KR20070098223A - Method for fabricating photo diode of image sensor - Google Patents

Abstract

A method for fabricating a photo diode of an image sensor is provided to implement an image characteristic with a high performance by optimizing a photo diode structure of a pixel according to blue, green, and red colors. A method for fabricating a photo diode of an image sensor includes the steps of: forming a transfer gate on a P-type silicon substrate(204) having an element isolation film(206); forming an N-type impurity layer(210) for the photo diode for charge accumulation in the lower part of the P-type silicon substrate(204) and one side of the transfer gate; forming a P1-type impurity layer(208) thinly on the P-type silicon substrate surface above the N-type impurity layer(210); and forming a P/N junction layer according to the N/P1-type impurity layer on the P-type silicon substrate surface(204).

Description

Photodiode manufacturing method of image sensor {METHOD FOR FABRICATING PHOTO DIODE OF IMAGE SENSOR}

1 is a cross-sectional view of a photodiode structure of a conventional image sensor,

2 is a cross-sectional view of a photodiode structure of an image sensor according to an embodiment of the present invention;

3 is an image sensor unit pixel layout diagram;

4 is an exemplary pixel array color arrangement of an image sensor;

5 is a diagram illustrating a light absorption graph in a silicon substrate according to the wavelength of light.

<Brief description of the major symbols in the drawings>

204: P-type silicon substrate 206: device isolation region

208: P1-type impurity layer 210: N-type impurity layer

212: gate electrode 214: gate oxide film

216 source / drain electrodes 218 P2-type impurity layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a photodiode of an image sensor, and more particularly, to fabricating a photodiode of an image sensor having a different photodiode structure of pixels for each color so as to obtain maximum light absorption at the photodiode. It is about a method.

In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal. By converting light into electrons, an electrical voltage at a location is determined by the amount of electrons in each pixel according to light intensity or wavelength. In order to realize the color of light, the color of each point is determined by the combination of neighboring pixels using a three primary color filter on the photodiode for each pixel.

A semiconductor device that converts light from an image sensor into an electron is a photodiode in a pixel. The principle is as follows. When voltage is applied to the junction part composed of PN junction formed on the silicon substrate in the reverse direction, charge deprivation region is formed around the junction. When light enters this region, photons called photons generate a pair of electrons and holes in this region. The hole moves to the P type region by the applied voltage, and the electron moves to the N type region. At this time, the N type region is used as a charge accumulation region, and the electrons accumulated therein are read out as a voltage through a circuit.

These photodiodes vary the light absorption within the silicon substrate of the photons depending on the wavelength of the light. The shorter the wavelength of light, the more the light is absorbed from the surface of the silicon. That is, for example, the blue color of the short wavelength visible light region is highest within about 0.1um of the surface of the silicon substrate, and the green color, which is the middle region of visible light, penetrates to a slightly deeper area. The case penetrates deep into the silicon substrate.

FIG. 1 illustrates a cross-sectional structure of a photodiode of a conventional image sensor. The photodiode is generally formed by PN bonding, and an isolation region 106 between elements is formed on a P-type silicon substrate 104. And an N1 type impurity layer 110 for forming a transistor by forming a gate oxide film 114, a gate electrode 112, a source / drain electrode 116, and the like, and accumulating electrons in forming a photodiode. There is a P1 type impurity layer 108 thereon, and a P2 type impurity layer is formed under the N1 type impurity layer 110 as necessary.

As described above, in the case of the image sensor according to the related art, the cross-section and layout of the photodiodes of the pixels for each color are all the same as in FIG. 1, which is for convenience of manufacturing. Although the manufacturing process is simple, the structure is not a structure that can obtain the maximum light absorption according to each wavelength of the three primary colors for the visible light band.

That is, as described above, although the light incident on the photodiode has different depths penetrating into the silicon according to the wavelength of each color, the blue light is used because a single photodiode junction structure is used for light having different wavelengths of three primary colors. There was a problem that optimum light absorption for green and red could not be obtained.

