29 August 2006 Off-plane grazing-incidence fan-groove blazed grating to serve as a high-efficiency spectral purity filter for EUV lithography
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Abstract
Reflecting large-blaze-angle diffraction gratings operating in the off-plane grazing configuration can be used to advantage as high-efficiency tools permitting separation and focusing of a 2%-wavelength about 13.5-nm. A cooled multiple grating with fan-groove geometry is used as a model to select the desired spectral range and obtain a record-high efficiency and stigmatic image focusing for a high dispersion in adjacent orders. A maximal relative efficiency of 0.96-0.99 and reflectances of 0.71-0.96 can be readily obtained with an off-plane fine-pitch grating intercepting at incidence angles of 70-85° a converging unpolarized light beam from an EUV collector, a figure higher than that of a grating in an in-plane mount. An absolute efficiency of ~0.72, calculated with a PCGrate-SX code using the AFM-measured groove profile, is reached in the -1st order of a Mo-coated 200-nm-pitch Si test grating in unpolarized light.
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Leonid I. Goray, Leonid I. Goray, } "Off-plane grazing-incidence fan-groove blazed grating to serve as a high-efficiency spectral purity filter for EUV lithography", Proc. SPIE 6317, Advances in X-Ray/EUV Optics, Components, and Applications, 63170O (29 August 2006); doi: 10.1117/12.678151; https://doi.org/10.1117/12.678151
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