newnergy9薄膜淀积技术课件

薄膜淀积技术半导体工艺中所涉及的常用薄膜：Evaporation(蒸发）Sputtering(溅射）使用加热、等离子体或紫外线等各种能源，使气态物质经化学反应（热解或化学合成）形成固态物质淀积在衬底上的方法，叫做化学汽相淀积(ChemicalVaporDeposition)技术，简称CVD技术。它与真空蒸发和溅射技术并列，是应用较为普遍的一种薄膜淀积技术。特点：1、淀积温度低；2、可以淀积各种电学和化学性质都符合要求的薄膜；3、均匀性好；4、操作简便，适于大量生产；CVD技术：CVD的分类：可按淀积温度，反应腔气压或淀积反应的激活方式分类—低温CVD(200-500°C)—中温CVD（500-1000°C)—高温CVD（1000-1300°C)—常压CVD—低压CVD—热CVD—等离子体CVD—光CVD等等热CVD系统：等离子体CVDMolecularBeamEpitaxy(MBE)分子束外延技术MBE自1960年开始就有人提出，是一种超精密和极精确的薄膜生长技术。其利用的是蒸发原理，将分子束射至单晶衬底上生长单晶外延层的方法。MBE的特点：超高真空；设备中外延生长室真空度可达5x10-11Torr,这样分子平均自由程L较大。例如：P=10-9Torr,L=5x106cm。这样大的自由程使分子碰撞几率很小，薄膜生长均匀，生长速率和组分可精确控制。可以实现低温过程；这样能减少杂质扩散和沾污的几率。利用MBE技术可生长出位错密度<102cm-2的外延层。原位监控；MBE设备上安装有许多原位监控仪器，可以实时监控外延薄膜的生长参数以及物理性能。(UHV=UltraHighVacuum)PhotoresistPhotolithographyisaprocessinwhichwaferiscoatedwithalightsensitivepolymercalledphotoresist.Polyisopreneisanexampleofacommonlyusedphotoactiveagent.AmaskisusedtoexposeselectedareasofphotoresisttoUVlight.TheUVlightinducespolymerizationintheexposedphotoresist.UVcausesittocrosslinkrenderingitinsolubleindevelopingsolution.Suchaphotoresistiscalledapositivephotoresist.Anegativephotoresistshowsanoppositebehavior.ThatisexposuretoUVmakesthephotoresistsolubleindevelopingsolution.!Remember:Therearetwotypesofphotoresist:*NEGATIVE-unexposedareasremoved*POSITIVE-exposedareasremovedNegativeresististhemostoftenusedbecauseitislessaffectedbyetchantsalthoughpositiveresistoffersbetterresolution.Positiveresistsaremorecapableofproducingthesmallsizeofmoderndevicefeatureswhicharetypicallybelow1.0μmbutmaybeassmallas0.15μm.光刻的大致工艺流程：涂胶：一般从高温炉中取出硅片立即涂胶或在180-200°C恒温干燥箱中烘烤30分钟后再进行涂胶。要求粘附性能良好，厚度均匀适当。前烘：在80°C恒温干燥箱中烘10-15分钟。目的是使胶膜体内溶剂充分挥发，使胶膜干燥，以增强胶膜与SiO2膜的粘附性和胶膜的耐磨坚膜：一般将显影后的硅片放在烘箱中热烘30分钟左右使经显影时软化、膨胀的胶膜坚固。这样可使胶膜与硅片贴得更牢，同时也增强了胶膜本身的抗蚀能力。腐蚀：在用正胶的情况下，利用适当的腐蚀液将SiO2或Al腐蚀掉，而有光刻胶覆盖的区域保存下来。去胶：腐蚀结束后，利用湿法去胶，氧气去胶或等离子体去胶等方法将覆盖在硅片表面的保护胶膜去除。ExposureMethod:*CONTACTPRINTING-1xmaskrequired；*DIRECTSTEP-5xmaskrequired；*E-BEAM-nomaskrequired；EtchProcessthatfollowsimmediatelyafterphotolithographystepistheremovalofmaterialfromareasunprotectedbyphotoresist.Thisprocessmustbeselective;thatisSiO2isremovedwhileleavingphotoresistandsiliconintact.Itmustalsobeanisotropic;thatisetchingshouldbeinonedirectiononly.EtchMethod:Twotypesofetchingprocessesareusedinpractice;namely,chemicalandphysicaletching.Inpurelychemicaletchingmaterialisremovedbydissolutionwhichishighlyselectivebutnotanisotropic.Inpurelyphysicalmethodmaterialisremovedbybombardmentofhighenergyionswhichisinherentlyanisotropicbutunselective.Asanexample,SiO2whichisusedasamaskfordriveindiffusionisremovedbyexposuretohydrogenfluoride.HydrogenfluoridereactswithSiO2toformvolatileSiF4whichissweptawaybyinertargongas.