18 April 2013 High accuracy CD matching monitor for CD-SEM beyond 20nm process
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In recent years, semiconductor makers have been developing 1Xnm HP (Half Pitch) node devices. It is a requirement for CD-SEM to improve measurement uncertainty of not only the basic short-term repeatability, but also of the long-term stability and tool-to-tool matching. A conventional method called “Common Site Method” has been used to evaluate the uncertainty of CD-SEM measurement. In this method, target patterns on an identical sample and identical measurement point, which is the common site, is measured repeatedly. Common Site Method has possible instability factors as follows; 1) Carry-over due to contamination and/or charging caused by repeated measurement on the same points 2) Dimensional variation caused by the use of non-identical patterns between the groups These issues cannot be solved by averaging the results from many measurement points. In this paper we introduce a new method: “Fresh Site Method” to check the long-term stability and tool-to-tool matching with high precision. In this method, a target on arbitrary point extracted randomly from a large area of dense pattern is measured on multiple dies. Precision of the measurement is improved by increasing the number of dies for the measurement because influence of the CD non-uniformity among the dies is reduced by the averaging effect of the measurement points. In addition, “Macro-Area Measurement” method[1][2] can reduce both the measurement uncertainty, caused by sample variation, and measurement time. As a result, the precision of CD-SEM monitoring using Fresh Site Method with Macro-Area Measurement produce sufficient results for the evaluation of CD-SEM measurement uncertainty, realizing a reproducibility performance below 0.1nm.
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K. Ueda, K. Ueda, T. Mizuno, T. Mizuno, K. Setoguchi, K. Setoguchi, "High accuracy CD matching monitor for CD-SEM beyond 20nm process", Proc. SPIE 8681, Metrology, Inspection, and Process Control for Microlithography XXVII, 868135 (18 April 2013); doi: 10.1117/12.2011389; https://doi.org/10.1117/12.2011389

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