In situ scanning electron microscopy indentation studies on multilayer nitride films: Methodology and deformation mechan
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W.M. Mook EMPA, Materials Science and Technology—Laboratory for Mechanics of Materials and Nanostructures, Thun, BE Switzerland
M. Parlinksa-Wojtan EMPA, Materials Science and Technology—Nanoscale Materials Science, D€ ubendorf, ZH Switzerland
J. Hejduk Polish Academy of Sciences—Institute of Electron Technology, Warsaw 02-668, Poland
J. Michler EMPA, Materials Science and Technology—Laboratory for Mechanics of Materials and Nanostructures, Thun, BE Switzerland (Received 31 July 2008; accepted 5 December 2008)
Systematic studies of the deformation mechanisms of multilayer transition metal nitride coatings TiN/CrN, TiN/NbN, and NbN/CrN, and corresponding reference coatings of TiN, NbN, and CrN deposited by a direct current (dc) magnetron sputtering process onto silicon h100i have been performed. Mechanical characterization was conducted using a combination of microindentation and nanoindentation in the load range 30 to 150 mN and 0.5 to 3.5 mN, respectively. For both load ranges, scanning electron microscopy (SEM) in situ indentation was used to observe the indentation process including any pileup, sink-in, and fracture mechanisms specific to each coating. The coatings’ microstructure, both before and after indentation, was analyzed using transmission electron microscopy (TEM). It was possible to both correlate the indentation load–displacement response to surface roughness effects and fracture modes (substrate and film cracking) and observe deformation mechanisms within the coatings.
I. INTRODUCTION
Transition metal nitride coatings have traditionally been used as protective coatings for different types of cutting tools and microelectronics and as diffusion barriers for the semiconductor industry, and they are now being considered for use as protective coatings in microelectromechanical systems (MEMS).1,2 This is due to their high hardness and reasonable toughness, which combine to give superior tribological performance compared to uncoated devices.3–5 Tribological issues are especially important for MEMS applications where excessive wear of the single- and polycrystalline silicon elements in motion drastically limit device designs and lifetimes. The most extensively explored transition metal nitride coatings are TiN, CrN, NbN, TaN, VN, and ZrN.1,2,6 This work focuses on three of these, namely TiN, CrN, and NbN, because of their outstanding mechanical properties. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0139
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http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 3, Mar 2009 Downloaded: 30 May 2014
All of these transition metal nitrides are relatively hard with values ranging from 21 to 25 GPa for TiN,7–9 from 14 to 22 GPa for CrN10,11 and from 6 to 45 GPa for NbN,12–14 depending on the deposition technique and its conditions. Moreover, all of these materials are reported to have good wear resistance6,14,15 and fracture toughness.1,16 These materials also possess some individual properties that differentiate them from each other. Both
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