A comparative study of kinetic and thermodynamic mechanisms of XH4 + H → XH3 + H2 reaction (X = Si, Ge, and Sn)

Extreme ultraviolet lithography (EUVL) systems face significant challenges in light source stability and equipment longevity due to contamination in the vacuum chamber caused by tin particle deposition. Hydrogen (H2) has been used as an in situ cleaning solution for tin, as the reaction between hydrogen radicals (H) and tin produces stannane (SnH4), most of which can then be pumped out of the vessel. However, there is limited availability of both experimental and theoretical kinetic data for the reaction of Sn with H2, which could be utilized in particle-in-cell or kinetics programs. Using first principles and transition state theory (TST) with Wigner and Eckart tunneling corrections, we reveal the thermodynamic and kinetic characteristics of the SnH4 + H → SnH3 + H2 reaction at the microscopic level. Our results show that this reaction is exothermic and thermodynamically spontaneous, with a significantly increasing rate as the temperature increases. Quantum tunneling effects dominate the reaction kinetics below 298 K, substantially enhancing the rate constant, whereas classical TST becomes increasingly valid at higher temperatures. As the central atom in Group IV A hydrides changes from Si to Sn, the overall reaction rate increases, while the influence of quantum tunneling gradually diminishes. We provide essential theoretical data for the reaction SnH4 + H → SnH3 + H2, as well as a theoretical foundation for other related reactions. This information could be utilized to optimize the decontamination process of EUVL light sources.