Zero MEF hole formation with Atten-PSM and modified illumination

Extremely fine hole pattern formation with dark spot image is investigated with Atten-PSM and specific modified illumination. In optical image calculation, by the application of tone reversed image in Atten-PSM under an optimized cross-pole illumination, dark spot image with zero MEF and iso-focal characteristics is obtained for very wide range of pattern pitch. In KrF wavelength, formation of ~110 nm size dark spot image with resolution DOF higher than ~0.50μm can be achieved for the pattern pitch of isolated to ~240 nm. In this imaging, MEF may become very low or exactly zero for the pitch of isolated to ~300 nm. Because of low or zero MEF, OPC is essentially difficult or may be performed imperfectly for this method. However, small OPE of ~10 nm in CD variation throughout pattern pitch could be expected by the application of optimized illumination. In preliminary experiments under KrF optics of NA=0.75, high DOF and zero MEF characteristics are successfully proven, even while the experiments are carried out with non-optimal modified illumination.