Variable-energy positron annihilation spectroscopy was applied to the study of the formation and evolution of vacancy-type defect structures in silicon and the 1.5μm thick Si top layer of silicon-on-insulator  samples. The samples were implanted with 2MeV Si ions at fluences between 1013 and 1015/cm2, and probed in the as-implanted state and after annealing for 30min at between 350 and 800C. In the case of silicon-on-insulator the ions were implanted such that their profile was predominantly in the insulating buried oxide layer, and thus their ability to combine with vacancies in the top Si layer, and that of other interstitials beyond the buried oxide, was effectively negated. No measurable differences in the positron response to the evolution of small clusters of n vacancies (Vn, n ∼ 3) in the top Si layer of the Si and silicon-on-insulator samples were observed after annealing up to 500C; at higher temperatures, however, this response persisted in the silicon-on-insulator samples as that in Si decreased toward zero. At 700 and 800C the damage in Si was below detectable levels, but the variable-energy positron annihilation spectroscopy response in the top Si layer in the silicon-on-insulator was consistent with the development of nanovoids.

The Evolution of Vacancy-Type Defects in Silicon-on-Insulator Structures Studied by Positron Annihilation Spectroscopy. P.G.Coleman, D.Nash, C.J.Edwardson, A.P.Knights, R.M.Gwilliam: Journal of Applied Physics, 2011, 110[1], 016104