Detection of Cl and chlorine-containing negative ions in rf plasmas by two-photon laser-induced fluorescence

Abstract

Chlorine atoms have been detected in rf etching plasmas of CClF3 and CCl2F2 with three-dimensional spatial resolution using a two-photon laser-induced fluorescence technique. The spin-forbidden 4p(4S0)–3p(2P0) transition is pumped by absorption of two 233.3-nm laser photons. Decay of the excited state results in 725–775 nm emission. Spatially resolved plasma concentration measurements under certain etching conditions indicate an anomalously large signal spike at the plasma/sheath boundary, an effect attributed to an aggregation of chlorine-containing negative ions which are also detected by this technique. The negative ions are detected by laser-induced photodetachment followed by two-photon excitation of atomic Cl.