A method for manufacturing structures of a CMOS image sensor. The method comprises the steps of depositing a gate insulating layer and a conductive layer on a semiconductor substrate; depositing an ion implantation barrier layer on the conductive layer; patterning the deposited gate insulating layer, conductive layer and ion implantation barrier layer to form a patterned, composite gate insulating layer, gate electrode and ion implantation barrier structure; forming a second photosensitive layer pattern to define a photodiode region; and implanting low-concentration dopant ions into the substrate using the second photosensitive layer pattern as an ion implantation mask to form a low-concentration dopant region within the photodiode region.