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2 April 2014 Improvement of inter-field CDU by using on-product focus control
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This paper introduces to improve inter-field CDU with on-product focus control by diffraction based focus (DBF) method. For DBF target selection, a robust focus metrology for focus control was obtained, and the selected DBF target was integrated on each seven spot of a product reticle. For on-product focus control, previously on-product focus monitoring was performed, and the monitored lots showed a stable focus fingerprint. Based on the result, Z and Z/ Rx/Ry corrections per field on wafers were applied. Focus uniformity of controlled wafers was improved up to 29% in comparison with non-corrected ones. To demonstrate the improvement of inter-field CDU, Full CDs on wafers were measured by SEM. As a result, inter-field CDU for controlled wafers was improved by 16% (3σ) compared with noncontrolled wafers.
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Kyeong Dong Park, Tony Park, Jong Hyun Hwang, Jin Phil Choi, and Young Seog Kang "Improvement of inter-field CDU by using on-product focus control", Proc. SPIE 9050, Metrology, Inspection, and Process Control for Microlithography XXVIII, 90500R (2 April 2014);

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