KR101201968B1 - Cmos image sensor and method for fabricating the same - 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 microlens for refracting and transmitting the incident light to the photodiode; And an insulating film for an optical waveguide disposed between a single material and the photodiode and the microlens.

The present invention comprises the steps of forming a photodiode on a 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 insulating film for an optical waveguide; And forming a microlens on the insulating film for the optical waveguide.

CMOS image sensor, microlens, photodiode.

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

Description of the Related Art [0002]

20: substrate 21: photodiode

22 interlayer insulating film 22a passivation film

23: wiring 25: photosensitive film pattern

28: etch stop film for borderless contact

29: device isolation layer 26: insulating film for optical waveguide

27: color filter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to CMOS image sensors, and more particularly, to CMOS image sensors and a method for 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 are being made to increase the photo sensitivity of the CMOS image sensor, one of which is a 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 converging technology that changes the path of light incident to a region other than the photodiode and collects the photodiode has emerged. This technique is a microlens forming technology.

However, even if the light is collected through the microlenses, the number of pixels to be integrated increases and the distance between the microlens and the photodiode disposed at the bottom of the microlens increases 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 the 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. The transfer transistor 101 for transporting the photocharges collected from the photodiode 100 to the floating diffusion region 102, and setting the potential of the floating diffusion region to a desired value and discharging the charge to discharge the floating diffusion region 102. A reset transistor 103 for resetting, a drive transistor 104 serving as a source follower buffer amplifier by applying a voltage of a floating diffusion region to a gate, and addressing as a switching role. The select transistor 105 performs a role. 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 4 Tr unit pixel. 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 converts an image of light incident through the microlens from 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 can pass through the microlenses 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 film 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 number of pixels included in the CMOS image sensor increases, the gap between the microlens and the photodiode increases more and more, so that light is hardly focused on the photodiode due to the multilayer interlayer insulating film.

The present invention has been proposed to solve the above-described problems, so that the light passing through the microlens can be focused on the photodiode as much as possible, so that 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 microlens for refracting and transmitting the incident light to the photodiode; And an insulating film for an optical waveguide disposed between a single material and the photodiode and the microlens.

The present invention comprises the steps of forming a photodiode on a 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 insulating film for an optical waveguide; And forming a microlens on the insulating film for the optical waveguide.

After the photodiode and the wiring process have been completed, the present invention provides a film on the exposed photodiode by removing the interlayer dielectric layer of the portion where the photodiode is formed by depositing a nitride film with a buffer oxide film and a passivation film. The present invention relates to a CMOS image sensor having improved light transmission characteristics by filling with FSG (Fluorinated Silica Glass, SiOF).

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

As shown in FIG. 4A, the method for manufacturing the CMOS image sensor according to the present embodiment first includes a photodiode 21 and a MOS transistor 28 corresponding to a photodiode on a substrate on which a device isolation layer 29 is formed. Four MOS transistors are provided, and a silicon nitride film 28 is formed as a borderless etch stop film on the top. Subsequently, a multilayer wiring 23 and an interlayer insulating film 22 for insulating each wiring 23 are formed thereon.

At this time, the interlayer insulating film formed on the uppermost wiring is the passivation film 22a. The plasma oxide chemical vapor deposition method (PE-CVD) forms a buffer oxide film in the range of 2000 to 3000 Pa, and the silicon nitride film is in the range of 3000 to 4000 Pa. Laminated to form. The buffer oxide film is formed of a TEOS (Tetra Ethyl Ortho Silicate) film.

Subsequently, an I-line photosensitive film is coated in a range of 10000 to 20000 kPa by a rotation coating method, and then a photosensitive film pattern 25 is formed by a photolithography process.

Subsequently, as shown in FIG. 4B, the silicon nitride film is etched using the photoresist pattern 25 as an etch mask under low etching selectivity, and then, as a result of etching with high etching selectivity. The insulating film 22 is etched.

At this time, the silicon nitride film 28 used as the borderless etch stop film serves as an etch stop film. Subsequently, the exposed silicon nitride film 28 is removed, and a hole A exposing the photodiode is formed.

Looking at the process of making the above-described hole (A) in detail, it is a large three-step etching process, the etching equipment is a device having a medium ion density (1x10 <10> ion / cm ³ ) I use it.

In the first etching process, the silicon nitride film used as the top passivation film is etched at a process pressure of 50 to 70 mT, a source power of 1500 to 2000 watts, and a bias power of 1500 to 1800 watts. In addition, the gas flow rate was 20 to 30 sccm for CHF ₃ , 50 to 80 sccm for CF ₄ , 10 to 20 sccm for O ₂ , and 400 to 600 sccm for Ar, and the etching selectivity between the silicon nitride film and the silicon oxide film formed at the bottom thereof was about 1.5 to 2.0. To proceed with the process.

