Method to correct EUVL mask substrate non-flatness

摘要

Methods to correct a non-flatness of a mask substrate are described. At least a pair of correction layers are formed on the substrate over a non-flat region of a front surface of a substrate. A thickness of the at least the pair of the correction layers is determined by a peak-to-valley distance of the non-flat region of the substrate. A portion of the correction layers over the non-flat region is heated locally. Heating changes the thickness of the portion of the correction layers and removes the non-flat region from a top surface of the correction layers without physically removing any materials. At least the pair of the correction layers is formed on a back surface of the substrate to compensate for a stress induced by the correction layers on the front surface of the substrate.