Surface carbonization and nucleation during chemical vapor deposition of diamond

The model presented considers surface kinetics processes, such as adsorption/desorption of hydrocarbon radicals, thermal dehydrogenation, evaporation, and carbon insertion into silicon, together with the bulk diffusion equation. The calculations performed show that surface protrusions present preferential locations for diamond nucleation due to a superposition of diffusion fluxes of carbon that is able to decrease the carbonization time on the protrusion tips by an order of magnitude compared with the untreated surfaces. This mechanism allows us to explain a number of observations in which the diamond is found to nucleate on the tips of surface protrusions. It is suggested that the surface carbon increases adsorption energy for hydrocarbon species and their concentration in the adlayer, resulting in high supersaturation which provokes nucleation. The analysis also shows that increased methane concentration in the feed gas and lower substrate temperature provide conditions for surface nucleation without a preliminary carbonization stage. The resulting diagram, outlining the operational parameters for both nucleation modes (via or without carbonization) on a Si (1,0,0) surface, is given. (C) 1999 American Institute of Physics. [S0021-8979(99)01115-9].