newnergy9薄膜淀積技術(shù)課件

薄膜淀積技術(shù)半導(dǎo)體工藝中所涉及的常用薄膜：Evaporation(蒸發(fā)）Sputtering(濺射）使用加熱、等離子體或紫外線等各種能源，使氣態(tài)物質(zhì)經(jīng)化學(xué)反應(yīng)（熱解或化學(xué)合成）形成固態(tài)物質(zhì)淀積在襯底上的方法，叫做化學(xué)汽相淀積(ChemicalVaporDeposition)技術(shù)，簡稱CVD技術(shù)。它與真空蒸發(fā)和濺射技術(shù)并列，是應(yīng)用較為普遍的一種薄膜淀積技術(shù)。特點(diǎn)：1、淀積溫度低；2、可以淀積各種電學(xué)和化學(xué)性質(zhì)都符合要求的薄膜；3、均勻性好；4、操作簡便，適于大量生產(chǎn)；CVD技術(shù)：CVD的分類：可按淀積溫度，反應(yīng)腔氣壓或淀積反應(yīng)的激活方式分類—低溫CVD(200-500°C)—中溫CVD（500-1000°C)—高溫CVD（1000-1300°C)—常壓CVD—低壓CVD—熱CVD—等離子體CVD—光CVD等等熱CVD系統(tǒng)：等離子體CVDMolecularBeamEpitaxy(MBE)分子束外延技術(shù)MBE自1960年開始就有人提出，是一種超精密和極精確的薄膜生長技術(shù)。其利用的是蒸發(fā)原理，將分子束射至單晶襯底上生長單晶外延層的方法。MBE的特點(diǎn)：超高真空；設(shè)備中外延生長室真空度可達(dá)5x10-11Torr,這樣分子平均自由程L較大。例如：P=10-9Torr,L=5x106cm。這樣大的自由程使分子碰撞幾率很小，薄膜生長均勻，生長速率和組分可精確控制?？梢詫?shí)現(xiàn)低溫過程；這樣能減少雜質(zhì)擴(kuò)散和沾污的幾率。利用MBE技術(shù)可生長出位錯(cuò)密度<102cm-2的外延層。原位監(jiān)控；MBE設(shè)備上安裝有許多原位監(jiān)控儀器，可以實(shí)時(shí)監(jiān)控外延薄膜的生長參數(shù)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.光刻的大致工藝流程：涂膠：一般從高溫爐中取出硅片立即涂膠或在180-200°C恒溫干燥箱中烘烤30分鐘后再進(jìn)行涂膠。要求粘附性能良好，厚度均勻適當(dāng)。前烘：在80°C恒溫干燥箱中烘10-15分鐘。目的是使膠膜體內(nèi)溶劑充分揮發(fā)，使膠膜干燥，以增強(qiáng)膠膜與SiO2膜的粘附性和膠膜的耐磨堅(jiān)膜：一般將顯影后的硅片放在烘箱中熱烘30分鐘左右使經(jīng)顯影時(shí)軟化、膨脹的膠膜堅(jiān)固。這樣可使膠膜與硅片貼得更牢，同時(shí)也增強(qiáng)了膠膜本身的抗蝕能力。腐蝕：在用正膠的情況下，利用適當(dāng)?shù)母g液將SiO2或Al腐蝕掉，而有光刻膠覆蓋的區(qū)域保存下來。去膠：腐蝕結(jié)束后，利用濕法去膠，氧氣去膠或等離子體去膠等方法將覆蓋在硅片表面的保護(hù)膠膜去除。ExposureMethod:*CONTACTPRINTING-1xmaskrequired；*DIRECTSTEP-5xmaskrequired；*E-BEAM-nomaskrequired；EtchProcessthatfollowsimmediatelyafterphotolithographystepistheremovalofmaterialfromareasunprotectedbyphotoresist.Thisprocessmustbeselective;thatisSiO2isremovedwhileleavingphotoresistandsiliconintact.Itmustalsobeanisotropic;thatisetchingshouldbeinonedirectiononly.EtchMethod:Twotypesofetchingprocessesareusedinpractice;namely,chemicalandphysicaletching.Inpurelychemicaletchingmaterialisremovedbydissolutionwhichishighlyselectivebutnotanisotropic.Inpurelyphysicalmethodmaterialisremovedbybombardmentofhighenergyionswhichisinherentlyanisotropicbutunselective.Asanexample,SiO2whichisusedasamaskfordriveindiffusionisremovedbyexposuretohydrogenfluoride.HydrogenfluoridereactswithSiO2toformvolatileSiF4whichissweptawaybyinertargongas.濕法刻蝕特點(diǎn)：選擇性高；生產(chǎn)量大；加工精度：~3μm裝置成本低；干法刻蝕特點(diǎn):可控性好；加工精度高,可達(dá)0.2μm；可加工設(shè)計(jì)形狀；對于硅系材料,最常用的是用在CF4中放電所產(chǎn)生的等離子體來腐蝕Si、多晶硅和Si3N4。主要反應(yīng)：在刻蝕過程中起主要作用的是原子態(tài)F和CF3游離基。近來人們發(fā)現(xiàn)在CF4中添加少量氧可使Si的腐蝕速率明顯提高。這是因?yàn)镺2與等離子體中的CF3、CF2或CF游離基作用而放出原子態(tài)F所致。