Oxidation Studies of Crystalline CVD Silicon Nitride

Oxidation studies of CVD α ‐ Si 3 N 4 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 Si 3 N 4 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 SiO 2 and evolution of N 2 could not account for the much lower parabolic rate constants and much higher activation energy for Si 3 N 4 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 SiO 2 and Si 2 N 2 O was formed when Si 3 N 4 was oxidized. The intermediate Si 2 N 2 O scale was identified as a single‐phase material, not a physical mixture of Si 3 N 4 and SiO 2 . The low oxidation rate and high activation energy for Si 3 N 4 during the oxidation were attributed to the formation of Si 2 N 2 O and low oxygen diffusivity in this structurally dense phase.