Light absorption is also important for image sensors, but among other factors that determine the sensor's performance is sensitivity to light and dynamic range, which are primarily the gate of the driver transistor that determines the capacitance (Cpd) and drive capability of the photodiode. It is determined by the ratio with the capacitance Cfd applied to the electrode, and the higher the ratio of Cpd / Cfd, the higher the sensitivity. The dynamic range of the sensor indicates how widely the sensor can accept both dark and bright areas at the same time, which is determined by the amount of Cpd in the photodiode.

However, in the photodiode structure of the conventional image sensor having the same cross-section and layout of the photodiode of the pixel for each color, as shown in FIG. 1, it is difficult to obtain optimal characteristics for each pixel even for sensor sensitivity and dynamic range characteristics for light. There was this.

Accordingly, an object of the present invention is to maximize the light absorption by utilizing the color filter arrangement of the pixel and the photodiode structure in the photodiode structure of the image sensor, and also the sensitivity to light or the dynamic range of the sensor for each wavelength By designing and implementing different photodiode structures of pixels according to each color of blue, green, and red, the photodiode of an image sensor capable of realizing higher performance image characteristics and realizing more integrated image pixels To provide a manufacturing method.

According to an aspect of the present invention, there is provided a method of manufacturing a photodiode of a blue color pixel of an image sensor, the method comprising: forming a transfer gate on a P-type silicon substrate on which an isolation layer is formed, and aligning one side of the transfer gate; Forming an N-type impurity layer for photodiodes for charge accumulation under the P-type silicon substrate, and forming a thin P1-type impurity region on the surface of the P-type silicon substrate on the N-type impurity layer; And forming a P / N junction layer due to the N / P1 type impurity layer on a surface portion of the P type silicon substrate.

In another aspect, the present invention provides a method for manufacturing a photodiode of a green color pixel of an image sensor, the method comprising: forming a transfer gate on a P-type silicon substrate on which an isolation layer is formed, and aligning one side of the transfer gate to a lower portion of the P-type silicon substrate; Forming an N-type impurity layer for photodiodes for charge accumulation in the semiconductor layer, forming a P2 type impurity layer in a central portion of the P-type silicon substrate below the N-type impurity layer, and Forming a thin P1 type impurity layer on the surface of the P type silicon substrate, and forming a P / N junction layer due to the N / P2 type impurity layer in the central portion of the P type silicon substrate below the N type impurity layer Characterized in that it comprises a.

In another aspect, the present invention provides a method for manufacturing a photodiode of a red color pixel of an image sensor, the method comprising: forming a transfer gate on a P-type silicon substrate on which a device isolation layer is formed, and aligning one side of the transfer gate to a lower portion of the P-type silicon substrate; Forming an N-type impurity layer for photodiodes for charge accumulation in the semiconductor substrate, forming a P2 type impurity layer under the P-type silicon substrate under the N-type impurity layer, Forming a thin P1 type impurity layer on a surface portion of the P type silicon substrate, and forming a P / N junction layer due to the N / P2 type impurity layer under the N type impurity under the N type impurity layer; It is characterized by including.

Hereinafter, with reference to the accompanying drawings will be described in detail the operation of the preferred embodiment according to the present invention.

2 illustrates a cross-sectional structure of a photodiode for each color of an image sensor according to an exemplary embodiment of the present invention. In FIG. 2, a photodiode region and a transfer gate device for a pixel including four transistors are illustrated for convenience of description.

Referring to FIG. 2, the photodiode is generally formed by a PN junction, but is shown here for a pinning type junction (PIN) type of PNP type structure, and this structure is shown on the P-type silicon substrate 204. An N1 type impurity that forms an isolation region 206 and forms a transistor by forming a gate oxide film 214, a gate electrode 212, a source drain electrode 216, and the like, and first accumulates electrons in forming a photodiode. There is a layer 210 and a P1 type impurity layer 208 thereon, and P2 type impurity layers 218 and 220 are formed under the N1 type impurity layer 210 as necessary.

In FIG. 3, three or four transistors are actually arranged for one unit pixel, and one photodiode PD is disposed. For example, photodiodes are arranged in each pixel for convenience.

