Automatic generation of phase-shifting mask patterns using shifter-edge lines

An algorithm for automatic phase-shifter generation has been developed for the fabrication of a gate layer by phase-shifting mask technology. Since the gate layer requires very fine patterns, the shifter-edge line technique is employed with a novel two-step exposure method. However, simple two-step exposure to eliminate undesired patterns along the shifter edge often gives rise to critical pattern deformation because of alignment error. Another difficulty is the occurrence of phase conflicts in automatic phase-shifter allocation. The new algorithm solves both of these problems. Experimental studies indicate that this algorithm should enable significant reductions in gate length and that it is applicable to practical circuit patterns.