Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2001-08-14
2002-09-10
Ng{overscore (o)}, Ng{overscore (a)}n V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S291000, C257S401000
Reexamination Certificate
active
06448596
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid-state imaging device, which uses the MOS image sensor of a threshold voltage modulation type used for a video camera, an electronic camera, an image input camera, a scanner, a facsimile or the like.
2. Description of the Related Art
As mass productivity is high for a semiconductor image sensor, e.g., a CCD image sensor, a MOS image sensor, and so on, the semiconductor image sensor has been used for almost all imaging devices with the progress made in a fine pattern technology.
In recent years, particularly the MOS image sensor has been reevaluated because it is advantageous in that power consumption is small compared with the CCD image sensor, and a sensor device and a peripheral circuit device can be manufactured by the same CMOS technology.
In line with such a tendency, the inventors made improvements on the MOS image sensor, and filed the application for a patent regarding a sensor device having a carrier pocket (heavily doped buried layer)
25
below the channel region of an insulated gate field effect transistor for light signal detection (hereinbelow, referred to as PXMOSFET) (Japanese Patent Application Hei 10 (1998)-186453). A patent therefor has been granted (registered No. 2935492).
The described MOS image sensor has a structure shown in FIGS.
1
and
2
:
FIG. 1
being a plan view; and
FIG. 2
being a sectional view taken on line I—I of FIG.
1
. In this structure as shown in
FIGS. 1 and 2
, a unit pixel
101
is composed of a photo-diode
111
, and a PXMOSFET
112
adjacent to the photo-diode
111
. The MOS image sensor is constructed by arraying such pixels
101
in a matrix form. The photo-diode
111
and the PXMOSFET
112
are communicated by p-type well regions
15
a
and
15
b
. In the PXMOSFET
112
, a gate electrode
19
has a ring shape, an n-type source region
16
is formed in the center thereof, and an n-type drain region
17
a
is formed to surround the outer periphery of the gate electrode
19
. A p-type hole pocket
25
is formed to surround the source region
16
in the well region
15
b
near the source region, below the gate electrode
19
.
Adjacent pixels
101
are isolated from each other by a pixel isolation region. The pixel isolation region is composed of an insulating isolation region
14
formed in a substrate surface by a local oxidation of silicon (LOCOS) method, and a p-type diffusing isolation region
13
formed in a semiconductor substrate provided below the insulating isolation region
14
.
During initialization period in the MOS image sensor, a high positive voltage is applied to each electrode to be depleted to sweep photo-generated holes remaining in the hole pocket
25
to the substrate. During storing period, the photo-diode
111
is irradiated with a light collected by a microlens to generate photo-generated holes, and then the holes are moved to be stored in the hole pocket
25
. Then, during reading period, a light signal is detected by detecting the threshold voltage of the PXMOSFET
112
modulated in proportion to the stored amount of photo-generated holes.
In the solid-state imaging device, the pixel isolation region formed by the LOCOS method is not suited for microfabrication of pixel
101
with respect to the structure. Thus, a further improvement may be required in order to meet a request for the microfabrication possibly made with a higher definition of an image in the future.
When a pixel pitch is reduced to achieve a higher density of a pixel array, since the structure of the peripheral part of the gate electrode
19
is complex compared with the photo-diode
111
, a reduction rate of the gate electrode
19
is limited compared with that of the photo-diode
111
. Consequently, at present or in the near future, an area of the gate electrode
19
may become to account for more than seventy percent to a total area of a pixel.
In the case of reducing a pixel pitch while maintaining an area of a light-detecting portion as wider as possible under such circumstances, the light-detecting portion of the photo-diode
111
is to be formed in a thin and long rectangular shape. Thus, if a light collection method by the microlens is applied, there may be caused a situation that an optical spot diameter is out of the light-detecting portion in the short side direction of the same finally as microfabrication is further advanced. In such a case, the quantity of incident light becomes short in both ends of the short side direction. Consequently, an output from the image sensor provably decreases and outputs between pixels provably results in a lack of uniformity even when a uniform pattern is photographed.
In addition, in the imaging device using the CCD device, resolution is improved by employing the three-plate system in which three CCD elements are arranged corresponding to primary colors separated by a prism. On the other hand, in the MOS image sensor, there has been expected an improvement of resolution by a single-plate system in which a light signal including primary colors is obtained with one imaging device element using a color filter. That leads to a good use of the features of the MOS image sensor, i.e., low power consumption, and a compact size.
SUMMARY OF THE INVENTION
The present invention provides a solid-state imaging device having a structure suited for microfabrication of a pixel, and capable of miniaturizing the imaging device as a whole.
It is an object of the present invention to provide a solid-state imaging device capable of improving resolution by a single-plate system.
Moreover, it is an object of the present invention to provide a solid-state imaging device having more effective pixel arrangement in preventing a decrease of output and a lack of uniformity of outputs among pixels.
The formation of an insulating film by a local oxidation of silicon (LOCOS) method is disadvantageous for microfabrication because the region for forming an isolation insulating film is expanded by an amount of more than a mask size due to the formation of bird's beak.
According to the present invention, as shown in
FIGS. 3
,
4
A,
4
C,
5
, and
6
, a pixel isolation region for isolating adjacent pixels
101
from each other is provided with a diffusing isolation region
53
having same conductivity as a drain region
57
a
. The diffusing isolation region
53
is formed deeper than the well regions
54
a
and
54
b
to contact the regions
52
a
and
52
b
under the well regions
54
a
and
54
b
while the diffusing isolation region
53
contact the impurity region
57
and the drain region
57
a
above the well regions
54
a
and
54
b
. Therefore, the well regions
54
a
and
54
b
are surrounded in the entire periphery thereof by the impurity region
57
, the drain region
57
a
, the regions
52
a
and
52
b
and the diffusing isolation region
53
. And during operating such imaging device, the photo-generated charges in the well regions
54
a
and
54
b
cannot move out of the well regions
54
a
and
54
b
due to a potential generated in the pn junction. In such manner, adjacent pixels can be separated from each other by the diffusing isolation region
53
.
In other words, since the pixel isolation is carried out only by the diffusing isolation region
53
without using any isolation insulating films by the LOCOS method, no bird's beak is formed to prevent the pixel isolation region from being expanded by an amount more than the mask size. Thus, the pixel
101
can be microfabricated, and thus the imaging device is miniaturized as a whole.
In the solid-state imaging device of the present invention, pixels
101
, each thereof having a PXMOSFET
112
, are arrayed in a matrix form, a plurality of gate electrodes
59
of PXMOSFETs
112
are disposed at at least four directions among the peripheral part of a photodiode
111
, and a plurality of photo-diodes
111
are disposed at at least four directions among the peripheral part of the gate electrode of the PXMOSFET
112
. In this case, one pixel
101
is provided with the
Kawajiri Kazuhiro
Miida Takashi
Innotech Corporation
Lorusso & Loud
Ng{overscore (o)} Ng{overscore (a)}n V.
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