Out-of-band radiation mitigation at 10.6 μm by molecular absorbers in laser-produced plasma extreme ultraviolet sources

Chimaobi Mbanaso; Alin O. Antohe; Horace Bull; Gregory Denbeaux; Frank Goodwin; Ady Hershcovitch

doi:10.1117/1.JMM.11.2.021116

10 May 2012 Out-of-band radiation mitigation at 10.6 μm by molecular absorbers in laser-produced plasma extreme ultraviolet sources

Chimaobi Mbanaso, Alin O. Antohe, Horace Bull, Gregory Denbeaux, Frank Goodwin, Ady Hershcovitch

Author Affiliations +

Journal of Micro/Nanolithography, MEMS, and MOEMS, Vol. 11, Issue 2, 021116 (May 2012). https://doi.org/10.1117/1.JMM.11.2.021116

Abstract

Out-of-band radiation in extreme ultraviolet (EUV) exposure tools remains one of the critical issues that must be addressed before the implementation of this lithography technique for high-volume manufacturing. The out-of-band spectrum at the intermediate focus of EUV sources that use a CO₂ laser-produced plasma is dominated by scattered radiation from the drive laser, which operates near 10.6-μm wavelength. To reduce the unwanted heating of optical components in the exposure tool caused by the infrared wavelength, a 10.6-μm wavelength-absorbing gas can be used to reduce the number of photons at this wavelength reaching the intermediate focus. Gaseous sulfur hexafluoride (SF₆), whose _U₃ infrared active mode is vibrationally excited by radiation around 10.6-μm wavelength, can be used to function as a molecular absorber and thus, mitigate part of the infrared radiation. In this work, the optical absorption of gaseous SF₆ is experimentally investigated at the CO₂ laser wavelengths close to 10.6 μm as well as the EUV wavelength. Various considerations affecting the use of a gas-based spectral filter are also discussed in this paper.

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Chimaobi Mbanaso, Alin O. Antohe, Horace Bull, Gregory Denbeaux, Frank Goodwin, and Ady Hershcovitch "Out-of-band radiation mitigation at 10.6 μm by molecular absorbers in laser-produced plasma extreme ultraviolet sources," Journal of Micro/Nanolithography, MEMS, and MOEMS 11(2), 021116 (10 May 2012). https://doi.org/10.1117/1.JMM.11.2.021116

Published: 10 May 2012

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