A THEORETICAL-STUDY OF THE INITIAL-STAGES OF SI(111)-7X7 OXIDATION .1. THE MOLECULAR PRECURSOR

We have studied the initial stages of the oxidation of the Si (111) su rface using extended Huckel tight-binding calculations. Due to the dif ferent dangling bond sites present on the reconstructed Si(111)-7 X 7 surface, one may expect more than one molecular precursor or dissociat ed Si-O configuration to be formed. As candidates for the main and kin etically most stable molecular precursor, structures involving O2 asso ciated with a single Si adatom site are proposed. Bridge structures ar e found to be less stable. However, dissociated species derived from b ridge structures play an important role in the oxidation process. In t his paper we introduce the computational approach used, and discuss th e nature of the molecular precursors. In a second paper the nature of the atomic oxygen containing products and the mechanism of SiO4 format ion are discussed.