26 March 2007 Flare effect of different shape of illumination apertures in 193-nm optical lithography system
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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.
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Young-Je Yun, Jeahee Kim, and Keeho Kim "Flare effect of different shape of illumination apertures in 193-nm optical lithography system", Proc. SPIE 6520, Optical Microlithography XX, 65202T (26 March 2007); doi: 10.1117/12.711634; https://doi.org/10.1117/12.711634

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