KR100698072B1 - Manufacturing Method 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, applying and patterning a positive photoresist on the planarization layer to form a plurality of microlens patterns corresponding to the photodiode, and reflowing the microlens pattern Forming a hemispherical microlens, and a front surface including the microlens And it characterized in that it performs a predetermined plasma processing is formed, including the step of reducing a gap between the microlens and the microlens.

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;

3A to 3D are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to the prior art.

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

5a and 5b is a photograph showing the shape of a microlens according to the prior art and 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

The present invention relates to an image sensor, and more particularly to a method for manufacturing a CMOS image sensor to improve the uniformity of the microlens.

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 element for an image sensor, 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. .

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.

As shown in FIG. 2, in the unit pixel of a general 3T CMOS image sensor, an 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, a method of manufacturing a CMOS image sensor according to the prior art will be described with reference to the accompanying drawings.

3A to 3D are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to the prior art.

As shown in FIG. 3A, an interlayer insulating layer 13 is formed on a semiconductor substrate 11 on which a plurality of photosensitive devices, for example, photodiodes 12 are formed.

Here, the interlayer insulating layer 13 may be formed in a multi-layer, and although not shown, after forming one interlayer insulating layer, a light shielding layer for preventing light from being incident to a portion other than the photodiode 12 region. After formation again an interlayer insulating layer is formed.

After coating using a salting resist on the interlayer insulating layer 13, exposure and development processes are performed to form color filter layers 14 for filtering light for each wavelength band.

Subsequently, the planarization layer 15 is formed on the color filter layer 14 to adjust the focal length and to secure the flatness for forming the lens layer.

As shown in FIG. 3B, a microlens resist layer 16a is applied onto the planarization layer 15, and the reticle 17 having an opening on the resist layer 16a is aligned.

Subsequently, light, such as a laser, is irradiated onto the entire surface including the reticle 17 to selectively expose the resist layer 16a corresponding to the opening of the reticle 17.

As shown in FIG. 3C, the exposed resist layer 16a is developed to form a microlens pattern 16b.

As shown in FIG. 3D, the microlens pattern 16b is reflowed at a temperature of 150 to 200 ° C. to form a hemispherical microlens 16.

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 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 entire surface including the color filter layer, and applying and patterning a positive photoresist on the planarization layer to correspond to the photodiode. Forming a hemispherical microlens by reflowing the microlens pattern, and performing an oxygen plasma treatment on the entire surface including the microlens to reduce a gap between the microlens and the microlens. Characterized by including The.

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

4A to 4G 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, and although not shown, a light shielding layer for preventing light from being incident to a portion other than the photodiode 32 region after forming one interlayer insulating layer. After forming, the 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. (silicon nitride) film is deposited to form a planarization layer 35.

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.

In addition, the space between the microlens patterns 37 is patterned to be narrower than before.

On the other hand, through the front exposure to the microlens pattern 37 as described above to increase the transmittance and generate 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.

Herein, the microlens 38 overlaps an edge between neighboring microlenses 38.

That is, as described above, when the space between the microlens patterns 37 is narrowed and the reflow process is performed, the edges of neighboring microlenses overlap.

As shown in FIG. 4G, an oxygen (O ₂ ) plasma is treated on the entire surface including the microlens 38 to reduce a gap between the neighboring microlens 38 and the microlens 38. Conduct.

Here, by performing an oxygen plasma treatment on the front surface of the microlens 38, the tails of the microlenses 38 generated by the reflow process are removed to remove the CD space and the microlenses between the microlenses 38. 38) can improve the uniformity.

In addition, in the oxygen plasma process, O ₂ is 10 to 40 sccm, Ar gas is 40 to 100 sccm, pressure is 30 to 100 Mt, and a wave source forms a plasma of 50 to 300 W to increase the uniformity of the microlens shape.

5A and 5B are photographs showing the shape of a microlens according to the prior art and the present invention.

In the conventional microlens, as shown in FIG. 5A, gaps between the microlenses are generated to reduce the uniformity of the microlenses.

On the contrary, in the microlens of the present invention, as shown in FIG. 5B, the uniformity of the microlens is improved as the gap of the microlens becomes zero.

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.

That is, 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 non-uniformity of the microlens and deterioration of color reproducibility due to a false signal. As a result, uniform color reproduction of the entire screen can be obtained, thereby improving color reproduction of the entire screen.

Claims (4)

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; Applying and patterning a positive photoresist on the planarization layer to form a plurality of microlens patterns corresponding to the photodiode; Reflowing the microlens pattern to form a hemispherical microlens; And reducing the gap between the microlens and the microlens by performing oxygen plasma treatment on the entire surface including the microlens. 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. The CMOS image of claim 1, wherein the oxygen plasma treatment is performed by forming a plasma having O ₂ of 10 to 40 sccm, Ar gas of 40 to 100 sccm, pressure of 30 to 100 Mt, and power of 50 to 300 W. Method of manufacturing the sensor.

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