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Proceedings Paper

Faster diffraction-based overlay measurements with smaller targets using 3D gratings
Author(s): Jie Li; Oleg Kritsun; Yongdong Liu; Prasad Dasari; Catherine Volkman; Jiangtao Hu
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Paper Abstract

Diffraction-based overlay (DBO) technologies have been developed to address the overlay metrology challenges for 22nm technology node and beyond. Most DBO technologies require specially designed targets that consist of multiple measurement pads, which consume too much space and increase measurement time. The traditional empirical approach (eDBO) using normal incidence spectroscopic reflectometry (NISR) relies on linear response of the reflectance with respect to overlay displacement within a small range. It offers convenience of quick recipe setup since there is no need to establish a model. However it requires three or four pads per direction (x or y) which adds burden to throughput and target size. Recent advances in modeling capability and computation power enabled mDBO, which allows overlay measurement with reduced number of pads, thus reducing measurement time and DBO target space. In this paper we evaluate the performance of single pad mDBO measurements using two 3D targets that have different grating shapes: squares in boxes and L-shapes in boxes. Good overlay sensitivities are observed for both targets. The correlation to programmed shifts and image-based overlay (IBO) is excellent. Despite the difference in shapes, the mDBO results are comparable for square and L-shape targets. The impact of process variations on overlay measurements is studied using a focus and exposure matrix (FEM) wafer. Although the FEM wafer has larger process variations, the correlation of mDBO results with IBO measurements is as good as the normal process wafer. We demonstrate the feasibility of single pad DBO measurements with faster throughput and smaller target size, which is particularly important in high volume manufacturing environment.

Paper Details

Date Published: 5 April 2012
PDF: 8 pages
Proc. SPIE 8324, Metrology, Inspection, and Process Control for Microlithography XXVI, 83241I (5 April 2012); doi: 10.1117/12.916747
Show Author Affiliations
Jie Li, Nanometrics Inc. (United States)
Oleg Kritsun, GLOBALFOUNDRIES Inc. (United States)
Yongdong Liu, Nanometrics Inc. (United States)
Prasad Dasari, Nanometrics Inc. (United States)
Catherine Volkman, GLOBALFOUNDRIES Inc. (United States)
Jiangtao Hu, Nanometrics Inc. (United States)

Published in SPIE Proceedings Vol. 8324:
Metrology, Inspection, and Process Control for Microlithography XXVI
Alexander Starikov, Editor(s)

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