We propose reactive gases, which can be easily decomposed, as the etching gas to avoid "greenhouse effects." In this article, the etching reaction between silicon and the trifluoro-acetyl-fluoride (CF3COF) gas is demonstrated, using a remote plasma at room temperature. The etching reaction is significantly enhanced by the addition of oxygen and remote-plasma excitation. The etch rate of silicon and oxide by CF3COF/O-2 is larger than that by CF4/O-2 and C2F6/O-2 at the same O-2 content. According to the optical emission study, however, the density of excited fluorine decreases in the plasma by the added oxygen into the CF3COF system. Photoelectron studies indicate that the major role of the additional oxygen is to remove the deposited fluorocarbon films from the surfaces.