RIM PHASE-SHIFT MASK COMBINED WITH OFF-AXIS ILLUMINATION - A PATH TO 0.5-LAMBDA NUMERICAL APERTURE GEOMETRIES

Phase-shift mask (PSM) approaches can be classified as either strong or weak. Weak PSM approaches, which are attractive because of their universal applicability to any pattern, are addressed. A simple design algorithm for rim PSM, called biased rim design (BiRD), is described. When used with normal stepper illumination (sigma=0.5), the modest benefits of rim PSMs are of questionable value in many cases. However, theoretical considerations show a synergy of weak PSM combined with off-axis illumination. One specific combination, termed BiRD/QUEST, is explored through a series of simulations. These results suggest that a properly biased weak PSM with appropriate illumination will allow robust manufacturing of 0.5lambda/NA lithographic patterns.