MS482MaterialsCharacterization(재료분석)

LectureNote4:XRF

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)

XRF:X-rayFluorescence

XRFmeasurescompositionandimpuritiesofbulkmaterialsandfilms.©Copyright EvansAnalyticalGroup®

Primary&SecondaryProcesses

X-ray(XPS,XRF),UV(UPS),Electrons(AES,EDS)

Emittedphotoelectron(XPS,UPS)

ExcitedIon

Augerelectronemission(AES)

FluorescentX-ray(XRF,EDS)RelaxationProcess1

RelaxationProcess2

XRFPrinciple

Moseley’slaw1𝝀�= 𝑘(𝒁 − 𝜎)

𝜆:wavelengthofanX-raycharacteristicline𝑘:constantforaparticularspectralseries𝑍:atomicnumber𝜎:screeningconstantfortherepulsion

correctionduetootherelectrons

XRFOverview• XRFspectralooksimilartoEDSspectra• Samplingdepthis~10XgreaterthanEDS(~10µm)• Detectionlimitsare~100XlowerthanEDS• Smallestanalysisareais~50µm• Vacuumnotrequired,butoftenusedtoimprovesensitivity• Lightelementdetectionverydifficult(typicallyNa-Udetected)• Nondestructive

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TypesofXRF

• Wavelength-dispersiveXRF(WDXRF):wavelengthoftheemittedX-raysdeterminedusingadiffractingcrystal

• Energy-dispersiveXRF(EDXRF):energyoftheemittedX-raysdirectlymeasuredbycollectingtheionizationproducedinasuitabledetectingmedium

• BetterenergyresolutionwithWDXRF thanEDXRF• HigherdetectionefficiencywithEDXRF thanEDXRF• SimultaneousdetectionofX-raysofdifferentenergies(wavelengths)possiblewithEDXRF,notwithWDXRF

WDXRF

• Foragivendiffractingcrystal(fixedd),Braggconditionatdifferentq fordifferentl ofemittedX-rays

• Angulardispersion(resolution)small l (large E) à small 2q

large l (small E) à large 2q

𝑑𝜃𝑑𝜆 =

𝑛2𝑑 cos 𝜃

(betterresolutionwithsmallerd)

WDXRFLimitationinspectralrangethatcanbemeasured• 2q fromafewdegreesto~150o possible,butoptimalrangeis15o – 70o- athigh2q:angulardispersionwidenspeakprofile- atlow2q:onlyasmallfractionofX-rayfromthesampleinterceptedbythe

diffractingcrystalsample

crystalq

sample

q

• LowZ-limit(lowElimit):l <2d

• HighZ-limit(highElimit)- byprimaryX-raysource(e.g.Wanode~50kVà Z<63)- bydiffractingcrystal,2q≥ 15o

Crystal 2d (nm) Elementrange

LiF (420) 0.18 Ni(28) – U

LiF (220) 0.29 V(23) – U

LiF (200) 0.40 K(19) – U

Si(111) 0.65

PX-1* 5.1 O(8) – Mg(12)

PX-2* 12 B(5) – C(6)

PX-3* 20 B(5)

OV-H** 24.2 Be(4) – B(5)

repeatingmultilayer*FromPhilips**OvonicSyntheticMaterialsCompany

WDXRF:Detector(Photon)detector:photonà electricalpulse

Gas-filleddetectorCurrentpulseI proportionalton ~KE/F ~hn/F,calledproportionalcounters

V

,Ve.g. B Ka (185 eV) creates ~6 pairs;

Mo Ka (17.4 keV) ~580 pairs

F = 27.8 eV (He), 27.4 eV (Ne), 26.4 eV (Ar), 22.8 eV (Kr), 20.8 eV (Xe)

Further amplification of nby the applied voltage

WDXRF:DetectorScintillationdetector

High energy photons à ionize NaI (Tl), F ~ 50 eV with e- (KE = hn – F ≈ hn) àexcitation of iodide atoms to 3 eV above the ground state, # of excited atoms ≈ hn / 3 eV à deexcitation with light, hn’ ~ 3 eV, emitted à photoelectrons from the photo-cathode (such as InSb) à multiplication of e- as large as 106

Poorer resolution compared to gas-filled detector

WDXRFatKARAhttps://kara.kaist.ac.kr http://www.rigaku.com/en/products/xrf/primus2

EDXRF

Semiconductordetector

cross-section of Si(Li) detector

n+

(serves as p+ contact)(intrinsic)

qVbias

p-n junction at reverse bias

n

p

# of e--h+ pairs generated in the intrinsic region proportional to hn

hn

# of e--h+ pairs collected by drift at Vbias

• Lessrestrictivegeometryinplacingadetectorà largesolidangleandincreaseddetectionefficiency

• SimultaneousdetectionofX-raysoverawiderange

• PoorresolutioncomparedtoWDXRF

XRFIntensityofaPureElement

𝑑𝑁RS 𝑥, 𝜆 = 𝑁V 𝜆 𝑑𝜆 W exp −𝜇[(𝜆) W𝑥

sin𝜑 W 𝑃RS W exp −𝜇[(𝛼) W𝑥

sin𝜓#ofKa fluorescencephotonsfromdx

#ofincidentphotonsbetweenl andl +dl

intensityatadepthx

• µK /(µK +µL +….)• Ka /(Ka +Kb +….)• WK /(WK +WA)

linearabsorptioncoefficient

attenuationofKafluorescencecreatedatdx

𝑁RS = ` ` 𝑑𝑁RS 𝑥, 𝜆ab

ac𝑑𝜆𝑑𝑥

d

V∝ ℎ (forathinfilmwithh <100nm)

