ABSTRACT
Electromigration is an intrinsic wearout mechanism, but due to interaction with defects, electromigration does not manifest itself until a circuit has been operated for months, or even years. Electromigration may be modeled either as a mass transport (pile up of aluminum atoms) or a vacancy transport mechanism. Polycrystalline aluminum films, which are typically used for interconnect in silicon chips, are most prone to electromigration due to the relatively loose binding of the aluminum atoms, especially at the surface of the individual crystal grains. The complex nature of the electromigration mechanism requires some empirical calibration. This is normally accomplished by performing accelerated life tests on simple discrete test structures, such as single metal lines, single lines crossing over underlying topography, or chains of metal links at different metallization levels. Electromigration can be managed by controlling the material factors, the enviromental factors, or both. The material factors are controlled by the process technology and the manufacturing practices.
