KR20110079330A

KR20110079330A - Image sensor and method for fabricating the same

Info

Publication number: KR20110079330A
Application number: KR1020090136348A
Authority: KR
Inventors: 김호수
Original assignee: 주식회사 동부하이텍
Priority date: 2009-12-31
Filing date: 2009-12-31
Publication date: 2011-07-07

Abstract

An image sensor according to the embodiment includes a substrate; A photodiode formed on the substrate; A gate insulating layer partially overlapping the photodiode; And a transfer transistor on the gate insulating layer and having a gate electrode made of a transparent material.

Image sensor, gate electrode

Description

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

Embodiments relate to an image sensor and a method of manufacturing the same.

An image sensor is a semiconductor device that detects light and converts it into an electrical signal. Among these, a charge coupled device (CCD) is a device in which charge carriers are stored and transported in a capacitor while individual metal-oxide-silicon (MOS) capacitors are located in close proximity to each other.

CMOS (Complementary MOS) image sensor uses CMOS technology that uses a control circuit and a signal processing circuit as peripheral circuits, and creates MOS transistors as many as the number of pixels and uses them sequentially to output Is a device that adopts a switching method for detecting.

In the conventional image sensor, the light incident on the photodiode in the region where the photodiode and the transfer transistor overlap is blocked and reflected by the transfer transistor, thereby reducing the amount of incident light.

According to the embodiment, a transparent transistor is used to fabricate a transfer transistor so that incident light is absorbed in the entire photodiode region, thereby improving light sensitivity, shading phenomenon, and significant difference in Gr / Gb signal, and capable of high-speed operation. It provides a sensor and a method of manufacturing the same.

In addition, the manufacturing method of the image sensor according to the embodiment comprises the steps of forming a photodiode on the substrate; Forming a gate insulating layer partially overlapping the photodiode; And forming a transfer transistor having a gate electrode made of a transparent material on the gate insulating layer.

According to the embodiment, the following effects are obtained.

First, since incident light is imaged over the entire photodiode area, the light sensitivity and dynamic range of the image sensor may be increased. Second, since the electrode of the transfer transistor is formed of a transparent material, the Gr signal generated in the 2 x 1 symmetrical pixel, the 2 x 2 symmetrical pixel, and the 4 x 1 symmetric pixel structure Significant difference in Gb signal can be improved. Third, it is possible to improve the shading caused by the electrodes of the transfer transistor blocking some of the photodiodes. Fourth, high-speed operation can be implemented by replacing the gate electrode with a metal of transparent material. Fifth, in the case of a gate electrode made of a transparent material, the ILD thickness can be reduced, so that an image sensor can be manufactured at a low stack height, thereby improving light sensitivity.

Hereinafter, an image sensor and a manufacturing method thereof according to an embodiment will be described in detail with reference to the accompanying drawings. In the description of an embodiment, each layer (film), region, pattern, or structure is formed “on” or “under” a substrate, each layer (film), region, pad, or pattern. In the case where it is described as "to", "on" and "under" include both "directly" or "indirectly" formed. Also, the criteria for top, bottom, or bottom of each layer will be described with reference to the drawings. In the drawings, the thickness or size of each layer is exaggerated, omitted, or schematically illustrated for convenience and clarity of description. In addition, the size of each component does not necessarily reflect the actual size.

The image sensor described in the embodiment is a semiconductor device that detects light and converts it into an electrical signal. Among them, a charge coupled device (CCD) is a device in which charge carriers are stored and transported in a capacitor while individual metal-oxide-silicon (MOS) capacitors are located in close proximity to each other.

1 is a diagram illustrating a circuit configuration of an image sensor according to an embodiment.

As shown in FIG. 1, the image sensor is formed in a 4T structure including a photodiode PD, a transfer transistor TX, a reset transistor RX, a drive transistor DX, and a selection transistor SX. It may be, but is not limited to such.

Photodiode PD is responsible for photoelectric conversion. The transfer transistor TX transmits the voltage of the floating diffusion region FD to the photodiode PD to reset the photodiode PD or to the photodiode PD. It acts as a switch for converting the incident optical signal into an electrical signal and transferring it to the floating diffusion region (FD). The reset transistor RX receives the voltage supplied from the power supply wiring PVDD and transfers the voltage to the photodiode PD through the floating diffusion region FD to initialize the photodiode PD. The drive transistor DX amplifies the voltage signal of the floating diffusion region FD. The selection transistor SX transfers the voltage signal output through the output terminal Vout connected to the bias unit to an external signal processor.

2 is a plan view of a unit pixel of an image sensor according to an exemplary embodiment, and FIG. 3 is a cross-sectional view of an AA ′ region of FIG. 2.

As illustrated in FIGS. 2 and 3, a photodiode PD and a capacitor CST are formed in a unit pixel area defined in the substrate 100, and a separation film FOX is formed to separate the devices. The printing layer 105 may be formed on the photodiode PD formed on the substrate 100. The transfer transistor TX is formed on the substrate 100 partially overlapping the printing layer 105 or the photodiode PD. In the region adjacent to the transistor transistor TX, the reset transistor RX, the drive transistor DX, and the selection transistor SX are formed.