XRFIntensityofanElementinMulticomponentMixture

𝑑𝑁RS,g 𝑥, 𝜆 = 𝑁V 𝜆 𝑑𝜆 W exp −𝜇(𝜆) W𝑥𝜌sin𝜑 W

𝐶g𝜇g 𝜆𝜇 𝜆 W 𝑃RS,g W exp −𝜇(𝛼) W

𝑥𝜌sin𝜓

𝑁RS,g = ` ` 𝑑𝑁RS,g 𝑥, 𝜆ab

ac𝑑𝜆𝑑𝑥

d

V∝ ℎg

averagemassabsorptioncoefficientµ(l)=CAµA(l)+CBµB(l)+CCµC(l)+….

#ofKa fluorescenceintensityofelementAfromdx

fractionabsorbedbytheelementA

Bestpracticeisusingstandards(pureA,pureB,pureC,….,ofknownthickness&mixtureofABC…withknowncompositionandthickness).

Matrix EffectCalibration curve for Pb La, Sn Ka, Sn Lain Pb-Sn binaries

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Example:RoHSandWEEEanalysis

XRFSpectrumfromreferencesample,1%Brinpolystyrene

CdHg,PbCr

Element ConcentrationCr <300ppm*Br 1%(reference)Cd <30ppmHg <100ppmPb <100ppm*InterferencefromhighFeconc.affectsCrdetectionlimit

• CandetectHg,Pb,Cd,Br,andCrdownto<100ppm• Isawidelyacceptedmeasurementtechnique• Cananalyzesmallareasandindividualcomponents• Spectralinterferencesandquantificationissuesmayaffectsome

analyses

BrFe Rh(source)

RoHS:RestrictionofHazardousSubstancesWEEE:WasteElectricalandElectronicEquipment ©CopyrightEvansAnalyticalGroup®

TXRF:TotalReflectionXRF

TXRFisanon-destructive,elementalsurveytechniquewhichcanmeasurewafersupto300mm.

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TXRFInstrumentation

X-RaySource

Slit

Monochromator

Chuck/Goniometer

Wafer SlitSlit

Si(Li)Detector

EDS

ScintillationDetector

IncidentAngle<<CriticalAngleforreflection

~0.05o

FluorescentX-RaysToEDSdetector

TXRFSpectra

ReflectedX-RaysToSCDetector

MonitorBeam

OverallBeamlineLayout

X-raySourceSelectionElementsquantifiedbyWLb excitation.

9kWrotating anode(~9.67keV)ElementsquantifiedbyMoKa excitation.

2kWtube,Motarget(~17.4keV)

LocationspecificSpectrum

Withtabulatedconcentrations

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ExampleofTXRF:SiWafers

TypicalDetectionLimitsInterferencefree,practicaldetectionlimits(1010 atoms/cm2)onSilicon*

*Insomecases,spectralinterferencespreventdetectionatlowlevels.

Element DL Element DL

S 50 Fe 0.3

Cl 20 Ni 0.3

K 10 Cu 0.3

Ca 10 Zn 0.8

Ti 2 As 3

V 2 Rh 20

Cr 0.7 Sb 20

Mn 0.6 Ta 3

W 3

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ExampleofTXRF:SiWafers

Table 1. TREX 630-T TXRF Results (Units of 1e10 atoms/cm2)S Cl K Ca Ti Cr Mn Fe Ni Cu Zn

Control WaferCenter 125±11 118±9 <10 <10 <1.1 <0.6 <0.5 0.4±0.2 <0.3 <0.3 <0.4

Implant WaferCenter 270±19 390±20 <10 <10 <0.9 1.5±0.3 <0.4 6±0.5 <0.3 <0.5 0.7±0.2

ControlWafer ImplantWafer

Si

SClAr

Fe

W Si

S

Cl

ArFe

W

SurfaceMetalContamination:Controlvs.Implantedwafers

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TXRFMapping

• Determinationmetalcontaminationdistributionacrossthewafer

• Bestsuitedfor“gross”contamination,suchasparticles• Commonusageforwaferbackside/handlingcontamination

2DElementalMappingcapabilities:

CuMapping Cu<3e9at/cm2

Cu=2e13at/cm2

VPD-ICPMSwouldyieldasinglevalueof1e11at/cm2 Cuforthewholewaferwithnodistributioninformation.

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TXRFatKARAhttps://kara.kaist.ac.kr

©Copyright2007EvansAnalyticalGroup®

SurfaceAnalysisTechniquesDetectionSensitivity

AES,XPS,ESCA,SEM,EDS

TXRF

VPD-TXRF,TOF-SIMS,SurfaceSIMS,VPD-ICPMS

~

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TXRFStrengthsandLimitations• Strengths

–Elementalsurveyanalysis–Quantitative,HighSensitivity–Non-destructive–Fast/Automatedanalysis–Fullwafers(upto300mm)–2DMappingcapable(sensitivetosingleparticles)

• Limitations–Cannotdetectlow-Zelements(Li,Na,K,Al)–Nodepthdistribution–10mmlateralspotsize–Polishedsurfacerequiredforbestsensitivity