KR20100079172A

KR20100079172A - Cmos image sensor and method for fabricating the same

Info

Publication number: KR20100079172A
Application number: KR1020080137588A
Authority: KR
Inventors: 박동빈
Original assignee: 주식회사 동부하이텍
Priority date: 2008-12-30
Filing date: 2008-12-30
Publication date: 2010-07-08

Abstract

According to the present invention, a CMOS image sensor includes a transfer transistor for transporting photocharges focused in a photodiode, first and second floating diffusion regions for receiving and storing photocharges through the transfer transistor, and first and second electrodes. A reset transistor for resetting the floating diffusion region, first and second drive transistors respectively connected to the first and second floating diffusion regions to serve as source follower-buffer amplifiers, and first and second drive transistors, respectively. And first and second select transistors to enable addressing by switching.

As described above, the present invention divides and stores charges transmitted through one transfer transistor into at least two floating diffusion regions, thereby reducing the area of one floating diffusion region and thus reducing the capacitor value. The sensitivity of the pixel can be increased by increasing the voltage conversion value.

Description

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

The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to a CMOS image sensor and a method of manufacturing the same for increasing the sensitivity of pixels by storing and storing charges transmitted through a transfer transistor in two floating diffusion regions. will be.

In general, in a CCD (Charge Couple Device) or CMOS image sensor, a photo diode (PD) is an introduction part for converting light incident to each wavelength into an electrical signal, and ideally photoelectric charge in all wavelength bands. Since the case where the efficiency (Quantum Efficiency) is 1 is focused on all incident light, efforts are being made to achieve this.

FIG. 1 is an equivalent circuit diagram of a unit pixel of a conventional CMOS image sensor, and includes one photodiode (PD) and four NMOSs (Tx Tr, Rx Tr, Sx Tr, and Dx Tr).

Four NMOS transistors are used to transfer the photo-generated charge from the photodiode (PD) to the floating diffusion region (FD). Reset transistor (Rx Tr) and Source Follower Buffer Amplif ier for setting potential and discharging charge Cpd to reset floating diffusion region FD. The drive transistor includes a drive transistor (Dx Tr) and a select transistor (Sx Tr) for addressing by switching.

2 is a plan view of a unit pixel of a CMOS image sensor according to the related art.

Referring to FIG. 2, a gate electrode of the transfer transistor Tx Tr (hereinafter, abbreviated as 'transfer gate Tx') is formed with one side overlapping a predetermined width in an active region in which the photodiode PD is to be formed. The floating diffusion region FD is formed in the active region below the other side of the transfer gate Tx. Here, the photodiode PD has a relatively large area, and the area of the photodiode PD becomes narrow while giving a bottle neck effect from the photodiode PD to the floating diffusion region FD.

The gate electrode of the reset transistor Rx Tr in the counterclockwise direction with respect to the floating diffusion region FD (hereinafter, abbreviated as 'reset gate Rx') and the gate electrode of the drive transistor Dx Tr , Abbreviated as 'drive gate Dx'], and gate electrodes of the select transistor Sx Tr (hereinafter, abbreviated as 'select gate Sx') are arranged to cross the upper portion of the active region at predetermined intervals. have.

In the CMOS image sensor having the above-described structure, the floating diffusion region FD has a floating diffusion region FD per pixel, as shown in FIG. 3. FD) The capacitor is in a large state.

Since the conventional floating diffusion region FD capacitor is in a large state, when the photocharges from the photodiode PD are converted into voltages, the voltage value thereof becomes small, thereby reducing the voltage swing due to the photocharge amount. There is this. That is, when strong light enters, there is no problem because the amount of photocharge is large, but in low light, leakage may be difficult to detect.

The present invention divides and stores the charges transmitted through one transfer transistor in at least two floating diffusion regions, thereby reducing the area of each floating diffusion region and thus reducing the capacitor value. It increases the sensitivity of the pixel.

According to the present invention, a CMOS image sensor includes a transfer transistor for transporting photoelectric charges focused in a photodiode, first and second floating diffusion regions for receiving and storing photocharges through the transfer transistor, and the first A reset transistor for resetting the second floating diffusion region, first and second drive transistors respectively connected to the first and second floating diffusion regions to serve as source follower-buffer amplifiers, and the first and second drives. And first and second select transistors respectively connected to the transistors to enable addressing through switching.

In addition, according to the present invention, a method of manufacturing a CMOS image sensor includes forming a transistor having a spacer on a semiconductor substrate, and etching a part of the semiconductor substrate exposed by the transistor gate to form a photodiode region. And forming a photodiode by performing an impurity ion implantation process on the photodiode region.

The present invention divides and stores charges transmitted through one transfer transistor into at least two floating diffusion regions, thereby reducing the area of one floating diffusion region and thus reducing the value of the capacitor. Since it can increase the sensitivity of the pixel can be increased.

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

In an embodiment of the present invention, by storing the charges transmitted through one transfer transistor in at least two floating diffusion regions, the area of each floating diffusion region can be reduced to reduce the capacitor value and thereby the voltage. A CMOS image sensor capable of increasing the sensitivity of a pixel by increasing a conversion value and a manufacturing method thereof will be described.

