WetEtchingandCleaningSur教学讲解课件

Raghavan1WetEtchingandCleaning:

SurfaceConsiderationsandProcessIssuesDr.SriniRaghavanDept.ofChemicalandEnvironmentalEngineeringUniversityofArizona1999ArizonaBoardofRegentsforTheUniversityofArizonaRaghavanWetEtchingandCleaniRaghavan2OutlineEtchingandcleaningsolutions/processesParticleadhesiontheorySurfacechargeandchemistryContaminationRaghavanOutlineEtchingandcleRaghavan3EtchingandCleaningSolutionsHFSolutionsDiluteHF(DHF)solutions-preparedbydiluting49%HFwithdionizedwaterBufferedHFsolutions-preparedbymixing49%HFand40%NH4Finvariousproportionsexample:BufferedOxideEtch(BOE)-patentedformofbufferedHFsolutionMaycontainsurfactantsforimprovingwettabilityofsiliconandpenetrationoftrenchescontaininghydrophobicbasenonionicoranionichydrocarbonorfluorocarbonRaghavanEtchingandCleaningSRaghavan4EtchRateofSiO2EtchRate(Å/min)atconstanttemp.Weight%HF0100EtchRate(Å/min)NH4F/HFRatiosTemperatureEtchrateofSiO2increaseswithincreasingweight%ofHFintheetchsolution,aswellashigherratiosofNH4FbufferinBHFsolutions.Etchratealsodirectlyincreaseswithincreasingtemperature.MoreNH4FLessNH4FRaghavanEtchRateofSiO2EtchRaghavan5EtchingandCleaningSolutions(cont’d)PiranhaH2SO4(98%)andH2O2(30%)indifferentratiosUsedforremovingorganiccontaminantsandstrippingphotoresistsPhosphoricacid(80%)SiliconnitrideetchNitricacidandHFSiliconetchRaghavanEtchingandCleaningSRaghavan6EtchingandCleaningSolutions(cont’d)SC-2(StandardClean2)HCl(73%),H2O2(30%),dionizedwaterOriginallydevelopedataratioof1:1:5UsedforremovingmetalliccontaminantsDilutechemistries(compositionswithlessHClandH2O2)arebeingactivelyconsideredRaghavanEtchingandCleaningSRaghavan7AlkalineCleaningSolutionsSC-1(StandardClean1)NH4OH(28%),H2O2(30%)anddionizedwaterClassicformulationis1:1:5Typicallyusedat70CDiluteformulationsarebecomingmorepopular

TetramethylAmmoniumHydroxide(TMAH)Example:BakerCleanTMAH(<10%),nonionicsurfactant(<2%),pHregulatorsforarangeof8-10,andchelating/complexingagentsCouldpossiblybeusedwithH2O2toreplaceSC1andSC2sequenceRaghavanAlkalineCleaningSoluRaghavan8SurfactantsAlkylphenoxypolyethyleneoxidealcoholNonioniccompoundsAlkylgroup:8-9carbons9-10ethyleneoxidegroupsExamples:NCW601A(WakoChemicals),TritonX-100(UnionCarbide)AlkylphenoxypolyglycidolsNonionicsurfactantsExample:OlinHuntSurfactant(OHSR)FluorinatedalkylsulfonatesAnionicsurfactantsTypically8carbonchainExample:FluoradFC-93(3M)RaghavanSurfactantsAlkylphenoRaghavan9Surfactants(cont’d)AcetylenicalcoholsUnsaturatedtriplebondinthestructureNonionicExample:Surfynol61(APCI)BetainesZwitterionicinnatureUsedmostlyinalkalinecleanExample:CocoamidopropylbetaineRaghavanSurfactants(cont’d)AcRaghavan10RCACleaningTwo-stepwetcleaningprocessinvolvingSC-1andSC-2:1)1:1:5NH4OH-H2O2-H2Oat~70COxidizingammoniacalsolutionAmmoniacomplexesmanymultivalentmetalions(e.g.CU++)Treatmentleavesathin“chemical”oxideWithoutH2O2,SiwillsufferstrongattachbyNH4OH2)1:1:5HCl-H2O2-H2Oat~70CHClremovesalkaliandtransitionmetals(e.g.Fe)RaghavanRCACleaningTwo-stepwRaghavan11ProblemswithSC1CleanSomemetals(e.g.Al)areinsolubleinthisoxidizing,highlybasicsolutionandtendtoprecipitateonthesurfaceofSiwafersHighFecontaminationofthewafersurfaceafteraSC1cleanRoughsurfaceaftercleaningSC1solutionswithlowerammoniacontent(X:1:5,X<1)arebeingactivelyinvestigatedRaghavanProblemswithSC1CleaRaghavan12ParticleRemovalDuringSC1CleanH2O2promotestheformationofanoxideNH4OHslowlyetchestheoxideIna1:1:5SC1,theoxideetchrateis~0.3nm/minat70ºC.AtthealkalinepHvalueofSC1solution,mostsurfacesarenegativelycharged.Hence,electrostaticrepulsionbetweentheremovedparticleandtheoxidesurfacewillpreventparticleredeposition.RaghavanParticleRemovalDurinRaghavan13ParticleRemovalEfficiencyvs.ImmersionTime

