KR20070071053A - CMOS image sensor and its manufacturing method - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor manufacturing technology, and more particularly, to a CMOS image sensor and a method of manufacturing the same, which increase the capacitance of the floating diffusion region to improve light sensitivity during semiconductor device manufacturing processes. To this end, the present invention, the CMOS image sensor is a photodiode that receives light to generate photocharge, a transfer transistor for transporting the photocharge collected from the photodiode to the floating diffusion region and the floating diffusion region in contact with the floating diffusion region A CMOS image sensor is provided that includes a trench capacitor that increases the capacitance of the transistor. The method may further include forming a trench in an active region of a semiconductor substrate, sequentially depositing a gate oxide film and a polysilicon film on the trench-formed substrate, selectively etching the gate oxide film and the polysilicon film, and forming a gate electrode of a transfer transistor. Forming a trench capacitor, forming a floating diffusion region in the semiconductor substrate on one side of the gate electrode of the transfer transistor, and forming a metal wiring connecting the floating diffusion region and the trench capacitor. A method of manufacturing an image sensor is provided.

Description

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

1 is a circuit diagram showing a unit pixel composed of one photodiode (PD) and four MOS transistors in a conventional CMOS image sensor.

2 is a circuit diagram illustrating a CMOS image sensor according to an exemplary embodiment of the present invention.

3A to 3C are cross-sectional views illustrating a process of forming the trench capacitor of FIG. 2.

Explanation of symbols on the main parts of the drawings

20 photodiode 21 transfer transistor

22: floating diffusion region 23: reset transistor

24: driver transistor 25: select transistor

26: load transistor 27: trench capacitor

TECHNICAL FIELD The present invention relates to semiconductor manufacturing technology, and more particularly, to a CMOS image sensor and a manufacturing method thereof.

In general, image sensors are used in a wide range of fields, from home products such as digital cameras and mobile phones, to endoscopes used in hospitals, and to satellite telescopes around the earth. The CMOS image sensor is a device that converts an optical image into an electrical signal, and employs a switching method in which a MOS transistor is formed by the number of pixels and the output is sequentially detected using the MOS transistor.

The CMOS image sensor is simpler to drive than the CCD image sensor, which is widely used as a conventional image sensor, enables various scanning methods, and can integrate signal processing circuits onto a single chip. In addition to the use of compatible CMOS technology, the manufacturing cost can be lowered and the power consumption is significantly lower. Therefore, it is used in low cost and low power fields such as mobile phones, PCs and surveillance cameras.

FIG. 1 is a circuit diagram illustrating a unit pixel composed of one photodiode (PD) and four MOS transistors in a conventional CMOS image sensor. 10), the transfer transistor 11 for transporting the photocharges collected from the photodiode 10 to the floating diffusion region 12, and setting the potential of the floating diffusion region to a desired value and discharging electric charges to discharge the floating diffusion region ( 12, a reset transistor 13 for resetting the voltage, a voltage of the floating diffusion region is applied to the gate, and a drive transistor 14 serving as a source follower buffer amplifier, and a switching role. It consists of a select transistor 15 which performs an addressing role. Outside the unit pixel, a load transistor 16 is formed to read an output signal.

Here, the capacitance of the floating diffusion region 12 is a very important parameter since the photosensitivity of the CMOS image sensor is determined. Thus, if the capacitance of the floating diffusion region 12 is too small, all the charges from the photodiode 10 cannot be loaded into the floating diffusion region 12, and if the capacitance of the floating diffusion region 12 is too large, the light Sensitivity is blunted and it is difficult to expect proper output

Accordingly, an object of the present invention is to provide a CMOS image sensor and a method of manufacturing the same, which have been proposed to solve the above-described problems of the prior art and improve the light sensitivity by increasing the capacitance of the floating diffusion region.

According to an aspect of the present invention for achieving the above object, the CMOS image sensor is a photodiode that receives light to generate a photocharge, a transfer transistor for transporting the photocharge collected from the photodiode to the floating diffusion region and the A CMOS image sensor is provided that includes a trench capacitor in contact with the floating diffusion to increase the capacitance of the floating diffusion.

The method may further include forming a trench in an active region of a semiconductor substrate, sequentially depositing a gate oxide film and a polysilicon film on the trench-formed substrate, selectively etching the gate oxide film and the polysilicon film, and forming a gate electrode of a transfer transistor. Forming a trench capacitor, forming a floating diffusion region in the semiconductor substrate on one side of the gate electrode of the transfer transistor, and forming a metal wiring connecting the floating diffusion region and the trench capacitor. A method of manufacturing an image sensor is provided.

