半导体工艺-复旦大学-蒋玉龙-Chapter11

Chapter11ChemicalVaporDepositionOutlineI.CVD–FormationofasolidfilmonasubstratebythereactionofvaporphasechemicalreactantsII.CVDprocesskineticsIII.PlasmaEnhancedCVDIV.Photo-EnhancedCVDV.CVDofSiO2andSi3N4I.CVD–Formationofasolidfilmonasubstratebythereactionofvaporphasechemicalreactants‹VariousmaterialsformedbyCVD*Dielectric:SiO2,Si3N4,SiNxOy……*Semiconductors:Si,SiC,Diamond…*Metals:W,WSi2,Al……‹Withdifferentcrystallinestructures*Amorphous,a-Si*Polycrystalline,poly-Si*Monocrystalline,c-Si‹Varietyofmethodsandchemicalreactantsources*ThermalCVD:APCVD,LPCVD,RTCVD,MOCVD,UHV-CVD*PlasmaCVD:PECVD,HDP-CVD,ECR-CVD*PhotoCVD:PCVD‹ByCVDsystemstructure:*Planar,Barrel,Furnacetube*HotWall,ColdWall‹Variousorganicandinorganiccompoundsourcesfordifferentfilms‹IncreasingapplicationofCVDfilmsinsemiconductortechnologyIICVDProcessKinetics‹RequirementsforCVDfilms•Controlledcompositionandstoichiometries•Goodthicknessuniformity•Highpurityanddensity•Goodelectricalproperties•Excellentadhesion•Goodstepcoverage•HighthroughputCVDprocesssteps1.Flowofreactantgasesintochamber2.Transportofspeciestothesubstrate3.Adsorptionofreactantbysubstrate4.Adatomsmigration,chemicalreaction,filmgrowth5.Desorption&removalofby-products‹Reactionatsurface:Heterogeneousreaction-desirableforhigh-qualityfilmdepositionΔReactioningasphase:HomogeneousreactionGasphaseclusterformationÆpooradhesion,lowerdensity–undesirable*“Raining”ofmaterialonsurface*Depositiononchamberwalls;etc‹CVDsystemmustbewelldesignedfromtwoviewpoints*Fluiddynamics(Transport:Supplyreactantsandremoveby-productscontinuously)*Chemistry(Reaction:Formationofuniformsolidfilmswithcertaincomposition)‹TwomajorfactorforCVDprocess*Transportofreactants*Surfacereactionrate‹Grovemodel*Diffusionfluxofreactanttosurface:hG-Gasphasemasstransportcoefficient*Fluxofreactantconsumedbysurfacereaction:KS-surfacereactionrateconstant)seccm)(CC(hFSGG121−−−=SSCKF=2FFF==21Insteadystate:ÆGSGSh/KCC+=1GGSGSChKhKF+=∴Depositionrate:NFR=N–DensityofCVDfilm(cm-3)NChKhKRGGSGS+=ΔMass-transportlimitedCVDprocessNChRKhGGSG≈→ΔSurfacereactionratelimitedCVDprocessNCKRKhGSSG≈→—Athermallyactivatedprocess)kT/Eexp(RRa−=0Ea–Activationenergy(athighT)III.PlasmaEnhancedCVD1.Gasdischargebyelectromagneticenergy—RFVoltage—Microwave(ECR)‹Plasma:*Ionizedgasmolecules,Electrons,Ionizedfragmentsofbroken-upgasmolecules,Neutralgasmolecules,freeradicals…*Fractionofionizedgasmolecules–0.1-1%*e-energy:1-20eV*Iondensity:108-1011cm-32.LowerTemperatureDeposition‹ReactantswithhigherenergyabsorbedfromE-MfieldÆSurfacereactionatlowerT(330oC)Amorphousfilmwithhigherpercentageofextraneousreactioncomponents(e.g.HinSiO2film)‹Negativeself-biasonsubstrateIonstrikingHigh-energye-strikingImprovementoffilmqualityRadiationdamagetosubstrate(Annealedbysubsequentthermalprocess)3.HighDensityPlasmaCVD(HDP-CVD)APECVDtechnologyfordeepsubμdevicefilmdepositionΔHighaspect-ratiogapfilling,moredensefilmΔTwoRFsourceswithaICP(Inductivecoupledplasma)ΔLowerpressure(~10-3torr)ΔLowertemperature(150-20oC)ΔPlasmadensity(~1011-1013cm-3)ΔVarioussystemsIVPhoto-EnhancedCVD—AnotherlowTCVDtechnology—UsingUVlight—Absorptionofphotoenergyby:(1)reactantdirectly(2)photosensitizer:e.g.Hgvaporλ2200ÅSiH4,NH3canabsorbphononλ≈2537ÅHgstronglyabsorbphononEnergyTransfertoreactantsbycollisionÆreaction24334HNSiNHSiH+→+V.CVDofSiO2andSi3N41.ApplicationofCVD-SiO2-Passivation-Interleveldielectric(insulation)-Cappinglayer(Out-diffusionbarrier)-Masking(duringionimplantation)-……2.SourcesandReactionforSiO2(1)OxidantSiH+4(400oC-900oC)2424424COSiH,ONSiH,NOSiH,OSiH++++↑+↑+↓→[phone]HNSiOONSiH(2)ilicateSrthoOtraethylTETEOS)OHC(Si−−452OHCOSiOO)OHC(Si222245210812++→+()CCoo700400−TEOS/O3:)C...(SiOO)OHC(Sio40023452+→+(3)422SiCl,ClSiHandother)CC(HClNSiOONClSiHoo95085022222222−++→+HClCOSiOHCOSiCl42222224++→++3.DepositionTemperature‹Ingeneral:SiO2filmquality-betterathigherTLowTdeposition:①ÆLowSurfacemobilityÆPoorstepcoverageandconformality②IncorporationofpartiallyreactedspeciesintoSiO2:SiH,SiH2,SiOH,etc‹LowTdeposition–preferredforICprocessintegration:morecompatiblewithmetallizationandotherprocess4.DopingforCVD-SiO2‹DopantsadditiontoCVD-SiO2ÆglassesΔPSG—SiO2dopedwithphosphorusΔBSG—SiO2dopedwithBoronΔBPSG—SiO2dopedwithB&P(1-4wt%B,4-6wt%P)ΔFSG—SiO2dopedwithFluorine‹EffectsofdopedSiO2ΔImprovedreflow—conformation,planarizationΔGetteringofimpuritiesΔDopingfromglassΔLowerdielectricconstant(FSG)‹DopedSiO2—Mixtureofdifferentglasses(SiO2+P2O5+B2O3…)‹Varietyofdopingchemicals—organic,inorganic252236254HOPOPH+→[phone]HOBOHB+→+...SiOFArOSiHSiF+→+++2445.CVD-Si3N4‹Primaryuses:Maskingagainstoxidation(LOCOS)PassivationSi3N4-goodbarriertodiffusionofH2O,O2,Na…‹Depositiontechniques-LPCVD-PECVD(atlowerT)‹Reaction:)C(HNSiNHSiHo900700124324334−+→+)C(HHClNSiNHClSiHo8007006643243322−++→+