That is, the image sensor is composed of a pixel region and a peripheral circuit portion on the silicon substrate, and the pixel region is made of a circuit composed of several transistors including a photodiode for converting light into electrons. In addition, in order to implement a color for each pixel, a color filter of three colors is generally formed on each pixel to implement the color of each pixel by a combination of neighboring pixels. The combination for the arrangement of the collars is shown.

In order to improve the various characteristics of the image sensor in the above-described image sensor, several key characteristics should be taken into consideration, that is, the maximum amount of light must be taken into account and the photodiode must convert the light to the maximum light absorption for each wavelength band. It is necessary to maximize the pixel output by the combination of photodiodes and transistors in the pixels.

Hereinafter, the photodiode structure of the present invention for maximizing the efficiency of an image sensor by absorbing light to the photodiode as described above will be described in more detail with reference to FIG. 2.

As shown in FIG. 2, photodiodes for three pixels having different colors are shown on the left side (200, 202, 203) and a cross-sectional view of the junction structure of the corresponding photodiode is shown on the right side.

When light in visible light is irradiated to the photodiode region, only light according to each filter is transmitted through the color filters to irradiate the photodiode. The irradiated light is caused by a reverse voltage in the PN junction structure in silicon constituting the photodiode. It is created by electrons and holes in the applied charge deprived region. At this time, depending on the wavelength of light, the shorter wavelength penetrates from the silicon surface and the longer wavelength penetrates into the silicon to form electrons and holes over a deeper junction region.

FIG. 5 is a graph illustrating light absorption in a silicon substrate according to the wavelength of light. As shown in FIG. 5, a blue color having a short wavelength has the highest light absorption just below the surface of the silicon substrate and moves into the silicon. As it enters, it is completely transparent. On the other hand, the green color is transmitted to a certain depth from the surface of the silicon substrate so that light absorption exists, and in the case of the red color, it is transmitted to a depth of several um, so that the light absorption is evenly distributed inside the silicon substrate than the surface of the silicon substrate. have.

Therefore, in order to maximize the light absorption of the blue color photodiode, it is necessary to form a PN junction on the surface of the silicon substrate to maximize the light absorption, and also be designed to increase the capacitance of the photodiode.

FIG. 2A illustrates a cross-sectional view of a photodiode junction structure of a pixel with respect to a blue color among photodiode structures having different structures for different colors, and a very thin P1 type impurity layer 208 is formed on a surface of a silicon substrate. In order to accumulate charge, an N1 type impurity layer 210 is formed thereon to form a PN junction layer between the two layers.

Then, when a reverse voltage is applied to the junction layer between these two layers, a charge depletion region occurs toward the P1 type impurity layer 208 and the P-type silicon substrate 204 around the N1 type impurity layer 210. In the case of the blue color, the electron holes are mostly generated in the impurity layer formed on the P1 type silicon substrate 204 and in the charge depletion region. At this time, the charge depletion region with the P type silicon substrate 204 formed under the N1 type impurity layer 210 contributes to increase the capacitance of the photodiode.

Next, in the case of the green color, as shown in (b) of FIG. 2, unlike the blue color, a capacitance of the photodiode is added by adding a P2 type impurity layer 218 directly below the N1 type impurity layer 210. Further enhancements improve the light sensitivity and dynamic range characteristics of the photodiode. Finally, referring to the red color photodiode structure shown in (c) of FIG. 2, in the photodiode structure of the pixel for the red color, the red color is more deeply emitted from the silicon substrate surface than the green color. Since light is transmitted and generated, the P2 type impurity layer 220 is formed at the bottom of the silicon substrate at a distance below the N1 type impurity layer 210 as compared to the green color photodiode structure, thereby increasing capacitance and light absorption.

Therefore, unlike the prior art, which has a photodiode junction of the same structure for each color and cannot realize the optimum light absorption rate for each color, the present invention has different colors for each color so as to have an optimal light absorption for each color for each color. By forming the photodiode structure as a junction structure, it is possible to make an image sensor with improved characteristics. In addition, since the present invention can separately control the photodiode of the pixel for each color, not only the impurity junction structure but also the layout of the drawing can be changed separately, so that the optimum sensor characteristics can be obtained in terms of layout.

