Growth Mechanism of SiC CVD: Surface Etching by H₂, H Atoms, and HCl

Silicon carbide is a wide bandgap semiconductor with unique characteristics suitable for high temperature and high power applications. Fabrication of SiC epitaxial layers is usually performed using chemical vapor deposition (CVD). In this work, we use quantum chemical density functional theory (B3LYP and M06-2X) and transition state theory to study etching reactions occurring on the surface of SiC during CVD in order to combine etching effects to the surface kinetic model for SiC CVD. H₂, H atoms and HCl gases are chosen in the study as the most likely etchants responsible for surface etching. We consider etchings of four surface sites, namely CH₃(ads), SiH₃CH₂(ads), SiH₂(CH₂)₂(ads), and SiH(CH₂)₃(ads), which represent four subsequent snapshots of the surface as the growth proceeds. We find that H atoms are the most effective etchant on CH₃(ads) and SiH₃CH₂(ads), which represent the first and second steps of the growth. HCl and H₂ are shown to be much less effective than H atoms and produce the etching rate constants which are ∼10⁴ and ∼10⁷ times slower. In comparison to CH₃(ads), SiH₃CH₂(ads) is shown to be less stable and more susceptible to etchings. Unlike the first and second steps of the growth, the third and fourth steps (i.e., SiH₂(CH₂)₂(ads) and SiH(CH₂)₃(ads)) are stable and much less susceptible to any of the three etchants considered. This implies that the growth species become more stable via forming Si-C bonds with another surface species. The formation of a larger surface cluster thus helps stabilizing the growth against etchings.