Competitive Etching and Oxidation of Vicinal Si(100) Surfaces
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Competitive Etching and Oxidation of Vicinal Si(100) Surfaces Marvin A. Albao1,2, Da-Jiang Liu1, Cheol H. Choi1,5 , Mark S. Gordon1,3, and J. W. Evans1,4 1 Ames Laboratory – U.S. Department of Energy, and Departments of Physics and Astronomy2, Chemistry3, and Mathematics4 Iowa State University, Ames, Iowa, 50010 5 Department of Chemistry, Kyungpook National University, Taegu 702-701, South Korea ABSTRACT Exposure of a vicinal Si(100) surface to oxygen at around 550 C produces etching-mediated step recession. In addition, some oxide islands are formed which locally pin receding steps. We develop an atomistic lattice-gas model for this process which accounts for the interplay between oxygen surface chemistry (adsorption, diffusion, oxide formation, and etching via SiO desorption) and the silicon surface and step dynamics (anisotropic diffusion and aggregation of di-vacancies formed by etching, and ad-dimer attachment-detachment dynamics at steps incorporating anisotropic energetics). Kinetic Monte Carlo simulation of this model produces step morphologies retaining some qualitative but not quantitative features of their equilibrium structure (alternating rough SB steps and smooth SA steps), except for pinning which produces protruding “fingers”. These features are seen in Scanning Tunneling Microscopy studies. INTRODUCTION Oxygen can react with silicon surfaces to produce either etching, described by the mechanism Si(solid) + ½ O2(gas) → SiO(gas) + surface vacancy, or alternatively surface oxide formation, described by Si(solid) + O2(gas) → SiO2(solid) [1]. Significantly, the formation of oxide islands on the surface protects or passivates the underlying Si from etching. At high surface temperatures (T), the lifetime of surface oxygen is small since SiO desorption is rapid, and etching or “active oxidation” dominates [2]. At low T, SiO desorption is effectively inoperative resulting in immediate oxide formation or “passive oxidation” [3]. For moderate T around 500 -700 C, and for typical oxygen pressures, there is a competition between both etching and oxide formation which can lead to complex surface morphologies [4-8]. Typical silicon surfaces are not perfectly flat, but crossed by arrays of steps [4,9]. Etching produces surface vacancies (primarily di-vacancies), anisotropic diffusion of which mediates nucleation and growth of vacancy pits on broad terraces, and which also produces step recession when these vacancies reach step edges [10]. Simultaneous formation of oxide islands produces pinning centers which interfere with this step recession process [4,5]. Many of these features are revealed in Scanning Tunneling Microscopy (STM) studies [4-7]. Thus, we are motivated to develop an atomistic model which can describe simultaneous etching and oxidation of vicinal Si(100) surfaces. Our goal is to elucidate the interaction between the surface chemistry of etching and oxidation, and the Si(100) surface step dynamics. The output of the model will be a detailed characterization of the complex morphology of the et
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