U.S. patent application number 14/150425 was filed with the patent office on 2014-05-01 for image sensing apparatus and imaging system.
This patent application is currently assigned to c/o CANON KABUSHIKI KAISHA. The applicant listed for this patent is c/o CANON KABUSHIKI KAISHA. Invention is credited to Yuu Arishima, Seiichirou Sakai, Hideaki Takada.
Application Number | 20140117211 14/150425 |
Document ID | / |
Family ID | 41012447 |
Filed Date | 2014-05-01 |
United States Patent
Application |
20140117211 |
Kind Code |
A1 |
Arishima; Yuu ; et
al. |
May 1, 2014 |
IMAGE SENSING APPARATUS AND IMAGING SYSTEM
Abstract
An image sensing apparatus includes a pixel array, a first color
filter, a second color filter, and a light shielding portion. The
amount of electric charges generated in a first pixel after light
of a first wavelength enters the first pixel is larger than that of
electric charges generated in a second pixel after light of a
second wavelength enters the second pixel. The light shielding
portion defines the aperture regions of the first and second pixels
so as to set the aperture area of the first pixel larger than that
of the second pixel.
Inventors: |
Arishima; Yuu;
(Yokohama-shi, JP) ; Takada; Hideaki;
(Yokohama-shi, JP) ; Sakai; Seiichirou;
(Ebina-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
c/o CANON KABUSHIKI KAISHA |
TOKYO |
|
JP |
|
|
Assignee: |
c/o CANON KABUSHIKI KAISHA
TOKYO
JP
|
Family ID: |
41012447 |
Appl. No.: |
14/150425 |
Filed: |
January 8, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13350273 |
Jan 13, 2012 |
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14150425 |
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12372099 |
Feb 17, 2009 |
8106343 |
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13350273 |
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Current U.S.
Class: |
250/208.1 |
Current CPC
Class: |
H01L 27/14621 20130101;
H01L 27/14623 20130101; H01L 27/14625 20130101; H01L 27/14605
20130101 |
Class at
Publication: |
250/208.1 |
International
Class: |
H01L 27/146 20060101
H01L027/146 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 29, 2008 |
JP |
2008-051120 |
Claims
1. An image sensing apparatus comprising: a pixel array in which a
plurality of pixels including a first pixel and a second pixel are
arrayed two-dimensionally; a first color filter which selectively
transmits light of a first wavelength so as to make light of the
first wavelength enter the first pixel; a second color filter which
selectively transmits light of a second wavelength so as to make
light of the second wavelength enter the second pixel; and a light
shielding portion which is interposed between the first color
filter, the second color filter, and the pixel array, and defines
an aperture region of each of the plurality of pixels, wherein an
amount of electric charges generated in the first pixel in
accordance with light of the first wavelength entering the first
pixel when white light having a continuous spectrum equivalent in
light energy per unit wavelength width between all wavelengths in a
visible region is partially transmitted by the first color filter
is larger than an amount of electric charges generated in the
second pixel in accordance with light of the second wavelength
entering the second pixel when the white light is partially
transmitted by the second color filter, and the light shielding
portion defines aperture regions of the first pixel and the second
pixel so as to set an aperture area of the first pixel larger than
an aperture area of the second pixel.
2-9. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an image sensing apparatus
and imaging system.
[0003] 2. Description of the Related Art
[0004] Image sensing apparatuses each having a pixel array in which
a plurality of pixels including photoelectric conversion elements
are arrayed in the row and column directions include an X-Y address
type CMOS image sensor having an amplifier for each pixel, in
addition to a CCD image sensor. The image sensing apparatus of this
type is used in an imaging system such as a digital camera or
digital video camera. Each pixel in the pixel array is generally
covered with a color filter which selectively transmits light of
the R (Red), G (Green), or B (Blue) wavelength to guide transmitted
light of the wavelength to a pixel below the color filter.
