Alternating phase shifting mask in EUV lithography

15 nm gate length in 35 nm node requires some resolution enhancement techniques in EUV lithography (EUVL). Alternating phase-shifting masks (Alt-PSMs) have demonstrated that narrow gate far below 0.6 of k/sub 1/ is available in optical lithography with sufficient flexibility to complex layout of gate layer. In EUVL, 15 nm gate length at NA 0.25 and 13.5 nm of exposure wavelength will requires alt-PSMs due to extremely low k/sub 1/ factor of 0.28. So far multi-layer structure in which Mo and Si are mutually stacked has not allowed to realize the alt-PSMs, because the consistency of 180 degree phase and the coincidence of reflectance in the two different area have suffered from controlling precisely etching depth in engraving multi-layer stack film. In order to realize alt-PSMs, we propose newly additive structure.