JPH08288493A - Color solid-state image pickup device - Google Patents

Abstract

PURPOSE: To provide a color solid-state image pickup device which can reduce white flaw while ensuring blooming resistance. CONSTITUTION: In a color solid-state image pickup device wherein a color of a processing object differs in a picture element unit or a substrate unit, a potential profile in a substrate depth direction of a sensor part 15 is made different in a picture unit or a chip unit corresponding to a color by changing a concentration of N-type impurities forming a signal charge storage layer 14, for example.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device,
In particular, the present invention relates to a color solid-state imaging device in which a color to be processed is different for each pixel or each substrate (chip).

[0002]

2. Description of the Related Art In a solid-state image pickup device, one of image defects
The challenge is to achieve both suppression of white scratches and ensuring blooming resistance. Here, the white defect is an image defect that appears as a white defect on the reproduction screen due to local dark current unevenness. The dark current, which causes the white defects, is more likely to be generated as the potential of the sensor portion becomes deeper. On the other hand, blooming is
This is a phenomenon in which, when strong light is incident, the sensor unit is saturated, signal charges overflow and enter the vertical charge transfer unit and the like, and a white portion spreads around the sensor unit. This phenomenon easily occurs as the potential of the sensor unit becomes shallower.

[0003]

By the way, in a single-plate type color solid-state image pickup device, for example, G (green) checkered R (red)
Since the color filters of the B (blue) line sequential arrangement are arranged, the color to be processed is different for each pixel, and G of the three primary colors is
Since the sensitivity is highest, the potential of each sensor unit is made to be equal among the pixels based on the G pixel. However, if the sensor potentials of all the pixels are made equal, white flaws, which are likely to occur due to the deeper sensor potential, will occur at the same probability for all the pixels, and thus the defect-free yield becomes a problem. Was becoming. On the other hand, if the sensor potential is made shallow in order to reduce the occurrence of white scratches, there is a problem that blooming resistance cannot be ensured.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a color solid-state image pickup device capable of reducing white scratches while ensuring blooming resistance. .

[0005]

According to the present invention, a sensor is provided in a single-plate color solid-state image pickup device in which a color to be processed is different for each pixel or in a multi-plate color solid-state image pickup device in which a color to be processed is different for each substrate (chip). The potential profile in the substrate depth direction of each part is different for each pixel or each substrate depending on the color.

[0006]

In the color solid-state image pickup device having the above-described structure, when the same incident light amount is considered, the pixel (or chip) of a color with low sensitivity is better than the pixel (or chip) of a color with high sensitivity. The amount of signal charges photoelectrically converted and accumulated in the sensor unit is small. Therefore, by making the potential of the sensor portion in the substrate depth direction shallower for the pixel (or chip) of the color having low sensitivity, the potential for the occurrence of the white defect is caused by making it shallower than the pixel (or chip) of the color having high sensitivity. It is possible to suppress the generation of a dark current, which does not impair the blooming resistance.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a sectional view of a unit cell of a color solid-state imaging device according to the present invention. In FIG. 1, on the surface side of the P well 12 on the N-type semiconductor substrate 11,
The hole storage layer 13 made of P ⁺ -type impurities is formed, and the signal charge storage layer 14 made of N-type impurities is formed under the hole storage layer 13, whereby the sensor unit 15 having a HAD (Hole Accumulated Diode) structure is formed. There is. The sensor unit 15 is two-dimensionally arrayed on the substrate 11, photoelectrically converts incident light into signal charge having a charge amount corresponding to the light amount, and stores the signal charge in the signal charge storage layer 14. A signal charge transfer region 17 made of N-type impurities is formed on the surface side of the P well 12 with the channel region 16 interposed therebetween.

Above the channel region 16 and the signal charge transfer region 17, a transfer electrode 1 made of polysilicon is formed.
8 are arranged via an insulating layer 19 made of a silicon oxide film (SiO ₂ ). The channel region 16 and a part of the transfer electrode 18 on the channel region 16 constitute a read gate unit 20 that reads out the signal charges accumulated in the sensor unit 15. The signal charge transfer region 17 and the transfer electrode 18 thereon form A vertical charge transfer unit 21 that vertically transfers the signal charges read by the read gate unit 20 is configured. The insulating layer 10 is covered with a light-shielding film 22 such as aluminum (Al) except for the sensor portion 15.

FIG. 2 shows the potential distribution from A to B in FIG. 1 in the direction parallel to the surface and the potential distribution from B to C in the substrate depth direction. In the figure, the solid line a
The potential distribution of is a state in which signal charges are accumulated in the sensor unit 15. When the amount of light incident on the sensor unit 15 increases and exceeds a certain amount of light, signal charges cross the barrier in the depth direction of the substrate, and overflow to the substrate 11 starts.
A substrate voltage Vsub. Applied to the substrate 11 so that a saturation signal amount set for each CCD chip (device) can be obtained under a determined light amount. Set the voltage value of.

