Development of Glyoxylic Acid Based Electroless Copper Deposition on Ruthenium
Figure 1 shows polarization analysis of glyoxylic acid and formaldehyde on Ru and PVD-Cu as a reference. All the measurements showed anodic oxidation. It indicates that the driving force of anodic oxidation of glyoxylic acid and formaldehyde is catalysis of Ru and Cu. Although the anodic oxidation of glyoxylic acid on Ru was weaker than formaldehyde, glyoxylic acid showed similar potential on Ru (-0.63 V) and Cu surface (-0.68 V) at -0.01 mA/cm2. They were -0.63 V on Ru and -0.83 V on Cu for the case of formaldehyde.
Furthermore, we found that 2,2’-bipyridyl worked as stabilizer, brightener and suppressor in the glyoxylic acid based bath. Figure 2 shows surface morphology, roughness and purity of ELD Cu using various concentrations of 2,2’- bipyridyl. The roughness and the purity of copper films improved by adding 2,2’-bipyridyl in the bath. The high purity of Cu might help to reduce void generation during the annealing process after filling. Figure 3 shows cross sectional TEM images of TSV after ELD on Ru. The ELD layer was defect free and worked as a seed layer for electrodeposition of copper. The advantage of depositing a conformal seed layer is that it also reduces the total Cu overburden, which is to be removed by CMP.
 F. Inoue, H. Philipsen, A. Radisic, S. Armini, Y.Civale, S. Shingubara, and P. Leunissen Journal of The Electrochemical Society, 159 (7) D437-D441 (2012)