20 April 2011 A CD-gap-free contour extraction technique for OPC model calibration
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Recently, optical proximity correction model calibration techniques that use SEM contours have enabled possibly significant improvements in complex mask design. However, compared to conventional CD-based calibration, contour-based calibration results in increased errors in 1D features. In fact, our research shows that there is a ~1-nm gap, which we call "CD-gap," between CD measurements directly calculated from a SEM image and CD measurements calculated from SEM contours. To achieve accurate calibration, SEM contours must match the corresponding CD measurements. We have developed a CD-gap-free contour extraction technique in response to this problem. In our technique, a mask edge is classified into shape structures and an optimized SEM contour extraction method is prepared for each shape structure to reduce the CD-gap. Experimental results show that the CD-gap can be decreased to sub-nm, which clearly demonstrates the potential of our proposed technique to play a vital role in the lithography process.
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T. Shibahara, T. Shibahara, T. Minakawa, T. Minakawa, M. Oikawa, M. Oikawa, H. Shindo, H. Shindo, H. Sugahara, H. Sugahara, Y. Hojyo, Y. Hojyo, } "A CD-gap-free contour extraction technique for OPC model calibration", Proc. SPIE 7971, Metrology, Inspection, and Process Control for Microlithography XXV, 79710O (20 April 2011); doi: 10.1117/12.878583; https://doi.org/10.1117/12.878583

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