JPH0536963A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To provide a solid-state imaging pickup device having a structure which does not allow any dark current to flow into its reading part. CONSTITUTION:A p<+> region 15 is formed on an area comprising an n<-> layer 25 and a p-well layer 23 with the exception of a reading part. In the region surrounding the reading part, there is formed a p<++> region 19 the impurity density of which is higher than that of the p<+> region 15 and the depth of which is shallower than that of the p<+> region 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device,
In particular, it relates to a photoelectric conversion unit of a solid-state imaging device.

[0002]

2. Description of the Related Art Conventionally, as a photoelectric conversion unit of an interline transfer type solid-state image pickup device, one having a sectional structure shown in FIG. 4 is known. The structure shown in FIG.
-Type well substrate 53 is formed on a p-type silicon substrate 51, and an N-type buried channel (vertical transfer shift register; VCC) formed in a double p-well (71, 73) on the p ^- well layer 53 is formed.
D) 55, 57 and oxide layer (SiO ₂ ) 59 thereon
An n ⁻ type layer 65 as a photoelectric conversion portion is formed between the two layers of gate electrodes 61 and 63 formed above. The n ^-
The mold layer 65 and the p ⁻ well layer 53 therebelow form a photodiode. In the more recent so-called high sensitivity type, a silicon substrate and an oxide layer 59 are formed on the surface of the diode, that is, on the n ⁻ type photodiode 65.
To shield the interface (Si-SiO ₂₎ and, p
^{A +} layer 67 is provided.

As shown in the planar structure in FIG. 5, p ⁺ layer 67 is formed so as to cover the main region of n ⁻ type layer 65 excluding the region of read section 69. This p ⁺
Function of layer 67 is that make the volume to one, also primarily by the Si-SiO ₂ interface and a non-depleted state to the other, will interface state is less likely to function as a generating center generates current The generation of dark current (leakage current) can be reduced.

However, in the device having such a structure, an etching damage due to etching unevenness at the time of manufacture, an interface state density of an interface of the photodiode increases due to metal contamination, etc., and an inversion state is caused, thereby causing a large dark current. I have something to do. This is because in the potential distribution of the photodiode shown by the line A in FIG. 3, the charge of electrons or holes tends to flow to a high potential (in the case of electrons) or low (in the case of holes), so that the barrier formed by the p ⁺ layer 67. However, there is a drawback that it flows through the Si—SiO ₂ interface and flows into the photodiode from the reading section.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks and to provide a solid-state image pickup device having a structure in which a dark current does not flow into the reading section.

[0006]

According to the present invention, in order to solve the above-mentioned problems, ap ⁺ region is formed on a region excluding a read portion for taking out charges of a photodiode formed of an n ^- layer and a p ^- well layer. in the solid-state imaging device that is, the impurity concentration than the p ⁺ region in the area surrounding the periphery of the reading unit is high, the solid-state imaging apparatus characterized by its depth to form a shallow p ⁺⁺ region than the p ⁺ region I will provide a.

[0007]

According to the present invention, when a large dark current is generated due to various external influences, it is possible to prevent the dark current from flowing into the reading section to some extent in the p ⁺ region. at high p ⁺⁺ regions in impurity concentration than the p ⁺ region provided so as to surround the peripheral read unit, substantially it can eliminate the flow of dark current in the reading unit, without affecting the reading unit, A clear image can be obtained.

As described above, for example, electrons generated between silicon and silicon oxide (Si-SiO ₂ ) cannot exceed the barrier formed by the p ⁺ layer, but easily flow to the highest potential, that is, Si. thus read with the signal from the reading unit transmitted the -SiO ₂ interface, but the p ⁺⁺ layer provided around the read unit, is possible to prevent the electron which has transmitted the Si-SiO ₂ interface It is possible.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a photoelectric conversion of a solid-state image pickup device (CCD).
It is a schematic plan view which shows a replacement part. First layer vertical roll
Between the sending electrodes (VCCD electrodes) 12 and 14 and the second layer
Between the vertical transfer electrodes (VCCD electrodes) 11 and 13,
P on the main surface of the diode ⁺Layer 15 is provided, p⁺
N not covered by layer 15^-Around the mold reading unit 17, p
⁺⁺The layer 19 surrounds the reading section 17 with a certain width.
It is arranged as follows.

