A Selection Rule of Solutes for Void-Resistant Crystalline Metallic Alloys Exposed to Electromigration

• Published in: Crystal research and technology (1979) 2002-08, Vol.37 (8), p.817-826
• Main Author: Zehe, A.
• Format: Article
• Language: English
• Subjects: Applied sciences; crystalline interconnects; electromigration; Electronic equipment and fabrication. Passive components, printed wiring boards, connectics; Electronics; Exact sciences and technology; metallic alloys; Testing, measurement, noise and reliability; void-resistance
• ISSN: 0232-1300; 1521-4079
• DOI: 10.1002/1521-4079(200208)37:8<817::AID-CRAT817>3.0.CO;2-6

This paper tries to predict electromigration resistance from basic properties of the involved atoms forming dilute alloys, and in particular of aluminium, copper and silver matrix metals with a number of chemically different solute elements. The leading property is generated by the formation of solute atom‐vacancy pairs, and its electronic charging state. A semi empirical rule is formulated, which considers the valence state of matrix‐ and solute atoms, and which allows a projection of the level of void formation or suppression during electromigration stressing. It is found, that the formation of voids is suppressed, if the valence electron number of the matrix atom and that of the alloying impurity atom sums up to an odd number. A broad literature scan was carried out indicating that there are only very few cases, where accordance between prediction and experimental result is violated. The rule is justified on microscopic considerations in the framework of the inhomogeneous electron gas model.