KR20060077079A - Cmos image sensor and method for fabricating the same - Google Patents

Abstract

The present invention is to provide a CMOS image sensor capable of realizing the image more realistic by removing the noise caused by removing all the electrons remaining in the sensing node even by the turn-on / turn-off operation of the reset transistor. The present invention is a photodiode; A sensing node doped with conductive impurities; A gate pattern of a reset transistor for transferring electrons transferred from the photodiode to the sensing node; A junction region doped with conductive impurities connected to the power supply voltage terminal; And a gate pattern of a reset transistor for transferring electrons generated by noise to the junction region in the sensing node, wherein the sensing node has a higher potential in the region of the gate pattern side of the reset transistor and a gate of a transfer transistor. The sensing node area of the pattern side provides a CMOS image sensor, characterized in that the potential is provided low.

CMOS image sensor, photodiode, reset transistor, noise.

Description

CMOS image sensor and its manufacturing method {CMOS IMAGE SENSOR AND METHOD FOR FABRICATING THE SAME}             

1 is a circuit diagram showing one unit pixel in a CMOS image sensor.

FIG. 2 is a process cross-sectional view of four MOS transistors forming a unit cycle shown in FIG.

3 is a process plan view of four MOS transistors shown in FIG.

4 is a view showing a problem of the CMOS image sensor according to the prior art.

5 illustrates a CMOS image sensor and its operation according to a preferred embodiment of the present invention.

6A to 6C are cross-sectional views showing a method of manufacturing the CMOS image sensor shown in FIG.

Explanation of symbols on the main parts of the drawings

20: substrate

22: sensing node 22a: high concentration impurity region of the sensing node

23: photodiode

24: gate pattern of the transfer transistor                 

25: gate pattern of reset transistor

The present invention relates to a CMOS image sensor, and more particularly to a CMOS image sensor that can reduce the reset noise.

In general, an image sensor of a semiconductor device is a semiconductor device that converts an optical image into an electrical signal. Representative image sensor devices include a charge coupled device (CCD) and a CMOS image sensor.

Among them, the charge-coupled device is a device in which charge carriers are stored and transported in the capacitor while individual metal-oxide-silicon (MOS) capacitors are located very close to each other. By using CMOS technology that uses a signal processing circuit as a peripheral circuit, a MOS transistor (typically four MOS transistors) corresponding to the number of pixels is made and sequentially output using the MOS transistor.

1 is a circuit diagram showing one unit pixel in a CMOS image sensor.

Referring to FIG. 1, one unit pixel includes one photodiode 10 and four an MOS transistors 11, 12, 13, and 14. As shown in FIG. Four NMOS transistors 11, 12, 13, and 14 are transfer MOS transistors 11 for transporting photocharges generated in the photodiode 10 to the charge sensing node N, and for the next signal detection. Addressing is performed by the reset MOS transistor 12 for discharging the charge stored in the charge sensing node 11, the drive MOS transistor 13 serving as a source follower, and the switching role. It is composed of a select MOS transistor 14 to enable it.

Four MOS transistors 11, 12, 13, and 14 and one photodiode 10 form one unit pixel, and are provided in the pixel array of the CMOS image sensor according to the number of unit pixels included in the CMOS image sensor. The number of photodiodes 10 and the number of MOS transistors for unit pixels corresponding thereto are determined.

FIG. 2 is a process cross-sectional view of four MOS transistors forming a unit circuit shown in FIG. 1, in which four MOS transistors 11, 12, 13, and 14 transfer signals Tx, Rx, Dx, and Sx to gates, respectively. The light transferred to the photodiode PD is transferred to the output terminal.

3 is a process plan view of four MOS transistors shown in FIG.

As shown in FIG. 3, the gate patterns Tx of the four MOS transistors 11, 12, 13, and 14 for transferring electrons collected by light transferred from the photodiode 10 to an output terminal. , Rx, Dx, and Sx are disposed, and active regions 101 to 104 are disposed to the left and right of the gate patterns Tx, Rx, Dx, and Sx, respectively.

The active region 101 is a sensing node SN that transfers electrons collected by the photodiode.                         

Looking at the operation of one unit device briefly, electrons collected by light transferred to the photodiode 10 are transferred to the sensing node 101 through the transfer transistor 11.

