Effect of germanium addition on the properties of reactively sputtered ZrN films D. Pilloud a , J.F. Pierson a, * , A. Cavaleiro b , M.C. Marco de Lucas c a De ´partement CREST, Institut FEMTO-ST (UMR CNRS 6174), Universite ´ de Franche-Comte ´, Po ˆle Universitaire, BP 71427, 25211 Montbe ´liard cedex, France b Departamento de Engenharia Meca ˆnica, Universidade de Coimbra, Polo II, ICEMS, FCTUC, Pinhal de Marrocos, 3030 Coimbra, Portugal c Laboratoire de Recherches sur la Re ´activite ´ des Solides (UMR CNRS 5613), Universite ´ de Bourgogne, 9 Av. Alain Savary, BP 47870, 21078 Dijon cedex, France Received 16 December 2004; received in revised form 13 June 2005; accepted 22 June 2005 Available online 26 July 2005 Abstract For the first time, Zr – Ge – N films were deposited on silicon and steel substrates by sputtering a Zr – Ge composite target in reactive Ar – N 2 mixture. The films were characterised by electron probe microanalysis, X-ray diffraction, micro-Raman spectroscopy and depth-sensing indentation. The effects of the Ge content and substrate bias voltage on the films’ structure, internal stress, hardness and oxidation resistance were investigated. Substrate bias strongly influenced the chemical composition of the films being observed by means of a steep decrease in the Ge content for negative bias voltages higher than 80 V. In these cases, a significant hardness improvement was registered. For 100 V biased films, in the Ge concentrations range tested in this study, only ZrN grains were evidenced by X-ray diffraction. The film compressive stresses increased with the germanium concentration. An unexpected effect of the Ge content on the films’ hardness was observed. In spite of the increase in the compressive stresses of the films with increasing Ge content, the hardness monotonously dropped from 38 GPa for pure ZrN down to 21.5 GPa for 4.6 at.% Ge. Addition of Ge into ZrN-based coatings induced an improvement of the oxidation resistance and it favoured the tetragonal form of zirconia in oxidised Zr – Ge – N coatings. D 2005 Elsevier B.V. All rights reserved. Keywords: Reactive sputtering; ZrN; Hardness; Oxidation 1. Introduction Transition metal nitrides coatings are widely used as diffusion barriers in microelectronics, hard wear-resistant coatings on cutting tools or as corrosion- and abrasion- resistant layers on optical and mechanical components [1]. Among the different transition metal nitrides (TiN, CrN, HfN, TaN, etc.) zirconium nitride is an attractive material due to its good chemical and physical properties. Although ZrN exhibits a slightly higher oxidation resistance than TiN, it is also sensitive to air oxidation at temperature as low as 600 -C [2,3]. To improve the oxidation resistance and/or the mechanical properties of zirconium nitride coatings, several elements have already been added: Al [4],C [5], Ce [6], Cu [7], Ni [8], Si [9], Ti [10],Y [11] etc. To the best of the author’s knowledge, there is no paper related to the effect of germanium addition on the properties of zirconium nitride coatings. Moreover, only little information is available in the literature concerning the effect of germa- nium addition on the properties of transition metal nitrides thin films. In previous papers, it was reported that hard Zr– Si–N films can be deposited by reactive sputtering a Zr–Si composite target [12] and that the oxidation resistance of ZrN films in the 600–750 -C range was improved by silicon addition [13]. Using the same deposition procedure, Zr–Ge–N coatings have been developed. The choice of germanium as doping element of ZrN films can be justified by the relative similar behaviour of silicon and germanium (atomic radius, ability to form a nitride, immiscibility with 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.06.051 * Corresponding author. Tel.: +33 3 81 99 46 72; fax: +33 3 81 99 46 73. E-mail address: jean-francois.pierson@pu-pm.univ-fcomte.fr (J.F. Pierson). Thin Solid Films 492 (2005) 180 – 186 www.elsevier.com/locate/tsf