KR20050039160A - Image sensor having color filter used for inner lens and the fabricating method thereof - Google Patents

Abstract

The present invention relates to an image sensor and a method for manufacturing the same, and more particularly, to an image sensor and a method for manufacturing the same using a color filter as an internal lens. The present invention relates to an image sensor and a method for manufacturing the same, which improves the light collection efficiency and color reproducibility by a simple process by patterning the color filter as if it were a microlens to perform the role of the color filter as well as the inner lens. The present invention for this purpose, an image sensor having a color filter and a microlens, comprising: a semiconductor substrate having a photodiode; A plurality of metal wirings formed on the substrate; A passivation film formed on the metal wiring; A color filter formed on the passivation film and serving as an internal lens; And a microlens formed on the color filter.

Description

IMAGE SENSOR HAVING COLOR FILTER USED FOR INNER LENS AND THE FABRICATING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor and a method of manufacturing the same, and more particularly, to an image sensor using a color filter as an internal lens and a method of manufacturing the same. In the present invention, the color filter is patterned as if it is a microlens, thereby simultaneously performing the role of the internal lens to improve the light collecting efficiency and color reproducibility of the image sensor by a simple process.

In addition, in the present invention, a thin overcoat layer (OCL) is introduced between the passivation film and the color filter to improve adhesion of the color filter. Therefore, in the present invention, the peeling phenomenon of peeling the color filter can be prevented, and thus the possibility of rework can be significantly reduced.

In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal, and may be roughly divided into a CMOS image sensor and a charge coupled device.

Among them, a charge coupled device (CCD) is a device in which charge carriers are stored and transported in a capacitor while individual metal-oxide-silicon (MOS) capacitors are located very close to each other. It is a device that adopts the switching method that detects the output by using MOS transistor as many as pixel by using CMOS technology that uses control circuit and signal processing circuit as peripheral circuit. .

In addition, the image sensor is composed of a light sensing portion for detecting light and a logic circuit portion for processing the detected light as an electrical signal to make data. The ratio of the area of the light sensing portion in the entire image sensor element is increased to increase the light sensitivity. Efforts have been made to increase the fill factor, but these efforts are limited in a limited area because the logic circuit part cannot be removed.

Therefore, a condensing technology has emerged to change the path of light incident to an area other than the light sensing portion to raise the light sensitivity, and to collect the light sensing portion. For this purpose, the image sensor uses a microlens on the Cali filter. The method of forming is used.

FIG. 1A is a circuit diagram showing a unit pixel composed of one photodiode PD and four MOS transistors in a conventional CMOS image sensor, and includes a photodiode 100 for generating photocharges by receiving light. The transfer transistor 101 for transporting the photocharges collected from the photodiode 100 to the floating diffusion region 102 and resets the floating diffusion region 102 by setting the potential of the floating diffusion region to a desired value and discharging electric charges. To the reset transistor 103, the drive transistor 104 to act as a source follower buffer amplifier, and the select transistor 105 to address to the switching role. It is composed. Outside the unit pixel, a load transistor 106 is formed to read an output signal.

FIG. 1B is a cross-sectional view showing an element cross section of a CMOS image sensor including such a unit pixel, a color filter, and microlenses.

Referring to this, the manufacturing process of the conventional CMOS image sensor is as follows. First, a field oxide film 11 defining an active region and a field region is formed on the semiconductor substrate 10.

Next, a unit pixel including the photodiode 12 is formed on the active region. In FIG. 1B, respective transistors constituting the unit pixel are not shown.

After the device isolation layer 11 and related elements including the photodiode 12 are formed, the interlayer insulating layer 13 is formed on the semiconductor substrate 10, and the first metal wiring 14 is formed on the interlayer insulating layer 13. Is formed.

Although FIG. 1B shows the case where two metal wires are used, more metal wires may be used, and the metal wires are intentionally laid out so as not to block the light incident on the photodiode 12. .

After the first metal wiring 14 is formed in this manner, the first interlayer insulating film 15 is coated on the first metal wiring. As the interlayer insulating film 15, a structure in which an oxide film / SOG film / oxide film is laminated is usually used.

Next, the second metal wiring 16 is formed on the first interlayer insulating film 15, and the second metal interlayer insulating film 17 is formed again on the second metal wiring 16.

In FIG. 1B, the metal wiring of two layers is used, the second metal wiring is the metal wiring located at the top, and then a passivation film forming process is performed.

In other words, the passivation film 18 is formed on the second interlayer insulating film 17 to protect the device from moisture, scratches and the like.

