Self-assembled monolayers are studied to replace metallic films used as barrier/adhesion layers between dielectric material and copper used for interconnects in semiconductor devices. In this study, alkoxysilane layers were deposited by SC CO2 processes on oxidized Si substrates using mainly two silanes: mercapto and aminopropyltrimethoxysilane. In order to obtain various layers, several process conditions were tuned such the process mode, static and dynamic, the temperature and the solvent. X-ray reflectometry was the main technique used to probe the structural and morphological characteristics of the films. All of these results show that the structure of the resulting organic layer depends on the molecule and on the process conditions. Aminoalkyltrimethoxysilanes lead to polycondensed layers formed with a thermally activated reaction while self-assembled monolayers are obtained with mercaptopropyltrimethoxysilane whatever the process condition. (C) 2009 Elsevier B.V. All rights reserved.