An Improvement of the Doerner-Nix Function for Substrate Effects in Ultrathin Films

摘要

Substrate effects continue to be an important issue in interrogating thin films by nanoindentation. In this study, we examined amorphous thin films of several different materials deposited onto a silicon wafer. These materials span from being considerably softer than the substrate to films significantly harder than the substrate. The thin film Young's modulus, E_f, was measured with an MTS Nanoindenter XP system and employing the continuous stiffness measurement (CSM). A so-called "flat region," where the substrate influence was negligible, was observed in the early stage of nearly every CSM modulus-displacement curve for all materials studied. The depth of this region (h_(cr)) was found to vary with the material. Based on the experimental data, we were able to modify the Doerner & Nix function for thin film indentation on a substrate, particularly their parameter alpha (α). The modified function was found to be adept at closely matching all experimental data collected, which spanned both soft films on hard substrates and hard films on soft substrates.