CN115241221B - Back-illuminated image sensor and manufacturing method thereof - Google Patents

Abstract

The invention provides a manufacturing method of a back-illuminated image sensor. The manufacturing method includes: providing a base, the base includes a first area and a second area, a grid material layer and a mandrel structure on the grid material layer are formed on the back of the base; side walls are formed on the side walls of the mandrel structure , remove the mandrel structure; use the side wall as a mask, etch the grid material layer to form a grid-like composite metal grid, the composite metal grid has multiple grid openings, the critical dimensions of the grid openings in the first zone Different from the critical dimension of the grille opening in the second zone. The manufacturing method of the back-illuminated image sensor can form a composite metal grid with a small size, and is beneficial to diversify the functions of the back-illuminated image sensor. The present invention also provides a back-illuminated image sensor manufactured by the above manufacturing method.

Description

Back-illuminated image sensor and manufacturing method thereof

technical field

The invention relates to the technical field of semiconductors, in particular to a back-illuminated image sensor and a manufacturing method thereof.

Background technique

At present, in the production of the back-illuminated image sensor (BSI), the production process of the composite metal grid (CompositeMetal Grid, CMG) has been introduced. In the manufacturing process of the composite metal grid, the composite metal grid is produced through a process of photolithography and etching. As the integration density of semiconductor chips increases, the size of the composite metal grid is also reduced. However, when the size (CD) of the composite metal grid shrinks to a certain extent, it cannot be formed by a simple photolithography and etching process. Composite metal grille. Therefore, how to make a composite metal grid with a smaller size needs to be solved urgently.

Contents of the invention

The purpose of the present invention is to provide a method for manufacturing a back-illuminated image sensor, which can manufacture a composite metal grid with a smaller size. The invention also provides a back-illuminated image sensor.

In order to achieve the above purpose, the manufacturing method of the back-illuminated image sensor provided by the present invention includes:

A substrate is provided, the substrate includes a first area and a second area, and a grid material layer and a mandrel structure on the grid material layer are formed on the back side of the base;

forming sidewalls at sidewalls of the mandrel structure, removing the mandrel structure; and

Using the side wall as a mask, etching the grid material layer to form a grid-like composite metal grid; the composite metal grid has a plurality of grid openings, and the grid openings in the first region The critical dimension is different from the critical dimension of the grid openings in said second zone.

Optionally, after removing the mandrel structure and before etching the grid material layer, the manufacturing method includes: trimming the topography of the bottom of the sidewall by an etching process to obtain a narrow top and a wide bottom. grille opening.

Optionally, the manufacturing method includes: after etching the grid material layer to form a grid-shaped composite metal grid, modifying the shape of the grid opening, so that the grid opening It is narrow at the top and wide at the bottom.

Optionally, the method for providing the substrate includes: forming the grid material layer, mask layer, core mold material layer and patterned photoresist layer stacked from bottom to top on the back of the substrate; and using the patterned photoresist layer as a mask to etch down the core material layer to form the core structure.

Optionally, the method for forming the side wall on the side wall of the mandrel structure includes: forming a side wall material layer, and the side wall material layer covers the top surface and the side wall of the mandrel structure and covers the lattice grid material layer; etching removes the side wall material layer on the top surface of the mandrel structure and part of the side wall material layer on the grid material layer, and retains the side wall material layer on the side wall of the mandrel structure as the side walls.

Optionally, the material of the core mold structure includes amorphous silicon.

Optionally, the grid material layer includes a metal layer and an oxide layer stacked from bottom to top on the back of the substrate.

Optionally, the manufacturing method includes: after etching the grid material layer to form a grid-shaped composite metal grid, forming an oxidation protection layer on sidewalls of the plurality of grid openings.

Optionally, the manufacturing method includes: after etching the grid material layer to form a grid-shaped composite metal grid, forming a color filter in the opening of the grid.

The invention also provides a back-illuminated image sensor. The back-illuminated image sensor is manufactured using the above-mentioned back-illuminated image sensor manufacturing method, and the back-illuminated image sensor includes a substrate and a composite metal grid. The substrate includes a first region and a second region. The composite metal grid is on the backside of the substrate and has a plurality of grid openings; wherein the critical dimensions of the grid openings in the first zone are different from the critical dimensions of the grid openings in the second zone.

