Simulation of porous silicon formation and silicon epitaxy on its surface

Processes of porous silicon formation and silicon epitaxy on its surface are studied using the Monte Carlo method. The model for porous silicon formation under anode etching allows for non-uniformity of charge distribution over the silicon-electrolyte interface. Processes of diffusion, generation and recombination of holes, as well as dimensional quantization, are also considered. Gilmer's model, extended to the case of a rough surface, is used to study epitaxy. The structures obtained by simulations at different levels of doping of the crystal substrate and for various parameters (temperature, HF concentration, and anode current density) are presented. Analysis of nanoporous structures showed that the porosity changes with depth, and fractal dimensionality exists below 10 nm. It has been shown that epitaxy, developing by formation of metastable nuclei at the edges of pores, by their subsequent growth along the perimeter and by formation of a thin continuous overhanging layer, may be described within the framework of this model. Three-dimensional images of near-surface layers formed at different stages of epitaxy have been obtained. The dependence of the epitaxy kinetics on the amount of deposited silicon for different structure porosities has been revealed. ©1999 Kluwer Academic/Plenum Publishers.