At this time, the depth of the junction for the layout and the impurities should be optimally designed in consideration of the characteristics of each wavelength of light for the silicon. For the blue, the depth of the junction should be within 0.5um from the silicon surface. It is desirable to be designed to be within 1.5um and within 5um for red.

Meanwhile, in the above description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the invention should be determined by the claims rather than by the described embodiments.

As described above, in the photodiode structure of the image sensor, the light absorption is maximized by utilizing the color filter arrangement of the pixel and the structure of the photodiode, and the sensitivity to light and the dynamic range of the sensor are also various. Designed by optimizing the photodiode structure of pixels according to each color of blue, green, and red so as to obtain the maximum for each wavelength, it is possible to realize higher performance image characteristics and higher density of image pixels There is this.

Claims (9)

A photodiode manufacturing method of a blue color pixel of an image sensor, Forming a transfer gate on the P-type silicon substrate on which the device isolation film is formed; Forming an N-type impurity layer for photodiodes for charge accumulation under the P-type silicon substrate by aligning to one side of the transfer gate; Forming a thin P1 type impurity region on the surface of the P type silicon substrate on the N type impurity layer; Forming a P / N junction layer due to the N / P1 type impurity layer on a surface portion of the P type silicon substrate; Photodiode manufacturing method of an image sensor comprising a. The method of claim 1, When a reverse voltage is applied to the P / N junction layer, a charge depletion region is generated toward the P1 type impurity layer and the P type silicon substrate around the N type impurity layer to generate electrons and holes due to the blue color light. Photodiode manufacturing method of an image sensor, characterized in that. The method of claim 2, The P / N junction layer for implementing the blue color pixel, the photodiode manufacturing method of the image sensor, characterized in that formed on the silicon substrate 0.5μm from the surface of the silicon substrate. As a method of manufacturing a photodiode of green color pixels of an image sensor, Forming a transfer gate on the P-type silicon substrate on which the device isolation film is formed; Forming an N-type impurity layer for photodiodes for charge accumulation under the P-type silicon substrate by aligning to one side of the transfer gate; Forming a P2 type impurity layer in a central portion of the P type silicon substrate under the N type impurity layer; Forming a thin P1 type impurity layer on a surface portion of the P type silicon substrate on the N type impurity layer; Forming a P / N junction layer due to the N / P2 type impurity layer in a central portion of the P type silicon substrate under the N type impurity layer Photodiode manufacturing method of an image sensor comprising a. The method of claim 4, wherein When a reverse voltage is applied to the P / N junction layer, a charge depletion region is generated toward the center of the P2 type impurity layer and the P type silicon substrate centering on the N type impurity layer to generate electrons and holes due to the green color light. Photodiode manufacturing method of an image sensor, characterized in that. The method of claim 5, The P / N bonding layer for implementing the green color pixel, the photodiode manufacturing method of the image sensor, characterized in that formed on the silicon substrate 1.5μm from the surface of the silicon substrate. A method of manufacturing a photodiode of red color pixels of an image sensor, Forming a transfer gate on the P-type silicon substrate on which the device isolation film is formed; Forming an N-type impurity layer for photodiodes for charge accumulation under the P-type silicon substrate by aligning to one side of the transfer gate; Forming a P2 type impurity layer under the P type silicon substrate under the N type impurity layer; Forming a thin P1 type impurity layer on a surface portion of the P type silicon substrate on the N type impurity layer; Forming a P / N junction layer under the N type impurity layer due to the N / P2 type impurity layer under the N type impurity substrate Photodiode manufacturing method of an image sensor comprising a. The method of claim 7, wherein When a reverse voltage is applied to the P / N junction layer, a charge depletion region is generated toward the lower portion of the P2 type layer and the P type silicon substrate around the N type impurity region to generate electrons and holes due to the red color light. Photodiode manufacturing method of an image sensor, characterized in that. The method of claim 8, The P / N junction layer for implementing the red color pixel, the photodiode manufacturing method of the image sensor, characterized in that formed on the silicon substrate 5μm from the surface of the silicon substrate.

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