MS482 Materials Characterization - KAISTenergymatlab.kaist.ac.kr/layouts/jit_basic_resources/... ·...
Transcript of MS482 Materials Characterization - KAISTenergymatlab.kaist.ac.kr/layouts/jit_basic_resources/... ·...
MS482MaterialsCharacterization(재료분석)
LectureNote5:RBS
Byungha ShinDept.ofMSE,KAIST
1
2016FallSemester
CourseInformationSyllabus1. Overviewofvariouscharacterizationtechniques (1lecture)2. Chemicalanalysistechniques (8lectures)
2.1. X-rayPhotoelectronSpectroscopy(XPS)2.2. UltravioletPhotoelectronSpectroscopy(UPS)2.3. AugerElectronSpectroscopy(AES)2.4. X-rayFluorescence(XRF)
3. Ionbeambasedtechniques (4lecture)3.1. RutherfordBackscatteringSpectrometry(RBS)3.2. SecondaryIonMassSpectrometry(SIMS)
4. Diffractionandimagingtechniques (7lectures)4.1. Basicdiffractiontheory4.2. X-rayDiffraction(XRD)&X-rayReflectometry(XRR)4.3. ScanningElectronMicroscopy(SEM)&
EnergyDispersiveX-raySpectroscopy(EDS)4.4. TransmissionElectronMicroscopy(TEM)
5. Scanningprobetechniques (1lecture)5.1. ScanningTunnelingMicroscopy(STM)5.2. AtomicForceMicroscopy(AFM)
6. Summary:Examplesofrealmaterialscharacterization (1lecture)*CharacterizationtechniquesinblueareavailableatKARA(KAISTanalysiscenterlocatedinW8-1)
RBS:RutherfordBackscatteringSpectrometry
RBSaccuratelymeasuresthecompositionanddepthprofileofthinfilms,includinghydrogen.
~
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Quantitative? Yes Destructive? No
Detectionlimits? 0.001– 10at% Lateral resolution(Probesize)? ³ 1 mm
Chemicalbonding? No Depthresolution? 5– 20nm
KeyApplications&InstrumentConfiguration• Determinethicknessandcompositionofthinfilms• Measurehydrogen• Determinefilmdensityfromafilmofknownthickness• Assessdamagetocrystalstructureasaresultofprocessing• Quantificationoffilmsonwholewafers(upto300mm)• Qualify&monitordepositionsystems(alsofab-to-fabcomparisons)
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• MeVionsfromanelectrostaticacceleratorarefocusedonasampleinavacuumchamberforanalysis.
• Typically,2MeVHe++ ionsareused.
PrinciplesKinematicsofelasticscattering
Conservationofenergyandmomentum12𝑀D𝑣F =
12𝑀D𝑣DF +
12𝑀F𝑣FF
v1
v2v
𝑀D𝑣 = 𝑀D𝑣D cos 𝜃 + 𝑀F𝑣F cos𝜙0 = 𝑀D𝑣D sin 𝜃 + 𝑀F𝑣F sin𝜙
ForM1 <M2 ,kinematicfactorK
𝐸D𝐸M=
𝑀FF − 𝑀D
F sinF 𝜃 D/F + 𝑀D cos 𝜃𝑀F + 𝑀D
F
(listedinHandout#5,Append.1)
• ForagivenM1 andM2,smallestK isatq =180o• Differenttypesofatoms,DM2à largestchangeinDE1 whenq =180o• Hence,backscatteringspectrometry,thoughq ~170o inpractice
PrinciplesScatteringCrossSection
Numberofparticlesscatteredinto𝑑Ω = 𝑄 W 𝑁Y W𝑑𝜎 𝜃𝑑Ω W 𝑑Ω
• E0 ofincidentparticleofM1àKM2E0 thatthisparticlepossessesatanyangleq afteranelasticcollisionwithaninitiallystationaryM2
• s(q), howfrequentlysuchacollisionoccuratacertainangleq?
