OXYGEN ATOM ACTINOMETRY REINVESTIGATED - COMPARISON WITH ABSOLUTE MEASUREMENTS BY RESONANCE-ABSORPTION AT 130 NM

Resonance absorption at 130 nm was used to measure absolute oxygen atom concentrations in O2-containing distributed electron cyclotron resonance plasmas. The dissociation fraction [O]/[O2] in pure O2 plasmas (1-6 m Torr) was in the range of 0.01-0.06, but was significantly increased by the addition of SF6, N2 or Kr. At 2 m Torr total pressure a maximum [O]/[O2] of 0.3 was observed for 10% SF6 added. The results were compared to those obtained by optical emission actionometry measurements. The quantity I0 (844 nm)/I(Ar) (750 nm) (with 0.1 m Torr Ar added) was poorly correlated with [O] but well correlated with [O2]. This suggests that, for dissociation fractions lower than 0.1, dissociative excitation, O2 + e-->O* (3p 3P) + O, is the most important mechanism for the production of 844 nm emission.