The second etching step is a process of removing a multilayer interlayer insulating film.

In the second etching step, by using a gas having a high C / F ratio (C ₄ F ₈ , C ₅ F ₈ , ...) so that the photoresist pattern 25, the lower silicon nitride layer 28 and the high etching selectivity are maintained. Proceed to the etching process that generates a large amount of polymer (Polymer).

The bottom temperature of the substrate proceeds to 20 to 40 degrees, which can be expected to change the polymer layer deposited on the lower layer into a carbon (CFx) structure containing a lot of carbon components. In addition, by adding hydrogen to remove the free fluorine gas which lowers the etching selectivity generated by the plasma by adding a hydrogen-containing gas (CH ₂ F ₂ , ..) in this process, the added hydrogen By using the property of the polymer generation (F + H-> HF) to advantageously use the method to the silicon nitride film 28 of the bottom to act as an etch stop film.

At this time, the process pressure is 30 ~ 50mT, the source power is 1800 ~ 2000watt, the bias power is 1500 ~ 1700watt. In addition, the gas flow rate of C ₅ F ₈ is 10 ~ 25sccm, CH ₂ F ₂ is 2 ~ 3sccm, O ₂ is 10 ~ 20sccm, Ar is 400 ~ 600sccm to ensure that the slope is formed in the hole generated by the process. At this time, the angle of the inclined surface to be etched is about 80` 85 degrees.

The third process step is to etch the silicon nitride film 28 to expose the photodiode region.

In the third process step, the process pressure proceeds at 50 to 70 mT, with a source power of 800 to 1200 watts and a bias power of 200 to 300 watts. In addition, the gas flow rate was 50 to 80 sccm for CF ₄ , 10 to 20 sccm for CH ₂ F ₂ , 10 to 20 sccm for O ₂ , and 400 to 600 sccm for Ar so that the etching selectivity of the silicon nitride film and the oxide film was about 1.5. To minimize the damage to the bottom surface of the silicon substrate to proceed with the process.

Subsequently, as illustrated in FIG. 4C, the photosensitive film pattern 25 is removed by using an O ₂ plasma apparatus using microwave downstream.

Photoresist removal process conditions are 1500 ~ 1800w of power, in order to increase the reactivity of oxygen radicals (Oxygen Raical) decomposed by plasma, W / F temperature is carried out at about 0 ~ 200, O ₂ gas flow rate is 200 Proceed to ~ 300sccm.

Subsequently, as shown in FIG. 4D, an optical waveguide insulating film 26 made of one material is formed in the hole A. FIG.

At this time, when the CMOS image sensor is operated by the optical waveguide insulating film 26 formed, only the optical waveguide insulating film 26 made of one material passes through the light transmitted through the microlens to the photodiode at the bottom. As a result, scattering, refraction, and absorption of light disappear, and more light can be focused on the lower photodiode.

Looking at the process of forming the optical waveguide insulating film 26 in detail, the optical waveguide with a silicon insulating film using an aqueous solution in which Boric Acid (H3BO3) is added to an aqueous solution of supersaturated Hydrofluosilicic Acid (H ₂ SiF ₆ ) in the range of 25 to 35 degrees. The insulating film 26 for forming is formed.

An optional LPD (Liquid Phase) for growing a silicon oxide film, which is an optical waveguide insulating film 26, in a region where the silicon nitride film is not grown, and in which the silicon exposed film is exposed to a photodiode region and an interlayer dielectric film. Deposition) method.

The optical waveguide insulating film 26 is formed up to a layer including the silicon nitride film 22a as a passivation film.                     

The mechanism of the LPD method of silicon dioxide is shown in Equation 1 below.

H ₂ SiF ₆ + ₂ H ₂ O <-> SiO ₂ + HF

Therefore, SiO2 is deposited from Hydrofluosilicic Acid (H ₂ SiF ₆ ) aqueous solution, and HF is generated to etch SiO2. To decompose HF, boric acid (H ₃ BO ₃ ) is added by 20-30%. The selectivity and deposition rate with the silicon nitride film were increased by the reaction as shown in Equation # 2.

H ₃ BO ₃ + 4HF <-> BF4- + H ₃ O + 2H ₂ O

Subsequently, as shown in FIG. 4E, the color filter 27 is formed in the order of blue, red, and green.

Subsequently, as shown in FIG. 4F, an over coating layer (OCL) film 30 for planarization is formed, and a microlens 31 and a protective film 32 are formed thereon.

As described above, the CMOS image sensor manufactured according to the present embodiment is only an optical waveguide insulating film 26 of one material in the process of transmitting the light transmitted through the microlens to the photodiode at the bottom when operating the CMOS image sensor As it passes through, light scattering, refraction, and absorption processes are eliminated, and more light can be focused on the lower photodiode.

