A method for forming a semiconductor device structure is provided. The method includes forming a dielectric layer over a semiconductor substrate and forming a hard mask layer over the dielectric layer. The method also includes performing a plasma etching process to etch the hard mask layer to form an opening, and a gas mixture used in the plasma etching process includes a nitrogen-containing gas, a halogen-containing gas, and a carbon-containing gas. The gas mixture has a volumetric concentration of the nitrogen-containing gas in a range from about 20% to about 30%. A volumetric concentration ratio of the carbon-containing gas to the halogen-containing gas in the gas mixture is equal to about 0.3. The method further includes etching the dielectric layer through the opening in the hard mask layer to form a feature opening in the dielectric layer. The method includes forming a conductive material in the feature opening.