Fig. 2. The appearance of grain boundary segregation due to annealing.

EDX mapping of a as-deposited 27 nm Cu PVD film and b 500 °C annealed 27 nm Cu PVD film. c EDX spectra of as-deposited and 500 °C annealed 27 nm PVD films. During annealing of 27 nm Cu at 500 °C, Ta undergoes diffusion along its grain boundaries (Fig. 2b) since it is not soluble in its grains^20,23. The oxygen already present along grain boundaries oxidizes Ta and leads to form TaO_x complexes, which act as the scattering centers for the electrons.