Simulation study on the influence of interface asymmetry on soft x-ray reflectivity of Mo/Si multilayers

Mo/Si multilayers have been gaining industry interest as a promising choice for the next generation soft-x-ray projection lithography. Usually, an asymmetrical interlayer transition zones is formed in sputtered Mo/Si multilayers and Mo-on-Si interface is thicker than Si-on-Mo one. In order to study the influence of interface asymmetry on soft X-ray reflectivity of Mo/Si multilayers, a four-layeT model is used to simulate soft X-ray reflectivity of Mo/Si multilayers at a given wavelength. The simulation study shows that interface asymmetry is not always disadvantageous to reflectivity of Mo/Si multilayers. When the sum of thickness of Mo-on-Si interface and Si-on-Mo interface is fixed, soft X-ray reflectivity of multilayers can be improved through increasing the thickness ratio of Mo-on-Si interface to Si-on-Mo interface. As the thickness of Si-on-Mo interface is fixed, only by increasing the thickness of of Mo-on-Si interface, soft X-ray reflectivity of multilayers can be improved. While the thickness of Mo-on-Si interface is fixed, only by increasing the thickness of Si-on-Mo interface, soft X-ray reflectivity of multilayers can be basically invariable.