The Role of Molybdenum in Enhancing Al/Sc Multilayers for EUV Applications

Researchers have been exploring the use of Aluminum/Scandium (Al/Sc) multilayers for optical applications in the extreme ultraviolet (EUV) range. These multilayers are particularly useful for wavelengths longer than the Sc M2, 3 absorption edge. One key challenge is improving the interface quality within these multilayers. This is where molybdenum (Mo) barrier layers come into play. They can significantly enhance the performance of Al/Sc multilayers. To understand how Mo barrier layers affect the interface and microstructure of Al/Sc multilayers, a variety of experiments were conducted. These included the fabrication of different multilayer structures: Al/Sc, Al/Sc/Mo, Al/Mo/Sc, and Al/Mo/Sc/Mo. The multilayers were created using a technique called direct-current magnetron sputtering. This method involves bombarding a target material with ions to deposit thin films onto a substrate. Several advanced techniques were used to analyze the impact of Mo barrier layers. These included grazing incidence X-ray reflectivity, transmission electron microscopy, selected area electron diffraction, energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray absorption spectroscopy. The findings revealed that Mo barrier layers, approximately 0. 5 nm thick, have distinct roles depending on their placement within the multilayer structure.

When Mo barriers are placed at the Al-on-Sc interfaces, they primarily suppress the columnar crystallization of Al layers. This means they help prevent the formation of column-like structures in the Al layers, which can lead to rough interfaces. By doing so, Mo barriers contribute to smoother interfacial surfaces. On the other hand, thin Mo layers at the Sc-on-Al interfaces act as antidiffusion barriers. They prevent the diffusion of Al atoms into the Sc layers, maintaining the integrity of the multilayer structure. The research established a model to explain how Mo barrier layers influence interface diffusion and microstructure in Al/Sc multilayers. This model provides a framework for understanding and optimizing the use of Mo barriers in future applications. It highlights the importance of strategic placement of Mo layers to achieve desired properties in Al/Sc multilayers. In summary, the incorporation of Mo barrier layers in Al/Sc multilayers offers a promising approach to enhancing their performance in the EUV range. By understanding the specific roles of Mo barriers at different interfaces, researchers can develop more effective optical elements for various applications.

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