A method for forming an improved TaN copper barrier for a copper damascene process is described which has improved adhesion to low-k dielectric layers and also improves the wetting of a copper seed layer deposited over it thereby improving the structure of the copper seed layer which is critical to achieving uniform, high quality electrochemical copper deposition. The copper barrier is a composite structure having an lower thin Ta rich TaN portion which mixes into and reacts with the surface of the low-k dielectric layer, forming a strongly bonded transition layer between the low-k material and the remaining portion of the barrier layer. The presence of the transition layer causes compressive film stress rather than tensile stress as found in the conventional TaN barrier. As a result, the barrier layer does not delaminate from the low-k layer during subsequent processing. A second thick central portion of the barrier layer is formed of stoichiometric TaN which benefits subsequent CMP of the copper damascene structure. An upper thin Ta portion improves barrier wetting to the copper seed layer. The three sections of the laminar barrier are sequentially deposited in a single pumpdown operation by IMP sputtering from a Ta target.