A method for forming a semiconductor structure includes providing a semiconductor substrate and forming a dielectric layer over the semiconductor substrate. An opening is formed in the dielectric layer. A conductive line is formed in the opening, wherein the conductive line has an open void formed therein. A sealing metal layer is formed overlying the conductive line, the dielectric layer, and the open void, wherein the sealing metal layer substantially fills the open void. The sealing metal layer is planarized so that a top surface thereof is substantially level with a top surface of the conductive line. An interconnect feature is formed above the semiconductor substrate, wherein the interconnect feature is electrically coupled with the conductive line and the sealing metal layer-filled open void.