リソグラフィ用 EUV(極端紫外)光源研究の現状と将来展望 3.EUV リソグラフィ光源としてのプラズマ その理論的な考察について

An extreme ultraviolet (EUV) radiation source is a critical factor for the success of EUV lithography. Although there are many methods and operating parameters for the generation of EUV light, none of the currently known sources meets the requirements of EUV lithography systems. In addition, the EUV source must be an integral part of a total lithography system, and must satisfy several criteria imposed by other parts of the entire system. For the purpose of examining the prospects for such sources, the emissivity from hot dense plasmas has been estimated with a model including opacity, ion abundance, hydrodynamics, and radiation transport. For quantitative estimation, the similarity of energy structure of Xe9+ and Xe10+ is considered. Only a small amount of data exists regarding Xe10+ ionization and energies of excited states. Various ideas for improvements are presented.