Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-05-16
2004-10-26
Tran, Minhloan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S291000, C257S290000, C257S118000, C257S233000, C257S257000
Reexamination Certificate
active
06809359
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid-state imaging device, a method for manufacturing the same, and a method for driving the same.
2. Related Background Art
Solid-state imaging devices such as CCD solid-state imaging devices and MOS solid-state imaging devices that include photoelectric conversion sections for converting light into electric charges are employed in various image input devices such as facsimiles, video cameras, and digital still cameras.
FIG. 20
is a cross-sectional view illustrating an example of a structure of a pixel in a conventional solid-state imaging device (this solid-state imaging device is hereinafter referred to as “first conventional example”). In this first conventional example, a N-type photoelectric conversion region
103
, a N-type transfer channel region
104
, a P-type readout region
105
, and a P
+
-type channel stop region
106
are formed in a P
−
-type well region
102
that is formed in a N
−
-type silicon substrate
101
. Further, a P
++
-type hole accumulation region
107
is formed in a topmost part of the photoelectric conversion region
103
, and a P-type well region
108
is formed immediately under the transfer channel region
104
. A transfer electrode
111
is formed above the transfer channel region
104
, the readout region
105
, and the channel-stop region
106
, with a gate insulation film
110
interposed therebetween. On a surface of the transfer electrode
111
, a first interlayer insulation film
113
is formed. Further, a conductive light-blocking film
115
is formed thereon with a second interlayer insulation film
114
interposed therebetween. The conductive light-blocking film
115
is formed so as to cover the transfer electrode
111
, and an opening
116
is provided at a position corresponding to at least a part of the photoelectric conversion region
103
. Furthermore, generally the conductive light-blocking film
115
is grounded. Furthermore, a protective film
117
, a flattening film
118
, a color filter layer
119
, and a microlens
120
are formed successively in the stated order.
FIG. 22
is a cross-sectional view illustrating another example of a conventional solid-state imaging device (this solid-state imaging device is hereinafter referred to as “second conventional example”). The second conventional example is disclosed in JP 7(1995)-94699 A, for instance. In the second conventional example, a transparent conductive film
121
is formed above the photoelectric conversion region
103
so as to be in direct contact with the P
++
-type hole accumulation region
107
. The transparent conductive film
121
is connected electrically with the conductive light-blocking film
115
, which is grounded. The structure of the second conventional example is identical to that of the first conventional example except for where the transparent conductive film
121
is formed.
In the first and second conventional examples, as described above, the P
++
-type hole accumulation region
107
is formed in a topmost part of the photoelectric conversion region
103
. This allows dark current generated thermally on the surface of the photoelectric conversion region to be trapped by the holes in the P
++
-type hole accumulation region
107
, thereby improving the image quality of the solid-state imaging device. The P
++
-type hole accumulation region
107
is a region in which P-type impurities are diffused at a high density, and which is formed by ion implantation.
FIG. 21
is a schematic view for explaining a method for forming the P
++
-type hole accumulation region. First, the P
−
-type well region
102
is formed in the N
−
-type silicon substrate
101
, and the N-type photoelectric conversion region
103
and the like are formed therein. Then, the transfer electrode
111
is formed on a surface of the silicon substrate
101
with the gate insulation film
110
interposed therebetween. Subsequently, the first interlayer insulation film
113
is formed on a surface of the transfer electrode
111
, and thereafter, self-aligned ion implantation of a P-type impurity such as boron (B) or boron fluoride (BF
2
) is carried out by using the transfer electrode
111
and the first interlayer insulation film
113
as masks. By so doing, the P
++
-type hole accumulation region
107
is formed.
The foregoing first and second conventional examples have the following drawbacks.
FIGS. 23 and 24
are schematic views for explaining the problems of the conventional solid-state imaging device, by referring to the configuration of the second conventional example.
In the first and second conventional examples, as described above, the P
++
-type hole accumulation region
107
is formed by the self-aligned ion implantation of a P-type impurity by using the transfer electrode
111
and the first interlayer insulation film
113
as masks. The ion implantation is carried out with a high dose of 10
13
to 10
14
cm
−2
and with a low energy of several to several tens of kilo electron volts, so as to minimize the incurred erosion of the photoelectric conversion region
103
while efficiently suppressing the dark current generated at a surface of the substrate. Furthermore, the P
++
-type hole accumulation region
107
is formed so as to cover a substantially entire face of the photoelectric conversion region
103
.
It is however difficult to suppress the expansion of a range of the impurity distribution, even with the ion implantation of the P-type impurity with a low energy, because of the relatively high impurity density in the P
++
-type hole accumulation region
107
as compared with the photoelectric conversion region
103
, and the influence of the channeling upon the ion implantation and the annealing for activation after the implantation. Therefore, in the conventional solid-state imaging device, a junction depth (X
J
) between the P
++
-type hole accumulation region
107
and the photoelectric conversion region
103
is 0.3 &mgr;m normally, and it is very difficult to decrease the same.
Consequently, as shown in
FIG. 23
, a part of signal charges
122
generated by the photoelectric conversion easily flow as surface diffusion current
123
into the transfer channel region
104
via the P
++
-type hole accumulation region
107
, thereby causing the problem of an increase in smear. Furthermore, when the signal charges
122
are read out from the N-type photoelectric conversion region
103
to the N-type transfer channel region
104
, a charge readout path
124
is formed, which sneaks around the P
++
-type hole accumulation region
107
. Therefore, the readout voltage increases.
Furthermore, problems as follows arise also. Since the P
++
-type hole accumulation region
107
is formed spreading in a horizontal direction, a space
125
between the P
++
-type hole accumulation region
107
and the transfer channel region is narrowed. As a result, when a readout pulse (normally about 15V) is applied to the transfer electrode
111
to read out the signal charges
122
, hot electrons are generated by a strong electric field between the P
++
-type hole accumulation region
107
and the N-type transfer channel
104
, which cause random noise.
Furthermore, as shown in
FIG. 24
, in the second conventional example, since the transparent conductive film
121
is formed in direct contact with a surface of the silicon substrate in an area of a photoelectric conversion section
109
, junction damage
126
occurs on the surface in the photoelectric conversion section
109
. As a result, even with an attempt for suppressing the depletion of a topmost face by grounding the P
++
-type hole accumulation region
107
, dark current is increased through the junction damage
126
, which degrades the image quality.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a sol
Matsushita Electric - Industrial Co., Ltd.
Tran Minhloan
Tran Tan
LandOfFree
Solid-state imaging device, method for manufacturing the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Solid-state imaging device, method for manufacturing the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solid-state imaging device, method for manufacturing the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3316714