薄膜技术英文课件-05Thin-Film-CVD

TechnologyofThinFilmChemicalVaporDepositionXuhaiZhangSchoolofMaterialScienceandEngineeringSoutheastUniversityOutlineIntroductionReactionTypesThermodynamicsofCVDGasTransportFilmgrowthKinetics2IntroductionCVDistheprocessofchemicallyreactingavolatilecompoundofamaterialtobedeposited,withothergases,toproduceanonvolatilesolidthatdepositsatomisticallyonasuitablyplacedsubstrate.Donotrequirevacuumorunusuallevelsofelectricpower,CVDswerepracticedcommerciallypriortoPVD.thefabricationofsolid-stateelectronicdevices,themanufactureofballbearingsandcuttingtools,andtheproductionofrocketengineandnuclearreactorcomponentshigh-qualityepitaxial(singlecrystal)filmsinbothsiliconandcompound-semiconductor,andassociatedinsulatingandpassivatingfilmsTheabilitytoproducealargevarietyoffilmsandcoatingsofmetals,semiconductors,andinorganicaswellasorganiccompoundsTheabilitytocontrollablycreatefilmsofwidelyvaryingstoichiometryAffordablecostoftheequipmentandoperatingexpenses,thesuitabilityforbothbatchandsemicontinuousoperation,andthecompatibilitywithotherprocessingsteps.e.g.high-qualityepitaxialfilmsGaNGaN/GaAsGaAs

e.g.diamondfilm：Si金刚石Schematiccross-sectionalviewofanMOStransistorstructuree.g.ProductsofCVD(epitaxial)Sisubstrate,polysilicon,variousSiO2films,low-temperatureoxide(LTO),borophosphosilicateglass(BPSG),WplugsManyvariantsofCVDprocessingatmosphericpressure(APCVD),low-pressure(LPCVD),plasma-enhanced(PECVD),laser-enhanced(LECVD)chemicalvapordepositionThefundamentalsequentialsteps1.Convectiveanddiffusivetransportofreactantsfromthegasinletstothereactionzone2.Chemicalreactionsinthegasphasetoproducenewreactivespeciesandby-products3.Transportoftheinitialreactantsandtheirproductstothesubstratesurface4.Adsorption(chemicalandphysical)anddiffusionofthesespeciesonthesubstratesurface5.Heterogeneousreactionscatalyzedbythesurfaceleadingtofilmformation6.Desorptionofthevolatileby-productsofsurfacereactions7.Convectiveanddiffusivetransportofthereactionby-products

awayfromthereactionzoneOutlineIntroductionReactionTypesThermodynamicsofCVDGasTransportFilmgrowthKinetics11PyrolysisThethermaldecompositionofsuchgaseousspeciesashydrides,carbonylsandorganometalliccompoundsonhotsubstrates.ReductionThesereactionscommonlyemployhydrogengastoeffectthereductionofsuchgaseousspeciesashalides,oxyhalides,orotheroxygen-containingcompounds.ProduceepitaxialSifilmsonsingle-crystalSiwafersWandMometalfilmsservedtointerconnectlevelsofmetallizationinintegratedcircuitsOxidationThedepositionofSiO2iscarriedoutatastageintheprocessingofintegratedcircuitswherehighersubstratetemperaturescannotbetolerated.HardaluminacoatingsthatextendthelifeofcuttingtoolsTheproductionofopticalfiberforcommunicationspurposes.Compoundformationthecompoundelementsexistinavolatileformandbesufficientlyreactiveinthegasphasee.g.GaAsepitaxicalfilmbyMOCVD：e.g.硬质涂层的化学气相沉积DisproportionationDisproportionationreactionsarepossiblewhenanonvolatilemetalcanformvolatilecompoundshavingdifferentdegreesofstabilitydependingonthetemperature.e.g.Gethinfilm：masstransportbetweenhotandcoldendsEarlyexperimentalreactorforepitaxialgrowthofSifilmsResersibletransferChemicaltransferortransportprocessesarecharacterizedbyareversalinthereactionequilibriumatsourceanddepositionregionsmaintainedatdifferenttemperatureswithinasinglereactor.epitaxialGaAsfilms（g）e.g.CdTethinfilmTwocommonfeaturesofCVDAllofthechemicalreactionscanbewritteninthesimplifiedgeneralizedformwhereA,B...refertothechemicalspeciesanda,b...tothecorrespondingstoichiometriccoefficientsSomereactionsarereversible,andthissuggeststhatstandardconceptsofchemicalthermodynamicsmayprovefruitfulinanalyzingthemOutlineIntroduction

ReactionTypesThermodynamicsofCVDGasTransportFilmgrowthKinetics21Free-energychangeinchemicalreactionReactionequation:FreeenergyFree-energychangeWheninstateofequilibriumEquilibriumconstantΔG>0，reactinreverse-directionΔG<0；reactinforward-directionJudgefeasibilityordirectionofreactione.g.