In particular, since the passivation silicon nitride film 22a and the silicon nitride film 28 used as the etch stop film for the borderless contact of the heterogeneous multilayer insulating films are removed from the light transmission path, more light is emitted. It can be focused on the photodiode of the sensor.

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, it will be understood by those of ordinary skill in the art that various embodiments are possible within the scope of the technical idea of the present invention.

In the CMOS image sensor manufactured by the present invention, since only one interlayer insulating film is formed on the path through which the light passing through the microlens is transmitted to the photodiode, the light does not occur due to refraction or scattering. This photodiode can be focused.

In addition, since only one film is present between the microlens and the photodiode, it is easy to adjust the focus of the microlens. In addition, since a film of one material is formed between the microlens and the photodiode in one single process, it is possible to maintain a uniform thickness between the microlens and the photodiode in all the pixels included in the image sensor.

As a result, more light is focused on the photodiode, resulting in a sharper and more accurate image.

Claims (13)

Photodiode; A microlens for refracting and transmitting the incident light to the photodiode; An optical waveguide insulating film made of a single material between the photodiode and the microlens; And A color filter provided between the insulating film for optical waveguide and the microlens Including, The optical waveguide insulating layer is directly connected to the color filter and the photodiode, The light transmitted through the microlens and the color filter passes only the insulating film for the optical waveguide before reaching the photodiode. CMOS image sensor. delete The method of claim 1, Further comprising a multi-layered insulating film for insulating the multi-layered wiring and the multi-layered wiring on the side of the optical waveguide insulating film, CMOS image sensor. 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 a single material to form an insulating film for an optical waveguide made of the single material; Forming a color filter on the insulating film for the optical waveguide; And Forming a microlens on the color filter Including, The optical waveguide insulating layer is directly connected to the color filter and the photodiode, The light transmitted through the microlens and the color filter passes only the insulating film for the optical waveguide before reaching the photodiode. Method for manufacturing a CMOS image sensor. 5. The method of claim 4, Forming the multilayer insulating film, A first step of forming a first silicon nitride film; A second step of forming at least two or more silicon oxide films on the first silicon nitride film; And And a third step of forming a passivation film stacked on the silicon oxide film by a silicon oxide film and a silicon nitride film. Method for manufacturing a CMOS image sensor. 6. The method of claim 5, The silicon oxide film formed of the passivation film is formed in the range of 2000 to 3000 Pa by plasma enhanced chemical vapor deposition method, Method for manufacturing a CMOS image sensor. The method of claim 6, The first step of forming the first silicon nitride film, The process pressure is 50 to 70 mT, the source power is 1500 to 2000 watts, the bias power is 1500 to 1800 watts, the gas flow rate of CHF ₃ is 20 to 30 sccm, and the CF ₄ gas flow rate is 50 to 80 sccm, O ₂ Carried out by a process in which the gas flow rate is 10 to 20 sccm, and the gas flow rate of Ar is 400 to 600 sccm, Method for manufacturing a CMOS image sensor. The method of claim 7, wherein The second step is performed by a process using C ₄ F ₈ or C ₅ F ₈ , Method for manufacturing a CMOS image sensor. 9. The method of claim 8, The second step is performed by the process of adding a gas containing hydrogen, Method for manufacturing a CMOS image sensor. The method of claim 9, The second step, The process pressure is 30 to 50 mT, the source power is 1800 to 2000 watts, the bias power is 1500 to 1700 watts, the gas flow rate of C ₅ F ₈ is 10 to 25 sccm, and the gas flow rate of CH ₂ F ₂ is 2 to 3 sccm , A gas flow rate of O ₂ is 10 to 20 sccm, and a gas flow rate of Ar is 400 to 600 sccm. Method for manufacturing a CMOS image sensor. 11. The method of claim 10, The third step, The process pressure is 50 to 70 mT, the source power is 800 to 1200 watts, the bias power is 200 to 300 watts, the gas flow rate of CF ₄ is 50 to 80 sccm, the gas flow rate of CH ₂ F ₂ is 10 to 20 sccm, O Carried out by a process in which a gas flow rate of ₂ is 10 to 20 sccm, and a gas flow rate of Ar is 400 to 600 sccm, Method for manufacturing a CMOS image sensor. 5. The method of claim 4, Filling the hole with the single material to form an insulating film for an optical waveguide made of the single material is performed by a process of an optional LPD method using an aqueous solution in which H ₃ BO ₃ is added to a supersaturated H ₂ SiF ₆ aqueous solution. felled, Method for manufacturing a CMOS image sensor. delete

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