Threading Dislocations in 4H-SiC Observed by Double-Crystal X-Ray Topography

Threading dislocations in 4H-SiC wafer were observed by using a double crystal X-ray topography technique. The incident beam was collimated by the first crystal so that the angular divergence was reduced to sufficiently smaller than the rocking curve of a diffraction of the specimen (the second crystal). At off-Bragg angles, cross-sectional projection of threading dislocations appeared on the topographic images. From these results, we found that outcrops of the screw dislocation at the wafer surfaces suffered from significant strain, giving strong contrast on the topograph even under the condition, $\vec{g}\cdot\vec{b}=0$. In addition, the edge and screw components in the mixed dislocations were clearly distinguished.