Low-Stress Molybdenum/Silicon Multilayer Coatings for Extreme Ultraviolet Lithography

概要

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Modified molybdenum/silicon(Mo/Si)multilayers were deposited by ion beam sputtering(IBS). We obtained low-stress multilayers by sub-multilayering each Mo-layer into a trilayer of Mo/Ru(ruthenium)/Mo, and by argon(Ar)ion beam polishing(IBP)after each Mo-layer deposition. Conventional Mo/Si multilayers have a compressive stress of about-450MPa, while the low-stress multilayers we have developed have a tensile stress of +14 MPa, on an average. Low-stress multilayers have similar reflectances to those of conventional Mo/Si multilayers, and exhibit no significant temporal changes in the layer period and the stress for up to one year. The method used for stress reduction is not a heating process such as annealing, thus it does not cause irreversible deformation of the precisely-figured mirror substrates of optics. It is expected that the application of low-stress multilayers to mirrors will make it possible to compose optics without worsening the optical properties due to deformation of substrates by the stress of multilayer coatings.
社団法人応用物理学会の論文
2000-12-30