Stress induced densification of thin porous low-k films during nanoindentation

Simultaneous impact of the substrate and pore densification hinders their differentiation during nanoindentation of porous thin low-k films, causing significant loss of valuable information in terms of nonlinear mechanical behavior. In this study, this issue is overcome by utilizing the substrate independent mechanical property solution with three nanoindenter probes that generate substantially different stress levels and elastic field distributions. Elastic moduli of porous thin films are found to be increasing with indenter sharpness in a non-linear fashion, indicating the influence of pore densification. Results obtained by finite element (FE) simulations with the Gurson model for porous media, qualitatively agree with experimental observations but quantitatively underestimates the pore densification. The proposed multiple-probe approach could facilitate non-linear property characterization of fabricated lowk materials.