SC1solutionsw/varyingNH4OHconcentrationParticleRemovalEfficiency01.0ImmersionTimeTheefficiencycurveissteeperwithahigherconcentrationofNH4OHintheSC1solution.1:1:5NH4OH:H2O2:H2ORaghavanParticleRemovalEfficRaghavan14StandardCleanforSiliconStep1-Piranha/SPM4:1H2SO4(40%):H2O2(30%)@90Cfor15minRemovesorganiccontaminantsStep2-DIwaterrinseStep3-DHFHF(2%)for30secStep4-DIwaterrinseStep5(SC-1/APM)1:1:5NH4OH(29%):H2O2(30%)H2Oat70Cfor10minremovesparticulatecontaminantsdesorbstracemetals(Au,Ag,Cu,Ni,etc.)RaghavanStandardCleanforSilRaghavan15StandardCleanforSilicon(cont’d)Step6-DIwaterrinseStep7-SC-21:1:5HCl(30%):H2O2(30%):H2Oat70Cfor10mindissolvesalkaliionsandhydroxidesofAl3+,Fe3+,Mg3+desorbsbycomplexingresidualmetalsStep8-DIwaterrinseStep9-SpinrinsedryRaghavanStandardCleanforSilRaghavan16AdhesionofParticlestoSurfacesAttractiveForces(AF)vanderWaalsforces(shortrange)Electrostatic(ifthechargeontheparticlesisoppositetothechargeonthesurface(typicallylongerrange)RepulsiveForces(RF)Electrostatic(chargeontheparticlehasthesamesignasthatonthesurface)Stericforces(duetoabsorbedpolymerlayersonthesurfaceoftheparticlesandwafer)(shortrange)WhenAF>RF,particledepositionisfavorableRaghavanAdhesionofParticlesRaghavan17ParticleDepositionModelParameterscontrollingdepositionzetapotentialofwaferssizeandzetapotentialofparticlesionicstrengthandtemperatureofsolutionTransportofparticlestowardsthewaferrequiresdiffusionthroughasurfaceboundarylayer(particlesmovealongtheflowinthesolutionanddepositbydiffusion).AlongtheflowDiffusionlayerSubstrateRaghavanParticleDepositionMoRaghavan18SurfaceChargeandSurfaceElectricityDevelopmentofsurfacechargeAdsorptionofH+andOH-ions(oxides)Selectiveadsorptionofpositiveornegativeions(hydrophobicmaterials)Ionizationofsurfacegroups(polymerssuchasnylon)Fixedchargesinthematrixstructureexposedduetocounterionreleaseexample:positivelychargedmodifiedfiltersusedinDIwaterpurificationRaghavanSurfaceChargeandSurRaghavan19SurfaceChargeDevelopmentonSiO2

