KR20090022357A

KR20090022357A - Cmos image sensor and method for manufacturing the sensor

Info

Publication number: KR20090022357A
Application number: KR1020070087654A
Authority: KR
Inventors: 여인근
Original assignee: 주식회사 동부하이텍
Priority date: 2007-08-30
Filing date: 2007-08-30
Publication date: 2009-03-04

Abstract

A CMOS image sensor and a manufacturing method thereof are provided to improve image quality by enlarging a ratio of a blue signal to a green signal and a ratio of a cyan signal to a yellow signal. An element isolation layer(202) is formed in an element isolation region of a semiconductor substrate(201) defined by the element isolation region and an active region. An element isolation layer is formed by an STI(Shallow Trench Isolation) process and an LOCOS(LoCal Oxidation of Silicon). A photo diode(203) with different sizes is formed in the active region of the semiconductor substrate. The photo diode is formed in the surface of the semiconductor substrate by injecting n type impurity ion with low density into the active region of the semiconductor substrate. The photo diode collects the electron generated by reacting the light on the silicon. An interlayer dielectric(204) is formed in the front surface of the semiconductor substrate including the photo diode.

Description

CMOS image sensor and method for manufacturing the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image sensors, and more particularly to CMOS image sensors widely used in various application areas such as digital still cameras or digital video cameras, and methods of manufacturing the same.

In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal, and is generally a charge coupled device (CCD) and CMOS metal (Complementary Metal Oxide Silicon) image. It is divided into Image Sensor.

CCD has a disadvantage in that the driving method is complicated, the power consumption is large, and the manufacturing process is complicated because a multi-step photo process is required. In addition, the CCD has a disadvantage in that it is difficult to integrate a control circuit, a signal processing circuit, an analog-to-digital converter (A / D converter), and the like into a charge coupled device chip, which makes it difficult to miniaturize a product. Recently, CMOS image sensors have attracted attention as next generation image sensors to overcome the disadvantages of CCDs. The CMOS image sensor uses CMOS technology that uses a control circuit and a signal processing circuit as a peripheral circuit to form MOS transistors corresponding to the number of unit pixels on a semiconductor substrate, thereby outputting each unit pixel by the MOS transistors. It is a device that employs a switching method that detects sequentially. That is, the CMOS image sensor implements an image by sequentially detecting an electrical signal of each unit pixel by a switching method by forming a photodiode and a MOS transistor in the unit pixel. The CMOS image sensor has advantages such as relatively low power consumption and a simple manufacturing process with a relatively small number of photo process steps due to the CMOS manufacturing technology. In addition, since the CMOS image sensor can integrate a control circuit, a signal processing circuit, an analog / digital conversion circuit, and the like into the CMOS image sensor chip, the CMOS image sensor has an advantage of easy miniaturization.

FIG. 1 is an equivalent circuit diagram of a general 4T CMOS image sensor, and FIG. 2 is a layout illustrating unit pixels of a typical 4T CMOS image sensor.

As illustrated in FIG. 1, the unit pixel 100 of the CMOS image sensor includes a photo diode (PD) 10 as a photoelectric converter and four transistors. Here, each of the four transistors is the transfer transistor 20, the reset transistor 30, the drive transistor 40 and the select transistor 50. The load transistor 60 is electrically connected to the output terminal OUT of each unit pixel 100. Here, reference numeral FD is a floating diffusion region, Tx is a gate voltage of the transfer transistor 20, Rx is a gate voltage of the reset transistor 30, Dx is a gate voltage of the drive transistor 40, Sx is It is the gate voltage of the select transistor 50.

As shown in FIG. 2, in a unit pixel of a general 4T type CMOS image sensor, an active region is defined, and an isolation layer is formed at a portion except the active region. One photodiode PD is formed in the wide portion of the active region, and gate electrodes 23, 33, 43, and 53 of four transistors are formed in the active region of the remaining portion, respectively. That is, the transfer transistor 20 is formed by the gate electrode 23, the reset transistor 30 is formed by the gate electrode 33, and the drive transistor 40 is formed by the gate electrode 43. The select transistor 50 is formed by the gate electrode 53. Impurity ions are implanted into the active region of each transistor except for the lower portion of each gate electrode 23, 33, 43, 53 to form a source / drain region S / D of each transistor.

