Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-12-19
2003-02-18
Whitehead, Jr., Carl (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S225000, C257S229000, C257S296000, C257S431000
Reexamination Certificate
active
06521924
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image sensor; and, more particularly, to an image sensor incorporating therein a capacitor structure for improving an optical efficiency of the image sensor.
DESCRIPTION OF THE PRIOR ART
As is well known, an image sensor is a semiconductor device for sensing a light reflected from an object to generate an image data. Especially, an image sensor fabricated by using a complementary metal oxide semiconductor (CMOS) technology is called a CMOS image sensor.
Generally, the CMOS image sensor includes a plurality of unit pixels. Each of the unit pixels also includes a light sensing element and a plurality of transistors. The light-sensing element such as a photodiode senses incident light reflected from an object and accumulates photoelectric charges that are generated due to the incident light. The transistors control a transfer of the photoelectric charges.
In
FIG. 1
, there is shown a prior art image sensor
100
including: a silicon substrate
102
, a photodiode
120
formed into the silicon substrate
102
for sensing a light beam incident thereto and generating photoelectric charges, a capacitor structure
130
formed on the silicon substrate
102
and the photodiode
120
, a diffusion region
106
, a transfer transistor
110
formed on the photodiode
120
, the diffusion region
106
and an isolation region
104
.
In the image sensor
100
, the transfer transistor
110
is provided with a gate dielectric
112
, a gate electrode
114
and a spacer
116
. The transfer transistor
110
is coupled to a sensing node for transferring the photoelectric charges to the sensing rode in response to a transfer control signal. The capacitor structure
130
is provided with an insulating film
132
, a bottom electrode
134
, a capacitor dielectric
136
and a top electrode
138
. In case when the photodiode
120
does not have sufficient capacitance, a certain portion of the photoelectric charges cannot be stored in the photodiode
120
, which will, in turn, leak out into the silicon substrate
102
, thereby decreasing an overall optical efficiency thereof and making noses in the image sensor
100
. These problems can be eliminated by using the capacitor structure
130
which is capable of providing additional capacitances to the photodiode
120
.
In
FIGS. 2A
to
2
D, there are illustrated manufacturing steps involved in manufacturing the conventional image sensor
100
.
The process for manufacturing the conventional image sensor
100
begins with the preparation of an active matrix having a silicon substrate
102
, a transfer transistor structure
110
formed thereon, an isolation region
104
and a photodiode
120
formed into the silicon substrate
102
, as shown in FIG.
2
A. An insulating layer
132
, e.g., made of SiOx, is formed over the entire surface by using a chemical vapor deposition (CVD) technique. The photodiode
120
is capable of converting a light beam incident thereto into photoelectric charges. The transfer transistor
110
includes a gate oxide
112
, a gate electrode
114
and a spacer
116
. The transfer transistor
110
is coupled to a sensing node
106
for transferring the photoelectric charges to the sensing node
106
in response to a transfer control signal. The sensing node
106
can be connected to a transistor such as a reset transistor or an amplification transistor not shown for the sake of simplicity.
Referring to
FIG. 2B
, an insulating layer
132
, e.g., made of silicon oxide (SiO
2
), is formed on top of the active matrix by using a method such as CVD. Thereafter, the insulating layer
132
is patterned into a first predetermined configuration to form a contact hole.
In a next step, a bottom electrode layer
134
, a capacitor dielectric layer
136
and a top electrode layer
138
are formed on the insulating layer
132
, successively, as shown in FIG.
2
C.
Finally, the top electrode layer
138
, the capacitor dielectric layer
136
and the bottom electrode layer
134
are patterned into a second predetermined configuration, thereby obtaining a capacitor structure
130
.
One of the major shortcomings of the above-described image sensor
100
is that it has complex manufacturing steps to form the capacitor structure
130
on the photodiode
120
.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an image sensor incorporating therein a capacitor structure for improving an optical efficiency thereof.
It is another object of the present invention to provide a method for manufacturing an image sensor incorporating therein a capacitor for improving an optical efficiency thereof.
In accordance with an aspect of the present invention, there is provided an image sensor provided with a plurality of unit pixels, each unit pixel comprising: a photoelectric element for sensing a light beam incident thereto and generating photoelectric charges; a transistor including a gate dielectric formed adjacent to the photoelectric element and a gate electrode formed on top of the gate dielectric; and a capacitor structure including an insulating film formed on a portion of the photoelectric element and a bottom electrode, wherein the insulating film and the gaze dielectric are made of a same material and the bottom electrode and the gate electrode are made of a same material.
In accordance with another aspect of the present invention, there is provided a method for manufacturing an image sensor, the method comprising the steps of: a) preparing a silicon substrate; b) forming a first dielectric layer and a first conductive layer, successively; c) patterning the first dielectric layer and the first conductive layer to obtain an insulating film and a bottom electrode of a capacitor structure and a gate dielectric and a gate electrode of a transistor, simultaneously; d) implanting a first type of dopants into a portion of the silicon substrate which is not covered with the insulating film and the gate dielectric and placed therebetween, thereby forming a photoelectric element; e) forming a second dielectric layer; f) removing a portion of the second dielectric layer which is located on top of the photoelectric element, thereby forming a contact hole; g) forming a second conductive layer on top of the second dielectric layer and the contact hole; and h) removing portions of the second conductive layer and the second dielectric layer which are placed on top of the gate electrode and the remaining portion of the photoelectric element.
REFERENCES:
patent: 5356826 (1994-10-01), Natsume
patent: 5760458 (1998-06-01), Bergemont et al.
patent: 6057572 (2000-05-01), Ito et al.
patent: 6103621 (2000-08-01), Huang
patent: 6204524 (2001-03-01), Rhodes
patent: 6255703 (2001-07-01), Hause et al.
patent: 5-13739 (1993-01-01), None
Han Jin-Su
Oh Hoon-Sang
Brophy Jamie L.
Hynix / Semiconductor Inc.
Jr. Carl Whitehead
Townsend and Townsend / and Crew LLP
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