Effect of 3-mercapto-1-propane sulfonate sulfonic acid and polyvinylpyrrolidone on the growth of cobalt pillar by electrodeposition

Cobalt is a promising material for electronic interconnections in the post-Moore law period. However, the vertical cobalt pillar is not fully compatible with the current electroplating-involved manufacturing process due to hydrogen evolution at the cathode and poor throwing power of the products. In this article, electrodeposition with multiple organic additives was employed to realize the fabrication of cobalt pillars. Electrochemical measurements were used to investigate the depolarization of 3-mercapto-1-propane sulfonate sulfonic acid (MPS) and the polarization of the polyvinylpyrrolidone (PVP) during cobalt electrodeposition. Notably, the competitive adsorption between MPS and PVP was verified and discussed in cobalt electrodeposition. In order to understand the adsorption and functional groups of the additives, quantum chemical calculations were performed to simulate the distribution of electrostatic potential and molecular orbital energy of the additives. Accordingly, the thiol group of MPS and the amide group of PVP were speculated to be the molecular adsorption sites in cobalt electrodeposition. The mechanism including three stages was proposed for cobalt pillar electrodeposition in solution with MPS and PVP. The electrodeposition of practical cobalt pillars with a depth of 50 µm and diameters of 60, 80, and 100 µm was successfully achieved by electroplating experiments, thereby promoting the application of metal cobalt for electronic packaging.