In the manufacturing method of the back-illuminated image sensor of the present invention, firstly, a grid material layer and a mandrel structure located on the grid material layer are formed on the back of the substrate, and the base includes a first region and a second region; and then A side wall is formed on the side wall of the mandrel structure, and then the mandrel structure is removed; then, the grid material layer is etched to form a grid-shaped composite metal grid by using the side wall as a mask. The manufacturing method of the back-illuminated image sensor can be used to form a composite metal grid with a small size. In addition, the composite metal grid has a plurality of grid openings, and the critical dimension of the grid openings in the first region is related to the The key dimensions of the grid openings in the second region are different, which is beneficial to diversify the functions of the back-illuminated image sensor.

In the back-illuminated image sensor of the present invention, the substrate includes a first area and a second area, the composite metal grid is located on the back side of the base and has a plurality of grid openings, the critical dimension of the grid opening in the first area is the same as the The key dimensions of the grid openings in the second region are different, which is beneficial to diversify the functions of the image sensor.

Description of drawings

FIG. 1 is a flowchart of a manufacturing method of a back-illuminated image sensor according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view after forming a patterned photoresist layer on a substrate in an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a mandrel structure formed on a substrate according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view of a sidewall material layer formed on a substrate according to an embodiment of the present invention.

Fig. 5 is a cross-sectional view after forming side walls on the side walls of the mandrel structure in an embodiment of the present invention.

FIG. 6 is a cross-sectional view after removing the mandrel structure on the substrate in an embodiment of the present invention.

Fig. 7 is a cross-sectional view of a trimmed side wall in an embodiment of the present invention.

FIG. 8 is a cross-sectional view after etching the grid material layer to form a composite metal grid in an embodiment of the present invention.

FIG. 9 is a cross-sectional view of a back-illuminated image sensor according to an embodiment of the present invention.

Explanation of reference signs: 10-substrate; 10a-first area; 10b-second area; 11-isolating oxide layer; 12-grid material layer; 121-first metal layer; 122-second metal layer; 123- Oxide layer; 13-mask layer; 131-amorphous carbon layer; 132-silicon oxynitride layer; 14-core mold material layer; 14a-core mold structure; 15-photoresist layer; 16-side wall material layer; 16a-side wall; 12a-composite metal grille; 17-grid opening; 18-oxidation protective layer; 19-color filter.

detailed description

The back-illuminated image sensor proposed by the present invention and its manufacturing method will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer from the following description. It should be noted that all the drawings are in a very simplified form and use imprecise scales, and are only used to facilitate and clearly assist the purpose of illustrating the embodiments of the present invention.

In order to manufacture a composite metal grid with a smaller size, the present application provides a method for manufacturing a back-illuminated image sensor. FIG. 1 is a flowchart of a manufacturing method of a back-illuminated image sensor according to an embodiment of the present invention. As shown in Figure 1, the manufacturing method of the back-illuminated image sensor of the present application includes:

S1, providing a substrate, the substrate includes a first region and a second region, and a grid material layer and a mandrel structure on the grid material layer are formed on the back of the substrate;

S2, forming side walls on the side walls of the mandrel structure, and removing the mandrel structure; and

S3, using the side wall as a mask, etching the grid material layer to form a grid-shaped composite metal grid; the composite metal grid has a plurality of grid openings, and the grid in the first area The critical dimensions of the openings are different from the critical dimensions of the openings of the grate in said second zone.

It should be understood that although the various steps in the flow chart of FIG. 1 are displayed sequentially as indicated by the arrows, these steps are not necessarily executed sequentially in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least some of the steps in FIG. 1 may include multiple steps or stages, and these steps or stages may not necessarily be executed at the same time, but may be executed at different times, and the execution sequence of these steps or stages may also be It is not necessarily performed sequentially, but may be performed alternately or alternately with other steps or at least a part of steps or stages in other steps.

The manufacturing method of the back-illuminated image sensor of the present application will be described below with reference to FIGS. 2 to 9 .

FIG. 3 is a cross-sectional view of a mandrel structure formed on a substrate according to an embodiment of the present invention. As shown in FIG. 3, the substrate 10 includes a first region 10a and a second region 10b. A grid material layer 12 and a mandrel structure 14a located on the grid material layer are formed on the back side of the substrate 10 .

FIG. 2 is a cross-sectional view after forming a patterned photoresist layer on a substrate in an embodiment of the present invention. The method for providing the substrate 10 may include: as shown in FIG. 2 , forming the grid material layer 12 , mask layer 13 , and core mold material layer 14 sequentially stacked from bottom to top on the back of the substrate 10 and a patterned photoresist layer 15; as shown in FIG. 3, using the patterned photoresist layer 15 as a mask, etch down the core mold material layer 14 to form the core mold structure 14a; The patterned photoresist layer 15 is then removed.

