Tantalum carbide and nitride diffusion barriers for Cu metallization

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 Si–Ta–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.