KR20080060450A - Cmos image sensor and method for fabricaing the same - Google Patents

Abstract

A CMOS image sensor and a manufacturing method thereof are provided to reduce a gap between micro lenses to increase the fill factor by forming a hole with a predetermined depth at a flattening layer between micro lenses. A plurality of photodiodes(32) are formed on a semiconductor substrate(31), and generate charges according to the incident light. An interlayer dielectric layer(33) is formed on a entire surface of the semiconductor substrate including the photodiodes. A plurality of color filter layers(34) are formed on the interlayer dielectric layer, corresponding to the photodiodes. A flattening layer(35) is formed on the entire surface of the substrate including the color filter layer. A hole(37) is formed as a predetermined depth on the flattening layer at a border site of the color filter layer. A micro lens(39) is formed at the flattening layer.

Description

CMOS image sensor and its manufacturing method {CMOS IMAGE SENSOR AND METHOD FOR FABRICAING THE SAME}

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

2 is a view for explaining the problem of the CMOS image sensor according to the prior art.

3 is a cross-sectional view showing a CMOS image sensor according to the present invention.

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

5 is a view for explaining the characteristics of the CMOS image sensor according to the present invention.

The present invention relates to an image sensor and a method of manufacturing the same.

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.

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

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

As shown in FIG. 1, 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.

2 is a view for explaining a problem of the CMOS image sensor according to the prior art.

That is, FIG. 2 is a diagram for explaining a problem that is structurally present when forming a microlens of a conventional CMOS image sensor.

As shown in FIG. 2, a gap of about 0.3 μm exists between the microlenses and the microlenses, and corner rounding is particularly performed at the corners of the microlenses, that is, the portions contacting the four microlenses. ) Is formed and unfocused light passes through and senses in the lower photodiode, which directly reduces the quality of the image. Although the microlens space is reduced to some extent during the reflow during the microlens formation process, the gap is rounded further as the photodiode becomes smaller and does not significantly decrease.

The present invention reduces the gap by reducing the corner rounding phenomenon of the microlenses, thereby increasing the fill factor by irradiating the photodiode to the light of the portion where the fill factor decreases due to the reduction of the photodiode size to the light which has not been reached. In addition, it is an object of the present invention to provide a CMOS image sensor and a method of manufacturing the same to improve the quality of the image sensor by reducing the light passing area between unnecessary gaps in addition to focusing.

CMOS image sensor according to the present invention comprises at least one photodiode formed on the semiconductor substrate to generate a charge according to the amount of incident light; An interlayer insulating layer formed on an entire surface of the semiconductor substrate including the photodiode; A plurality of color filter layers formed on the interlayer insulating layer to correspond to the photodiodes; A planarization layer formed on an entire surface of the semiconductor substrate including the color filter layer; A hole formed at a predetermined depth in the planarization layer of the color filter layer boundary; And a microlens formed on the planarization layer such that a corner portion extends in the hole of the planarization layer.

A method of manufacturing a CMOS image sensor according to the present invention may include forming an interlayer insulating film on an entire surface of a semiconductor substrate on which a plurality of photodiodes are formed; Forming a plurality of color filter layers on the interlayer insulating layer so as to correspond to the respective photodiodes; Forming a planarization layer on a front surface of each color filter layer; Selectively removing the planarization layer corresponding to the boundary portion of each color filter layer to form a plurality of holes having a predetermined depth from a surface; And forming a microlens on the planarization layer such that corner portions extend to both sides of each hole.

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

3 is a cross-sectional view showing a CMOS image sensor according to the present invention.

As shown in FIG. 3, at least one photodiode 32 is formed on the semiconductor substrate 31 to generate electric charges according to the amount of incident light, and a front surface of the semiconductor substrate 31 including the photodiode 32. The interlayer insulating layer 33 formed on the interlayer insulating layer 33, the color filter layers 34 of R, G, and B which respectively pass light of a specific wavelength band, and the color filter layer 34 A planarization layer 35 formed on the entire surface of the semiconductor substrate 31 including a hole, a hole 37 formed at a predetermined depth in the planarization layer 35 at the boundary of the color filter layer 34, and the planarization layer 35. The micro lens 39 is formed in a convex shape having a predetermined curvature and extends into the hole 37 to pass through the color filter layer 34 to condense light to the photodiode 32. It is composed.

