Michaelquirk半导体制造技术-第章光刻气相成底膜到软烘课件

SemiconductorManufacturingTechnology

MichaelQuirk&JulianSerda

©October2001byPrenticeHall

Chapter13

Photolithography:SurfacePreparationtoSoftBake©2000byPrenticeHallSemiconductorManufacturingTechnologybyMichaelQuirkandJulianSerda

SemiconductorManufacturingTeObjectivesAfterstudyingthematerialinthischapter,youwillbeableto:1. Explainthebasicconceptsforphotolithography,includingprocessoverview,criticaldimensiongenerations,lightspectrum,resolutionandprocesslatitude.2. Discussthedifferencebetweennegativeandpositivelithography.3. Stateanddescribetheeightbasicstepstophotolithography.4. Explainhowthewafersurfaceispreparedforphotolithography.5. Describephotoresistanddiscussphotoresistphysicalproperties.6. Discussthechemistryandapplicationsofconventionali-linephotoresist.7. DescribethechemistryandbenefitsofdeepUV(DUV)resists,includingchemicallyamplifiedresists.8. Explainhowphotoresistisappliedinwafermanufacturing.9. Discussthepurposeofsoftbakeandhowitisaccomplishedinproduction.

ObjectivesAfterstudyingthemWaferFabricationProcessFlowImplantDiffusionTest/SortEtchPolishPhotoCompletedwaferUnpatternedwaferWaferstartThinFilmsWaferfabrication(front-end)UsedwithpermissionfromAdvancedMicroDevicesFigure13.1

WaferFabricationProcessFlowPatterningProcessPhotomaskReticleCriticalDimensionGenerationsLightSpectrumResolutionOverlayAccuracyProcessLatitudePhotolithographyConcepts

PatterningProcessPhotolithogrPhotomaskandReticleforMicrolithographyPhotographprovidedcourtesyofAdvancedMicroDevices4:1Reticle1:1MaskPhoto13.1

PhotomaskandReticleforMicrThreeDimensionalPatterninPhotoresistLinewidthSpaceThicknessSubstratePhotoresistFigure13.2

ThreeDimensionalPatterninPSectionoftheElectromagneticSpectrumVisibleRadiowavesMicro-wavesInfraredGammaraysUVX-raysf(Hz)1010101010101010101046810121416221820

(m)420-2-4-6-8-14-10-1210101010101010101010365436405248193157ghiDUVDUVVUVl(nm)CommonUVwavelengthsusedinopticallithography.Figure13.3

SectionoftheElectromagneticImportantWavelengthsforPhotolithographyExposureTable13.1

ImportantWavelengthsforPhotImportanceofMaskOverlayAccuracyPMOSFETNMOSFETCrosssectionofCMOSinverterTopviewofCMOSinverterThemaskinglayersdeterminetheaccuracybywhichsubsequentprocessescanbeperformed.Thephotoresistmaskpatternpreparesindividuallayersforproperplacement,orientation,andsizeofstructurestobeetchedorimplanted.Smallsizesandlowtolerancesdonotprovidemuchroomforerror.Figure13.4

ImportanceofMaskOverlayAccPhotolithographyProcessesNegativeResistWaferimageisoppositeofmaskimageExposedresisthardensandisinsolubleDeveloperremovesunexposedresistPositiveResistMaskimageissameaswaferimageExposedresistsoftensandissolubleDeveloperremovesexposedresist

PhotolithographyProcessesNegaNegativeLithographyUltravioletlightIslandAreasexposedtolightbecomecrosslinkedandresistthedeveloperchemical.Resultingpatternaftertheresistisdeveloped.WindowExposedareaofphotoresistShadowonphotoresistChromeislandonglassmaskSiliconsubstratePhotoresistOxidePhotoresistOxideSiliconsubstrateFigure13.5

NegativeLithographyUltraviolePositiveLithographyFigure13.6

photoresistsiliconsubstrateoxideoxidesiliconsubstratephotoresistUltravioletlightIslandAreasexposedtolightaredissolved.Resultingpatternaftertheresistisdeveloped.ShadowonphotoresistExposedareaofphotoresistChromeislandonglassmaskWindowSiliconsubstratePhotoresistOxidePhotoresistOxideSiliconsubstratePositiveLithographyFigure13.RelationshipBetweenMaskandResistDesiredphotoresiststructuretobeprintedonwaferWindowSubstrateIslandofphotoresistQuartzChromeIslandMaskpatternrequiredwhenusingnegativephotoresist(oppositeofintendedstructure)Maskpatternrequiredwhenusingpositivephotoresist(sameasintendedstructure)Figure13.7