Since the sensing node 101 is connected to the gate of the driving transistor 13, the driving transistor 13 adjusts the voltage level of the active region 103 bonded to one end in accordance with the voltage applied to the sensing node 101. Driving. Subsequently, the select transistor 104 is turned on to output a voltage applied to the active region 103 through an output terminal.

In the process of transferring data once, a reset process is performed. The reset process is a process of removing the electrons accumulated in the sensing node due to noise by turning on the reset transistor. In the reset process, the difference between the output value and the data by the actual image is processed as actual information.

4 is a view showing a problem of the CMOS image sensor according to the prior art.

When the image sensor operates, the difference between the reset output value and the data output value for the incident light is processed as an image, which is called correlated double sampling (CDS).

When the reset transistor is turned on, all of the charge remaining in the sensing node must escape to the power supply voltage, but not all of the charge remains.

Noise caused by the remaining electrons at this time becomes very difficult to remove even by using the above-described CDS method.                         

In the left figure of FIG. 4, if the level when the reset transistor is turned on is b, and the time when the reset transistor is turned off is a, the sensing node is turned on and the sensing node is removed even after the reset transistor is turned off. The electrons remain in the device, resulting in noise.

The noise at this time causes a problem that the image is distorted even when using the CDS method, which causes a problem in that the image cannot be properly implemented.

The present invention has been proposed to solve the above-mentioned problems, and by removing all the electrons remaining in the sensing node even by the turn-on / turn-off operation of the reset transistor, it is possible to implement the image more closely by removing the noise caused by the noise. It is an object to provide a CMOS image sensor.

The present invention is a photodiode; A sensing node doped with conductive impurities; A gate pattern of a reset transistor for transferring electrons transferred from the photodiode to the sensing node; A junction region doped with conductive impurities connected to the power supply voltage terminal; And a gate pattern of a reset transistor for transferring electrons generated by noise to the junction region in the sensing node, wherein the sensing node has a higher potential in the region of the gate pattern side of the reset transistor and a gate of a transfer transistor. The sensing node area of the pattern side provides a CMOS image sensor, characterized in that the potential is provided low.

In addition, the present invention comprises the steps of forming a gate pattern of the reset transistor and the gate pattern of the transfer transistor on the substrate; Forming a sensing node by doping an impurity between the gate pattern of the reset transistor and the gate pattern of the transfer transistor; Doping an impurity in a portion of the sensing node so that the region of the gate pattern side of the reset transistor has a higher potential, and the sensing node region of the gate pattern side of the transfer transistor has a lower potential. Provided is a method of manufacturing a CMOS image sensor.

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.

5 is a diagram illustrating a CMOS image sensor and its operation according to a preferred embodiment of the present invention.

Referring to FIG. 5, the CMOS image sensor according to the present exemplary embodiment does not make the potential of the sensing node flat but is formed to have a constant slope.

By adjusting the doping concentration of the sensing node, the potential on the gate pattern side of the reset transistor is higher, and the sensing node on the gate pattern side of the transfer transistor forms a lower potential.                     

By forming the sensing node, the electrons accumulated in the sensing node can easily move toward the gate pattern of the reset transistor regardless of the external image due to the naturally generated internal electric field.

By doing so, all the electrons due to the noise generated in the reset operation are removed to the reset transistor, so that the data related to the pure image from which the noise component is removed can be safely processed in the process of receiving and processing the image.

6A to 6C are cross-sectional views illustrating a method of manufacturing the CMOS image sensor shown in FIG. 5.

Referring to FIG. 6A, the method of manufacturing an image sensor according to the present embodiment first forms a gate pattern 25 of a reset transistor and a gate pattern 24 of a transfer transistor on a substrate 20.

Subsequently, the n-type impurity regions 21 and 22 are formed on one side and the other side of the gate pattern of the reset transistor, and the photodiode 23 is formed on one side of the transistor transistor. Herein, the n-type impurity region 22 becomes a sensing node.

6B, a photosensitive film pattern 26 is formed to expose a portion of the sensing node of the gate pattern side of the transfer transistor. At this time, the area about half of the sensing node is exposed.

