半导体工艺-复旦大学-蒋玉龙-Chapter07

Chapter7LithographyOutlineI.Finelinelithography-keyformicro-fabricationII.ProgressforpatterningtechnologyIII.OpticalalignmentandexposuresystemIV.PhotoresistV.Opticallithographyforsub-microfabricationVI.LightsourcesforopticallithographyVII.PhaseshiftingmasktechnologyVIII.NovellithographytechnologyfornanometerCMOSIX.ImmersionlithographyX.EUVandX-raylithographyXI.ElectronbeamlithographyI.Finelinelithography–Keyformicrofabrication‹Maincharacteristicforadvancedmicrolithography(1)HighresolutionResolution–Abilitytodistinguishcloselyspacedobjects(Min.linewidthorspacecanberesolved&printed)(2)Finepatternregistrationcapability---Tightfitofthepatterntoapreviousprintedpattern(3)Precisedimensionalcontrol---Abilitytoproducedevicefeaturesizesovertheentirewafersurfacewithhighaccuracy&precision(4)Highthroughput---EssentialrequirementforlowercostofmassproductionResolutionlimitedbylightdiffractionandinterference‹Resolutionandnumericalaperture(NA)ofanopticalsystemTheminimumfeature(W)thatmaybeprintedwithanopticalsystemisdeterminedbytheRayleighequation:W=K1λ/NANA=nSinαn≅1,k1---TheresolutionfactorDepthoffocusneedstobeconsideredtoo:σ=k2λ/(NA)2‹Forbetterresolution¾Shorterwavelength¾LargerNA(Resolutionisameasureoftheabilityofasystemtoformseparateimagesofcloselyspacedobjects)Ⅱ.ProgressofpatterningtechnologyMainphotolithographyprocesses‹Mask(Reticle)making:OpticalÆE-beam‹Photoresist:NegativeÆPositive,Multilayer(Plasma-developableresistforall-drylithographicprocess)‹Alignment&exposureContactÆProjection,DSWOpticalÆE-beam,X-ray,ionbeam‹EtchingWetÆDry,RIEIsotropicÆAnisotropic(directional)‹从设计到硅片曝光不同光刻技术流程图设计计算机程序光台10X掩模版1X母版1X光刻版对准，曝光光刻硅片电子束系统分步重复投影曝光DSWDirectWritingContact/ProximityScanningProjectionⅢ.Opticalalignmentandexposuresystem(1)Contactprinting¾Lowyieldbecauseofdamage&defects¾Canbeofgooddefinition&highresolution(0.5μmresolutionreported)(Limiteddiffraction)(2)OpticalproximityprintingMin.linewidth:Wm=(dλ)1/2λ--Wavelengthofthelightd--Mask-waferseparation(3)Full-waferscanningprojectionprinter(1stintroducedbyPerkin-Elmerin1973)¾Full-sizemaskimageprojectionbysynchronouslymovingthemaskandwaferwhilethemaskisilluminatedbyasegmentofacircularbandoflightMax.resolution~1μm(4)DirectStepperonWafer(DSW)projectionlithography(硅片直接分步重复—对准曝光系统)系统计算机生产控制计算机激光干涉仪系统光源掩模版定位调节器透镜硅片平台操作员Highresolutionexcimerlaserprojectionstepper‹Usinghigh-resolutionmulti-elementlenswitharelativelysmallfield¾Reductionlens:5X,10X,2.5X,1X,4X¾Projectionimagefield:15X15mm2,22X22mm2…¾Lens–comprisedofalargenumberofrefractingelementsinordertocompensateforvariousopticalaberrations‹RayleighlimitforresolutionofanopticallithographyW=K1λ/NAW–Separationoftwobarelyresolvableobjectsλ–WavelengthoflightNA–Numericalaperture:NA≅D/2fD–Diameterofthelensentrancepupilf–Focallengthofthelensk1—theprocessrelatedfactor—ameasureoflithographyaggressivenessk1isacomplexfactorofseveralvariablesinthephotolithographyprocesssuchasthequalityofthephotoresistandtheuseofresolutionenhancementtechniquessuchasphaseshiftmasks,off-axisilluminationandopticalproximitycorrection.‹Precisetemperaturecontrolandvibration-freefacilityrequiredSi:α≈2.5×10-6/°C,For200mmwafer:ΔT=1°C;ÆΔl≈0.5μm‹Modulationtransferfunction(MTF)ofaprojectionsystem¾FeaturesizeresolutionisdeterminedbyMTFofopticalsystemandMTFofresist(MTF–光学传递函数)9Capabilityofanopticalprojectionsystemtoreproduceamaskonawafersurface9MTFdependson:–Illuminationwavelength（λ）–NAofthelens–Maskfeaturesize–SpatialcoherenceoflightsourcediameterpupildiametersourceLightS=(Pupildiameter∼Condenserlensdiameter)Usually,S≈0.5-0.7inmodernsystem*Modulation:minmaxminmaxIIIIM+−=Foridealtransfer:10min=→≈MI*MTFofanexposuresystemimmaskimMMMMTF≈=1≈maskM*Spatialcoherenceoflightsource‹Spatialfrequency–lines/mm(Cutoff)ResolutionbyRayleighcriterionForsystemwithλ=0.436μmandNA=0.35→NAb/61.0100021000λν==1316/(/)cutofflinesmmcirclesmmν≈2b=0.76μm(b,λ---μm)‹TRANSISTORDENSITIESonintegratedcircuitshaveincreasedatanexponentialrate,asshownonthislogarithmicplot.Theratehasbeensustainedbyasuccessionoflithographysystems,whichareusedinchip-makingtoprojectpatternsontowafers.Higherdensitieshavebeenachievedinmemorychipsbecauseoftheirmoreregularandstraightforwarddesign.IV.PhotoresistFinelithographyrequiresphotoresist:¾HighResolution¾HighPhotosensitivity1.Composition¾Matrixmaterial(resin树脂)¾Sensitizer–photoactivecompound¾Solvent(2-3%innegativeresist;~20%inpositiveresist)2.Negativephotoresist¾Photochemistry:hνadsorption→Crosslinkednetwork→Insoluble¾Applicationto≥3µm¾Resistcontrast:γ≈1.5¾Moresevereswelling→Lowerresolution(Resistvolume↑duringdevelopment,duetoabsorptionofdeveloperbyexposedresist)3.PositivePhotoresist¾Photochemicaltransformationofthephotosensitivecomponent(sensitizer):Byphoto-scission(“光分裂”)ofsensitizermolecules¾Adissolutioninhibitor→Adissolutionenhancer¾Highercontrastandresolution→Popularapplication4.Multi-layerresistprocessforbetterresolution*PlanarizedsurfacewiththinimaginglayerÆBetterresolutionÆBetterdimensionalcontrolDisadvantage:Complexity5.R&Donnewhigh-resolution,high-sensitivityresists¾DeepUVoptica