A method embodiment includes forming a hard mask over a dielectric layer and forming a first metal line and a second metal line extending through the hard mask into the dielectric layer. The method further includes removing the hard mask, wherein removing the hard mask defines an opening between the first metal line and the second metal line. A liner is then formed over the first metal line, the second metal line, and the dielectric layer, wherein the liner covers sidewalls and a bottom surface of the opening.