JP2002124659A - Solid-state image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state image pickup device which can reduce a reading voltage. SOLUTION: The image pickup device includes a photodiode 10 and a transfer channel formed within a semiconductor substrate, and first and second gate electrodes 11 and 8 formed on the transfer channel region 4 via an insulating film; and functions as a read electrode for reading out signal charge to the channel region 4 from the photodiode 10. A straight line connecting a center A of a region of the channel region 4 covered with the first gate electrode 11 and not covered with the second gate electrode 8 and a center B of the photodiode 10 is arranged to be vertical to a charge transfer direction (X direction).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a solid-state imaging device capable of realizing a low read voltage.

[0002]

2. Description of the Related Art In recent years, charge coupled devices (charge coupled devices) have been developed.
evice; hereinafter, “CCD”. ) Is widely used in consumer and commercial video cameras. FIG. 8 is a schematic plan view showing the structure of a conventional solid-state imaging device. This solid-state imaging device has a structure in which a plurality of pixels are arranged in a matrix on a semiconductor substrate plane, and each pixel includes a photodiode 10 and a charge transfer unit. The charge transfer section includes a transfer channel section 4 formed in a semiconductor substrate, and a first gate electrode 11 and a second gate electrode 8 formed above the transfer channel section 4 via an insulating film. The first gate electrode 11 includes:
It functions not only as a transfer electrode of the CCD, but also as a read electrode for reading signal charges accumulated in the photodiode 10 to the transfer channel unit 4. Further, a read control unit 7 which is a p-type region is formed between the transfer channel unit 4 and the photodiode 10 formed in the same pixel, and the transfer channel unit 4 and the photodiode formed in different pixels are formed. 10, an isolation portion 6 which is a p-type region is formed.

[0003] In such a solid-state imaging device, the miniaturization of video cameras, the progress of high definition for HDTV,
With the advent of all-pixel CCDs for multimedia applications, the area per pixel tends to be increasingly reduced. For example, in a digital still camera, a solid-state imaging device having a pixel size of 3 μm square is becoming mainstream. In order to cope with such a tendency, it is required to miniaturize the CCD and the photodiode without deteriorating characteristics such as D range, transfer efficiency, sensitivity, smear, and afterimage. As a means for achieving this, a method is employed in which diffusion regions forming a CCD, a photodiode, and the like are formed using high-acceleration ion implantation and low-temperature heat treatment. As a result, unnecessary diffusion of the impurity species from each diffusion region to the undesired region can be suppressed, and the diffusion region can be formed in a desired minute region with a desired concentration and diffusion depth. it can.

[0004]

In the above-mentioned solid-state imaging device, when reading out the signal charges accumulated in the photodiode to the transfer channel section, the purpose is to prevent crosstalk, suppress blooming, reduce dark output and suppress smear. Therefore, the voltage applied to the second gate electrode 8 is fixed at 0 V or a negative voltage. Therefore, the p-type region existing on the substrate surface below the second gate electrode 8 (the shaded portion in FIG. 8 includes not only the selectively formed p-type region but also a p-type well. In this case, the surface potential is 0V.

On the other hand, a positive voltage is applied to the first gate electrode 11, which is a read electrode, whereby a depletion layer expands from the transfer channel portion 4 toward the photodiode 10, and a read channel is formed. The curve in FIG. 8 shows a read channel formed from the minimum potential point B of the photodiode to the minimum potential point A of the transfer channel portion. In this manner, in the conventional solid-state imaging device, a curve is drawn such that the read channel reaches the transfer channel unit 4 while approaching the 0V region.

As described above, in the conventional solid-state imaging device, since the read channel passes near the 0V region,
There is a problem that the spread of the depletion layer for forming the read channel is hindered, and the read voltage increases. This problem has been particularly prominent in a fine solid-state imaging device having a pixel size of 3 μm square or less.

FIG. 9 is a diagram showing a potential distribution at the time of reading out signal charges in a conventional solid-state imaging device. In this potential distribution diagram, it can be seen from the fact that the potential gradient between the 0 V region and the read channel is too steep to cause the above-described read hindrance.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a solid-state imaging device capable of lowering a read voltage.

