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24 May 2004 High-resolution optical overlay metrology
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Optical methods are often thought to lose their effectiveness as a metrology tool beyond the Rayleigh criterion. However, using advanced modeling methods, the conventional resolution limitations encountered in well-defined edge-to-edge measurements using edge thresholds do not apply. In fact, in this paper we present evidence that optics can be used to image and measure features as small as 10 nm in dimension, well below the imaging wavelength. To understand the limits of optical methods we have extensively studied both linewidth and overlay metrology applications. Although overlay applications are usually thought to involve pitch or centerline measurements of features from different process levels, some target designs present optical proximity effects which pose a significant challenge. Likewise, line width measurements require determination of the physical edges and geometry which created that profile. Both types of measurements require model-based analysis to accurately evaluate the data and images. In this paper we explore methods to optimize target geometry, optical configurations, structured illumination, and analysis algorithms with applications in both critical dimension and overlay metrology.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Richard M. Silver, Ravikiran Attota, Michael Stocker, Michael Bishop, Jau-Shi Jay Jun, Egon Marx, Mark P. Davidson, and Robert D. Larrabee "High-resolution optical overlay metrology", Proc. SPIE 5375, Metrology, Inspection, and Process Control for Microlithography XVIII, (24 May 2004);

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