15 October 2012 Technology of focus detection for 193nm projection lithographic tool
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With the shortening printing wavelength and increasing numerical aperture of lithographic tool, the depth of focus(DOF) sees a rapidly drop down trend, reach a scale of several hundred nanometers while the repeatable accuracy of focusing and leveling must be one-tenth of DOF, approximately several dozen nanometers. For this feature, this article first introduces several focusing technology, Obtained the advantages and disadvantages of various methods by comparing. Then get the accuracy of dual-grating focusing method through theoretical calculation. And the dual-grating focusing method based on photoelastic modulation is divided into coarse focusing and precise focusing method to analyze, establishing image processing model of coarse focusing and photoelastic modulation model of accurate focusing. Finally, focusing algorithm is simulated with MATLAB. In conclusion dual-grating focusing method shows high precision, high efficiency and non-contact measurement of the focal plane, meeting the demands of focusing in 193nm projection lithography.
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Chengliang Di, Chengliang Di, Wei Yan, Wei Yan, Song Hu, Song Hu, Feng Xu, Feng Xu, Jinglong Li, Jinglong Li, "Technology of focus detection for 193nm projection lithographic tool", Proc. SPIE 8418, 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Smart Structures, Micro- and Nano-Optical Devices, and Systems, 84180Y (15 October 2012); doi: 10.1117/12.971448; https://doi.org/10.1117/12.971448

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