On the Prospects of Lithography in the Region of Wavelengths Shorter than 13.5 nm

A brief historical overview of the development of projection lithography in the extreme ultraviolet (EUV) range at a wavelength of 13.5 nm is presented. Using an eleven-mirror X-ray optical system as an example, the efficiency of a source—X-ray optics system for wavelengths of 13.5 nm (Mo/Si multilayer mirrors, tin laser-plasma source), 11.2 nm (Ru/Be multilayer mirrors, xenon source), and 10.8 nm (multilayer mirrors Ru/Sr, xenon source) is compared. Calculation is carried out taking into account experimental data on the reflection coefficients of multilayer mirrors and the conversion efficiency of laser-plasma X-ray sources based on multiply charged Sn and Xe ions. The maximum reflection coefficients of multilayer mirrors achieved are: RMo/Si = 70.15%, RRu/Be = 72.2%, and RRu/Sr = 62.2%. The efficiency of conversion of laser-radiation energy into X-ray radiation based on Sn ions at a wavelength of 13.5 nm corrected for the actual transmission band of the X-ray optical system is taken equal to CE13.5 = 5.4%. The conversion efficiency of the source based on Xe ions is taken equal to: CE11.2 = 1.0% and CE10.8 = 1.6%. The calculated productivity of lithographs expressed in arbitrary units at various wavelengths is: LP13.5 = 0.1091, LP11.2 = 0.0278, and LP10.8 = 0.0089. Despite the lower productivity, due to significant simplification of the lithograph design and the lower cost of both the equipment and its operation, lithography at a wavelength of 11.2 nm has good prospects for practical application.