Introduction-of-IC-Fabrication

1Chapter2IntroductionofICFabrication2Objectives•Defineyieldandexplainitsimportance•Describethebasicstructureofacleanroom.•Explaintheimportanceofcleanroomprotocols(協議規範）•ListfourbasicoperationsofICprocessing•Nameatleastsixprocessbays（區間）inanICfab•Explainthepurposesofchippackaging•Describethestandardwirebondingandflip-chipbumpbondingprocesses（覆晶接合製程）3WaferProcessFlowMaterialsDesignMasksICFabTestPackagingFinalTestThermalProcessesPhoto-lithographyEtchPRstripImplantPRstripMetallizationCMPDielectricdepositionWafers4FabCost•Fabcostisveryhigh,$1Bfor8”fab•Cleanroom•Equipment,usually$1Mpertool•Materials,highpurity,ultrahighpurity•Facilities•People,trainingandpay5Yield•Waferyield–•Dieyield–•Packagingyield–•YT=YWxYDxYC•OverallYielddetermineswhetherafabismakingprofitorlosingmoneytotalgoodWWafersWafersY=totalgoodDDiesDiesY=totalgoodCChipsChipsY=6HowDoesFabMake(Loss)Money•Cost:–Wafer(8”):~$150/wafer*–Processing:~$1200($2/wafer/step,600steps)–Packing:~$5/chip•Sale:–~200chips/wafer–~$50/chip(low-endmicroprocessorin2000)*Costofwafer,chipsperwafer,andpriceofchipvaries,numbersherearechoosingrandomlybasedongeneralinformation.7HowDoesaFabMake(Loss)Money•100%yield:150+1200+1000=$2350/wafer•50%yield:150+1200+500=$1850/wafer•0%yield:150+1200=$1350/wafer•100%yield:200×50=$10,000/wafer•50%yield:100×50=$5,000/wafer•0%yield:0×50=$0.00/wafer•100%yield:10000−2350=$7650/wafer•50%yield:5000−1850=$3150/wafer•0%yield:0−1350=−$1350/waferCost:Sale:ProfitMargin:8Question•Ifyieldforeveryprocessstepis99%,whatistheoverallprocessingyieldafter600processsteps?•Answer–Itequalsto99%times99%600times–0.99600=0.0024=0.24%–Almostnoyield9Throughput•Numberofwafersabletoprocess–Fab:wafers/month(typically10,000)–Tool:wafers/hour(typically60)•Athighyield,highthroughputbrought10DefectsandYield•Toachieve100%yield,thekillerdefectdensitymustbezeroforeveryprocessstep.•Atthesamedefectdensityandchipsize,themoreprocessstep,thelowertheyield•Atthesamedefectdensitylevel,thelargerchipsize,thelowertheyieldnDAY)1(1+∝D:thekillerdefectdensityA:thechipareaN:thenumberofprocessstepsY=28/32=87.5%Y=2/6=33.3%KillerDefects11IllustrationofaProductionWaferTestdieDieTransistorandtestcircuitsarebuiltduringwaferprocessing12IllustrationofaProductionWaferScribeLinesDiesTestStructures13CleanRoom•Artificialenvironmentwithlowparticlecounts•Startedinmedicalapplicationforpost-surgeryinfectionprevention•Particleskillsyield•ICfabricationmustinacleanroom•Firstusedforsurgeryroomtoavoidbacteriacontamination•Adoptedinsemiconductorindustryin1950•Smallerdeviceneedshighergradecleanroom•Lessparticle,moreexpensivetobuild14CleanroomClasses•Class10isdefinedaslessthan10particleswithdiameterlargerthan0.5μmpercubicfoot.•Class1isdefinedaslessthan1suchparticlespercubicfoot.•0.18mmdevicerequirehigherthanClass1gradecleanroom.0.1110100100010000100000Class100,000Class10,000Class1,000Class100Class10Class1#ofparticles/ft0.11.010Particlesizeinmicron3ClassM-115DefinitionofAirborneParticulateCleanlinessClassperFed.Std.209EClassParticles/ft30.1μm0.2μm0.3μm0.5μm5μmM-19.82.120.8650.281357.5311035075301010075030010010001000710000100007016EffectofParticlesonMasks(1)ParticlesonMaskStumpon+PRHoleon−PRFilmSubstrateFilmSubstrate17EffectofParticleContamination(2)PartiallyImplantedJunctionsParticleIonBeamPhotoresistScreenOxideDopantinPR18EffectofParticleContamination(3)•Aparticleevenone-tenthoftheminimumfeaturesizecancontaminatethechip–At0.18umfeaturesize,aparticleassmallas0.018umcouldbeakillerparticleifitfallsonacriticalarea•Largerparticles(1umindiameter)–Canbehandlebyhigh-pressureairflow–High-pressureairornitrogenblowersarewidelyusedinolder,100mm(4-inches)fabs•Smallerparticles–Cann’tbehandlebyhigh-pressureairflow–Anairbloweraddmoreparticles19CleanroomStructureProcessAreaEquipmentAreaClass1000EquipmentAreaClass1000RaisedFloorwithGridPanelsReturnAirHEPAFilterFansPump,RFandetc.ProcessToolProcessToolMakeupAirMakeupAirClass120Cleanroomstructure•For0.18umprocess–Betterthanclass1cleanroomisneedforprocessingarea•Class1000isgoodenoughfortheequipmentarea•Toachievebetterthanclass100cleanness–Itisimportanttokeepalinearairflow,usuallycalledlaminarflow,andavoidairturbulence(擾流)–Withlaminarflow,airborneparticlesarecarriedawayquicklybytheairflow–Class100isthedividinglinebetweenlaminarflowandturbulentflow(lowercosts)•Acleanroomisalwayskeptathigherpressurethannoncleanareas–Keepingairflowoutwardagainstairborneparticleswhenadoorisopened21Mini-environment•Class1000cleanroom,lowercost•Boardroomarrangement,nowallsbetweenprocessandequipment•Betterthanclass1environmentaroundwafersandtheprocesstools•Automaticwafertransferbetweenprocesstools22Mini-EnvironmentCleanroomClass1000Class1000RaisedFloorwithGridPanelsReturnAirHEPAFilterFansPump,RFandetc.ProcessToolMakeupAirMakeupAirProcessToolHEPAFilterClass123GowningArea（無塵室更衣區）GownRacks無塵衣掛架BenchesShelfofGloves,HairandShoeCoversDisposalBins棄物箱Wash/CleanStationsStorageShelfofGlovesShelfofGlovesEntranceToCleanroom24Cleanroomprotocols•Differfromcompanytocompany,evenfromfabtofabinthesamecompany•Theobjectives–Keep