Improved contrast and reflectivity of multilayer reflective optics for wavelenghts beyond the Extreme UV

We present a computational and experimental study on interface passivation of B4C/La multilayers for photolithography at wavelengths beyond 13.5 nm. We successfully applied N-plasma treatment to form interface-localized BN and LaN layers, preventing LaB6 and LaC2 interlayer formation and increasing the optical contrast. Experiments suggest an improvement of absolute reflection by up to 20% for 200 period multilayers, with a best-so-far result of 41.5 % at near-normal incidence of 6.7 n