JPH05291554A - Solid-state image sensing element - Google Patents

Abstract

PURPOSE:To promote high density of a pixel by eliminating deviation in each black level between an effective pixel region and an ineffective pixel region and by stabilizing the black level in a dark state and during image sensing of high illuminance subject. CONSTITUTION:Each pixel of an ineffective pixel region for detecting optical black is constituted as follows. A sensor part opening 27 is provided on a sensor part 13. A first P-type well region is not provided for over-flow barrier formation formed in adjacent to the sensor part 13 of each pixel in an effective pixel region for image sensing. That is, the N-type sensor part 13 is formed directly on the N-type silicon substrate 11.

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 sensor,
In particular, the present invention relates to a CCD linear sensor or a CCD image sensor having an effective pixel area for detecting light information of an object and an invalid pixel area for detecting optical black.

[0002]

2. Description of the Related Art Generally, a CCD linear sensor or a CCD image sensor has an effective pixel area for detecting optical information of a subject and an invalid pixel area for detecting optical black. The invalid pixel areas are usually provided at the left and right ends and the upper and lower ends of the effective pixel area.

The structure of each pixel in the conventional effective pixel area and ineffective pixel area will be described based on a CCD image sensor (vertical overflow type). First, the pixel structure in the effective pixel area is as shown in FIG. 9A. , N in the first P-type well region 42 on the N-type silicon substrate 41.
A mold sensor portion 43, a vertical register 44, and a P-type channel stopper region 45 are formed.

A P-type positive charge storage region 46 is formed on the surface of the sensor portion 43, and a second P-type well region 47 is formed immediately below the vertical register 44. Further, the vertical register 44 is formed.
A transfer electrode 49 made of a polycrystalline silicon layer is selectively formed on the transfer electrode 49 via a gate insulating film 48, and an Al light shielding film 51 is formed on the transfer electrode 49 via an interlayer insulating film 50.
For example, plasma SiN is formed on the entire surface including the Al light shielding film 51.
The surface protective layer 52 made of a film is formed to form one pixel in the effective pixel area. The P-type region 53 formed between the sensor unit 43 and the vertical register 44 is a read gate.

Further, the Al light shielding layer 51 is provided in the sensor portion 4
3 has been selectively removed by etching, and the light L
Is incident on the sensor section 43 through the sensor section opening 54 formed by this etching removal.

On the other hand, the configuration of each pixel in the invalid pixel region is as shown in FIG. 10A, except that the sensor section opening 54 for light incidence is not provided on the sensor section 43, as shown in FIG. 9A.
This is the same as the pixel configuration in the effective pixel area indicated by.
In FIG. 10A, the same symbols are given to those corresponding to FIG. 9A.

Therefore, the potential distributions in the vertical direction in the effective pixel region and the invalid pixel region are shown in FIGS. 9B and 10.
As shown in B, the overflow barrier OFB by the first P-type well region 42 is formed adjacent to the sensor portion 43.

Next, a horizontal overflow type CCD
As shown in FIGS. 11A and 12A, the configuration of each pixel in the effective pixel region and the invalid pixel region in the image sensor overflows in the lateral direction of the N-type sensor unit 43 formed on the P-type silicon substrate 61. An N-type overflow drain region 63 is formed via a control P-type gate region 62, and a sensor section opening 54 for light incidence on the sensor section 43 is formed in each pixel of the effective pixel area. Each pixel in the pixel area has an A on the sensor unit 43.
The 1 light-shielding film 51 is formed to block the light L from entering the sensor unit 43. Note that, in FIGS. 11A and 12A, the same symbols are given to those corresponding to FIG. 9A.

Therefore, as shown in FIGS. 11B and 12B, the electrostatic potential distribution in the horizontal direction in the effective pixel region and the invalid pixel region is such that the overflow barrier OFB due to the P-type gate region 62 is adjacent to the sensor unit 43. It has a formed shape.

[0010]

By the way, the above-mentioned CCD
Hydrogen annealing is performed in the process of manufacturing the image sensor. This hydrogen anneal is performed in order to reduce the interface state between the vertical register 44 and the sensor unit 43 and reduce the dark current to a practical level. The effect of reducing the interface state by this hydrogen annealing treatment is generally called the hydrogen annealing effect.

