19 March 2015 Overlay improvement using Legendre-Zernike model-based overlay corrections and monitoring with interpolated metric
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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.
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Md Zakir Ullah, Rajanish Javvaji, Alan Lim, Lieu Chia Chuen, Boris Habets, Stefan Buhl, Georg Erley, Steven Tottewitz, Enrico Bellmann, "Overlay improvement using Legendre-Zernike model-based overlay corrections and monitoring with interpolated metric", Proc. SPIE 9424, Metrology, Inspection, and Process Control for Microlithography XXIX, 942420 (19 March 2015); doi: 10.1117/12.2085013; https://doi.org/10.1117/12.2085013
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