LASER-PLASMA SOURCES FOR SOFT-X-RAY PROJECTION LITHOGRAPHY

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