Characterization and optimization of tin particle mitigation and EUV conversion efficiency in a laser produced plasma EUV light source

A laser produced plasma (LPP) extreme ultraviolet (EUV) light source of 13.5 nm has been developed for next generation lithography. Sn plasma is an efficient generator of 13.5 nm EUV light. On the other hand, deposition of Sn particles which strongly affects EUV collector mirror lifetime is a critical issue for long-term stable operation of the high-power EUV light source. In this paper we describe about the optimization of tin debris mitigation with a compact EUV generation system. We observe almost all of Sn fragments generated after a pre-pulse irradiation are vaporized by a main CO 2 pulse laser with a droplet of 20 μm in diameter. An EUV conversion efficiency (CE) of 3.4% at a maximum is obtained for the 20 μm droplet. These results indicate the debris mitigation can be achieved without degradation of the high EUV CE.