Structure of Silicon Films Evaporated onto a Clean NaCl Substrate

Abstract

Silicon films, 30–300 Å in thickness, evaporated (using an electron beam evaporation technique) onto NaCl substrates cleaved in ultrahigh vacuum and held at 25–500 °C at various deposition rates (0.1–8 Å/sec) have been investigated by reflection electron diffraction and transmission electron microscopy. It was found that the structure and epitaxy of films were markedly influenced by the purity of the Si source, ambient pressure during evaporation, substrate surface condition, deposition rate, and substrate temperature. Decoration of imperfections of the substrate surface was obtained with Si deposited at relatively slow rate (0.1–0.3 Å/sec). Films produced on the substrates at 25–300 °C were amorphous. The amorphous to crystalline transition temperature was in the range of 300–400 °C. Epitaxial orientation of films (001)Si‖(001)NaCl with [100]Si‖ [100]NaCl was observed on the substrates at 400 °C at the slow deposition rate. The epitaxial films included microtwins with the twinning planes of {111}. The growth and structure of films were also influenced considerably by an electron beam bombardment applied to the substrate during evaporation.