Investigation of the barrier properties of copper-vanadium alloys with a sub-tantalum layer on low-k dielectrics

- We reported the effects of Cu-V alloy with sub-Ta layer on the self-forming barrier process.
- The reliability and barrier properties of the Cu-V barrier layer could be enhanced by sub-Ta layer (∼2 nm).
- The sub-Ta layer disturbed the formation of the V-based diffusion barrier.

In this study, we investigated the effects of a sub-Ta layer on the self-forming barrier process of a Cu-V alloy on low-k dielectrics. To determine how the sub-Ta layer affects the V-based self-forming barrier performance, Cu-V/low-k and Cu-V/Ta/low-k samples were compared using various analysis methods. The thickness, chemical composition, and reliability performance of the V-based interlayer with or without the sub-Ta layer were determined by transmission electron microscopy (TEM), X-ray photoemission spectroscopy (XPS), and thermal stability analysis, respectively. Although the sub-Ta layer adversely affected the decrease of the sheet resistance of the Cu alloy and the formation of a V-based interlayer, the experimental results revealed that the Cu-V/Ta/low-k samples exhibited good reliability and barrier properties, indicating that these properties for a Cu-V barrier layer can be enhanced by introducing a thin Ta sub-layer. XPS analysis showed that the sub-Ta layer affects the formation of a V oxide layer not only by blocking the diffusion of V atoms, but also due to the formation of Ta oxide. In the case of a V-based interlayer with a sub-Ta layer, both Ta2O5 and V2O5 compounds were formed on the low-k layer. Furthermore, according to the leakage current results, although the introduction of the sub-Ta layer improved the reliability and thermal stability of the self-forming barrier process, the Cu-V/Ta/low-k/Si structures demonstrated increased current densities under the 550 °C thermal stress condition. This indicates that the Cu-V alloy with the sub-Ta layer needs to be further investigated to improve the thermal stability.