Scale-up of a cluster jet laser plasma source for Extreme Ultraviolet Lithography

A high-average-power extreme ultraviolet (EUV) source based on a laser plasma cluster jet is being developed for EUV lithography. The source employs a cooled supersonic nozzle expansion to produce a dense beam of Xe clusters as the plasma source target. The cluster beam is irradiated with a pulsed laser to create a high-temperature plasma radiating efficiently in the EUV spectral region. To accommodate drive laser repetition rates of up to 6000 Hz, a continuous jet expansion with full Xe gas recycling is employed, rather than earlier pulsed jet expansions. The continuous jet employs an efficient high-throughput pumping scheme to minimize the ambient pressure of highly-attenuating Xe gas. Source power scale-up is achieved by increasing laser repetition rate, keeping laser pulse parameters nominally fixed. In the first phase of EUV power scale-up, the continuous cluster jet source has been integrated with a 200 W laser driver operating at repetition rates up to 500 Hz. With this system, a laser-to-EUV conversion efficiency of 0.69% is achieved. In the second phase, the jet is being integrated with a 1700 W diode-pumped solid state laser driver operating at repetition rates up to 6000 Hz. A brief description of the 1700 W laser system and its integration with the continuous cluster jet are discussed.