JP2853778B2 - Solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device widely used in video cameras and the like.

[0002]

2. Description of the Related Art In recent years, solid-state imaging devices have been widely used in video cameras and the like. The solid-state imaging device has achieved miniaturization and high sensitivity, enabling imaging at low illuminance, but on the other hand, white blemishes due to dark current generated by the photoelectric conversion unit in low illuminance, especially in darkness, have become a problem. ing.

Hereinafter, a conventional solid-state imaging device will be described. FIG. 2 is a sectional structural view of a conventional solid-state imaging device. In FIG. 2, 1 is an n-type silicon substrate, 2 is a p-type well,
3 is an n ^- type region, 4 is an n-type region, 5 is a p ⁺ type region, and 6 is a p-type region.
^{A +} type region, 7 is a p ⁺⁺ type region, 8 is an insulating film, and 10 is a second-layer polysilicon electrode.

[0004] The solid-state imaging device configured as described above is described.
The operation will be described below. First, the p-type wafer
N, which is a photoelectric conversion unit formed in the^-Type area (below
The intensity of the incident light is indicated by 3
Depending on the degree, signal charge is generated by electron-hole pair generation
You. Next, a high level is applied to the second-layer polysilicon electrode 10.
Read potential by applying a pulse of
Controlling p⁺Lower the potential of the mold region 5,
An n-type region (hereinafter, referred to as a vertical
(Referred to as CCD) 4. Therefore, the first layer
Polysilicon electrode (not shown) and second layer polysilicon electrode
Alternating middle and low level pulses on pole 10
And the signal charges are sequentially transferred in the vertical CCD 4.
Where p ⁺The mold area 6 is a photo adjacent to the vertical CCD 4.
This is to perform electrical isolation between the diodes 3. Also p
⁺⁺The mold region 7 is a fully depleted photodiode 3
On the surface of the photodiode 3
Form a hole accumulation layer with the potential fixed at ground level, for example.
And the noise generated at the interface order on the photodiode 3
Reduces sound charge (dark current).

In the conventional solid-state imaging device described above,
P formed on the surface of the photodiode 3⁺⁺Potential of mold region 7
Is fixed to the ground level,
In the imaging device, p⁺⁺Mold area 7
There was no. With such a solid-state imaging device,
An oxide film exists on the surface of the depleted photodiode 3
As a result, the crystallinity of the oxide film and the silicon substrate 1 is disturbed.
The interface level generated due to the surface of the photodiode 3
Existed. This interface state is distributed in the forbidden band, for example,
A donor that emits one electron and becomes positively charged or neutral
Indicates type behavior. The photodiode on the surface of the photodiode 3
Electrons (noise charge) generated by the scanner read to the vertical CCD4
And detected as dark current. Photodiode 3
If there is an interface state on the surface of the
Always bad, p shown in FIG.⁺⁺Type region 7 as photodiode
3 shows a value about 10 times that of the conventional example formed on the surface.
Was. In that case, p⁺⁺The effect of the mold region 7 is that the dark current value
Of the surface of the photodiode 3 ⁺⁺Depends on the area of the mold region 7
The result became clearer. Therefore, the dark current
To reduce, p⁺⁺It is necessary to increase the area of the mold region 7.
It is important.

[0006]

However, in the above conventional structure, if the n ⁻ -type region of the photodiode is completely covered with the p ⁺⁺ -type region serving as a hole accumulation layer, the second-layer polysilicon electrode becomes Even if a high-level voltage is applied, the surface of the photodiode is fixed at, for example, the ground level, so that the potential immediately below the polysilicon electrode does not change, and the signal charges in the photodiode are completely transferred to the vertical CCD.
In this case, it is difficult to read out the image, and a so-called afterimage is generated. In order to solve this problem, the area of the hole accumulation layer in the photodiode is reduced, and the fully depleted n ⁻ -type region is placed on the silicon substrate with a length substantially equal to the width of the polysilicon read electrode. There has been proposed a structure in which the exposed n ⁻ -type region is entirely covered with a polysilicon readout electrode so that signal charges can be easily read out. However, when the area of the hole accumulation layer is reduced as a measure against image lag as in this structure, on the contrary, electrons are emitted from the surface of the photodiode from the increased interface state, dark current is generated, and an image with many white scratches is generated. Had the problem of becoming

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a solid-state imaging device free from afterimages and free from white spots.

[0008]

In order to achieve this object, a solid-state imaging device according to the present invention is provided on a semiconductor substrate of a first conductivity type.
A photoelectric conversion unit comprising a region of the second conductivity type;
Second signal receiving and sequentially transferring the signal charges generated in the section
A transfer section composed of an electric type region and a signal charge from a photoelectric conversion section.
To the transfer section to transfer charges through the transfer section.
And a readout electrode, wherein the readout electrode is a part of the photoelectric conversion unit.
Protrudes to the signal charge reading side so as to cover part of the side
A surface layer comprising a region of the first conductivity type,
The surface of the photoelectric conversion unit is covered except for the vicinity of the protruding portion .