Next, after forming the planarization film (not shown) on the passivation film 18, the color filter 19 is formed on the planarization film or the color filter 19 is formed directly on the passivation film 18. May be

FIG. 1B shows a case where the color filter 19 is formed directly on the passivation film 18. As the color filter 19, a dyed photoresist is generally used, and one color filter 19 is formed for each unit pixel to separate colors from incident light.

All three color filters of blue, red, and green shown in FIG. 1B are formed using photoresist, and neighboring color filters are formed to overlap each other slightly.

Since the adjacent color filters are formed to overlap each other slightly in this way, a step occurs due to this, and to compensate for this, an overcoat layer (OCL) 20 is formed on the color filter 19.

Microlenses for collecting light must be formed on the flattened surface, which eliminates the step caused by the color filter. Therefore, as described above, the overcoating layer 20 formed on the color filter 19 serves to eliminate the step, and the overcoating layer is also made of a photoresist-based film.

Thereafter, the microlens 21 is formed on the overcoating layer 20 having the planarized surface. A method of forming the microlens 21 will be described below.

First, a photosensitive photoresist of a silicon oxide film series having high light transmittance is applied by using a spin-on-coater. Next, a patterning process using an appropriate mask is performed to form an angular microlens corresponding to each unit pixel.

Next, when a microlens having an angular form is flowed by applying a thermal process, a dome-shaped microlens as shown in FIG. 1B may be obtained.

In the CMOS image sensor according to the related art, as shown in FIG. 1B, all the light entering the chip passes through the microlens 21 and enters the photodiode through the color filter 19.

However, in the prior art, since light incident through the microlenses does not enter all of the photodiodes and the amount of light lost in the middle is not small, there is a disadvantage in that the light sensitivity characteristic is reduced.

That is, even if light is collected through a microlens, the incident light is refracted and reflected by the metal wiring, the oxide film, or the like, so that a considerable amount of light loss occurs.

In addition, when the color filter 19 is formed directly on the passivation film 18, the phenomenon that the color filter 18 is often lifted due to poor adhesion between the passivation film 18 and the color filter 19. This resulted in a deterioration of color reproducibility.

Since the color filters are not constituted as a whole but are patterned one by one for each unit pixel, the adhesion to the passivation film should be excellent, but this was not the case in the prior art.

In addition, if any one of the millions of color filters falls, it has to be reworked, which increases productivity and production cost.

An object of the present invention is to provide an image sensor and a method of manufacturing the same, which improve the light sensitivity characteristics of an image sensor by a simple process by using a color filter as an internal lens.

According to an aspect of the present invention, there is provided an image sensor including a color filter and a microlens, comprising: a semiconductor substrate on which a photodiode is formed; A plurality of metal wirings formed on the substrate; A passivation film formed on the metal wiring; A color filter formed on the passivation film and serving as an internal lens; And a microlens formed on the color filter.

In addition, the present invention provides a method of manufacturing an image sensor having a color filter and a microlens, the method comprising: forming a photodiode on a semiconductor substrate; Forming a plurality of metal wirings on the substrate; Forming a passivation film on the metal wiring; Forming a photoresist-based first overcoating layer on the passivation film; Forming a color filter serving as an inner lens on the first overcoating layer; Forming a planarization film on the color filter; And forming a microlens on the planarization layer.

In the present invention, the color filter is formed as a dome like a micro lens, so that the color filter also serves as an internal lens. In other words, rather than forming a separate internal lens to improve the light condensation, the shape of the color filter is implemented as a dome type, and the color filter can also be used as the internal lens, thereby improving the light sensitivity characteristics by a simple process.

To this end, in the present invention, a material having a refractive index larger than that of the conventional color filter forming material is used, and the shape of the color filter is also changed to a dome shape.

In addition, in the present invention, a thin overcoat layer is introduced between the passivation film and the color filter to improve the adhesion of the color filter. At this time, the newly introduced overcoating layer has a thin thickness of about 100 ~ 500Å, thereby minimizing the increase of the distance from the photodiode to the top layer to prevent performance degradation of the image sensor.

Hereinafter, the most preferred embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art can easily implement the technical idea of the present invention.

Figure 2 is a cross-sectional view showing a cross-sectional view of the CMOS image sensor formed according to an embodiment of the present invention with reference to this it will be described an embodiment of the present invention.

The process up to forming the passivation film 38 in Fig. 2 is the same as in the prior art. Referring to this point, first, a field oxide film 31 defining an active region and a field region is formed on the semiconductor substrate 30.

Next, a unit pixel including the photodiode 32 is formed on the active region. In FIG. 2, respective transistors constituting the unit pixel are not shown.

After the related devices including the device isolation layer 31 and the photodiode 32 are formed in this manner, the interlayer insulating layer 33 is formed on the semiconductor substrate 30, and the first metal wiring 34 is formed on the interlayer insulating layer 33. ).

