The plasma oxidation of CF4 in a tubular-alumina fast-flow reactor

Mass-spectrometric analyses were made of the plasma reactions of 50-W CF4 and CF4-O2 discharges as functions of pressure (0.15–0.6 Torr), flow rate (2–80 cm3/min) or the O2 level in the feed. Discharges were investigated both in the presence and absence of single-crystal Si. The products from CF4 alone were F, F2, and C2F6; in the presence of Si the products were SiF4, C2F6, and small amounts of F. The products from CF4-O2 were F, F2, COF2, CO2, and CO; in the presence of Si the products were SiF4, F, F2, COF2, CO2, and CO. The conversion of CF4 to products increased monotonically with residence time in the discharge and the O2 concentration in the feed. It appears that F2 was produced in the plasma zone and that the SiFx (x<4) species reacted with F2 to give SiF4.