Patent Number: 
Section: claims

1. A method comprising:obtaining a target layout including at least one substantially square target shape having four edges;modifying the at least one substantially square target shape in the target layout to form a rectangular shape by at least one of: moving at least one edge of the substantially square target shape in the target layout or pre-defining at least one dimension of a final modified mask layout; andperforming, by a computer, an optical proximity correction (OPC) on the target layout after the modifying to produce the final modified mask layout having a pattern that will form the rectangular shape circular to within a predefined tolerance when the final modified mask layout is transferred into a resist layer. 2. The method of claim 1, wherein the rectangular shape has an aspect ratio of larger than about 1:1. 3. The method of claim 1, wherein the at least one substantially square target shape includes a plurality of substantially square target shapes. 4. The method of claim 3, wherein the modifying is applied to all of the plurality of substantially square target shapes to form a plurality of rectangular shapes. 5. The method of claim 3, wherein the modifying is applied to only those substantially square target shapes in at least one highest density region. 6. The method of claim 1, wherein the at least one edge of the at least one substantially square target shape that is elongated is determined by a density of targets in any given direction. 7. The method of claim 1, further comprising limiting movement of an edge during the OPC performing. 8. A system comprising:at least one computing device;an obtainer for obtaining a target layout including at least one substantially square target shape having four edges;a modifier for modifying the at least one substantially square target shape in the target layout to form a rectangular shape by at least one of: moving at least one edge of the substantially square target shape in the target layout or pre-defining at least one dimension of a final modified mask layout; andan optical proximity correction (OPC)module for performing an optical proximity correction on the target layout after the modifying to produce the final modified mask layout having a pattern that will form the rectangular shape circular to within a predefined tolerance when the final modified mask layout is transferred into a resist layer. 9. The system of claim 8, wherein the rectangular shape has an aspect ratio of larger than about 1:1. 10. The system of claim 8, wherein the at least one substantially square target shape includes a plurality of substantially square target shapes. 11. The system of claim 10, wherein the modifying means modifies all of the plurality of substantially square target shapes to form a plurality of rectangular shapes. 12. The system of claim 10, wherein the modifying means modifies only those substantially square target shapes in at least one highest density region. 13. The system of claim 8, wherein the at least one edge of the at least one substantially square target shape that is elongated is determined by a density of targets in any given direction. 14. The system of claim 8, further comprising means for limiting movement of an edge during the OPC performing. 15. A program product stored on a non-transitory computer-readable medium, which when executed by a computer system, performs the process comprising:obtaining a target layout including at least one substantially square target shape having four edges;modifying the at least one substantially square target shape in the target layout to form a rectangular shape by at least one of: moving at least one edge of the substantially square target shape in the target layout or pre-defining at least one dimension of a final modified mask layout; andperforming an optical proximity correction (OPC) on the target layout after the modifying to produce the final modified mask layout having a pattern that will form the rectangular shape circular to within a predefined tolerance when the final modified mask layout is transferred into a resist layer. 16. The program product of claim 15, wherein the rectangular shape has an aspect ratio of larger than about 1:1. 17. The program product of claim 15, wherein the at least one substantially square target shape includes a plurality of substantially square target shapes. 18. The program product of claim 17, wherein the modifying is applied to all of the plurality of substantially square target shapes to form a plurality of rectangular shapes. 19. The program product of claim 15, wherein the at least one edge of the at least one substantially square target shape that is elongated is determined by a density of targets in any given direction. 20. The program product of claim 15, the process further comprising limiting movement of an edge during the OPC performing.