ImmersedinAqueousSolutions-O-Si...-Si-O...-Si-O...-O-Si...-O-Si-OH2+-O-Si-OH2+-O-Si-OH-O-Si-O--O-Si-O--O-Si-OHBulkSolidSolutionBulkSolidSolutionH+OH-BulkSiO2AqueousSolutionAcidicSolutions(lowpH)BasicSolutions(highpH)H+OH-RaghavanSurfaceChargeDevelopRaghavan20PointofZeroCharge(PZC)ofMaterialsPZC=thesolutionpHvalueatwhichthesurfacebearsnonetcharge;i.e.surf=00surf(microcoulombs/cm2)pH20-20PZCMaterial pHPZCSiO2 2-2.5TiO2 5.5-6Al2O3 ~9Si ~4Nylon ~6Developmentof+or-chargeatagivenpHdependsonthenatureofthemetal-oxygenbondandtheacid/basecharacterofthesurfaceMOHgroups.AcidicoxideshavealowerPZCthanbasicoxides.RaghavanPointofZeroCharge(Raghavan21SurfacePotential(o)andZetaPotential()SolidLiquid+--++-+-+---+-0oSurfacePotential(o):NotexperimentallymeasurableOxidesimmersedinaqueoussoln’s,o=0.059(PZC-pH)voltsZetaPotential():Potentialinthedoublelayeratashortdistance(typicallythediameterofahydratedcounterion)fromthesolidsurfaceExperimentallymeasurablethroughelectrokinetictechniques

Decreases(morenegative)withincreasingpHRaghavanSurfacePotential(o)Raghavan22ZetaPotential

ElectrophoreticMethod=dielectricconstantofliquid=viscosityofliquidK=constantdependentonparticlesize>>1/or<<1/(1/istheelectricaldoublelayerthickness)Techniqueusefulforparticlessuspendedinaqueousornon-aqueousmediaERaghavanZetaPotential

ElectrRaghavan23ZetaPotentialfromStreamingPotentialV(+)and(-)chargesLIQUIDINPLIQUIDOUTGenerationofanelectricalpotentialduetotheflowofliquidpastachargedsurfacePotentialgenerated=streamingpotential(Estr),whichisrelatedtozetapotential,,andkareviscosity,dielectricconstant,andconductivityofsolution;Es/Pistheslopeofthestreamingpotentialvs.pressuredrop.RaghavanZetaPotentialfromStRaghavan24StreamingPotentialCell

SchematicSketch-6”wafersBlockCellLIQOUTLIQINChannelElectrodeLIQINLIQOUTElectrodeRaghavanStreamingPotentialCeRaghavan25ZetaPotentialvs.pH

OxideWafer-ActivationEtch0(-)ZetaPotential,mVpHRaghavanZetaPotentialvs.pH

Raghavan26ContaminationMechanismsLiquidfilmdraining(liquid/airinterface)BulkdepositionfromliquidsContaminantpick-upfromairALHydrophilicHydrophobicAL(OR)RaghavanContaminationMechanisRaghavan27WetEtchingandCleaning:

