THE INTERACTION OF ATOMIC-HYDROGEN WITH ADSORBED ETHYLENE AND ACETYLENE ON SI(100)

The effect of atomic hydrogen on the adsorbed layers formed on Si(100) from ethylene and acetylene exposure has been studied using thermal desorption spectroscopy. Considerable changes in surface reactivity patterns have been measured, with surface conversion reactions being favoured over the competition between thermal decomposition and molecular thermal desorption that is apparent for these species in the absence of atomic hydrogen. Abstraction by atomic hydrogen from adsorbed ethylene is found to give rise to adsorbed acetylene, which then undergoes C-C scission to form adsorbed CH2 groups when further exposed to atomic H. These species associate to desorb as ethylene at a higher temperature than is measured for the molecular form. CH2 formation is also apparent when atomic H interacts directly with adsorbed acetylene. Surface addition reactions are observed leading to the formation of C3 species. The results are compared to the reactions which occur when Si(100) is exposed to hot filament activated methane-hydrogen mixtures and are discussed in terms of the surface intermediates which may play an active role in the initiation of thin film chemical vapour deposition of diamond on silicon.