《半导体生产过程》PPT课件.ppt

EE4345-SemiconductorElectronicsDesignProject,SiliconManufacturingGroupMembersYoungSoonSongNghiaNguyenKeiWongEyadFanousHannaKimStevenHsu,HISTORY,19thCentury-Solid-StateRectifiers1907-ApplicationofCrystalDetectorinRadioSets1947-BJTConstructedbyBardeenandBrattain1959IntegratedCircuitConstructedbyKilby,SemiconductorManufacturingProcess,SemiconductorManufacturingProcess,FundamentalProcessingSteps,1.SiliconManufacturinga)Czochralskimethod.b)WaferManufacturingc)Crystalstructure2.Photolithographya)Photoresistsb)PhotomaskandReticlesc)Patterning,3.OxideGrowth&Removala)OxideGrowth&Depositionb)OxideRemovalc)Othereffectsd)LocalOxidation4.Diffusion&IonImplantationa)Diffusionb)Othereffectsc)IonImplantation,SemiconductorManufacturingProcess(cont),SiliconManufacturing,CrystalGrowthandWaferManufacturing,FABRICATINGSILICON,Quartz,orSilica,ConsistsofSiliconDioxideSandContainsManyTinyGrainsofQuartzSiliconCanbeArtificiallyProducedbyCombiningSilicaandCarboninElectricFurniceGivesPolycrystallineSilicon(multitudeofcrystals)PracticalIntegratedCircuitsCanOnlybeFabricatedfromSingle-CrystalMaterial,CRYSTALGROWTH,CzochralskiProcessisaTechniqueinMakingSingle-CrystalSiliconASolidSeedCrystalisRotatedandSlowlyExtractedfromaPoolofMoltenSiRequiresCarefulControltoGiveCrystalsDesiredPurityandDimensions,CYLINDEROFMONOCRYSTALLINE,TheSiliconCylinderisKnownasanIngotTypicalIngotisAbout1or2MetersinLengthCanbeSlicedintoHundredsofSmallerCircularPiecesCalledWafersEachWaferYieldsHundredsorThousandsofIntegratedCircuits,WAFERMANUFACTURING,TheSiliconCrystalisSlicedbyUsingaDiamond-TippedSawintoThinWafersSortedbyThicknessDamagedWafersRemovedDuringLappingEtchWafersinChemicaltoRemoveanyRemainingCrystalDamagePolishingSmoothesUnevenSurfaceLeftbySawingProcess,THECRYSTALSTRUCTUREOFSILICON,AUnitCellHas18SiliconsAtomsWeakBondingAlongCleavagePlanesWaferSplitsinto4or6Wedge-ShapedFragmentsMillerIndicesisUsedtoAssigntoEachPossiblePlanePassingThroughtheCrystalLattice,SiliconManufacturing,Photolithography,Photolithography,Photolithographyisatechniquethatisusedtodefinetheshapeofmicro-machinedstructuresonawafer.,PhotolithographyPhotoresist,Thefirststepinthephotolithographyprocessistodevelopamask,whichwillbetypicallybeachromiumpatternonaglassplate.Next,thewaferisthencoatedwithapolymerwhichissensitivetoultravioletlightcalledaphotoresist.Afterward,thephotoresististhendevelopedwhichtransfersthepatternonthemasktothephotoresistlayer.,PhotolithographyPhotoresist,TherearetwobasictypesofPhotoresistsPositiveandNegative.Positiveresists.Positiveresistsdecomposesultravioletlight.TheresistisexposedwithUVlightwherevertheunderlyingmaterialistoberemoved.Intheseresists,exposuretotheUVlightchangesthechemicalstructureoftheresistsothatitbecomesmoresolubleinthedeveloper.Theexposedresististhenwashedawaybythedevelopersolution,leavingwindowsofthebareunderlyingmaterial.Themask,therefore,containsanexactcopyofthepatternwhichistoremainonthewafer.,PhotolithographyPhotoresist,NegativeresistsExposuretotheUVlightcausesthenegativeresisttobecomepolymerized,andmoredifficulttodissolve.Therefore,thenegativeresistremainsonthesurfacewhereveritisexposed,andthedevelopersolutionremovesonlytheunexposedportions.Masksusedfornegativephotoresists,therefore,containtheinverse(orphotographicnegative)ofthepatterntobetransferred.,PhotolithographyModel,Figure1ashowsathinfilmofsomematerial(eg,silicondioxide)onasubstrateofsomeothermaterial(eg,asiliconwafer).Photoresistlayer(Figure1b)Ultravioletlightisthenshonethroughthemaskontothephotoresist(figure1c).,PhotolithographyModel(cont),Thephotoresististhendevelopedwhichtransfersthepatternonthemasktothephotoresistlayer(figure1d).Achemical(orsomeothermethod)isthenusedtoremovetheoxidewhereitisexposedthroughtheopeningsintheresist(figure1e).Finallytheresistisremovedleavingthepatternedoxide(figure1f).,PhotolithographyPhotomasksandReticles,PhotomaskThisisasquareglassplatewithapatternedemulsionofmetalfilmononeside.Themaskisalignedwiththewafer,sothatthepatterncanbetransferredontothewafersurface.Eachmaskafterthefirstonemustbealignedtothepreviouspattern.,PhotolithographyPhotomasksandReticles,Whenaimageonthephotomaskisprojectedseveraltimesidebysideontothewafer,thisisknownassteppingandthephotomaskiscalledareticle.,Ancommonreticleisthe5XThepatternsonthe5Xreticlearereduced5timeswhenprojectedontothewafer.Thismeansthediesonthephotomaskare5timeslargerthantheyareonthefinalproduct.Thereareotherkindsofreductionreticles(2X,4X,and10X),butthe5Xisthemostcommonlyused.Reductionreticlesareusedonavarietyofsteppers,themostcommonbeingASM,Canon,Nikon,andGCA.,PhotolithographyPhotomasksandReticles,Examplesof5XReticles:,PhotolithographyPhotomasksandReticles,Oncethemaskhasbeenaccuratelyalignedwiththepatternonthewaferssurface,thephotoresistisexposedthroughthepatternonthemaskwithahighintensityultravioletlight.Therearethreeprimaryexposuremethods:contact,proximity,andprojection.,PhotolithographyPatterning,ThelaststageofPhotolithographyisaprocesscalledashing.Thisprocesshastheexposedwaferssprayedwithamixtureoforganicsolventsthatdissolvesportionsofthephotoresist.Conventionalmethodsofashingrequireanoxygen-plasmaash,oftenincombinationwithhalogengases,topenetratethecrustandremovethephotoresist.Usually,theplasmaashingprocessalsorequiresafollow-upcleaningwithwet-chemicalsandacidstoremovetheresiduesandnon-volatilecontaminantsthatremainafterashing.Despitethistreatment,itisnotunusualtorepeattheashpluswet-cleancycleinordertocompletelyremoveallphotoresistandresidues.,SiliconManufacturing,OxidationofSilicon,SiO2growthisakeyprocessstepinmanufacturingallSidevices-Thick(1m)oxidesareusedforfieldoxides(isolatedevicesfromoneanother)-Thingateoxides(100)controlMOSdevices-SacrificiallayersaregrownandremovedtocleanupsurfacesThestabilityandeaseofformationofSiO2wasoneofthereasonsthatSireplacedGeasthesemiconductorofchoice.,Thesimplestmethodofproducinganoxidelayerconsistsofheatingasiliconwaferinanoxidizingatmosphere.,Dryoxide-PuredryoxygenisemployedDisadvantage-Dryoxidegrowsveryslowly.Advantage-Oxidelayersareveryuniform.-Relativelyfewdefectsexistattheoxide-siliconinterface(Thesedefectsinterferewiththeproperoperationofsemiconductordevices)-IthasespeciallylowsurfacestatechargesandthusmakeidealdielectricsforMOStransistors.,Wetoxide-Inthesamewayasdryoxides,butsteamisinjectedDisadvantage-Hydrogenatomsliberatedbythedecompositionofthewatermoleculesproduceimperfectionsthatmaydegradetheoxidequality.Advantage-Wetoxidegrowsfast.