Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2002-06-21
2003-12-02
Fahmy, Wael (Department: 2814)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C257S291000, C257S292000, C257S293000
Reexamination Certificate
active
06656777
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid state imaging device, a method of manufacturing the same, and a solid state imaging system and, more particularly, a solid state imaging device using a MOS image sensor of a threshold voltage modulation system employed in a video camera, an electronic camera, an image input camera, a scanner, a facsimile, or the like, a method of manufacturing the same, and a solid state imaging system.
2. Description of the Prior Art
Since a semiconductor image sensor such as a CCD image sensor, a MOS image sensor, etc. is excellent in mass productivity, such semiconductor image sensor is applied to most of the image input devices with the progress of the fine pattern technology.
In particular, the MOS image sensor is reconsidered in recent years because of its merits that the power consumption is small rather than the CCD image sensor and that the sensor element and peripheral circuit elements can be fabricated by the same CMOS technology.
In view of the trend in the times, the applicant of this application has improved the MOS image sensor, and then secured the Patent (Registration Number 2935492) by filing the Patent Application (Patent Application Hei 10-186453) in connection with the image sensor device which has the carrier pocket (high concentration buried layer) under the channel region.
In the invention of this Patent (Registration Number 2935492), in order to suppress the injection of the light emitting charges into the surface defects of the semiconductor layer and thus reduce the noise, the photo diode has the buried structure for the light emitting charges (in this case, holes). More particularly, the n-type impurity region is formed on the surface layer of the p-type well region. This p-type well region is formed integrally with the p-type base region of the light signal detecting MOS transistor, and this n-type impurity region is formed integrally with the n-type drain region. As a result, the configuration can be formed in which the light emitting charges generated in the p-type well region of the photo diode portion can contribute to the detection of the light signal.
Meanwhile, in the MOS image sensor, normally the spectral sensitivity characteristic, especially the red-color sensitivity is low. Therefore, in order to broaden much more the applications of the MOS image sensor in the future, it is desired to achieve the improvement of the red-color sensitivity. In addition, it is desired to achieve the improvement of the blue-color sensitivity. At the same time, the higher integration degree of the solid state imaging device is also desired.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a solid state imaging device using a MOS image sensor capable of achieving improvement in red-color sensitivity and improvement in blue-color sensitivity while maintaining the performance of a light signal detecting MOS transistor, a method of manufacturing the same, and a solid state imaging system.
With reference to
FIG. 2A
in order to improve the red-color sensitivity, it is desired that the n-type epitaxial layer (n-type layer)
12
on the p-type substrate
11
should be formed thicker than in the structure of applicants' Patent Registration Number 2935492. However, if the n-type epitaxial layer (n-type layer)
12
is formed thicker, the reset voltage for the initialization to discharge the carriers must be increased and thus the performance of the light signal detecting MOS transistor is lowered. In other words, in order to improve the red-color sensitivity and to maintain/improve the reset efficiency, structures are needed which are incompatible with each other.
In the present invention, as exemplified by the embodiment shown in
FIGS. 1 and 2A
. in the store period during when the carriers are generated by the light in the photo diode
111
having the above structure and then stored in the high concentration buried layer (carrier pocket)
25
of opposite conductivity type, the depletion layer can spread from a boundary surface between the one conductivity type impurity region
17
and the opposite conductivity type first well region
15
a
in the photo diode
111
to the overall first well region
15
a
by the applied voltage. Further, the depletion layer can spread from a boundary surface between the opposite conductivity type substrate
11
and the one conductivity type buried layer
32
in the photo diode
111
to the first semiconductor layers
12
and
32
. Therefore, the light emitting charges generated in the depleted first well region
15
a
and the first semiconductor layers
12
and
32
can contribute to the detection of the light signal.
In other words, since the thicknesses of the first semiconductor layers
12
and
32
are increased, the thickness of the light receiving region can be extended effectively with respect to the long wavelength light such as the red-color. Accordingly, the improvement of the red-color sensitivity can be achieved.
In contrast, in the sweep period (initialization period) during when the carriers are swept out from the high concentration buried layer
25
and the second well region
15
b
in the light signal detecting MOS transistor
112
portion, the depletion layer can spread from a boundary surface between the one conductivity type channel doped layer
15
c
and the opposite conductivity type second well region
15
b
into the second well region
15
b
by the applied voltage, and also the depletion layer can spread from a boundary surface between the opposite conductivity type sixth semiconductor layer
33
and the one conductivity type third semiconductor layer
12
into the third semiconductor layer
12
under the second well region
15
b.
As a result, the electric field from the gate electrode
19
can extend mainly to the depleted second well region
15
b
and the third semiconductor layer
12
formed under the second well region
15
b.
In the case of the present invention, the thickness of the third semiconductor layer
12
under the second well region
15
b
is small and the opposite conductivity type high concentration sixth semiconductor layer
33
is formed in the neighborhood of the one conductivity type third semiconductor layer
12
on the substrate
11
side. Therefore, extension of the depletion layer from the boundary surface between the opposite conductivity type sixth semiconductor layer
33
and the one conductivity type third semiconductor layer
12
into the sixth semiconductor layer
33
in the sweep period can be limited, and also the width of the depletion layer extending from the boundary surface to the third semiconductor layer
12
can be reduced. That is, the voltage from the gate electrode
19
is mainly applied to the second well region
15
b.
Accordingly, since the abrupt potential change that is fitted to sweep out the carriers is caused in the second well region
15
b
and thus the strong electric field is applied. Therefore, the stored carriers can be swept out effectively from the high concentration buried layer (carrier pocket)
25
and the second well region
15
b
by the low reset voltage, whereby the reset efficiency can be improved.
In addition, according to the present invention, since the low concentration drain (LDD) structure is employed as the structure of the light signal detecting MOS transistor
112
, the short channel of the light signal detecting MOS transistor
112
can be achieved and thus the higher integration degree of the solid state imaging device can be achieved.
Also, the impurity region
117
is formed at the same time when the low concentration drain region
117
a
is formed. That is, since the impurity concentration of the impurity region
117
is set to the low concentration, the impurity region
117
can be formed at the shallow position from the surface. Accordingly, the blue-color that has the short wavelength and attenuates suddenly in the vicinity of the surface can be received at the sufficient intensity.
In addition, since the one conductivi
Fahmy Wael
Ha Nathan W.
Innotech Corporation
Lorusso, Loud & Kelly
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