EUV Source Developments on Laser-Produced Plasmas using Cryogenic Xe and Lithium New Scheme Target

摘要

We intended to use deposition-free target such as cryogenic Xe target as a laser produced plasma EUV source. We reported an enhancement of conversion efficiency (CE) by double pulse irradiation and a CE dependence on wavelength of drive laser. Lithium target used with hot multi-layer mirror was proposed by Cymer, as a new deposition-free target. We made EUV source studies experimentally on cryogenic Xe target and lithium new scheme target. In this paper, we report newly made double pulse irradiation experiments on cryogenic Xe target and an enhanced EUV generation with new "forced recombination" and/or "expansion energy re-conversion" lithium target. Laser systems used in the experiments were a 320 Hz repetition rate Nd:YAG slab laser and a 10 Hz Nd:YAG rod laser with maximum pulse energy of 1J. EUV emissions were measured by a time resolved and a time integrated imaging cameras, a transmission and a grazing incidence spectrometers, fast EUV photo-diodes and a Flying Circus 3 for power monitor. Temporal resolved EUV images from Li target indicate relatively long emission time and large emission area. The size of emission area is improved and the emission intensity is enhanced by adding a wall in front of the Li target. Experimental results indicate the expected forced recombination and expansion energy re-conversion characteristics.