JPH05190829A - Solid-state image-sensing element - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the charge transfer efficiency in a charge transfer device. A photoelectric conversion element array including a plurality of photoelectric conversion elements 1 arranged side by side and a charge transfer element provided adjacent to the photoelectric conversion element array are provided, and the charge transfer element includes a charge transfer path 35. In the solid-state imaging device including the charge read electrode 30A and the charge transfer electrode 30B provided for each photoelectric conversion element on the charge transfer path, except for the side portion of each photoelectric conversion element on the charge transfer element side. While the element isolation diffusion layer 10 is formed on the side of the charge transfer electrode, even if a charge transfer voltage is applied to the charge transfer electrode, the voltage causes the charge from the photoelectric conversion element to reach the charge transfer path of the charge transfer element. Means are provided to prevent transfer.

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, it relates to improvement of a diffusion layer for element isolation surrounding the photoelectric conversion element.

[0002]

2. Description of the Related Art A solid-state image pickup device generates an amount of electric charge corresponding to the light intensity in each photoelectric conversion device when a light image is projected on a region where a plurality of photoelectric conversion devices are formed. Each charge is transferred to the outside of the light image projection area by the charge transfer element, the charge amount corresponding to each photoelectric conversion element is converted into, for example, a voltage value, and the signal obtained by this is output as a video signal. ing.

The charge transfer element is formed by arranging a charge transfer electrode and a charge read electrode in parallel along the transfer direction on each charge transfer path adjacent to one photoelectric conversion element. Element conversion diffusion layers are formed on the sides of the conversion element other than under the charge read electrode.

The solid-state image pickup device having such a structure is
For example, the document “Video Information 1986 May Issue Vo
L. 18 Industrial Development Organization KK Issue ”.

[0005]

However, in the solid-state image pickup device having the above-mentioned structure, the region (where the device isolation diffusion layer is formed at the boundary between the charge transfer path and the photoelectric conversion device in the charge transfer device). There is a region under the charge transfer electrode) and a region not formed (region under the charge read electrode). Due to this, the impurity concentration in the charge transfer path cannot be made uniform in the transfer direction. However, since the element isolation diffusion layer and the diffusion layer forming the charge transfer path are diffusion layers of different conductivity types, the part of the charge transfer path adjacent to the element isolation diffusion layer is different from the other part. This is because the impurity concentration becomes thin as compared with the above.

For this reason, the potential of the charge transfer path varies along the transfer direction, causing a problem in that the charge transfer becomes defective.

Therefore, the present invention has been made under such circumstances, and an object of the present invention is to provide a solid-state image pickup device having an improved charge transfer efficiency in the charge transfer device. Especially.

[0008]

In order to achieve such an object, the present invention basically provides a photoelectric conversion element array composed of a plurality of photoelectric conversion elements arranged in parallel, and this photoelectric conversion element array. And a charge transfer element provided adjacently to the charge transfer element. The charge transfer element includes a charge transfer path and a charge read electrode and a charge transfer electrode provided on the charge transfer path for each photoelectric conversion element. In the solid-state image pickup device, a diffusion layer for element isolation is formed on the side portions other than the side portion on the charge transfer element side of each photoelectric conversion element, and even if a charge transfer voltage is applied to the charge transfer electrodes. It is characterized in that a means is provided for preventing charges from the photoelectric conversion element from being transferred to the charge transfer path of the charge transfer element by the voltage.

[0009]

In the solid-state image pickup device thus constructed, the element isolation diffusion layer is formed on each side of the photoelectric conversion elements except the side on the charge transfer element side. This is because no element isolation diffusion layer is formed on the side of each photoelectric conversion element on the charge transfer element side.

Therefore, in the charge transfer path of the charge transfer element, the effect of the element isolation diffusion layer becomes almost the same along the longitudinal direction thereof, and the impurity concentration is lowered by the element isolation diffusion layer. No area is formed.

This means that the height of the potential becomes uniform along the charge transfer path of the charge transfer element, so that the transfer failure unlike the conventional case does not occur.

In addition, the present invention adopts the above-mentioned configuration, and even if a charge transfer voltage is applied to the charge transfer electrode, the voltage causes the charge from the photoelectric conversion element to reach the charge transfer path of the charge transfer element. A means for preventing the transfer is provided.