[0009]

In order to achieve the above object, a solid-state imaging device according to the present invention has a plurality of pixels arranged in a matrix on a semiconductor substrate, and each of the pixels is arranged in the semiconductor substrate. A photodiode and a transfer channel portion formed, and a first gate electrode and a second gate electrode formed on the transfer channel portion via an insulating film, wherein the first gate electrode includes A solid-state imaging device that functions as a read electrode for reading a signal charge from a diode to the transfer channel unit, wherein the transfer channel unit is covered by the first gate electrode and not covered by the second gate electrode. A straight line connecting the center of the region and the center of the photodiode,
Each of the pixels is configured to be perpendicular to a charge transfer direction in the transfer channel section.

According to such a configuration, when reading charges from the photodiode to the transfer channel section, the read channel formed from the minimum potential point of the photodiode to the minimum potential point of the transfer channel section is transferred to the transfer channel section. It can be formed perpendicular to the direction. As a result, it is possible to sufficiently secure the expansion of the depletion layer from the transfer channel portion, and it is possible to reduce the read voltage.

In the solid-state imaging device, it is preferable that a p-type region is formed in a surface layer of the semiconductor substrate so as to surround a periphery of the photodiode.
It is preferable that the impurity concentration of the p-type region is higher than the impurity concentration of the semiconductor substrate or a p-type well formed in the semiconductor substrate.

The dark current of the solid-state imaging device is caused by a leak current generated around the transfer channel section flowing into the transfer channel section. As a method of reducing the dark current, a method of forming a high-concentration p-type region in the surface layer portion of the semiconductor substrate except for the photodiode and the transfer channel portion can be considered. However, when a high-concentration p-type region is formed in the vicinity of the read channel, diffusion of impurity species from the p-type region to the read channel occurs, and as a result, reading of signal charges is inhibited.

In a conventional solid-state imaging device, as shown in FIG.
When the periphery of the photodiode 10 is surrounded by a high-concentration p-type region in order to draw a curve approaching the end of the high-concentration p-type region, a high-concentration p-type region is formed in the vicinity of the read channel, causing an increase in the read voltage. There was a problem.

However, according to the above-described preferred embodiment of the present invention, the distance from the read channel to the end of the photodiode can be sufficiently widened, so that the read voltage does not increase around the photodiode without increasing the read voltage. Can be surrounded by a p-type region. Therefore, it is possible to reduce the dark current while reducing the read voltage.

In the solid-state imaging device, it is preferable that a p-type region is formed on the photodiode, and a recess is formed on a surface of the semiconductor substrate on the transfer channel portion. In this case, it is further preferable that the depth of the concave portion is deeper than the diffusion depth of the p-type region formed in the semiconductor substrate on the photodiode. According to this preferred example, the read voltage can be further reduced.

In the solid-state imaging device, it is preferable that a part of the first gate electrode overlaps with the photodiode. This is because the read voltage can be further reduced.

Further, in the solid-state imaging device, the first and second gate electrodes formed on the transfer channel portion from which signal charges are read out from the photodiodes are the first and second gate electrodes.
The position of the end of the gate electrode on the side of the photodiode is equal to the position of the end of the second gate electrode on the side of the photodiode, or the gate electrode protrudes further to the side of the photodiode. preferable. This is because the read voltage can be further reduced. Note that “positions are equal” means that the positions in the direction perpendicular to the charge transfer direction are equal.

In the solid-state imaging device, in the transfer channel portion, a length of a region covered by the second gate electrode in a charge transfer direction, and a length of the region covered by the first gate electrode and the second It is preferable that the length of the region not covered by the gate electrode is equal to the length in the charge transfer direction. This is because deterioration of the maximum handled charge amount in the transfer channel portion can be suppressed.

In the solid-state imaging device, it is preferable that the first gate electrode and the second gate electrode do not overlap. Since the distance from the substrate surface to the protective film can be reduced, vignetting of incident light (a phenomenon that incident light collected by the lens formed on the protective film cannot enter the photodiode due to the thickness of the gate electrode and the light shielding film) ) Can be reduced, and the sensitivity can be improved.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, an example of a solid-state imaging device according to a first embodiment of the present invention will be described.

This solid-state imaging device includes an imaging area in which a plurality of pixels are arranged, and a non-imaging area in which peripheral circuits for driving the pixels are arranged.

FIG. 1 is a schematic plan view showing an example of the structure of the solid-state imaging device according to the present embodiment. FIG. 2 is a sectional view taken along the line II ′ of FIG. These drawings show the structure of the imaging region.

