A few new reactants for the wet cleaning of silicon surfaces, for example, ozone dissolved in ultrapure water (UPW), have been proposed to replace the original RCA process using H2O2 solutions. In the present work we describe, for the first time, the mechanism of silicon surface oxidation by dilute solutions of elemental chlorine. Upon reaction with this highly oxidizing agent, the open circuit potential (OCP) shifted immediately to positive values, the effect being identical for both n- and p-type Si substrates. The surface transformation was firstly investigated by electrochemical impedance spectroscopy which showed successive semicircles representing RC equivalent circuits, showing a gradual growth of an insulating layer. X-ray photoelectron spectroscopy (XPS) recordings demonstrated unequivocally the formation of a pure and uniform chemical oxide layer, the possible contamination by Cl element being negligible. Moreover, the strong oxidizing and complexing properties of chlorinated aqueous solutions afford this reactant a high efficiency in surface cleaning from metal impurities. The effectiveness of this treatment was proven by AFM observation of the surface which was beforehand intentionally contaminated by Cu nuclei. The original flat surface was easily restored after a short cleaning using this new chemical reactant. This novel technique of surface treatment is promising with respect to the economy and environmental requirements, and also for the possible subsequent growth of multi-layer high-k dielectric structures. (C) 2004 Elsevier Ltd. All rights reserved.