This means is implemented by means other than the diffusion layer for element isolation described above. For example, even if a transfer voltage is applied to the charge transfer electrode, photoelectric conversion is performed on the surface of the semiconductor layer below the charge transfer electrode. The channel layer for connecting the element and the charge transfer path of the charge transfer element is not formed.

[0014]

FIG. 2 is a schematic configuration diagram showing an embodiment of a solid-state image pickup device according to the present invention.

In the figure, each element is formed in the arrangement as shown on the main surface of a one-chip semiconductor substrate. In the figure, a plurality of photodiodes 1 are formed in a matrix in a light image projection area on the main surface of the semiconductor substrate.

Here, the photodiode 1 is a photoelectric conversion element which generates an electric charge according to the intensity of the light upon irradiation with the light.

Further, there is a vertical shift register 2 formed along the column direction for each group of photodiodes 1 arranged in the column direction (vertical direction in the figure), and each of these vertical shift registers 2 is a CCD element. It consists of

The vertical shift registers 2 read the charges generated in the photodiodes 1 arranged in the column direction and transfer the charges to the outside of the optical image projection area along the column direction. Is becoming

The charge read from each photodiode 1 to the vertical shift register 2 is performed by a charge read electrode (not shown).

Further, the charges respectively transferred from the respective vertical shift registers 2 are outputted to the horizontal shift register 4 and transferred by the horizontal shift register 4 in the horizontal direction. The horizontal shift register 4 is composed of CCD elements like the vertical shift registers 2.

The output from the horizontal shift register 4 is input to the output circuit 5, converted into, for example, a voltage in the output circuit 5, and taken out to the outside.

Then, in the main surface of the semiconductor substrate on which each element is formed in this way, an opening is formed in the region where each photodiode 1 is formed, so that only each photodiode 1 is exposed to light. A film (not shown) is formed.

FIG. 3 is a plan view showing in detail the relationship between the CCD element which is the vertical shift register 2 and the photodiode 1.

In the figure, the formation region of the N-type diffusion layer 23 shown by the dotted region in the figure is the formation region of the photodiode 1, and these photodiodes 1 are arranged in a matrix. Although not shown in the figure, on the surface of the N-type diffusion layer 23 of the photodiode 1, a P-type diffusion layer 24 for preventing so-called dark current (see FIG. 4).
(See) has been formed.

A charge transfer path 35 is formed between the photodiode groups arranged in the column direction (vertical direction in the drawing). The charge transfer path 35 is adapted to transfer charges after reading out the charges from each photodiode 1 positioned on the left side in the drawing.

The charges are read out and transferred by the transfer electrode 30A formed in the second layer (this transfer electrode 30A is hereinafter referred to as the read electrode 30A) and the transfer electrode 30B formed in the first layer. It has become so.

The transfer electrodes 30B and the read electrodes 30A are alternately arranged along the charge transfer paths 35, and the read electrodes 30A in the direction of the charge transfer paths.
Both ends of the (second layer) are positioned above the transfer electrodes 30B (first layer) and have overlapping regions.

Further, both sides of the read electrode 30A (sides parallel to the charge transfer path 35) are positioned on an extension of the corresponding side of the transfer electrode 30B on one side, but the other side. It extends over the region of the photodiode 1. The readout electrode 30A has a function as a transfer electrode, but the extension portion has a function for reading out the charge of the photodiode 1.

The transfer electrode 30B and the readout electrode 30A on each charge transfer path 35 are connected to the adjacent charge transfer path 3
5, the transfer electrodes 30B and the readout electrodes 30A on the upper electrode 5 are connected to each other so that a transfer signal is commonly applied.

FIG. 1 is a plan view showing the diffusion layer exposed on the surface of the semiconductor substrate by removing the transfer electrode 30B, the read electrode 30A, and the gate oxide film (not shown) in FIG. In the figure, a plurality of N-type diffusion layers 25 forming the charge transfer path 35 are formed in parallel. On the left side of each charge transfer path 35 in the drawing, a plurality of N-type diffusion layers 23 forming the photodiode 1 are arranged in parallel along the extending direction of the charge transfer path 35.

