Use of stress-engineered material layers for the measurement of interfacial fracture toughness of nanoscale thin films

A new technique employing stress-engineered material layers for the measurement of interfacial fracture toughness of nanoscale thin films has been developed. This technique has been implemented to measure the interfacial fracture toughness of patterned Titanium (Ti) film on a Silicon (Si) substrate. This test employs a stress-engineered super layer deposited on Ti to provide the energy for the delamination propagation of Ti thin film from the Si substrate. The amount of energy available for the delamination propagation is varied by depositing a selectively-etchable thin release layer between the film strips and the substrate. By designing a decreasing area of the release layer, it is possible to arrest the delamination at a given location, and the interfacial fracture toughness or the critical energy release rate can be found at the location where the delamination ceases to propagate. For Ti film with thickness of 90 nm, the results show that the interfacial fracture toughness of Ti/Si ranges from 3.45 to 5.70 J/m² when the mode mixity increases from 6.8 to 38.4°. The methodology presented in this paper is generic in nature, and can be used to measure the process-dependent interfacial fracture toughness of various nanoscale thin film interfaces.