The image sensor, which is composed of a plurality of dense pixels arranged in a row and column, includes photodiodes (PD) for generating photons by sensing light from the outside, floating diffusions (FD) for transferring charges generated from the photodiodes, and photos. And a transfer transistor Tx for transferring charge generated from the photodiode PD to the floating diffusion region FD between the diode PD and the floating diffusion region FD.

Hereinafter, a general CMOS image sensor will be described.

3 is a cross-sectional view illustrating a general CMOS image sensor.

The CMOS image sensor shown in FIG. 3 includes a photodiode region 103, an interlayer insulating layer 104, and first and second planarization formed on the semiconductor substrate 101 in an active region between the device isolation layers 102. Layers 105 and 107 and color filter layer 106 and microlens 108 of red (R), green (G), blue (B) or magenta (M), yellow (Y), cyan (C) Has Here, various transistors (not shown) and metal wirings (not shown) are formed in the active region of the semiconductor substrate 101. The general CMOS image sensor configured as described above has a color filter layer 107 for each color to receive signals of various colors on top of the photodiode region 103 and the microlens 108 is adapted to receive more light. It is formed at the top of the light receiving unit.

Brief description of the operation of the CMOS image sensor configured as described above is as follows.

First, as the reset transistor Rx is turned on, the potential of the output floating diffusion node becomes VDD. At this time, a reference value is detected. Subsequently, when light is incident on the photodiode PD, which is a light receiving unit, outside of the image sensor, EHP is generated in proportion thereto. The potential of the source node of the transfer transistor Tx is changed in proportion to the amount of signal charge generated by the signal charge generated by the photodiode PD. Subsequently, when the transfer transistor Tx is turned on, the accumulated signal charge is transferred to the floating diffusion region FD, and the potential of the output floating diffusion node changes in proportion to the transferred signal charge amount, and at the same time, the gate bias of the drive transistor Dx gate bias is changed. This eventually causes a change in the source potential of the drive transistor Dx. At this time, when the select transistor Sx is turned on, data is read out to the column. When the reset transistor Rx is turned on, the potential of the output floating diffusion node becomes VDD. This process is repeated.

4 is a diagram illustrating a general pixel array in the CMOS image sensor, and FIG. 5 is a diagram illustrating an array of color filters.

In the CMOS image sensor, pixels are arranged in a lattice shape as shown in FIG. 4, and each pixel represents a single color, and a single color is combined to form an image. Light in each wavelength band has different responsiveness to silicon. In particular, since blue light is halfway between violet light and green light, as can be seen from Table 1, electrons gathered into a photodiode mainly react at the silicon surface, despite the same light intensity. Less than green and red.

Photon Wavelength Single photon energy Half-absorption depth 400 nm (Violet) 3.1 eV 0.093 μm 530 nm (Green) 2.3 eV 0.790 μm 600 nm (Yellow) 2.0 eV 1.200㎛ 700 nm (Red) 1.77 eV 3.000㎛

Here, the depth of half absorption refers to a depth at which the intensity of light absorbed by the material is reduced by half.

Therefore, the blue signal is smaller than the green and red signals, and the magnitude of the blue signal with respect to the green signal is about 0.5 to 0.7. The magnitude ratio of each color signal greatly affects the color of the image, and in particular, the ratio of the blue signal and the green signal (B / G ratio) is included in the yield test condition and is strictly managed. In order to improve this, various angles of efforts have been made, such as increasing the depletion layer, reducing the thickness of the blue color filter layer, or adjusting the order of the color filter layer forming process by performing p-type doping on the silicon surface. to be.

An object of the present invention is to provide a CMOS image sensor and a method of manufacturing the same that can improve the quality of the image by improving the ratio of the blue signal to the green signal.

