A method for manufacturing a semiconductor structure includes: forming a dielectric layer over a conductive layer on a semiconductor substrate; etching the dielectric layer to form a via hole that exposes the conductive layer; depositing a barrier layer to line the via hole; after depositing the barrier layer, depositing a first metal layer to fill a remainder of the via hole; performing a chemical mechanical polishing (CMP) process on the first metal layer until the barrier layer is exposed; after performing the CMP process, depositing a second metal layer over the barrier layer and the first metal layer; and etching the second metal layer to form a metal line.