Thin wafer grinding 超薄晶圆减薄

RecentDevelopmentsinThinwafergrinding–AnApplicationReviewThomasPuthanangady,RamaVedantham,JIkedaPhD.SaintGobainAbrasives-NortonSalKassir–StrasbaughSamKaoPhD–Tru-SiOutline•Introduction•WheredoesB/Gfitin•Whydoit•Whataresometypicalproblemsencountered•ObjectiveofPresentation•Experimentalmethod•Machineusedtogrind,Wheelsusedtogrind,metrology•equipment,recipeused•ExperimentalResults5.ConclusionsWaferFabsWorkFlowBackgrindingWaferManufacturingDepositionEtchingEpitaxySEMInspectRTPCMPIonImplantMaskLithographyBack-endSpinOnPhotoThinWaferProcessingWaferTestWaferMountDicingDieAttachWirebondEncapsulationFlipChipBackGrindDe-TapeEtchhandlingProfileofTypicalSiliconWaferLeftsideofthiswaferwasground.GrindingWaferswithBevelCADDrawingsillustratetheeffectofthebevelongrindingthinwafers.1in=200µmDeviceThinWaferwithBevelandDeviceBevelFullRadius1inCloseUpofThinWaferWithBevel•Closeupshowsthatthetipofthethinwaferisverythin.•Thethintipleadstochippingaroundtheedgeofthewafer.•Thedamagepropagatesaroundwaferandfurtherintowafer.1in=200µmxyx=TotalWaferThickness-CircuitryThicknessy=Function(x)VeryThin0.25in.ThinWaferGrinding•Thinnerwafersdonothavetheinherentmasstoresistbendingstressesdueto•Gravity•Residualgrinding/machiningstresses•ThisresultsinBowandWarp•Createshandlingissuesandmayultimatelyresultinwaferbreakage•Thiseffectismorepronouncedin200mmandlargerwafersObjectiveEvaluateeffectofgrindingwheelspecificationon8”thinwafersforoptimumtoolselectionEffectofgritsizeandgrade(wheelhardness)onthinwafer•Surfacestresses•Waferstrength•SurfaceRoughnesscharacteristicsFinalwaferthickness:125umTestMethodoloy-8”wafersmanuallytapedusingavacuumchuck-Testwheelsusedtogrind25nosof8”waferseachto125umthicknessontheStrasbaugh7AFgrinder-Theforceduringgrinding,cycletimeandthewheelwearratesweremonitored.-Waferswerede-tapedmanually-Surfacefinish(Ra,Rt),WaferBowandStrengthmeasured-ChippingwasclassifiedaspernumberandsizeofchipsusingamicroscopeCleanedges:NC(NoChippageatall)Roughedgewithnovisiblechippage:RE(RoughEdge)Onechipwithin1x1mm:MC(Mediumchippage)Morethanonechiporonechipbiggerthan1x1mm:LC(Largechippage)GrindingProcessDemonstration–EquipmentusedforTestsSTRASBAUGHTestRecipeandProcessParametersFineWheelTruingProgramPad:6”ExtraFineCoarseWheelTruing/DressingProgramPad:6”CoarseWheelspeed=1923RPMstep1step2dwellliftDressingamount(µm)1901010Feedrate(µm/s)20.25rev1Chuckspeed(rpm)50505050Wheelspeed=1200RPMstep1dwellliftDressingamount(µm)5020Feedrate(µm/s)575rev2Chuckspeed(rpm)200200200TestRecipeandProcessParametersCoarseGrindingProgramWheelspeed=137RPMStep1Step2Step3dwellliftWaferthickness(µm)165155150160Feedrate(µm/s)6315rev5Chuckspeed(rpm)100100100100100FineGrindingProgramWheelspeed=4350RPMStep1Step2Step3dwellliftWaferthickness(µm)135130125127Feedrate(µm/s)10.50.3100rev0.5Chuckspeed(rpm)590590590590590TestRecipeandprocessparametersAbrasivetoolstested•Coarse•Coarse#3R7B•Fine•Polish#1A•Polish#3A•Polish#4A•Polish#6A•Polish#3B•Polish#3C(HardnessABC,Gritsize#1#3#4#6)•Tapethickness=150um•Thewheelsonboththespindleswererotatinganticlockwiseandthechuckswerealsorotatinganticlockwise(lookingfromtop)MetrologyEquipmentThefinish,Waferbowandstrengthweremeasured.Theforcesduringgrindingweredownloadedusingthedataacquisitionsysteminthe7AF.WYKOMHT-IIIWhiteLightInterferometerSettingformeasuringfinegroundwafers:ModePSIObjective40XMagnification40.000=40.000x1.000OpticalFilterHighMag.ClearModThresh2.0%Resolution238x184FullViewNumberofAverages3AnalysisFilterNoneSmartscope250formeasuringtheflatness/bowofwafersEffectofGritSizeonGrindingThinWafersEffectofGritSizeonGrindingForces0510152025300102030405060WafernumberNormalGrindingForce[Lbs]Polish#1SPolish#3APolish#4APolish#6AEffectofGritSizeonGrindingProcesstime0204060801001201401600102030405060WafernumberProcesstime[seconds]Polish#1SPolish#3APolish#4APolish#6AEffectofgritsizeonFinish050100150200Polish#1APolish#3APolish#4APolish#6AWheelSpecificationRainA01000200030004000RtinARainARtinACoarsergritsizeEffectofgritsizeontheWaferBow0100200300400500600700Polish#1APolish#3APolish#4APolish#6AWheelSpecificationBowinumCoarsergritsizeEffectofGritSizeongrindingthinwafersCleanedges:1NC(NoChippageatall)Roughedgewithnovisiblechippage:2RE(RoughEdge)Onechipwithin1x1mm:3MC(Mediumchippage)Morethanonechiporonechipbiggerthan1x1mm:4LC(Largechippage)Effectofgritsizeonwheellife07005101520253035WafernumberWearPolish#3A(Normalizedlife100)Polish#4A(Normalizedlife81)Polish#6A(Normalizedlife200)CoarsergritsizeEffectofgritsizeondiefractureload00.511.52012345WheelspecificationFractureloadinlbsPolish#1APolish#6APolish#4APolish#3ACoarsegritsizeEffectofgritsizeonChipping012345Polish#1APolish#3APolish#4APolish#6AWheelspecificationChipping(Qualitative)ChippingEffectofgritsizeonchippingPolish#1APolish#3APolish#4APolish#6AEffectofGradeongrindingthinwafersEffectofWheelHardnessonGrindingForces0510152025303540450102030405060WafernumberNormalGrindingForcein[Lbs]Polish#3APolish#3BPolish#3CEffectofWheelHardnessongrindingProcesstime0204060801001200102030405060WafernumberProcesstime[se