Although FIG. 2 shows the case where two metal wires are used, more metal wires may be used, and the metal wires are intentionally laid out so as not to block the light incident on the photodiode 12. .

After the first metal wire 34 is formed in this manner, the first interlayer insulating film 35 is coated on the first metal wire. As the interlayer insulating film 35, a structure in which an oxide film / SOG film / oxide film is laminated is usually used.

Next, the second metal interconnection 36 is formed on the first interlayer insulating film 35, and the second interlayer insulation layer 37 is again formed on the second metal interconnection 36. In FIG. 2, the metal wiring of two layers is used, the second metal wiring is the metal wiring located at the top, and then the passivation film forming process is performed.

That is, the passivation film 38 is formed on the second interlayer insulating film 37 to protect the device from moisture, scratches and the like.

Next, a first overcoat layer 39 is formed on the passivation film 38. The first overcoating layer 39 is formed for the purpose of improving the adhesion of the color filter 40 to be subsequently formed.

The color filter 40 is made of a photosensitive film series material. When the color filter is directly formed on the passivation film 38, the color filter is often dropped because the adhesion between the passivation film and the color filter is not good.

In the present invention, in order to prevent this, a first overcoating layer 39 of the same photoresist layer is introduced between the color filter 40 and the passivation film 38. That is, in the present invention, since the color filter is formed on the same photoresist-based first overcoating layer, the adhesive force may be improved to prevent the floating phenomenon as in the prior art.

In addition, the first overcoating layer 39 used in the embodiment of the present invention has a thin thickness of about 100 to 500 mW. This is to avoid increasing the distance from the photodiode to the top layer.

The distance from the photodiode to the uppermost layer is an important factor in the optical characteristics of the image sensor. In the present invention, the first overcoating layer 39 is newly introduced to increase the distance. The first overcoating layer 39 having a thin thickness of ˜500 mm 3 was used.

After forming the first overcoating layer in this manner, an internal lens combined color filter is formed.

In an embodiment of the present invention, a material having a larger refractive index than the conventional one is used to use the color filter as an internal lens. That is, the color filter photosensitive film used in the prior art had a refractive index of about 1.55, the color filter photosensitive film used in one embodiment of the present invention has a refractive index of about 1.69, preferably in the range of about 1.64 to 1.74. Have

As such, in the present invention, the color filter 40 is made of a material having a higher refractive index, and the color filter 40 is also implemented in a dome shape to serve as a lens.

Patterning the color filter in the dome form is similar to the method of forming the microlens, and a method of forming the blue filter will be described as an example.

First, the refractive index is about 1.64 to 1.74 and a color filter photosensitive film 40 dyed blue is coated on the first overcoating layer 39. Next, an exposure / development process using an appropriate mask (not shown) is performed to leave an angled photosensitive film only in a portion where the blue filter is to be formed, and the photosensitive film formed on the remaining portion is removed.

Then, blank exposure (Bleaching) using a stepper or the like is performed.

The above-described blank exposure process decomposes the PAC (Photo Active Compound) component present in the color filter-forming photosensitive film 40, and the flow proceeds smoothly when the thermal process is subsequently performed.

In other words, when the PAC component is decomposed through the exposure process, the binding force is reduced, so that the flow characteristics are also changed, and the dome-shaped color filter can be obtained through the flow process for a proper temperature (for example, 150 ° C.) and a proper time. have.

The red filter is formed using the above-described method of forming a blue filter, and the green filter is also formed in the same manner.

In the present invention, a material having a high refractive index is used as the photoresist for the color filter, and the shape of the color filter also has a hemispherical dome shape, so that the color filter also serves as an internal lens.

In the present invention, since the color filter focuses the light passing through the microlens once more, the efficiency of condensing the light into the photodiode without losing the light can be increased, thus increasing the amount of photocharges condensed into the photodiode. Therefore, color reproducibility can be improved.

As in the present invention, the color filter may not be used as the internal lens, but the internal lens may be improved, but condensation efficiency may be improved.

First, there is a disadvantage that the process is complicated because a separate internal lens must be added. Second, since a new layer is added, the distance from the photodiode to the top layer is increased. However, in the present invention, since the color filter also serves as the inner lens, it can be free from the above-mentioned disadvantages.

After forming the internal lens combined color filter 40 as described above, the second overcoating layer 41 is formed to compensate for the step difference caused by the color filter. Microlenses for collecting light must be formed on the flattened surface, which eliminates the step caused by the color filter.

Accordingly, the second overcoating layer 41 is formed on the first overcoating layer 39 including the color filter, and the second overcoating layer 41 is also formed of a photoresist film-based film.

