www.DRAFT.ugent.be

Magnetron sputter deposition,the role of the ions

D. DeplaGhent UniversityDepartment of Solid State SciencesResearch group DRAFT

Join us in Ghent: December 13 and 14, 2012

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ICMCTF 2012, San Diego, US2

The target level

Sputter yield and angular distribution

Ion induced secondary electron yield

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ICMCTF 2012, San Diego, US3

Measuring sputter yield

4

3

2

1

0

sputter yield

600500400300200

discharge voltage (V)

Al Ag Cu Cr

Mg Nb Ta Ti

Y Zr

ISEE

matoms nMion

MI

1

Y

+ γ

=

∆

=

Reason: quantification of the MC simulation of compositional profiles

Measuring mass difference and discharge currentat constant discharge voltage

Difficulties1) Electron yield (see further)2) Neutrals

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US4

Powder targets

4

3

2

1

0

effective sputter yield

700600500400300200

discharge voltage (V)

Al solid Al powder

Ag solid Ag powder

Cu solid Cu powder

Ti solid Ti powder

Why do we measure differences with calculated sputter yields (Matsunami, Yamamura, Eckstein, Sigmund, TRIDYN, SRIM, ACAT, Marlowe, …) ?

F. Boydens, W.P. Leroy, R. Persoons, D. Depla Physica Status Solidi A 209 (2012) 524-530

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US5

Powder targets : before and after

Al before Al after

Cu before Cu after

We are sputtering from real surfaces, which evolve during the experiment.

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US6

Powder targets : a model

Sputter yield depends on angle of incidence

Shadowing effect due to target surface geometry

Ar+

θ

5

4

3

2

1

0relative sputter yield

806040200

angle of incidence (°)

Al 425 eV Ag 500 eV Cu 450 eV Ti 380 eV

www.srim.org

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US7

Powder targets : results

3.0

2.5

2.0

1.5

1.0

0.5

0.0

corrected pow

der yields

3.02.52.01.51.00.50.0

corrected solid yields

After correction for the surface, both target types give the same results.

Is only the effective value of the sputter yield important ?

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US8

Powder targets : angular distributions

3.0

2.5

2.0

1.5

1.0

0.5

0.0

1.00.80.60.40.20.0

cos θ

aluminum

solid target powder target

5

4

3

2

1

0

1.00.80.60.40.20.0

cos θ

copper

solid target powder target

Complete different angular distributionsThe angular distribution of a solid target is not cosine !

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US9

Ion induced electron yield : metals

4.0

3.5

3.0

2.5

2.0

1.5inverse of the discharge voltage (x10

-31/V)

0.200.150.100.050.00

ion induced electron yield

Ag Al AuCe Cu CrIn Mg MoNb PbPd PtReTaTiYZr

0disch arg e

0 i ISEE

WV

mf=

ε ε γ

W0 : effective ionisation energyεεεεi : ion collection efficiencyεεεε0 : fraction of maximum possible number of ionsm : multiplication factor : accounts for ionisation in the sheathf : effective ionisation probability : influenced by electron recaptureγγγγISEE : ion induced secondary electron emission yield

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US10

Ion induced electron yield : oxides/nitrides

-100 0 100 200

Mg

Al

Y

Ce

Pb

Zr

Au

Ag

Cu

Cr

Ti

In

Pt

Re

Nb

Ta

Mo

nitride oxide

γC,nitride γC,oxide

0.0840.067

0.22 0.19

0.0310.036

0.22 0.27

0.0960.086

0.0550.092

0.27 0.40

0.0790.036

0.0970.044

0.0590.092

0.0490.022

0.0710.038

0.0940.057

0.11 0.078

0.18 0.37

0.12 0.13

0.0710.067

(γC-γM)/γM (%)

Nitrides

Conducting : yield decreaseIsolating : yield increase

Oxides

Reduction by sputtering: yield decreaseCongruent sputtering, i.e. isolating, yield increase

D. Depla, S. Mahieu, R. De Gryse, Thin Solid Films 517 (2009) 2825–2839

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US11

0.5

0.4

0.3

0.2

0.1

0.0

1.81.61.41.21.00.80.6

AgAlAuCeCrCuInLiMgMoNbPbPtReTaTiYZr

reduction R

SE

EY

Ion induced electron yield : reduction

J.B. Malherbe, S. Hofmann, J.M. Sanz, Appl. Surf. Sci. 27 (1986) 355.

