An image sensor may include a main photodiode formed in a substrate, a first inter-layer dielectric layer formed over a lower surface of the substrate, and phase difference detectors formed over the first inter-layer dielectric layer. The phase difference detectors include a left phase difference detector that is vertically overlapping and aligned with a left side region of the main photodiode, and a right phase difference detector that is vertically overlapping and aligned with a right side region of the main photodiode.