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