1. An image sensor comprising: a semiconductor substrate having a first conductivity type; a deep well having a second conductivity type, the deep well being formed at a predetermined depth in the semiconductor substrate to divide the semiconductor substrate into a first conductivity type upper substrate area and a lower substrate area; and a plurality of unit pixels integrating charges corresponding to incident light and comprising first conductivity type ion-implantation areas said first conductivity type ion-implantation areas are separated from one another, at least one unit pixel among the plurality of unit pixels further comprising the first conductivity type upper substrate area that is positioned under a first conductivity type ion-implantation area included in the unit pixel, extends beyond the first conductivity type ion-implantation area and is electrically isolated from first conductivity type ion-implantation areas included in adjacent unit pixels of said plurality of unit pixels.