A method for fabricating semiconductor device includes the steps of: forming a dielectric layer on a substrate; forming a stop layer between the dielectric layer and the substrate, wherein the stop layer contacts the substrate directly and the dielectric layer covers the top surface of the stop layer; forming an opening in the dielectric layer, wherein the dielectric layer comprises a damaged layer adjacent to the opening; forming a dielectric protective layer in the opening; forming a metal layer in the opening; removing the damaged layer and the dielectric protective layer to form a void, wherein the void exposes a top surface of the substrate; and forming a cap layer on and covering the dielectric layer, the void, and the metal layer.