Procurement specification requirements for protection against electromigration failures in aluminium metallizations

• Published in: Microelectronics and reliability Vol. 19; no. 3; pp. 207 - 218
• Main Author: Sim, S.P.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 1979
• ISSN: 0026-2714; 1872-941X
• DOI: 10.1016/0026-2714(79)90335-4

Electromigration failure in aluminium metallizations has been widely investigated over the past decade, but continues to be a problem. Published work has not produced consistent results-reporting a variety of acceleration factors for temperature and current densities. Therefore, a detailed investigation was undertaken to enable the formulation of a meaningful specification test requirement to reduce the risk of premature failure of integrated circuits by electromigration. Life tests on aluminium metallizations from different sources have confirmed the sensitivity of electromigration to aluminium microstructure. Temperature and current density acceleration factors for the degradation of aluminium tracks have been found. Activation energies were in the range 0.4–0.6 eV for the films tested, and comparison with published results confirms that large grain films generally have a higher activitation energy and better reliability than small grain films. Current density acceleration was proportional to J −2 with no significant dependence on the grain size. However, it was found that testing at excessive current densities or temperatures could cause significant variations in lifetime, accounting for some of the spread in published acceleration factors. Test methods are recommended embodying an activation energy of 0.45eV and a current density acceleration proportional to J −2, within constraints which minimize risks due to the spread in activation energies and variations due to excessive dissipation or temperature. Tests have shown that other failure mechanisms occur during high current lifetests on completed integrated circuits, requiring the use of a metallization test pattern for the tests that are recommended.