Investigation of interdiffusion in copper–nickel bilayer thin films

Auger depth profiling technique and X-ray diffraction analysis have been employed to study the interdiffusion in vacuum-deposited copper–nickel bilayer thin films. An adaptation of the Whipple model was used to determine the diffusion coefficients of both nickel in copper and copper in nickel. The calculated diffusion coefficient is (2.0×10−7 cm2/s)exp(−1.0 eV/kT) for nickel in copper, and (6×10−8 cm2/s)exp(−0.98 eV/kT) for copper in nickel. The difference between the diffusion parameters obtained in the present work and those extracted by other investigators is attributed essentially to the difference in the films microstructure and to the annealing ambient. It is concluded that interdiffusion in the investigated films is described by type-B kinetics in which rapid grain-boundary diffusion is coupled to defect-enhanced diffusion into the grain interior. The present data raise a question about the effectiveness of nickel as a diffusion barrier between copper and the silicon substrate.