Carbon film growth on model electron-irradiated MLM cap layer: interaction of benzene and MMA vapor with TiO2 surface

Our aim is to characterize the surface processes that affect the reflectivity of TiO2 - capped multilayer mirrors used in EUV lithography. Low energy electron beam is employed to mimic excitations initiated by EUV radiation. Temperature programmed desorption (TPD), x-ray photoelectron spectroscopy (XPS), and low energy ion scattering (LEIS) are used to analyze the surface reactions. Carbon film growth on the TiO2 (011) crystalline surface is measured during 10 to 100 eV electron bombardment in benzene or methyl methacrylate (MMA) vapor over a wide range of pressures and temperatures near 300 K. Low energy secondary electrons excited by EUV photons contribute substantially to 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 photoexcitations appear to dominate. The adsorption energy, the steady-state coverage of the molecules on the surface and the cross-sections for electron-stimulated dissociation are key parameters for understanding and modeling the processes on the EUVL mirrors.

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