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Process Considerations for Manufacturing 50 μm Thinned III-V Wafers.pdf

Process Considerations for Manu…

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2012-07-25 0人阅读 0 0 0 暂无简介 举报

简介:本文档为《Process Considerations for Manufacturing 50 μm Thinned III-V Waferspdf》,可适用于人文社科领域

ProcessConsiderationsforManufacturingμmThinnedIIIVWafersGCobb,HIsom,CSellers,VWilliamsTriQuintSemiconductorWRennerRdRichardson,TX,email:hisomtqscomKeywords:μmthinnedIIIVmaterial,backsideprocessing,mount,demount,manufacturability,saw,pickandplaceABSTRACT:DeviceperformancerequirementsforheatdissipationcontinuetodriveproductstothinnersubstratethicknessHowever,processingofwafersthinnedtoμmcreatesnewchallengesforhandlingthesefragilesubstratesBreakageofsubstratesduringmanufacturingcancreatesignificantexpenseandtheriskofdamageisincreasedasthenumberofstepsforbacksideprocessingincreasesTriQuintSemiconductorhassuccessfullydevelopedanddemonstratedaprocessformanufacturingdevicesonμmthinnedIIIVsubstratesThispaperfocusesontheprocesscontrolsandconsiderationsneededtomanufacturedevicesonthinnedsubstratesProcessconsiderationsatseveralpointsinthethinwaferflow(includingwafermounting,backsidemetallization,demountinganddiesingulation)willbediscussedWAFERMOUNT:DuetotheintrinsicbrittlenessofIIIVcompoundsemiconductormaterials,wafersmustbetemporarilybondedtoarigidcarrierwhilebeingprocessedthroughbackgrind,photolithography,metallizationandsubstrateviaetchstepsduringbacksideprocessingBondingcanbeachievedbyvariousmethods,suchasthermalorUVreleasefilm,waxorUVcuredopticaladhesiveWithallofthesebondingmethods,additionalprecautionsmustbetakentoensurethatthedevicesideofthewaferisprotectedfrombothchemicalandmechanicaldamageTriQuintSemiconductorutilizesaUVcurableopticaladhesiveandprotectivenegativeresistcoatingtobondwaferstoasapphirecarriersubstrateThenegativeresistcoatingmustbeofsufficientthicknesstocompletelycoverallfrontsidetopographysothattheopticaladhesivelayerdoesnotcontactanyofthefrontsidemetallizationDebondingisachievedbydissolvingthenegativeresistlayersince,oncecuredtheopticaladhesivebecomesvirtuallyinsolubleinsolventscommonlyusedinsemiconductordeviceprocessingWehavefoundthatthecuredopticaladhesiveisrequiredtokeepthethinnedwafersbondedtothesupportingsapphirecarrierduringthesubstrateviaplasmaprocessingBACKSIDEMETALLIZATION:Wafersthinnedtoμm,μmorlessbecomeincreasinglysusceptibletothestresseffectsofappliedthinfilmsThestressofepitaxialfilmscancausesignificantbowingofIIIVwafersafterthecarriersubstratehasbeendebondedfromthewaferIfnotaccountedandcompensatedfor,thisstresscanleadtoyieldlossduetowaferbreakageduringthewaferdebondingprocessorparametricyieldlossduetopoorthermalcontactduringelectricalprobeFollowingsubstrateviaformation,TriQuintSemiconductorsputtersacoatingofTiWNiAuthatactsastheseedmetalforthegoldplatingonthebacksideofthedeviceThestressinthislayerisadjustedtocompensateforcurvatureofthewaferinducedbytheepitaxiallayersThisadjustmentismadebyvaryingthedepositionpressureasseeninFigureBycarefultuningofthestressintheseedmetallayer,thecurvatureofthethinnedwaferisminimizedTiWStressvsDepositionPressurePressure(mTorr)Stress(mPa)Stress(mPa)FigureTiWfilmstressasafunctionofdepositionpressureWAFERDEMOUNT:Asindicatedbytheterminologyof“temporarybonding”,wafersmustberemovedfromthecarriersubstrateattheconclusionofbacksideprocessingThisdemountstepcanbethesourceofsignificantwaferbreakagewithμmthinnedsubstratesThedemountstepmustcompletelydebondthewafersfromthecarriersubstratewithnoresidueremainingonthewaferTriQuintSemiconductorhasdevelopedademountprocessthatconsistsofamultistepchemicalprocessthatdebondsthewaferfromsubstrateandalsoremovestheprotectiveresistlayeratthesametimeCSMANTECHConference,May,,Austin,Texas,USAAswithanychemicalprocess,thefirstconsiderationmustbetoselectchemicalsthatarecompatiblewiththesubstratewaferused,thematerialsdepositedduringthedevicefabricationprocessandthatcanbesafelyimplementedintothefabricationenvironmentSecondly,theprocessdevelopedmustberobustandminimizecycletimeTriQuintSemiconductorhasdevelopedadebondingprocessthatutilizeschemicalscommonlyfoundinsemiconductorprocessingThesechemicalsareusedtodissolvethesacrificialnegativeresistlayerappliedtothewaferspriortobondingthemtothesupportingsapphireusingtheopticaladhesiveAsstatedpreviously,theopticaladhesiveisnotnormallysolubleinthesechemicalsandremainsonthesapphiresupportswhichmustbecleanedinaseparatecleaningprocessWhendevelopingthedebondingprocessforμmthinnedwafers,itbecameapparentthattheturbulencegeneratedbynormalprocessinginoverflowweirtankswascausingwaferstocrackandbreakduringtheprocessAttemptstoadjusttheturbulencebyadjustingflowratesfailedtoimprovethedebondingresultsWefoundthatbafflingtheincomingflowresultedinasubstantialimprovementtothedebondingprocess(Figure)umDebondProcessRun#UnitsUnitFigureDIESINGULATION:DiesingulationmaybeachievedbyutilizingeitherwaferscribeandbreakmethodsorsawingTriQuintSemiconductorutilizesbothmethodsfordiesingulationforμmthinnedwafersThispaperwillfocusontheprocessconsiderationsforsawingμmthinnedwafersTapeselectionforthesawprocesswasdeterminedtobetheyieldlimitingcharacteristicinachievinghighyieldsatdiepickonμmthinnedIIIVsubstratesGreaterthandieyieldfrompickhasbeenachievedwithexcellentqualityafteroptimizationofthetapeselectionanddiepickprocessIndevelopingasawprocessforμmthinnedwafersitisimportanttoconsiderthephysicalnatureoftheprocessintermsofforcefromthesawblademovingthroughthematerial,thedepthofthecutintothesupportingtapeandthecoolingwaterbeingacceleratedacrossthewaferbythebladeTapemustbeselectedsothatdieareheldsecurelyduringthesingulationprocessbutcanbeeasilyremovedduringthediepickprocessaftersingulationDesignedexperimentswereconductedfocusingontapesfromvariousvendors(Table)tooptimizethediesingulationprocessTable:TapeDesignationAdhesiveThickness(μm)AdhesionaftercureAgmmBgmmCgmmOneexperimentallayoutandtheresultsofthetestarefoundinTableThefigureofmeritusedinthisexperimentwasthepercentageofdieexhibitingdefectsafterdiepickThebestresultswereobtainedusingtapeCwhichhasthethinnestadhesivelayerandlowestadhesionaftercureTable:TheseresultssupportatheorythatduringthesawprocesstheadhesiveispushedupintothesubstrateviaandissubsequentlyprotectedfromtheUVexposuretoreducethetackleveloftheadhesiveWhenattemptsaremadetoremovethedieatthepickprocessthishightackareacausesaplugofadhesivetobeleftinthesubstrateviaThereductioninadhesivethicknessminimizestheamountofhightackmaterialontheinteriorofthesubstrateviaandallowsfordietoberemovedwithoutresidualmaterialCSMANTECHConference,May,,Austin,Texas,USACONCLUSIONSDevelopingprocessesforIIIVsemiconductorwafersthinnedtoμmandbeyondposesanentirelynewrealmofdifficultiesasthinfilmeffectsbegintodominatetheintrinsicstrengthofthesubstratematerialSpecialconsiderationsmustbetakenwithregardstostressmanagementofdepositedfilmsandtothestressinducedbythechemicalandmechanicalprocessingthatmustbedonetoproducethefinaldevicesAsdeviceperformancerequirementscontinuetodrivesubstratethicknesstoprogressivelysmallersizes,newprocessdevelopmentwillfollowtoallowformanufacturabilityofthosedevicesACKNOWLEDGEMENTSTheauthorswouldliketothankthefollowingindividualsfortheirsupportincompletingthetestingandexperimentationrequiredforthisproject:GlenBronson,DrAndrewMacInnes,RodneyBrownandJamesMillerACRONYMSUV:ultravioletCSMANTECHConference,May,,Austin,Texas,USACSMANTECHConference,May,,Austin,Texas,USAOMNIBLANK:

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