Particularly, in the effective pixel region, a large amount of hydrogen ions easily diffuse from the surface protective layer (plasma SiN film) 52 to the silicon substrate 41 (or 61) side.
The dark current level is sufficiently reduced. However, in the invalid pixel area, the Al light shielding film 51 is laminated on the sensor portion 43, so that hydrogen diffusion from the surface protection layer 52 is not easily performed, and the dark current level is not reduced as much as the effective pixel area. ..

As a result, a black level shift occurs between the effective pixel area and the invalid pixel area. In the signal processing in the subsequent stage, since the signal processing is performed with the black level in the invalid pixel region as a reference, there is a problem in that black floats on the white side in the actual reproduced image and the gradation accuracy becomes rough.

When the strong light L hits the invalid pixel area, the light L passes through the Al light-shielding film 51 and reaches the lower sensor section 43, and as a result, the electric charge e is generated in the sensor section 43. In addition, since the overflow barrier OFB exists adjacent to the sensor unit 43, the generated electric charge e is accumulated in the sensor unit 43.
Because, during the read period, the accumulated charge e
Is read out to the vertical register 44 as it is, and as a result, the black level is deviated. As a countermeasure against this, a method of increasing the film thickness of the Al light shielding film 51 can be considered, but there is a disadvantage that it cannot cope with the recent high density of pixels.

That is, the width of the sensor section opening 54 is becoming narrower due to the higher density of pixels. In such a situation, if the Al light shielding film 51 is made thick, the sensor section opening 54 is made thicker.
Has a disadvantage that the effective aperture ratio of the sensor unit 43 becomes smaller and the noise (shot noise) due to the fluctuation of the signal charge at the time of low illuminance and the dark noise become larger.

The present invention has been made in view of the above problems, and an object thereof is to capture a dark state and a high-luminance object without any deviation in black level between the effective pixel area and the invalid pixel area. An object of the present invention is to provide a solid-state image sensor which can stabilize the black level at the time and can promote high density of pixels.

[0016]

In the solid-state imaging device of the present invention, a photoelectric conversion region 13 and an opening 27 for light incidence are formed on the photoelectric conversion region 13 and the potential is adjacent to the photoelectric conversion region 13. An effective pixel region 1 in which a large number of imaging pixels having the upper barrier OFB are arranged, a photoelectric conversion region 13, and an opening 27 for light incidence on the photoelectric conversion region 13.
And the ineffective pixel region 2 in which a large number of pixels for optical black detection without the barrier OFB on the potential are arranged next to the photoelectric conversion region 13.

[0017]

According to the above-described configuration of the present invention, the invalid pixel region 2
Since the opening 27 for light incidence is provided in each pixel constituting the above, during the hydrogen annealing treatment in the manufacturing process,
Hydrogen diffusion to each pixel in the invalid pixel area 2 is effective pixel area 1
The dark current level can be reduced to the same level as that of the effective pixel region 1. In addition, the photoelectric conversion region 13
Since the barrier OFB on the potential is not provided adjacent to, the electric charge e generated by the incident light L can be completely swept away.

From the above, it is possible to stabilize the black level in the dark state and at the time of photographing a high-luminance object without causing a deviation in each black level between the effective pixel area 1 and the invalid pixel area 2. it can.

Further, since all the electric charges e generated by the incident light L can be swept away, the film thickness of the light shielding film 25 formed in each pixel can be made thin, and the effective aperture according to the miniaturization design of the pixel can be achieved. It is possible to prevent the rate from decreasing. This leads to promotion of higher pixel density,
High resolution of the reproduced image can be realized.

[0020]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a plan view showing a total pixel image area of a CCD image sensor according to this embodiment.

As shown in the figure, this CCD image sensor has an effective pixel area 1 for detecting light information of an object and an ineffective pixel area 2 for detecting optical black. The illustrated example shows an example in which the invalid pixel regions 2 are provided at the left and right ends and the upper and lower ends of the effective pixel region 1.

Next, the structure of each pixel in the effective pixel region 1 and the invalid pixel region 2 will be described separately for the vertical overflow type (first embodiment) and the horizontal overflow type (second embodiment).

