Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
2002-11-08
2003-11-25
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S048000
Reexamination Certificate
active
06653164
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Present Invention
The present invention relates to a solid state imaging device, its manufacturing method and a solid state imaging apparatus. More particularly, the present invention relates to a solid state imaging device which uses a MOS image sensor based on a threshold voltage modulation system used for a video camera, an electronic camera, an image input camera, a scanner, a facsimile or the like, its manufacturing method and a solid state imaging apparatus.
2. Description of the Prior Art
Because of its high mass productivity, a semiconductor image sensor such as a CCD image sensor, a MOS image sensor or the like has been applied to almost all types of image input devices following the progress in a pattern microfabrication technology.
Particularly, in recent years, the applicability of the MOS image sensor has been recognized again because of its advantages, i.e., lower power consumption compared with that of the CCD image sensor, and the capability of making a sensor device and a peripheral circuit device by the same CMOS technology.
FIG. 1
is a sectional view showing such a MOS image sensor.
In the drawing, a photodetection diode
311
and a MOS transistor
312
for optical signal detection constitute one unit pixel. To isolate adjacent unit pixels from each other, an element isolation insulating film
214
is formed on a semiconductor layer
212
in an element isolation region. In addition, a light shielding film
223
is formed on a coating insulating film
226
in such way as to cover the MOS transistor for optical signal detection. The light shielding film
223
includes a light receiving window
224
formed on the light receiving portion of the photodetection diode
311
to transmit an optical signal.
In both of the forming regions of the photodetection diode
311
and the MOS transistor
312
for optical signal detection, well regions
215
a
and
215
b
are formed on the surface of the-semiconductor layer
212
.
Source and drain regions
216
and
217
a
are formed in the well region
215
b
of the MOS transistor
312
. On the other hand, on the surface of the well region
215
a
of the photodetection diode
311
, a region
217
of one conductivity type is formed to be connected to the drain region
217
a
of one conductivity type and, thus, a buried structure is formed for optically generated charges.
A source electrode
220
is connected to the source region
216
, and a drain electrode
222
is connected to the region
217
of one conductivity type, i.e., the drain region
217
a
. Further, a gate electrode
219
is formed above a channel region
215
c
between the source and drain regions
216
and
217
a
by interpolating a gate insulating film
218
.
In the vicinity of the source region
216
, a hole pocket (carrier pocket)
225
is formed in the well region
215
b
. In this pocket, light generation holes are stored, and a threshold of the MOS transistor
312
is changed in proportion to the storage amount of such light generation holes.
A series of operations of the MOS image sensor are passed through an initializing period, a storing period and a reading period. During the initializing period, a high reverse voltage is applied to each electrode for depletion, and light generation holes remaining in the hole pocket
225
are discharged. During the storing period, light generation holes are formed by light irradiation and then stored in the hole pocket
225
. Then, during the reading period, an optical signal proportional to the storage amount of light generation holes is detected.
By the way, In the MOS image sensor, defects tend to occur in an interface between the element isolation insulating film
214
and the semiconductor layer
212
and, in most cases, holes are captured in the defects. These holes are discharged during the initializing or storing period. The holes are injected through the depleted n type semiconductor layer
212
into the p type well regions
215
a
and
215
b
, and then stored in the hole pocket
225
. The holes discharged from the defects and stored in the hole pocket
225
result in the generation of fixed pattern noise.
SUMMARY OF THE INVENTION
The object of the present present invention is to provide a solid state imaging device, which employs a MOS image sensor capable of suppressing fixed pattern noise generated by charges discharged from defects in an interface or the like between an element isolation insulating film and a semiconductor layer, and performing much more microfabrication. The object of the present invention is also to provide a manufacturing method of the solid state imaging device and a solid state imaging apparatus equipped with the solid state imaging device.
The present invention is directed to a solid state imaging device. As shown in
FIG. 3A
, the present invention includes a unit pixel
101
which, in turn, includes a photodetection diode
111
and an insulated gate field effect transistor (MOS transistor)
112
adjacent to the photodetection diode
111
for optical signal detection, wherein an element isolation insulating film
14
is formed so as to isolate adjacent unit pixels
101
from each other, and an element isolation region
13
of an opposite conductivity type to that of a second semiconductor layer
12
, the element isolation region
13
isolating the second semiconductor layer
12
, is formed under a lower surface of the element isolation insulating film
14
, so as to reach first semiconductor layer
11
.
Either an impurity region
17
or a drain region
17
b
is formed so as to be extended near the element isolation region
13
, and a drain electrode
22
is formed near the element isolation region
13
so as to be connected to either the impurity region
17
or the drain region
17
b.
The photodetection diode
111
and the insulated gate field effect transistor (MOS transistor)
112
for optical signal detection are formed in well regions
15
a
and
15
b
connected to each other, and comprise a buried layer having a high concentration (carrier pocket)
25
for storing optically generated charges in the well region
15
b
in the peripheral portion of a source region of the MOS transistor
112
for optical signal detection.
Generally, there are many levels in an interface between the insulating film and the semiconductor layer. Especially, in the case that the element isolation insulating film
14
is formed by local oxidation of silicon (LOCOS), defects caused by thermal distortion tend to occur in addition to an interface state. In the case that the drain regions
17
a
and
17
b
are adjacent to the element isolation insulating film
14
, in the end portions of the drain regions
17
a
and
17
b
, a pn junction tail end of the drain regions
17
a
and
17
b
is in contact with the surface, and a surface state is included in a depletion layer extending transversely from the drain regions
17
a
and
17
b
. Consequently, current leakage is apt to occur. As described above, according to the present invention, the element isolation region
13
of a conductivity type opposite that of the second semiconductor layer
12
, which isolates the second semiconductor layer
12
to reach the first semiconductor layer
11
, is formed under the entire lower surface of the element isolation insulating film
14
. Thus, in initializing and storing periods, when a positive voltage is applied to the n type drain regions
17
a
and
17
b
, a depletion layer extending from the p type well regions
15
a
and
15
b
or the p type substrate
11
reaches only the outer peripheral portion of the element isolation region
13
without extending to therein and, hence, the defects in the interface are not covered with the depletion layer. Therefore, charges captured in the defects of the interface can be prevented from being discharged into the depletion layer, and it is possible to suppress fixed pattern noise generated by the storage of charges in the hole pocket (carrier pocket)
25
caused by such defects in the interface.
A drain electrode
22
is provided in the
Innotech Corproation
Lorusso, Loud & Kelly
Owens Beth E.
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