacent grains Grain growth eliminatesfree surface and thus the total surface energy decreasesaccordingly However for thicker films grain growth is underthe control of strain energy minimization For face-centeredcubic (fcc) metals grain orientation which has the lowestplastic strain energy is the (220) plane [24] Development ofstrain energy minimizing textures does not minimize surfaceand interface energies [25 26] Therefore surface struc-ture of the copper films with different thicknesses reflects

016

020

024

028

032

036

040

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 7 Texture coefficients of the 30 120583m Cu film annealed atdifferent temperatures

a dynamic equilibrium between surface energy and strainenergy Surface energy is very important for the structure ofthinner films whereas strain energy is very important for thestructure of thicker films

During the annealing processes the intensity of the(220) grain increases but that of the (111) grain decreases Apreferred grain orientation (220) after annealing is observedwhile (111) is the preferred orientation before annealing Theeffect of yield in grain is proposed to explain the (220)preferred orientation during annealing When the annealingtemperatures increase thin films will start to yield Also theminimum strain energy will control the grain growth In-plane stress in a grain is a function of grain orientation factor119862119894119895119896 and the yield stress of the grain also varies depending

on its orientationThe orientation factor 119862119894119895119896

of (220) has thesmallest one of 142 while that of (111) has the largest one of346 [27] When the thin films start to yield for grains ofequal initial sizes the (220) grains will yield before the (111)grains thus the (220) grains have an energetic advantage forfurther growth [28] This yielding process also leads to strainenergy minimization This may explain why the (220) grainsgrow faster than other grains and become the final preferredorientation

In addition initial grain size also has an effect on thetexture evolution With a certain volume the smaller andthe more uniform the grain is the more evenly the strainenergy will disperse to all the grain So the distribution ofinternal stress (the stress due to difference in the thermalexpansion coefficients and thickness between films and sub-strates during annealing) will be more even which will makethe grain with minimization strain energy grow easily andquickly Grain size in thin films is smaller than thick filmsWe can see from Figures 5ndash7 that the finial texture coefficientafter annealing at 500∘C in thick films is less than thin films

33 Mechanical Properties Nanoindentation was performedon all the Cu films annealed at different temperatures

6 Advances in Materials Science and Engineering

The typical load-indentation depth curves for the 30 120583mfilmannealed at different annealing temperatures are shown inFigure 8 It can be seen from Figure 8 that the loadunloadcurves for all the samples are nearly similar which maybe attributed to the similar crystalline nature of Cu filmsFigure 9 shows the hardness as a function of the annealingtemperature for the Cu films with various thicknesses Morerecent and systematic experiments indicate that both thegrain size and the film thickness have a marked influence onthe strength of thin films [29ndash32] Relationship between thehardness and the yield stress can be expressed as119867 = 3120590

119910 120590119910

is the yield stress and119867 is the hardnessEffect of different parts of microstructure on the yield

stress can be expressed as [29]

120590119910= 1205900+ 119896119889minus119899

+ 1198961015840

119905minus119898

(2)

where 1205900is the bulk yield stress (large-grained polycrystal)

119896119889minus119899 is the contribution from the grain boundaries (119889 grain

size) 1198961015840119905minus119898 is the contribution from the film surface orinterface (119905 film thickness) The first two terms togetherform the well-known Hall-Petch relation where 119899 = 05commonly Combining the data in Table 2 and Figure 9Figure 10 can be obtained which shows that the grain sizedependence of strength in Cu thin films on Si substratesfollowed a Hall-Petch type relation This is the describedHall-Petch effect that establishes a linear dependency ofthe hardness with the reciprocal square root of grain sizeClearly the strengthening of the sputtered copper films wasmainly attained by grain refinement The Hall-Petch effect isexplained in terms of a restriction in the movement of grainsthat is strengthening due to the formation of pileups in thelarger grain boundaries associated with low grain size FromFigure 8 we can see that the indentation depth increases withthe annealing temperatures under the same load which maybe a factor affecting the Hall-Petch type relation In additiongrain size changes with the films thickness which may beanother reason for the yield stress variation

Different load-indentation depth curves for the Cu filmsannealed at different temperatures imply different indenta-tion plastic characteristics for these films These curves canbe separated into the following three stages pure elasticdeformation stage at the beginning of the load elastic-plastic deformation stage after displacement jump and elasticresponse during unload It agrees with the Hertz contacttheory well during the elastic deformation stage The lowerthe annealing is the less the elastic displacement is Displace-ment jump caused by the dislocation pileup and incrementon the plastic deformation region increase with the increaseof the grain size With the decrease of the grain size thedensity of the grain boundaries increases It cannot only actas the source of dislocation but also decrease the dislocationactivation energy

The values of elastic modulus can also be obtainedby nanoindentation The Young modulus decreased 20compared to that of the traditional coarse-grained Cu Theelastic modulus is one of the intrinsic properties of a material[33] Elastic modulus is an important indicator to reflect thebond strength between the atoms Many factors can affect

0

5

10

15

20

25

30

35

40

As-deposited

0 100 200 300 400 500 600 700 800 900

Annealing temperature 500∘C

Annealing temperature 400∘C

Annealing temperature 300∘C

Load

P(m

N)

Indentation depth h (nm)

Figure 8 Load-indentation depth curves for the 30 120583m Cu filmsannealed at different temperatures

20

21

22

23

24

25

26

27

28

29

10 120583m16 120583m30 120583m

100 200 300 400 500

Annealing temperature T (∘C)

Har

dnes

sH(G

Pa)

Figure 9 Hardness versus annealing temperature for the Cu filmswith different thicknesses

the elastic modulus such as texture [33] grain coalescenceandmicrocrack [34] Elasticmodulus of the Cu thin filmswilldecrease 20when 13 of grain boundaries is destroyed basedon the microcrack mechanism

XRD diffraction technique was carried out to investi-gate the residual stress by the well-know sin2Ψ methodFigure 11 shows the relationship between residual stressand TC(111)TC(220) ratio in Cu films The film with (111)-orientated grains had the highest tensile one and that with(220)-orientated grains had the lowest tensile one Theresidual stress in as-deposited copper films reached a highvalue but decreased down to a minimum value after samplesannealing This was obviously due to the thermal relaxationof residual stresses and the annealing effect onmicrostructuredefects This may be due to the preferred growth of grainswhich leads to a change of residual stress

Advances in Materials Science and Engineering 7

05

06

07

08

09

10

004 005 006 007 008 009 010 011 012 013

Yield

stre

ss120590y

(GPa

)

dminus05 (nmminus05)

10 120583m16 120583m30 120583m

Figure 10 Trend of yield stress dependency on grain size for the Cufilms

03

06

09

12

15

18

21

0

20

40

60

80

100

Resid

ual s

tress

(MPa

)

TC(1

11)

TC(2

20)

Annealing temperature T (∘C)0 50 100 150 200 250 300 350 400 450

minus20

TC(111)TC(220) of 10 120583mTC(111)TC(220) of 16 120583mTC(111)TC(220) of 30 120583m

Residual stress of 10 120583mResidual stress of 16 120583mResidual stress of 30 120583m

Figure 11 TC(111)TC(220) ratio and residual stress versus anneal-ing temperatures of 10 120583m 16 120583m and 30 120583m

4 Conclusions

The effect of annealing treatment on magnetron sputteredCu films is investigated using AFM XRD and nanoinden-tation techniques Surface topography and microstructuralevolution after annealing is studied in detail Relationshipbetween themicrostructure and themechanical properties ofthe thin films is also proposed The higher the texture of (111)is the lower the resistivity isWith the increase of (111) texturetensile stress increases For microelectronic application largeresidual stress will cause cavity crack and peeling of Cu filmswhich will cause circuit deformation and even produce shortcircuit or open circuit Annealing is usually taken during ICAlthough the resistivity of Cu films decreased a little thereliability of the system is greatly increased

The following are our main conclusions

(1) Annealing treatment can provide enough energy forthe grain to growWhen the annealing temperature isless than 400∘C the higher the annealing temperatureis the more the energy for the grain growth will beWith the grain growth surface void is filled and thesurface RMS decreases However when the annealingtemperature is gt400∘C grain grows abnormally andcoalescence occurs Surface void defects and microc-racks increase and the surface RMS increases

(2) Films thickness grain size and annealing tempera-tures are the main factors that affect the microstruc-ture of the annealed Cu films The minimization ofenergy including surface energy interface energy andstrain energy (elastic strain energy and plastic strainenergy) controls the microstructural evolution

(3) The grain size dependence of strength in the Cuthin films on the Si substrates followed a Hall-Petchtype relation In addition grain size changes with thefilms thickness which may be another reason for theyield stress variationThe as-deposited Cu films are intensile state and have strong (111) orientation Duringthe annealing with the decreasing of (111) orientationtensile stress decreased The ratio of TC(111)TC(220)can be used as a merit for the state of residual stress

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project is supported by National Basic Research Devel-opment Program of China (973 Program Grant no 2009CB724200) Research Fund for the Doctoral Program ofHigher Education of China (Grant no 20111415120002) andShanxi Provincial Science Foundation for Youths of China(Grant no 2010021023-4)

References

[1] A A Volinsky J Vella I S Adhihetty et al ldquoMicrostructureand mechanical properties of electroplated Cu thin filmsrdquo inProceedings of the Materials Research Society Symposium vol649 pp Q 531ndashQ 536 Boston Mass USA November 2001

[2] S P Murarka ldquoMultilevel interconnections for ULSI and GSIerardquo Materials Science and Engineering R Reports vol 19 no3-4 pp 87ndash151 1997

[3] S P Murarka R J Gutmann A E Kaloyeros and W ALanford ldquoAdvanced multilayer metallization schemes withcopper as interconnection metalrdquoThin Solid Films vol 236 no1-2 pp 257ndash266 1993

[4] R W Vook ldquoElectrical control of surface electromigrationdamagerdquoThin Solid Films vol 305 no 1-2 pp 286ndash291 1997

[5] A Wiatrowski W M Posadowski G Jozwiak J SerafinczukR Szeloch and T Gotszalk ldquoStandard and self-sustainedmagnetron sputtering deposited Cu films investigated bymeans

8 Advances in Materials Science and Engineering

of AFM and XRDrdquoMicroelectronics Reliability vol 51 no 7 pp1203ndash1206 2011

[6] M-T Le Y-U Sohn J-W Lim and G-S Choi ldquoEffect ofsputtering power on the nucleation and growth of Cu filmsdeposited by magnetron sputteringrdquo Materials Transactionsvol 51 no 1 pp 116ndash120 2010

[7] AK Siker AKumar P Shukla P B Zantye andM SanganarialdquoEffect of multistep annealing on mechanical and surfaceproperties of electroplated Cu thin filmsrdquo Journal of ElectronicMaterials vol 32 no 10 pp 1028ndash1033 2003

[8] P Shukla A K Sikder P B Zantye A Kumar and MSanganaria ldquoEffect of annealing on the structural mechanicaland tribological properties of electroplated Cu thin filmsrdquoMaterials Research Society Symposium Proceedings vol 182 ppF3161ndashF3167 2004

