Solid-state image pickup device, with purposefully displaced color filters, method of manufacturing same and camera incorporating same

The displacement amount of a color filter which is displaced with respect to an opening of a light-shielding film along the surface of a substrate increases as the distance from the substantial center of an image pickup region to the opening of the light-shielding film increases, and the height from the surface of the substrate to the substantial center in the direction of thickness of the color filter increases. For this reason, whole light incident on the sensor of each pixel can pass through only a corresponding color filter and also pass through the entire thickness of the color filter. Even when the thickness or height of the color filter changes in units of pixels, a high-quality image having no color irregularity can be obtained.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a solid-state image pickup device having a 
plurality of color filters corresponding to a plurality of pixels, a 
method of manufacturing the same and a camera having this solid-state 
image pickup device. 
2. Description of the Related Art 
FIG. 1 is a plan view of an entire CCD solid-state image pickup device of 
an interline transfer type. A chip 11 of this CCD solid-state image pickup 
device has an image pickup region 12 formed by arraying a plurality of 
pixels. FIG. 2 schematically shows a camera using the chip 11. In this 
camera, the image of light from a target object is formed in the image 
pickup region 12 of the chip 11 through an optical system 14 including a 
lens 13. The chip 11 of the CCD solid-state image pickup device is driven 
by a driving system 15 including a timing generator. The output signal 
from the chip 11 is converted into an image signal through various signal 
processing operations in a signal processing system 16. FIG. 3 is an 
enlarged view of a portion of the camera near the chip 11 and the optical 
system 14. 
FIGS. 4A to 5B show a CCD solid-state image pickup device having an on-chip 
color filter for a complementary color system according to the first 
related art of the present invention. 
FIGS. 4A and 5A show a central portion 12a of the image pickup region 12. 
FIGS. 4B and 5B show a peripheral portion 12b of the image pickup region 
12. In this first related art, a p-type well 22 is formed in an Si 
substrate 21. A p-type region 23 as a hole accumulated region and an 
n-type region 24 closer to the surface of the Si substrate 21 than the 
p-type well 22 constitute a sensor 25. 
A p-type region 26 adjacent to the sensor 25 serves as a read out portion, 
and an n-type region 27 adjacent to the p-type region 26 serves as a 
vertical transfer portion. A p-type well 31 is formed under the n-type 
region 27. A p-type region 32 adjacent to the n-type region 27 serves as a 
pixel separation portion. An SiO.sub.2 film 33 as a gate insulating film 
is formed on the surface of the Si substrate 21. A polysilicon film 34 on 
the Si substrate 21 forms a transfer electrode. 
The polysilicon film 34 is covered with an SiO.sub.2 film 35 or the like as 
an insulating film. The Si substrate 21 and the SiO.sub.2 film 35 are 
covered with an SiO.sub.2 film 36 as a passivation film. A light-shielding 
film 37 consisting of an Al film, a W film or the like is formed on the 
SiO.sub.2 film 36. An opening 37a corresponding to the sensor 25 is formed 
in the light-shielding film 37. 
The light-shielding film 37 and so on are covered with an SiN or SiO film 
41 as a passivation film. A planarizing film 42 is formed on the SiN or 
SiO film 41. A red filter 43a, a blue filter 43b and a yellow filter 43c 
on the planarizing film 42 are patterned into a checkerboard pattern 
corresponding to pixels, which constitute an on-chip color filter 43. 
The on-chip color filter 43 of this first related art is used for a 
complementary system, so the blue filter 43b and the yellow filter 43c are 
stacked to form a green filter, as shown in FIGS. 4A and 4B. A planarizing 
film 44 and an on-chip lens 45 are sequentially formed on the on-chip 
color filter 43. 
FIGS. 6A and 6B show a CCD solid-state image pickup device having an 
on-chip color filter for a primary color system according to the second 
related art of the present invention. The second related art substantially 
has the same arrangement as that of the first related art shown in FIGS. 
4A to 5B except that the on-chip color filter 43 has a single-layer 
structure. 
When the exit pupil of the lens 13 of the camera shown in FIGS. 2 and 3 is 
close to the chip 11, light 46 is incident on the on-chip lens 45 at the 
central portion 12a of the image pickup region 12 almost in parallel to 
the optical axis of the on-chip lens 45, as shown in FIGS. 4A and 6A. At 
the peripheral portion 12b of the image pickup region 12, however, the 
light 46 is incident on the on-chip lens 45 obliquely with respect to the 
optical axis of the on-chip lens 45, as shown in FIGS. 4B and 6B. 
For this reason, in the first and second related arts, the optical axis of 
the on-chip lens 45 is made to match the center of the opening 37a of the 
light-shielding film 37 at the central portion 12a of the image pickup 
region 12, as shown in FIG. 5A, although the displacement amount between 
the optical axis of the on-chip lens 45 and the center of the opening 37a 
of the light-shielding film 37 is increased toward the peripheral portion 
12b, as shown in FIG. 5B. 
