Three-dimensional structure of dislocations in silicon determined by synchrotron white x-ray topography combined with a topo-tomographic technique

We have studied the propagation and elimination of dislocations generated at the early stage of Czochralski silicon crystal growth using synchrotron white x-ray topography combined with a topo-tomographic technique. Two silicon crystals with [001] growth-axes were examined. One was intentionally grown without enlarging its diameter to easily observe the features of the dislocation propagation, and the other was grown with Dash necking, followed by a 2 inch enlargement of its diameter in order to observe the elimination of the dislocations. The three-dimensional structure of the individual dislocation, i.e. the direction of the dislocation line, its Burgers vector and the glide plane, were determined. These investigations revealed that dislocation half loops, which were generated from tangled dislocations, were expanded on their glide planes and were often deformed by their interaction, cross slip and collision with the crystal surface, followed by a gradual decrease in their density. The dislocation-elimination effect of the Dash necking was caused by the expansion of the dislocation half loops being terminated within the crystal and by their pinning on the crystal surface.