providing a substrate;

forming a bottom layer over the substrate, wherein the bottom layer includes a polymer, a first cross-linking agent and a second cross-linking agent different from the first cross-linking agent, the second cross-linking agent including one or more functional groups including fluorine;

thermally treating the bottom layer;

forming a hard mask layer over the thermally treated bottom layer;

forming a photoresist layer over the hard mask layer;

exposing the photoresist layer to a radiation source according to a pattern;

developing the photoresist layer;

performing a first etching process to form the pattern in the bottom layer and the hard mask layer but not in the substrate; and

performing a second etching process to form the pattern in the substrate.