Mo/Si Multilayers with Different Barrier Layers for Applications as Extreme Ultraviolet Mirrors

Abstract

Pulsed laser deposition (PLD) and magnetron sputter deposition (MSD) have been used to prepare different types of Mo/Si multilayers for the extreme ultraviolet (EUV) spectral range. In the case of PLD prepared Mo/Si multilayers the deposition of 0.3–0.5 nm thick carbon barrier layers at the interfaces leads to a substantial improvement of the interface quality. This can be deduced from Cu-Kα reflectivity measurements and HRTEM observations. Consequently the EUV reflectivity has been substantially increased. For pure Mo/Si-multilayers prepared by MSD the deposition parameters have been optimized so that a normal incidence reflectivity of REUV=68.7% could be realized. Although this is one of the best experimental results achieved so far, there is still a gap between this experimental value and the theoretical limit (REUV=75.5%). One of the main reasons for this discrepancy is the formation of intermixing zones at the interfaces. With B4C and C barrier layers at the interfaces interdiffusion can be reduced. The resulting EUV reflectivity of this new type of EUV multilayers is 69.8% (λ=13.42 nm, α=1.5°) and 71.4% (λ=12.52 nm, α=22.5°).