Diamond Deposition and Behavior of Atomic Carbon Species in a Low-Pressure Inductively Coupled Plasma

Diamond was successfully synthesized by using H2-rich CH4/CO/H2 and H2-rich CH4/H2 inductively coupled plasmas at a pressure of 11 Pa. The ratio of particle size to deposition time, as a criterion of the diamond growth rate, in H2-rich CH4/CO/H2 mixture gas plasmas was higher than that in H2-rich CH4/H2 mixture gas plasmas. The deposits in H2-rich CH4/H2 and H2-rich CH4/CO/H2 mixture gas plasmas were found to contain nondiamond phases, as confirmed by Raman spectroscopy. In order to investigate the mechanism involved in diamond formation, C-atom densities in the plasmas were measured by vacuum ultraviolet absorption spectroscopy with a carbon hollow cathode lamp. In addition, CH, OH and H-atom emission intensities were measured by optical emission spectroscopy. As a result, it was found that the C-atom densities increased considerably with increasing mixture ratio of CO to CH4. On the basis of the correlation between the quality of deposits and the C-atom densities, C-atoms were determined to probably contribute to the formation of nondiamond phases in the deposits.