Measurement of the Mode Mix Dependent Interfacial Fracture Toughness for a Ti/Si Interface Using a Modified Decohesion Test

The Modified Decohesion Test (MDT), developed by the authors, eliminates shortcomings of current interfacial fracture toughness testing methods. In this approach, a highly stressed super layer is used to drive delamination and create any mode mix at the crack tip. MDT uses the change in crack surface area to vary the available energy per unit area for crack growth and thus to bound the interfacial fracture toughness. Therefore, this technique uses a single sample to measure the interfacial fracture toughness, as opposed to the decohesion test that uses several samples to be able to bound the interfacial fracture toughness. Since the deformations remain elastic, a mechanics-based solution can be used to correlate test parameters to the energy release rate. Common IC fabrication techniques are used to prepare the sample and execute the test, thereby making the test compatible with current microelectronic or MEMS facilities. In this paper, the mechanics based solution used in the MDT to correlate test parameters to the fracture metrics is discussed and compared against other analytical models. Interfacial fracture toughness results are provided for a Ti/Si interface at several mode mixes.