Silicon carbide (SiC) is a promising semiconductor material for fabricating a high voltage power device. SiC has several polytypes such as 3C-SiC, 4H-SiC and 6H-SiC. In particular, 3C-SiC-based MOSFET shows higher channel mobility compared to other polytype because of low density of interface traps between SiO2/SiC ^[1]. We have developed the bulk growth technique of high quality 3C-SiC using top-seeded solution growth (TSSG) method. For the development, the most important issues were the polytype control of 3C-SiC and the elimination of double positioning boundaries (DPBs). In this paper, we review our trials for them: the kinetic approach of the polytype-selective growth and the elimination of DPBs by utilizing the step advance velocity depending on crystal orientation.

(1) Selective growth of polytype 3C-SiC is often grown on Si, 4H-SiC or 6H-SiC heteroepitaxially because of the lack of a high quality 3C-SiC bulk crystal. However, various polytypes can grow simultaneously during 3C-SiC growth on hexagonal SiC. In this study, we have achieved the selective growth of 3C-SiC single polytype by using the difference of growth rate among the polytepes. On the growth of 3C-SiC on the (0001) plane of hexagonal SiC seed, the 3C-SiC could grow via 2D nucleation mode, whereas the hexagonal polytype could grow via spiral growth mode from screw dislocations in the seed. Each polytype has the supersaturation dependence of growth rate as shown in Figure 1 ^[2]. This graph means that 6H-SiC preferentially grows in the range of A, and 3C-SiC grows in the range of B. In actual, we demonstrated the 3C-SiC growth regulating the supersaturation in TSSG method. At a higher supersaturation, only 3C-SiC grew on 6H-SiC seed. In contrast, at a lower supersaturation, 6H-SiC overgrew 3C-SiC ^[3]. Moreover, we performed the bulk crystal growth of 3C-SiC, of which the size 10×10 mm² and the thickness is approximately 1 mm in the maximum ^[4]. The conventional method of growth polytype control, e.g. step-controlled epitaxy ^[5], is based on the concept of the inheritance of stacking sequence. In contrast, our method based on growth kinetics is quite different from conventional techniques.

(2) Suppression of double positioning boundary Two twinned variants of 3C-SiC can grow on hexagonal SiC (0001) plane and DPBs are formed between them. The DPBs is the critical issue because they cause a leakage current. When 3C-SiC domain grows by the step-flow growth toward [1-100] of hexagonal SiC, the step of each variant advances toward [11-2] and [-1-12]. The step velocity of each variant is different from each other due to the discrepancy between their atomic structures. Therefore, the grown surface could be covered with the variant of higher step advance velocity as shown in Figure 2. In actual, we performed the 3C-SiC growth on 6H-SiC off-oriented toward [1-100] by TSSG method. Consequently, we obtained the DPB-free 3C-SiC with a range of about 10 mm².

This study was supported by a Grant-in-Aid for JSPS Fellows (22·8543), Industrial Technology Research Grant Program in 2007 from NEDO, and Adaptable and Seamless Technology Transfer Program through targetdrive R&D from JST.

Reference

1) H. Uchida et al., Mater. Sci. Forum, 717-720 (2012) 1109,

2) K. Seki et al., J. Cryst. Growth, 335 (2011) 94,

3) K. Seki et al., J. Cryst. Growth, 360 (2012) 176,

4) K. Seki et al., Mater. Sci. Forum, 740-742 (2013) 311,

5) H. Matsunami et al., Mater. Sci. Eng: R, 20 (1997) 125.

Figure 1. 3C-SiC and 6H-SiC have the different supersaturation dependence of growth rate. The 6H-SiC preferentially grows in the supersaturation range of A, whereas 3C-SiC grows over the 6H-SiC in the range of B.

Figure 2. Two variants of 3C-SiC have the different step velocity toward [1-100] of hexagonal SiC seed crystal. The variant growing faster (blue) grows on the other (red).

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