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4 April 2012 Overlay accuracy with respect to device scaling
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Abstract
Overlay metrology performance is usually reported as repeatability, matching between tools or optics aberrations distorting the measurement (Tool induced shift or TIS). Over the last few years, improvement of these metrics by the tool suppliers has been impressive. But, what about accuracy? Using different target types, we have already reported small differences in the mean value as well as fingerprint [1]. These differences make the correctables questionable. Which target is correct and therefore which translation, scaling etc. values should be fed back to the scanner? In this paper we investigate the sources of these differences, using several approaches. First, we measure the response of different targets to offsets programmed in a test vehicle. Second, we check the response of the same overlay targets to overlay errors programmed into the scanner. We compare overlay target designs; what is the contribution of the size of the features that make up the target? We use different overlay measurement techniques; is DBO (Diffraction Based Overlay) more accurate than IBO (Image Based Overlay)? We measure overlay on several stacks; what is the stack contribution to inaccuracy? In conclusion, we offer an explanation for the observed differences and propose a solution to reduce them.
© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Philippe Leray, David Laidler, and Shaunee Cheng "Overlay accuracy with respect to device scaling", Proc. SPIE 8324, Metrology, Inspection, and Process Control for Microlithography XXVI, 832409 (4 April 2012); https://doi.org/10.1117/12.918017
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