Phase Shift Mask (PSM) approaches may be classified as either strong or weak. This paper addresses 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 ($sigma $EQ .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 allows robust manufacturing of 0.5 $lambda@/NA lithographic patterns.
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