Preanneal effect on the ring-shaped distribution of oxygen precipitates in Czochralski-grown silicon

An anomalous ring-shaped distribution of oxygen precipitates in Czochralski-grown Si is investigated, using x-ray-diffraction topography and Fourier transform infrared spectroscopy. The appearance of the ring area, corresponding to a region of oxidation-induced stacking faults, strongly depends on the preanneal before the precipitation anneal at 1000 °C. The single precipitation anneal at an elevated temperature without any preanneal maintains the distribution of precipitation nuclei formed at 450 °C during cooling from crystal growth; however, the ring-shaped distribution is not affected by the existence of thermal donors. Therefore, it is concluded that the precipitation nuclei formed at 450 °C do not have any relationship to thermal donors.