title: Wavefront measurement interferometry at the operational wavelength of extreme-ultraviolet lithography.
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.
authors: EUVA Sagamihara R&D Center, 1-10-1 Asamizodai, Sagamihara, Kanagawa 228-0828, Japan. zhu.yucong@nikon.co.jp
authors: Yucong
authors: Y
authors: Zhu
authors: Katsumi
authors: K
authors: Sugisaki
authors: Masashi
authors: M
authors: Okada
authors: Katsura
authors: K
authors: Otaki
authors: Zhiqiang
authors: Z
authors: Liu
authors: Jun
authors: J
authors: Kawakami
authors: Mikihiko
authors: M
authors: Ishii
authors: Jun
authors: J
authors: Saito
authors: Katsuhiko
authors: K
authors: Murakami
authors: Masanobu
authors: M
authors: Hasegawa
authors: Chidane
authors: C
authors: Ouchi
authors: Seima
authors: S
authors: Kato
authors: Takayuki
authors: T
authors: Hasegawa
authors: Akiyoshi
authors: A
authors: Suzuki
authors: Hideo
authors: H
authors: Yokota
authors: Masahito
authors: M
authors: Niibe