EFFECT OF OXIDE PRECIPITATE SIZES ON THE MECHANICAL STRENGTH OF CZOCHRALSKI SILICON-WAFERS

The effect of oxide precipitate sizes on the mechanical strength of Cz ochralski silicon (CZ-Si) wafers has been studied with emphasis on the mechanism of slip dislocation generation by oxide precipitates. Therm al stresses, which are larger than those set up in wafers during actua l device processes, were applied to two-step annealed wafers. It was d etermined by X-ray topography and transmission electron microscopy obs ervations that both platelet and polyhedral precipitates can generate slip dislocations when their size is larger than approximately 200 nm. With further experiments, it is concluded that the precipitates canno t generate slip dislocations during actual device processing when the precipitate size is smaller than 200 nm, and this conclusion is indepe ndent of the precipitate density. The stress concentration of compress ive thermal stresses applied to oxide precipitates should be the cause of slip dislocation generation. Three critical stress curves of slip dislocation generation were obtained for the wafers, in which the plat elet sizes are approximately 70 nm, 200 nm and from 330 nm to 490 nm.