KR20090085828A - Image sensor decresing crosstalk between pixels and method for manufacturing the image sensor - Google Patents

Abstract

An image sensor and a manufacturing method thereof are provided to reduce an electrical crosstalk and an optical crosstalk at a time by blocking an incident light in a photo diode of adjacent unit pixels. An image sensor(300) includes a semiconductor substrate(201), a plurality of photo diodes(202), and a plurality of isolation regions. A plurality of photo diodes is formed inside the semiconductor substrate. A plurality of isolation regions is formed inside a plurality of trenches for isolating a plurality of photo diodes. Each isolation region includes a first isolation film(203a) and a second isolation film(301). The first isolation film is formed according to a trench surface. The second isolation film is formed inside the first isolation film in order to block an incident light from an adjacent photo diode.

Description

IMAGE SENSOR DECRESING CROSSTALK BETWEEN PIXELS AND METHOD FOR MANUFACTURING THE IMAGE SENSOR}

The present invention relates to an image sensor and a method for manufacturing the same, and more particularly, to an image sensor and a method for manufacturing the same that can reduce the crosstalk between the pixels by filling the light-absorbing material in the device isolation region.

An image sensor is a semiconductor device that converts light into an electrical signal, and is divided into a charge coupled device (CCD) and a complementary metal oxide silicon (CMOS) image sensor. CCDs have complex drive methods, high power consumption, and complex manufacturing processes.

Recently, the demand for CMOS image sensors is rapidly increasing in various fields such as digital cameras, camcorders, personal communication systems (PCS), and gaming devices. Hereinafter, the image sensor means a CMOS image sensor.

First, the operation of a general image sensor is briefly described.

1 is a circuit diagram illustrating a unit pixel 100 constituting an image sensor. Referring to FIG. 1, the unit pixel 100 having a 4T (transistors) type includes a photodiode 101, a floating diffusion region 103, and a plurality of transistors 102, 104, 105, and 106. .

The image sensor includes a plurality of unit pixels 100 arranged in a matrix, but the plurality of unit pixels 100 have the same structure and operation principle as each other, and thus, for the sake of brief description, FIG. Only one unit pixel 100 is shown.

The photodiode 101 generates photoelectrons in response to light incident from the outside. The transfer transistor 102 transmits the photoelectrons generated by the photodiode 101 to the floating diffusion region 103 in response to a transmission signal TG. The reset transistor 104 resets the floating diffusion region 103 to a predetermined voltage VDD in response to the reset signal RG.

The drive transistor 105 outputs a voltage varying in response to the voltage level of the floating diffusion region 103 through the vertical signal line 107. The selection transistor 106 selects a unit pixel to output a signal in response to the selection signal SEL.

In recent years, the demand for high resolution image sensors has increased, and the size of the unit pixel of the image sensor has been rapidly decreased due to the development of the CMOS manufacturing process. As the size of the unit pixel decreases, the size of the photodiode decreases, which causes a decrease in the sensitivity of the photodiode.

In order to minimize degradation of the sensitivity of the photodiode, the size of the photodiode in the unit pixel is designed to be the maximum possible size. As a result, the distance between the photo diodes of the adjacent unit pixels is closer to each other, thereby increasing the frequency of crosstalk between the adjacent pixels.

2 is a partial cross-sectional view of a general image sensor 200. 2, the image sensor 200 includes a semiconductor substrate 201, a plurality of photo diodes 202, an isolation region 203a, a first insulating layer 203b, and a second insulating layer 204. , And wiring metal 205.

The device isolation region 203a separates adjacent photodiodes from each other. In general, the device isolation region 203a is formed of an oxide film filled in a trench formed by a shallow trench isolation (STI) process. The oxide film, which is an electrical insulator, can reduce electrical crosstalk between adjacent unit pixels by electrically separating adjacent photodiodes.

However, since the oxide film has a transparent property, light may pass easily, and thus there is a problem in that it is vulnerable to optical crosstalk. Referring to FIG. 2, light incident from an adjacent photodiode passes through the device isolation region 203a to generate electron (e) and hole (h) pairs (EHP) inside the photodiode. It can be seen that.

After the EHP is generated, holes (h) can be easily absorbed into the semiconductor substrate 201, which is a high concentration of P-type, while electrons (e) move to adjacent photodiodes, resulting in a data mix between adjacent pixels, That is, crosstalk can be generated.

Accordingly, a technical problem of the present invention is to provide an image sensor and a method of manufacturing the same capable of simultaneously reducing electrical crosstalk and optical crosstalk by blocking light incident on photodiodes of adjacent unit pixels.

An image sensor for achieving the above technical problem includes a semiconductor substrate, a plurality of photo diodes, and a plurality of device isolation regions. The plurality of photodiodes is formed inside the semiconductor substrate. The plurality of device isolation regions are formed in a plurality of trenches for separating the photodiodes from each other.

