Solid state image sensor

Abstract

Solid state image sensor of an improved charge transfer efficiency, including a first conductive type semiconductor substrate; a plurality of photodiodes each formed on a surface of the first conductive type semiconductor substrate; a second conductive type first well formed under the surface of the first conductive type substrate; a second conductive type second well formed under the surface of the first conductive semiconductor substrate so that a part of the second well forms an overlapped region with the first well; a plurality of first conductive type vertical charge coupled devices (VCCDs) each formed under a surface of a region of the first well for transferring signal charges generated in the photodiodes toward output side of the VCCD in response to external vertical transfer clock signals; vertical transfer gates formed extended over the plurality of the VCCDs for applying the external vertical transfer clock signals; a first conductive type horizontal charge coupled device (HCCD) formed in a region of the second conductive type second well for transferring the image signal charges transferred from the VCCDs toward an output side of the HCCD in response to external horizontal transfer clock signals; and, a plurality of horizontal transfer gates formed extended over the HCCDs for applying the horizontal transfer clock signals, characterized in that the overlapped region of the first well for forming the vertical charge coupled devices and the second well for forming the horizontal charge coupled device is only formed under the horizontal transfer gates within the horizontal charge coupled device.