Reverse Biased Electrochemical Etching of SiC-SBD
With development of very-low-micropipe-density substrate, reduction of other device killer defects becomes important for large size power devices. We employed reverse biased electrochemical etching (RECE) method in order to elucidate where the current leaks out in Schottky barrier diode. Low concentration 4H-SiC epi-layer with Al implanted guard rings was electrochemically etched under reverse bias voltage up to 400V in HF-based electrolyte. The surface of the substrate was observed with Nomarski microscopy before and after RECE. In guard ring area, holes appeared which are aligned toward off-direction of the substrate. The length of the aligned holes is about 25μm. The guard ring surrounding the holes were etched uniformly but limited as though there exists a boundary parallel to the steps. In Schottky contact area, not all but some of carrot defects showed an etched feature after RECE. Such etching features are also observed at different position without carrot. We consider that threading screw dislocation is one cause of leakage current in SBD. An etching feature like tangled strings also appeared. Its outer dimension is more than 1mm with thickness of about 50μm. The origin of tangled-string-like feature is not clear yet.
N. Wright, C.M. Johnson, K. Vassilevski, I. Nikitina and A. Horsfall
K. Nishikawa et al., "Reverse Biased Electrochemical Etching of SiC-SBD", Materials Science Forum, Vols. 556-557, pp. 419-422, 2007