Thermodynamics analyses of the effect of CH3 and C2H2 on morphology of CVD diamond films

CH3 and C2H2 are the dominant growth precursors during chemical vapor deposition diamond process. The ratio of C2H2 to CH3 concentration will affect the growth orientation of diamond film. In this paper the dependence of C2H2 and CH3 concentrations on substrate temperature is calculated under 4 kPa pressure according to a non-equilibrium thermodynamic coupling model reported previously. The concentrations of C2H2 and CH3 increase when the substrate temperature rises. C2H2 concentration rises more highly. The dependence of the ratio of C2H2 to CH3 concentration ([C2H2]/[CH3]) on substrate temperature is also calculated. Diamond (111) and (100) facets growth is discussed with the ratio of C2H2 to CH3 concentration under various substrate temperatures and CH4 concentrations. With the increase of substrate temperature or CH4 concentration, the value of [C2H2]/[CH3] will rise. So the growth rate of diamond (111) facets controlled by C2H2 concentration is higher than that of diamond (100) facets controlled by CH3, and thus (100) facets appear. These results are well consistent with many experiments reported by other researchers. (C) 2000 Elsevier Science S.A. All rights reserved.