Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-06-04
2001-05-15
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S226000, C257S294000, C257S432000, C348S311000, C438S069000
Reexamination Certificate
active
06232590
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid state image sensor, and more particularly, to a solid state image sensor and a method for fabricating the same, which can improve a sensitivity and a smear of a CCD(Charge Coupled Device).
2. Background of the Invention
In general, a solid state image sensor is a device which uses a photoelectric conversion device and a charge coupled device in taking an image of an objective and providing the image as an electrical signal. The charge coupled device is used in transmission of a signal charge generated in a photoelectric conversion device(a photodiode) through a microlens and a color filter in a particular direction in a substrate utilizing a potential variation. The solid state image sensor is provided with a plurality of photoelectric conversion regions, vertical charge coupled devices(VCCDs) each one formed between the photoelectric conversion regions for vertical transmission of charges generated in the photoelectric conversion regions, a horizontal charge coupled device(HCCD) for horizontal transmission of the charge transmitted in the vertical direction by the VCCDs, and a floating diffusion region for sensing and amplifying the charges transmitted in the horizontal direction and providing to a peripheral circuit.
A related art method for fabricating an HCCD will be explained with reference to the attached drawings.
FIGS. 1
a
~
1
d
illustrate sections showing the steps of a related art method for fabricating a solid state image sensor.
Referring to
FIG. 1
a
, the related art method for fabricating a solid state image sensor starts from forming a first planar layer
14
on a black and white solid state image sensor
11
which is provided with a plurality of photodiode regions PD
12
each for converting an optical image signal into an electrical signal, a plurality of vertical charge coupled devices(VCCDs)
13
each for transmitting video charges generated in the photodiode region
12
in a vertical direction, and a horizontal charge coupled device(not shown) for transmission of the video charges transmitted in the vertical direction to a horizontal direction. Then, as shown in
FIG. 1
b
, first, second and third color filter layers
15
,
16
and
17
are formed on the first planar layer
14
over the photodiode regions
12
in succession to correspond to the photodiodes
12
, selectively. The color filter layers are formed by coating and patterning a dyeable resist and dying and fixing the dyeable resist layer. As shown in
FIG. 1
c
, a second planar layer
18
is formed on an entire surface inclusive of the first, second and third color filter layers
15
,
16
and
17
. Then, as shown in
FIG. 1
d
, microlenses
19
are formed on the second planar layer
18
to correspond to respective photodiode regions
12
.
The operation of the related art solid state image sensor formed by the aforementioned method will be explained.
A light incident to the solid state image sensor is focused by a microlens
19
, passes through one of the first, second and third color filter layers
15
,
16
and
17
each of which is adapted to transmit only a particular waveform of light, and is incident to a corresponding diode
12
. The light incident to the photodiode
12
is converted into an electrical signal at the photodiode region
12
, and transmitted in a vertical direction and a horizontal direction in response to clock signals applied to gates on the VCCDs and the HCCD of the solid state image sensor, sensed and amplified at the floating diffusion region(not shown) at an end of the HCCD, and provided to a peripheral circuit.
FIG. 2
illustrates focal distances of a short axis and a long axis of a related art microlens.
Referring to
FIG. 2
, the rectangular microlens formed in conformity to the rectangular pixel in the CCD, with a difference of radii of curvatures of the long axis and the short axis, forms different focal distances of the lights incident to the photodiode through the microlens. That is, a focal distance differs depending on refractive indices of the air and a lens, and since refractive indices of the air are fixed at the same place, focal distances of the lights transmitted through the microlens to be incident to the photodiode become different due to a difference of refractive indices coming from a difference of radii of curvatures; a focal distance from the long axis is greater than a focal distance from the short axis.
However, the related art method for fabricating a solid state image sensor has the following problem.
That is, the rectangular microlens formed in conformity to the rectangular pixel in the CCD causes a loss of CCD sensitivity as much as a difference of focal distances of the lights incident to the photodiode through the microlens.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a solid state image sensor and a method for fabricating the same that substantially obviates one or more ofthe problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a solid state image sensor and a method for fabricating the same, which can provide the same focal distances of lights incident to a photodiode through a microlens for improving a sensitivity of a CCD.
Additional features and advantage s of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the solid state image sensor includes photodiode regions for generating video charges from incident lights, and charge coupled devices each formed between the photodiodes for transferring the video charges in one direction, wherein impurity ions are implanted in a portion of each of microlenses formed over, and one to one matched to the photodiode regions for varying a refractive index.
In another aspect of the present invention, there is provided a method for fabricating a solid state image sensor, including the steps of (1) forming photodiode regions for generating video charges from incident lights, (2) forming charge coupled devices between the photodiode regions for transferring the video charges in one direction, (3) forming a first planar layer on all surfaces of the photodiode regions and the charge coupled devices, (4) forming color filter layers on the first planar layer to be one to one matched to the photodiode regions, (5) forming a second planar layer on an entire surface inclusive of the color filter layers, (6) forming microlenses on the second planar layer to be one to one matched to the photodiode regions, (7) forming a mask layer on an entire surface to expose a portion of the microlens, and (8) using the mask layer as a mask in injecting impurity ions into the exposed portions of the microlenses.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 5306926 (1994-04-01), Yonemoto
patent: 5323052 (1994-06-01), Koyama
patent: 5371397 (1994-12-01), Maegawa et al.
patent: 5420634 (1995-05-01), Matsumoto
patent: 5796154 (1998-08-01), Sano et al.
patent: 5854091 (1998-12-01), Back et al.
patent: 6127668 (2000-10-01), Baek
Lee John R.
LG Semicon Co. Ltd.
Morgan & Lewis & Bockius, LLP
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