Post-discharge study of laser-triggered vacuum discharge for highly repetitive powerful EUV source

Extreme ultraviolet (EUV) source remains a key issue for industrial application of EUV lithography. Currently, laser-triggered discharge (LTD) tin plasma is the most promising discharge produced plasma EUV source scheme. High frequency discharge of up to tens of kHz is required to achieve sufficient average radiation power. However, the choice of discharge frequency is restricted by the recovery time of the remnant plasma in the post discharge stage. Although much work has been performed to investigate discharge plasma dynamics and its corresponding EUV radiation process during main discharge, study regarding post-discharge stage of LTD tin plasma EUV source is scant. In this paper, we present a post-discharge study of a laser-triggered vacuum discharge for high repetition rate EUV source. The insulation strength recovery curve of tin fuel residual between electrodes was measured by time lapse electrical breakdown voltage test. In addition, the two-laser triggered discharge system was built to model the high frequency operation of the laser-triggered discharge plasma EUV source. The intensity recovery process of EUV radiation with different discharge time intervals was measured. Time relation between two recovery processes of electrical insulation strength and EUV radiation has been discussed for the estimation of optimal frequency in our LTDPP EUV source.