The transfer transistor TX, the reset transistor RX, the drive transistor DX, and the select transistor SX are disposed on the gate insulating layers 111 to 141 and the gate insulating layers 111 to 141 formed on the substrate 100. Each of the gate electrodes 115 to 145 is positioned. A floating diffusion region FD 106 is formed between the transfer transistor TX and the reset transistor RX, and a source / drain region is formed between the reset transistor RX, the drive transistor DX, and the selection transistor SX. Ion implantation regions 106 to 109 including 107, 108 and 109 are formed.

The passivation layer 150 is formed on the transfer transistor TX, the reset transistor RX, the drive transistor DX, and the select transistor SX. The passivation layer 150 may be formed of BPSG including boron (B), but is not limited thereto. The metal electrodes M1 170 may be formed on the passivation layer 150 to be connected to the transfer transistor TX, the reset transistor RX, the drive transistor DX, and the selection transistor SX. The metal electrodes M1 170 are connected to the electrodes 115 to 145 and the regions 106 to 109 by the contact electrodes 160.

An interlayer insulating layer 180 is formed on the passivation layer 150.

In the case of the transfer transistor TX according to the embodiment, the gate electrode 115 is made of a transparent material. The transparent material may be made of any one of SnO, ZnO, indium tin oxide (ITO), InO, and graphene, but is not limited thereto.

In order to fabricate the transfer transistor TX according to the embodiment, the photodiode PD is formed on the substrate 100, and the gate insulating layer 111 partially overlapping the photodiode PD is thermally oxidized. Form. Subsequently, the gate electrode 115 is formed of a transparent material such as SnO, ZnO, ITO, InO, and Graphene, and manufactured to act as a transfer transistor TX through a photolithography process. On the other hand, for the transistors RX, DX, and SX except for the transfer transistor TX, the gate electrodes 125 to 145 are formed of polysilicon, metals, silicides of metals, and the like, followed by photo etching. It is manufactured to act as a transistor (RX, DX, SX) through a process.

As described above, the image sensor including the transfer transistor TX made of the gate electrode 115 made of a transparent material may be formed in a 4T structure as shown in FIG. 1, and the basic operation method may be the same. It is not limited.

When the gate electrode 115 of the transfer transistor TX is formed of a transparent material, an area in which the photodiode PD is blocked by light incident by the transfer transistor TX is removed, as in region B of FIG. 2, As shown in FIG. 3, since light is incident on the entire photodiode PD region, light sensitivity is increased.

Meanwhile, the reset transistor RX, the driver transistor DX, and the selection transistor SX are increased in order to increase the fill factor of the area of the photodiode PD in the overall image sensor area due to the reduction of the area of the unit pixel. ) Can be used in common. In a so-called shared structure that forms a plurality of photodiodes (PD) and transfer transistors (TX), a signal is generated in each photodiode (PD) by blocking the photodiode (PD) from the transfer transistor (TX). Significant differences and shading can be improved.

By configuring the gate electrode 115 of the transfer transistor TX with a transparent material, a parasitic cap and resistance of poly may be reduced to configure a CMOS image sensor for high speed operation that is required in a specific field. In addition, as the gate electrode 115 of the transfer transistor TX is formed of a transparent material, the thickness of the insulating layer is lower than that of the related art, thereby reducing the length of the path through which light flows from the photodiode PD. Light sensitivity can be improved.

Features, structures, effects, etc. described in the above embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to only one embodiment. Furthermore, the features, structures, effects, and the like illustrated in the embodiments may be combined or modified with respect to other embodiments by those skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

In addition, the above description has been made with reference to the embodiment, which is merely an example, and is not intended to limit the present invention. Those skilled in the art to which the present invention pertains will be illustrated as above without departing from the essential characteristics of the present embodiment. It will be appreciated that various modifications and applications are possible. For example, each component specifically shown in the embodiment can be modified. And differences relating to such modifications and applications will have to be construed as being included in the scope of the invention defined in the appended claims.

1 is a diagram for explaining a circuit configuration of an image sensor according to an embodiment.

2 is a plan view of a unit pixel of an image sensor according to an exemplary embodiment.

3 is a cross-sectional view taken along the line AA ′ of FIG. 2;

Claims

Board;

A photodiode formed on the substrate;

A gate insulating layer partially overlapping the photodiode; And

And a transfer transistor on the gate insulating layer and having a gate electrode made of a transparent material.

The method of claim 1,

The transparent material,

An image sensor comprising any one of SnO, ZnO, ITO, InO, and Graphene.

The method of claim 1,

At least one of the unit pixels included in the image sensor is

The image sensor, characterized in that formed with the transfer transistor.

Forming a photodiode on the substrate;

Forming a gate insulating layer partially overlapping the photodiode; And

Forming a transfer transistor having a gate electrode made of a transparent material on the gate insulating layer.

5. The method of claim 4,

The transparent material,

SnO, ZnO, ITO, Graphene any one of the manufacturing method of the image sensor, characterized in that made of.