A method for treating a substrate is disclosed. The method includes forming a film stack on the substrate, the film stack comprising an underlying layer, a coating layer disposed above the underlying layer, and a patterning layer disposed above the coating layer. In the method, portions of the patterning layer are removed to form sidewalls of the patterning layer and expose portions of the coating layer, a carbon-containing layer is deposited on the exposed portions of the coating layer and non-sidewall portions of the patterning layer, and the carbon-containing layer and a portion of the coating layer are removed to expose other portions of the coating layer and the patterning layer. The method further includes repeating the deposition and removal of the carbon-coating layer at least until portions of the underlying layer are exposed.