Modeling the substrate effects on nanoindentation mechanical property measurement

Nanoindentation technique is commonly used to characterize the mechanical properties of thin films. However, the validity of the measurements is greatly affected by the indentation depth and the substrate properties. The purpose of this study is to understand the influence of the substrate properties, the thin film thickness and the mechanical properties of the thin film itself on force-displacement curves obtained by nanoindentation. The experimentally obtained force versus indentation depth curves of single and bi-layer thin film systems on silicon wafers were simulated using finite element modeling (FEM). The materials properties of the thin film layers were extracted by fitting the load-displacement curves obtained by FEM and experiments. The experimental part of this study includes nanoindentation tests performed on low-k films deposited on a silicon substrate. These films were treated during different periods of time (Os, 20s, 35s, 70s, 140s, 350s and 700s) with He/H2 downstream-plasma (DSP) at a fixed temperature of 280degC, thereby resulting in a double layered structure with the same total film thickness, but with different thickness and mechanical properties of the "modified" top layer. The results of this work provide considerable insight for the determination of the mechanical properties of layered systems.