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STRESA,ITALY,2527APRIL20070LEVELVACUUMPACKAGINGRTPROCESSFORMEMSRESONATORSNICOLASABEL1,3,DANIELGROGG1,CYRILLEHIBERT2,FABRICECASSET4,PASCALANCEY3,ADRIANMIONESCU11LEG,ECOLEPOLYTECHNIQUEFDRALEDELAUSANNEEPFL,SWITZERLAND,2CMIEPFL,3STMICROELECTRONICS,FRANCE,4CEALETIMINATEC,FRANCEABSTRACTANEWROOMTEMPERATURERT0LEVELVACUUMPACKAGEISDEMONSTRATEDINTHISWORK,USINGAMORPHOUSSILICONASIASSACRIFICIALLAYERANDSIO2ASSTRUCTURALLAYERTHEPROCESSISCOMPATIBLEWITHMOSTOFMEMSRESONATORSANDRESONANTSUSPENDEDGATEMOSFET1FABRICATIONPROCESSESTHISPAPERPRESENTSASTUDYONTHEINFLUENCEOFRELEASINGHOLEDIMENSIONSONTHERELEASINGTIMEANDHOLECLOGGINGITDISCUSSESMASSPRODUCTIONCOMPATIBILITYINTERMSOFPACKAGINGSTRESSDURINGBACKENDPLASTICINJECTIONPROCESSTHEPACKAGINGISDONEATROOMTEMPERATUREMAKINGITFULLYCOMPATIBLEWITHICPROCESSEDWAFERSANDAVOIDINGANYSUBSEQUENTDEGRADATIONOFTHEACTIVEDEVICES1INTRODUCTIONMEMSRESONATORSPERFORMANCESHAVEBEENDEMONSTRATEDTOSATISFYREQUIREMENTSFORCMOSCOINTEGRATEDREFERENCEOSCILLATORAPPLICATIONS23DIFFERENTPACKAGINGPOSSIBILITIESWEREPROPOSEDINPREVIOUSYEARSUSINGEITHERA0LEVELAPPROACHES4,5ORWAFERBONDINGAPPROACHES6ACCORDINGTOINDUSTRYREQUIREMENTS,0LEVELTHINFILMPACKAGINGUSINGSTANDARDFRONTENDMANUFACTURINGPROCESSESISHOWEVERLIKELYTOBETHEMOSTCOSTEFFICIENTTECHNIQUETOACHIEVEVACUUMENCAPSULATIONOFMEMSCOMPONENTSFORVOLUMEPRODUCTION2DEVICEDESCRIPTIONANDPACKAGINGDESIGNTHEPACKAGINGPROCESSHASBEENDONEONAMEMSRESONATORHAVINGMOSFETDETECTION1THEDEVICEISBASEDONASUSPENDEDGATERESONATINGOVERAMOSFETCHANNELWHICHMODULATESTHEDRAINCURRENTTHEADVANTAGEOFTHISTECHNIQUEISTHEMUCHLARGERTHEOUTPUTDETECTIONCURRENTTHANFORTHEUSUALCAPACITIVEDETECTIONTYPE,DUETOTHEINTRINSICGAINOFTHETRANSISTORTHERSGMOSFETDEVICEFABRICATIONPROCESSANDPERFORMANCESWEREPREVIOUSLYDESCRIBEDIN7THEPROCESSSTEPSAREPRESENTEDINFIG1,WHEREA5MTHICKAMORPHOUSSILICONASILAYERISSPUTTEREDONTHEALREADYRELEASEDMEMSRESONATORFOLLOWEDBYA2MRFSPUTTEREDSIO2FILMDEPOSITIONAQUASIZEROSTRESSASIFILMDEPOSITIONPROCESSHASBEENDEVELOPEDTHEQUASIVERTICALDEPOSITIONAVOIDSDEPOSITINGMATERIALUNDERTHEBEAMLOWERINGTHERELEASINGTIMERELEASINGHOLESOF15MWEREETCHEDTHROUGHTHESIO2LAYERANDTHERELEASINGSTEPISDONEBYDRYSF6PLASMADUETOPURECHEMICALETCHING,HIGHSELECTIVITYOFLESSTHAN1NM/MINONSIO2WASOBTAINEDTHEHOLESWERECLOGGEDBYANONCONFORMALSPUTTERSSIO2DEPOSITIONATROOMTEMPERATUREFIG1SCHEMATICOFTHE0LEVELVACUUMPACKAGEFABRICATIONPROCESSOFARSGMOSFETPACKAGINGPROCESSHASBEENPERFORMEDONTHEMETALGATESGMOSFETANDFIG2ASHOWSANSEMPICTUREOFARELEASEDALSIBASEDRSGMOSFETWITHA500NMAIRGAP,ABEAMLENGTHANDWIDTHOFRESPECTIVELY125MAND6MWITHA40NMGATEOXIDEAVACUUMPACKAGEDRSGMOSFETISSHOWNINFIG2BHIGHLIGHTINGTHESTRONGBONDSOFTHEREFILLEDRELEASINGHOLEAFTERCLOGGINGCROSSSECTIONOFARELEASINGHOLEINFIG2CSHOWSMORETHAN1MBONDINGSURFACETOENSURECAVITYSEALINGAFIBCROSSSECTIONINFIG2DSHOWSTHESUSPENDEDSIO2EDAPUBLISHING/DTIP2007ISBN9782355000003NICOLASABEL,DANIELGROGG,CYRILLEHIBERT,FABRICECASSET,PASCALANCEY,ADRIANMIONESCU0LEVELVACUUMPACKAGINGRTPROCESSFORMEMSRESONATORSMEMBRANEABOVETHESUSPENDEDGATETHEVACUUMATMOSPHEREINSIDETHECAVITYISOBTAINEDBYDEPOSITINGTHETOPSIO2LAYERUNDER5X107MBARGIVENBYTHEEQUIPMENTSUSPENDEDGATEDRAINSOURCEBULKCONTACTA10MDRAINSOURCESUSPENDEDGATE6M1MBSIO2C1MHOLEDIAMETER15MVACUUMEDCAVITY1UMSIO2DDRAINSUSPENDEDGATE50MFIG2SEMPICTURESOFAALSIBASEDRSGMOSFET,BTOPVIEWOFASIO2CAPCOVERINGTHERSGMOSFET,CCROSSSECTIONOFRELEASINGHOLESFILLEDWITHSPUTTEREDSIO2,DFIBCROSSSECTIONOFTHEPACKAGEDRSGMOSFET,MATERIALREDEPOSITEDDURINGTHEFIBCUTISSURROUNDINGTHESUSPENDEDGATEANDTHESIO2MEMBRANETHESLIGHTLYCOMPRESSIVESIO2MEMBRANESSHOWVERYGOODBEHAVIORFORTHETHINFILMPACKAGING,ASSEENINFIG3WHERECAVITIESWEREFORMEDONLARGEOPENINGSIZEDURINGTHECLOGGINGPROCESS,DUETOTHEHIGHLYNONCONFORMALDEPOSITION,THEAMOUNTOFMATERIALENTERINGINTHECAVITYHASBEENMEASUREDTOBEONLY80NMCOMPAREDTOTHE25MOXIDEDEPOSITEDRESIDUESINSIDETHECAVITYARECONFINEDINAN8TO10MDIAMETERCIRCLE,BUTSTRONGLYDEPENDONTHETOPOLOGYINSIDETHECAVITYTHEOXIDETHICKNESSNEEDEDTOCLOGTHEHOLESSTRONGLYDEPENDSONTHEHOLEWIDTHOVERHEIGHTRATIO,WHICHTHEREFOREDETERMINESTHEAMOUNTOFRESIDUESINTHECAVITY40MSUSPENDEDSIO2MEMBRANESA2M11MASI05MWETOXIDE45MSPUTTEREDSIO2BFIG3ABCROSSSECTIONOFA2UMSIO2SUSPENDEDMEMBRANEHAVINGARELEASINGHOLECLOGGEDBYA25MSIO2SPUTTERINGDEPOSITION3EFFECTOFOPENINGSIZEONRELEASINGRATEANDCLOGGINGEFFECTETCHINGRATEVARIATIONONASIRELATEDTOTHEHOLEOPENINGSIZEANDTHEASITHICKNESSISSHOWNINFIG4SMALLHOLESOPENINGSDECREASETHEETCHINGRATEADUALUNDERETCHINGBEHAVIORDUETOASITHICKNESSVARIATIONANDHOLESDIAMETERSISOBSERVEDAFTERA2MINRELEASESTEPFORASMALLHOLEAPERTURE2MDIAMETER,EXPOSEDSURFACEFACTORISDOMINANTANDETCHINGRATEIS3TIMESGREATERFORTHETHINASIHOWEVERFORLARGEOPENINGS9MDIAMETERFORWHICHUNDERETCHDISTANCEISMOREIMPORTANT,PATHFACTORREPRESENTINGTHELATERALOPENINGHEIGHTFORSPECIESEDAPUBLISHING/DTIP2007ISBN9782355000003NICOLASABEL,DANIELGROGG,CYRILLEHIBERT,FABRICECASSET,PASCALANCEY,ADRIANMIONESCU0LEVELVACUUMPACKAGINGRTPROCESSFORMEMSRESONATORSTOREACHASIBECOMESIMPORTANTANDTHENETCHINGRATIODECREASESTO13012345612345678910HOLEDIAMETERUMUNDERETCHRATEUM/MIN11UMASI33UMASIFIG4UNDERETCHRATEFORVARIOUSRELEASINGHOLESDIAMETERSWITHAMORPHOUSSILICONSACRIFICIALLAYERSOF11MAND33M,AFTER2MINRELEASINGAFTERRELEASE,ENCAPSULATIONISPERFORMEDBYSPUTTEREDDEPOSITIONOFSIO2UNDERHIGHVACUUMOF5X107MBARUSINGTHEINTRINSIC,NONCONFORMALDEPOSITIONTOCLOGHOLES,ASSHOWNINFIG5CLOGGINGEFFECTISSTRONGLYMATERIALDEPENDENTANDISRELATEDTOTHESTICKINGCOEFFICIENTTHATDEFINESPROBABILITYFORAMOLECULETOSTICKTOTHESURFACETHECOEFFICIENTISBELOW001FORLPCVDPOLYSIBUT026FORSIO2,THEREFOREBEINGMORESUITABLEFORCLOGGINGPURPOSESIO2MEMBRANE2MCLOGGINGHOLEAPERTURESIO2REDEPOSITIONREMAININGAPERTUREFIG5SCHEMATICOFACROSSSECTIONOFTHESIO2MEMBRANECLOGGEDBYSIO2SPUTTERINGDEPOSITIONHOLECLOGGINGHASASTRONGDEPENDENCEONTHEOPENINGASPECTRATIOASPRESENTEDINFIG6HOLESWITHDIAMETEROVERHEIGHTASPECTRATIOBELOW1ARECLOGGEDFORSIO2THICKNESSOF2MHOLEWITHOPENINGRATIOOF15COULDONLYBECLOGGEDFORA3MTHICKSIO2DEPOSITIONTHEHOLECLOGGINGRATEISMEASUREDTOBE330NMPERDEPOSITEDMICRONOFSIO2010002000300040000123OPENINGASPECTRATIOREMAININGAPERTURENM2MSIO2INITIALSIO2MEMBRANETHICKNESS2M3MSIO2REMAININGAPERTURENMFIG6HOLECLOGGINGEFFECTDEPENDINGONTHEDIAMETEROVERHEIGHTRATIOINTHE2MSIO2MEMBRANERIGHTREMAININGAPERTUREDIAMETERINNMFOR2MAND3MSIO2DEPOSITIONFORHOLECLOGGINGTHEEFFECTOFHOLEGEOMETRYONUNDERETCHRATEANDCLOGGINGHASBEENSTUDIEDONSQUAREANDRECTANGULARHOLESINFIG7RECTANGULAROPENINGHASAQUASIIDENTICALUNDERETCHINGTHANSQUARESHAPEOFTHESAMEOPENINGAREA,WHILECLOGGINGIS10TIMESMOREIMPORTANT0510152025303505101520RELASINGTIMEMINUNDERETCHUM2UM2UMXETCHINGDIRECTIONYETCHINGDIRECTIONXYXXFIG7UNDERETCHLENGTHAFTER16MINRELEASEFOR291M2SQUAREANDRECTANGLERELEASEHOLESREDDOTTEDRECTANGLESTHEINITIALSIO2THICKNESSISA2MANDTHETHICKNESSOFASIIS11MREMAININGHOLESIZEAFTER25MSIO2DEPOSITIONIS14MFORTHESQUAREAND140NMFORTHERECTANGLE4PACKAGINGISSUESFORPRODUCTIONENVIRONMENTFORINDUSTRIALPRODUCTIONOFINTEGRATEDMEMS,0LEVELPACKAGEHASTOSUSTAINPLASTICMOLDING,WHICHCORRESPONDSTOANISOSTATICPRESSUREOFAROUND100BARENCAPSULATIONFILMTHICKNESSHASBEENDESIGNEDTOLOWERTHEIMPACTOFTHEPRESSUREDURINGMOLDINGFEMSIMULATIONSDONEWITHCOVENTORINFIG8SHOWTHATTHEEDAPUBLISHING/DTIP2007ISBN9782355000003NICOLASABEL,DANIELGROGG,CYRILLEHIBERT,FABRICECASSET,PASCALANCEY,ADRIANMIONESCU0LEVELVACUUMPACKAGINGRTPROCESSFORMEMSRESONATORSMOLDINGINDUCEDPACKAGEDEFLECTIONISREDUCEDTO25NM,HAVINGA45MTHICKSIO2FILM,WHICHMAKESITCOMPATIBLEWITHSTANDARDINDUSTRIALBACKENDPROCESSES015131925NMDISPLACEMENTACOVENTOR004081216MPASTRESSBCOVENTORFIG8FEMMODELLINGOFTHEPACKAGEDRESONATORUNDERAPPLIEDISOSTATICPRESSUREMIMICKINGPLASTICINJECTIONPROCESSSTEPEFFECTOFLTOANDPECVDNITRIDEMATERIALSONCAPPINGDEFLECTIONUNDERMOLDINGSTRESSAREPRESENTEDINTABLEIMEMBRANETHICKNESSCANTHENBEOPTIMIZEDTOLOWERTHEMOLDINGINDUCEDDEFLECTIONBYCONSIDERINGYOUNGSMODULUSANDMAXIMUMSTRESSBEFOREFAILUREOFTHETWOMATERIALSSTRUCTURALLAYERMATERIALLTONITRIDEPECVDFILMTHICKNESS45M25MMAXSTRESSBEFOREFAILURE2GPA9GPASTRESSDUETOMOLDING16MPA4MPAMOLDINGINDUCEDDEFLECTION25NM36NMTABLEIFEMSIMULATIONSOFTHESTRUCTURALLAYERTHICKNESSNEEDEDTOSUSTAINPLASTICMOLDINGOVER0LEVELPACKAGINGCOMPOSEDOFA30MX30MMEMBRANECOMPARISONWITHPECVDNITRIDETHICKNESSNEEDEDTOINDUCETHESAMEDEFLECTIONONTHEDEVELOPEDPROCESSFLOW,FURTHERINVESTIGATIONSONVACUUMLEVELANDLONGTERMSTABILITYSTILLTOBESTUDIEDINORDERTOFULLYCHARACTERIZETHEPACKAGINGTHISCHARACTERIZATIONCANEITHERBEDONEDIRECTLYBYUSINGHELIUMLEAKAGETEST9,ORINDIRECTLYBYACTUATINGTHEPACKAGEDRESONATORFORWHICHQUALITYFACTORISDIRECTLYRELATEDTOTHEVACUUMLEVEL5CONCLUSIONANOVEL0LEVELPACKAGINGPROCESSWASPRESENTEDUSINGASIASSACRIFICIALLAYERANDSIO2ASENCAPSULATINGLAYERRSGMOSFETRESONATORSHAVEBEENSUCCESSFULLYENCAPSULATEDUNDERHIGHVACUUMIMPACTOFBACKENDOFLINEINDUSTRIALPROCESSOVERTHEENCAPSULATIONHASBEENINVESTIGATED,RESULTINGINOPTIMALCOVERTHICKNESSNEEDEDTOSUSTAINPLASTICMOLDINGINFLUENCEOFHOLEDIMENSIONSONRELEASINGTIMEANDCLOGGINGEFFECTFORENCAPSULATIONWEREINVESTIGATED,ANDOPTIMIZEDPACKAGINGPARAMETERSAREIDENTIFIEDFORTHISPROCESS11REFERENCES1NABELETAL,“ULTRALOWVOLTAGEMEMSRESONATORBASEDONRSGMOSFET“,MEMS06,PP8828