Radiative properties and hydrodynamics of laser-produced tin plasma for efficient extreme ultraviolet light source

A laser-produced tin (Sn) plasma is an attractive extreme-ultraviolet (EUV) light source for the next generation lithography in terms of its brightness and compactness. Radiative properties and hydrodynamics of the laser-produced Sn plasmas are quite important for investigating the optimum conditions for EUV generation. Several experiments have been performed to clarify the above issues; (i) EUV spectra emitted from isolated Snq+ (5 < q < 15) ions and opacity spectrum of a 30-eV Sn plasma have been measured as fundamental data for accurate modeling radiation energy transport in plasmas, (ii) electron density profile in 13.5 nm emission dominant region of a laser-produced Sn plasma was measured with a laser interferometer for understanding hydrodynamics of an EUV source plasma. (iii) benchmarking one-dimensional (ID) radiation-hydrodynamic simulation code with multiple laser beam irradiated spherical ID Sn plasma. Based on the experimental results and calculations, it was found that optically thinner plasma emits 13.5 nm light more efficiently. Optical depth of Sn plasma is actively controlled with changing laser pulse duration and the use of low-density porous target.