We report a comparative study on the diffusion barrier performance of transition metal nitride thin films, including TiNx, TaNx, and WNx, between Al and Cu deposited by ionized physical vapor deposition (IPVD) or atomic layer deposition (ALD), which is particularly important for the integration of the Cu interconnect into memory devices such as dynamic random access memory and NAND Flash. Without a suitable diffusion barrier, various kinds of Al-Cu intermetallic compounds were formed, even after annealing at 200°C for 30 min. Sheet resistance measurements, X-ray diffractometry, and cross-sectional view transmission electron microscopy analysis combined with energy-dispersive spectroscopy consistently showed that the insertion of a 10-nm-thick IPVD- TiNx or IPVD- TaNx layer between the two layers retarded the interdiffusion of Al and Cu during the annealing at 400 or 450°C, respectively, for 30 min in a high vacuum (<5× 10-5 Torr). Noticeably, ALD- WNx prepared using a sequential supply of B2 H6, WF6, and NH3, could effectively prevent the interdiffusion of Al and Cu and the formation of Al-Cu intermetallic compounds up to an annealing temperature of 550°C for 30 min.