Effect of substrate bias voltage on the thermal stability of Cu/Ta/Si structures deposited by ion beam deposition

The interfacial reactions of the Cu (100nm)/Ta (50nm)/Si structures and their relationship with the microstructure of Ta diffusion barrier are investigated. Ta films were deposited on Si (100) substrates using a non-mass separated ion beam deposition system at various bias voltages ranging from 0 to - 200V. An optimum applied substrate bias voltage of - 125V was found to yield a dominant α-Ta film with a noncolumnar structure, low electrical resistivity (about 40 μΩcm) and smooth surface. A Ta diffusion barrier which was deposited at the optimum bias voltage prevented Cu-Si interaction up to 600°C for 60 min in flowing purified H₂, whereas a Ta layer with a columnar structure, deposited at zero bias voltage, degraded at 300°C. Two different reactions of the Cu/Ta (0 V)/Si and the Cu/Ta (-125 V)/Si structures concerning the thermal stability were investigated and discussed on the basis of the experimental results.