Energy loss and angular dispersion of 2-200 keV protons in amorphous silicon

AbstractTheenergylossof2–200keVprotonsinthinamorphoussiliconfoilshasbeenmeasuredforprojectilestransmittedintheforwarddirectionandasafunctionoftheexitangle.Atthelowestenergies,differencesofupto30%withrecentlypublishedvaluesareobserved.Angulareffectsintheenergyloss,atlowandhighenergies,havebeeninvestigated.Thelow-energyresultsarereproducedbymodelcalculationsandMonteCarlosimulations,whichindicatethattheinelasticenergylossdoesnotshowadependenceupontheimpactparameterinthelowenergyregion.Afittingformulaforthepresentenergylossvaluesisprovided. 2002ElsevierScienceB.V.Allrightsreserved. PACS:34.50.Bw;34.50.-s;34.20.Cf;02.70.LqKeywords:Silicon;Stoppingpower;Energyloss;Angulardistributions;Multiplescattering 1. IntroductionSilicon is the most frequently used semicon-ductor material in electronic devices. Thereforethereisaspecialneedtoinvestigateitsproperties.One of the many questions of interest is theslowingdownandangulardispersionoffastionsinsiliconbecauseoftherelevancetoionimplan-tation.ThestoppingcrosssectionofionsinSihasbeen investigated mainly in the intermediate andhigh ion-energy ranges. However, for energiescorresponding to ion velocities below the Bohrvelocity, the data is very scarce and shows no-ticeable dispersion. This is so because obtainingreliable data from back-scattering measurementsbecomes extremely difficult, whereas for trans-mission experiments, very thin and uniform foilsarerequired.Thislackofdataatverylowenergiesisreflectedinthespreadof 50%betweenmoderntheoretical predictions and recent extrapolatedfitting curves as will be shown in a figure. Toevaluatethecharacteristicmagnitudesforionim-plantation, such as ranges and angular spread,computersimulationsareused[1,2].Suchsimula-tionsrequirepreciseinelasticenergylossdataandinteraction potentials. In addition, the shallowimplantation that is required by the miniaturiza-tion ofsemiconductor devicesdemands a preciseknowledge of the stopping cross sections at verylowenergies.The existing simulations in the low-energyrange make use of simplified electronic stopping