Fabrication and Characterization of Tio2 and Sio2 as Protective Coating for Mo/Si Multilayer by Ion Beam Sputtering

Abstract

Mo/Si multilayer mirrors have been widely used in extreme ultraviolet (EUV) astronomy, microscopy, and advanced lithography. To extend the lifetime of Mo/Si multilayer, the protective coating is important for actual application. In this paper, TiO2 and SiO2 have been chosen as the protective coating for Mo/Si multilayers. To investigate the fabrication process of TiO2 and SiO2 by ion beam sputtering (IBS), a comparative study on the choice of sputtering targets has been detailed conducted. Oxide monolayer samples were characterized by grazing incidence X-ray reflectivity (GIXRR), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). The Mo/Si multilayer deposited with ultra-thin TiO2 and SiO2 protective coating was analyzed by transmission electron microscope (TEM) and angle-resolved XPS. The results indicated the protective coating has low surface roughness and the dioxide component is higher than 95%. The reflectivity of Mo/Si multilayer with and without protective coating have been measured at synchrotron radiation facility. The reflectivity drop was similar with theoretically calculation based on the precise thickness control.

Keywords: Protective coating, Mo/Si multilayer, ion beam sputtering, X-ray photoelectron spectroscopy