Copper thin films are deposited by thermal evaporation on unetched and etched monocrystalline silicon. The study by alpha particles backscattering (RBS) raises a strong diffusion of copper in silicon substrates with and without native suboxide layer. On the other hand, the X-rays diffraction shows the formation and the growth Of CU3Si and Cu4Si silicides. Whereas the scanning microscopy underlines large crystallites growth surrounded by black zones of silicon coming from the uncovered substrate, independently to the surface state of the substrate, after annealing at high temperature. The presence of native silicon suboxide at Cu/Si interface, influences in a drastic way the minimal temperature to which the interfacial reaction occurs. The oxygen impurities detected by microanalysis, after heat treatment under vacuum, are closely related to the growth of silicides crystallites. (c) 2006 Published by Elsevier B.V.