|| For several years interconnection of semiconductor industry is advanced and then feature size is gradually reduced. However it causes some problems such as RC(resistive-capacitive) delay and gap filling difficulty. To solve this problems, low dielectric constant material is applied to substitute SiO2. Furthermore self-forming diffusion barrier process to prevent Cu diffusion into the dielectrics without barrier layer deposition also researched. Self-forming barrier process is one of the solution to increase Cu filling ratio. But it is very sensitive to the Cu alloy material composition and it causing Cu penetration during annealing for barrier formation. In this work, Cu-Mn alloy and Ta were used for seed layer and sub-layer on low-k substrates to fine the solution of this problems. Cu-Mn/Ta/low-k structure was prepared and annealed at 400 oC during 1 hr to barrier formation. Deposited film and barrier layer properties were analyzed by four-point-probe, transmission electron microscopy, Auger electron microscopy, atomic force microscopy and I-V analysis. We were confirmed that the Ta layer is sufficient to support the self-forming barrier process by prevention of Cu diffusion into the dielectric during annealing. Moreover its thermal stability is good compared to the self-forming barrier without Ta layer. The results shows Cu-Mn/Ta layer on low-k substrates is suitable for Cu diffusion barrier so it is expected to enhance device performance potentially.