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

Analytical models for growth by metal organic vapor phase epitaxy. I.Isothermal models

For a proper description of growth by metal organic vapour phase epitaxy the three-dimensional Navier-Stokes partial differential equations need to be solved which govern the following series of processes: (i) transport by diffusion and flow through the gas phase, (ii) reactions which take place in this gas phase, (iii) reactions which take place at the surface. The authors are at first interested in the medium- and higher-temperature regions, which cover the growth determined by diffusion through the gas phase (medium temperature) and the growth that is determined by the desorption of growth species (higher temperature). Using a number of well justified assumptions one can reduce the problem to a two-dimensional one. For the diffusion-limited region (i.e. medium-temperature region) the effect of different flow profiles (plug flow, parabolic flow, linear increasing velocity and combination of plug and linear profile) on the growth rate has been studied under isothermal conditions. It was found that all profiles yield the same growth rate within a few per cent, so that it suffices to use the simple plug flow profile in growth rate calculations. It is also shown that axial diffusion is an important effect only at the end of long reactors. Finally a model is derived in which surface reaction kinetics is combined with the diffusion-limited model for the isothermal case