Here, in order to secure the blooming resistance, that is, in order to prevent signal charges from entering the vertical charge transfer portion 21 and the like when the sensor portion 15 is saturated by the incidence of strong light, the substrate depth is set. Barrier height h1
Is limited to be lower than the barrier height h2 of the front side read gate section 20. Under this condition, if the sensor potential is increased, the read voltage applied when reading the signal charges from the sensor unit 15,
When the signal charge is swept to the substrate 11, the substrate voltage Vsu
b. Shutter voltage ΔVsub. It becomes necessary to increase the voltage value of.

The potential distribution when the signal charge is read from the sensor unit 15 to the vertical charge transfer unit 21 is indicated by a chain double-dashed line b in FIG. 2, and the potential distribution when the signal charge is swept away from the sensor unit 15 to the substrate 11 is shown. 2 is indicated by a dotted line c. Further, if the sensor potential is deepened, the frequency of occurrence of white scratches will increase. FIG. 3 shows the relationship between the number of white defects generated per chip and the sensor potential in a CCD chip having a certain number of effective pixels. As is clear from the figure, the number of white scratches increases as the sensor potential becomes deeper.

Considering the case where the CCD chip having the above-mentioned configuration is applied to a single-plate color solid-state image pickup device, for example, a color filter 41 having a G checkered R / B line sequential arrangement (Bayer arrangement) as shown in FIG. It will be arranged on each sensor unit 15 on-chip. In this single-plate type color solid-state imaging device, the sensitivity for each color is as shown in FIG. 5, though it depends on the thickness of the color filter layer. That is, among the three primary colors R, G, and B of light, G has the highest sensitivity, R has the second highest sensitivity, and B has the lowest sensitivity. In FIG. 5, the sensitivity ratios R / G = 0.7 and B / G =
The case of 0.3 is shown.

As is clear from this, the sensor unit 1
Among the colors of the color filters 41 arranged on the color filters 5, the saturation signal charge amount of the color having relatively low sensitivity does not need to be the same as that of the color having the highest sensitivity. The present invention has been made paying attention to this point. That is, in the single-plate color solid-state imaging device in which the color to be processed is different for each pixel, the potential profile in the substrate depth direction is made different for each pixel corresponding to the color. Specifically, the sensor potential of the R pixel is shallower than that of the G pixel, and the sensor potential of the B pixel is shallower than that. The dependency of the output signal (signal amount) on the incident light amount in this case is as shown in FIG.

In order to make the sensor potential different for each pixel on a color-by-pixel basis, for example, the concentration of the N-type impurity forming the signal charge storage layer 14 of the sensor section 15 is set for each color using energy, dose, or heat treatment time as parameters. It can be realized by corresponding changes. Further, in the process of changing the sensor potential for each color, for example, in the case of changing the sensor potential corresponding to three colors, a step of opening only a pixel of a specific color in the resist pattern and ion-implanting N-type impurities is performed. It can be realized by repeating the process once. Therefore, the number of steps is increased as compared with the conventional manufacturing step in which the ion implantation of the N-type impurity is performed once by using the resist pattern in which the sensor portions of all pixels are windowed regardless of the color.

As described above, in the single-plate color solid-state image pickup device in which the color to be processed is different for each pixel, the sensor potential is made to be different for each pixel for each color.
Although the number of manufacturing steps is increased by making the sensor potential for low-sensitivity colors shallow, it is possible to reduce the occurrence of dark current, which causes white defects, for pixels with low-sensitivity colors. Can be reduced. Moreover, as described above, the saturation signal charge amount of the color having relatively low sensitivity does not have to be the same amount as that of the color having the highest sensitivity, and may be small, so that the sensor potential of the color having low sensitivity is made shallow. However, blooming resistance can be secured.

In the above embodiment, when the color filter 41 of the G checkered R / B line sequential arrangement (Bayer arrangement) is used, the sensor potential is set to 3 for each of the three colors.
Although different stages are used, the present invention is not limited to this, and for R and B, a common sensor potential of 2 is set on the basis of the color (R) having a higher sensitivity.
The steps may be different. According to this, although the dark current reduction effect is slightly inferior in the B pixel, which has the lowest sensitivity, the process of ion-implanting the N-type impurity into the sensor unit 15 can be performed only twice, so that compared with the above embodiment. Therefore, the number of processes can be reduced by one (+1 compared to the conventional method).

Further, in the above embodiment, the case where the color filter having the G checkered R / B line sequential arrangement is used has been described, but the present invention is not limited to this, and is shown in FIG. 7, for example. The same applies to the case of using a color arrangement of other colors such as a complementary color checkered arrangement.

