常压化学气相沉积(APCVD).ppt

AtmosphericPressureCVD（APCVD）,Luomin(罗敏),1,HistoryofCVD,WhatisAPCVD?Chemicalvapordepositionmaybedefinedasthedepositionofasolidonaheatedsurfacefromachemicalreactioninthevaporphase.Itbelongstotheclassofvapor-transferprocesseswhichisatomisticinnature,thatisthedepositionspeciesareatomsormoleculesoracombinationofthese.APCVDisaCVDmethodatnormalpressure(atmosphericpressure)whichisusedfordepositionofdopedandundopedoxides.Thedepositedoxidehasalowdensityandthecoverageismoderateduetoarelativelylowtemperature.,2,CVDisnotanewprocessitsfirstpracticalusewasdevelopedinthe1880sintheproductionofincandescentlampstoimprovethestrengthoffilamentsbycoatingthemwithcarbonormetal.1960:IntroductionofthetermsCVDandPVDtodistinguish“chemicalvapordeposition”from“physicalvapordeposition.”1960:IntroductionofCVDinsemiconductorfabrication.1960:CVDTiCcoatingoncementedcarbidetoolsintroducedanddevelopmentofCVDtungsten.,3,1963:IntroductionofplasmaCVDinelectronics.1968:StartofindustrialuseofCVDcoatedcementedcarbides.1980s:IntroductionofCVDdiamondcoatings.1990s:Rapidexpansionofmetallo-organicCVD(MOCVD)forceramicandmetaldeposition.,4,ThermodynamicofCVD,ACVDreactionisgovernedbythermodynamics,thatisthedrivingforcewhichindicatesthedirectionthereactionisgoingtoproceed(ifatall),andbykinetics,whichdefinesthetransportprocessanddeterminestherate-controlmechanism,inotherwords,howfastitisgoing.Chemicalthermodynamicsisconcernedwiththeinterrelationofvariousformsofenergyandthetransferofenergyfromonechemicalsystemtoanotherinaccordancewiththefirstandsecondlawsofthermodynamics.InthecaseofCVD,thistransferoccurswhenthegaseouscompounds,introducedinthedepositionchamber,reacttoformthesoliddepositandby-productsgases.,5,GCalculationsandReactionFeasibility,ThefirststepofatheoreticalanalysisistoensurethatthedesiredCVDreactionwilltakeplace.Thiswillhappenifthethermodynamicsisfavorable,thatisifthetransferofenergythefree-energychangeofthereactionknownasGrisnegative.TocalculateGr,itisnecessarytoknowthethermodynamicpropertiesofeachcomponent,specificallytheirfreeenergiesofformation(alsoknownasGibbsfreeenergy),Gf.Therelationshipisexpressedbythefollowingequation:,6,Eq.(1),reactants,Thefreeenergyofformationisnotafixedvaluebutvariesasafunctionofseveralparameterswhichincludethetypeofreactants,themolarratioofthesereactants,theprocesstemperature,andtheprocesspressure.Thisrelationshipisrepresentedbythefollowingequation:,Eq.(2),where:,7,=stoichiometriccoefficientofspecies“i”intheCVDreaction(negativeforreactants,positiveforproducts)=standardfreeenergyofformationofspecies“i”attemperatureTand1atm.R=gasconstantT=absolutetemperatureQ=activityofspecies“i”whichis=1forpuresolidsand=forgases=partialpressureofspecies“i”=molefractionofspecies“i”=totalpressure,8,(Kistheequilibriumconstant),Itistheequilibriumconditionsofcompositionandactivities(partialpressureforgases)thatarecalculatedtoassesstheyieldofadesiredreaction.,Bydefinition,thefreeenergychangeforareactionatequilibriumiszero,hence:,Eq.(3),9,DepositionSequence,Reactantgasesenterthereactorbyforcedflow.Gasesdiffusethroughtheboundarylayer.Gasescomeincontactwithsurfaceofsubstrate.Depositionreactiontakesplaceonsurfaceofsubstrate.Gaseousby-productsofthereactionarediffusedawayfromthesurface,throughtheboundarylayer.,ThesequenceofeventstakingplaceduringaCVDreactioncanbesummarizedasfollows:,10,FundamentalsofAPCVD,11,IllustrationofahorizontalAPCVDreactor,GasVelocityReactant-GasConcentrationTemperature,Mainfactorsinfluencethedeposition,12,13,IllustrationofstructuresofAPCVDsystem,Equipmentstructures,14,DepositionofSiO2onthesubstrate,APCVDisoftenusedfordepositionofdopedandundopedoxides.Thedepositedoxidehasalowdensityandthecoverageismoderateduetoarelativelylowtemperature.Becauseofimprovedtools,theAPCVDundergoesarenaissance.Thehighwaferthroughputisabigadvantageofthisprocess,SiH4+O2SiO2+2H2(T=430C,p=105Pa),AsprocessgasessilaneSiH4(highlydelutedwithnitrogenN2)andoxygenO2areused.Thegasesaredecomposedthermalatabout400Candreactwitheachothertoformthedesiredfilm.,Example,15,Characteristics(advantages),simplereactionsystemDepositionalspeedisfastLowtemperature,16,Characteristics(limitations),particlescontaminat