Copper electromigration failure times evaluated over a wide range of voiding phases

Electromigration failure times of 100 nm wide dual damascene Cu interconnects have been evaluated over a very wide range of different stages of void formation and growth. Voids that did not span the whole line width and height have been monitored using the so-called local sense structures, while standard single via structures were used to study fully grown voids. The activation energy E_a did not change over the whole experimental range of failure times indicating that the main diffusion path during void formation and growth does not change in our semi-bamboo lines. The earlier reported increase in distributional spread σ after full void formation is less pronounced during void formation which is due to different kinetics before and after full void formation. The use of defining failure criteria before full void formation has been explored as a tool to reduce electromigration test times. Due to the constant E_a, test times can be reduced by over a factor of two.