A photomask ensures the transfer of a pattern having a uniform and desired CD onto a substrate from which an electronic device or the like is made. The photomask includes a transparent substrate, a light-shielding film on the front side of the substrate and defining a mask pattern of transmission regions dedicated for pattern formation, and an auxiliary pattern on the front side of the substrate that alters the intensity of the light beam passing through the substrate. After the mask pattern is formed, the photomask is tested to determine variations between the desired (target) CD and the CDs of the features of a pattern transcribed onto a test wafer using the photomask. A density function in which characteristics of the auxiliary pattern to be formed, e.g., the size, depth and/or pitch of recesses, is developed as a prediction of the intensity distribution of the light beam transmitted through the substrate once the auxiliary pattern is present at the front side of the substrate. The photomask is then repaired/corrected by designing and forming the auxiliary pattern according to the density function so as to prevent local or global variations between the desired CD and the actual CD from occurring.