Subsequently, the photoresist pattern 26 is used as an etch mask to dope the n-type impurity into the sensing node to form a high concentration impurity region 22a of the sensing node.

Subsequently, as illustrated in FIG. 6C, the photoresist pattern 26 is removed.                     

As described above, instead of uniformly doping the sensing node, the doping concentration of the sensing node is adjusted so that the area of the gate pattern side of the reset transistor has a higher potential, and the sensing node area of the gate pattern side of the transfer transistor has a potential. By forming a lower value, it is possible to remove all accumulated electrons generated regardless of the image in the sensing node by giving a tilt rather than flattening the potential.

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.

For example, the sensing node may be formed to have a multi-stage doping concentration instead of forming the sensing node in a two-step impurity doping process.

In addition, the process may be performed by doping the impurity in the opposite region without further doping the anneal impurity in order to give the sensing node a slope in potential.

According to the present invention, since the electrons accumulated as noise components in the sensing node of the CMOS image sensor can be removed through the reset transistor more easily than in the related art, a high quality image can be easily implemented in receiving and implementing the image. .

Claims (10)

Photodiode; A sensing node doped with conductive impurities; A gate pattern of a reset transistor for transferring electrons transferred from the photodiode to the sensing node; A junction region doped with conductive impurities connected to the power supply voltage terminal; And A gate pattern of a reset transistor configured to transfer electrons generated by noise to the junction region in the sensing node, And the sensing node has a higher potential at the gate pattern side of the reset transistor, and has a lower potential at the sensing node region of the gate pattern side of the transfer transistor. The method of claim 1, The sensing node The CMOS image sensor, characterized in that at least two or more regions have different doping concentrations so that the potential at the gate pattern side of the reset transistor is higher and the sensing node region at the gate pattern side of the transfer transistor has a lower potential. . The method of claim 1, The sensing node The area on the gate pattern side of the reset transistor has a higher potential, and the sensing node area on the gate pattern side of the transfer transistor has a lower potential. And an N-type impurity concentration of 1/2 region of the gate transistor side of the transformer transistor is higher. The method of claim 1, The sensing node The area on the gate pattern side of the reset transistor has a higher potential, and the sensing node area on the gate pattern side of the transfer transistor has a lower potential. The CMOS image sensor, characterized in that the concentration of the implanted impurity in the 1/2 region of the gate pattern side of the transformer transistor is lower. Forming a gate pattern of the reset transistor and a gate pattern of the transfer transistor on the substrate; Forming a sensing node by doping an impurity between the gate pattern of the reset transistor and the gate pattern of the transfer transistor; Doping impurities in a portion of the sensing node so as to make the potential at the gate pattern side of the reset transistor higher and the sensing node area at the gate pattern side of the transfer transistor lower the potential. Method of manufacturing a CMOS image sensor. The method of claim 5, The method of manufacturing a CMOS image sensor comprising doping an impurity in a portion of the sensing node comprises doping an impurity in a half region of the sensing node. The method of claim 5, Doping an impurity in a portion of the sensing node And a doped N-type impurity in a portion of the sensing node on the gate pattern side of the transfer transistor in the sensing node region. The method of claim 5, Doping an impurity in a portion of the sensing node And a dopant impurity in a portion of the sensing node of the sensing transistor in a gate pattern side of the reset transistor. The method of claim 5, Doping an impurity in a portion of the sensing node Doping an N-type impurity at a first doping concentration to a first partial region of the sensing transistor region on a gate pattern side of a transfer transistor; And The second partial region (the region of the gate pattern side of the transfer transistor of the area smaller than the first partial region) of the sensing node region of the gate pattern side of the transfer transistor is higher than the second doping concentration (the first doping concentration). The method of manufacturing a CMOS image sensor comprising the step of doping the n-type impurity. The method of claim 5, Doping an impurity in a portion of the sensing node Doping impurity impurities at a first doping concentration to a first partial region of the sensing transistor region on the gate pattern side of a reset transistor; And The second partial region (the region of the gate pattern side of the transfer transistor having the smaller area than the first partial region) of the sensing transistor region of the gate pattern side of the reset transistor is higher than the second doping concentration (the first doping concentration). The method of manufacturing a CMOS image sensor comprising the step of doping the impurity of the object (at a concentration).

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