Wavefront measurement interferometry at the operational wavelength of extreme-ultraviolet lithography |
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Authors: | Zhu Yucong Sugisaki Katsumi Okada Masashi Otaki Katsura Liu Zhiqiang Kawakami Jun Ishii Mikihiko Saito Jun Murakami Katsuhiko Hasegawa Masanobu Ouchi Chidane Kato Seima Hasegawa Takayuki Suzuki Akiyoshi Yokota Hideo Niibe Masahito |
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Affiliation: | EUVA Sagamihara R&D Center, 1-10-1 Asamizodai, Sagamihara, Kanagawa 228-0828, Japan. zhu.yucong@nikon.co.jp |
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Abstract: | Two basic types of interferometer, a point diffraction interferometer (PDI) and a lateral shearing interferometer (LSI) suitable for operation in the extreme-ultraviolet (EUV) wavelength region, are described. To address the challenges of wavefront measurement with an accuracy of 0.1 nm rms, we present a calibration method for the PDI that places a mask with two large windows at the image plane of the illumination point light source and a general approach to deriving the phase-shift algorithm series that eliminates the undesired zeroth-order effect in the LSI. These approaches to improving the measurement accuracy were experimentally verified by the wavefront measurements of a Schwarzschild-type EUV projection lens. |
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