KR100801850B1 - Image sensor and method of manufacturing the same - Google Patents

Abstract

An image sensor and a method for manufacturing the same are provided to reduce aberration of a micro-lens by forming an aspheric micro-lens having a parabolic shape. A photodiode structure(100) is formed on a pixel region of a semiconductor substrate(10) in order to generate an electrical signal by using incident light. An aspheric micro-lens(250) is arranged on the photodiode structure. The aspheric micro-lens includes a first photoresist pattern(200a) having a first planar area and first sensitivity with respect to the light, and a second photoresist pattern(210a) having a second planar area and second sensitivity with respect to the light. The second photoresist pattern is arranged on the first photoresist pattern. The second planar area is smaller than the first planar area. The second sensitivity is higher than the first sensitivity.

Description

Image sensor and manufacturing method thereof {IMAGE SENSOR AND METHOD OF MANUFACTURING THE SAME}

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

FIG. 2 is a layout diagram illustrating the photodiode pixel illustrated in FIG. 1.

3 is a plan view of the photodiode pixel of FIG. 2.

4 is a flowchart illustrating a manufacturing method of an image sensor according to an exemplary embodiment of the present invention.

FIG. 5 is a cross-sectional view illustrating the first and second photoresist thin films of FIG. 4.

6 is a cross-sectional view illustrating the preliminary micro lens of FIG. 4.

<Explanation of symbols for the main parts of the drawings>

10: semiconductor substrate 100: photodiode structure

110: photodiode pixel 120: wiring

130: interlayer insulating film 140: color filter

150 planarization layer 200 first photoresist thin film

210: second photoresist thin film 230: preliminary microlens

250: aspherical micro lens

The present invention relates to an image sensor and a method for manufacturing the same, and more particularly to an image sensor having a microlens having an aspheric surface and a method for manufacturing the same.

In general, an image sensor is defined as a semiconductor device that converts an optical image into an electrical signal. Conventional image sensors are typically a charge coupled device (CCD), CMOS image sensor (CMOS image sensor) and the like.

The charge coupling device is formed between a plurality of photo diodes for converting a signal of light into an electrical signal, and a plurality of vertical diodes formed in a matrix to transfer charges generated in each photo diode in a vertical direction. A directional charge transfer region, a horizontal charge transfer region (HCCD) for transmitting charges transferred by each vertical charge transfer region in a horizontal direction, and a sense amplifier (Sense) for sensing an electric charge transferred in the horizontal direction and outputting an electrical signal Amplifier).

However, such a charge coupling device has a disadvantage in that the driving method is complicated, the power consumption is high, and the manufacturing process is complicated because a multi-step photo process is required.

In addition, the charge coupling device has a disadvantage in that it is difficult to integrate a control circuit, a signal processing circuit, an analog-to-digital conversion circuit (A / D converter), and the like into a charge coupling 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 charge-coupled devices. 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.

CMOS image sensor has advantages such as low power consumption, simple manufacturing process according to few photo process steps because of CMOS 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. Therefore, CMOS image sensors are now widely used in various application areas such as digital still cameras, digital video cameras, and the like.

A general CMOS image sensor includes a plurality of pixels disposed in a pixel area and detecting a light amount, and a micro lens corresponding to the pixel to focus light to the pixel.

The micro lens of the conventional CMOS image sensor has a spherical shape. Since the microlens has a spherical shape, as the resolution of the CMOS image sensor increases, the pixel size of the CMOS image sensor is reduced by the microlens having the spherical shape of the CMOS image sensor, thereby decreasing the size of the microlens. It is becoming. For this reason, when the size of the microlens is reduced, a problem arises in that the focus of the microlens having the spherical surface is not accurately focused on the pixel area due to the spherical aberration.

Accordingly, the present invention has been made in view of such a conventional problem, and an object of the present invention is to provide an image sensor that can solve the spherical aberration problem caused by the size reduction of the microlens.

Another object of the present invention is to provide a method of manufacturing the image sensor.

In order to realize one object of the present invention, an image sensor according to the present invention is formed in a pixel region of a semiconductor substrate, and is disposed on a photodiode structure and a photodiode structure generating an electrical signal by incident light. Aspherical microlenses.

Meanwhile, a method of manufacturing an image sensor for realizing another object of the present invention includes forming a photodiode structure having photodiode pixels for generating an electrical signal by light incident on a pixel region of a semiconductor substrate. Forming a first photoresist thin film having a first sensitivity to light on the first photoresist thin film, and forming a second photoresist thin film having a second sensitivity higher than a first sensitivity to the light on the first photoresist thin film And patterning the first and second photoresist thin films using a pattern mask so as to have a first photoresist pattern having a first planar area on the photodiode structure and a smaller than the first planar area on the first photoresist pattern. Forming a preliminary microlens including a second photoresist pattern having a second planar area And heat treating the preliminary microlens to form a microlens having an aspheric surface.

