Determining the Size of the EUV Laser-Plasma Source for a Microscope

In this paper, the size and intensity of laser-plasma sources based on pulsed argon gas jets operating at a wavelength of 13.84 nm are studied. The gas jet is 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 are used to form the jet of a pulsed gas target: using a jet with a supersonic nozzle and using a capillary. The capillary source is commercially available. The sources are certified using a mirror microscope operating in the extreme ultraviolet region at a wavelength of 13.84 nm. Due to the possibility of supplying a higher pressure of the operating 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 is found to increase six times. The width at half maximum of the injector-based source diameter is 250 +/- 10 mu m with a profile close to Gaussian. In the field of view of a microscope of 25 x 25 mu m, the nonuniformity of illumination from the "source on the injector" is similar to 1%, and in the field of view of 50 x 50 mu m, it is similar to 4%. The width at half maximum of the source diameter based on a commercial valve with a capillary source is 330 +/- 10 mu m with a profile close to U-shaped. Based on the results of the comparison, an upgraded version of the microscope with up to 350x magnification will use an injector-based source.