In order to increase the failure temperature of a Ta diffusion barrier for Cu, the suppression of silicide formation in a Ta/Si system by ion-beam-assisted deposition of Ta film was investigated. When the Ta layer was deposited without ion bombardment, the reaction between Ta and Si started at 600 °C. In the case where the Ta film was prepared with concurrent ion bombardment, however, the silicide formation was retarded up to 700 °C. The suppression of Ta silicide formation can be attributed to a densification of grain boundaries in the Ta film by ion bombardment, followed by a reduction of the chemical driving force for the initial stage of silicide formation. The Ta diffusion barrier deposited by ion-beam-assisted deposition effectively suppressed the reaction between Si and Cu layers up to 650 °C for 30 min. ©1997 American Institute of Physics.