30 July 2002 Method of Zernike coefficients extraction for optics aberration measurement
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With recent progress in resolution enhancement techniques, requirements for exposure tools, specifically optics aberration, are becoming severer. Some simple ways to allow aberration measurements to be performed on exposure tools have been reported and made commercially available. These methods, however, do not seem to go much beyond monitoring of aberration changes while the accuracy of absolute values is left unclear. This paper describes a new approach of optics aberration measurement. With this approach, an optimum effective light source and patterns to be measured have been designed for analysis of Zernike polynomials that represent the wavefront of optics. By measuring the shift of images printed from the patterns with the light source, specific Zernike coefficients can be extracted. This new technique can also be applied to any conventional lens aberration tests using SEM. Same as the above Zernike coefficients extraction, just measuring the displacement of the images that are formed from optimum mask patterns with an optimum light source will provide a conventional SEM value. Simulations to compare the new technique with the conventional SEM showed a very good correlation with each other as expected. Experimental results are discussed to determine the accuracy of the new technique.
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Yoshihiro Shiode, Yoshihiro Shiode, Shuuichi Okada, Shuuichi Okada, Hiroki Takamori, Hiroki Takamori, Hideki Matsuda, Hideki Matsuda, Sachiko Fujiwara, Sachiko Fujiwara, } "Method of Zernike coefficients extraction for optics aberration measurement", Proc. SPIE 4691, Optical Microlithography XV, (30 July 2002); doi: 10.1117/12.474530; https://doi.org/10.1117/12.474530

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