Deposition of multilayer mirrors with arbitrary period thickness distributions

Abstract

In this paper we will 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 lateral varying particle transmission is placed in front of the substrate to be coated. Planar and curved substrates have been used to deposit multilayers with prescribed period thickness gradients. The realized laterally graded multilayer interference mirrors have been investigated by using X-ray and EUV-reflectometry. For the example of Mo/Si multilayers as normal incidence reflectors for EUV light at 13.5 nm it has been demonstrated that high-reflection multilayer mirrors can be deposited using the new deposition technique. Typical EUV reflectance of Mo/Si multilayer 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 have been coated. The nominal thicknesses were compared with the actual values. Furthermore, steep gradients of the period thickness with thickness changes of typically 5% along a length of 5mm have been prepared and characterized.