[9] S KMukherjee L Joshi and P K Barhai ldquoA comparative studyof nanocrystalline Cu film deposited using anodic vacuum arcand dc magnetron sputteringrdquo Surface amp Coatings Technologyvol 205 no 19 pp 4582ndash4595 2011

[10] Z H Cao H M Lu and X K Meng ldquoBarrier layer andannealing temperature dependent microstructure evolution ofnanocrystalline Cu filmsrdquoMaterials Chemistry and Physics vol117 no 1 pp 321ndash325 2009

[11] B Okolo P Lamparter UWelzel TWagner and E JMittemei-jer ldquoThe effect of deposition parameters and substrate surfacecondition on texture morphology and stress in magnetron-sputter-deposited Cu thin filmsrdquo Thin Solid Films vol 474 no1-2 pp 50ndash63 2005

[12] Q X Zhao F Bian Y Zhou et al ldquoOptical emission electrontemperature and microstructure of Cu film prepared by mag-netron sputteringrdquo Materials Letters vol 62 no 25 pp 4140ndash4142 2008

[13] W D Nix J R Greer G Feng and E T Lilleodden ldquoDefor-mation at the nanometer and micrometer length scales effectsof strain gradients and dislocation starvationrdquoThin Solid Filmsvol 515 no 6 pp 3152ndash3157 2007

[14] Z P Bazant Z Guo H D Espinosa Y Zhu and B PengldquoEpitaxially influenced boundary layer model for size effect inthin metallic filmsrdquo Journal of Applied Physics vol 97 no 7Article ID 073506 2005

[15] H D Espinosa M Panico S Berbenni and K W SchwarzldquoDiscrete dislocation dynamics simulations to interpret plas-ticity size and surface effects in freestanding FCC thin filmsrdquoInternational Journal of Plasticity vol 22 no 11 pp 2091ndash21172006

[16] D S Gianola S van PetegemM Legros S Brandstetter H vanSwygenhoven and K J Hemker ldquoStress-assisted discontinuousgrain growth and its effect on the deformation behavior ofnanocrystalline aluminum thin filmsrdquo Acta Materialia vol 54no 8 pp 2253ndash2263 2006

[17] E Arzt ldquoSize effects in materials due to microstructural anddimensional constraints a comparative reviewrdquo Acta Materi-alia vol 46 no 16 pp 5611ndash5626 1998

[18] N-J Park D P Field M M Nowell and P R Besser ldquoEffect offilm thickness on the evolution of annealing texture in sputteredcopper filmsrdquo Journal of Electronic Materials vol 34 no 12 pp1500ndash1508 2005

[19] G M Pharr ldquoMeasurement of mechanical properties by ultra-low load indentationrdquoMaterials Science and Engineering A vol253 no 1-2 pp 151ndash159 1998

[20] J-M Zhang K-W Xu and V Ji ldquoCompetition between surfaceand strain energy during grain growth in free-standing and

attached Ag and Cu films on Si substratesrdquo Applied SurfaceScience vol 187 no 1-2 pp 60ndash67 2002

[21] V Weihnacht and W Bruckner ldquoAbnormal grain growth in 111textured Cu thin filmsrdquoThin Solid Films vol 418 no 2 pp 136ndash144 2002

[22] C V Thompson and R Carel ldquoTexture development in poly-crystalline thin filmsrdquoMaterials Science and Engineering B vol32 no 3 pp 211ndash219 1995

[23] C S Barret and T B Massalski Structure of Metals PergamonPress Oxford UK 1980

[24] J-M Zhang K-W Xu and M-R Zhang ldquoTheory of abnormalgrain growth in thin films and analysis of energy anisotropyrdquoActa Physica Sinica vol 52 no 5 pp 1207ndash1211 2003

[25] H LWei HHuang CHWoo R K Zheng GHWen andXX Zhang ldquoDevelopment of ⟨110⟩ texture in copper thin filmsrdquoApplied Physics Letters vol 80 no 13 pp 2290ndash2292 2002

[26] RCarel CVThompson andH J Frost ldquoComputer simulationof strain energy effects vs surface and interface energy effects ongrain growth in thin filmsrdquo Acta Materialia vol 44 no 6 pp2479ndash2494 1996

[27] J E Sanchez Jr and E Arzt ldquoEffects of grain orientation onhillock formation and grain growth in aluminum films onsilicon substratesrdquo Scripta Metallurgica et Materiala vol 27 no3 pp 285ndash290 1992

[28] F Spaepen ldquoSubstrate curvature resulting from the capillaryforces of a liquid droprdquo Journal of the Mechanics and Physics ofSolids vol 44 no 5 pp 675ndash681 1996

[29] Y-J Choi and S Suresh ldquoSize effects on the mechanicalproperties of thin polycrystalline metal films on substratesrdquoActa Materialia vol 50 no 7 pp 1881ndash1893 2002

[30] M A Meyers A Mishra and D J Benson ldquoMechanicalproperties of nanocrystalline materialsrdquo Progress in MaterialsScience vol 51 no 4 pp 427ndash556 2006

[31] D Y W Yu and F Spaepen ldquoThe yield strength of thin copperfilms on Kaptonrdquo Journal of Applied Physics vol 95 no 6 pp2991ndash2997 2004

[32] W D Nix and H Gao ldquoIndentation size effects in crystallinematerials a law for strain gradient plasticityrdquo Journal of theMechanics and Physics of Solids vol 46 no 3 pp 411ndash425 1998

[33] S H Hong K S Kim Y-M Kim J-H Hahn C-S Leeand J-H Park ldquoCharacterization of elastic moduli of Cu thinfilms using nanoindentation techniquerdquoComposites Science andTechnology vol 65 no 9 pp 1401ndash1408 2005

[34] N R Shamsutdinov A J Bottger and B J Thijsse ldquoGrain coa-lescence and its effect on stress and elasticity in nanocrystallinemetal filmsrdquo Acta Materialia vol 55 no 3 pp 777ndash784 2007

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

4 Advances in Materials Science and Engineering

Table 1 Surface roughness Sq (nm) for the Cu films with differentthicknesses annealing temperatures

Annealing temperature (∘C) Thickness (120583m)10 16 30

As-deposited 388 34 298300 366 309 261400 163 291 216500 288 408 948

Table 2Grain size119889 (nm) for theCufilmswith different thicknessesand annealing temperatures

Annealing temperature (∘C) Thickness (120583m)10 16 30

As-deposited 66 88 91300 100 124 143400 120 165 170500 375 405 550

from the ideal value implies the preferred growth Quan-titative information concerning the preferential crystalliteorientation was obtained from the texture coefficient TC

ℎ119896119897

defined as [23]

TCℎ119896119897=119868(ℎ119896119897)1198680(ℎ119896119897)

sum119899

119894=1119868(ℎ119896119897)1198680(ℎ119896119897)

times 100 (1)

where 119868(ℎ119896119897)

is the measured relative intensity of a plane (ℎ119896119897)and 1198680(ℎ119896119897)

is the standard intensity of the plane (ℎ119896119897) takenfrom the JCPDS data The value TC

ℎ119896119897= 1119899 = 025 (ie

119899 = 4 for our case as four planes are included in our XRDstudy) represents films with randomly oriented crystalliteswhile higher values indicate the abundance of grains orientedin a given (ℎ119896119897) direction [23]

321 Effect of Thickness on Texture From Figures 2 and 3we can see that the preferred orientation and texture in thethin films change with the thickness The strongest X-rayreflections are visible from Cu(111) planes This indicates thatthe crystallization occurs preferentially in the (111) planesWhile the polycrystalline films are thin growth of grainwith (111) texture is favored by surface and interface energyminimization especially in very thin films [24 25] Withthe increase of the thickness the (111) orientation decreaseswhereas the (220) orientation increases Strain energy (theenergy stored by a system undergoing deformation includingelastic strain energy and plastic strain energy) controls thegrain growth gradually as the thickness increases Elasticstrain energy is the potential mechanical energy stored in theconfiguration of a material as work is performed to distort itsvolume or shape Plastic strain energy is the energy stored bya system undergoing plastic deformation

322 Effect of Annealing Temperatures on Texture Figure 4shows the XRD patterns of the Cu films with a thick-ness of 10 120583m under different annealing temperatures All

(311)(220)(200)

(111)

40 50 60 70 80 90 100

Inte

nsity

I(a

u)

10 120583m

16 120583m

30 120583m

2120579 (∘)

Figure 2 XRD patterns of the Cu films with different thicknesses

010

015

020

025

030

035

040

045

050

Text

ure c

oeffi

cien

t TC

(111)(200)

(220)(311)

Thickness h (120583m)10 15 20 25 30

Figure 3 Texture coefficients of the Cu films with different thick-nesses

(311)(200)As-deposited

(220)

(111)

2120579 (∘)

Inte

nsity

I(a

u)

40 50 60 70 80 90

Annealing temperature 500∘CAnnealing temperature 400∘C

Annealing temperature 300∘C

Figure 4 XRD patterns of the 10 120583m Cu film annealed at differenttemperatures

the films exhibit X-ray reflections from Cu (111) (200) (220)and (311) To investigate the evolution of crystallite orien-tations with different annealing temperatures the texturecoefficient under different annealing temperatures is shownin Figures 5ndash7 for the films with thickness of 10 16 and30 120583m respectively

Advances in Materials Science and Engineering 5

0001020304050607080910

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 5 Texture coefficients of the 10 120583m Cu film annealed atdifferent temperatures

01

02

03

04

05

06

07

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 6 Texture coefficients of the 16 120583m Cu film annealed atdifferent temperatures

The main driving force for subsequent grain growth isminimum total free energy (surface energy grain interfaceenergy and film strain energy) [21] For thinner films graingrowth is under the control of surface energy minimizationOnly a few grains can grow whose surface energy is relativelylower than the others Grains whose surface energy is higherwill be merged into adjacent grains Grain growth eliminatesfree surface and thus the total surface energy decreasesaccordingly However for thicker films grain growth is underthe control of strain energy minimization For face-centeredcubic (fcc) metals grain orientation which has the lowestplastic strain energy is the (220) plane [24] Development ofstrain energy minimizing textures does not minimize surfaceand interface energies [25 26] Therefore surface struc-ture of the copper films with different thicknesses reflects

016

020

024

028

032

036

040

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 7 Texture coefficients of the 30 120583m Cu film annealed atdifferent temperatures

a dynamic equilibrium between surface energy and strainenergy Surface energy is very important for the structure ofthinner films whereas strain energy is very important for thestructure of thicker films

