JP2001127275A - Solid-state imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a white spot from occurring when a dark signal is acquired with a photoelectric conversion element in an invalid imaging region by reducing the depletion region of the photoelectric conversion element in the invalid imaging region. SOLUTION: Related to a valid imaging region 100A, an N- type impurity region 132 is formed on a P- type well layer 130 provided at the deep layer of an N- type Si substrate 110, over which an N- type photoelectric conversion region 134 and a P+ type impurity region 136 which constitute a photodiode 112 are formed. The N- type impurity region 132 deepens the overflow barrier of the valid imaging region 100A, for improved sensitivity in a near infrared region. Related to an invalid imaging region 100B, the N- type photoelectric conversion region 134 and the P+ type impurity region 136 which constitute the photodiode 112 are formed, with no N- type impurity region 132 formed on the P- type well layer 130. Thus, the depletion region of the invalid imaging region 100B is reduced, and a white spot at dark signal is suppressed to accurately decide a black level.

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 which photoelectric conversion elements such as photodiodes are provided in a matrix on a semiconductor substrate, and a central area of the matrix is an effective imaging area and a peripheral area is an invalid imaging area. The present invention relates to an imaging device.

[0002]

2. Description of the Related Art FIG. 5 is a plan view showing a pattern shape of each pixel portion in a conventional solid-state imaging device. As shown in FIG. 5, this solid-state imaging device includes a photodiode unit 12 (shown by a solid line in FIG. 5) for performing photoelectric conversion on a semiconductor substrate 10 and a signal charge stored in the photodiode unit 12 which is transferred to a horizontal transfer register. Vertical transfer register unit 14 (indicated by a dashed line in FIG. 5) for transferring data to a unit (not shown).
And polycrystalline Si electrode portions 16 and 18 (shown by two-dot broken lines in FIG. 5) for applying a drive signal voltage to the vertical transfer register portion 14, and an inter-pixel channel stop portion 20 (see FIG. 5) for separating adjacent pixel portions. 5 is indicated by a broken line).

FIG. 6 is a sectional view taken along the line ZZ of FIG. With reference to FIG. 6, a stacked structure in the solid-state imaging device shown in FIG. 5 will be described. The photodiode of the solid-state imaging device described here has a light wavelength of 700 to 1000.
The structure has a sensitivity in the vicinity of nm (near-infrared region), and the semiconductor substrate 10 has an overflow barrier that limits the overflow of excess charge from the photodiode as compared with a photodiode of a general solid-state imaging device. It is located in the deep part of.

In the example shown in FIG. 6, first, an N-type Si substrate 1
A P-type well layer (P # 1) 30 is formed at a depth of 0. Next, an N-type impurity region 32 constituting an N-type well layer (NW) is formed in the upper layer of the P-type well layer 30 corresponding to the imaging pixel shape of the photodiode section 12, and the photodiode section 12 is formed thereon. Are formed, an N-type impurity region (photoelectric conversion region) 34 and a P + -type impurity region 36 are formed. These are formed by sequentially performing ion implantation or the like on the N-type Si substrate 10.

[0005] The N-type impurity region 32 (shown as a hatched region in FIG. 5) is formed in the photodiode section 12 as described above.
Is provided as a potential barrier for disposing the overflow barrier in a deep part of the semiconductor substrate 10,
An overflow barrier is arranged on the deep side of the N− type impurity region 32. Then, the photodiode section 12
When the excess electric charge accumulated in the N-type Si substrate 1 exceeds a certain potential, the electric charge exceeds the overflow barrier and the N-type Si substrate 1
This constitutes a vertical overflow drain structure discharged to zero.

A P-type read gate section 40 is provided adjacent to the left side of the upper P + -type impurity region 36 in the figure, and a vertical transfer register section 14 having a CCD structure is formed outside the P-type read gate section 40. A P + type inter-pixel channel stop portion 20 is formed adjacent to the P + type impurity region 36 on the right side in the drawing. These are also formed by sequentially performing ion implantation or the like on the N-type Si substrate 10.

On the surface of the N-type Si substrate 10, the above-mentioned polycrystalline Si electrode portion 16 is provided via an insulating film 42. In addition, on the upper surface of the polycrystalline Si electrode portion 16,
A light shielding film 44 for light shielding is provided. The light-shielding film 44 is formed so as to cover the periphery of the photodiode portion 12. The opening portion 44A formed in the light-shielding film 44 exposes the photodiode portion 12 to the outside and receives external light. It has become.

