Oxygen and fluorine atom kinetics in electron cyclotron resonance plasmas by time-resolved actinometry

The kinetics of O and F atoms in O₂-based plasmas has been studied by time-resolved optical emission spectroscopy (actinometry) in modulated plasmas. The sticking coefficient α_O of O atoms on the stainless-steel reactor walls was 0.09±0.01 in O₂ plasmas containing fluorine (added as either SF₆ or F₂), but was about 0.5 in a pure O₂ plasma. This explains the significant increase in steady-state O density as a few percent of fluorinated gas is added. The corresponding value for F atoms, α_F, was 0.06±0.01, almost independent of conditions. The method also indicates the relative importance of the different electron-impact-induced mechanisms (direct excitation of ground-state atoms and dissociative excitation of feedstock molecules) for the production of emitting atoms [O 3p³P (844 nm) and F 3s²P (703 nm)] in plasmas. These results show that the widely used (steady-state) actinometry technique using 844-nm emission from O 3p ³P atoms is an unreliable measure of ground-state [O] variations.