KR20070024787A - Cmos image sensor and method for fabricating the same - Google Patents

Abstract

A CMOS image sensor is provided to irradiate more light to a micro lens by avoiding deterioration of an optical characteristic generated by refraction or reflection of light wherein the refraction or reflection happens by a difference of refractivity between a micro lens protection layer and air. A photodiode(31) is formed in a substrate(30). A micro lens(38) is formed on the photodiode, aligned with the photodiode. A sub layer(40) is formed on the micro lens, having an intermediate index of refraction between those of the micro lens and the air. The sub layer comes in contact with the air, made of a porous low dielectric layer. A protection layer for protecting the micro lens is formed along the surface of the micro lens between the micro lens and the sub layer.

Description

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

1 is a circuit diagram showing one unit pixel in a CMOS image sensor.

FIG. 2 is a process cross-sectional view of four MOS transistors forming a unit cycle shown in FIG.

3 is a process plan view of four MOS transistors shown in FIG.

Figure 4 is a schematic cross-sectional view of an image sensor according to the prior art.

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

Explanation of symbols on the main parts of the drawings

30 substrate 31 photodiode

32: device isolation layer 33: interlayer insulating film

34: wiring 35: planarization film

36: color filter 37: planarization film

38: microlens 39: lens protective film

40: auxiliary film for improving the light sensitivity

The present invention relates to a CMOS image sensor and a manufacturing method thereof, and more particularly, to an optical characteristic improvement of the CMOS image sensor.

In general, an image sensor of a semiconductor device is a semiconductor device that converts an optical image into an electrical signal. Representative image sensor devices include a charge coupled device (CCD) and a CMOS image sensor.

Among them, the charge-coupled device is a device in which charge carriers are stored and transported in the capacitor while individual metal-oxide-silicon (MOS) capacitors are located very close to each other. By using CMOS technology that uses a signal processing circuit as a peripheral circuit, a MOS transistor (typically four MOS transistors) corresponding to the number of pixels is made and sequentially output using the MOS transistor.

1 is a circuit diagram showing one unit pixel in a CMOS image sensor.

Referring to FIG. 1, one unit pixel includes one photodiode 10 and four an MOS transistors 11, 12, 13, and 14. As shown in FIG. Four NMOS transistors 11, 12, 13, and 14 are a transfer MOS transistor 11 for transporting the photocharge generated in the photodiode 10 to the charge sensing node N, and a charge for the next signal detection. The reset MOS transistor 12 for discharging the charge stored in the sensing node 11, the drive MOS transistor 13 serving as a source follower 13, and the switching role can be addressed. It is composed of a select MOS transistor 14 to enable.

Four MOS transistors 11, 12, 13, and 14 and one photodiode 10 form one unit pixel, and are provided in the pixel array of the CMOS image sensor according to the number of unit pixels included in the CMOS image sensor. The number of photodiodes 10 and the number of MOS transistors for unit pixels corresponding thereto are determined.

FIG. 2 is a process cross-sectional view of four MOS transistors constituting a unit circuit shown in FIG. 1, and four MOS transistors 11, 12, 13, and 14 respectively transmit signals Tx, Rx, Dx, and Sx to gates. The light transmitted to the photodiode PD is transmitted to the output terminal.

3 is a process plan view of four MOS transistors shown in FIG.

As shown in FIG. 3, gate patterns Tx of four MOS transistors 11, 12, 13, and 14 for transferring electrons collected by light transmitted from the photodiode 10 to an output terminal. , Rx, Dx, and Sx are disposed, and active regions 101 to 104 are disposed to the left and right of the gate patterns Tx, Rx, Dx, and Sx, respectively.

In this case, the active region 101 is a charge sensing node that receives electrons collected by the photodiode.

Referring to the operation of one unit device briefly, electrons collected by light transmitted to the photodiode 10 are transferred to the charge sensing node 101 through the transfer transistor 11.

Since the charge sensing node 101 is connected to the gate of the driving transistor 13, the driving transistor 13 is the voltage of the active region 103 bonded to one end in accordance with the voltage applied to the charge sensing node 101. Drive the level. Subsequently, the select transistor 104 is turned on to output a voltage applied to the active region 103 through an output terminal.

4 is a cross-sectional view schematically showing an image sensor according to the prior art.

