Sputtering(溅射镀膜)课件

GlowDischargeGlow-dischargesputteringmeanstheenergeticparticlesusedtostriketargetisgeneratedbyglow-discharge.Creationofglow-dischargeTubefilledwithargon,neutral,nochargedparticlesbetweencathodeandanodeElasticcollision,noenergyexchangeInelasticcollisionEnergynotenoughhigh,exciteelectrons,emittingphotonsEnergyhighenough,ionizeelectrons,causesecondaryfreeelectronsBothfreeelectronsareacceleratedagain,socausecascadingorgasbreakdown

Flowofelectronsiscollectedbyanode,currentwillquicklydecaytozeroGLOWDISCHARGEPROCESSESAtomsintogasstate

attarget:targetatomsejectedtargetionsejected(1-2%)electronsemittedhelpskeepplasmagoingAr+ionsreflectedasArneutralsArburiedintargetphotonsemittedSputterDepositionFundamentalsofSputterDepositionSputterDepositionmomentumtransferprocessinvolvestop10Åmodelashardspherecollisionsgoodforenergies<50keV95%ofincidentenergygoesintotarget=>COOLthetarget5%ofincidentenergyiscarriedoffbytargetatomstypicalenergiesof5-100eVtargetatomscomeoffwithanon-uniformdistributionmoreatomsnormaltothesurfacecosinedistribution(likesurfacesource)characterizeprocessbysputteryield(S)S=numberejected/numberincidentSputteringprocessSdependson:targetmaterialbindingenergymassofatomssputteringgasmassofatoms(Sincreasesforheaviergasses)incidentenergy(Sincreasesforhigherenergies)geometrymostefficient20-30degreesfromglancingfornormalincidencesputtering:maximumaround10kVsputteringthresholdSisabout1-10typicallyForcalculatingSweneed:numberofatomsejecteddependsonmomentumandenergytransferredthesedependonrelativemassesandcollisionanglemaximumenergytransferredtotargetatominhardspherecollisiondependsonbindingenergyoftargetatomnumberoflayersinvolvedinprocessmeanfreepathofionintargettypicallyabout2layerssurfacedensityoftargetatomscollisioncrosssectionofionwithtargetatomPVDSputteringToolPVDbySputteringSputtering:Sputteringisaprocesswherebycoatingmaterialisdislodgedandejectedfromthesolidsurfaceduetothemomentumexchangeassociatedwithsurfacebombardmentbyenergeticparticles.Processes:Gasionsareacceleratedbyahighvoltage,producingaglowdischargeorplasmaAsource(thecathode,alsocalledthetarget)isbombardedinhighvacuumbygasionsAtomsfromthetargetareejectedbymomentumtransferandmoveacrossthevacuumchamberAtomsaredepositedonthesubstratetobecoatedandformathinfilm.SputteringMechanismBounceback: whenverylowenergy(<5eV);whenthecollisionishead-onornearlysoEmbedded: whenmuchhigherenergy(>10KeV),theimpingingparticlesaremostlikelytobeembeddedinthetarget,whichisthebasisofIonImplantationIfenergylevelisbetweenthetwoextremes:somefractionoftheenergyoftheimpingingionsistransferredtothesolidintheformofheat,andlatticedamageanotherfractionofsuchenergycausesatomsfromthesurfacetobedislodgedandejectedintothegasphase----SputteringThekineticenergyoftheimpingingparticleslargelydictateswhateventwillhappenUniqueCharacteristicsUniformthicknessoverlargearea.Simplethicknesscontrol.Thealloycompositionmaintainsstoichiometrywiththeoriginaltargetcomposition.Depositionratesdonotdifferagreatdealfromonematerialtoanother.Sputtering-cleaningpriortoinitiatingfilmdeposition.Thesurfaceisnotagainexposedtoambientaftersuchcleaning.Thelifetimeofasputteringtargetmaybeaslongashundredsofrunsandisseldomlessthan20.CoatingMaterialsMetals:Al,Cu,Zn,Au,Ni,Cr,W,Mo,TiAlloysAg-Cu,Pb-Sn,Al-Zn,Ni-CrNonmetals:

graphite,MoS2,WS2,PTFERefractoryoxides:

Al2O3,Cr2O3,Al2O3-Cr2O3,SiO2,ZrO2-Y2O3

Refractorycarbides:

TiC,ZrC,HfC,NbC,Tic-Ni,Tic-ZrC

Refactorynitrides:

TiN,Ti2N,ZrN,HfN,TiN-ZrN,TiN-AlN-ZrN

Refractoryborides:

TiB2,ZrB2,HfB2,CrB2,MoB2Refactory

silicides:

MoSi2,WSi2,Cr3Si2Thinfilmsputteringlines6chamberthinfilmsputteringlineSputteringSystemDCsputteringRFSputterDepositionCathodesputterarrangementCathodeplanarsputteringsystemSputteringalloytargetscompositionofalloyinfilmisapproximatelythesameasalloyintarget(unlikeevaporation)rapidmixinginliquids(evaporation)slowdiffusionmixinginsolids(sputtering)targetreachessteadystatesurfacecompositionbalancessputteryieldProcess:InitialalloyofAandB..........................ABABABABABABABIfSA>SB,removemoreAenrichessurfaceinB.....................BAB.B.BA.B.ABMoreBonsurface=>moreBsputtered.......ABABBABABBABsurfacecompositionreachessteadystatesurfaceenrichedinBbulkcompositionsputteredfASA/CA=fBSB/CBwheref=surfacefractionandC=bulkcompositionalloytargetsneedtobeconditionedbysputteringafewhundredÅbeforedepositing2.TransporttosubstrateTargetatomspassthroughArgasandplasmaenvironmentoneAr+ionforevery10,000ArneutralselectronsinplasmacollidewithArneutralstoformionsandmoreelectronsTargetatomscollidewithAratoms,Ar+ionsandelectronstreatasrandomwalk"diffusion"throughgastargetatomsloseenergy(downto1-10eV)chemicalreactionsmayoccuringasnotalineofsightprocess(unlesspressurereduced)cancoataroundcorners3.DepositonsubstratetargetatomsandionsimpingeelectronsimpingeAratomsimpingeArpressureabout0.1torrArmaybeincorporatedintofilmenergeticparticlesmaymodifygrowthsubstratesheatup100-200Ciscommonforathermallyisolatedsample(noheatconduction)r=substratedensity(g/cm3)c=substrateheatcapacity(J/gûC)d=substratethickness(cm)W=filmatomicvolume(cm3/atom)D-DOT=depositionrate(Å/min)t=time(secs)energiesareineV/atomnote:theconstantdoeshaveunitsParameters:ArgonPressure

optimumdepositionratearound100mTorrcompromisebetweenincreasingnumberofArionsincreasingscatteringofArionswithneutralAratomsifyoucanincreasethenumberofionswithoutincreasingthenumberofneutrals,youcanoperateatlowerpressuresSputtervoltage

maximizesputteryield(S)typically-2to-5kVSubstrateBiasVoltage

substrateisbeingbombardedbyelectronsandionsfromtargetandplasmasputteringfilmwhileyoudepositneutralatomsdepositindependentlyputnegativebiasonthesubstratetocontrolthiscansignificantlychangefilmpropertiesSubstratetemperature

controlwithsubstrateheaterheatingfromdepositedmaterialincreaseswithincreasingsputtervoltagedecreaseswithincreasingsubstratebiasDepositionrate

changeswithArpressureincreaseswithsputteryieldusuallyincreaseswithhighvoltageParticleEnergy

increaseswithincreasingsputtervoltagedecreaseswithincreasingsubstratebiasdecreaseswithincreasingArpressureGoodforinsulatingmaterialsinDCsystems,positivechargebuildsuponthecathode(target)need1012voltstosputterinsulators!!avoidchargebuildupbyalternatingpotential................TIME------->sputterdepositionoccurswhentargetisnegativesubstrateandchambermakeaverylargeelectrode-sonotmuchsputteringofsubstratePhysicalprocessfrequencieslessthanabout50kHzelectronsandionsinplasmaaremobilebothfollowtheswitchingoftheanodeandcathodebasicallyDCsputteringofbothsurfacesfrequenciesaboveabout50kHzions(heavy)cannolongerfollowtheswitchingelectronscanneutralizepositivechargebuildupAdvantages:EasiertokeepplasmagoingundertheseconditionsCanoperateatlowerArpressures(1-15mTorr)fewergascollisions=>morelineofsightdepositionMagnetronSputterDepositionusewithDCorRFgoal:increaseionizationofArWhy?HighersputterratesatlowerArpressures(downto0.5mTorr)fewergascollisions-morelineofsightHow?increaseprobabilityofelectronsstrikingAr

increaseelectronpathlengthuseelectricandmagneticfieldsMostcommonconfigura