SurfaceConsiderationsandProcessIssuesDr.SriniRaghavanDept.ofChemicalandEnvironmentalEngineeringUniversityofArizona1999ArizonaBoardofRegentsforTheUniversityofArizonaRaghavanWetEtchingandCleaniRaghavan28OutlineEtchingandcleaningsolutions/processesParticleadhesiontheorySurfacechargeandchemistryContaminationRaghavanOutlineEtchingandcleRaghavan29EtchingandCleaningSolutionsHFSolutionsDiluteHF(DHF)solutions-preparedbydiluting49%HFwithdionizedwaterBufferedHFsolutions-preparedbymixing49%HFand40%NH4Finvariousproportionsexample:BufferedOxideEtch(BOE)-patentedformofbufferedHFsolutionMaycontainsurfactantsforimprovingwettabilityofsiliconandpenetrationoftrenchescontaininghydrophobicbasenonionicoranionichydrocarbonorfluorocarbonRaghavanEtchingandCleaningSRaghavan30EtchRateofSiO2EtchRate(Å/min)atconstanttemp.Weight%HF0100EtchRate(Å/min)NH4F/HFRatiosTemperatureEtchrateofSiO2increaseswithincreasingweight%ofHFintheetchsolution,aswellashigherratiosofNH4FbufferinBHFsolutions.Etchratealsodirectlyincreaseswithincreasingtemperature.MoreNH4FLessNH4FRaghavanEtchRateofSiO2EtchRaghavan31EtchingandCleaningSolutions(cont’d)PiranhaH2SO4(98%)andH2O2(30%)indifferentratiosUsedforremovingorganiccontaminantsandstrippingphotoresistsPhosphoricacid(80%)SiliconnitrideetchNitricacidandHFSiliconetchRaghavanEtchingandCleaningSRaghavan32EtchingandCleaningSolutions(cont’d)SC-2(StandardClean2)HCl(73%),H2O2(30%),dionizedwaterOriginallydevelopedataratioof1:1:5UsedforremovingmetalliccontaminantsDilutechemistries(compositionswithlessHClandH2O2)arebeingactivelyconsideredRaghavanEtchingandCleaningSRaghavan33AlkalineCleaningSolutionsSC-1(StandardClean1)NH4OH(28%),H2O2(30%)anddionizedwaterClassicformulationis1:1:5Typicallyusedat70CDiluteformulationsarebecomingmorepopular

TetramethylAmmoniumHydroxide(TMAH)Example:BakerCleanTMAH(<10%),nonionicsurfactant(<2%),pHregulatorsforarangeof8-10,andchelating/complexingagentsCouldpossiblybeusedwithH2O2toreplaceSC1andSC2sequenceRaghavanAlkalineCleaningSoluRaghavan34SurfactantsAlkylphenoxypolyethyleneoxidealcoholNonioniccompoundsAlkylgroup:8-9carbons9-10ethyleneoxidegroupsExamples:NCW601A(WakoChemicals),TritonX-100(UnionCarbide)AlkylphenoxypolyglycidolsNonionicsurfactantsExample:OlinHuntSurfactant(OHSR)FluorinatedalkylsulfonatesAnionicsurfactantsTypically8carbonchainExample:FluoradFC-93(3M)RaghavanSurfactantsAlkylphenoRaghavan35Surfactants(cont’d)AcetylenicalcoholsUnsaturatedtriplebondinthestructureNonionicExample:Surfynol61(APCI)BetainesZwitterionicinnatureUsedmostlyinalkalinecleanExample:CocoamidopropylbetaineRaghavanSurfactants(cont’d)AcRaghavan36RCACleaningTwo-stepwetcleaningprocessinvolvingSC-1andSC-2:1)1:1:5NH4OH-H2O2-H2Oat~70COxidizingammoniacalsolutionAmmoniacomplexesmanymultivalentmetalions(e.g.CU++)Treatmentleavesathin“chemical”oxideWithoutH2O2,SiwillsufferstrongattachbyNH4OH2)1:1:5HCl-H2O2-H2Oat~70CHClremovesalkaliandtransitionmetals(e.g.Fe)RaghavanRCACleaningTwo-stepwRaghavan37ProblemswithSC1CleanSomemetals(e.g.Al)areinsolubleinthisoxidizing,highlybasicsolutionandtendtoprecipitateonthesurfaceofSiwafersHighFecontaminationofthewafersurfaceafteraSC1cleanRoughsurfaceaftercleaningSC1solutionswithlowerammoniacontent(X:1:5,X<1)arebeingactivelyinvestigatedRaghavanProblemswithSC1CleaRaghavan38ParticleRemovalDuringSC1CleanH2O2promotestheformationofanoxideNH4OHslowlyetchestheoxideIna1:1:5SC1,theoxideetchrateis~0.3nm/minat70ºC.AtthealkalinepHvalueofSC1solution,mostsurfacesarenegativelycharged.Hence,electrostaticrepulsionbetweentheremovedparticleandtheoxidesurfacewillpreventparticleredeposition.RaghavanParticleRemovalDurinRaghavan39ParticleRemovalEfficiencyvs.ImmersionTime

