KR100688584B1 - Cmos image sensor and method of fabricating the same sensor - Google Patents

Abstract

A CMOS image sensor is provided to increase reflectivity caused by an isolation layer by forming the isolation layer made of two material layers having different refractivity. An epitaxial layer(200) of first conductivity type is formed on a substrate(100) of first conductivity type. Photodiodes(400) are formed on the epitaxial layer in each active region. Two material layers having different refractivity are alternately and vertically formed on the substrate to form an isolation layer(300) for isolating the active regions. The two material layers can be a silicon layer and a silicon oxide layer. The isolation layer can be composed of three layers of the silicon layer and silicon oxide layers formed on both sides of the silicon layer. The silicon oxide layers are connected to each other through the lower part of the silicon layer.

Description

CMOS image sensor and method of manufacturing the sensor {CMOS image sensor and method of fabricating the same sensor}

1 is a schematic cross-sectional view of a conventional CMOS image sensor.

2 is a schematic cross-sectional view of a CMOS image sensor according to an exemplary embodiment.

3A and 3B are enlarged cross-sectional views illustrating structures of two material films applicable to the device isolation film of FIG. 2.

4A and 4B are graphs illustrating reflectances according to wavelengths of the device isolation layer structure applied to the present invention.

5A to 5E are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to another exemplary embodiment of the present invention.

Description of the main parts of the drawing

100: p-type Substrate ... 200: p-type Epilayer

300, 300a: device isolation film ... 320: silicon oxide film

320a: air film ............ 340,340a: silicon film

350: trench ... 400: photodiode

The present invention relates to a CMOS image sensor, and more particularly, to a CMOS image sensor and a method of manufacturing the same, which block visible light from penetrating into surrounding pixels through an isolation layer.

In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal. Among the image sensors, a charge coupled device (CCD) is a charge carrier in which individual capacitors are located very close to each other. Is a device in which capacitors are stored and transferred, and CMOS image sensors use CMOS technology that uses control circuits and signal processing circuits as peripheral circuits to make as many MOS transistors as pixels, and to sequentially detect the output using them. It is an element employing a switching method.

CCD has a number of disadvantages such as complicated driving method, high power consumption, high number of mask process steps, complicated process, and difficulty in making one chip because signal processing circuit cannot be implemented in CCD chip. In order to overcome the shortcomings, the development of CMOS image sensors using sub-micron CMOS manufacturing techniques has been studied.

Since CMOS image sensor uses unit MOS manufacturing technology, it consumes less power and has fewer mask processes, making the process very simple compared to CCD process and enabling one-chip with various signal processing circuits.

The CMOS image sensor is typically a complex of unit pixels consisting of one photodiode (PD) and four MOS transistors.

FIG. 1 is a cross-sectional view schematically illustrating a conventional image sensor, and a photo diode and a transfer transistor are illustrated in a unit pixel, and the remaining transistors are omitted.

Referring to FIG. 1, a low concentration p-type epitaxial layer 20 epitaxially grown on a relatively high concentration p-type semiconductor substrate 10 is illustrated, and the p-type epitaxial layer 20 is illustrated. In the upper portion, an isolation layer 30 for separating the active region is formed using a trench structure. Typically, a channel stop ion implantation region (not shown) is formed below the device isolation layer 30 having the trench structure, and spacers 62 are formed on both sidewalls of the gate electrode 60 of the transfer transistor.

One side of the p-type ion implantation region 42 constituting the p / n / p type photodiode 40 is aligned with the spacer 62 and the other side is aligned with the device isolation layer 30 to form the p-type epitaxial layer 20. It is formed at a predetermined depth from the surface, and the n-type ion implantation region 44 is formed deep in the epi layer 20 below the p-type ion implantation region 42. In this case, the device isolation layer may be formed thinner or deeper than the n-type ion implantation region 44. On the other hand, it can be seen that the p-type epitaxial layer 20 is connected to adjacent pixels.

In the conventional image sensor configured as described above, light incident in the direction of the arrow penetrates the device isolation layer 30 to generate an electron-electron pair in adjacent pixels, thereby causing crosstalk (CT) between adjacent pixels. That is, light incident on a specific unit pixel must be photoelectrically converted by a photodiode of a specific unit pixel to output data. The light penetrates into the adjacent pixel through the device isolation layer, thereby causing a problem of lowering the sensitivity of the photodiode. This CT phenomenon is mainly caused by reflected, diffracted or scattered light and side light incident on the side of the device isolation layer.

