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In electronics, and especially in integrated circuits, electromigration refers to the gradual movement of the atoms in a conductor due to moving electrons (current) colliding with those atoms. Electromigration is exacerbated by high current densities and the Joule heating of the conductor (see electrical resistance), and can lead to eventual failure of electrical components.

Electromigration occurs when some of the momentum of a moving electron is transferred to a nearby atom, causing the atom to move from its original position. Over time, if this force knocks enough atoms far enough from their original positions, a break or gap can develop in the conducting material, preventing the flow of electricity. In narrow interconnect conductors, such as those linking transistors and other components in integrated circuits, this is known as a void (or internal) failure (open circuit). Electromigration can also cause the atoms of a conductor to pile up and drift toward other nearby conductors, creating an unintended electrical connection known as a hillock failure (short circuit). Both of these situations can lead to a malfunction of the circuit.

In an ideal conductor, where atoms are arranged in a perfect lattice structure, the electrons moving through it would experience no collisions and electromigration would not occur. In real conductors, defects in the lattice structure and the random thermal vibration of the atoms about their positions causes electrons to collide with the atoms and scatter, which is the source of electrical resistance (at least in metals; see electrical conduction). Normally, the amount of momentum imparted by the relatively low-mass electrons is not enough to permanently displace the atoms. However, in high-power situations (such as with the increasing current draw and decreasing wire sizes in modern VLSI microprocessors), enough electrons bombard the atoms with enough force to become significant.

The two main factors contributing to electromigration are heat and current density. Heat, often arising from the Joule heating of the conductor, accelerates the process of electromigration by causing the atoms of the conductor to vibrate further from their ideal lattice positions, increasing the amount of electron scattering. High current density increases the number of electrons scattering against the atoms of the conductor, and hence the speed at which the atoms are displaced.

In integrated circuits, electromigration does not occur in semiconductors directly, but in the metal interconnects deposited onto them (see semiconductor device fabrication).

See Also: Integrated circuit, semiconductor, electromagnetism, electrical conduction

[edit] References

[1] What is Electromigration?, Computer Simulation Laboratory, Middle East Technical University, http://www.csl.mete.metu.edu.tr/Electromigration/emig.htm.