Multilayer lifetime has emerged as one of the major issues for the commercialization of extreme-ultraviolet lithography (EUVL). We describe the performance of an oxidation-resistant capping layer of Ru atop multilayers that results in a reflectivity above 69% at 13.2 nm, which is suitable for EUVL projection optics and has been tested with accelerated electron-beam and extreme-ultraviolet (EUV) light in a water-vapor environment. Based on accelerated exposure results, we calculated multilayer lifetimes for all reflective mirrors in a typical commercial EUVL tool and concluded that Ru-capped multilayers have approximately 40x longer lifetimes than Si-capped multilayers, which translates to 3 months to many years, depending on the mirror dose.

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Articles you may be interested inResonance effects in photoemission from TiO2-capped Mo/Si multilayer mirrors for extreme ultraviolet applications J. Appl. Phys. 109, 083112 (2011); 10.1063/1.3575319 Iridium/silicon capping layer for soft x-ray and extreme ultraviolet mirrors

The transmission of soft x rays with photon energies from 1606 eV to 2106 eV was measured for tungsten using thin-film samples and a synchrotron source. This region includes the M IV and M V edges. The two tungsten films had thicknesses of 107.7Ϯ10 nm and 51.5Ϯ10 nm; the intensity of the transmitted x rays was measured with a silicon photodiode. The values for the mass absorption coefficient reported here were determined from the ratios of the transmission through the two samples, i.e., through a net 56.2Ϯ14 nm of tungsten, and some additional constant factors. The M V,IV edges have widths ͑10%-90% after background subtraction͒ of 33Ϯ5 eV and 28Ϯ5 eV, respectively, compared to zero width in all x-ray tables based on atomic form factors and to 41 eV and 44 eV within a real-space multiple-scattering theory. The measurements are relevant to microspectroscopy and microtomography of integrated circuit interconnects and may be applicable to accurate measurement of the mass absorption coefficients of similar dense elements.