Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1997-09-29
2001-04-10
Ho, Tuan (Department: 2612)
Television
Camera, system and detail
Solid-state image sensor
C348S316000
Reexamination Certificate
active
06215521
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid state image sensor and a method for manufacturing the same, and more specifically to a solid state image sensor having an unnecessary electric charge exhausting section formed adjacent to a horizontal electric charge transfer section, and a method for manufacturing the same.
2. Description of Related Art
A solid state image sensor, which has been conventionally widely incorporated as an image pickup means in a single-unit video camera recorder, is now increasing the number of pixels included therein, and at present, has started to be used, in place of an optical camera exposing a film, as an electronic still camera which converts optical information into an electric signal and stores the electric signal in a memory medium, to make it possible to produce a hard copy from the stored electric signal, or to reproduce the optical information on a monitor display screen.
The solid state image sensor as mentioned above, includes a photoelectric conversion section, and an electric charge transfer section for vertically and horizontally transferring a signal electric charge accumulated in the photoelectric conversion section. Actually, in addition to the signal electric charge which will become an essentially required video signal, there exists an unnecessary electric charge including an electric charge photoelectrically converted in an unnecessary period and an electric charge due to a current generated at a silicon-oxide film boundary. When the solid state image sensor is incorporated as the image pickup means in the single-unit video camera-recorder, even if the unnecessary electric charge is generated, the unnecessary electric charge will lower at an negligible level after a few frames, and therefore, the unnecessary electric charge will not become a large problem. However, when the solid state image sensor is used as the image pickup means of the electronic still camera, the unnecessary electric charge is superposed on the signal charge which should become the essentially required video signal, with the result that an image quality is deteriorated. In addition, if a substantial time is required to remove the unnecessary electric charge, there occurs a time delay from the moment a shutter button is triggered to the moment the shutter is actually opened and closed, with the result that a so-called shutter chance may be lost.
Therefore, differently from the solid state image sensor incorporated in the single-unit video camera-recorder, the solid state image sensor used as the image pickup means of the electronic still camera, is required to momentarily remove all unnecessary electric charges existing in the photoelectric conversion section and the vertical and horizontal electric charge transfer sections, at the same time as the shutter button is triggered.
As a means for removing the unnecessary electric charges, for example, Y. Ishihara et al proposes an “Interline CCD Image Sensor with Vertical Overflow Drain”, in Journal of Society of Television of Japan, Vol. 37, No. 10, 1983, pages 782-787. In brief, in order to remove the unnecessary electric charges existing in the photoelectric conversion section, a P
−
semiconductor region having a low impurity concentration is formed directly under an N type semiconductor region constituting the photoelectric conversion section, and a reverse biasing is applied to an N
−−
semiconductor substrate so that an excess electric charge is removed into the N
−−
semiconductor substrate for a blooming suppression, and the N type semiconductor region itself is depleted so that all the signal electric charge is removed into the N
−−
semiconductor substrate.
In addition, the unnecessary electric charge existing in the horizontal electric charge transfer section, can be removed into a reset drain provided at an end of the horizontal electric charge transfer section in a conventional operation, since the horizontal electric charge transfer section can operate at a high speed.
On the other hand, in order to remove the unnecessary electric charge existing in the vertical electric charge transfer section, it is necessary to transfer at least one to a few frames.
For example, Japanese Patent Application Pre-examination Publication No. JP-A-02-205359 (the content of which is incorporated by reference in its entirety into this application, and an English abstract of JP-A-02-205359 is available from the Japanese Patent Office, and the content of the English abstract is also incorporated by reference in its entirety into this application), proposes one method for removing the unnecessary electric charge existing in the vertical electric charge transfer. In brief, an unnecessary electric charge exhausting section is provided adjacent to the horizontal electric charge transfer section, so that the unnecessary electric charge existing in the vertical electric charge transfer section is removed by transferring the unnecessary electric charge existing in the vertical electric charge transfer section in a forward direction.
Referring to
FIG. 1
, there is shown a layout diagram of the solid state image sensor having the unnecessary electric charge exhausting section provided adjacent to the horizontal electric charge transfer section. The shown solid state image sensor includes an image sensor section
100
, which comprises a number of photoelectric conversion cells
101
(each of which is formed of, for example, a photodiodes, and each of which will be called a “photocell” hereinafter) arranged in the form of a matrix, a plurality of vertical electric charge transfer sections
103
each of which extends along a corresponding vertical column of photocells, and a number of transfer gates
102
each provided between a corresponding photocell and a corresponding adjacent vertical electric charge transfer section
103
. The vertical electric charge transfer sections
103
are driven, by four-phase drive pulses &phgr;V
1
to &phgr;V
4
to transfer signal charges through the vertical electric charge transfer section.
The shown solid state image sensor also includes a horizontal electric charge transfer section
300
formed along lower ends of the vertical electric charge transfer sections
103
and connected to the lower ends of the vertical electric charge transfer sections
103
through vertical-horizontal junction sections
200
. The horizontal electric charge transfer section
300
has one end connected through an electric charge detection section
301
to an output amplification section
302
.
Furthermore, the shown solid state image sensor includes an unnecessary electric charge exhausting section
500
extending along the horizontal electric charge transfer section
300
, and a potential barrier section
400
formed between the horizontal electric charge transfer section
300
and the unnecessary electric charge exhausting section
500
, and an N
+++
semiconductor region
501
formed at one end of the unnecessary electric charge exhausting section
500
and connected to a power supply voltage V
D
.
Referring to
FIG. 2
, there is shown an enlarged layout pattern diagram, in accordance with the prior art, of a portion confined by a two-dot chain line in
FIG. 1
, which shows a portion of a region including the potential barrier section
400
and the unnecessary electric charge exhausting section
500
formed adjacent to the horizontal electric charge transfer section
300
. The shown portion includes a transfer channel
15
of the vertical electric charge transfer sections
103
, a transfer channel
14
of the vertical-horizontal junction sections
200
, an electric charge barrier region
5
and an electric charge storage region
6
of a transfer channel of the horizontal electric charge transfer section
300
, a potential barrier region
11
of the potential barrier section
400
, an unnecessary electric charge exhausting region
12
of the unnecessary electric charge exhausting section
500
.
The shown portion al
Nakashiba Yasutaka
Surisawa Yuji
Hayes, Soloway, Hennessey Grossman & Hage, P.C.
Ho Tuan
NEC Corporation
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