Nucleation Kinetics of Electroless Cu Deposition on Ruthenium Using Glyoxylic Acid as a Reducing Agent

Glyoxylic acid is seen as a promising candidate to replace formaldehyde as reducing agent in electroless Cu baths. For deposition on ruthenium, the anodic reaction of glyoxylic acid has been evaluated and compared to formaldehyde using linear sweep voltammetry. Significant differences were observed for the deposition of copper on ruthenium. First of all, a faster nucleation was inferred from open-circuit potential measurements, which is beneficial as it reduces the total process time. Secondary, we found 2,2′ bipyridyl worked as stabilizer and brightener in this glyoxylic acid-based electroless bath. Thirdly, the purity of the copper films improved when 2,2′ bipyridyl was present in the solution. Using the optimized composition, we demonstrate a conformal Cu seed layer deposition (∼100 nm) inside high aspect ratio (16.7) through-Si vias. This work shows the feasibility for electroless Cu seeding in a through-Si via metallization sequence.