EUV spectral purity filter: optical and mechanical design, grating fabrication, and testing

Abstract

The radiation emitted from an EUV source is collected and focused by a suitable collector system. A reflective blazed grating is used in -1st diffraction order to select a definite spectral band around 13.5 nm wavelength from the broad-band emission spectrum of the source. The effective grating area is segmented into a set of different plane gratings, mounted on a common base plate. In order to focus the light from the collector system, the grating segments are tilted and form a best-fit polygon surface. A specific groove density variation on the grating segments significantly improves the imaging performance. In this paper, we report on design, fabrication and testing of the grating system.