Alternating phase mask

An alternating phase mask for exposing a photosensitive layer in a photolithographic process, the alternating phase mask comprising:

• at least two opaque segments including a first opaque segment with a longitudinal side and a second opaque segment ending at the longitudinal side of the first opaque segment, the second opaque segment subdividing the first opaque segment into two opaque partial segments on either side of an end region of the second opaque segment;
• transparent surface segments, one of the transparent surface segments disposed on each side of each of the two opaque partial segments and of the second opaque segment and extending over an entire length of the opaque segments, mutually adjacent ones of the transparent surface segments in each case having phases displaced by 180°±Δ α with respect to each other, and Δ α being at most 25°;
• and
• a surface boundary segment disposed between two of the transparent surface segments and having a phase situated between the phases of the two of the transparent surface segments, the transparent surface segments separated by the surface boundary segment and situated opposite of the longitudinal side of the first opaque segment having the phases displaced by 180°±Δ α with respect to each other, the
• surface boundary segment having a shape of an elongated rectangle with a width being substantially equivalent to a width of the second opaque segment.