A method for forming an opening is disclosed. First, a semiconductor substrate is provided, in which the semiconductor substrate includes at least one metal interconnects therein. A stacked film is formed on the semiconductor substrate, in which the stacked film includes at least one dielectric layer and one hard mask. The hard mask is used to form an opening in the stacked film without exposing the metal interconnects, and the hard mask is removed thereafter. A barrier layer is later deposited on the semiconductor substrate to cover a portion of the dielectric layer and the surface of the metal interconnects.