薄膜技术Film

SiliconVLSITechnologyThinFilmsEECS322/415ThinfilmsdominateICstructures1SiliconVLSITechnologyThinFilmsEECS322/415DesirableTraitsofFilmsUsedinIC’s•Highpurity,desirableproperties(electrical,mechanical)•Highuniformityacrosslarge-areasubstrates•Goodstepcoverage(conformality)•Goodfill•Highplanarity2SiliconVLSITechnologyThinFilmsEECS322/4153SiliconVLSITechnologyThinFilmsEECS322/415ExamplesSputteredAlCVDOxide4SiliconVLSITechnologyThinFilmsEECS322/415AspectRatio•Appliestopatternedstructuresandetchedtrenches5SiliconVLSITechnologyThinFilmsEECS322/415ProjectedDemandsofThinFilms6SiliconVLSITechnologyThinFilmsEECS322/415DepositionCategories•ChemicalVaporDeposition–APCVD,LPCVD,PECVD•PhysicalVaporDeposition–Evaporation,sputtering•SpinCasting–viscousfluids•Dipcoating–monolayers7SiliconVLSITechnologyThinFilmsEECS322/415AtmosphericPressureChemicalVaporDeposition•TypicalSystemSetup8SiliconVLSITechnologyThinFilmsEECS322/415APCVD•GeneralProcess–Transportofreactantsthroughthemaingasflowtothedepositionregion–Diffusionthroughtheboundarylayertosubstratesurface–Absorptionofreactantsonsubstratesurface–Executionofsurfacereactions–Dissociationofreactants,surfacemigration,reactions–Desorptionofbyproducts–Transportofbyproductsthroughboundarylayer–Transportofbyproductsthroughmaingasflow9SiliconVLSITechnologyThinFilmsEECS322/415•GeneralProcess(continued)–Theprocesscanbedescribedintermsoffluxes–Deal-Groveappliesandcanbeusedtodeterminedepositionrates10SiliconVLSITechnologyThinFilmsEECS322/415DepositionRate(fromDeal-Groveanalysis)•Oneoftworegimeswilldominate•DependsonwhichfluxisdominantSurfacereactioncontrolledkShGMasstransfercontrolledhGkS11SiliconVLSITechnologyThinFilmsEECS322/415SiliconCVD•RequiresSi-containinggas•Inallcases,theslopeinthereactionlimitedregimeisaboutthesame(i.e.,activationenergyof1.6eV)surfacereactionisaboutthesame•Differencesinoverallratemaybeduetohydrogendesorption•Epitaxialgrowthdoneinmasstransferlimitedregimetoensurethatallreactantsareusedandpresumablyincorporatedintothelattice12SiliconVLSITechnologyThinFilmsEECS322/415GasFlowsandAPCVD•Masstransferdependsonthicknessofaboundarylayer(seeFig9.9)–Unfortunately,theboundarylayerthicknessisnotuniformacrossalargeareasubstrate,butincreases–Solutiontiltthesubstratetodecreasethegasflowcross-sectionalareaalongitslength13SiliconVLSITechnologyThinFilmsEECS322/415GasDepletion•Canbeaproblemresultinginageometrydependentdepositionratealongthesubstratelength•AddressedbysubstratetiltingtocapturemorereactantsoutsidethestagnantboundarylayerAutodoping•Canoccurbyvariouspathways14SiliconVLSITechnologyThinFilmsEECS322/415LowPressureChemicalVaporDepositionSetup•TypicalSystemSetup15SiliconVLSITechnologyThinFilmsEECS322/415WhyLPCVD?•APCVDoperatesinmasstransportlimitedregime–Requirescontrolofgeometrytoensureuniformity•Couldswitchtosurfacereactionregimebyloweringtemperature–Depositionrategoesdown–Filmqualitysuffersatthelowertemps•Loweringpressureaddressestheseissues–Increasesdiffusion–Extendsreactionrateregimetohighertemps16SiliconVLSITechnologyThinFilmsEECS322/415WhyLPCVD?17SiliconVLSITechnologyThinFilmsEECS322/415WhyLPCVD?•Increasesdiffusion–Recall–And–AttTorr,DGincreasesby760XwhileδSincreasesby7X,sohGincreasebyabout100X18SiliconVLSITechnologyThinFilmsEECS322/415WhyLPCVD?•Diffusionagain–Tomaintainreasonabledepositionrates,onedecreasestotalpressurewhilemaintaininghighpartialpressuresofreactants19SiliconVLSITechnologyThinFilmsEECS322/415PlasmaEnhancedChemicalVaporDeposition1.Lowpressures:50mTorrto5Torr2.13.56MHz3.Highfield4.Highenergyelectronsstrikegasmoleculesandionizethem.Lowpressuresinsurehighcollisionenergies20SiliconVLSITechnologyThinFilmsEECS322/415PECVD•MuchlikeLPCVDbutusesaplasmadischargeasasourceofenergy–Resultsinloweringofsubstratetemperature•Whatisaplasma?–Anenergeticgaseouscollectionofelectronschargedmolecules,neutralmolecules,neutralandchargedmolecularfragmentsofenergeticallyexcitedmoleculesandfreeradicals–Freeradicalselectricallyneutralspeciesthathaveincompletechemicalbonds21SiliconVLSITechnologyThinFilmsEECS322/415PECVD–Theplasmaanditsreactive/energeticcomponentsresultsinlessthermalenergyrequiredforfilmgrowth•Commonuses–SiO2,Si3N4•Characteristics–Filmsusuallynotstoichiometric–Oftentheycontainhydrogendecreasesdensity–Mustcontainatleastthedesiredpropertyplusgoodadhesiontobeuseful22SiliconVLSITechnologyThinFilmsEECS322/415HighDensityPlasmaCVD•LikePECVDexceptplasmageneratedremotely•Alsouseshigherfrequencytogenerateplasma•Hashighdensityofionsinplasma•Goodforviafilling–Ionskeepsidewallscleanduringdep.23SiliconVLSITechnologyThinFilmsEECS322/415PhysicalVaporDeposition(PVD)•Reliesonphysicalprocessestoproducereactants–Evaporation–Sputtering•Requireslongmeanfreepathtoinsurethefollowing:–Reactionsdon’toccuringasphase–Physicalprocesseshavemaximumavailableenergy–Reactantshavemaximumenergywhenadsorbedonsurface.•GenerallylowertemperatureprocessthanCVD•Popularformetals24SiliconVLSITechnologyThinFilmsEECS322/415Evaporation•Sourcematerialheatedinvacuum–Resistanceheating–Heatsentiresource–Electronb