100-picometer interferometry for EUVL

Gary E. Sommargren; D. W. Phillion; Michael A. Johnson; Nhan Q. Nguyen; Anton Barty; Franklyn J. Snell; Daren R. Dillon; Lloyd S. Bradsher

doi:10.1117/12.472305

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1 July 2002 100-picometer interferometry for EUVL

Gary E. Sommargren, D. W. Phillion, Michael A. Johnson, Nhan Q. Nguyen, Anton Barty, Franklyn J. Snell, Daren R. Dillon, Lloyd S. Bradsher

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Proceedings Volume 4688, Emerging Lithographic Technologies VI; (2002) https://doi.org/10.1117/12.472305
Event: SPIE's 27th Annual International Symposium on Microlithography, 2002, Santa Clara, California, United States

Abstract

Future extreme ultraviolet lithography (EUVL) steppers will, in all likelihood, have six-mirror projection cameras. To operate at the diffraction limit over an acceptable depth of focus each aspheric mirror will have to be fabricated with an absolute figure accuracy approaching 100pm rms. We are currently developing visible light interferometry to meet this need based on modifications of our present phase shifting diffraction interferometry (PSDI) methodology where we achieved an absolute accuracy of 250pm. The basic PSDI approach has been further simplified, using lensless imaging based on computational diffractive back-propagation, to eliminate auxiliary optics that typically limit measurement accuracy. Small remaining error sources, related to geometric positioning, CCD camera pixel spacing and laser wavelength, have been modeled and measured. Using these results we have estimated the total system error for measuring off-axis aspheric EUVL mirrors with this new approach to interferometry.

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Gary E. Sommargren, D. W. Phillion, Michael A. Johnson, Nhan Q. Nguyen, Anton Barty, Franklyn J. Snell, Daren R. Dillon, and Lloyd S. Bradsher "100-picometer interferometry for EUVL", Proc. SPIE 4688, Emerging Lithographic Technologies VI, (1 July 2002); https://doi.org/10.1117/12.472305

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