During the annealing processes the intensity of the(220) grain increases but that of the (111) grain decreases Apreferred grain orientation (220) after annealing is observedwhile (111) is the preferred orientation before annealing Theeffect of yield in grain is proposed to explain the (220)preferred orientation during annealing When the annealingtemperatures increase thin films will start to yield Also theminimum strain energy will control the grain growth In-plane stress in a grain is a function of grain orientation factor119862119894119895119896 and the yield stress of the grain also varies depending

on its orientationThe orientation factor 119862119894119895119896

of (220) has thesmallest one of 142 while that of (111) has the largest one of346 [27] When the thin films start to yield for grains ofequal initial sizes the (220) grains will yield before the (111)grains thus the (220) grains have an energetic advantage forfurther growth [28] This yielding process also leads to strainenergy minimization This may explain why the (220) grainsgrow faster than other grains and become the final preferredorientation

In addition initial grain size also has an effect on thetexture evolution With a certain volume the smaller andthe more uniform the grain is the more evenly the strainenergy will disperse to all the grain So the distribution ofinternal stress (the stress due to difference in the thermalexpansion coefficients and thickness between films and sub-strates during annealing) will be more even which will makethe grain with minimization strain energy grow easily andquickly Grain size in thin films is smaller than thick filmsWe can see from Figures 5ndash7 that the finial texture coefficientafter annealing at 500∘C in thick films is less than thin films

33 Mechanical Properties Nanoindentation was performedon all the Cu films annealed at different temperatures

6 Advances in Materials Science and Engineering

The typical load-indentation depth curves for the 30 120583mfilmannealed at different annealing temperatures are shown inFigure 8 It can be seen from Figure 8 that the loadunloadcurves for all the samples are nearly similar which maybe attributed to the similar crystalline nature of Cu filmsFigure 9 shows the hardness as a function of the annealingtemperature for the Cu films with various thicknesses Morerecent and systematic experiments indicate that both thegrain size and the film thickness have a marked influence onthe strength of thin films [29ndash32] Relationship between thehardness and the yield stress can be expressed as119867 = 3120590

119910 120590119910

is the yield stress and119867 is the hardnessEffect of different parts of microstructure on the yield

stress can be expressed as [29]

120590119910= 1205900+ 119896119889minus119899

+ 1198961015840

119905minus119898

(2)

where 1205900is the bulk yield stress (large-grained polycrystal)

119896119889minus119899 is the contribution from the grain boundaries (119889 grain

size) 1198961015840119905minus119898 is the contribution from the film surface orinterface (119905 film thickness) The first two terms togetherform the well-known Hall-Petch relation where 119899 = 05commonly Combining the data in Table 2 and Figure 9Figure 10 can be obtained which shows that the grain sizedependence of strength in Cu thin films on Si substratesfollowed a Hall-Petch type relation This is the describedHall-Petch effect that establishes a linear dependency ofthe hardness with the reciprocal square root of grain sizeClearly the strengthening of the sputtered copper films wasmainly attained by grain refinement The Hall-Petch effect isexplained in terms of a restriction in the movement of grainsthat is strengthening due to the formation of pileups in thelarger grain boundaries associated with low grain size FromFigure 8 we can see that the indentation depth increases withthe annealing temperatures under the same load which maybe a factor affecting the Hall-Petch type relation In additiongrain size changes with the films thickness which may beanother reason for the yield stress variation

Different load-indentation depth curves for the Cu filmsannealed at different temperatures imply different indenta-tion plastic characteristics for these films These curves canbe separated into the following three stages pure elasticdeformation stage at the beginning of the load elastic-plastic deformation stage after displacement jump and elasticresponse during unload It agrees with the Hertz contacttheory well during the elastic deformation stage The lowerthe annealing is the less the elastic displacement is Displace-ment jump caused by the dislocation pileup and incrementon the plastic deformation region increase with the increaseof the grain size With the decrease of the grain size thedensity of the grain boundaries increases It cannot only actas the source of dislocation but also decrease the dislocationactivation energy

The values of elastic modulus can also be obtainedby nanoindentation The Young modulus decreased 20compared to that of the traditional coarse-grained Cu Theelastic modulus is one of the intrinsic properties of a material[33] Elastic modulus is an important indicator to reflect thebond strength between the atoms Many factors can affect

0

5

10

15

20

25

30

35

40

As-deposited

0 100 200 300 400 500 600 700 800 900

Annealing temperature 500∘C

Annealing temperature 400∘C

Annealing temperature 300∘C

Load

P(m

N)

Indentation depth h (nm)

Figure 8 Load-indentation depth curves for the 30 120583m Cu filmsannealed at different temperatures

20

21

22

23

24

25

26

27

28

29

10 120583m16 120583m30 120583m

100 200 300 400 500

Annealing temperature T (∘C)

Har

dnes

sH(G

Pa)

Figure 9 Hardness versus annealing temperature for the Cu filmswith different thicknesses

the elastic modulus such as texture [33] grain coalescenceandmicrocrack [34] Elasticmodulus of the Cu thin filmswilldecrease 20when 13 of grain boundaries is destroyed basedon the microcrack mechanism

XRD diffraction technique was carried out to investi-gate the residual stress by the well-know sin2Ψ methodFigure 11 shows the relationship between residual stressand TC(111)TC(220) ratio in Cu films The film with (111)-orientated grains had the highest tensile one and that with(220)-orientated grains had the lowest tensile one Theresidual stress in as-deposited copper films reached a highvalue but decreased down to a minimum value after samplesannealing This was obviously due to the thermal relaxationof residual stresses and the annealing effect onmicrostructuredefects This may be due to the preferred growth of grainswhich leads to a change of residual stress

Advances in Materials Science and Engineering 7

05

06

07

08

09

10

004 005 006 007 008 009 010 011 012 013

Yield

stre

ss120590y

(GPa

)

dminus05 (nmminus05)

10 120583m16 120583m30 120583m

Figure 10 Trend of yield stress dependency on grain size for the Cufilms

03

06

09

12

15

18

21

0

20

40

60

80

100

Resid

ual s

tress

(MPa

)

TC(1

11)

TC(2

20)

Annealing temperature T (∘C)0 50 100 150 200 250 300 350 400 450

minus20

TC(111)TC(220) of 10 120583mTC(111)TC(220) of 16 120583mTC(111)TC(220) of 30 120583m

Residual stress of 10 120583mResidual stress of 16 120583mResidual stress of 30 120583m

Figure 11 TC(111)TC(220) ratio and residual stress versus anneal-ing temperatures of 10 120583m 16 120583m and 30 120583m

4 Conclusions

The effect of annealing treatment on magnetron sputteredCu films is investigated using AFM XRD and nanoinden-tation techniques Surface topography and microstructuralevolution after annealing is studied in detail Relationshipbetween themicrostructure and themechanical properties ofthe thin films is also proposed The higher the texture of (111)is the lower the resistivity isWith the increase of (111) texturetensile stress increases For microelectronic application largeresidual stress will cause cavity crack and peeling of Cu filmswhich will cause circuit deformation and even produce shortcircuit or open circuit Annealing is usually taken during ICAlthough the resistivity of Cu films decreased a little thereliability of the system is greatly increased

The following are our main conclusions

(1) Annealing treatment can provide enough energy forthe grain to growWhen the annealing temperature isless than 400∘C the higher the annealing temperatureis the more the energy for the grain growth will beWith the grain growth surface void is filled and thesurface RMS decreases However when the annealingtemperature is gt400∘C grain grows abnormally andcoalescence occurs Surface void defects and microc-racks increase and the surface RMS increases

(2) Films thickness grain size and annealing tempera-tures are the main factors that affect the microstruc-ture of the annealed Cu films The minimization ofenergy including surface energy interface energy andstrain energy (elastic strain energy and plastic strainenergy) controls the microstructural evolution

(3) The grain size dependence of strength in the Cuthin films on the Si substrates followed a Hall-Petchtype relation In addition grain size changes with thefilms thickness which may be another reason for theyield stress variationThe as-deposited Cu films are intensile state and have strong (111) orientation Duringthe annealing with the decreasing of (111) orientationtensile stress decreased The ratio of TC(111)TC(220)can be used as a merit for the state of residual stress

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project is supported by National Basic Research Devel-opment Program of China (973 Program Grant no 2009CB724200) Research Fund for the Doctoral Program ofHigher Education of China (Grant no 20111415120002) andShanxi Provincial Science Foundation for Youths of China(Grant no 2010021023-4)

References

[1] A A Volinsky J Vella I S Adhihetty et al ldquoMicrostructureand mechanical properties of electroplated Cu thin filmsrdquo inProceedings of the Materials Research Society Symposium vol649 pp Q 531ndashQ 536 Boston Mass USA November 2001

[2] S P Murarka ldquoMultilevel interconnections for ULSI and GSIerardquo Materials Science and Engineering R Reports vol 19 no3-4 pp 87ndash151 1997

[3] S P Murarka R J Gutmann A E Kaloyeros and W ALanford ldquoAdvanced multilayer metallization schemes withcopper as interconnection metalrdquoThin Solid Films vol 236 no1-2 pp 257ndash266 1993

[4] R W Vook ldquoElectrical control of surface electromigrationdamagerdquoThin Solid Films vol 305 no 1-2 pp 286ndash291 1997

[5] A Wiatrowski W M Posadowski G Jozwiak J SerafinczukR Szeloch and T Gotszalk ldquoStandard and self-sustainedmagnetron sputtering deposited Cu films investigated bymeans

8 Advances in Materials Science and Engineering

of AFM and XRDrdquoMicroelectronics Reliability vol 51 no 7 pp1203ndash1206 2011

[6] M-T Le Y-U Sohn J-W Lim and G-S Choi ldquoEffect ofsputtering power on the nucleation and growth of Cu filmsdeposited by magnetron sputteringrdquo Materials Transactionsvol 51 no 1 pp 116ndash120 2010

[7] AK Siker AKumar P Shukla P B Zantye andM SanganarialdquoEffect of multistep annealing on mechanical and surfaceproperties of electroplated Cu thin filmsrdquo Journal of ElectronicMaterials vol 32 no 10 pp 1028ndash1033 2003

[8] P Shukla A K Sikder P B Zantye A Kumar and MSanganaria ldquoEffect of annealing on the structural mechanicaland tribological properties of electroplated Cu thin filmsrdquoMaterials Research Society Symposium Proceedings vol 182 ppF3161ndashF3167 2004

[9] S KMukherjee L Joshi and P K Barhai ldquoA comparative studyof nanocrystalline Cu film deposited using anodic vacuum arcand dc magnetron sputteringrdquo Surface amp Coatings Technologyvol 205 no 19 pp 4582ndash4595 2011

[10] Z H Cao H M Lu and X K Meng ldquoBarrier layer andannealing temperature dependent microstructure evolution ofnanocrystalline Cu filmsrdquoMaterials Chemistry and Physics vol117 no 1 pp 321ndash325 2009

[11] B Okolo P Lamparter UWelzel TWagner and E JMittemei-jer ldquoThe effect of deposition parameters and substrate surfacecondition on texture morphology and stress in magnetron-sputter-deposited Cu thin filmsrdquo Thin Solid Films vol 474 no1-2 pp 50ndash63 2005

[12] Q X Zhao F Bian Y Zhou et al ldquoOptical emission electrontemperature and microstructure of Cu film prepared by mag-netron sputteringrdquo Materials Letters vol 62 no 25 pp 4140ndash4142 2008

