LAUSR

The combination of an all-wet barrier/seed process and Cu electrodeposition can be used to fabricate conformal Cu interconnects. This process usually uses a Co-based barrier deposited by electroless plating. However, as Co is more electrochemically active than Cu, the Co dissolves readily in the acidic Cu 2+ electrolyte during the subsequent Cu electrodeposition. This paper describes the trisodium citrate enhanced deposition of Cu on a Co/SiO2/Si substrate via alternating the underpotential deposition of Pb and surface-limited redox replacement of Cu. The nucleation mechanisms and properties of the Cu films were evaluated using scanning electron microscopy, X-ray diffraction, and an electrochemical analyzer. The results show that the complexation of Pb 2+ -Cit 3induced a low coverage of the Pb adlayer during the underpotential deposition. The grain growth led to progressive nucleation for 1 mM trisodium citrate, and shifted gradually toward instantaneous nucleation as the trisodium citrate concentration was increased to 5 mM. The Cu (111) texture was obtained with the 1 mM trisodium citrate addition. However, a high trisodium citrate concentration tended to cause Cu oxidation. The enhancement of the formation of a Cu film by the addition of trisodium citrate via the proposed processes was demonstrated..