A method for fabricating a semiconductor device is disclosed. In an embodiment, the method may include providing a semiconductor substrate; forming gate material layers over the semiconductor substrate; forming a multi-layer hard mask layer over the gate material layers, wherein the multi-layer hard mask layer includes a plurality of film stacks, each film stack having a silicon oxide layer and a carbon-containing material layer, each film stack having a thickness equal to or less than about 10 angstrom; patterning the multi-layer hard mask layer, forming an opening of the multi-hard mask layer; etching the gate material layers within the opening of the multi-layer hard mask layer, forming a gate structure; performing a tilt-angle ion implantation process to the semiconductor substrate, wherein a first remaining thickness of the multi-layer hard mask layer is less than a first thickness; and thereafter performing an epitaxy growth to the semiconductor substrate, wherein a second remaining thickness of the multi-layer hard mask layer is greater than a second thickness.