Reactive deposition of AleN coatings in Ar/N 2 atmospheres using pulsed-DC or high power impulse magnetron sputtering discharges A. Guillaumot a, * , F. Lapostolle a , C. Dublanche-Tixier b , J.C. Oliveira c , A. Billard a , C. Langlade a a LERMPS-UTBM, Site de Montbéliard, F-90010 Belfort Cedex, France b E.N.S.I.L-SPCTS, 16 rue d’Atlantis, Parc Ester Technopôle, BP 6804, F-87068 Limoges Cedex, France c SEG-CEMUC, Mechanical Engineering Department, University of Coimbra, Polo II, 3030-788 Coimbra, Portugal article info Article history: Received 7 September 2009 Received in revised form 17 March 2010 Accepted 19 April 2010 Keywords: Aluminium nitride HIPIMS OES measurements Structural properties Hardness abstract In this paper, the metal to ceramic transition of the AleN 2 system was investigated using classical reactive pulsed-DC magnetron sputtering and HIgh Power Impulse Magnetron Sputtering (HIPIMS) at a constant average current of 3 A. Optical emission spectroscopy measurements revealed more ionised aluminium species in the HIPIMS discharge compared to pulsed-DC sputtering. It also showed excited N 0 and ionised N þ species in reactive Ar/N 2 HIPIMS discharges. The corresponding evolution of the consumed nitrogen flow as a function of the N 2 partial pressure revealed that a higher amount of reactive gas is needed to achieve stoichiometric AlN with HIPIMS. Electron probe micro-analysis and X-ray diffraction measurements confirmed that a partially poisoned aluminium target is enough to allow the deposition of stoichiometric hcp-AlN thin films via HIPIMS. To go further in the comparison of both processes, two stoichiometric hexagonal aluminium nitride thin films have been deposited. High power impulse magnetron sputtered hcp-AlN exhibits a higher nano-hardness (18 GPa) than that of the coating realised with conventional pulsed-DC sputtering (8 GPa). Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Hexagonal aluminium nitride (hcp-AlN) is a reliable coating for optical and electrical applications due to its large band gap in the 5.9e6.2 eV range [1,2]. Also known for its good chemical stability, high hardness and high resistance to corrosion at high temperature [3,4], hcp-AlN could also be a convenient candidate for tribological and mechanical applications at high temperature. Recent work in the field of physical vapour deposition processes has shown a great interest in the use of processes giving very dense plasmas with a high ionisation fraction of the sputtered particles [5e8]. The metalemetalloid reactivity is increased and the transi- tion mode in reactive sputtering tends to stabilise [9,10]. It also becomes possible to control the metallic ion bombardment by biasing the substrates, leading to an improvement of the film density [11,12] and adhesion [13,14]. This last decade, a new deposition technique in the field of ionised physical vapour depo- sition, called High Power Impulse Magnetron Sputtering has shown a real alternative to enhance thin films properties. The aim of this work is to compare conventional unipolar pulsed-DC sputtering and HIPIMS for the elaboration of AleN thin films. First, optical emission spectroscopy measurements will be performed, both in a pure Ar and in Ar/N 2 atmospheres, to bring information about the plasmas characteristics. Then, the influence of nitrogen partial pressure on the AleN thin films properties is investigated. Finally, two transparent hcp-AlN coatings are syn- thesised with these two sputtering techniques and their morphology and hardness are compared. 2. Experimental details AleN films were deposited on stainless steel (z520 HV), glass and silicon substrates. They were set at floating potential, at a distance of 140 mm from the target surface, on a one-fold rotating substrate holder (18 rpm) whose axis is parallel to the target surface, in a Balzers 640R unit. A pure aluminium target (99.9% purity) was mounted on a 125 Â 250 mm 2 balanced rectangular cathode. This last was powered either by a high power pulsed (Sinex 3, Chemfilt) or a pulsed-DC (Pinnacle Plus, Advance Energy) power supply, both equipped with an arc handling system. The HIPIMS discharge voltage was measured using a GMW-GE 3421 voltage probe capable of supporting up to 2 kV (AC and DC), * Corresponding author. Tel.: þ33 3 84 58 37 08; fax: þ33 3 84 58 37 37. E-mail address: amelie.guillaumot@utbm.fr (A. Guillaumot). Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum 0042-207X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2010.04.012 Vacuum 85 (2010) 120e125