Electromigration experiments indicate that the copper interconnect lifetime decreases at every new interconnect generation. Modern interconnects, due to their reduced size, show a smaller void volume for failure, while a larger fraction of atoms is transported along fast diffusivity paths at copper interfaces to the surrounding layers and grain boundaries. This increasing dependence on fast diffusivity paths causes significant variation in the interconnect performance and electromigration degradation. In order to produce more reliable interconnects, these fast diffusivity paths must be particularly addressed, when introducing new designs and materials. The electromigration lifetime depends on the variability of material properties at the microscopic and atomistic level. Microscopic properties are grain boundaries and grains with their proper crystal orientation. Atomistic properties are configurations of atoms of the grain boundaries, at the interfaces of the surrounding layers, and at the cross-section between grain boundaries and interfaces. Modern Technology Computer-Aided Design (TCAD), in order to meet the challenges of contemporary interconnects, must cover three major areas: physically based continuum modeling, first-principle/atomic-level modeling, and statistical compact modeling. Our research work comprises all of these three areas. Results and methods from different levels of modeling need to be efficiently combined and for this purpose a comprehensive study of their theoretical background is a prerequisite.
The source of electromigration performance variability lies in the atomistic level, for which first-principle methods must be employed. We use the results from such first principle methods in order to parameterize and modify the continuum level models. Furthermore, to investigate realistic three-dimensional interconnect layouts, continuum level models are used. The results of the corresponding simulations are applied to study failure scenarios and discuss implications to future interconnect designs. Finally, in order to interpret the results of accelerated electromigration tests and their utilization for long time prediction of interconnect behavior under realistic operating conditions, compact models and statistical methods are used.