ObtaintheO2partialpressureΔG

0=-202kcal(1273K)；PO2=2×10-30Pa

whenrealO2partialpressureislargertheequilibriumpressure,thethinfilmtendtobesubjecttooxidatione.g.ForCuthinfilm：ΔG0≈-25kcal(1273K)；PO2≈5×10-5atm≈5PaAlismoreliketooxidizethanCuApplicationofthermaldynamicsinCVDSELICTIONOFREACTIVEROUTECALCULATIONOFCHEMICALREACTIVEEQUILIBRIUMSELICTIONOFREACTIVEROUTEMicroeletronicdevice：substrate：SiO2；Materialforcondutiveline：Cu和Al；Depositetemperature：400℃；CuandAl,whichissuittodepositeonSiO2？e.g.1FreeenergychangeforreactionbetweenconductivematerialandsubstrateSiO2+Cu

isOKSELICTIONOFREACTIVEROUTEe.g.1EpitaxyofY2O3thinfilmbyCVDUseofYCl3：K=e30，reactinforwarddirection，Butdrivingforceislarge,polycrystalstructure；UseofYBr3haslargerdrivingforcethanUseofYCl3SELICTIONOFREACTIVEROUTEe.g.2EpitaxyofY2O3thinfilmbyCVDUsingCO2

insteadofO2？CannotobtainY2O3

thinfilme.g.2SELICTIONOFREACTIVEROUTEEpitaxyofY2O3thinfilmbyCVDYBr3+CO2：Thisroutismorefeasiblee.g.2SELICTIONOFREACTIVEROUTE

e.g.Pressureofdifferentspecies

Application:OptimizationofdepositionparametersuchasT

Quantitativeinformationofequilibriume.g.Si-Cl-Hsystem

aSi=1e.g.Si-Cl-H

systemSummaryofthermodynamicdataingtheSi-Cl-Hsysteme.g.Si-Cl-HsystemKiisfixedbyspecifyingTandFromationreactonsforSiCl4andHClat1500KK2,K3,K4,K5,K6couldbeobtainedinthiswaye.g.Si-Cl-H

systemTotalpressureP0inthereactorisfixed：Cl/Hmolarratioisfixed：Partialpressureofvariousspeciesunderdifferenttemperature温度（K）分压（atm）单晶硅薄膜生长：气压为P0,[Cl]/[H]=0.01时，Si-Cl-H系统平衡气相组分Areactoroperatingtemperaturein1400Kissuggested,becauseasaresultoffilmdepositiontheSicontentinthegasspahseisminimized!

e.g.Si-Cl-HsystemKineticsinCVDGastransportViscousflowinmostCVDsystem1.Thedepositedfilmorcoatingthicknessuniformitydependsonthedeliveryofequalamountsofreactantstoallsubstratesurfaces.2.Rapiddepositiongrowthratesaredependentonoptimizingtheflowofreactantsthroughthesystemandtosubstrates.3.Moreefficientutilizationofgenerallyexpensiveprocessgasescanbeachievedasaresult.4.ComputermodelingofCVDprocesseswillbemoreaccurateenablingimprovedreactordesignandbetterpredictivecapabilitywithregardtoperformance.

Diffusioningases:diffusioninvolvesthemotionofindividualatomicormolecularspeciesBulkflowprocesses:partsofthegasmoveasawhole,suchasviscousfloworconvectionTheflowvelocityhasauniformvalue,onlypriortoimpingingontheleadingedgeoftheplate.VelocitygradientsformbecausethegasclingstotheplateFarawaythevelocityisstilluniformbutdropsrapidlytozeroattheplatesurface,creatingaboundarylayer.TheboundarylayergrowswithdistancealongtheplateLaminargasflowpatterns.Laminargasflowpatterns.ThethicknessofboundarylayerReynoldsmunber容器气体的流速分布

Aftergasmoveinthedistanceof0.07r0Re,theflowisfullydevelopedandthevelocityprofilenolongerchangesLaminargasflowpatterns.Becausehotgaseousreactantsandproductsmustpassthroughtheboundarylayerseparatingthelaminarstreamandfilmdeposit,lowvaluesofboundarylayeraredesirableHowtoreduacethenegtiveeffectofboundarylayeronthedepositionrate？Increasingthegasflowrate,whichraisesthevalueofRe.However,Reexceedsapproximately2100,atransitionfromlaminartoturbulentflowoccurs,whichisharmforuniform,defect-freefilmgrouth.Practicalstrategy:decreasethepressuretopromotediffusion.BoundarylayerDiffusioningasesFilmMassfluxDiffusivityvaluesMassfluxthroughboundarylayerninExperimentallyfoundtobe1.8ReducegaspressureMassfluxincreaseasawholeMassfluxthroughboundarylayer

Convection

：drivenbygravitaltionforce.inCVDreactor,itcausebyverticalgas-densityortrmperautregradients.

Methodtodepressconvertion：Increasegasvelocity；Hotzonegethigherposition；Reducepressure；Improveuniformityoftemperature。高流速低流速

usageofconvectionAxialgrowth-rateuniformityFilmgrowthkineticsAnexponentialdecayinthegrowthratewithdistancealongthereactorispredictedGrowthrate:InprovetheuniformdopositioninaxialgrowthTiltingthesubstrate.Becausethevelocityofgasflowinthetaperedspaceabovethesubstratesisforcedtoincreasewithdistance.ContinuouslyincreasingthetemperaturedownstreamwithinthereactorJgJsDiffusionalmassflowJg:FluxconsumedbythereacionJs:Temperatureedependenceinfilmgrowth动态平衡关系:反应流=扩散流Diffusion-controlledcondition：ks>>hg,

Surface-reactioncontrolledcondition:ks<<hg,

HighTgrowth：ks>>hg,mass-tramsfercontrol;lowTgrowth：ks<<hg,surface-reactioncontrol;GrowthrateDepositionrateofSifromdifferentprecursorgasesasafunctionoftemperature外延Si薄膜沉积模型温度与生长速率关系ActualfilmgrowthprocessessExothermicreaction:ReachesamaximumandthendropswithtemperatureNetreactiverate：InfluenceofthermodynamicsEndothermicreactions：Netreactiverate:Van’tHoffequationΔH0

<0ΔH0>0ExothermicreactionsEndothermicreactionshigherTcausesdecreaseofKlowerTcausesdecreaseofKe.g.：

Hot–wallreactore.g.：

Cold-wallreactorClassofCVDtemperatureHigh-temperature/low-temperatureCVDpressureAtmosphericpressure/low-pressure