第十二章、材料表征与分析

HenryRadamson1DepartmentofMicroelectronicsandInformationTechnologyKTH,RoyalInstituteofTechnologyBandgapandmobilityingroupIVmaterialsystemsbyHenryH.RadamsonHenryRadamson2Increasingthenumberoftransistorsinthechip/yearDown-scalingthesizeofthetransistors(junctions,thresholdvoltagegateoxidethickness)ThisoccursforbothlateralandverticalsizesoftransistorsThedopantconcentrationsinsource/drainandinthechannelhastobemodifiedThemobilityisanimportantissueinthedown-scalingwhichhastobekepthigh.Roadmapofthemicrotechnology(atransitiontonanotechnology)StrainengineeringinchannelregionisdemandedHenryRadamson3StrainandbandgapingroupIVmaterialHenryRadamson4StrainandBandgapEngineeringMismatchofSiandSiGe,SiC,SiGeC,SiSn,GeSn,SnGeSiGeGe1-xSnxorSi1-xGexlayerSnSiaSn=0.6489,aGe=0.5646&aSi=0.5431nm(Sn/Ge~15%,Sn/Si17%andGe/Si~4.2%mismatch).SiSubstrateSiyC1-ylayerCompressiveStrainTensilStrainStrainrelaxedStraincompensatedCHenryRadamson5SiGeGehasnearlydirectbandgapof0.85eVBandstructureofSiandGeHenryRadamson6Bandgapofalloysisdeterminedfromactivecomponent:1.alloying2.Strain(consistsoftwocomponents:hydrostatic,uniaxial)Types:Compressive&Tensile(Ge/GeSn&Ge/GeSi)Designs;Biaxial&Uniaxial(ortwo-&one-dimstrain)Fourcasescanbeoccured:*Straincompensated(e.g.ternarysystemsGeSnSi&GeSiC)*Strainrelaxed(GeorGeSivirtualbufferlayer)(alloyingcomponentbutdefectstateswithinthebandgap)*Nostrainedlayers(e.g.ternarysystemsGeSnSi)(latticematche.g.ternarysystemsGeSnSi)*Locallystrained(Ge,Si&Sndots)strainedindivitualdots,relaxeddotsinaburiedlayerStrainandBandgapEngineering:-GeSnalloysystem-GeSnSialloysystem-strainedGeonGeSnorSiGeSnfordirectbandgap(viatensilestrain)-UnstrainGe(orSiGe)onSiGeSnforintersubbandapplications–quantumcascadelasers(QCLs)-SiSnalloyonGeSnforcommunicationwavelengths(1.3mm–1.55mm)Transitionofindirect-bandgaptoadirectbandgapwithSncontent6-8%HenryRadamson8StrainengineeringinMOSFETsHenryRadamson9SiGebandstructure(compressiveBiaxialstrain)SiGe/Sisystemscreateacompressivestrainwhichactonthevalenceband(thebandgapnarrowingisonlyfromvalencebandshift)SiGeSiHenryRadamson10Conductionbandsplit(tensileBiaxialstrain)TensilestrainshiftsΔ2electronsdownwards(thesearelightelectrons).Twowayshavebeenusedtogeneratetensilestrain:Electronsinconductionbandofunstrained-SiStrained-SihaselectronsΔ2atminimumconductionbandedgeSiC(tensile)onSiSi(tensile)onrelaxed-SiGeConductionbandofSicontainsΔ4andΔ2electrons.HenryRadamson11FormationofbiaxialanduniaxialstraininSi1)GrowthofSi1-xGexorSiC2)Formationofgatestack2)ImplantationBorPtoformS/D1)Formationofgatestack2)EtchofSitoformrecess3)SelectivegrowthtoformS/DUniaxialstrainBiaxialstrainHenryRadamson12InducinguniaxialstrainRecessedjunctions(dry-etched)werefilledbyB-dopedSiGelayers(selectiveepitaxy).ThiscreatesacompressivestraininSichannellayer.DepositionofSiNlayeronthetopofthenMOSinordertocreateatensilestraininSichannellayer.Alt.TherecessisfilledbyAs/P-dopedSi1-yCyHenryRadamson13Inducingstressof1GPainpMOSFETsTunningSiNstressfromhighlytensiletocompressivestressinLPCVDandPECVD.ThemechanicalpropertyofnitridelayersisdeterminedbycontrollingthegasphasedissociationofSilane,AmoniaandgasesinaplasmaenvironmentArghavanietal.IEEEElectronDeviceLetters,V27(2006)114ThesenitridelayerscanbegrownonembeddedSiGelayers.TheinducedstressisadditivetotheinducedSiGestress.HenryRadamson14ScatteringandmobilityManyscatteringcontributionsLowerdopantconcentrationcauseshighermobilityAlwaysholehaslowermobilitythanelectron(thisisaprobleminCMOSdesign)HenryRadamson15Carriermobilityinstrained-SiThecalculationsshowthehighestmobilitywillbeobtainedalong110channeldirection.HenryRadamson16ElectronmobilityinStrained-SiHenryRadamson17ScatteringprocessesinacrystalLatticescattering:electronschangesitsmomentumandenergywithphononwithconservationofenergyandmomentum.IntravalleyscatteringwhenthefinalpositionoftheelectroninE-Kspaceareinthesamevalleyotherwiseintervalleyscatteringoccurswhentheelectron’sfinalpositionisindifferentvalleys.Alloyscattering:periodicpotentialisdistortedbyalloyingDeformationpotentialscattering:whentheacousticphononschangesthepositionoflatticeatomleadingtoconductionandvalencebandedgeisvaried.Pizzoelectricscattering:IftheatomsinthecrystalcanbeionizedbyacousticphononsCarrier-carrierscattering:whentheelectroncollidewitheachotherandissignificantND1017cm-3HenryRadamson18HowtoincreasethemobilityTwoways:decreasingthescatteringordecreasingthem*BothcasescanbeobtainedbyinducingstraininSiCompressivestrain(strainedSiGeonSi)splitsthevalencebandwhereastensilestrain(strainedSionrelaxedSiGeorSiConSi)reformtheconductionband.HenryRadamson19WhatweneedtomeasureStrainDefectdensityMaterialphasesinsilicides(loweringcontactresistanceinMOSFETs)InterfaceroughnessinheterostructuresHowtomeasureThislecturefocusesonlyonXRDtechniqueHenryRadamson20Departmentof