Unexpected Sources of Basal Plane Dislocations in 4H-SiC Epitaxy

Abstract

The suppression of degradation inducing basal plane dislocations (BPDs) in the critical drift layer of SiC power devices has occurred mainly by preventing BPDs in the substrate from propagating into the drift layer. As optimized epitaxial growth has produced drift layers free of BPDs over a large fraction of the wafer, other sources of BPDs have become important. Two alternate sources are discussed. The first is epitaxial inclusions, which mainly consist of grossly misoriented 4H-SiC. The local stress field around the inclusion introduces a cluster of BPDs. In low-BPD epitaxy, the outermost BPDs can glide centimeters forming halfloop arrays that have BPD segments along their whole length. The second source of BPDs not normally considered is BPDs that are converted to threading edge dislocation before reaching the drift layer. Experiments suggest that for high current levels and/or over time, device degradation is possible.