The electromigration effect revisited: non-uniform local tensile stress-driven diffusion.

Area of Science:

• Materials Science
• Solid-State Physics
• Computational Materials Science

Background:

• Electromigration (EM) describes atomic diffusion in metals under electrical stress.
• Current theories focus on electrostatic and electron-wind forces but lack lattice stability coupling.
• Understanding EM is crucial for microelectronic device reliability.

Purpose of the Study:

• To investigate the interplay between electromigration and lattice stability in pure copper.
• To elucidate the fundamental driving forces behind the electromigration effect.
• To validate theoretical models with experimental observations.

Main Methods:

• In situ current-stressing experiments on pure copper strips.
• Synchrotron X-ray diffractometry for lattice analysis.
• Scanning electron microscopy for microstructural observation.
• Ab initio calculations using density functional theory.

Main Results:

• Identified intrinsic, non-uniform lattice expansion induced by electron flow, greater at the cathode.
• Observed elastic deformation for small strains and diffusion-driven stress relaxation (hillocks, voids) for strains exceeding the yield point.
• Validated the fundamental driving force for electromigration.

Conclusions:

• Electron flow-induced lattice strain is a fundamental aspect of electromigration.
• The magnitude of this strain dictates whether deformation is elastic or leads to material failure.
• This work provides a unified understanding of electromigration mechanisms and their link to lattice stability.