A method for forming an interconnect structure is provided. The method includes: forming a dielectric layer on a substrate, and forming an opening in the dielectric layer; forming a first metal layer, a second metal layer, and a third metal layer sequentially over the dielectric layer. The opening of the dielectric layer is filled with the first metal layer to form a conductive via. The method also includes: performing one or multiple etch operation to etch the first metal layer, the second metal layer, and the third metal layer, so as to form a metal line corresponding to the first metal layer, an intermediate metal layer corresponding to the second metal layer, and a metal pillar corresponding to the third metal layer. In particular, the width of the metal line is greater than the width of the metal pillar.