生产管理知识_半导体生产过程培训课件

EE4345 SemiconductorElectronicsDesignProject SiliconManufacturingGroupMembersYoungSoonSongNghiaNguyenKeiWongEyadFanousHannaKimStevenHsu HISTORY 19thCentury Solid StateRectifiers1907 ApplicationofCrystalDetectorinRadioSets1947 BJTConstructedbyBardeenandBrattain1959 IntegratedCircuitConstructedbyKilby 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 orphotographic negative 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 Oncethemaskhasbeenaccuratelyalignedwiththepatternonthewafer ssurface thephotoresistisexposedthroughthepatternonthemaskwithahighintensityultravioletlight Therearethreeprimaryexposuremethods contact proximity andprojection PhotolithographyPatterning ThelaststageofPhotolithographyisaprocesscalledashing Thisprocesshastheexposedwaferssprayedwithamixtureoforganicsolventsthatdissolvesportionsofthephotoresist Conventionalmethodsofashingrequireanoxygen plasmaash oftenincombinationwithhalogengases topenetratethecrustandremovethephotoresist Usually theplasmaashingprocessalsorequiresafollow upcleaningwithwet chemicalsandacidstoremovetheresiduesandnon volatilecontaminantsthatremainafterashing Despitethistreatment itisnotunusualtorepeatthe ashpluswet clean cycleinordertocompletelyremoveallphotoresistandresidues SiliconManufacturing OxidationofSilicon SiO2growthisakeyprocessstepinmanufacturingallSidevices Thick 1 m 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 notusedtoetchfeatureslessthan 3 m achievehighselectivitiesformostfilmcombinations capableofhighthroughputs usecomparablycheapequipment canhaveresistadhesionproblems canetchjustaboutanything ExampleWetProcesses ForSiO2etching HF NH4F H20 bufferedoxideetchorBOE ForSi3N4 Hotphosphoricacid H3PO4at180 C needtouseoxidehardmaskSilicon Nitric HF aceticacids HNO3 HF CH3COOH H2OAluminum Acetic nitric phosphoricacidsat35 45 C CH3COOH HNO3 H3PO4 Whatisaplasma glowdischarge Aplasmaisapartiallyionizedgasmadeupofequalpartspositivelyandnegativelychargedparticles Plasmasaregeneratedbyflowinggasesthroughanelectricormagneticfield Thesefieldsremoveelectronsfromsomeofthegasmolecules Theliberatedelectronsareaccelerated orenergized bythefields Theenergeticelectronsslamintoothergasmolecules liberatingmoreelectrons whichareacceleratedandliberatemoreelectronsfromgasmolecules thussustainingtheplasma DryorPlasmaEtching DryorPlasmaEtching DryorPlasmaEtching Combinationofchemicalandphysicaletching ReactiveIonEtching 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