スズ貫通孔ターゲットを用いたレーザ生成プラズマEUV(Extreme Ultraviolet)光源 : −円錐および円筒型貫通孔内アブレーション過程とEUV放射−

概要

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In a future system of EUV (extreme ultraviolet) lithography, a high power light source with 13.5nm wavelength is demanded for long operation life time under high repetition rate. Tin target has significant potential for high conversion efficiency. This paper presents a new method to develop a debris-free EUV light source by using tin targets with conical and cylindrical through-holes, which have advantages for increasing EUV emission and reducing debris in the direction of the through-hole exit. The strong EUV intensity from plasma produced by Q-switched Nd:YAG SHG (second harmonic generation) laser is measured with a detector, that consists of Mo/Si deposited photodiode, Zr filter and Au mirror. For commercial EUV light source, repetitive use of the target is required. The emission stability for repeated operation is evaluated using these through-hole targets. Also, the visible light emission from the confined plasma in the through-hole is observed using a high-speed camera, and then the laser ablation process is considered. Finally the feasibility of the tin target with cylindrical through-hole is discussed for development of commercial EUV lithography system.