Optical EngineeringRim phase-shift mask combined with off-axis illumination: a path to 0.5λ/numerical aperture geometries
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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 (σ=0.5), the modest benefits of rim PSMs are of questionable value in many cases. However, theoretical considerations show a synergy of weak PSM cornbined 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 0.5λ/NA lithographic patterns.