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 hydrofluorie acid (HF) solution has been investigated using synchroton radiation (SR) in the vacuum-ultraviolci (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 VUVSR. 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 O H bond scission in a surface Si-OH 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.