Investigation of the elastic modulus of thin films using simple biaxial bending techniques

Abstract

The increasing use of thin films in numerous applications has raised the interest in the mechanical behavior of thin films; particularly the hardness and the elastic modulus of these films. The aim of the present study is to evaluate a simple biaxial bending technique to measure the elastic modulus of films with thicknesses ranging from 0.1 to 2 μm. In this range, it can be difficult to use simple indentation techniques owing to the influence of the substrate, and in order to determine the performance of these systems it is often essential to be able to determine the elastic modulus unambiguously. Tests have been carried out on glass substrates, and magnetron sputtered metal films (copper and aluminium) have been deposited on glass discs to evaluate the film properties. The samples were loaded in biaxial flexure using a point load on the disc supported by three point supports. The bending apparatus uses a commercially available micromechanical probe (UMIS 2000) that enables the measurement of very low loads and small displacements. Comparison is made between the force-displacement response of the disc with and without the sputtered film. Analysis of the bending response gave values of the elastic modulus for the glass discs of E=54.7±0.4 GPa, while E=116±8 GPa for the copper films and E=84±5 GPa for the aluminium films.