THINTARGET:NS ATOMS/cm2 (=N·t)
(average)scatteringcrosssection[cm2/steradian]
,Q
(inRBS,solidangleW issmall,10-2steradian orless,soaveragecanbeusedinsteadofdifferential)
= 𝑄 W 𝑁Y W1Ω[
𝑑𝜎 𝜃𝑑Ω 𝑑Ω
\W Ω= 𝑄 W 𝑁Y W [
𝑑𝜎 𝜃𝑑Ω 𝑑Ω
\
NumberofparticlesscatteredintothedetectorwithW
differentialscatteringcrosssection
= 𝑄 W 𝑁Y W 𝜎 𝜃 W Ω
PrinciplesScatteringCrossSection
𝜎 𝜃 =𝑞F𝑍D𝑍F4𝐸
F 1sin`𝜃/2
Z1:atomicnumberofincidentparticleZ2:atomicnumberoftargetatomq:elementalchargeE:energyofincidentparticle(forthederivation,readpp.21-24ofHandout#8)
• Withoutconsideringrecoilofthetargetatom(M1 <<M2),i.e.,thetargetatomisstationaryallthetime
• Includingtherecoileffect,
𝜎 𝜃 =𝑞F𝑍D𝑍F4𝐸
F
sina`𝜃2 − 2
𝑀D
𝑀F
F+ ⋯
~4%correctioninthecaseofHe(M1=4)incidentonSi(M1=28)
• Rutherford ScatteringCrossSection,s(q)for1MeV4HeislistedinHandout#5,Appendix2.
PrinciplesDeviationfromRutherfordScattering
• AssumptiontoderiveRutherfordscatteringcrosssection:scatteringduetotherepulsionoftwopositivelychargednucleiofatomicnumberZ1 andZ2
• Meaningthatincidentatompenetrateswellinsidetheorbitaloftheatomicelectronsà closestdistance<Kshellelectronradiusà
𝐸 >𝑞F𝑍D𝑍F𝑎M
, wherea0 isBohrradius.~10keV forHescatteringfromSi~340keV forHescatteringfromAu
• At lowenergy,correctionfromthescreeningshouldbeconsidered. 𝜎fg = 𝜎 𝜃 F
• Athigherenergy,departurefromtheRutherfordscatteringcrosssectionduetotheinteractionoftheincidentparticlewiththenucleusofthetargetatom
~9.6MeVforHeionsincidentonSi
PrinciplesStoppingpower(stoppingcrosssection)
−𝑑𝐸𝑑𝑥 =
2𝜋𝑞`𝑍DF
𝐸 W 𝑁𝑍F W𝑀D
𝑚 ln2𝑚𝑣F
𝐼
EnergylossofMeVlightions(suchasHe)insolids:• electronicenergyloss (interactionwithelectrons,excitedorejected)
• Negligiblenuclearenergyloss
dE/dx:eV/Å(1/r)dE/dx:eV/(µg/cm2),wherer ismassdensity(1/N)dE/dx:eV/(atoms/cm2),whereN isatomicdensity
listedinAppendix3(Handout#5)
N:targetatomconcentration(#/cm3)m:electronmassI:averageexcitationenergyofanelectron
Principles
• Energytransferfromaprojectiletoatargetatominanelastictwo-bodycollisionà conceptofkinematicfactorandcapabilityofmassperception
• Likelihoodofoccurrenceofsuchatwo-bodycollisionàconceptofscatteringcrosssection andcapabilityofquantitativeanalysisofatomiccomposition
• Averageenergylossofanatommovingthroughadensemediumà conceptofstoppingcrosssection andcapabilityofdepthperception
HowtoInterpretRBSData
• Channelnumber=Backscatteringenergy
• Surfaceisontheright(highenergy)greaterdepthstotheleft(lowerenergy)à DE~t
• Heavierelementsproducehigherenergybackscattering.Why?
• Heavierelementsproducelargerpeaksperunitconcentration.Why?
• Shapeofspectrum.Why?
PtonSi
200nmPt
𝜎 𝜃 =𝑞F𝑍D𝑍F4𝐸
F
sina`𝜃2 − 2
𝑀D𝑀F
F+ ⋯
Rutherfordscatteringcrosssection
SifromSi/Ptinterface
(t)
energycorrespondingtoSiatsurface
Ptatsurface
DE
EnergyWidth
𝐾no𝐸M 𝐾np𝐸M
• SurfaceAupeakathigherenergythansurfaceAlpeak
•
t=
∆𝐸rs = [𝑑𝐸𝑑𝑥
t
𝑑𝑥 ≈𝑑𝐸𝑑𝑥vrs
W 𝑡
Att, 𝐸 𝑡 = 𝐸M − ∆𝐸rs = 𝐸M −xyxz{rsW 𝑡
𝐸D
𝐸D = 𝐾no𝐸 𝑡 − t|}~ �
xyxz{�pt
= −𝑡 𝐾noxyxz{rs+ t
|}~ �xyxz{�pt
+ 𝐾no𝐸M
∆𝐸no = 𝐾no𝐸M − 𝐸D = 𝒕[S]
• Surfaceenergyapproximation(for<100nm):xyxz{rs~ xyxz{y�, xyxz{�pt
~ xyxz{�y�
• Meanenergyapproximation:xyxz{rs~ xyxz{y�a
��∆y
, xyxz{�pt
~ xyxz{y��
��∆y
?