Each of the device isolation regions includes a first device isolation layer formed along the trench surface and a second device isolation layer formed inside the first device isolation layer to block light incident from an adjacent photodiode.

The plurality of trenches may be formed by etching according to a shallow trench isolation (STI) process. The first device isolation layer may be an oxide layer, and the second device isolation layer may be a light absorbing material layer for reducing crosstalk between pixels by absorbing light incident from adjacent photodiodes.

An image sensor manufacturing method for solving the technical problem comprises the steps of forming a plurality of photodiodes inside a semiconductor substrate; Forming a plurality of trenches to separate the photo diodes from each other; And forming a plurality of device isolation regions within the plurality of trenches.

Each of the device isolation regions includes a first device isolation layer formed along the trench surface and a second device isolation layer formed inside the first device isolation layer to block light incident from an adjacent photodiode. The forming of the plurality of trenches may be an etching process according to an STI process.

The forming of each of the plurality of device isolation regions may include forming a first device isolation layer including the first device isolation layer; Forming a second device isolation layer including the second device isolation layer; And forming the first device isolation layer and the second device isolation layer by etching.

 The first device isolation layer may be an oxide layer, and the second device isolation layer may be a light absorbing material layer for reducing crosstalk between pixels by absorbing light incident from adjacent photodiodes. The forming of the first device isolation layer and the second device isolation layer may include forming the first device isolation layer and the second device isolation layer by etching according to a chemical mechanical polishing (CMP) process.

The depth of etching according to the CMP process may be deeper than the trench start surface formed by etching according to the STI process.

As described above, the image sensor and the manufacturing method thereof according to the present invention have the effect of simultaneously reducing the electrical crosstalk and the optical crosstalk between adjacent unit pixels.

In order to fully understand the present invention, the operational advantages of the present invention, and the objects attained by the practice of the present invention, reference should be made to the accompanying drawings which illustrate preferred embodiments of the present invention and the contents described in the accompanying drawings.

In the present specification, when one component 'transmits' data or a signal to another component, the component may directly transmit the data or signal to the other component, and at least one other component. Through this means that the data or signal can be transmitted to the other component.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

3 is a partial cross-sectional view of an image sensor 300 according to an embodiment of the present invention. Referring to FIG. 3, the image sensor 300 includes a semiconductor substrate 201, a plurality of photo diodes 202, isolation regions 203a and 301, a first insulating layer 230b, and a second insulating layer ( 204, and wiring metal 205. In FIG. 3, only two adjacent photodiodes are shown for simplicity.

The semiconductor substrate 201 may be composed of a high concentration P ++ layer and a P-epi layer stacked thereon, but is briefly referred to as a semiconductor substrate. The plurality of photodiodes 202 are formed in the semiconductor substrate 201 and convert incident light into an electrical signal.

The image sensor 300 is positioned above the photodiode 202 and has a color filter (not shown) for filtering incident light, a micro lens (not shown) for concentrating incident light, and the image sensor ( A plurality of transistors (not shown) and various metal wires (not shown) for driving 300 may be further provided.

The plurality of device isolation regions 203a and 301 are formed in the plurality of trenches for separating the photodiodes 202 from each other. The trenches may be formed by a shallow trench isolation (STI) process.

Each of the device isolation regions 203a and 301 is formed in the first device isolation layer 203a formed along the trench surface and in the first device isolation layer to block light incident from an adjacent photodiode. The separator 301 is included.

The first device isolation layer 203a is generally an oxide film, which is electrically insulated or transparent, and thus cannot effectively block light incident from adjacent photodiodes. The second device isolation layer 301 may be a light absorbing material layer for reducing crosstalk between pixels by absorbing light incident from adjacent photodiodes. The second device isolation layer 301 may be formed of metal, polysilicon, silicon, or the like having light absorbing properties.

That is, the second device isolation layer 301 may compensate for the weakness of the first device isolation layer 203a against optical crosstalk, thereby reducing optical crosstalk by blocking light incident from an adjacent photodiode.

The first insulating layer 203b may be formed of the same oxide film as the first device isolation layer 203a and may be used to form a plurality of transistors included in the image sensor 300. The second insulating layer 204 may be implemented as a nitride (SiN) layer, and the image sensor 300 may perform an anti-reflection (ARL) function.

The wiring metal 205 may be a power line connecting a plurality of transistors included in the image sensor 300. As shown in FIG. 3, the wiring metal 205 may serve as a shield to block light incident to an adjacent photodiode.

The first device isolation layer 203a, the second device isolation layer 301, the first insulation layer 203b, the second insulation layer 204, and the like may be formed by a high density plasma oxide film deposition process. Can be.

4 is a flowchart illustrating a manufacturing method of an image sensor 300 according to an exemplary embodiment of the present invention. 5A to 5F are cross-sectional views illustrating processes of a method of manufacturing the image sensor 300 according to an exemplary embodiment of the present invention. Hereinafter, the process will be described in detail with reference to FIGS. 3, 4, and 5A to 5F.