On the other hand, since long wavelengths such as red light have a deep penetration depth, they are a major cause of CT phenomenon, and often penetrate deeper than the n-type ion implantation region 44 to generate electron-electron pairs in the epi layer 20. In other words, it acts as a factor causing the CT phenomenon through the epi layer 20 connected to the adjacent pixels.

These CT phenomena are becoming a fatal weakness of the sensor in terms of sensitivity as the pixel size of the CMOS image sensor becomes smaller.

Accordingly, an object of the present invention is to provide a CMOS image sensor and a method of manufacturing the same which can block light from penetrating into adjacent pixels through a new device isolation layer structure.

In order to achieve the above technical problem, the present invention is a first conductivity type substrate; An epitaxial layer of a first conductivity type formed on the substrate; Photodiodes formed in respective active regions above the epitaxial layer; And device isolation layers having two refractive indexes having different refractive indices, which are alternately formed in the vertical direction on the substrate, to separate the active regions from each other.

According to an embodiment of the present invention, the two material films are preferably a silicon film and a silicon oxide film or a silicon film and an air film, but not limited thereto. The two material films may be formed using other materials having a refractive index difference of 2 or more. Of course. The first conductivity type is p type, that is, the first conductivity type substrate is a p type substrate and the first conductivity type epi layer is preferably a p type epi layer.

The present invention also comprises the steps of growing an epitaxial layer of the first conductivity type on the first conductivity type substrate to achieve the above technical problem; Forming an isolation layer on the epi layer to alternately form two material films having different refractive indices in a direction perpendicular to the substrate to separate active regions; And implanting ions into the epitaxial layer to form a photodiode.

In an embodiment, the device isolation layer may include forming a trench in the epitaxial layer; Forming a silicon oxide film on a lower surface and a sidewall of the trench; And forming a silicon film by filling the inside of the trench in which the silicon oxide film is formed with silicon. In addition, the device isolation layer may be configured by forming at least two air layers spaced apart from each other through dry etching in the epitaxial layer.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention; In the following description, when a component is described as being on top of another component, it may be directly on top of another component, and a third component may be interposed therebetween. In addition, in the drawings, the thickness or size of each component is omitted or exaggerated for clarity and convenience of explanation, the same reference numerals in the drawings refer to the same elements. On the other hand, the terms used are used only for the purpose of illustrating the present invention and are not used to limit the scope of the invention described in the meaning or claims.

2 is a cross-sectional view schematically illustrating a CMOS image sensor according to an exemplary embodiment of the present invention, and a transfer transistor, a floating diffusion region, and the like are omitted for convenience of description.

Referring to FIG. 2, the CMOS image sensor includes a p-type semiconductor substrate 100, a p-type epi layer 200 formed on the substrate 100, a device isolation layer 300 and an epi layer ( 200 includes a photodiode 400 formed thereon.

The device isolation layer 300 in the present embodiment is formed deeper than the photodiode 400, and is formed by alternately disposing two material films having different refractive indices in a direction perpendicular to the substrate 100. By forming the device isolation layer 300 using two material films having different refractive indices, the reflectance of the device isolation layer can be increased, thereby preventing side light or the like from penetrating into adjacent pixels. The greater the difference between the refractive indices of the two material layers, the greater the reflectance of the device isolation layer. Therefore, it is preferable to form the device isolation layer using different materials having a large difference in refractive index.

On the other hand, in the present embodiment, three element isolation films are formed using two material films, but it is of course possible to form more than that as necessary. In addition, it is preferable to prevent the CT phenomenon through the epi layer 200 by forming the device isolation layer 300 near the substrate 100.

The photodiode 400 includes a p-type ion implantation region at an upper portion and an n-type ion implantation region at a lower portion thereof, and a transfer transistor or the like is formed on the side of the photodiode.

3A and 3B are enlarged cross-sectional views illustrating structures of two material films applicable to the device isolation film of FIG. 2.

Referring to FIG. 3A, the device isolation layer 300 is formed using the silicon oxide film 320 and the silicon film 340, and has three layers of film. The silicon oxide layer 320 is formed by forming a trench in the epitaxial layer and then depositing silicon oxide (SiO ₂ ) on the bottom and sidewalls of the trench, and the silicon layer 340 is filled with silicon (Si) between the silicon oxide layer 320. Is formed.

In this case, it is preferable that the width d1 of the silicon oxide film 320 is formed to be about 550 GPa, and the width d2 of the silicon film 340 is formed to be about 500 GPa. Generally, silicon oxide has a refractive index of about 1.46, and silicon has a refractive index of about 3.7 to 5.7 depending on the wavelength. Therefore, the refractive index difference is 2.2 or more, and the device isolation layer 300 formed of the silicon oxide film 320 and the silicon film 340 has a high reflectance.

3B illustrates a structure in which the device isolation layer 300a is formed using two material films different from those of FIG. 3A. That is, the device isolation layer 300a is formed by forming two air layers 320a spaced apart by etching on the epi layer. Etching is preferably dry etching to form an air film 320a having a uniform thickness. In the device isolation film 300a, the air film 320a and the silicon film 340a between the air film form two material films.

The width d3 of the air film 320a is formed to be about 740 mW, and the width d4 of the silicon film 340a between the air film 320a is formed to be about 520 mW. Since the refractive index of air is almost 1, the refractive index difference between the two material films is larger than in FIG. 3A. Therefore, the reflectance of the device isolation layer 300a formed of the air film 320a and the silicon film 340a is further increased.

Here, the two material films used for the device isolation layers 300 and 300a are merely examples, and the device isolation layer may be formed using materials having a large refractive index difference, preferably, having a refractive index difference of 2 or more. In addition, not only three layers but also two material films may be alternately formed to form three or more layers.

4A and 4B are graphs of reflectances according to wavelengths of the device isolation layer structure according to the present invention. FIG. 4A is a view showing the device isolation layer structure of FIG. 3A and FIG. 4B is a view of FIG. 3B.

Referring to FIG. 4A, the graph calculates the reflectance of the device isolation layer with respect to the visible light region incident perpendicularly to the device isolation layer having the structure of FIG. 3A. The horizontal x-axis represents the wavelength of light and the vertical y-axis is Indicate reflectance. It can be seen that the reflectance is very high in the remaining wavelength region except for two places (410 nm and 450 nm) of the blue light region, and in particular, in the red light region, which is a long wavelength region which contributes to the CT phenomenon, it has an average reflectance of 80% or more.

Referring to FIG. 4B, the graph calculates the reflectance of the device isolation film with respect to the visible light region incident perpendicularly to the device isolation film of FIG. 3B. Except for one portion (450 nm) of the blue light region, the overall reflectance is high, and in particular, the red light region has a reflectance of about 90% or more. This is because the difference in refractive index between the silicon film and the air film is larger than the difference in refractive index between the silicon film and the silicon oxide film as described above.

By forming the device isolation film using two material films having different refractive indices as in the present embodiment, the conventional CT phenomenon can be significantly reduced by reflecting most of light, especially long wavelength light in the visible light region.

5A to 5E are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to another exemplary embodiment of the present invention.

Referring to FIG. 5A, first, a p-type epitaxial layer 200 is grown on a p-type substrate 100.

Referring to FIG. 5B, after the epi layer 200 is formed, the trench 350 for the device isolation region is formed on the epi layer 200. The trench 350 is formed by etching an oxide layer (not shown) and a nitride layer (not shown) on the epitaxial layer 200 to protect the epitaxial layer 200 and using a photoresist (not shown) pattern on the nitride layer. do. The trench is preferably formed as deep as possible to reduce the CT phenomenon through the epi layer 200.

Referring to FIG. 5C, the silicon oxide layer 320 may be formed by depositing silicon oxide on the lower surface and the sidewalls of the trench 350. In this case, the silicon oxide film 320 has a width d1 of about 550 Å.

Referring to FIG. 5D, a trench in which the silicon oxide layer 320 is formed is filled with silicon to form a silicon layer 340. Accordingly, the device isolation film 300 formed of two material films, a silicon oxide film and a silicon film, is completed. In this case, the width d2 of the silicon film 340 is preferably about 500 mW. Therefore, it is desirable to form the first trench so as to be about 1050 GPa.

The device isolation film 300 structure according to the present embodiment adopts the structure of the device isolation film of FIG. 3A, but may be formed by adopting the device isolation film structure of FIG. 3B. That is, the device isolation layer may be completed by forming two air layers spaced through the selective dry etching on the epi layer 200.

Referring to FIG. 5E, after the device isolation layer 300 is formed, a photodiode is formed by doping ions in the doped region for the photodiode. Although not shown in the drawings, a transfer transistor, a floating diffusion region, and the like are formed at this time. In more detail, a gate (not shown) of the transfer transistor is formed on the epi layer 200, and an ion implantation mask for forming an n-type ion implantation region of the photodiode 400 is formed. Since the n-type ion implantation region is aligned by the device isolation layer 300 and one side of a gate (not shown), an n-type ion implantation region is formed deep under the epi layer 200 using an ion implantation mask suitable for this. Subsequently, spacers (not shown) are formed on both sidewalls of the gate (not shown), and a p-type ion implantation region aligned with the device isolation layer 300 and the spacer on one side of the gate is formed over the surface of the epi layer 200. do. Thereafter, an n-type impurity region constituting the floating diffusion region is formed on the other side of the gate to manufacture a CMOS image sensor.

So far, the present invention has been described with reference to the embodiments shown in the drawings, which are merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. will be. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described in detail above, the CMOS image sensor according to the present invention forms an element isolation layer using two material films having different refractive indices, thereby increasing the reflectance by the element isolation layer, thereby reducing the CT phenomenon caused by incident light invading adjacent pixels. You can.

Claims (17)

A first conductivity type substrate; An epitaxial layer of a first conductivity type formed on the substrate; Photodiodes formed in respective active regions above the epitaxial layer; And And two material layers having different refractive indices are alternately formed in the vertical direction on the substrate to separate the active regions from each other. 2. According to claim 1, The two material films are silicon film and silicon oxide film, characterized in that the CMOS image sensor. The method of claim 2, The device isolation layer is composed of a three-ply film of the silicon film and the silicon oxide film formed on both sides of the silicon film, The silicon oxide film on both sides of the CMOS image sensor, characterized in that connected to each other through the lower portion of the silicon film. The method of claim 3, wherein And the silicon film has a width of 500 mW, and each of the silicon oxide films on both sides of the silicon film has a width of 550 mW. According to claim 1, The two material films are silicon film and air film, characterized in that the CMOS image sensor. The method of claim 5, The device separator is The CMOS image sensor comprising a three-ply film of the silicon film and the air film formed on both sides of the silicon film. The method of claim 6, Each of the air membranes has a width of 740 kPa, and the silicon film has a width of 520 kPa. According to claim 1, The first conductivity type is p-type, The photodiode includes a p-type ion implantation region and an n-type ion implantation region at the bottom of the CMOS image sensor. According to claim 1, The difference between the refractive index of the two material film is CMOS image sensor, characterized in that more than two. According to claim 1, And a reflectance of the red light in the visible light region by the device isolation layer is 80% or more. Growing an epitaxial layer of a first conductivity type on the first conductivity type substrate; Forming an isolation layer on the epi layer to alternately form two material films having different refractive indices in a direction perpendicular to the substrate to separate active regions; And And implanting ions into the epitaxial layer to form a photodiode. The method of claim 11, wherein Forming the device isolation layer Forming a trench in the epi layer; Forming a silicon oxide film on a lower surface and a sidewall of the trench; And And forming a silicon film by filling the inside of the trench in which the silicon oxide film is formed with silicon. The method of claim 12, The silicon oxide film is formed to have a width of 550 Å, The silicon film manufacturing method of the CMOS image sensor, characterized in that formed to have a width of 500 kHz. The method of claim 12, Forming the device isolation layer And forming at least two air films spaced apart from each other by dry etching in the epitaxial layer. The method of claim 14, Two air membranes are formed, Wherein each air film has a width of 740 kPa, and the silicon film of the epi layer between the air films has a width of 520 kPa. The method of claim 11, wherein The first conductivity type is p-type, In the photodiode forming step And implanting n-type ions into the lower portion of the epi layer and implanting p-type ions into the upper surface to form an n-type ion implantation region and a p-type ion implantation region. The method of claim 11, wherein The device isolation film manufacturing method of the CMOS image sensor, characterized in that formed by two material films having a refractive index difference of 2 or more.

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