A method and system for patterning a dielectric film such as a low dielectric constant (low-k) material. A dry non-plasma etching process can be implemented to transfer a pattern from a photo-lithographic layer to a hard mask layer, while minimizing the evolution of surface roughness in the sidewall of the etched pattern in the hard mask layer. Once a pattern is transferred to the hard mask layer, the photo-lithographic layer can be removed in order to minimize the exposure of the underlying low-k dielectric film to the ashing or wet stripping process that facilitates removal of the photo-lithographic layer. The dry non-plasma removal process comprises a chemical treatment of the exposed hard mask layer, followed by a thermal treatment of the chemically treated exposed layer. The two steps, chemical and thermal treatment, can be repeated.