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US12

Ion induced electron yield : estimating the work function

(((( ))))ISEE i0.032 E0.78 2γ = − φγ = − φγ = − φγ = − φ

(((( ))))iISEE 0.016 2Eγ = − φγ = − φγ = − φγ = − φ

(((( ))))ISEE i F0.2 0 8 EE. 2γ = − φγ = − φγ = − φγ = − φ6.5

6.0

5.5

5.0

4.5

4.0

3.5Published work function (averaged) (eV)

6.56.05.55.04.54.03.5

Calculated work function (eV)

ZrN

TiNNbN

TaN

MoNslope 45°

In2O3

ReO3

TiO2

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US13

Ion induced electron yield : oxides/nitrides

We could reason : Removing electrons from the solid, influences the bond distance, and hence electron emission should be related in general to the bulk modulus of materials.

0.6

0.5

0.4

0.3

0.2

0.1

0.0

SEEY

4003002001000

bulk modulus (GPa)

123

4

567

89

10111213

1415

1617

18

19123

45612

3451

23

45

6

1

2

34

5

12

3

4

metals (Al, Au, Ce, Cr, Cu, In, Li,

Mg, Mo, Nb, Pb, Pd, Pt, Re, Ta, Ti, Y, Zr)

nitride (low SEEY) (Nb, Ti, Zr, Mo, Ta, Cr)

oxide (low SEEY) (Cr, Cu, In, Re, Ta, Zr)

nitride (high SEEY) (Al, Ce, Mg, Y)

oxide (high SEEY) (Al, Ce, Li, Mg, Y)

titania targets (1.75; 1.4; 1, 0.75; 0.5)

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US14

Negative oxygen ejection

350

300

250

200

150

Vd (V)

4.03.53.02.52.01.51.00.50.0

O2 (sccm)

1.0

0.8

0.6

0.4

0.2

0.0

Cps (a.u.)

O-

O2-

YO-

YO2-

On poisoning the target, the discharge voltage changes.This is the result, in this case, of the increase of ISEE yield.But… we also notice a drastic increase of the ejection of negative ions

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US15

Ion induced electron yield : negative oxygen

Oxidized surfaces emit negative ions

The amount of emitted O- is correlated with the ion induced electron yield.

18

16

14

12

10

8

6

4

Ln(O-/O) = Ln((IO-Vd/2+I O

-Vd)/(Yield

O*I

Ar))

-4.0 -3.0 -2.0 -1.0 0.0 1.0

ln (electron yield oxide)

AlCeCr

CuLiMgNb

TaTiRePtYZr

S. Mahieu, W. P. Leroy, K. Van Aeken, and D. Depla

J. Appl. Phys. 106 (2009) 093302

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US16

Negative ion emission

100

101

102

103

104

105

Cps (a.u.)

30025020015010050

E (eV)

exp O SiMTRA O2 SiMTRA

AlO SiMTRA AlO2 SiMTRA

O-

O2- =>

O + O-

AlO- =>

Al + O-

AlO2- =>

AlO + O-

The measured O- originates from different negative species emitted from the target.

d

d

d2

2

d

M(O)V x 108 V

M(AlO)

M(O)V

M(O)V x 290 V

M(O)V x

M(O

x 145 VM

78 VM(A

O

)

)

lO

(

)

=

=

=

=

S. Mahieu, W. P. Leroy, K. Van Aeken, and D. Depla

J. Appl. Phys. 106 (2009) 093302

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US17

Negative ion emission : properties

intensity (a.u.)

-30 -20 -10 0 10 20 30

angle (°)

Cps O- (a.u.)

Itot

3000

2000

1000

0

intensity (counts)

60504030

2θ (°)

(222) (400) (440) (622)

Crystalline

Amorphous

Crystalline Y2O3 can only be grown under a low flux of negative ions

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US18

The plasma level : creating ions

Target poisoning

Recycling ions

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ICMCTF 2012, San Diego, US19

Noble gas retention

T i

Sputtering Ti in Xe/N2 while examining with in-situ RBS

Steady-state concentration of Xe in the race track 3.4% (Ti) 9.8% (TiN)

No changes are noticed after sputtering.

S. Mahieu, W.P. Leroy, D. Depla, S. Schreiber, W. Möller

Appl. Phys. Lett. 93 (2008) 061501 (3pp)

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US20

Noble gas retention

Energy distribution of Ti+ ions

Clearly sputtered from the target

1.0

0.8

0.6

0.4

0.2

0.0

intensity (a.u.)

2520151050-5

energy (eV)

0.25 Pa 0.35 Pa 0.45 Pa 0.55 Pa 0.65 Pa 0.75 Pa 0.85 Pa 1.05 Pa

Two distributions are noticed.

Thermal species originating from the sputter gas.

Species sputtered from the target.Peak energy : 3.2 eV ?

1.0

0.8

0.6

0.4

0.2

0.0

intensity (a.u.)

