US Patent 7264907 Photomask having central and peripheral line patterns

Each of patterns on two types of photomasks, including identical central pattern portions, each having a line pattern on the center of a substrate, and peripheral pattern portions around the central pattern portions, and having distances between the central pattern portion and the peripheral pattern portion different from each other, is transferred onto a wafer. Thereafter, each line width of the transferred patterns corresponding to the line pattern of each photomask is measured. The difference between each of line widths is obtained, from which the flare rate is calculated.