[0005] Recently, as the number of pixels of an image sensing
apparatus has increased, the pixels of the pixel array have been
shrinked. Along with the shrinkage of pixels, the dimension of the
aperture region of the pixel comes close to the half-wavelength of
light entering the pixel. As a result, it becomes difficult for the
pixel to receive light of the R wavelength which is longest among
the R, G, and B wavelengths.
[0006] To solve this problem, Japanese Patent Laid-Open No.
2007-005629 discloses an image sensing apparatus in which the
aperture size of an R pixel is set larger than those of the
apertures of pixels of the remaining colors (G and B). According to
Japanese Patent Laid-Open No. 2007-005629, this structure can
reduce degradation of the image quality caused by shrinkage of
pixels.
[0007] A case where white balance is adjusted in an imaging system
having the image sensing apparatus disclosed in Japanese Patent
Laid-Open No. 2007-005629 and a signal processing unit which
processes a signal output from the image sensing apparatus to
generate image data will be examined. In this case, upon receiving
R, G, and B pixel signals output from the image sensing apparatus,
the signal processing unit amplifies them with different gains so
as to obtain a proper white level in a display or recording image.
The gains of the respective colors are often determined to satisfy
R gain>G gain>B gain in accordance with the characteristics
(spectral characteristic and absorption characteristic) of the
color filter, and the wavelength dependence of utilization
efficiency of electric charges when, for example, a photoelectric
conversion element is arranged on a silicon semiconductor
substrate.
[0008] Assume that light (stray light) enters at least some pixels
of the pixel array at a large incident angle. At this time, the
mixture of colors (leakage of signal charges to an adjacent pixel)
owing to stray light occurs to the same degree per unit aperture
area in two adjacent pixels of different colors (e.g., R and G
pixels, or B and G pixels). After output from the image sensing
apparatus, pixel signals of different colors containing the mixed
color component are amplified with different gains by the signal
processing unit. The influence of stray light, i.e., the intensity
of the mixed color component generated by stray light differs
between colors in an obtained display or recording image.
[0009] Particularly in the image sensing apparatus disclosed in
Japanese Patent Laid-Open No. 2007-005629, the aperture size of an
R pixel is larger than those of pixels of the remaining colors (G
and B). Thus, the mixture of colors by stray light in the R pixel
becomes more serious than that by stray light in the G and B
pixels. When R gain>G gain>B gain, the intensity of a mixed
color component in the R pixel signal becomes higher than those of
mixed color components in the G and B pixel signals in an image
signal amplified by the signal processing unit.
[0010] As a result, the influence of stray light on a specific
color (R) may stand out in an obtained image.
SUMMARY OF THE INVENTION
[0011] It is an aim of the present invention to make the influence
of stray light on an obtained image uniform between colors.
[0012] According to the first aspect of the present invention,
there is provided an image sensing apparatus comprising: a pixel
array in which a plurality of pixels including a first pixel and a
second pixel are arrayed two-dimensionally; a first color filter
which selectively transmits light of a first wavelength so as to
make light of the first wavelength enter the first pixel; a second
color filter which selectively transmits light of a second
wavelength so as to make light of the second wavelength enter the
second pixel; and a light shielding portion which is interposed
between the first color filter, the second color filter, and the
pixel array, and defines an aperture region of each of the
plurality of pixels, wherein an amount of electric charges
generated in the first pixel in accordance with light of the first
wavelength entering the first pixel when white light having a
continuous spectrum equivalent in light energy per unit wavelength
width between all wavelengths in a visible region is partially
transmitted by the first color filter is larger than an amount of
electric charges generated in the second pixel in accordance with
light of the second wavelength entering the second pixel when the
white light is partially transmitted by the second color filter,
and the light shielding portion defines aperture regions of the
first pixel and the second pixel so as to set an aperture area of
the first pixel larger than an aperture area of the second
pixel.
