KR100660328B1 - Method for manufacturing of cmos image sensor - Google Patents

Abstract

A method for manufacturing a CMOS image sensor is provided to uniformly form a micro lens and to improve characteristics of an image sensor by using an imprint manner. An interlayer dielectric(203) is formed on the whole surface of a semiconductor substrate(201) where plural photo diodes(202) and all sorts of transistors are formed. A color filter layer(204) is formed on the interlayer dielectric to be opposite to each photo diode. A planarization layer(205) is formed on the whole surface including the color filter layer. The planarization layer is selectively removed to form a trench having a predetermined depth from the surface. A photoresist(207) is applied on the whole surface of the semiconductor substrate including the trench. A mold(208) where a lens shape is patterned is aligned to the semiconductor substrate where the photoresist is applied. The mold is overlapped with the semiconductor substrate where the photo resist is applied. A predetermined pressure and heat are given to the mold to transfer the patterned lens shape of the mold to the photo resist. The mold is removed from the semiconductor substrate to form a micro lens in the trench of the planarization layer.

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 5H 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

201: semiconductor substrate 202: photodiode

203: interlayer insulation layer 204: color filter layer

205: planarization layer 206: trench

207: photosensitive liquid 208: mold

209: Micro Lens

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 select 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 select 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, a process of forming a microlens after reducing the thickness of the semiconductor passivation may be applied. In this case, the uniformity of application of the photoresist may be reduced due to the step difference. 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 on the entire surface including the color filter layer, selectively removing the planarization layer to form a trench having a predetermined depth from a surface, and forming the trench; Applying a photoresist to the entire surface of the semiconductor substrate, including aligning a mold having a desired lens pattern on the semiconductor substrate to which the photoresist is applied, and overlaying the mold with a semiconductor substrate coated with the photoresist The patterned lens shape is applied to the mold by applying heat at the same time. It characterized by forming, including the steps of forming a micro lens in the trench of the planarization layer to remove the mold from the semiconductor substrate for transferring the group photoresist.

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 on the mold 31 to the polymer thin film 33 formed on the semiconductor substrate 32 to form a polymer thin film 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 5H 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 203 is formed on a semiconductor substrate 201 on which a plurality of photosensitive devices, for example, photodiodes 202 and various transistors (see FIG. 1) are formed. do.

Here, the interlayer insulating layer 203 may be formed in multiple layers, and although not shown, a light shielding layer for preventing light from being incident on a portion other than the photodiode 202 after forming one interlayer insulating layer. After formation, an interlayer insulating layer is formed again.

As shown in FIG. 5B, color filter layers R, G, and B are applied to the interlayer insulating layer 203 using a salty resist and then subjected to an exposure and development process to filter light for each wavelength band. 204).

Here, each color filter layer 204 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 of a single color filter layer 204 Form into layers.

As shown in FIG. 5C, silicon nitride is applied to the front surface of the semiconductor substrate 201 including the color filter layer 204 to prevent moisture and heavy metals from penetrating the EMC and the outside. (silicon nitride) film is deposited to form a planarization layer 205.

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 205.

Here, in the state in which the planarization layer 205 is formed, the pad and the scribe line portion of the planarization layer 205 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, in order to increase the amount of light incident on the photodiode 202, a trench 206 having a predetermined depth from a surface is selectively removed by selectively removing the planarization layer 205 of a portion where a microlens is to be formed. To form.

As shown in FIG. 5E, a microlens photosensitive liquid 207 is coated on the entire surface of the semiconductor substrate 201 including the trench 206.

As shown in FIG. 5F, the mold 208 having a pattern formed in a desired lens shape (for example, hemispherical shape) is aligned on the semiconductor substrate 201 to which the photosensitive liquid 207 is applied.

In this case, the material of the mold 208 uses poly dimethylsiloxane (PDMS).

As shown in Fig. 5G, the mold 208 and the semiconductor substrate 201 to which the photosensitive liquid 207 is applied are opposed to each other, and then a thermal process is performed in a state where pressure is applied.

Here, the thermal process is performed so that the photoresist 207 can maintain an accurate shape after overlapping a mold on the semiconductor substrate 201 to which the photoresist 207 is applied.

As shown in FIG. 5H, the mold 208 is separated from the semiconductor substrate 201 to have a microlens having the same shape as the pattern formed in the mold 208 in the trench 206 of the planarization layer 205. 209 is formed.

Meanwhile, in the present invention, after the trench 206 is formed in the planarization layer 205, the microlens 209 is formed in the trench 206 to reduce the distance between the microlens 209 and the photodiode 202. The sensitivity of the image sensor may be improved by minimizing the loss of light incident to the photodiode 202 through the lens 209.

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 lens shape is changed depending on the conditions of the thermal process and the overexposure process, the present invention can reduce the factor of the lens shape change by fixing after overlapping the mold accurately designed.

Third, the conventional lens forming method has to proceed with the thermal process and the overexposure process again after the general photographic process, the present invention can improve the productivity by shortening this process.

Fourth, when the microlens is formed after the step is made to improve the capability of the image sensor, there may be a disadvantage that the lens shape formed around the step may not be uniform in the conventional method. Microlenses can be formed uniformly.

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 on the entire surface including the color filter layer; Selectively removing the planarization layer to form a trench having a predetermined depth from a surface; Applying a photoresist to the entire surface of the semiconductor substrate including the trench; Arranging a mold in which a desired lens shape is patterned on the semiconductor substrate to which the photosensitive liquid is applied; Overlapping the mold with a semiconductor substrate coated with a photosensitive liquid, applying a predetermined pressure, and simultaneously applying heat to transfer the patterned lens shape to the photosensitive liquid; And removing the mold from the semiconductor substrate to form a microlens in the trench of the planarization 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. The method of claim 1, wherein the material of the mold is PDMS. The method of claim 1, wherein the mold has a hemispherical pattern formed thereon.

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