Kinetics of photon-stimulated desorption of positive ions from a HF-treated Si surface

Kinetics of photon-stimulated-desorption (PSD) of positive ions from a Si surface treated with a hydrofluoric acid (HF) solution has been investigated using synchroton radiation (SR) in the vacuum-ultraviolet (VUV) region. Mass analysis of the PSD ions is performed with a time-of-flight technique. PSD of H⁺ and O⁺ ions is observed during exposure of the surface to VUV-SR. It is found that the O⁺ ion desorption rate initially rises and subsequently decreases as the amount of photon exposure is increased, while the H⁺ ion desorption rate decreases exponentially with photon exposure. The photon-exposure dependence of the O⁺ desorption rate is interpreted in terms of a two-step first-order process in which OH bond scission in a surface SiOH complex initially occurs to give rise to desorption of H⁺ and then the remaining Si-O bond is ruptured to produce O⁺ PSD ions. The H⁺ PSD reaction is found to be a single-step process.