Referring to FIG. 4, a color filter array (CFA) such as blue, red, and green, which form unit pixels on the substrate 20 on which the photodiodes 10 and PD are formed, is formed. A color filter array 24 is disposed, and a flattening film called an overcoating layer (OCL) 25 is formed thereon, and an upper portion of the region overlapping with the color filter array 14; Convex microlenses 16 are formed.

Multi-layered wirings 23 are formed between the multi-layered insulating films 22, and the wirings 23 are disposed in regions not overlapping with the photodiode 10. The wirings formed of metal serve as a light blocking film. do.

In addition, a plurality of MOS transistors (region A) are formed on the substrate 20 adjacent to the photodiode 10, which is a transfer transistor, a select transistor, a reset transistor, and a drive as described above in the case of a 4Tr unit pixel. The transistor is placed.

A protective film 27 is formed on the microlens 26 to protect the microlens 26 from scratches and the like. Reference numeral 29 denotes a device isolation film.

Also, although not shown here, a macro lens is disposed on the upper portion of the micro lens to directly receive light incident from the outside and transmit the light to the micro lens.

As described above, the voltage applied to the gate of the driving transistor is controlled by electrons transferred from the photodiode to the charge sensing node SD, and the source terminal of the driving transistor is driven in response to the regulated voltage.

Since the CMOS image sensor is a semiconductor device that converts an optical image into an electrical signal, an area for receiving light is very important.

Efforts have been made to increase the ratio of the area of the light-sensing portion of the entire image sensor element to increase the light sensitivity. However, since the logic circuit portion cannot be removed, these efforts are under limited area, but there are limitations. .

Therefore, in order to increase the light sensitivity, a light condensing technology that changes the path of light incident to a region other than the light sensing region and collects the light sensing portion has emerged. This technique is a micro lens technology.

In addition, the image sensor for implementing a color image is a color filter array is arranged on the upper part of the light sensing portion for generating and measuring the photocharge by receiving light from the outside. Color filter arrays generally consist of three color filters: red, green and blue.

These micro lenses and color filters are formed using a photosensitive film, and have a light film quality.

Looking at the manufacturing process of the CMOS image sensor currently used to form a protective film 27 as a final layer on the micro lens of the pixel portion. Therefore, the protective film is in contact with air.

At this time, the refractive index of the microlens is 1.6, the refractive index of the insulating film used as the protective film is 1.5, and the air coming into contact with the protective film is 1.0. The difference in refractive index between the microlens and the protective film is hardly noticeable, but the difference in refractive index between the air and the protective film is about 0.5.

This difference in refractive index reduces the amount of light that does not transmit all the light into the pixel and is refracted or reflected and reaches the photodiode, which may eventually cause deterioration of optical characteristics.

This problem is exacerbated as the difference between the refractive index of the top surface of the CMOS image sensor, that is, the film in contact with the air and the refractive index between the air is larger.

The present invention has been proposed to solve the above problems, and provides a CMOS image sensor and a method of manufacturing the same, by reducing the difference in refractive index between the top end of the CMOS image sensor and the air, more light can be incident to the micro lens. The purpose.

The present invention comprises the steps of forming a photodiode on the substrate; Forming a micro lens on the photodiode to be aligned with the photodiode; And forming an auxiliary film having a value between a refractive index of the microlens and a refractive index of the air on the microlens, wherein the auxiliary film is manufactured to be in contact with the air. to provide.

The present invention also provides a photodiode, a microlens formed on the photodiode so as to be aligned with the photodiode, and disposed on the microlens, and having a value between a refractive index of the microlens and a refractive index of air. It is provided with an auxiliary film, it provides a CMOS image sensor, characterized in that the auxiliary film is configured to contact with air.

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

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

As shown in FIG. 5A, a method of manufacturing a CMOS image sensor according to the present embodiment will be described. First, a photodiode 31 is formed on a substrate 30 on which an element isolation film 32 is formed, and a multilayered structure is formed thereon. A multilayer insulating film 33 for insulating the wiring 34 and the multilayer wiring 34 is formed.

Subsequently, as shown in Fig. 5B, a planarization film 35 called an OCL (over coating layer) film is formed.

Subsequently, as shown in FIG. 5C, the color filter 36 is formed to be aligned with the photodiode 31.

Subsequently, as shown in FIG. 5D, a planarization film 37 called an over coating layer (OCL) film is formed so as to cover the color filter 36. As shown in FIG.

