Alternating phase mask

An alternating phase mask is described in which a propagation of a T phase conflict which occurs in the case of a T pattern structure is avoided by producing a phase jump at one of the 90° corners of the T pattern structure. First and second transparent area segments, which produce a mutual phase difference of 180°, are separated by a narrow slot running approximately at 45° toward the corner of the T pattern structure. The structure containing the transparent area segments, which are separated by the slot running at 45°, can also be provided at the other corner of the T structure providing a solution for each T conflict. The trimming mask for eliminating the dark line artificially produced by the 180° phase jump is a conventional mask and requires no additional coloration. Moreover, alignment errors are minimal on account of the small number of trimming openings.