CH3 and CH Densities in a Diamond Growth DC Discharge

A highly sensitive multi-element optical absorption technique is used to measure the absolute column density of both CH 3 and CH radicals in a dc hollow cathode plasma-assisted chemical vapor deposition (CVD) system with CH 4 and H 2 used as the input gases. The plasma gas temperature is determined at different spatial points using the H 2 emission spectrum near 460 nm. The spatial maps of the temperature and the radical densities provide information on the chemical processes taking place in the discharge. The CH 3 and CH radical density measurements made in the dc discharge system are compared with similar measurements made in a hot filament CVD system. The [H]/[H 2 ] ratio is derived from the CH 3 and CH densities using an analysis based on partial thermodynamic equilibrium of the single carbon hydrocarbon abstraction reactions.