Role of O(1D) in the oxidation of Si(100)

Abstract

Oxidation of silicon with neutral atomic oxygen species generated in a rare gas plasma has recently been shown to produce high-quality thin oxides. It has been speculated that atomic oxygen in the first excited state, O(1D), is a dominant reactive species in the oxidation mechanism. In this study, we investigate the role of O(1D) in silicon oxidation in the absence of other oxidizing species. The O(1D) is generated by laser-induced photodissociation of N2O at 193 nm. We find that, at 400 °C, O(1D) is effective in the initial stages of oxidation, but the oxide growth rate decreases dramatically past 1.5 nm. Oxide films thicker than 2 nm were not achieved regardless of oxidation time or N2O partial pressure (0.5–90 mTorr), indicating O(1D) cannot be a dominant reactive species in thicker rapid oxidation mechanisms. We suggest that quenching of O(1D) to O(3P) (ground state) during diffusion through thicker oxides results in drastically slower oxidation kinetics. In contrast, oxidation with a vacuum ultraviolet excimer lamp operating at 172 nm resulted in rapid oxide growth up to 4 nm. Thus, other species produced in plasmas and excimer lamps, such as molecular and atomic ions, photons, and free and conduction band electrons, likely play a dominant role in the rapid oxidation mechanism of thicker oxides (>2 nm).