Characterization of TiO2 thin films in the EUV and soft X-ray region A. Comisso* 1,2 , A. Giglia 3 , M. Nardello 1,2 , E. Tessarolo 1,2 , L. Calvillo 4 , M.G. Sertsu 1,2 , G.Granozzi 4 , F. Gerlin 1,2 , L. Brigo 5 , P. Nicolosi 1,2 1 University of Padova, Department of Information Engineering, via Gradenigo 6B, 35131 Padova, Italy. 2 Consiglio Nazionale delle Ricerche—Institute for Photonics and Na notechnologies Laboratory for Ultraviolet and X-Ray Optical Research, via Trasea 7, 35131 Padova, Italy. 3 CNR- Istituto Officina Materiali, I-34149 Trieste, Italy 4 Department of Chemical Sciences, University of Padova, Vi a Marzolo 1, 35131 Padova, Italy 5 University of Padova, Industrial Engineering Department and INSTM Padova RU, Via Marzolo 9, 35131 Padova, Italy ABSTRACT In this work, three TiO 2 thin films with thicknesses of 22.7, 48.5 and 102.9 nm were grown on Si (100) substrates by the technique of electron beam evaporation. The films were deposited at a substrate temperature of 150°C with a deposition rate of 0.3 - 0.5 A/sec. The films thicknesses were characterized by spectroscopic ellipsometry and profilometry. The surface roughness was measured by AFM obtaining RMS of less than 0.7nm. Investigations performed by XPS method have shown that stoichiometric TiO 2 was obtained on all the samples with no suboxide presences. Reflectance measurements of the samples were performed in EUV and SX spectral regions from 25.5 to 454.2eV using synchrotron radiation. Analyzing the refractive index N=n+ik of TiO 2 thin films, optical constants (n,k) in this energy range were both determined by fitting the Fresnel equations with least-square fitting methods. Keywords: TiO 2 , thin films, e-beam, optical constants, extreme ultraviolet, soft x-rays, optical coatings. 1. INTRODUCTION The demand to enhance knowledge and the interest in developing optical coatings with high reflectance efficiency in the extreme ultraviolet (EUV) and soft x-ray (SX) spectral region, are induced by activities such as synchrotron-based research, EUV x-ray lithography, x-ray astronomy, and plasma application. Recent research has evidenced TiO 2 to be a very promising and important materials in EUV and SX applications. Some examples of its competent use are: effective capping layers for Mo/Si multilayer (ML) mirrors [1,2], beam splitter (BS) for high-order harmonics [3] and as a component on novel MLs for “water window” wavelength [4], just to name a few. In order to predict performance, design and improve optical devices used in the EUV and SX, it is vital to have knowledge and accurate information on the refractive index of the materials used in this wavelength spectrum, together with the way they grow when interfaced with other materials. Thus, a full characterization of these materials and an analysis of interfaces are of great interest for development of new high performance components, along with improving the development of thin film single layer and multilayer coatings. In the EUV/SX energy regions, near-edge x-ray absorption fine structures (NEXAFS) are expected to occur, that depends on material properties like the microstructure and chemical composition. These in turn can depend on a variety of parameters such as the deposition condition of the film. Because NEXAFS can depend on subtle effects, it cannot always be calculated accurately through modeling and atomic approximations, especially for composite materials [5,6] such as TiO 2 . For these reasons we considered valuable to experimentally measure index of refraction of TiO 2 thin films, which as far as we know and literature goes, it´s never been measured in SX and EUV wavelength region. The optical properties of a material in the EUV and SX region are described by its complex index of refraction (Eq.1) N=n+ik (1) being n the real part or refractive index, and k the imaginary part or extinction coefficient. Both n and k are functions of wavelength. Various methods are used to determine the optical constants (n,k), in this work we´ve used the method EUV and X-ray Optics: Synergy between Laboratory and Space IV, edited by René Hudec, Ladislav Pina, Proc. of SPIE Vol. 9510, 95100Z · © 2015 SPIE CCC code: 0277-786X/15/$18 · doi: 10.1117/12.2178142 Proc. of SPIE Vol. 9510 95100Z-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/25/2015 Terms of Use: http://spiedl.org/terms