Adsorption and surface diffusion of silicon growth species in silicon carbide chemical vapour deposition processes studied by quantum-chemical computations

摘要

The effect chlorine addition to the gas mixture has on the surface chemistry in the chemical vapour deposition (CVD) process for silicon carbide (SiC) epitaxial layers is studied by quantum-chemical calculations of the adsorption and diffusion of SiH2 and SiCl2 on the (000-1) 4H–SiC surface. SiH2 was found to bind more strongly to the surface than SiCl2 by approximately 100 kJ mol−1 and to have a 50 kJ mol−1 lower energy barrier for diffusion on the fully hydrogen-terminated surface. On a bare SiC surface, without hydrogen termination, the SiCl2 molecule has a somewhat lower energy barrier for diffusion. SiCl2 is found to require a higher activation energy for desorption once chemisorbed, compared to the SiH2 molecule. Gibbs free energy calculations also indicate that the SiC surface may not be fully hydrogen terminated at CVD conditions since missing neighbouring pair of surface hydrogens is found to be a likely type of defect on a hydrogen-terminated SiC surface.