A semiconductor structure includes a substrate having thereon a dielectric layer. An opening is formed in the dielectric layer. The opening includes a bottom surface and a sidewall surface. A diffusion barrier layer is conformally disposed along the sidewall surface and the bottom surface of the opening. A nucleation metal layer is conformally disposed on the diffusion barrier layer. A bulk metal layer is disposed on the nucleation metal layer. A film-growth retarding layer is disposed between the nucleation metal layer and the bulk metal layer.