The present disclosure provides a mask. The mask includes a substrate; an etch stop layer disposed on the substrate, wherein the etch stop layer includes at least one of ruthenium oxide, tungsten nitride, and titanium nitride and is doped with at least one of phosphorous (P), calcium (Ca), and sodium (Na); and a material layer disposed on the etch stop layer and patterned to have an opening, wherein the etch stop layer completely covers a portion of the substrate within the opening.