A p-type well 2 is formed in an n-type semiconductor substrate 1. The impurity concentration of the p-type well 2 is not particularly limited, but is, for example, 1 × 10 ¹⁶ cm ⁻³ or less. A bias voltage is applied to the p-type well 2 to determine the amount of charge stored in the photodiode 10, and a discharge voltage higher than the bias voltage is used to discharge unnecessary charges stored in the photodiode 10. The bias voltage is set to 15 V or less by setting the impurity concentration of the p-type well to 1 × 10 ¹⁶ cm ⁻³ or less,
The discharge voltage may be 20 V or less.

A plurality of pixels are arranged in a matrix on the plane of the semiconductor substrate on which the p-type well 2 is formed.
Each pixel has a photodiode 10 for performing photoelectric conversion.
And a charge transfer unit for reading and transferring charges generated by photoelectric conversion.

The photodiode 10 is an n-type diffusion region formed deep in the p-type well 2. The impurity concentration is not particularly limited as long as the photoelectric conversion can be performed. For example, the impurity concentration is 1.0 × 10 ¹⁵ cm ^{−3 to} 1.0 ×
10 ¹⁷ cm ^-3 . The diffusion depth is, for example, 0.5 μm to 2.2 μm.

In order to reduce dark current, a p-type region 12 is formed on the surface layer of the semiconductor substrate on the photodiode 10.
May be formed. The impurity concentration of the p-type region 12 is, for example, 1.0 × 10 ¹⁷ cm ^{−3 to} 5.0 × 10 ¹⁹ cm.
^-3 , and the diffusion depth is, for example, 0.1 μm to 0.5
μm. In addition, as shown in FIG.
Is preferably formed so as not to overlap with gate electrodes 8 and 11.

The charge transfer section is a CCD having a transfer channel section 4 formed in the p-type well 2 and a gate electrode disposed on the transfer channel section 4 via an insulating film.

The transfer channel 4 is an n-type diffusion region formed in the surface of the p-type well 2. The impurity concentration is, for example, 1.0 × 10 ¹⁶ cm ^{−3 to} 1.0 × 10 ¹⁸ cm.
⁻³ , and the diffusion depth is, for example, 0.1 μm to 0.5 μm.
It is.

[0029] At least two gate electrodes are arranged for one photodiode, and these gate electrodes are arranged so as to partially overlap each other. For example, in the structure shown in FIGS. 1 and 2, a second gate electrode 8 is formed on the transfer channel section 4 via an insulating film 5, and further above the insulating film 9
By forming the first gate electrode 11 through the first gate electrode 11, the first gate electrode 11 and the second gate electrode 8 are arranged so as to partially overlap each other.

The first gate electrode 11 is an electrode serving as both a read electrode and a transfer electrode. As shown in FIG. 1, the first gate electrode 11 is formed so as to be adjacent to the photodiode 10, and is preferably formed so that a part thereof overlaps the photodiode 10.
The second gate electrode 8 is a transfer electrode, and is formed in a region corresponding to a gap between the first gate electrodes 11. Further, as shown in FIG. 1, pixels adjacent in the direction perpendicular to the charge transfer direction (X direction in FIG.
The gate electrodes 11 and the second gate electrodes 8 are connected to each other.

As shown in FIG. 1, the first gate electrode 11
And the second gate electrode 8 has a center (A) of a region covered by the first gate electrode 11 and not covered by the second gate electrode 8 of the transfer channel portion 4 on the plane of the semiconductor substrate; The straight lines connecting the centers (B) of the ten are perpendicular to the charge transfer direction. This makes it possible to reduce the read voltage when reading the signal charge from the photodiode 10 to the transfer channel unit 4. The reduction in the read voltage will be described later in detail.

On the side from which signal charges are read from the photodiode 10 to the transfer channel section 4, the position of the end of the first gate electrode 11 is equal to or equal to the position of the end of the second gate electrode. It is more preferable that the projection extends toward the photodiode 10 than the photodiode 10. Thus, the potential of the first gate electrode 11 at the time of reading can be transmitted over a wide range, so that the reading voltage can be reduced.

