A method of manufacturing a mask, the method including forming initial ribs such that forming the initial ribs includes forming at least two photoresist patterns such that the at least two photoresist patterns have different widths, are formed on at least one side of a mask substrate, and overlap each other, and performing an etching process at least two times; and forming final ribs such that the final ribs have curved sides having a different curvature radius than a curvature radius of initial curved sides of the initial ribs and have defined slit patterns, forming the final ribs including removing all but one of the at least two photoresist patterns, and performing an etching process.