Interfacial properties and characterization of Sc/Si multilayers T.N. Shendruk a, ⁎, A. Moewes a , E.Z. Kurmaev b , P. Ochin c , H. Maury d,e , J.-M. André d,e , K. Le Guen d,e , P. Jonnard d,e a Department of Physics and Engineering Physics, University of Saskatchewan, 116 Science Place, Saskatoon, SK, Canada S7N 5E2 b Institute of Metal Physics, Russian Academy of Sciences-Ural Division, 620041 Yekaterinburg, Russia c ICMPE Institut de Chimie et Matériaux Paris Est, CNRS-Université Paris XII UMR 7182, 2-8 rue Henri Dunant F-94320 Thiais, France d Laboratoire de Chimie Physique-Matiére et Rayonnement, UPMC Univ Paris 06, 11 rue Pierre et Marie Curie, F-75231 Paris Cedex 05, France e CNRS-UMR 7614, 11 rue Pierre et Marie Curie, F-75231 Paris Cedex 05, France abstract article info Article history: Received 26 September 2008 Received in revised form 8 January 2010 Accepted 23 January 2010 Available online 1 February 2010 Keywords: Multilayers Extreme ultraviolet optics Diffusion barriers Scandiumsilicon Intermixing X-ray absorption spectroscopy X-ray emission spectroscopy We investigate the intermixing of layers in Sc/Si and Sc/B 4 C/Si/B 4 C multilayers using electron and synchrotron excited soft X-ray emission and absorption spectroscopy. The multilayers are annealed at 100, 200, 300, 400 and 500 °C after preparation by magnetron sputtering. Silicon K β emission and reflectivity measurements verify that the non-annealed multilayer systems are composed of distinct layers with only a minor interdiffusion in Sc/Si samples whereas annealing Sc/Si multilayers at 400 °C leads to a degradation of the multilayer structure and the formation of intermittent scandium silicide, ScSi. The presence of B 4 C barriers in Sc/B 4 C/Si/B 4 C hinders this degradation from developing for the entire temperature range considered. The barrier layers continue to be effective for the entire temperature range even after an extended shelf-life. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Since the development of the tabletop X-ray laser [1] and free- electron lasers [2], a need for highly reflective coatings in the soft X-ray range of 35–50 nm has emerged. However, this extreme ultraviolet (EUV) spectral range is difficult to access because of the lack of high reflectivity materials. Sc/Si multilayers show promising reflectivity in this wavelength range [3–5]; however, it is found that the Si species tend to interdiffuse into Sc layers [6], especially at temperatures above 150 °C. This interdiffusion can be reduced by placing thin barrier layers, such as W, Cr, ScN or B 4 C [7–10], between the Sc and Si layers. ScN and B 4 C are preferable because tungsten and chromium are highly absorbent and significantly reduce the reflectivity. B 4 C barrier layers show a slightly better reflectivity than ScN [9]. Theoretical predictions of Sc/Si multilayers give values of up to 72% reflectivity, although the experimental reflectivities do not yet exceed 54% [3]. This is due to the phase instability of the Sc–Si binary material system, resulting in an interaction and intermixing of layers in the as-deposited state as well as after production. To overcome this intermixing, it is necessary to study the degradation of multilayers. We do so by studying the local structure of Sc and Si atoms in Sc/Si and Sc/B 4 C/Si/B 4 C multilayer dependence on a series of annealing temperatures. X-ray absorption (XAS) and emission spectroscopy (XES) directly probe conduction band and valence band states respectively and are unique in the sense that they can non-destructively provide bulk-sensitive information of buried interfaces. This becomes particularly important where the optical properties of the multilayer structures depend on the structure at the interfaces. For these reasons, the techniques have been employed to analyze multilayers [11–19]. 2. Experimental details The reflective coatings are produced by a periodic magnetron sputtering deposition of nanolaminate layers onto a silicon substrate [20]. To create highly reflective films for the 35–50 nm range, scandium is selected for its low absorption index and high refractive index, which result from scandium's small number of valence electrons and intense transitions between core electrons and the partially empty 3d-band. Silicon is chosen as the spacer material due to its familiarity. Although sample preparation by sputtering is chosen for its improved thermal stability over other techniques [2], the system is inevitably metastable and interdiffusion of Si and Sc layers readily occurs. The studied samples are multilayers having a 10 nm period, with 5 nm thick layers of Sc and Si. The number of bilayers for each sample is Thin Solid Films 518 (2010) 3808–3812 ⁎ Corresponding author. Present address: University of Ottawa, Department of Physics, MacDonald Hall, 150 Louis Pasteur, Ottawa, ON, Canada K1N 6N5. E-mail address: tshen098@uottawa.ca (T.N. Shendruk). 0040-6090/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2010.01.036 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf