Electroless plating of copper on metal-nitride diffusion barriers initiated by displacement reaction

摘要

We found that copper could be deposited by electroless-plating on the surface of metal-nitride barrier films such as TaN and WN without any sputtered Cu seed layer or Pd catalysis adsorption pretreatnaent. When the metal nitride barrier films were pretreated with proper wet chemical etchings to remove a surface oxygen-rich layer and immersed into an electroless Cu plating solution with a glyoxylic acid reducing agent, the copper was deposited immediately on them. Electroless deposited Cu on sputtered TaN had good adhesion properties to endure against CMP and the electrical resistivity of 0.42 μm damascene interconnection formed by electroless deposition only was 2.1 μΩ cm. The electrical potential measurements of the barrier layers against the Ag/AgCl reference electrode in the plating solution showed that the reduction oxidation (REDOX) potentials of TaN and WN were lower than that of copper. We also found that the REDOX potential of TiN was higher than that of Cu, and the electroless-plated-copper was not deposited 6n the surface of TiN without catalysis treatment. As a consequence, the deposition mechanism of electroless copper plating on the surfaces of TaN and WN is considered to be the displacement plating reaction between metal-nitrides and copper ions.