半导体工艺-复旦大学-蒋玉龙-Chapter12

Chapter12DryEtchingbyPlasmaProcessingOutlineI.Dryetching---oneofthekeytechnologiesforVLSI/ULSIII.PlasmaetchingmechanismsIII.Variousplasma-etchingreactorsIV.EtchingAnisotropyV.DryetchingfordifferentmaterialsVI.ContaminationduringPlasmaEtchingVII.RadiationDamageVIII.EndpointDetectionIDryetching---oneofthekeytechnologiesforVLSI/ULSI‹Predominantdryetchingtechnology—PlasmaandReactionIonEtching(RIE)¾Etchingprocessingasplasmadischarge(at10-3-100torr)¾Gaseousreactants¾Gaseousproducts‹Advantages:¾Anisotropicetching¾Formationofsmall-geometrydevicestructure¾Highdensityofreactivespeciesavailable¾Environmentallylesshazardous‹Otherdryetchingtechniques:¾Ionbeamenhancedetching¾Electron－beamenhancedetching¾Photonassistedetching¾Gas－phaseetching:AnhydrousHFvaporIIPlasmaetchingmechanisms‹Physicalprocess:Surfacebombardmentbyionsacceleratedacrosssheath‹Chemicalprocess:Activespeciesreactwithsubstrateatomsformingvolatileproducts1.Physical－sputteringetching¾Byanyionswithenoughenergy(thresholdenergy)¾Withnoorlessselectivity(Mask&substrateetching)¾ContaminationSolutions:¾Keeppotentialbelowsputteringthreshold¾UsechambermaterialwithhighthresholdApplicationofpuresputteringetching:---Fordepthprofilinginanalyticaltools(SIMS,AES)---Ionmilling2.Complexphysicalandchemicalprocessduringplasma/RIE‹4fundamentallydifferentetchingmechanisms:¾Sputtering¾Chemicaletchingviaplasmaspecies→Isotropicetching¾Chemical/physicaletchingviareactiveionbombardment→Anisotropicetching¾Ionassistedorioninduced:Ionbombardment+chemicalspecie→EffectiveetchingUsuallynoreactionoftheetchinggasorgasmixturewithoutthepresenceoftheplasma(3)PossiblemechanismsofionbombardmentinetchingprocessIonEnhancedEtching¾Ionscreatedamage/defectswhichcatalyseschemicalreaction(SeeFig.(a)below)¾Ionbombardmentdirectlydissociatesreactantmolecules¾Ionbombardmentremovesinvolatileresiduesthatcouldinhibitetching(SeeFig.(b)below)Mechanismofionenhancedetching(4)Importanceofradicals:¾Radical－atomicormolecularspeciewhichisneutralbutincompletelybonded,veryreactiveExample:EtchingSiO2byCF4plasmaF,CF3－radicals¾Radicals－responsibleformostofthechemicaletchinginmostprocesses¾F-atoms(radicals)－ActiveetchanteFCFCFe234++→++eFCFCFe++→+34IIIVariousplasma-etchingreactors‹Componentsofplasmaetchingsystems:¾Etchingchamberwithelectrodes¾Pumpingsystemforestablishing&maintainingprocessinggaspressure¾Pressuregaugestomonitorpressureinthechamber¾Variableconductancebetweenthepumpandchamberforindependentcontrollingpressureandflowrate¾Gashandlingcapabilitytotestandcontroltheflowofreactantgas¾Powersource¾Processmonitorandendpointdetector‹Variousreactorsdifferentinconfigurations,etchingmodesandpowersources:¾Barrelvs.ParallelPlatevs.Hexode¾Batchvs.SingleWafer¾Plasmavs.RIE¾Directvs.Downstream¾RFvs.Microwave•Highdensityplasmaetcher--byInductivecoupledplasma(ICP)IVEtchingAnisotropy‹Patterningfeatureprofilecontrol－VitalimportanceforVLSI/ULSI‹Thedegreeofanisotropyofanetchprocess:RL:lateraletchrateRV:verticaletchrate.‹Purechemicalreaction:Isotropicetching‹Ionicbombardment:AnisotropicetchingVLRRA−=1RIEandPlasmaetching‹Plasmaetch:Waferongroundedelectrode---lessanisotropic‹RIE:Waferonpoweredelectrode---moreanisotropicVt~50-500VatlowerP(5-100mtorr)Vp20Vat0.1-2Torr‹Mechanismsforanisotropicetching:¾Ionenhancedetching:9Increasedetchratebyionbombardment9Slightetchingwithoutions¾Ioninducedetching:9Ionbombardmentinitiateschemicaletching9Noetchingwithoutions¾Sidewallpassivation:Stablefilmsformedonsidewallduetolackofbombardment9Sidewallfilmpreventsetchingbyotherisotropicetchant9Sidewallfilmdeposition:*BydepositionofpolymericmaterialfromC-containingplasmas:－CF2－polymers¾Perfectanisotropicetchingnotalwaysdesired(becausemetalcontinuityfailureatsteps,contacts,non-removalofresidues…)Non-verticaletchprofiles:byusingmoreisotropicetch(P↑→V↓)…VDryetchingfordifferentmaterials1)Generaletchingprocessrequirements:¾Featureprofile¾Selectivity(SAB=EA/EB)¾UniformityandReproducibility¾Throughout¾Lowcontaminationanddamage2)SiO2etching:¾ByF-basedetchants(etchingproduct---SiF4):CHF3,CF4+H2,C2F6,C3F8，mixtures¾TogetgoodselectivityoverSi,needF-deficientplasmaCF4+H2→F/Cratio↓→Sietchrate↓3)Si3N4etching:¾SimilaretchantswithSiO2+NF3－betterselectivityoverSiO2(9-10)4)Sietching¾Variousetchants:(etchingproducts:SiCl2,SiCl4,SiF2,)Cl2,CCl4,BCl3+Cl2,CFCl3,CF4+O2,SF6,NF3orotherCl-containingmixture¾Highselectivityrequired(forpoly-Sigate):Cl-basedplasma－veryselective¾Highanisotropyrequired:fortrenchisolation,DRAMcapacitors5)Aletching¾ByCl-basedetchants:BCl3,CCl4,SCl4,Cl2,,¾KeytoAl-etching:FormationofAlCl3－highvaporpressurecompound¾Corrosionproblem:Clresidues+H2Ovapor→HClcorrosion¾Nativeoxide(Al2O3)~(30A):Mustberemovedfirst(CCl4,BCl3+Cl2)6)ResistPlasmaAshing(Plasmastripping)¾ByO2plasma:e+O2→O+O+e…resisit+O2→CO,CO2,H2O¾Downstreamprocessingtoeliminatedevicedamagefromionbombardment(bymicrowaveplasmaasher)¾Additionofothergases(forminggas,fluorinecompounds)toimprovethestriprateatlowTandtohydrogenatetheremainingresiduesforeasyaqueousremoval(O2+CF4…)7)Usingmixture-gasetchantstoimproveetchi