KR20060136076A - method for manufacturing of CMOS image sensor - Google Patents

Abstract

The present invention provides a CMOS image sensor that realizes a clear color by zeroing the gap between microlenses to improve light condensing efficiency and preventing extra light from entering the adjacent pixels. A method of fabricating a semiconductor device, the method comprising: forming an interlayer insulating film on an entire surface of a semiconductor substrate on which a plurality of photodiodes and various transistors are formed; forming a color filter layer corresponding to each photodiode on the interlayer insulating film; Forming a planarization layer on the entire surface including the filter layer, forming a microlens on the planarization layer corresponding to the photodiode, forming an organic material layer on the front surface of the semiconductor substrate including the microlens; Removing the organic material layer and simultaneously forming a groove in the planarization layer between the microlenses. Characterized in that the formed box.

Microlenses, color filter layers, organic materials, concave lenses

Description

Method for manufacturing of CMOS image sensor

1 is an equivalent circuit diagram of a typical 3T CMOS image sensor

2 is a layout diagram showing unit pixels of a general 3T CMOS image sensor;

3 is a cross-sectional view showing a CMOS image sensor according to the prior art

4A to 4H are cross-sectional views illustrating a method of manufacturing the CMOS image sensor according to the present invention.

Explanation of symbols for the main parts of the drawings

31 semiconductor substrate 32 photodiode

33: interlayer insulation layer 34: color filter layer

35 planarization layer 36 photoresist

37: microlens pattern 38: microlens

39: organic material layer 40: groove

The present invention relates to an image sensor, and more particularly to a method of manufacturing a CMOS image sensor to improve the light receiving capability of the image sensor.

In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal, and may be broadly classified into a charge coupled device (CCD) image sensor device and a complementary metal oxide semiconductor (CMOS) image sensor device.

The CMOS image sensor includes a photodiode unit for detecting irradiated light and a CMOS logic circuit unit for converting the detected light into an electrical signal and converting the data into electrical signals. As the amount of light received by the photodiode increases, the photosensitivity of the image sensor is increased. ) The characteristics become good.

In order to increase the light sensitivity, a technique in which the fill factor of the photodiode in the total area of the image sensor is increased or the path of light incident to a region other than the photodiode is changed to focus the photodiode is used. .

A representative example of the condensing technique is to form a microlens, which is a method of irradiating a larger amount of light to a photodiode by refracting the path of incident light by making a convex microlens with a material having a high light transmittance on the photodiode. to be.

In this case, light parallel to the optical axis of the microlens is refracted by the microlens to form a focal point at a predetermined position on the optical axis.

On the other hand, in manufacturing an image sensor device, since the number of photodiodes that accept an image determines the resolution, the pixels are miniaturized due to the progress and miniaturization of high pixels. have.

Accordingly, as the miniaturization and the high pixel development progress, the focus of the external image is focused through the microlens in the image plane.

The color filter forms a color filter layer in primary or complementary colors for color separation. In the primary colors, red, green, and blue colors are used, and in the complementary colors, cyan ( Cyan, Yellow, and Magenta colors are formed to be separated in color so that they can be formed on-chip to reproduce colors.

On the other hand, in order to efficiently utilize the incident light, and to maximize the utilization of the microlens is formed to increase the light collection efficiency, the microlens is formed by thermal reflow of the photo resist (photo resist) .

However, when reflowing to focus more light by making the microlens size as large as possible, a bridge is formed between neighboring microlenses, which maintains a certain degree of CD and improves uniformity. Done.

Among the image sensors having the above characteristics, CMOS image sensors are classified into 3T type, 4T type, and 5T type according to the number of transistors. The 3T type consists of one photodiode and three transistors, and the 4T type consists of one photodiode and four transistors. An equivalent circuit and layout of the unit pixels of the 3T-type CMOS image sensor will be described as follows.

FIG. 1 is an equivalent circuit diagram of a general 3T CMOS image sensor, and FIG. 2 is a layout diagram illustrating unit pixels of a general 3T CMOS image sensor.

