KR100390824B1 - Image sensor having double filter - Google Patents

Abstract

In order to overcome the limitation of the color material of the conventional color filter, to reduce the noise signal, and to increase the driving range of the sensor, the light filter passing through the color filter of at least the first color is composed of an oxide film and a nitride film. Its feature is to provide a passing image sensor.

Description

Image sensor having double filter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of image sensor manufacturing, and more particularly, to an image sensor having a double filter to improve color reproducibility.

An image sensor is an apparatus that converts optical information of one or two dimensions or more into an electrical signal. The types of image sensors are broadly classified into imaging tubes and solid-state imaging devices. Imaging tubes are widely used in measurement, control, and recognition using image processing technology centering on televisions, and applied technologies have been developed. There are two types of solid-state image sensors on the market: metal-oxide-semiconductor (MOS) type and charge coupled device (CCD) type.

CMOS image sensor is a device that converts an optical image into an electrical signal using CMOS fabrication technology, and employs a switching method that makes MOS transistors as many as the number of pixels and uses them to sequentially detect the output. The CMOS image sensor is simpler to drive than the CCD image sensor, which is widely used as a conventional image sensor, and can realize various scanning methods, and can integrate a signal processing circuit into a single chip, thereby miniaturizing the product. The use of compatible CMOS technology reduces manufacturing costs and significantly lowers power consumption.

FIG. 1 is a circuit diagram showing a unit pixel of a CMOS image sensor composed of four transistors and two capacitance structures, and a unit pixel of a CMOS image sensor composed of a photodiode (PD) and four NMOS transistors. . Of the four NMOS transistors, the transfer transistor Tx serves to transport the photocharges generated by the photodiode PD to the floating diffusion region, and the reset transistor Rx is stored in the floating diffusion region for signal detection. It serves to discharge the charge, the drive transistor (Dx) serves as a source follower (Source Follower), the select transistor (Sx) is for switching (Switching) and addressing (Addressing). In the drawing, "Cf" represents capacitance of the floating diffusion region, and "Cp" represents capacitance of the photodiode, respectively.

Operation of the image sensor unit pixel configured as described above is performed as follows. Initially, the reset pixel Rx, the transfer transistor Tx, and the select transistor Sx are turned on to reset the unit pixel. At this time, the photodiode PD starts to deplete, and the capacitance Cp generates carrier charging, and the capacitance Cf of the floating diffusion region is charged and stored up to the supply voltage VDD. The transfer transistor Tx is turned off, the select transistor Sx is turned on, and the reset transistor Rx is turned off. In this operation state, after reading the output voltage V1 from the unit pixel output terminal Out and storing it in the buffer, the transfer transistor Tx is turned on to move the carriers of the capacitance Cp changed according to the light intensity to the capacitance Cf. The output voltage V2 is read again from the output terminal, and the analog data for V1-V2 is converted into digital data, thereby completing one operation cycle for the unit pixel.

An image sensor used as an image recognition device is important in its ability to convert incident light into electrons without loss. A device that converts incident light into electrons is a photodiode. As shown in FIG. 1, a photodiode as well as a photodiode and a circuit for signal processing inside a unit pixel are complex in a unit pixel of an image sensor. There is a limit on the area of the diode. In order to overcome this problem, a microlens is formed on the unit pixel to collect light incident to a region other than the photodiode region of the light incident on the unit pixel. As such, the light collecting speed of the image sensor may be improved by forming the microlens.

FIG. 2 is a cross-sectional view illustrating the formation of color filters R, G, and B in a conventional image sensor manufacturing process, and includes a passivation layer on a semiconductor substrate 20 on which a substructure including light receiving means such as a photodiode is completed. 21 is formed, and color filters R, G, and B are formed on the passivation layer 21.

In the conventional image sensor, the color reproducibility characteristics of the red, green, and blue color materials are broadly overlapped with each other. Due to this, there is a problem of causing a noise signal and greatly reducing the relative signal strength of each of the red, green, and blue lives.

The present invention for solving the above problems is to provide an image sensor having a double filter for improving color reproducibility.

1 is a circuit diagram schematically showing a unit pixel structure of a CMOS image sensor according to the prior art;

Figure 2 is a cross-sectional view showing a color filter formed in a conventional image sensor manufacturing process,

3 is a cross-sectional view showing a color filter structure of an image sensor according to an embodiment of the present invention;

4 is a graph showing that the light transmittance is changed according to the wavelength by the color filter of the image sensor according to an embodiment of the present invention;

Figure 5 is a graph showing a comparison of the transmittance according to the wavelength in the color filter of the image sensor according to the prior art and the present invention.

