What is Electromigration???
Electromigration is the gradual displacement of metal atoms in a semiconductor. It occurs when the current
density is high enough to cause the drift of metal ions in the direction of the electron flow, and is characterized
by the ion flux density. This density depends on the magnitude of forces that tend to hold the ions in place,
i.e., the nature of the conductor, crystal size, interface and grain-boundary chemistry, and the magnitude of
forces that tend to dislodge them, including the current density, temperature and mechanical stresses.
Failure mechanism
There are two different EM failure mechanisms that occur due to asymmetry in the ion flow. The first example
in Figure shows a void where the outgoing ion flux exceeds the incoming ion flux, resulting in an open circuit.
The second example shows a hillock where the incoming ion flux exceeds the outgoing ion flux, resulting in
a short circuit.
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| Void (open circuit) and hillock (short circuit) |