2520151050-5

energy (eV)

0.25 Pa 0.35 Pa 0.45 Pa 0.55 Pa 0.65 Pa 0.75 Pa 0.85 Pa 1.05 Pa

3.2 eV

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US21

Sputter conditions:

• Target Al or Y (D = 5.08 cm)• Process gas Ar• Reactive gas O2

• S = 55 L/s or 112 L/s• Pbase = ~10-4 Pa• PAr = 0.45 Pa or 0.37 Pa• I = 0.4 A, 0.5 A or 0.6 A

Hysteresis experiment = stepwise in/decreasing the O2 flow while collecting:

• discharge voltage V and current I• total pressure Ptot = PAr + PO2

steady state values !

Experimental : hysteresis experiments

magnetron

Vacuum chamber

tube

shield

opening

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US22

• RSD model describes three parts:

� vacuum chamber by the gas flow balance� target composition� substrate composition

• RSD model parameters

More quantitative…

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US23

What can we learn?

After fitting, including the sputter yield of the oxide as a fitting parameter, we compare with the experimental sputter yield (see before). From this we learn: the reaction rate constant is for both systems quite similar. This agrees also with the expectations as we implant highly reactive O atoms.

K. Strijckmans, W.P. Leroy, R. De Gryse, D. Depla

Surface and Coatings Technology 206 (2012) 3666-3675,

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US24

Fraction vs. pressure

( )rs s m r

nv n f2 Ip x kzn n

t

∂= − ∇ + −

∂�

tt

t c

2F

2F zIY

αθ =

α +

Chemisorption depends on pressure

Fk

P

2 m T=

π

Ion implantation depends on fractionAr

Pf

P P=

+

Increasing the argon pressure, decreases the fraction, but the partial pressure remains the same.

300

350

400

450

1086420

300

350

400

450

1086420

normalized oxygen flow (sccm)

300

350

400

450

1086420

300

350

400

450

1086420

300

350

400

450

dis

charg

e v

olta

ge (

V)

1086420

300

350

400

450

1086420

300

350

400

450

1086420

300

350

400

450

1086420

300

350

400

450

1086420

300

350

400

450

1086420

300

350

400

450

1086420

on oxygen addition

on oxygen removal

0.40 Pa 0.52 Pa 0.71 Pa

1.21 Pa 1.51 Pa 1.86 Pa 2.16 Pa

0.92 Pa

2.51 Pa 3.06 Pa 5.02 Pa

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US25

Hysteresis free: ideal solution?

2000

1800

1600

1400

1200

1000

time (s)

6543210

argon pressure (Pa)

procuduresputter cleaning in pure Ar5 minutes (0.4A)addition of 7 sccm O2

Arcing starts faster at higher pressure

50

40

30

20

10

0

fraction (%)

6543210

argon pressure (Pa)

Origin: redeposition of sputtered atoms increases almost linearly with the argon pressure (simulations performed with SiMTRA)

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US26

The substrate level : bombardment and growth

HIPIMS: energy per arriving atom

Momentum flux

Bended columns

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ICMCTF 2012, San Diego, US27

Microstructure and orientation versus diffusion length

substrate

substrate

substrate

Direct relation betweenMicrostructure/orientation and diffusion length

8x10-8

7

6

5

4

3

2

1

0

L (a.u.)

181512963N2 flow (sccm)

zone Ic

zone T

zone II

random/zone Ic

[111]/zone T

[200]/zone T

[111]+[200]/zone II

[200]/zone II

− −≈ ≈ tot

bEE1ln(D) kT

Ti

tot

Ti

1expD

L D tE

− = ∗ ≈ ≈

Θ Θ

S. Mahieu, D. Depla

J. Phys. D: Appl. Phys. 42 (2009) 053002 (16pp)

S. Mahieu, D. Depla

J. Phys. D: Appl. Phys. 42 (2009) 053002 (16pp)

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US28

Ion-to-atom ratio…

But what is the idea behind this choice?Ions, reflected atoms and sputtered atoms contribute not only in energy, but also in momentum.

Atomic peening, recoil effects, sputtering not only ask energy but also momentum.

16

12

8

4

0

Hardness (GPa)

16141210864

ion-to-atom ratio I

300

200

100

0

Elastic modulus (GPa)

hardness (Z:1.7)

elastic modulus (Z:2.4)

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US29

Momentum flux

Torsion wire

Front plate

Opening area A

Rotatable wire holder

d

22

2

p A F Mbp

A A 3dATP

∆ φ= ∆ φ = = = π θ

Due to the impact of the particles there is a force F. In equilibrium we will get:

300

250

200

150

100

50

Elastic M

odulus (GPa)

40x10-21

3020100

Momentum flux/Metallic flux (kgm/s)

16

12

8

4

0

Hardness (G

Pa)

elastic modulus hardness

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US30

HIPIMS

W. P. Leroy, S. Konstantinidis S. Mahieu, R. Snyders, D. Depla,

J. Phys. D: Appl. Phys. 44 (2011) 115201

• Only limited drop in total energy flux

• Change in the angular distribution

Measuring the angular distribution of the total Energy Flux

0

0.05

0.1

0.15

0.2

0.25

0.3

0.05 0.1 0.15 0.2 0.25 0.3

020

40

60

80

DC

HIPIMS 5µs HIPIMS 15µs

HIPIMS 15µs

Total energy Flux (a.u.)

