A Study on Seed Damage in Plating Electrolyte and Its Repairing in Cu Damascene Metallization

In this study, we observed the changes in the film properties of a Cu seed layer with its damage and repair. The immersion of the Cu seed layer in a sulfuric-acid-based plating electrolyte can result in damage to the Cu seed layer by the dissolution of the native Cu oxide and corrosion of Cu, leading to defects in the subsequent electrodeposited layer. The damaged seed layer was repaired using electroless plating. Cu re-covered the surface and the crystal structure of the seed layer was rebuilt and, finally, the filling characteristic was improved into superfilling in Cu electroplating for the damascene process. Electroless repairing, however, increased the seed roughness due to the low nucleation on the exposed barrier surface and the accompanying three-dimensional Cu growth. To refine the repairing process by inducing the nucleation on the barrier surface, Sn–Pd activation was adopted before the repair, and it reduced the surface roughness and improved the continuity of the seed layer effectively.