First-Principles Analyses of O2 Molecules around Ultrathin SiO2/Si(100) Interface

Abstract

The microscopic structures and reaction mechanisms of O2 molecules at ultrathin SiO2/Si(100) interface are investigated based on first-principles total-energy calculations. It is found that the molecular-type oxygen is stable in the SiO2 region of the interface, while the O2 in the Si substrate dissociates and two Si-O-Si bonds are formed. It is also found that the O2 in the SiO2 region can directly react with the Si substrate. The energy barrier for its reaction (0.2 eV) does not correspond to (previously consented) severing process of interfacial Si-Si bonds, but to the formation of weak Si-O bonds between the O atoms of oxidant and the interfacial Si atoms: The hybridization of the oxygen-2p orbitals of the oxidant and the valence band states of the Si substrate is the principal factor of the reaction. The calculated results imply that other microscopic mechanisms such as accumulation of interfacial strain or its release mechanisms are involved in the interfacial reaction during Si oxidation.