Onset of slip in silicon containing oxide precipitates

Abstract

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 (108−1011 cm−3), and background oxygen concentrations (7.7×1017−10.35×1017 cm−3) using a bending technique with annular knife edges causing a biaxial stress distribution in the samples. The main advantage of the method we use is the possibility of detecting single slip events that may be caused by precipitates with special properties. We found that the stress level at which dislocation movement can be detected around precipitates depends mainly on the mean-precipitate diameter. The stress threshold at which dislocations begin to move can be increased by a thermal 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 prior to any external stress being applied. It has been shown that such heat treatments can lead to a mechanical strengthening of the wafers in certain circumstances.