Electromigration phenomena in 0.13 micron copper interconnects

Cu/low-k interconnects have replaced many A1 interconnects recently in Integrated Circuits with 0.13 pm technology and beyond. These technologies confine many recent fabrication processes, such as Chemical Mechanical Polishing with dual-damascene Cu electrodepositing, new materials and via processes. This thesis focuses on new reliability challenges that have developed with the changes in materials and processes. In particular, electromigration dominates the failure mechanisms in interconnects. We report an unusual circuit failure mode induced by short-lived extrusions observed during DC and bidirectional electromigration tests. This novel "soft" failure mode consists of extrusions forming, then self-dissolving before the traditional permanent void or extrusion failure. These failures shorten the lifetime significantly and bring new challenges to reliability tests. Two self-dissolution mechanisms under DC test conditions are discussed and extrusion shape evolution is modeled assuming both capillary and electron wind forces are present. Our model confirms that the electrical stress will accelerate the shape evolution process.