用于高温SiC传感器的集成与封装技术

AssemblyandPackagingTechnologiesforHigh-TemperatureSiCSensorsRoderichZeiser,PhillipWagnerandJuergenWildeUniversityofFreiburg-IMTEKGeorges-Koehler-Allee10379110Freiburg,[e-mail]isapromisingsemiconductormaterialforsensorapplicationsinharshenvironments.TooperateSiC-MEMSathightemperature,reliableassemblyandpackagingtechnologiesareneeded.Inthispaper,packagingtechnologiesfordie-attachmentandinterconnectionsuitableforSiC-Sensorsarepresented.Theyareinvestigatedontheirstability,reliabilityandtheirthermo-mechanicalinfluenceonthesensorelement.Activemetalbrazing,glasssolderingandceramicbondingareusedasmountingtechnologiesandPlatinumandPalladiumwiresforelectricalinterconnection.Differentmaterialcombinationswereexamined.Silicontest-chipsprocessedinthinfilmtechnologywithametallizationsuitableforharshenvironmentswereusedforconductingandcharacterizationofthetechnologies.Thetest-chipsweremountedonAl2O3,AlNandSi3N4substratestoexaminetheinfluenceofthesensorsubstrate.Themechanicalstressinthechipinducedbythepackagingprocesswasanalyzedbyanopticalmeasurementofthechipssurface,correlatedtoananalyticalapproachandcomparedtoFEM-simulations.Theinvestigationofthemechanicalstabilityofthematerialcompoundswascarriedoutbyshear-testsbeforeandafter100hoursstorageat500°C.Inthisstudytheglass-solderprocesswithanAlNsensorsubstrateisthemostsuitedtechnologyincaseofthereliabilityofSiC-MEMS. IntroductionInthefieldofindustryfacilities,automotiveandaerospaceindustrythereisagrowingdemandforsensorsystemsthatarecapableofcollectingreliableanddurabledatainhightemperatureenvironments.In[1,2]pressuresensorsarepresented,whichcanoperatealreadybetween400-600°C.Bothsensorsarebasedonsiliconcarbide(SiC)asafunctionalsemiconductorlayer.Unlikesilicon-basedsemiconductors,withamaximaloperatingtemperatureupto200°C,SiCcanbeusedasasensormaterialforapplicationsatmuchhighertemperaturesduetoitslargerbandgapandtheresulting,muchlowerintrinsiccarrierconcentrationathightemperatures[3].ThesensorscanberealizedonaSiCwaferbymeansofbulkmicromachining[2]orbydepositionoftheSiCsemiconductorlayeronasiliconwafer[1].Examplesforapplicationsare,agassensorincorrosive,hotatmosphereofachemicalfacility,ahigh-pressuresensorinthecombustionchamberofacarengineoranaccelerationsensorlocatedonaturbinebladeinaviation.Thesemeasurementsystemsmustbemountedandelectricallyinterconnectedstableandreliable.Thosesystemsmustwithstandnotonlymorethan100,000hoursofhighpressureorhightemperature,butalsolargenumbersoftemperatureandpressurecyclesaswellasvibration.Thereforenotonlyarobustsensorelement,butalsohighlystableassemblyandpackagingtechnologiesareneeded.Intheliterature,differentmaterialsystems,suitableforthepackagingofSiCsensorshavebeendescribed[4,5].Therangeofmaterialsandpackagingprocessesisdrasticallyreducedbyincreasingtemperature.Furthermore,thematerialchosenassubstrateandfordie-attachshouldfittothethermo-mechanicalpropertiesofthesensorelementtoreducethermallyinducedstressafterthepackagingprocess.Organicadhesives,suchasepoxideswhicharetypicallyusedformountingsiliconsensorscannolongerbeusedattemperaturesabove200°C.Softsoldersusedfordie-attachofsensorsorpowerdevicescanbeusedupto50Kbelowtheirmeltingtemperature,whichistypicallyinarangeof210-320°C.Inthisworkglasssoldering,brazingandceramicbondingfordie-attachofSiC-sensors,technologieswhichareabletowithstandextremetemperaturesareinvestigatedandcomparedtoeachotherrelatingtostabilityandreliability.Test-chips,substratesandsimulationmodelThedie-attachtechniques,activemetalbrazing,glass-solderingandceramicbondingwereimplementedwithsilicontest-chips,processedwiththinfilmtechnology.Thetest-chipismadeofstandardSi(100)havingalmostthesamematerialpropertiesasforexampleahightemperaturepressuresensor,withathinfunctionallayerofSiC,depositedonasiliconwafer[1].Figure1:Thinfilmtestsensorassembledwithtemperaturestabletechnologiesupto600°CFigure1exhibitsamicrographoftheprototypeofourthinfilmstress-sensorpackagedwithtechnologiesdescribedinthiswork.Onthestress-chipthereisatemperaturestablemetallizationmeandrous-structuredwithanelectricalresist-ivityproportionaltothestrainandsotostressinthechipssurface.Atthemomentinastageofdevelopment,thechipismountedonaSi3N4substrateandconnectedwithplatinumwirebondstothesensorsubstrate.978-1-4673-1965-2/12/$31.00©2012IEEE338Forthisstudy,thetest-chipsaremountedonAluminiumoxide(Al2O3),Aluminiumnitride(AlN)andSiliconnitride(Si3N4)sub-strates,ceramicswhichwereproposedinpreviousworkaswellsuitedforSiC-Packaging[4,5,6].Table1showsim-portantmaterialpropertiesoftheusedceramicsincomparisontosilicon.SiliconAl2O3AlNSi3N4[ppm/K]2.67.35.23[W/mK]1502417070[GPa]161340310314Table1:Materialspropertiesoftheceramicsubstratesatroomtemperaturegivenbythemanufacturersandreference[6]Afinite-elementsimulationusingthesoftwareAnsyswascarriedouttoobtainthemechanicalstressinsidethetest-chipaftertheassemblyprocess.Themodelofthetest-chipwasthree-dimensionalandincludedmaterialdataofthesimulatedmaterial-compoundsgivenbythemanufacturers.Figure2showsthe