Doubly exposed patterning using mutually one-pitch step shifted alternating phase shift masks

A double exposure using mutually one-pitch-step shifted alt. PSM's is proposed to eliminate the DeltaCD and CD reversal. By doubly exposing mutually one-pitch-step shifted alt. PSM's, the DeltaCD and CD reversal is observed to disappear, The phase and undercut margins of 8degrees and 40 nm are observed, respectively by simulation for 1.2 mum DOF margin. The alignment tolerance is calculated to be 75 nm which is enough for considerring recent lithographic systems. By doubly exposing mutually one-pitch-step shifted alt. PSM, almost identical CD's of 141 nm and 142 nm are measured, The phase margin of 15degrees (from 169degrees to 184degrees) and the undercut margin of 50 nm (from 100 nm to 150 nm) are observed for DOF margin of 1.0 mum. Our double exposing technique prove to have advantages over alt. PSM not only in removal of DeltaCD and CD reversal, but also in the phase and undercut margin.