[13] W D Nix J R Greer G Feng and E T Lilleodden ldquoDefor-mation at the nanometer and micrometer length scales effectsof strain gradients and dislocation starvationrdquoThin Solid Filmsvol 515 no 6 pp 3152ndash3157 2007

[14] Z P Bazant Z Guo H D Espinosa Y Zhu and B PengldquoEpitaxially influenced boundary layer model for size effect inthin metallic filmsrdquo Journal of Applied Physics vol 97 no 7Article ID 073506 2005

[15] H D Espinosa M Panico S Berbenni and K W SchwarzldquoDiscrete dislocation dynamics simulations to interpret plas-ticity size and surface effects in freestanding FCC thin filmsrdquoInternational Journal of Plasticity vol 22 no 11 pp 2091ndash21172006

[16] D S Gianola S van PetegemM Legros S Brandstetter H vanSwygenhoven and K J Hemker ldquoStress-assisted discontinuousgrain growth and its effect on the deformation behavior ofnanocrystalline aluminum thin filmsrdquo Acta Materialia vol 54no 8 pp 2253ndash2263 2006

[17] E Arzt ldquoSize effects in materials due to microstructural anddimensional constraints a comparative reviewrdquo Acta Materi-alia vol 46 no 16 pp 5611ndash5626 1998

[18] N-J Park D P Field M M Nowell and P R Besser ldquoEffect offilm thickness on the evolution of annealing texture in sputteredcopper filmsrdquo Journal of Electronic Materials vol 34 no 12 pp1500ndash1508 2005

[19] G M Pharr ldquoMeasurement of mechanical properties by ultra-low load indentationrdquoMaterials Science and Engineering A vol253 no 1-2 pp 151ndash159 1998

[20] J-M Zhang K-W Xu and V Ji ldquoCompetition between surfaceand strain energy during grain growth in free-standing and

attached Ag and Cu films on Si substratesrdquo Applied SurfaceScience vol 187 no 1-2 pp 60ndash67 2002

[21] V Weihnacht and W Bruckner ldquoAbnormal grain growth in 111textured Cu thin filmsrdquoThin Solid Films vol 418 no 2 pp 136ndash144 2002

[22] C V Thompson and R Carel ldquoTexture development in poly-crystalline thin filmsrdquoMaterials Science and Engineering B vol32 no 3 pp 211ndash219 1995

[23] C S Barret and T B Massalski Structure of Metals PergamonPress Oxford UK 1980

[24] J-M Zhang K-W Xu and M-R Zhang ldquoTheory of abnormalgrain growth in thin films and analysis of energy anisotropyrdquoActa Physica Sinica vol 52 no 5 pp 1207ndash1211 2003

[25] H LWei HHuang CHWoo R K Zheng GHWen andXX Zhang ldquoDevelopment of ⟨110⟩ texture in copper thin filmsrdquoApplied Physics Letters vol 80 no 13 pp 2290ndash2292 2002

[26] RCarel CVThompson andH J Frost ldquoComputer simulationof strain energy effects vs surface and interface energy effects ongrain growth in thin filmsrdquo Acta Materialia vol 44 no 6 pp2479ndash2494 1996

[27] J E Sanchez Jr and E Arzt ldquoEffects of grain orientation onhillock formation and grain growth in aluminum films onsilicon substratesrdquo Scripta Metallurgica et Materiala vol 27 no3 pp 285ndash290 1992

[28] F Spaepen ldquoSubstrate curvature resulting from the capillaryforces of a liquid droprdquo Journal of the Mechanics and Physics ofSolids vol 44 no 5 pp 675ndash681 1996

[29] Y-J Choi and S Suresh ldquoSize effects on the mechanicalproperties of thin polycrystalline metal films on substratesrdquoActa Materialia vol 50 no 7 pp 1881ndash1893 2002

[30] M A Meyers A Mishra and D J Benson ldquoMechanicalproperties of nanocrystalline materialsrdquo Progress in MaterialsScience vol 51 no 4 pp 427ndash556 2006

[31] D Y W Yu and F Spaepen ldquoThe yield strength of thin copperfilms on Kaptonrdquo Journal of Applied Physics vol 95 no 6 pp2991ndash2997 2004

[32] W D Nix and H Gao ldquoIndentation size effects in crystallinematerials a law for strain gradient plasticityrdquo Journal of theMechanics and Physics of Solids vol 46 no 3 pp 411ndash425 1998

[33] S H Hong K S Kim Y-M Kim J-H Hahn C-S Leeand J-H Park ldquoCharacterization of elastic moduli of Cu thinfilms using nanoindentation techniquerdquoComposites Science andTechnology vol 65 no 9 pp 1401ndash1408 2005

[34] N R Shamsutdinov A J Bottger and B J Thijsse ldquoGrain coa-lescence and its effect on stress and elasticity in nanocrystallinemetal filmsrdquo Acta Materialia vol 55 no 3 pp 777ndash784 2007

Submit your manuscripts athttpwwwhindawicom

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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CeramicsJournal of

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CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

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NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Advances in Materials Science and Engineering 5

0001020304050607080910

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 5 Texture coefficients of the 10 120583m Cu film annealed atdifferent temperatures

01

02

03

04

05

06

07

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 6 Texture coefficients of the 16 120583m Cu film annealed atdifferent temperatures

The main driving force for subsequent grain growth isminimum total free energy (surface energy grain interfaceenergy and film strain energy) [21] For thinner films graingrowth is under the control of surface energy minimizationOnly a few grains can grow whose surface energy is relativelylower than the others Grains whose surface energy is higherwill be merged into adjacent grains Grain growth eliminatesfree surface and thus the total surface energy decreasesaccordingly However for thicker films grain growth is underthe control of strain energy minimization For face-centeredcubic (fcc) metals grain orientation which has the lowestplastic strain energy is the (220) plane [24] Development ofstrain energy minimizing textures does not minimize surfaceand interface energies [25 26] Therefore surface struc-ture of the copper films with different thicknesses reflects

016

020

024

028

032

036

040

Text

ure c

oeffi

cien

t TC

100 200 300 400 500

Annealing temperature T (∘C)

(111)(200)

(220)(311)

Figure 7 Texture coefficients of the 30 120583m Cu film annealed atdifferent temperatures

a dynamic equilibrium between surface energy and strainenergy Surface energy is very important for the structure ofthinner films whereas strain energy is very important for thestructure of thicker films

During the annealing processes the intensity of the(220) grain increases but that of the (111) grain decreases Apreferred grain orientation (220) after annealing is observedwhile (111) is the preferred orientation before annealing Theeffect of yield in grain is proposed to explain the (220)preferred orientation during annealing When the annealingtemperatures increase thin films will start to yield Also theminimum strain energy will control the grain growth In-plane stress in a grain is a function of grain orientation factor119862119894119895119896 and the yield stress of the grain also varies depending

on its orientationThe orientation factor 119862119894119895119896

of (220) has thesmallest one of 142 while that of (111) has the largest one of346 [27] When the thin films start to yield for grains ofequal initial sizes the (220) grains will yield before the (111)grains thus the (220) grains have an energetic advantage forfurther growth [28] This yielding process also leads to strainenergy minimization This may explain why the (220) grainsgrow faster than other grains and become the final preferredorientation

In addition initial grain size also has an effect on thetexture evolution With a certain volume the smaller andthe more uniform the grain is the more evenly the strainenergy will disperse to all the grain So the distribution ofinternal stress (the stress due to difference in the thermalexpansion coefficients and thickness between films and sub-strates during annealing) will be more even which will makethe grain with minimization strain energy grow easily andquickly Grain size in thin films is smaller than thick filmsWe can see from Figures 5ndash7 that the finial texture coefficientafter annealing at 500∘C in thick films is less than thin films

33 Mechanical Properties Nanoindentation was performedon all the Cu films annealed at different temperatures

6 Advances in Materials Science and Engineering

The typical load-indentation depth curves for the 30 120583mfilmannealed at different annealing temperatures are shown inFigure 8 It can be seen from Figure 8 that the loadunloadcurves for all the samples are nearly similar which maybe attributed to the similar crystalline nature of Cu filmsFigure 9 shows the hardness as a function of the annealingtemperature for the Cu films with various thicknesses Morerecent and systematic experiments indicate that both thegrain size and the film thickness have a marked influence onthe strength of thin films [29ndash32] Relationship between thehardness and the yield stress can be expressed as119867 = 3120590

119910 120590119910

is the yield stress and119867 is the hardnessEffect of different parts of microstructure on the yield

stress can be expressed as [29]

120590119910= 1205900+ 119896119889minus119899

+ 1198961015840

119905minus119898

(2)

where 1205900is the bulk yield stress (large-grained polycrystal)

119896119889minus119899 is the contribution from the grain boundaries (119889 grain

size) 1198961015840119905minus119898 is the contribution from the film surface orinterface (119905 film thickness) The first two terms togetherform the well-known Hall-Petch relation where 119899 = 05commonly Combining the data in Table 2 and Figure 9Figure 10 can be obtained which shows that the grain sizedependence of strength in Cu thin films on Si substratesfollowed a Hall-Petch type relation This is the describedHall-Petch effect that establishes a linear dependency ofthe hardness with the reciprocal square root of grain sizeClearly the strengthening of the sputtered copper films wasmainly attained by grain refinement The Hall-Petch effect isexplained in terms of a restriction in the movement of grainsthat is strengthening due to the formation of pileups in thelarger grain boundaries associated with low grain size FromFigure 8 we can see that the indentation depth increases withthe annealing temperatures under the same load which maybe a factor affecting the Hall-Petch type relation In additiongrain size changes with the films thickness which may beanother reason for the yield stress variation

Different load-indentation depth curves for the Cu filmsannealed at different temperatures imply different indenta-tion plastic characteristics for these films These curves canbe separated into the following three stages pure elasticdeformation stage at the beginning of the load elastic-plastic deformation stage after displacement jump and elasticresponse during unload It agrees with the Hertz contacttheory well during the elastic deformation stage The lowerthe annealing is the less the elastic displacement is Displace-ment jump caused by the dislocation pileup and incrementon the plastic deformation region increase with the increaseof the grain size With the decrease of the grain size thedensity of the grain boundaries increases It cannot only actas the source of dislocation but also decrease the dislocationactivation energy

The values of elastic modulus can also be obtainedby nanoindentation The Young modulus decreased 20compared to that of the traditional coarse-grained Cu Theelastic modulus is one of the intrinsic properties of a material[33] Elastic modulus is an important indicator to reflect thebond strength between the atoms Many factors can affect

0

5

10

15

20

25

30

35

40

As-deposited

0 100 200 300 400 500 600 700 800 900

Annealing temperature 500∘C

Annealing temperature 400∘C

Annealing temperature 300∘C

Load

P(m

N)

Indentation depth h (nm)

Figure 8 Load-indentation depth curves for the 30 120583m Cu filmsannealed at different temperatures

20

21

22

23

24

25

26

27

28

29

10 120583m16 120583m30 120583m

100 200 300 400 500

Annealing temperature T (∘C)

