Development of Glyoxylic Acid Based Electroless Copper Deposition on Ruthenium

Abstract

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 to shorten the total process time, was inferred from open-circuit potential measurements. Secondary, we found 2,2’ bipyridyl worked as stabilizer, brightener, and suppressor 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 for the electroless bath, we demonstrate a conformal Cu seed layer deposition (~100 nm) inside high aspect ratio (16.7) through Si vias. This work shows the potential for electroless Cu seeding for a through Si via metallization.