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