Further, in the solid-state imaging device having the above-described configuration, as shown in FIG. 7, the entire light receiving surface is formed by a central effective imaging region 1A and an invalid imaging region (so-called OB (Op
tical Black) section) 1B, an imaging signal is obtained by the photodiode section 12 in the effective imaging area 1A, and a dark signal from the photodiode section 12 in the invalid imaging area 1B is used to determine the black level. I have. For example, as shown in FIG. 5, the invalid imaging region 1B is provided with a light shielding film 46 that entirely covers the invalid imaging region 1B from above the light shielding film 44, or the invalid imaging region 1B is shielded. This can be realized by providing a light-shielding film 44 that blocks input of light to the photodiode unit 12 without forming the opening 44A of the film 44.

FIG. 8 is an explanatory diagram showing potential curves of respective parts in the above-mentioned conventional solid-state imaging device. In FIG. 8, the vertical axis indicates the level of the potential,
The horizontal axis indicates the position in the depth direction of the Si substrate. The curve shown in FIG. 8 indicates the point A on the photodiode unit 12 in the effective imaging area 1A shown in FIG.
5 shows a potential curve at a point B on the photodiode section 12 in the section. As illustrated, in the solid-state imaging device illustrated in FIGS. 5 and 6, the structure of the photodiode unit 12 is common between the effective imaging region 1A and the invalid imaging region 1B, and thus the potential curves are also common. And
An overflow barrier serving to control the amount of accumulated charge in each photodiode section 12 is formed at point C in FIG.

[0010]

By the way, in the solid-state imaging device as described above, the N- type impurity region 32 for arranging the overflow barrier deep in the photodiode section 12 is provided with the effective imaging region 1A and the invalid imaging region. 1B. However, when the black level is determined by using the dark signal from the photodiode unit 12 provided in the invalid imaging region 1B as described above, the occurrence rate of white spots included in the dark signal is determined by S in the photodiode unit 12.
This is proportional to the width of the depletion region formed in the depth direction of the i-substrate 10. For this reason, the above-described N− type impurity region 32 is provided in a deep portion of the photodiode portion 12 in the invalid imaging region 1B.
Is formed, the depth of the depletion region becomes deeper,
White spots easily occur at the time of dark signals.

For the above reasons, a solid-state image pickup device having a photodiode having a structure having sensitivity also in the near-infrared region has a large depletion region in the depth direction as compared with a normal solid-state image pickup device. When a black point is determined using a dark signal from the invalid imaging area 1B, a white point included in the dark signal cannot make a proper determination, and a large defect occurs in the image. There is a problem.

Accordingly, an object of the present invention is to reduce the depletion region in the photoelectric conversion element in the invalid image pickup area, thereby suppressing the occurrence of white spots when a dark signal is obtained by the photoelectric conversion element in the invalid image pickup area. Another object of the present invention is to provide a solid-state imaging device capable of determining an appropriate black level.

[0013]

According to the present invention, in order to achieve the above object, a large number of photoelectric conversion elements constituting image pickup pixels are arranged in a matrix on a semiconductor substrate, and a central area of the photoelectric conversion elements is arranged. A solid-state imaging device in which an effective imaging region is formed by photoelectric conversion elements disposed in the solid-state imaging device, and a photoelectric conversion element disposed in a peripheral region of the effective imaging region is shielded by a light-shielding film to form an invalid imaging region. Has a well layer of the second conductivity type in a deep portion formed of the first conductivity type, and the photoelectric conversion element has a first impurity region of the second conductivity type formed on a surface portion of the semiconductor substrate. And a first conductivity type photoelectric conversion region formed on the deep side of the first impurity region. The photoelectric conversion element of the effective imaging region further includes the photoelectric conversion region, the second conductivity type well layer, 1st conductivity between The second impurity region is provided, and the,
The photoelectric conversion element in the invalid imaging region is configured such that the second impurity region is not provided between the photoelectric conversion region and a well layer of the second conductivity type.

In the solid-state imaging device according to the present invention, in the photoelectric conversion element in the effective imaging region, a charge corresponding to the amount of light received in the first impurity region from the opening of the shielding film is accumulated in the photoelectric conversion region. Is taken out as an imaging signal. On the other hand, in the photoelectric conversion element in the invalid imaging area, the light receiving surface is shielded, and no light is incident. Therefore, the charge accumulated in the photoelectric conversion element corresponds to a dark signal, and the signal charge , The black level can be determined.

