阅读说明：本技术 前照式cmos图像传感器的形成方法 (Forming method of front-illuminated CMOS image sensor ) 是由 徐涛 李�杰 郑展 付文 于 2019-02-02 设计创作，主要内容包括：本发明提供一种前照式CMOS图像传感器的形成方法,包括：依次形成器件层、多层金属层,所述器件层包括感光区域和非感光区域；形成顶层金属层,刻蚀顶层金属层形成预设图案；在感光区域和非感光区域上方依次形成第一阻挡层和介质层；研磨所述介质层,停止至所述非感光区域的第一阻挡层区域表面；在所述研磨后的表面上形成第二阻挡层；刻蚀所述感光区域的第二阻挡层、介质层至暴露出第一阻挡层表面；其中,通过第一阻挡层的阻挡,可以提高研磨和刻蚀工艺的均匀性,并在保证感光区域表面与非感光区域表面相对较低高度差的同时可以获得感光区域相对较短的光程。(The invention provides a method for forming a front-illuminated CMOS image sensor, which comprises the following steps: sequentially forming a device layer and a plurality of metal layers, wherein the device layer comprises a photosensitive area and a non-photosensitive area; forming a top metal layer, and etching the top metal layer to form a preset pattern; sequentially forming a first barrier layer and a dielectric layer above the photosensitive area and the non-photosensitive area; grinding the dielectric layer and stopping till the surface of the first barrier layer area of the non-photosensitive area; forming a second barrier layer on the ground surface; etching the second barrier layer and the dielectric layer of the photosensitive area until the surface of the first barrier layer is exposed; the first barrier layer can improve the uniformity of the grinding and etching processes, and can obtain a relatively short optical path of the photosensitive area while ensuring a relatively low height difference between the surface of the photosensitive area and the surface of the non-photosensitive area.)

1. A method for forming a front-illuminated CMOS image sensor, comprising:

sequentially forming a device layer and a plurality of metal layers, wherein the device layer comprises a photosensitive area and a non-photosensitive area;

forming a top metal layer, and etching the top metal layer to form a preset pattern;

sequentially forming a first barrier layer and a dielectric layer above the photosensitive area and the non-photosensitive area;

grinding the dielectric layer and stopping till the surface of the first barrier layer area of the non-photosensitive area;

forming a second barrier layer on the ground surface;

etching the second barrier layer and the dielectric layer of the photosensitive area until the surface of the first barrier layer is exposed;

the first barrier layer can improve the uniformity of the grinding and etching processes, and can obtain a relatively short optical path of the photosensitive area while ensuring a relatively low height difference between the surface of the photosensitive area and the surface of the non-photosensitive area.

2. The method of forming a front-illuminated CMOS image sensor as in claim 1, wherein: forming a buffer layer between the top metal layer and the first barrier layer before forming the first barrier layer.

3. The method of forming a front-illuminated CMOS image sensor as in claim 1, wherein: the first barrier layer and the second barrier layer are made of any one or a combination of more of SiN, SiON, SiC, SiNC and SiONC.

4. The method of forming a front-illuminated CMOS image sensor as in claim 2, wherein: the buffer layer is made of SiO₂。

5. The method of forming a front-illuminated CMOS image sensor as in claim 1, wherein: and grinding the medium layer through chemical mechanical grinding or physical mechanical grinding.

6. The method of forming a front-illuminated CMOS image sensor as in claim 1, wherein: and forming a color filter layer and a micro-lens layer on the first barrier layer of the photosensitive area after the step of etching the second barrier layer and the dielectric layer of the photosensitive area.

7. The method of forming a front-illuminated CMOS image sensor as in claim 1, wherein: the thickness of the first barrier layer is 10-50nm, and the thickness of the second barrier layer is 30-200 nm.

Technical Field

The invention relates to a method for forming a front-illuminated CMOS image sensor.

Background

An image sensor is a sensor that can sense optical image information and convert it into a usable output signal, and is an important component that constitutes a digital camera. Depending on the Device, the Device can be classified into two categories, namely, a CCD (Charge Coupled Device) and a CMOS (Complementary Metal-oxide semiconductor).

The CMOS image sensor has the advantages of simple process, easy integration with other devices, small volume, light weight, low power consumption, low cost and the like. Therefore, as the technology is developed, CMOS image sensors are increasingly used in various electronic products instead of CCD image sensors. At present, CMOS image sensors are widely used in still digital cameras, camera phones, digital video cameras, medical imaging devices (e.g., gastroscopes), vehicle imaging devices, and the like.

