ABSOLUTE DENSITY DETERMINATION OF CH RADICALS IN A METHANE PLASMA

Laser-induced fluorescence was applied at the B-X transition of the CH radical to measure absolute densities of the CH radicals in an electron cyclotron resonance methane plasma. The absolute experimental uncertainty is only about 30% due to a new calibration procedure. The CH density correlates well with optical emission from the CH A-X and B-X transitions over a wide pressure range. Experimental results are in satisfactory agreement with predictions from a model based on rate equations for the electron-induced dissociation and ionization of the parent methane gas. This model also includes the interaction of the plasma species with the surrounding walls and the particle transport due to pumping.