Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
1999-12-02
2002-05-07
Thomas, Tom (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S232000, C257S233000, C438S048000
Reexamination Certificate
active
06384436
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a photoelectric transducer and a solid-state image sensing device using the photoelectric transducer, and more particularly to, a solid-state image sensing device in which smear or crosstalk is reduced.
BACKGROUND OF THE INVENTION
Typical solid-state image sensing devices using CCD have an interline transfer type two-dimensional CCD solid-state image sensing device and a buried photodiode structure. This is described in, for example, Japanese patent application laid-open No. 57-62557 (1982).
FIG. 1A
is a plan view showing an interline transfer type two-dimensional CCD solid-state image sensing device, and
FIG. 1B
is a cross sectional view cut along the line F—F in FIG.
1
A. In this type of solid-state image sensing device, many photodiodes
1
to generate signal charge by the incidence of light are arrayed. A vertical CCD register
2
is provided for each row of photodiodes. One end of the vertical CCD register
2
is connected to a horizontal CCD register
3
, which is connected to an output section
4
. The photodiode and the vertical CCD register are formed on a n-well
9
formed on a n-substrate
19
. The photodiode is composed of n-region
6
to accumulate signal charge and p
+
-region the surface. The vertical CCD register is composed of n-well
7
and p-well
8
. Between the photodiode and vertical CCD register, there is p
+
-device separation region
10
or p-region
11
forming a transfer gate. At the upper part of the vertical CCD register, there is provided a gate electrode
12
to apply drive pulse voltage through gate insulator film
13
to the vertical CCD register. Further on the gate electrode
12
, light-shielding film
14
is formed sandwiching insulation film
15
, and thereby light-generated charge can be prevented from occurring in the vertical CCD register. The whole surface is covered with insulation film
15
. The transfer gate is controlled by the gate electrode
12
of vertical CCD register. When positive voltage is applied to the gate electrode, signal charge moves from the n-accumulation region
6
through a channel formed at the transfer gate to the n-well
7
.
Here, the end of p
+
-region
5
adjacent to the transfer gate and on the surface of photodiode is separated from the p-region
11
so as to make signal charge easy to read out from the n-accumulation region
6
to the n-well
7
of vertical CCD register. Thus, the n-region
6
is formed between the p
+
-region
5
and the p-region
11
.
Also, a solid-state image sensing device called frame transfer type other than the interline transfer type is known. The frame transfer type solid-state image sensing device is characterized by its high numerical aperture.
FIG. 2
is a plan view showing a frame transfer type two-dimensional CCD solid-state image sensing device. Different from the interline transfer type, its vertical CCD register functions as both transfer section and light-receiving section. One end of multiple rows of vertical CCD registers
51
is connected to a horizontal CCD register
52
, which is connected to output section
53
. The occurrence of charge by the incidence of light is performed in the vertical CCD register. In the frame transfer type, since the incidence of light is performed through the gate electrode of vertical CCD register, the sensitivity of the short-wavelength component is not good. Therefore, by providing the vertical CCD register
2
with a window
54
with no gate electrode on its top, the sensitivity of the short-wavelength component can be enhanced.
FIG. 3
is an enlarged view showing the pixel region. Gate electrodes
71
to
74
are periodically disposed in the transfer direction and windows
54
are formed therebetween. The gate electrodes in
FIG. 3
are of single layer, but maybe of multiple layers. Light-shielding film
64
to prevent the crosstalk is formed over the gate electrode between pixels. The light-shielding film
64
is connected to the gate electrode by the contact and may be also used as electric interconnection.
FIG. 4A
is a schematic plan view showing the surface of substrate below the gate electrode.
FIG. 4B
is a cross sectional view cut along the line G—G in FIG.
4
A. The n-region
56
is formed below the gate electrode, and p-device separation region
60
is formed below the light-shielding film
64
. Also, p-well
59
is formed on n-substrate
69
, and n-well
56
is further formed thereon. The n-well
56
is a charge accumulation region for the incidence of light and is also used as a transfer section. In the opening section (window), p
+
-region
55
is formed on the n-well
56
. In the transfer section, a gate electrode
62
to which the drive voltage pulse of CCD is applied through gate insulator film
63
is formed. The p-device separation region
60
is formed between pixels, and light-shielding film
64
is formed sandwiching insulation film
65
thereon. Also, the whole surface is covered with insulation film
65
.
In the CCD image sensing device, cell area per one pixel continues to reduce, according to an increase in pixel number and a reduction in device size. In the interline transfer type CCD image sensing device, the distance between the light-receiving section and the transfer section shortens with the reduction of cell area. Therefore, there is a problem that even when the transfer gate is turned off, smear is likely to flow into the transfer section beyond the device separation region. Such smear occurs especially when light with high luminance is supplied. In the buried photodiode structure disclosed in Japanese patent application No. 57-062557 (1982), the smear component due to diffusion of signal charge to generate in the semiconductor substrate becomes an issue. The diffusion-caused smear explained below, referring to the drawings.
FIG. 5
is an enlarged cross sectional view showing the end of p
+
-region
5
on the side of the p
+
-device separation region
10
in FIG.
1
B. When light is supplied to the image-sensing device, signal charge due to the photoelectric conversion occurs in the surface p
+
-region
5
and n-accumulation region
6
of the photodiode. Most of the signal charge that occurs in the surface p
+
-region
5
moves to the n-accumulation region
6
. But, part of the light-generated charge occurring at the p
+
-region
5
near the end of the light-shielding film
14
passes through near the surface of the p
+
-device separation region
10
, then flows into n-well
7
of vertical CCD register to cause a smear.
The same phenomenon is also seen in the case of frame transfer type CCD image-sensing device. In this case, the window incurs crosstalk.
FIG. 6
is an enlarged cross sectional view showing the vicinity of the device separation region of the frame transfer type CCD image-sensing device in FIG.
4
B. Signal charge generated in the surface p
+
-region
55
of the window's end where light-shielding film
64
opens by the incidence of light passes through the p
+
-device separation region
60
, flowing into then-region
56
for the neighboring pixel to affect the sensitivity of that pixel.
Methods of reducing the diffused smear component have been suggested. For example, Japanese patent application No. 08-130299 (1996) discloses a structure that surface p
+
-region
25
of photodiode and device separation region
30
are connected by p
++
-region
38
with high concentration of impurity as shown in FIG.
7
A. In
FIG. 7A
, the composition except the surface p
+
-region
25
of photodiode and device separation region
30
is the same as that in FIG.
1
B. For this composition, the potential distribution of a cross section cut along the line H—H is shown in FIG.
7
B. According to this method, since the potential barrier is formed by built-in voltage by the difference of impurity concentration, the possibility that signal charge comes into a smear component due to the diffusion can be reduced.
However, due to insufficient height of potential barrier, th
Kudoh Yoshiharu
Tanabe Akihito
Kang Donghee
NEC Corporation
Thomas Tom
Whitham Curtis & Christofferson, P.C.
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