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Modeling of very thin aluminum nitride film mechanical properties from nanoindentation measurements


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Authors: F. Roudet, D. Chicot, X. Decoopman, A. Iost, J. Bürgi, J. García Molleja, L. Nosei, J. Feugeas.

Thin Solid Films 594 (2015) 129-137.

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Modeling of very thin aluminum nitride film mechanical properties from nanoindentation measurements

  1. 1. Modeling of very thin aluminum nitride film mechanical properties from nanoindentation measurements F. Roudet a, ⁎, D. Chicot a , X. Decoopman a , A. Iost a,b , J. Bürgi c , J. Garcia-Molleja e , L. Nosei d , J. Feugeas c a Université Lille Nord de France, USTL, LML, CNRS, UMR 8107, F-59650 Villeneuve d'Ascq, France b Arts et Métiers ParisTech — Centre de Lille, 8, Boulevard Louis XIV, 59000 Lille Cedex, France c Instituto de Física Rosario (CONICET-UNR), Bvrd. 27 de Febrero 210 Bis, 2000 Rosario, Argentina d Instituto de Mecánica Aplicada y Estructuras—FCEIA-UNR, Berutti y Riobamba, 2000 Rosario, Argentina e School of Physics, Yachay Tech, Yachay City of Knowledge, 100119 Urcuquí, Ecuador a b s t r a c ta r t i c l e i n f o Article history: Received 13 October 2014 Received in revised form 5 October 2015 Accepted 5 October 2015 Available online 8 October 2015 Keywords: Nanoindentation Elastic modulus Hardness Modeling Aluminum nitride Thin films The mechanical property determination of thin films by nanoindentation can be affected by the substrate depending on the indentation testing conditions and the film thickness. In this condition and especially for very thin films, application of models is required for separating the substrate influence of the indentation mea- surement. In this paper, hardness and elastic modulus of columnar aluminum nitride of 250 nm (thickness) have been determined by nanoindentation. The hardness versus the indenter displacement variation has been studied applying a variety of models to compare their prediction. A specific methodology avoiding the knowledge of the film thickness is proposed. Concerning the elastic modulus determination, different weight functions have been applied without any success since the elastic modulus variation versus the indenter displacement shows typically an ‘S’ curve whereas the standard models predict a linear variation. Consequently to adequately repre- sent this variation, the models are modified accordingly to Avrami's law. As a main result, the hardness is found to be equal to 10 GPa and the elastic modulus close to 150 GPa. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Aluminum and its alloys are usually employed for their low density. Aluminum alloys with zinc are used in the aeronautic industry; they are commonly classified in the series 7xxx. On the other hand, the automo- bile industry prefers the series 5xxx with addition of magnesium, or the series 2xxx with copper. The advantage of the series 5xxx is mainly its good corrosion resistance in a saline environment. However, corrosion phenomena could appear in a saline and wet environment [1]. Corro- sion protection can be achieved by covering the surface with a painted layer. But to improve the wear resistance it is possible to increase the hardness at the surface with chemical, mechanical, electrochemical, diffusion or heat treatment [2]. In this work, we focused the study on the series 5xxx, because the proportion of magnesium increases the hardness of the aluminum alloy, which gives a good weldability, a good resistance to saline environments and a good capability to work in a cold environment. For specific and severe application in tribology, Leyland and Matthews [3] suggest the use of materials having a high hardness to elastic modulus ratio. This can be obtained with hard mate- rials presenting a low elastic modulus. To replace classical heat treat- ment [4], which can modify the quantity of Al–Mg precipitates in the specific case of series 5xxx of aluminum alloys, we prefer the use of a thin layer of aluminum nitride deposited by magnetron sputtering, for which the hardness can reach more than 20 GPa. Aluminum nitride (AlN) is a III-N compound with a large variety of interesting properties. AlN has a wurtzite structure [5] and develops piezoelectric properties with a high sound speed [6], AlN density is near to 3.26 g/cm3 and its band gap is 6.2 eV, consequently AlN has excellent dielectric properties [7]. On the other hand, doping AlN develops a remarkable semiconduc- tor behavior. According to these properties, aluminum nitride has sever- al technological and industrial applications like optics [8], mechanics [9] and electronics [10] domains. Indeed, AlN can act as high-pass filters, pressure gauges, bulk acoustic wave resonator, biological sensors [11], micro-motors [12] and as protective coating against oxidation [2]. The objective of this work is the determination of the mechanical properties, i.e. the hardness and the elastic modulus, of the aluminum nitride by means of nanoindentation using the continuous stiffness measurement mode. The main difficulty in this case is the relative low thickness of the film, around 250 nm. Indeed, for such very thin film, the substrate necessarily interferes into the measurement for low in- dentation depth to thickness ratio, close to 0.1 for the hardness determi- nation [13,14] and until 0.01 for the elastic modulus determination [15, 16]. In addition, a very precise value of the film thickness is required for obtaining consistent mechanical properties. Among the hardness models available in literature [17–21], we selected the model of Jönsson and Hogmark [17], Korsusnky et al. [19] and the model of Puchi-Cabrera [20,21]. As compared to the others, the model of Jönsson and Hogmark Thin Solid Films 594 (2015) 129–137 ⁎ Corresponding author. E-mail address: (F. Roudet). 0040-6090/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Thin Solid Films journal homepage: