Solid imaging device

Details Solid imaging device Solid imaging device

2000-01-05

2001-11-13

Ngô, Ngân V. (Department: 2814)

Active solid-state devices (e.g., transistors, solid-state diode

Responsive to non-electrical signal

Electromagnetic or particle radiation

C257S232000, C257S233000, C257S249000

Reexamination Certificate

active

06316814

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an imaging device, and particularly relates to an imaging device in which the generation of smear is prevented.
2. Background Art
A basic cell of a CMOS sensor, an active type XY address-type solid imaging device is shown in FIG.
10
. In
FIG. 10
, the reference numeral
10
denotes a solid imaging system (a CMOS sensor),
11
denotes a P-type silicon substrate,
12
a P-type well,
14
an N-type region (photoelectric conversion region) forming a photodiode,
16
a gate SiO
2
film,
18
a polysilicon film forming a reset gate,
20
an N
+
region for forming a reset drain,
21
a field oxide film for element separation, and
22
a metal film for forming a light shield film in which an aperture
23
is formed for defining a light admitting area.
An interlayer insulating film
24
and a plurality of wiring layers
13
,
15
,
17
,
19
are provided between the photoelectric conversion region
14
and the light shielding film
22
, and the photoelectric conversion layer
14
is connected with a source-follower-amplifier
24
by a wiring layer (not shown).
The source-follower-amplifier
24
comprises a selection switch MOD transistor
26
, a MOS transistor
28
for detection, and a MOD transistor
29
as a load, and the gate of the MOS transistor
28
is connected with the photoelectric conversion region
14
.
An operation of such a CMOS sensor constituted as shown above is described as follows. First, by applying a high pulse &phgr;
R
to the reset gate
18
, the potential of the N-type region forming the photodiode
14
(photoelectric conversion region) is set. Next, by applying a low pulse &phgr;
R
to the reset gate
18
, electric charge generated by the photoelectric conversion is stored in the depleted layer. Depending upon the amount of the stored electric charge, the potential of the N-type region (photoelectric conversion region)
14
is changed, and the potential change is output from an output terminal
30
of the source-follower-amplifier
24
.
In the structure of the conventional CMOS sensor
10
, since there are many components intervening in between the light shielding film
22
defining the aperture
23
and the photoelectric conversion region
14
on the silicon substrate
11
such as the interlayer insulating film
24
and a plurality of wiring layers
13
,
15
,
17
,
19
, the interval L
0
between the light shielding film
22
and the photoelectric conversion region
14
becomes as large as a few &mgr;m which is far larger than the wavelength of visible light (approximately 80 to 770 nm), and the diffracted light
25
diffracted by the aperture
23
is admitted to the periphery of the photoelectric conversion region
14
as shown in FIG.
10
(
a
).
Therefore, in the structure of the conventional CMOS sensor, a problem arises that false signals (generally called “smear”) are generated by the photoelectric conversion due to the expanded beam of light admitted to the periphery of the photoelectric conversion by the light diffraction effect and, thus, the S/N ratio of image signals is degraded.
Although a technique has been proposed in which the size of the aperture
23
(e.g. the width W
0
) is reduced relative to the size of the photoelectric conversion region
14
(e.g. the width W
14
), a problem has been encountered that this technique causes reduction of the amount of light incident to the photoelectric conversion region, which results in reducing the sensitivity.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problems and to attain at least one of three objectives described below. That is, the objectives include (1) to reduce smear, (2) to improve the S/N ratio of the image signals, and (3) to provide a solid imaging device having a higher sensitivity than the conventional devices.
The above objects are achieved by providing a solid imaging device comprising: a photoelectric conversion region; a light shielding film having an aperture above said photoelectric conversion region; a plurality of wiring layers disposed at intermediate positions between said light shielding layer and said photoelectric conversion region; wherein, a portion of said wiring layer is disposed protruding inside of said light shielding layer when viewed from the top of the aperture so as to shield the incident light for defining the light admitting region by shielding the incident light admitted to the peripheral area of the photoelectric conversion region.
It is preferable that said wiring layer is made of metal or polysilicon, and it is also preferable that said wiring layer is selected from the group consisting of a Vdd layer connected to said reset drain region, a reset gate wiring layer connected to said reset gate electrode, a reset gate, an XY address wiring layer, and an output wiring layer.
In the present invention, said wiring layer is disposed so as to surround said photoelectric conversion region, disposed so as to intermittently surround said photoelectric conversion region, or said wiring layer is disposed so as to cover at least a portion of said photoelectric conversion region.
In the present invention, a plurality of the wiring layers are located at different heights from said photoelectric conversion region and a plurality of the wiring layers are disposed so as to surround said photoelectric conversion area in combinations of two or more wiring layers.
The solid imaging device of the present invention may be applied as MOS sensors and CCD sensors.
In the solid imaging device of the present invention, since a metal or polysilicon wiring layer disposed inside of the light shielding film is used for shielding the light incident to the photoelectric conversion region and since the wiring layer is disposed close to the photoelectric conversion layer, bending of the incident light by diffraction can be reduced, so that it is possible to reduce the false signals (smears) and to avoid the degradation of the S/N ratio caused by smears trapped in the adjacent photoelectric conversion layer or the diffusion layer in the output circuit.
In the solid imaging device of the present invention, since the wiring layer, protruded inside from the edge of the aperture of the light shielding film is used for shielding the light incident to the peripheral area around the photoelectric conversion region, it becomes possible to increase the light admitting area in the same photoelectric conversion region, which results in increasing sensitivity in the photoelectric conversion and the sensitivity of the solid imaging device.
In the solid imaging device of the present invention, disposition of various wiring layers such as the Vdd wiring layer connected to the reset drain layer, the reset gate layer connected to the reset gate, the reset gate, the XY address wiring layer, or the output wiring layers, having different heights from the photoelectric conversion region, make it possible to reduce the relative distance from the wiring layer to the photoelectric conversion layer, when two or more layers are used in combination for surrounding the photoelectric region.


REFERENCES:
patent: 5028972 (1991-07-01), Watanabe et al.
patent: 5250825 (1993-10-01), Negishi et al.
patent: 5514888 (1996-05-01), Sano et al.
patent: 5929470 (1999-07-01), Harada et al.
patent: 6133595 (2000-10-01), Senda

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