Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
2001-03-19
2003-04-08
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S215000, C257S222000, C257S225000, C257S227000, C257S228000, C257S232000, C257S233000, C257S219000, C257S249000, C257S244000, C257S292000, C257S301000, C257S302000, C257S303000, C257S304000, C257S305000, C257S461000, C257S466000, C257S514000, C257S515000, C438S048000
Reexamination Certificate
active
06545302
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an image sensor, and, more particularly, to a CMOS image sensor and/or a charge coupled device (CCD), which is capable of decreasing leakage current between photodiodes and a method for fabricating the same.
BACKGROUND OF THE INVENTION
As is well known, an image sensor is an apparatus for sensing light reflected from an object and for generating image data. In particular, an image sensor fabricated by using CMOS (Complementary Metal Oxide Semiconductor) technology is called a CMOS image sensor.
Generally, the CMOS image sensor includes a plurality of pixel units having a light sensing region and a peripheral circuit region. Each of the pixel units also includes a light sensing element formed on the light sensing region and a plurality of transistors formed on the peripheral circuit region. The light sensing elements, such as a pinned photodiode, senses incident light reflected from an object and accumulates photoelectric charges that are generated due to the incident light. The transistors control the transfer of the photoelectric charges.
A prior art method for fabricating a photodiode region of a conventional image sensor will be described with reference to
FIGS. 1A and 1B
.
As shown in
FIG. 1A
, field oxide layers
102
for isolating devices are formed in a p-type silicon substrate
101
. The field oxide layers
102
are formed by a LOCOS (Local Oxidation of Silicon) or an STI (Shallow Trench Isolation) method. Thereafter, P-type field stop layers
103
are formed beneath the field oxide layers
102
to prevent the generation of leakage current between devices.
As shown in
FIG. 1B
, after forming an ion implantation mask (not shown) to open the photodiode regions
3
a
and
3
b
on the p-type silicon substrate
101
, a low-concentration and high-energy ion implantation is performed to form n-type doping regions
104
in the p-type silicon substrate
101
. Thereafter, a high-concentration and low-energy ion implantation is performed to form p-type doping regions
105
beneath the surfaces of the p-type silicon substrate
101
. After that, a thermal treatment process is performed to diffuse the impurities in the n-type doping regions
104
and the p-type doping regions
105
, whereby pinned photodiodes are formed. Each pinned photodiode includes a p-type doping region
105
, an n-type doping region
104
under the p-type doping region
105
and the p-type substrate
101
under the n-type doping region
104
.
The pinned photodiode has several merits in comparison with a source/drain PN junction type diode and a MOS capacitor type diode. For example, the n-type doping region of the pinned photodiode having a PNP structure can be fully depleted and the depth of the depletion layer can be increased. Thereby, an incident photon can easily generate an electron. That is, the quantum efficiency and the light sensitivity of the pinned photodiode is improved relative to the aforementioned diodes.
A major shortcoming of the conventional CMOS image sensor is the generation of leakage current (LKG) between pinned photodiodes formed in adjacent pixel units. Although, the field stop layers
103
are formed beneath the field oxide layers
102
, the generation of the leakage current (LKG) cannot be prevented effectively because of the doping regions
104
formed by the high-energy ion implantation.
If the doping concentration of the field stop layers
103
is increased to prevent the generation of the leakage current, then the impurities in the field stop layers
103
are diffused to the photodiodes. As a result, the characteristics of the photodiodes are deteriorated.
SUMMARY OF THE INVENTION
In accordance with an aspect of the invention, an image sensor is provided which contains a first pixel unit and a second pixel unit, each of the first and second pixel units having a photodiode region. The image sensor includes a semiconductor substrate of a first conductivity type; a device isolation layer formed in the semiconductor substrate; a field stop layer formed beneath the device isolation layer; a trench formed in the semiconductor substrate between the photodiode region of the first pixel unit and the photodiode region of the second pixel unit; a first doping region of the first conductivity type formed beneath the surface of the semiconductor substrate of the first photodiode region of the first pixel unit; an insulating member within the trench; and a second doping region of a second conductivity type formed in the semiconductor substrate under the first doping region.
In accordance with another aspect of the invention, an image sensor is provided which contains a first pixel unit and a second pixel unit, each of the first and second pixel units having a photodiode region. The image sensor includes: a semiconductor substrate of a first conductivity type; a device isolation layer formed in the semiconductor substrate; a field stop layer formed beneath the device isolation layer; a trench formed in the semiconductor substrate between the photodiode region of the first pixel unit and the photodiode region of the second pixel unit; an insulating layer covering a surface of the field oxide layer and a surface of the semiconductor substrate including a surface of the trench; a conducting member within the trench, wherein the conducting member covers the device isolation layer and exposes the semiconductor substrate of the photodiode region of the first pixel unit; a first doping region of the first conductivity type formed beneath the surface of the semiconductor substrate of the photodiode region of the first pixel unit; and a second doping region of a second conductivity type formed in the semiconductor substrate under the first doping region.
In accordance with another aspect of the invention, a method for fabricating an image sensor having a first pixel unit and a second pixel unit is provided, each of the first and second pixel units having a photodiode region, the method comprising the steps of: providing a semiconductor substrate of a first conductivity type; forming a device isolation layer in the semiconductor substrate; forming a field stop layer beneath the device isolation layer; forming a trench in the semiconductor substrate between the photodiode region of the first pixel unit and the photodiode region of the second pixel unit; forming a first doping region of the first conductivity type beneath the surface of the semiconductor substrate of the photodiode region of the first pixel unit; forming an insulating member within the trench; forming a second doping region of a second conductivity type in the semiconductor substrate under the first doping region; and performing a thermal treatment process to diffuse impurities in the first doping region and the second doping region.
In accordance with still another aspect of the invention, a method for fabricating an image sensor having a first pixel unit and a second pixel unit is provided, wherein each of the first and second pixel units has a photodiode region, the method comprising the steps of: providing a semiconductor substrate of a first conductivity type; forming a device isolation layer in the semiconductor substrate; forming a field stop layer beneath the device isolation layer; forming a trench in the semiconductor substrate between the photodiode region of the first pixel unit and the photodiode region of the second pixel unit; forming an insulating layer on a surface of the device isolation layer and on a surface of the semiconductor substrate including on a surface of the trench; forming a conducting member within the trench and covering the insulating layer formed on the device isolation layer; forming a first doping region of the first conductivity type beneath the surface of the semiconductor substrate in the photodiode region of the first pixel unit; forming a second doping region of a second conductivity type in the semiconductor substrate under the first doping region; and performing a thermal treatment process to diffuse impurities in the first dop
Hyundai Electronics Industries Co,. Ltd.
Lee Eddie
Marshall Gerstein & Borun
Ortiz Edgardo
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