The effect of microstructure on the resistance to electromigration of AlCu thin film conductors

Abstract

Aluminum-copper alloy films were prepared by vacuum evaporation under varying conditions of deposition rate and substrate temperature. They were subsequently subjected to electromigration testing using the median time to failure (MTF) and temperature-ramp resistance analysis to characterize electromigration (TRACE) methods and the resulting activation energies for electromigration were extracted. It was found that certain microstructural configurations affected the beneficial effects of copper on the resistance of thin films to electromigration. The magnitude of the activation energies ranged from 0.25 eV up to 0.95 eV. The differences in the activation energies Q were related to the deposition conditions, the films' grain size distributions, the copper content of the films, the Al 2Cu precipitate distributions in the films, and the possible presence of Guinier-Preston zones. The Avrami analysis of the resistometric data for the lifetime experiments was also employed. It was found that a single failure mechanism dominated over the temperature range of the MTF experiments, but this mechanism was dependent on the deposition conditions.