Preferred diffusion paths for copper electromigration by in situ transmission electron microscopy.

Area of Science:

• Materials Science
• Solid-State Physics
• Electrical Engineering

Background:

• Electromigration (EM) is a major cause of copper interconnect failure in integrated circuits.
• Understanding EM mechanisms is crucial for enhancing device reliability under operational stress.

Purpose of the Study:

• To investigate copper (Cu) self-diffusion pathways under electrical bias.
• To elucidate the role of grain boundaries and crystallographic orientation in EM-induced Cu movement.

Main Methods:

• In situ transmission electron microscopy (TEM) to observe Cu movement under electrical current.
• Application of electrical bias to multigrain Cu lines for extended durations (up to 10^4 s).
• Integration with scanning nanobeam diffraction for detailed microstructural analysis.

Main Results:

• High-angle grain boundaries, particularly those at free surfaces, were identified as the primary pathways for Cu EM.
• Cu movement was observed to be grain-boundary-dominated rather than dependent on specific intra-grain crystallographic orientation.
• Direct observation of grain growth on Cu hillocks, facilitated by the formation of highly mobile Σ7 and Σ3 twin coincidence site lattice boundaries.

Conclusions:

• This research provides critical insights into the fundamental mechanisms of electromigration in copper interconnects.
• The findings highlight the importance of grain boundary engineering for improving the electromigration resistance and long-term reliability of integrated circuits.