Actinic defect counting statistics over 1-cm2 area of EUVL mask blank
As a continuation of comparison experiments between EUV inspection and visible inspection of defects on EUVL mask blanks, we report on the result of an experiment where the EUV defect inspection tool is used to perform at-wavelength defect counting over 1 cm2 of EUVL mask blank. Initial EUV inspection found five defects over the scanned area and the subsequent optical scattering inspection was able to detect all of the five defects. Therefore, if there are any defects that are only detectable by EUV inspection, the density is lower than the order of unity per cm2. An upgrade path to substantially increase the overall throughput of the EUV inspection system is also identified in the manuscript.
At-wavelength detection of extreme ultraviolet lithography mask blank defects
We report the design and operation of an at-wavelength system for extreme ultraviolet lithography mask blank defect detection. Initial results demonstrate sensitivity to submicron size phase defects. The performance of the system is compared with the practical requirements for a mask blank inspection system in terms of the sensitivity and scanning time.
A new optical design method and its application to an extreme ultraviolet varied line spacing plane grating monochromator
Abstract A new design method has been developed for a double-element optical system. The method incorporates a very simple ray tracing procedure into an analytic merit function that closely represents the variance of an infinite number of ray-traced spots in the image plane. A 174° constant-deviation objective Monk-Gillieson monochromator consisting of a highly demagnifying ( ∼ 1 10 ) spherical mirror, varied spacing plane grating, and elliptic cylindrical focusing mirror has been designed for a bending-magnet beamline using the new design method. Ray-tracing results show that the new design can provide higher spectral purity and throughput as compared to a design based on the light path function and that the monochromator design gives slit-width-limited resolutions over a wavelength range of 2–5 nm.