CHARACTERIZATION OF POINT-DEFECT GENERATION AT SILICON SURFACES USING GOLD DIFFUSION

The utility of observations of Au diffusion for the characterization of point defect generation and annihilation rates at surfaces and of vacancy distributions and diffusivity in the substrate is demonstrated. Particularly noted are the effects of ambient gases and surface finish on the diffusion process and on the resultant distributions of electrically active Au. Au was deposited on commercial float-zone Si in a vacuum system after the Si had reached the diffusion temperature (1233 K) and had been annealed in various ways. Contrary to a previously published report, electrically active Au with a one-sided profile is found when the Au is deposited and annealed in a vacuum. Previously reported two-sided profiles for electrically active Au are obtained when millitorr levels of O2 are present in the ambient gas during diffusion or during a preanneal prior to Au deposition. It is concluded that the polished or etched silicon surfaces lack the imperfections needed to make them effective sources or sinks for vacancies or self-interstitials, but that surface roughening caused by O2-induced evaporation of SiO is sufficient to create very effective sources or sinks.