-Usefultogrowathicklayeroffieldoxide,DepositedOxides,Oxideisfrequentlyemployedasaninsulatorbetweentwolayersofmetalization.Insuchcases,someformofdepositedoxidemustbeusedratherthanthegrownoxides.Depositedoxidescanbeproducedbyvariousreactionsbetweengaseoussiliconcompoundsandgaseousoxidizers.Depositedoxidestendtopossesslowdensitiesandlargenumbersofdefectsites.NotsuitableforuseasgatedielectricsforMOStransistorsbutstillacceptableforuseasinsulatinglayersbetweenmultipleconductorlayers,orasprotectiveovercoats.,KeyVariablesinOxidation,Temperature-reactionrate-solidstatediffusionOxidizingspecies-wetoxidationismuchfasterthandryoxidationSurfacecleanliness-metalliccontaminationcancatalyzereaction-qualityofoxidegrown(interfacestates),Etching,Etchingistheprocesswhereunwantedareasoffilmsareremovedbyeitherdissolvingtheminawetchemicalsolution(WetEtching)orbyreactingthemwithgasesinaplasmatoformvolatileproducts(DryEtching).Resistprotectsareaswhicharetoremain.Insomecasesahardmask,usuallypatternedlayersofSiO2orSi3N4,areusedwhentheetchselectivitytophotoresistislowortheetchingenvironmentcausesresisttodelaminate.Thisispartoflithography-patterntransfer.,WetChemicalEtching,Wetetches:-areingeneralisotropic(notusedtoetchfeatureslessthan3m)-achievehighselectivitiesformostfilmcombinations-capableofhighthroughputs-usecomparablycheapequipment-canhaveresistadhesionproblems-canetchjustaboutanything,ExampleWetProcesses,ForSiO2etching-HF+NH4F+H20(bufferedoxideetchorBOE)ForSi3N4-Hotphosphoricacid:H3PO4at180C-needtouseoxidehardmaskSilicon-Nitric,HF,aceticacids-HNO3+HF+CH3COOH+H2OAluminum-Acetic,nitric,phosphoricacidsat35-45C-CH3COOH+HNO3+H3PO4,Whatisaplasma(glowdischarge)?,Aplasmaisapartiallyionizedgasmadeupofequalpartspositivelyandnegativelychargedparticles.Plasmasaregeneratedbyflowinggasesthroughanelectricormagneticfield.Thesefieldsremoveelectronsfromsomeofthegasmolecules.Theliberatedelectronsareaccelerated,orenergized,bythefields.Theenergeticelectronsslamintoothergasmolecules,liberatingmoreelectrons,whichareacceleratedandliberatemoreelectronsfromgasmolecules,thussustainingtheplasma.,DryorPlasmaEtching,DryorPlasmaEtching,DryorPlasmaEtching,CombinationofchemicalandphysicaletchingReactiveIonEtching(RIE)Directionaletchingduetoionassistance.InRIEprocessesthewaferssitonthepoweredelectrode.Thisplacementsetsupanegativebiasonthewaferwhichacceleratespositivelychargeionstowardthesurface.Theseionsenhancethechemicaletchingmechanismsandallowanisotropicetching.Wetetchesaresimpler,butdryetchesprovidebetterlinewidthcontrolsinceitisanisotropic.,OtherEffectsofOxideGrowthandRemoval,OxideStepThedifferencesinoxidethicknessandinthedepthsofthesiliconsurfacescombinetoproduceacharacteristicsurfacediscontinuityThegrowthofathermaloxideaffectsthedopinglevelsintheunderlyingsiliconThedopingofsiliconaffectstherateofoxidegrowth,LocalOxidationofSilicon(LOCOS),LOCOS:localizedoxidationofsiliconusingsiliconnitrideasamaskagainstthermaloxidation.Atechniquecalledlocaloxidationofsilicon(LOCOS)allowstheselectivegrowththickoxidelayersCMOSandBiCMOSprocessesemployLOCOStogrowathickfieldoxideoverelectricallyinactiveregionsofthewafer,SiliconManufacturing,DiffusionandIonImplantation,WN-JunctionFabrication(Earliestmethod),Process:OppositepolaritydopingatomsareaddedtomoltensiliconduringtheCzochralskiprocesstocreatein-grownjunctionsintheingot.Repeatedcounterdopingscanproducemultiplejunctionswithinthecrystal.DisadvantagesInabilitytoproducedifferentlydopedareasindifferentpartsofthewafer.Thethicknessandplanarityofgrownjunctionsaredifficulttocontrol.Repeatedcounterdopingsdegradetheelectricalpropertiesofthesilicon.,ThePlanarProcess,Advantages:Theplanarprocessdoesnotrequiremultiplecounterdopingsofthesiliconingot.Thisprocessallowsmoreprecisecontrolofjunctiondepthsanddopantdistributions.,Methodsofplanarprocess,DiffusionAuniformlydopedingotisslicedintowafers.Anoxidefilmisthengrownonthewafers.Thefilmispatternedandetchedusingphotolithographyexposingspecificsectionsofthesilicon.Thewafersare