Profile Changes and Self-sputtering during Low Energy Ion Implantation.
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Profile Changes and Self-sputtering during Low Energy Ion Implantation. W.Vandervorst, T.Janssens, B.Brijs, R.Lindsay, IMEC, Kapeldreef 75, B-3001 Leuven, Belgium E. J. H. Collart, David A. Kirkwood, Applied Materials UK Ltd, Parametric and Conductive Implant Division,Foundry Lane, Horsham, W-Sussex RH13 5PX, United Kingdom, G. Mathot, G.Terwagne, Univ. Namur, LARN, rue de Bruxelles 61, B-5000 Namur, Belgium ABSTRACT Continued device scaling requires the formation of ever-shallower junctions with low resistance. A desirable option to form these junctions is still the use of conventional ion implantation. However in order to meet the junction depth/sheet resistance goals, a strong reduction in implant energy and increase in implant dose is required. Earlier work for B and BF2implants, has suggested that during low energy ion implantation self-sputtering may become an important factor influencing/limiting the retained dose. The basic mechanism for the selfsputtering with increasing dose is the increasing dopant concentration at the surface leading to an increased probability for re-emission by the sputtering process. Simple models describing ion retention in combination with sputtering are based on this concept and indeed predict a selfsputtering process limiting the final retained dose. Unfortunately the theoretical calculations only predict a significant sputtering at doses >51016 at/cm2 whereas experimental results already show a limit in retained dose at 5 10 15at/cm2. In order to confirm the experimental data, low energy B, BF2, As and Sb implants have been made. Dose retention was monitored using nuclear reaction analysis and RBS whereby details of the dopant profile (redistribution) were studied using high resolution SIMS. For As and Sb no self-sputtering up to a dose of 1 1016at/cm2 can be found. For B a small dose loss (
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