KR20060077075A - CMOS image sensor and its manufacturing method - Google Patents

Abstract

The present invention provides a CMOS image sensor that prevents light from being reflected, absorbed, and scattered in the transmission path of light passing through the microlens so that the light passing through the microlens can be focused on the photodiode as much as possible. To provide a method, to which the present invention comprises a photodiode; A micro lens for refracting and transmitting the incident light to the photodiode; And an optical waveguide disposed between a single material and the photodiode and the microlens.

In addition, the present invention comprises the steps of forming a photodiode on the substrate; Forming a multilayer insulating film on the photodiode; Selectively removing the multilayer insulating film to form a hole to expose the photodiode; Filling the hole with one material to form an optical waveguide; And forming a micro lens on the insulating film for optical waveguide.

Image sensor, micro lens, optical waveguide, photosensitive film.

Description

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

1 is a block diagram of a conventional CMOS image sensor.

2 is a circuit diagram showing the configuration of unit pixels of a conventional CMOS image sensor.

Figure 3 is a schematic cross-sectional view of an image sensor according to the prior art.

4A through 4D are cross-sectional views illustrating a manufacturing process of an image sensor according to a preferred embodiment of the present invention.

5 is a cross-sectional view showing a light transmission path when the manufactured image sensor according to the present embodiment operates.

Figure 6 is a cross-sectional view showing a path of light transmission when the image sensor according to the prior art and the present invention operates.

7 is a conceptual diagram showing a parasitic capacitor influencing one wiring.

8 is a sectional view showing an image sensor according to a second embodiment of the present invention;

Explanation of symbols on the main parts of the drawings

20: substrate 21: photodiode                 

22: device isolation film 23: interlayer insulating film

24: wiring 25: passivation film

26: photosensitive film A: hole for the optical waveguide

27: micro lens

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to CMOS image sensors, and more particularly to a CMOS image sensor and a method of manufacturing the same, wherein light transmitted through a microlens is focused more on a photodiode.

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, and the CMOS image sensor is a control circuit and a signal processing circuit. It is a device that adopts a switching method of making MOS transistors by the number of pixels by using CMOS technology using a signal processing circuit as a peripheral circuit and sequentially detecting the output using the MOS transistors.

Efforts have been made to increase the photo sensitivity of the CMOS image sensor, one of which is the light condensing technology. CMOS image sensor is composed of photodiode for detecting light and CMOS logic circuit for processing the detected light as electrical signal and data.In order to increase the light sensitivity of image sensor, photodiode occupies the area of total photo sensor area. Efforts have been made to increase the size (commonly referred to as "fill factor"), but there is a limit to such efforts under a limited area since the logic circuit part cannot be removed.

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 photodiode and collects the photodiode has emerged. Such a technique is a microlens forming technology.

However, even if light is collected through the microlenses, the number of pixels accumulated is gradually increased, and the distance between the microlens and the photodiode disposed at the bottom thereof is gradually increased so that the light passing through the microlens cannot be focused. Effective delivery to photodiodes is becoming increasingly difficult.

1 is a block diagram of a conventional CMOS image sensor.

Referring to FIG. 1, a conventional CMOS image sensor includes a pixel array in which a plurality of unit pixels are arrayed, an ADC block for converting an analog signal output from the pixel array into a digital signal, and a digital value output from the ADC block. And a line buffer to store, a decoder / pixel driver for decoding the input address to select a unit pixel of the pixel array, and a control register and logic for controlling the decoder / pixel driver.

2 is a circuit diagram showing the configuration of unit pixels of a conventional CMOS image sensor.

FIG. 2 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 upon receiving light. A 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 a potential of the floating diffusion region to a desired value and discharging electric charge. A reset transistor 103 for supplying voltage, a drive transistor 104 serving as a source follower buffer amplifier by applying a voltage of a floating diffusion region to a gate, and an addressing role as a switching role. It consists of a select transistor 105 that performs the following. Outside the unit pixel, a load transistor 106 for reading an output signal is formed.

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

Referring to FIG. 3, a color filter array (CFA) such as blue, red, and green, which form unit pixels on the substrate 10 on which the photodiodes 11 and PD are formed, is formed. A color filter array 14 is disposed, and a flattening film called an overcoating layer (OCL) 15 is formed thereon, and an upper portion of the region overlapping the color filter array 14 is formed. Convex microlenses 16 are formed.                         

Multi-layered wiring 13 is formed between the multi-layered insulating films 12, and the wiring 13 is disposed in an area not overlapping with the photodiode 11, and the wiring formed of metal serves as a light blocking film. do.

In addition, a plurality of MOS transistors 18 regions are formed on the substrate 10 adjacent to the photodiode 11, which includes a transfer transistor, a select transistor, a reset transistor, and a drive transistor in the case of a unit pixel having a 4 Tr structure. do.

A protective film 17 is formed on the microlens 16 to protect the microlens 16 from scratches and the like. Reference numeral 9 denotes a device isolation film.

As described above, the CMOS image sensor collects an image of light incident through the microlens in the photodiode and converts the image into a voltage signal. At this time, a charge is generated in proportion to the intensity of light incident on the photodiode, and the generated charge is transferred to the internal circuit.

