A MIXED INTERFACE REACTION DIFFUSION CONTROL MODEL FOR OXIDATION OF SI3N4

The observed parabolic rate constants for the oxidation of Si3N4 at 1100 to 1400-degrees-C are 10 to 1000 times lower than those for the oxidation of silicon. Calculations are performed to determine parabolic rate constants from the existing oxygen tracer diffusivity values and from the diffusivity and solubility values of the dissolved diatomic oxygen. These calculations suggest that the rate oxidation is not controlled by oxygen diffusion. Instead, it is controlled by a mixed process involving reaction at the Si2N2O/SiO2 interface and nitrogen diffusion through SiO2. A detailed analysis indicates that the rate law can be nearly parabolic for this mixed control process.