Some embodiments of the present disclosure provide a back side illuminated (BSI) image sensor. The back side illuminated (BSI) image sensor includes a semiconductive substrate and an interlayer dielectric (ILD) layer at a front side of the semiconductive substrate. The ILD layer includes a dielectric layer over the semiconductive substrate and a contact partially buried inside the semiconductive substrate. The contact includes a silicide layer including a predetermined thickness proximately in a range from about 600 angstroms to about 1200 angstroms.