Adhesive layers residing at an interface between metal lines and dielectric diffusion barrier (or etch stop) layers are used to improve electromigration performance of interconnects. Adhesion layers are formed by depositing a precursor layer of metal-containing material (e.g., material containing Al, Ti, Ca, Mg, etc.) over an exposed copper line, and converting the precursor layer to a passivated layer (e.g., nitridized layer). For example, a substrate containing exposed copper line having exposed Cu—O bonds is contacted with trimethylaluminum to form a precursor layer having Al—O bonds and Al—C bonds on copper surface. The precursor layer is then treated to remove residual organic substituents and to form Al—N, Al—H bonds or both. The treatment can include direct plasma treatment, remote plasma treatment, UV-treatment, and thermal treatment with a gas such as NH3, H2, N2, and mixtures thereof. A dielectric diffusion barrier layer is then deposited.