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Proceedings Paper

Overlay improvement using Legendre-Zernike model-based overlay corrections and monitoring with interpolated metric
Author(s): Md Zakir Ullah; Rajanish Javvaji; Alan Lim; Lieu Chia Chuen; Boris Habets; Stefan Buhl; Georg Erley; Steven Tottewitz; Enrico Bellmann
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Paper Abstract

This paper focuses on orthogonal model corrections where model parameters do not influence each other as long as the measurement layout is sufficiently symmetric. For the grid correction we used Zernike polynomials, and for the intrafield correction we used a two-dimensional set of Legendre polynomials. We enabled these corrections by developing a transformation matrix as an exposure tool is incapable of correcting such orthogonal polynomials. Simulation with OVALiS shows that the linear parameters get stabilized by several factors when using a combined Zernike/Legendre model. The correlation between linear and higher order parameters disappears, and overlay mean plus 3-sigma improves up to ~15–20%. Simulated data agrees well with experimental and electrical data. Additionally, we introduced an interpolated metric that probed the wafer and field with a dense grid. This interpolated metric showed that the Zernike/Legendre model-based correction does not cause over-correction like that seen on standard polynomial models. We have tested higher order process corrections comprehensively by enabling an orthogonal model, as well as by making use of interpolated metrics to monitor the overlay performance. These orthogonal models can be implemented in the production line based on inline overlay data where interpolated metrics will ensure that there is no over-correction and no negative impact on product.

Paper Details

Date Published: 19 March 2015
PDF: 14 pages
Proc. SPIE 9424, Metrology, Inspection, and Process Control for Microlithography XXIX, 942420 (19 March 2015); doi: 10.1117/12.2085013
Show Author Affiliations
Md Zakir Ullah, Micron Semiconductor Asia Pte. Ltd. (Singapore)
Rajanish Javvaji, Micron Semiconductor Asia Pte. Ltd. (Singapore)
Alan Lim, Micron Semiconductor Asia Pte. Ltd. (Singapore)
Lieu Chia Chuen, Micron Semiconductor Asia Pte. Ltd (Singapore)
Boris Habets, Qoniac GmbH (Germany)
Stefan Buhl, Qoniac GmbH (Germany)
Georg Erley, Qoniac GmbH (Germany)
Steven Tottewitz, Qoniac GmbH (Germany)
Enrico Bellmann, Qoniac GmbH (Germany)

Published in SPIE Proceedings Vol. 9424:
Metrology, Inspection, and Process Control for Microlithography XXIX
Jason P. Cain; Martha I. Sanchez, Editor(s)

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