Gas-phase reactions in plasmas of SF6 with O2: Reactions of F with SOF2 and SO2 and reactions of O with SOF2

Abstract

The plasma chemistry of SF6/O2 mixtures is particularly complicated because of the large number of possible reactions. Over a wide range of conditions, products including SF4, SOF4, SOF2, and SO2F2 can be formed but thre is considerable uncertainty about the major reactions which contribute to the formation of these species. In this work reactions of oxygen atoms with SOF2 and fluorine atoms with SOF2 and SO2 have been studied in order to determine the principal sources of SO2F2 in these plasmas. Reactions were studied at 295 K in a gas flow reactor sampled by a mass spectrometer. No reaction could be detected between oxygen atoms and SOF2, which for the conditions employed, means that the upper limit for the reaction rate coefficient is 1×10−14 cm3 sec−1. The reaction of fluorine atoms with SOF2 was studied with the helium bath gas number density ranging from 3.1×1016 to 2.0×1017 cm−3. Within this range the rate coefficient increased with increasing [He] from (4.1 to 10.8)×10−14 cm3 sec−1. SO2 was found to react with fluorine atoms with a rate coefficient which appeared to be independent of the helium bath gas number density over the range given above. The possibility that this reaction occurred entirely on the walls of the reactor is discussed.