Hereinafter, an image sensor and a method of manufacturing the same according to embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. Those skilled in the art can implement the present invention in various other forms without departing from the technical spirit of the present invention.

Image sensor

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

Referring to FIG. 1, an image sensor according to the present invention includes a grape diode structure and an aspherical lens.

The photodiode structure 100 is formed in the pixel region of the semiconductor substrate and generates an electrical signal by incident light. The photodiode structure 100 may be formed on the photodiode pixel 110 formed on the upper surface of the semiconductor substrate 10, the interlayer insulation layer 130 formed on the photodiode pixel 110, and the interlayer insulation layer 130. And a flattening layer 150 disposed on the color filter 140 formed on the color filter 141.

Hereinafter, the photodiode pixel 110 will be described in more detail.

FIG. 2 is a layout diagram illustrating the photodiode pixel illustrated in FIG. 1, and FIG. 3 is a plan view of the photodiode pixel of FIG. 2.

2 and 3, the photodiode pixel 110 may include a photodiode PD, a transfer transistor Tx, a reset transistor Rx, a select transistor Sx, and an access transistor Ax for sensing the amount of light. It includes.

The transfer transistor Tx and the reset transistor Rx are connected in series to the photodiode PD. The source of the transfer transistor Tx is connected to the photodiode PD, and the drain of the transfer transistor Tx is connected to the source of the reset transistor Sx. A power supply voltage Vdd is applied to the drain of the reset transistor Sx.

The drain of the transfer transistor Tx serves as a floating diffusion (FD). The floating diffusion layer FD is connected to the gate of the select transistor Sx. The select transistor Sx and the access transistor Ax are connected in series. That is, the source of the select transistor Sx and the drain of the access transistor Ax are connected to each other. A power supply voltage Vdd is applied to the drain of the access transistor Ax and the source of the reset transistor Rx. The drain of the select transistor Sx corresponds to the output terminal Out, and the select signal Row is applied to the gate of the select transistor Sx.

Referring back to FIG. 1, the interlayer insulating layer 130 insulates the wiring 120 formed of a multilayer, and the wiring 120 includes a photodiode PD, a transfer transistor Tx, a reset transistor Rx, and a select transistor. (Sx) and the access transistor (Ax) are electrically connected to each other to provide a drive signal or output a signal corresponding to the amount of light. Accordingly, the interlayer insulating layer 130 covers and insulates the wirings 120 disposed on different layers as shown in FIG. 1.

On the other hand, the color filter 140 is formed on the upper surface of the interlayer insulating film located on the uppermost layer of the above-described interlayer insulating film 130 and is formed corresponding to the photodiode pixel 110. In the present embodiment, the color filter 140 may be formed of unit color filters 142 such as a red color filter, a green color filter, and a blue color filter.

Referring to FIG. 1, the aspherical micro lens 250 is disposed on an upper surface of the planarization layer 150 of the photodiode structure 100 and has a parabolic shape. The parabolic aspherical microlens 250 is formed by the first and second photoresist patterns 200a and 210a having different sensitivity.

The first photoresist pattern 200a has a first sensitivity with respect to the first planar area, for example, the same area and light as each unit color filter 142. The second photoresist pattern 210a is disposed on the first photoresist pattern 200a and has a second sensitivity higher than the first sensitivity to light and a second planar area smaller than the first plane area.

Preferably, the thicknesses of the first photoresist pattern 200a and the second photoresist pattern 210a are the same, and the second sensitivity is 1.5 to 2 times higher than the first sensitivity.

As described in detail in the present embodiment, a parabolic shape is formed using the first photoresist pattern 200a and the second photoresist pattern 210 having different sensitivity on the top surface of the planarization layer 150 of the photodiode structure 100. If the aspherical microlens 250 is formed, the problem of spherical aberration due to the size reduction of the microlens can be solved.

Manufacturing Method of Image Sensor

4 is a flowchart illustrating a manufacturing method of an image sensor according to an exemplary embodiment of the present invention.

4 and 1, in step S10, to manufacture an image sensor, first, the photodiode structure 100 shown in FIG. 1 is fabricated on a semiconductor substrate 10. The photodiode structure 100 is also formed in the active region AR and a peripheral region (not shown) disposed around the active region AR.

