KR20070003007A - Method for fabricating cmos image sensor - Google Patents

Abstract

A method for manufacturing a CMOS image sensor is provided to improve photo efficiency by obtaining an aiming curvature from a microlens in spite of the decrease of size of a pixel. A plurality of microlens resin layers are formed on a predetermined structure corresponding to each pixel. A pin type rod reaches for each resin layer. A microlens(36) with an aiming curvature is formed by performing a heat treatment on the resultant structure. The pin type rod is made of a silicon oxide layer. The pin type rod reaches a predetermined position adjacent to the resin layer. The predetermined position and the resin layer are spaced apart from as much as 0.1 micrometer.

Description

Manufacturing method of CMOS image sensor {METHOD FOR FABRICATING CMOS IMAGE SENSOR}

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 5B are sectional views showing the manufacturing method of the image sensor according to the prior art.

Figure 6 is a cross-sectional view showing a problem of the image sensor according to the prior art.

7A to 7B are cross-sectional views illustrating a method of manufacturing a CMOS image sensor according to a preferred embodiment of the present invention.

8 is a cross-sectional view of the CMOS image sensor of the present invention.

Explanation of symbols on the main parts of the drawings

32, 35 insulating film 34 color filter

36: microlens 37: pin-shaped insulator

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CMOS image sensor and a manufacturing method thereof, and more particularly, to an inter-element insulation of a 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 may 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 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 sensing node 101 through the transfer transistor 11.

Since the sensing node 101 is connected to the gate of the driving transistor 13, the driving transistor 13 has a voltage level of the active region 103 bonded to one end in accordance with a voltage applied to the sensing node 101. Will drive. 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.

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

In addition, although not shown here, a macro lens that directly receives light incident from the outside and transmits the light to the micro lens is disposed above 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 floating node SD, and the source terminal of the driving transistor is driven in response to the regulated voltage.

5A to 5B are cross-sectional views illustrating a manufacturing method of an image sensor according to the prior art.

As shown in FIG. 5A, the method of manufacturing an image sensor according to the related art forms a flattening film 22 in a state where a predetermined process is completed, and forms a color filter 25 thereon.

Subsequently, a flattening film 24 called an OCL film (over coating layer) is formed to cover the color filter 25.

Next, the resin film pattern 26a is formed so as to be aligned with the color filter 25.

Subsequently, as shown in Fig. 5B, the microlens 26 aligned with the color filter 25 is formed using the resin film pattern 26a.

6 is a cross-sectional view showing a problem of the image sensor according to the prior art. Hereinafter, the operation of the CMOS image sensor and the problems of the CMOS image sensor according to the related art will be described.

The CMOS image sensor consists of a light-receiving unit for integrating light and a circuit for converting light into an electrical signal. Efforts have been made to increase the ratio of the area of the light sensing portion to the overall image sensor element in order to increase the light sensitivity. However, since the logic circuit portion cannot be essentially removed, this effort is limited under the limited area.

Therefore, in order to increase the light sensitivity, a condensing technology that changes the path of light incident to a region other than the light sensing portion and collects it into the light sensing portion has emerged. For this purpose, the image sensor uses a method of forming a microlens on the color filter. I use it.

The microlens is formed by applying a solution of a resin composition to be used as a lens on a surface of a substrate, developing the microlens on each pixel, and baking and performing a heat-out process to form a convex lens. In this case, if the size of the resin composition to be formed as a micro lens is also reduced in order to achieve high resolution, the micro lens formed after the heat treatment is brought into contact with a neighboring micro lens to form a lens having a desired curvature. Will not.

Therefore, the light coming through the micro lens is very large and the focal length cannot collect the light properly in the lower photodiode, and also causes interference with neighboring lenses.

As shown in FIG. 6, when the micro lens and the micro lens are stuck together, the focal point F may not be formed in the photodiode formed at the bottom of the micro lens.

The present invention has been proposed to solve the above-described problems, and aims to provide a CMOS image sensor capable of collecting as much light as possible on a photodiode by increasing the curvature of the microlens.

The present invention comprises the steps of forming a plurality of resin film for microlenses corresponding to each pixel; Approaching a plurality of stick-shaped sticks corresponding to the plurality of resin films to the resin film; And performing a heat treatment process so that the resin film becomes a micro lens having a curvature around the pin (due to surface tension).

The present invention is to solve the problem that the size of one pixel is small, it is difficult to maintain the curvature of the micro lens formed on each pixel, so that it is difficult to focus the light, and after forming a lens shape of the resin material on each pixel, In order to form a lens shape, the invention is an invention in which a pin-shaped fine insulating film is brought into contact with an upper portion of a lens.

This acts to hold the resin film with surface tension on each pixel that flows during heat treatment, thereby preventing cohesion with neighboring resin films, thereby making it possible to form small microlenses with a large curvature radius. Can be effectively focused on the photodiode.

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. .

7A to 7B 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. 7A, in the method of manufacturing the CMOS image sensor according to the present embodiment, after forming a photodiode corresponding to each pixel and an upper wiring structure, a planarization film 32 is formed, and the color filter 34 is formed. Is formed, and a planarization film 35 called an OCL film is formed.

Subsequently, a resin film 36a formed of a microlens is formed to align with the color filter 34. Subsequently, an insulating film having a pin shape is placed on top of each resin film 36a to 0.1um of each resin film 36a.

Here, the resin film can use all the photosensitive film materials.

Subsequently, as shown in Fig. 7B, the resin film 36a is heat treated (processed at 250 degrees or less) to form the microlens 36.

As the temperature increases during the heat treatment, the resin film rises as it flows and contacts the upper fin. Contact with the upper pins prevents contact with neighboring lenses by surface tension.

The pin-shaped insulating film uses a silicon wafer or a glass substrate. In addition, the pin-shaped insulating film may be formed by forming a silicon oxide film about 5000 ~ 5um on the silicon substrate, and then selectively etched at the same interval as the microlens interval. Limit the pin width to within 1.5um.

At this time, if the temperature is dropped to about 150 degrees or less so that the upper pin falls, it is possible to make a micro lens having a small radius of curvature of a desired shape. The process of forming a multi-layered metal wiring and a multi-layered insulating film is the same as a conventional process and is omitted.

8 is a cross-sectional view of the CMOS image sensor of the present invention.

As shown in Fig. 8, it can be seen that the focal point F is formed on the photodiode due to the microlens with a large radius of curvature, whereby more light is focused.

Reference numeral 39 is an isolation layer, 31 is a photodiode, 32 is an interlayer insulating film, and 33 is a metal wiring.

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.

Highly integrated by the present invention, even if the size of one pixel is small, the curvature of the micro lens can be formed to the desired degree, so that more light can be collected.

In addition, even if the size of the pixel is small, the phenomenon of sticking with the neighboring micro lenses is eliminated, and the phenomenon in which light incident between neighboring pixels interferes with each other disappears, thereby realizing a clearer image.

Claims (3)

Forming a plurality of resin films for microlenses corresponding to each pixel; Approaching a plurality of stick-shaped sticks corresponding to the plurality of resin films to the resin film; And Performing a heat treatment process so that the resin film becomes a micro lens having curvature around the pin (due to surface tension) CMOS image sensor comprising a. The method of claim 1, The plurality of pins in the form of pins CMOS image sensor, characterized in that formed using a silicon oxide film. The method of claim 1, Proximity of the pin-shaped stick The CMOS image sensor, characterized in that the pin-shaped sticks to each of the plurality of resin films to the nearest 0.1um.

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