半導(dǎo)體生產(chǎn)過程(編輯修改稿)
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【文章內(nèi)容簡介】 60。Silicon ManufacturingOxidation of Siliconw SiO2 growth is a key process step in manufacturing all Si devices 173。 Thick (173。 1181。m) oxides are used for field oxides (isolate devices from one another )173。 Thin gate oxides (173。100 197。) control MOS devices 173。 Sacrificial layers are grown and removed to clean up surfaces w The stability and ease of formation of SiO2 was one of the reasons that Si replaced Ge as the semiconductor of choice.Thesimplestmethodofproducinganoxidelayerconsistsofheatingasiliconwaferinanoxidizingatmosphere.wDry oxide 173。PuredryoxygenisemployedDisadvantage Dryoxidegrowsveryslowly.AdvantageOxidelayersareveryuniform.Relativelyfewdefectsexistattheoxidesiliconinterface(Thesedefectsinterferewiththeproperoperationofsemiconductordevices)IthasespeciallylowsurfacestatechargesandthusmakeidealdielectricsforMOStransistors.wWet oxide 173。 Inthesamewayasdryoxides,butsteamisinjectedDisadvantage Hydrogenatomsliberatedbythedepositionofthewatermoleculesproduceimperfectionsthatmay degradetheoxidequality. Advantage Wetoxidegrowsfast.UsefultogrowathicklayeroffieldoxideDeposited Oxidesw Oxideisfrequentlyemployedasaninsulatorbetweentwolayersofmetalization.Insuchcases,someformofdeposited oxidemustbeusedratherthanthegrownoxides.w Depositedoxidescanbeproducedbyvariousreactionsbetweengaseoussiliconpoundsandgaseousoxidizers.Depositedoxidestendtopossesslowdensitiesandlargenumbersofdefectsites.NotsuitableforuseasgatedielectricsforMOStransistorsbutstillacceptableforuseasinsulatinglayersbetweenmultipleconductorlayers,orasprotectiveovercoats.KeyVariablesinOxidationw Temperature 173。 reaction rate 173。 solid state diffusion w Oxidizing species 173。 wet oxidation is much faster than dry oxidation w Surface cleanliness 173。 metallic contamination can catalyze reaction 173。 quality of oxide grown (interface states)EtchingEtchingistheprocesswhereunwantedareasoffilmsareremovedbyeitherdissolvingtheminawetchemicalsolution(Wet Etching )orbyreactingthemwithgasesinaplasmatoformvolatileproducts(Dry Etching).Resistprotectsareaswhicharetoremain.Insomecasesahardmask,usuallypatternedlayersofSiO2orSi3N4,areusedwhentheetchselectivitytophotoresistislowortheetchingenvironmentcausesresisttodelaminate.Thisispartoflithographypatterntransfer.Wet Chemical Etchingw Wet etches: 173。 are in general isotropic (not used to etch features less than ≈ 3 181。m) 173
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