Doping(DiffusionandIonImplantation)Dopingisageneraltermwhichreferstotheintroductionofimpuritiesintoasemiconductormedium.Dopingusedindependentlyisnonselective,whereasifusedinconjunctionwithpatterndefinition,itcanbeselective;introducingimpuritiesintoonlythoseareasthatyoudesire.THEREARETWOTECHNIQUESOFDOPING:*SOLID-STATEDIFFUSION*IONIMPLANTATIONDiffusion:Diffusionistheprocesswherebyparticlesmovefromregionsofhigherconcentrationtoregionsoflowerconcentration.Althoughthisincludestheselfdiffusionphenomena,ourinterestisinthediffusionofimpurityatoms.硅平面擴(kuò)散工藝是在硅集成電路中廣泛使用的一種摻雜技術(shù)。其利用硅片表面的SiO2作為擴(kuò)散掩膜，把待摻入的元素從窗口擴(kuò)散到硅片內(nèi)。固態(tài)源擴(kuò)散裝置氣態(tài)源擴(kuò)散裝置液態(tài)源擴(kuò)散裝置擴(kuò)散原理：空位擴(kuò)散復(fù)合擴(kuò)散格子間隙擴(kuò)散MathematicalModelforDiffusion：Thebasicone-dimensionaldiffusionprocessfollowsFick'sfirstlawofdiffusion:J=-D?N/?xwhereJistheparticlefluxofthedonororacceptorimpurityspecies,Nistheconcentrationoftheimpurity,andDisthediffusioncoefficient.Fick'ssecondlawofdiffusionmaybederivedusingthecontinuityequationfortheparticleflux:?N/?t=D?2N/?x2inwhichthediffusioncoefficientDhasbeenassumedtobeindependentofposition.Thisassumptionisviolatedathighimpurityconcentrations.Twospecifictypesofboundaryconditionsareimportantinmodelingimpuritydiffusioninsilicon.Thefirstistheconstant-sourcediffusion(恒定表面濃度擴(kuò)散),inwhichthesurfaceconcentrationisheldconstantthroughoutthediffusion.N(x,t)=Noerfc[x/2(Dt)1/2]Whereerfciscomplementaryerrorfunction(相補(bǔ)誤差函數(shù)).Thesecondiscalledalimited-sourcediffusion(限定源擴(kuò)散),inwhichafixedquantityoftheimpurityspeciesisdepositedinathinlayeronthesurfaceofthesilicon.SOLID-STATEDIFFUSIONUSUALLYCONSISTSOFTWOSTEPS:1)PRE-DEPOSITION；2)DRIVE-IN；Duringthepre-depositionstep,impuritiesareintroducedbuttypicallydonotdiffuseveryfarintothesubstrate.恒定表面濃度擴(kuò)散Beforethedrive-in,alayerofoxideisdepositedtocapthewaferthuspreventingimpuritiesfromescaping.Duringthedrive-in,thewaferisheatedandtheimpuritiesdiffusefurtherintothewaferuntilthedesiredproreached.限定源擴(kuò)散在熱擴(kuò)散中，摻雜原子通過掩膜向硅片中擴(kuò)散時(shí)，除了在深度方向形成一定分布外，在窗口邊緣同樣有橫向擴(kuò)散。另外，在大面積摻雜時(shí)的摻雜量、結(jié)深和濃度分布可控性重復(fù)性等方面，高溫?cái)U(kuò)散法有著一定不足之處，限制了其應(yīng)用。目前，在低濃度高精度摻雜方面已被離子注入技術(shù)所替代。IonImplantation:Ionsofdopantatomsareacceleratedtoahighvelocityinanelectricfieldandimpingeontargetwafer.Theionspenetratethroughtheoxidelayerandenterintosilicon.Penetrationdepthsof500to5000Aareeasilyachieved.Penetrationdepthdependsonsizeofionandenergyapplied.Theionsdonotpenetratethephotoresistlayerswhicharetypically10,000Athick.Bymanipulatingtheaccelerationvoltage,theaverageimplantationdepthcanbepreciselycontrolled.Thedopantconcentratio