The evolution of vacancy-type defects in silicon-on-insulator structures studied by positron annihilation spectroscopy

Variable-energy positron annihilation spectroscopy (VEPAS) has been applied to the study of the formation and evolution of vacancy-type defect structures in silicon (Si) and the 1.5 mu m thick Si top layer of silicon-on-insulator (SOI) samples. The samples were implanted with 2 MeV Si ions at fluences between 10(13) and 10(15) cm(-2), and probed in the as-implanted state and after annealing for 30 min at temperatures between 350 and 800 degrees C. In the case of SOI 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 (V(n), n similar to 3) in the top Si layer of the Si and SOI samples were observed after annealing up to 500 degrees C; at higher temperatures, however, this response persisted in the SOI samples as that in Si decreased toward zero. At 700 and 800 degrees C the damage in Si was below detectable levels, but the VEPAS response in the top Si layer in the SOI was consistent with the development of nanovoids.