High temperature brittle film adhesion measured from annealing-induced circular blisters

Testing high temperature brittle film adhesion is necessary for understanding interfacial failure at elevated temperatures. However, current brittle film adhesion measurement methods are limited to room temperature. Experimental techniques to characterize high temperature brittle film adhesion are lacking, and temperature effects on brittle film adhesion remain poorly understood. Here, a simple, yet reliable method is developed to measure the adhesion of TiN films on Si substrates with native SiO2 oxide layer from 300 degrees C to 500 degrees C, based on circular blisters induced by annealing. The circular blister size was proven to remain the same after cooling down to room temperature, based on in situ observations. Experimental results show that film adhesion energy gradually increases and then drops with annealing temperature. Thermally activated dislocation glide promotes easier nucleation of dislocations in Si substrate near the interface. This in turn increases dislocation shielding effects on the interfacial crack tip during its dynamic propagation, resulting in the initially increased adhesion with temperature. Plastic deformation of TiN film is not considered because the combination of the small grain size of less than 10 nm and the amorphous/nanocrystalline structure limits dislocation emission and grain sliding. Local phase film transformation from amorphous to nanocrystalline at the TiN/SiO2 interface was demonstrated by high resolution transmission electron microscopy, causing adhesion reduction due to interfacial embrittlement and contact mismatch at 500 degrees C. In addition, the drop in adhesion induces circular blisters' transition from axisymmetric to non-axisymmetric. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.