Addition of strong interaction element Fe(or Sn) to improve the stability of solid solution Cu(Ge) film

In order to apply solid solution Cu(Ge) film to a barrierless structure for Cu interconnection, a binary Cu(Ge) solid solution film was prepared on the single-crystal Si(100) substrate by magnetron sputtering, followed by vacuum annealing. It was found that the individual addition of Ge led to serious interfacial diffusion promoting Cu-Si reaction. Therefore, Fe (or Sn) was chosen as the third element to prepare Cu(Ge-Fe(or Sn)) ternary films. The strong interactions from the negative mixing enthalpy between Ge-Fe(or Sn) stabilizes Ge in the Cu lattice, improving the thermal stability of the film. After 400 °C/1 h annealing, the Cu99.19Ge0.73Fe0.08 and Cu99.22Ge0.69Fe0.09 films with the largest lattice distortion remained stable with the resistivity as low as 2.54-2.80 μΩ cm. For Cu(Ge-Sn) films, the Cu-Si reaction did not occur in the Cu99.01Ge0.90Sn0.09 films with the largest lattice distortion, and the resistivity was maintained at 2.51 μΩ cm. The results proved that strong interaction elements Fe and Sn could prevent the diffusion of Ge and enhance the stability of Cu alloy films. The addition of small atomic radius element Fe, which has large diffusion activation energy and small diffusion coefficient in Cu, could inhibit diffusion for a wide range of composition.