Study of near-surface layers modified by ion implantation in Si wafers by grazing incidence X-ray reflectometry

The grazing incidence X-ray reflectivity (GIXR) curves recorded from two se ts of Si(111) samples implanted with As+ ions of energy 80 keV with a numbe r of doses above the amorphization limit are reported. The first, 'clean' s et of samples, was implanted in ultra high and clean vacuum to avoid contam ination. The second, 'contaminated' set, was implanted under less rigorous conditions, and contaminated with carbon and oxygen. The reflectivities for the 'contaminated' samples show that a formation of near-surface layer of lower electron density (about 10-15% for the highest dose) comparing to the pure Si occurs. The thickness of the layer increases with ion dose, and co mplicated in-depth electron density profiles are necessary to fit the refle ctivities. The results for the 'clean' samples show quite different, dose d ependent, features, and suggest a qualitative change in layer properties oc curring between the doses of 1x10(16) and 5x10(16) I cm(-2). The reflectivi ty at higher doses indicate a densification of the near-surface layers due to implantation of about 7-12% higher comparing to the pure Si. (C) 1999 El sevier Science S.A. All rights reserved.