A plurality of photodiodes 202 are formed in the semiconductor substrate 201 by ion implantation (S100). As is well known, a photodiode is composed of a deep N-type impurity region (deep N−) and a shallow P0 impurity region formed through ion implantation. In FIG. 5A, only two photodiodes are shown for simplicity.

After the photodiodes 202 are formed, a trench for separating between the photodiodes 202 is formed by etching according to an STI process (S200). Referring to FIG. 5A, it can be seen that a trench having a predetermined depth is formed between the photodiodes 202.

After the trenches are formed, device isolation regions are formed in the plurality of trenches (steps S300, S400, and S500). The process of forming the device isolation region will be described in more detail.

First, a first device isolation layer including the first device isolation layer 203a is formed (S300). Referring to FIG. 5C, the first device isolation layer is formed on the trench surface, the semiconductor substrate 201, and the photodiode 202, and a portion of the first device isolation layer formed along the trench surface is formed. Finally, the first device isolation layer 203a is formed. The first device isolation layer may be an oxide film.

A second device isolation layer including the second device isolation layer 301 is formed on the first device isolation layer (S400). Referring to FIG. 5D, the portion of the second device isolation layer formed inside the first device isolation layer 203a is a portion that finally becomes the second device isolation layer 301. In addition, the dotted line illustrated in FIG. 5D indicates a surface on which the first device isolation layer 203a and the second device isolation layer 301 are finally formed by etching. The second device isolation layer 301 may be formed of a nitride or oxide-based inorganic film, silicon, polysilicon, metal, or the like having light absorbing properties.

After the second device isolation layer is formed, the first device isolation layer 203a and the second device isolation layer 301 are formed by etching (S500). The etching may be performed according to the CMP process. 5D and 5E, it can be seen that the depth of etching (CMP surface) according to the CMP process is deeper than the trench starting surface (STI surface) formed by etching according to the STI process.

The first device isolation layer 203a may reduce electrical crosstalk between the photodiodes 202 as an electrical insulator, but the second device isolation layer 301 absorbs light incident from an adjacent photodiode. Optical crosstalk between the photodiodes 202 can be reduced.

After the first device isolation layer 203a and the second device isolation layer 301 are formed, a first insulating layer 203b is formed on the viewing surface again (S600). The first insulating layer 203b may be an oxide film like the first device isolation layer 203a. In FIG. 5F, the first device isolation layer 203a and the first insulating layer 203b are the same oxide layer.

An image sensor manufacturing process after the first insulating layer 203b is formed is well known to those skilled in the art, and a detailed description thereof will be omitted.

Although the invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a circuit diagram illustrating a unit pixel constituting an image sensor.

2 is a partial cross-sectional view of a general image sensor.

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

4 is a flowchart illustrating a manufacturing method of an image sensor according to an exemplary embodiment of the present invention.

5A to 5F are cross-sectional views illustrating processes of a method of manufacturing an image sensor according to an embodiment of the present invention.

Claims (9)

Semiconductor substrates; A plurality of photo diodes formed in the semiconductor substrate; And A plurality of device isolation regions formed in the plurality of trenches for separating the photodiodes from each other, Each of the device isolation regions includes a first device isolation layer formed along the trench surface and a second device isolation layer formed inside the first device isolation layer to block light incident from an adjacent photodiode. The method of claim 1, wherein the plurality of trenches, Image sensor formed by etching according to STI (Shallow Trench Isolation) process. The method of claim 1, wherein the first device separator, An oxide film, The second device separation membrane, An image sensor, which is a film of light absorbing material for reducing crosstalk between pixels by absorbing light incident from adjacent photo diodes. Forming a plurality of photo diodes inside the semiconductor substrate; Forming a plurality of trenches to separate the photo diodes from each other; And Forming a plurality of device isolation regions within the plurality of trenches, Each of the device isolation regions includes a first device isolation layer formed along the trench surface and a second device isolation layer formed inside the first device isolation layer to block light incident from an adjacent photodiode. . The method of claim 4, wherein the forming of the plurality of trenches comprises: And forming the plurality of trenches by etching according to an STI process. The method of claim 4, wherein forming each of the plurality of device isolation regions comprises: Forming a first device isolation layer including the first device isolation layer; Forming a second device isolation layer including the second device isolation layer; And And forming the first device separator and the second device separator by etching. The method of claim 6, wherein the first device separator, An oxide film, The second device separation membrane, A method of manufacturing an image sensor, which is a film of light absorbing material for reducing crosstalk between pixels by absorbing light incident from adjacent photodiodes. The method of claim 6, wherein the forming of the first device isolation layer and the second device isolation layer comprises: And forming the first device separator and the second device separator by etching according to a chemical mechanical polishing (CMP) process. The method of claim 8, wherein the depth of etching according to the CMP process, The image sensor manufacturing method deeper than the trench start surface formed by the etching according to the STI process.

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