The chemical interaction of Al on a Si02 dielectric layer and the addition of Al into Ru thin films on Si02 for use as copper diffusion barrier layers are assessed in situ using X-ray photoelectron spectroscopy. Thin (-1-2 nm) Al films were deposited on a Si02 substrate and in a separate experiment on a 3 nm Ru liner layer on Si02, and both A1/Si02 and A1/Ru/Si02 structures were subsequently thermally annealed. Results indicate the reduction of Si02 and the subsequent formation of Al203 with the release of Si from the dielectric. The Al/Ru/Si02 structure showed evidence for the diffusion of Al through the Ru layer and the subsequent interaction of the Al with the underlying 5i02 dielectric to form Al203. In this case, the reduction of 5i02 leads to the release of Si from the dielectric and the subsequent chemical interaction of Ru with Si. 2014 Published by Elsevier B.V.