KR20060127498A - Manufacturing Method of CMOS Image Sensor for Reducing Dark Current - Google Patents

Abstract

A method of manufacturing a CMOS image sensor for reducing dark current is provided. This method uses a photoresist that covers the upper front surface of the polysilicon conductive film forming the transfer gate to form the photodiode of the CMOS image sensor as a mask, thereby preventing dopant ion penetration into the lower portion of the transfer gate generated during the dopant ion implantation process. It is characterized by preventing. As a result, there is an effect of reducing the defect that generates a dark current in the CMOS image sensor.

Description

Method of fabricating CMOS image sensor to reduce dark current {Method Of Fabricating CMOS Image Sensor To Reduce The Dark Current}

1 is an equivalent circuit diagram of a general CMOS image sensor pixel.

2 is a plan view of a general CMOS image sensor pixel.

3A to 3E are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to the prior art.

4A to 4E are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to an exemplary embodiment of the present invention.

The present invention relates to a method of manufacturing a CMOS (Complementary MOS) image sensor, and more particularly to a method of manufacturing a CMOS image sensor to reduce the dark current (dark current).

In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal. The image sensor may be classified into two types, a charge coupled device (CCD) method and a CMOS method.

The charge coupling device is a device in which charge carriers are stored in a capacitor and transported while each MOS capacitor is located in close proximity to each other. CMOS is a peripheral circuit of a control circuit and a signal processing circuit. A device employing a switching method that sequentially detects the output signals of MOS transistors in the order of pixels.

The CMOS image sensor has a simpler driving method than the charge-coupled device image sensor, and uses CMOS technology to lower manufacturing cost and lower power consumption. On the other hand, in the case of the charge-coupled device, the process is relatively difficult compared to the CMOS, and in the case of the charge-coupled device, random access is not possible, but the CMOS image sensor has an advantage that can be applied.

However, the CMOS image sensor has been found to have disadvantages such as noise and clarity, making it difficult to use. In the late 1990s and recently, the quality of products has been gradually improved due to the development of CMOS process technology and the improvement of signal processing algorithms.

The general CMOS image sensor pixel may include a photodiode (PD) and at least one transistor. 1 is a unit pixel circuit diagram illustrating a CMOS image sensor including one photodiode and four NMOS transistors.

Referring to FIG. 1, the CMOS image sensor pixel may include a transfer transistor Tx for transporting photocharges collected in a photodiode PD to a floating diffusion region (F / D), and floating at a desired value. Reset transistor Rx, source follower buffer amplifier for setting the potential of the diffusion region F / D and discharging the charge to reset the floating diffusion region F / D. A drive transistor Dx acts as a role and a select transistor Sx which allows addressing to a switching role.

The operation method of the CMOS image sensor pixel is as follows.

First, when the reset transistor Rx is turned on, the potential of the floating diffusion region F / D becomes the applied voltage Vdd. When light is incident on the photodiode PD from the outside, an electron-hole pair (EHP) is generated, and signal charges are accumulated in the source of the transfer transistor Tx. When the transfer transistor Tx is turned on, the accumulated signal charge is transferred to the floating diffusion region F / D to change the potential of the floating diffusion region F / D and at the same time the gate potential of the drive transistor Dx. Is changed. At this time, when the select transistor Sx is turned on by the selection signal Row, data is output to the output terminal Out. When the reset transistor Rx is turned on again, the potential of the floating diffusion region F / D becomes the applied voltage Vdd, and this process can be repeated to output an image signal.

2 is a plan view illustrating such a CMOS image sensor pixel.

Referring to FIG. 2, the CMOS image sensor pixel includes a device isolation pattern 16 formed on a substrate to define a diode region 40 and an active region 42. Typically, the diode region 40 is formed wide to increase the light efficiency, and the active region 42 extends from one side of the diode region 40. The transfer gate 24, the reset gate 26, and the selection gate 28 are sequentially formed on the active region 42 at predetermined intervals. Although not shown, an access gate is formed in the active region 42 spaced apart from the selection gate 28 by a predetermined distance. The transfer gate 24 is formed on the active region 42 adjacent to the diode region 40. The floating diffusion region 30 is formed in the active region 42 between the transfer gate 24 and the reset gate 26. Although not shown, the floating diffusion region 30 and the selection gate 28 are electrically connected by wiring.

3A to 3E are cross-sectional views illustrating processes for manufacturing CMOS image sensor according to the related art, and are cross-sectional views taken along the line A-A of FIG. 2.

