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首页 Carrier techniques for thin wafer processing

Carrier techniques for thin wafer processing.pdf

Carrier techniques for thin waf…

kukuka6
2012-07-25 0人阅读 0 0 0 暂无简介 举报

简介:本文档为《Carrier techniques for thin wafer processingpdf》,可适用于工程科技领域

CarriertechniquesforthinwaferprocessingCLandesberger,SScherbaum,KBockFraunhoferInstituteforReliabilityandMicrointegrationIZM,Munichbranchoftheinstitute,Hansastrassed,Munich,Germanyemail:christoflandesbergerizmmfraunhoferde,phone:()Keywords:reversiblebonding,mobileelectrostaticcarriers,thinwaferprocessing,waferhandlingAbstractThreedifferenttypesofcarriertechniqueshavebeeninvestigatedanddeveloped:thermalreleasetapes,solvablethermoplasticgluelayerandmobileelectrostaticcarrierThesecarrierswereappliedformanufactureofultrathinRFIDchips,µmthinCMOSimagesensorsandtoanewprocesssequencethatenablestheformationofsolderballsatthefrontsideofanalreadythinneddevicewaferTechnicalcapabilitiesofdifferentcarriertechniquesarecomparedwithrespecttoallowedtemperaturerange,typeofbondinganddebondingmechanismandtheircompatibilitywithtypicalwaferfabprocessesMobileelectrostaticcarrierswereusedtoperformsolderballbumpingatµmthinsiliconwafersTheprocesssequencedemonstratesthecapabilityofelectrostaticcarriertechnologytoenablethinwaferprocessingatelevatedtemperaturesINTRODUCTIONTheincreasingdemandforthinsemiconductordeviceshaverequiredmoreandmoresophisticatedsolutionsfortheirmanufacturingprocessesAppropriatesupportsystemsareabasicneedforsecurehandlingandprocessingofverythinsemiconductordevicewafersGenerallythisisaccomplishedbytemporarilybondingarigidcarriersubstrateontothefrontsideofadevicewaferbeforethinningWellknowntechniquesusepolymericbondingagentslikewax,solvablegluesorthermallyreleasableadhesivetapesFurthermanufactureconceptsarebasedonbondingmaterialsthatcanbereleasedafterUVlaserirradiationthroughatransparentglasscarrierApplicationofpolymerbasedbondingtechniquesislimitedtothetemperaturerangebelow°CFurtherincreasedtemperaturestabilityisrequiredinordertoallowprocessstepslikesinteringofbacksidemetalorplasmaetchingofdielectriclayersIncontrarytoadhesivebondingelectrostaticattractionhasthepotentialtoenablethinwaferprocessingatelevatedtemperaturesRecentdevelopmentworkattheauthors’institutehasleadtoanewtypeofmobileelectrostaticcarriersbasedonsiliconwafersubstrateswhichweresuccessfullyappliedtoprocessstepslikephotolithographyandplasmaetchingNextsectionswilldescribefollowingdifferenttypesofcarriertechniques:thermalreleasetapes,thermoplasticgluelayersandmobileelectrostaticcarriersTHERMALRELEASETAPESApplicationofthermalreleasetapeshasbecomeawidespreadmethodinordertosupportwaferswithlowtopographiesduringthinningprocessesAcarrierisattachedtotheprocesswaferbymeansofadoublesidedadhesivetapewithonesidethermalreleasableSubsequently,backsidegrindingandetchingdowntoµmcanbeperformedRemovalofthecarrierisperformedbyaheatingtreatmentbetweenand°CThismethodwasalsoappliedforwaferswithhighsurfacetopographyInthiscase,devicetopographywasembeddedbyanadditionaltapeFurthermorethismethodcanbecombinedwiththeDicingbyThinningtechnology(DbyT)asillustratedinFigDicinggroovesarepreparedatwaferfrontsidewiththetrenchdepthcorrespondingtotheprojectedchipthicknessPreparationofthesechipgroovescanbeaccomplishedbymeansofawafersaworbysilicondryetchingAftermountingthetrencheddevicewafertothecarriersubstratethewaferpairisthinnedfromitsbacksideuntilthechipgroovesareopenedCarriersubstratea)b)c)CMOSwaferCarriersubstrateCMOSwaferEmbeddingmaterialTemperaturereleasetapeEmbeddingmaterialTemperaturereleasetapeCarriersubstratea)b)c)CMOSwaferCMOSwaferCarriersubstrateCMOSwaferEmbeddingmaterialTemperaturereleasetapeCMOSwaferEmbeddingmaterialTemperaturereleasetapeEmbeddingmaterialTemperaturereleasetapeEmbeddingmaterialTemperaturereleasetapeFig:DicingbyThinningprocessforwaferswithhightopographies:a)Prepatterningofscribelines,b)Embeddingoftopographiesandreversiblebondingtocarriersubstrate,c)ResultafterthinningprocessProblemsmayarisewhenchemicals(etchantsorpolishingslurries)getincontactwiththeembeddingmaterialthroughtheseparationgroovesInordertoovercomethesedifficultiesweintroducedaprotectivelayerwhichisspunontothewafersurfacebeforetapingAfterwaferthinningthecarriersubstrateisliftedoffbyinitiatingthethermalreleasefunctionofthethermaltapeSubsequently,allseparatedchipsyetattachedtotheembeddingtapeweretransferredontoafilmframecarrier(seeFig)TheprotectivecoatingwasremovedafterdelaminatingtheembeddingtapeWaferthinning,chipseparationandtransferwassuccessfullyconductedwithµmthinandflexibleRFIDchipsforsmartlabelapplicationsCSMANTECHConference,May,,Austin,Texas,USAFig:FilmframecarrierwithµmthinchipsonthermalreleasepickuptapesinglechipswereremovedontheleftsideSOLVABLETHERMOPLASTICGLUELAYERAssecondmethodforreversiblebondingtechniquebymeansofpolymericmaterialsweinvestigatedthermoplasticgluelayerswhichcanbeappliedbyspincoatingprocessUsingthismethodallowsforverythinanduniformadhesivelayersThisisofutmostimportancewhenwafersofafinalthicknessintherangeofµmaretobepreparedThicknessvariationsintheadhesivefilmwoulddirectlyresultinanonuniformwaferthicknesswhichisinmostcasesnottolerableThere’sasecondbenefitwhenusingsuchgluelayers:thecapabilitytoembedsurfacetopographyEspeciallywhencombining“DicingbyThinning”technologywithafinalCMPpolishingprocessperformedattoµmthindevicewaferswesucceededinbestthinningresultsThethermoplasticgluefillsthefrontsidechiptrenchestoalargeextentandtherebypreventschipcrackingduringfinalCMPstepFigshowsacrosssectionofaµmthinwaferprocessedaccordingtoDbyTconceptChipsarealreadyseparatedandarestillattachedtoacarrierwaferbythermoplasticadhesiveFig:Crosssectionofthinnedwafer,mountedonacarriersubstratebymeansofathinsolvablegluelayerInordertoremoveallthindiesthecarrierwaferisimmersedintoasolventbathandtheglueisdissolvedAlldiesarereleasedwithoutanymechanicalforceandcanbefishedoutofthebathTheprocessflowwasappliedtosiliconCMOSimagesensorwafers(diametermm)–µmthinsensorchipswerepreparedandtheirelectricalfunctionalitywasprovenFig:µmthinCMOSimagesensorplacedonasheetofpaper(left)andcomparedtoachipofstandardthickness(right)MOBILEELECTROSTATICCARRIERSElectrostaticforcesoffertheuniqueopportunitytorealizeareversiblebondingtechniquewithoutusingpolymericbondingmaterialsThereforebondinganddebondingofthinwafersontoelectrostaticcarrierscanbeachievedwithinveryshorttime,inarepeatablemannerandwithoutanyconstraintsregardingsurfacecontaminantsfrombondingagentsFigshowsanexampleofamobileelectrostaticcarrierpreparedonasiliconwafersubstrateandtheadjacentchargingunitwhichprovidesVDCvoltagetoinitiatetheelectrostaticfixationFig:MobileelectrostaticcarriermadeonsiliconwafersubstrateandhandheldpowersupplyMostimportantfeatureofthiscarriertechniqueisitsabilitytomaintainelectrostaticattractionafterdisconnectionofpowersupplyforalongperiodoftimeItwasalreadyshownthatpermanentpolarizationstateremainsactiveattemperaturesevenabove°CFigshowsthevoltagedecayatthecontactpadsofamobileelectrostaticcarrier,measuredatroomtemperatureandwithathinwaferattachedontothecarrierRoomtemperaturestabilityofthechargingstatuskeepsconstantformanydaysandtherebyoffersanewandeasytechnicalsolutionfortransport,storageandhandlingofthinandfragilewafersThelongdurationtimeofthepolarizedstateofthecarrierisalsoCSMANTECHConference,May,