KR20080062063A - Cmos image sensor and method of manufaturing thereof - Google Patents

Abstract

A CMOS image sensor and a manufacturing method thereof are provided to prevent a punch-through effect between a photodiode and a floating diffusion region by forming a punch-though prevention layer at an upper side of the floating diffusion region. An epitaxial layer(200) is formed on a semiconductor substrate. A photodiode region is formed in the epitaxial layer. A color filter(221) is formed at an upper side of the photodiode region. A floating diffusion region(240) is separated from the photodiode region. A punch-through prevention layer(250) is formed at an upper side of the floating diffusion region. A transfer transistor(230) is formed in the epitaxial layer between the photodiode region and the floating diffusion region. The punch-through prevention layer includes Ge or As and has a thickness of 120-139 Å.

Description

CMOS Image Sensor and Method of Manufaturing Thereof}

1A is a plan view showing a conventional CMOS image sensor.

FIG. 1B is a cross-sectional view of the CMOS image sensor cut along line A-A 'shown in FIG. 1A;

2 is a cross-sectional view of the CMOS image sensor according to an embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

200: P-type epi layer 220: photodiode

221: color filter 230: transfer transistor

240: floating diffusion region 250: punch through layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CMOS image sensor and a method of manufacturing the same, and more particularly, to a CMOS image sensor capable of preventing the occurrence of a punch through phenomenon between a photodiode (PD) and a floating diffusion region (FD). will be.

An image sensor is an element that transforms an optical image into an electrical signal and is largely classified into a complementary metal-oxide-silicon (CMOS) image sensor and a charge coupled device (CCD) image sensor. The CCD image sensor has better photo sensitivity and noise characteristics than the CMOS image sensor, but has high integration difficulty and high power consumption. In contrast, a CMOS image sensor has simpler processes, suitable for high integration, and lower power consumption than a CCD image sensor.

Therefore, in recent years, as the manufacturing technology of semiconductor devices is highly developed, the manufacturing technology and characteristics of the CMOS image sensor have been greatly improved, and research on the CMOS image sensor has been actively conducted.

Typically, a pixel of a CMOS image sensor includes photodiodes that receive light and transistors that control image signals input from the photodiodes. According to the number of these transistors, CMOS image sensors are classified into 3T type and 4T type. Here, the 3T type is composed of one photodiode and three transistors, and the 4T type is composed of one photodiode and four transistors.

Hereinafter, the layout of the unit pixels of the 4T type CMOS image sensor will be described.

Referring to FIG. 1A, a conventional CMOS image sensor includes an isolation layer 10 for separating a semiconductor substrate into an active region 1 and an isolation region, and a photodiode having the largest area in the active region 1. A region PD, a transfer transistor Tx, a reset transistor Rx, and a drive transistor Dx, which are formed to overlap the active region 1 other than the photodiode region PD, are provided.

The photodiode PD detects incident light and generates electric charges according to the amount of light.

The transfer transistor Tx serves to transport charges generated in the photodiode PD to a floating diffusion region (FD). Before transport, the floating diffusion region FD is set to a predetermined low charge state by turning on the reset transistor Rx for electrons from the photodiode PD.

The reset transistor Rx serves to discharge charge stored in the floating diffusion region FD for signal detection.

The drive transistor Dx serves as a source follower for converting the charges into a voltage signal.

The conventional CMOS image sensor converts the charge generated in the photodiode region PD into a voltage signal in the drive transistor Dx.

However, the conventional CMOS image sensor punch-through between the photodiode PD and the floating diffusion region FD as shown in FIG. 1B showing a cross section taken along the line AA ′ of FIG. 1A. ) Is difficult to control the electron flow (Electron Current) by the transfer transistor (Tx).

In particular, as it becomes difficult to control the transfer transistor Tx, the dark signal characteristic, which is the most important part of the CMOS image sensor characteristic, is degraded. That is, even when there is no light, the CMOS image sensor is driven, and when the temperature rises, such characteristics are intensified and the characteristics of the CMOS image sensor are degraded.

