A1/A1-Oxide Interface Diffusion During Electromigration

Abstract

This paper presents new results concerning diffusion at the interface between Al and its oxide, due to electromigration in Al interconnects. The results show that the phenomenon is an important and general one. Significant large-scale modification of the surface of Alalloy conductors was observed after electromigration stress under a wide range of different conditions: 1) in a number of different alloys (Al-Si, Al-Cu, Al-Si-V & Al-Si-V-Pd), 2) with and without passivation, 3) over an extended temperature range, 4) over an extended range of current density, and 5) with a number of different underlayers (SiO2, W-Ti (no vacuum-break before Al deposition) and W-Ti (oxidized surface before Al deposition)). After electromigration stressing, the surface showed height variations: at certain locations the original thickness remained, while at adjacent locations the thickness was reduced; as much as 150nm in 2500 hrs, for Al-Si on oxidized W-Ti metallization. Damage by thinning has received little attention in the past. Based on the results presented, a model for the underlying mechanism is proposed. In this model Al atoms diffuse concurrently along the interface between the Al-metal and its oxide, and through the grain boundaries, even at low stress conditions and in non-bamboo lines.

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Augur, R.A., Wolters, R., Schmidt, W. et al. A1/A1-Oxide Interface Diffusion During Electromigration. MRS Online Proceedings Library 391, 264 (1995). https://doi.org/10.1557/PROC-391-259

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