Har

dnes

sH(G

Pa)

Figure 9 Hardness versus annealing temperature for the Cu filmswith different thicknesses

the elastic modulus such as texture [33] grain coalescenceandmicrocrack [34] Elasticmodulus of the Cu thin filmswilldecrease 20when 13 of grain boundaries is destroyed basedon the microcrack mechanism

XRD diffraction technique was carried out to investi-gate the residual stress by the well-know sin2Ψ methodFigure 11 shows the relationship between residual stressand TC(111)TC(220) ratio in Cu films The film with (111)-orientated grains had the highest tensile one and that with(220)-orientated grains had the lowest tensile one Theresidual stress in as-deposited copper films reached a highvalue but decreased down to a minimum value after samplesannealing This was obviously due to the thermal relaxationof residual stresses and the annealing effect onmicrostructuredefects This may be due to the preferred growth of grainswhich leads to a change of residual stress

Advances in Materials Science and Engineering 7

05

06

07

08

09

10

004 005 006 007 008 009 010 011 012 013

Yield

stre

ss120590y

(GPa

)

dminus05 (nmminus05)

10 120583m16 120583m30 120583m

Figure 10 Trend of yield stress dependency on grain size for the Cufilms

03

06

09

12

15

18

21

0

20

40

60

80

100

Resid

ual s

tress

(MPa

)

TC(1

11)

TC(2

20)

Annealing temperature T (∘C)0 50 100 150 200 250 300 350 400 450

minus20

TC(111)TC(220) of 10 120583mTC(111)TC(220) of 16 120583mTC(111)TC(220) of 30 120583m

Residual stress of 10 120583mResidual stress of 16 120583mResidual stress of 30 120583m

Figure 11 TC(111)TC(220) ratio and residual stress versus anneal-ing temperatures of 10 120583m 16 120583m and 30 120583m

4 Conclusions

The effect of annealing treatment on magnetron sputteredCu films is investigated using AFM XRD and nanoinden-tation techniques Surface topography and microstructuralevolution after annealing is studied in detail Relationshipbetween themicrostructure and themechanical properties ofthe thin films is also proposed The higher the texture of (111)is the lower the resistivity isWith the increase of (111) texturetensile stress increases For microelectronic application largeresidual stress will cause cavity crack and peeling of Cu filmswhich will cause circuit deformation and even produce shortcircuit or open circuit Annealing is usually taken during ICAlthough the resistivity of Cu films decreased a little thereliability of the system is greatly increased

The following are our main conclusions

(1) Annealing treatment can provide enough energy forthe grain to growWhen the annealing temperature isless than 400∘C the higher the annealing temperatureis the more the energy for the grain growth will beWith the grain growth surface void is filled and thesurface RMS decreases However when the annealingtemperature is gt400∘C grain grows abnormally andcoalescence occurs Surface void defects and microc-racks increase and the surface RMS increases

(2) Films thickness grain size and annealing tempera-tures are the main factors that affect the microstruc-ture of the annealed Cu films The minimization ofenergy including surface energy interface energy andstrain energy (elastic strain energy and plastic strainenergy) controls the microstructural evolution

(3) The grain size dependence of strength in the Cuthin films on the Si substrates followed a Hall-Petchtype relation In addition grain size changes with thefilms thickness which may be another reason for theyield stress variationThe as-deposited Cu films are intensile state and have strong (111) orientation Duringthe annealing with the decreasing of (111) orientationtensile stress decreased The ratio of TC(111)TC(220)can be used as a merit for the state of residual stress

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project is supported by National Basic Research Devel-opment Program of China (973 Program Grant no 2009CB724200) Research Fund for the Doctoral Program ofHigher Education of China (Grant no 20111415120002) andShanxi Provincial Science Foundation for Youths of China(Grant no 2010021023-4)

References

[1] A A Volinsky J Vella I S Adhihetty et al ldquoMicrostructureand mechanical properties of electroplated Cu thin filmsrdquo inProceedings of the Materials Research Society Symposium vol649 pp Q 531ndashQ 536 Boston Mass USA November 2001

[2] S P Murarka ldquoMultilevel interconnections for ULSI and GSIerardquo Materials Science and Engineering R Reports vol 19 no3-4 pp 87ndash151 1997

[3] S P Murarka R J Gutmann A E Kaloyeros and W ALanford ldquoAdvanced multilayer metallization schemes withcopper as interconnection metalrdquoThin Solid Films vol 236 no1-2 pp 257ndash266 1993

[4] R W Vook ldquoElectrical control of surface electromigrationdamagerdquoThin Solid Films vol 305 no 1-2 pp 286ndash291 1997

[5] A Wiatrowski W M Posadowski G Jozwiak J SerafinczukR Szeloch and T Gotszalk ldquoStandard and self-sustainedmagnetron sputtering deposited Cu films investigated bymeans

8 Advances in Materials Science and Engineering

of AFM and XRDrdquoMicroelectronics Reliability vol 51 no 7 pp1203ndash1206 2011

[6] M-T Le Y-U Sohn J-W Lim and G-S Choi ldquoEffect ofsputtering power on the nucleation and growth of Cu filmsdeposited by magnetron sputteringrdquo Materials Transactionsvol 51 no 1 pp 116ndash120 2010

[7] AK Siker AKumar P Shukla P B Zantye andM SanganarialdquoEffect of multistep annealing on mechanical and surfaceproperties of electroplated Cu thin filmsrdquo Journal of ElectronicMaterials vol 32 no 10 pp 1028ndash1033 2003

[8] P Shukla A K Sikder P B Zantye A Kumar and MSanganaria ldquoEffect of annealing on the structural mechanicaland tribological properties of electroplated Cu thin filmsrdquoMaterials Research Society Symposium Proceedings vol 182 ppF3161ndashF3167 2004

[9] S KMukherjee L Joshi and P K Barhai ldquoA comparative studyof nanocrystalline Cu film deposited using anodic vacuum arcand dc magnetron sputteringrdquo Surface amp Coatings Technologyvol 205 no 19 pp 4582ndash4595 2011

[10] Z H Cao H M Lu and X K Meng ldquoBarrier layer andannealing temperature dependent microstructure evolution ofnanocrystalline Cu filmsrdquoMaterials Chemistry and Physics vol117 no 1 pp 321ndash325 2009

[11] B Okolo P Lamparter UWelzel TWagner and E JMittemei-jer ldquoThe effect of deposition parameters and substrate surfacecondition on texture morphology and stress in magnetron-sputter-deposited Cu thin filmsrdquo Thin Solid Films vol 474 no1-2 pp 50ndash63 2005

[12] Q X Zhao F Bian Y Zhou et al ldquoOptical emission electrontemperature and microstructure of Cu film prepared by mag-netron sputteringrdquo Materials Letters vol 62 no 25 pp 4140ndash4142 2008

[13] W D Nix J R Greer G Feng and E T Lilleodden ldquoDefor-mation at the nanometer and micrometer length scales effectsof strain gradients and dislocation starvationrdquoThin Solid Filmsvol 515 no 6 pp 3152ndash3157 2007

[14] Z P Bazant Z Guo H D Espinosa Y Zhu and B PengldquoEpitaxially influenced boundary layer model for size effect inthin metallic filmsrdquo Journal of Applied Physics vol 97 no 7Article ID 073506 2005

[15] H D Espinosa M Panico S Berbenni and K W SchwarzldquoDiscrete dislocation dynamics simulations to interpret plas-ticity size and surface effects in freestanding FCC thin filmsrdquoInternational Journal of Plasticity vol 22 no 11 pp 2091ndash21172006

[16] D S Gianola S van PetegemM Legros S Brandstetter H vanSwygenhoven and K J Hemker ldquoStress-assisted discontinuousgrain growth and its effect on the deformation behavior ofnanocrystalline aluminum thin filmsrdquo Acta Materialia vol 54no 8 pp 2253ndash2263 2006

[17] E Arzt ldquoSize effects in materials due to microstructural anddimensional constraints a comparative reviewrdquo Acta Materi-alia vol 46 no 16 pp 5611ndash5626 1998

[18] N-J Park D P Field M M Nowell and P R Besser ldquoEffect offilm thickness on the evolution of annealing texture in sputteredcopper filmsrdquo Journal of Electronic Materials vol 34 no 12 pp1500ndash1508 2005

[19] G M Pharr ldquoMeasurement of mechanical properties by ultra-low load indentationrdquoMaterials Science and Engineering A vol253 no 1-2 pp 151ndash159 1998

[20] J-M Zhang K-W Xu and V Ji ldquoCompetition between surfaceand strain energy during grain growth in free-standing and

attached Ag and Cu films on Si substratesrdquo Applied SurfaceScience vol 187 no 1-2 pp 60ndash67 2002

[21] V Weihnacht and W Bruckner ldquoAbnormal grain growth in 111textured Cu thin filmsrdquoThin Solid Films vol 418 no 2 pp 136ndash144 2002

[22] C V Thompson and R Carel ldquoTexture development in poly-crystalline thin filmsrdquoMaterials Science and Engineering B vol32 no 3 pp 211ndash219 1995

[23] C S Barret and T B Massalski Structure of Metals PergamonPress Oxford UK 1980

[24] J-M Zhang K-W Xu and M-R Zhang ldquoTheory of abnormalgrain growth in thin films and analysis of energy anisotropyrdquoActa Physica Sinica vol 52 no 5 pp 1207ndash1211 2003

[25] H LWei HHuang CHWoo R K Zheng GHWen andXX Zhang ldquoDevelopment of ⟨110⟩ texture in copper thin filmsrdquoApplied Physics Letters vol 80 no 13 pp 2290ndash2292 2002

[26] RCarel CVThompson andH J Frost ldquoComputer simulationof strain energy effects vs surface and interface energy effects ongrain growth in thin filmsrdquo Acta Materialia vol 44 no 6 pp2479ndash2494 1996

[27] J E Sanchez Jr and E Arzt ldquoEffects of grain orientation onhillock formation and grain growth in aluminum films onsilicon substratesrdquo Scripta Metallurgica et Materiala vol 27 no3 pp 285ndash290 1992

[28] F Spaepen ldquoSubstrate curvature resulting from the capillaryforces of a liquid droprdquo Journal of the Mechanics and Physics ofSolids vol 44 no 5 pp 675ndash681 1996

[29] Y-J Choi and S Suresh ldquoSize effects on the mechanicalproperties of thin polycrystalline metal films on substratesrdquoActa Materialia vol 50 no 7 pp 1881ndash1893 2002

[30] M A Meyers A Mishra and D J Benson ldquoMechanicalproperties of nanocrystalline materialsrdquo Progress in MaterialsScience vol 51 no 4 pp 427ndash556 2006

[31] D Y W Yu and F Spaepen ldquoThe yield strength of thin copperfilms on Kaptonrdquo Journal of Applied Physics vol 95 no 6 pp2991ndash2997 2004

