The critical role of hydrocarbon source and growth optimization for high-quality thick 4H-SiC epitaxial layers

Abstract

The development of ultra-high power electronic devices based on 4H-SiC relies on the growth of high-quality thick epitaxial layers. Chloride-based chemical vapor deposition is preferred for this purpose, and in this study we show that optimizing the process also requires a careful selection of hydrocarbons as the carbon source. Propane, a common precursor, limits control over the C/Si ratio at high growth rates, leading to defects and even loss of crystallinity. In contrast, methane offers a wider window for C/Si ratio adjustment, enabling further optimization of the epitaxial growth process. Using methane, an optimal growth rate of $25\mu m$/h is identified at which the minority carrier lifetime is maximized. Additionally, a saturation limit for minority carrier lifetime is observed in layers exceeding a thickness of $\sim$ $100\mu m$. It is also shown that, although the formation of characteristic surface morphological defects is inevitable, their severity can be controlled by adding additional HCl or increasing the growth rate; however, at a cost of reduced minority carrier lifetime. The growth of $125\mu m$ thick epitaxial wafers with methane and propane demonstrates the advantage of using methane as the carbon source. This is evidenced by a smoother surface, better doping uniformity, and nearly double the minority carrier lifetime compared to the propane-grown wafer. These findings highlight the benefits of methane in growing thick 4H-SiC epitaxial layers for high-power devices.