Therefore, as much light as possible must pass through the microlens and connected to the photodiode disposed at the bottom thereof to provide an image close to the real object.

However, as described above, as more pixels are integrated in the image sensor, the distance between the photodiode and the microlens is gradually increased, thereby decreasing the intensity of light transmitted to the photodiode.

In addition, due to the interlayer insulating layer disposed between the photodiode and the microlens in multiple layers, the light passing through the microlens is reflected, absorbed, scattered, and many parts are lost.

As the CMOS image sensor becomes smaller and more highly integrated, the number of layers of wiring increases, and the increase in the wiring increases the distance between the photodiode and the microlens so that the entire focus is formed and the light is scattered as the light reaches the photodiode. There is a problem that the amount of light that reaches the diode is small.

In addition, the scattered light escapes through the interlayer insulating film, which affects other photodiodes, thereby reducing the vividness of colors. In order to improve this problem, the radius of curvature of the microlenses should be increased. However, the thickness of the microlenses is limited, and the limit of the curvature radius is also reached.

The present invention has been proposed to solve the above-mentioned problems, and in order to focus the light passing through the microlens as much as possible on the photodiode, the light is reflected, absorbed, scattered, etc. An object of the present invention is to provide a CMOS image sensor and a method of manufacturing the same.

The present invention is a photodiode; A micro lens for refracting and transmitting the incident light to the photodiode; And an optical waveguide disposed between a single material and the photodiode and the microlens.                     

In addition, the present invention comprises the steps of forming a photodiode on the substrate; Forming a multilayer insulating film on the photodiode; Selectively removing the multilayer insulating film to form a hole to expose the photodiode; Filling the hole with one material to form an optical waveguide; And forming a micro lens on the insulating film for optical waveguide.

DETAILED DESCRIPTION Hereinafter, exemplary 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. do.

4A to 4D are cross-sectional views illustrating a manufacturing process of an image sensor according to a preferred embodiment of the present invention.

As shown in FIG. 4A, a method of manufacturing a CMOS image sensor according to the present embodiment includes a photo transistor 21 and a MOS transistor corresponding to a photo diode on a substrate on which an element isolation film 22 is formed. Four morph transistors). Subsequently, a multilayer wiring 23 and an interlayer insulating film 24 for insulating each wiring 23 are formed thereon. Subsequently, a passivation film 25 is formed at the top.

Subsequently, as shown in FIG. 4B, the interlayer insulating film 24 is selectively removed to expose the photodiode to form the hole A for optical waveguide.

When forming the optical waveguide hole A, all the films including the interlayer insulating film / passivation film between the microlens and the photodiode are selectively removed so that the photodiode is exposed.

Subsequently, as illustrated in FIG. 4C, a photoresist having an etch reflectance of 2 to 2.5 or more is embedded in the hole A for the optical waveguide.

Then, as shown in Fig. 4D, a micro lens is formed.

Therefore, since the CMOS image sensor manufactured according to the present embodiment has only one photosensitive film on the path through which the light passing through the microlens is transmitted to the photodiode, the phenomenon of light refraction, scattering, etc. does not occur. Light can be focused on the photodiode.

By embedding a photoresist film having a reflectance in the range of 2 to 2.5 in the optical waveguide through which light is transmitted, since the silicon insulating film used as the interlayer insulating film has a reflectance of about 1.46, the light input through the microlens is adjacent to the adjacent interlayer insulating film in contact with the optical waveguide. Total reflection occurs at the interface with the. Therefore, the light reaches all the photodiodes at the bottom without being consumed in the optical waveguide.

As described above, total reflection occurs at or above the critical angle when light travels from the medium having the large refractive index to the small medium. The equation for obtaining the critical angle when the refractive index n1 progresses from n1 to n2 is sinφ = n2 / n1.

Since the refractive index of the photosensitive film used as the optical waveguide is 2.0 to 2.5, the refractive index of the silicon oxide film used as the interlayer insulating film is 1.45, so the critical angle is about 47 to 38 degrees.

The light passing through the microlenses is incident at a sufficient angle of 50 or more at the interface between the waveguide photosensitive film and the neighboring insulating film, so that the light is totally reflected to reach the photodiode.

5 is a cross-sectional view showing a light transmission path when the manufactured image sensor according to the present embodiment operates.

As shown in Fig. 5, the optical waveguide formed of the photosensitive film can be formed in a cylindrical shape. When the optical waveguide is formed in the shape of a cylinder, the angle of incident light may be higher, thereby making it easier to totally reflect the light on the lower photodiode. In addition, the lower region may be formed into a wider cylindrical shape or the upper portion of a wider cylindrical shape.

In addition to forming an optical waveguide using a photosensitive film, an optical waveguide may be formed of a silicon oxide film of SOG (Spin On Glass) series or a silicon oxide film or a silicon insulating film using HDP (High Density plasma). Also in this case, it may be formed with a difference between the adjacent insulating film and the refractive index.

6 is a cross-sectional view showing a light transmission path when the image sensor according to the related art and the present invention operate.

