Toward a high average power and debris free soft X-ray source for microlithography, pumped by a long pulse excimer laser

We present the exciting results obtained by using a natural (i.e. as long as the active medium gain) 120 ns-duration excimer laser pulse focused on relatively thick targets (100 micrometer): a conversion efficiency exceeding 20% has been obtained in the 40 - 70 eV (170 - 300 Angstrom) spectral interval from Cu and Ta targets, with more than 100-ns-FWHM X- ray pulses and low speed (less than 100 m/s) emitted debris. A fast CCD camera is used to reveal the debris and to measure their speed for different laser parameters. These values of debris speed are compatible with the use of a mechanical device to separate them from the X-ray beam and hence to protect the optics of a projection-microlithography system.