1 June 1992 Accuracy of overlay measurements: tool and mark asymmetry effects
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Definitions of centerline and centerline overlay (O/L) are built on the implicit assumptions of certain symmetries. Verification of these symmetries, and the use of redundancies built into the design of O/L measurement marks, can estimate the relative accuracy of O/L measurements, even in the absence of certified reference materials (standards). Verification carried out as of paired comparison is shown to be very effective; in addition, it constitutes the basis for data culling. Several sources of O/L measurement inaccuracy, associated with O/L measurement tools and with O/L measurement marks, are pointed out and some are illustrated using modeling. A simple measure of tool-related inaccuracy, tool-induced shift (TIS), is proposed and utilized as a performance estimate of O/L measurement tools relative to accuracy. Inaccuracies of O/L measurements, caused by O/L measurement tools and marks, on the order of 100 nm, are observed and their causes identified. Examples are given of significant improvements in accuracy. A roadmap toward accurate O/L measurement is outlined. This approach is also applicable to alignment systems.
Alexander Starikov, Alexander Starikov, Daniel J. Coleman, Daniel J. Coleman, Patricia J. Larson, Patricia J. Larson, Alexander D. Lopata, Alexander D. Lopata, William A. Muth, William A. Muth, } "Accuracy of overlay measurements: tool and mark asymmetry effects," Optical Engineering 31(6), (1 June 1992). https://doi.org/10.1117/12.56172 . Submission:

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