Diagnostics of inductively coupled chlorine plasmas : Measurement of Cl 2 ¿ and Cl ¿ densities

The absolute densities of positive ions ~Cl2 1 and Cl! are obtained over a 2–20 mTorr pressure range and 5–1000 W input radio-frequency rf power range in a transformer-coupled Cl2 plasma. The relative number density of Cl2 1 is measured by laser-induced fluorescence. These laser-induced fluorescence data are calibrated by Langmuir-probe measurements of total positive-ion density at low powers to yield absolute values for nCl 2 1 and are corrected for changes in rotational temperature with rf power. In turn, the nCl 2 1 data are used to determine the effective-mass correction for refined Langmuir-probe measurements of the total positive-ion density. The density of Cl is then the difference between the total positive-ion and Cl2 1 densities. For all the pressures, Cl2 1 is found to be the dominant ion in the capacitively coupled regime ~input powers below 100 W!, while Cl is the dominant ion at higher powers ~.300 W! of the inductively coupled regime. Experimental results are compared to those from a simple global model. This work is a continuation of a study that provides a complete set of experimentally measured plasma parameters over a broad range of conditions in a chlorine plasma, produced with a commercial, inductively coupled rf source. © 2000 American Institute of Physics. @S0021-8979~00!01718-7#