[0013] According to the second aspect of the present invention,
there is provided an image sensing apparatus comprising: a pixel
array in which a plurality of pixels including a first pixel and a
second pixel are arrayed two-dimensionally; a first color filter
which selectively transmits light of a first wavelength so as to
make light of the first wavelength enter the first pixel; a second
color filter which selectively transmits light of a second
wavelength so as to make light of the second wavelength enter the
second pixel; and a light shielding portion which is interposed
between the first color filter, the second color filter, and the
pixel array, and defines an aperture region of each of the
plurality of pixels, wherein the first wavelength is shorter than
the second wavelength, and the light shielding portion defines
aperture regions of the first pixel and the second pixel so as to
set an aperture area of the first pixel larger than an aperture
area of the second pixel.
[0014] According to the third aspect of the present invention,
there is provided an imaging system comprising: an image sensing
apparatus defined, according to the first and second aspects of the
invention, an optical system which forms an image on an image
sensing surface of the image sensing apparatus; and a signal
processing unit which processes a signal output from the image
sensing apparatus to generate image data, wherein the image sensing
apparatus senses a reference white object before sensing an object,
and the signal processing unit determines a gain for a signal
output from the first pixel to have a value smaller than a value of
a gain for a signal output from the second pixel so as to obtain a
proper white level for the reference white object in a display or
recording image.
[0015] The present invention can make the influence of stray light
on an obtained image uniform between colors.
[0016] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a block diagram of the configuration of an imaging
system 90 to which an image sensing apparatus 100 according to an
embodiment of the present invention is applied;
[0018] FIG. 2 is a diagram of the arrangement of the image sensing
apparatus 100 according to the embodiment of the present
invention;
[0019] FIG. 3 is a plan view showing the layout of an image sensing
apparatus according to the first embodiment of the present
invention;
[0020] FIG. 4 is a sectional view taken along a line a-a' in FIG.
3;
[0021] FIG. 5 is a sectional view taken along a line b-b' in FIG.
3;
[0022] FIG. 6 is a plan view showing the layout of an image sensing
apparatus according to the third embodiment of the present
invention;
[0023] FIG. 7 is a plan view showing the layout of an image sensing
apparatus according to the fourth embodiment of the present
invention;
[0024] FIG. 8 is a sectional view showing the sectional structure
of an image sensing apparatus according to the fifth embodiment of
the present invention;
[0025] FIG. 9 is a plan view showing the layout of an image sensing
apparatus under design according to the sixth embodiment of the
present invention; and
[0026] FIG. 10 is a plan view showing the layout of the image
sensing apparatus according to the sixth embodiment of the present
invention.
DESCRIPTION OF THE EMBODIMENTS
[0027] An imaging system 90 to which an image sensing apparatus 100
according to an embodiment of the present invention is applied will
be explained with reference to FIG. 1. FIG. 1 is a block diagram of
the configuration of the imaging system 90 to which the image
sensing apparatus 100 according to the embodiment of the present
invention is applied.
[0028] As shown in FIG. 1, the imaging system 90 mainly includes an
optical system, the image sensing apparatus 100, and a signal
processing unit. The optical system mainly includes a shutter 91,
lens 92, and stop 93. The signal processing unit mainly includes a
sensed signal processing circuit 95, A/D converter 96, image signal
processor 97, memory 87, external I/F 89, timing generator 98,
overall control/arithmetic unit 99, recording medium 88, and
recording medium control I/F 94. The signal processing unit may not
include the recording medium 88.
[0029] The shutter 91 is arranged in front of the lens 92 on the
optical path to control the exposure.
[0030] The lens 92 refracts incident light to form an object image
on the pixel array (image sensing surface) of the image sensing
apparatus 100.
[0031] The stop 93 is interposed between the lens 92 and the image
sensing apparatus 100 on the optical path. The stop 93 adjusts the
quantity of light guided to the image sensing apparatus 100 after
passing through the lens 92.
[0032] Before sensing an object, the image sensing apparatus 100
senses a reference white object. The image sensing apparatus 100
converts the reference white object image formed on the pixel array
into the first image signal. The image sensing apparatus 100 reads
out and outputs the first image signal from the pixel array. The
image sensing apparatus 100 also senses an object. The image
sensing apparatus 100 converts the object image formed on the pixel
array into the second image signal. The image sensing apparatus 100
reads out and outputs the second image signal from the pixel
array.
