Carbon film growth on model electron-irradiated MLM cap layer: interaction of benzene and MMA vapor with TiO 2 surface

Abstract

Our aim is to characterize the surface processes that affect the reflectivity of TiO 2 - 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 TiO 2 (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 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 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.