Theoretical Studies on Surface Electronics States. Theory of Initial Oxidation Processes on Si Surface.

Abstract

Oxidation of the Si(001) surface, one of the most important processes in the modern Si technology, was studied by using the first-principles calculation technique with spin-polarized gradient approximation. The inclusion of spin degrees of freedom greatly suppresses the reactivity of an O2 molecule. As a result, at most sites, incoming O2 molecules do not show spontaneous dissociative chemisorption. The activation energy needed for direct oxidation increases from ca 1.0eV to ca 2.5eV, as the chemisorbed site becomes deeper from the Si surface. We found, however, there exist narrow channels, along which O2 molecules are chemisorbed onto the Si surface without extra energy. We have also clarified the apparent barrierless reaction mechanism of the backbond oxidation through diffusion of O atoms from the metastable site on the surface towards the backbond site.