THE SIO2-SI3N4 INTERFACE .2. O-2 PERMEATION AND OXIDATION REACTION

Previous analyses of Si3N4 oxidation on the basis of diffusion control by a suboxide layer yielded impossibly high N-2 pressures. Those models assumed interfacial reactions as the oxidation mechanism. However, it is now thought that the oxidation process is in situ substitution of O for N in silicon oxynitride of graded composition rather than interfacial reaction. In this paper, diffusional and thermodynamic analyses appropriate to this mode of oxidation are developed for both the permeation and reaction aspects of oxidation; O-2 diffusivities are calculated from permeation energies;gas pressures in the oxide are derived from solution thermodynamics and found to be moderate.