As shown in FIG. 1, a unit pixel of a general 3T CMOS image sensor includes one photodiode (PD) and three nMOS transistors T1, T2, and T3. The cathode of the photodiode PD is connected to the drain of the first nMOS transistor T1 and the gate of the second nMOS transistor T2. The sources of the first and second nMOS transistors T1 and T2 are all connected to a power supply line supplied with a reference voltage VR, and the gate of the first nMOS transistor T1 has a reset signal RST. It is connected to the reset line supplied. Further, the source of the third nMOS transistor T3 is connected to the drain of the second nMOS transistor, the drain of the third nMOS transistor T3 is connected to a read circuit (not shown in the drawing) via a signal line, The gate of the third nMOS transistor T3 is connected to a column select line to which a selection signal SLCT is supplied. Accordingly, the first nMOS transistor T1 is referred to as a reset transistor Rx, the second nMOS transistor T2 is referred to as a drive transistor Dx, and the third nMOS transistor T3 is referred to as a selection transistor Sx.

In the unit pixel of the general 3T CMOS image sensor, as shown in FIG. 2, the active region 10 is defined so that one photodiode 20 is formed in a wide portion of the active region 10. Gate electrodes 30, 40, and 50 of three transistors are formed in the active region 10 of the remaining portion, respectively.

That is, the reset transistor Rx is formed by the gate electrode 30, the drive transistor Dx is formed by the gate electrode 40, and the selection transistor Sx is formed by the gate electrode 50. Is formed.

Here, impurity ions are implanted into the active region 10 of each transistor except for lower portions of the gate electrodes 30, 40, and 50 to form source / drain regions of each transistor. Therefore, a power supply voltage Vdd is applied to a source / drain region between the reset transistor Rx and the drive transistor Dx, and a source / drain region on one side of the select transistor Sx is shown in a read circuit (not shown). Not used).

Although not illustrated in the drawings, the gate electrodes 30, 40, and 50 described above are connected to respective signal lines, and each of the signal lines has a pad at one end thereof and is connected to an external driving circuit.

Hereinafter, the CMOS image sensor according to the related art will be described with reference to the accompanying drawings.

3 is a cross-sectional view showing a CMOS image sensor according to the prior art.

As shown in FIG. 3, at least one photodiode 12 is formed on the semiconductor substrate 11 to generate charges according to the amount of incident light, and a front surface of the semiconductor substrate 11 including the photodiode 12. The interlayer insulating layer 13 formed on the interlayer insulating layer 13, the color filter layers 14 of R, G, and B formed through the interlayer insulating layer 13 to pass light of a specific wavelength band, respectively, and the color filter layer 14. And a planarization layer 15 formed on the entire surface of the semiconductor substrate 11 including the semiconductor substrate 11 and a convex shape having a predetermined curvature on the planarization layer 15 and passing through the corresponding color filter layer 14 to allow the photodiode 12. It consists of a micro lens 16 for condensing light.

Although not shown in the drawings, an optical shielding layer is formed in the interlayer insulating layer 13 to prevent light from being incident on portions other than the photodiode region.

The device for sensing light may be configured in the form of a photo gate, not in the form of a photo diode.

Here, the color filter layer 14 is composed of a color filter of R (red), G (green), B (blue), each color filter is a photolithography process using a photosensitive material and applying a separate mask Is formed.

However, due to the miniaturization of the image sensor and the change to multiple pixels, more pixels are made per unit area, and as the pixel size becomes smaller, the color filter and the microlens formed on-chip on the top The size is also smaller. As the unit pixel size decreases, the sensitivity decreases as the area of the photodiode receiving light decreases.

Therefore, in order to compensate for the reduced sensitivity, more light must be received. In order to do so, there is a method of increasing the opening and forming a condensing microlens on the upper part, and the opening is mostly formed of a metal layer.

The metal layer serves as a wiring and a light shielding layer, and when the incident light incident on the unit pixel and incident on the light shielding layer is refracted by focusing the light through the opening of the condensing microlens, the microlens increases as the condensing microlens is raised. The degree of sticking or dropping is slightly different, resulting in poor image uniformity.

In addition, the lower color separation layer is affected, and the information of the adjacent color separation layer is mixed, resulting in poor color reproducibility and contrast. In addition, it is difficult to form a pattern having a desired shape during alignment exposure due to a decrease in photo resolution due to the mixing of pigments when forming a color separation layer, and an additional process in which an upper flat layer is necessary by overlapping or forming a space between the color separation layers. This is necessary.

