AlSiV and AlSiVPd films as alternatives for AlSiCu interconnect: microstructure and its impact on reliability

In this paper new data on highly reliable interconnect materials based on aluminium will be presented. Compared with AlSiCu alloy films, alternative alloys such as AlSiV and AlSiVPd combine excellent plasma etchability with good corrosion resistance. Addition of V to AlSi increases the electrical resistivity, but if the concentration of V does not exceed 0.2–0.3 at.%, the increase is not a problem for most practical applications in ultralarge-scale integration. AlSiV and AlSiVPd films have been subjected to electromigration stress (180°C, 2 × 10 6 A cm −2). AlSiVPd films showed suprisingly high resistance to damage. Understanding the microstructure becomes increasingly important as integrated circuit feature sizes become smaller than the average grain size of the aluminium alloy films used for interconnect. Therefore the microstructural details of the above alloys have been studied using transmission electron microscopy. Based on the results, a model has been developed which explains the action of V and Pd in the aluminium lattice. According to this model, both V and Pd are needed concurrently to obtain a high reliability Al-based interconnect. Furthermore, recent findings suggest that electromigration failure of narrow lines may be dominated by diffusion along the Al/Al-oxide interface, such that lines fail by thinning. The above model and the reliability results presented here are consistent with an interface diffusion mechanism. Finally, the (Al, Pd) precipitates observed have been characterized and identified as the decagonal “Al 75Pd 25”-type phase.