Another object of the present invention is to provide a CMOS image sensor capable of improving the quality of an image by improving a ratio of a cyan signal to a yellow signal, and a method of manufacturing the same.

According to an embodiment of the present disclosure, a CMOS image sensor may include photodiodes of different sizes provided on a semiconductor substrate, color filter layers of different sizes and corresponding color filter layers provided on the photodiodes. It is preferable that the lens is composed of micro lenses of different sizes.

According to another aspect of the present invention, there is provided a method of manufacturing a CMOS image sensor, including forming photodiodes of different sizes on a semiconductor substrate, and forming color filters having different sizes corresponding to the photodiodes. It is preferable that the step of forming on top of the photodiode and forming micro lenses of different sizes corresponding to the color filter layers.

As described above, the CMOS image sensor and a method of manufacturing the same according to the present invention express the ratio of the blue signal representing the blue light to the green signal representing the green light or the cyan light representing the yellow signal representing the yellow light. By increasing the ratio of the cyan signal, an image quality of the image can be improved.

Hereinafter, an embodiment of a CMOS image sensor and a method of manufacturing the same according to the present invention will be described with reference to the accompanying drawings.

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

Referring to FIG. 6, a device isolation layer 202 is formed in a device isolation region of a semiconductor substrate 201 defined as a device isolation region and an active region. The device isolation layer 202 may be formed by a shallow trench isolation (STI) process or a LOCOS (LoCal Oxidation of Silicon) process. A single crystal silicon substrate may be used as the semiconductor substrate 201. Photodiodes 203 having different sizes are formed in the active region of the semiconductor substrate 201. For example, when the semiconductor substrate 201 is P ++ type, the low concentration n-type impurity ions may be implanted into the active region of the semiconductor substrate 201 to form the photodiode 203 on the surface of the semiconductor substrate 201. The photodiode 203 collects electrons generated by reaction of light and silicon.

An interlayer insulating film 204 is formed on the entire surface of the semiconductor substrate 201 including the photodiode 203. The interlayer insulating film 204 uses an oxide film such as USG (Undoped Silicate Glass). The first planarization layer 205 is formed on the interlayer insulating film 204.

Colors of red (R), green (G), blue (B) or magenta (M), yellow (Y), and cyan (C) on the first planarization layer 205 corresponding to each photodiode 203. The filter layer 206 is formed. Here, the color filter layers 206 of R, G, B or M, Y, and C have different sizes. For example, after applying a blue, red, and green salty resist layer on the first planarization layer 205, the exposure, development process is performed, and the colors of R, G, and B that filter light by each wavelength band. The filter layer 206 is formed.

The second planarization layer 207 is formed on the entire surface of the semiconductor substrate 201 including the color filter layers 206. Microlenses 208 having different sizes are formed on the second planarization layer 207 to correspond to the color filter layers 206. For example, by depositing a material layer on the second planarization layer 207, selectively patterning the material layer to form a microlens pattern, and reflowing the microlens pattern to a temperature of 200 to 700 ℃ to hemispherical micro Lens 208 can be formed. Subsequently, the microlens 208 reflowed by heat treatment is cooled. A resist or TEOS oxide film can be used as the material layer for forming the microlens.

Here, various transistors (not shown) and metal wirings (not shown) are formed in the active region of the semiconductor substrate 201.

The light entering the CMOS image sensor according to the present invention is refracted by the microlens 208 and travels with a path focused on the photodiode 203 in the pixel, and then passes through the color filter layer 206 to produce a desired component (mainly monochromatic light). When the light meets a single crystal silicon substrate, it produces a photoelectric effect to produce electrons. Among the electrons generated by the photoelectric effect, electrons generated in the depletion layer around the photodiode are collected in the photodiode, and are read to form a signal.