Referring to FIG. 3A, the P-type semiconductor layer 10a is formed on the semiconductor substrate 10. An isolation layer 16 is formed on the P-type semiconductor layer 10a to define an active region (42 in FIG. 2) and a diode region (40 in FIG. 2). The diode region is a region where a photodiode is subsequently formed, and the active region is connected to one side of the diode region.

N-type dopant ions are selectively implanted into the surface of the active region and the diode region to form a channel diffusion layer 21, and then P-type dopant ions are selectively implanted to channel doping the surface of the channel diffusion layer 21. The area 22 is formed.

Referring to FIG. 3B, an oxide layer is formed on the diode region and the active region, a conductive layer is formed of a material such as polysilicon on the oxide layer, and then the conductive layer and the oxide layer are patterned to transfer gates. 24 and a gate oxide film 23 are formed.

Referring to FIG. 3C, a first photoresist 32 is formed to cover the upper portion of the transfer gate 24 while exposing the diode region. N-type dopant 34 ions are implanted using the first photoresist 32 to form an N-type photodiode region 18 in the diode region connected to one side of the transfer gate 24.

The photodiode 40 is formed by implanting P-type dopant ions into the N-type photodiode region 18 to form a P-type photodiode region 20.

Referring to FIG. 3D, the first photoresist 32 is removed, and a second photoresist 36 covering the photodiode 40 and the transfer gate 24 is formed. The floating diffusion region 30 is formed by selectively implanting N-type dopant ions into the active region on one side of the transfer gate 24 using the second photoresist 36. The floating diffusion region 30 may be formed before forming the transfer gate 24. It may also be formed before forming the photodiode 40.

Referring to FIG. 3E, the second photoresist 36 is removed to manufacture a CMOS image sensor.

As the CMOS image sensor device is miniaturized, the thickness of the transfer gate 24 is gradually reduced. Meanwhile, misalignment with the side surfaces of the transfer gate 24 may not be avoided in the process of forming the first photoresist 32. Accordingly, referring to FIG. 3C, the channel doped region 22 under the transfer gate 24 through the partial surface B of the transfer gate 24 in the ion implantation process of the N-type dopant 34. The N-type dopant 34 ions may penetrate into. As a result, the penetrated N-type dopant 34 ions may generate a dark current in the pixel of the image sensor device by changing the P-type concentration of the channel doped region 22.

Meanwhile, the same problem may occur due to misalignment even in the process of forming the floating diffusion region 30 using the second photoresist 36.

The present invention is to solve the above problems, and to provide a manufacturing method for reducing the dark current of the CMOS image sensor.

In order to achieve the above technical problem, a method of manufacturing a CMOS image sensor is provided. The method includes forming an isolation layer on a semiconductor substrate to define an active region and a diode region, and forming an oxide film and a conductive film on the diode region and the active region; Forming a first photoresist covering the conductive film and exposing a diode region; Etching the conductive film and the oxide film on the exposed diode region using the first photoresist, and implanting a dopant into the diode region to form a photodiode; Removing the first photoresist; Forming a second photoresist covering the photodiode and a portion of the conductive film; Etching the conductive layer and the oxide layer using the second photoresist to form a transfer gate, and implanting an N-type dopant to form a floating diffusion region; And removing the second photoresist.

In the dopant ion implantation process to form the photodiode of the CMOS image sensor device, a photoresist covering the entire upper surface of the transfer gate formation region is formed without using a conventional self-aligned structure using the transfer gate as a mask. As a result, dopant ions may be prevented from penetrating into the channel doped region under the transfer gate, thereby suppressing dark current generation of the CMOS image sensor device.

The method may further include forming the channel doped region under the transfer gate. The forming of the photodiode may include forming an N-type photodiode region by ion implanting an N-type dopant into the diode region, and forming a P-type photodiode region by ion implanting a P-type dopant into the N-type photodiode region. It may include the step. The P-type photodiode region is formed on the N-type photodiode region.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosure may be made thorough and complete, and to fully convey the spirit of the invention to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Also, if a layer is said to be on another layer or substrate it may be formed directly on the other layer or substrate or a third layer may be interposed therebetween.

4A to 4E are cross-sectional views taken along line AA of FIG. 2 to illustrate a manufacturing process of the CMOS image sensor according to an exemplary embodiment of the present invention.

