Kinetics of Thermal Growth of Silicon Dioxide Films in Water Vapor‐Oxygen‐Argon Mixtures

Abstract

The kinetics of growth of silicon dioxide films in mixtures of water vapor, oxygen, and argon have been studied in the range of water partial pressures from 4.6 to 355 Torr and the temperature range 850° to 1217°C. A combined linear‐parabolic law of growth adequately represents the data over the complete region of temperatures and partial pressures studied. In the absence of oxygen, the linear and parabolic growth constants have first order dependence on the water vapor pressure at low pressures. In the case of the parabolic constant a saturation effect is evidenced by strong negative deviations from the first order law at higher water vapor pressures. This deviation is explained in terms of an adsorption isotherm at the oxide surface. The adsorption calculated from the growth behavior accurately fits the Langmuir adsorption isotherm. The apparent activation enthalpies of the parabolic and linear rate constants are 1.1 ev and approximately 3.3 ev, respectively, over the region of linear dependence upon the water vapor pressure. The enthalpy change calculated from the temperature dependence of the Langmuir adsorption isotherm is near zero. The measured enthalpies correspond to a superposition of the enthalpies of adsorption, desorption, generation of active sites for adsorption, and diffusion through the oxide film. The data do not enable the resolution of these several enthalpies. In the mixed water, oxygen argon ambient, the effect of introducing small vapor pressures of water at fixed oxygen partial pressure is to catalyze that part of the total growth rate due to the presence of oxygen. Higher vapor pressures of water repress the oxygen contribution to the growth rate at 850°. The latter effect was not observed at 1000°C over the partial pressure range investigated.