Embodiments of the present invention provide increased distance between vias and neighboring metal lines in a back end of line (BEOL) structure. A copper alloy seed layer is deposited in trenches that are formed in a dielectric layer. The trenches are then filled with copper. An anneal is then performed to create a self-forming barrier using a seed layer constituent, such as manganese, as the manganese is drawn to the dielectric layer during the anneal. The self-forming barrier is disposed on a shoulder region of the dielectric layer, increasing the effective distance between the via and its neighboring metal lines.