Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal
Reexamination Certificate
2001-10-03
2004-03-09
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
C438S069000, C438S070000, C438S300000, C438S309000
Reexamination Certificate
active
06703256
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a solid-state image sensor and a method of fabricating the same, and more particularly to a solid-state image sensor capable of preventing occurrence of smear, and a method of fabricating the same.
2. Description of the Related Art
FIG. 1
illustrates a unit cell of a CMOS sensor which is an active XY address type solid-state image sensor.
The illustrated unit cell is comprised of a p-type silicon substrate
10
, a p-type well
12
formed in the p-type silicon substrate
10
, an n-type region
14
formed in the p-type well
12
and acting as a photodiode, a gate insulating film
16
formed on a surface of the p-type silicon substrate
10
and composed of silicon dioxide (SiO
2
), a reset gate
18
formed on the gate insulating film
16
and composed of polysilicon, a reset drain region
20
composed of an n
+
type region, a field oxide film
21
for electrical isolation between regions in each of which a device is to be fabricated, and a light-impermeable film
22
composed of metal and having an opening
23
through which light enters the n-type region
14
.
An interlayer insulating film and a wiring layer are formed between the light-impermeable film
22
and the n-type region
14
in which light is converted into electricity.
The n-type region
14
is electrically connected to a source follower amplifier
24
. As illustrated in
FIG. 1
, the source follower amplifier
24
is comprised of (a) a first MOS transistor
26
acting as a selector switch, (b) a second MOS transistor
28
having a source electrically connected to a drain of the first MOS transistor
26
, a source electrically connected to a voltage Vdd, and a gate electrically connected to the n-type region
14
, (c) a third MOS transistor
29
acting as a load, and having a drain electrically connected to a source of the first MOS transistor
26
, and a source electrically connected to a voltage Vss, and (d) an output terminal
30
electrically connected to a source of the first MOS transistor
26
and a drain of the third MOS transistor
29
.
The CMOS sensor illustrated in
FIG. 1
operates as follows.
First, a high pulse &PHgr;
R
is applied to the reset gate
18
to thereby cause the n-type region
14
acting as a photodiode, to have a certain potential. Then, a low pulse &PHgr;
R
is applied to the reset gate
18
to thereby accumulate electric charges in a depletion layer which electric charges have been generated by converting light into electricity.
A potential of the photodiode
14
varies in accordance with the thus accumulated electric charges. Variation in the potential is output through the output terminal
30
of the source follower amplifier
24
.
In such a conventional CMOS sensor as illustrated in
FIG. 1
, since an interlayer insulating film and a plurality of wiring layers are sandwiched between the light-impermeable film
22
and the n-type region or light-electricity converting region
14
, the light-impermeable film
22
is much spaced away from the n-type region
14
. Hence, light
25
diffracted due to diffraction effect of light having passed through the opening
23
reaches a border area of the light-electricity converting region
14
, as illustrated in FIG.
1
.
Thus, the conventional CMOS sensor is accompanied with a problem of so-called smear that light reaching a border of the light-electricity converting region or n-type region
14
due to diffraction effect is converted into electricity to thereby generate a false signal.
In addition, the thus generated false signal is trapped in adjacent light-electricity converting regions or in a diffusion layer of the source follower amplifier
24
, resulting in another problem that a S/N ratio of image signals is degraded.
SUMMARY OF THE INVENTION
In view of the above-mentioned problem, it is an object of the present invention to provide a solid-state image sensor which is capable of preventing generation of smear or the above-mentioned false signal. It is also an object of the present invention to provide a method of fabricating such a solid-state image sensor.
In one aspect of the present invention, there is provided a solid-state image sensor including a first region in which light is converted into electricity, and a second region composed of silicide, the second region at least partially forming a border area of the first region at a surface of the first region.
The second region can interrupt light which would cause smear, from entering the region.
It is preferable that the solid-state image sensor is constituted as a CMOS sensor or a CCD sensor.
It is preferable that the second region is composed of silicide of refractory metal.
There is further provided a solid-state image sensor including a first region in which light is converted into electricity, a reset gate electrode, a reset drain region, and a second region composed of suicide, the second region at least partially forming a border area of the first region at a surface of the first region.
There is still further provided a solid-state image sensor including a first region in which light is converted into electricity, a reset gate electrode, a reset drain region, a second region composed of suicide, the second region at least partially forming a border area of the first region at a surface of the first region, and a third region composed of suicide, the third region covering a surface of the reset drain region therewith.
It is preferable that the second and third regions are formed from a common layer.
There is yet further provided a solid-state image sensor including a first region in which light is converted into electricity, a light-impermeable film having an opening situated above the first region, and a second region composed of silicide, the second region at least partially forming a border area of the first region at a surface of the first region such that the second region interrupts diffracted light coming through the opening, from entering the first region.
There is still yet further provided a solid-state image sensor including a first region in which light is converted into electricity, a light-impermeable film having an opening situated above the first region, a reset gate electrode, a reset drain region, and a second region composed of silicide, the second region at least partially forming a border area of the first region at a surface of the first region such that the second region interrupts diffracted light coming through the opening, from entering the first region.
There is further provided a solid-state image sensor including a first region in which light is converted into electricity, a light-impermeable film having an opening situated above the first region, a reset gate electrode, a reset drain region, a second region composed of silicide, the second region at least partially forming a border area of the first region at a surface of the first region such that the second region interrupts diffracted light coming through the opening, from entering the first region, and a third region composed of silicide, the third region covering a surface of the reset drain region therewith.
In another aspect of the present invention, there is provided a method of fabricating a solid-state image sensor, including the steps of (a) forming a first region in which light is converted into electricity, in a silicon substrate, the first region having an electrical conductivity opposite to an electrical conductivity of the silicon substrate, and (b) forming a second region composed of silicide, the second region forming a border area of the first region at a surface of the first region.
For instance, the step (b) may be carried out by silicifying a border area of the first region or deposition a refractory metal film and heating the refractory metal film.
It is preferable that the method further includes the step of forming a light-impermeable film having an opening situated above the first region.
There is further provided a method of fabricating a solid-state image sensor, including the steps of (a)
Nagata Tsuyoshi
Nakashiba Yasutaka
Luu Chuong A
Smith Matthew
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