[32] W D Nix and H Gao ldquoIndentation size effects in crystallinematerials a law for strain gradient plasticityrdquo Journal of theMechanics and Physics of Solids vol 46 no 3 pp 411ndash425 1998

[33] S H Hong K S Kim Y-M Kim J-H Hahn C-S Leeand J-H Park ldquoCharacterization of elastic moduli of Cu thinfilms using nanoindentation techniquerdquoComposites Science andTechnology vol 65 no 9 pp 1401ndash1408 2005

[34] N R Shamsutdinov A J Bottger and B J Thijsse ldquoGrain coa-lescence and its effect on stress and elasticity in nanocrystallinemetal filmsrdquo Acta Materialia vol 55 no 3 pp 777ndash784 2007

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

6 Advances in Materials Science and Engineering

The typical load-indentation depth curves for the 30 120583mfilmannealed at different annealing temperatures are shown inFigure 8 It can be seen from Figure 8 that the loadunloadcurves for all the samples are nearly similar which maybe attributed to the similar crystalline nature of Cu filmsFigure 9 shows the hardness as a function of the annealingtemperature for the Cu films with various thicknesses Morerecent and systematic experiments indicate that both thegrain size and the film thickness have a marked influence onthe strength of thin films [29ndash32] Relationship between thehardness and the yield stress can be expressed as119867 = 3120590

119910 120590119910

is the yield stress and119867 is the hardnessEffect of different parts of microstructure on the yield

stress can be expressed as [29]

120590119910= 1205900+ 119896119889minus119899

+ 1198961015840

119905minus119898

(2)

where 1205900is the bulk yield stress (large-grained polycrystal)

119896119889minus119899 is the contribution from the grain boundaries (119889 grain

size) 1198961015840119905minus119898 is the contribution from the film surface orinterface (119905 film thickness) The first two terms togetherform the well-known Hall-Petch relation where 119899 = 05commonly Combining the data in Table 2 and Figure 9Figure 10 can be obtained which shows that the grain sizedependence of strength in Cu thin films on Si substratesfollowed a Hall-Petch type relation This is the describedHall-Petch effect that establishes a linear dependency ofthe hardness with the reciprocal square root of grain sizeClearly the strengthening of the sputtered copper films wasmainly attained by grain refinement The Hall-Petch effect isexplained in terms of a restriction in the movement of grainsthat is strengthening due to the formation of pileups in thelarger grain boundaries associated with low grain size FromFigure 8 we can see that the indentation depth increases withthe annealing temperatures under the same load which maybe a factor affecting the Hall-Petch type relation In additiongrain size changes with the films thickness which may beanother reason for the yield stress variation

Different load-indentation depth curves for the Cu filmsannealed at different temperatures imply different indenta-tion plastic characteristics for these films These curves canbe separated into the following three stages pure elasticdeformation stage at the beginning of the load elastic-plastic deformation stage after displacement jump and elasticresponse during unload It agrees with the Hertz contacttheory well during the elastic deformation stage The lowerthe annealing is the less the elastic displacement is Displace-ment jump caused by the dislocation pileup and incrementon the plastic deformation region increase with the increaseof the grain size With the decrease of the grain size thedensity of the grain boundaries increases It cannot only actas the source of dislocation but also decrease the dislocationactivation energy

The values of elastic modulus can also be obtainedby nanoindentation The Young modulus decreased 20compared to that of the traditional coarse-grained Cu Theelastic modulus is one of the intrinsic properties of a material[33] Elastic modulus is an important indicator to reflect thebond strength between the atoms Many factors can affect

0

5

10

15

20

25

30

35

40

As-deposited

0 100 200 300 400 500 600 700 800 900

Annealing temperature 500∘C

Annealing temperature 400∘C

Annealing temperature 300∘C

Load

P(m

N)

Indentation depth h (nm)

Figure 8 Load-indentation depth curves for the 30 120583m Cu filmsannealed at different temperatures

20

21

22

23

24

25

26

27

28

29

10 120583m16 120583m30 120583m

100 200 300 400 500

Annealing temperature T (∘C)

Har

dnes

sH(G

Pa)

Figure 9 Hardness versus annealing temperature for the Cu filmswith different thicknesses

the elastic modulus such as texture [33] grain coalescenceandmicrocrack [34] Elasticmodulus of the Cu thin filmswilldecrease 20when 13 of grain boundaries is destroyed basedon the microcrack mechanism

XRD diffraction technique was carried out to investi-gate the residual stress by the well-know sin2Ψ methodFigure 11 shows the relationship between residual stressand TC(111)TC(220) ratio in Cu films The film with (111)-orientated grains had the highest tensile one and that with(220)-orientated grains had the lowest tensile one Theresidual stress in as-deposited copper films reached a highvalue but decreased down to a minimum value after samplesannealing This was obviously due to the thermal relaxationof residual stresses and the annealing effect onmicrostructuredefects This may be due to the preferred growth of grainswhich leads to a change of residual stress

Advances in Materials Science and Engineering 7

05

06

07

08

09

10

004 005 006 007 008 009 010 011 012 013

Yield

stre

ss120590y

(GPa

)

dminus05 (nmminus05)

10 120583m16 120583m30 120583m

Figure 10 Trend of yield stress dependency on grain size for the Cufilms

03

06

09

12

15

18

21

0

20

40

60

80

100

Resid

ual s

tress

(MPa

)

TC(1

11)

TC(2

20)

Annealing temperature T (∘C)0 50 100 150 200 250 300 350 400 450

minus20

TC(111)TC(220) of 10 120583mTC(111)TC(220) of 16 120583mTC(111)TC(220) of 30 120583m

Residual stress of 10 120583mResidual stress of 16 120583mResidual stress of 30 120583m

Figure 11 TC(111)TC(220) ratio and residual stress versus anneal-ing temperatures of 10 120583m 16 120583m and 30 120583m

4 Conclusions

The effect of annealing treatment on magnetron sputteredCu films is investigated using AFM XRD and nanoinden-tation techniques Surface topography and microstructuralevolution after annealing is studied in detail Relationshipbetween themicrostructure and themechanical properties ofthe thin films is also proposed The higher the texture of (111)is the lower the resistivity isWith the increase of (111) texturetensile stress increases For microelectronic application largeresidual stress will cause cavity crack and peeling of Cu filmswhich will cause circuit deformation and even produce shortcircuit or open circuit Annealing is usually taken during ICAlthough the resistivity of Cu films decreased a little thereliability of the system is greatly increased

The following are our main conclusions

(1) Annealing treatment can provide enough energy forthe grain to growWhen the annealing temperature isless than 400∘C the higher the annealing temperatureis the more the energy for the grain growth will beWith the grain growth surface void is filled and thesurface RMS decreases However when the annealingtemperature is gt400∘C grain grows abnormally andcoalescence occurs Surface void defects and microc-racks increase and the surface RMS increases

(2) Films thickness grain size and annealing tempera-tures are the main factors that affect the microstruc-ture of the annealed Cu films The minimization ofenergy including surface energy interface energy andstrain energy (elastic strain energy and plastic strainenergy) controls the microstructural evolution

(3) The grain size dependence of strength in the Cuthin films on the Si substrates followed a Hall-Petchtype relation In addition grain size changes with thefilms thickness which may be another reason for theyield stress variationThe as-deposited Cu films are intensile state and have strong (111) orientation Duringthe annealing with the decreasing of (111) orientationtensile stress decreased The ratio of TC(111)TC(220)can be used as a merit for the state of residual stress

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project is supported by National Basic Research Devel-opment Program of China (973 Program Grant no 2009CB724200) Research Fund for the Doctoral Program ofHigher Education of China (Grant no 20111415120002) andShanxi Provincial Science Foundation for Youths of China(Grant no 2010021023-4)

References

[1] A A Volinsky J Vella I S Adhihetty et al ldquoMicrostructureand mechanical properties of electroplated Cu thin filmsrdquo inProceedings of the Materials Research Society Symposium vol649 pp Q 531ndashQ 536 Boston Mass USA November 2001

[2] S P Murarka ldquoMultilevel interconnections for ULSI and GSIerardquo Materials Science and Engineering R Reports vol 19 no3-4 pp 87ndash151 1997

[3] S P Murarka R J Gutmann A E Kaloyeros and W ALanford ldquoAdvanced multilayer metallization schemes withcopper as interconnection metalrdquoThin Solid Films vol 236 no1-2 pp 257ndash266 1993

[4] R W Vook ldquoElectrical control of surface electromigrationdamagerdquoThin Solid Films vol 305 no 1-2 pp 286ndash291 1997

[5] A Wiatrowski W M Posadowski G Jozwiak J SerafinczukR Szeloch and T Gotszalk ldquoStandard and self-sustainedmagnetron sputtering deposited Cu films investigated bymeans

8 Advances in Materials Science and Engineering

of AFM and XRDrdquoMicroelectronics Reliability vol 51 no 7 pp1203ndash1206 2011

[6] M-T Le Y-U Sohn J-W Lim and G-S Choi ldquoEffect ofsputtering power on the nucleation and growth of Cu filmsdeposited by magnetron sputteringrdquo Materials Transactionsvol 51 no 1 pp 116ndash120 2010

[7] AK Siker AKumar P Shukla P B Zantye andM SanganarialdquoEffect of multistep annealing on mechanical and surfaceproperties of electroplated Cu thin filmsrdquo Journal of ElectronicMaterials vol 32 no 10 pp 1028ndash1033 2003

[8] P Shukla A K Sikder P B Zantye A Kumar and MSanganaria ldquoEffect of annealing on the structural mechanicaland tribological properties of electroplated Cu thin filmsrdquoMaterials Research Society Symposium Proceedings vol 182 ppF3161ndashF3167 2004

[9] S KMukherjee L Joshi and P K Barhai ldquoA comparative studyof nanocrystalline Cu film deposited using anodic vacuum arcand dc magnetron sputteringrdquo Surface amp Coatings Technologyvol 205 no 19 pp 4582ndash4595 2011

[10] Z H Cao H M Lu and X K Meng ldquoBarrier layer andannealing temperature dependent microstructure evolution ofnanocrystalline Cu filmsrdquoMaterials Chemistry and Physics vol117 no 1 pp 321ndash325 2009

[11] B Okolo P Lamparter UWelzel TWagner and E JMittemei-jer ldquoThe effect of deposition parameters and substrate surfacecondition on texture morphology and stress in magnetron-sputter-deposited Cu thin filmsrdquo Thin Solid Films vol 474 no1-2 pp 50ndash63 2005

[12] Q X Zhao F Bian Y Zhou et al ldquoOptical emission electrontemperature and microstructure of Cu film prepared by mag-netron sputteringrdquo Materials Letters vol 62 no 25 pp 4140ndash4142 2008

[13] W D Nix J R Greer G Feng and E T Lilleodden ldquoDefor-mation at the nanometer and micrometer length scales effectsof strain gradients and dislocation starvationrdquoThin Solid Filmsvol 515 no 6 pp 3152ndash3157 2007

[14] Z P Bazant Z Guo H D Espinosa Y Zhu and B PengldquoEpitaxially influenced boundary layer model for size effect inthin metallic filmsrdquo Journal of Applied Physics vol 97 no 7Article ID 073506 2005