The present invention can improve the image characteristics by solving the problem that the dark signal characteristic of the punch-through between the photodiode PD and the floating diffusion region FD is degraded. An object of the present invention is to provide a method for manufacturing a CMOS image sensor.

Another object of the present invention is to provide a CMOS image sensor having improved image characteristics by suppressing the occurrence of a punch-through phenomenon between the photodiode PD and the floating diffusion region FD.

The present invention for achieving the above object is an epi layer formed on a semiconductor substrate; A photodiode provided on the epi layer and a color filter provided on the photodiode area; A floating diffusion region FD spaced apart from the photodiode region; A punch-through layer disposed on the floating diffusion region FD; And a transfer transistor provided on the epitaxial layer between the photodiode region and the floating diffusion region FD.

In addition, the present invention comprises the steps of forming an epitaxial layer by performing an epitaxial (epitaxial) process on the semiconductor substrate; Providing a transfer transistor comprising a gate pattern and a space on the epi layer; Implanting a dopant into the photodiode region spaced apart from the transfer transistor to sequentially form a photodiode region and a color filter above the photodiode region; Providing a hard mask to open a floating diffusion region spaced apart from the photodiode and opposed to the photodiode region; And implanting GE or As in the floating diffusion region to provide a punch-through prevention layer on top of the floating diffusion region.

In the present invention, the providing of the transfer transistor may include sequentially depositing a gate insulating film and a gate poly film on the epi layer; Forming a gate pattern by patterning the gate insulating layer and the gate poly layer using a mask provided on the gate poly layer; And forming gate spacers formed of SiN on both sidewalls of the gate pattern.

In the present invention, the step of providing the punch-through prevention layer is characterized in that the GE or As is implanted at a dose of 3 to 4E14 atoms with an energy of 10 to 15 KeV and provided at a thickness of 120 to 130 kPa.

In the present invention, the semiconductor substrate is a high concentration P + + type semiconductor substrate and the epi layer is characterized in that the P- type epi layer formed by an epitaxial (epitaxial) process.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

As shown in FIG. 2, in the CMOS image sensor according to the exemplary embodiment of the present invention, Ge or As is doped on the floating diffusion region 240 to induce Si damage by inducing amorphous damage. ) To prevent punch-through from being caused by the dopant doped in the floating diffusion region 240.

Thus, the charge transport between the photodiode 220 and the floating diffusion region 240 is well controlled by the transfer transistor 230 such that electron flows into the channel of the transfer transistor 230 without the occurrence of a punch through. Current can be well formed .

Hereinafter, a method of manufacturing the CMOS image sensor including the punch-through prevention layer 250 according to the embodiment of the present invention will be described.

As shown in FIG. 2, an epitaxial process is performed on a high concentration P ++ type semiconductor substrate (not shown) to form a low concentration P-type epi layer 200.

Next, a gate pattern formed of a gate insulating film and a gate poly is provided on the P-type epitaxial layer 200.

A process of providing the gate pattern will be described in detail. A gate insulating film and a gate poly film are sequentially formed on the P-type epitaxial layer 200 through a deposition method. Subsequently, the gate insulating film and the gate poly pattern may be formed by patterning the gate insulating film and the gate poly film by a photolithography process using a mask provided on the gate poly film.

Thereafter, as shown in FIG. 2, gate spacers are formed on both sidewalls of the gate pattern to form the transfer transistor 230. The gate spacers may be formed as gate spacers on both sidewalls of the gate pattern by forming an insulating film SiN on the P-type epitaxial layer 200 including the gate pattern and performing an etch back process.

After the transfer transistor 230 is formed, a dopant is injected into the photodiode region spaced apart from the transfer transistor 230 to sequentially form the photodiode 220 and the color filter 221.