Further, the first gate electrode 11 and the second gate electrode 8 are covered with the first gate electrode 11 and the second gate electrode 8 of the transfer channel portion 4 in the charge transfer direction. It is preferable that the dimension (L1) of the uncovered area is equal to the dimension (L2) of the area covered by the second gate electrode 8. Thus, it is possible to suppress the deterioration of the maximum handled charge amount in the charge transfer unit.

It is preferable that the first gate electrode 11 and the second gate electrode 8 do not overlap each other.
Thus, the thickness of the gate electrode on the substrate can be reduced to one layer. Therefore, the protective film 1 is removed from the substrate surface.
6, the vignetting of the incident light (a phenomenon that the incident light collected by the lens formed on the protective film cannot enter the photodiode due to the thickness of the gate electrode and the light shielding film) can be reduced. , The sensitivity can be improved.

The first gate electrode 11 and the second gate electrode 8 may be made of, for example, polysilicon, and the insulating films 5 and 9 may be made of, for example, a silicon oxide film, a silicon nitride film, Alternatively, a film in which these are superposed in two layers can be used.

Photodiode 1 formed in the same pixel
A read control unit 7 that is a p-type diffusion region is formed between the transfer channel unit 0 and the transfer channel unit 4. The impurity concentration of the read control unit 7 is, for example, 2.0 × 10 ¹⁵ cm ⁻³ to 2.
It is 0 × 10 ¹⁷ cm ⁻³ . Further, in order to suppress mixing of signal charges between adjacent pixels, an isolation portion 6 which is a p-type diffusion region is formed between the photodiode 10 and the transfer channel portion 4 formed in different pixels. I have. The impurity concentration of the separation part 6 is, for example, 1.0 × 10 ¹⁶ cm ⁻³ or more.
It is 5.0 × 10 ¹⁸ cm ⁻³ .

Further, a p-type region 3 is formed immediately below the transfer channel section 4 in the p-type well 2. The p-type region 3 is a region that separates the transfer channel unit 4 from the semiconductor substrate, and together with the read control unit 7 and the separation unit 6,
It is formed so as to surround the transfer channel unit 4.

On the surface of the semiconductor substrate above the photodiode 10, an antireflection film 13 is formed with an insulating film 5 interposed. As the antireflection film 13, for example, a silicon nitride film or the like is used. Above the semiconductor substrate, an insulating film 14, a light shielding film 15, and a protective film 16 are formed in this order. The light-shielding film 15 is formed of the photodiode 1
This is a metal film having an opening above zero, for example, an aluminum film, a titanium film, a tungsten silicide film, a tungsten film, or the like is used. Further, as the insulating film 14 and the protective film 16, for example, a silicon oxide film, a silicon nitride film, or the like is used.

FIG. 3 is a diagram showing a potential distribution at the time of reading signal charges of the solid-state imaging device. Hereinafter, the operation of the solid-state imaging device will be described with reference to FIGS. 1 and 3, and the readout improvement effect obtained by the solid-state imaging device will be described.

First, in the photodiode 10, charges are generated and accumulated by photoelectric conversion of incident light. Subsequently, the charges stored in the photodiode 10 are read out to the transfer channel unit 4.

At the time of reading out signal charges, the voltage applied to the second gate electrode 8 is 0 V or a negative voltage (V) for the purpose of preventing crosstalk of each pixel signal, suppressing blooming, reducing dark output and suppressing smear. For example, -7
V). Therefore, the surface potential of the p-type region (hatched portion in FIG. 1; hereinafter, referred to as “0V region”) existing between the photodiodes 10 adjacent to each other in the charge transfer direction becomes 0V.

On the other hand, a positive voltage is applied to the first gate electrode 11 also serving as a readout electrode. As a result, FIG.
As shown in (2), a potential well is formed in a region of the transfer channel portion 4 that is covered by the first gate electrode 11 and not covered by the second gate electrode 8. At the same time, a depletion layer expands from the transfer channel section 4 toward the photodiode 10, and a read channel is formed. The charges of the photodiode 10 flow into the transfer channel unit 4 through the read channel.

The read channel is formed from the minimum potential point of the photodiode 10 to the minimum potential point in a region where a potential well is formed at the time of reading charges. In the solid-state imaging device, as shown in FIG.
A configuration is such that a straight line connecting point A corresponding to the minimum potential point of the region where the potential well is formed at the time of charge reading and point B corresponding to the minimum potential point of the photodiode is perpendicular to the charge transfer direction. Therefore, the read channel is formed perpendicular to the charge transfer direction.

