Behavior of laser scattering tomography defects along the radial and the in-depth directions in a CZ Si wafer with ring-OSF

The behavior of defects along the radial and the in-depth directions was st udied in P-type (100) Si wafers by using laser scattering tomography and pr eferential etching. In as-grown wafers, grown-in laser scattering tomograph y defects(LSTDs) were observed inside ring-oxidation-induced stacking fault s(ring-OSFs) with a density of about 10(6) ea/cm(3), and these defects were uniform with the depth from the wafer surface. After 4-step annealing, the distribution of the defect density was different from that of the grown-in LSTD density, which was greatly increased just inside and outside the ring -OSFs. It was found that this radial distribution depended considerably on the depth from the wafer surface. The characteristics of the radial distrib ution, which was of high density around a ring-OSF, were not obvious near t he surface, but were clear in the bulk because of the out-diffusion of oxyg en during the heat treatment. Besides, the defect density on and inside/out side a ring-OSF increased with the depth from the wafer surface while the d ensity at the wafer center was uniform with depth after a 4-step heat treat ment. This behavior is due to annihilation of the residual vacancies formin g oxygen precipitates. Therefore, the ring-OSF position in the radial direc tion could be defined from the results for the LSTDs measured below a depth of 24 mum from the wafer surface after 4-step heat treatment. This result corresponded to that of bulk micro-defects(BMDs) caused by using the prefer ential etching method.