US Patent 7843063 Microstructure modification in copper interconnect structure

Cobalt is added to a copper seed layer, a copper plating layer, or a copper capping layer in order to modify the microstructure of copper lines and vias. The cobalt can be in the form of a copper-cobalt alloy or as a very thin cobalt layer. The grain boundaries configured in bamboo microstructure in the inventive metal interconnect structure shut down copper grain boundary diffusion. The composition of the metal interconnect structure after grain growth contains from about 1 ppm to about 10% of cobalt in atomic concentration. Grain boundaries extend from a top surface of a copper-cobalt alloy line to a bottom surface of the copper-cobalt alloy line, and are separated from any other grain boundary by a distance greater than a width of the copper-cobalt alloy line.