Electronegativity-dependent cleaning of tin and tin hydride containing contamination of EUV optics

Extreme ultraviolet lithography (EUVL) uses emission from a tin plasma as a light source. The mirrors that collect the light are subject to a hostile environment, consisting of hydrogen, background gases, as well as tin in gas, liquid, and ionized states. Understanding how this environment interacts with the mirror surface is critical to designing plasma-facing surfaces that are cleanable and have a sufficiently long lifetime. We hypothesize that the lifetime and clean-ability of a facing surface depends on the relative electronegativities of the metal, tin, and the cleaning agent. In this study, metal surfaces, which model the plasma-facing surface, were deposited onto a silicon wafer. The deposition of tin and subsequent cleaning via hydrogen radicals was studied using in situ ellipsometry, atomic force microscopy, and X-Ray photoelectron spectroscopy. Early results on Si, and Ru show different cleaning rates and different deposition morphologies, in agreement with published results.