Synthetic diamond particles and films were deposited on Si(100), Si (111), polycrystalline titanium, and MgO(100) from the decomposition of a gas mixture of $H_2$ and $CH_4$ using a hot-filament chemical vapor deposition (HFCVD) method. In order to obtain a fundamental information for the nucleation behavior of diamond, the role of carbide layer, the role of scratch, the effect of deposition parameters (filament temperature, substrate temperature, $CH_4$ concentration in $H_2$, flow rate, and pressure), and the role of atomic hydrogen have been studied.
The TiC was formed on titanium substrate during deposition. It was observed that scratches which existed on the initial Ti surface, disappeared after the TiC has formed; this TiC had a rough and porous structure. The TiC layer formed in this experimental condition did not influence the nucleation behavior of diamond. The nucleation behavior depended entirely on the initial surface condition of the Ti substrate, i.e., whether or not it was scratched with the diamond powder.
In order to understand the role of scratch for diamond nucleation, the Si (100) substrate surface was observed after scratching with diamond knife. A lot of stepped surface were generated and diamond particles were nucleated on stepped surfaces. It is believed that the changes in the surface nature due to the scratching process can create the new nucleation sites which has strong binding energies and that the formation of these new sites can alter the nucleation behavior.
The nucleation density increased with increasing flow rate(50-200 sccm), $CH_4$ concentration in $H_2$ (0.6-2.0 vol%), and pressure (10-60 Torr). This was attributed to the increase in the carbon-containing species which can contribute to the deposition with increasing flow rate, $CH_4$ concentration, and pressure. The nucleation density with increasing filament temperature (1800-2300 ℃) and substrate temperature (600-950 ℃) showed maximum, which was closely related to the substrate surface etching.
The nucleation density of diamond was decreased dramatically with increasing hydrogen treatment time prior to deposition. The etching of substrate surface was observed and enhanced with increasing hydrogen treatment time. These results were explained in terms of the etching of nucleation sites due to atomic hydrogen.
The changes in nucleation behavior of diamond with deposition condition can be explained in terms of the formation rate of adsorbed phase.