Vapour growth of silicon: growth anisotropy and adsorption

The development of facets on hemispherical single crystal substrates is investigated for growth in a near-equilibrium hot-wall CVD system, in order to study the orientation dependence of silicon crystal growth as a function of gas phase parameters in the Si-H-Cl system. It is found that only faces with indices {hhk} are stable. On the basis of their different behaviour as a function of experimental conditions, these faces are divided into {hhk}h k and {hhk}h < k faces. The {111} and {001} faces have to be considered separately. From the experimental dependencies it is concluded that the adsorption of chlorine and hydrogen plays a dominant yet ambivalent role: it stabilizes the {001} and the {hhk}h k faces, but destabilizes the {hhk}h < k faces. In order to explain these effects, it has to be assumed that under CVD conditions dimer-like reconstructions are present on all silicon faces. The interplay between surface dimer reconstructions and adsorption processes also shows up in the kinetic roughening of the different faces at high supersaturations. Theoretical calculations of the probabilities of adsorption of growth species on the different faces are used to explain the differences in kinetic roughening of these faces and the observed change in orientation of growth hillocks on the {111} faces which occurs when the supersaturation is increased.