RelationshipBetweenMaskandClearFieldandDarkFieldMasksSimulationofcontactholes(positiveresistlithography)Simulationofmetalinterconnectlines(positiveresistlithography)ClearFieldMaskDarkFieldMaskFigure13.8

ClearFieldandDarkFieldMasEightStepsofPhotolithographyTable13.2

EightStepsofPhotolithographEightStepsofPhotolithography8)Developinspect5)Post-exposurebake6)Develop7)HardbakeUVLightMask

4)AlignmentandExposureResist2)Spincoat3)Softbake1)VaporprimeHMDSFigure13.9

EightStepsofPhotolithographPhotolithographyTrackSystemPhotocourtesyofAdvancedMicroDevices,TELTrackMarkVIIIPhoto13.2

PhotolithographyTrackSystemPVaporPrimeTheFirstStepofPhotolithography:PromotesGoodPhotoresist-to-WaferAdhesionPrimesWaferwithHexamethyldisilazane,HMDSFollowedbyDehydrationBakeEnsuresWaferSurfaceisCleanandDry

VaporPrimeTheFirstStepofPSpinCoatProcessSummary:WaferisheldontovacuumchuckDispense~5mlofphotoresistSlowspin~500rpmRampupto~3000to5000rpmQualitymeasures:timespeedthicknessuniformityparticlesanddefectsVacuumchuckSpindleconnectedtospinmotorTovacuumpumpPhotoresistdispenserFigure13.10

SpinCoatProcessSummary:VacuuSoftbakeCharacteristicsofSoftBake:ImprovesPhotoresist-to-WaferAdhesionPromotesResistUniformityonWaferImprovesLinewidthControlDuringEtchDrivesOffMostofSolventinPhotoresistTypicalBakeTemperaturesare90to100°CForAbout30SecondsOnaHotPlateFollowedbyCoolingSteponColdPlate

SoftbakeCharacteristicsofSoAlignmentandExposureProcessSummary:Transfersthemaskimagetotheresist-coatedwaferActivatesphoto-sensitivecomponentsofphotoresistQualitymeasures:linewidthresolutionoverlayaccuracyparticlesanddefectsUVlightsourceMaskResist

Figure13.11

AlignmentandExposureProcessPost-ExposureBakeRequiredforDeepUVResistsTypicalTemperatures100to110°ConahotplateImmediatelyafterExposureHasBecomeaVirtualStandardforDUVandStandardResists

Post-ExposureBakeRequiredforPhotoresistDevelopmentProcessSummary:SolubleareasofphotoresistaredissolvedbydeveloperchemicalVisiblepatternsappearonwafer -windows -islandsQualitymeasures: -lineresolution -uniformity -particlesanddefectsVacuumchuckSpindleconnectedtospinmotorTovacuumpumpDevelopdispenserFigure13.12

PhotoresistDevelopmentProcessHardBakeAPost-DevelopmentThermalBakeEvaporateRemainingSolventImproveResist-to-WaferAdhesionHigherTemperature(120to140°C)thanSoftBake

HardBakeAPost-DevelopmentThDevelopInspectInspecttoVerifyaQualityPatternIdentifyQualityProblems(Defects)CharacterizethePerformanceofthePhotolithographyProcessPreventsPassingDefectstoOtherAreasEtchImplantReworkMisprocessedorDefectiveResist-coatedWafersTypicallyanAutomatedOperation

DevelopInspectInspecttoVeriVaporPrimeWaferCleaningDehydrationBakeWaferPrimingPrimingTechniquesPuddleDispenseandSpinSprayDispenseandSpinVaporPrimeandDehydrationBake

VaporPrimeWaferCleaningEffectofPoorResistAdhesionDuetoSurfaceContaminationFigure13.13

ResistliftoffEffectofPoorResistAdhesionHMDSPuddleDispenseandSpinPuddleformationSpinwafertoremoveexcessliquidFigure13.14

HMDSPuddleDispenseandSpinPHMDSHotPlateDehydrationBake

andVaporPrimeWaferExhaustHotplateChambercoverProcessSummary:DehydrationbakeinenclosedchamberwithexhaustHexamethyldisilazane(HMDS)Cleananddrywafersurface(hydrophobic)Temp~200to250

CTime~60sec.Figure13.15

HMDSHotPlateDehydrationBakThePurposeofPhotoresistinWaferFabTotransferthemaskpatterntothephotoresistonthetoplayerofthewafersurfaceToprotecttheunderlyingmaterialduringsubsequentprocessinge.g.etchorionimplantation.

