Electromigration Simulation

Highly integrated microelectronic circuits (e.g. microprocessors) require dense interconnects with dimensions down to some 150 nm. With the resulting increase in current density in the interconnects, electromigration induced failure becomes a more and more challenging issue. Significant advance has been made by choosing copper instead of aluminum as interconnect metal, because copper has an improved electromigration bulk resistance. State of the art copper interconnect technology imposes new challenges for electromigration reliability Technology Computer-Aided Design (TCAD) solutions. One major problem of copper interconnects is high diffusivity at the interfaces to cap and barrier layers. In particular, when new materials and processes are introduced, the adhesion between copper and the attached layers is increased so that the interfacial diffusivity is reduced to the level of the diffusivity of grain boundaries. This means that the microstructure of interconnects, i.e. network of grain boundaries, crystal orientation inside the grains, and stress dependence of grain bulk diffusivity plays a crucial role in determining interconnect behavior under the impact of electromigration. Current electromigration models used for simulation and analysis of interconnect reliability lack appropriate description of metal microstructure and consequently have a very limited predictive capability. In the scope of this project we will evaluate the available electromigration models. In addition we will analyze models which describe the microstructure impact on electromigration induced material transport in interconnects. The models will be implemented in a simulation tool following a careful study of the corresponding numerical algorithms. A final decision about best suited models for simulation will be made after comparison of simulation results with relevant experiments.

Highly integrated microelectronic circuits (e.g. microprocessors) require dense interconnects with dimensions down to some 150 nm. With the resulting increase in current density in the interconnects, electromigration induced failure becomes a more and more challenging issue. Significant advance has been made by choosing copper instead of aluminum as interconnect metal, because copper has an improved electromigration bulk resistance. State of the art copper interconnect technology imposes new challenges for electromigration reliability Technology Computer-Aided Design (TCAD) solutions. One major problem of copper interconnects is high diffusivity at the interfaces to cap and barrier layers. In particular, when new materials and processes are introduced, the adhesion between copper and the attached layers is increased so that the interfacial diffusivity is reduced to the level of the diffusivity of grain boundaries. This means that the microstructure of interconnects, i.e. network of grain boundaries, crystal orientation inside the grains, and stress dependence of grain bulk diffusivity plays a crucial role in determining interconnect behavior under the impact of electromigration. Current electromigration models used for simulation and analysis of interconnect reliability lack appropriate description of metal microstructure and consequently have a very limited predictive capability. In the scope of this project we will evaluate the available electromigration models. In addition we will analyze models which describe the microstructure impact on electromigration induced material transport in interconnects. The models will be implemented in a simulation tool following a careful study of the corresponding numerical algorithms. A final decision about best suited models for simulation will be made after comparison of simulation results with relevant experiments.