As shown in FIG. 2 and FIG. 3 , the grid material layer may include a first metal layer 121 , a second metal layer 122 and an oxide layer 123 stacked in sequence, but is not limited thereto. In the present application, the material of the first metal layer 121 may include titanium (Ti) and/or titanium nitride (TiN), and the thickness of the first metal layer 121 may be 30 angstroms to 120 angstroms, for example, a titanium layer of 50 angstroms or A titanium nitride layer of 10 angstroms; the material of the second metal layer 122 can include aluminum-copper alloy (AlCu), and the thickness of the second metal layer 122 can be 2500 angstroms to 3000 angstroms, for example, 2800 angstroms; the material of the oxide layer 123 can be Including silicon oxide, the thickness of the oxide layer 123 may be 6000-7000 angstroms, such as 6500 angstroms, but not limited thereto. Those skilled in the art can adjust the materials and thicknesses of the first metal layer 121 , the second metal layer 122 and the oxide layer 123 as required.

In order to protect the grid material layer 12 during subsequent etching to form side walls, a mask layer 13 is formed between the mandrel structure 14a and the grid material layer 12, and the subsequent patterned mask layer 13 is also combined with the side walls. Together, they serve as a mask for etching the grid material layer 12, so as to subsequently form a grid opening with a narrow top and a wide bottom. As an example, the mask layer 13 includes an amorphous carbon layer 131 (a-Carbon) and a silicon oxynitride layer 132 stacked in sequence, or the mask layer 13 includes an amorphous carbon layer 131 and a silicon oxide layer (not shown in the figure). The thickness of the amorphous carbon layer 131 may range from 5500 angstroms to 6500 angstroms, for example, 6000 angstroms. The thickness of the silicon oxynitride layer 132 may be 270 angstroms to 350 angstroms, for example, 320 angstroms. The silicon oxide layer on the amorphous carbon layer 131 may have a thickness of 30 angstroms to 70 angstroms, for example, 50 angstroms. It should be noted that those skilled in the art can adjust the material and thickness of each material layer in the mask layer 13 as needed.

The core material layer 14, or the core structure 14a is made of amorphous silicon, but not limited thereto. The material of the substrate 10 can be silicon, germanium, silicon germanium, silicon carbide, gallium arsenide or indium gallium, or silicon-on-insulator, germanium-on-insulator; or other materials, such as gallium arsenide and other III-V compounds.

FIG. 9 is a cross-sectional view of a back-illuminated image sensor according to an embodiment of the present invention. Referring to FIG. 3 and FIG. 9 , before the grid material layer 12 is formed on the back surface of the substrate 10 , various devices have been formed in the substrate 10 , for example, a plurality of pixel units Pix have been formed in the substrate 10 .

Before forming the grid material layer 12 on the back of the substrate 10, the back side of the substrate 10 can also be ground and thinned, and then an isolation oxide layer 11 is formed on the back of the substrate 10, and the isolation oxide layer 11 can repair the back of the substrate 10 due to Surface defects caused by grinding. The material of the isolation oxide layer 11 may be silicon oxide. The thickness of the isolation oxide layer 11 may be 1600 angstroms to 2000 angstroms, such as 1800 angstroms, but not limited thereto. The isolation oxide layer 11 can be formed by a thermal oxidation process.

After the core mold structure 14a is formed, sidewalls are formed on the sidewalls of the core mold structure 14a.

FIG. 4 is a cross-sectional view of a sidewall material layer formed on a substrate according to an embodiment of the present invention. Fig. 5 is a cross-sectional view after forming side walls on the side walls of the mandrel structure in an embodiment of the present invention. The method for forming the side wall on the side wall of the mandrel structure 14a may include: as shown in FIG. 4 , forming a side wall material layer 16, and the side wall material layer 16 covers the top surface of the mandrel structure 14a and sidewalls and cover the grid material layer 12, specifically covering the exposed surface of the mask layer 13; as shown in FIG. A part of the side wall material layer on the mask layer 13 is reserved as the side wall 16a on the side wall of the mandrel structure 14a.

The material of the sidewall material layer 16 may include silicon oxide, but is not limited thereto. In order to improve the thickness uniformity of the sidewall material layer 16 , the sidewall material layer 16 may be formed by an atomic layer deposition (ALD) process, but is not limited thereto. The side wall material layer 16 can also be formed by other chemical vapor deposition processes known in the art. During the process of etching the sidewall material layer 16 to form the sidewall 16 a, the etching stops on the surface of the mask layer 13 , for example, stops on the surface of the silicon oxynitride layer 132 .

