Electrochemical study for the characterisation of wet silicon oxide surfaces

Because wet ultra-thin silicon oxides are extensively used in the microelec tronic industry, we have investigated the growth of these oxides in various aqueous solutions using three main electrochemical techniques: (i) open ci rcuit potential variation with time; (ii) linear voltammetry in a narrow ra nge of potential; and (iii) electrochemical impedance spectroscopy under va rious polarisation potentials, to collect quantitative data regarding the g rowth kinetics of silicon oxide passivating layer, mainly at room temperatu re (r.t.). In oxidising alkaline solutions, the surface silicon oxide layer reached a limiting thickness value with time, related to oxidation/dissolu tion stationary behaviour. This observation was confirmed using ellipsometr y. It was possible to reach with electrochemical techniques and ellipsometr y the etching rate of the silicon substrate under the oxide layer in alkali ne solution. Another interesting observation in this study was that the oxi de layer showed a pronounced permeability to ions and oxidising agents in a lkaline media, while this phenomenon vanished in acidic solutions. (C) 2001 Elsevier Science Ltd. All rights reserved.