Subsequently, as shown in FIG. 5E, the microlens 38 is formed to be aligned with the color filter 36.

Next, as shown in FIG. 5F, a protective film 39 is formed to cover the microlens.

Then, as shown in Fig. 5G, a porous low-K on the protective film 39 is coded as an auxiliary film 40 for improving light sensitivity. At this time, the auxiliary layer 40 coats a solution containing a matrix and porogen using a coater. In addition, the heating process may be further performed to facilitate the curing of the matrix and the decomposition of the porogen.

As described above, in the exemplary embodiment of the present invention, the refractive index of the microlens protective film and the refractive index of the air are reduced in order to reduce a phenomenon in which optical characteristics deteriorate due to the refraction or reflection of light caused by the difference in refractive index between the protective film of the microlens and the air. A material having a value of between is formed on the protective film of the microlens as an auxiliary film 40 for improving light sensitivity.

By doing so, the light transmittance can be increased, thereby increasing the amount of light incident on the microlens.

As a result of the calculation using Snell's law, it is expected that the required refractive index of the auxiliary film 40 for the improvement of light sensitivity is about 100% when the required refractive index is about 1.22.

However, it is difficult to form a film having such a low refractive index by the CVD method currently used. In order to solve this difficulty, the refractive index can be easily adjusted by facilitating the adjustment of the film formed through the introduction of pore (all values between about 1.1 and 1.5 can be realized). It is possible to form a dielectric low-k.

In addition, as an auxiliary film 40 for improving the photosensitivity, a SOG (spin on glass) film of about 1.35 may be used, but a porous low-K having a lower refractive index by adjusting pore size and pore distribution. It is more effective than this.

In addition, as the size of the pattern becomes smaller, the wiring is used as copper. In this case, a porous low-K film is absolutely necessary as an insulating film of the copper wiring. In this case, therefore, process troubles can be reduced.

In addition, in order to increase the incident amount of light, a porous low-K may be formed in addition to the protective film of the microlens, which may be formed at a position having a required refractive index between 1.1 and 1.5. In this case, when the pattern is formed using the photoresist film, the porous low-K film may serve as an antireflction film.

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.

According to the present invention, a problem of deterioration of optical characteristics caused by refraction or reflection of light due to the difference in refractive index between the microlens passivation layer and the air may be solved, and more light may be incident on the microlens.

In particular, by using the auxiliary film 40 for improving the light sensitivity of about 1.22, the optical properties can be improved without replacing the other film, the improvement is 5% or more.

Claims (12)

Forming a photodiode on the substrate; Forming a micro lens on the photodiode to be aligned with the photodiode; And Forming an auxiliary film on the microlens having a value between a refractive index of the microlens and a refractive index of air; And a method of manufacturing the CMOS image sensor, wherein the auxiliary film is manufactured to be in contact with air. The method of claim 1, The auxiliary film is a method of manufacturing a CMOS image sensor, characterized in that it has a refractive index within 1.0 ~ 1.5. The method of claim 2, The auxiliary layer has a refractive index of 1.22 manufacturing method of the CMOS image sensor. According to claim 1, The auxiliary film is a method of manufacturing a CMOS image sensor, characterized in that formed by a porous low-k (porous low-K). The method of claim 4, wherein The auxiliary film is a method of manufacturing a CMOS image sensor, characterized in that for forming a solution containing a matrix and porogen (porogen) by using a coater (coater). The method of claim 5, The method of manufacturing a CMOS image sensor further comprising the step of performing a heating process for facilitating curing of the matrix and decomposition of porogen. The method of claim 1, And forming a protective film along the surface of the microlens to protect the microlens between the microlens and the auxiliary film. Photodiode; A micro lens formed on the photodiode to be aligned with the photodiode; And An auxiliary film disposed on the microlens and having a value between a refractive index of the microlens and a refractive index of air; And a secondary film is configured to be in contact with air. The method of claim 8, The auxiliary film is a CMOS image sensor, characterized in that it has a refractive index within 1.0 ~ 1.5. The method of claim 9, The auxiliary film has a refractive index of 1.22 CMOS image sensor. According to claim 10, The auxiliary film is a CMOS image sensor, characterized in that the poros low-k (porous low-K). The method of claim 11, wherein And a microlens protective film disposed between the microlens and the auxiliary film along the surface of the microlens to protect the microlens.

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