半导体工艺-复旦大学-蒋玉龙-Chapter08

Chapter8IonImplantationOutlineI.BasicPrincipleandMethodII.InteractionbetweenIncidentIonsandSubstrateAtomsIII.StoppingPowerandProjectedRangeIV.IonChannelingEffectV.ImplantDamageVI.ThermalAnnealingI.BasicPrincipleandMethod1.SurfacePropertyModificationbyIonImplant‹IonImplantation---PowerfulMethodforBuildingaSurfaceLayerwithParticularPropertiesinSelectionRegion(IonModification)InteractionbetweenIncidentIonBeamandSolidSurface:3basiceffects(1)Sputtering:LowEnergy(102-103eV)(2)Backscattering(Reflection)(3)Injection,Penetration-Implantation*ItDependsonEnergy(Velocity),Ionmass,Targetmass.*Modificationofthematerialpropertiesbyimplant:Chemical,Electrical,Mechanical,Optical‹Applications(Expanding):¾SemiconductorDopingandPN-JunctionFormation¾OxideorNitrideFormation¾Corrosion-ResistingSurface(Cr,Ta,Steel)¾OpticalDevice¾Superconductor(RiseCriticalTemperature)‹Ionimplant---dominantdopingtechnologyforCMOSandothersemiconductordevicesAvarietyofapplicationofionimplantbydifferentimpurity,energy,doseandprocessing2.IonImplantationSystem(1)IonSourceandDoseMeasurement*Gaseoussource(commonlyused):BF3,PH5,PF5,AsH5,AsF5*SolidSource---SputteringSource*Apowersupplytoenergizetheionsource---plasma(Idealionsource---highI,lowervoltage,E=0)*Beamcurrent---importantfordosecontrolandimplantorefficiency‹Beamcurrentprecisemeasurement:¾Needtakeintoaccounttheparticlesotherthantherightpositiveionssuchas:Neutrals;NegativeIons;Secondaryeemittedfromtargetbyionbombardment¾UsingFaradaycage(withnegativevoltage)toeliminatethesecondarye-current‹BeamCurrent---oneofmajorperformanceparameterofimplantor¾LowCurrentImplantor:10-50uA¾MediumCurrentImplantor:400uA-4mA¾HighCurrentImplantor:5mA-25mA-100mA‹Ex:EatonNova10-80:20-80KeV;B-4.0mA,P-10mA,As-12.5mA(2)MassSeparation---MagneticAnalyzer---Ionsourcematerialsareusuallycompounds---Productionotherkindchargedspeciesuponionization---Contaminantimpurities*LorentzForce:*CentrifugalForce:][→→→×=BvnqFrMvF21=1FF=rMvvBnq2)(=nqBMvr=∴nqVMv=221B-MagneticFluxDensityv-IonVelocity;M-IonmassV-AcceleratingPotentialR0-Radiusofmagnetcurvaturen-Numberofcharge∴21)2(1nqMVBr=210)2(1nqMVrB=KBnM=(3)TheAccelerator‹TheIonEnergyisdeterminedbytheacceleratingpotentialoftheaccelerationtubeV=80KVAsSinglecharged:80KeVAsDoublecharged:160KeV¾Lowenergyimplantor100KeV¾Mediumenergyimplantor100-400KeV¾Highenergyimplantor400KeV¾Ultra-lowenergyimplantor0.2-10KeV(Forultra-shallowjunctionformation)EinVEoutI+25KeV300KV325KeVI++50KeV300KV650KeVOut+-highvoltageBeamIn2.AdvantagesofIonImplantation(1)Lowcontaminationdopingmethod¾Massseparationtechniques¾Vacuum(P10-10Torr)Probabilityofnocollisionincertainlength:(L)~exp(-L/λ)λ=MeanFreePath∝AtP10-10Torr:λ107cmSinglemachineforawidevarietyofimpuritiespressure1(2)Precisecontrolofimpuritydosebybeamcurrent&time1011-1018Ions/cm2,±1%(1011-1016)fordoping;(1017-1018)forlayers(Evencaninducedopantaboveequilibriumsolidsolubility)Diffusion:T°C,t:±5%~10%Difficultyforlowconcentrationdiffusion(1014cm-2)Typical“ERFC”,SolidSolubilityPredeposition:Q=ForBoronat1000°C,30minD≅3×10-14cm2/sec;N≅4×1020cm-3;Q≅3.3×1015cm-202NDtπ(3)DepthandprofilecontrolbyimplantationenergyImpurityprofilescanbecustomizedbyperformingmultipleimplantsatvariousdosageandenergy(Example:InternalBase,ExternalBase)(4)Uniformityacrosswaferandreproducibilityfromwafertowafer(5)Lowtemperatureoperation---Awidevarietyofmasks(SiO,SiN,Al,Resist……)canusedforimplant→Selectivedoping→Freedomindesignofself-alignment---Compoundsemiconductordoping,avoiddissociationathightemperaturediffusion3.IonImplant⎯extendedapplicationinmicroelectronicsIIInteractionBetweenIncidentIons&SubstrateAtoms1.Physicalprocessofionimplantation¾Ionimplantation(II)---non-equilibriumprocessDiffusion---equilibriumprocessBymolecule/atomthermalmotion(BrownMotion)II---InteractionbetweenchargedparticlesandlatticeatomsandinjectionofenergeticionsintoasolidM,qAtonetimeioninteractsorcolloidswithonetargetatom∴IIprocess---asuccessionofbinarycollisions‹Collision---processofenergylossandscattering¾Elastic&inelasticcollisions¾Elasticcollisionbetweenion&nuclei:(consideredastwohardspheres)Followingenergyconservationlawandmomentumconservationlaw→Energy&momentumexchangebetweentwoparticles¾Inelasticprocess:--Directinteractionbetweenmovingion&electrons→Dragforce:non-localelectronicstopping--Electronperturbation:excitation&ionization→localelectronicstoppingDecayofexcitedelectron→photon/eemission2.EnergyExchangeDuringElasticCollision‹KinematicalEquationInteratomicforce---repulsiveCoulombtype2221)(rqZZrFeffeff=rqZZrVeffeff221)(=Rangeofinteractiondistances:(Head-on)→mrm101110)31(10−−×−←21(InteratomicLatticeSpacing)¾Perfectelastichard(rigid)spherecollision21RRRM+=:MRr0)(=rV:MRr0)(≠rV*ConservationofKineticEnergy:210EEE+=;222101122111222MvMvMv=+(1)*ConservationLawforMomentum:Paralleltolineofcenters:221101)cos(cosvMvMvM++=ψθψ(2)Perpendiculartolineofcenters:)sin(sin1101ψθψ+=vMvM(3)From(3):θθψcos2sinsin1021201vvvvv−+=θθψcos2coscos10212010vvvvvv−+−=From(2):)cos2(102120222122θvvvvMMv−+=Subto(1):2021Kvv=→;01KEE=K---Kinematicalfactor22