,Austin,Texas,USAconfirmedbyfittingexperimentaldatawithanexponentialdecaycurveFitresultsindicateanimpressivelyhighportionofconstantpolarization,whichisaroundVwheninitialchargingwasperformedatV(seeFig)Data:DataSiESTModel:ExpDecChi^DoF=R^=y±A±t±Sicarrier(type)fitexponentialdecayVoltageatelectrodesVTimeindaysFig:Electrostaticpotentialmeasuredatamobileelectrostaticcarrielectrostaticcarriershavebeenpreparedonceramic,glassUMPINGOFTHINWAFERSBYMEANSOFMOBILEsedforflipchipassembliesandFig:µmthintestwaferfixedontoamobileelectrostaticcarrierFigIERTECHNIQUESapplyandenablerafterremovalofchargingunitperformedat°CEandsiliconwafersubstratesForapplicationsinGaAstechnologyalsosapphiresubstrateswouldbeverydesirableinordertomatchcoefficientsofthermalexpansionofcarrieranddevicewaferBELECTROSTATICCARRIERSSolderbumpsarewidelyuchipscalepackage(CSP)technologiesHowever,thinningofwaferswithsolderballshavingadiameterof–µmisachallengingtaskActuallywaferthicknessbelowµmcouldn’tbereachedbybacksidegrindingduetohighriskforwaferbreakageMobileelectrostaticcarriersnowofferthepossibilityforanewprocesssequence:Afterdepositionoftheunderbumpmetallisation(UBMegNiAu,–µminthickness)thewaferisfirstthinnedbystandardbackgrindingprocessThegroundwafermaythenbeattachedontoamobileelectrostaticcarrierandundergoesfurtherstressreliefprocesseslikespinetchingordryetchingAfterwardsthethinwaferistransferredontoanotherelectrostaticcarrierandsubsequentlyisintroducedintothebumpingsequenceThiscomprisessolderpastedepositionbystencilprintingandsolderreflowinabeltfurnaceattemperaturesaround°CFigshowsaµmthintestwafer,diametermm,attachedontoamobileelectrostaticcarrierSolderballsarealreadyformedandarevisiblealongthechiplayoutAfterbumpingwaferswereremovedfromthecarrieranddicedbyaconventionalwafersawFinalSEMinspection,seeFig,showstheamazingrelationbetweenchipthicknessandsolderballdimensionsItshouldbementionedthatgrindingofwaferhavingsolderballsofµmindiameterontopwoulddefinitelyresultinbrokenwafersubstrateThereforebumpingofathinwaferissuggestedinsteadofthinningabumpedwaferAccordingtothisnewconceptnorestrictioninwaferthicknessandorwaferdiameterdoesappear:SEMpictureofµmthinsinglechipssolderballbumpingwasperformedafterthinningCOMPARISONOFCARRThermalreleasetapesareeasytomanufactureandhandlingof–µmthin,flexiblewafersanddiesDifficultieshavebeenfoundwhenCMPpolishingincombinationwithDicingbyThinningconceptsshouldberealizedforchipthicknessbelowµmDuetolowthermalresistanceofpolymertapesthepossibilitytorunprocessesatthebacksideofthinnedwafersisstronglylimitedFurthermoretapescannotsealthewaferedgeduring“underwater”processesPenetrationofprocessliquidslikewaterandsolventsoftenleadstodelaminationofthetapeclosetowaferedgeThinthermoplasticgluelayersallowforhighlyuniformwaferthickness,alsoincombinationwithCMPpolishingandDbyTtechniquesTemporaryadhesivebondingbythingluelayersalsoenablelowtemperaturebacksideprocesseslikephotolithographyandmetalsputteringHowever,dissolvingofgluelayersandremovalofresiduesrequirefurthertechnicaleffortsCSMANTECHConference,May,,Austin,Texas,USAMobileelectrostaticcarriersopenthedoorforhightemperaturebacksideprocessingofthinwafersTechnicalESThermalrmoplasticMobilelimitationsoccurwithprocessesinliquidenvironmentsduetopenetrationoffluidsbetweencarrieranddevicewaferInprinciplethisriskmightbereducedorstoppedbyapplyingasoftsealringorlayerontopoftheelectrostaticcarrierHowever,thiswouldthenreducethermalstabilityTABLECOMPARISONOFREVERSIBLEBONDINGTECHNIQUreleasetapesadhesiveelectrostaticThecarrierApplicationofBondlayerlaminationTapeSpincoatingnoneThicknessofbondlayer–µm–µmnoneTemperaturestability–°Cca°C°C>Processcapabilitesgrinding,spin,etching,g,layerdeposition,Waferetchinggrinding,polishing,sputtering,lithographyDryetchinlithography,sintering,…DebondingmechanismHeatinduceddischargeDissolvechemicallyElectricalNecessityfocleaningrInsomecasesyesnoPossibleproduapplicatioctnssemiconductorstegration,ultrathiner,discrete,solarcell,Thin,flexibledindevicesPowGaAs,optoelectronicdevicesithrespecttothisshortdiscussionitiscdthatere’syetnotasinglecarriersolutionthatfulfillsallFERecauseofthesimplebondinganddebondingmechanismriersarespecificallyqualifiedforWthoncluderequirementsofthinwafertechnologyAsconsequencethisleadstoanewtask:developmentofappropriatewafertransferconceptswhichallowacombinationofdifferentcarriertechniquesTHINWAFERTRANSBmobileelectrostaticcartransferprocessesofverythinwafersFigshowsanexamplehowtotransferathinnedwaferfromacarrierwiththermalreleasetapeontoanelectrostaticcarriermobileESChotplatemobileESChotplatemobileESChotplatemobileESChotplateFig:Transferofathinnedwaferfroanadhesivetapebasedcarrier(leftontop)ontoanelectrostaticcarrier(rightsideatbottom)dstoatripleferontoastandardporousvacuumchuckandthenTemporarybondingtechniquesenablesecurehandlingofverythinandfragilesemiconductorbcessstepswillleadtonewmanufactureNTSothankRainerPatzeltfromlinfortheaccomplishmentofsolderalSPargfrieder,PLindner,GMittendorfer,JWeixlbergerUltrathinsingUsingTemporaryBondingSemiconductorrevices”,mFirstthebacksideofthethinnedwaferisputontotheelectrostaticcarrierChargingtheecarrierleawaferstackByheatingtheunderlyingvacuumhotplatetheadhesionofthethermalreleasetapegetslostandthefirstcarrierontopofthestackcaneasilyberemovedThethinwaferitselfisalwaysconnectedtoarigidcarrierThistransferconceptwasusedsuccessfullyforthedemonstrationofsolderballbumpingafterwaferthinningInthiscasewaferbacksidewasattachedontotheelectrostaticcarrier,subsequentfrontsideprocessescouldbeperformedstraightforwardOfcourseitwillbealsopossibletofirsttransferathinneddevicewaattachthesurfaceofthisdevicewaferontoanelectrostaticcarrierSuchhandlingsequenceenablesfurtherbacksideprocessstepsforthinwafersattachedontoamobileelectrostaticcarrierCONCLUSIONSandprocessingsustratesUltrathinsilicondeviceswerepreparedbymeansofreversibleadhesivetapesandsolvablegluelayersElectrostaticcarrieropenthedoortohightemperatureprocessingoftemporarilyattachedthinwafersInordertodemonstratetheapplicabilityofmobileecarriersabumpingprocessforµmthinsiliconwaferscouldberealizedsuccessfullyItissupposedthatappropriateselectionofcarriertechniquesforspecificproconceptsforverythinandfragilesemiconductorsubstratesinthenearfutureACKNOWLEDGEMETheauthorswouldliketFraunhoferIZMinBerblbumpingREFERENCESWaferProcesInternational,JanuaryCKessel,KSaito,FWeimarWaferThinningbyusingMWafeSupportSystemWorkshop”ThinSemiconductorDNovember,Munich,GermanyKBock,CLandesberger,MBleier,DBollmann,DHemmetzberger,„Characterizationofelectrostaticcarriersubstratestobeusedasasupportforthinsemiconductorwafers”,InternationalConferenceonCompoundSemiconductorManufacturingTechnology“GaAsMantech”,NewOrleans,Louisiana,AprilCLandesberger,DBollmann,ADrost,USchaber,KBockHandlingandprocessingofthinsemiconductorsubstratesbymeansofmobileelectrostaticcarriersInternationalMEMSMSTIndustryForum,SemiconEuropa,Munich,GermanyMFeil,CAdler,DHemmetzberger,MKönig,KBockTheChallengeofUltraThinChipAssemblyElectronicsComponentsandTechnologyConference,,LasVegas,Nevada,USAFRobert,DTomuta,JvanSpijker,CKallmayer,CLandesbergerBacksidethinnedSiimagesensorsinUHVdevicesWorkshop”ThinSemiconductorDevices”,November,Munich,Germanysee:wwwbeflexibledeUSpatentUS,,BGermanpatentapplicationDEACSMANTECHConference,May,,Austin,Texas,USA

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