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0911-B01-05

Investigation of Dislocation Behavior during Bulk Crystal Growth of SiC Noboru Ohtani, Masakazu Katsuno, Masashi Nakabayashi, Hiroshi Tsuge, Tatsuo Fujimoto, Hirokatsu Yashiro, Mitsuru Sawamura, Takashi Aigo, and Taizo Hoshino Advanced Technology Research Laboratories, Nippon Steel Corporation, 20-1 Shintomi, Futtsu, Chiba, 293-8511, Japan ABSTRACT Dislocation behavior during physical vapor transport (PVT) growth of silicon carbide (SiC) single crystals has been investigated by defect selective etching and transmission electron microscopy (TEM). It was found that foreign polytype inclusions introduced a high density of basal plane dislocations at the polytype boundary, while in the polytype-transformed areas of the crystal, the density of medium size hexagonal etch pits due to threading screw dislocations was significantly reduced, indicating that the polytype transformation tended to cease the propagation of threading screw dislocations. Oval-shaped etch pit arrays observed on the etched vicinal (0001)Si surface, indicative of the dislocation multiplication in the basal plane, showed characteristic distribution around micropipes and low angle grain boundaries. Based on the results, we have argued dislocation behavior in PVT grown SiC crystals, suggesting that dislocation interaction and conversion are relevant processes to understanding the behavior. INTRODUCTION It is well-known that SiC crystal deficiencies are delaying the realization of outstandingly superior SiC power electronics. The efforts to date have centered on eradicating micropipes, and 4H-SiC substrates with extremely low micropipe densities (less than 1 cm-2) have been achieved. Nevertheless, SiC substrates and epilayers still contain several types of dislocations in densities to the order of thousands per square centimetres that are nearly 10000-fold micropipe densities. While not nearly as detrimental to SiC device performance as micropipes, it has recently been demonstrated that dislocations existing in SiC crystals degrade several characteristics of SiC devices, e.g., the forward bias characteristics of the SiC pin diodes and the gate oxide reliability of SiC MOSFETs. This paper investigates dislocation behavior during the growth of hexagonal SiC bulk crystals using defect selective etching and transmission electron microscopy (TEM). Particularly, we focus on the dislocation propagation and multiplication processes in 4H-SiC crystals grown by the physical vapor transport (PVT) growth method. EXPERIMENTAL 4H-SiC single crystals were grown by the physical vapor transport (PVT) growth (modified-Lely) method on a 4H-SiC (0001)C seed crystal. The growth conditions employed in this study were almost the same as those previously described [1], and the crystals were nitrogen-doped. The grown crystals were sliced approximately perpendicular to the growth direction into (0001)Si wafers off-oriented toward [1100] or [1120]. Chemical wet etching in molten KOH was used to reveal the types and distribution of

dislocations on the off-oriented (00