4 is a diagram illustrating unit pixels of a CMOS image sensor including a floating diffusion region according to an exemplary embodiment of the present invention, wherein the photocharges focused on the photodiode PD are first and second floating diffusion regions FD1 and FD2. A transfer transistor (Tx) for transporting through the circuit, a reset transistor (Rx) for setting the potential of the node to a desired value, and discharging electric charges to reset the first and second floating diffusion regions (FD1, FD2). , The first and second drive transistors Dx1 and Dx2 connected to the two floating diffusion regions FD1 and FD2 to act as source follower-buffer amplifiers, and the first and second select transistors to enable addressing by switching. Sx1, Sx2).

The first floating diffusion region FD1 is connected to the first drive transistor Dx1 through the first floating diffusion contact FD CT1, and the second floating diffusion region FD2 is connected to the second floating diffusion contact (FD1). FD CT2 is connected to the second drive transistor Dx2.

The first drive transistor Dx1 is connected to the first select transistor Sx1 and the second drive transistor Dx2 is connected to the second select transistor Sx2.

As shown in FIG. 4, one transfer transistor Tx is connected to two, that is, the first and second floating diffusion regions FD1 and FD2 in one unit pixel, and the turn-on of the transfer transistor Tx is turned on. Charges transported by the operation are stored in the first and second floating diffusion regions FD1 and FD2, and the reset transistor Rx and the first and second drive transistors Dx1 and Dx2 are commonly supplied with a power supply voltage.

The driving method of the unit pixel having the above configuration will be described. First, the transfer transistor Tx, the reset transistor Rx, and the first and second select transistors Sx1, Sx, and 2 are turned off. In this case, it is assumed that the photodiode PD is completely depleted.

Next, the photocharges are focused on the photodiode PD, and the first and second floating diffusion regions FD1 and FD2 are first reset by pulsing the gate of the reset transistor Rx (high). The gates of the first and second select transistors Sx1 and Sx2 are pulsed high to turn on the unit pixels, and the output voltages V1 and V1 'of the first and second drive transistors Dx1 and Dx2 are measured, respectively. The value means a DC level shift of the first and second floating diffusion regions FD1 and FD2.

Next, the transfer transistor Tx is pulsed high and turned on, in which all photoelectric charge is transferred to the first and second floating diffusion regions FD1 and FD2.

Next, the transistors Tx are pulsed low and turned off, and then the output voltages V2 and V2 'of the first and second drive transistors Dx1 and Dx2 are measured.

After all, the output signal difference V1-V2 (V1-V2) is the result of the photocharge obtained at the difference (V1'-V2 ') between V1 (V1') and V2 (V2 '), which is a pure signal value without noise. Becomes This method is called correlated double sampling (CDS).

As described above, according to the present invention, by storing the charges transmitted through one transfer transistor in two floating diffusion regions, the area of one floating diffusion region can be reduced to reduce the value of a capacitor. The conversion value can be made large.

As described above, since the first and second drive transistors Dx1 and Dx2 are required to process voltages in the first and second floating diffusion regions FD1 and FD2, respectively, the structure shown in FIG. A photodiode (PD) region is formed.

5 is a view showing a photodiode region structure according to the present invention.

Referring to FIG. 5, a p-type epitaxial layer 502 is formed on a semiconductor substrate 500, for example, a p-type semiconductor substrate 500, and an isolation layer (not shown) is formed on a predetermined surface of the p-type epitaxial layer 502. ) Is formed, and the transfer transistor Tx is formed by forming a transfer gate having a spacer (not shown) formed on the p-type epi layer 502.

Then, in order to isolate the photodiode region and the channel region of the transfer transistor Tx, a portion of the semiconductor substrate 500 corresponding to the photodiode region is etched and an impurity ion implantation process is performed on the etched portion to deep n. The photodiode PD is formed by forming the type diffusion layer 504 and the shallow p-type diffusion layer 506.

The capacitor of the photodiode PD may be adjusted by increasing the dose of impurity ions during the impurity ion implantation process for forming the n-type diffusion layer 504 and the p-type diffusion layer 506.

It has been described so far limited to one embodiment of the present invention, it is obvious that the technology of the present invention can be easily modified by those skilled in the art. Such modified embodiments should be included in the technical spirit described in the claims of the present invention.

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

2 is a plan view of a unit pixel of a CMOS image sensor according to the prior art,

3 is a view for explaining a conventional problem,

4 is a diagram illustrating unit pixels of a CMOS image sensor including a floating diffusion region according to an exemplary embodiment of the present invention.

5 is a view showing a photodiode region structure according to the present invention. It is a cross section.

Description of the Related Art

500: p-type semiconductor substrate 502: p-type epi layer

504: n-type diffusion layer 506: p-type diffusion layer

Claims

A transfer transistor for transporting the concentrated photocharges in the photodiode,

First and second floating diffusion regions configured to receive and store photocharges through the transfer transistor;

A reset transistor for resetting the first and second floating diffusion regions;

First and second drive transistors respectively connected to the first and second floating diffusion regions to serve as source follower-buffer amplifiers;

First and second select transistors respectively connected to the first and second drive transistors to enable addressing by switching.

CMOS image sensor comprising a.

Forming a transport gate having a spacer on the semiconductor substrate;

Etching a portion of the semiconductor substrate exposed by the transistor gate to form a photodiode region;

Forming a photodiode by performing an impurity ion implantation process on the photodiode region

CMOS image sensor manufacturing method comprising a.