KR100872289B1 - COMS image sensor with improved light focusing ability and method of fabricating thereof - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CMOS image sensor and a method of manufacturing the same, and in particular, to improve light receiving characteristics of a device by using a passivation film as a lens. The present invention for this purpose is a substrate formed with a related element, including a light receiving element; A metal wiring formed on the substrate; An interlayer insulating layer formed on the metal line, wherein a portion of the interlayer insulating layer is removed so that the region corresponding to the light receiving element is convex and the other region is concave and convex; A passivation film formed on the interlayer insulating film; A planarization film formed on the passivation film; And a color filter formed on the planarization film.

Image sensor, micro lens, passivation film, unit pixel, focal length

Description

MOS image sensor with improved light focusing ability and method of fabricating             

1A is a circuit diagram showing a unit pixel of a CMOS image sensor according to the prior art;

Figure 1b is a cross-sectional view showing a cross section of the CMOS image sensor according to the prior art,

2a to 2b are cross-sectional views showing the manufacturing process of the CMOS image sensor according to the present invention.

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

10: substrate

11: field oxide film

12: photodiode

13: interlayer insulating film

14, 16, 18: metal circuit for unit pixel

15, 17, 19: interlayer insulating film

30: passivation film

31: planarization film for color filter formation                 

32: color filter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CMOS image sensor, and more particularly, to a CMOS image sensor having improved light receiving characteristics of a device and a method of manufacturing the same.

In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal. Among them, a charge coupled device (CCD) includes individual metal-oxide-silicon (MOS) capacitors. A device in which charge carriers are stored and transported in a capacitor while being in close proximity to each other. Complementary MOS image sensors use CMOS technology that uses a control circuit and a signal processing circuit as peripheral circuits. A device employing a switching scheme that creates MOS transistors as many as pixels and sequentially detects outputs using the MOS transistors.

CCD (charge coupled device) has several disadvantages such as complicated driving method, high power consumption, high number of mask process steps, complicated process, and difficult to implement signal processing circuit in CCD chip. In order to overcome such drawbacks, the development of a CMOS image sensor using a sub-micron CMOS manufacturing technology has been studied in recent years. The CMOS image sensor forms an image by forming a photodiode and a MOS transistor in a unit pixel and sequentially detects signals in a switching method, and implements an image. The CMOS manufacturing technology uses less power and uses 20 to 30 masks with 20 masks. Compared to CCD process that requires two masks, the process is very simple, and it is possible to make various signal processing circuits and one chip, which is attracting attention as the next generation image sensor.

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 for generating photocharges by receiving light and a photodiode ( A transfer transistor (Tx) for transporting the photocharge collected from the photo diodes to the floating diffusion region (FD), and for resetting the floating diffusion region (FD) by setting the potential of the floating diffusion region to a desired value and discharging electric charges. A reset transistor Rx, a drive transistor Dx serving as a source follower buffer amplifier, and a select transistor Sx capable of addressing by switching. . Outside the unit pixel, a load transistor is formed to read an output signal.

Figure 1b is a cross-sectional view showing a cross-sectional view of the CMOS image sensor including such a unit pixel with reference to this description of the manufacturing method of a conventional image sensor as follows.

First, after forming the field oxide film 11 for electrical insulation between devices on the semiconductor substrate 10, a gate electrode is formed by successively applying and patterning polysilicon and tungsten silicide films. Not shown in 1b)

Thereafter, an appropriate ion implantation process is performed to form the photodiode 12 and to perform ion implantation for forming a source / drain and a sensing node of the transistor.

Next, an interlayer insulating film 13 is formed on the entire structure including the photodiode 12 and the field oxide film 11 and the planarization process is performed.

Thereafter, metal circuits 14, 16, and 18 constituting unit pixels are formed on the interlayer insulating film 13. In this case, the metal circuits 14, 16, and 18 are formed to be disposed so as not to block light incident on the photodiode 12.

The unit pixel of an image sensor is composed of a plurality of transistors for signal processing including a photodiode. Reference numerals 14, 16 and 18 shown in Fig. 1B show a metal circuit for constructing such unit pixels.

Interlayer insulating films 15, 17 and 19 for electrical insulation are formed between the metal circuits of the unit pixel constituting layers of each layer, and the device is removed from moisture or scratches on the final interlayer insulating film 19. For protection purposes, the passivation film 20 composed of an oxide film or a nitride film is formed, thereby completing a general CMOS process.

