Efficient EUV Light Plasma Sources Driven by a 2-μm-Wavelength Laser
The aim of this Thesis is to experimentally investigate and understand plasmas as used in extreme ultraviolett (EUV) lithography, and learn what conversion efficiencies (CE) and which in-band energies can be achieved by irradiating tin targets with 2-μm-wavelength laser light. To do so, we built a 2-μm-wavelength system, based on the parametric conversion of 1-μm- into 2-μm-wavelength, and applied it in our investigations of EUV light generation. This laser system is not envisioned to be used in any industrial application since it runs at a low 10 Hz repetition rate, but it is valuable as a first plasma driver to characterize the EUV emission from 2-μm-wavelength driven tin plasmas. Our studies include a comparison of 1-μm- and 2-μm-driven plasmas to gain insight on how the expected reduction in optical depth affects the CE and obtainable overall in-band energy. This insight is valuable to characterize and understand the effects of different laser irradiation parameters (i.e., laser intensity, laser pulse duration, laser beam spot size, and intensity distribution) and tin target morphology. We systematically investigate how the in-band energy that could be used in EUVL scales with laser irradiation parameters and tin target size. The goal is to determine if the in-band energy could be scaled to energy levels relevant to the industry without impairing the CE. Showing high obtainable CEs from 2-μm-wavelength driven EUV plasma close to those from the CO2-gas laser, at relevant in-band energies would be a critical first step towards demonstrating the feasibility to enhance the overall energy efficiency of EUV sources by using 2-μm solid-state-lasers.