ATOMIC CARBON VAPOR AS A DIAMOND GROWTH PRECURSOR IN THERMAL PLASMAS

A detailed surface chemistry mechanism is proposed for chemical vapor deposition of diamond films, which extends the growth-by-methyl mechan ism proposed by Harris to treat any CH(m) radical, m = 0-3, as a growt h monomer. Numerical computations were performed in which the mechanis m was coupled to a model for the boundary layer above the substrate, f or conditions typical of diamond deposition in an atmospheric-pressure thermal plasma. The predicted linear growth rate increases strongly a s the boundary layer thickness delta is decreased and the results indi cate a strong dependence of the diamond growth chemistry on delta. For relatively thick boundary layers (modest velocities of the reactant j et) growth is dominated by CH3. For very thin boundary layers (high ve locities) the model predicts that growth is dominated by C. For the tr ansition region where C and CH3 each contribute about 40% to growth, C H2 abo contributes about 17%. The carbon conversion efficiency is also predicted to peak in the transition region, and drops sharply for ver y thin boundary layers.