Electromigration — Induced failure mechanism and lifetime prediction in NiCu thin film

NiCu is one of the widely used thin-film materials, which is now commonly used as sensor and resistor in very-large-scale-integration (VLSI) because of its high resistivity and stability. However, with the scale decreasing and the temperature increasing in service condition, the limited reliability of NiCu thin-film material has been a key issue in microelectronics and packaging industry mainly due to the current induced electromigration (EM). In this paper, a sandwich-like NiCu thin-film resistor (Ta/NiCu/Ta) with the thickness of 120 nm was fabricated on the glass substrate by sputtering technique. The resistance of the thin-film structure was proved to increase with time during test. The mean-time-to-failure (MTTF) analysis based on the Black´s equation found that the activation energy (Ea) was 0.99 eV and the model parameter for current density of Black´s equation was close to 3. Additionally, multi-voids were observed in the thin-film, which can be explained by the Ni diffusion along the barrier layers of Ta crystals. The results in this study proved that multi-voids formation by Ni diffusion is the main reason that leads to EM failure.