Onset of slip in silicon containing oxide precipitates

We report a study of the behavior of dislocations at oxide precipitates in (001) Czochralski silicon wafers for different oxide-precipitate sizes (100 -600 nm), densities (10(8)-10(11) cm(-3)), and background oxygen concentrat ions (7.7x10(17)-10.35x10(17) cm(-3)) using a bending technique with annula r knife edges causing a biaxial stress distribution in the samples. The mai n advantage of the method we use is the possibility of detecting single sli p events that may be caused by precipitates with special properties. We fou nd that the stress level at which dislocation movement can be detected arou nd precipitates depends mainly on the mean-precipitate diameter. The stress threshold at which dislocations begin to move can be increased by a therma l treatment prior to application of an external stress. This effect is due to the diffusion of oxygen to the dislocations causing a locking effect and shows that the dislocations are associated with the oxide precipitates pri or to any external stress being applied. It has been shown that such heat t reatments can lead to a mechanical strengthening of the wafers in certain c ircumstances. (C) 2001 American Institute of Physics.