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7 July 1997 Overlay error of fine patterns by lens aberration using modified illumination
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Overlay errors of fine patterns using modified illumination are experimentally measured and analyzed. Overlaid `vernier' patterns which fine lines and holes are overlaid on standard line patterns are used to measure the overlay errors. The experimental results using a KrF excimer laser stepper with various illumination conditions show that the overlay errors depend on the illumination coherence factor (sigma) and the pattern feature. These overlay errors consist of magnification and offset and these errors depend on the pattern feature. The offset error between line pattern and hole pattern are considerably large for device fabrication. The magnification component originates from coma aberration of the projection lens. We will confirm and estimate the effect of coma aberration on the overlay error by optical simulation. The origin of the offset error is considered to be coma aberration due to lens element decentering. This `decentering' coma aberration causes the offset error and the effect of `decentering' coma aberration has the feature dependence.
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Takashi Saito, Hisashi Watanabe, and Yoshimitsu Okuda "Overlay error of fine patterns by lens aberration using modified illumination", Proc. SPIE 3051, Optical Microlithography X, (7 July 1997); doi: 10.1117/12.275988;

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