Synthesis and purification of diamond films using the microwave plasma of a CO-H2 system

A variety of diamond films were deposited using the microwave plasma of a CO-H₂ system. Qualities of the synthesized films were correlated with the gas phase atomic hydrogen concentration monitored using optical emission spectroscopy. The amorphous components contained in the synthesized films were of a polyacetylene structure, which was possibly formed by the successive polymerization of C₂H₂ in the gas phase.Excess atomic hydrogen allowed highly crystallized diamond films to be deposited at high growth rates which included only a small amount of polyacetylene components. Two possible explanations for these results were proposed: the suppression of polyacetylene formation and the production of appropriate precursor (CH₃) for diamond synthesis under the excess atomic hydrogen condition.Finally, the ratioI_H/I_Ar (whereI is the optical emission intensity) was suggested as a decisive parameter indicating the suitability of the plasma conditions for the growth of pure diamond with good crystallinity.