Analysis and minimization of temperature-induced adsorption effects caused by 3 Å molecular sieves in diffusion-cooled carbon dioxide (CO₂) lasers

The operational stability and performance of diffusion-cooled CO₂ lasers, crucial for generating extreme ultraviolet (EUV) radiation for microchip production, depend critically on maintaining a constant gas composition and pressure within the resonator. Conventional zeolitic 3 Å molecular sieves are frequently employed for the drying of laser gas; however, they have a tendency to adsorb both water (H₂O) and the laser-active component, CO₂. Furthermore, they cause undesirable temperature-dependent gas pressure fluctuations resulting from the adsorption or desorption of gas molecules under changing external conditions, making them unsuitable for use in long-term operations that require high accuracy. The situation becomes problematic for all negative pressure or vacuum systems requiring high pressure accuracy, that need to be transported for example to a customer, or that do not have a service life under operating or cleanroom conditions. The study examines a previously uninvestigated approach by systematically comparing conventional potassium-ion (K⁺)-exchanged 3 Å LTA molecular sieves with specially manufactured caesium-ion (Cs⁺)-exchanged 3 Å LTA sieves, aiming to suppress temperature-dependent gas composition fluctuations while preserving efficient H₂O removal. Thermal desorption analyses and long-term pressure monitoring indicate that Cs⁺-exchanged sieves exhibit markedly reduced CO₂ adsorption and desorption dynamics, resulting in significantly improved gas pressure stability against ambient temperature changes. Furthermore, integrating engineering controls such as isolating valves can further minimize pressure fluctuations. These results demonstrate that the combination of optimized molecular sieve material and proactive system design enables reliable, high-stability operation of CO₂ lasers under changing environmental conditions.