Propagation mechanism of non-step-flow direction BPDs into 4H-SiC epitaxial layers and their stacking fault expansion behavior

Abstract

Basal plane dislocations (BPDs) are a primary reliability concern for SiC power electronics. Almost all BPDs propagating from the substrate to the epitaxial layer in 4H-SiC have line directions and Burgers vectors almost parallel to the step-flow growth direction. A novel and unexpected propagation mechanism of a BPD with the dislocation vectors 120° to the step-flow direction is reported. Direct imaging with multiple techniques, including after carrier injection, was performed to investigate the propagation mechanisms, microstructural analysis, and associated stacking fault (SF) expansion. It was found that the Burgers vector of this BPD was 13[2¯110] as opposed to the typical ±13[112¯0] and that its propagation was made possible through the interaction between the BPD and a threading mixed dislocation (TMD), which provided spiral growth steps in multiple directions. The interaction also causes the multiplication of SFs, which is described. Additionally, the TMD gets deflected on to the basal plane inside the epitaxial layer and forms a Frank + Shockley fault. The three physical mechanisms identified in SiC wafers increase a power device’s on-state resistance and reverse current leakage, thereby jeopardizing the device’s reliability.