US Patent 7687831 Solid state image pickup device

P type semiconductor well regions 8 and 9 for device separation are provided in an upper and lower two layer structure in conformity with the position of a high sensitivity type photodiode PD, and the first P type semiconductor well region 8 at the upper layer is provided in the state of being closer to the pixel side than an end portion of a LOCOS layer 1A, for limiting a dark current generated at the end portion of the LOCOS layer 1A. In addition, the second P type semiconductor well region 9 at the lower layer is formed in a narrow region receding from the photodiode PD, so that the depletion layer of the photodiode PD is prevented from being obstructed, and the depletion is secured in a sufficiently broad region, whereby enhancement of the sensitivity of the photodiode PD can be achieved.