As is apparent from FIGS. 4B and 6B, the ratio of the light 46 which is 
focused by the on-chip lens 45 and made incident on the sensor 25 of each 
pixel is high even at the peripheral portion 12b. Therefore, shading due 
to the incident angle of the light 46, i.e., a phenomenon that the 
sensitivity gradually changes from the central portion to the peripheral 
portion on the image pickup output screen is suppressed. 
Recently, the displacement amount between the on-chip lens 45 and the 
opening 37a at the peripheral portion 12b is increasing along with a 
reduction of the effective size of an optical system. When the exit pupil 
distance of a lens is 3 mm, the incident angle of the light 46 is about 
50.degree. and the displacement amount of the on-chip lens 45 almost 
reaches 1/2 the pixel pitch. 
However, in the first and second related arts, the center of the on-chip 
color filter 43 of each pixel matches the center of the opening 37a even 
at the peripheral portion 12b, as shown in FIGS. 4B and 6B. 
As is apparent from FIGS. 4B and 6B, the light 46 incident on the sensor 25 
of each pixel passes through the on-chip color filter 43 of an adjacent 
pixel, resulting in a mixed color, or the light 46 passes through only 
part of the thickness of the on-chip color filter 43 of the pixel, 
resulting in a deviation of the spectral characteristics from desired 
characteristics. For this reason, in the first and second related arts, a 
high-quality image having no color irregularity can hardly be obtained. 
To prevent color irregularity, displacement of the on-chip color filter 43 
of each pixel from the opening 37a has also been examined. In this case, 
however, only the distance from the central portion 12a of the image 
pickup region 12 to the opening 37a of each pixel is taken into 
consideration, and the thickness of the on-chip color filter 43 or the 
height from the surface of the Si substrate 21 is not taken into 
consideration. For this reason, it is still difficult to obtain a 
high-quality image having no color irregularity. 
SUMMARY OF THE INVENTION 
According to a solid-state image pickup device, a method of manufacturing 
the device and a camera having the device of the present invention, the 
displacement amount of a color filter with respect to an opening of a 
light-shielding film is determined in accordance with both the distance 
from the substantial center of an image pickup region and the height from 
the surface of a substrate. For this reason, even when the thickness or 
height of the color filter changes in units of pixels, and light is 
incident through a lens having a short exit pupil distance, the whole 
light incident on the sensor of each pixel can pass through only a color 
filter corresponding to the pixel and can pass through the entire 
thickness of the color filter. Therefore, a high-quality image having no 
color irregularity can be obtained. 
Even when the color filter has a multilayer structure, the whole light 
incident on the sensor of each pixel can readily pass through only a color 
filter corresponding to the pixel and can pass through the entire 
thickness of the color filter as far as the upper layer portion and the 
lower layer portion of the color filter have different displacement 
amounts with respect to the opening of the light-shielding film. 
Therefore, a high-quality image having no color irregularity can be easily 
obtained. 
Even when the color filter has a single-layer structure in which the 
thickness of the color filter changes in units of colors, the whole light 
incident on the sensor of each pixel can pass through only a color filter 
corresponding to the pixel and can pass through the entire thickness of 
the color filter. Therefore, a high-quality image having no color 
irregularity can be obtained.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The first to third embodiments of the present invention applied to a CCD 
solid-state image pickup device of an interline transfer type and a camera 
having the CCD solid-state image pickup device will be described below 
with reference to FIGS. 7A to 11B. The first to third embodiments have the 
same arrangement as in FIG. 1 as a whole. 
FIGS. 7A to 8C show the first embodiment having an on-chip color filter for 
a complementary color system. The first embodiment substantially has the 
same arrangement as that of the first related art shown in FIGS. 4A to 5B, 
so the optical axis of an on-chip lens 45 matches the center of an opening 
37a of a light-shielding film 37 at a central portion 12a of an image 
pickup region 12, as shown in FIGS. 7A and 8A. 
In the first embodiment, however, at a peripheral portion 12b of the image 
pickup region 12, not only the optical axis of the on-chip lens 45 but 
also the substantial center of an on-chip color filter 43 is displaced 
from the substantial center of the opening 37a of the light-shielding film 
37, as shown in FIGS. 7B and 8B. The on-chip color filter 43 is displaced 
in the same direction as the displacement direction of the on-chip lens 45 
although the displacement amount is smaller than that of the on-chip lens 
45. The displacement amount of the on-chip color filter 43 corresponds to 
the distance from the substantial center of the opening 37a to the 
substantial center of the on-chip color filter 43 along the surface of the 
Si substrate 21. 
These displacement amounts increase toward the peripheral portion 12b. The 
displacement direction at a peripheral portion on an opposite side of the 
peripheral portion 12b of the image pickup region 12 is reverse to that at 
the peripheral portion 12b. The displacement direction at a corner portion 
12c of the image pickup region 12 shown in FIG. 1 is not a one-dimensional 
direction as in FIG. 8B but a two-dimensional direction, as shown in FIG. 
