1. Field of the Invention
The present invention relates to an image pickup device and a camera, and more particularly to an image pickup device and a camera in which charges are converted into a voltage in a pixel region to be read as a voltage signal like an active pixel sensor (APS).
2. Description of Related Art
In recent years, a demand for a digital single lens reflex camera has been developing, and a sensor used in the digital single lens reflex camera is sized to be large one from APS-C size to a 35 mm film size.
Moreover, the used sensor itself widely varies from a CCD to an APS and the like.
Japanese Patent Application Laid-Open No. 2001-230400 (corresponding U.S. application was published as U.S. Publication 2001012133A) discloses an amplifying type image pickup device having a plurality of two-dimensionally arranged pixels, each including a photoelectric conversion element and an amplifying transistor, wherein: a first conductivity type semiconductor region constituting each photoelectric conversion element is formed in a common well composed of a second conductivity type semiconductor formed in a first conductivity type semiconductor substrate; a first conductivity type semiconductor region constituting a source and a drain of each of the amplifying transistors is formed in the common well; and a plurality of electric contacts for supplying a reference voltage to the common well is provided in the inside of the pixel array area in the common well.
In the APS sensor which has the large image pickup surface mentioned above, it is necessary to perform a voltage conversion of charges based on certain reference potential. When the reference potential is distributed on the image pickup surface, also the optical signal having received the voltage conversion has shading according to the distribution. Thus, there is a problem in which image performance is seriously damaged.
For coping with the problem, the prior art disclosed in the publication mentioned above provides an electrode for fixing the potential of the well in which a source follower is arranged to the reference potential when the source is used as an amplifying portion in a pixel, for example.
FIG. 10 is a sectional view showing the cross-sectional structure of prior art. In FIG. 10, an electrode region for taking well potential is denoted by a reference numeral 2.
A reference numeral 1 denotes n-type semiconductor region forming a photoelectric conversion region. A reference numeral 2 denotes p-type semiconductor region. A reference numeral 3 denotes a well contact wiring. A reference numeral 4 denotes P-well. A reference numeral 12 denotes an element isolation region. Reference numerals 13–17 denote source and drain regions of MOS transistor. A reference numeral 101 denotes a photoelectric conversion unit. A reference numeral 102 denotes a transfer MOS transistor. A reference numeral 103 denotes a reset MOS transistor. A reference numeral 104 denotes a selection MOS transistor. And, a reference numeral 105 denotes an amplifying MOS transistor.
FIG. 11 is a plan view showing the planar structure of the prior art. The well region 2 of FIG. 10 corresponds to a well electrode 1101 in FIG. 11.
A reference numeral 1104 denotes a photodiode. A reference numeral 1102 denotes a poly wiring (poly gate). A reference numeral 1103 denotes a MOS transistor unit (N+). Lmin denotes element isolation width. And, Smin denotes an area of the well electrode 1101.
Generally, between a well region and a light receiving unit, an insulating isolation region represented by the localized oxidation of silicon (LOCOS), the shallow trench isolation (STI) and the like is arranged. In FIG. 10, LOCOS 12 is arranged as such an element isolation region.
In arranging the element isolation region, the following restrictions are especially given from a viewpoint of an exposure process on production. Those are (1) the securement of the minimum separation width Lmin and (2) the securement of the minimum electrode area Smin.
In performing the miniaturization of a pixel, by the restrictions mentioned above, the light receiving area of a photodiode used as the light receiving unit becomes small, and the sensor performance has been worsened in terms of the optical property thereof, the saturated charge amount thereof, and the like.
Accordingly, it is an object of the present invention to provide a solid state image pickup device and a camera which do not worsen the sensor performance in terms of the optical property thereof, the saturated charge amount thereof, and the like.