Optimizing 13.5 nm laser-produced tin plasma emission as a function of laser wavelength

摘要

Extreme ultraviolet lithography requires a light source at 13.5 nm to match the proposed multilayer optics reflectivity. The impact of wavelength and power density on the ion distribution and electron temperature in a laser-produced plasma is calculated for Nd:YAG and CO_2 lasers. A steady-state figure of merit, calculated to optimize emission as a function of laser wavelength, shows an increase with a CO_2 laser. The influence of reduced electron density in the CO_2 laser-produced plasma is considered in a one-dimensional radiation transport model, where a more than twofold increase in conversion efficiency over that attainable with the Nd:YAG is predicted.