Nucleation and growth studies of polycrystalline covalent materials

The chemical vapor deposition of different covalent polycrystalline materials—including diamond, silicon carbide, and carbon nitride—in stagnation flow reactors was rigorously simulated to determine the nucleation and growth mechanisms of these materials. Kinetic models were used to predict the rates of gas-phase and surface chemistry, the temperature and velocity profiles, potential gaseous film growth precursors, the time evolution of nucleation and intermediate layer formation, and the morphological evolution of continuous polycrystalline films. Numerical studies were also carried out to determine the dependence of the kinetics of nucleation and subsequent polycrystalline film growth on operating conditions.; The calculated results for carbon nitride deposition indicate that the experimentally measured bond types in the carbon nitride films must result from chemical bond rearrangement occurring on the deposition surface or in the bulk phase once gaseous film growth precursors, including C, CH₂ , CH₃, C₂H₂, N, NH, NH₂, HCN, and H₂CN, are adsorbed. Of these precursors, C and CH ₃ dominate the carbon contribution to carbon nitride film growth, and atomic nitrogen is the principal nitrogen bearing species. When the evolution rates of a silicon carbide intermediate layer and diamond clusters are calculated by accounting for gas-phase and surface reactions, surface and bulk diffusion, the mechanism for intermediate layer formation, and heterogeneous diamond nucleation kinetics, it is predicted that higher adsorption energies, in the range of 3.7 to 4.5 eV, lead to larger surface adatom densities, lower saturated nucleation densities, and larger silicon carbide intermediate layer thicknesses. The intermediate layer thickness becomes saturated while the growing diamond nuclei still cover a very small fraction of the silicon carbide. Reports of heteroepitaxial diamond nucleation without silicon carbide intermediate layer formation may be readily explained by a significant decrease in the intermediate layer thickness at lower substrate temperatures and at higher diamond nucleation densities. Further, the results of the morphology evolution model reveal that the crystallographic texture and surface morphology—surface roughness, film texture, and grain size—of polycrystalline silicon carbide films, as well as diamond films deposited on the silicon carbide layer, are strongly dependent upon the saturated nucleation density, the deposition condition, and film thickness.