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

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.