Set of at least two masks for the projection of structure patterns

1. A set of at least two masks for the projection of structure patterns, each structure pattern being formed on the masks and coordinated with one another by a projection system into the same photosensitive layer arranged on a semiconductor wafer, the projection system having a resolution limit for a lateral dimension of an opening projected onto the semiconductor wafer from a mask, comprising:

a first mask including a semitransparent or nontransparent first layer, which is arranged on a first substrate and in which at least one first opening is formed at a first position, the first opening having a first lateral dimension, which is greater than the resolution limit; and

a second mask assigned to the first mask, the second mask including a semitransparent or nontransparent second layer, which is arranged on a second substrate and in which at least one dummy structure assigned to the first opening is formed at a second position, the dummy structure having a second lateral dimension, which is smaller than the resolution limit of the projection system wherein the first position on the first mask identically corresponds to the second position on the second mask,

wherein one of the first and second masks is an alternating phase mask,

wherein the other of the first and second masks is a trimming mask having at least one further opening for the exposure of a region in the photosensitive layer, which arises on account of a phase conflict in the case of an exposure with said one of the first and second masks, and

wherein the second lateral dimension is selected to improve a depth of focus in a combined double exposure by the first and second masks.

2. The set of masks as claimed in claim 1 , wherein the first opening, a second opening, and at least one third opening are arranged as gaps in a periodic line-gap pattern on the first mask.

3. The set of masks as claimed in claim 2 , wherein the first opening, the second opening, and the at least one third opening, as gaps, are separated from one another by first, second and third webs formed by the semitransparent or nontransparent first layer, the first opening, the second opening, and the at least one third opening in each case have the same first lateral dimension, the first, second and third webs in each case have identical third lateral dimensions, but the first and the third lateral dimensions are different from one another.

4. The set of masks as claimed in claim 3 , wherein the first opening, the second opening, and the at least one third opening are in each case assigned a dummy structure, the position of the first opening, the second opening and the at least one third opening on the first mask each corresponding identically to that position of the dummy structure assigned thereto on the second mask.

5. The set of masks as claimed in claim 1 , wherein at least one further transparent opening is formed at a further first position on the first mask, and at least one semitransparent region is arranged at a further second position on the second mask, the further second position corresponding to the further first position on the first mask.