Indentation fracture of low dielectric constant materials

This work is the development of a method to estimate the fracture toughness of thin (∼1 mum), porous, silicate-based dielectric films with pre-existing tensile film stresses. These films are under development by the microelectronic industry for their low permittivity (low dielectric constant, or low- k). The porosity needed to create the low dielectric constant also degrades mechanical integrity, and a fracture toughness estimation method is needed for material comparisons and integration engineering.; Instrumented indentation experiments are performed with sharp, geometrically similar probes of varying acuity on a wide range of bulk materials in order to understand general phenomena of varying the probe acuity. The occurrence of fracture at the indentation site is related to load and displacement behavior. It is shown that the compliance of the radial cracks is transmitted to the indenting probe only when the probe is very acute.; Indentation fracture development during the indentation load-unload cycle on transparent specimens was monitored with a custom indentation instrument. Careful examination of fracture development at indentations by acute probes on silicate glasses shows that the conventional elastic-plastic residual mismatch mechanism of radial fracture at indentation in brittle materials is not applicable for these or such acute mechanical probes.; The instrumented indentation and in-situ indentation results lead to the proposal of a new mechanism of radial fracture, indentation wedging. A scaling model is derived to relate material properties to the forces that drive and resist radial fracture. The general behavior of the model is explored, and model predictions compare favorably with experiment.; A wide survey of low-k indentation fracture phenomena, using four low-dielectric constant organosilicate films in varying thicknesses, is made to determine some of the general phenomena of radial fracture at very low-load indentations. Drawing heavily on the indentation wedging model, a model for the extraction of low-k film fracture properties is created and compared with experiment. The model incorporates the pre-existing stresses in the film, the influence of the stiff silicon substrate on the indentation stress fields, and the constraint that the substrate has on the crack shape.