Optimization of LaN/B multilayer mirrors for 6.x nm wavelength

In this article we present an overview of the optimization of LaN/B multilayers that enabled the deposition of a multilayer with a normal incidence reflectance of 57.3 % at 6.6 nm wavelength, the highest value reported to date. Two different ways of nitridation of the La layers were investigated: firstly N-ion post treatment of the La layer and secondly reactive magnetron sputtering of La in N2 atmosphere. Initially the optimization of the multilayers was performed for 50 period test multilayers, followed by the selection of the best process to study the stability of the full stack deposition and the optical performance of the mirrors. The scaling of reflectivity with increasing number of periods for LaN/B multilayer mirrors will also be discussed