KINETIC-ENERGY DEPENDENCE OF THE REACTIONS OF O+ AND O2+ WITH CF4 AND C2F6

Guided ion beam techniques are used to measure cross sections as a function of kinetic energy for reaction of O+ and O2+ with CF4 and C2F6. The predominant ions formed in these fluorocarbon systems correspond to dissociative charge-transfer reactions, with small amounts of FCO+ and F2CO+ being formed. The thresholds and shapes of dissociative charge-transfer cross sections are explained in terms of vertical ionization to various electronic states of CF4+ and C2F6+. In the O+ reactions, fluoride transfer to form CF3+ in the CF4 system and C2F5+ in the C2F6 system is also observed at thermal energies. The formation of carbon oxyfluoride ions in these systems is postulated to occur by insertion of the oxygen ions into C-F bonds of the fluorocarbon molecules. From the O2+ + CF4 and O+ + C2F6 systems, DELTA-(f)H(F2CO+) is determined. The relationship of these reactions to plasma deposition and etching is discussed.