Comparison study for sub-150-nm DUV lithography between high-NA KrF and ArF lithography

Critical issues for 150nm DUV lithography using 0.70 NA KrF and 0.60 NA ArF had been investigated. Aberration, coherence variation, mask error effect, and process margin for each case had been analyzed. Current projection lens and illumination optics are getting better and better. However, for 150nm lithography using high NA scanner, a large portion of beam should be traced on the outside of lens pupil and traced on the resist surface with a large incident angle. In such a case, lens aberration effect was observed on field edge, even though strehl ratio of projection lens and coherence variation on field edge had been improved. These effects had been investigated. One other critical issue in high NA scanner is depth of focus. The common depth of focus between dense and isolated patterns in real process using high NA scanner is mainly affected by photoresist thickness. That issue had been also investigated. Another important issue for 150nm DUV lithography is mask error effect. In the case of same design rule, lower (lambda) /NA lens is more favored than higher (lambda) /NA. Mask error issue in high NA KrF and ArF was also analyzed. Total comparisons between high NA KrF and 0.60 NA ArF have been discussed.