Electron-induced interaction of selected hydrocarbons with TiO2 surfaces: the relevance to extreme ultraviolet lithography

The aim of this work is to characterize desorption induced by electronic transition processes that affect the reflectivity of TiO 2 -capped multilayer mirrors used in extreme ultraviolet (EUV) lithography. A low energy electron beam is employed to mimic excitations initiated by EUV radiation. Temperature programmed desorption, x-ray photoelectron spectroscopy, and low energy ion scattering are used to analyze the surface reactions. Carbon film growth on the TiO 2 (011) crystalline surface is measured during 10-100 eV electron bombardment in benzene or methyl methacrylate vapor over a wide range of pressures and temperatures near 300 K. Low energy secondary electrons excited by EUV photons contribute substantially to the carbon accumulation on clean TiO 2 cap layers. For benzene on clean TiO 2 , secondary electron effects dominate in the initial stages of carbon accumulation, whereas for C-covered TiO 2 , direct excitations appear to dominate. We report on the adsorption energy, the steady-state coverage of the molecules on the surface and the cross sections for electron-stimulated dissociation: all key parameters for understanding and modeling the processes relating to the EUV lithography mirrors.