Mitigation of fast ions generated from laser-produced Sn plasma for extreme ultraviolet light source by H2 gas

Abstract

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.

Ablation dynamics of tin micro-droplet irradiated by double pulse laser used for extreme ultraviolet lithography source

“…Therefore, mitigation of the debris is of importance for the development of a practical EUV lithography system. Although several methods have been developed for the debris mitigation [5][6][7], the fundamental and general approach is the use of a minimum amount of Sn that can still provide a sufficient EUV power. This type of Sn target is called a mass-limited or a minimum-mass target [8][9][10].…”

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

“…Therefore, a mitigation of the debris is of importance for the development of a practical EUV lithography system. Although several methods have been developed for the debris mitigation, including a magnetic field trap of ions [7], foil trap [8], and so on [9], it is difficult to mitigate the neutral particle debris because they can not be controlled by electromagnetic field. In the previous study, it was found that the neutral atoms are originated from the low-intensity part of the laser spot and the deep layer from the target surface [10] and large size debris must be also generated from the same parts.…”

Measurements of hydrogen gas stopping efficiency for tin ions from laser-produced plasma

“…9 In order to protect the source optics from the plasma debris, various approaches for the debris mitigation are being developed. These are deflection of the ion and plasma fluxes with a strong magnetic field, [15][16][17] stopping of these corpuscular fluxes with a background gas, 18,19 and combination of the two approaches. 9,20 The application of the background gas is important because it also allows us to mitigate the neutral atom flux (if such is present).…”

“…20 The interaction of Sn plasma plume with background gases has been studied in various experimental conditions. [18][19][20][21][22] However, direct measurements of Sn ion stopping in the above-mentioned gases are still lacking. This paper reports on the experimental studies of Sn þ and Sn 2þ ion stopping by hydrogen for ion energies in the range of $0.1-10 keV.…”