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Proceedings Paper

High-radiance LDP source: clean, reliable, and stable EUV source for mask inspection
Author(s): Yusuke Teramoto; Bárbara Santos; Guido Mertens; Ralf Kops; Margarete Kops; Alexander von Wezyk; Klaus Bergmann; Hironobu Yabuta; Akihisa Nagano; Noritaka Ashizawa; Yuta Taniguchi; Takahiro Shirai; Kiyotada Nakamura; Kazuya Aoki; Kunihiko Kasama
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Paper Abstract

High-throughput and -resolution actinic mask inspection tools are needed as EUVL begins to enter into volume production phase. To realize such inspection tools, a high-radiance EUV source is necessary. Ushio’s laser-assisted discharge-produced plasma (LDP) source is able to meet industry’s requirements in radiance, cleanliness, stability and reliability. Ushio’s LDP source has shown the peak radiance at plasma of 180 W/mm2/sr and the area-averaged radiance in a 200-μm-diameter circle behind the debris mitigation system of 120 W/mm2/sr. A new version of the debris mitigation system is in testing phase. Its optical transmission was confirmed to be 73 %, which is 4 % lower than that of the previous version and therefore will be improved. Cleanliness of the system is evaluated by exposing Ru mirrors placed behind the debris mitigation system. Ru sputter rate was proven to be sufficiently low as 3~5 nm/Gpulse at 7 kHz, whereas frequency-dependent sputter rate was 1~3 nm/Gpulse at 5~9 kHz as previously reported. Sn deposition remained very low (< 0.05 nm) and did not grow over time. A new technique to suppress debris was tested and preliminary results were promising. Time-of-flight signal of fast ions was completely suppressed and Ru sputter rate of exposed mirrors at 3 kHz was approximately 1.3 nm/Gpulse, whereas the conventional mitigation system (new version) resulted in Ru sputter rate of 0.7 nm/Gpulse. This new technique also allows increasing the radiance efficiency by 30 %. Stability tests were done at several different discharge frequencies. Pulse energy stability was approximately 10 %. Dose energy stability dropped from approximately 2 % to 0.1 % when feedback control was activated. EUV emission position stability was studied at 3 kHz. Deviation of the plasma center of gravity was 6 μm, which is 3 % of plasma diameter and therefore considered to be negligible. Reliability tests were performed on both R and D and prototype machines and up to 200 hours of non-interrupted operation was demonstrated.

Paper Details

Date Published: 18 March 2016
PDF: 8 pages
Proc. SPIE 9776, Extreme Ultraviolet (EUV) Lithography VII, 97760L (18 March 2016); doi: 10.1117/12.2219219
Show Author Affiliations
Yusuke Teramoto, BLV Licht-und Vakuumtechnik Gmbh (Germany)
Bárbara Santos, BLV Licht-und Vakuumtechnik Gmbh (Germany)
Guido Mertens, BLV Licht-und Vakuumtechnik Gmbh (Germany)
Ralf Kops, BLV Licht-und Vakuumtechnik Gmbh (Germany)
Margarete Kops, BLV Licht-und Vakuumtechnik Gmbh (Germany)
Alexander von Wezyk, Fraunhofer ILT (Germany)
Klaus Bergmann, Fraunhofer ILT (Germany)
Hironobu Yabuta, Ushio Inc. (Japan)
Akihisa Nagano, Ushio Inc. (Japan)
Noritaka Ashizawa, Ushio Inc. (Japan)
Yuta Taniguchi, Ushio Inc. (Japan)
Takahiro Shirai, Ushio Inc. (Japan)
Kiyotada Nakamura, Ushio Inc. (Japan)
Kazuya Aoki, Ushio Inc. (Japan)
Kunihiko Kasama, Ushio Inc. (Japan)

Published in SPIE Proceedings Vol. 9776:
Extreme Ultraviolet (EUV) Lithography VII
Eric M. Panning, Editor(s)

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