A method for preventing the formation of voids and contaminants in vias during the fabrication of a metal interconnect structure such as a dual damascene structure is disclosed. The method includes providing a substrate; providing a dielectric layer having trench openings and via openings on the substrate, wherein the ratio of the sum of the areas of the trench openings to the sum of the areas of the via openings is between 1 and 300; wherein the via opening bottom has a width of less than about 25 μm; and electroplating a metal in the trench openings and via openings. An interconnect structure having at least one void-free via is further disclosed.