DEAu
Q:whichoneislarger,DEAu orDEAu?
DepthProfiles
𝐻�r𝐻Yr
=𝑁�r𝑁Yr
𝜎�r(𝐸M)𝜎Yr(𝐸M)
≅𝑁�r𝑁Yr
𝑍�r𝑍Yr
F
E1
𝐻�r𝐻Yr
=𝑁�r𝑁Yr
𝜎�r(𝐸M)𝜎Yr(𝐸D)
≅𝑁�r𝑁Yr
(𝑍�r/𝐸M)F
(𝑍Yr/𝐸D)F
𝜎 𝜃 =𝑞F𝑍D𝑍F4𝐸
F
sina`𝜃2 − 2
𝑀D𝑀F
F+ ⋯
𝐻�r∆𝐸�r𝐻Yr∆𝐸Yr
=𝑁�r𝑁Yr
𝜎�r𝜎Yr
orbetterapproximation
MeasuringConcentration&Thickness
ComparisonofThreeWSix FilmswithvaryingWconcentrations
ComparisonofThreeTiFilmswithvaryingthickness
2.27meVHe,160° RBS
Si SiO2
Si
O
SiinSiO2
Depth
OatSurface
Depth
SiatSurface
ExampleofRBSSpectrum
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ScatteringGeometryAffectsDepthResolution
Sample
~100°
~160°
GrazingExit
Detector
Normal AngleDetector
Incident He++ IonsBackscattered
He Ion
• Grazingangledetectorimprovesdepthresolutionforthinlayers
ScatteringGeometryAffectsDepthResolution
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EffectofFilmDensityonThicknesses
• FundamentalunitofmeasurementforRBSisatoms/cm2
• Density× thickness=atoms/cm2
• TocalculateafilmthicknessusingRBSaloneonemustassumeafilmdensity• Ifthefilmthicknessisknown(byTEM,SEM,profilometry,etc.),thenthefilm
densitycanbecalculated
2.27meVHe,160° RBS
Thetotalatomsineachfilmareequal(1.13x1018 atoms/cm2)
Bothsamplesproducethisspectrum200nm
density=5.66x1022 Ti atoms/cm3
Si Ti
Si Ti
ChannelNumber0
26
24
22
20
18
16
14
12
10
8
6
4
2
0200 400
Si Ti
400nm
density=2.83x1022Ti atoms/cm3
HydrogenForwardScatteringSpectrometry(HFS)
• AlsocalledForwardRecoilSpectrometry• HeisheavierthanH,sonoHebackscattersfromH(orD)• Hedoesforward scatterHatsignificantenergy• EnergyofrecoilingHismeasured
RBS/HFSAnalysisofSiliconNitrideFilm
RBSspectrum
HFSspectrum
Filmcomposition:Si- 38.4%N- 49.1%H- 12.5%
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Channeling
Conceptualimageofchannelingprocess
Ref.ScientificAmerican
ApplicationsofChanneling
• Quantitativecrystaldamageprofiling– IonImplants– Regrowthofdamagedcrystals– Polishingdamage– Ionetching– Epitaxiallayers– Thicknessofamorphouslayers
• Damagedetectionlimit:1x1015 to1x1017 displacedat/cm2
• Substitutionality ofdopants/impurities
Channeling:CrystalDamage
0
Measurementofdamageincrystalstructure
Disorderincrystalstructureresultsinhigherbackscatteringyield
Region without Region with disorderdisorder
MeV He ions
Energy
Yiel
d
Random
Crystal with disorder
AlignedPerfect crystal
0
Channeling:EpitaxialGrowth
• Depositedatomsareinperfectregistrywiththesubstrate(i.e.,epitaxy)à shadowconesbytheabsorbedatoms
Channeling:Substituionality ofimpurities
Yb-implantedSi
• Yb innotsubstitutionalbutislocatednearthe<110>channels
StrengthsandWeaknesses
• Strengths–Non-destructivedepthprofiling–Quantitativewithoutstandards–Analysisofwholewafers(150,200,300mm),irregularandlargesamples
–Cananalyzeconductorsandinsulators–Canmeasurehydrogen
• Weaknesses–Largeanalysisarea(1mm)–PoorsensitivityforlowZelements–Inmanycases,usefulinformationlimitedtothinfilms(<0.5µm)–Generallynotgoodforbulksamples