Effect of radio frequency and direct current modes of deposition on protective metallurgical hard silicon carbon nitride coatings by magnetron sputtering A.S. Bhattacharyya a , G.C. Das b , S. Mukherjee b , S.K. Mishra a, * a Materials Science and Technology Division, National Metallurgical Laboratory, Burmamines, Jamshedpur 831007, Jharkand, India b Department of Metallurgical and Material Engineering, Jadavpur University, Kolkata 700019, India article info Article history: Received 25 May 2009 Received in revised form 13 June 2009 Accepted 14 June 2009 Keywords: Si–C–N coatings RF–DC magnetron sputtering abstract Siliconcarbonitride (Si–C–N) coatings were deposited on silicon (100) by magnetron sputtering using radio frequency alternating current and direct current. The mechanical performance of the coatings in the two modes was compared through static indentation and scratch test in both microlevel and nanolevel. A structure–property correlation was attempted to establish mechanical behavior, micro- structure and bond present in the film. Studies showed RF films to be mechanically tougher and having higher scratch resistance compared to the DC films. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Hard coatings are required for the protection of machine parts under wear and abrasion. Conventional superhard coatings of diamond, cBN, transition metal carbides and nitrides are expensive and brittle and cannot be used at high temperatures [1,2]. Nano- composite and multilayer coatings are the alternatives with consecutive alternate layers of low and high elastic modulus which results in the inhibition of dislocation motion giving high hardness along with toughness [3,4]. Si–C–N nanocomposite coatings have shown improved properties like thermal stability (up to 1500  C), oxidation resistance, high hardness, wide band gap, chemical inertness, excellent mechanical, thermal and optical properties [5–7], which make them a promising material for wear and oxidation resistance, optoelectronics, MEMS and high temperature applications [8–14]. Si–C–N system is expected to have different superhard phases in amorphous Si–C–N matrix namely SiC, b-Si 3 N 4 and even b-C 3 N 4 phase. Chemical vapour deposition, magnetron sputtering, microwave and electron cyclotron resonance PECVD, ion implantation and pulsed laser deposition processes have been used to fabricate Si–C–N films. Out of all these processes, sputtering is a promising technique for deposition of good, adherent coatings and to tailor the properties of films by varying deposition condi- tions. The deposition conditions, electric source such as radio frequency (RF) or direct current (DC), used influence the ultimate properties of the coatings to a good extent. Due to alternate current cycles in RF, the deposition rate is lower compared to the DC mode. Therefore the time span available for the adatoms to undergo thermal accommodation and coalescence at the substrate is different in both the cases, which affects the properties of the coatings deposited in the two different modes. To our knowledge such comparative study on Si–C–N is not available. We report our studies on the effect of electric sources such as RF and DC during magnetron sputtering of nanocomposite Si–C–N film on micro- structural and mechanical properties. 2. Experimental procedures Si–C–N coatings were deposited on Si (100) and SS 304 substrates by RF and DC magnetron sputtering (HHV, Bangalore, India) using single SiC target of 50 mm diameter and 3 mm thick- ness, made by sintering SiC powder compacted into disc and sin- tering at 1950  C in graphite furnace, under argon and nitrogen atmosphere. The base pressure of the chamber, prior to deposition of film, was 5  10 4 Pa and during deposition argon was fed into the chamber up to 0.1 Pa and rest nitrogen was introduced to reach the deposition pressure of 1 Pa. The substrate temperature was fixed at 500  C during deposition. The substrates were cleaned ultrasonically with acetone, dried and immediately kept inside the chamber. In case of deposition in the DC mode, the voltage was kept at 1.2 kV and the current was in the range of 0.3–0.35 A so that the power is maintained around 400 W (360–420 W). The deposition time was kept low for the DC mode due to higher deposition rate so that the film thickness is around 4 mm in both RF and DC modes. In RF mode the coatings were deposited at 500  C, 1 Pa and 400 W. * Corresponding author. E-mail address: skm_smp@yahoo.co.in (S.K. Mishra). Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum 0042-207X/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2009.06.051 Vacuum 83 (2009) 1464–1469