Referring to FIG. 4A, a P-type semiconductor layer 110a is formed on the semiconductor substrate 110. A deep P well 112 is formed in the semiconductor substrate 110. The deep P well 112 may be formed between the P-type semiconductor layer 110a and the semiconductor substrate 110.

An isolation layer 116 is formed on the P-type semiconductor layer 110a to define an active region (42 in FIG. 2) and a diode region (40 in FIG. 2). The diode region is a region where a photodiode is subsequently formed, and the active region is connected to one side of the diode region.

N-type dopant ions are selectively implanted into surfaces of the active region and the diode region to form an N-type channel diffusion layer 121, and then P-type dopant ions are selectively implanted to form the N-type channel diffusion layer 121. P-type channel doped region 122 is formed on the surface.

Referring to FIG. 4B, an oxide film 123 is formed on the diode region and the active region. The conductive film 124 is formed of a material such as polysilicon on the oxide film 123. After forming the first photoresist 132 covering the entire upper surface of the conductive film 124 and exposing the diode region, the conductive film 124 and the oxide film 123 using the first photoresist 132. Pattern).

Referring to FIG. 4C, the N-type dopant 134 ions are implanted using the first photoresist 132 to form an N-type photodiode region 118 aligned with one side of the conductive layer 124. Subsequently, a P-type photodiode region 120 is formed by implanting P-type dopant ions into the N-type photodiode region 118 to form a P-N junction photodiode 140. Although the P-type photodiode region 120 is formed using the first photoresist 132 as an ion implantation mask, the P-type photodiode region 120 is not limited thereto and may be formed using another ion implantation mask.

Referring to FIG. 4D, the first photoresist 132 is removed and a second photoresist 136 is formed to cover the photodiode 140 and a portion of the conductive layer 124. The conductive gate 124 and the oxide layer 123 are etched using the second photoresist 136 to form a transfer gate 124a. Subsequently, the floating diffusion region 130 is formed by selectively implanting N-type dopant ions into one side of the transfer gate 124a using the second photoresist 136. The floating diffusion region 130 may be formed before the transfer gate 124a is formed. In addition, it may be formed before forming the photodiode 140.

Referring to FIG. 4E, the second photoresist 136 is removed to manufacture a CMOS image sensor.

When a reverse bias is applied between the N-type photodiode region 118 and the P-type semiconductor layer 110a in the CMOS image sensor having such a structure, the N-type photodiode region 118 and the P-type semiconductor layer ( Impurity concentrations of 110a) are mixed. When the impurity concentration is properly mixed, the N-type photodiode region 118 is in a fully depletion state, and the P-type semiconductor layer 110a and the N-type that exist below the N-type photodiode region 118. As the depletion region extends to the P-type photodiode region 120 on the photodiode region 118, a wider depletion layer expansion occurs to the P-type semiconductor layer 110a having a relatively low dopant concentration. The depletion region may accumulate and store photocharges generated by incident light. The image is reproduced using the photocharge.

In the method of manufacturing the CMOS image sensor, the first photoresist 132 for forming the photodiode 140 covers the entire upper surface of the conductive layer 124. Accordingly, the N-type dopant 134 ions are blocked in the first photoresist 132 so that the channel doped region 122 and the channel diffusion layer 121 under the transfer gate 124a are formed. Protected. This minimizes the dark current.

As described above, according to the present invention, the photodiode is formed using a photoresist covering the entire upper surface of the transfer gate, thereby preventing the dopant from penetrating into the channel doping region and the channel diffusion layer under the transfer gate. Accordingly, the conventional dark current can be minimized.

Claims (3)

Forming an isolation layer on the semiconductor substrate to define an active region and a diode region, and forming an oxide layer and a conductive layer on the diode region and the active region; Forming a first photoresist covering the conductive film and exposing a diode region; Etching the conductive film and the oxide film on the exposed diode region by using the first photoresist, and implanting a dopant into the diode region to form a photodiode; Removing the first photoresist; Forming a second photoresist covering the photodiode and a portion of the conductive film; Etching the conductive layer using the second photoresist to form a transfer gate, and implanting an N-type dopant to form a floating diffusion region; And Removing the second photoresist. The method of claim 1, And forming a channel doped region between the photodiode region and the floating diffusion region. The method of claim 1, Forming the photodiode, Implanting an N-type dopant into the diode region to form an N-type photodiode region; And Ion implanting a P-type dopant into the photodiode N-type region to form a P-type photodiode region, And the P-type photodiode region is formed on the N-type photodiode region.

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