As shown in FIG. 2A, the configuration of each pixel in the effective pixel region 1 of the CCD image sensor according to the first embodiment is such that the N-type is formed in the first P-type well region 12 on the N-type silicon substrate 11. The sensor section 13, the vertical register 14 and the P-type channel stopper region 15 are formed. Further, the P-type positive charge accumulation region 1 is formed on the surface of the sensor unit 13.
6 is formed, and the second P-type well region 17 is formed immediately below the vertical register 14. The P-type region 18 formed between the sensor unit 13 and the vertical register 14 is a read gate.

Then, an oxide film 19 of SiO _{2 is formed on} the entire surface.
And the oxide film 19 is formed on the vertical register 14, the channel stopper region 15 and the read gate 18.
The Si ₃ N ₄ film 20 and the SiO ₂ film 21 are sequentially laminated via the. The vertical register 14, the channel stopper region 15, and the oxide film 19 on the read gate 18, Si ₃ N
_{The four} film 20 and the SiO ₂ film 21 form a gate insulating film 22 having a three-layer structure.

Then, a transfer electrode 23 of a polycrystalline silicon layer is selectively formed on the gate insulating film 22,
An Al light-shielding film 25 is formed on the transfer electrode 23 via an interlayer insulating film 24, and a surface protection layer 26 made of, for example, a plasma SiN film is formed on the entire surface including the Al light-shielding film 25, so that pixels in the effective pixel region 1 are It is configured.

The Al light-shielding film 25 is selectively etched and removed on the sensor portion 13, and the light L is opened by the sensor portion opening 27 formed by this etching and removal.
The light is incident on the inside of the sensor unit 13 through.

The vertical potential distribution of each pixel in the effective pixel region 1 is such that an overflow barrier OFB formed by the first P-type well region 12 is formed adjacent to the sensor portion 13 as shown in FIG. 2B. Has become.

Therefore, the light L that has entered through the sensor opening 27 is p between the sensor 13 and the positive charge accumulation region 16.
n-junction surface and sensor portion 13 and first P-type well region 12
Electrons that are photoelectrically converted at the pn junction surface with
Hole pairs are generated, and among the generated electron-hole pairs, holes are positive charge accumulation region 16 and first P-type well region 12.
The electrons e pass through to the silicon substrate 11 side and are accumulated in the potential well P formed in the sensor unit 13. When the accumulated amount of electrons e exceeds the maximum handled charge amount of the vertical register 14, the excess electrons e are overflow barrier O due to the first P-type well region 12.
It is swept to the silicon substrate 11 side beyond the FB.

On the other hand, the configuration of each pixel in the invalid pixel region 2 is as shown in FIG.
The configuration is the same as that of the pixel in the effective pixel region 1 shown in FIG. 2A, except that is not provided. In this FIG. 3A,
The same reference numerals are given to those corresponding to FIG. 2A. Therefore, each pixel in the invalid pixel area 2 is also provided with the sensor opening 27 for light incidence as in the case of the effective pixel area 1.

As shown in FIG. 3B, the vertical potential distribution of each pixel in the invalid pixel region 2 does not have the overflow barrier OFB (see FIG. 2B) formed next to the sensor portion 13 and faces the silicon substrate 11. And the distribution becomes a downward slope. Therefore, even if the electric charge e is generated in the sensor unit 13 by the light L incident through the sensor unit opening 27, the generated electric charge e is directly discharged to the silicon substrate 11 side.

Therefore, even if the light L is incident on each pixel in the invalid pixel region 2, the signal charge e corresponding to the light L is not accumulated and a stable black level can be obtained. This leads to stabilization of the black level regardless of the amount of incident light.

As described above, according to the first embodiment,
Since the sensor portion opening 27 for light incidence is provided in each pixel forming the invalid pixel region 2, hydrogen diffusion to each pixel of the invalid pixel region 2 is effective pixel region 1 during hydrogen annealing in the manufacturing process. The dark current level can be reduced to the same level as that of the effective pixel region 1.

In addition, each pixel in the invalid pixel area 2 has a first P
The sensor portion 13 is formed without providing the mold well region 12.
Since the overflow barrier OFB is not provided next to the substrate 1, all the charges e generated by the incident light L are transferred to the substrate 1.
Can be swept to the 1 side. From such a thing,
It is possible to stabilize the black level between the effective pixel area 1 and the ineffective pixel area 2 without causing a deviation in each black level, and in a dark state and when capturing a high-luminance object.

Further, as described above, since all the electric charges e generated by the incident light L can be swept away to the substrate 11 side, the Al light shielding film 25 formed in each pixel can be thinned. It is possible to prevent a reduction in the effective aperture ratio due to the pixel miniaturization design. This leads to promotion of high density of pixels, and high resolution of reproduced image can be realized.

Next, some modifications of the first embodiment will be described with reference to FIGS. In these modified examples, the configuration of each pixel in the effective pixel region 1 is the same as that in the first embodiment, and therefore the description thereof is omitted, and the configuration of each pixel in the invalid pixel region 2 will be described exclusively.

FIGS. 4A and 4B show a first modification, which has substantially the same structure as that of the first embodiment,
The difference is that the first P-type well region 12 is formed under the vertical register 14. According to the first modification, the effect of the first embodiment can be obtained, and the smear can be reduced.

5A and 5B show a second modification, which has substantially the same structure as that of the first embodiment,
The difference is that the N-type sensor unit 13 is not formed. This second
According to this modified example, in addition to the effect of the first embodiment, the electric field in the vertical direction becomes weak because the sensor unit 13 is not formed, and as a result, breakdown can be suppressed.

FIGS. 6A and 6B show a third modified example, which has a structure obtained by combining the first modified example and the second modified example. That is, the first P-type well region 12 is formed under the vertical register 14, and the N-type sensor portion 13 is not provided. According to the third modified example, in addition to the effect of the first example, the effect of the first modified example (reduction of smear) and the effect of the second modified example (suppression of breakdown) are obtained. be able to.

Next, the configuration of each pixel, particularly in the invalid pixel area 2 of the second embodiment applied to the horizontal overflow type will be described with reference to FIGS. 7 and 8. still,
Components corresponding to those in FIG. 1 are designated by the same reference numerals.

As shown in FIG. 7A, the configuration of each pixel in the invalid pixel region 2 according to the second embodiment is as shown in FIG. 7A, in the lateral direction of the N type sensor portion 13 formed on the P type silicon substrate 31. An N-type overflow drain region 32 is directly formed without forming a P-type gate region (see reference numeral 62 in FIG. 12) for overflow control. Further, a sensor portion opening 27 for light incidence is formed on the sensor portion 13.

As shown in FIG. 7B, the horizontal potential distribution of each pixel in the invalid pixel region 2 is such that the overflow barrier OFB (shown by a chain double-dashed line) is not formed next to the sensor portion 13 and the direct overflow drain is formed. The potential well DP is formed by the region 32. Therefore, even if the electric charge e is generated in the sensor unit 13 by the light L incident through the sensor unit opening 27, the generated electric charge e remains as it is in the potential well D.
You will get to P.

Also in the second embodiment, as in the first embodiment, each pixel forming the invalid pixel region 2 is provided with the sensor opening 27 for light incidence, so that hydrogen in the manufacturing process is used. During the annealing process, hydrogen diffusion to each pixel in the invalid pixel region 2 is performed similarly to the effective pixel region 1,
The dark current level can be reduced to the same level as the effective pixel region 1.

In addition, the P-type gate region for overflow control is not provided in each pixel of the invalid pixel region 2, and the overflow barrier O is provided next to the sensor unit 13.
Since the FB is not provided, all the charges e generated by the incident light L can be swept to the potential well DP formed by the drain region 32. For this reason, it is possible to stabilize the black level between the effective pixel area 1 and the invalid pixel area 2 without causing a deviation in each black level, and in the dark state and when capturing a high-luminance object.

Further, as described above, since all the charges e generated by the incident light L can be swept to the potential well DP, the Al light shielding film 25 formed in each pixel.
It is possible to reduce the film thickness, and it is possible to prevent a reduction in the effective aperture ratio due to the pixel miniaturization design. This leads to promotion of high density of pixels, and high resolution of reproduced image can be realized.

Next, a modification of the second embodiment will be described with reference to FIG. This modification has almost the same configuration as the second embodiment, but is configured by further increasing the concentration of donor impurities in the sensor section 13. With this configuration, as shown in FIG. 8B, the potential of the sensor unit 13 becomes deeper, and the charge e generated in the sensor unit 13 by the incidence of the light L is increased.
Can be easily extracted into the potential well DP by the overflow drain region 32.

In the above example, the example applied to the CCD image sensor is shown, but the present invention can also be applied to a CCD linear sensor.

[0047]

According to the solid-state image pickup device of the present invention, there is no deviation in each black level between the effective pixel region and the invalid pixel region, and the black level is stabilized in the dark state and when capturing a high-luminance object. It is possible to promote high density of pixels.

[Brief description of drawings]

FIG. 1 is a plan view showing a total pixel image area of a CCD image sensor according to this embodiment.

FIG. 2A is a sectional view showing a configuration of one pixel in an effective pixel region of the CCD image sensor according to the first embodiment. B is a potential diagram in the vertical direction of the pixel (on the line AA in FIG. 2A).

FIG. 3A is a sectional view showing a configuration of one pixel in an invalid pixel region of the CCD image sensor according to the first embodiment. B is a potential diagram in the vertical direction of the pixel (on the line BB of FIG. 3A).

FIG. 4A is a CCD according to a first modification of the first embodiment.
FIG. 3 is a cross-sectional view showing the configuration of one pixel in the invalid pixel region of the image sensor. B is a potential diagram in the vertical direction of the pixel (on the line CC of FIG. 4A).

FIG. 5A is a CCD according to a second modification of the first embodiment.
FIG. 3 is a cross-sectional view showing the configuration of one pixel in the invalid pixel region of the image sensor. B is a potential diagram in the pixel vertical direction (on the line D-D in FIG. 5A).

FIG. 6A is a CCD according to a third modification of the first embodiment.
FIG. 3 is a cross-sectional view showing the configuration of one pixel in the invalid pixel region of the image sensor. B is a potential diagram in the vertical direction of the pixel (on the line EE in FIG. 6A).

FIG. 7A is a sectional view showing a configuration of one pixel in an invalid pixel region of the CCD image sensor according to the second embodiment. B is a potential diagram in the lateral direction of the pixel (on the line FF in FIG. 7A).

FIG. 8A is a cross-sectional view showing a configuration of one pixel in an invalid pixel region of a CCD image sensor according to a modification of the second embodiment. B is a potential diagram in the lateral direction of the pixel (on the line GG in FIG. 8A).

FIG. 9A is a cross-sectional view showing a configuration of one pixel in an effective pixel region of a CCD image sensor according to a conventional example. B
Is a potential diagram in the vertical direction of the pixel (on the line HH in FIG. 9A).

FIG. 10A is a cross-sectional view showing a configuration of one pixel in an invalid pixel region of a CCD image sensor according to a conventional example.
B is a potential diagram in the vertical direction of the pixel (on the line I-I in FIG. 10A).

FIG. 11A is a sectional view showing a configuration of one pixel in an effective pixel region of a CCD image sensor according to another conventional example. B is a potential diagram in the horizontal direction of the pixel (on the line JJ of FIG. 11A).

FIG. 12A is a cross-sectional view showing a configuration of one pixel in an invalid pixel region of a CCD image sensor according to another conventional example. B is a potential diagram in the horizontal direction of the pixel (on the line KK in FIG. 12A).

[Explanation of symbols]

 1 Effective Pixel Region 2 Invalid Pixel Region 11 N-type Silicon Substrate 12 First P-type Well Region 13 Sensor Part 14 Vertical Register 15 Channel Stopper Region 16 Positive Charge Storage Region 17 Second P-type Well Region 18 Read Gate 22 Gate Insulation Film 23 Transfer Electrode 24 Interlayer Insulating Film 25 Al Light Shielding Film 26 Surface Protective Layer 27 Sensor Opening OFB Overflow Barrier 31 P-type Silicon Substrate 32 Overflow Drain Region DP Potential Well

Claims (1)

[Claims] 1. An effective arrangement in which a photoelectric conversion region and an opening for light incidence are formed on the photoelectric conversion region, and a large number of imaging pixels having a potential barrier are arranged adjacent to the photoelectric conversion region. A pixel area, a photoelectric conversion area, and an opening for light incidence are formed on the photoelectric conversion area, and a large number of pixels for optical black detection having no potential barrier are arranged next to the photoelectric conversion area. A solid-state image sensor having an invalid pixel region.