Optical elements for Extreme ultraviolet (EUV) Photolithography fall into several categories: most notably mirrors, but also (transmissive) beam splitters, spectral filters, diffusers, sensors and fiducial reference plates. All these components are challenged to the extreme by the stringent demands of photolithography at roughly 10 nm resolution, and the high-power EUV sources of up to 500 W today. This puts stringent requirements on materials, manufacturing and pretreatments of EUV optical elements, and requires deep understanding of the interaction between these optical elements and the EUV irradiation and the low-pressure background gas. While much is known about the interaction between EUV and mirrors, also elements like membranes are integral parts of today’s lithography tools. In this paper, we will give an overview of these interactions, and will dive deeper in the recent improvements in highpower transmissive membranes, and will also address some options being considered to extend the power limits even further to beyond 1000 W.
|