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19 March 2015 Signal response metrology (SRM): a new approach for lithography metrology
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CD uniformity requirements at 20nm and more advanced nodes have challenged the precision limits of CD-SEM metrology, conventionally used for scanner qualification and in-line focus/dose monitoring on product wafers. Optical CD metrology has consequently gained adoption for these applications because of its superior precision, but has been limited adopted, due to challenges with long time-to-results and robustness to process variation. Both of these challenges are due to the limitations imposed by geometric modeling of the photoresist (PR) profile as required by conventional RCWA-based scatterometry. Signal Response Metrology (SRM) is a new technique that obviates the need for geometric modeling by directly correlating focus, dose, and CD to the spectral response of a scatterometry tool. Consequently, it suggests superior accuracy and robustness to process variation for focus/dose monitoring, as well as reducing the time to set up a new measurement recipe from days to hours. This work describes the fundamental concepts of SRM and the results of its application to lithography metrology and control. These results include time to results and measurement performance data on Focus, Dose and CD measurements performed on real devices and on design rule metrology targets.
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Stilian Pandev, Fang Fang, Young Ki Kim, Jamie Tsai, Alok Vaid, Lokesh Subramany, Dimitry Sanko, Vidya Ramanathan, Ren Zhou, Kartik Venkataraman, and Ronny Haupt "Signal response metrology (SRM): a new approach for lithography metrology", Proc. SPIE 9424, Metrology, Inspection, and Process Control for Microlithography XXIX, 94241P (19 March 2015);

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