The mechanism of slip dislocation generation by oxide precipitates was studied by applying thermal stresses to 2-step annealed Czochralski wafers. It was found, using X-ray topography, that slip dislocations in the center of the wafers were generated during withdrawal, while those in the peripheral regions were generated on insertion. Transmission electron microscopic observations showed that oxide precipitates rather than punched-out dislocations were the nuclei of slip dislocations. Compressive thermal stress concentrations at oxide precipitates were suggested to be the cause of slip dislocation generation. The effect of precipitate size upon the mechanical strength of Czochralski wafers was studied by applying thermal stresses which were far higher than those normally set up in wafers. It was found that both platelet and polyhedral precipitates could generate slip dislocations when their size was greater than about 200nm. It was concluded that the precipitates could not generate slip dislocations during device processing if the precipitates were smaller than 20nm; regardless of the precipitate density.

K.Sueoka, M.Akatsuka, H.Katahama, N.Adachi: Solid State Phenomena, 1997, 57-58, 137-42