Thereafter, the microlens 42 is formed on the second overcoating layer 41 having the planarized surface. A method of forming the microlens 42 will be described below.

First, a photosensitive photoresist of a silicon oxide film series having high light transmittance is applied by using a spin-on-coater. Next, a patterning process using an appropriate mask is performed to form an angular microlens corresponding to each unit pixel.

Next, when a microlens having an angular shape is flowed by applying a thermal process, a dome-shaped microlens as shown in FIG. 2 may be obtained.

Referring to the flow process for forming a dome-shaped microlens is as follows. First, after obtaining the angular form by patterning the microlens-forming photoresist film 32, blank exposure using a stepper is performed.

In one embodiment of the present invention, a blank exposure process was performed using light having a wavelength of 248 nm. Through this exposure process, the PAC (Photo Active Compound) component present in the microlens forming photosensitive film 42 is decomposed, and when the thermal process is subsequently performed, the flow proceeds smoothly.

That is, since the bonding force decreases when the PAC component is decomposed through the exposure process, a dome-type microlens can be obtained through a flow process for 5 minutes at a temperature of 150 ° C., and 200 ° C. again after such a flow process. Curing process is performed for 5 minutes to harden the shape of the microlens.

Thereafter, in order to protect the microlens, a process of forming a microlens passivation layer (not shown) including a low temperature oxide layer may be performed.

Referring to FIG. 2, in the image sensor according to the exemplary embodiment of the present disclosure, since the light primarily collected through the microlens is focused once again through the color filter, the light collecting efficiency may be increased without the conventional light loss.

The present invention having the features described above is applicable to other image sensors (for example, charge coupled devices) using color filters and micro lenses in addition to the CMOS image sensor.

As described above, the present invention is not limited to the above-described embodiments and the accompanying drawings, and the present invention may be variously substituted, modified, and changed without departing from the spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

When the present invention is applied to the image sensor, the light collecting efficiency of the image sensor can be increased by a simple process, and the color reproducibility can be drastically improved. Also, the color filter can be prevented from being lifted, thereby improving productivity and reducing the production cost. Can be.

1A is a circuit diagram showing a unit pixel structure of a conventional CMOS image sensor;

1B is a cross-sectional view showing a cross section of a conventional CMOS image sensor including a color filter and a micro lens;

2 is a cross-sectional view of the CMOS image sensor according to an embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

30: substrate

31: device isolation film

32: photodiode

33: interlayer insulating film

34: first metal wiring

35: first interlayer insulating film

36: second metal wiring

37: second interlayer insulating film

38: passivation film

39: first OCL membrane

40: Color filter with internal lens

41: planarization film

41: the second OCL membrane

42 microlens

Claims (9)

In the image sensor having a color filter and a micro lens, A semiconductor substrate on which a photodiode is formed; A plurality of metal wirings formed on the substrate; A passivation film formed on the metal wiring; A color filter formed on the passivation film and serving as an internal lens; And Micro lens formed on the color filter Image sensor made, including. In the image sensor having a color filter and a micro lens, A semiconductor substrate on which a photodiode is formed; A plurality of metal wirings formed on the substrate; A passivation film formed on the metal wiring; A first overcoating layer formed on the passivation film, the first overcoating layer having a thickness of 100 to 500 kPa; A color filter formed on the first overcoating layer and serving as an internal lens; A planarization film formed on the color filter; And Microlenses formed on the planarization layer Image sensor made, including. The method of claim 1, The color filter is an image sensor, characterized in that the refractive index is 1.64 ~ 1.74. The method of claim 3, wherein The color filter is an image sensor, characterized in that having a hemispherical dome shape. The method of claim 2, The color filter is an image sensor, characterized in that the refractive index is 1.64 ~ 1.74. The method of claim 5, wherein The color filter is an image sensor, characterized in that having a hemispherical dome shape. In the manufacturing method of an image sensor having a color filter and a micro lens, Forming a photodiode on the semiconductor substrate; Forming a plurality of metal wirings on the substrate; Forming a passivation film on the metal wiring; Forming a photoresist-based first overcoating layer on the passivation film; Forming a color filter serving as an inner lens on the first overcoating layer; Forming a planarization film on the color filter; And Forming a microlens on the planarization layer Method of manufacturing an image sensor comprising a. The method of claim 7, wherein Forming a color filter that also serves as an internal lens, A method of manufacturing an image sensor, characterized by forming a color filter having a hemispherical dome shape using a dyed photosensitive film having a refractive index of 1.64 to 1.74. The method of claim 7, wherein The first overcoating layer is a manufacturing method of the image sensor, characterized in that having a thickness of 100 ~ 500Å.