14 November 2003 Precise in-situ transmission measurement system at 157 nm
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Precise in-situ transmission testing is necessary for evaluation of materials to be used in lithography systems, which use light source at the wavelength of 157 nm. Fluorine (F2) excimer lasers have pulse-to-pulse energy variation (< 9 %, 3 sigma, from manufacturer's specification), and pulse energy monitoring is required for precise evaluation. Due to the uncontrolled fluctuations of the polarization and high pulse energy of the laser, it is difficult to monitor the laser pulse energy and to achieve precision measurement. We have built a precise in-situ transmittance measurement system, employing polarization insensitive beam splitters for precision pulse energy monitoring. The beam splitter consists of three parallel plates. This scheme eliminates the effects of polarization fluctuation and decreases the energy to the detector. We have obtained 0.1 % (3 sigma) stability in our transmission measurement using this assembly.
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Seiji Takeuchi, Yasuhiro Kishikawa, Minoru Yoshii, Akiyoshi Suzuki, "Precise in-situ transmission measurement system at 157 nm", Proc. SPIE 5192, Optical Diagnostic Methods for Inorganic Materials III, (14 November 2003); doi: 10.1117/12.506614; https://doi.org/10.1117/12.506614

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