MEMS原理-02-Lithography

02微机械加工技术图形转移（光刻）工艺OpticalLithographyUsesofLithographyOutlinesLithographyoverviewPhotoresistsNegativephotoresistPositivephotoresistLithographyprocessesSpincoatingprimerandPRPre-bakeAlignmentandexposureDevelopmentHardbakeEtchStripPRFutureTrendsSummaryLithographyoverviewEpitaxialGrowthOxidationLithographyBoronDiffusionOxidationLithographyPDiffusionOxidationLithographyAldepositionLithographyDicingSinterBondingPackageTestMainfabricationtechnologyprocessesoftransistorPhotoresists(PR)•Photosensitivematerial•Temporarilycoatedonwafersurface•Transferdesignimageonitthroughexposure•VerysimilartothephotosensitivecoatingonthefilmforcameraPhotoresistComposition•Polymer(resinorbasematerials)•Sensitizers(photoactivecompound,PAC)•Solvents•AdditivesMostutilitarianmetricsofthephotoresist•Sensitivity(mJ/cm2)•Resolution(smallestfeature)Polymer•Solidorganicmaterial•Transfersdesignedpatterntowafersurface•ChangessolubilityduetophotochemicalreactionwhenexposedtoUVlight.•PositivePR:frominsolubletosoluble•NegativePR:fromsolubletoinsolubleSensitizers•Controlsand/ormodifiesphotochemicalreactionofresistduringexposure.•DeterminesexposuretimeandintensitySolvent•DissolvespolymersintoliquidthinningPR•AllowapplicationofthinPRlayersbyspinningAdditives•Variousaddedchemicaltoachievedesiredprocessresults,suchasdyestoreducereflection.TypesofPhotoresistsNegativePhotoresist•Becomesinsolubleafterexposure•Whendeveloped,theunexposedpartsdissolved.•CheaperPositivePhotoresist•Becomessolubleafterexposure•Whendeveloped,theexposedpartsdissolved•BetterresolutionMask/reticleExposureAfterDevelopmentNegativePhotoresistUVlightPositivePhotoresistSubstrateSubstrateSubstratePhotoresistNegativeandPositivePhotoresistsSubstratePhotoresistNegativePhotoresistMaskExposeDevelopmentNegativePhotoresistNegativeResist•MostnegativePRarepolyisoprene(聚异戊二烯)type•ExposedPRbecomescross-linkedpolymer•Cross-linkedpolymerhashigherchemicaletchresistance.•Unexposedpartwillbedissolvedindevelopmentsolution.PositivePhotoresist•Novolacresinpolymer（酯醛树脂）•Acetatetypesolvents(醋酸酯)•Sensitizercross-linkedwithintheresin•Energyfromthelightdissociatesthesensitizerandbreaksdownthecross-links•Exposedpartdissolveindevelopersolution•Imagethesamethatonthemask•Higherresolution•CommonlyusedinICfabricationsMask/reticleExposureAfterDevelopmentUVlightPositivePhotoresistSubstrateSubstrateSubstratePhotoresistPositivePhotoresistsSubstratePhotoresistDisadvantagesofNegativePhotoresist•Polymerabsorbsthedevelopmentsolvent•PoorresolutionduetoPRswelling•Environmentalandsafetyissuesduetothemainsolventsxylene(二甲苯).ComparisonofPhotoresists-PRFilm+PRFilmSubstrateSubstrateQuestion•Positivephotoresistcanachievemuchhigherresolutionthannegativephotoresist,whydidn’tpeopleuseitbeforethe1980s?Answer•Positivephotoresistismuchmoreexpensivethereforenegativephotoresistwasuseduntilithadtobereplacedwhentheminimumfeaturesizewasshrunktosmallerthan3mmLithographyprocesses•SpincoatingprimerandPR•Pre-bake•Alignmentandexposure•Development•Hardbake•Etch•StripPRBasicSteps-OldTechnology•Waferclean•Dehydrationbake•SpincoatingprimerandPR•Softbake•Alignmentandexposure•Development•Patterninspection•HardbakePRcoatingDevelopmentBasicSteps-AdvancedTechnology•Waferclean•Pre-bakeandprimercoating•Photoresistspincoating•Softbake•Alignmentandexposure•Postexposurebake•Development•Hardbake•PatterninspectionPRcoatingDevelopmentTrack-stepperintegratedsystemHardbakeStripPREtchPreviousProcessIonImplantRejectedSurfacepreparationPRcoatingSoftbakeAlignment&ExposureDevelopmentInspectionPEBApprovedCleanTracksystemPhotoBayPhotocellLithographyprocessesWaferClean•Removecontaminants•Removeparticulate•Reducepinholesandotherdefects•Improvephotoresistadhesion•Basicsteps–Chemicalclean–Rinse–DryPrimerVaporCoatingDehydrationBakeWaferPrepChamberPrimerLayerPre-bakeandPrimerVaporCoatingWaferHotPlateHotPlateHMDSVaporHMDS:六甲基二硅亚胺•Dehydrationbake•Removemoisturefromwafersurface•PromoteadhesionbetweenPRandsurface•Usuallyaround100°C•IntegrationwithprimercoatingPhotolithographyProcess,Prebake•PromotesadhesionofPRtowafersurface•Wildlyused:Hexamethyldisilazane(HMDS)•HMDSvaporcoatingpriortoPRspincoating•Usuallyperformedin-situwithpre-bake•ChillplatetocooldownwaferbeforePRcoatingPhotolithographyProcess,PrimerWaferCooling•Waferneedtocooldown•Water-cooledchillplate•TemperaturecanaffectPRviscosity–AffectPRspincoatingthickness•Wafersitonavacuumchuck•Slowspin~500rpm•Liquidphotoresistappliedatcenterofwafer•Rampupto~3000-7000rpm•Photoresistspreadbycentrifugalforce•EvenlycoatonwafersurfacePhotoresistCoating-SpinCoatingSpinCoater•Automaticwaferloadingsystemfromrobotoftracksystem•Vacuumchucktoholdwafer•Resistcontainmentanddrain•Exhaustfeatures•Controllablespinmotor•Dispenseranddispenserpump•EdgebeadremovalPhotoresistSpinCoaterVacuumPREBRWaferChuckWaterSleeveDrainExhaustEBR:乳化丁二烯橡胶PhotoresistApplyingSpindlePRdispensernozzleChuckWaferTovacuumpumpPhotoresistSuckBackSpindleTovacuumpumpPRdispensernozzleChuckPRsuckbackWaferPhotoresistSpinCoatingSpindleTovacuumpumpPRdispensernozzleChuckPRsuckbackWaferPho