Therefore, in the solid-state imaging device,
Distance from read channel to 0V area (D in FIG. 1)
1 and D2) can each be equally long. That is, the read channel reaches the transfer channel unit 4 from the photodiode 10 without passing near the 0V region. As a result, at the time of reading, the expansion of the depletion layer from the transfer channel unit 4 is less likely to be inhibited, and the reading voltage can be reduced. Such a read improvement effect can also be seen from the fact that the potential gradient between the 0 V region and the read channel is gentle in the potential distribution diagram of FIG.

Next, after reading out the signal charges to the transfer channel section 4, an appropriate voltage is applied to the first gate electrode 11 and the second gate electrode 8, and a potential well is formed below the second gate electrode 8. Form. As a result, the signal charges read below the first gate electrode 11 move below the second gate electrode 8. By repeating such a cycle, signal charges are transferred one-dimensionally in the transfer channel unit 4.

(Second Embodiment) Next, an example of a solid-state image pickup device according to a second embodiment of the present invention will be described.

FIG. 4 is a schematic plan view showing an example of the structure of the solid-state imaging device according to this embodiment. FIG. 5 is a sectional view taken along line II ′ of FIG. These drawings show the structure of the imaging region of the solid-state imaging device. In FIGS. 4 and 5, the same members as those in FIGS. 1 and 2 are denoted by the same reference numerals.

A plurality of pixels are arranged in a matrix on an n-type semiconductor substrate 1 on which a p-type well 2 is formed. Each pixel includes a photodiode 10 and a charge transfer unit. The charge transfer section includes a transfer channel section 4 formed in the p-type well 2, a second gate electrode 8 formed above the transfer channel section 4 via an insulating film 5, and a charge transfer section formed via an insulating film 9. This is a CCD having one gate electrode 11. The first gate electrode 11 is an electrode that serves both as a readout electrode and a transfer electrode, and the second gate electrode 8 is a transfer electrode.

The first gate electrode 11 and the second gate electrode 8 are, in the plane of the semiconductor substrate, a region covered by the first gate electrode 11 of the transfer channel portion 4 and not covered by the second gate electrode 8. And a straight line connecting the center (A) of the photodiode 10 and the center (B) of the photodiode 10 is arranged to be perpendicular to the charge transfer direction (X direction in FIG. 3).

On the side where signal charges are read from the photodiode 10 to the transfer channel section 4, the position of the end of the first gate electrode 11 is equal to or equal to the position of the end of the second gate electrode. It is more preferable that the projection extends toward the photodiode 10 than the photodiode 10. Further, in the charge transfer direction, the dimension (L1) of the region of the transfer channel portion 4 covered by the first gate electrode 11 and not covered by the second gate electrode 8, and the size of the region covered by the second gate electrode 8, It is preferable that the size (L2) of the divided area is equal. Further, it is preferable that the first gate electrode 11 and the second gate electrode 8 do not overlap.

Photodiode 1 formed in the same pixel
A readout control unit 7 is formed between the transfer channel unit 0 and the transfer channel unit 4, and a separation unit 6 is formed between the transfer channel unit 4 and a photodiode 10 formed in another pixel adjacent to each other. ing. Further, a p-type region 3 is formed immediately below the transfer channel portion 4 in the p-type well 2.

Further, in the present embodiment, the p-type region 17 is formed in the surface layer of the p-type well 2 and in the gap between the photodiodes 10 adjacent in the charge transfer direction. One end of the p-type region 17 is closer to the transfer channel 4 than the end of the photodiode 10 in the direction perpendicular to the charge transfer direction.
0 is a transfer channel portion formed in the same pixel. ) Overhangs to the side. In other words, the p-type region 17
Is formed so as to surround the photodiode 10 together with the read control unit 7 and the separation unit 6. The impurity concentration of the p-type region 17 is, for example, 1.0 ×
10 ¹⁶ cm ^{-3 to} 1.0 × 10 ¹⁹ cm ^-3 , and the diffusion depth is, for example, 0.3 μm to 1.5 μm.

On the surface of the semiconductor substrate above the photodiode 10, an anti-reflection film 13 is formed via an insulating film 5. Above the semiconductor substrate, an insulating film 14, a light shielding film 15, and a protective film 16 are formed in this order.

