Tin fluid dynamics driven by laser-produced plasmas relevant to EUV nanolithography

Abstract

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.