Growth study and theoretical investigation of the ultrathin oxide SiO2-Si heterojunction

The local atomic structure of ultrathin gate oxides and its effect and that of the corresponding SiO2-Si interface on the band offset of a MOS structu re are investigated theoretically. To generate a physically realistic inter face, we perform a "direct oxidation" simulation using quantum molecular dy namics. The critical thickness at which the oxidation rate switches from be ing limited by chemical kinetics to being diffusion limited is estimated. A novel method is introduced to evaluate the band offset within local orbita l density functional theory. The valence band offset for the ultrathin oxid e is found to be smaller (by 0.3 eV) than that of oxides thicker than simil ar to 10 Angstrom in accord with the recent XPS results.