Custom-tailored nm-multilayers for EUV and X-ray optical applications

We describe a new approach for the deposition of multilayers with arbitrary period thickness distributions. The standard technique of magnetron sputter deposition has been extended to a design where a special mask with laterally varying particle transmission is placed in front of the substrate to be coated. Initially, a mask with laterally uniform transmission was applied to characterize the resulting uniformity of the coating. The optical performance has been investigated by reflectance measurements. For the example of Mo/Si multilayers as normal incidence reflectors for EUV light of λ=13.5 nm it has been demonstrated that hig h-reflection multilayer mirrors can be deposited using the new deposition technique. Typical EUV reflectances of Mo/Si multilayers with carbon barrier layers are in the order of 70 %. In addition, non-uniform masks have been used and several 1- and 2-dimensional period thickness gradients were coated and the measured a nd nominal thicknesses have been compared.