Double exposure using mutually one-pitch-step shifted alt. PSM's is proposed to eliminate the ⊿CD and CD reversal. By doubly exposing mutually one-pitch-step shifted alt. PSM's, the ⊿CD and CD reversal is observed to disappear. The phase margin of 8° and the undercut margin of 40 nm are obtained for 1.2μm DOF margin. Comparing with alt. PSM, double exposure using mutually one-pitch-step shifted alt. PSM has larger margin in undercut and phase, which allows mask to be manufactured easily. The alignment tolerance is calculated to be 75 nm which is enough compared with recent lithographic systems. By doubly exposing mutually one-pitch-step shifted alt. PSM, the equal CD's of 141 nm and 142 nm were observed. Our double exposing technique proved to have large advantages over alt. PSM not only in removal of ⊿CD and CD reversal, but also in the phase and undercut margin.
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