Experimental study of the dynamics and extreme ultraviolet radiation of laser produced colliding Sn plasmas

Abstract

The advanced research on bright 13.5 nm extreme ultraviolet (EUV) light sources with low debris is of crucial importance for the semiconductor industry. The scheme of laser produced colliding plasma holds the potential to significantly improve the conversion efficiency (CE) from the laser energy to the required EUV light sources. A pulsed Nd:YAG laser beam was split into two beams using a polarizing cube and focused on a planar Sn target surface at a distance of 2.5 mm to generate two colliding plasmas. It was found that the optical radiation intensity of the stagnation layer generated in the colliding plasmas region was much higher than that of a single-pulse plasma under the same laser energy. Furthermore, the stagnation layer could exist for a longer time with a higher optical radiation intensity, which meant that the formation of the stagnation layer effectively converted the ion kinetic energy into optical radiation energy. The time-of-flight (TOF) ion signal of the colliding plasma exhibited a much narrower distribution compared to the seed plasma. At the same laser energy, the ion kinetic energy of the colliding plasma was lower than that of the single-pulse plasma. The TOF peak voltage and total charge showed a stronger angular dependence for the colliding plasma. At high laser energy, the colliding plasma could significantly reduce the ion's kinetic energy without changing the CE of the EUV.