20. The method of claim 15 , wherein the first, second, and third photomasks are designed according to an IC design layout having a plurality of IC features to be formed on the substrate.
20. The method of claim 15 , wherein the first, second, and third photomasks are designed according to an IC design layout having a plurality of IC features to be formed on the substrate. 21. The method of claim 20 , wherein: the first photomask includes a first layout having a first subset of the IC features, wherein the first layout does not violate design rules; the second photomask includes a second layout having a second subset of the IC features and connecting features, wherein the second subset of the IC features violate the design rules and the second layout does not violate the design rules; and the third photomask includes a third layout having a plurality of trimming features that correspond to the connecting features.