第二章-1(光学光刻技术)

第二章：光学光刻ChapterII:PhotoLithography主流的微电子制造过程中，光刻是最复杂、昂贵和关键的工艺。大概占成本的1/3以上。2ContentResolutioninPhotolithographyExposuremodesandtheiradvantagesanddisadvantagesPhotolithographyresolutionenhancementtechnologyPlanarizationAlignment3Historicalnote:lithography’sorigins1822,France,NicéphoreNiépce,copyanetchprintonoiledpaperusingbitumenmask---theadventofphotography;1827,France,Lemaître,usingstrongacidmadeanengravingofCardinald’Amboise(一位红衣主教的雕像).Lithography[stone(lithos)+write(gráphein)]refertoaprocessinventedin1796byAloysSenefelder.Hefoundthatstonewhenproperlyinkedandtreatedwithchemicals,couldtransferacarvedimageintopaper.Resolution:0.5~1mm4130yearslater,in1961,photo-etchingprocessbeenusedtoproducealargenumberoftransistoronathinsliceofSiwafer.Today,photolithography,X-raylithography,charge-particlelithography,allachievedsubmicroresolution.Resolution:5mmHistoricalnote:lithographydevelopingResolution:~10-190nmLithographyOverviewMask(掩模版)Photoresist(光刻胶)Spinningresistandsoftbaking(涂胶/前烘)Exposureandpost-exposuretreatment(曝光)Development(显影)De-scummingandpost-baking（去胶）Inspections（检测）67光刻胶/光阻(Photoresist)光诱导化学反应8光刻胶的涂覆WhereK=overallcalibrationC=polymerconcentrationing/100mLsolution=intrinsicviscosityW=rotationsperminute(rpm)T=(KC)/W1/2910掩模版(Mask)lightfielddarkfieldGlass(玻璃)Cr(铬)11NegativeandPositivePhotoresist12CriticalDimension(特征尺寸)TheabsolutesizeofminimumfeatureinanICoraminiaturedevice,whetheritinvolvesalinewidth,spacing,orcontactdimension,iscalledthecriticaldimension.13MaskAligners对准机/光刻机主要性能标准：1,分辨率(即可以曝光出来的最小特征尺寸)2,对准(套刻精度的度量)3,产量14Resolution分辨率通常表达为可分辨的且仍能保持一定尺寸容差的最小特征尺寸，典型值是取线宽分布三倍标准偏差值不超过线宽的10％。15MaskAligner(光学光刻机)Exposuresystem(maskaligner)consistofalightsource,illuminationoptics,amask,projectionoptics,analignmentsystemandawaferstage.16ExposureModes(曝光模式)1,ContactMode2,ProximityModeSimpleequitmentDirectcontact,pollute,particleResolution:submicronComplicatesystemNodirectcontact,longlifeResolution:3mm173,ProjectionModeWorklikeaprojectoroverheadMasktowafer1:1Resolution:1mm18ScanningProjectionSystemResolution:0.25mm194,Step&RepeatAlignment/Exposure20ProjectionPrinter(步进式投影曝光机)Stepandrepeat21FactorontheExposureSystemResolutionResolutionmainlylimitsby:LightsourceOpticalsystemMaskDiffractionoflightResistsensitivityAlignmentofmasktowaferNon-uniformitiesinwaferormaskflatnessDebrisbetweenwaferandmask22ExpusureLightsource•Shortwavelength•Highintensity•Stable•Highpressuremecurylamp•Excimerlaser23SpectrumoftheMercuryLamp24PhotolithgraphyLightSources25Theoreticalresolution(曝光精度)26ContactPrinting(接触式曝光)27ProximityPrinting(接近式曝光)28LightDiffractionWithoutLens29LightDiffractionWithLens30ProjectionPrinting(投影式曝光)k1:experimentallydeterminedparameter:wavelengthofthelightNA:numericalapertureofthelenssystem31NumericalAperture(数值孔径)透镜收集衍射光的能力称为透镜的数值孔径(NA)NA=nsinm32通过增加透镜半径,达到增加NA的目的k=0.75NA=0.6=365nmR=0.4mm33Exercise1,34ThewaytoimproveresolutionIncreaseNALargerlens,couldbetooexpensiveandunpraticalReduceDOFandcausefabricationdifficultiesReducewavelengthNeeddeveloplightsource,PRandequipmentLimitationforreducingwavelengthUVtoDUV,toEUV,andtoX-RayReducek1Phaseshiftmask35Phase-shiftingMasks(移相掩膜技术—以相消干涉原理为基础)3637DepthofFocus(焦深)=365nmNA=0.4DOF=2.3mm透镜焦点周围的一个范围，在这个范围内图像连续地保持清晰，这个范围被称为焦深。2)(2NADOF38Exercise2,2)(2NADOF39Planarization(表面平整化)Liquidfilms:Spin-onglass,resistSolidfilms:CVDdepositiondioxideChemical-mechanicalpolishing(CMP)[oxide,polysilicon,metal]40光刻系统分辨率与焦深的关系2)(2NADOF41光刻系统分辨率与焦深的关系42表面反射和驻波对曝光精度的影响造成侧壁粗糙43表面反射和驻波对曝光精度影响的消除44StandingWaveEffectonPhotoresist45PostExposureBakePhotoresistglasstransitiontemperuatureTgBakingtemperaturehigherthanTgThermalmovementofphotoresistmoleculesRearrangementoftheoverexposedandunderexposedPRmoleculesAverageoutstandingwaveeffectSmoothPRsidewallandimproveresolution46PEBMinimizesStandingWaveEffect47Alignment(套刻对准)套准精度：对准系统把版图套准到硅片上图形的能力。套准容差：要形成的图形层和前一层图形的最大相对位移。一般而言，套准容差为特征尺寸的1/3。48Alignment(套刻对准)49对准标记对准标记：置于掩模版和硅片上用来确定它们的位置和方向的定位图形。投影掩模版的对准标记(RA)在投影掩模版的左右两侧。它将与安装在步进光刻机机身上的对准标记对准。整场对准标记(GA)在第一次曝光时被光刻在硅片左右两边，它被用于每个硅片的粗对准。精对准标记(FA)是在每个场曝光时被光刻，它被用于每个硅片曝光场和投影掩模版的对准调节。50Alignment(套刻对准)51环境条件的影响温度：热膨胀湿度：光刻胶和基片的粘附性、干涉定位NA和聚焦振动：定位错误、离焦和不均匀曝光大气压力：光学系统中的折射率和激光干涉计，导致线宽不均匀和套准精度变差52GreyMasks(灰度曝光技术)Usingamorphouscarbon,lighttransmittancecanbeadjustedbychangingthefilmthicknessbetween0-200nm.53GreyMasksfor3DStructuresLimitsofPhotolithography(光学的极限)曝光波长的缩短：从G线(436nm)，I线(365nm)到深紫外(248nm,193nm)，目前正在研发的真空紫外光源(157nm).分辨率增强技术的使用：高分辨力、高灵敏度、高对比度光刻胶的使用，移相掩模技术、光学临近效应的校正，离轴照明技术，空间滤波技术。将因为其高可靠性和成熟的工艺技术成为微加工的重要技术手段。NextGenerationLithography(后光学时代的光刻技术)最后一代光学曝光技术将可能是应用氟分子激光器的157nm波长光源，预计曝光能力将可实现40-70nm的最小图形尺寸。下一代光刻技术：电子束光刻技术、离子束曝光技术、X射线曝光技术、极紫外曝光技术。56Summary主要介绍了光学曝光的方式、原理和几种影响光学曝光精度的主要因素及解决方法。