Frank Dislocations Generation and Behavior Investigation in PVT-Grown 4H-SiC Crystals

Threading mixed, screw, and edge dislocations (TMDs/TSDs/TEDs), as well as basal plane dislocations (BPDs), in 4H-SiC crystals are known to be harmful to the performance of power devices. Additionally, Frank dislocations and associated stacking faults formed by deflection of TSDs/TMDs during physical vapor transport growth are also deleterious. Using synchrotron x-ray topography of 4H-SiC off-axis and axial wafers, a systematic analysis has been carried out on the generation and behavior of Frank dislocations. The distribution of Frank dislocations has been found to be related to the as-grown surface shape of the boule. When the angle between the surface of the boule and the basal plane is larger than a critical angle of 7°~10°, the height of the macrosteps is large enough to deflect the TSDs/TMDs and form Frank dislocations. The conversion between TSDs/TMDs and Frank dislocations form different contrast on x-ray topographic images. Detailed analysis of the configurations of Frank dislocations and BPDs reveals that the stress field of Frank dislocations is large enough to affect the movement of BPDs in a layer of ~ 60 µm thick during crystal growth.