Effect of annealing atmosphere on void formation in copper interconnects

Abstract

In order to understand the void formation mechanism in electroplated Cu interconnects used in Si-semiconductor devices, microstructure of Cu/CuO/Cu layered films which were prepared on the Si3N4/Si substrates by the sputter-deposition technique was observed by transmission electron microscopy (TEM) and scanning ion microscopy (SIM). A high density of macro and micro voids were observed in the samples annealed in atmosphere containing hydrogen, whereas no voids were observed in the samples annealed in Ar atmosphere. TEM observation suggested that a small amount of oxygen contained in the Cu films (even a native oxide layer) formed water vapor at elevated temperatures, causing formation of the micro-voids when the samples were annealed in hydrogen atmosphere. The present result suggested that the void formation in the electroplated Cu films was induced by existence of impurities such as oxygen in the Cu films, and that the void growth was strongly enhanced by annealing in hydrogen atmosphere.