Electromigration in Double-Layer Metallization

The electromigration of the top stripe in aluminum double-layer metallization systems was investigated. The current density dependence and the activation energy characterization are important in double-layer metallization. The step-coverage and coating effects of SiN is better than that of Si02. New phenomena associated with electromigration have been observed as follows: 1. The mean lifetime is affected by the material of the dielectric layer. This material effect might be related to the hardness of layer. 2. The mean lifetime due to electromigration depends on the magnitude and polarity of the electric field applied between adjacent stripes. Ordinary stress tests for electromigratfon are done where current is conducted only in the top stripe and not in the bottom stripe. Our results show that this situation is realistic under conditions existing in microelectronic circuits. The proposed method for stress testing should be used to simulate actual condition in microelectronic circuits. We emphasize that the stress test method used to disclose this electric field effect is important for accelerated stress testing, especially for metallization in VLSI circuits and multi-layer systems. The failure mechanism due to the electric field effect can be explained in terms of the applied electric field deflecting current-carrying electrons in the metal stripe, and is independent of leakage current between stripes.