Initial oxide-growth process on the Si(100) surface

We investigate the initial growth of oxide on the Si(100) surface by means of first-principles molecular-dynamics calculations. By inserting oxygen atoms successively into the backbonds and the dimer bonds, the variation in surface geometry and in adsorption energy is studied. Once a backbond is oxidized, substitution at the rest backbond of the dimer atom gets much less favorable. The other bonds show a similar reactivity to that on the clean surface. Thus, the oxide growth of the first atomic layer proceeds rather uniformly until one monolayer coverage. This process seems compatible with the recent observation of layer-by-layer oxidation by scanning reflection electron microscopy [H. Watanabe et al., Phys. Rev. Lett. 80 (1998) 345]. However, the energetics of the second-layer oxidation lead to preferential inward growth rather than lateral growth. (C) 1999 Elsevier Science B.V. All rights reserved.