Fast ion debris generated in laser-tin droplet interaction is known to degrade the reflectivity of the EUV collector mirror, posing a challenge to the commercial use of the EUV source. In the present work, we conduct one-dimensional fully kinetic Particle-In-Cell simulations using PSC code that is capable of capturing fast ion debris formation. We discuss the progress in the implementation of physics modules for the PSC code that is required to replicate the EUV generation process in detail. We demonstrate decent agreement between our kinetic simulations and radiation hydrodynamics simulations in terms of macroscopic plasma parameters. We also discuss the role of the kinetic effects in EUV and next-generation BEUV sources.
State-of-the-art nanolithography machines employ extreme ultraviolet (EUV) light to pattern nanometer-scale features on silicon wafers for the production of integrated circuits. This radiation is generated in a laserproduced plasma formed on tin microdroplet targets. In this contribution, we give an overview of our recent experimental and theoretical studies on the properties of tin plasmas driven by short-wavelength lasers and the subsequent tin fluid dynamics. First, we will present a comprehensive characterization of the properties of laserproduced tin plasmas driven by lasers with wavelengths in the 1–10 µm range. Second, we present absolutely calibrated, charge-state-resolved measurements of the ion kinetic energy distribution recorded under multiple detection angles. Through extensive radiation-hydrodynamic simulations of the plasma formation, growth and expansion, we demonstrate that a single-fluid approach accurately reproduces the angular dependence of the ion energy distribution. Moreover, we identify the origin of a high-energy peak in the distribution as a high-speed shell generated at early times in the expansion. Finally, we show that the time evolution of the droplet target morphology is entirely determined by the early-time plasma-driven pressure impulse on the droplet.
Extreme ultraviolet (EUV) light generated by tin-plasma is used for state-of-the-art nanolithography. Currently, the plasma is generated by irradiating tin-microdroplets with 10-micometer wavelength light from CO2-gas lasers.
Energy efficient solid-state lasers providing 2-micron wavelength main-pulses may present a viable option for driving EUV-emitting plasma. The 2-micron drive wavelength is situated between the well-studied cases of 1- and 10-micron. Our experiments, using pre-pulse deformed tin droplet targets, show that a 2-micron main-pulse has the potential to provide a higher-brightness source, compared to the 10-micron laser case, with a higher conversion efficiency than in the 1-micron laser case.
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