Wet-chemical deposition of metals for advanced semiconductor technology nodes: Rh3+ solution stability and Rh electrodeposition

For back end of line metallization, the wet-chemical deposition of Rh requires investigation as the metal can improve the performance of semiconductor devices, due to its low resistivity and expected favourable electromigration characteristics. This study reports the Rh electrochemistry features in four background electrolytes (KCl, NH4Cl, K2SO4, and (NH4)2 SO4) as well as the stability of Rh3+ in the electrolytes and ultrapure water using UV-vis spectroscopy and it was found that various complexes were formed depending on storage time and mixing time. The onset potentials of the Rh3+ reduction reaction(s) and hydrogen evolution reaction were determined by linear sweep voltammetry. For chloride-based solutions, a much slower stabilization was observed than for sulphate-based solutions, as evidenced by the gradual disappearing of multiple reduction peaks over the course of days. After stabilization, Rh is deposited with a single reduction peak. Although Rh has a high catalytic activity for hydrogen evolution, the adsorption/desorption of hydrogen ions on the metal surface and the onset of Rh3+ reduction occur at well-separated potentials, which allowed us to use an electrochemical quartz crystal microbalance to determine the Rh deposition potential as well as quantify the amount of metal deposited on a Pt-coated electrode.