[0033] The sensed signal processing circuit 95 is connected to the
image sensing apparatus 100, and processes the first or second
image signal output from the image sensing apparatus 100.
[0034] The A/D converter 96 is connected to the sensed signal
processing circuit 95. The A/D converter 96 converts the first or
second image signal (analog signal) processed by and output from
the sensed signal processing circuit 95 into the first or second
image signal (digital signal).
[0035] The image signal processor 97 is connected to the A/D
converter 96. The image signal processor 97 performs various
arithmetic processes such as correction for the first or second
image signal (digital signal) output from the A/D converter 96.
[0036] For example, the image signal processor 97 determines gains
for R, G, and B by using the first image signal (digital signal)
received from the A/D converter 96 so as to obtain a proper white
level for a reference white object in a display or recording image.
After that, the image signal processor 97 amplifies, with different
gains, R, G, and B pixel signals in the second image signal
(digital signal) received from the A/D converter 96 so as to obtain
a proper white level in a display or recording image, thereby
generating image data. The image signal processor 97 supplies the
image data to the memory 87, external I/F 89, overall
control/arithmetic unit 99, recording medium control I/F 94, and
the like.
[0037] The memory 87 is connected to the image signal processor 97,
and stores image data output from the image signal processor
97.
[0038] The external I/F 89 is connected to the image signal
processor 97. Image data output from the image signal processor 97
is transferred to an external device (e.g., a personal computer)
via the external I/F 89.
[0039] The timing generator 98 is connected to the image sensing
apparatus 100, sensed signal processing circuit 95, A/D converter
96, and image signal processor 97. The timing generator 98 supplies
timing signals to the image sensing apparatus 100, sensed signal
processing circuit 95, A/D converter 96, and image signal processor
97. The image sensing apparatus 100, sensed signal processing
circuit 95, A/D converter 96, and image signal processor 97 operate
in synchronism with the timing signals.
[0040] The overall control/arithmetic unit 99 is connected to the
timing generator 98, image signal processor 97, and recording
medium control I/F 94, and controls all of them.
[0041] The recording medium 88 is detachably connected to the
recording medium control I/F 94. Image data output from the image
signal processor 97 is recorded on the recording medium 88 via the
recording medium control I/F 94.
[0042] With this arrangement, the image sensing apparatus 100 can
provide a high-quality image (image data) as long as it can obtain
a high-quality image signal.
[0043] The arrangement of the image sensing apparatus 100 according
to the embodiment of the present invention will be explained with
reference to
[0044] FIG. 2. FIG. 2 is a diagram of the arrangement of the image
sensing apparatus 100 according to the embodiment of the present
invention.
[0045] The image sensing apparatus 100 includes a pixel array PA,
color filter array CFA, wiring pattern (light shielding portion)
LP, vertical scanning circuit 10, readout circuit 20, horizontal
scanning circuit 30, and output circuit 40.
[0046] In the pixel array PA, a plurality of pixels are arrayed
two-dimensionally (in the row and column directions). The pixels
include the first and second pixels. For example, the first and
second pixels are arranged adjacent to each other in the row or
column direction. Each pixel includes a photoelectric conversion
element (e.g., photodiode).
[0047] In the color filter array CFA, a plurality of color filters
are arrayed two-dimensionally (in the row and column directions).
Each color filter is arranged above each pixel (front side in FIG.
2) in the pixel array PA. The color filters include the first and
second color filters. The first color filter selectively transmits
light of the first wavelength so that light of the first wavelength
enters the first pixel. The second color filter selectively
transmits light of the second wavelength so that light of the
second wavelength enters the second pixel.
[0048] The amount of electric charges generated in the first pixel
in accordance with light of the first wavelength entering the first
pixel when white light is partially transmitted by the first color
filter is larger than that of electric charges generated in the
second pixel in accordance with light of the second wavelength
entering the second pixel when white light is partially transmitted
by the second color filter. The white light has a continuous
spectrum equivalent in light energy per unit wavelength width
between all wavelengths in the visible region.
