Dislocation-Related Etch Protrusions Formed on 4H-SiC (000-1) Surfaces by Molten KOH Etching
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0911-B05-22
Dislocation-Related Etch Protrusions Formed on 4H-SiC (000-1) Surfaces by Molten KOH Etching Masahide Gotoh1, Takeshi Tawara1, Shun-ichi Nakamura1, Tae Tamori2, Yoshiyuki Kuboki2, Yoshiyuki Yonezawa1, and Masaharu Nishiura1 1 Device Technology Laboratory, Fuji Electric Advanced Technology, 4-18-1, Tsukama, Matsumoto, Nagano, 390-0821, Japan 2 Material and Science Laboratory, Fuji Electric Advanced Technology, 1, Fuji-machi, Hino, Tokyo, 191-8502, Japan
ABSTRACT In this study, we investigated surface features formed by molten KOH etching of (000-1) substrates and epilayers, using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (TEM). We found the surface features formed on (000-1) are protrusions, in contrast to well-known dimples on (0001).
INTRODUCTION 4H-SiC has a wider band gap (3.26eV) and a higher breakdown field (2.5–3.0 MV/cm) than silicon, and is expected to realize high-power semiconductor devices with a MOSFET structure instead of IGBT. Recently, MOS devices fabricated on a (000-1) surface are taken notice owing to high channel mobility and oxidation speed [1]. In spite of extensive and intensive improvements in crystal quality of SiC, commercial SiC wafers still contain a large number of dislocations (104–105 cm-2) that cause degradation of electrical properties. For example, forward voltage degradation of SiC bipolar devices is caused by expansion of stacking faults originating from basal plane dislocations (BPDs) [2]; threading screw dislocations cause reduction in breakdown voltage of p-n junctions and Schottky barriers [3, 4]. For detailed investigation of dislocations, cross-sectional transmission electron microscopy (TEM) is a powerful technique, which, however, requires precise locations of the targeted dislocations. For a (0001) face, molten KOH etching is an easy way to recognize dislocations. Etch pits produced by molten KOH have already been correlated to several kinds of dislocations [5]. However, there are only a few studies about a (000-1) face. The anisotropy in etching rate by molten KOH etching, where the (0001) face is etched slowest and the (000-1) face is etched fastest, makes it much harder to reveal dislocations by the etching of a (000-1) face. Bondokov et al. reported using KOH vapor for etching, but quite high temperatures (900–1000°C) are needed to produce clear etch pits comparable to those on (0001) faces [6]. In this study, we investigated the surface features produced by molten KOH etching of 4H-SiC (000-1) faces. Varieties of surface features, difference between substrate and epitaxial layers, and types of dislocations are discussed.
EXPERIMENTAL The samples were diced into 1×1 cm2 chips from n-type 4H-SiC (000-1) substrates and epitaxial layers with 8° of off-axis toward . The net donor concentration of substrates was around 1018 cm-3. Three different donor concentrations (5.0×1016 cm-3, 3.7×1018 cm-3, and 2.4×1019 cm-3) were employed for the epilayers. The thickness of epilayers was typically 7–10 µm, with an excepti
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