Step selectivity of the oxidation on Si(001) surfaces
B. D. Yu
Department of Physics, University of Seoul, Seoul 130-743, Korea
Oxidation of silicon surfaces has attracted much attention as one of the most important processes in current and future Si technology. Particularly, control of initial reactions of oxygen with Si surfaces on atomic scale is one of important issues required for better stability and function of Si devices. In this work, we report possible oxygen adsorption structures and oxidation reaction at single-layer steps of Si(001) using first-principles total-energy calculations based on density-functional theory (DFT). In the calculations, we used a (1,1,19) vicinal surface. On each terrace, the orientation of the reconstruction is different, resulting in the formation of alternate single-layer SA and SB steps. By employing the DFT calculations, we found that oxygen molecules are preferentially incorporated into sites at the SB step edges. The resulting oxidation structures consist of -Si-O- chain structures along the step edge, thereby eliminating the energetically unfavorable step-edge dangling bonds. Our results and analysis of the preferential oxidation at the rebonded SB step provides a natural explanation for the experimental observation that the rebonded step edge acts as strong sink for the oxidation of Si.