[0049] As the wavelength of incident light is shorter,
photoelectric conversion occurs closer to the surface of a
semiconductor substrate. As the wavelength of incident light is
longer, photoelectric conversion occurs at a deeper position in the
semiconductor substrate. Hence, a pixel corresponding to a short
wavelength tends to output a larger amount of electric charges
available as a signal. This phenomenon becomes conspicuous when a
silicon substrate is used as a semiconductor substrate.
[0050] The wiring pattern LP is interposed between the color filter
array CFA (first and second color filters) and the pixel array PA
in a direction perpendicular to the sheet surface of FIG. 2. The
wiring pattern LP defines the aperture region of each pixel. The
wiring pattern LP defines the aperture regions of the first and
second pixels so that the aperture area of the first pixel becomes
larger than that of the second pixel.
[0051] The vertical scanning circuit 10 scans pixels on the
respective rows of the pixel array PA in the vertical direction
(column direction) to output, from the pixels on the respective
rows, signals corresponding to the amounts of electric charges
generated in the pixels on the respective rows. Since the amount of
electric charges generated in the first pixel is larger than that
of electric charges generated in the second pixel, the level of a
signal output from the first pixel is higher than that of a signal
output from the second pixel.
[0052] Upon receiving signals output from pixels on the respective
columns of the pixel array PA, the readout circuit 20 temporarily
holds the received signals.
[0053] The horizontal scanning circuit 30 scans the readout circuit
20 in the horizontal direction (row direction) to sequentially
transfer, to the output circuit 40, the signals of pixels on the
respective columns that are held by the readout circuit 20.
[0054] The output circuit 40 generates an image signal from the
transferred signals, and outputs the generated image signal to a
subsequent stage (the sensed signal processing circuit 95).
[0055] The level of a signal output from the first pixel is higher
than that of a signal output from the second pixel. In accordance
with this, the signal processing unit subsequent to the image
sensing apparatus 100 determines a gain for a signal output from
the first pixel to have a value smaller than that of a gain for a
signal output from the second pixel so as to obtain a proper white
level in a display or recording image.
[0056] As described above, the aperture area of the first pixel is
set larger than that of the second pixel. When the mixture of
colors by stray light occurs to the same degree per unit aperture
area in the first and second pixels, the mixture of colors by stray
light in the first pixel becomes more serious than that by stray
light in the second pixel. Even in this case, a gain used in a
subsequent signal processing unit (the image signal processor 97
shown in FIG. 1) for the signal of the first pixel is determined to
have a value smaller than that of a gain for the signal of the
second pixel in correspondence with the fact that the amount of
electric charges generated in the first pixel is larger than that
generated in the second pixel. Thus, the intensity of the mixed
color component in the signal of the first pixel can be made equal
to that of the mixed color component in the signal of the second
pixel in an image signal amplified by the signal processing unit.
As a result, the influence of stray light on an obtained image can
be made uniform.
FIRST WORKING EXAMPLE
[0057] The first working example will be described as an example in
which the first wavelength is shorter than the second one. An image
sensing apparatus according to the first working example of the
present invention will be explained with reference to FIG. 3. FIG.
3 is a plan view showing the layout of the image sensing apparatus
according to the first working example of the present
invention.
[0058] A problem arising from the first wavelength (e.g., B
wavelength) and the second wavelength (e.g., R wavelength) will be
explained.
[0059] In FIG. 3, a partial region of a pixel array PA is extracted
and illustrated. A partial region of a wiring pattern LP is
hatched. The wiring pattern LP includes a plurality of wiring
layers 101 to 103. The wiring layer 101 is the lowermost wiring
layer (first wiring layer) in the wiring pattern LP. The wiring
layer 103 is the uppermost wiring layer (third wiring layer) in the
wiring pattern LP. The wiring layer 102 is an intermediate wiring
layer (second wiring layer) between the wiring layers 101 and
103.
[0060] In FIG. 3, a microlens for improving focusing conditions is
not illustrated. The optical design of the microlens has a purpose
of minimizing the loss of light owing to reflection by the
uppermost wiring layer 103 of the wiring pattern LP. Hence, the
wiring layer 103 serves as a light shielding layer.
