Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-11-26
2004-02-10
Jackson, Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S223000, C257S229000, C257S432000, C257S435000, C348S273000, C348S340000
Reexamination Certificate
active
06690049
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid-state image sensor having a function of decreasing a shading amount, a production method for the solid-state image sensor, and a digital camera using the solid-state image sensor, and particularly to a solid-state image sensor wherein micro-lenses are placed on the photodetecting cells belonging to the incident side, the production method of the solid-state image sensor, and a digital camera using the solid-state image sensor.
2. Description of the Related Art
Recently, video cameras and digital cameras have become wide-spread in general. CCD-type or MOS-type solid-state image sensors are used in these cameras. In such solid-state image sensors, a plurality of photodetecting cells having a light-receiving part (a photoelectric converter) are arranged to form a matrix. The energy of the light incident to each photodetecting cell undergoes photoelectric conversion in the light-receiving part, generating a signal charge. The generated signal charge is outputted to the external parts, via a CCD and a signal channel.
As shown in
FIG. 32
, a CCD-type solid-state image sensor
10
of the related art has a photodetecting cell
13
having a light-receiving part
2
, a vertical CCD
15
and a horizontal CCD
16
constituting the light-receiving part
2
for transferring signal charges, and an output amplifier
17
.
Among the photodetecting cells placed in the light receiving area (the area to which the light is incident) of the solid-state image sensor
10
, there are valid cells wherein the energy of the light, incident to the light-receiving part
2
, undergoes a photoelectric conversion into a signal charge for outputting said signal charge, and there are photodetecting cells for outputting dark currents without photoelectric conversion.
A photodetecting cell which outputs dark currents is known, for instance as a black dummy. Such a photodetecting cell has an incident side which is shielded from the light, and is generally placed in one row and/or one column surrounding the valid cell area wherein a plurality of valid cells are arranged to form a matrix, or in a row at the extremity of any side of the valid cell area where a plurality of valid cells are arranged to form a matrix.
In addition, the solid-state image sensor
10
is equipped with a light-blocking layer such that the light is only incident to the light-receiving part
2
of the valid cells, and with signal driving channels for applying voltage to CCD electrodes, not shown in FIG.
32
.
In addition, color filters are placed above each light-receiving part, for taking color pictures with the solid-state image sensor
10
.
FIG. 33
is a layout view showing an example of an array of color filters. The plurality of color filters together forms a layer. R, G and B represent red, green and blue filters, respectively. One of the R, G or B filters is placed above the light-receiving part
2
.
In addition, to improve the converging power, a micro-lens is sometimes placed above each light-receiving part
2
.
FIG. 34
is a cross-sectional view showing the structure of a photodetecting cell of the solid-state image sensor
10
of the related art.
In the above-mentioned solid-state image sensor
10
, the light-receiving part
2
is formed on top of the semiconductor substrate
1
(for example a silicon substrate), a light blocking layer
9
with apertures
8
is placed on the incident side of the light-receiving part
2
.
Above each light-receiving part
2
, one of the R, G and B color filter
4
is placed in an on-chip fashion. In addition, a micro-lens
7
for improving the converging power is placed immediately above the light-receiving part
2
, via a flattening layer
6
.
In fact, in such a solid-state image sensor
10
, a phenomenon called shading is known which gives rise to sensitivity fluctuations in the valid cell area.
Shading originates from the fact that incident lights incident to the peripheral part of the valid cell area, when compared to incident lights incident to the central part of the valid cell area, have incidences which are oblique. In other words, when the light is obliquely incident, it generates eclipses and a degradation of the photoelectric conversion rate at the level of the light-receiving part
2
.
In this case, since the quantity of incident lights in the central part of the valid cell area is greater, for the same quantity of incident lights, the output signal is greater for the photodetecting cells of the central part when compared to the photodetecting cells of the peripheral part. Therefore, a “sensitivity fluctuation” is generated between the photodetecting cells of the central part and the photodetecting cells of the peripheral part. Also, in this document, the “sensitivity fluctuation (or the difference in the output value)” is called the shading amount. The shading amount increases when the number of photodetecting cells increases, and the size of the valid cell area increases.
FIG. 35
shows an example of results obtained when the shading amount is measured for a solid-state image sensor.
The measurements of the shading amount shown in
FIG. 35
have been obtained by measuring the output of a valid cell area, whose size was 25.1 mm in the horizontal direction and 16.9 mm in the vertical direction.
In the drawing, &Dgr;
0
is the G output voltage of the central part (sensitivity, equivalent to the actual aperture rate), &Circlesolid; is the calculated value for the latter, X is the actual measurement of the G output voltage for the peripheral part, and □ is the calculated value of the latter.
From this figure, it is clear that the shading amount between the central part and the peripheral part depends on the F number of the digital camera, the result of which is displayed as the difference in the G output voltage (sensitivity).
A so-called “micro-lens positional offsetting” method, wherein the center of micro-lens belonging to the peripheral part is moved towards the central part of the valid cell area, taking the center of the corresponding light-receiving part as the reference, and a method wherein the aperture width of the light blocking layer is larger the closer to the periphery it is, taking the center of the corresponding light-receiving part as the reference, have been proposed as methods for decreasing such shading amounts.
Of these, the “micro-lens positional offsetting” is publicly known, for instance, as disclosed in Japanese patent No. 2600250.
In the “micro-lens positional offsetting”, as shown in
FIG. 36
, the center of a micro-lens
27
installed above a light-receiving part (for example a photovoltaic such as a photodiode)
22
, is matched with the center of a light-receiving part
22
(double-broken lines in the drawing) in case the light-receiving part belongs to the central part
21
A of the valid cell area
21
, and offset by a specified distance d
1
towards the central part of the valid cell area
21
, in case the light-receiving part belongs to the peripheral part
21
E of the valid cell area.
The specified distance d
1
is defined so it becomes greater at a constant rate, the further from the center
21
X of the solid-state image sensor
20
. In addition, optimal values are determined for the specified distance d
1
, taking into consideration the characteristics of the camera lenses and the solid-state image sensor
20
actually used. In addition, in the drawing, numeral
23
is an inter-level isolation layer, numeral
24
is a color filter and numeral
26
is a flattening layer.
The “micro-lens positional offsetting” shading countermeasure mentioned above has been recognized to be effective to some extent, but it is still not sufficient. The reasons are explained concretely in the following.
First, the above-mentioned shading countermeasure has the problem of not taking into account the solid-state image sensors wherein color filters are placed on the incident side, thereby generating color shading due to said color filters. Color shading designates the offset of c
Ohkouchi Naoki
Suzuki Satoshi
Gilster Peter S.
Greensfelder Hemker & Gale, P.C.
Jackson Jerome
Nikon Corporation
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