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Growth Mechanism of SiC Chemical Vapor Deposition: Adsorption and Surface Reactions of Active Si Species

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journal contribution
posted on 06.12.2017, 00:00 by Pitsiri Sukkaew, Emil Kalered, Erik Janzén, Olof Kordina, Örjan Danielsson, Lars Ojamäe
Silicon carbide is a wide bandgap semiconductor ideally suitable for high temperature and high power applications. An active SiC layer is usually fabricated using halide-assisted chemical vapor deposition (CVD). In this work, we use quantum chemical density functional theory (B3LYP and M06-2X) and transition state theory to study adsorptions of active Si species in the CVD process on both the Si face and the C face of 4H-SiC. We show that adsorptions of SiCl, SiCl2, SiHCl, SiH, and SiH2 on the Si face likely occur on a methylene site, CH2(ads), but the processes are thermodynamically less favorable than their reverse or desorptions. Nevertheless, the adsorbed products become stabilized with the help of subsequent surface reactions to form a larger cluster. These cluster formation reactions happen with rates that are fast enough to compete with the desorption processes. On the C face, the adsorptions likely occur on a surface site terminated by a dangling bond, *­(ads), and produce the products which are thermodynamically stable. Lastly, we present the Gibbs free energies of adsorptions of Si atoms, SiX, SiX2, and SiHX, for X being F and Br. Adsorptions of Si atoms are shown to be the most thermodynamically favorable among all the species in the study. Among the halide-containing species, the Gibbs free energies (ΔRG°) from smallest to largest are observed in the adsorptions of SiX, SiHX, and SiX2, for X being the halides. The results in this study suggest that the major Si contributors in the SiC–CVD process are Si atoms, SiX (for X being the halide) and SiH.