Referring to FIG. 2, in order to form the photodiode structure 100, first, a photodiode PD, a transfer transistor Tx, a reset transistor Rx, and a select transistor sensing the amount of light on the semiconductor substrate 10 may be used. A plurality of photodiode pixels 110 including Sx and an access transistor Ax are formed, and the photodiode pixels 110 having the above-described configuration are formed through a semiconductor thin film process.

The operation of the photodiode pixel 110 having the above-described structure will be briefly described. First, the reset transistor Rx is turned on to make the potential of the floating diffusion layer FD equal to the power supply voltage Vdd, and then the reset transistor Rx is turned off. This operation is defined as a reset operation.

When external light is incident on the photodiode PD, electron-hole pairs (EHP) are generated in the photodiode PD and signal charges are accumulated in the photodiode PD. Subsequently, as the transfer transistor Tx is turned on, the signal charges accumulated in the photodiode PD are output to the floating diffusion layer FD and stored in the floating diffusion layer FD.

Accordingly, the potential of the floating diffusion layer FD is changed in proportion to the amount of charges output from the photodiode PD, thereby changing the potential of the gate of the access transistor Ax. At this time, when the select transistor Sx is turned on by the selection signal Row, data is output to the output terminal Out.

After the data is output, the photodiode pixel 110 performs a reset operation again. Each photodiode pixel 110 repeats these processes to convert light into an electrical signal and output the same.

When the photodiode pixel 110 having the above-described structure is formed, a plurality of lines for insulating the wiring 120 and the wiring 120 for providing a driving signal or outputting a signal corresponding to the amount of light to the photodiode pixel 110 are provided. Interlayer insulating films 130 are formed.

Subsequently, a color filter 140 is formed on an upper surface of the uppermost interlayer insulating layer formed on the uppermost layer of the interlayer insulating layer 130, and each color filter 140 is formed corresponding to each photodiode pixel 110. In the present embodiment, the color filter 140 may be formed of unit color filters 142 such as a red color filter, a green color filter, and a blue color filter. In the present embodiment, the unit color filters 142 measured from the surface of the uppermost interlayer insulating film may have different thicknesses. Alternatively, the thickness of each unit color filter 142 measured from the surface of the uppermost interlayer insulating layer may be the same.

The color filter 140 may be formed by applying a photosensitive material including a photosensitive material, a pigment, and / or a dye on the interlayer insulating layer 130, and patterning them by a photo-etching method.

After the color filter 140 is formed, the planarization layer 150 is formed on the color filter 140 to form the photodiode structure 100. In the present exemplary embodiment, the planarization layer 150 is preferably formed when the unit color filters 142 have different thicknesses.

FIG. 5 is a cross-sectional view illustrating the first and second photoresist thin films of FIG. 4.

4 and 5, in step S20, the first photoresist thin film 200 is formed on the photodiode structure 100. The first photoresist thin film 200 is formed on the entire upper surface of the planarization film and has a first sensitivity.

4 and 5 again, in step S30, the second surface having a second sensitivity higher than the first sensitivity of the first photoresist thin film 200 with respect to light on the upper surface of the first photoresist thin film 200. The photoresist thin film 210 is formed.

In the present embodiment, the first and second photoresist thin films 200 and 210 may be formed by, for example, a spin coating process. For example, the first and second photoresist thin films 200 and 210 may include a positive type photosensitive material which is removed by reacting with light.

Preferably, the thickness and optical refraction coefficient of the second photoresist thin film 210 are the same as the thickness and optical refraction coefficient of the first photoresist thin film 200. Also, the melting point of the second photoresist thin film 210 that is melted by heat and the melting point of the first photoresist thin film 200 are also the same.

In addition, the second sensitivity of the second photoresist thin film 210 is preferably 1.5 to 2 times the first sensitivity of the first photoresist thin film 200.

6 is a cross-sectional view illustrating the preliminary micro lens of FIG. 4.

4 and 6, in step S40, the first and second photoresist thin films 200 and 210 are patterned using a pattern mask to have a first planar area on the photodiode structure 100. A preliminary microlens 230 including a second photoresist pattern 210a having a second plane area smaller than the first plane area is formed on the photoresist pattern 200a and the first photoresist pattern 200a.

