A method for manufacturing metal interconnects. The method includes following steps. A substrate including a dielectric layer formed thereon is provided, and a plurality of trenches are formed in the dielectric layer. Next, a seed layer is formed in the trenches and on the dielectric layer and followed by masking regions of the seed layer to define a plurality of masked regions and a plurality of exposed regions for the seed layer. Subsequently, a surface treatment is performed to the exposed regions of the seed layer to form a plurality of rough surfaces on the exposed regions of the seed layer. Then, a metal layer is formed on the substrate, and the trenches are filled up with the metal layer.