We have found that besides a Ta absorber thickness reduction an illumination pupil optimization is necessary to fully remove these CD asymmetries. The pupil optimization is achieved by relating the aerial image decomposition (here: symmetrization and balancing of intensities across the diffracted orders) with lithographic metrics per pupil plane location. The resulting pupil allows us (i) to lift the focus-dependent CD asymmetries and (ii) to co-optimize a number of lithographic metrics such as overlapping process window, contrast, non-telecentricity and pattern shift. The importance of subsidiary conditions (e.g. symmetry of the pupil, required DOF) will be discussed.
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T. Last, L. de Winter, P. van Adrichem, J. Finders, "Illumination pupil optimization in 0.33NA EUVL by intensity balancing for semi-iso dark field two-bar M1 building blocks ," Proc. SPIE 10032, 32nd European Mask and Lithography Conference, 100320A (20 October 2016);