Edge defocus can be reduced by several techniques on a Nikon S204 scanner. By using main software MCSV version 3.44 or above, as well as disable range, and scan direction. Edge defocus can be reduced but is not eliminated at 3 o'clock and 4 o'clock. Wafer flatness is studied to investigate the cause of this defocus. The chuck shape is the key to avoid to defocusing at these two positions. Modification of chuck shape can reduce yield loss.
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