An optical mask for forming a pattern is provided. The optical mask includes: a substrate including a light blocking pattern formed on portions of the substrate, wherein the light blocking pattern includes a halftone layer and a light blocking layer formed on the halftone layer, and the halftone layer and the light blocking layer overlap such that at least an edge portion of the halftone layer is exposed. A pitch of the light blocking pattern may about 6 μm, and a transmission ratio of the halftone layer may range from about 10% to about 50%.