In order to form the preliminary microlens 230, the first and second photoresist thin films 200 and 210 are exposed using a reticle (not shown). In the present embodiment, the reticle includes a light blocking portion (not shown) that blocks light directed toward the photodiode pixel 110. Accordingly, after all of the remaining portions of the first photoresist thin film 200 except for the portion corresponding to the unit color filter 142 are exposed by light, the exposed portions are removed by the developer, and the first photoresist pattern ( 200a) has the same planar area as the unit color filter 142. The second photoresist thin film 210, which is 1.5 to 2 times higher in optical sensitivity than the first photoresist thin film 200, is removed more than the first photoresist thin film 200, so that the second photoresist is thinner. The resist pattern 210a has a planar area smaller than that of the first photoresist pattern 200a.

Meanwhile, the focusing of the light exposing the first and second photoresist thin films 200 and 210 is matched to the upper surface of the second photoresist thin film 210. When the focusing of the light to be exposed is aligned with the upper surface of the second photoresist thin film 210, the sidewalls 202 and 212 have a constant slope when the first and second photoresist thin films 200 and 210 are patterned. .

Preferably, the inner sidewalls of the sidewalls 202 of the first photoresist pattern 200a and the top surface of the photodiode structure 100 and the top surface of the first photoresist pattern 200a and the sidewalls of the second photoresist pattern 210 are formed. Each cabinet formed by 212 is an acute angle.

1 and 4, in step S50, after the preliminary microlens 230 is formed, the preliminary microlens 230 is heat-treated at a high temperature, for example, at a temperature at which the first and second photoresist thin films are melted. An aspherical micro lens 250 is manufactured. That is, the preliminary microlens 230 is changed into a chemically / physically stable aspherical microlens 250 by processing and heat treatment in a parabolic shape by heat.

As described in detail above, two photoresist thin films having different sensitivity are formed on the planarization film, and are developed after exposure to form a preliminary microlens having a smaller area toward the top photoresist thin film, and then subjected to heat treatment and parabolic. Formation of the aspherical microlenses of the shape can easily reduce the micro lens aberration for condensing light with the photodiode, and the image quality can be improved even if the size of the microlenses is reduced.

Although the detailed description of the present invention has been described with reference to the embodiments of the present invention, those skilled in the art or those skilled in the art will have the spirit and scope of the present invention as set forth in the claims below. It will be appreciated that various modifications and variations can be made in the present invention without departing from the scope of the art.

Claims (11)

A photodiode structure formed in the pixel region of the semiconductor substrate and generating an electrical signal by incident light; And An aspherical micro lens disposed on the photodiode structure, The aspherical micro lens A first photoresist pattern having a first sensitivity to the first planar area and to light; And And a second photoresist pattern disposed on the first photoresist pattern, the second photoresist pattern having a second planar area smaller than the first planar area and a second sensitivity higher than the first sensitivity to the light. The method of claim 1, wherein the photodiode structure is A photodiode pixel formed on the semiconductor substrate; An interlayer insulating film formed on the photodiode pixel; A color filter formed on the interlayer insulating layer corresponding to each of the photodiode pixels; And And a planarization layer disposed on the color filter. delete The image sensor of claim 1, wherein thicknesses of the first photoresist pattern and the second photoresist pattern are the same. The image sensor of claim 1, wherein the second sensitivity is 1.5 to 2 times higher than the first sensitivity. Forming a photodiode structure having photodiode pixels for generating an electrical signal by light incident on the pixel region of the semiconductor substrate; Forming a first photoresist thin film having a first sensitivity to light on the photodiode structure; Forming a second photoresist thin film having a second sensitivity higher than a first sensitivity to the light on the first photoresist thin film; Patterning the first and second photoresist thin films using a pattern mask to form a first photoresist pattern having a first planar area on the photodiode structure and a second smaller than the first planar area on the first photoresist pattern Forming a preliminary microlens including a second photoresist pattern having a planar area; And Heat-treating the preliminary microlens to form a microlens having an aspheric surface. The method of claim 6, Forming the photodiode structure Forming a photodiode pixel on the semiconductor substrate; Forming an interlayer insulating film covering the photodiode pixel; Forming a color filter corresponding to each of the photodiode pixels on the interlayer insulating film; And And forming a planarization layer covering the color filter to planarize the planarization layer. The method of claim 6, And a thickness of the first photoresist thin film and the second photoresist thin film are the same. The method of claim 6, And the second sensitivity of the second photoresist thin film is 1.5 to 2 times the first sensitivity of the first photoresist thin film. The method of claim 6, In the forming of the preliminary microlens, an internal angle formed by a sidewall of the first photoresist pattern and an upper surface of the photodiode structure and an internal angle formed by an upper surface of the first photoresist pattern and a sidewall of the second photoresist pattern A manufacturing method of an image sensor, characterized in that each acute angle. The method of claim 6, And the optical refraction coefficients of the first and second photoresist thin films are the same.

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