Growth Control of Epitaxial Graphene and SiC Film for Remote Epitaxy

In remote epitaxy, epitaxial films can grow on compound semiconductor substrates through 2D materials and be transferred from the substrates to others [1]. This technique is effective for cost reduction of wafer process because it enables the reuse of the expensive substrates. SiC is one of the most promising materials for next generation of power transistors [2], and application of remote epitaxy to SiC is needed for the development of semiconductor industry. Graphene can be grown on SiC directly by thermal decomposition of SiC substrates (generally in atmospheric pressure or vacuum) [3], and these composite substrates are ideal for SiC remote epitaxy. However, step-bunching arises during annealing SiC substrates in graphene growth processes. This phenomenon leads to rough surface of the substrates, and these are not suitable as epi-ready substrates.<br/> In this study, we show an effective technique to suppress the step-bunching during graphene growth. We prepared 4-degree off-cut (in the [11-20] direction) 4H-SiC (0001) substrates. The growth process is divided into two steps: step-bunching suppression (step1) and graphene growth (step2). In the first step, the SiC substrates are annealed in vacuum atmosphere to grow only graphene buffer layer (so-called zero-layer graphene). Since decomposition of SiC occurs from low temperature in this condition, the buffer layer can grow with almost no step-bunching. In the second step, the substrates are annealed in Ar atmospheric pressure at higher temperature than step1. The pre-covered buffer layer effectively suppressed the step-bunching, and graphene grown in the atmospheric pressure has good controllability of the number of layers.<br/> Next, we investigated the SiC growth on graphene/SiC substrates. Propane and silane are used as gas sources to produce SiC. To understand the effects of the gases on graphene, single gas of each source was flowed on graphene at 1300°C and more. These experiments revealed that silane can react with graphene to be SiC in high temperature though propane has little effect on etching of graphene. SiC growth experiments were carried out after these investigations, and we confirmed Si poor condition is needed for survival of graphene especially at the beginning of SiC growth. Our simulation of vapor phase reaction also supports the experiment results. Although complete balance of growth and etching of graphene in SiC growth process have not been achieved, these results will be a great help for future SiC remote epitaxy studies. This work was partly implemented under a joint research project of Tsukuba Power Electrics Constellations (TPEC).<br/><br/>[1] Y. Kim, <i>et al</i>., Nature, <b>544</b>, 340-343 (2017).<br/>[2] M. Bhantnager and B. J. Baliga, IEEE Trans. Electron Devices <b>40</b>, 645 (1993).<br/>[3] C. Berger, <i>et al</i>., J. Phys. Chem. <b>708</b>, 19912 (2004), C. Virojanadara, et al., Phys. Rev. B <b>78</b>, 245403 (2008).