Referring to the left side of FIG. 6, conventionally, light incident through a microlens passes through a multi-layered insulating layer and cannot be focused on a lower photodiode, but a large amount of light has spread to other portions.

However, as shown in the right figure of FIG. 6, since the image sensor according to the present embodiment is a photosensitive film having one optical waveguide, total reflection occurs at the interface with neighboring insulating films, so that most of the incident light is lowered. Can be focused on a photodiode of

In addition, since light does not spread to neighboring areas, light scattering disappears and a clearer image can be realized.

7 is a conceptual diagram showing a parasitic capacitor influencing one wiring.

As shown in Fig. 7, in the signal transmission through the wiring, the signal transmission speed is determined by the magnitude of the resistance in the parasitic capacitor and the wiring generated in the wiring and the surrounding insulating film.

As shown, the smaller the parasitic capacitor generated by the adjacent insulating surface and the adjacent insulating surface, and the smaller the magnitude of the resistance of the wiring, the higher the speed at which the signal is transmitted through the wiring.

Previously, the most commonly used material for wiring was aluminum. Aluminum has many advantages that are easy to process in the manufacturing process, but as the image sensor becomes more integrated, it is difficult to form a considerable thickness of aluminum for wiring in order to have the desired conductivity.

Therefore, the image sensor according to the second preferred embodiment of the present invention is formed by using copper having better conductivity because of low resistance as wiring.

If copper is used as the wiring, the thickness of the wiring can be made thinner than before, so the gap between the micro lens and the photodiode can be further reduced.

8 is a cross-sectional view illustrating an image sensor according to a second exemplary embodiment of the present invention.                     

As shown in the right side of FIG. 8, it can be seen that the distance between the microlens and the photodiode is significantly reduced than before by using copper as a wiring instead of aluminum. In this case, the copper wiring may be formed by a well-known damascene process.

Therefore, if all the wiring used for the CMOS image sensor is used as copper, and an optical waveguide is formed of one material, most of the light incident through the micro lens can be focused on the photodiode.

In this case, a photosensitive film may be used as the material for the optical waveguide. In addition to forming an optical waveguide using the photosensitive film, an optical waveguide may be formed of a silicon oxide film of SOG (Spin On Glass) series or HDP (High Density plasma). An optical waveguide may be formed of a silicon oxide film or a silicon insulating film. Also in this case, it may be formed with a difference in refractive index between neighboring insulating films (so that a total reflection shape can occur).

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

According to the present invention, the light transmitted to the CMOS image sensor can focus more light on the photodiode.                     

In addition, the light can be prevented from being scattered through the interlayer insulating film, so that the scattered light can be fundamentally blocked to realize a vivid color as an image.

Claims (15)

Photodiode; A micro lens for refracting and transmitting the incident light to the photodiode; And An optical waveguide disposed of a single material between the photodiode and the microlens CMOS image sensor having a. The method of claim 1, The optical waveguide is a CMOS image sensor, characterized in that provided as a photosensitive film. The method of claim 1, The optical waveguide is a CMOS image sensor, characterized in that provided with a silicon oxide film of SOG series. The method of claim 1, The optical waveguide is a CMOS image sensor, characterized in that provided with a silicon oxide film or a silicon insulating film using HDP. The method of claim 1, And a multilayer insulating film in contact with the optical waveguide, wherein total reflection occurs at an interface with the insulating film adjacent to the optical waveguide. The method of claim 5, The material used as the optical waveguide is a CMOS image sensor, characterized in that it has a refractive index of 2.0 ~ 2.5. The method of claim 6, And a multilayer insulating film in contact with the optical waveguide is a silicon oxide film having a refractive index of 1.46. The method of claim 1, The optical waveguide is a CMOS image sensor, characterized in that provided in a cylindrical shape. The method of claim 8, The cylindrical image sensor, characterized in that the top surface is a wider shape than the bottom surface or the bottom surface is wider than the top surface. The method of claim 5 The CMOS image sensor, characterized in that the multilayer copper wiring is further provided between the multilayer insulating film. Forming a photodiode on the substrate; Forming a multilayer insulating film on the photodiode; Selectively removing the multilayer insulating film to form a hole to expose the photodiode; Filling the hole with one material to form an optical waveguide; And Forming a micro lens on the optical waveguide insulating film Method for manufacturing a CMOS image sensor comprising a. The method of claim 11, The method of manufacturing a CMOS image sensor, characterized in that the refractive index of the material embedded in the optical waveguide has a 2.0 ~ 2.5. The method of claim 11, The material embedded in the optical waveguide is a method of manufacturing a CMOS image sensor, characterized in that the photosensitive film. The method of claim 11, The material embedded in the optical waveguide is Method of manufacturing a CMOS image sensor, characterized in that formed by the silicon oxide film or silicon oxide film or silicon insulating film of the SOG series. The method of claim 12, Forming the multilayer insulating film A first step of forming a first silicon nitride film; Forming a silicon oxide film of at least two layers on the first silicon nitride film; And And forming a passivation film on the silicon oxide film using a silicon nitride film.

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