Tantalum Carbide and Nitride Diffusion Barriers for Cu Metallisation

The reactions in the Si/TaC/Cu and Si/Ta2N/Cu metallisation systems were investigated by x-ray diffraction, Rutherford backscattering, scanning electron microscope and the transmission electron microscopy. The results were then combined with the assessed ternary SiTa-C, Ta-C-Cu, Si-Ta-N and Ta-N-Cu phase diagrams. It was found that both barriers ultimately failed due to diffusion of Cu through the barrier and accompanied formation of Cu3Si at temperatures higher than 725 °C. However, in the TaC barriers the formation of amorphous TaOx layer with significant amounts of C took place at the TaC/Cu interface already at 600 °C. Similar behaviour at "low" temperatures was also noted in the Ta2N barriers.