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 TiO2-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 TiO2(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 TiO2 cap layers. For benzene on clean TiO2, secondary electron effects dominate in the initial stages of carbon accumulation, whereas for C-covered TiO2, 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.