ESD基础课程

Chapter7SD(EleetrostaticDischargeProtectionDesignforanoeectronicsinCMOSecnoloProf.Ming-DouKerNanoelectronicsandGigascaleSystemsLaboratoryInstituteofElectronics,NationalChiao-TungUniversity,Taiwanmdker~ieee.orgAbstract.Inthistutorial,weteachusefulon-chipESDprotectionde-signsforCMOSintegratedcircuits.Thecontentsinclude(1)IntroductiontoElectrostaticDischarge,(2)DesignTechniquesofESDProtectionCir-cuit,(3)Whole-ChipESDProtectionDesign,and(4)ESDProtectionforMixed-VoltageIJOInterface.TheclearESDprotectiondesignconceptsanddetailedcircuitimplementationsarepresentedinthiscourse.ESDprotectiondesignismoreimportantinthenanoscaleCMOStechnology.HighESDrobustnesscannotbeachievedwithonlyprocesssolutions.Thecircuitdesignsolutionsshouldbeaddedintothechipswithsuitablelayoutarrangementtoachievethepurposeofwhole-chipESDprotectionforICproducts.1-4244-0460-6/06/$20.00©)2006IEEE.217CHAPTER7.ESDPROTECTIONDESIGNINNANOCMOS7.1IntroductiontoElectrostaticDischarge(ESD)Electrostaticdischarge(ESD)phenomenonoftenhappensbetweentwoormoreobjectswithdifferentelectrostaticpotentials.ESDphenomenonhasbeenknownasaseriousproblemforICproductsfabricatedbythead-vanceddeep-submicronandnanoscalesemiconductorprocesstechnolo-gies.Inthescaled-downCMOSprocesses,theMOSdeviceswithshal-lowerjunctiondepth,thinnergateoxide,lightly-dopeddrain(LDD)struc-ture,andslicideddiffusionhavebettercircuitperformanceofhigherop-eratingspeedandloweroperatingpower,buttheybecomeweakertoESDstresses.DevicesareusuallydamagedbyESDduetotherapidlygeneratedheatortherapidlycreatedstrongelectricalfield.TopredicttheESDim-munitylevel,ortofindtheESDsensitive(weak)pointoftheICs,thereareseveralorganizationstoissueESDteststandards.TheyareESDA(Elec-trostaticDischargeAssociation),AEC(AutomotiveElectronicsCouncil),EIA/JEDEC(ElectronicIndustriesAlliance/JointElectronDeviceEngi-neeringCouncil),andMIL-STD(USMilitaryStandard).ThedominantESDtestmethodsoncomponent-levelICproductsareknownasHBM(HumanBodyModel)[1],MM(MachineModel)[2],andCDM(ChargedDeviceModel)[3].7.1.1ESDStandardsandModels7.1.1.1HumanBodyModel(HBM)TheactualESDeventfromthechargedhumanbodytotheICisshowninFig.7.1(a).ApersonwithelectrostaticpotentialtohandletheICtoagroundedsurfacewillcausetheESDcurrentthroughthefingersofhumanbodytotheIC,andthentothegroundedsurface.ThecircuitdiagramusedtomodelthisESDevent(calledasHumanBodyModel,HBM)isshowninFig.7.1(b).TheequivalentcapacitanceintheHBMtostoretheelectrostaticchargesisstandardizedas100pF,andtheresistanceintheFIBMtodischargetheelectrostaticchargesthroughhuman'sfingerisstandardizedas1.5kohm.Thetypicalcurrentpeakof2-kVHBMESDeventis1.3Ampwitharisetimeof51Ons.WithsuchfastESDcurrentdischargingthroughtheIC,iteasilycausessomeseriousdamagesontheI/0devicesoftheICs,ifthereisnosuitableESDprotectiondesignintheICs.ThetypicalHBMESDfailureontheI/Odevicesofa0.18-nmCMOSICisshowninFig.7.1(c),wheretheI/Opiniszappedbya1-kVHBMESDstress.Theobviousdamageslocatealongthepoly-gatebetweenthe2187.1.INTRODUCTIONTOELECTROSTATICDISCHARGE(ESD)drainandsourceregionsotanNMO4Stocausethel/(pinshortingtoground.(a)/i#f~~~DEVUN1l01(b)(c)Figure7.1:(a)ESDeventfromthechargedhumanbodytotheIC.(b)Theequivalentcircuitofhumanbodymodel(I{BM)ESDevent.(c)ThetypicalESDfailurecausedbyHBMESDstressonthe1/0devicesofCMOSIC.219CHAPTER7.ESDPROTECTIONDESIGNINNANOCMOS(a)(b)Figure7.2:(a)Theequivalentcircuitofmachinemodel(MM)ESDevent.(b)ThetypicalESDfailurecausedbyMMESDstressontheoutputNMOSofCMOSIC.7.1.1.2Mach'ineModel(MM)TheICproductsoftenhavehugevolumeformassproduction.Tohandlesuchhugeproductionvolume,theautomaticmachinesareusedtoprocessICproductsduringfabrication,assembly,andtesting.Theautomaticma-chinescouldgeneratetheESDeventtocausetheESDstressontheICproducts.ThecircuitdiagramfortheMachineModel(MM)ESDeventisshowninFig.7.2(a).TheequivalentcapacitanceintheMMtostoretheelectrostaticchargesisstandardizedas200pF,andtheresistanceintheMMtodischargetheelectrostaticchargesisideallyzero.But,actually,theparasiticresistanceofseveralohmandtheparasiticinductanceofseveralnHalongtheconnectionlinefromthecapacitor(200pF)tothedeviceun-dertest(DUT)willcauselittleringingintheMMESDcurrentwaveform.Thetypicalcurrentpeakof200-VMMESDeventis3.8Ampwithacur-rentringingfrequencyof16MHz.Therisetime(1-3ns)ofMMESDeventisslightlyfasterthanthatofHBMESDevent,duetotheabsenceofthedischargingresistanceof1.5kohm(HBM).WithsuchfasterESDcur-rentdischargingthroughtheIC,iteasilycausesmoreseriousdamagesontheI/OdevicesoftheICs.ThetypicalESDfailureontheII/devicesofa0.18-imCMOSICisshowninFig.7.2(b),wheretheI/Opiniszappedbya200-VMMESDstress.Theobviousdamagelocatesacrossthefinger'sendofthepoly-gatebetweenthedrainandsourceregionsofanoutputNMOStocausetheII/pinshortingtoground.2207.1.INTRODUCTIONTOELECTROSTATICDISCHARGE(ESD)7.1.1.3Charged-DeviceModel(CDM)TheelectrostaticchargescouldbealsostoredinthefloatingICduringthefabrication/assembly/testingprocesses.IfthechargedICtouchestothegroundedsurface,theelectrostaticchargeswillbedischargedfromthebodyofICtotheexternalgroundtocausetheChargedDeviceModel(CDM)ESDevent.T