FIG. 6 is a cross-sectional view after removing the mandrel structure on the substrate in an embodiment of the present invention. After the side wall 16a is formed on the side wall of the core mold structure 14a, as shown in FIG. 6, the core mold structure 14a is removed. For example, the core mold structure 14a may be etched and removed by a dry etching process.

As shown in FIG. 6, there is a first distance between adjacent side walls 16a in the first region 10a, and there is a second distance between adjacent side walls 16a in the second region 10b. The first distance It is different from the second pitch, so that grid openings with different critical dimensions can be formed by subsequent etching.

FIG. 8 is a cross-sectional view after etching the grid material layer to form a composite metal grid in an embodiment of the present invention. Referring to FIG. 6 and FIG. 8 , using the sidewall 16 a as a mask, the grid material layer is etched to form a grid-shaped composite metal grid 12 a. Specifically, using the sidewall 16a as a mask, the mask layer 13 is etched downward, and stops on the grid material layer 12 to form a patterned mask layer; the sidewall 16a and the patterned mask layer are jointly As a mask, etch the oxide layer 123, the second metal layer 122 and the first metal layer 121 downwards and stop on the isolation oxide layer 11 to form the composite metal grid 12a; then remove the spacer 16a and the patterned mask layer.

The composite metal grid 12a has a plurality of grid openings 17, the critical dimension of the grid openings 17 in the first zone 10a is CD1, the critical dimension of the grid openings 17 in the second zone 10b is CD2, and CD1 and CD2 are not equal . By forming the grille openings 17 with different key dimensions, it is beneficial to improve the diversification of functions of the back-illuminated image sensor.

8 and 9, in order to increase the amount of light received by the pixel unit Pix under the grid opening 17 and improve the performance of the back-illuminated image sensor, in this embodiment, the shape of the grid opening 17 is made to be narrow at the top and narrow at the bottom. Wide, or in other words, the cross-sectional figure of the grille opening 17 is narrow at the top and wide at the bottom. For example, the cross-sectional figure of the grille opening 17 may be a trapezoid with a narrow top and a wide bottom.

Fig. 7 is a cross-sectional view of a trimmed side wall in an embodiment of the present invention. In order to obtain a grid opening 17 with a narrow top and a wide bottom, in some embodiments, after removing the core mold structure 14a, before etching the mask layer 13 downward using the sidewall 16a as a mask, as shown in FIG. The topography of the bottom of the sidewall 16a is trimmed by an etching process to obtain a grid opening 17 with a narrow top and a wide bottom. For example, the sidewall at the bottom of the sidewall 16a is etched by a dry etching process, so that the bottom spacing of adjacent sidewalls is enlarged, or the bottom spacing of adjacent sidewalls is larger than the top spacing, so as to obtain a grid with a narrow top and a wide bottom. Opening 17.

It should be noted that, when modifying the topography of the bottom of the sidewall 16a, the mask layer 13 may include protecting the grid material layer 12 below. The topography of the bottom of the sidewall 16a is trimmed, and the mask layer 13 is arranged between the sidewall 16a and the grid material layer 12, which is beneficial to etching to form the grid opening 17 with a narrow top and a wide bottom.

In some embodiments, referring to FIG. 8, after etching the grid material layer 12 to form a grid-like composite metal grid 12a, the shape of the grid opening 17 of the composite metal grid 12a is modified, so that the grid opening 17 is a shape with a narrow top and a wide bottom. Specifically, the sidewall at the bottom of the grid opening 17 may be etched by a dry etching process, so as to enlarge the size of the bottom of the grid opening 17 .

Referring to FIG. 9 , after the grid material layer 12 is etched to form a grid-shaped composite metal grid 12 a , an oxidation protection layer 18 may be formed on the sidewalls of the plurality of grid openings 17 . The material of the oxidation protection layer 18 may be silicon oxide.

Referring to FIG. 9, after etching the grid material layer to form a grid-shaped composite metal grid 12a, specifically, after forming an oxidation protection layer 18 on the sidewall of the grid opening 17, it can be formed in the grid opening 17. color filter 19 . A convex lens array (not shown in the figure) can also be formed on the composite metal grid 12a and the color filter 19, and one color filter 19 corresponds to one convex lens.

