A method for forming a metal interconnect structure provides a conformal layer of barrier material, such as a nitride, within a patterned opening in a dielectric layer. The barrier material is deposited after the opening is etched to the dielectric layer, stopping on a diffusion barrier. A first layer of a metal barrier material, such as tantalum, is conformally deposited on the barrier material. A directional etch is performed that removes horizontal nitride and tantalum, leaving the nitride and tantalum on the sidewalls of the patterned opening. The barrier material prevents contamination of the dielectric layer from conductive material, such as copper, during the etching of the diffusion barrier overlying the conductive material, and during subsequent sputter etch cleaning. A thin, second metal layer is conformally deposited and forms a suitable barrier on the sidewalls of the opening, while providing low contact resistance between the second metal layer and the underlying substrate.