Fracture in stress engineered, high density, thin film interconnects.

摘要

The micro-contact spring is a new technology that is based on physically vapor deposited thin film cantilevers with a purposely-imposed stress gradient through the thickness of the film. These “springs” have the potential to meet the long and near term high-density packaging and probing challenges, as outlined by the International Technology Roadmap for Semiconductors. The success of this technology is, in part, dependent on the ability to create springs that are reliable against interfacial fracture during fabrication, microelectronic probing, and microelectronic packaging applications. Through this research, a framework to understand the interfacial integrity of thin film cantilevers under monotonic and cyclic loading has been established.; This research has developed a modified decohesion test (MDT) that eliminates the shortcomings of current interfacial fracture toughness measurement methods for thin film interfaces. This highly flexible and robust test gives tight bounds on the fracture toughness using a single sample, generates any mode mix, creates an interface representative of microelectronic or MEMS applications, and remains in the linear elastic fracture mechanics regime. The MDT was applied to investigate the interfacial fracture toughness of two material systems relevant to micro-contact spring applications: titanium/silicon and titanium/Al ₂O₃. A von Karman Plate Theory (VKPT) based analytical method was applied and further enhanced in this research to analytically model the large, nonlinear behavior of intrinsically stressed, thin film, cantilever strips. The multilayer analytical approach, based on simply supported plates, was shown to predict the energy release rate of cantilevered strips during monotonic fracture remarkably well and showed the importance of bifurcation of curvature in understanding the nonlinear behavior of intrinsically stressed thin film cantilever plates. A framework for numerical modeling of micro-contact springs in fabrication, packaging, and probing applications was developed in this research. Based on the these models, the VKPT analytical framework, and the interfacial fracture toughness measured through the MDT, comprehensive design guidelines were established to achieve micro-contact spring fabrication design goals and ensure continuing reliability in subsequent probing and free-air packaging applications.