[15] H D Espinosa M Panico S Berbenni and K W SchwarzldquoDiscrete dislocation dynamics simulations to interpret plas-ticity size and surface effects in freestanding FCC thin filmsrdquoInternational Journal of Plasticity vol 22 no 11 pp 2091ndash21172006

[16] D S Gianola S van PetegemM Legros S Brandstetter H vanSwygenhoven and K J Hemker ldquoStress-assisted discontinuousgrain growth and its effect on the deformation behavior ofnanocrystalline aluminum thin filmsrdquo Acta Materialia vol 54no 8 pp 2253ndash2263 2006

[17] E Arzt ldquoSize effects in materials due to microstructural anddimensional constraints a comparative reviewrdquo Acta Materi-alia vol 46 no 16 pp 5611ndash5626 1998

[18] N-J Park D P Field M M Nowell and P R Besser ldquoEffect offilm thickness on the evolution of annealing texture in sputteredcopper filmsrdquo Journal of Electronic Materials vol 34 no 12 pp1500ndash1508 2005

[19] G M Pharr ldquoMeasurement of mechanical properties by ultra-low load indentationrdquoMaterials Science and Engineering A vol253 no 1-2 pp 151ndash159 1998

[20] J-M Zhang K-W Xu and V Ji ldquoCompetition between surfaceand strain energy during grain growth in free-standing and

attached Ag and Cu films on Si substratesrdquo Applied SurfaceScience vol 187 no 1-2 pp 60ndash67 2002

[21] V Weihnacht and W Bruckner ldquoAbnormal grain growth in 111textured Cu thin filmsrdquoThin Solid Films vol 418 no 2 pp 136ndash144 2002

[22] C V Thompson and R Carel ldquoTexture development in poly-crystalline thin filmsrdquoMaterials Science and Engineering B vol32 no 3 pp 211ndash219 1995

[23] C S Barret and T B Massalski Structure of Metals PergamonPress Oxford UK 1980

[24] J-M Zhang K-W Xu and M-R Zhang ldquoTheory of abnormalgrain growth in thin films and analysis of energy anisotropyrdquoActa Physica Sinica vol 52 no 5 pp 1207ndash1211 2003

[25] H LWei HHuang CHWoo R K Zheng GHWen andXX Zhang ldquoDevelopment of ⟨110⟩ texture in copper thin filmsrdquoApplied Physics Letters vol 80 no 13 pp 2290ndash2292 2002

[26] RCarel CVThompson andH J Frost ldquoComputer simulationof strain energy effects vs surface and interface energy effects ongrain growth in thin filmsrdquo Acta Materialia vol 44 no 6 pp2479ndash2494 1996

[27] J E Sanchez Jr and E Arzt ldquoEffects of grain orientation onhillock formation and grain growth in aluminum films onsilicon substratesrdquo Scripta Metallurgica et Materiala vol 27 no3 pp 285ndash290 1992

[28] F Spaepen ldquoSubstrate curvature resulting from the capillaryforces of a liquid droprdquo Journal of the Mechanics and Physics ofSolids vol 44 no 5 pp 675ndash681 1996

[29] Y-J Choi and S Suresh ldquoSize effects on the mechanicalproperties of thin polycrystalline metal films on substratesrdquoActa Materialia vol 50 no 7 pp 1881ndash1893 2002

[30] M A Meyers A Mishra and D J Benson ldquoMechanicalproperties of nanocrystalline materialsrdquo Progress in MaterialsScience vol 51 no 4 pp 427ndash556 2006

[31] D Y W Yu and F Spaepen ldquoThe yield strength of thin copperfilms on Kaptonrdquo Journal of Applied Physics vol 95 no 6 pp2991ndash2997 2004

[32] W D Nix and H Gao ldquoIndentation size effects in crystallinematerials a law for strain gradient plasticityrdquo Journal of theMechanics and Physics of Solids vol 46 no 3 pp 411ndash425 1998

[33] S H Hong K S Kim Y-M Kim J-H Hahn C-S Leeand J-H Park ldquoCharacterization of elastic moduli of Cu thinfilms using nanoindentation techniquerdquoComposites Science andTechnology vol 65 no 9 pp 1401ndash1408 2005

[34] N R Shamsutdinov A J Bottger and B J Thijsse ldquoGrain coa-lescence and its effect on stress and elasticity in nanocrystallinemetal filmsrdquo Acta Materialia vol 55 no 3 pp 777ndash784 2007

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Advances in Materials Science and Engineering 7

05

06

07

08

09

10

004 005 006 007 008 009 010 011 012 013

Yield

stre

ss120590y

(GPa

)

dminus05 (nmminus05)

10 120583m16 120583m30 120583m

Figure 10 Trend of yield stress dependency on grain size for the Cufilms

03

06

09

12

15

18

21

0

20

40

60

80

100

Resid

ual s

tress

(MPa

)

TC(1

11)

TC(2

20)

Annealing temperature T (∘C)0 50 100 150 200 250 300 350 400 450

minus20

TC(111)TC(220) of 10 120583mTC(111)TC(220) of 16 120583mTC(111)TC(220) of 30 120583m

Residual stress of 10 120583mResidual stress of 16 120583mResidual stress of 30 120583m

Figure 11 TC(111)TC(220) ratio and residual stress versus anneal-ing temperatures of 10 120583m 16 120583m and 30 120583m

4 Conclusions

The effect of annealing treatment on magnetron sputteredCu films is investigated using AFM XRD and nanoinden-tation techniques Surface topography and microstructuralevolution after annealing is studied in detail Relationshipbetween themicrostructure and themechanical properties ofthe thin films is also proposed The higher the texture of (111)is the lower the resistivity isWith the increase of (111) texturetensile stress increases For microelectronic application largeresidual stress will cause cavity crack and peeling of Cu filmswhich will cause circuit deformation and even produce shortcircuit or open circuit Annealing is usually taken during ICAlthough the resistivity of Cu films decreased a little thereliability of the system is greatly increased

The following are our main conclusions

(1) Annealing treatment can provide enough energy forthe grain to growWhen the annealing temperature isless than 400∘C the higher the annealing temperatureis the more the energy for the grain growth will beWith the grain growth surface void is filled and thesurface RMS decreases However when the annealingtemperature is gt400∘C grain grows abnormally andcoalescence occurs Surface void defects and microc-racks increase and the surface RMS increases

(2) Films thickness grain size and annealing tempera-tures are the main factors that affect the microstruc-ture of the annealed Cu films The minimization ofenergy including surface energy interface energy andstrain energy (elastic strain energy and plastic strainenergy) controls the microstructural evolution

(3) The grain size dependence of strength in the Cuthin films on the Si substrates followed a Hall-Petchtype relation In addition grain size changes with thefilms thickness which may be another reason for theyield stress variationThe as-deposited Cu films are intensile state and have strong (111) orientation Duringthe annealing with the decreasing of (111) orientationtensile stress decreased The ratio of TC(111)TC(220)can be used as a merit for the state of residual stress

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project is supported by National Basic Research Devel-opment Program of China (973 Program Grant no 2009CB724200) Research Fund for the Doctoral Program ofHigher Education of China (Grant no 20111415120002) andShanxi Provincial Science Foundation for Youths of China(Grant no 2010021023-4)

References

[1] A A Volinsky J Vella I S Adhihetty et al ldquoMicrostructureand mechanical properties of electroplated Cu thin filmsrdquo inProceedings of the Materials Research Society Symposium vol649 pp Q 531ndashQ 536 Boston Mass USA November 2001

[2] S P Murarka ldquoMultilevel interconnections for ULSI and GSIerardquo Materials Science and Engineering R Reports vol 19 no3-4 pp 87ndash151 1997

[3] S P Murarka R J Gutmann A E Kaloyeros and W ALanford ldquoAdvanced multilayer metallization schemes withcopper as interconnection metalrdquoThin Solid Films vol 236 no1-2 pp 257ndash266 1993

[4] R W Vook ldquoElectrical control of surface electromigrationdamagerdquoThin Solid Films vol 305 no 1-2 pp 286ndash291 1997

[5] A Wiatrowski W M Posadowski G Jozwiak J SerafinczukR Szeloch and T Gotszalk ldquoStandard and self-sustainedmagnetron sputtering deposited Cu films investigated bymeans

8 Advances in Materials Science and Engineering

of AFM and XRDrdquoMicroelectronics Reliability vol 51 no 7 pp1203ndash1206 2011

[6] M-T Le Y-U Sohn J-W Lim and G-S Choi ldquoEffect ofsputtering power on the nucleation and growth of Cu filmsdeposited by magnetron sputteringrdquo Materials Transactionsvol 51 no 1 pp 116ndash120 2010

[7] AK Siker AKumar P Shukla P B Zantye andM SanganarialdquoEffect of multistep annealing on mechanical and surfaceproperties of electroplated Cu thin filmsrdquo Journal of ElectronicMaterials vol 32 no 10 pp 1028ndash1033 2003

[8] P Shukla A K Sikder P B Zantye A Kumar and MSanganaria ldquoEffect of annealing on the structural mechanicaland tribological properties of electroplated Cu thin filmsrdquoMaterials Research Society Symposium Proceedings vol 182 ppF3161ndashF3167 2004

[9] S KMukherjee L Joshi and P K Barhai ldquoA comparative studyof nanocrystalline Cu film deposited using anodic vacuum arcand dc magnetron sputteringrdquo Surface amp Coatings Technologyvol 205 no 19 pp 4582ndash4595 2011

[10] Z H Cao H M Lu and X K Meng ldquoBarrier layer andannealing temperature dependent microstructure evolution ofnanocrystalline Cu filmsrdquoMaterials Chemistry and Physics vol117 no 1 pp 321ndash325 2009

[11] B Okolo P Lamparter UWelzel TWagner and E JMittemei-jer ldquoThe effect of deposition parameters and substrate surfacecondition on texture morphology and stress in magnetron-sputter-deposited Cu thin filmsrdquo Thin Solid Films vol 474 no1-2 pp 50ndash63 2005

[12] Q X Zhao F Bian Y Zhou et al ldquoOptical emission electrontemperature and microstructure of Cu film prepared by mag-netron sputteringrdquo Materials Letters vol 62 no 25 pp 4140ndash4142 2008

[13] W D Nix J R Greer G Feng and E T Lilleodden ldquoDefor-mation at the nanometer and micrometer length scales effectsof strain gradients and dislocation starvationrdquoThin Solid Filmsvol 515 no 6 pp 3152ndash3157 2007

[14] Z P Bazant Z Guo H D Espinosa Y Zhu and B PengldquoEpitaxially influenced boundary layer model for size effect inthin metallic filmsrdquo Journal of Applied Physics vol 97 no 7Article ID 073506 2005

[15] H D Espinosa M Panico S Berbenni and K W SchwarzldquoDiscrete dislocation dynamics simulations to interpret plas-ticity size and surface effects in freestanding FCC thin filmsrdquoInternational Journal of Plasticity vol 22 no 11 pp 2091ndash21172006

