The thermal stability of Cu/Ta/Cr/Si structure is analyzed and compared with that of Cu/Ta/Si and Cu/Ta/Cr/Ta/Si structures. The Cu/Ta/Si and Cu/Ta/Cr/Ta/Si systems retained their structures up to 600 °C without increase in resistivity but the Cu/Ta/Cr/Si structure was degraded after annealing at 400 °C. In the latter case, the degradation was dominated by the outdiffusion of free Si, probably released from the substrate in the formation of CrSi2. It is suggested that the released Si is reactive and its outdiffusion through Ta layer is facilitated by the high affinity of Si toward Ta, as expected from the large negative value of mixing enthalpy between Ta and Si. ©1996 American Institute of Physics.