High-irradiance illumination system for transmission extreme ultraviolet microscopy

Abstract

Abstract A high-irradiance illumination system with normal-incidence multilayer mirrors is developed. The system consists of two concave Mo/Si multilayer mirrors with aspherical substrates that provide critical illumination by imaging a laser-produced plasma (LPP) light source at a wavelength of 13.6 nm with a magnification of almost unity. By effectively correcting spherical aberration, a raytracing computation indicates that the irradiance on the sample can be increased by about four times compared to that for a conventional system with spherical mirrors. We experimentally confirmed the enhancement by combining a LPP light source with aspherical mirrors fabricated by magneto rheological finishing.