Decomposition of electron ionization mass spectra and calculation of electron ionization cross sections of Sn_<i>x</i>H_<i>y</i> for extreme ultraviolet lithography

Abstract The contamination of collector mirrors by Sn debris is one of the key factors affecting the lifespan of manufacturing machines in extreme ultraviolet lithography (EUVL). Hydrogen has been used as an in situ cleaning solution for Sn. The reaction of H radicals with Sn produces SnH 4 , which can be pumped out of the vessel. Electron impact ionization (EII) mass spectrometry will be used to monitor the reaction products. However, the isotopic effect complicates the deconvolution of the EII mass spectrum. In this investigation a Monte Carlo method for deconvolution of the mass spectrum is proposed and successfully applied to SnH 4 and Sn 2 H 6 , taking into account the natural isotopic distribution of Sn. Additionally, the simplex method for function minimization, which employs the Nelder-Mead optimization algorithm, is utilized as a benchmark. Both methods show good agreement with the experimental measurements. Furthermore, the EII cross section of the Sn atom is calculated using the level-to-level distorted-wave (LLDW) method and the experimental cross sections can be accurately reproduced by scaling the distorted-wave cross sections. The cross sections of SnH, SnH 2 , SnH 3 , Sn 2 H 4 and Sn 2 H 6 are calculated based on the Binary-Encounter-Bethe (BEB) model, utilizing the adiabatic ionization potential (AIP) and vertical ionization potential (VIP). This investigation in mass spectrum deconvolution and ionization cross sections provides a foundation for studying quantum yields in in situ tin cleaning.