Further, in the above-mentioned embodiment, it is described that the present invention is applied to the single-plate type color solid-state image pickup device in which the color to be processed is different for each pixel, but the present invention is not limited to this, and C
It is also applicable to a multi-plate color solid-state imaging device in which the color to be processed is different for each CD chip. For example, in the case of a three-plate color solid-state image pickup device, as shown in FIG. 8, a three-color separation prism 81 is provided in an optical system that takes in incident light to separate the incident light into three primary colors of R, G, and B. , Three CCD chips (solid-state imaging device) 82R, 8 provided corresponding to each color
It is configured to lead to 2G and 82B.

The three-color separating prism 81 is composed of three prism blocks, and B-reflecting (R, G-transmitting) and R-reflecting (G-transmitting) dichroic layers 83a, 83b are provided at the boundaries between the blocks. , The incident light is divided into light of each color. The reflected lights of B and R are reflected again on the respective total reflection surfaces. Then, by arranging CCD chips 82R, 82G, and 82B of the same size at the image forming positions of the lights of the respective colors, R, G, and B signals are derived from the respective outputs.

The color to be processed is different for each chip.
When the present invention is applied to a plate-type color solid-state imaging device,
The sensor potential may be different for each chip. To make the sensor potential different for each chip, in each CCD chip, for example, the sensor unit 1
5 can be realized by changing the concentration of the N-type impurity forming the signal charge storage layer 14 of No. 5 according to the color of the processing target of each chip with the energy, dose amount or heat treatment time as parameters.

As described above, when the present invention is applied to a three-plate color solid-state image pickup device in which the color to be processed is different for each chip,
Since the step of ion-implanting N-type impurities to form the sensor portion 15 is only required once, the color having low sensitivity can be treated with the same number of steps as the conventional manufacturing step, that is, without increasing the number of manufacturing steps. With regard to the CCD chip, it is possible to reduce the occurrence of dark current that causes white defects and reduce the frequency of white defects. Further, even if the sensor potential of the CCD chip for processing a color having low sensitivity is made shallow, the blooming resistance can be ensured for the same reason as in the above embodiment.

In the three-plate color solid-state image pickup device, as described above, three CCD chips are used corresponding to the three primary colors, respectively, and R, G, and B signals are independently obtained. In addition to the above, two CCD chips are used for G, and one CCD chip is used for R and B.
Signal obtained by time division multiplexing (so-called,
Dual-Green method) is also available. In the case of such a three-plate color solid-state image pickup device, CCs for R and B are used.
In the D chip, the color to be processed differs for each pixel.

Therefore, regarding the CCD chips for R and B, as described in the previous embodiment, the sensor potential is set to a common depth between the colors with reference to the color (R) having the higher sensitivity. Alternatively, the sensor potential may be different for each pixel for each color (R, B). This is because the color separation prism is used in the optical system to divide the incident light into G, R, and B, and two CCD chips are arranged at each image forming position for G, R, and B. The same applies to the two-plate color solid-state imaging device.

[0024]

As described above, according to the present invention,
In a color solid-state imaging device in which a color to be processed differs depending on a pixel unit or a substrate unit, by making the potential profile of the sensor unit in the substrate depth direction different on a pixel unit basis or a chip unit basis depending on the color, a white defect may occur. Since it is possible to reduce the generation of dark current, which is a cause of the generation, it is possible to reduce the frequency of occurrence of white scratches and ensure the blooming resistance.

[Brief description of drawings]

FIG. 1 is a sectional view of a unit cell of a color solid-state imaging device according to the present invention.

FIG. 2 is a diagram showing a potential distribution from A to B in FIG. 1 in a direction parallel to a surface and a potential distribution from B to C in a substrate depth direction.

FIG. 3 is a diagram showing the relationship between the number of white scratches generated per chip and the sensor potential.

FIG. 4 is a diagram showing a color arrangement of a color filter of a G checkered R / B line sequential arrangement.

FIG. 5 is a diagram showing dependence of an output signal on an incident light amount according to a conventional example.

FIG. 6 is a diagram showing the dependence of an output signal on the amount of incident light according to the present invention.

FIG. 7 is a diagram showing a color arrangement of a color filter having a complementary color checkered arrangement.

FIG. 8 is a diagram showing an example of a configuration of an optical system of a three-plate color solid-state imaging device.

[Explanation of symbols]

 11 N-type semiconductor substrate 14 Signal charge storage layer 15 Sensor part 20 Read gate part 21 Vertical charge transfer part

Claims (2)

[Claims] 1. A color solid-state imaging device in which a sensor unit for photoelectrically converting incident light is two-dimensionally arranged on a substrate, and a color to be processed is different on a pixel-by-pixel or substrate-by-substrate basis. A color solid-state imaging device characterized in that the potential profile in the vertical direction differs depending on the color in pixel units or substrate units. 2. The color solid-state image pickup device according to claim 1, wherein the impurity concentration of the impurity layer forming the sensor unit is different for each pixel in each pixel or each substrate.