8C. 
In FIGS. 7B, 8B and 8C, and in the second and third embodiments to be 
described later, the on-chip lens 45 and the on-chip color filter 43 are 
displaced by a uniform amount near the peripheral portion 12b and the 
corner portion 12c for the illustrative convenience. In fact, the 
displacement amount is determined in accordance with both the distance 
from the substantial center of the image pickup region 12 to the opening 
37a of each pixel and the height from the surface of the Si substrate 21 
to the substantial center in the direction of thickness of the on-chip 
color filter 43, so the displacement amount of a high on-chip color filter 
43 is large. 
More specifically, as the absolute value of the exit pupil distance 
decreases, the incident angle of light 46 incident on the peripheral 
portion 12b of the image pickup region 12 increases, as shown in FIG. 9A. 
However, as the absolute value of the exit pupil distance decreases, and 
the height from the surface of the Si substrate 21 to the substantial 
center in the direction of thickness of the on-chip color filter 43 
increases, the displacement amount of the on-chip color filter 43 becomes 
large, as shown in FIGS. 9B and 9C. 
More specifically, a normal camera has an exit pupil distance of about -20 
mm. In the first embodiment, if the exit pupil distance is, e.g., -3 mm, 
and the incident angle of the light 46 is large, the displacement amount 
of the on-chip color filter 43 is increased. Therefore, a high-quality 
image can be obtained even with a camera such as an endoscope having a 
short exit pupil distance. 
As is apparent from FIG. 9B, the height of the on-chip color filter 43 is 
substantially proportional to its displacement amount. As a specific value 
of the displacement amount of the on-chip color filter 43, a median value 
between a displacement amount of zero and the displacement amount of the 
on-chip lens 45 is employed to most effectively guide the light 46 focused 
by the on-chip lens 45 to a sensor 25. 
The on-chip color filter 43 can be formed by a conventionally known 
technique of dying casein or gelatin or patterning a photosensitive 
material mixed with coloring agents. The on-chip lens 45 can also be 
formed by a conventionally known technique. 
In the above-described first embodiment, the light 46 incident on the 
sensor 25 of each pixel is prevented from passing through the on-chip 
color filter 43 of an adjacent pixel, and simultaneously, the light 46 is 
prevented from passing through only part of the thickness of the on-chip 
color filter 43 of the pixel, as is apparent from FIG. 7B, so a 
high-quality image having no color irregularity can be obtained. 
FIG. 10 shows a peripheral portion 12b of an image pickup region 12, which 
is shown in FIG. 1, of the second embodiment having an on-chip color 
filter for a complementary color system. The second embodiment 
substantially has the same arrangement as that of the first embodiment 
shown in FIGS. 7A to 8C except that a blue filter 43b and a yellow filter 
43c which constitute a green filter have different displacement amounts, 
and the displacement amount of the yellow filter 43c on the upper side is 
larger than that of the blue filter 43b on the lower side. 
In the second embodiment, the displacement amounts of the blue filter 43b 
and the yellow filter 43c can be independently determined. For this 
reason, it is easier than in the first embodiment to prevent light 46 
incident on a sensor 25 of each pixel from passing through an on-chip 
color filter 43 of an adjacent pixel or prevent the light 46 from passing 
through only part of the thickness of the on-chip color filter 43 of the 
pixel, as is apparent from FIG. 10. 
FIGS. 11A and 11B show the third embodiment having an on-chip color filter 
for a primary color system. The third embodiment also has the same 
arrangement as that of the first embodiment shown in FIGS. 7A to 8C except 
that an on-chip color filter 43 has a single-layer structure. 
In the above first to third embodiments, the height from the surface of the 
Si substrate 21 to the lower surface of the on-chip color filter 43 is 
equal for all pixels because of a planarizing film 42. Even when this 
height changes in units of pixels due to some reason, the displacement 
amount of the on-chip color filter 43 is determined in accordance with the 
height from the surface of the Si substrate 21 to the substantial center 
in the direction of thickness of the on-chip color filter 43, so a 
high-quality image having no color irregularity can be obtained. 
In the first to third embodiments, as is apparent from a comparison of the 
position of the peripheral portion 12b of the image pickup region 12 
between FIG. 7B and FIG. 1, the on-chip color filter 43 is displaced along 
a direction from the substantial center of the opening 37a of the 
light-shielding film 37 to the central portion 12a of the image pickup 
region 12. 
However, when the size of the lens of, e.g., a video camera is much larger 
than that of the image pickup region 12, and the lens is mounted close to 
a chip 11, i.e., when the lens has a positive exit pupil, the on-chip 
color filter 43 may be displaced in a direction reverse to that in the 
first to third embodiments.