Patent ID: 7566516

Claim:
A method of designing a photomask for defining a photoresist layer formed on a wafer, wherein the wafer has at least two alignment marks formed thereon, the method comprising: providing a shot size; creating an optimal shot map, wherein the optimal shot map is composed of a plurality of shots and the optimal shot map matches with a profile of the wafer to have maximum number of complete shots inside the profile; obtaining an optimal relative position of an alignment mark region on the wafer with respect to the optimal shot map and a relative position of the alignment mark in the alignment mark region; and designing a layout of a photomask to have a shot region and at least an alignment mark pattern region having a profile equal to the profile of the alignment mark region on the wafer, wherein a first ratio of the size of the shot region to the shot size is equal to a second ratio of the size of the alignment mark pattern region to the size of the alignment mark region and the alignment mark pattern region comprises: a block region with a position in the alignment mark pattern region corresponding to the relative position of the alignment mark in the alignment mark region; a clean-out region adjacent to one side of the block region; and a dummy pattern region adjacent to another side of the block region.