Rim phase-shift mask combined with off-axis illumination: A path to 0.5Λ/NA geometries

Abstract

Phase Shift Mask (PSM) approaches may be classified as cither strong or weak. This paper will address weak PSM approaches which are attractive because of their universal applicability to any pattern. A simple design algorithm for rim PSM, called Biased Rim Design (BiRD), is described. When used with normal stepper illumination (σ=.5), the modest benefits of rim PSM 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 0.5Λ/NA lithographic patterns.