Effect of Rare Gas Dilution on CH3 Radical Density in RF-Discharge CH4 Plasma

The behavior of the CH3 radical density in a parallel-plate RF CH4 plasma diluted with rare gases (He, Ne, Ar, Kr, and Xe) was investigated systematically using infrared diode laser absorption spectroscopy. The CH3 radical density increased in CH4/Xe and CH4/Kr plasmas with increasing rare gas dilution. The Xe* atom densities in the lowest metastable state 3 P 2 and the resonant state 3 P 1 were measured in CH4/Xe plasma through absorption spectroscopy using a Xe hollow cathode lamp in order to clarify the role of Xe* (3 P 2 and 3 P 1) atoms. It was shown that the increase in the CH3 radical density in CH4/Xe plasma was mainly caused by the collision of Xe* atoms with CH4 molecules.