Therefore, the conventional technique maintains the uniformity of the microlens by maintaining the space between the microlenses at 0.2 ~ 0.5㎛ when forming the microlenses, the space between the microlenses is the loss of incoming incident light and ) The incident causes a color blurring.

The microlens is formed on top of the planarization layer to match the pixel size and length of the device, and then coated with a photoresist. After forming a pattern by exposure and development, the microlens is reflowed by applying thermal energy. Form.

The photoresist for microlenses uses g-Line or I-Line photoresist with good flow ability, and generally uses a material that reacts in a g, h, I-Line complex wavelength region.

After the pattern is formed by I-Line to 0.2-0.5 μm that can be defined by I-Line, it is hardened and thermally reflowed, and fine CD (Critical) in the pattern process is performed during the thermal reflow. The difference in dimension appears as it is during reflow, and there is a local bridge, resulting in unevenness of microlens size, resulting in a difference in uniformity and deterioration of sensitivity and color clarity.

The present invention has been made to solve the above problems by zeroing the gap (gap) between the microlenses to increase the light condensing efficiency and to prevent extra light from entering the adjacent pixels It is an object of the present invention to provide a method for manufacturing a CMOS image sensor to realize a vivid color.

The method for manufacturing the CMOS image sensor according to the present invention for achieving the above object comprises the steps of forming an interlayer insulating film on the front surface of the semiconductor substrate on which a plurality of photodiodes and various transistors are formed; Forming a color filter layer corresponding to the diode, forming a planarization layer on the front surface including the color filter layer, forming a microlens on the planarization layer corresponding to the photodiode, and including the microlens. And forming a groove in the planarization layer between the microlenses while removing the organic material layer.

Hereinafter, a method of manufacturing the CMOS image sensor according to the present invention will be described in detail with reference to the accompanying drawings.

4A to 4H are cross-sectional views illustrating a method of manufacturing the CMOS image sensor according to the present invention.

As shown in FIG. 4A, an interlayer insulating layer 33 is formed on a semiconductor substrate 31 on which a plurality of photosensitive devices, for example, photodiodes 32 and various transistors (see FIG. 1), are formed. do.

Here, the interlayer insulating layer 33 may be formed in multiple layers. Although not shown, a light shielding layer is formed to prevent light from being incident on a portion other than the photodiode 32 region after the formation of one interlayer insulating layer. Later, an interlayer insulating layer is formed again.

As shown in FIG. 4B, color filter layers R, G, and B are applied to the interlayer insulating layer 33 using a salty resist, and then subjected to an exposure and development process to filter light for each wavelength band. 34).

Here, each of the color filter layers 34 is coated with a photosensitive material to have a thickness of 1 to 5 μm, and is patterned by a photolithography process using a separate mask to filter light by each wavelength band. Form into layers.

As shown in FIG. 4C, silicon nitride is applied to the front surface of the semiconductor substrate 31 including the color filter layer 34 to prevent moisture and heavy metals from penetrating into the EMC and the outside when packaged. A planarization layer 35 is formed by depositing a (silicon nitride) film.

On the other hand, since the optical transmission is very important, the image sensor is formed to a thickness of 1000 ~ 6000Å in order to exclude the interference phenomenon of the thin film due to the thickness of the planarization layer 35.

Here, in the state in which the planarization layer 35 is formed, the pad and the scribe line portion of the planarization layer 35 are opened by using a bonding pad for wiring as a mask. ) And dry or wet etching to form any desired bonding pads (not shown).

As shown in FIG. 4D, the photoresist 36 for microlenses is coated on the photodiode 32 in order to efficiently focus light on the entire surface of the semiconductor substrate 31 including the planarization layer 35.

As shown in FIG. 4E, the photoresist 36 is selectively patterned by an exposure and development process to form a microlens pattern 37.

In this case, when the photoresist 36 is a positive resist, since the transmittance is improved only by dissolving the photo active compound of the initiator, which is an absorber of the photoresist 36, the front exposure is increased. exposure) decomposes the photo active compound remaining in the microlens pattern 37.

On the other hand, through the front exposure to the microlens pattern 37 as described above to increase the transmittance and generate a photo acid (photo acid) to increase the flow (flow ability) of the microlens.