Next, three kinds of color filters 21 are formed on the passivation film 20 for color image realization. As the color filters, usually dyed photoresists are used.

After the color filter is formed in this way, the overcoating layer 22 is deposited on the color filter 21 and flattened so that the microlens 23 can be formed on the flattened overcoating layer 22.                         

The microlens 23 is coated with a photoresist for forming a microlens, and then patterned to form a rectangular shape. Thereafter, the rectangular photoresist is flowed through a thermal process to form a dome-shaped microlens.

As described above, since not only the photodiode but also a circuit for signal processing inside the unit pixel are configured in the unit pixel of the conventional image sensor, the area of the photodiode is limited.

Accordingly, the light receiving characteristics of the device may be improved by forming a microlens on the unit pixel to collect light incident to a region other than the photodiode region among the light incident on the unit pixel.

However, as the size of the unit pixel decreases, the height of the upper structure is increased due to the interlayer insulating films 15, 17, and 19 and the metal wirings 14, 16, and 18 formed on the photodiode compared to the size of the photodiode. do.

Therefore, in the case of using a method of forming a color filter on the unit pixel and forming a microlens on the upper part as in the related art, a planarization layer having a predetermined thickness is required to implement the microlens during the process. The process was complicated and the increase in height was not significant.

In addition, since the distance from the center of the photodiode to the center of the microlens is several times the length of one side of the photodiode, the microlens that can focus on the photodiode is not easy.

In addition, since the distance from the photodiode to the microlens is far from the focal length of the lens, the light (AA) refracted by the microlens is lost to the photodiode.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object thereof is to provide a CMOS image sensor and a method of manufacturing the same, which have improved light receiving characteristics by using a passivation film as a lens.

In order to achieve the above object, the present invention provides a substrate on which a related element including a light receiving element is formed, a metal wiring formed on the substrate, and a region formed on the metal wiring, the region corresponding to the light receiving element being convex and other. The region of is an interlayer insulating film having a predetermined portion removed to have concave and convex irregularities, a passivation film formed of a material having a refractive index greater than that of the interlayer insulating film along the step of the interlayer insulating film, a planarization film formed on the passivation film, and It provides a CMOS image sensor including a color filter formed on the planarization film.

The present invention also provides a method of forming a related device including a light receiving element on a substrate, forming a metal wiring on the substrate, forming an interlayer insulating film on the metal wiring, and responding to the light receiving element. Removing a portion of the interlayer dielectric layer so that the convex region is convex and other regions are concave and convex, and forming a passivation layer on the interlayer dielectric layer with a material having a higher refractive index than the interlayer dielectric layer along the step of the interlayer dielectric layer. And forming a planarization film on the passivation film, and forming a color filter on the planarization film.

According to an aspect of the present invention, a passivation film performs a lens function by etching irregular portions of a final interlayer insulating film and forming a passivation film having a large refractive index along the step of the final interlayer insulating film.

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.

2A to 2B are cross-sectional views illustrating a manufacturing process of the CMOS image sensor according to an exemplary embodiment of the present invention and will be described with reference to the same.

First, referring to FIG. 2A, after forming a field oxide film 11 for electrical insulation between devices on a semiconductor substrate 10, a gate electrode is formed by successively applying and patterning a polysilicon and a tungsten silicide film. (The gate electrode is not shown in Fig. 2A.)

The field oxide layer 11 may be formed by a local oxide of silicon (LOCOS) method or may have a trench structure.

Thereafter, an appropriate ion implantation process is performed to form the photodiode 12 and to perform ion implantation for forming a source / drain and a sensing node of the transistor.

Next, an interlayer insulating film 13 is formed on the entire structure including the photodiode 12 and the field oxide film 11 and the planarization process is performed.

Subsequently, metal circuits 14, 16, and 18 constituting unit pixels are formed on the interlayer insulating film 13. In this case, the metal circuits 14, 16, and 18 are formed to be disposed so as not to block light incident on the photodiode 12.

The unit pixel of an image sensor is composed of a plurality of transistors for signal processing including a photodiode. Reference numerals 14, 16, and 18 shown in FIG. 1B show a metal circuit for unit pixel configuration, and interlayer insulating films 15, 17, and 19 for electrical insulation between the metal circuits for unit pixel configuration in each layer. ) Is formed.

