Low-Order Aberrations Correction of Extreme Ultraviolet Imaging Objective with Deformable Multilayer Mirrors

Mitsunori Toyoda, Ryo Sunayama, Mihiro Yanagihara, Schaa, Volker RW (Ed.)
For at-wavelength observation of a lithography mask, recently, we proposed an EUV microscope consisting of multilayer-mirror objective (operating wavelength: 13.5 nm, numerical aperture: 0.25). To provide diffraction-limited spatial resolution below 30 nm, reduction of wave aberrations of low order, i.e., spherical aberration, coma, and astigmatism, should be key technical challenge for the microscope. In this paper, firstly, we describe detail of optical design and instrumentation of the point
more » ... tation of the point diffraction interferometer (PDI), so as to provide high enough sensing accuracy of 100 pm, which would be required for an optical axis adjustment of the EUV objective. Next, experimental results of wave front correction on the EUV objective are reported. We corrected spherical aberration and coma by precisely aligning an optical axis of the mirrors, while effects of astigmatism were also minimized with a figure-deformable mirror which can control radius of curvature in two mutually orthogonal directions. We confirmed that these low order terms should be less than 0.3 nm RMS.
doi:10.18429/jacow-medsi2016-tupe22 fatcat:stkjtjluavedreme56hph3vg4y