第四章-化学气相沉积

ChemicalVaporDeposition化学气相沉积•要点：化学气相淀积的基本原理－过程、反应、速度CVD特点CVD装置低压CVD等离子体化学气相淀积PECVD金属有机物化学气相沉淀（MOCVD）4.1简介Hardestmat.-Damagedthehardnesssensor2.5mmhigh,grownin1daysingle-crystaldiamondgrownbyCVDC.S.Yanetal.,PhysicaStatusSolidi(a)201,R25(2004)].•化学气相淀积，简称CVD(ChemicalVaporDeposition)是把含有构成薄膜元素的一种或者几种化合物或单质气体供给基片，借助气相作用或在基片上的化学反应生成所需薄膜。gasinletgasdecompositiongasreactionsubstrateadsorptiongasexhaust定义1)气体分解方式gasdecomposition•(1)thermaldeposition•(2)plasmadeposition•(3)photon(laser,UV)deposition2)CVD种类－accordingtotemp.,pressure,…•CVDchemicalvapordeposition•APCVDatmosphericpressure...•LPCVDlow-pressure...•VLPCVDverylowpressure…•PECVDplasma-enhanced...•LECVDlaser-enhanced...•MOCVDmetal-organic...•ECRCVDelectron-cyclotronresonance...•VPEvapor-phaseepitaxy3)优势－advantages•lowcostdielectric(poly-silicon,Si3N4,SiO2)andmetalthinfilm•highdepositionrate•highorlowpressure•controlthickness,defectandresistivity•highfilmquality•LTCVDforsemiconductors,ex.,Si3N4,SiO2andepilayer•lowradioactivedamage•Buthighdepositiontemperatureandenvironmentdamage4)沉积参数－parametersforthinfilmstructure(1)temperatureofsubstrateandchamber(2)growthrate(3)gaspressure–Theseparametersaffectonsurfacespeedoftheinvolvedatoms.OverviewnotallcomponentsarefoundinallCVDsystems:SourcegasReactsonsubstratetodepositfilm4.2化学反应类型1.热分解－Pyrolysis-thermaldecompositionAB(g)---A(s)+B(g)ex:SidepositionfromSilaneat650oCSiH4(g)---Si(s)+2H2(g)usetodeposit:Al,Ti,Pb,Mo,Fe,Ni,B,Zr,C,Si,Ge,SiO2,Al2O3,MnO2,BN,Si3N4,GaN,Si1-xGex,...2.还原－ReductionoftenusingH2(metal,substrate)AX(g)+H2(g)===A(s)+HX(g)-oftenlowertemperaturethanpyrolysis-reversible=canuseforcleaningtooex:Wdepositionat300oCWF6(g)+3H2(g)===W(s)+6HF(g)-usetodeposit:Al,Ti,Sn,Ta,Nb,Cr,Mo,Fe,B,Si,Ge,TaB,TiB2,SiO2,BP,Nb3Ge,Si1-xGex,...3.氧化/氮化反应－Oxidation/NitritionoftenusingO2/N2AX(g)+O2(g)---AO(s)+[O]X(g)ex:SiO2depositionfromsilaneandoxygenat450oC(lowertempthanthermaloxidation)SiH4(g)+O2(g)---SiO2(s)+2H2(g)usetodeposit:Al2O3,TiO2,Ta2O5,SnO2,ZnO,...4.置换反应－ExchangeoftenusingamoniaorwatervaporAX(g)+NH3(g)---AN(s)+HX(g)AX(g)+H2O(g)---AO(s)+HX(g)ex:depositwearresistantfilm(BN)at1100oCBF3(g)+NH3(g)---BN(s)+3HF(g)usetodeposit:TiN,TaN,AlN,SiC,Al2O3,In2O3,SnO2,SiO2,...5.歧化反应－Disproportionationcompoundsinvolvingelementswithmultiplevalencestates（多种价态）2AB(g)===A(s)+AB2(g)ex:usetodeposit:Al,C,Ge,Si,III-Vcompounds,...6.可逆输运－ReversibleTransferex:usetodeposit:GaInAs,AlGaAs,InP,FeSi2,...Howdoesreactiongo?Dependsonparameters:–Temperature–Pressure–reactants(purity,concentration…)Thermodynamicsanddynamics4.3Reactionlaw1.CVD热力学判断反应、方向、平衡•ignoresrateinformationDGristhecriteria.DGr0(Textbookp111)•notstrictlycorrectinflowingsystem(nonequilibrium)•Ellinghamplotscanbeuseful•MoCl5,ReCl3andAsCl3areallreducedbyHtometalsandHCl•Ni,Fe,andCochloridesreduceatintermediatetemperatures•SiCl4reducesathightemperature•manyothermetalchloridesaretoostable•CrCl2isclose-butnotquiteFig.4.24.4CVD过程动力学气体输入气体对流气相扩散表面吸附表面反应表面脱附薄膜成核生长1.CVDFilmGrowthStepsoncereactionisidentified,considertheprocessindetail:–源source:productionofappropriategas–气相传输transportofgastosubstrate–沉积depositionoffilm:•吸附－adsorptionofgasonsubstrate•反应－reactiononsubstrate–phasetransformation–recrystallization,graingrowth–废气排除transportofwasteproductsawayfromsubstrateA.CVDSources•源类型typesofsources–gasses(easiest)–volatileliquids–sublimablesolids–combination•materialsshouldbe–稳定stableatroomtemperature–挥发性sufficientlyvolatile•highenoughpartialpressuretogetgoodgrowthrates–reactiontemperaturemeltingpointofsubstrate–producedesiredelementonsubstratewitheasilyremovableby-products–lowtoxicityB.Substratesneedtoconsider--besidesitsproperties–adsorption–surfacereactions–ex:WF6depositsonSibutnotonSiO2C.Growthoffilmsdependson–transportofgastosurface–adsorptionofgasonsubstrate–reactionratesonsubstrate–transportofproductsawayfromsubstrate2.质量传递过程Masstransportingas–goals–delivergasuniformlytosubstrate(uniformfilms)–optimizeflowformaximumdepositionrateA.Twoflowregimes–分子流Molecularflow•diffusioningas–D~T3/2/PfromKineticTheoryofGasses–reducePressureforhigherDandhigherdepositionrate–粘滞流Viscousflow•lowflowratesproduceslaminarflow(desired)•highflowratesproducesturbulentflow(avoid)层流laminarflow:simplecase--flowpastaplatenearplatevelocity=0==stagnantlayer(滞流层、边界层)•diffusegasthroughstagnantlayertosurfacemasstransportdependsonfundamentalparametersexperimentalparameters反应物浓度reactantconcentrationpressure扩散diffusivitygasvelocity边界层厚度boundarylayerthicknesstemperaturedistributionreactorgeometrygasproperties(viscosity...)B.气相扩散模型(Grove,1967)•AB(g)---A(s)+B(g)F1=fluxtosurfaceF2=fluxconsumedinfilmCG=concentrationofABingasCS=concentrationofABatsurfaceF1=hG(CG-CS)=D/δ*(nG-nS)wherehG=gasdiffusionrateconstant,orDF2=kSCSwhereks=surfacerateconstantinsteadystate:F1=F2=FgrowthrateoffilmisproportionaltoF∝T3/2/pC.Tworate-limitingcasesa传质限制机制－masstransferlimited–smallhG–growthcontrolledbytransfertosubstrate–hGisnotverytemperaturedependent–commonlimitathighertemperatureslowerpressure,higherT→Quickerdiffusionb表面反应限制－surfacereactio