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Mechanical properties by indentation of aluminium nitride nanometric thin film

Abstract:

The mechanical properties of thin film are usually determined by nanoindentation in order to circumvent the influence of the substrate. Indeed, it is recognized that the substrate interferes into the measurement when the indenter penetrates more than 10% of the film thickness for the hardness determination and 1% for the elastic modulus determination. For very thin films for which a direct measurement of the mechanical properties is not possible, models must be applied to separate the contribution of the substrate into the measurement. In this work, hardness and elastic modulus of aluminum nitride film of 250 nm of thickness deposited by Magnetron Sputtering have been determined by nanoindentation. In order to reduce the influence of the uncertainty of the film thickness value on the mechanical property determination, we suggest to introduce the thickness term into the fitting parameters of the different models and to study the convergence of these models. Concerning the elastic modulus, we observed that the experimental data varied following a typical S-curve between tow asymptotes, one which tends toward the value of the film modulus for very low indenter displacements and the other toward that of the substrate for the highest indentation loads. In these conditions, the model proposed by Antunes et al. using the Gao's function in which no fitting parameters are involved cannot adequately represent the experimental data variation. That is the reason why we propose to apply similarly to the Avrami's law which allows to take into account the tendencies at the two extremum. Finally, we obtained values close to 10 GPa and 150 GPa for the hardness and the elastic modulus, respectively, in accordance with the literature data.