EUV-induced oxidation of carbon on TiO₂

Previously we reported estimates of the maximum etch rates of C on TiO₂ by oxidizers including NO, O₃ and H₂O₂ when irradiated by a spatially-non-uniform beam of extreme ultraviolet (EUV) radiation at 13.5 nm (Faradzhev et al., 2013). Here we extend that work by presenting temporally and spatially resolved measurements of the C etching by these oxidizers as a function of EUV intensity in the range (0.3 to 3) mW/mm² [(0.2 to 2) × 10¹⁶ photons s^-1 cm^-2]. We find that the rates for NO scale linearly with intensity and are smaller than those for O₃, which exhibit a weak, sub-linear intensity dependence in this range. We demonstrate that these behaviors are consistent with adsorption of the oxidizing precursor on the C surface followed by a photon-stimulated reaction resulting in volatile C-containing products. The kinetics of photon-induced C etching by hydrogen peroxide, however, appear to be more complex. The spatially resolved measurements reveal that C removal by H₂O₂ begins at the edges of the C spot, where the light intensity is the lowest, and proceeds toward the center of the spot. This localization of the reaction may occur because hydroxyl radicals are produced efficiently on the catalytically active TiO₂ surface.