Negative ion density in inductively coupled chlorine plasmas

Summary form only given, as follows. The negative ion density in radio-frequency (RF) inductively-coupled chlorine discharges has been inferred using laser photodetachment spectroscopy. A gaseous electronics conference (GEC) RF reference cell with an inductively coupled plasma source was used to produce the plasma. For this experiment, the chlorine pressure was between 20 and 50 mTorr and the RF power into the plasma was 150 to 250 Watts at 13.56 MHz. Light from a frequency quadrupled Nd:YAG laser (266 nm) was used to photodetach electrons from C1/sup -/. The time dependent excess electron density was then detected by a microwave interferometer operating at 80 GHz. Based upon the cross section for photodetachment and the measurement geometry, negative ion densities can be calculated. The inferred negative ion densities are at least an order of magnitude higher than the steady state electron density over the parameter space investigated. The dependence of the negative ion density on RF power, gas pressure, flow rate and RF phase will be discussed.