Intro to Plasma Etching

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1、PlasmaEtchingOutline•Plasmavs.WetEtching•ThePlasmaState-Plasmacomposition,DC&RFPlasma•PlasmaEtchingPrinciplesandProcesses•Equipment•AdvancedPlasmaSystemsPhilipD.RackUniversityofTennesseeTerminologyEtching-theprocessbywhichmaterialisremovedfromasurfaceMaskLayer-Us

2、edtoprotectregionsofthewafersurface.ExamplesarephotoresistoranoxidelayerWetEtching-substratesareimmersedinareactivesolution(etchant).Thelayertobeetchedisremovedbychemicalreactionorbydissolution.Thereactionproductsmustbesolubleandarecarriedawaybytheetchantsolution

3、.DryEtching-Substratesareimmersedinareactivegas(plasma).Thelayertobeetchedisremovedbychemicalreactionsand/orphysicalmeans(ionbombardment).Thereactionproductsmustbevolatileandarecarriedawayinthegasstream.Anisotropic-etchrateisnotequalinalldirections.Isotropic-etch

4、rateisequalinalldirections.Selectivity-theratioofetchrateoffilmtoetchrateofsubstrateormask.AspectRatio-ratioofdepthtowidthofanetchedfeature.PhilipD.RackUniversityofTennesseePage11WhyPlasmaEtching?AdvancedICFabricationwithsmallgeometriesrequiresprecisepatterntrans

5、ferGeometryinthe<1.0micrometerrangeiscommonLinewidthscomparabletofilmthicknessSomeapplicationsrequirehighaspectratioSomematerialswetetchwithdifficultyDisposalofwastesislesscostlyPhilipD.RackUniversityofTennesseeAnisotropicEtch,HighAspectRatioPhilipD.RackUniversit

6、yofTennesseePage22IdealEtchingProcessmaskfilmtobeetchedBeforeetchsubstratemaskAfteretchsubstrateNoprocessisideal,butsomeplasmaetchesareclose.PhilipD.RackUniversityofTennesseeDirectionalityofEtchingxresistxzDegreeofAnisotropyA=(z-x)/zsubstratezAnisotropicEtch(x

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8、ler&GuidePlateGenerallyWetEtchingisIsotropicPhilipD.RackUniversityofTennesseeWetEtchingProblemsMaskresistBeforeEtchsubstrateisotropicpoorBlockingundercutadhesi