Dislocations Preferentially Generated in Compressed Regions of Saddle-Shaped Deformed, Precipitation-Softened, Czochralski-Grown Silicon Wafers

Abstract

Distribution of dislocations in Czochralski-grown (CZ) silicon (Si) circular wafers thermally deformed in a saddle shape at 1273 K was investigated by using X-ray topography (for the bulk Si) and an etching technique (for the surface). In such deformed wafers softened by oxygen precipitation (density of oxide precipitates, including all secondary microdefects, was less than 2×1015 m-3), slip dislocations were preferentially generated and randomly distributed in the concave side (compressed region) of the wafer. This preference is due to the lattice mismatch between oxide precipitates and Si matrix, which causes internal stress that compresses the Si matrix and results in an externally applied stress to the concave side of the wafer. When the density of microdefects was less than 2×1013 m-3, slip dislocations were introduced along the <110> slip direction in a line from the top surface of the wafer to a neutral plane. At this density, dislocations were initiated at wafer surfaces where thermal stresses were the highest and then propagated into the neutral plane in both the concave and convex sides. Based on our results and on previous numerical analyses of the relationship between the critical stress required to multiply slip dislocations and the microdefect density, we developed a model that explains how slip dislocations multiply in saddle-shaped deformed wafers.