Oxidation studies of CVD α-Si3N4 were performed in dry oxygen, oxygen-argon, and oxygen-nitrogen-argon gas mixtures of various oxygen and nitrogen partial pressures at a total pressure of 1 atm at 1100°–1400°C. Parallel oxidation studies of single-crystal silicon were also conducted for direct comparison. It was observed that the oxidation of both Si3N4 and Si followed parabolic growth kinetics with activation energies of about 115 kcal/mol and about 30 kcal/mol, respectively. The formation of a single layer of SiO2 and evolution of N2 could not account for the much lower parabolic rate constants and much higher activation energy for Si3N4 than for Si during the oxidation. Detailed characterization of the oxidation scales using ellipsometry, step-by-step etching, SIMS, and XPS techniques indicated that a duplex oxidation scale consisting of SiO2 and Si2N2O was formed when Si3N4 was oxidized. The intermediate Si2N2O scale was identified as a single-phase material, not a physical mixture of Si3N4 and SiO2. The low oxidation rate and high activation energy for Si3N4 during the oxidation were attributed to the formation of Si2N2O and low oxygen diffusivity in this structurally dense phase.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry