KR20060077118A - Cmos image sensor having optical shield layer using photonic crystal - Google Patents

Abstract

The present invention is applied to a CMOS image sensor using a photonic crystal as a color filter. A photonic crystal is a structure having a characteristic of blocking or passing light of a specific wavelength in a specific direction by showing a photonic band gap in a dielectric material having a three-dimensional periodicity. Periodically changing the dielectric constant of a material over space (1 to 3 dimensions) results in a photonic band gap in which electromagnetic waves are not transmitted in a specific frequency band, a concept similar to the electron band gap in semiconductors. to be.

It is now available as a light-blocking layer in CMOS image sensors, and theoretically can only selectively reflect light in a very fine frequency range and 100% reflectivity for specific wavelengths.

Therefore, by applying the light blocking layer using the photonic crystal to the CMOS image sensor, it is possible to replace the current color filter to the light blocking layer to which the metal is applied, thereby improving light blocking characteristics.

Image sensor, light blocking layer, photonic crystal, photonic band gap.

Description

CMOS Image Sensor with Light-Blocking Layer Using Photonic Crystal {CMOS IMAGE SENSOR HAVING OPTICAL SHIELD LAYER USING PHOTONIC CRYSTAL}             

1 is a plan view showing an arrangement of unit pixels of a CMOS image sensor;

FIG. 2 is a cross-sectional view illustrating a unit pixel of an image sensor taken along the direction of a-a 'in FIG. 1 so that all RGB colors appear.

3 is a view showing the structure of a two-dimensional photonic crystal and the formation of a photonic band gap.

4 illustrates a multidimensional structure of a photonic crystal.

5 is a cross-sectional view of a CMOS image sensor using a photonic crystal as a light blocking layer in accordance with an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

500: P type substrate 501: P type epi layer

502: field oxide film 503: gate insulating film

504: gate conductive film 505: n- region

506 spacer 507 floating diffusion region                 

508: source / drain 509: P0 area

510: insulating film for borderless contact 511: all insulating film

512: first metal line 513: insulating film between metal lines

514: second metal line 515: first overcoating layer

516: light blocking layer 517: second overcoating layer

518: color filter array 519: second overcoating layer

520: Micro Lens

The present invention relates to an image sensor, and more particularly, to a CMOS image sensor using a photonic crystal as a light blocking layer.

The image sensor is a semiconductor device that converts an optical image into an electrical signal. Among them, a charge coupled device (CCD) is a device in which charge carriers are stored and transported in capacitors while individual MOS (Metal-Oxide-Silicon) capacitors are located in close proximity to each other.

On the other hand, CMOS (Complementary MOS) image sensors use CMOS technology that uses a control circuit and a signal processing circuit as peripheral circuits. It is a device that adopts a switching method that detects an output sequentially.

1 is a plan view showing an arrangement of unit pixels of a CMOS image sensor.

Referring to FIG. 1, each unit pixel for capturing a color of RGB which is three primary colors of light is arranged in a grid structure.

FIG. 2 is a cross-sectional view illustrating a unit pixel of an image sensor taken along the direction of a-a 'so that all RGB colors appear.

Referring to FIG. 2, a field oxide film 101 is locally formed on a substrate 100 having a structure in which a high concentration of a P-type (P ++) region and an epi layer (P-epi) are stacked, and on the substrate 100. A plurality of gate electrodes including a transfer gate (not shown) are formed, for example, an N-zero region (not shown) by deep ion implantation under the surface of the substrate 100 aligned on one side of the transfer gate. A photodiode 102 (hereinafter referred to as PD) formed of a P-type region (not shown) positioned in a region in contact with the surface of the substrate 100 is formed. Although not shown in the drawing, in this case, a high concentration N-type (N +) floating diffusion region is formed at the bottom of the surface of the substrate 100 aligned on the other side of the transfer gate by ion implantation.

On the upper side where the PD 102 and the transfer gate are formed, a structure 103 in which a plurality of metal lines and a plurality of insulating films, which form a stacked structure, are mixed is formed.

The plurality of metal lines are used to connect power lines or signal lines, unit pixels, and logic circuits, and serve as shields, that is, light blocking layers, to prevent light from being incident on regions other than the PD 102.                         

On the structure 103 in which a plurality of metal lines and a plurality of insulating films are mixed, a first overcoating layer 104 (hereinafter, referred to as OCL1) is formed to reduce the generation of steps due to metal line formation. On the OCL1, a color filter array 105 (hereinafter referred to as CFA) for implementing RGB color is formed for each unit pixel.

R (Red) G (Green) B (Blue), which is the three primary colors of ordinary light, is used. In addition, yellow, magenta (Mg), and cyan (Cy), which are complementary colors, may be used. .

On the CFA 105, a second overcoating layer 106 (hereinafter referred to as OCL2) is formed on the CCL 105 so as to reduce a step generated by forming the CFA 105 to secure a process margin when forming a microlens. , Micro-Lens (hereinafter referred to as ML) is formed.

A protective film is formed on the ML to prevent the ML from being scratched or broken, and the protective film is omitted here.

Thus, the incident light is focused by the ML 107 and enters the PD 102.

In order to suppress the generation of noise in the image sensor, light must be blocked in a region other than the light receiving region including the photodiode.

As can be seen from the above structure, in the conventional case, a plurality of metal lines serve as a light blocking layer.

However, when the thickness of the metal line is thin, it cannot block all the light entering the bottom of the metal line, and if the metal line used as the light blocking layer is used for the purpose of signal transmission instead of the light blocking layer at a specific portion, The process and the like will be restricted. In addition, in the case of prolonged light exposure, light may be partially absorbed rather than reflected by 100%, and thus noise may be generated due to heat due to the absorbed light.

The present invention proposed to solve the above problems of the prior art, an object thereof is to provide an image sensor that can improve the light blocking characteristics.

In order to achieve the above object, the present invention includes a light-receiving element and a light blocking layer covering all regions except the light-receiving element in order to block light incident from the upper portion of the light-receiving element to a region other than the light-receiving element. The monolayer provides an image sensor characterized in that a plurality of dielectrics having different refractive indices are arranged periodically to form a photonic crystal through which light of a specific wavelength passes.

The present invention is to replace the conventional metal shield, that is, light blocking layer using a metal using a photonic crystal. Photonic crystals can periodically combine materials with different dielectric constants to block light in a particular wavelength range. The wavelength range can be selected simply by changing the spatial combination without changing the composition of the material.

FIG. 3 is a diagram illustrating the structure of a 2-dimensional photonic crystal and the formation of a photonic band gap, showing the basic principle of the photonic crystal.

When light is passed in the direction of a wave vector of a photonic crystal in a two-dimensional array having different dielectric constants, it can be seen that there are regions where light is prohibited in a specific wavelength band. This is called a photonic band gap, and it is possible to select a specific wavelength band by applying the selectivity of the wavelength to the color filter.

By changing the material and structure of the photonic crystal used, the selection of the wavelength band can be changed. The photonic band gap can be controlled by changing the type of the material without changing the structure of the material or vice versa without changing the type of the material.

This has advantages in terms of process change, since it is only necessary to change the structure without changing the material to select different wavelengths.

Theoretically, photonic crystals can have 100% reflectivity for specific wavelengths, resulting in high light shielding efficiency and low temperature rises, unlike conventional metal shields, even when exposed to light for extended periods of time. Reflect.

In addition, since it is formed on the existing metal line, it is functionally separated from the metal line so that the wiring design can be freely made.

DETAILED DESCRIPTION Hereinafter, exemplary 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.

4 illustrates a multidimensional structure of a photonic crystal.

Photonic crystals can be largely divided into three types: the one-dimensional photonic crystal shown in (a) of FIG. 4 and the two-dimensional photonic crystal shown in (b) of FIG. There are three types of photonic crystals (Periodic in two directions) and three-dimensional photonic crystals (Periodic in three directions) shown in FIG.

In the case of the one-dimensional photonic crystal as shown in (a) of FIG. 4, since the different materials only need to be periodically stacked, the manufacture thereof is the simplest. In addition, the production of two- and three-dimensional photonic crystals is also possible.

In the case of a one-dimensional photonic crystal, two or more different materials having different dielectric constants (or refractive indices) may be periodically stacked. At this time, there is a photonic band gap with respect to the wavelength in the stacked direction, that is, the vertical direction of each layer. This can be used as a light blocking layer.

In other words, changing the laminated structure (thickness of each layer, etc.) results in photonic band gaps for different wavelengths. Thus, shield characteristics can be obtained as close as 100% to incident light using an appropriate thickness and period.

5 is a cross-sectional view illustrating a CMOS image sensor having a 4-transistor structure using a photonic crystal as a light blocking layer according to an embodiment of the present invention.

Referring to FIG. 5, a field oxide film 502 is formed locally on a semiconductor layer having a structure in which a high concentration P-type (P ++) substrate 500 and a P-type epitaxial layer (P-epi, 501) are stacked. On the semiconductor layer, a transistor (Tx), a reset transistor (Rx), a drive transistor (Dx) and a select transistor (Sx) including a gate electrode and a source / drain 508 formed on the semiconductor layer aligned with the side thereof are formed. Formed.

Each transistor is composed of a stacked structure of the gate lead film 503 and the gate conductive film 504 and a spacer 506 on the sidewall thereof, and has a high concentration N type (n +) between the transfer transistor Tx and the reset transistor Rx. A floating diffusion region 507 is formed.

N-zero region (505, hereinafter referred to as n-region) by deep ion implantation under the semiconductor layer surface aligned to one side of the transfer gate, and P-type region 509 (hereinafter referred to as P0 region) located in the region in contact with the semiconductor layer surface. Photodiode PD is formed.

The insulating layer 510 for borderless contact is formed on the photodiode PD and the plurality of transistors. The borderless contact insulating film 510 is a nitride film-based insulating film.

Pre-metal dielectric (hereinafter referred to as PMD) is formed on the borderless contact insulating layer 510, and a first metal line M1 is formed on the PMD 511. An inter-metal insulating film 513 (hereinafter referred to as IMD) is formed on the metal line M1, a second metal line M2 is formed on the IMD 513, and a second metal line A plurality of metal lines (not shown) and a first overcoating layer 515 (hereinafter referred to as OCL1) are formed on M2.

On the OCL1 515, a light blocking layer 516 for blocking light incidence to regions other than the photodiode PD is formed so as to cover all regions other than the light receiving region including the photodiode PD.

Conventionally, the metal line is used to act as the light blocking layer 516. However, in the present invention, a photonic crystal having a very simple manufacturing process is used in the present invention.

In the case of the photonic crystal, only two kinds of materials, a and b, are used, but the stack structure can be reflected to almost 100% through the photomic band gap by varying the stack structure such as the thickness of each layer.

It is also possible to form a laminate structure of a nitride film and an oxide film commonly used as an insulating film during a CMOS process, and a laminate structure of a nitride film and a low temperature oxide (LTO) used for the role of passivation after metal line formation is repeated. It can also be used.

When the light blocking layer 516 using photonic crystals is used, materials having two different refractive indices or dielectric constants are formed by spatially different combinations. It is possible to change the choice of wavelength by changing only the spatial arrangement of the two materials.

Of course, it is possible to have a light blocking property by changing the type of the material used, and can be filtered by applying not only 1-dimensional photonic crystal but also 2-dimensional and 3-dimensional photonic crystal.

A second overcoating layer 517 (hereinafter referred to as OCL2) is formed on the light blocking layer 516, and a color filter array 518 is formed on the OCL2 517 to implement RGB colors for each unit pixel.

R (Red) G (Green) B (Blue), which is the three primary colors of ordinary light, is used. In addition, yellow, magenta (Mg), and cyan (Cy), which are complementary colors, may be used. .

On the color filter array 518, a third overcoating layer 519 (hereinafter referred to as OCL3) is formed on the color filter array 518 so as to reduce a step generated by forming the color filter array 518 to secure a process margin when forming a microlens. The microlens 520 is formed on the 519.

A protective film is formed on the microlens 520 to prevent the microlens 520 from being scratched or broken, and the protective film is omitted here.

As the protective film, LTO is used to prevent deformation of the microlens 520 by the thermal process.

As such, the materials used for the preparation of the photonic crystal need only be materials having different refractive indices (dielectric constants), thereby greatly deviating from the constraints of the use of the materials. In addition, in the case of the one-dimensional photonic crystal, only the adjustment of the laminated structure is required, the manufacturing process is simple.

As described above, the present invention obtains a light blocking effect by stacking a dielectric material having different materials, that is, different dielectric constants (or refractive indices), instead of the conventional metal, and is particularly effective for an image sensor that must be transparently packaged. When the light blocking layer is formed using a photonic crystal, it may be manufactured at any place after the conventional metal line.

In addition, by changing the structure of LTO and the like used in the conventional passivation it is possible to block light with the addition process of several layers including other materials, it is possible to give a design margin to the metal line of the lower layer just by adding a simple process, In addition, the metal line may be further reduced.

In addition, the present invention has been found that the light blocking layer using the photonic crystal may be formed on the metal line in parallel with the existing metal line shield, thereby maximizing the light blocking property.

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

For example, in the above-described embodiment of the present invention, the CMOS image sensor is taken as an example, but it is also applicable to all image sensors having the light receiving unit and the microlens.

The present invention described above, by implementing a light blocking layer using a photonic crystal, to maximize the light blocking effect, there is an effect of improving the performance of the image sensor.

Claims (4)

And a light blocking layer covering all regions except the light receiving element to block light incident from an upper portion of the light receiving element to an area except the light receiving element. The light blocking layer is a plurality of dielectrics having different refractive indices are arranged periodically to form a photonic crystal passing light of a specific wavelength. The method of claim 1, And the refractive indexes of the plurality of dielectrics are different from each other. The method according to claim 1 or 2, The photonic crystal is an image sensor, characterized in that the structure of any one, two-dimensional or three-dimensional. The method according to claim 1 or 2, The plurality of dielectrics comprises an oxide film or a nitride film.

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