Comparative study of methods for counting of dislocations in 4H-SiC

Three experimental techniques to determine the density of the three relevant dislocation types (basal plane, threading edge and threading screw) in SiC were investigated: etching by molten KOH with and without the addition of Na2O2 and X-ray topography. The applicability to implement these techniques for a reliable full-wafer scale analysis is tested experimentally. The limitations are found to be mainly determined by the feature sizes. Based on simple considerations, the range of acceptable sizes of the dislocation-related features is estimated. Etching with Na2O2 allows to distinguish between all three types of dislocations, but a reliable detection is difficult to set up due to a too large spread of etch pit size. Without the addition of Na2O2, TSD and TED cannot be distinguished, but etch pit sizes become more homogeneous, enabling robust etch pit detection over a wider range of dislocation densities. X-ray topography gives reliable results for TSDs and BPDs whereas the measurement of TEDs is limited.