EFFECT OF ADDED HYDROGEN ON THE RF DISCHARGE CHEMISTRY OF CF4, CF3H, AND C2F6

The products of 50-W 0.5 Torr rf discharges of CF4, CF 3H, C2F6, and mixtures of these gases with H2 were investigated as a function of mass-flow rate (5-80 STD cm3/min) or H2 concentration. In addition, the C 2F6 discharge was studied as a function of pressure (0.2-0.8 Torr) and power (50-200 W). Products from the CF4 discharge included F, F2, and C2F6; from CF3H: HF, CF4, C2F4, C2F6, C2HF and C2H2 were produced; from C 2F6: essentially CF4 and C2F 4. The addition of H2 to CF4 or C 2F6 gave the same products as those from CF3H. The product distribution was a function of H2 concentration. The extent of conversion of starting material was a monotonic function of the residence time in the discharge zone. A mechanistic rationalization follows: CF4e-⇄F +CF3 e-⇄F+CF2e -⇄F+CF. The various radicals formed underwent abstraction and recombination reactions. Addition of hydrogen altered the above equilibria as well as the nature of the discharge.