Internship: Shaping laser-induced tin targets for EUV generation

In our lab, we investigate the interaction of laser pulses with liquid tin microspheres to advance the knowledge of the physical processes that rule the extreme ultraviolet light (EUV) generation currently used in state-of-the-art nanolithography machines. These machines use a two-step process to generate EUV light that is later on used to inscribe the smallest microchips with the highest spatial resolution. In the first step, a laser-pulse illuminates one side of a tin droplet creating a plasma at its surface, whose rapid expansion transfers momentum to the droplet inducing a controlled propulsion and deformation into a pizza-like shape. A few microseconds after the initial kick, a second, more intense, laser pulse illuminates the expanding material and generates a tin plasma that preferentially generates EUV light at a wavelength of 13.5 nm.

In this (BSc) project, we propose to investigate the above-mentioned first step by establishing a link between the experimental observations of the initial plasma kick and the subsequent propulsion and expansion dynamics. In order to quantify the fluid dynamic properties, movies of the dynamic process will be used to track the center-of-mass position and the radius as a function of time to extract the propulsion and expansion velocities. The intensity of the plasma (bright spot on the image) will be systematically studied and will serve as a link between the initial laser features and the subsequent fluid dynamics. During the first stage of the (BSc) project there will be lab tours where we will explain the experimental systems and methods. The core of the project will focus on data analysis of pre-existing experimental data with the possibility of acquiring new data later on. Overall, this project will help us to understand collectively different stages of the laser-tin interaction process, involving mechanisms that are explained using laser physics, plasma physics and fluid dynamics.

Recommended articles for further reading on this subject:

• Liu, R.A. Meijer, J. Hernandez-Rueda, D. Kurilovich, Z. Mazzotta, S. Witte and O.O. Versolato, Laser-induced vaporization of a stretching sheet of liquid tin, J. Appl. Phys 129, 5: 053302: 1-7 (2021)
• Liu, D. Kurilovich, H. Gelderblom and O.O. Versolato, Mass loss from a stretching semitransparent sheet of liquid tin, Phys. Rev. Applied 13, 2: 024035: 1-10 (2020)
• O.O. Versolato, Physics of laser-driven tin plasma sources of EUV radiation for nanolithography, Plasma Sources Sci. Technol. 28, 8: 083001:1-17 (2019)