ThePurposeofPhotoresistinSuccessiveReductionsinCDsLeadtoProgressiveImprovementsinPhotoresistBetterimagedefinition(resolution).Betteradhesiontosemiconductorwafersurfaces.Betteruniformitycharacteristics.Increasedprocesslatitude(lesssensitivitytoprocessvariations).

SuccessiveReductionsinCDsLPhotoresistTypesofPhotoresistNegativeVersusPositivePhotoresistsPhotoresistPhysicalPropertiesConventionalI-LinePhotoresistsNegativeI-LinePhotoresistsPositiveI-LinePhotoresistsDeepUV(DUV)PhotoresistsPhotoresistDispensingMethodsSpinCoat

PhotoresistSpinCoatTypesofPhotoresistsTwoTypesofPhotoresistPositiveResistNegativeResistCDCapabilityConventionalResistDeepUVResistProcessApplicationsNon-criticalLayersCriticalLayers

TypesofPhotoresistsTwoTypesNegativeVersusPositiveResistsNegativeResistWaferimageisoppositeofmaskimageExposedresisthardensandisinsolubleDeveloperremovesunexposedresistPositiveResistMaskimageissameaswaferimageExposedresistsoftensandissolubleDeveloperremovesexposedresistResolutionIssuesClearFieldVersusDarkFieldMasks

NegativeVersusPositiveResisPhotoresistPhysicalCharacteristicsResolutionContrastSensitivityViscosityAdhesionEtchresistanceSurfacetensionStorageandhandlingContaminantsandparticles

PhotoresistPhysicalCharacterResistContrastPoorResistContrastSlopedwallsSwellingPoorcontrastResistFilmGoodResistContrastSharpwallsNoswellingGoodcontrastResistFilmFigure13.16

ResistContrastPoorResistConSurfaceTension Lowsurfacetension Highsurfacetension fromlowmolecular fromhighmolecular forces forcesFigure13.17

SurfaceTension LowsurfaceteComponentsofConventionalPhotoresistAdditives:chemicalsthatcontrolspecificaspectsofresistmaterialSolvent:givesresistitsflowcharacteristicsSensitizers:photosensitivecomponentoftheresistmaterialResin:mixofpolymersusedasbinder;givesresistmechanicalandchemicalpropertiesFigure13.18

ComponentsofConventionalPhoNegativeResistCross-LinkingAreasexposedtolightbecomecrosslinkedandresistthedeveloperchemical.Unexposedareasremainsolubletodeveloperchemical.Pre-exposure-photoresistPost-exposure-photoresistPost-develop-photoresistUVOxidePhotoresistSubstrateCrosslinksUnexposedExposedSolubleFigure13.19

NegativeResistCross-LinkingAPACasDissolutionInhibitor

inPositiveI-LineResistResistexposedtolightdissolvesinthedeveloperchemical.Unexposedresist,containingPACs,remaincrosslinkedandinsolubletodeveloperchemical.Pre-exposure+photoresistPost-exposure+photoresistPost-develop+photoresistUVOxidePhotoresistSubstrateSolubleresistExposedUnexposedPACFigure13.20

PACasDissolutionInhibitor

GoodContrastCharacteristicsofPositiveI-linePhotoresistPositivePhotoresist:SharpwallsNoswellingGoodcontrastFilmResistFigure13.21

GoodContrastCharacteristicsDUVEmissionSpectrum*Intensityofmercurylampistoolowat248nmtobeusableinDUVphotolithographyapplications.Excimerlasers,suchasshownontheleftprovidemoreenergyforagivenDUVwavelength.MercurylampspectrumusedwithpermissionfromUSHIOSpecialtyLightingProductsFigure13.22

100806040200248nmRelativeIntensity(%)KrFlaseremissionspectrumEmissionspectrumofhigh-intensitymercurylamp120100806040200200 300 400 500 600Wavelength(nm)RelativeIntensity(%)g-line436nmi-line365nmh-line405nmDUV*248nmDUVEmissionSpectrum*IntensiChemicallyAmplified(CA)DUVResistResistexposedtolightdissolvesinthedeveloperchemical.UnexposedresistremainscrosslinkedandPAGsareinactive.Pre-exposure+CAphotoresistPost-exposure+CAphotoresistPost-develop+CAphotoresistUVOxidePhotoresistSubstrateUnchangedExposedUnexposedAcid-catalyzedreaction(duringPEB)PAGPAGPAGPAGH+PAGPAGPAGH+H+PAGPAGFigure13.23

ChemicallyAmplified(CA)DUVExposureStepsforChemically-AmplifiedDUVResist