KR100720464B1 - Manufacturing Method of CMOS Image Sensor - Google Patents

Abstract

The present invention relates to a method of manufacturing a CMOS image sensor to form a microlens using an imprint method to uniformly form the microlens and to improve the characteristics of the image sensor. Forming an interlayer insulating film on an entire surface of the semiconductor substrate on which various transistors are formed; forming a color filter layer on the interlayer insulating film to correspond to each photodiode; and forming a 1000 nm silicon nitride material on the entire surface including the color filter layer. Forming a planarization layer having a thickness of ˜6000 와, applying a photoresist on the planarization layer, and arranging a mold of a PDMS material patterned with a desired lens shape on the semiconductor substrate to which the photoresist is applied And overlapping the mold with the semiconductor substrate to which the photoresist is applied. Transferring a patterned lens shape to the photosensitive liquid by applying heat of 300 ° C. to 500 ° C. while applying MPa pressure, and forming a microlens on the planarization layer by removing the mold from the semiconductor substrate. It characterized in that it comprises a.

Micro Lens, Photoresist, Imprint Method, Image Sensor

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 4D are cross-sectional views illustrating a method of forming a pattern having a desired shape by using an imprint lithography method.

5A to 5G 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

101 semiconductor substrate 102 photodiode

103: interlayer insulation layer 104: color filter layer

105: planarization layer 106: photosensitive liquid

107 mold 108 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 multiple layers, and although not shown, a light shielding layer is formed to prevent light from being incident on portions other than the photodiode 12 region after the formation of one interlayer insulating layer. Later, an interlayer insulating layer is formed again.

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, the resist layer 16a is selectively exposed to the opening of the reticle 17 by irradiating light such as a laser on the entire surface including 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 predetermined temperature to form a hemispherical microlens 16.

However, the CMOS image sensor according to the related art has some problems as follows by forming a microlens through a reflow method.

First, due to the sensitivity of the microlens photoresist itself, it is very difficult to control the process in the bleach and reflow processes after the exposure and development processes.

That is, as shown in A and B of FIG. 3D, the spacing between the microlenses is not uniform.

Second, it is very sensitive to the thermal process requires expensive equipment capable of fine temperature control, it is difficult to form a complete spherical lens if the temperature control is not properly.

In other words, if the temperature is not properly adjusted, the lens and the lens are connected to each other or too far apart to obtain an accurate image. Accurately forming such spherical lens determines the quality of the complementary oxide semiconductor image sensor. This is becoming an important factor.

In recent years, technologies for shortening the light path to improve the quality of the image sensor have been shown. Among these technologies, the microlens formed after the completion of the complementary metal oxide semiconductor process is formed. The technology for this is introduced.

Finally, before forming the lens of the image sensor, the process of forming the microlens after reducing the passivation thickness of the image sensor is sometimes applied. In the case of the lens being formed and the lens adjacent to the step when forming the lens may have a disadvantage that the lens aperture, the shape is bad.

The present invention has been made to solve the above problems, by forming a microlens using an imprint method to form a microlens uniformly and at the same time to improve the characteristics of the image sensor of the CMOS image sensor The purpose is to provide a manufacturing method.

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 having a thickness of 1000 to 6000 로 with a silicon nitride material on the front surface including the color filter layer, and applying a photoresist on the planarization layer; And arranging a mold made of PDMS material having a pattern of a desired lens shape on the semiconductor substrate to which the photoresist is applied, and applying the pressure to 30 MPa to 50 MPa while overlapping the mold with the semiconductor substrate to which the photoresist is applied. Transferring a patterned lens shape to the mold to the photosensitive liquid by applying a heat of 500 ° C to 500 ° C; And removing a mold from the semiconductor substrate to form a microlens on the planarization layer.

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

In the present invention, research and development on new pattern forming methods (lithographic methods by non-traditional methods) that can overcome the limitations of the conventional photolithography method are actively conducted everywhere, and among such non-traditional lithography methods One feature is the formation of microlenses using imprint lithography.

4A to 4D are cross-sectional views illustrating a method of forming a pattern having a desired shape by using an imprint lithography method.

As shown in Fig. 4A, a rigid mold 31, such as silicon (Si), on which a desired pattern is formed is prepared.

Subsequently, the thermoplastic polymer thin film 33 is coded and formed on the semiconductor substrate 32.

The mold 31 on which the pattern is formed is aligned on the semiconductor substrate 32 coated with the polymer thin film 33.

