DOI: 10.1051/jp3:1994232
J. Phys. III France 4 (1994) 1669-1677

Laser plasma sources for soft X-ray projection lithography

F. Bijkerk¹, L. Shmaenok¹, A. van Honk¹, R. Bastiaensen¹, Yu. Ya. Platonov², A. P. Shevelko³, A. V. Mitrofanov³, F. Voß⁴, R. Désor⁴, H. Frowein⁴ and B. Nikolaus<sup>4

1</sup>  FOM-Institute for Plasma Physics Rijnhuizen, Edisonbaan 14, 3439 MN Nieuwegein, The Netherlands
²  Institute of Applied Physics of the Russian Academy of Science, Ulyanov 46, Nizhny Novgorod 603600, Russia
³  P. N. Lebedev Physical Institute of the Russian Academy of Science, Leninsky Prospekt 53, 117924 Moscow B-333, Russia
⁴  Lambda Physik Forschung GmbH, Hans Böcklerstraße 12, D-3400 Göttingen, Germany

(Received 19 November 1993, accepted 20 January 1994)

Abstract
Results are reported concerning high-repetition-rate excimer lasers with average powers up to 415 W and their usage for generating laser-plasma soft X-ray sources. A conversion efficiency of laser light into monochromatized soft X-ray radiation of 0.7% at 13.5 nm (2% bandwidth) was achieved using an excimer laser of which the beam quality was adapted for this application. Two methods to mitigate the production of plasma debris have been analyzed : tape targets and the use of Kr as a buffer gas. The optimum coating thickness of tape targets coated with Ta has determined to be 1  m. Ta tape targets and the Kr buffer were used in a debris contamination test of 10 ⁵ pulses. After this exposure, the reflectivity of a normal incidence Mo-Si multilayer mirror that faced the plasma, was found to be 18% lower. The contamination could be removed by cleaning, which restored the reflectivity to 97% of the initial value.

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