A method of manufacturing a semiconductor device includes forming a first dielectric layer over a substrate, forming a metal layer in the first dielectric layer, forming an etch stop layer on a surface of the first dielectric layer and the metal layer, removing portions of the metal layer and the etch stop layer to form a recess in the metal layer, and forming a tungsten plug in the recess. The recess is spaced apart from a bottom surface of the etch stop layer.