Smoothing of diamond-turned substrates for extreme-ultraviolet lithography illuminators

Regina Soufli; Eberhard Spiller; Mark A. Schmidt; Jeffrey C. Robinson; Sherry L. Baker; Susan Ratti; Michael A. Johnson; Eric M. Gullikson

doi:10.1117/12.509220

13 January 2004 Smoothing of diamond-turned substrates for extreme-ultraviolet lithography illuminators

Regina Soufli, Eberhard Spiller, Mark A. Schmidt, Jeffrey C. Robinson, Sherry L. Baker, Susan Ratti, Michael A. Johnson, Eric M. Gullikson

Author Affiliations +

Proceedings Volume 5193, Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications; (2004) https://doi.org/10.1117/12.509220
Event: Optical Science and Technology, SPIE's 48th Annual Meeting, 2003, San Diego, California, United States

Abstract

Condenser optics in extreme ultraviolet lithography (EUVL) systems are subjected to frequent replacement as they are positioned close to the illumination source, where increased heating and contamination occur. In the case of aspherical condenser elements made by optical figuring/finishing, their replacement can be very expensive (several hundred thousand dollars). One approach to this problem would be to manufacture inexpensive illuminator optics that meet all required specifications and could be replaced at no substantial cost. Diamond-turned metal substrates are a factor of 100 less expensive than conventional aspherical substrates but have insufficient finish, leading to unacceptably low EUV reflectance after multilayer coating. In this work it is shown that, by applying a smoothing film prior to multilayer coating, the high spatial frequency roughness of a diamond-turned metal substrate is reduced from 1.76 to 0.27 nm rms while the figure slope error is maintained at acceptable levels. Metrology tests performed at various stages of the fabrication of the element demonstrated that it satisfied all critical figure and finish specifications as illuminator. Initial experimental results on the stability and performance of the optic under a real EUVL plasma source environment show no accelerated degradation when compared to conventional substrates.

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Regina Soufli, Eberhard Spiller, Mark A. Schmidt, Jeffrey C. Robinson, Sherry L. Baker, Susan Ratti, Michael A. Johnson, and Eric M. Gullikson "Smoothing of diamond-turned substrates for extreme-ultraviolet lithography illuminators", Proc. SPIE 5193, Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications, (13 January 2004); https://doi.org/10.1117/12.509220

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