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MEMSVACUUMPACKAGINGTECHNOLOGYANDAPPLICATIONSJINYUFENG,ZHANGJIAXUNPEKINGUNIVERSITYSHENZHENGRADUATESCHOOL,SHENZHEN,518055,CHINANATIONALKEYLABOFMICRO/NANOFABRICATIONTECHNOLOGYOFCHINATEL861062752536,FAX861062751789,JINYFIMEPKUEDUCNABSTRACTMANYMEMSMICROELECTROMECHANICSYSTEMSPARTSHAVETOMEETTHEREQUIREMENTSFORVACUUMPACKAGINGINVACUUMPACKAGING,LEAKAGEANDGASPERMEATION,WHICHWILLAFFECTTHENORMALFUNCTIONOFTHECOMPONENTS,AREMAJORPROBLEMSHERMETICSEALINGISONEOFTHEMOSTIMPORTANTTECHNOLOGIESFORRELIABLEVACUUMPACKAGINGINTHISPAPER,SEVERALHERMETICSEALINGTECHNOLOGIESFORVACUUMPACKAGINGWILLBEPRESENTED,INCLUDINGEUTECTICBONDING,ADHESIVEBONDING,GLASSFRITBONDING,ANDSILICONGLASSANODICBONDINGFURTHERFORE,THEAUTHORWILLINTRODUCEDTWOAPPROACHESTODEALWITHSEALINGIMPERFECTSURFACECAUSEDBYELECTRICFEEDTHROUGHS,WHICHLINKTOTHEOUTSIDEOFTHESMALLCAVITYOFMEMSSENSORSTHEGETTERWILLBEDISDUSSEDASITISESSENTIALTOKEEPTHEVACUUMENVIRONMENTINSIDETHECAVITYOFDEVICESINCETHEINNERWALLSMIGHTRELEASEGASAFTERHERMETICSEAL1MATERIALSUSEDINMEMSVACUUMPACKAGING1GASPERMEATIONINVACUUMPACKAGINGHASTOBECONSIDERED,WHENCHOOSINGMATERIALSAPPLIEDINMEMSPACKAGINGFORTHESAMEQUANTITYPERMEATEDGAS,THEPRESSUREDETERIORATIONCAUSEDBYGASPERMEATIONINMEMSISMUCHMORETHANTHATINCONVENTIONALSTRUCTURE,SINCETHEVOLUMEISSMALLERINMEMSCAVITYFURTHERMORE,THINNERSTRUCTURESAREOFTENUSEDINMEMSVACUUMPACKAGINGTHISWILLCAUSEMORESERIOUSPERMEATIONPROBLEMFORTHEMEMSDEVICESFORINSTANCE,THEPERMEATEDGASISHUNDREDTIMESMOREWHENTHETHICKNESSOFAWALLORDIAPHRAGMISREDUCEDFROM1MMTO10MINCASEOFTHEGASPERMEATION,WESHOULDCHOOSETHEPACKAGINGMATERIALSWITHLOWPERMEATIONRATEFIG1COMPARESTHEPERMEATIONRATEOFMOISTUREORWATERMOLECULESTHROUGHSEVERALKINDSOFPACKAGINGMATERIALS,WHICHAREUSEDINMODERNELECTRONICFABRICATIONANDPACKAGINGTHEIRPERMEATIONRATERANGESFROM1018CM3/SECTO1010CM3/SECFIG1PERMEABILITYOFWATERTHROUGHNONHERMETICANDHERMETICMATERIALSFEATURINGLOWERPERMEATIONRATE,GLASSES,CERAMICS,SILICONNITRIDES,METALS,ANDSOMEPURECRYSTALSARESUGGESTEDTOBETHECANDIDATESFORHERMETICPACKAGINGTHOSEWITHHIGHERPERMEATIONRATE,WHICHAREREGARDEDASNONHERMETICMATERIALS,MUSTBEKEPTAWAYFROMTHECATALOGUEFORHERMETICPACKAGINGINOURWORKS,GLASS,CERAMIC,ANDADHESIVEMATERIALSWITHLOWPERMEATIONRATEWERECHOSENASTHEPACKAGINGSTRUCTURES/MATERIALS2HERMETICALSEALINGFORMEMSSTRUCTUREHERMETICPACKAGINGPLAYSANIMPORTANTROLEINMANYMICROSYSTEMSHERMETICSEALING,WHICHPROTECTSTHEMICROSYSTEMSFROMHARMFULENVIRONMENTALINFLUENCES,CANSIGNIFICANTLYINCREASETHERELIABILITYANDLIFETIMEOFTHEMBESIDESANODICBONDING,ANUMBEROFOTHERBONDINGTECHNIQUESHAVEALSOBEENUSEDFORHERMETICPACKAGING,INCLUDINGSILICONTOGOLDEUTECTICBONDING,GLASSFRITBONDING,FUSIONBONDING,ANDBONDINGUSINGEVAPORATEDGLASSTHEHERMETICSEALINGPROCESSESDEVELOPEDINTHISRESEARCHWORKINCLUDEELECTROSTATICBONDINGORANODICSILICONGLASSBONDING,EUTECTICBONDING,GLASSFRITBONDING21SOLDERBONDINGANDEUTECTICBONDINGSOLDERBONDINGFORHERMETICALLYSEALINGWAFERSISBASEDONSOLDERJOININGTWOWAFERTOGETHEROFTHEM,EUTECTICBONDINGISWIDELYAPPLIEDINMEMSPACKAGING,WHICHTAKESTHEADVANTAGEOFTHEEUTECTICALLOYTOREALIZEABONDBETWEENTWOSUBSTRATESATALOWERTEMPERATURESOLDEROFASUITABLEMATERIALSETCANBEFORMEDINTHEBONDINGAREABETWEENSUBSTRATESOFPACKAGEANDDEVICERAISETHETEMPERATUREUNTILTHESOLDERFLOWSANDCREATESABONDTOSEALTWOSUBSTRATESTHEMOSTOBVIOUSMATERIALSTOUSEARETHOSESTANDARDSOLDERSUSEDINMICROELECTRONICAPPLICATIONS,BUTMANYOFSUCHSOLDERMATERIALSCONTAINEITHERFLUXORSUFFICIENTIMPURITIESTHESEFLAWSCAUSESIGNIFICANTOUTGASSINGDURINGTHEREFLOWPROCESSTHISBECOMESAMAJORPROBLEMWHENTRYINGTOUSESUCHSOLDERSFORVACUUMPACKAGINGRECENTDEVELOPMENTRESEARCHONNEWFLUXLESSSOLDERMATERIALSMAYOVERCOMESUCHPROBLEMANDSEVERALGROUPSAREPURSUINGTHIS2COMPARINGWITHSTANDARDSOLDER,ITISALSOPOSSIBLETOUSEALLOYSOFDIFFERENTMATERIALSINTHEFORMOFEUTECTICSOLDERONEOFTHEMOSTCOMMONMATERIALSETSISTHEEUTECTICOFGOLDANDSILICONSILICONGOLDEUTECTICISQUITEATTRACTIVEBECAUSEITISFORMEDATATEMPERATUREOF363CWITHONEPARTSILICONANDFOURPARTSGOLDTHISMATERIALSISCOMMONLYUSEDINMEMSFABRICATION,ANDWHENTHEEUTECTICISFORMED,THEOUTGASSINGPROBLEMISRESOLVEDSINCETHEMIXTUREISSIMPLYFORMEDBYRAISINGTHETEMPERATUREANDTHESTARTINGMATERIALSAREPUREINADDITION,THETEMPERATUREISLOWENOUGHFORMOSTAPPLICATIONS0780394496/05/20002005IEEE20056THINTERNATIONALCONFERENCEONELECTRONICPACKAGINGTECHNOLOGYONONEHAND,FORSILICONGOLDEUTECTICBONDING,ALTHOUGHTHEEUTECTICPOINTIS363OC,THEBONDINGTEMPERATUREMUSTBEHIGHERAHIGHERTEMPERATURECANPROMOTETHEDIFFUSIONOFGOLDANDSILICONINTOEACHOTHER,ANDINCREASETHETHICKNESSOFTHEDIFFUSIONLAYERWHERETHECHEMICALCOMPOSITIONCANMATCHWITHWHATISNEEDEDFOREUTECTICBONDINGTHEREFORE,AHIGHERTEMPERATUREANDALONGERBONDINGTIMEAREBENEFICIALTOAGOODBONDINGONTHEOTHERHAND,IFTHEBONDINGTEMPERATUREISTOOHIGH,ITMAYCAUSESERIOUSDIFFUSIONOFGOLDINTOSILICON,WHICHWILLDEGRADETHEFUNCTIONOFTHESILICONDEVICESFIG2SHOWSTHESCANNINGACOUSTICMICROSCOPESAMMICROGRAPHSOFEUTECTICALLYBONDEDSENSORWAFERANDSILICONCAPWAFERATABONDINGTEMPERATUREOF400450OCDURINGSAMANALYZINGPROCESS,THEBONDEDWAFERSAREIMMERSEDINDEIONIZEDWATERBUBBLEFREEINTERFACESAREOBSERVEDANDNOWATERISSUCKEDINTOTHECAVITIESITINDICATESTHATTHECAVITIESAREWELLSEALEDTHEPULLTESTRESULTSSHOWTHATTHEBONDSTRENGTHISMORETHAN5MPAFIG2SAMMICROGR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