Methods of reducing a registration error of a photomask, and related photomasks and methods of manufacturing an integrated circuit

A method of reducing a registration error of a photomask, the method comprising:

• measuring the registration error with respect to a pattern element in a main pattern region configured to transfer main patterns for an integrated circuit on a chip region of a wafer, wherein the photomask comprises the main pattern region, an auxiliary pattern region configured to transfer auxiliary patterns on a scribe line region of the wafer, and a black border region around the main pattern region and the auxiliary pattern region, and wherein the photomask comprises a photomask substrate and a multi-layer pattern on the photomask substrate;
• identifying a first direction, to which the pattern element is shifted from a nominal position, using a result of measuring the registration error;
• and
• changing a strain of the photomask at a location of the pattern element by physically deforming a portion of the multi-layer pattern of the photomask at a selection point that is spaced apart from the location of the pattern element in a second direction that is different from the first direction and is in at least one of the auxiliary pattern region and the black border region.