Atomic chlorine concentration and gas temperature measurements in a plasma etching reactor

The technique of diode laser absorption has been used to measure gas temperatures and atomic chlorine concentrations in a Cl2 glow discharge. The infrared transition used is between the 2P1/2←2P3/2 spin-orbit levels and occurs at 882.36 cm−1. The measured atomic chlorine translational temperature was 770±100 K, and was relatively independent of plasma conditions over the range studied. This temperature was confirmed by an analysis of the rotational band shape of nitrogen second-positive emission which yields a nitrogen rotational temperature. Measured atomic chlorine concentrations ranged from 1.8×1014 to 6.6×1014 cm−3, representing atomic chlorine fractions from 3% to 8%. Atomic chlorine concentration increased with both increasing discharge power and pressure.