[0061] In FIG. 3, partial regions of the color filter array CFA are
represented by colors (R, Gb, Gr, and B) being transmitted by color
filters. The color filter array CFA is, e.g., a Bayer array. In
FIG. 3, assume that stray light enters the light receiving surface
at an acute angle (large incident angle) with respect to the light
receiving surface in a direction indicated by an arrow along the
long side (row direction) of the pixel array. In this case, the
optical mixture of colors occurs to the same degree per unit
aperture area between R and Gr pixels or Gb and B pixels adjacent
to each other in the row direction. Since adjacent pixels are not
completely shielded from each other, the mixture of colors occurs
to a certain degree. If pixels are completely shielded by a wiring
layer or the like, the yield may decrease, so such a structure is
not generally employed.
[0062] The number of electrons generated for each color (amount of
electric charges generated in a pixel of each color) changes
depending on the spectral characteristic of the color filter and a
spectral characteristic corresponding to the wavelength of the
photoelectric conversion element. Thus, white balance is adjusted
by multiplying signals of respective colors by gains by a
subsequent signal processing unit. For example, Rgr, Grgg, Gbgg,
and Bgb represent outputs multiplied by gains for the respective
colors in order to adjust white balance. In this case, gr
represents a gain to multiply R in a subsequent stage, gg
represents a gain to multiply Gr and Gb in the subsequent stage,
and gb represents a gain to multiply B in the subsequent stage. As
for optical mixture of colors by light entering at an acute angle
(large incident angle), ab represents the amount of optical mixture
of Gb to B along a line a-a' in FIG. 3, and ar represents that of
optical mixture of Gr to R along a line b-b'. If the layout of
elements in a pixel is the same for the respective colors,
ar=ab.
[0063] Assume that the amounts of signal charges in R and B pixels
in accordance with light entering at a small incident angle are
R:B=1:2. In this case, letting gr:gb=2:1, the signals of the R and
B pixels after amplification by the signal processing unit become
equal to each other:
Rgr=Bgb (1)
[0064] The amount of electric charges generated by light entering
at an acute angle (large incident angle) is (R+Grar) for the R
pixel and (B+Gbab) for the B pixel in consideration of the amount
of optical mixture of colors. In this case, letting gr:gb=2:1, the
signals of the R and B pixels after amplification by the signal
processing unit become different from each other:
(R+Grar)gr>(B+Gbab)gb (2)
Assuming that outputs from G pixels are equal to satisfy Gr=Gb, the
final intensity of optical mixture of colors apparently becomes
different between R and B more than expected.
[0065] Since the influence of stray light in an image differs
between colors, the influence of stray light on a specific color (R
in this case) stands out in an obtained image (white balance is
lost). The visual characteristic of a human is particularly
sensitive to R, so the image looks very poor.
[0066] To solve this, the working example sets ar<ab so that the
final intensity of optical mixture of colors becomes equal between
R and B, or the image becomes bluish to make the optical mixture of
colors less noticeable. The working example sets ar<ab by
changing the wiring pattern LP between a-a' and b-b' in FIG. 3,
i.e., setting the aperture area of the B pixel larger than that of
the R pixel. This provides a condition to mix B having a small gain
more readily than R having a large gain. Accordingly, the
difference between colors in the intensity of optical mixture of
colors in an amplified image signal can be minimized, reducing
unexpected coloring upon development.
[0067] Similar to Japanese Patent Laid-Open No. 2007-005629, the
aperture of the light shielding layer of an R pixel may also be
widened to make R and B outputs equal and set gains in the
subsequent stage to gr=gb. However, to increase the sensitivity of
each pixel as much as possible along with miniaturization of
pixels, it is appropriate to widen the aperture sizes of all pixels
as much as possible.
[0068] A characteristic structure in the working example will be
explained with reference to FIGS. 3 to 5. FIG. 4 is a sectional
view taken along the line a-a' in FIG. 3. FIG. 5 is a sectional
view taken along the line b-b' in FIG. 3.