CMOS image sensor products can be classified into FSI (front Illumination) and BSI (back Illumination). In a front-illuminated CMOS image sensor product, BEOL (Back end of Line) processes have at least two or more layers of metal wiring, i.e., a plurality of layers of metal wiring and dielectric layers. For the photosensitive area, the distance from the chip surface to the photosensitive surface is large, so that incident light rays can be absorbed by the photosensitive area only after passing through a long path (optical path), the light ray attenuation is large, the light ray sensitivity is reduced, the CRA (Chiefray Angle, the included Angle between the main light ray and the normal direction of an imaging surface) of the chip cannot be too large, the application range is limited, and the performance of the image sensor is greatly influenced.

Referring specifically to fig. 1-5, there are shown partial schematic views of a method of fabricating a prior art front-illuminated CMOS image sensor.

Referring to fig. 1 and fig. 2, a device layer 10 and a plurality of metal layers 20 are sequentially formed, wherein the device layer 10 includes a photosensitive region 12 and a non-photosensitive region 11; a top metal layer 30 is formed, and the top metal layer 30 is etched to form a predetermined pattern (as shown in fig. 2).

Referring to fig. 3 and 4, a dielectric layer 40 is formed above the photosensitive region 12 and the non-photosensitive region 11, and the polishing dielectric layer 40 stops at a position having a distance H1 of at least 200nm from the surface of the top metal layer 30, because the polishing process has a fast edge and a slow edge, if the polishing dielectric layer 40 stops at a position having a distance H1 of less than 200nm from the surface of the top metal layer 30, damage may be caused to the surface of the top metal layer 30 at the edge of the wafer during the polishing process, and the uniformity of polishing between wafers is difficult to be ensured, thereby affecting the performance of the image sensor. Subsequently, a barrier layer 60 is formed on the polished surface, preferably, the material of the barrier layer 60 is any one or a combination of more of SiN, SiON, SiC, SiNC, and SiONC, and the thickness is usually 30 to 200 nm.

Referring to fig. 5, the barrier layer 60 and the dielectric layer 40 in the photosensitive region are etched, in order to ensure that the color filter layer at the boundary between the final photosensitive region and the non-photosensitive region, the microlens layer has a good shape, and it is necessary to control the height difference H2 between the surface of the photosensitive region and the surface of the non-photosensitive region to be not too large, usually 300-.

Disclosure of Invention

The invention aims to provide a method for forming a front-illuminated CMOS image sensor, which improves the uniformity of grinding and etching processes, ensures relatively low height difference between the surface of a photosensitive area and the surface of a non-photosensitive area, obtains relatively short optical path of the photosensitive area and improves the performance of the image sensor.

In view of the above, the present invention provides a method of forming a front-illuminated CMOS image sensor, comprising: sequentially forming a device layer and a plurality of metal layers, wherein the device layer comprises a photosensitive area and a non-photosensitive area; forming a top metal layer, and etching the top metal layer to form a preset pattern; sequentially forming a first barrier layer and a dielectric layer above the photosensitive area and the non-photosensitive area; grinding the dielectric layer and stopping till the surface of the first barrier layer area of the non-photosensitive area; forming a second barrier layer on the ground surface; etching the second barrier layer and the dielectric layer of the photosensitive area until the surface of the first barrier layer is exposed; the first barrier layer can improve the uniformity of the grinding and etching processes, and can obtain a relatively short optical path of the photosensitive area while ensuring a relatively low height difference between the surface of the photosensitive area and the surface of the non-photosensitive area.

Preferably, before forming the first barrier layer, a buffer layer is formed between the top metal layer and the first barrier layer.

Preferably, the first barrier layer and the second barrier layer are made of any one or a combination of more of SiN, SiON, SiC, SiNC and SiON.

Preferably, the buffer layer is made of SiO₂。

Preferably, the dielectric layer is polished by chemical mechanical polishing or physical mechanical polishing.

Preferably, the method for forming a front-illuminated CMOS image sensor further includes forming a color filter layer and a microlens layer on the first barrier layer of the photosensitive region after the step of etching the second barrier layer and the dielectric layer of the photosensitive region.

Preferably, the thickness of the first barrier layer is 10-50nm, and the thickness of the second barrier layer is 30-200 nm.

The forming method of the front-illuminated CMOS image sensor can improve the uniformity of grinding and etching processes by the blocking of the first blocking layer, can obtain relatively short optical path of a photosensitive area while ensuring relatively low height difference between the surface of the photosensitive area and the surface of a non-photosensitive area, and improves the performance of the image sensor.

Drawings

Other features, objects and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments thereof, which proceeds with reference to the accompanying drawings.

Fig. 1-5 are partial schematic views of a method of fabricating a front-illuminated CMOS image sensor according to the prior art;

FIG. 6 is a flow chart of a method of fabricating a front-illuminated CMOS image sensor of the present invention;

fig. 7 to 12 are partial schematic views illustrating a method for fabricating a front-illuminated CMOS image sensor according to the present invention.

In the drawings, like or similar reference numbers indicate like or similar devices (modules) or steps throughout the different views.

