This document summarizes a study that used nanoindentation to determine the mechanical properties, specifically the hardness and elastic modulus, of a very thin (250 nm) aluminum nitride film. Various models were applied and compared to account for the substrate influence at such low film thickness. For hardness, models by Jönsson and Hogmark, Korsunsky et al., and Puchi-Cabrera were selected. For elastic modulus, standard models using weight functions were not successful due to an "S-curve" variation with indentation depth, so the models were modified based on Avrami's law. The main results found the hardness to be 10 GPa and elastic modulus close to 150 GPa.

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: francine.roudet@univ-lille1.fr (F. Roudet).
http://dx.doi.org/10.1016/j.tsf.2015.10.010
0040-6090/© 2015 Elsevier B.V. All rights reserved.
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