Microelectronic industry is driven by the continuous miniaturization process conducing to the introduction of materials with better performance. These materials are subjected to stresses mainly due to thermal mismatch, microstructural changes or process integration which can be in the origin of mechanical reliability issues. To study these phenomena and even electromigration a good mechanical characterization of the materials is needed. This work aims at developing tests to assess fracture and elastoplastic behavior of thin Cu films. The tests developed are based on the deflection of microbeams (micromachined using a focused ion beam) using a nanoindenter. Different test geometries for microbeams have been evaluated and quantitative data have been obtained combining experimental results with analytical or numerical models, depending on the property under study. Microbeam response shows a strong dependence on the orientation of the grains close to the fixed end. Grain orientation has been measured by electron backscatter diffraction and the plastic behavior has been modeled by the finite element method using an in-house crystal plasticity subroutine. The effect of film thickness on fracture energy has been determined from tests of notched beams. (C) 2014 Elsevier B.V. All rights reserved.

The continuous miniaturization process in the microelectronic industry, along with the introduction of Interlayer Dielectrics (ILDs) with poorer mechanical properties, makes necessary the development of characterization techniques to evaluate the mechanical performance of very thin films. This work presents a mechanical characterization technique for thin films based on membrane testing. Membranes, micromachined with anisotropic wet etching of Si, are tested to fracture using a nanoindenter to apply the load and register the provoked deflection. The technique is applied to the fracture characterization of two different ILDs with four thicknesses ranging from 100 nm to 500 nm. Combination of experiments and finite element simulations allows for the calculation of the strength of the materials from the fracture load. The technique permits to discriminate both ILDs and to establish clear thickness dependence: for both materials, 100 nm films show a significant lower strength while no effect of film thickness on strength is observed in the range between 200 and 500 nm. A sensitivity analysis of the outcome of the technique, the fracture stress, to the variability of the input parameters is presented, showing the robustness of the proposed approach: the experimental error in the fracture stress is smaller than the variation in the input parameters.

The continuous process of miniaturization in the microelectronics industry requires the introduction of new, thinner interlayer dielectric (ILD) materials with poorer mechanical properties. As a consequence, new mechanical characterization techniques are needed in the industry to evaluate very thin films. This work presents a new fracture characterization technique for thin films, called "dual tip indentation" (DTI). The technique takes advantage of a particular geometry of the indentation tip to provoke shallow and controlled cracking on the targeted brittle thin film. The technique is applied to the fracture characterization of two different ILD with four thicknesses, ranging from 100 nm to 500 nm. Further fractographic analysis, along with finite element modeling, shows that it is possible to extract intrinsic fracture properties from the fracture load. The technique allows one to discriminate between the ILD and, for both materials, 100 nm films show lower strength. No effect of film thickness on strength is observed in the range between 200 and 500 nm. The results from DTI compare well with those previously obtained for the same materials from membrane testing, taking into account the differences in volume tested.

This work presents a finite element analysis of the indentation size effect (ISE) experimentally observed in tests performed at submicron scale. A 3D model of a conical rigid surface indenting on a Nb single crystal at different depths has been developed. The bcc Nb material has been characterized within a finite-strain framework through a crystal plasticity model incorporating strain-gradient hardening. The hardness evolution for different material orientations and for different initial dislocation densities has been studied. The numerical results are compared with predictions of existing analytical models and with experimental results. (C) 2013 Elsevier B.V. All rights reserved.