A method for filling a metal is disclosed. First, a substrate is provided. The substrate includes a metal material layer, a dielectric layer covering the metal material layer and a hard mask layer covering the dielectric layer. The hard mask layer has at least one opening to expose the underlying dielectric layer. Second, a dry etching step is performed to etch the dielectric layer through the opening to remove part of the dielectric layer to expose the metal material layer and to form a recess and leave some residues in the recess. Then a cleaning step is performed to remove the residues and to selectively remove part of the hard mask to substantially enlarge the opening. Later, a metal fills the recess through the enlarged opening.