The solid-state imaging device of this embodiment has the same structure as that of the first embodiment except that the p-type region 17 is formed in the surface layer of the semiconductor substrate. The operation is also the same as in the first embodiment.

According to the present embodiment, it is possible to reduce the dark current while reducing the read voltage as in the first embodiment. This effect will be described below.

As described above, the dark current in the solid-state imaging device is caused by the leakage current flowing into the transfer channel. This dark current can be reduced, for example, by forming a p-type region around the photodiode. In the present embodiment, by forming the p-type region 17, the periphery of the photodiode can be surrounded by the p-type region, so that dark current can be reduced.

Further, in this embodiment, a straight line connecting point A corresponding to the minimum potential point of the region where the potential well is formed at the time of reading the electric charge and point B corresponding to the minimum potential point of the photodiode 10 is defined as It is formed so as to be perpendicular to the charge transfer direction. Therefore, as shown in FIG. 4, a large distance between the read channel and the p-type region 17 can be ensured. Therefore, it is possible to suppress an increase in the read voltage due to the formation of the p-type region 17.

(Third Embodiment) Next, an example of a solid-state imaging device according to a third embodiment of the present invention will be described.

FIG. 6 is a schematic plan view showing an example of the structure of the solid-state imaging device according to the present embodiment. FIG. 7 is a sectional view taken along the line II ′ of FIG. These drawings show the structure of the imaging region of the solid-state imaging device. 6 and 7, the same members as those in FIGS. 1 and 2 are denoted by the same reference numerals.

A plurality of pixels are arranged in a matrix on an n-type semiconductor substrate 1 on which a p-type well 2 is formed. Each pixel includes a photodiode 10 and a charge transfer unit. The photodiode 10 is an n-type region formed in the p-type well 2, and has a p-type region 12 formed thereon in order to reduce dark current.

The charge transfer section includes a transfer channel section 4 formed in the p-type well 2 and the transfer channel section 4.
First gate electrode 11 disposed thereon with insulating film 5 interposed
And a CCD having a second gate electrode 8.

The transfer channel section 4 is an n-type diffusion region formed in the surface layer of the semiconductor substrate. In the present embodiment, a concave portion is formed on the surface of the semiconductor substrate on the transfer channel portion 4. This concave portion is formed in a groove shape along the charge transfer direction (X direction in FIG. 6) by the transfer channel portion 4. The depth of the concave portion is deeper than the diffusion depth of the p-type region 12 formed on the photodiode 10, for example, 0.1 to 0.6 μm.

The first gate electrode 11 is an electrode serving as both a read electrode and a transfer electrode, and the second gate electrode 8 is a transfer electrode. The first gate electrode 11 and the second
The gate electrode 8 of the semiconductor substrate plane is covered by the first gate electrode 11 of the transfer channel portion 4 and not covered by the second gate electrode 8 (A), and the center of the photodiode 10 (B) is arranged so as to be perpendicular to the charge transfer direction (X direction in FIG. 6).

On the side from which signal charges are read from the photodiode 10 to the transfer channel section 4, the position of the end of the first gate electrode 11 is equal to or equal to the position of the end of the second gate electrode. It is more preferable that the projection extends toward the photodiode 10 than the photodiode 10. Further, in the charge transfer direction, the dimension (L1) of the region of the transfer channel portion 4 covered by the first gate electrode 11 and not covered by the second gate electrode 8, and the size of the region covered by the second gate electrode 8, It is preferable that the size (L2) of the divided area is equal. Further, it is preferable that the first gate electrode 11 and the second gate electrode 8 do not overlap.

A readout control unit 7 is formed between the photodiode 10 formed in the same pixel and the transfer channel unit 4, and the readout control unit 7 is connected to the photodiode 10 formed in another adjacent pixel. A separation section 6 is formed between the section 4 and the section 4. Furthermore, p-type well 2
The p-type region 3 is formed immediately below the transfer channel section 4 in the inside.

On the surface of the semiconductor substrate above the photodiode 10, an antireflection film 13 is formed with an insulating film 5 interposed. Above the semiconductor substrate, an insulating film 14, a light shielding film 15, and a protective film 16 are formed in this order.

