MS482MaterialsCharacterization(재료분석)

LectureNote3:AES

Byungha ShinDept.ofMSE,KAIST

1

2015FallSemester

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)

AES(AugerElectronSpectroscopy)

AESprovidesexcellentsurfacesensitivityandsmallspotsize

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AugerProcessX-rayinXPS

ElectroninAES

ExcitedIon

Augerelectronemission

FluorescentX-rayRelaxationProcess1

RelaxationProcess2

X-ray(XPS)vsElectronbeam(AES)tocreateAugerelectrons• Electronbeamcanbeobtainedwithordersofmagnitudegreaterintensitythanis

possiblewithX-ray• Electronbeamfocuseddowntonm-scale

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BackgroundCompared to SEM-EDS, Auger electrons originate closer to the surface and are localized to a smaller lateral location.

Incident electron beamSourceofAugerelectronsignal

Sourceofsecondaryelectronsignal(SEM)

YieldofSEcanbelargerthan1dependingonE

SourceofBackscatteredelectrons(SEM)

Sourceofelectron-excitedcharacteristicX-rays(SEM-EDS)

SourceofBremsstrahlung

Sourceofsecondaryfluorescence

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Nomenclature

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WXY

initialvacancy

finalvacancies

KLL Transition• KL1L1:2s02p6 (1S)• KL1L2:2s12p5(1P)• KL1L3:2s12p5(3P)• KL2L2:2s22p4(1S)• KL2L3:2s22p4(3P)• KL3L3:2s22p4(1D)

inXPS

AugerEnergiesAugerdeexcitationprocessesinSi

2pspin-orbitsplit~0.6eV EKL1L2,3 ~1839– 149– 99=1591eV

EL2,3VV ~90eV

EWXY=EW (Z)– EX (Z)– EY (Z+∆) Z:atomicnumberoftheinvolvedatom∆:½- ¼

EWXY=EW (Z)– ½[EX (Z)+EX (Z+1)]– ½[EY (Z)+EY (Z+1)]Example:KL1L1 AugerTransitioninNi𝐸CDEDFGH = 𝐸CGH −

KL𝐸DEGH + 𝐸DE

NO − KL𝐸DFGH + 𝐸DF

NO ~ 6.369keV (fromHandout#5,Append.5)=6.384keV (fromHandout#5,Append.7)

AugerEnergies

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From“HandbookofAugerElectronSpectroscopy(PhysicalElectronicsIndustries,Inc.)”

AESInstrumentation

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Path of primary electrons

Path of Auger Electrons

CylindricalMirrorAnalyzer(CMA)• largetransmissionfactor(probabilitythatanelectrontransmittedthroughtheanalyzer)• Largeangularacceptance• Noretardingfieldtofixedpassenergy:energyresolutionvarieswithAugerelectronKE

(butstilllessthanpeakFWHM)

(CMA)

negativevoltageappliedtooutercylinder

TypicalDataElasticallyscatteredelectrons(noenergyloss)

Electronswithcharacteristicenergylossduetoelectronicandplasmonic excitations

Augerfeaturessuperimposedonthelargebackgroundofsecondaryelectrons

Derivativemode:“differentiation”electronicallybysuperimposingasmallacvoltageontheoutercylindervoltageanddetectingthein-phasesignal

TypicalData

RawData

Derivative

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QuantitativeAnalysis

YieldofAugerelectrons,YA(d)producedfromathinlayerofwidth∆d atadepthd

𝑌R 𝑑 [#/cmL X sec] = 𝐶[∆𝑑 X 𝜎^ 𝑑 1 − 𝜔[ 𝑒a b cde f

g X 𝐼(𝑑) X 𝑇 X 𝑑Ω/4𝜋

Cx concentrationofelementxse(d) ionizationcross-sectionatdepthdwx fluorescenceyield[fortransitionstovacanciesintheKshell,WX/(WX+WA)]l escapedepthq analyzerangleI(d) theelectronexcitationfluxatdepthd,I(d) =IP(d) + IB(d) = IP(d)[1+RB(d)],

whereRBisthebackscatteringfactorT transmissionoftheanalyzerdW solidangleoftheanalyzer

QuantitativeAnalysis

perKvacancy

AugerYieldvs.FluorescenceYield

• ForelementslighterthanZ=32,AESisabetterchoicethanXRForEDS• Q:WhataboutHandHe,canyouseeHorHefromAES?

perKvacancy perL

vacancy

QuantitativeAnalysis

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Withanexternalstandardwithaknownconcentrationof𝐶[m ofelementx,theconcentrationof𝐶[n inthetestsamplecanbefoundfromtheratioofAugeryield:

𝐶[m

𝐶[n=𝑌[m

𝑌[n𝜆n

𝜆m1 + 𝑅qn

1 + 𝑅qm

Inaddition,ifthecompositionofthestandardisclosetothatofthetestsample:

𝐶[m

𝐶[n≈𝑌[m

𝑌[n

Al

O

Ti

Ti+N

C

400 800 1200 1600 2000Kinetic Energy (eV)

dEN

(E)/d

E

On metal line

400 800 1200 1600 2000

AlAl

F

O

C N

Kinetic Energy (eV)dE

N(E

)/dE

On defect

TiN/Al lineson SiO2 Green=Ti Red=Al

ExampleofAESAnalysis:ThinContaminationLayer

AugeranalysisshowsthethinresidueisanAlflake,probablyoriginatingfromtheetchchamber.

SEM image

AES map

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• Strengths– Surfacesensitive(sub-monolayeranalysis)– Gooddepthresolution– Smallspotsize(particlesassmallas25nmcanbeanalyzed)

• Limitations– Bestquantificationrequiresstandards– Insulatorsaredifficult– Samplesmustbevacuumcompatible– Relativelylowsensitivity(1%-0.1at%)

StrengthsandLimitations

ComplementaryTechniques

• XPS:Largerspotsize,canprovidechemicalstateinformation,betterquantification,betterhighzsensitivity.

• SEM-EDS:Largerspotsize,muchdeeperanalysisdepth,betterhighz,worselowZsensitivity.

• RBS:largerspotsize(notforimaging),betteratthinfilmcomposition(morequantitative),morepeakoverlap.

• STEM-EDS:Smallerspotsize,longertopreparesamples.Notasgoodforsurfacecontamination.