US Patent 7790335 Photomask and manufacturing method of semiconductor device

A double exposure process is performed using a halftone phase shift mask (11) including gate patterns (1), assist patterns (2a) and (2b) with different resoluble line widths, and an assist pattern (2c) with a line width equal to or smaller than a resolution limit which are respectively inserted into portions in each of which a distance between the gate patterns (1) is large, and a Levenson phase shift mask (11) including shifter patterns (3) corresponding to the gate patterns (1) of the photomask 11. On this occasion, the assist patterns (2a), (2b), and (2c) are erased and only the gate patterns (1) are transferred. Consequently, when patterns are transferred by the double exposure process, a common depth of focus of the patterns is improved and highly uniform line widths are realized, which makes it possible to manufacture a highly reliable semiconductor device.