Physical Transport
Gradual material displacement in metallic conductors arises from the momentum transfer between conducting electrons and the metal lattice atoms. In sub-micron semiconductor interconnects, electromigration leads to the formation of voids and hillocks. These physical voids increase localized electrical resistance, while hillocks can cause electrical shorts to adjacent metal lines.
Degradation Rate
Mathematical calculation of the mean time to failure in metallic interconnects relies on Black’s equation. This relation incorporates both current density and activation energy to predict how electromigration progresses under specific thermal conditions. Engineers use these calculated rates to specify maximum current density limits for metallization lines.
Circuit Impact
Localized changes in conductor resistance alter the propagation delay of signals across complex semiconductor networks. As electromigration thins the conductive paths, the increased heating further speeds up the degradation of the metal line. This self-heating feedback loop accelerates the circuit failure.
Circuit designers balance line widths and current profiles to maintain reliable signal path performance over the intended service life of the microchip.
Test Profile
Verification of conductor endurance involves high temperature operating life testing at elevated currents. These stress conditions accelerate the action of electromigration to expose design weaknesses within a compressed timeframe. The resulting acceleration factor calculation guides the qualification of the production process.
