Trace Rare Gases Optical Emission Spectroscopy for Determination of Electron Temperatures and Species Concentrations in Chlorine-Containing Plasmas

Abstract

Trace rare gas optical emission spectroscopy has been used to obtain electron temperatures (Te) and percent dissociation of Cl2 in chlorine-containing, high-density inductively (transformer) coupled plasmas. In this method, a small amount of an equal mixture of the rare gases is added to the plasma and emission spectra that include lines from the rare gases are recorded. Modeling of the dependence of the rare gas emission intensities on Te allows Te to be derived from the best match between the observed and computed intensities. Te in Cl2 plasmas increases from 1.7 eV at 20 mTorr to 3.4 eV at 0.5 mTorr. These values are 1.3 to 1.8 times lower than those recorded with a Langmuir probe. This discrepancy is due at least in part to artifacts associated with using a single Langmuir probe in a reactor with semiinsulating walls. Absolute percent dissociations of Cl2 were determined by monitoring the intensity of an emission band of Cl2, normalized to emission from Ar and Xe. Cl2 percent dissociation increased with power and decreased with pressure. At 1.0 mTorr, Cl2 is about 85% dissociated at a power density of 0.1 W/cm3 and 95% dissociated at 0.3 W/cm3 in a Cl2 plasma. Addition of BCl3 to Cl2 increases the dissociation of Cl2.