[0069] The gain in the subsequent stage is set to be largest for R,
and decreases in the order of G and B. As shown in FIG. 3, the
number of wiring lines of a wiring layer 101 is small on the left
side of Gb and B pixels, but large on the left side of R and Gr
pixels. These structures are shown in the sectional views of FIGS.
4 and 5.
[0070] In FIG. 4, an N-type diffusion region 112 is formed in a
P-type well region 110, and electric charges generated by incident
light are transferred using a transfer electrode 109. Reference
numeral 108 denotes an element isolation region; and 101, 102, and
103, wiring layers between which an interlayer insulation film 106
exists. Reference numeral 111 denotes a color filter layer for
color separation; and 113, a microlens. Since no wiring line of the
wiring layer 101 exists between Gb and B, the adjacent pixels are
not shielded by a wiring line.
[0071] For example, in FIG. 4, assume that x .mu.m is 5.2 .mu.m,
and that y .mu.m is 4.9 .mu.m. When a light beam 107 enters at an
incident angle of about .theta.=50.degree. or more, it leaks as
stray light to an adjacent pixel.
[0072] As shown in FIG. 5 which is a sectional view of R and Gr, a
wiring line 101b exists in addition to the same wiring lines as
those in FIG. 4 and a wiring line 101a of the wiring layer 101.
This structure makes it difficult to leak an incident light beam as
stray light to an adjacent pixel. Under the condition of FIG. 5,
when the wiring line 101b is extended from the end of a pixel to
above a photoelectric conversion element by about 1.15 .mu.m, the
quantity of light of about .theta.=50.degree. or more leaking to an
adjacent pixel can be decreased.
[0073] From this relationship, the area of an aperture formed by
the wiring layer above the photoelectric conversion element becomes
relatively large in Gb and B pixels. When light enters at a large
incident angle, the ratio at which the light is captured as stray
light increases. The mixture of colors between Gr and B pixels
becomes greater than that between R and Gr pixels. Although the B
output is multiplied by gain and emphasized, the gain for B is
smaller than that for R, suppressing the degree of degradation of
the image quality. Hence, degradation of the image quality by light
entering at an unexpectedly large incident angle can be
reduced.
[0074] The manufacturing yield can also be increased by decreasing
the wiring area as shown in FIG. 3.
[0075] It should be noted that, when the magnitude relationship
between R and B gains is reversed, pixels along which wiring lines
are arranged are changed to Gb and B, satisfying the same
relationship of the mixture of colors as the above-described one.
Similarly, the gain in the subsequent stage is set to R>G>B,
but even if the order changes, the same effects can be achieved by
increasing the aperture area of a pixel having a smaller gain.
SECOND WORKING EXAMPLE
[0076] The second working example of the present invention will be
explained.
[0077] In the second working example, a pixel having the largest
aperture area above a photoelectric conversion element is a pixel
corresponding to the shortest wavelength. In this case, such a
pixel is a pixel using the B color filter. This is because the
visual characteristic of a human eye is more sensitive to R than B.
When light enters at an acute angle, a large aperture area of B
promotes the mixture of colors. When the image is developed upon
multiplying the output by a gain which is set in accordance with
general incident light to adjust white balance, the image becomes
bluish. However, degradation of the bluish image is less
conspicuous than that of a reddish image. Even when light enters at
a large incident angle, which is generally not expected,
degradation of the image quality can be suppressed.
THIRD WORKING EXAMPLE
[0078] The third working example of the present invention will be
explained with reference to FIG. 6. FIG. 6 is a plan view showing
the layout of an image sensing apparatus according to the third
working example of the present invention.