* Description of reference numerals for the main parts of the drawings *

30: semiconductor substrate 31: passivation layer

32: laminated filter 33: OCL layer

R: Red color filter G: Green color filter

B: blue color filter

The present invention for achieving the above object, the passivation layer covering the semiconductor substrate is completed, the lower structure formation including a light sensing means; A first laminated filter and a second laminated filter, each of which is composed of a plurality of nitride films and oxide films alternately stacked on the passivation layer and spaced apart from each other; A transparent planarization layer covering the first multilayer filter, the second multilayer filter, and the passivation layer; A color filter of a first color formed on the transparent flattening layer and overlapping the first stacked filter; A color filter of a second color formed on the transparent flattening layer and overlapping the second stacked filter; And a color filter having a third color overlapping the transparent planarization layer between the first and second stacked filters.

The present invention consists of an oxide film and a nitride film of light passing through a color filter of at least a first color in order to overcome the limitations of the color material of the conventional color filter, to reduce the noise signal, and to increase the dynamic range of the sensor. It is characterized by providing an image sensor that passes through the stacked filter.

3 is a cross-sectional view illustrating a schematic structure of an image sensor according to an exemplary embodiment of the present invention, which includes a passivation layer 31 covering a semiconductor substrate 30 on which a substructure such as a photodiode (not shown) is completed. ), At least two stacked filter patterns 32 including the plurality of nitride films N and oxide films O alternately stacked on the passivation layer 31, the passivation layer 31, and the stacked filter pattern ( A red color filter (R), a blue color filter (B), and a stacked filter pattern respectively formed on the OCL flattening layer 33 covering the 32, the OCL flattening layer 33, and overlapping the stacked filter pattern 32. The green color filter G covering the OCL planarization layer 33 between 32 is shown.

The multilayer filter pattern 32 includes a plurality of nitride layers N and oxide layers O alternately stacked on the passivation layer 31. In the exemplary embodiment of the present invention, the nitride film N having a refractive index of 1.8 to 2.2 and the oxide film O having a refractive index of 1.29 to 1.57 are alternately stacked six times, and the oxide film is formed to have a thickness of about 0.0846 μm to 0.1034 μm. The nitride film is formed to have a thickness of 0.0477 μm to 0.0583 μm to form a quarter wavelength reflector stack (QWRS).

Figure 4 is a graph showing the change in transmittance according to the wavelength by the color filter of the image sensor according to an embodiment of the present invention, Figure 5 is a color filter of the image sensor according to the prior art (A) and the present invention (B) As a graph comparing the change in transmittance according to the wavelength, the color reproducibility of an image sensor having a dual color filter is improved as in the present invention.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be apparent to those of ordinary knowledge.

The present invention made as described above can improve the color reproducibility characteristics in the color image sensor, and can increase the relative signal size and driving range of each color.

Claims (7)

delete In the image sensor, A passivation layer covering a semiconductor substrate on which a lower structure including photosensitive means is completed; A first laminated filter and a second laminated filter, each of which is composed of a plurality of nitride films and oxide films alternately stacked on the passivation layer and spaced apart from each other; A transparent planarization layer covering the first multilayer filter, the second multilayer filter, and the passivation layer; A color filter of a first color formed on the transparent flattening layer and overlapping the first stacked filter; A color filter of a second color formed on the transparent flattening layer and overlapping the second stacked filter; And A color filter of a third color overlapping the transparent planarization layer between the first and second stacked filters Image sensor comprising a. The method of claim 2, Each of the first stacked filter and the second stacked filter, And an oxide film and a plurality of nitride films alternately stacked on the passivation layer. The method of claim 3, wherein Each of the first stacked filter and the second stacked filter, An image sensor comprising a nitride film having a refractive index of 1.8 to 2.2 and an oxide film having a refractive index of 1.29 to 1.57. The method of claim 4, wherein Each of the first stacked filter and the second stacked filter, An image sensor comprising a nitride film and an oxide film which are alternately stacked six times each. The method of claim 5, The oxide film has a thickness of 0.0846 μm to 0.1034 μm, The thickness of the nitride film is an image sensor, characterized in that 0.0477 ㎛ to 0.0583 ㎛. The method according to any one of claims 2 to 6, The color filter of the first color is a red color filter, The color filter of the second color is a blue color filter, And the color filter of the third color is a green color filter.