Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
2000-08-11
2002-01-15
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
Reexamination Certificate
active
06338978
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sensor and a method for fabricating the same, and more particularly, to an image sensor and a method for fabricating the same.
2. Background of the Related Art
FIG. 1
is a layout illustrating a conventional solid state image sensor, and
FIG. 2
is a sectional view illustrating a conventional solid state image sensor.
FIGS. 3A
to
3
F are sectional views illustrating a method for fabricating a conventional solid state image sensor of
FIGS. 1 and 2
.
As shown in
FIG. 1
, a solid state image sensor includes a plurality of photodiode regions
300
, vertical charge transfer regions
400
, a horizontal charge transfer region
500
, and a sense amplifier
600
. The plurality of photodiode regions
300
converts a signal of light to an electrical image transfer signal. Each of the vertical charge transfer region
400
transfers the image charge formed by the photodiodes
300
in a vertical direction. The horizontal charge transfer region
500
transfers the image charge transferred in a vertical direction by the vertical charge transfer region
400
to a horizontal direction. The sense amplifier
600
senses the image signal charge transferred in the horizontal direction by the horizontal charge transfer region
500
.
As shown in
FIG. 2
, a conventional solid state image sensor includes a p-type well
12
formed in a surface of an n-type semiconductor substrate
11
in which a photoelectric conversion region is defined. A photodiode is formed of a PD-N region
13
and a PD-P region in a surface of the p-type well
12
in the photoelectric conversion region, for converting a signal of light to an electrical signal. A vertical charge transfer region
14
is formed in the surface of the p-type well
12
in which the photodiode is not formed, and a channel stop layer
15
is formed in the surface of the p-type well
12
around the photodiode except for a portion between one side of the photodiode and the vertical charge transfer region
14
.
A gate insulating film
16
is formed on the semiconductor substrate
11
including the vertical charge transfer region
14
and the photodiode, and a transfer gate
17
is formed on the gate insulating film
16
except for the photodiode. A first insulating film
18
is formed on a surface of the transfer gate
17
, and a second insulating film
20
is formed on the gate insulating film
16
including the first insulating film
18
. A light-shielding layer
21
is formed on the second insulating film
20
except for the photodiode, and a third insulating film
22
is formed on the light-shielding layer
21
including the second insulating film
20
.
A conventional method for fabricating a solid state image sensor will be described with reference to
FIGS. 3A
to
3
F. As shown in
FIG. 3
a
, a p-type impurity ion is selectively implanted into a predetermined region in a surface of an n-type semiconductor substrate
11
in which a photoelectric conversion region is defined. A p-type well
12
is then formed by a drive-in diffusion process.
As shown in
FIG. 3B
, an n-type impurity ion is implanted into a surface of the p-type well
12
in the photoelectric conversion region. A PD-N region
13
is then formed by drive-in diffusion process. Subsequently, a heavily doped n-type impurity ion is implanted into the surface of the p-type well
12
in which the PD-N region
13
is not formed. A vertical charge transfer region
14
is then formed by a drive-in diffusion process.
As shown in
FIG. 3C
, a heavily doped p-type impurity ion of energy lower than that to form the PD-region
13
is implanted into the surface of the p-type well
12
around the PD-N region
13
except for a portion between one side of the PD-N region
13
and the vertical charge transfer region
14
. A channel stop layer
15
is then formed by a drive-in diffusion process. A gate insulating film
16
is formed on an entire surface of the semiconductor substrate
11
in which the vertical charge transfer region
14
and the channel stop layer
15
are formed.
As shown in
FIG. 3D
, a polysilicon and a first photoresist are sequentially formed on the gate insulating film
16
. The first photoresist is selectively patterned by exposure and developing processes to remain over the vertical charge transfer region
14
. Subsequently, the polysilicon is selectively etched using the patterned first photoresist as a mask to form a transfer gate
17
. The first photoresist is then removed. A first insulating film
18
is grown on a surface of the transfer gate
17
by a thermal oxidation process.
As shown in
FIG. 3E
, the heavily doped p-type impurity ion of energy lower than that to form the channel stop layer
15
is implanted into the surface of the p-type well
12
in the photoelectric conversion region. A PD-P region
19
is then formed with a thin thickness by a drive-in diffusion process. Thus, a photodiode with the PD-N region
13
and the PD-P region
19
is formed.
A second insulating film
20
and a light-shielding layer
21
are sequentially formed on the entire surface including the first insulating film
18
. As shown in
FIG. 3F
, a second photoresist is deposited on the light-shielding layer
21
and then the second photoresist is selectively patterned by exposure and developing processes, so that the second photoresist over the photodiode is removed.
Subsequently, the light-shielding layer
21
is selectively etched using the second patterned photoresist as a mask. The second photoresist is then removed. A third insulating film
22
is formed on the entire surface including the selectively etched light-shielding layer
21
.
In the conventional solid state image sensor, a signal charge stored in the photodiode is transferred to the vertical charge transfer region
14
by a clock signal applied to the transfer gate
17
and then is moved in the vertical direction. A hole or the positive charge is then removed in the PD-P region
19
.
The PD-N region
13
is originally floating. However, if a high clock signal is If applied to the transfer gate
17
, the signal charge in the PD-N region
13
is transferred to the vertical charge transfer region
14
and electrons are thus lost. As a result, the PD-N region
13
is pinched off. In this state, if the signal charge occurs again, the potential of the PD-N region
13
ascends, but fails to ascend more than Vsdl (saddle potential) of the p-type well
12
.
The vertical charge transfer region
14
has high potential because a voltage of the transfer gate
17
is added to the pinched off potential of the PD-N region
13
. At this time, a high voltage is applied to the transfer gate
17
because the device is operated by deep depletion mode.
However, the conventional solid state image sensor and the method for fabricating the same have several problems and disadvantages. If a surface of the photodiode is damaged or contaminated by a heavy metal in the course of the process steps, a noise charge occurs, and the noise charge flows to the photodiode. In addition, since the gate insulating film is formed on the semiconductor substrate including the photodiode, the incident light directly flows to the vertical charge transfer region through the gate insulating film, thereby causing a Smear phenomenon.
SUMMARY OF THE INVENTION
An object of the present invention is to obviate one or more of the problems and/or disadvantages of the related art.
Another object of the present invention is to prevent the occurrence of a Smear phenomenon.
A further object of the present invention is to prevent a noise charge from flowing to a photodiode.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a solid state image sensor according to the present invention includes a semiconductor substrate, a plurality of photoelectric conversion devices in a matrix arrangement in a surface of the semiconductor substrate, a plurality of vertical charge transfer regions formed in one direction in a su
Bowers Charles
Fleshner & Kim LLP.
Hyundai Electronics Industries Co. Ltd
Thompson Craig
LandOfFree
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