A Study of Cu/CuMn Barrier for 22-nm Semiconductor Manufacturing

The barrier properties of self-forming barrier are sensitive to the thickness, annealing temperature, annealing time, and impurity concentration of itself. In this paper, the properties of Cu/CuMn/ SiO₂ bilayer structures were investigated, and an optimized thickness of Cu and CuMn alloy used as barrier layers in these bilayer structures was also determined. The bilayer structure could reduce the resistance of barrier and improve the surface morphology in electroplating process because Mn is easier to be corroded and oxidized than Cu in sulfuric acid. The electrical and material properties of Cu/CuMn/ SiO₂ were studied. A diffusion barrier layer self-formed at the interface during annealing, and the growth behavior followed a logarithmic rate law. The microstructures of the metal films were analyzed by transmission electron microscopy (TEM) and then correlated with the electrical properties of the CuMn films. After annealing, the thermal stability of Cu/ CuMn films was better than single Cu film and CuMn film. When Cu layer was capped, the Mn atoms diffused easily to the interface due to high chemical potential of the Cu layer. Thus, Mn atoms tend to move to SiO₂, and the amount of surplus Mn atoms in Cu will reduce after heat treatment.