Optimization of conditions for excitation of Xe laser plasma in an extreme ultraviolet radiation source for nanolithography in order to increase its efficiency

Subject of study. The study focuses on laser plasma excited by a Xe gas-jet target. Aim of study. The aim of this study is to increase the output of extreme ultraviolet radiation from such a plasma to a level that meets the requirements of industrial production, specifically for use as a radiation source in a new branch of lithography with a wavelength near 11.2 nm. Method. The primary method used involves changing the diameter of the laser beam by moving a Xe gas-jet target along its axis. This adjustment leads to a change in the interaction area between the beam and the target, which in turn alters the size of the laser spark. The intensity of plasma radiation at wavelengths of 11.2 nm and 13.5 nm was measured using a surface-barrier Si photosensor and a Bragg mirror. Additionally, the energy of the laser radiation absorbed by the plasma was measured. Main results. The results show that, when the diameter of the laser beam illuminating the target increases from 46 µm to 344 µm, the energy emitted in the extreme ultraviolet range increases by approximately 5 times. In the identified irradiation mode, the efficiency of converting laser radiation into radiation with a wavelength of 11.2 nm was 3.9%. Recent measurements of the plasma lifetime have shown that it depends on the size of the plasma and, in several experiments, is significantly shorter than the laser pulse duration. This finding suggests that the plasma lifetime can be used as an optimization parameter when selecting the laser pulse duration. Practical significance. A record-high efficiency is obtained for the conversion of laser pulse energy into extreme ultraviolet radiation by a laser-plasma radiation source with a gas target. This achievement opens up the prospect of using such sources in the industrial production of microcircuits.