Kinetics and mechanism of low-pressure,high-temperature oxidation of silicon-II

The reaction of oxygen at low pressures with silicon layers on tungsten ribbons was studied. An abrupt transition was observed between a condition of passivation, in which a thin film of SiO₂ formed at low temperatures, and a steady-state combustion condition at high temperatures. The latter state is characterized by the formation of volatile SiO. The boundary between these two states has been defined in terms of the pressure-temperature relation. Oxygen consumption in the combustion state is represented by first-order reaction kinetics with an activation energy of 13 ± 1 kcal/mole. The stability of the two states has been defined by a thermodynamic analysis of the SiO₂ layer stability. The oxygen consumption dependence on temperature has been described by a kinetic model which involves a consideration of the various elementary steps in the reaction.