SC1solutionsw/varyingNH4OHconcentrationParticleRemovalEfficiency01.0ImmersionTimeTheefficiencycurveissteeperwithahigherconcentrationofNH4OHintheSC1solution.1:1:5NH4OH:H2O2:H2ORaghavanParticleRemovalEfficRaghavan40StandardCleanforSiliconStep1-Piranha/SPM4:1H2SO4(40%):H2O2(30%)@90Cfor15minRemovesorganiccontaminantsStep2-DIwaterrinseStep3-DHFHF(2%)for30secStep4-DIwaterrinseStep5(SC-1/APM)1:1:5NH4OH(29%):H2O2(30%)H2Oat70Cfor10minremovesparticulatecontaminantsdesorbstracemetals(Au,Ag,Cu,Ni,etc.)RaghavanStandardCleanforSilRaghavan41StandardCleanforSilicon(cont’d)Step6-DIwaterrinseStep7-SC-21:1:5HCl(30%):H2O2(30%):H2Oat70Cfor10mindissolvesalkaliionsandhydroxidesofAl3+,Fe3+,Mg3+desorbsbycomplexingresidualmetalsStep8-DIwaterrinseStep9-SpinrinsedryRaghavanStandardCleanforSilRaghavan42AdhesionofParticlestoSurfacesAttractiveForces(AF)vanderWaalsforces(shortrange)Electrostatic(ifthechargeontheparticlesisoppositetothechargeonthesurface(typicallylongerrange)RepulsiveForces(RF)Electrostatic(chargeontheparticlehasthesamesignasthatonthesurface)Stericforces(duetoabsorbedpolymerlayersonthesurfaceoftheparticlesandwafer)(shortrange)WhenAF>RF,particledepositionisfavorableRaghavanAdhesionofParticlesRaghavan43ParticleDepositionModelParameterscontrollingdepositionzetapotentialofwaferssizeandzetapotentialofparticlesionicstrengthandtemperatureofsolutionTransportofparticlestowardsthewaferrequiresdiffusionthroughasurfaceboundarylayer(particlesmovealongtheflowinthesolutionanddepositbydiffusion).AlongtheflowDiffusionlayerSubstrateRaghavanParticleDepositionMoRaghavan44SurfaceChargeandSurfaceElectricityDevelopmentofsurfacechargeAdsorptionofH+andOH-ions(oxides)Selectiveadsorptionofpositiveornegativeions(hydrophobicmaterials)Ionizationofsurfacegroups(polymerssuchasnylon)Fixedchargesinthematrixstructureexposedduetocounterionreleaseexample:positivelychargedmodifiedfiltersusedinDIwaterpurificationRaghavanSurfaceChargeandSurRaghavan45SurfaceChargeDevelopmentonSiO2

ImmersedinAqueousSolutions-O-Si...-Si-O...-Si-O...-O-Si...-O-Si-OH2+-O-Si-OH2+-O-Si-OH-O-Si-O--O-Si-O--O-Si-OHBulkSolidSolutionBulkSolidSolutionH+OH-BulkSiO2AqueousSolutionAcidicSolutions(lowpH)BasicSolutions(highpH)H+OH-RaghavanSurfaceChargeDevelopRaghavan46PointofZeroCharge(PZC)ofMaterialsPZC=thesolutionpHvalueatwhichthesurfacebearsnonetcharge;i.e.surf=00surf(microcoulombs/cm2)pH20-20PZCMaterial pHPZCSiO2 2-2.5TiO2 5.5-6Al2O3 ~9Si ~4Nylon ~6Developmentof+or-chargeatagivenpHdependsonthenatureofthemetal-oxygenbondandtheacid/basecharacterofthesurfaceMOHgroups.AcidicoxideshavealowerPZCthanbasicoxides.