Characterization of deformation properties of metals in 3D ICs

The properties of the materials involved in the set-up of 3D ICs need to be known, when the occurring mechanical stresses are to be modeled. Especially elastic-plastic properties are relevant for the metal layers, which form redistribution layers and the through silicon vias. These can be characterized by the nanoindentation experiment, which is an established technique for the determination of Hardness and Young's modulus of thin films. But this standard data set is not sufficient to be used as input to finite element simulations, because stress strain curves are required for the analysis of reliability of metal layers. These stress-strain curves can be obtained by fitting the force displacement curves of the experiment with a finite-element model. This approach enables additionally a solution for the so called substrate effect, because the stiffness of the substrate can be considered in the fitting model. This known approach is being applied and tested on thin (300 nm ) gold layers deposited on silicon. It is shown that a good sensitivity for Young's Modulus can be reached even for indents that exceed 10 % of the film thickness, but for the plastic data the results are not unique and a range of plastic properties can be fitted.