Flare has been important variable to achieve good CD control in low k1 lithography. Early works on flare
have focused on long-range DC and local flare, with an attention on how to measure flare and how flare
impact on CD control within theoretical model for ideal situation. As pattern size decreases below 100 nm,
however, short-range flare begins to appear prominently beyond that technology node. It has been pointed
out that process conditions such as photo resist thickness, substrate film stacks, and even some times
photo masks can be important variables for short-range flare but impact of process variables on flare at
illumination level has less been understood yet. Recently, Yun et al. have shown that the illumination
conditions such as coherence factor and illumination aperture shapes also give impact on short-range flare.
They found that the amount of short-range flare, the additional portion of the diffraction image to the
ideal one, increases as the illumination aperture size increases but inner radius of the annular illumination
apertures affect little on the amount of the short-range flare.
In this paper, as the series of the experiments by Yun et al., we will prove detailed relation between
illumination aperture shapes and the short range flare by exploring its impact with number of off-axis
illumination apertures including multi-pole illumination apertures, in addition to the previous data on
partially coherent conventional and simple annular illumination apertures. We utilize the 193-nm scan-and-step exposure tool and evaluate the short-range flare by measuring CD on the 100 nm lines surrounded by clear window having various open ratios. The extended data on various off-axis
illumination apertures reveal clarify the impact of illumination aperture shape on the short-range flare.