Proton Sensitive Additive for Cobalt Electrodeposition

Cobalt electrodeposition involves hydrogen reduction reaction, and the proton supply in feature filling varies depending on the location because of the topographical characteristics, thereby resulting in changes on the electrode surface, such as changes in pH and hydrogen adsorption. Based on this phenomenon, void-free trench filling was performed using benzimidazole (BZI) as an additive, which has different suppression effects depending on pH. Linear sweep voltammetry experiments confirmed the change in suppression behavior of the additive according to pH. Chronoamperometric transients were performed at a fixed BZI concentration to confirm the potential region, wherein actual cobalt deposition was suppressed. Chronoamperometric analysis with various rotation rates was also conducted to demonstrate the effect of proton concentration near the electrode on the suppression effect of BZI. Finally, a void-free filling working mechanism in a low aspect ratio trench using BZI was proposed. This study proposes, a single additive, whose suppression behavior changes according to the change in pH of the electrode surface, by considering the pH of the cobalt deposition solution and pK a value of the additive. Furthermore, it was demonstrated that void-free filling can be performed even in a trench with a low aspect ratio.