An element isolation diffusion layer 10 for electrically isolating the photodiode 1 and the charge transfer path 35 located on the left side of the drawing is formed of a P type diffusion layer. However, in this embodiment, in particular, it is not formed at all on the side on the charge transfer path 35 side where the charges are read out, but is formed only on the portion corresponding to the remaining side. Especially.

As described above, since the element isolation diffusion layer 10 surrounding the photodiode 1 is not formed on the charge transfer path 35 side from which the charges are read from the photodiode 1, the charge transfer path is formed. The element 35 is not affected by the influence of the element isolation diffusion layer 10 such that its impurity concentration is reduced. Therefore, the impurity concentration along the charge transfer direction in the charge transfer path 35 is maintained uniform.

In the charge transfer path 35 in FIG. 1, aa (below the transfer electrode 30B) and bb (below the read electrode 30A).
As shown in FIG. 7, it can be seen that the potential φ distributions at are the same in all cases. Therefore, it is possible to improve the charge transfer efficiency due to the uniformity of the potential φ distribution.

Here, the effect of the solid-state image sensor of this embodiment will be clarified by comparing the conventional solid-state image sensor and the solid-state image sensor of this embodiment.

FIG. 8 is a diagram showing the structure of a conventional solid-state image pickup device, which is associated with the structure of FIG. 1 according to the present embodiment. In FIG. 8, the isolation element diffusion layer 10 is not formed only under the readout electrode 30A, and except for this portion, the N-type diffusion layer 23 that substantially constitutes the photodiode 1 is formed.
Is formed so as to surround. Therefore, the diffusion layer 10 for separating element is formed below the transfer electrode 30B as compared with the case of FIG. In this case, when the potential φ distribution is similarly examined at the location corresponding to FIG. 1,
As will be apparent from the dotted line portion of FIG.
The potential is low under B.

FIG. 4 is a constitutional view showing a cross section taken along line VI-VI in FIG.

In the figure, there is an N-type semiconductor substrate 21, and a P-type well layer 22 made of a P-type semiconductor layer having a low concentration is formed on the surface of the N-type semiconductor substrate 21.
An N-type diffusion layer 23 is formed on the surface of the P-type well layer 22 and constitutes the photodiode 1 together with the P-type well layer 22.

On the surface of the N type diffusion layer 23 constituting the photodiode 1, a high concentration P type diffusion layer 24 is formed.
Are formed. The P-type diffusion layer 24 is a diffusion layer for preventing so-called dark current.

Further, N constituting the photodiode 1
An N-type diffusion layer 25, which is a charge transfer path (indicated by a charge transfer path 35 in FIG. 1) of the vertical shift register 2, is formed on the surface of the P-type well layer 22 in the vicinity of the type diffusion layer 23. There is. The N-type diffusion layer 25 is formed on the surface of the high-concentration P-type well layer 26 formed in the P-type well layer 22 in order to prevent so-called smear.

A read electrode 30A is formed on the main surface on which the various diffusion layers are thus formed, with an insulating film 27 made of, for example, a silicon oxide film interposed therebetween.

The read electrode 30A is formed so as to cover the surface of the P type diffusion layer 26 between the N type diffusion layer 23 of the photodiode 1 and the N type diffusion layer 25 which is the charge transfer path 35, By applying a read voltage to the read electrode 30A, a channel layer is formed on the surface to read charges.

Further, an insulating film 27 made of an oxide film is formed so as to cover the read electrode 30A and the region of the photodiode 1, and the upper surface of the insulating film 27 except the region where the photodiode 1 is formed (hence the opening). The light shielding film 28 made of, for example, aluminum is formed.

FIG. 5 is a sectional view taken along line VV in FIG.

The same reference numerals as in FIG. 4 indicate the same parts. In the figure, the structure different from that of FIG.
B and the N-type diffusion layer 23 forming the photodiode 1. That is, the edge of the transfer electrode 30B on the side of the photodiode 1 and the edge of the N-type diffusion layer forming the photodiode 1 on the side of the transfer electrode 30B are formed so as to be separated by α in the figure. Even if a transfer voltage is applied to 30B, a channel layer or the like is formed on the surface of the P-type diffusion layer 26 so that charge reading cannot be performed.

