Thermo-correction of quasi-static optical distortions in optical reducing systems for EUV projection lithography

摘要

Optical reducing systems for the extreme ultraviolet projection lithography are actively developed in the last few years. Optical elements of these systems are required to be of super-high optical quality. For the systems operating in the 13-nm wavelength range, their optical distortions should not exceed 1 nm in magnitude. Manufacturing of such elements requires large financial injections, In this report, we consider how to use thermal deformation of an optical element exposed to light for improvement of optical quality of the element. It is shown, in particular, that residual quasi-static large-scale (20% of diameter of the element) optical distortions, about 15 nm in magnitude, can be compensated with the proposed technique down to 0.5 nm (i.e. ≈ λ_0/20 - λ_0/30 in the EUV).