Optical emission diagnostics and film growth during microwave-plasma-assisted diamond CVD

High-resolution spectroscopy of atomic and molecular lines in a hydrogen-methane-argon plasma was used for the investigation of the gas temperature and the atomic hydrogen concentration as a function of process parameters (power, pressure, and methane concentration) during microwave-plasma-assisted CVD of oriented diamond films on silicon(100) substrates. Translational temperatures were derived from the Doppler broadening of H-2 lines and the H-alpha line. Rotational temperatures of H-2 as calculated from the Q-branch of the Fulcher-alpha system yield much lower temperatures which can be explained by theoretical considerations. Information about the changes in hydrogen concentration is obtained by actinometry, i.e. by relating the intensity of the Balmer lines to an argon line. The results are relatively independent of the choice of the Balmer and actinometer lines, except when varying the methane concentration. The diamond films show distinct changes in morphology with increasing microwave power or methane concentration. From the growth rate at constant methane content, limits for the activation energy of diamond growth have been derived by using a simple growth law which takes into account the influence of substrate temperature and gas phase activation. Microstructure formation at high temperatures is controlled by the growth competition between {100} and {111} facets, while twinning dominates in the low-temperature range.