湿法刻蚀特点：选择性高；生产量大；加工精度：~3μm装置成本低；干法刻蚀特点:可控性好；加工精度高,可达0.2μm；可加工设计形状；对于硅系材料,最常用的是用在CF4中放电所产生的等离子体来腐蚀Si、多晶硅和Si3N4。主要反应：在刻蚀过程中起主要作用的是原子态F和CF3游离基。近来人们发现在CF4中添加少量氧可使Si的腐蚀速率明显提高。这是因为O2与等离子体中的CF3、CF2或CF游离基作用而放出原子态F所致。Doping(DiffusionandIonImplantation)Dopingisageneraltermwhichreferstotheintroductionofimpuritiesintoasemiconductormedium.Dopingusedindependentlyisnonselective,whereasifusedinconjunctionwithpatterndefinition,itcanbeselective;introducingimpuritiesintoonlythoseareasthatyoudesire.THEREARETWOTECHNIQUESOFDOPING:*SOLID-STATEDIFFUSION*IONIMPLANTATIONDiffusion:Diffusionistheprocesswherebyparticlesmovefromregionsofhigherconcentrationtoregionsoflowerconcentration.Althoughthisincludestheselfdiffusionphenomena,ourinterestisinthediffusionofimpurityatoms.硅平面扩散工艺是在硅集成电路中广泛使用的一种掺杂技术。其利用硅片表面的SiO2作为扩散掩膜，把待掺入的元素从窗口扩散到硅片内。固态源扩散装置气态源扩散装置液态源扩散装置扩散原理：空位扩散复合扩散格子间隙扩散MathematicalModelforDiffusion：Thebasicone-dimensionaldiffusionprocessfollowsFick'sfirstlawofdiffusion:J=-D∂N/∂xwhereJistheparticlefluxofthedonororacceptorimpurityspecies,Nistheconcentrationoftheimpurity,andDisthediffusioncoefficient.Fick'ssecondlawofdiffusionmaybederivedusingthecontinuityequationfortheparticleflux:∂N/∂t=D∂2N/∂x2inwhichthediffusioncoefficientDhasbeenassumedtobeindependentofposition.Thisassumptionisviolatedathighimpurityconcentrations.Twospecifictypesofboundaryconditionsareimportantinmodelingimpuritydiffusioninsilicon.Thefirstistheconstant-sourcediffusion(恒定表面浓度扩散),inwhichthesurfaceconcentrationisheldconstantthroughoutthediffusion.N(x,t)=Noerfc[x/2(Dt)1/2]Whereerfciscomplementaryerrorfunction(相补误差函数).Thesecondiscalledalimited-sourcediffusion(限定源扩散),inwhichafixedquantityoftheimpurityspeciesisdepositedinathinlayeronthesurfaceofthesilicon.SOLID-STATEDIFFUSIONUSUALLYCONSISTSOFTWOSTEPS:1)PRE-DEPOSITION；2)DRIVE-IN；Duringthepre-depositionstep,impuritiesareintroducedbuttypicallydonotdiffuseveryfarintothesubstrate.恒定表面浓度扩散Beforethedrive-in,alayerofoxideisdepositedtocapthewaferthuspreventingimpuritiesfromescaping.Duringthedrive-in,thewaferisheatedandtheimpuritiesdiffusefurtherintothewaferuntilthedesiredproreached.限定源扩散在热扩散中，掺杂原子通过掩膜向硅片中扩散时，除了在深度方向形成一定分布外，在窗口边缘同样有横向扩散。另外，在大面积掺杂时的掺杂量、结深和浓度分布可控性重复性等方面，高温扩散法有着一定不足之处，限制了其应用。目前，在低浓度高精度掺杂方面已被离子注入技术所替代。IonImplantation:Ionsofdopantatomsareacceleratedtoahighvelocityinanelectricfieldandimpingeontargetwafer.Theionspenetratethroughtheoxidelayerandenterintosilicon.Penetrationdepthsof500to5000Aareeasilyachieved.Penetrationdepthdependsonsizeofionandenergyapplied.Theionsdonotpenetratethephotoresistlayerswhicharetypically10,000Athick.Bymanipulatingtheaccelerationvoltage,theaverageimplantationdepthcanbepreciselycontrolled.Thedopantconcentratio