Among the photodiodes shown in FIG. 6, the photodiode of the blue pixel is the largest, the color filter layer of the blue pixel is the largest among the color filter layers of R, G, and B, and the micro-array provided on the color filter layer of the blue pixel among the micro lenses. The lens is the largest. As described above, since the size of the photodiode, the color filter layer, and the microlens of the blue pixel is larger than that of the photodiode, the color filter layer, and the microlens of the green or red pixel, the amount of light received by the blue pixel is increased and blue light is increased. The depletion layer, which can collect electrons generated by silicon and photoelectric effect, is widened. Alternatively, the photodiode of the cyan pixel is the largest among the photodiodes, the color filter layer of the cyan pixel is the largest among the color filter layers of M, Y and C, and the microlens provided on the color filter layer of the cyan pixel among the micro lenses. Big. As described above, since the size of the photodiode, the color filter layer, and the microlens of the cyan pixel is larger than the size of the photodiode, the color filter layer, and the microlens of the magenta or yellow pixel, the amount of light received by the cyan pixel is increased and cyan light is increased. The depletion layer, which can collect electrons generated by silicon and photoelectric effect, is widened.

7 is a diagram illustrating a pixel array of the CMOS image sensor according to the present invention.

In the case of the general CMOS image sensor illustrated in FIG. 4, the size of the photodiodes of the blue pixel and the other pixels are all constant, whereas in the CMOS image sensor according to the present invention, as shown in FIG. 7, the photodiode of the blue pixel ( 301 is larger than photodiodes 303, 305, and 307 of other color pixels, such as green or red, and microlens 300 of blue pixel, microlenses 302, 304, and 306 of other color pixels, such as green or red. It is greater than). In addition, in the CMOS image sensor according to the present invention, as shown in FIG. 7, the photodiode 301 of the cyan pixel is larger than the photodiodes 303, 305, and 307 of other color pixels such as magenta or yellow, and the cyan pixel. It can be seen that the microlens 300 is larger than the microlenses 302, 304, and 306 of other color pixels such as magenta or yellow.

As long as the photodiode, color filter layer and microlens related to the generation of the blue (or cyan) signal are larger than those related to the generation of the signal of the different color, the CMOS image sensor according to the present invention is shown in the cross section shown in FIG. It is not limited. For example, a plurality of interlayer insulating films 204 may be provided between the photodiode 203 and the color filter layer 206, and the first and second planarization layers 205 and 207 may also be selectively provided. The shape of the lens 208 is not limited to hemispherical.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and it is common in the art that various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

1 is an equivalent circuit diagram of a general 4T CMOS image sensor.

2 is a layout illustrating unit pixels of a general 4T CMOS image sensor.

3 is a cross-sectional view illustrating a general CMOS image sensor.

4 is a diagram illustrating a general pixel array in the CMOS image sensor.

5 is a diagram illustrating an arrangement of color filters.

* Explanation of symbols for main parts of the drawings

201: semiconductor substrate 202: device isolation film

203: photodiode 204: interlayer insulating film

205: first planarization layer 206: color filter layer

207: second planarization layer 208: micro lens

Claims

Photodiodes of different sizes provided on the semiconductor substrate;

Color filter layers having different sizes corresponding to the photo diodes; And

And CMOS lenses having different sizes of microlenses provided on the color filter layers.

The CMOS image sensor according to claim 1, wherein the photodiode of the blue pixel is the largest among the photodiodes.

The CMOS image sensor according to claim 1, wherein the color filter layer of the blue pixel is the largest among the color filter layers.

The CMOS image sensor according to claim 1, wherein, among the micro lenses, the micro lens provided on the color filter layer of a blue pixel is the largest.

The CMOS image sensor according to claim 1, wherein the photodiode of the cyan pixel is the largest among the photodiodes.

The CMOS image sensor according to claim 1, wherein the color filter layer of the cyan pixel is the largest among the color filter layers.

The CMOS image sensor according to claim 1, wherein, among the micro lenses, the micro lens provided on the color filter layer of the cyan pixel is the largest.

Forming photodiodes of different sizes on the semiconductor substrate;

Forming color filters of different sizes on the photodiode in correspondence with the photodiodes; And

And forming micro lenses having different sizes corresponding to the color filter layers.