Such a structure is a necessary structure which must be made with the improvement of the element isolation diffusion layer in this embodiment.

In short, even if a transfer voltage is applied to the transfer electrode 30B, means for preventing charges from the photodiode 1 from being transferred to the charge transfer path 35 by the voltage is provided by means other than the element isolation diffusion layer. This is intended to eliminate the adverse effect of the element isolation diffusion layer.

Therefore, as shown in FIG. 6, the surface of the P type diffusion layer 26 between the N type diffusion layer 23 forming the photodiode 1 and the N type diffusion layer 25 forming the charge transfer path 35 is covered. Even if the transfer electrode 30B is formed, the N
The same means as described above is formed by forming the extending portion 60 in which the P-type diffusion layer 24 for preventing so-called dark current formed on the surface of the type diffusion layer 23 is extended below the transfer electrode 30B. Can be configured.

According to the solid-state image pickup device according to the embodiment described above, the element isolation diffusion layer 10 is formed on the other side portions of the respective photodiodes 1 except the side portion on the CCD element side. Therefore, in particular, each photodiode 1
The diffusion layer 10 for element isolation is not formed at all on the side of the CCD element side.

Therefore, in the charge transfer path 35 of the CCD element, the influence of the element isolation diffusion layer 10 becomes almost the same along the longitudinal direction, and the impurity concentration is lowered by the element isolation diffusion layer 10. There is no possibility that a region such as a dead end will be formed.

This means that the charge transfer path 35 of the CCD element is
Since the height of the potential becomes uniform along the line, there is no problem of transfer failure as in the conventional case.

In addition, this embodiment adopts the above-mentioned structure, and even if a transfer voltage is applied to the transfer electrode 30B, the charge from the photodiode 1 is transferred to the charge transfer path 35 of the CCD element by the voltage. It is provided with a means for preventing this.

This means is based on the above-mentioned element isolation diffusion layer 10.
The present embodiment is intended to eliminate the harmful effects of the element isolation diffusion layer 10.

In the above-mentioned embodiment, the solid-state image pickup device called a so-called area sensor has been described, but the present invention is not limited to this. For example, photoelectric conversion devices are arranged in a line. It goes without saying that the present invention can also be applied to a solid-state image sensor including a line sensor.

[0054]

As is clear from the above description,
According to the solid-state imaging device of the present invention, the charge transfer efficiency of the charge transfer device can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of a solid-state image pickup device according to the present invention, and is a plan view showing a pattern of a device isolation diffusion layer in particular.

FIG. 2 is an overall schematic diagram showing an embodiment of a solid-state image sensor according to the present invention.

FIG. 3 is a plan view showing an example of patterns of a charge read electrode and a charge transfer electrode in the solid-state image sensor according to the present invention.

FIG. 4 is a cross-sectional view taken along the line VV of FIG.

5 is a sectional view taken along line VI-VI in FIG.

FIG. 6 is a sectional view showing another embodiment of the solid-state image sensor according to the present invention.

FIG. 7 is a graph comparing the effects of the solid-state image sensor according to the present invention with the conventional case.

FIG. 8 is a configuration diagram showing an example of a conventional solid-state imaging device, and is a plan view showing a pattern of a device isolation diffusion layer in particular.

[Explanation of symbols]

1 ... Photodiode, 10 ... Element isolation diffusion layer, 30
A ... Read electrode, 30B ... Transfer electrode, 35 ... Charge transfer path.

Claims (1)

[Claims] 1. A photoelectric conversion element array comprising a plurality of photoelectric conversion elements arranged in parallel, and a charge transfer element provided adjacent to the photoelectric conversion element array, the charge transfer element being a charge transfer path. In a solid-state imaging device including a charge read electrode and a charge transfer electrode provided for each photoelectric conversion element on the charge transfer path, other sides of the photoelectric conversion element except a side portion on the charge transfer element side. A diffusion layer for element isolation is formed in the portion, and even if a charge transfer voltage is applied to the charge transfer electrode, the voltage prevents the charge from the photoelectric conversion element from being transferred to the charge transfer path of the charge transfer element. A solid-state image sensor, comprising: