Amorphous Ta-N as a Diffusion Barrier for Cu Metallization

摘要

Amorphous Ta-N thin films (14 and 62 nm thick) arc deposited on Si substrates by reactive magnetron sputtering followed by Cu film deposition. The intcrlaycr reaction and failure mechanism of the annealed metallization stacks arc investigated by resistance measurements, x-ray diffraction (XRD) and detailed electron microscopy analysis accompanied with electron energy-loss spectroscopy (EELS). Amorphous Ta-N crystallizes at 600℃ by a polymorphous transformation to Ta_2N. The crystallized Ta_2N barrier prevents Cu-Si interaction and intermixing up to 700-800℃, depending on the barrier thickness. Copper appears to be the main diffusing species and reacts with Si at the Ta-N/Si interface to form η"-Cu3Si. Local Cu-Si reaction enhances the formation of TaSi_2 precipitates. Silicon also diffuses, though at a much slower rate, to the surface and reacts with Cu. Local oxidation of Cu_3Si occurs upon exposure to air, accompanied by SiO_2 formation.