High reflectance La/B based multilayer mirrors for 6.x nm wavelength

For future photolithography processes, the wavelength of 6 nm may offer improved imaging specs. The perspective of this technology however, will depend critically on the performance of multilayer reflective mirrors, which are likely to be based on La/B. One of the issues is formation of LaxBy compounds at the interfaces, which decreases the optical contrast and reduce the reflectivity. To prevent such chemical interaction, passivation of La by nitrogen has been investigated. We successfully synthesized LaN layers that resulted in a new world record reflectivity of 64% at 6.6 nm at near normal incidence. This reduces the gap to the target of 70%, desired for a next generation lithography.