In the solid-state imaging device according to the present invention, in the photoelectric conversion element in the effective imaging region, a second impurity region is provided on a deep side of the photoelectric conversion region, and the photoelectric conversion region is formed by the second impurity region. An overflow barrier that limits the overflow of the excess charge is disposed deeper in the semiconductor substrate than the photoelectric conversion region. With this structure, the amount of charge stored in the photoelectric conversion region increases,
It is possible to obtain an imaging device having sensitivity in the near infrared region. On the other hand, in the photoelectric conversion element in the invalid imaging region, the second impurity region is not provided on the deep side of the photoelectric conversion region. Therefore, the depletion region in the depth direction of the photoelectric conversion element in the invalid imaging region is effective. It is smaller than the photoelectric conversion element in the imaging area. Therefore,
When a dark signal is obtained by the photoelectric conversion element in the invalid imaging region, generation of a white point can be suppressed, and an appropriate black level can be determined.

As described above, in the solid-state imaging device of the present invention,
To provide a solid-state imaging device with high sensitivity and high image quality that can accurately determine a black level by changing the structure of an impurity profile between a photoelectric conversion element in an effective imaging area and a photoelectric conversion element in an invalid imaging area. Becomes possible.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the solid-state imaging device according to the present invention will be described below. FIG. 1 is a plan view showing a pattern shape of each pixel unit in a solid-state imaging device according to an embodiment of the present invention. This solid-state imaging device includes a photodiode unit 11 for performing photoelectric conversion on a semiconductor substrate 110.
2 (shown by a solid line in FIG. 1), a vertical transfer register 114 (shown by a dashed line in FIG. 1) for transferring signal charges accumulated in the photodiode 112 to a horizontal transfer register (not shown), This vertical transfer register section 1
Polycrystalline Si electrode portion 116 for applying a drive signal voltage to
And 118 (indicated by a two-dot broken line in FIG. 1) and an inter-pixel channel stop unit 120 for separating adjacent pixel units.
(Shown by a broken line in FIG. 1).

In the solid-state image pickup device of this embodiment, as in the conventional example shown in FIG. 7, the entire light receiving surface is formed by a central effective image pickup region 100A and an invalid image pickup region (a so-called OB (Optical Black) portion) around the central effective image pickup region 100A. 100B), an imaging signal is obtained by the photodiode unit 112 in the effective imaging region 100A, and a dark signal from the photodiode unit 112 in the invalid imaging region 100B is used for determining the black level. FIG. 2 is a cross-sectional view taken along line XX of FIG. 1 and shows the element structure of the photodiode unit 112 in the effective imaging region 100A. FIG.
FIG. 2 is a sectional view taken along line YY of FIG.
4 shows the element structure of the photodiode unit 112 in B. That is, the solid-state imaging device according to the present embodiment has different element structures in the effective imaging region 100A and the invalid imaging region 100B.

First, based on FIG.
The element structure of 0A will be described. The photodiode in the effective imaging area 100A according to the present embodiment has the same structure as that shown in FIG. 6 and has a structure having sensitivity even in the vicinity of a light wavelength of 700 to 1000 nm (near infrared region). An overflow barrier that limits the overflow of excess charge from the photodiode as compared to the photodiode of the device is located deep in the semiconductor substrate 110.

In the example shown in FIG. 2, first, the N-type Si substrate 1
A P-type well layer (P # 1) 130 is formed at a depth of 10. Next, an N-type well layer (N-type well layer) is formed on the P-type well layer 130 corresponding to the shape of the imaging pixel of the photodiode unit 112.
An N-type impurity region 132 constituting W) is formed, and an N-type impurity region (photoelectric conversion region) 134 and a P + type impurity region 136 constituting the photodiode portion 112 are formed thereon.
To form These are formed by sequentially performing ion implantation or the like on the N-type Si substrate 110.

The N-type impurity region 132 (indicated by the hatched region in FIG. 1) has the photodiode portion 1 as described above.
Twelve overflow barriers are provided as potential barriers to be disposed deep in the semiconductor substrate 110, and the overflow barrier is disposed deep in the N− type impurity region 132. When the excess charge accumulated in the photodiode unit 112 exceeds a certain potential, the charge passes through the overflow barrier and becomes N-type S
A vertical overflow drain structure discharged to the i-substrate 110 is configured.

Further, a P-type read gate section 140 is provided adjacent to the left side of the upper P + type impurity region 136 in the figure, and outside the vertical transfer register section 11 having a CCD structure.
4 are formed. A P + type inter-pixel channel stop portion 120 is formed adjacent to the P + type impurity region 136 on the right side in the drawing. These are also N-type Si substrates 110
Is formed by sequentially performing ion implantation or the like on the substrate.

