KR100790229B1 - Image sensor and fabricating method of the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor, and in particular, to form a low concentration N-type impurity region under the depletion region to change the potential distribution under the PD, thereby preventing cross talk between PDs by blocking the flow of photoelectrons generated by dead light. To provide an image sensor and a method of manufacturing the same, for this purpose, the present invention, the first conductive semiconductor layer; A photodiode formed at a predetermined depth from the surface of the semiconductor layer and having a first impurity region of a second conductivity type thereunder; A second impurity region of a second conductivity type formed under the photodiode in the semiconductor layer and having a second potential lower than a first potential of the depletion region formed by the semiconductor layer and the photodiode; A channel stop region of a first conductivity type formed in the semiconductor layer and in contact with one side of the photodiode; And a light blocking metal layer formed on the semiconductor layer to overlap the channel stop region.

In addition, the present invention provides an image sensor manufacturing method of the above structure.

Photodiode, cross talk, channel stop area, depletion area, saddle point.

Description

Image sensor and fabrication method {Image sensor and fabricating method of the same}             

1 is a unit pixel circuit diagram of a conventional CMOS image sensor;

2 is a cross-sectional view showing an image sensor according to the prior art,

3 is a schematic diagram showing the potential distribution when FIG. 2 is cut at A-A ';

4 is a cross-sectional view showing an image sensor according to the present invention;

FIG. 5 is a schematic diagram showing a potential distribution when FIG. 4 is cut at A-A ';

Explanation of symbols on the main parts of the drawings

10: semiconductor layer

PD: Photodiode

CST: Channel Stop Area

SM: Light Blocking Metal Layer

The present invention relates to a semiconductor device, and more particularly, to an image sensor, and more particularly, to an image sensor and a method of manufacturing the same that can minimize cross talk.

In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal. In a double charge coupled device (CCD), individual metal-oxide-silicon (MOS) capacitors are very different from each other. A device in which charge carriers are stored and transported in a capacitor while being located in close proximity, and CMOS (Complementary MOS) image sensor is a CMOS technology that uses a control circuit and a signal processing circuit as peripheral circuits. Is a device that employs a switching method that creates MOS transistors by the number of pixels and sequentially detects the output using them.

In the manufacture of such various image sensors, efforts are being made to increase the photo sensitivity of the image sensor, one of which is a condensing technology. For example, a CMOS image sensor is composed of a photodiode for detecting light and a portion of a CMOS logic circuit for processing the detected light into an electrical signal to make data. To increase light sensitivity, the ratio of the photodiode to the total image sensor area is increased. Efforts have been made to increase (usually referred to as Fill Factor).

1 is a circuit diagram of a unit pixel of a conventional CMOS image sensor, and a submicron CMOS Epi process is applied to increase sensitivity and reduce cross talk between unit pixels.

The unit pixel is composed of one low voltage buried photodiode and four NMOS transistors. Unlike the conventional photo gate structure, the low voltage buried photodiode has a polysilicon with a light sensing region. Not only is it covered, it has excellent light sensitivity for short wavelength blue light as well as increase the depth of depletion in the light sensing area, so the light sensitivity for long wavelength red or infrared light is also excellent. On the other hand, the low-voltage buried photodiode structure allows photogenerated charges in the photosensitive area to be completely transported to the Floating Sensing Node, which significantly increases the charge transfer efficiency. There are advantages to it.

In addition, the transfer gate (Tx), that is, the gate electrode and the reset gate (Rx), which transfer photocharges among the four transistors, is caused by a voltage drop due to a positive threshold voltage. In order to prevent the loss of charge transport efficiency, the NMOS transistor has a negative threshold voltage. In this case, the N-LDD ion implantation is omitted so that the overlap capacitance between the gate electrode and the reset gate and the floating sensing node is reduced. (Overlap Capacitance) can be lowered, so that the potential change of the floating sensing node can be amplified according to the amount of charge carried. (△ V-ΔQ / C)

Meanwhile, the drive gate (Sx) serving as a source follower is composed of a general submicron NMOS transistor. This structure was constructed with minimal changes to the submicron CMOS Epi process, and specifically the thermal cycle was designed to be completely unchanged. On the other hand, a color filter array composed of red, green, blue, or yellow, magenta, cyan, and the like on a unit pixel array for implementing a color image. (Color Filter Array) The process of forming.

The operation principle of obtaining an output from such a unit pixel is as follows.

end. Turn off Tx, Rx, Sx. The low voltage buried photodiode is then fully depletion.

I. Photogenerated charge is collected in a low voltage buried photo diode.

All. After a proper integration time, the Rx is turned on to reset the floating sensing node first.

la. The unit pixel is turned on by turning on Sx.

hemp. Measure the output voltage (V1) of the source follower buffer. This value simply means the CD level shift of the Floating Sensing Node.

bar. Turn on Tx.

four. All photogenerated charges are transported to Floating Sensing Nodes.

Ah. Turn off Tx.                         

character. Measure the output voltage (V2) of the source follower buffer.

car. The output signals V1-V2 are the result of the photocharge transport resulting from the difference between V1 and V2 and are pure signal values without noise. This method is called CDS (Corelated Double Sampling).

Ka. Repeat the process of 'a' to 'tea'. However, the low voltage buried photodiode is fully depleted during the 'dead' process.

2 is a cross-sectional view showing an image sensor according to the prior art.

Referring to FIG. 2, a P0 and an n- structure photodiode (hereinafter referred to as PD) are formed in the semiconductor layer 10 through a process such as ion implantation, and the data interference between neighboring PDs is prevented. A P-type channel stop region (hereinafter referred to as CST) is formed to prevent cross talk, and CST is typically formed under a field insulating film (not shown) through P-type impurity ion implantation. . In addition, a light blocking metal layer (hereinafter referred to as SM) is formed on the upper portion which does not overlap with the PD to prevent the light incident to the transfer gate (not shown) and the throttle torque between the PD due to the dead light α. have.

Here, the gate electrodes, that is, the transfer gate and the source / drain, are omitted for simplicity of the drawings, and the planarization film under the SM is also omitted. In addition, the semiconductor layer 10 may include a structure in which a high concentration P ++ layer P-Epi layer is stacked or a P-well.

In the conventional image sensor made as described above, when the external strong incident light is irradiated, the dead light α due to the multilayer reflection between the layers having different refractive indices or the refraction generated by the surface of the non-uniform film is generated. As shown in the drawing, the distance from the surface of the semiconductor layer 10 to the SM is far, that is, the film between them is thick, and thus, it is impossible to prevent cross talk due to the ray of light such as α.

Here, X represents a saddle point, which is a boundary point where the P-type semiconductor layer 10 is depleted by the n- region and remains as a neutral region. It can be said that the level of 10) is the first point at which the level becomes 0V.

FIG. 3 schematically shows the potential distribution when FIG. 2 is cut at A-A ', and the photoelectrons α' generated inside the P-type semiconductor layer 10 by α-radiation also exhibit drift. And diffusion into the depletion region by the potential difference to cause cross talk.

On the other hand, in order to prevent crosstalk between the PD due to the light projection, the distance between the SM and the surface of the semiconductor layer 10 may be shortened, that is, the intermediate film may be omitted or thinned. It adversely affects the characteristics of the device. Therefore, there is a need for a fundamental solution for preventing cross talk caused by such light.

The present invention proposed to solve the problems of the prior art as described above, by forming a low concentration of the N-type impurity region under the depletion region to change the potential distribution of the lower PD to fundamentally block the flow of optoelectronic generated by the dead light It is an object of the present invention to provide an image sensor and a method of manufacturing the same that can prevent cross talk between PDs.

In order to achieve the above object, the present invention, the first conductive semiconductor layer; A photodiode formed at a predetermined depth from the surface of the semiconductor layer and having a first impurity region of a second conductivity type thereunder; A second impurity region of a second conductivity type formed under the photodiode in the semiconductor layer and having a second potential lower than a first potential of the depletion region formed by the semiconductor layer and the photodiode; A channel stop region of a first conductivity type formed in the semiconductor layer and in contact with one side of the photodiode; And a light blocking metal layer formed on the semiconductor layer to overlap the channel stop region.

In addition, the present invention to achieve the above object, the first step of forming a second impurity region of the second conductive type inside the semiconductor layer of the first conductive type; Forming a channel stop region of a first conductivity type in the semiconductor layer to be in contact with a surface of the semiconductor layer; A third step of forming a first impurity region of a second conductivity type for photodiode on the second impurity region in the semiconductor layer through ion implantation, wherein the first impurity region is in contact with one side of the channel stop region; A fourth step of forming a third impurity region of a first conductivity type at an interface in contact with the semiconductor layer above the first impurity region; And a fifth step of forming a light blocking metal layer on the semiconductor layer so as to overlap the channel stop region.                     

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. do.

4 is a cross-sectional view showing an image sensor of the present invention.

Referring to FIG. 4, the image sensor of the present invention is formed with a P-type semiconductor layer 10, a predetermined depth from the surface of the semiconductor layer 10, and has an N-type impurity region n1- below. N having a photodiode PD and a second potential lower than the first potential of the depletion region formed by the semiconductor layer 10 and the photodiode PD formed under the photodiode PD in the semiconductor layer 10. Type impurity region n2-, a P-type channel stop region CST formed in the semiconductor layer 10 and in contact with one side of the photodiode PD, and a channel stop region on the semiconductor layer 10. The light blocking metal layer SM is formed to overlap the CST, and the gate electrodes, that is, the transfer gate and the source / drain, are omitted for the sake of simplicity, and the planarization film under the SM is omitted. In addition, the semiconductor layer 10 may include a structure in which a high concentration P ++ layer P-Epi layer is stacked or a P-well. Further, a P-type impurity region P0 for photodiode PD is formed at an interface in contact with the semiconductor layer 10 above the impurity region n1-.

In the image sensor of the present invention having the above-described configuration, P / N / P / is formed by additionally forming n2-region in the conventional P / N / P-type PD structure formed of P0 region, n1-region, and semiconductor layer. Since it has an N / P structure, cross talk is prevented by processing the photoelectron generated by incident light like 'ga' in the n2- region.

That is, as shown in FIG. 5 schematically showing the potential distribution by cutting FIG. 4 in the AA 'direction, Ga' is blocked by a kind of potential barrier by the n2- region with lower potential at the saddle point X '. It does not spread to the PD region. Therefore, it is possible to fundamentally prevent the crosstalk caused by the photoelectron generated by the dead light.

At this time, the n2- region may have a ground potential, and a constant DC may be applied. In addition, the depletion region may be formed wider by forming at a deeper level.

On the other hand, looks at the manufacturing process of the image sensor having the above configuration.

First, an n2- region is formed in the semiconductor layer 10 through ion implantation, and is formed with an energy of 1MeV to 5MeV by using impurities having a concentration of 1.0E15 / cm 3 to 1.0E18 / cm 3, followed by n1-n for PD. It is possible to adjust the saddle point of the depletion region to be formed according to the concentration and depth of the region.

Subsequently, a P-type channel stop region CST is formed in the semiconductor layer 10 to be in contact with the surface of the semiconductor layer 10. A field insulating film (not shown) is formed, followed by ion implantation to form a field insulating film ( It is formed in the lower portion, not to reduce the width of the PD at this time.

Next, an ion implantation is to form an N-type impurity region (n1-region) for photodiode on the n2- region in the semiconductor layer 10, and to be in contact with one side of the channel stop region (CST). Energy of 100KeV to 250KeV which is lower than the ion implantation energy for n2-region formation is used.

Subsequently, the P-type impurity region P0 for PD is formed so that the photodiode region has a P / N / P / N / P structure by forming the P-type impurity region P0 at an interface in contact with the semiconductor layer 10 above the n1-region. A sensor is formed, and a light blocking metal layer SM is formed on the upper portion which does not overlap with the PD for preventing incident light to the transfer gate (not shown) and thrust torque between the PD due to the dead light.

Therefore, even if the distance between the SM and the surface of the semiconductor layer 10 is far, crosstalk between the PDs due to the flow of photoelectrons formed by the oblique light by the n2-region is effectively prevented.

According to the present invention as described above, an N-type impurity region is formed below the PD to form a potential well, thereby suppressing the flow of photoelectrons generated by dead light to fundamentally prevent cross talk between PDs. It can be seen through the examples.

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

The present invention described above, by minimizing the cross talk of the data between the photodiode, it can be expected to have an excellent effect that can ultimately greatly improve the performance of the image sensor.

Claims (8)

In the image sensor, A first conductive semiconductor layer; A photodiode formed at a predetermined depth from the surface of the semiconductor layer and having a first impurity region of a second conductivity type thereunder; A second impurity region of a second conductivity type formed under the photodiode in the semiconductor layer and having a second potential lower than a first potential of the depletion region formed by the semiconductor layer and the photodiode; A channel stop region of a first conductivity type formed in the semiconductor layer and in contact with one side of the photodiode; And A light blocking metal layer formed to overlap the channel stop region on the semiconductor layer; And the photodiode further comprises a third impurity region of a first conductivity type at an interface in contact with the semiconductor layer above the first impurity region. The method of claim 1, And the second impurity region has a ground potential. delete The method according to claim 1 or 2, The first conductive type is a P-type, the second conductive type is an image sensor, characterized in that the N-type. In the image sensor manufacturing method, A first step of forming a second impurity region of a second conductive type in the semiconductor layer of the first conductive type; Forming a channel stop region of a first conductivity type in the semiconductor layer to be in contact with a surface of the semiconductor layer; A third step of forming a first impurity region of a second conductivity type for photodiode on the second impurity region in the semiconductor layer through ion implantation, wherein the first impurity region is in contact with one side of the channel stop region; A fourth step of forming a third impurity region of a first conductivity type at an interface in contact with the semiconductor layer above the first impurity region; And A fifth step of forming a light blocking metal layer on the semiconductor layer to overlap the channel stop region; Image sensor manufacturing method comprising a. The method of claim 5, Upon formation of the second impurity region of the first step, An ion sensor is implanted using impurities of 1.0E15 / cm 3 to 1.0E18 / cm 3 concentration. The method of claim 6, When the ion implantation, the image sensor manufacturing method, characterized in that using the energy of 1MeV to 5MeV. The method of claim 5, The first conductive type is a P-type, the second conductive type is an image sensor manufacturing method, characterized in that the N-type.

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