A study of nucleation in chemically grown epitaxial silicon films using molecular beam techniques III. Nucleation rate measurements and the effect of oxygen on initial growth behaviour

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Abstract
Epitaxial silicon layers have been grown on (111) silicon substrates by the pyrolysis of silane using a molecular beam method (Joyce and Bradley 1966). It has been shown that growth is completely inhibited in the presence of a surface oxide film. The removal of this film as SiO by silicon formed from the beam corresponds to an induction period which is observed before growth centres form. After completion of the induction period, the number density of growth centres rapidly reaches an equilibrium value. The centres then have a small size distribution, but with respect to position obey a Maxwellian distribution about a most probable separation distance. The equilibrium number density of centres follows an exponential dependence on substrate temperature and a power law dependence on beam intensity. The activation energy and order of reaction for the heterogeneous pyrolysis of silane on a (111) silicon surface have been determined mass spectrometrically. These results have been analysed in terms of a growth theory which assumes complete condensation with subsequent addition of adatoms to existing nuclei. From this analysis a value for the number of silicon atoms in the smallest stable nucleus was deduced, together with an activation energy for the surface diffusion of silicon on silicon.