The solid-state imaging device of this embodiment has the same structure as that of the first embodiment except that a concave portion is formed on the surface of the semiconductor substrate on the transfer channel portion 4. The operation is also the same as in the first embodiment. Also in the present embodiment, the second
Similarly to the embodiment, a p-type region may be formed in a gap between the photodiodes 10 adjacent in the charge transfer direction.

According to the present embodiment, similarly to the first embodiment, the read voltage can be reduced. Furthermore,
In the present embodiment, as shown in FIG. 7, since the concave portion is formed on the surface of the transfer channel portion 4, the transfer channel portion 4 is covered with the first gate electrode 11 and covered with the second gate electrode. The minimum potential point of the region where no potential well is formed at the time of reading (FIG. 7
Corresponding to the point A. ) Can be made equal to the depth of the minimum potential point (corresponding to the point B in FIG. 7) of the photodiode. As a result, it is possible to further reduce the read voltage.

[0069]

As described above, according to the solid-state imaging device of the present invention, when electric charges are read out from the photodiode to the transfer channel section, the charge is transferred from the minimum potential point of the photodiode to the minimum potential point of the transfer channel section. The read channel formed by the above method can be formed perpendicular to the charge transfer direction, and as a result, the read voltage can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic plan view illustrating a structure of a solid-state imaging device according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view taken along the line I-I 'of FIG.

FIG. 3 is a potential distribution diagram when reading out signal charges in the solid-state imaging device shown in FIG. 1;

FIG. 4 is a schematic plan view illustrating a structure of a solid-state imaging device according to a second embodiment of the present invention.

FIG. 5 is a schematic sectional view taken along the line I-I ′ of FIG. 4;

FIG. 6 is a schematic plan view illustrating a structure of a solid-state imaging device according to a third embodiment of the present invention.

FIG. 7 is a schematic sectional view taken along the line I-I ′ of FIG. 6;

FIG. 8 is a schematic plan view showing the structure of a conventional solid-state imaging device.

FIG. 9 is a potential distribution diagram at the time of reading out signal charges in the solid-state imaging device shown in FIG. 8;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 semiconductor substrate 2 p-type well 3, 6, 7, 12, 17 p-type region 4 transfer channel section 5, 9, 14 insulating film 8 second gate electrode 10 photodiode 11 first gate electrode 13 anti-reflection film 15 Light shielding film 16 Protective film

Claims (8)

[Claims] A plurality of pixels arranged in a matrix on a semiconductor substrate, wherein each of the pixels includes a photodiode and a transfer channel formed in the semiconductor substrate;
A first gate electrode and a second gate electrode formed on the transfer channel portion via an insulating film, wherein the first gate electrode reads signal charges from the photodiode to the transfer channel portion Solid-state imaging device that functions as a read electrode for the transfer channel portion, the center of the transfer channel portion being covered with the first gate electrode and not being covered with the second gate electrode, and the center of the photodiode. So that a straight line connecting to the transfer channel portion is perpendicular to the charge transfer direction,
A solid-state imaging device, wherein each of the pixels is configured. 2. The solid-state imaging device according to claim 1, wherein a p-type region is formed in a surface portion of said semiconductor substrate so as to surround a periphery of said photodiode. 3. The solid-state imaging device according to claim 1, wherein a p-type region is formed on the photodiode, and a recess is formed on a surface of the semiconductor substrate on the transfer channel portion. 4. The solid-state imaging device according to claim 3, wherein the depth of the recess is larger than the diffusion depth of the p-type region formed on the photodiode. 5. The solid-state imaging device according to claim 1, wherein a part of said first gate electrode overlaps with said photodiode. 6. The photodiode of the first gate electrode with respect to the photodiode and the first and second gate electrodes formed on the transfer channel from which signal charges are read from the photodiode. The position of the end on the side of the second gate electrode is equal to the position of the end of the second gate electrode on the side of the photodiode, or the position protrudes further toward the side of the photodiode. The solid-state imaging device according to claim 1. 7. The transfer channel portion, wherein a length of the region covered by the second gate electrode in the charge transfer direction is covered by the first gate electrode and covered by the second gate electrode. The solid-state imaging device according to claim 1, wherein the lengths of the non-existing regions are equal to each other in the charge transfer direction. 8. The solid-state imaging device according to claim 1, wherein said first gate electrode and said second gate electrode do not overlap with each other.