Controlled Fracture and Mode-Mixity Dependence of Nanoscale Interconnects

Mechanical failures of back-end-of-line (BEoL) interconnects represent a critical yield and reliability concern for integrating new materials such as ultralow-permittivity (ultralow-k) dielectrics in advanced integrated circuits and for introducing new packaging technologies. The actual failure mode of the interconnects could vary with the BEoL processes, packaging, and assembly technology, as well as reliability and in-field stressing conditions. In this paper, we present a fundamental study of the crack propagation behavior of BEoL interconnects and its dependence on the mode mixity imposed by the external boundary condition. The effective fracture resistance has been measured for representative structures from upper, middle, and lower level interconnects. Under certain conditions where the failure path is uniform, the intrinsic fracture properties of the interlayer dielectric material and vias can be determined separately that allows a direct assessment of process-induced impacts on the integrated materials and their geometrical scaling properties.