A method for processing a substrate that includes: patterning a carbon-based hardmask layer over a dielectric layer to form a first recess in the carbon-based hardmask layer, the first recess having a tapered profile such that a width of the first recess at a first height is greater than a width of the first recess at a second height that is lower than the first height; depositing a metal-containing layer over the patterned carbon-based hardmask layer, the metal-containing layer being physically in contact with sidewalls of the patterned carbon-based hardmask layer in the first recess, the metal-containing layer being thicker at the first height than at the second height; and etching the dielectric layer using the patterned carbon-based hardmask layer as an etch mask by an anisotropic plasma etch process to form a second recess in the dielectric layer.