4A to 4F 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 a multi-layer, although not shown, after forming one interlayer insulating layer to form a light shielding layer for preventing light from being incident to a portion other than the photodiode 32 region. After that, 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 is applied onto the planarization layer 35, and then the photoresist 36 is selectively patterned by an exposure and development process.

In this case, the patterned photoresist 36 has a boundary portion of the color filter layer 34 open. That is, it is an area where corner portions of the microlenses to be formed later are formed.

In addition, the photoresist 36 is exposed to light using a photomask after the photomask is formed so that a cross-shaped hole is formed at a point where four microlenses to be formed subsequently meet.

In addition, the hole 37 is formed in the shape of any one of the cross-shaped, rhombic, octagonal, circular.

Subsequently, the planarization layer 35 is selectively removed using the patterned photoresist 36 as a mask to form a hole 37 having a predetermined depth from the surface.

As shown in FIG. 4E, in order to remove the photoresist 36 and focus light efficiently on the photodiode 32 on the entire surface of the semiconductor substrate 31 including the hole 37. Apply photoresist.

Subsequently, the photoresist is selectively patterned by an exposure and development process to form a microlens pattern 38.

In the case where the photoresist is a positive resist, the microlens may be exposed to a front exposure because the transmittance is improved only when the photo active compound of the initiator, which is an absorber of the photoresist, is decomposed. The photo active compound remaining in the pattern 38 is decomposed.

On the other hand, through the front exposure to the microlens pattern 38 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 portion of a heat treatment of 150 ° C. or higher in a state where the semiconductor substrate 31 on which the microlens pattern 38 is formed is placed on a hot plate (not shown). The lens pattern 38 is reflowed to form a hemispherical microlens 39.

Subsequently, the microlens 39 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.

On the other hand, when the microlens pattern 38 is reflowed, the microlens pattern 38 is reflowed to the inside of the hole 36 formed in the surface of the planarization layer 34 to become a corner portion of the microlens 39.

5 is a view for explaining the characteristics of the CMOS image sensor according to the present invention.

That is, to form a hole having a predetermined depth in the planarization layer and to form a cross-shaped hole (hole) at the point where the four microlenses meet as shown in Figure 5 so that the corner portion of the microlens extends to the hole portion After that, the etching process of the planarization layer is performed. If the microlens pattern is formed and reflowed after the hole is formed, photoresist flows along the wall between the holes to reduce the gap.

On the other hand, the shape of the hole is formed cross-shaped to have a maximum ML surface area, but may also be a rhombus or octagonal shape.

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 CMOS image sensor and its manufacturing method according to the present invention have the following effects.

First, by forming a hole having a predetermined depth in the planarization layer between the microlenses, the gap between the microlenses may be reduced to increase the fill factor to increase the amount of irradiated light, thereby improving the quality of the image sensor.

Second, it is possible to improve the quality of the image sensor by reducing the noise caused by conventionally unfocused through the gap.

Claims (4)

A photodiode formed on at least one semiconductor substrate and generating charges according to the amount of incident light; An interlayer insulating layer formed on an entire surface of the semiconductor substrate including the photodiode; A plurality of color filter layers formed on the interlayer insulating layer to correspond to the photodiodes; A planarization layer formed on an entire surface of the semiconductor substrate including the color filter layer; A hole formed at a predetermined depth in the planarization layer of the color filter layer boundary; And And a microlens formed on the planarization layer such that a corner portion extends in the hole of the planarization layer. The method of claim 1, The hole is a CMOS image sensor, characterized in that formed in the shape of any one of cross-shaped, rhombic, octagonal, circular. Forming an interlayer insulating film on an entire surface of the semiconductor substrate on which the plurality of photodiodes are formed; Forming a plurality of color filter layers on the interlayer insulating layer so as to correspond to the respective photodiodes; Forming a planarization layer on a front surface of each color filter layer; Selectively removing the planarization layer corresponding to the boundary portion of each color filter layer to form a plurality of holes having a predetermined depth from a surface; And And forming a microlens on the planarization layer such that corner portions extend to both sides of each of the holes. The method of claim 3, wherein The hole manufacturing method of the CMOS image sensor, characterized in that formed in any one shape of cross, rhombus, octagon, circle.

Images