ENHANCED OXYGEN PRECIPITATION IN ELECTRON-IRRADIATED SILICON

The precipitation of oxygen has been investigated for 2 MeV electron irradiated silicon samples, with irradiation doses 10(15)-10(18) cm-2, at an annealing temperature of 900-degrees-C for up to 444 h. The samples initially contained either different concentrations of the vacancy-oxygen (VO) center created at the irradiation, or the vacancy-dioxygen (VO2) center created by annealing at 350-degrees-C after the irradiation. It was found that the incubation time and oxygen decay rate for the precipitation process was irradiation dose dependent. Among the VO samples this could be caused by a supersaturation of vacancies, which would both decrease the critical precipitate radius and enhance oxygen diffusion. It was also found that an enhanced precipitation among VO samples appeared as a transient process, which has not been observed at this high temperature before. A different mechanism could account for the enhanced precipitation rate for samples with VO2. For these samples results from transmission electron microscopy studies, Wright etching, and growth of precipitate related infrared (IR)-absorption bands all indicate increased precipitate number densities. High temperature rapid thermal annealing shows that VO2 develops into VO2 + O(i). It is therefore suggested that the VO2 center is a nucleus for oxygen precipitation. Different incubation times were observed for the growth of the precipitate IR bands, which is explained by the appearance of differently shaped precipitate particles.