Silicon anodic oxides grown in the oscillatory anodisation regime - kinetics of growth, composition and electrical properties

The work presents the results of studying the anodic oxide growth at silicon in a special regime when the values of the anodic current or potential are oscillating in time. The oscillatory kinetics is ranging from intermittent and damped oscillations to very regular and long-lasting ones. The critical experimental factors allowing to observe well-defined oscillations are the composition of electrolyte, its temperature, anodic-current density (or voltage), electrolyte stirring, etc. Direct electron microscopy measurements show that the oscillations are due to the cyclic process of the formation of thin oxide films (10-100 nm, depending on the conditions of growth) and their pealing off from the surface of Si wafer. The surface works as a generator of these oxide films which according to the data of infrared measurements and secondary ton mass spectroscopy are composed of SiO2. Crystallographic orientation of Si wafers is an important factor in determining the shape of oscillations, presumably due to a specifics of the dissolution of different crystallographic planes of silicon. Analysis of the morphology of the samples and their kinetics of growth shows that the oscillatory anodisation kinetics is a self-organisation phenomenon emerging as a result of collective interactions in the electrolyte/Si system. DC and AC electrical conductivity of the formed oxide films are studied and shown to obey the hopping conductivity mechanisms. Transient effects in DC conductivity (charge trapping, structural relaxation, etc.) are studied using the frequency noise spectroscopy (FNS). It is shown that the FNS method allows to improve the reproducibility of the data due to its insensitivity towards macrostructural inhomogeneities of the oxide films. (C) 2001 Published by Elsevier Science Ltd.