Interface structure and interdiffusion in Mo/Si multilayers

This thesis refers to the design, fabrication and characterization of Mo/Si multilayers mainly used as optics in EUV lithography. At Mo-Si interfaces, subnanometer interlayers are formed which influence microscopic (density, crystallinity) as well as macroscopic (reflectivity, stress) multilayer properties. The composition of the sub-nanometer interlayers formed at Mo/Si interfaces is not possible to determine directly with the standard techniques. This thesis focuses on the structural analysis of the Mo and Si layers and the interdiffusion along Mo/Si interfaces during and after ion bombardment and thermal treatment. The structural and chemical changes were analyzed by soft and hard X-ray measurements, in combination with TEM, XPS, XES, and AFM analysis. The structure of Mo/Si multilayers changes as a function of the Mo fraction of a multilayer period. For multilayers having low and high Mo fractions, applicable to plasma diagnostics or stress compensation, a two layer system is formed, consisting of Mo/MoXSiY or Si/MoXSiY, depending on Mo fraction. For intermediate Mo fractions, used in EUV reflective multilayer mirrors, a four layer system is formed, containing pure Mo and Si layers, as well as MoXSiY interlayers. This thesis presents a detailed study of Mo/Si multilayers for a wide range of Mo fractions, directly after deposition, as well as after thermal treatment.