A method of processing a substrate includes: depositing an etch stop layer atop a first dielectric layer; forming a feature in the etch stop layer and the first dielectric layer; depositing a first metal layer to fill the feature; etching the first metal layer to form a recess; depositing a second dielectric layer to fill the recess wherein the second dielectric layer is a low-k material suitable as a metal and oxygen diffusion barrier; forming a patterned mask layer atop the substrate to expose a portion of the second dielectric layer and the etch stop layer; etching the exposed portion of the second dielectric layer to a top surface of the first metal layer to form a via in the second dielectric layer; and depositing a second metal layer atop the substrate, wherein the second metal layer is connected to the first metal layer by the via.