Imaging Diagnostics of Debris from Laser-Produced Tin Plasma with Droplet Target for EUV Light Source

The dynamics of debris from laser-produced tin (Sn) plasma was investigated for a practical extreme ultraviolet (EUV) lithography source. The kinetic behaviors of the Sn atoms and of the dense particles from Sn droplet target irradiated by double pulses from the Nd:YAG laser and the CO 2 laser were also investigated by the laser-induced fluorescence imaging method and a high-speed imaging, respectively. After the pre-pulse irradiation of the Nd:YAG laser, the Sn atoms were ejected in all direction from the target with a speed of as fast as 20 km/s and the dense particle cloud expanded by a reaction force due to the plasma expansion with a speed of approximately 500 m/s. The expanding target was subsequently irradiated by the main-pulse of CO 2 laser and the dense cloud was almost disappeared by main-pulse irradiation.