A method includes providing a substrate, wherein the substrate includes a conductive feature in a top portion of the substrate; forming a buffer layer over the substrate; forming a dielectric layer over the buffer layer; performing a first etching process to form an opening in the dielectric layer, thereby exposing a top surface of the buffer layer; and performing a second etching process to extend the opening downwardly into the buffer layer, thereby exposing a top surface of the conductive feature, wherein the performing of the second etching process includes laterally enlarging a footing profile of the opening.