Detailed Description

In order to solve the problems in the prior art, the invention provides a method for forming a front-illuminated CMOS image sensor, which can improve the uniformity of the grinding and etching processes by the blocking of the first blocking layer, and can obtain a relatively short optical path of a photosensitive area while ensuring a relatively low height difference between the surface of the photosensitive area and the surface of a non-photosensitive area, thereby improving the performance of the image sensor.

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof. The accompanying drawings illustrate, by way of example, specific embodiments in which the invention may be practiced. The illustrated embodiments are not intended to be exhaustive of all embodiments according to the invention. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

As shown in fig. 6, the present invention provides a method for forming a front-illuminated CMOS image sensor, comprising: sequentially forming a device layer and a plurality of metal layers, wherein the device layer comprises a photosensitive area and a non-photosensitive area; forming a top metal layer, and etching the top metal layer to form a preset pattern; sequentially forming a first barrier layer and a dielectric layer above the photosensitive area and the non-photosensitive area; grinding the dielectric layer and stopping till the surface of the first barrier layer area of the non-photosensitive area; forming a second barrier layer on the ground surface; etching the second barrier layer and the dielectric layer of the photosensitive area until the surface of the first barrier layer is exposed; the first barrier layer can improve the uniformity of the grinding and etching processes, and can obtain a relatively short optical path of the photosensitive area while ensuring a relatively low height difference between the surface of the photosensitive area and the surface of the non-photosensitive area.

Referring specifically to fig. 7-12, there are shown partial schematic views of a method of fabricating a front-illuminated CMOS image sensor of the present invention.

Referring to fig. 7 and 8, a device layer 110 and a plurality of metal layers 120 are sequentially formed, wherein the device layer 110 includes a photosensitive region 112 and a non-photosensitive region 111; a top metal layer 130 is formed, and the top metal layer 130 is etched to form a predetermined pattern (as shown in fig. 8).

Referring to fig. 9, a first blocking layer 140 and a dielectric layer 150 are sequentially formed above the photosensitive region 112 and the non-photosensitive region 111, and preferably, the first blocking layer 140 is made of any one or a combination of SiN, SiON, SiC, SiNC, and SiONC, and has a thickness of 10 to 50 nm.

In other preferred embodiments not shown, a buffer layer, preferably made of SiO, may be formed between the top metal layer 130 and the first barrier layer 140 before the first barrier layer 140 is formed₂The thickness is 10-50 nm.

Referring to fig. 10, the dielectric layer 150 is polished to stop at the surface of the first barrier layer 140 in the non-photosensitive region 111, and the first barrier layer 140 serves as a polishing stop layer, so that there is no fear of damage to the surface of the top metal layer 30 during polishing, and the uniformity of the polishing process can be improved by the barrier of the first barrier layer 140. Preferably, the grinding process is chemical mechanical grinding or physical mechanical grinding.

Referring to fig. 11, a second barrier layer 160 is formed on the polished surface, and preferably, the second barrier layer 160 is made of any one or a combination of SiN, SiON, SiC, SiNC, and SiONC, and has a thickness of 30-200 nm.

Referring to fig. 12, the second barrier layer 160 and the dielectric layer 150 of the photosensitive region 112 are etched until the surface of the first barrier layer 140 is exposed, and the first barrier layer 140 serves as an etch stop layer, so that there is no need to worry about damage to the surface of the underlying multi-layer metal layer 120 during the etching process, and the uniformity of the etching process can be improved by the barrier of the first barrier layer 140.

By controlling the thickness of the first barrier layer 140 to be 10-50nm and the thickness of the buffer layer (if any) to be 10-50nm, the distance H1 ' between the surface of the first barrier layer 140 and the surface of the top metal layer 30 in the present invention is much smaller than the distance H1 between the surface of the dielectric layer 40 and the surface of the top metal layer 30 in the prior art, so that a relatively short optical path H3 ' of the photosensitive region can be obtained while a relatively low height difference H2 ' between the surface of the photosensitive region and the surface of the non-photosensitive region is ensured, thereby reducing the loss of light, improving the light sensitivity, and improving the performance of the image sensor.

In addition, the method for forming the front-illuminated CMOS image sensor of the present invention further includes forming a color filter layer and a microlens layer on the first barrier layer 140 of the photosensitive region 112 after the step of etching the second barrier layer 160 and the dielectric layer 150 of the photosensitive region 112, thereby forming a complete image sensor structure.

The forming method of the front-illuminated CMOS image sensor can improve the uniformity of grinding and etching processes by the blocking of the first blocking layer, can obtain relatively short optical path of a photosensitive area while ensuring relatively low height difference between the surface of the photosensitive area and the surface of a non-photosensitive area, and improves the performance of the image sensor.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. Furthermore, it will be obvious that the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. Several elements recited in the apparatus claims may also be implemented by one element. The terms first, second, etc. are used to denote names, but not any particular order.