微机电系统2课件

CHAPTER2.MicrofabricationtechnologySemi-conductorindustryandMEMSmaterials.IntroductiontomodernSemiconductorindustrySemiconductorindustryisplayingmoreandmoreimportantroleinmodernsociety.Wecansay,nosemiconductorindustry,nomoderncivilization!2)CommonlyusedMEMSmaterials

CategoryMaterialPropertyorapplicationMetalAu,Al,Cu,Ni,CrConductorSemiconductorSiliconStructure,semiconductorPoly-crystallinesiliconStructure,semiconductorSingle-crystallinesiliconStructure,AnisotropicetchpropertiesGaAsStructure,opticalpropertiesQuartzCrystallineSiO2Substrate,structuresPolymerParylene-C

NafionPolymericmaterialsNon-metalsDiamond(C)structure3)CrystalstructureofSilicon4)Crystalplanes5)Typesofsiliconwafer6)WhydowechoosesiliconasaMEMSstructuralmaterial?Semiconductorsareaclassofmaterialswhichhavetheuniquepropertythattheirelectricalconductivitycanbecontrolledoveraverywiderangebytheintroductionofdopants.Whilethispropertycaneasilybeobservedincrystalline,polycrystalline,oramorphoussemiconductormaterials,crystallinematerialsprovidethemostreproduciblepropertiesandthehighestperformancedevicesand

arealmostalwaysused

inintegratedcircuits.Dopantsareatomsthatgenerallycontaineitheronemoreoronefewerelectronsintheiroutermostshellthanthehostsemiconductor.Theyprovideoneextraelectronoronemissingelectron(a"hole")comparedtothehostatoms.Theseexcesselectronsandholesarethecarriers,whichcarrycurrentinsemiconductordevices.Thekeytobuildingsemiconductordevicesandintegratedcircuitsliesintheabilitytocontrolthelocaldopingandhencethelocalelectronicpropertiesofasemiconductorcrystal.7)SemiconductorDevicesUnderstandingofhowthebasicdevicesusedICsoperateisuseful,becauseitprovidessomeunderstandingoftheobjectiveswehaveforICtechnology.ThemostcommonlyusedICdevicesare:1)PNDiodes2)BipolarJunctionTransistors3)MOSTransistors☼Basicstepoflithography:1）Themaximumresolutionofadevice:whereλisthewavelengthoflightusedtomakeimagetransfer.e.g.UVλ=500nm2）Steps:substratepreparation→thinfilmaddition→castPR→pre-designedmask→exposeinUVlight→developPRindevelopingsolution→EtchthethinfilmcoveredwithPRinasolutionthatwillattackthethinfilmbutnotthePR→removePR

2)PhotoresistSpinCoatingDefinitionofclean-roomclass:numberofparticlesofsize>ofair.100class,10class3.X-Raylithography

AtypeoflightlithographytechniquesusingshortwavelengthX-RaysProsFastprocessHighaspectratioSolvesdepthoffocusproblemHighresolutionsof~.5µmReductionindiffraction,reflection,andscatteringeffectsNotaffectedbyorganicdefectsinmask

ConsShadowprintingLateralmagnificationerrorBrighterx-raysourcesneededMoresensitiveresistsneededDifficultfabricationofx-raymask

ProsComputer-controlledbeamNomaskisneededCanproducesub-1µmfeaturesDiffractioneffectsareminimizedElectronbeamcandetectsurfacefeaturesforveryaccurateregistrarConsSwellingoccurswhendevelopingnegativeelectronbeamresists,limitingresolutionExpensiveascomparedtolightlithographysystemsSlowerascomparedtolightlithographysystemsForwardscatteringintheresistandbackscatteringinthesubstratelimitresolution

5.DiffusionandImplantationofDopantsThermaloxidation--growingonSiDryoxidation:(1150°C,4hr)Wetoxidation:(800°C~1200°C)o.44dSidWheret:time;A、B:constant;whent<<

d≈Bt/A

AandBcanbeobtainedfrom‘handbook’2)Deposition(nochemicalreactiononsurface)--Vacuumchambersareneeded+thinfilmdeposition--Al,Au,Cr4)CVD(ChemicalVaporDeposition)(1)(300~500°C)TypicallyCVDfilmsare0.1~2umthicknessinMEMSuse.(2)(700°C~900°C)(3)(600°C~700°C)5um~50umpoly-SiLPCVD（低压CVD）P<102PaPECVD(等离子增强CVD)（二）Bulkmicromachining1.BasicconceptforBulkMicromachiningSelectivity—Aprocessisselectivityifitetchesthedesireddirectionatahigherrateandallothersurfaceatalowerrate.Isotropic--Sameetchingrateatalldirections.Anisotropic–directionselected4)WetetchingThisisthesimplestetchingtechnology.Allitrequiresisacontainerwithaliquidsolutionthatwilldissolvethematerialinquestion.Isotropicenchants(HNA):HF,HNO3,CH3COOHAnisotropicenchants:KOH,EDP,TMAH54.74°(100)<100>Note:theadvantageofwetetchingisthatyouwillgetgoodselectivity,buthardtocontroletchrate.5)DryetchingPlasmaetchpolySi:Cl,Fbasedgases,suchasCl2,CF4Oxides:CHF3,C2F6etc.b.RIE(reactiveironetch)c.DRIE（三）Surfacevs.BulkmicromachingSurfacemicromachingBulkmicromachingSurfaceMicromachi