应力的经典解释-Stress-Class-PresentionPPT课件

IntroductiontoStressMeasurementontheASET-F5xObjectivesDefinestressasusedinICmanufacturingDefinebow,coefficientofexpansionandradiusofcurvature.DifferentiatebetweentensileandcompressivestressIdentifythevariablesinStoney’sEquationandrelatethemtothephysicalparametersofthesubstrateandthefilmDescribecalculations,signconventionsanddatacollectionforstressListthesequenceofeventsinthemeasurementprocessDescribethedifferencebetweenstagewhenusedforstressandfilms.Describehowtherawdataiscollectedandprocessed.ListtheapplicationforstressWhatisStress?Stress=Force/Area=F/AForce=FFArea=AStressisdefinedasaforcevectordividedbytheareaofapplication.StressinaFilmonaWaferSiSubstrateForcesactintheplaneofthefilmStress=Force/Area=Force/(FilmThickness*FilmUnitWidth)WhatisThinFilmStress?ThinFilmStressisdevelopedduringdeposition.Typically,depositiontakesplaceathightemperatures.Thefilmandsubstratehavedifferentcoefficientsofthermalexpansion.Whenthefilmandsubstratecoolandremainattached,thematerial(eitherthefilmorthesubstrate)thathasthehighercoefficientofexpansionwillbeundertensilestressandtheothermaterialwillbeundercompressivestress.Theforcesattheinterfacewillbeequalandopposite;sincethefilmisusuallyverythin,itcanexperienceveryhighstresslevels.Similarly,sincethesubstrateissothick,itexperiencesverylowstresslevels.WhatisThinFilmStress?1.Filmatroomtemperature,noforceapplied3.Forcerequiredtostretchfilmuponcooling(sothatitstaysattachedtosubstrate)2.Filmatdeposition(high)temperature,noforceapplied4.Forcesactonsubstrate,anddeformwaferWhatareindicatorsofstressinafilm?Stressgoesthroughasystem,likegravityandmagneticforces,itisconsideredafieldvariable.Wecanonlydetermineitsvaluebyseeinghowitbendsthewafer.Bylookingatthebendingofthewaferbeforeandafterthedepositionofthefilmlayer,itcanbedeterminedwhatthestressisinthefilm.SilconSubstratefilm:tensilestressSubstrate:compressiveWhichofthesefilmsareunderthegreateststress?Assumethethicknessofallthefilmsareofthesamematerialandthickness.Placeinorderfromhigheststresstoloweststress.187654321t1c2t3t2c3cNoStress?MathematicalModelforStressIfitcannotbeexpressedinnumbers,itisnotfactbutmerelyanopinion.LazarusLongzr_scanBowtfFilmthicknessRRadiusofCurvaturew(r)HeightChangetsSubstratethicknessStoney’sEquation=--------------ts2tfE1R1-16n=Poisson’sratioE=Young’sModulusElasticModulusisameasureofthestiffnessofthematerialElasticModulusAnimportantmaterialspropertyistermedthetensileelasticmodulus,orYoung'sModulus.ThisisusuallygiventhesymbolE.Loosely,themodulusisdefinedastheforceyouneedtoprovidetoelongateyourmaterial. Young'sModulusforTypicalMaterialsSemiconductorsandMaterials:Diamond(C)1000SiliconCarbide(SiC)450Silicon(Si)107Silicaglass(SiO2)94 MetalsPolymers:Nylon2-4Polyethylene0.2-0.7Rubber0.01-0.1Tungsten(W)406Copper(Cu)124Aluminum(Al)69 StretchStoney’sEquationAssumptionsSubstrateisassumedtobe:thinelasticallyisotropic(equallystiffinalldirectionsintheplane)“perfectly”flatDepositedfilmisassumedtobe:ofuniformthicknessmuchthinnerthanthesubstrateunderisotropicplanestress(thestressisequalinalldirectionsintheplane)TemperatureofthewaferisuniformMaximumwaferdeflectionislessthanhalfthewaferthicknessThewaferismechanicallyfreeSignConventiontftszrRw(r)r_scanbow=w(r_scan)Inthisdiagram:thefilmisunderpositive(tensile)stressR(radiusofcurvature)ispositivebowispositiveFromTheoryIntoApplication…HowdoestheASETF5xmeasurestress?F5xMeasurementBasicsMeasuresthedeflectionofthewaferalongascanlineWaferscannedinasingleaxison3pinsupportSensorstationary–Tilt,4xDBSor15xDBSfocusesFitalinetothederivativeofthedeflectiondatatogetcurvatureCalibratedusingaflatmirror,50mconvexmirrorandatleasttwowafers(canbearbitrarywafers)Officiallyfor300mm,alsosupports200mmDataCollectionNotethat:WaferisnotperfectlyflattobeginwithStageistiltedStep1:Measuredeflectionbeforefilmdeposition-“pre”measurementDataCollectionNotethat:Wafertiltcanbedifferentthan“pre”measurement,duetopinrepeatabilityStep2:Measuredeflectionafterfilmdeposition-“post”measurementDataCollectionNotethat:DeflectiondifferenceiscircularCirculararccouldbetiltedStep3:Subtract“pre”-“post”datatogetdeflectiondifference.Thisisthestressinduceddeflection.CalculationofRTwodifferentmethodsFitaseconddegreepolynomialtothedeflectiondifferencedata(z)Fitalinetothederivativeofthedeflectiondifferencedata(dz/dr)Defaultislinearfitofdz/dr,controlledbyakestrel.inisettingDeterminationofRadiusofCurvatureRRscanRW(r)10.022.734.546.458.369.279.188.196.2104.1112.312-0.2DATACurvefittoaquadraticz=ar2+br+cNote:Beforeandafterfilmdepositionscansaremadetodeterminechangeinstress.CalculationofRFitaquadratictoz:z=ar2+br+cverticaloffsetcurvaturetiltSlope=dz/drCurvature=C(r)=d2z/dr2C(r)=constant=C=2aR=1/C=1/(2a)R=1/(2a)=1/mFitalinetodz/dr:dz/dr=2ar+b=mr+bCalculatedz/drbyfinitedifference(dz/dr)i=(zi+1-zi)/(ri+1-ri)=--------------ts2tfE1R1-1CalculationofStressandBowStress:UseStoney’sEquationBow:Usegeometrybow=(|R|-sqrt(R2-r_scan2))*sign(R)bowr_scanR6MeasurementMechanicsWaferplacedontoplaten,heldinplaceusingvacuumMeasurefilmthickness(ifneeded):SinglemeasurementorAverageofDiameterScanSequenceofEventsMeasurementMechanicsWaferliftedontothreepins:a)Vacuumoffb)Lowerstage1mmtoensureclearancec)Liftpins-checkpinsensorsd)Slidestresshardstopin--checkhardstopsensorse)SwitchtostresslimitswitchforCZcontrolf)ReduceXYaccelerationandvelocitytopreventwaferslippageSequenceofEventsMeasurementMechanicsMeasurewaferdeflection:a)Scandiameter,focusateachsiteb)UseSEcoarseor15xDBSfocusc)RecordstageCZ&FZpositionsDropwafertoplaten,reversingpreviousstepsReturnwafertocassetteMonitorwaferalignment(optional)SequenceofEventsFocus(FZ)IsusedtoDetermineheightCZ/FZDiscontinuities–Why?IdeallykeepCZfixedanduseFZonlytomeasurewaferdisplacementduringastressscanSeveralfactorscontributetopreventthisUseableFZfocusrange=240umWaferbowrangetobemeasured=+/-250umBowfor“flat”waferduetogravity=-60umWafertiltrelativetoopticalaxis=250ummax,variesfromsystem-to-systemCalibration-DataCollectionScanaflatmirrorScanaconvexcurvedmirror,R-50mScanavarietyofwafersatboth0ºand180ºwaferloadanglesMirrorsareonly150mmlongandsitintheslotintheplatenforthehandlerfinger.This0º-180ºdataisusedto“reflect”themirrordatatotheothersideoftheplaten.Calibration-DataProcessingFZmapUseflatmirrorasthe“pre”andconvexmirrorasthe“post’measurementsFindtheFZmapthatgivesthebestmatchtotheactualmirrorradiusoveralldatascans.ThingstoConsiderSensitivitytoairflowacrossthewaferWhenuponthestresspins,waferactsasawingandlifts,mainlyattheedges,withairflowacrossthewaferDynamicflowvariations(turbulence)causevibrationswhichdegradefocusrepeatabilityandstressprecisionStaticflowvariationscauseaccuracyshiftsO-ringsarenotanidealpointsupportforwaferEffectivepointofcontactlikelydifferentfornegativeandpositivebowedwafersLikelycauseofmeasurementshiftsandmatchingissuesKLAQualificationTestsUsebareSiwaferforthe“pre”measurementUsethermaloxidewafer(s)forthe“post”measurement(s)UseaconstantfilmthicknessInternalKLAwafersetconsistsof5wafersref,+/-170umbow,+/-40umbowFieldKLAwafersetconsistsof2wafersref,+170umbowApplicationsofStressMeasurementintheSemiconductorIndustryAluminumstressinducedvoidsPassivationcracking(nitride,oxide)StressinduceddislocationsinsiliconElectricaltestyielddegradationTungstensilicidecrackingApplicationsofStressMeasurementintheSemiconductorIndustry(cont.)StressincreaseinoxidesduringtemperaturecyclingConstantcurrentstresstest(CCST)degradationMatchingmetallizationexpansiononGaAsSiliconcrackingduetohighfilmstressDiecrackingApplicationsofStressMeasurementinMicroelectronicsAluminumstressinducedvoidsFilmcrackingFilmdelaminationWaferwarpageHillockformation.Electricaleffects(TDDB)Diecracking