The reactions of hydrocarbons on silicon and diamond surfaces and their role in the chemical vapour deposition of diamond

A range of surface sensitive probes including thermal desorption spectroscopy, Auger electron spectroscopy and low energy electron diffraction have been employed to investigate interfacial reactions on Si(100) and polycrystalline CVD diamond. The systems studied encompass the adsorption of CH4, C2H4, C2H2 and CH3I on Si(100) and the effect of atomic H on the adsorbed phases formed. The interaction of H2 and CH4 with CVD diamond has also been investigated. The chemistry observed is considered in the context of chemical vapour deposition (CVD) of diamond. Bound hydrocarbon species, both C2H4 and C2H2, are formed on Si(100) after flowing CH 4 over a hot filament. A conversion of adsorbed C2H 4 to C2H2 by atomic H abstraction is observed. Further atomic H abstraction enables catenation to occur giving rise to C3 forms. This formation provides direct experimental insight into the surface reactions which occur during the onset of hot-filament activated CVD diamond formation on Si. Abstraction by atomic H from directly adsorbed C2H 4 is found to give rise to adsorbed C2H2, which then undergoes C-C scission to form adsorbed CH2 groups when further exposed to atomic H. CH2 formation is also apparent when atomic H interacts directly with adsorbed C2H2. The importance of CH2 as surface intermediate in diamond CVD process is discussed. CH3I undergoes dissociation upon adsorption on Si(100) giving rise to surface CH3 and I. Comparison of the effect of atomic H on this adsorbed layer with the other systems indicates the relative efficiency of CH3 and C2H2 species in CVD diamond formation on Si. A preliminary investigation of a CH3 source is also described. The reactivity of polycrystalline CVD diamond surfaces with respect to the interaction with atomic H and activated CH4 suggests that single crystal diamond surfaces could provide useful model substrates for the investigation of diamond CVD processes