Interface characterization in B-based multilayer mirrors for next generation lithography

The interfaces in La/B4C and LaN/B4C multilayer mirrors designed for near normal incidence reflection of 6.x nm EUV light were investigated by grazing incidence X-ray reflectometry, high-resolution transmission electron microscopy and EUV reflectometry. The thickness and roughness asymmetries of the different interfaces in both studied systems have been identified. A development of interface roughness with an increasing number of bilayers was found by different investigation methods. For near normal incidence, R = 51.1% @ λ = 6.65 nm could be reached with our La/B4C multilayer mirrors, whereas R = 58.1% was achieved with LaN/B4C multilayers at the same wavelength.