DETAILED SURFACE AND GAS-PHASE CHEMICAL-KINETICS OF DIAMOND DEPOSITION

A chemical kinetic model is developed that includes detailed descriptions of both gas-phase and surface processes occurring in gas-activated deposition of diamond films on diamond (111) surface. The model was 'tested by simulating diamond film deposition in a hot-filament reactor using methane-hydrogen, methane-argon, and methane-oxygen-hydrogen gas mixtures. The gas-phase part of the model includes transport phenomena and predicts correctly the measured concentrations of major gaseous species. The surface part of the model reproduces the general experimental trends-the effects of temperature, pressure, initial methane concentration, and the addition of oxygen-for the growth rate and film quality. Analysis of the computational results revealed the factors controlling the growth phenomena. Among several reaction pathways describing deposition of diamond initiated by different gaseous species, including CH3 and several C2H(x) species, the H-abstraction-C2H2-addition mechanism appears to dominate. The key role of hydrogen and oxygen is identified to be the suppression of the formation of aromatic species in the gas phase, which prevents their condensation on the deposition surface. Activation of the growing surface by H atoms and gasification of sp2 carbon by OH radicals are other important factors. The developed model does not support the theory of preferential etching by H atoms advanced to explain the kinetic competition between diamond and nondiamond phases. Instead, it establishes the critical role of aromatics condensation and interconversion of sp2 and sp3 carbon phases mediated by hydrogen atoms.