Investigating phase-shifting mask layout issues using a CAD toolkit

Phase-shifting mask layout issues for nonregular designs are investigated using a new CAD (computer-aided design) toolkit. Using this toolkit, the periphery cells of a nonregular 16-Mb DRAM scaled for 64-Mb design rules are analyzed for their phase-shifting potential. On average, a 0.5 shrink factor applied to a layer of the DRAM periphery mask results in an effective shrink factor of 0.53, since some areas of the mask have phase conflicts. In this case, 94% of the cell area is easily shiftable using two phases. Possible solutions are recommended for the remaining difficult areas. The toolkit contains components for the global shrinking, phase-assignment, design-rule checking, region extraction, and region replacement of a mask layer. Using the initial shrink factor and violation data generated by the toolkit, an effective shrink factor based on phase-conflicts can be calculated for a particular design. The toolkit can also be used to assist in translating a traditional design into a phase-shifted one interactively from within a mask layout editor.<>