张世广118-119-b07

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1、118CHAPTER3TheSemiconductorinEquilibrium3.7.2ImpurityAtomIonImplantationInasecondmethodofdoping,high-energyimpurityionsareimplantedintothesemiconductor.Abeamofimpurityionsareacceleratedtoenergiesrangingfrom1keVto1MeVandimpingesthesurfaceofthesemiconductor.Suchaprocessisreferredtoasionimplantation.T

2、woprimaryadvantagesofionimplantationarethemoreprecisecontrolandreproducibilityofimpuritydopingandthelowerprocessingtemperaturecomparedtodiffusion.Figure3.23showsabasicschematicofanionimplantationsystem.Thedepthofpenetrationorprojectedrangeisafunctionoftheimplantedionssincethereisacertainrandomnessi

3、ntheinteractionoftheimplantedionswiththehostsemiconductoratoms.Figure3.24showsatypicalimpurityprofile.Byperformingseveralimplantsatdifferentenergies,itispossibletocreatearegionthatisalmostuniformlydoped.Whenenergeticionsimpingeonthesemiconductor,theylosetheirenergybyaseriesofcollisionswiththesemico

4、nductoratoms.Asaresultofthisinteraction,semiconductoratomsaredisplacedfromtheirnormalsingle-crystalpositions.Adamagedregioniscreatedinthesemiconductorandmostoftheimplantedionsarenotlocatedinsubstitutionalpositions.Toactivatetheimplantedionandrepairthedamagedarea,thesemiconductormustbeannealedatanel

5、evatedtemperatureforaparticularperiodoftime.Theconventionalannealingtemperatureisontheorderof600℃andtheannealingtimeisontheorderof30min.Rapidthermalannealingprocessarealsoused.Theannealtemperaturesandtimesareconsiderablylowerthanthoseusedinthediffusionprocess.Theimplantionscanbeblockedfromenteringt

6、hesemiconductorbymetal,photoresist,oroxides.Bydefiningspecificpatternsonthesurface,onlyspecificdesiredregionsofthesemiconductorwillbedoped.Thistechniqueisthenusedtocreatethemanysemiconductordevicesintheintegratedcircuit.Figure3.23Schematicofanionimplanter.(CourtesyofRunyanandBean)3.8Summary119Figur

7、e3.24Typicalimplantedimpurityprofile.Thepeakoftheimplantedconcentrationcanoccurbelowthesurfaceofthesemiconductor.3.7SUMMARY1.A.Theconcentrationofelectronsintheconductionbandisfoundbyintegratingtheproductoft