Reliability of Al metallization is strongly influenced by electromigration. In Al lines there are at least two competing failure modes. On the one hand, mass flow divergencies can produce stripe interruptions, and on the other hand, homogeneous mass flow, which is described by the Al drift velocity, can lead to contact openings. Test results indicate that the drift velocity limits the lifetime of metallization. Worst case failure behavior should be measured in long test lines, since there is an electromigration threshold, which affects mass flow in shorter lines. Al reliability can be improved by reducing the total mass flow.
This might be done by influencing electromigration mechanisms. Considering electromigration threshold, grain boundary and interface electromigration can be eliminated in large-grained, narrow lines. The extremely low mass flow of the remaining mechanism is beneficial for the reliability of metallization.