One of the major challenges in the integrated circuit beyond 90 nm is to fabricate low resistivity Cu diffusion barrier layer in the metal multilevel interconnect. Ta/TaN bilayer is one of the best candidates for Cu metal diffusion layer. It provides the advantage good diffusion performance between Cu and low-k dielectric layer. However, the resistivity is large deviation from tantalum phase variation. This is because of Tantalum of bilayer easily found in beta-phase, which is high resistance. This paper proposed a low resistivity alpha-Ta thin films were grown by treatment-TaN using Argon plasma treatment on TaN substrate. The argon treatment redistribute nitrogen profile between Ta and TaN and create a Ta(N) interface. X-ray diffraction analyses show that the interface film is composed of b.c.c.-Ta(N) grains. This Ta/treatment TaN provide new method to fabricated b.c.c.-Ta(N) difference from the previously report deposition by sputtering process. The resistivity will decrease nitrogen concentration to provide a favorable environment to promote low resistivity Tantalum alpha-phase formation.