[16] D S Gianola S van PetegemM Legros S Brandstetter H vanSwygenhoven and K J Hemker ldquoStress-assisted discontinuousgrain growth and its effect on the deformation behavior ofnanocrystalline aluminum thin filmsrdquo Acta Materialia vol 54no 8 pp 2253ndash2263 2006

[17] E Arzt ldquoSize effects in materials due to microstructural anddimensional constraints a comparative reviewrdquo Acta Materi-alia vol 46 no 16 pp 5611ndash5626 1998

[18] N-J Park D P Field M M Nowell and P R Besser ldquoEffect offilm thickness on the evolution of annealing texture in sputteredcopper filmsrdquo Journal of Electronic Materials vol 34 no 12 pp1500ndash1508 2005

[19] G M Pharr ldquoMeasurement of mechanical properties by ultra-low load indentationrdquoMaterials Science and Engineering A vol253 no 1-2 pp 151ndash159 1998

[20] J-M Zhang K-W Xu and V Ji ldquoCompetition between surfaceand strain energy during grain growth in free-standing and

attached Ag and Cu films on Si substratesrdquo Applied SurfaceScience vol 187 no 1-2 pp 60ndash67 2002

[21] V Weihnacht and W Bruckner ldquoAbnormal grain growth in 111textured Cu thin filmsrdquoThin Solid Films vol 418 no 2 pp 136ndash144 2002

[22] C V Thompson and R Carel ldquoTexture development in poly-crystalline thin filmsrdquoMaterials Science and Engineering B vol32 no 3 pp 211ndash219 1995

[23] C S Barret and T B Massalski Structure of Metals PergamonPress Oxford UK 1980

[24] J-M Zhang K-W Xu and M-R Zhang ldquoTheory of abnormalgrain growth in thin films and analysis of energy anisotropyrdquoActa Physica Sinica vol 52 no 5 pp 1207ndash1211 2003

[25] H LWei HHuang CHWoo R K Zheng GHWen andXX Zhang ldquoDevelopment of ⟨110⟩ texture in copper thin filmsrdquoApplied Physics Letters vol 80 no 13 pp 2290ndash2292 2002

[26] RCarel CVThompson andH J Frost ldquoComputer simulationof strain energy effects vs surface and interface energy effects ongrain growth in thin filmsrdquo Acta Materialia vol 44 no 6 pp2479ndash2494 1996

[27] J E Sanchez Jr and E Arzt ldquoEffects of grain orientation onhillock formation and grain growth in aluminum films onsilicon substratesrdquo Scripta Metallurgica et Materiala vol 27 no3 pp 285ndash290 1992

[28] F Spaepen ldquoSubstrate curvature resulting from the capillaryforces of a liquid droprdquo Journal of the Mechanics and Physics ofSolids vol 44 no 5 pp 675ndash681 1996

[29] Y-J Choi and S Suresh ldquoSize effects on the mechanicalproperties of thin polycrystalline metal films on substratesrdquoActa Materialia vol 50 no 7 pp 1881ndash1893 2002

[30] M A Meyers A Mishra and D J Benson ldquoMechanicalproperties of nanocrystalline materialsrdquo Progress in MaterialsScience vol 51 no 4 pp 427ndash556 2006

[31] D Y W Yu and F Spaepen ldquoThe yield strength of thin copperfilms on Kaptonrdquo Journal of Applied Physics vol 95 no 6 pp2991ndash2997 2004

[32] W D Nix and H Gao ldquoIndentation size effects in crystallinematerials a law for strain gradient plasticityrdquo Journal of theMechanics and Physics of Solids vol 46 no 3 pp 411ndash425 1998

[33] S H Hong K S Kim Y-M Kim J-H Hahn C-S Leeand J-H Park ldquoCharacterization of elastic moduli of Cu thinfilms using nanoindentation techniquerdquoComposites Science andTechnology vol 65 no 9 pp 1401ndash1408 2005

[34] N R Shamsutdinov A J Bottger and B J Thijsse ldquoGrain coa-lescence and its effect on stress and elasticity in nanocrystallinemetal filmsrdquo Acta Materialia vol 55 no 3 pp 777ndash784 2007

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

8 Advances in Materials Science and Engineering

of AFM and XRDrdquoMicroelectronics Reliability vol 51 no 7 pp1203ndash1206 2011

[6] M-T Le Y-U Sohn J-W Lim and G-S Choi ldquoEffect ofsputtering power on the nucleation and growth of Cu filmsdeposited by magnetron sputteringrdquo Materials Transactionsvol 51 no 1 pp 116ndash120 2010

[7] AK Siker AKumar P Shukla P B Zantye andM SanganarialdquoEffect of multistep annealing on mechanical and surfaceproperties of electroplated Cu thin filmsrdquo Journal of ElectronicMaterials vol 32 no 10 pp 1028ndash1033 2003

[8] P Shukla A K Sikder P B Zantye A Kumar and MSanganaria ldquoEffect of annealing on the structural mechanicaland tribological properties of electroplated Cu thin filmsrdquoMaterials Research Society Symposium Proceedings vol 182 ppF3161ndashF3167 2004

[9] S KMukherjee L Joshi and P K Barhai ldquoA comparative studyof nanocrystalline Cu film deposited using anodic vacuum arcand dc magnetron sputteringrdquo Surface amp Coatings Technologyvol 205 no 19 pp 4582ndash4595 2011

[10] Z H Cao H M Lu and X K Meng ldquoBarrier layer andannealing temperature dependent microstructure evolution ofnanocrystalline Cu filmsrdquoMaterials Chemistry and Physics vol117 no 1 pp 321ndash325 2009

[11] B Okolo P Lamparter UWelzel TWagner and E JMittemei-jer ldquoThe effect of deposition parameters and substrate surfacecondition on texture morphology and stress in magnetron-sputter-deposited Cu thin filmsrdquo Thin Solid Films vol 474 no1-2 pp 50ndash63 2005

[12] Q X Zhao F Bian Y Zhou et al ldquoOptical emission electrontemperature and microstructure of Cu film prepared by mag-netron sputteringrdquo Materials Letters vol 62 no 25 pp 4140ndash4142 2008

[13] W D Nix J R Greer G Feng and E T Lilleodden ldquoDefor-mation at the nanometer and micrometer length scales effectsof strain gradients and dislocation starvationrdquoThin Solid Filmsvol 515 no 6 pp 3152ndash3157 2007

[14] Z P Bazant Z Guo H D Espinosa Y Zhu and B PengldquoEpitaxially influenced boundary layer model for size effect inthin metallic filmsrdquo Journal of Applied Physics vol 97 no 7Article ID 073506 2005

[15] H D Espinosa M Panico S Berbenni and K W SchwarzldquoDiscrete dislocation dynamics simulations to interpret plas-ticity size and surface effects in freestanding FCC thin filmsrdquoInternational Journal of Plasticity vol 22 no 11 pp 2091ndash21172006

[16] D S Gianola S van PetegemM Legros S Brandstetter H vanSwygenhoven and K J Hemker ldquoStress-assisted discontinuousgrain growth and its effect on the deformation behavior ofnanocrystalline aluminum thin filmsrdquo Acta Materialia vol 54no 8 pp 2253ndash2263 2006

[17] E Arzt ldquoSize effects in materials due to microstructural anddimensional constraints a comparative reviewrdquo Acta Materi-alia vol 46 no 16 pp 5611ndash5626 1998

[18] N-J Park D P Field M M Nowell and P R Besser ldquoEffect offilm thickness on the evolution of annealing texture in sputteredcopper filmsrdquo Journal of Electronic Materials vol 34 no 12 pp1500ndash1508 2005

[19] G M Pharr ldquoMeasurement of mechanical properties by ultra-low load indentationrdquoMaterials Science and Engineering A vol253 no 1-2 pp 151ndash159 1998

[20] J-M Zhang K-W Xu and V Ji ldquoCompetition between surfaceand strain energy during grain growth in free-standing and

attached Ag and Cu films on Si substratesrdquo Applied SurfaceScience vol 187 no 1-2 pp 60ndash67 2002

[21] V Weihnacht and W Bruckner ldquoAbnormal grain growth in 111textured Cu thin filmsrdquoThin Solid Films vol 418 no 2 pp 136ndash144 2002

[22] C V Thompson and R Carel ldquoTexture development in poly-crystalline thin filmsrdquoMaterials Science and Engineering B vol32 no 3 pp 211ndash219 1995

[23] C S Barret and T B Massalski Structure of Metals PergamonPress Oxford UK 1980

[24] J-M Zhang K-W Xu and M-R Zhang ldquoTheory of abnormalgrain growth in thin films and analysis of energy anisotropyrdquoActa Physica Sinica vol 52 no 5 pp 1207ndash1211 2003

[25] H LWei HHuang CHWoo R K Zheng GHWen andXX Zhang ldquoDevelopment of ⟨110⟩ texture in copper thin filmsrdquoApplied Physics Letters vol 80 no 13 pp 2290ndash2292 2002

[26] RCarel CVThompson andH J Frost ldquoComputer simulationof strain energy effects vs surface and interface energy effects ongrain growth in thin filmsrdquo Acta Materialia vol 44 no 6 pp2479ndash2494 1996

[27] J E Sanchez Jr and E Arzt ldquoEffects of grain orientation onhillock formation and grain growth in aluminum films onsilicon substratesrdquo Scripta Metallurgica et Materiala vol 27 no3 pp 285ndash290 1992

[28] F Spaepen ldquoSubstrate curvature resulting from the capillaryforces of a liquid droprdquo Journal of the Mechanics and Physics ofSolids vol 44 no 5 pp 675ndash681 1996

[29] Y-J Choi and S Suresh ldquoSize effects on the mechanicalproperties of thin polycrystalline metal films on substratesrdquoActa Materialia vol 50 no 7 pp 1881ndash1893 2002

[30] M A Meyers A Mishra and D J Benson ldquoMechanicalproperties of nanocrystalline materialsrdquo Progress in MaterialsScience vol 51 no 4 pp 427ndash556 2006

[31] D Y W Yu and F Spaepen ldquoThe yield strength of thin copperfilms on Kaptonrdquo Journal of Applied Physics vol 95 no 6 pp2991ndash2997 2004

[32] W D Nix and H Gao ldquoIndentation size effects in crystallinematerials a law for strain gradient plasticityrdquo Journal of theMechanics and Physics of Solids vol 46 no 3 pp 411ndash425 1998

[33] S H Hong K S Kim Y-M Kim J-H Hahn C-S Leeand J-H Park ldquoCharacterization of elastic moduli of Cu thinfilms using nanoindentation techniquerdquoComposites Science andTechnology vol 65 no 9 pp 1401ndash1408 2005

[34] N R Shamsutdinov A J Bottger and B J Thijsse ldquoGrain coa-lescence and its effect on stress and elasticity in nanocrystallinemetal filmsrdquo Acta Materialia vol 55 no 3 pp 777ndash784 2007

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials