Studies of porous silicon aging by ellipsometry

Abstract

Polarization characteristics of the film formed on porous silicon sample surface after its fabrication by electrochemical monocrystalline silicon etching have been studied by the method of multiple-angle-of-incidence ellipsometry which allows, in a number of cases, to determine the parameters of those parts of the reflecting system, which forms the reflected wave. Consequently, of the film existence, a strong ellipsometric parameter tanψ maximum appearing at a certain angle of light incidence on the sample was found. This means that the p-component of the electric field vector in the reflected beam significantly exceeds the s-component and as a result, the reflected light is predominantly p-polarized. Over a long period of observation the maximum gradually decreases in amplitude and a minimum appears instead it. It is assumed that the ellipsometric phenomena observed are due to time changes in characteristics of the film formed as a result of silicon and electrochemical reactions products interaction with atmospheric oxygen. Dependences of ellipsometric parameters on the angle of incidence are approximately described by two-layer model of the film investigated. It was found that the outer film layer has a refractive index of approximately 1.1 that is noticeable lower than natural silicon dioxide refractive index (1.45). This indicates a significant porosity of the near-surface layer of the film.