Sizing the EUV Laser-Plasma Source for a Microscope

Abstract

The size and intensity of laser-plasma sources based on pulsed argon gas jets operating at a wavelength of 13.84 nm were studied. The gas jet was excited by laser radiation at a wavelength of 1064 nm with a pulse duration of 4.4 ns, a repetition frequency of 10 Hz, and a pulse energy of 0.5 J. Two methods of forming a jet of a pulsed gas target were studied: using a jet with a supersonic nozzle and using a capillary. The capillary source is commercially available. The sources were certified using a mirror microscope operating in the extreme ultraviolet region at a wavelength of 13.84 nm. It was found that due to the possibility of supplying a higher pressure of the working gas to the nozzle inlet, increasing the density and reducing the exit angle of the gas jet in the supersonic nozzle compared to the capillary, the peak radiation intensity at a wavelength of 13.84 nm increased six times. The full width at half maximum of the nozzle-based source diameter was 250 ± 10 μm with a profile close to Gaussian. In the field of view of a microscope of 25 × 25 μm, the nonuniformity of illumination from the “source on the nozzle” is about 1%; in the field of view of 50 × 50 μm, it is about 4%. The full width at half maximum of the source diameter based on a commercial valve with a capillary source was 330 ± 10 µm with a profile close to П-shaped. Based on the results of the comparison, an upgraded version of the microscope with up to 350× magnification will use a nozzle-based source.