In the manufacturing method of the back-illuminated image sensor of the present application, firstly, a grid material layer and a mandrel structure 14a located on the grid material layer are formed on the back surface of the substrate 10, and the substrate 10 includes a first region and a first region 10a. The second zone 10b; then form a sidewall 16a on the sidewall of the mandrel structure 14a, and then remove the mandrel structure 14a; then use the sidewall 16a as a mask to etch the grid material layer to form a network Grid-shaped composite metal grid 12a. The manufacturing method of the back-illuminated image sensor can form a composite metal grid 12a with a smaller size. In addition, the composite metal grid 12a has a plurality of grid openings 17, and the grid openings 17 in the first region 10a The critical dimension of is different from the critical dimension of the grid opening 17 in the second region 10b, which is beneficial to diversify the functions of the back-illuminated image sensor.

The present application also provides a back-illuminated image sensor, which can be manufactured by the above manufacturing method.

Referring to FIG. 9, the back-illuminated image sensor includes a substrate 10 and a composite metal grid 12a.

The substrate 10 includes a first region 10a and a second region 10b. A plurality of pixel units Pix are formed in the substrate 10 , and the plurality of pixel units are isolated by an isolation structure. An interconnection layer is formed on the front side of the substrate 10 .

A composite metal grid 12a is located on the back side of the substrate 10 and has a plurality of grid openings 17 . The critical dimensions of the grate openings 17 in the first zone 10a are different from the critical dimensions of the grate openings 17 in the second zone 10b.

Further, the grille opening 17 may have a shape with a narrow top and a wide bottom, so as to increase the amount of light received by the pixel units under the grille opening 17 and improve the performance of the back-illuminated image sensor.

It should be noted that, unless otherwise specified or pointed out, the terms “first”, “second”, and “third” in the description are only used to distinguish each component, element, step, etc. It is used to express the logical relationship or sequence relationship between various components, elements, and steps.

The above description is only a description of the preferred embodiments of the present invention, and is not any limitation to the scope of rights of the present invention. Anyone skilled in the art can use the methods and technical contents disclosed above to analyze the present invention without departing from the spirit and scope of the present invention. Possible changes and modifications are made in the technical solution. Therefore, any modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention are protected by the technical solution of the present invention. scope.

Claims (7)

1. A method for fabricating a backside illuminated image sensor, comprising:

providing a substrate, wherein the substrate comprises a first area and a second area, and a grid material layer and a core mold structure positioned on the grid material layer are formed on the back surface of the substrate; the method of providing the substrate comprises: forming the grid material layer, the mask layer, the core mold material layer and the graphical photoresist layer which are stacked from bottom to top on the back surface of the substrate, etching the core mold material layer downwards by taking the graphical photoresist layer as a mask to form the core mold structure, and then removing the graphical photoresist layer;

forming a side wall on the side wall of the core mold structure, and removing the core mold structure; and

etching the mask layer by taking the side wall as a mask to form a patterned mask layer; etching the grid material layer by taking the side wall and the patterned mask layer as masks to form a latticed composite metal grid; the composite metal grid having a plurality of grid openings, the critical dimensions of the grid openings in the first zone being different from the critical dimensions of the grid openings in the second zone;

after the mandrel structure is removed and before the grid material layer is etched, the appearance of the bottom of the side wall is trimmed through an etching process, so that a grid opening with a narrow top and a wide bottom is obtained.

2. The method of claim 1, wherein forming the sidewall on the sidewall of the mandrel structure comprises:

forming a side wall material layer, wherein the side wall material layer covers the top surface and the side wall of the core mold structure and covers the grid material layer;

and etching to remove the side wall material layer on the top surface of the core mold structure and part of the side wall material layer on the grid material layer, and reserving the side wall material layer on the side wall of the core mold structure as the side wall.

3. The method of claim 1, wherein the material of the mandrel structure comprises amorphous silicon.

4. The method of claim 1, wherein the layer of grid material includes a metal layer and an oxide layer stacked from bottom to top on the back side of the substrate.

5. The method of manufacturing of claim 1, comprising:

and after the grid material layer is etched to form a grid-shaped composite metal grid, forming an oxidation protection layer on the side wall of the plurality of grid openings.

6. The method of manufacturing of claim 1, comprising:

and after the grid material layer is etched to form a grid-shaped composite metal grid, forming a color filter in the grid opening.

7. A back-illuminated image sensor manufactured by the method for manufacturing a back-illuminated image sensor according to any one of claims 1 to 6, the back-illuminated image sensor comprising:

a substrate comprising a first region and a second region; and

a composite metal grid on the back side of the substrate having a plurality of grid openings; wherein a critical dimension of the grid openings in the first zone is different from a critical dimension of the grid openings in the second zone.

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