Diffusion and Barrier Layers.pdf

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1、Chapter3DiffusionandBarrierLayers3.1Diffusion3.1.1IntroductionDiffusionisafrequentlyusedtechniquetoincorporateimpuritiesintoasemicon-ductor.Imperfectioninanearlyperfectcrystalistheprimethemeofintentionalimpuritydiffusioninsiliconcrystals[1]fortheformationofp-njunctions,conduc-tionchannels,andso

2、urcedrainregions.Theperformanceofthedevicesdependscriticallyontheimpurityconcentrationandtheimpurityprofile.Forthisreasonthediffusionofvariousimpuritiesinsemiconductorshasbeenstudiedextensively.Figure3.1showsthepandnjunctionsinsideasilicon(Si)transistorformedbydiffusionofimpuritiesinsideSi.Thesu

3、rfaceofthediffusedlayerismetallized(granularstructures)withaluminum(orAl-alloy)whichistheconventionalmetaltomakeohmiccontactsbeforetheCu-damasceneprocess.IntheCu-damasceneprocess,copper(Cu),theprimarymetalinthesub-100nmsilicondevice,isconsideredamajorinsidiousimpuritythataffectstheminoritycarri

4、erlifetimeanddeviceyield.However,foralongtime,thedetrimentaleffectofCuonSi-deviceyieldwasuncertain.Theextremelyhighdiffusivityofcopperinsilicon,itssmallionicradius,anditsrelativelyweakinteractionwiththesiliconlattice,makeithighlymobileatroomtemperatureandimpactsonthestabilityofCu-complexes[2].F

5、igure3.2showsaninsituX-raydiffractionpatternrecordedduringheating(200◦C)ofaCu-filmdepositedoversilicon.Asamatteroffact,thediffusionofcopperatelevatedtemperaturesanditsprecipitationinsilicondependuponvariousfactors[2].Thusthereexistsaneedtostudythediffusionmechanismofcopperinsilicon,becauseintheC

6、u-damasceneprocessinterconnectinglinesareformedfromelectrodepositedcopperfilm.Figure3.3showstheCu-interconnectdamascenestructure,whichhasreplacedtheconventionalaluminuminterconnectinmodernsub-100nmnodetechnology.Asthestateof250nmback-endprocesseschangedto130nm,thepropagationdelays,signaldispersi

7、on,and/orcross-talknoiseassociatedwithAl/SiO2systemlimitedthechipperformance.ReductionofpropagationdelayduetoRCeffectsoftheinterconnectinglinescanminimizethecapacitivecross-talknoise.ThustheobviouschoicewillbetoreplacetheAl-interc