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 mode ls assumed interfacial reactions as the oxidation mechanism. However, it is now thought that the oxidation process is in situ substitution o f O for N in silicon oxynitride of graded composition rather than inte rfacial reaction. In this paper, diffusional and thermodynamic analyse s appropriate to this mode of oxidation are developed for both the per meation and reaction aspects of oxidation; O-2 diffusivities are calcu lated from permeation energies;gas pressures in the oxide are derived from solution thermodynamics and found to be moderate.