Embodiments of methods for forming Cu diffusion barriers for semiconductor interconnect structures are provided. The method includes oxidizing an exposed outer portion of a copper line that is disposed along a dielectric substrate to form a copper oxide layer. An oxide reducing metal is deposited onto the copper oxide layer. The copper oxide layer is reduced with at least a portion of the oxide reducing metal that oxidizes to form a metal oxide barrier layer. A dielectric cap is deposited over the metal oxide barrier layer.