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

Abstract

In the development of extreme ultraviolet (EUV) light source for EUV lithography systems by laser-produced plasma (LPP), mass-limited targets such as a micro-droplet were considered as promising targets for debris mitigation. In our study, the dynamics of debris from the tin (Sn) droplet target was investigated in order to establish the guideline for the optimum design of the mitigation system. The Sn micro-droplet targets used in the experiment were made with a help of pulsed-laser. The behaviors of the Sn atoms from the droplet target irradiated by the Nd:YAG laser were investigated using the laser-induced fluorescence (LIF) imaging method. Sn atoms were observed even from a small amount target such as several ten µm droplets, indicating the droplet of this size was not ionized completely by the single pulse of Nd:YAG laser. Furthermore, the ablation dynamics of the irradiated droplet was observed by a high-speed time-resolved imaging camera simultaneously with the LIF imaging.