Measurement of the mechanical properties of copper thin films by microbeam bending

In an effort to devise a simple method for studying the mechanical properties of thin films on substrates, a microbeam bending technique has been developed. The method is similar to previous microbeam bending studies, except that triangular shaped silicon microbeams are used. These triangular beams have the advantage that the entire film on the top surface of the beams is subjected to a uniform state of strain as the beams are deflected, unlike the standard rectangular geometry where the bending is concentrated at the support.; Rectangular and triangular silicon beams have been fabricated using micromachining processing techniques. Copper films are deposited on top of the Si beams, and the bi-layer beams are deflected using a nanoindenter. To extract the stress-strain behavior of the film on the triangular beams, a simple numerical model has been developed. The yielding behavior of the film can be modeled using a Ramburg-Osgood constitutive law, which is then used to predict the stress-strain relation for the film while attached to its substrate. This model has also been used to show that although in beam bending there is a gradient of stress and strain through the thickness of the film, this effect does not obscure the measurement of the yield stress in our analysis.; Utilizing this technique, the yielding and strain hardening behavior of Cu thin films have been investigated. A Cu film was thermally cycled from room temperature to 500°C to examine the effect of thermal processing on the stress-strain behavior of the film. Cu films with dual texture as well as strong <111> texture have also been deposited. For the dual textured film, an analysis of the onset of yielding in the different orientations has been preformed using orientation imaging microscopy and a Schmid Factor analysis. Strongly textured <111> films were deposited at three different film thicknesses to examine the effect of texture as well as film thickness on the yield properties of the film. The <111> textured films show very high rates of work hardening, and an increase in yield stress with decreasing film thickness. These trends are consistent with current dislocation models.