Section 5: Thin Film Deposition Part 2: Chemical MethodsChemical Vapor Deposition (CVD)LPCVD ExamplesLPCVD ExamplesCVD MechanismsCVD Deposition Rate [Grove Model]Grove model of CVD (cont’d)Deposition Rate versus TempGrowth Rate Dependence on Flow VelocityLPCVD FeaturesComments about LPCVDPlasma Enhanced CVDAtomic Layer DepositionEE143 – Ali JaveySection 5: Thin Film Deposition Part 2: Chemical MethodsJaeger Chapter 6EE143 – Ali JaveyChemical Vapor Deposition (CVD)filmsubstratechemical reactionsourceMore conformal deposition vs. PVDstepttShown hereis 100% conformaldepositionEE143 – Ali Javey[]()↑+→↑+→++→++↑+→+ZYXOHCSiOHOCSiateorthosilicenetetraethylTEOScHSiOOSiHHOPOPHSiOOPglasssilicatephosphoPSGbHSiOOSiHSiOa24522224252225222242.:)(262534.:)(2)(gas 350oC-500oCsolid350oC-500oCgasLPCVD ExamplesEE143 – Ali Javey↑+→++⎯⎯→⎯−+→+HFWHWFWfHSiSiHSiPolyeHNSiNHSiHNSidCo63)(2)(123)(26260042433443LPCVD ExamplesEE143 – Ali JaveyCVD Mechanismsreactant12543stagnantgas layersurfacediffusionsubstrate1 = Diffusion of reactant to surface2 = Absorption of reactant to surface3 = Chemical reaction4 = Desorption of gas by-products5 = Outdiffusion of by-product gasEE143 – Ali JaveyCVD Deposition Rate [Grove Model]FF==31kTEosGekkhDΔ−==δF1F3Sifilmδ= thickness of stagnant layer31FF=δD [ CG -CS ] / δkS CSEE143 – Ali JaveyGsGCkhF ⋅+=∴1113timewithcontantNFdtdx==∴3N = atomic densityof deposited filmFilm growth rate = F3/ NNote: This result is exactly the same as the Deal-Grove modelor thermal oxidation with oxide thickness =0 Grove model of CVD (cont’d)EE143 – Ali JaveyDeposition Rate versus Temp[log scale] Rate0RT∝32gas transport limitedsurface-reactionlimited1/Tlow Thigh TEE143 – Ali JaveyGrowth Rate Dependence on Flow VelocityEE143 – Ali Javey(1) More conformal deposition, if T is uniform(2) Inter-wafer and intra-wafer thickness uniformity less sensitive to gas flow patterns. (i.e. wafer placement).Wafer topographyLPCVD FeaturesEE143 – Ali JaveyComments about LPCVD(2) Mass depletion probleminoutmore less(1) Sensitivity to gas flow patternFurnace tubewafersEE143 – Ali Javey• Ionized chemical species allows a lower process temperature to be used.• Film properties (e.g. mechanical stress) can be tailored by controllable ion bombardment with substrate bias voltage.Plasma Enhanced CVDAtomic Layer DepositionEE143 – Ali Javey• The process involves two self-limiting half reactions that are repeated in cycles• Unlike CVD, in ALD pulses of precursors are introduced in each cycle• ALD is highly conformal and enables excellent thickness uniformity and control down to
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