The structure of the p ⁺⁺ layer 19 will be described with reference to FIG. Explaining the entire structure, the N-type substrate 2
1, a p ^- well layer 23 is formed on the p ^- well layer 23, and an n ^- layer 25 is formed on the p ^- well layer 23 to form a p ^- n ^- well photodiode. Further, the p ⁺ layer 15 as a dead region is formed on the n ⁻ layer 25, and the reading section 17 is formed.
A p ⁺⁺ layer 19 according to the present invention is provided in the vicinity of, by ion implantation or the like. An n-type channel region 27 as a transfer path is formed below the vertical transfer electrode 13 which also serves as a read electrode, and a p layer 29 is formed below the n-type channel region 27 to form p ^−.
Together with the layers, they form a double well structure.

[0012] The depth of the p ⁺⁺ layer 19, it is only necessary to shallower than the depth of the p ⁺ layer 15. Examples of impurities of the p ⁺⁺ layer 19 include BF ₂ ⁺ . The impurity concentration of the p ⁺⁺ layer 19, it is preferable to appropriately select the impurity concentration in accordance with the impurity concentration of the p ⁺ layer 15. Impurity concentration of p ⁺ layer 15 and p ^{+ +} layer 1
When the relation with the impurity concentration of 9 is shown by the ratio thereof, it is preferably about 1: 1 or more.

The width of the p ⁺⁺ layer 19 in the plane direction is preferably about 1 μm or more. Further, the p ⁺⁺ layers 19 may be provided in multiple layers in addition to the single layer provided around the read section.

The operation of the p ⁺⁺ layer 19 will be described with reference to FIG. 2. The Si—SiO ₂ interface of the photoelectric conversion part is damaged by abrupt etching irregularities or metal contamination, and a large amount of darkness occurs. When a current is generated, the p ⁺ layer 15
The electric charges that have been transmitted through the interface with the insulating layer and cannot be blocked by the p ⁺ layer 15 are blocked by the p ⁺⁺ layer 19, and the charges do not flow into the reading section 17.

By forming a barrier in the p ⁺⁺ layer 19 as shown by the line B in FIG. 3, it is possible to prevent the potential of the potential distribution of the photodiode from rising. Therefore, the charge of dark current is blocked by the barrier region of the p ⁺⁺ layer 19 and is hardly taken into the reading section.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications and changes can be made.

[0017]

According to the present invention, in the case where the dark current by various external influences occur significantly also in the p ⁺ region, although it is possible to prevent the inflow of a certain degree charge, further prevented by the p ⁺ region The charge of the dark current that did not exist is prevented from flowing into the p ⁺⁺ region where the impurity concentration is higher than that of the p ⁺ region that is provided so as to surround the periphery of the reading part, and the inflow of dark current to the reading part is almost eliminated. And shallower than the p ⁺ region p ⁺⁺
Since the area is provided, it is possible to obtain a clear image without hindering the movement of the photoelectrically converted charges transferred to the reading unit and without affecting the reading operation of the reading unit.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a photoelectric conversion unit showing an example of a solid-state imaging device according to the present invention.

FIG. 2 is an explanatory diagram showing a cross section of the photoelectric conversion unit shown in FIG.

FIG. 3 is a graph showing a potential distribution of a phototransistor.

FIG. 4 is an explanatory diagram showing a cross-sectional structure of a solid-state imaging device.

FIG. 5 is a diagram schematically showing a photoelectric conversion unit of a conventional solid-state imaging device.

[Explanation of symbols]

11, 12, 13, 14 Charge transfer electrode 15 p ⁺ layer 17 Read-out portion 19 p ⁺⁺ layer 21 N-type silicon substrate 23 p ^- well 25 n ^- well 27 n-type channel layer 29 p-well

Claims (1)

Claim: What is claimed is: 1. A solid-state imaging device, comprising: a p ⁺ region formed on a region excluding a readout portion for extracting charges of a photodiode formed of an n ^- layer and a p ^- well layer. A solid-state image pickup device, wherein a p ^{+ +} region having a higher impurity concentration than the p ⁺ region and a shallower depth than the p ⁺ region is formed in a region surrounding the area.