Electrodeposition of Platinum Group Metals for Interconnects Beyond 5nm Technology Node
Authors: Pacquette Adele , O'Sullivan Eugene J. , Krishnan Mahadevaiyer 
Published: July 2021

For technology nodes beyond 5 nm, copper metal may not be feasible as conductor material in Damascene interconnects.1 The bulk resistivity of copper increases exponentially and electromigration of copper is possible with the scaling down of the technology nodes. Metals such as inert platinum group metals have been proposed as alternative metal conductors for interconnects.2 Platinum group metals exhibit less electron scattering and lower electromigration in narrow line widths compared to copper; the electron scattering is proportional to the bulk resistivity. Thus, certain platinum group metals, e.g., ruthenium2, have been proposed as alternative conductors for interconnects.3 Ruthenium electrodeposition needs further development because of slow kinetics, resulting in poor control of morphology, and defects in the film due to hydrogen evolution at the high overpotential required to initiate ruthenium deposition.4 Another challenge is that ruthenium has multiple oxidation states, which may result in disproportionate reactions, and, thus, electrodeposition may not occur reproducibly.3
This study investigates the electrodeposition of ruthenium from nitrosyl ruthenium complexes, and/or inorganic ruthenium compounds such as chlorides, sulfates or phosphates in acidic electrolytes. Figure 1 shows ruthenium electrodeposited on an ultrathin seed layer with high sheet resistance. Electrodeposition techniques such as chronoamperometry and chronopotentiometry are compared for the initiation of ruthenium nuclei on such highly-resistive (up to 400 Ω/sq) seed layers. In this study, a multi-step electrodeposition process was developed for the nucleation, then growth of a uniform, void-free ruthenium film. A constant voltage was applied for a short time (few seconds) to initiate plating by providing the overpotential necessary to form ruthenium nuclei. Next, a low current density was applied to grow the film to the desired thickness (50 – 100 nm). This method allows for minimal hydrogen evolution and prevents void formation since the high potential is applied for a short time compared to other typical pulse plating methods. The multi-step method is reproducible and results in uniform plating on 200 mm wafer scale by utilizing plating tool shields that can control center and edge plating rates. This talk describes the effect of electrolyte bath composition and plating parameters on the morphology, adhesion and uniformity of the electrodeposited ruthenium.
Figure 1: Electrodeposited ruthenium on Si substrate with ultrathin seed layer.
1) Chen, Q.; Lin, X.; Valvede, C.; Paneccasio, V.; Hurtubise, R.; Ye, P.; Kudrak, E.; Abys, J., Electroless copper deposition on ruthenium for damascene interconnects. ECS Transactions. 2007, 6 (8), 179-184.
2) Mainka, G.; Beitel G.; Schnabel R.F.; Saenger, A.; Dehm, C., Chemical mechanical polishing of iridium and iridium oxide for damascene process. Journal of the Electrochemical Society. 2001, 148, G552-G558.
3) Bernasconi, R.; Magagnin, L., Review—Ruthenium as diffusion barrier layer in electronic interconnects: Current literature with a focus on electrochemical deposition methods. Journal of the Electrochemical Society. 2019, 166 (1), D3219-D3225.
4) Oppedisano, D.K.; Jones, L.A.; Junk, T.; Bhargava, S.K., Ruthenium electrodeposition from aqueous solution at high cathodic overpotential. Journal of the Electrochemical Society. 2014, 161 (10), D489-D494.
Acknowledgement
The authors acknowledge the researchers of the Microelectronics Research Laboratory (MRL) at the IBM T. J. Watson Research Center, for the fabrication work.

Figure 1