Hereinafter, the preferred 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. .

2 is a circuit diagram illustrating a CMOS image sensor according to an exemplary embodiment of the present invention.

Referring to FIG. 2, the CMOS image sensor includes a photodiode 20 that receives light to generate photocharges, and a transfer transistor 21 for transporting the photocharges collected from the photodiode 20 to the floating diffusion region 22. ), A reset transistor 23 for resetting the floating diffusion region 22 by setting the potential of the floating diffusion region to a desired value and discharging electric charges, and a voltage of the floating diffusion region is applied to the gate to supply a source follower buffer. A drive transistor 24 serving as an amplifier (Source Follower Buffer Amplifier), a select transistor 25 serving as an addressing role as a switching role, and an adjacent region of the floating diffusion region 22. It is provided with a trench capacitor 27 to increase the capacitance of the floating diffusion region (22). Outside the unit pixel, a load transistor 26 is provided to read an output signal. In this case, the trench capacitor 27 is made of polysilicon-insulating film-polysilicon (PIP).

3A to 3C are cross-sectional views illustrating a process of forming the trench capacitor 27 of FIG. 2. The reference numerals in FIG. 2 will be described with reference.

In the process of forming the trench capacitor 27, first, as shown in FIG. 3A, an isolation layer 302 defining an active region and an isolation region is formed on the semiconductor substrate 301.

In this case, the semiconductor substrate 301 is formed with a low concentration p epi layer on the p + type substrate, the reason for using a low concentration p epi layer on the high concentration p + type substrate, First, a low concentration p epi layer is It can increase the depth of the photodiode's depletion region largely and deeply, thereby increasing the photodiode's ability to collect photocharges. Second, the high concentration of p + at the bottom of the p-type epilayer. Having a substrate allows the charge to quickly recombine before it spreads to neighboring pixels, thus reducing the random diffusion of the photocharge, thus reducing the change in the transfer function of the photocharge. to be.

In addition, the device isolation layer 302 is formed through an STI process that hardly has a bird's beak and thus may reduce an area to be electrically separated between devices according to high integration of devices.

Subsequently, a pad layer is formed to partially expose the active region of the semiconductor substrate 301, and the trench 303 is formed by etching the semiconductor substrate 301 using an etching barrier.

Next, as shown in FIG. 3B, the gate oxide film 304 and the polysilicon film 305 are sequentially deposited on the substrate on which the trench 303 is formed. In this case, the trench 303 is buried by the polysilicon film 305.

Next, as shown in FIG. 3C, the gate oxide layer 304 and the polysilicon layer 305 are selectively etched to form the gate electrodes 304 and 305 and the semiconductor substrate 301 / gate oxide layer of the transfer transistor Tx. A trench capacitor 27 having a structure of 304 / polysilicon film 305 is formed.

Subsequently, impurities are injected into one side of the gate electrodes 304 and 305 of the transfer transistor Tx to form a photodiode PD, and a floating diffusion region FD is formed on the other side.

A metal wiring 306 is formed to contact the polysilicon layer 305, which is an upper layer of the trench capacitor 27, and to contact the floating diffusion region FD.

As described above, the present invention increases the capacitance of the floating diffusion region 22 by forming a trench capacitor 27 that can increase the capacitance of the floating diffusion region 22 without being affected by the size of the unit pixel.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made in the art without departing from the technical spirit of the present invention. It will be clear to those of ordinary knowledge.

As described above, the present invention forms a trench capacitor in contact with the floating diffusion region to increase the capacitance of the floating diffusion region without being affected by the size of the unit pixel.

The capacitance of the trench capacitor can be easily adjusted to adjust the capacitance of the floating diffusion region according to the chip characteristics.

Claims (2)

Photodiodes that receive light to generate photocharges; A transfer transistor for transporting the photocharges collected by the photodiode to a floating diffusion region; And A trench capacitor in contact with the floating diffusion region to increase the capacitance of the floating diffusion region CMOS image sensor comprising a. Forming a trench in an active region of the semiconductor substrate; Sequentially depositing a gate oxide film and a polysilicon film on the trench-formed substrate; Selectively etching the gate oxide layer and the polysilicon layer to form a gate electrode and a trench capacitor of a transfer transistor; Forming a floating diffusion region in the semiconductor substrate on one side of a gate electrode of the transfer transistor; And Forming a metal interconnection connecting the floating diffusion region and the trench capacitor Method of manufacturing a CMOS image sensor comprising a.

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