The behavior of debris generated from a laser-produced plasma (LPP) for the extreme ultraviolet light source at 13.5nm has been studied using a laser induced fluorescence (LIF) imaging system. Tin (Sn) LPPs were produced by irradiating a flat Sn plate and Sn thin films perpendicularly with a Nd:YAG laser beam. When a thin Sn film was used as a target material, the depletion of the Sn atoms was clearly observed along the Nd:YAG laser beam. The LIF system was also used for visualizing the sputtering process of a mirror substrate by the fast ions generated from the plasma.

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One of the serious problems in the laser-produced plasma for an extreme ultraviolet (EUV) light source used for the next generation lithography is the generation of fast ions that damage the EUV collector optics. In this study, the mitigation of fast ions from a laser-produced Sn plasma by a H2 background gas was investigated. It has been confirmed that H2 buffer gas at a pressure of 13.3Pa has little influence on the transmission of 13.5nm light with an optical path length of 200mm. The sputtering of a dummy mirror by the fast ions generated from the laser-produced Sn plasma and their mitigation were investigated by visualizing the spatial distributions of sputtered atoms using the laser-induced fluorescence (LIF) imaging method. It was evaluated that the sputtering rate by the fast ions was reduced to less than approximately 5% by H2 gas with a column density of 1.2×1021l∕m2. The dynamics and the chemical reaction of the plasma plume containing the high energy and high density ions in a H2 background gas were also investigated by a time-resolved emission spectroscopy as well as by LIF.

The ablation dynamics of a tin (Sn) micro-droplet by double pulse laser irradiation for the development of an extreme ultraviolet lithography source was investigated. The solid state Sn droplet target with a diameter of 30 µm was irradiated by double laser pulses from a Q-switched Nd : YAG laser and a CO2 laser, and the kinetic behaviour of debris such as Sn atoms, ions and of the dense particles from the droplet was investigated by the laser-induced fluorescence imaging method, Faraday cups and high-speed imaging, respectively. After the pre-pulse irradiation of the Nd : YAG laser, the ions were emitted towards the laser incident direction with an average kinetic energy of 3–6 keV and the dense particle cloud moved in the direction opposite to the laser incident direction with expansion by a reaction force due to the plasma expansion at a speed of approximately 500 m s−1. On the other hand, the Sn atoms were ejected in all directions from the target with a speed as fast as 20 km s−1. The expanding target was subsequently irradiated by the main pulse of the CO2 laser with a delay of 800 ns and the dense cloud almost disappeared due to main-pulse irradiation.

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