Mass Spectrometric Study of Oxidation of SiC in Low-Pressure Oxygen

Passive-to-active oxidation transitions in chemical vapor deposited (CVD) SiC under low total pressures (0.8-440 Pa) in the temperature range 1250-1700°C have been investigated. A mass spectrometer sampling system equipped with a xenon image furnace was used to detect the transition points. As the temperature increased under fixed oxygen pressure, the ion current at 28, which corresponds to the partial pressure of CO(g) on the surface of CVD-SiC samples, indicated two distinct changes in the measured partial pressure of CO(g). One can be assigned to a transition from the passive oxidation to bubble formation and the other can be assigned to a transition from bubble formation to active oxidation. An explanation is proposed based on available kinetic and thermodynamic data for these.