The surface treatment of ultralow-kappa dielectric layers by exposure to atomic oxygen is presented as a potential mechanism to modify the chemical composition of the dielectric surface to facilitate copper diffusion barrier layer formation. High carbon content, low-kappa dielectric films of varying porosity were exposed to atomic oxygen treatments at room temperature, and x-ray photoelectron spectroscopy studies reveal both the depletion of carbon and the incorporation of oxygen at the surface. Subsequent dynamic water contact angle measurements show that the chemically modified surfaces become more hydrophilic after treatment, suggesting that the substrates have become more "SiO2-like" at the near surface region. This treatment is shown to be thermally stable up to 400 degrees C. High resolution electron energy loss spectroscopy elemental profiles confirm the localised removal of carbon from the surface region. Manganese (approximate to 1 nm) was subsequently deposited on the modified substrates and thermally annealed to form surface localized MnSiO3 based barrier layers. The energy-dispersive X-ray spectroscopy elemental maps show that the atomic oxygen treatments facilitate the formation of a continuous manganese silicate barrier within dense low-k films, but significant manganese diffusion is observed in the case of porous substrates, negatively impacting the formation of a discrete barrier layer. Ultimately, the atomic oxygen treatment proves effective in modifying the surface of non-porous dielectrics while continuing to facilitate barrier formation. However, in the case of high porosity films, diffusion of manganese into the bulk film remains a critical issue. Published by AIP Publishing.