Electroless Plating of Copper on Metal-Nitride Diffusion Barriers Initiated by Displacement Plating

Copper is deposited on TaN and WN barrier layers by electroless plating without the need for activation preprocessing when substrates are (i) pretreated by wet chemical etching to remove surface oxides, and (ii) immersed in an electroless Cu plating solution containing glyoxylic acid as a reducing agent. Electrical potential measurements indicate that the redox potentials of TaN and WN in the plating solution are lower than that of copper, driving displacement plating of Cu in the initial stage of deposition. The adhesion between electroless-plated Cu and the TaN barrier layer after annealing is 0.11 kgf/cm as determined by a peeling test, which is sufficient for reliability during chemical mechanical polishing. A damascene Cu interconnect was successfully fabricated without delamination and exhibited an electrical resistivity of 2.2 μΩ cm after annealing for a 0.42 μm wide interconnect track. These results indicate that the proposed electroless process is suitable for the formation of a Cu seed layer prior to electrodeposition for the fabrication of ultralarge scale inteerated interconnects.