In one embodiment of the present invention, the process up to forming the final interlayer insulating film 19 on the final metal wiring 18 is the same as in the prior art. However, subsequent processes are different from the prior art. This will be described below.

After the final interlayer insulating film 19 is formed, a mask process is performed to etch a portion of the final interlayer insulating film 19 to form the unevenness 19a as shown in FIG. 2A.

The unevenness 19a formed on the final interlayer insulating film 19 is formed to be convex in the region corresponding to the photodiode 12 and concave in the region corresponding to the metal wirings 14, 16, and 18.

In addition, the height of the unevenness 19a may be adjusted through experiments so that incident light may be collected by the photodiode 12.                     

Next, as shown in FIG. 2B, the passivation film 30 is deposited on the curved final interlayer insulating film 19 along the step of the final interlayer insulating film 19. Since the passivation film 30 is formed along the lower step, as shown in FIG. 2B, the passivation film 30 is formed to have the shape of a gate spacer at the end of the unevenness 19a.

Such a passivation film 30 allows the passivation film 30 to function as a lens, and the silicon nitride film may be used as the passivation film 30, or may have a refractive index lower than that of the lower interlayer insulating film. It is formed using large materials.

As described above, when the height of the unevenness 19a is experimentally adjusted and a passivation film is formed using a material having a large refractive index, a lens capable of condensing incident light with a photodiode can be obtained. 2B shows that incident light is focused onto the photodiode by the lens according to the embodiment of the present invention.

The curved passivation film 30 is formed in this manner, and then the planarization film 31 is applied on the curved passivation film 30. The planarization layer 31 enables the subsequent color filter 32 to be formed on the planarized surface, and the overcoat layer, which is a photoresist-based material, may be used as the planarization layer 31.

Next, when the color filter 32 is formed using the dyed photoresist on the planarization film 31, the CMOS image sensor manufacturing process according to an embodiment of the present invention is completed.

In an embodiment of the present invention, the lens is formed using a passivation film instead of forming a microlens on the color filter. Therefore, the position where the incident light is refracted is close to that of the photodiode, and this advantage can reduce the amount of light lost by the lens even when the focal length of the lens is not accurate. .

In addition, the CMOS image sensor manufacturing process according to an embodiment of the present invention has the advantage that the process is simplified because a series of mask processes and flow processes for forming a conventional microlens is omitted.

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 the art.

When the present invention is applied, since the location where the light is refracted is close to the photodiode, the amount of light lost by refraction can be reduced even when the focal length is not accurate. In addition, by controlling the thickness of the irregularities, there is an advantage that the focal length of the light refracted at the uneven end can also be adjusted experimentally.

In addition, since a series of mask processes for forming a conventional microlens can be omitted, the effect of process simplification can also be obtained.

Claims (7)

A substrate on which a related element including a light receiving element is formed; A metal wiring formed on the substrate; An interlayer insulating layer formed on the metal line, wherein an area corresponding to the light receiving element is convex and other portions are removed to have concave and convex irregularities; A passivation film formed of a material having a larger refractive index than the interlayer insulating film along the step of the interlayer insulating film; A planarization film formed on the passivation film; And Color filter formed on the planarization film CMOS image sensor comprising a. The method of claim 1, The height of the unevenness formed in the interlayer insulating film is adjusted so that the incident light can be focused to the light receiving element. The method of claim 1, The passivation film is a CMOS image sensor made of a silicon nitride film. Forming a related element including a light receiving element on the substrate; Forming a metal wire on the substrate; Forming an interlayer insulating film on the metal wiring; Removing a portion of the interlayer insulating film so that a region corresponding to the light receiving element is convex and other regions have concave and convex irregularities; Forming a passivation film on the interlayer insulating film with a material having a refractive index greater than that of the interlayer insulating film along the step of the interlayer insulating film; Forming a planarization film on the passivation film; And Forming a color filter on the planarization layer Method for manufacturing a CMOS image sensor comprising a. The method of claim 4, wherein Removing a portion of the interlayer insulating film to have the unevenness The method of manufacturing a CMOS image sensor, characterized in that for determining the height of the irregularities so that incident light is focused on the light receiving element. The method of claim 4, wherein The passivation film is a method of manufacturing a CMOS image sensor, characterized in that formed using a silicon nitride film. delete

Images