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

The absolute densities of positive ions (Cl-2(+) 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 Cl-2 plasma. The relative number density of Cl-2(+) 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 n(Cl2+) and are corrected for changes in rotational temperature with rf power. In turn, the n(Cl2+) 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 Cl-2(+) densities. For all the pressures, Cl-2(+) 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. (C) 2000 American Institute of Physics. [S0021-8979(00)01718-7].