As shown in FIG. 4B, the semiconductor substrate 32 on which the polymer thin film 33 is formed is opposed to the mold 31 on which the pattern is formed.

As shown in FIG. 4C, the semiconductor substrate 32 and the mold 31 are placed between the press plates in a state in which the semiconductor substrate 32 and the mold 31 face each other to be treated at high temperature and high pressure.

As shown in FIG. 4D, the semiconductor substrate 32 and the mold 31 are separated to transfer the pattern formed in the mold 31 to the polymer thin film 33 formed on the semiconductor substrate 32. The pattern 33a is formed.

Since the imprint lithography method uses a rigid mold such as silicon, the imprint lithography method has an advantage of easily implementing a pattern up to about 6 nm.

5A to 5G are cross-sectional views illustrating a method of manufacturing the CMOS image sensor according to the present invention.

As shown in FIG. 5A, an interlayer insulating layer 103 is formed on a semiconductor substrate 101 on which a plurality of photosensitive devices, for example, photodiodes 102 and various transistors (see FIG. 1), are formed. do.

Here, the interlayer insulating layer 103 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 102 region. After formation, an interlayer insulating layer is formed again.

As illustrated in FIG. 5B, color filter layers R, G, and B are applied to the interlayer insulating layer 103 using a salty resist and then subjected to an exposure and development process to filter light for each wavelength band. 104).

Here, each color filter layer 104 is applied to the photosensitive material to have a thickness of 1 ~ 5㎛ and patterned by a photolithography process using a separate mask to filter the light for each wavelength band single unit Form into layers.

As shown in FIG. 5C, in order to prevent the penetration of moisture or heavy metals from the EMC and the outside during reliability and packaging on the front surface of the semiconductor substrate 101 including the color filter layer 104. (silicon nitride) film is deposited to form a planarization layer 105.

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 105.

Here, in the state in which the planarization layer 105 is formed, the pad and the scribe line portion of the planarization layer 105 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. 5D, a photoresist 106 for microlenses is applied to the photodiode 102 in order to focus light efficiently on the entire surface of the semiconductor substrate 101 including the planarization layer 105.

As shown in FIG. 5E, the mold 107 having the pattern formed in a desired lens shape (for example, hemispherical shape) is aligned on the semiconductor substrate 101 to which the photosensitive liquid 106 is applied.

Here, the material of the mold 107 uses poly dimethylsiloxane (PDMS).

As shown in FIG. 5F, a process of applying heat of 300 ° C. to 500 ° C. in a state in which a pressure of 30 MPa to 50 MPa is applied after overlapping the mold 107 and the semiconductor substrate 101 to which the photosensitive liquid 106 is applied. The lens pattern patterned on the mold 107 is transferred to the photosensitive liquid 106.
Here, the step of applying the heat of 300 ° C to 500 ° C is carried out in order to maintain the correct shape of the photosensitive liquid 106 after the mold is overlapped with the semiconductor substrate 101 to which the photosensitive liquid 106 is applied.

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As shown in FIG. 5G, the mold 107 is separated from the semiconductor substrate 101, and the microlens 108 having the same shape as the pattern formed on the mold 107 is formed on the planarization layer 105. Form.

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, the present invention can expect the following effects by forming a microlens having a desired shape using the imprint method.

First, the conventional method of forming a lens through a thermal process and an overexposure process has a difficulty in that the shape of the lens may not be accurately formed according to the processing conditions, but through the present invention the correct lens without the shape of the microlens undisturbed It can form a shape.

Second, the conventional lens forming method has a disadvantage in that the shape of the lens changes depending on the conditions of the thermal process and overexposure process, the present invention can reduce the factor of the lens shape change by fixing after overlapping the mold accurately designed.

third. In the conventional lens forming method, a thermal process and an overexposure process must be performed again after a general photographic process, but the present invention can improve productivity by shortening such a process.

Claims (5)

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 having a thickness of 1000 to 6000 microns on a front surface including the color filter layer; Applying a photoresist on the planarization layer; Arranging a mold of a PDMS material patterned with a desired lens shape on the semiconductor substrate to which the photoresist is applied; Transferring the patterned lens shape to the photosensitive liquid by applying a heat of 300 ° C. to 500 ° C. while applying a pressure of 30 MPa to 50 MPa while overlapping the mold with a semiconductor substrate coated with a photoresist; And removing the mold from the semiconductor substrate to form a microlens on the planarization layer. delete delete delete The method of claim 1, wherein the mold has a hemispherical pattern formed thereon.

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