High-efficiency clean EUV plasma source at 10-30 mn, driven by a long-pulse-width excimer laser

A long-pulse-width high-output energy (120 ns FWHM, 7J) XeCl laser has been focused on thin tape targets (Cu and Ta) to generate more than 100-ns-long (FWHM) EUV pulses in the 10-30 nm spectral region, suitable for projection microlithography. The conversion efficiency was more than 20% over a 27pi solid angle. We observed debris emission using a gated CCD camera, and measured the debris speed for different irradiation conditions. We found irradiation conditions such that the measured velocities were low enough that simple mechanical devices combined with krypton at low-pressure could efficiently stop both ionic debris and cluster debris. Our results show that a suitable combination of driving-laser characteristics, target material and thickness, environment gas and mechanical choppers can make clean and increase the power of EUV solid-target laser-plasma sources.