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12 March 2008 Focus, dynamics, and defectivity performance at wafer edge in immersion lithography
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We evaluate several types of wafers and investigate the effect of wafer edge geometry on focus, dynamics and defectivity performance in ArF immersion lithography. Wafer edge geometry includes both edge shape (e.g. short, long, full round etc.) and edge roll-off (ERO) here. We found that focus accuracy at wafer edge depends on ERO, especially on ZDD (Z double derivative) and if we use the specified wafer which has low ZDD value, it keeps same good focus accuracy at the edge area as the one at the wafer center area. Dynamics (stage synchronization accuracy) was independent of wafer diameter, thickness and edge geometry. We also found that defectivity was strongly dependent on the edge shape. More bridging defects were found on the short edge wafer than the long edge wafer. This is related with wafer edge conditions after coating and during exposure.
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Takao Tamura, Naka Onoda, Masafumi Fujita, and Takayuki Uchiyama "Focus, dynamics, and defectivity performance at wafer edge in immersion lithography", Proc. SPIE 6924, Optical Microlithography XXI, 692419 (12 March 2008);

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