dry-etch-introduction[1]

ETCHProcessIntroduction„Whereisetchusedinchipmanufacturingflow„Generaletchconceptandterminology„Etchequipmentprinciples„Etchprocessoverview„SummaryWhereisetchusedinmanufacturingflowofintegratedcircuitDryEtchandWetEtchIsotropicEtch:Anetchthatproceedslaterallyandverticallyatthesametime,sometimesatequalrates.Wetchemicaletchesareusuallyisotropicinnature.An-isotropicetch:Anetchthathasverylittlelateralactivity.Mostoftheetchingoccursintheverticaldirection.Dryetchsystemsareprimarilyanisotropic.WhyUseDryEtch?DimensionShrinkageRequirementSEMCross-section3DstructureGeneralEtchConcept&TerminologyDCGlowDischargee-+M--M++2e-e-+M--M*+e-e-+M2--M+M+e-•LowPressuretoIncreaseParticleMeanFreePath•HighEnergytoGiveEnoughParticleCollisionParallel-PlatePlasmaReactorsDisadvantagesofDCglowdischargeinplasmaetch:(1)Requireshighpowerconsumption.(i.e.Lowiondensity)(2)Requiresionbombardmenttoemitsecondarye-fromelectrodes.(Electrodematerialconsumption)(3)Requiresconductionmaterialforelectrode.(Notsuitableforwaferprocessing)ElectrodeConfigurationinPlasma-AssistedEtchReactorsInductivelyCoupledPlasma(ICP)EtchReactorsTCP:BasisofOperation“TCPsource”--Theelectricalfieldofthecoilisparalleltotheplaneofthecoil--ElectronsfollowtheoscillatingRFcurrentplanartothecoil.--Ionsarecreatedbytheacceleratingelectrons,ionshavelittledirectionality.--Thehighionefficiencycreatesahighdensityplasma.TCP:BasisofOperation“Biassource”DryEtchingDefinition:Dryetchingiscomposedofplasmaandplasmageneratedmethodsemployingenergeticgasmolecules,ions,and/orfreeradicalstoremovesurfacematerialsfromthewafer.Application:•definepattern(dimension,shape)•definethicknessWhatisplasma?A“PartialIonized”Gaswith“EqualNumber”ofpositiveandNegativechargedparticles.„Itcontainshighlyreactivegasspecies-FreeRadicalsandIons„Itemitslight-Glow„Itisdrivenbyelectricenergy-ElectricFieldPlasmaGenerationDiagramPlasmaGenerationProcedureDisadvantagesofDCglowdischargeinplasmaetch:(1)Requireshighpowerconsumption.(i.e.Lowiondensity)(2)Requiresionbombardmenttoemitsecondarye-fromelectrodes.(Electrodematerialconsumption)(3)Requiresconductionmaterialforelectrode.(Notsuitableforwaferprocessing)IonizationTheory„In-elasticCollision„KeyReactioninsustainingastableplasmae-e-e-+„Collisionrate(MeanFreepath)Pressure↑ÖCollisionRate↑FlowRate↑ÖCollisionRate↑Power↑ÖCollisionrate↑„ElectronEnergyPressure↑ÖEnergy↓FlowRate↑ÖNoEffectPower↑ÖEnergy↑„MeanFractionEnergyLossPerCollisionDependsongas,energy„IonizationPotentialdependsongasIonizationPotential--Theminimumenergyrequiredtoionizeaparticle.--Example:1.Lowpower:H2dominatesionization2.Highpower:N2dominatesionization3.Heneverplaysanimportantroleinplasmaformation.GeneralPlasmaEtchDoing“Chemicalreaction”inthePlasmaEnvironmentatLowTemperature.„Plasmaprovidesthesourceof(1)ReactiveRedicalsÖEtchantSource(2)ReactiveionsÖDirectionality&EtchantSource(3)ExcitedMoleculars/AtomsÖEPDSignal(4)IonBombardmentonSurfaceÖReducingSurfacePotentialtoenhanceaserieschemicalEtcheswhichrequirehightemperatureinthenormalsituation.GeneralPlasmaEtch„IonBeamEtch(PurePhysicalSputtering)hastwobigdisadvantages:(A)LowSelectivity(B)LowEfficiency„ChemicalEtchhastwodisadvantages:(A)IsotropicEtch(B)NotScalabletoSubmicronSize.(C.D.&Uniformity)GeneralPlasmaEtchMechanismGeneralPlasmaEtchMechanismExample:OxideetchingOxideEtchapplicationMainlyforPatterndefinition,mostlycombinewithphotoresist:„SpacerEtch:DefineLDDWidth„ContactandViaEtch:DefineContactandViaSize„SOGEtchback:ForSurfacePlanarization„PadEtch:OpenBondingPadBasicPlasmaEtchProcedureStep1:Breakthrough(ME1)–EtchnativeoxidelayerForexample:Al2O3onAl-Si-CuSurfaceSiO2onPolysiliconsurface–Etchhardmaskoranti-reflectionLayerForexample:Oxide,NitrideorSiONonPolysilicongate.PE-oxide,TiN/TiorSiONonAl-Si-CuStep2:Mainetch(ME2toEPD)ProfileandC.D.arethemosttwoimportantconcerns.SelectivitytophotoresistisimportantwhenC.D.at0.35umorbelow.Step3:OverEtch(OE)Selectivitytobottomlayerandresidue-freearethetwomostimportantfactorstobeconsidered.BasicPlasmaEtchProcedure:(1)„Polycide/Polyetchmechanism:WSi2Etch(ME1)*WSi2+Cl2→WClx↑byionbombardmentSiCl4(g)Verticalside-wallcausedby(1)WClxpassivation(2)Directionion(3)Polymerfromphotoresistknock-out.BasicPlasmaEtchProcedure:(2)„Polycide/Polyetchmechanism:PolyEtch(ME2EPcatch)*Si+Cl2+HBr+He/O2(afewonly)→SiCl4(g)SiBr4↑byionbombardmentBrxOy↑byionbombardmentVerticalside-wallcausedby(1)SiBr4&BrxOypassivation(2)Directionion(3)Polymerfromphotoresistknock-out.BasicPlasmaEtchProcedure:(3)„Polycide/Polyetchmechanism:OverEtch*Si+HBr+He/O2→SiBr4↑byionbombardmentBrxOy↑byionbombardmentHighselectivitytooxideisachievedbyBrxOyformationandpassivation.EndpointDetectionAnyparameterwhichcanindicatethecompletionofaplasmaetchcanbeusedastheendpointdetection,EPD.(1)OpticalspectrumEmissionofetchantorby-product.(2)OpticalIntensityInterference.(3)PlasmaImpedance,(MatchingCKT)(4)DCBiasVariation(5)PressureVariationOpticalEmission„AtomorMolecularwasexcitedtohighenergylevelsbye-collision.ThoseunstablehighenergylevelswilldecaytoGRDlevelorsomemeta-stablelevelandemitlightwhichcontains