Addition of silver in copper nitride films deposited by reactive magnetron sputtering J.F. Pierson * and D. Horwat Laboratoire de Science et Ge ´nie des Surfaces (UMR CNRS 7570), Ecole des Mines, Parc de Saurupt, CS 14234, 54042 Nancy Ce ´dex, France Received 2 October 2007; revised 11 November 2007; accepted 12 November 2007 Silver–copper nitride thin films were deposited on glass substrates by reactive co-sputtering of silver and copper targets. The films were characterized by energy dispersive X-ray spectroscopy to determine the silver to copper atomic ratio and by X-ray diffraction to determine the film structure. From the experimental values of lattice constant and UV–visible reflectance measurements, the position of silver atoms in Cu 3 N films was discussed. Finally, the effect of silver on the film electrical resistivity was presented. Ó 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Reactive sputtering; Copper nitride; Structure The well-known thermal decomposition of copper nitride (Cu 3 N) at low temperatures has been successfully used for write-once recording media [1–4], to generate microscopic copper lines by maskless laser writing [5] or to form copper dots [6]. Such kinds of applications in- duce a great interest in the thin films community for the deposition of copper nitride films. Cu 3 N coatings have been deposited using various processes: molecular beam epitaxy [7], pulsed laser deposition [8], atomic layer deposition [9] or RF magnetron reactive sputtering [10–17]. Copper nitride has a cubic anti-ReO 3 type structure (space group: Pm3m, lattice constant: 0.3819 nm). In this structure, nitrogen atoms are positioned at the cor- ners of the cell, and copper atoms are positioned at the centre of the cube edges. Thus, this crystal structure exhibits a vacant site at the centre of the cell. Using ab initio total energy calculations, Moreno-Armenta et al. [18] have shown that copper nitride is an indirect semi- conducting material with a band gap close of 0.25 eV. They also study the effect of metal insertion (M@Ni, Cu, Zn, Pd, Ag and Cd) at the centre of the cell on the electronic structure [19]. Whatever the nature of the metal, the authors show that Cu 3 MN exhibits metal- lic properties. Although copper nitride has been widely studied, little information is available in the literature concerning Cu 3 N doped by a transition metal element. Zachwieja and Jacobs [20] have synthesized Cu 3 Pd 0.02 N and Cu 3 Pd 0.989 N. Both compounds crystallize in the Pm3m structure with a lattice constant of 0.3810 and 0.3854 nm, respectively. Very recently, Fan et al. [21] doped sputtered Cu 3 N films with titanium. The titanium concentration ranged between 0 and 1 at.%. The authors observed that increasing the Ti content induces a modi- fication of the film preferred orientation, of the surface morphology and of the electrical and optical properties. In this study, silver has been added to copper nitride films. The choice of silver is due to the fact that this ele- ment does not react with nitrogen during sputtering deposition [22]. Contrary to the work of Fan et al. [21], the silver content is >20 at.% to obtain clear evi- dence of the localization of foreign atoms in the Cu 3 N films. The aims of this manuscript are to show that, for the first time, silver can be added into copper nitride films and to clarify the position of silver atoms into the films (i.e., centre of the Cu 3 N cell, substitution of copper atoms into Cu 3 N cell, or formation of a bi-phased struc- ture Ag and Cu 3 N). Copper nitride and silver–copper nitride films were deposited on glass substrates by reactive magnetron co-sputtering of silver and copper targets (50-mm diam- eter, 3-mm thick and purity >99.9%). The experimental device is a 40-L sputtering chamber pumped down via a mechanical pump and a turbomolecular pump allow- ing a base vacuum of 10 4 Pa and equipped with two 1359-6462/$ - see front matter Ó 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2007.11.016 * Corresponding author. Tel.: +33 3 83584342; e-mail: jean-francois. pierson@mines.inpl-nancy.fr Available online at www.sciencedirect.com Scripta Materialia 58 (2008) 568–570 www.elsevier.com/locate/scriptamat