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1、BulkMicromachiningofSiliconGREGORYT.A.KOVACS,MEMBER,IEEE,NADIMI.MALUF,MEMBER,IEEE,ANDKURTE.PETERSEN,FELLOW,IEEEInvitedPaperBulksiliconetchingtechniques,usedtoselectivelyremoveThegeometriesofetchedfeaturesliealongacontinuumsiliconfromsubstrates,havebeenbro
2、adlyappliedinthebetweenfullyisotropic(rounded,duetoequaletchratesfabricationofmicromachinedsensors,actuators,andstructures.inalldirections)toanisotropic(typicallyexhibitingper-Despitethemorerecentemergenceofhigherresolution,surface-fectlyflatsurfacesandwel
3、l-defined,sharpangles).Thisismicromachiningapproaches,themajorityofcurrentlyshippingsiliconsensorsaremadeusingbulketching.ParticularlyinillustratedinFig.1(a)and(b).Thesepropertiesaredefinedlightofnewlyintroduceddryetchingmethodscompatiblewithbythenatureofth
4、echemicalreactions,thediffusionofcomplementarymetal±oxide±semiconductors,itisunlikelythatreactantsandproducts,andanumberofotherfactors,bulkmicromachiningwilldecreaseinpopularityinthenearincludingtheshapesofthemasksusedtodefinetheetchedfuture.Theavailableet
5、chingmethodsfallintothreecategoriesinregions.termsofthestateoftheetchant:wet,vapor,andplasma.Foreachcategory,theavailableprocessesarereviewedandcomparedAnotherkeydistinguishingfeatureofetchantsistheintermsofetchresults,cost,complexity,processcompatibility
6、,phaseofthereactants:liquid(orªwetºetchants,almostandanumberofotherfactors.Inaddition,severalexampleexclusivelyrelyingonaqueouschemistries),vapor,andmicromachinedstructuresarepresented.plasma(thelattertwobeingreferredtoasªdryºetchants).KeywordsÐBulk,etchi
7、ng,micromachining,silicon.Asmightbeexpected,thereactionmechanisms,reactionrates,chemistries,anddiffusionpropertiesofthesethreeI.INTRODUCTIONmodesarequitedifferent,asaretheassociatedequipmentcosts.ThepurposeofbulkmicromachiningistoselectivelyTheetchingreac
8、tionsrelyontheoxidationofsiliconremovesignificantamountsofsiliconfromasubstrate.toformcompoundsthatcanbephysicallyremovedfromThisissometimesdonetoªundercutºstructuresthatarethesubstrate.Inaqueouschemistries,thistends