Diagnostics of inductively coupled chlorine plasmas: Measurement of Cl2+ and Cl+ densities

The absolute densities of positive ions (Cl2+ 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+ 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 nCl2+ and are corrected for changes in rotational temperature with rf power. In turn, the nCl2+ 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+ densities. For all the pressures, Cl2+ 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.