[0079] FIG. 6 is a plan view in consideration of optical mixture of
colors in the vertical direction (column direction) of a Bayer
array (pixel array). The "vertical direction" corresponds to the
short side direction (column direction) of a rectangular image
sensing region (pixel array). At this time, the gain in a
subsequent stage is set to be largest for R, and decreases in the
order of G and B. Similar to the first working example, the B pixel
has a large aperture area and suffers serious mixture of colors
owing to stray light. However, a gain for the signal of the B pixel
in the subsequent signal processing unit is small, so fluctuation
(poor white balance) of the influence of stray light on an image
signal are reduced. The manufacturing yield can also be increased
by decreasing the wiring area as shown in FIG. 6.
FOURTH WORKING EXAMPLE
[0080] The fourth working example of the present invention will be
explained with reference to FIG. 7. FIG. 7 is a plan view showing
the layout of an image sensing apparatus according to the fourth
working example of the present invention.
[0081] In the fourth working example, an R pixel is a pixel having
a small-area aperture formed by wiring lines (a lowermost wiring
layer 101 in a wiring pattern LP) closest to an N-type region 112
(see FIG. 4) of a photoelectric conversion element. In the pixel,
the area of an aperture area formed by wiring lines (the lowermost
wiring layer 101 in the wiring pattern LP) closest to the
photoelectric conversion element (the N-type region 112) determines
whether to photoelectrically convert light entering at an acute
angle. Degradation of the image quality can be reduced by
decreasing the aperture area of R which stands out upon
development.
FIFTH WORKING EXAMPLE
[0082] The fifth working example of the present invention will be
explained with reference to FIG. 8. FIG. 8 is a sectional view
showing the sectional structure of an image sensing apparatus
according to the fifth working example of the present invention.
FIG. 8 is a sectional view taken along a line c-c' in FIG. 7.
[0083] In the fifth working example, the aperture area of only a Gb
pixel is increased without increasing that of a B pixel. Reference
numeral 116 denotes a locus of a light beam which enters a pixel
adjacent to one that receives a light beam 107. A wiring line 101b
exists on only the B side among the Gb and B pixels. A light beam
such as the light beam 107 leaks from the Gb pixel to the adjacent
B pixel. To the contrary, a light beam as indicated by the locus
116 does not leak to an adjacent pixel. Even if light enters at an
acute angle (large incident angle) .theta., an image can be
prevented from becoming reddish, reducing degradation of the image
quality.
SIXTH WORKING EXAMPLE
[0084] The sixth working example of the present invention will be
explained with reference to FIGS. 9 and 10. FIG. 9 is a plan view
showing the layout of an image sensing apparatus under design
according to the sixth working example of the present invention.
FIG. 10 is a plan view showing the layout of the image sensing
apparatus according to the sixth working example of the present
invention.
[0085] In the sixth working example, the influence of mixture of
colors when light enters at an acute angle is reduced by arranging
a dummy wiring line for a Gb pixel in a layout in which a pixel
does not share a wiring line with an adjacent pixel. When each
pixel includes one amplification transistor, all pixels have the
same layout as shown in FIG. 9. For descriptive convenience, a
wiring layer 103 is not hatched in FIG. 9. In FIG. 9, wiring lines
117 and 118 are used to connect a P- or N-type diffusion region to
the wiring layer 103 in order to apply a given voltage to the
diffusion region. When sharing the diffusion region between
adjacent pixels, the wiring line 117 or 118 suffices to be formed
on only one side.
[0086] After determining the layout as shown in FIG. 9, dummy
wiring lines 119 are arranged in pixels except for Gb pixels as
shown in FIG. 10. This causes great mixture of colors from the Gb
pixel to the B pixel when light enters at a large incident angle
which is an acute angle with respect to the surface. As a result,
an image can be prevented from becoming reddish owing to
fluctuation (poor white balance) of the influence of stray light on
an image signal between colors, reducing degradation of the image
quality.
[0087] While the present invention has been described with
reference to exemplary embodiment or working examples, it is to be
understood that the invention is not limited to the disclosed
exemplary embodiment or working examples. The scope of the
following claims is to be accorded the broadest interpretation so
as to encompass all such modifications and equivalent structures
and functions.
[0088] This application claims the benefit of Japanese Patent
Application No. 2008-051120, filed Feb. 29, 2008, which is hereby
incorporated by reference herein in its entirety.
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