The mechanical strength of wafers was investigated by using indentation methods. The sizes of rosette patterns which were generated during annealing (900C, 0.5h) were measured in as-grown float-zone and Czochralski wafers. It was found that the rosette size in float-zone wafers was larger than that in Czochralski wafers. The rosette size decreased as the -2/3 power of the interstitial O concentration (3.7 x 1017 to 1.6 x 1018/cm3), Oi, in Czochralski wafers. On the basis of the experimental results, it was concluded that wafers in which Oi numbered more than about 2 x 1017/cm3 had the ability to pin dislocations. The pinning effect of oxide precipitates and stacking faults was also investigated by using the indentation method. It was found that precipitates with a density of about 109/cm3 and an average size of less than some 500nm, did not affect the rosette size. On the other hand, stacking faults whose density was about 107/cm3 and whose average size was some 50μ, exhibited pinning effects.

M.Akatsuka, K.Sueoka, H.Katahama, N.Morimoto, N.Adachi: Japanese Journal of Applied Physics - 2, 1997, 36[11A], L1422-5