Electrical and morphological change of Ag-Ni films by annealing in vacuum

Ag and Ag-Ni films (Ni: 0.6, 2.0 and 4.8 at.%) with a thickness of 95 nm were deposited on SiO2/Si substrates and the thermal stability of the films was evaluated. The films were annealed at temperatures from 400 to 700 °C for 1 h in vacuum. The as-deposited Ag and Ag-Ni films had a smooth surface. The Ag-Ni films had an electrical resistivity higher than that of the Ag film because of the impurity scattering effect. However, the resistivity of Ag-Ni films decreased until 600 °C by annealing. As the morphological change after annealing, void formation was observed for the Ag film at 500 °C. Then after the annealing at 600 °C, agglomeration with a partly uncovered substrate was clearly observed for the Ag film. On the other hand, void formation was also observed for the Ag-Ni films at 600 °C. Further annealing at 650 °C caused agglomeration of the Ag-Ni films with an increase in their resistivity. Due to the insolubility of Ni into Ag, small islands of Ni appeared at this temperature. Consequently, Ag-Ni films are useful for suppressing agglomeration up to the annealing temperature of 600 °C. The resistivity of the Ag-Ni (0.6 at.%) film was 2.1-2.4 μΩ cm after annealing from 400 to 550 °C comparable with that of the Ag film (1.9-2.2 μΩ cm) and it remained low, though that of the pure Ag film increased significantly at 600 °C.