Neutral Debris Mitigation in Laser Produced Extreme Ultraviolet Light Source by the Use of Minimum-Mass Tin Target

Neutral tin (Sn) atoms expanding from laser-produced Sn plasmas, called neutral atomic Sn debris, were characterized for application to the extreme ultraviolet (EUV) lithography. Laser-induced-fluorescence (LIF) technique was used to observe spatial distribution and temporal evolution of the neutral atomic debris. Dependence of LIF intensity on number of the neutral atomic Sn debris was calibrated by coupling with 13.5-nm EUV light backlight technique. Dominant source of the neutral atomic debris was found to be periphery of the laser spot heated thermally by high-temperature EUV source plasma. Sufficient conversion efficiency from driver laser energy to 13.5-nm light one was obtained with a very thin Sn dot coated on a glass substrate. With the use of such a minimum-mass Sn target, total amount of the neutral atomic debris can be reduced down to 1% of that from bulk Sn target.

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