14 June 1999 Optical linewidth models: then and now
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In the late 1970's Dr. Diane Nyyssonen demonstrated that the NIST could optically calibrate photomask linewidth standards that were narrower than the classical resolution limit of a conventional bright-field microscope. She equated the unknown edge position on the observed image profile to the known edge position on a theoretically calculated image profile of that line. Since at that time, there was no other way to accurately identify the position of the geometrical edge of micrometer-sized lines on their observed optical images, NIST would not have been able to issue accurate photomask linewidth standards without her theoretical model. NIST has initiated a program to re-examine Nyyssonen's model to see how well it meets today's requirements for linewidth standards. Fortunately, one of the authors conferred with Dr. Diana Nyyssonen about her model before her untimely death, and he was able to improve the utility and accuracy of her model. He removed some of her assumptions and improved the efficiency of computations to the point where they could be done on a desktop computer. This paper will detail the result of the initial comparison of the Nyyssonen and Davidson models as applied to photomasks and will identify any significance of the differences as applied to the calibration of NIST photomask standards.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Robert D. Larrabee, Robert D. Larrabee, Richard M. Silver, Richard M. Silver, Mark P. Davidson, Mark P. Davidson, "Optical linewidth models: then and now", Proc. SPIE 3677, Metrology, Inspection, and Process Control for Microlithography XIII, (14 June 1999); doi: 10.1117/12.350855; https://doi.org/10.1117/12.350855

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