4H-SiC 표면의 극성 및 오프컷 각도에 따른 다이아몬드 성장거동 연구

Abstract

In this study, we investigated the effects of surface polarity and off-cut orientation of 4H- SiC substrates on the growth behavior and interfacial characteristics of diamond layers grown by microwave plasma chemical vapor deposition (MPCVD). Owing to its ultra-wide bandgap (~5.5 eV) and superior thermal conductivity (~2000 W/m·K), diamond is a highly promising material for high-power and high-frequency electronic applications. However, limitations in homo-growth of diamond, substrate scalability and cost have driven interest in alternative substrate materials with favorable lattice compatibility and thermal properties. Among them, 4H-SiC offers a relatively low lattice mismatch (~18.2%) and high thermal and chemical stability. In this work, N-type 4H-SiC substrates with 0° and 4° off-axis orientations were prepared using both Si-face and C-face surfaces. Prior to growth, surface roughening was conducted through ultrasonic agitation in a solution of diamond powder (170–250 μm) dispersed in ethanol. Diamond growth was carried out using MPCVD at 1150 °C, 5 kW power, 120 Torr pressure, and 6% of CH₄/H₂ for 1 hour. Atomic Force Microscopy (AFM) and Optical Microscope (OM) confirmed that the C-face exhibited higher RMS surface roughness compared to the Si-face after roughening. Field- Emission Scanning Electron Microscopy (FE-SEM) revealed that diamond grains on the C- face were smaller but uniform, while those on the Si-face were larger with lower density. X-ray Diffraction (XRD) confirmed diamond crystallinity across all samples. The sharpest (111) peak was observed on the C-face with a 4° off-cut, suggesting improved crystal quality. Raman spectroscopy identified a G peak (~1520 cm⁻¹) on the Si-face, indicating the presence of a diamond-like carbon (DLC) interfacial layer. Transmission Electron Microscopy (TEM) - Fast Fourier Transform (FFT) patterns demonstrated polycrystalline features for all samples, but distinct diffraction spots on the 4° C-face implied locally better- aligned crystallites, supporting the XRD results. Hall effect measurements were performed only on the C-face samples due to the continuous diamond coverage; further validation is needed, and the electrical characteristics of the Si-face samples with interfacial DLC layers will be explored in subsequent studies. Conclusively, it clearly demonstrates that the surface polarity of 4H-SiC significantly affects the diamond growth mechanism. Nevertheless, the correlation between surface roughness (RMS) and growth behavior was not directly established in this study, suggesting the need for more quantitative and systematic investigation in future work.