DISSOCIATION AND PYROLYSIS OF SI2H6 ON SI SURFACES - THE INFLUENCE OFSURFACE-STRUCTURE AND ADLAYER COMPOSITION

The reaction of disilane, Si2H6, with the Si(100) and Si(111) surfaces has been examined with supersonic molecular beam scattering technique s. The emphasis has been on elucidating the reaction mechanism operati ve under conditions leading to steady-state Si epitaxial growth. Two r eaction mechanisms have been identified: (i) complete pyrolysis to for m two adsorbed Si atoms and gas phase hydrogen; and (ii) a reaction fo rming one adsorbed Si atom, gas phase hydrogen, and silane, SiH4, as a gas phase product. The relative predominance of these two channels is sensitive to surface structure, adlayer composition, and incident kin etic energy. In particular, only complete pyrolysis is observed on the clean Si(100)-(2 X 1) and Si(11)-''(1 X 1 )'' surfaces. The silane pr oduction channel, on the other hand, is observed on the Si(111)-(7 X 7 ) surface, and on the Si(100)-(2 X 1) surface in the presence of a fin ite coverage of either adsorbed hydrogen or phosphorus atoms. Examinat ion of the reaction dynamics reveals that the probability of complete pyrolysis increases with increasing incident kinetic energy. Angular-r esolved measurements of the scattered SiH4(g) product on the Si(111)-( 7 X 7) surface suggest that silane is formed from the reaction of a ch emisorbed intermediate. Comparison of the reaction probability of SiH4 and Si2H6 on the Si(111)-(7 X 7) surface as a function of incident ki netic energy suggests a similar decomposition mechanism for these two molecules, namely, Si-H bond activation. In this scenario, SiH4(g) is formed via unimolecular thermal decomposition of an adsorbed Si,HS(a) species. (C) 1995 American Institute of Physics.