A ROUTE FOR THE FORMATION OF CH2 SPECIES DURING DIAMOND CVD

The reactions of atomic hydrogen with ethylene and acetylene adsorbed on Si(100) have been studied. In the absence of atomic hydrogen, acetylene and ethylene display a comparatively simple surface chemistry, both adsorbing molecularly at low temperatures and dissociating irreversibly to gaseous hydrogen and surface carbon as the temperature is raised. This situation changes dramatically in the presence of atomic hydrogen, which stimulates C-H and C-C bond making/breaking processes. It is observed consequently that adsorbed ethylene is converted to acetylene and ultimately to adsorbed CH2 species in the presence of an atomic hydrogen flux. Acetylene is similarly converted to CH2 species, which are found to react with acetylene to produce volatile C-3 hydrocarbons. The work provides experimental insight into the nature of the reactions of atomic hydrogen within hydrocarbon phases adsorbed on semiconductor surfaces, which play an important role in CVD diamond nucleation and growth.