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US31

HIPIMS

0

0.001

0.002

0.001 0.002

020

40

60

80

DC

HIPIMS 5µs

HIPIMS 15µs

HIPIMS 20µs

SIMTRA

Dep Rate / Pav

• Huge decrease of deposition rate

• Angular distribution of adparticles looks similar

Measuring the angular distribution of the deposition rate

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US32

Ions in the structure

Mg(Al)O15%

Mg(Cr)O19%

Mg(Ti)O8%

Mg(Zr)O11%

Mg(Y)O15%

-30

-20

-10

0

10

20

30

tilt angle (°)

-35 -25 -15 -5 5 15 25 35

cation radius change (%)

Dual magnetron sputtering on an inclined substrate

Biaxial alignment Inhomogeneous distribution

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US33

Ions in the structure

Mg(Al)O15%

Mg(Mg)O

Mg(Zr)O11%

-25

-15

-5

5

15

25

tilt (111) planes (°)

-25 -15 -5 5 15 25

column tilt (°)An almost 1:1 relationship is found between the microstructure and the texture.

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US34

Conclusions

4

3

2

1

0effective sputter yield

700600500400300200

discharge voltage (V)

Al solid Al powder

Ag solid Ag powder

Cu solid Cu powder

Ti solid Ti powder

Deposition rate depend on the effective yield and the angular distribution. Single measurements above the target don’t give you the right answer when discussing changes in deposition rate.

0.6

0.5

0.4

0.3

0.2

0.1

0.0

SEEY

4003002001000

bulk modulus (GPa)

123

4

567

89

10111213

1415

1617

18

19123

45612

3451

23

45

6

1

2

34

5

12

3

4

metals (Al, Au, Ce, Cr, Cu, In, Li,

Mg, Mo, Nb, Pb, Pd, Pt, Re, Ta, Ti, Y, Zr)

nitride (low SEEY) (Nb, Ti, Zr, Mo, Ta, Cr)

oxide (low SEEY) (Cr, Cu, In, Re, Ta, Zr)

nitride (high SEEY) (Al, Ce, Mg, Y)

oxide (high SEEY) (Al, Ce, Li, Mg, Y)

titania targets (1.75; 1.4; 1, 0.75; 0.5)

Discharge voltage behaviour during reactive magnetron sputtering can easily be predicted.

300

350

400

450

1086420

300

350

400

450

1086420

normalized oxygen flow (sccm)

300

350

400

450

1086420

300

350

400

450

1086420

300

350

400

450

dis

ch

arg

e v

oltag

e (

V)

1086420

300

350

400

450

1086420

300

350

400

450

1086420

300

350

400

450

1086420

300

350

400

450

1086420

300

350

400

450

1086420

300

350

400

450

1086420

on oxygen addition

on oxygen removal

0.40 Pa 0.52 Pa 0.71 Pa

1.21 Pa 1.51 Pa 1.86 Pa 2.16 Pa

0.92 Pa

2.51 Pa 3.06 Pa 5.02 Pa

Target poisoning is more complicated than currently described.

300

250

200

150

100

50

Elastic M

odulus (GPa

)

40x10-21

3020100

Momentum flux/Metallic flux (kgm/s)

16

12

8

4

0

Hardn

ess (GPa)

elastic modulus hardness Ion-to-atom ratio : decouple energy from

momentum

Target

Plasma

Substrate

Conclusions

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ICMCTF 2012, San Diego, US35

Acknowledgements

DRAFT : R. De GryseW. LeroyM. SaraivaF. BoydensS. Mahieu (now at AGC Europe)

UMons : R. Snyders (HIPIMS)S. Konstandinitis (HIPIMS)

Uppsala University : S. BergT. NybergE. Sarhammar

VITO Research Centre : R. Persoons (Profilometry)

University of Antwerp : S. Van Tendeloo (TEM)

Join us in Ghent: December 13 and 14, 2012

www.rsd2012.be

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ICMCTF 2012, San Diego, US36

If you ever wonder why DRAFT (Design, Research And Feasibility of Thin films) is named DRAFT…Here is another answer.