Si transfer and self-limiting chemisorption on Ru thin film surface in hydrogen radicals environment

Surface contamination and its level control play a crucial role in modern technologies and industries. One of the contamination mechanisms in industries which use hydrogen plasma is so-called hydrogen induced outgassing (HIO) when hydrogen species interact with surface contaminants forming volatile hydrides. Thus, these volatile hydrides may be adsorbed on chemically active surfaces spreading contamination. Our goal is to understand the HIO process and develop a dedicated surface cleanliness metrology. One of the approaches is to find a material that acts as getter for HIO species, such that the presence of HIO species on large surface area components can be detected by post-mortem analysis of the getter sample after simultaneous hydrogen radicals exposure of the component of interest and the getter sample. We have started to test this approach with Si as HIO material and a Ru thin film as the getter material. The interaction of hydrogen radicals with the Si surface leads to the formation of volatile silane which subsequently adsorbs on the getter material. In equilibrium conditions, when the silicon ‘source’ and Ru getter are placed next to each other and exposed to the same hydrogen radical flux, one monolayer of chemisorbed Si is observed. We propose that silane adsorption in hydrogen radicals environment is a self-limiting process, where the reaction terminates once all the reactive Ru sites on the surface are occupied by chemisorbed Si.