The thermal stability of the Cu/Ta2Al/Ta/Si contact system, in which the intermetallic compound film of Ta2Al is used as a diffusion barrier to copper penetration, has been studied using Auger electron spectroscopy analysis. Although the examined contact system degrades by the interfacial reaction of silicide formation at the Ta/Si interface due to annealing, the system tolerates annealing at 650 degrees C for 1 h if the Ta layer is considered as a consumable barrier, The replacement of Ta with a Ta-W alloy film results in a decrease of the resistivity and an increase of the silicidation temperature due to alloying. By using this alloy film as a layer adjoining to Si, the system of Cu/Ta2Al/Ta-W/Si tolerates annealing at 680 degrees C for 1 h. Even after this annealing, any penetration of Cu is not observed at the Cu/Ta2Al interface, suggesting that Ta2Al is a promising material as a diffusion barrier to copper overlayer films.