HEAVY HITTERS

This thesis investigates the atomic-scale interactions of tin ions (Sn) in EUV light sources, which are essential for modern chip lithography. EUV light, with a wavelength of 13.5 nm, is generated by irradiating a tin droplet with a laser, creating a hot plasma of tin ions. In addition to the desired light, energetic tin particles are also released, which can damage the collector mirror; a hydrogen buffer gas is used to slow these particles down. Optimizing these sources requires a detailed understanding of how tin ions interact with gases and surfaces. The research is built around three pillars. First, ion–gas interactions were studied: the stopping power of hydrogen for Sn1+ ions was measured and found to be lower than previously assumed. A transition in the energy dependence around 600 eV was observed, in good agreement with the results of a new semi-classical collision model. Second, ion–surface interactions were investigated: argon, krypton, and xenon ions were directed at a polycrystalline ruthenium surface. The results show that surface roughness only partly explains the absence of an expected scattering peak, pointing to the role of many-body interactions for heavy projectiles. Measurements of ion-induced electron emission from Sn1-5+ show that kinetic electron emission occurs at velocities much lower than expected, while potential electron emission increases with charge state, as expected. Third, measurement instrumentation was improved: conventional retarding field analyzers were found to produce unreliable energy distributions due to electrostatic lensing caused by their grids. A new gridless design exhibits a constant, energy-independent transmission. In summary, this work shows that simplified models fall short of fully describing these interactions, but that a more complete atomic-scale description is now within reach.