A method for forming a metal interconnection in an image sensor includes forming a first interlayer dielectric (ILD) layer having a contact plug over a substrate, forming a diffusion barrier layer over the first ILD layer, performing a forming gas annealing, forming a second ILD layer over the diffusion barrier layer, etching the second ILD layer and the diffusion barrier layer to form a trench, forming a conductive layer to fill the trench, and planarizing the conductive layer to form a metal interconnection electrically connected to the contact plug.