Glyoxylic Acid as Reducing Agent for Electroless Copper Deposition on Cobalt Liner

Abstract

Electroless deposition of Cu was investigated on thin Co layer for through Si via with high aspect ratio structure. The electroless deposition bath was optimized for minimizing Co corrosion during Cu nucleation by using electrochemical analysis. Glyoxylic acid, which is known as non-toxic reducing agent for electroless Cu deposition, showed anodic oxidation on Co, which did not appear for the case of formaldehyde. Furthermore, ratio of complexing agent and Cu ion also impacted Co corrosion; free complexing agent in the electroless deposition bath accelerated corrosion of Co. The optimized electroless bath which contained glyoxylic acid as reducing agent and non-free EDTA performed in 3 μm × 50 μm TSV, the electroless deposited Cu layer could serve as a seed layer for TSV filling by electrodeposition. The electroless Cu layer was continuously deposited without missing of continuity of Co layer even close to the bottom of TSV.