Achieving long-term gas pressure stability in diffusion-cooled carbon dioxide (CO2) lasers by minimizing CO2 adsorption from 3Å molecular sieves with optimized cesium exchange rates

Abstract

The smallest computer chip structures currently available are produced using state-of-the-art EUV radiation. The established concept utilizes CO₂ lasers to pump a laser-induced plasma, generating 13 nm EUV radiation. In diffusion-cooled carbon dioxide lasers, long-term stability of the gas mixture is extremely important for stable performance because there is no gas exchange. Minimal amounts of water disturb the gas equilibrium. Molecular sieves enable rapid drying of the resonator and long-term water adsorption. However, conventional 3 Å molecular sieves and molecular sieves from previously published studies adsorb not only water molecules but also other laser gas components such as carbon dioxide in parallel. This leads to both a drop in pressure and a loss of laser power making them inappropriate for use in a diffusion-cooled laser. In this work, the chemical and selectivity properties with regard to water and carbon dioxide molecules of specially manufactured cesium-ion exchanged 3Å LTA molecular sieves were systematically investigated and their suitability for the laser was tested. Applying molecular sieves with an optimum exchange rate of 40.5% cesium content prepared with a high regeneration temperature of 673.2 K, a condition was finally found in which the water from the laser gas is adsorbed in sufficient quantity (15.9% of the molecular sieve’s self-weight), even the adsorption of carbon dioxide was prevented to a negligible extent. Despite a very small difference in molecular diameter between water and carbon dioxide of only 0.2 Å, long-term continuous operation of the system became possible.