Subsequently, a punch-through prevention layer is formed on the floating diffusion region 240 of the P-type epi layer 200 by implanting GE or As, which is a heavy dopant, with a hard mask that opens the floating diffusion region 240. 250.

Specifically, a hard mask is provided to open the floating diffusion region 240 of the P-type epitaxial layer 200, and through this hard mask, GE or As is formed of 3 to 4E14 atoms at an energy of 10 to 15 KeV. The dose amount may be implanted into the floating diffusion region 240 of the P-type epitaxial layer 200 to form a punch-through prevention layer 250 having a thickness of 120 to 130 Å.

As such, when GE or As is implanted into the floating diffusion region 240 of the P-type epitaxial layer 200, Si damage is induced to the upper side of the floating diffusion region 240 to form an amorphous phase. In the floating diffusion region 240, if the boron implantation process is subsequently performed by the amorphous Si in the floating diffusion region 240, the N-type ions are floated by the punch through prevention layer 250. It will not be injected deep into), preventing the punch-through phenomenon.

Thus, in the CMOS image sensor having the punch-through prevention layer 250 according to the present invention, the charge transport between the photodiode 220 and the floating diffusion region 240 is well controlled by the transfer transistor 230 so that the punch-through Electron current may be well flowed into a channel generated under the transfer transistor 230 without generation .

Although the technical spirit of the present invention has been described in detail according to the above-described preferred embodiment, it should be noted that the above-described embodiments are for the purpose of description and not of limitation.

In addition, those skilled in the art will understand that various implementations are possible within the scope of the technical idea of the present invention.

As described above, the present invention includes a punch-through prevention layer on the upper side of the floating diffusion region FD, thereby preventing the occurrence of punch-through between the photodiode and the floating diffusion region FD, thereby transferring charge transport. It is possible to provide a CMOS image sensor that is well controlled by the transistor Tx and has an improved image characteristic in which electron current flows well into a channel of a transfer transistor without the occurrence of a punch through .

Claims (7)

An epitaxial layer formed on the semiconductor substrate; A photodiode provided on the epi layer and a color filter provided on the photodiode area; A floating diffusion region FD spaced apart from the photodiode region; A punch-through layer disposed on the floating diffusion region FD; And A transfer transistor provided on the epitaxial layer between the photodiode region and the floating diffusion region FD. CMOS image sensor configured to include. The method of claim 1, The punch-through prevention layer is CMOS image sensor, characterized in that provided with a thickness of 120 ~ 130Å by using GE or As. The method of claim 1, The semiconductor substrate is a high concentration P ++ type semiconductor substrate The epi layer is a CMOS image sensor, characterized in that the P-type epi layer formed by an epitaxial process. Forming an epitaxial layer by performing an epitaxial process on the semiconductor substrate; Providing a transfer transistor comprising a gate pattern and a space on the epi layer; Implanting a dopant into the photodiode region spaced apart from the transfer transistor to sequentially form a photodiode region and a color filter above the photodiode region; Providing a hard mask to open a floating diffusion region spaced apart from the photodiode and opposed to the photodiode region; And Implanting GE or As into the floating diffusion region to provide a punch-through prevention layer on top of the floating diffusion region Method of manufacturing a CMOS image sensor comprising a. The method of claim 4, wherein The step of providing the transfer transistor Sequentially depositing a gate insulating film and a gate poly film on the epi layer; Forming a gate pattern by patterning the gate insulating layer and the gate poly layer using a mask provided on the gate poly layer; And Forming a gate spacer made of SiN on both sidewalls of the gate pattern Method of manufacturing a CMOS image sensor comprising a. The method of claim 4, wherein The step of providing the punch through prevention layer A method of manufacturing a CMOS image sensor comprising GE or As at a dose of 3 to 4E14 atoms at an energy of 10 to 15 KeV and having a thickness of 120 to 130 kPa. The method of claim 4, wherein The semiconductor substrate is a high concentration P ++ type semiconductor substrate And the epi layer is a P-type epi layer formed by an epitaxial process.

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