【正文】 cid: H3PO4 at 180 176。 can etch just about anythingExample Wet Processesw For SiO2 etching 173。 use parably cheap equipment 173。 achieve high selectivities for most film binations 173。 are in general isotropic (not used to etch features less than ≈ 3 181。patternlithographypartThistocausesetchingoristoetchwhenareorofpatternedmask,asometowhichprotectsproductsformplasmainwithreactingorsolutionwetindissolvingbyareofunwantedprocessis metallic contamination can catalyze reaction 173。 solid state diffusion w Oxidizing species 173。Oxidationw Temperature 173。Variablesovercoats.aslayers,multiplelayersasforstilltransistorsforgateusesuitabledefectnumbersandlowtooxidesgaseouspoundsgaseousreactionsbybeoxidesgrownthanusedmustofsomesuchoftwoinsulatorasfrequentlyw Oxidefieldlayeratofast.oxide Advantage oxidedegrade thatproducewateroftheliberatedHydrogenisbutdrywaythetransistors.wWet oxide 173。foridealthusandstatelowhasdevices)ofproperwithdefectsinterfacetheexistfewuniform.areOxideslowly.growsDryisdryoxidizinginsiliconheatingconsistsoxideproducingmethod 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.The100 197。m) oxides are used for field oxides (isolate devices from one another )173。 Thick (173。residues.photoresistremovetoinwetcleanashrepeatunusualistreatment,Despiteashing.remaincontaminantsandthetoandwithfollowuprequiresprocessplasmaUsually,photoresist.removecrustperategases,withinash,anashingmethodsphotoresistofdissolvessolventsofasprayedexposedhasThiscalledaPhotolithographystages surface, the photoresist is exposed through the pattern on the mask with a high intensity ultraviolet light. There are three primary exposure methods: contact, proximity, and projection. PhotolithographyPatterningTheaistheasiswafer,ontobyseveralistheimagePhotolithographyModelw Figure 1a shows a thin film of some material (eg, silicon dioxide) on a substrate of some other material (eg, a silicon wafer).w Photoresist layer (Figure 1b )w Ultraviolet light is then shone through the mask onto the photoresist (figure 1c). PhotolithographyModel (cont)w The photoresist is then developed which transfers the pattern on the mask to the photoresist layer (figure 1d). w A chemical (or some other method) is then used to remove the oxide where it is exposed through the openings in the resist (figure 1e). w Finally the resist is removed leaving the patterned oxide (figure 1f). PhotolithographyPhotomasks and ReticlesPhotomask This is a square glass plate with a patterned emulsion of metal film on one side. The mask is aligned with the wafer, so that the pattern can be transferred onto the wafer surface. Each mask after the first one must be aligned to the previous pattern. PhotolithographyPhotomasks and ReticlesWhenlayer.themaskonthewhichthenphotoresistphotoresist.Afterward,calledultravioletsensitivewhichacoatedistheplate.apatternatypically