SPIE photomask technology
1 December 2022
High-brightness LDP source for EUVL mask inspection
Ryuta Furuya1, Kazuya Aoki1, Yusuke Teramoto1, Takahiro Shirai1, Shunichi Morimoto1,
Hidenori Watanabe1, Akihisa Nagano1, Daisuke Yajima1, Noritaka Ashizawa1 ,Yoshihiko Sato1,
1Ushio Inc. (Japan)
Ushio has been delivering LDP sources for EUV mask actinic inspection. Our LDP source is suitable for mask inspection purposes because of its good position stability, high brightness, and sufficient cleanliness. In the field, availability of LDP sources keeps about 90% and additional improvement measures will be deployed to achieve 95%. In recent progress, we are investigating the plasma shape control guideline by changing discharge conditions. Also, we have decreased the debris emission from the plasma by optimizing laser conditions, and additional cleanliness improvement is expected by optimization of debris shield structure. High pulse frequency LDP sources are also under investigation which have an advantage in temporal stability. We have demonstrated 14 kHz operation in the laboratory and extensive study is undergoing.
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