On the surface of the N-type Si substrate 110,
The polycrystalline Si electrode portion 116 described above via the insulating film 142
Is provided. Further, a light-shielding film 144 for light-shielding is provided on the upper surface of the polycrystalline Si electrode portion 116. The light-shielding film 144 is formed so as to cover the periphery of the photodiode portion 112.
The photodiode portion 112 is exposed to the outside by the opening 144A formed at the bottom and receives external light.

Next, based on FIG.
The element structure of 0B will be described. This invalid imaging area 100B
Is a light shielding film 1 that entirely covers the invalid imaging region 100B from above the light shielding film 144, as in the example shown in FIG.
46 or the invalid imaging area 1
00B can be realized by providing the light-shielding film 144 that blocks light input to the photodiode 112 without forming the opening 144A of the light-shielding film 144.

The structure of the effective imaging region 100B is the same as that of the effective imaging region 100A except that the N− type impurity region 132 is not provided.
In the same step as 00A, a P-type well layer (P # 1) 130 and an N-type impurity region (photoelectric conversion region) 13 forming the photodiode portion 112 are formed in a deep layer of the N-type Si substrate 110.
4 and P + type impurity regions 136 are formed.
However, in the invalid imaging region 100B, a mask or the like is applied to the invalid imaging region 100B in the above-described step of forming the N − -type impurity region 132 by ion implantation of the effective imaging region 100A. Is implanted, and the N- type impurity region 1 is
32 is not formed. Therefore, in the solid-state imaging device according to the present embodiment, as shown by the hatched area in FIG. 1, the N − -type impurity region 132 is provided on the effective imaging region 100A side, and the N − -type impurity region 13 is provided on the invalid imaging region 100B side.
2 is not provided.

As a result, in the photodiode section 112 on the side of the effective imaging area 100A, the overflow barrier is disposed deep in the semiconductor substrate 110 by the N-type impurity region 132, and the overflow wavelength is near 700 to 1000 nm (near infrared region). Also has a structure having sensitivity. On the other hand, the photodiode section 112 on the side of the invalid imaging region 100B has N-
By not having the type impurity region 132 and reducing the depletion region in the depth direction, the generation of a white point when a dark signal is obtained by the photodiode unit 112 in the invalid imaging region 100B is suppressed, and an appropriate The black level can be determined. The other structure of the invalid imaging region 100B is the same as that of the effective imaging region 100A, and a description thereof will not be repeated.

FIG. 4 is an explanatory diagram showing potential curves of respective parts in the solid-state imaging device according to the present embodiment.
In FIG. 4, the vertical axis indicates the level of the potential, and the horizontal axis indicates the position in the depth direction of the Si substrate. A curve D shown in FIG. 4 shows a potential curve at a point D on the photodiode 112 in the effective imaging region 100A shown in FIG. 5, and a curve E shown in FIG. 4 shows a potential curve in the invalid imaging region 100B. Point E on photodiode section 112
5 shows a potential curve at.

As shown in the figure, in the solid-state imaging device of the present embodiment, the potential curve D of the effective imaging region 100A is shown.
Is similar to the conventional potential curve shown in FIG.
An overflow barrier serving to control the amount of accumulated charges in the photodiode section 112 is formed at a point F in FIG. On the other hand, in the potential curve E of the invalid imaging region 100B, the depletion region is narrowed in the depth direction because the N− type impurity region 132 is not provided, and the white point at the time of a dark signal is suppressed by that amount. It becomes possible. Therefore, in the present embodiment, it is possible to provide a solid-state imaging device that has sufficient sensitivity even in the near-infrared region and can obtain a high-quality image by determining an appropriate black level.

In the solid-state imaging device according to the above-described embodiment, an example is described in which a photodiode having sensitivity even in the vicinity of a light wavelength of 700 to 1000 nm (near infrared region) is provided, but the present invention is not limited to this. Shall be. Also,
The configuration shown in FIGS. 1 and 2 described above exemplifies a specific example necessary to explain the present invention, and the present invention is also limited to specific components of a solid-state imaging device to the above-described example. However, the present invention can be applied to various solid-state imaging devices having a second impurity region for a potential barrier in an effective imaging region.

