Method for measuring fracture toughness of thin films

摘要

A nanoindentation apparatus is used to measure the in-plane fracture toughness of a thin film formed on a substrate. One or more notches are formed in the thin film. An indenter is applied to the thin film near the notch or notches and a load is applied to the indenter to force it into the thin film. Because the substrate is softer than the thin film, the indenter does not penetrate the thin film, but "sinks in" to the soft substrate. The sink in effect enhances the tensile strain and stress at the notch. In one embodiment, both the penetration of the indenter into the thin film and substrate and the load on the indenter are measured. When the thin film fractures at the notch or notches, the indenter sharply sinks into the substrate. The thin film fracture toughness is then calculated based on the value of the load and penetration at the point of fracture using either finite element analysis or an analytical model. In a second embodiment, the cross- section of the notch or notches is measured after removing the indenter which has formed an indentation in the thin film. The indenter acts as a crack extension force. The thin film fracture toughness is then calculated based upon the geometry of a crack tip at the tip of the notch and using finite element analysis, or an analytical model, such as a Crack Tip Opening Displacement (CTOD) method.