Reactive ion etching (RIE) of poly-beta-SiC was investigated in the NF3/O-2 mixture gas plasma. The addition of 10% oxygen concentration to the NF3 plasma increased the etching rate to similar to 80 nm/min at a total pressure of 10 Pa and 997. nm/min at a total pressure of 20 Pa. The ratio of increase in etching rate against that in the pure NF3 plasma was similar to 43%. RIE for longer than 30 min in the 90% NF3 and 10% O-2 mixture gas plasma gave a much smoother surface than that etched in the pure NF3 plasma. However, the further addition of O-2 decreased the etching rate. Optical-emission spectra indicated the presence of an oxygen radical, in addition to fluorine radical and molecular nitrogen cations, in the NF3/O-2 mixture gas plasma. X-ray photoemission spectroscopy analysis of the etched samples revealed that the SiO2 layer was formed on the surface at the higher O-2 concentration. The role of oxygen in the NF3/O-2 mixture gas plasma was elucidated. Scanning electron microscopy observation revealed that many thornlike substances, i.e., spikes, were formed on the SiC surface during RIE at the total pressure of 10 Pa. Images of the cross section, of spike formed during RIE at the total pressure of 2 Pa also indicated that the sputtered aluminum particle from a mask may be preferentially deposited on the top of carbon-rich island formed on the SiC surface and act as a micromask together with carbon on the carbon-rich island to form a thornlike spike. An etching model of the SiC surface and the mechanism on formation and growth of the spike on the SiC surface in the NF3/O-2 mixture gas plasma are proposed. (c) 2007 American Vacuum Society.