Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
2003-02-14
2004-04-06
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S233000, C257S240000
Reexamination Certificate
active
06717190
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid-state image pick-up device, and particularly to the structure of a signal charge transfer electrode in the image pick-up apparatus.
2. Description of the Related Art
When the image pick-up of a still image is conducted by an electronic still camera, a solid-state image pick-up device of all pixel (progressive) reading system is appropriate as an image pick-up device, rather than the system so-called interlaced scanning which is corresponding to a standard television signal.
In the conventional interline transfer type charge coupled device (hereinafter, called IT-CCD), as shown in
FIG. 20
, an image pick-up device of the checker board arrangement in which a light receiving portion
51
having an embedded photodiode composed of P type low density impurity area (P-well), N type high density impurity layer
51
a
, and P type high density impurity layer
51
b
of the surface is widely used. In order to conduct the all pixel reading in the IT-CCD, at least 3 electrodes (3 phase transfer pulse &phgr;1, &phgr;2, and &phgr;3) is necessary per one pixel. Therefore, in the IT-CCD of the all pixel reading type of the IT-CCD, triple layered polysilicon electrode structure polysilicon having the first layer
61
, second layer
62
, and third layer
63
is adopted for the charge transfer electrode, and an electrode wiring area between pixels is reduced as small as possible, and that is realized.
In the IT-CCD, the electrode wiring area in the row direction of each light receiving portion as mentioned above, is a space for the wiring of polysilicon electrode, and in order not to sacrifice the sensitivity, it is required that its width is reduced as narrow as possible. When the width of the electrode wiring area is reduced, the width of the polysilicon electrode is also reduced, and the electric resistance of the charge transfer electrode is increased. Accordingly, conventionally, the width of the polysilicon electrode of this electrode wiring area is reduced, and inversely, the electrode thickness is increased to cancel out the increase of the electrical resistance. In general, the thickness of the polysilicon electrode is about 0.4 &mgr;m-0.7 &mgr;m, and the electrical resistance of the transfer electrode is reduced to the allowable level. However, when the film thickness of the polysilicon electrode is increased, it might bring about another problem. in its lithography process, thus increasing the thickness of the electrode is somewhat limited one. In the future, when the increase of the pixels (for example, more than 5000×10
3
) or the increase of the CCD image size (APS size or 135 size) advances, due to such electrical resistance of the polysilicon charge transfer electrode, it becomes difficult for the high charge transfer efficiency to be maintained during the charge transfer process.
Further, by using the progressive solid-state image pick-up device, a full electronic shutter capability is realized in which any mechanical component is not required. In the case of such a full electronic shutter, the light is always on the solid-state image pick-up device, which is not experienced in the case of the mechanical shutter being used, it is important to suppress a smear (the bleeding of the light which appears in the image in the row direction when the high luminance object such as the sun is photographed). In order to reduce the smear level, as shown in
FIG. 21
, a frame interline transfer type CCD (hereinafter, called FIT-CCD) is developed. The FIT-CCD has another CCD portion
54
which stores the electronic charges from the light receiving area
53
. The charge storage portion
54
where the incoming light is shielded, is provided on the adjoining area of the light receiving area
53
in which a light receiving portion
51
and a charge transfer electrode
52
are arranged. In such the FIT-CCD, by quickly moving the charge to the storage area
54
, the reduction of smear is conducted. Therefore, because the high speed charge transfer in the VCCD is required, the reduction of the resistance of the charge transfer electrode corresponding to the high speed driving is necessary.
In order to reduce the electrical resistance of the charge transfer electrode in the IT-CCD, other than the case where the thickness of the polysilicon electrode is increased, it is considered that the dopant density of phosphorus or arsenic in the polysilicon electrode is increased and the resistivity is reduced. However, in this method, even when the dopant density is increased more than the solubility limit of the impurity element, because the resistivity is not enough reduced, in the same manner as the case of the increase of the thickness, there is a limit in the correspondence of the increase of the pixels, increase of the size, or the high speed driving. Accordingly, as another method to reduce the electrical resistance of the charge transfer electrode, the structure in which a backing metallic wiring, so called metallic backing is over-coated on the polysilicon electrode as disclosed in JP-A-2001-223352, is proposed.
When the metallic backing is provided on the IT-CCD, as shown in
FIG. 22
, it is the structure in which the metallic wiring
55
is extended in the vertical row direction on the upper portion of the VCCD charge transfer electrode
52
and through the contact hole
56
, the metallic wiring
55
is electrically connected to the polysilicon electrode of each phase. In such a IT-CCD, there remains only limited room for the layout arrangements for both the metallic wiring and the contact hole by which the metallic wiring and the polysilicon electrode are electrically connected. Further, in the charge transfer electrode of the of triple layered polysilicon structure of the progressive IT-CCD, triple layered electrodes are vertically folded between the light receiving portions of
51
in the row direction, which becomes difficult to expose enough area of each electrode for the electrical contact with the metallic backing being provided on every polysilicon electrode layer.
As described above, in the conventional IT-CCD, in order to reduce the electrical resistance of a charge transfer electrode, the method in which the thickness of a polysilicon electrode is increased, or the dopant density of phosphorous or arsenic in the polysilicon electrode is increased, is adopted, but, by these methods, it is difficult to meet further requirements such as increase of pixels, increase of the chip size or the high charge transfer speed. Further, when the metallic backing is used, in its structure in the IT-CCD, the given room is limited for the layouts of the metallic wiring and the contact hole where the metalic wiring and the polysilicon electrode are electrically connected, and lithography/process for increasing the density of the pixels becomes difficult. Particularly, in the charge transfer electrode of the triple layered polysilicon structure by which all pixels can be read, it is difficult to provide the metallic backing on every polysilicon electrode.
SUMMARY OF THE INVENTION
The present invention is attained in view of the above circumference, and the object of the present invention is to provide with a solid-state image pick-up device, more specifically IT-CCD, such that although integration of the device becomes much more high density, the equivalent electrical resistance of the charge transfer electrode can be reduced to achieve high speed transfer of the electric charge.
Referring to the drawings, embodiments of the present invention will be described below.
FIG. 1
is a view showing the outline structure of a CCD image pick-up device used for the embodiment of the present invention. In the present embodiment, so called honeycomb arrangement CCD image pick-up device (hereinafter, called honeycomb CCD) is used as the IT-CCD in the image pick-up area (light receiving area) provided with the light receiving portion composed of the photoelectric conversion devices such as photodiodes. The pixel arrangeme
Fuji Photo Film Co. , Ltd.
Ngo Ngan V.
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