[0030]

As described above, according to the present invention, a large number of photoelectric conversion elements constituting image pickup pixels are arranged in a matrix on a semiconductor substrate, and a photoelectric conversion element arranged in a central region of the photoelectric conversion elements is provided. In the solid-state imaging device in which the effective imaging region is configured by the elements and the ineffective imaging region is configured by shielding the photoelectric conversion element arranged in the peripheral region of the effective imaging region with a light shielding film, the photoelectric conversion element in the effective imaging region includes: A second impurity region of the first conductivity type is provided between the photoelectric conversion region and the well layer of the second conductivity type, and the photoelectric conversion element in the invalid imaging region includes the photoelectric conversion region and the well of the second conductivity type. The second impurity region was not provided between the layer and the layer. Therefore, in the solid-state imaging device of the present invention, by changing the structure of the impurity profile between the photoelectric conversion element in the effective imaging area and the photoelectric conversion element in the invalid imaging area, an image with good sensitivity and capable of accurately determining the black level can be obtained. It is possible to provide a high-quality solid-state imaging device.

[Brief description of the drawings]

FIG. 1 is a plan view showing a pattern shape of each pixel unit in a solid-state imaging device according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line XX of FIG.

FIG. 3 is a sectional view taken along line YY of FIG. 1;

FIG. 4 is an explanatory diagram showing a potential curve in the solid-state imaging device shown in FIG.

FIG. 5 is a plan view showing a pattern shape of each pixel unit in a conventional solid-state imaging device.

FIG. 6 is a sectional view taken along line ZZ of FIG. 5;

FIG. 7 is a plan view showing an entire effective imaging area and an invalid imaging area in the conventional solid-state imaging device shown in FIG.

8 is an explanatory diagram showing a potential curve in the conventional solid-state imaging device shown in FIG.

[Explanation of symbols]

100A effective imaging area, 100B invalid imaging area, 110 semiconductor substrate (N-type Si substrate), 112
... Photodiode section 114... Vertical transfer register section 116 and 118... Polycrystalline Si electrode section 120.
Channel stop portion between pixels, 130 P-type well layer (P # 1), 132 N-type impurity region, 134
N-type impurity regions (photoelectric conversion regions), 136 P + -type impurity regions, 140 read gate portions, 142 insulating films, 144, 146 light-shielding films, 144A opening.

Claims (6)

[Claims] 1. A large number of photoelectric conversion elements constituting image pickup pixels are arranged in a matrix on a semiconductor substrate, and an effective image pickup area is formed by a photoelectric conversion element arranged in a central area among the photoelectric conversion elements. A solid-state imaging device in which a photoelectric conversion element disposed in a peripheral region of the effective imaging region is shielded by a light-shielding film to form an invalid imaging region; wherein the semiconductor substrate is formed of a first conductivity type, A second conductivity type well layer, wherein the photoelectric conversion element includes a second conductivity type first impurity region formed on a surface portion of the semiconductor substrate, and a first impurity region formed on a deep side of the first impurity region. A conductive type photoelectric conversion region, and a first conductive type second impurity region is provided between the photoelectric conversion region and a second conductive type well layer in the photoelectric conversion element of the effective imaging region. And the invalid imaging area In the photoelectric conversion element in the region, the second impurity region is not provided between the photoelectric conversion region and the well layer of the second conductivity type.
A solid-state imaging device characterized by the above-mentioned. 2. A second conductivity type read gate region formed adjacent to one side of the first impurity region on a surface of the semiconductor substrate; and the first impurity region of the read gate region. A vertical transfer register region formed adjacent to a side opposite to the side, and a second conductivity type channel formed adjacent to the other side of the first impurity region on a surface of the semiconductor substrate. A stop region, an insulating film formed on the surface of the semiconductor substrate except for the photoelectric conversion element, a driving electrode film of a vertical transfer register formed on an upper surface of the insulating film, and the driving electrode film The solid-state imaging device according to claim 1, further comprising: a shielding film provided on an upper surface of the photoelectric conversion element, the shielding film having an opening corresponding to a light receiving region of the photoelectric conversion element. 3. The solid-state imaging device according to claim 1, wherein the invalid imaging region is formed by not forming an opening of a shielding film in the invalid imaging region. 4. The solid-state imaging device according to claim 1, wherein the invalid imaging region is formed by shielding a further upper surface of the shielding film from light. 5. The solid-state imaging device according to claim 1, wherein an output from the photoelectric conversion element in the invalid imaging region is used for determining a black level. 6. The first conductivity type is an N type, and the second conductivity type is an N type.
The solid-state imaging device according to claim 1, wherein the conductivity type is a P-type.