As shown in FIG. 4F, the microstructure present in the upper part of a heat treatment of 150 ° C. or higher in a state where the semiconductor substrate 31 on which the microlens pattern 37 is formed is placed on a hot plate (not shown). The lens pattern 37 is reflowed to form a hemispherical microlens 38.

Subsequently, the microlens 38 reflowed by the heat treatment is cooled. In this case, the cooling process is performed in a state where the semiconductor substrate 31 is placed on a cool plate.

As shown in FIG. 4G, an organic material layer 39 is deposited on the entire surface of the semiconductor substrate 31 including the microlenses 38 to a thickness of 30 to 100 nm and then cured.

Herein, the organic material layer 39 may have a thickness of 100 nm or less on the microlens 38. The space portion of the microlens 38 may be formed by the microlens 38 during dry etching using oxygen (O ₂ ) plasma. It is a layer for flowing a zero gap.

In addition, the organic material layer 39 uses photoresist.

In addition, in the case of using a thermosetting resin as the organic material layer 39 formed on the microlens 38, the thermosetting resin after UV treatment to the microlens 38 to remove the reaction with the microlens 38 To form.

As shown in FIG. 4H, the organic material layer 39 is dry-etched by O ₂ plasma treatment to zero the space portion of the microlens 38. The space portion is formed in a concave shape.

That is, when the organic material layer 39 formed on the front surface including the microlens 38 is removed by O ₂ plasma etching, the planarization layer 35 between the microlenses 38 is removed by a predetermined thickness from the surface. Grooves 40 are formed in the planarization layer 35 between the microlenses 38.

Here, unevenness due to the enlargement of the size of the microlens 38, unevenness caused by sub influence, and bonding exposed to the developer when the color filter layer 34, the planarization layer 35, and the microlens 38 are formed. In order to prevent corrosion of the pad, the pad portion may be blocked by a barrier layer such as an oxide film.

In addition, the tails of the non-uniform microlenses 38 between the microlenses 38 and the microlenses 38 can be removed, and also shadows between the gaps of the microlenses 38 during the O ₂ plasma treatment. Shallow etch enables concave lenses to be formed, enabling zero gaps between the microlenses 38 and condensing the pixel area with 100% photodiode 32 for improved sensitivity and proximity. It is possible to implement a clean image by preventing entering into the pixel.

In the manufacture of the CMOS image sensor according to the present invention, after forming the microlens 38, an organic material layer 39 such as a photoresist (or thermosetting resin) is formed on the microlens 38. Oxygen plasma treatment to improve the uniformity of the microlens with a buffer layer formed to a thickness of 30 to 100nm to guide the concave lens shape between the microlenses 38 for the zero gap of the microlens 38. It is possible to improve the uniformity of the microlens gap.

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.

As described above, the method for manufacturing the CMOS image sensor according to the present invention has the following effects.

First, in manufacturing an image sensor, the efficiency of the microlens is maximized, and the uniformity of the microlens is improved by preventing noise caused by nonuniformity of the microlens and deterioration of color reproducibility due to a false signal. It is possible to obtain uniform color reproduction of the entire screen.

Second, by maximizing the size of the microlenses, the sensitivity can be improved to realize a bright image without noise even in a dark environment.

Claims (7)

Forming an interlayer insulating film on an entire surface of the semiconductor substrate on which a plurality of photodiodes and various transistors are formed; Forming a color filter layer on the interlayer insulating layer so as to correspond to each photodiode; Forming a planarization layer on the entire surface including the color filter layer; Forming a microlens on the planarization layer to correspond to the photodiode; Forming an organic material layer on an entire surface of the semiconductor substrate including the microlens; Forming a groove in the planarization layer between the microlenses while removing the organic material layer. The method of claim 1, wherein the organic material layer uses a photoresist or a thermosetting resin. The method of claim 1, wherein the organic material layer is formed to a thickness of 30 to 100 nm. The method of claim 1, wherein the organic material layer is removed by an oxygen plasma treatment. The method of claim 1, further comprising irradiating UV to the microlenses prior to forming the organic material layer. The method of claim 1, wherein the planarization layer is formed of silicon nitride. The method of claim 1, wherein the planarization layer is formed to a thickness of 1000 ~ 6000 kHz.

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