[0009]

According to this configuration, the vertical C
By reducing the width of the second-layer polysilicon electrode serving as the readout electrode and increasing the area of the hole accumulation layer in the direction in which the signal charges move to the CD, the dark current generated at the interface state can be reduced. A solid-state imaging device free from afterimages can be realized because there is no white flaw caused by the cause and the second layer of polysilicon is present partially on the photodiode.

[0010]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1A is a plan view of a main part of a solid-state imaging device according to an embodiment of the present invention, and FIG.
It is sectional drawing cut | disconnected by the -A 'line. In FIG. 1, 1 is an n-type silicon substrate, 2 is a p-type well, 3 is an n ^- type region (photodiode), 4 is an n-type region (vertical CCD),
Reference numeral 5 denotes a p ⁺ -type region for performing read potential control when reading signal charges from the photodiode 3 to the vertical CCD 4, 6 denotes a p ⁺ -type region for electrically separating the vertical CCD 4 from an adjacent photodiode 3, and 7 a denotes a p ⁺ -type region. A p ⁺⁺ type region as a hole accumulation layer, 8 is an insulating film, 9 is a first-layer polysilicon electrode, 10a is a photodiode 3 from a vertical CCD.
4 is a second-layer polysilicon electrode constituting a readout electrode for reading out signal charges to the fourth.

First, a photodiode 3, a vertical CCD 4, a first-layer polysilicon electrode 9, and a second-layer polysilicon electrode 10a having a different shape from the conventional example are formed on an n-type silicon substrate 1. Second layer polysilicon electrode 10a
The width in the direction in which signal charges are read from the photodiode 3 to the vertical CCD 4 is set to, for example, 1/3 or less of the conventional example. From the opposite viewpoint, a part of the second-layer polysilicon electrode 10a has a shape protruding above the photodiode 3 (hereinafter referred to as protruding). The length of the second-layer polysilicon electrode 10a (the length of the gate electrode with respect to the direction in which the signal charge moves) in a region where there is no protrusion above the photodiode 3 is substantially equal to the length of the first-layer polysilicon electrode 9. The photodiode 3 also exists below the region where the second-layer polysilicon electrode 10a is not formed. In a region where the second-layer polysilicon electrode 10a is not formed, the p ⁺⁺ -type region 7a serving as a hole accumulation layer is formed.
Completely cover the photodiode 3, and the area of the region where the p ⁺⁺ type region 7a does not cover the photodiode 3 is less than one third of the conventional example. When the same high-level pulse voltage as that of the conventional example is applied to the second-layer polysilicon electrode 10a, the afterimage is equal to or less than the same measurement limit as that of the conventional example (0%) even though the protrusion area is reduced. And the p ⁺⁺ type region 7a on the photodiode 3
As a result, the decrease in yield due to the occurrence of defective white spots is reduced to about 1/3 as compared with the conventional method.

In this embodiment, the area of the protrusion of the second-layer polysilicon electrode 10a is set to about 1/3 or less of the conventional example.
As the ratio is reduced to 3, 1/2, and 1/3, the incidence of white spot defects decreases. Therefore, by setting the area of the protrusion to an optimal area, for example, about １ ／ of the conventional example, it is possible to realize a solid-state imaging device free from white spot defects.

[0014]

As described above, according to the present invention, the area of the hole accumulation layer on the photodiode is reduced by reducing the width of the second polysilicon electrode for reading signal charges from the photodiode to the vertical CCD. By increasing, the number of white flaws and the output value thereof can be greatly reduced. In addition, since a part of the second-layer polysilicon electrode protrudes above the photodiode, the after-image characteristic is lower than the measurement limit. An excellent solid-state imaging device capable of reading out signal charges can be realized.

[Brief description of the drawings]

FIG. 1A is a plan view of a main part of a solid-state imaging device according to an embodiment of the present invention. FIG. 1B is a cross-sectional view taken along line AA ′ of FIG.

FIG. 2 is a cross-sectional view of a conventional solid-state imaging device.

[Explanation of symbols]

Reference Signs List 1 n-type silicon substrate (semiconductor substrate) 2 p-type well (p-type region) 3 n ^- type region (photoelectric conversion unit) 4 n-type region (transfer unit) 7a p ⁺⁺ type region (p-type region) 10a 2 layers Eye polysilicon electrode (readout electrode)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-30183 (JP, A) JP-A-2-126778 (JP, A) JP-A-2-168670 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H01L 27/14-27/148 H01L 29/762-29/768

Claims (1)

(57) [Claims] A first conductive type semiconductor substrate formed on a first conductive type semiconductor substrate;
A photoelectric conversion unit comprising a region of a second conductivity type, a transfer unit comprising a region of a second conductivity type for receiving and sequentially transferring signal charges generated by the photoelectric conversion unit, and a photoelectric conversion unit comprising the photoelectric conversion unit. Or
To transfer to the transfer section and transfer charges in the transfer section
A solid-state imaging device having a readout electrode for
The readout electrode is formed on a part of one side of the photoelectric conversion unit.
A protruding part is provided on the signal charge reading side to cover
And the surface layer comprising the first conductivity type region is
The surface of the portion is covered except for the vicinity of the protruding portion.
A solid-state imaging device according to.