An amorphous Ta-Zr binary alloy diffusion barrier was studied in the Cu metallization. A Cu/Ta50Zr50/Si stack with 50 nm thick amorphous film was prepared by cosputtering can effectively suppress the penetration of Cu atoms into substrate upon annealing up to 650 degrees C. Examining the thermal stability of the barrier revealed that the crystallization of these amorphous Ta50Zr50 films occurred at 800 degrees C, higher than its failure temperature. The results show that the existence of Cu layer first induced the formation of TaSi2 and ZrSi2 crystalline phases at 650 degrees C, followed by the formation of Cu3Si. A failure mechanism of the diffusion barrier is proposed based on the relation between the thermal stress and the activation energy of barrier/substrate interface reaction. (C) 2008 American Vacuum Society.