The formation of grown-in defects, which were assumed to be O precipitates that formed during Czochralski growth, was investigated by means of infra-red light-scattering tomography. It was found that the density of the infra-red light-scattering defects decreased with decreasing crystal pulling rate. Also, the defects did not form just after solidification, but grew to a size that was detectable by light-scattering tomography during cooling to about 1100C. The defect density decreased during slow cooling at temperatures ranging from to 1500 to 1000C, while their size increased. The formation mechanism of the defects was considered in terms of interactions between O atoms and point defects. Account was taken of free energy changes and of the critical nucleus radius for O precipitation. It was suggested that the formation of the defects depended upon the vacancy concentration. In the case of a constant vacancy concentration, their density and size were governed by the cooling rate at temperatures ranging from 1150 to 1000C.

M.Hourai, T.Nagashima, E.Kajita, S.Miki, T.Shigematsu, M.Okui: Journal of the Electrochemical Society, 1995, 142[9], 3193-201