Professor N Cheung, U.C. BerkeleyLecture 9EE143 F201011) Implant Profile depends only on incident ion momentum,NOT on charge stateA+AA-Same implantprofileSamemomentumNote : Kinetic Energy = (momentum)2/2M2) Charge carried by ions will be neutralized by charges inthe substrate after implantation.3) n, p, Nd+, Na- charges in semiconductors are causedby the chemistry of the implanted dopants, and are NOTrelated to charges carried by the ions.Professor N Cheung, U.C. BerkeleyLecture 9EE143 F20102Kinetic Energy of Multiply Charged IonsWith Accelerating Voltage = x kVB+P+As+Kinetic Energy = x · keVB+++B++Kinetic Energy = 2x · keVKinetic Energy = 3x · keVSinglychargedDoublychargedTriplychargedNote: Kinetic energy is expressed in eV . An electronic charge q experiencing avoltage drop of 1 Volt will gain a kinetic energy of 1 eVProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F20103Molecular Ion ImplantationBF2+Kinetic Energy = x keVBFFB has 11 amuF has 19 amuaccelerating voltage= x kV+-%2019191111BFof.E.KBof.E.Kvm21Fof.E.Kvm21Bof.E.KvvvVelocity22BF2BBFFBMolecular ion willdissociate immediatelyinto atomic componentsafter entering a solid.All atomic componentswill have same velocityafter dissociation.SolidSurfaceProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F20104FBFBFFSame velocity V = VBF(move together as a molecule)V = VFB' 'afterProof : Dissociated atomic components having same velocityBinding energy of molecule (~ several eV)is negligible compared with ion energy(many keV).12mBvB2 + 212mFvF2) =12mBvB2 + 2(12mFvF2) [1](mB + 2mF)vB = mBv'B + 2mFv'F [2]The only way to satisfy both [1] and [2] is :vB = vF = vB = vF.Professor N Cheung, U.C. BerkeleyLecture 9EE143 F20105B+Beam current (B+) as acceleratingvoltage < 1kVBF2+Beam current (BF2+) can still bemaintained high with 5kVaccelerating voltage but the effectiveB implantation energy is only ~1 keVMolecular Implantation for Shallow JunctionsFor conventional beamline implanters,Beam current as accelerator voltage Professor N Cheung, U.C. BerkeleyLecture 9EE143 F20106Implantation DamageProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F20107Amount and type of Crystalline DamageProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F20108Solid Epitaxial “Growth” through theImplant Damaged RegionProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F20109Solid Epitaxial “Growth” through theImplant Damaged Region – cont.Professor N Cheung, U.C. BerkeleyLecture 9EE143 F201010Interstitial-VacancyrecombinationAgglomerationof secondary defectsSecondary defectsAnnealed outDopant Activation Versus Annealing TempProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F201011* Sheet Resistance is limited by dopant solid solubility* Shallower junctions will have higher RSDopant ActivationProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F201012(1) Restore Si crystallinity.(2) Place dopants into Si substitutional sitesfor electrical activationAfter implantation, we need an annealing step.A typical ~900oC, 30min will:Post-Implantation Annealing SummaryProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F201013Ion ChannelingTo minimize channeling, we tilt wafer by 7owith respect to ion beam.To minimize channeling, we tilt wafer by 7owith respect to ion beam.random scattering pathdeeperpenetrationSi CrystalRandom componentchanneledcomponentC(x)xAxial ChannelingPlanar ChannelingRandomProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F201014Chaneling with “Lucky Ions”Some scatteredions can still fallinto othercrystallographicchannelingdirections.Some scatteredions can still fallinto othercrystallographicchannelingdirections.xC(x)xjCBwithchanneling tail of “lucky ions”xj’NoChanneling7oSi substrate+Ion beamalready tilted7oaway from normalof surfaceProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F201015Si+1 E15/cm2Si crystalDisadvantage : Needs an additional high-dose implantation stepDisadvantage : Needs an additional high-dose implantation stepB+Si crystalAmorphous SiStep 1High dose Si+implantation to covertsurface layer intoamorphous SiStep 2Implantation ofdesired dopantinto amorphoussurface layerPrevention of Channeling by Pre-amorphizationProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F201016Transverse (or Lateral) Straggle (Rtor R)RtRtRp>1RtRpProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F201017yMaskC(y) at x=Rpx = RpImplanted speciehas lateral distribution,larger than mask openingImplanted speciehas lateral distribution,larger than mask openingxyHigher concentrationLowerconcentrationLateral Ion Scattering Causes Feature EnlargementProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F201018 ttaaRyyRayerfcRayerfcxCKdyexCKyxCt22,222'masky=-ay=+axA 2-D formulation of Implantation ProfileProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F201019()( ) ( )( ) ( ) ( ) ( )[ ]( ) ( )For a i e no maskC x y C xC x y C x K erfc erfcC x C x KK == -= =. .,,212A 2-D formulation of Implantaion Profile – cont.Professor N Cheung, U.C. BerkeleyLecture 9EE143 F201020(details of erfcfunction alsocovered inDiffusion sectionof EE143Reader)[Curves alsogiven inJaeger]Semi-log Plotsof Gaussian and erfc functionsProfessor N Cheung, U.C. BerkeleyLecture 9EE143 F201021Transmission Factor of Implantation MaskWhat fraction ofdose gets intoSi substrate?x=0 x=dC(x)Mask material (e.g. photoresist)Si substrateC(x)Mask material withd=x=0 x=d-Professor N Cheung, U.C. BerkeleyLecture 9EE143 F201022Transmitted FractionT C x dx C x dxerfcd RRerfc x e dyC x dC x Rdppyxp000412 212102Rule of thumb Good masking thickness:d R Rp p4 3. ~are values offor ions intothe masking materialRpRp,Professor N Cheung, U.C. BerkeleyLecture 9EE143 F201023SIMOX depends on a peaked implant profile. The sharp interfaces areformed during high temperature annealing.4000 Å of buried oxide requires a high oxygen dose of 2E18/cm2Slow process using beam-line implantersSOI WaferExample Application : SIMOX(Separation by IMplantation of OXygen)Professor N Cheung, U.C. BerkeleyLecture 9EE143 F201024H+1. H+IonImplantation~ 6E16 dose2. Direct WaferBondingHandle waferSi donorSi donorSi donorBondinginterface3. Donor wafer cleavagewith heat treatmentor mechanical cleavageThermal
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