Image sensor and preparation method thereof

Abstract

The invention discloses an image sensor and a preparation method thereof, the surface of a substrate is provided with a concave-convex absorption enhancement structure, and one end of at least part of grids is embedded into the absorption enhancement structure. On the basis of the original absorption enhancement structure and grid forming process, the embedded grid can be formed without additional process flow or cost. According to the image sensor and the preparation method thereof, on one hand, the effective area of the absorption enhancement structure is increased, the quantum efficiency of the image sensor is further improved, and on the other hand, optical crosstalk between adjacent pixel units is reduced.

Description

Technical Field

[0001] The present invention relates to the field of integrated circuits, and particularly to an image sensor and a method for manufacturing the same. Background Art

[0002] An image sensor uses the photoelectric conversion function of optoelectronic devices in a pixel array to convert an optical signal into an electrical signal corresponding to the optical signal in proportion, and then forms image information through processing, storage, etc. by a peripheral circuit.

[0003] As Figure 1 shown, it is a schematic diagram of an existing image sensor. The image sensor includes a substrate 1, a photodetector unit 2 disposed in the substrate 1, a filter layer 3 corresponding to the photodetection unit, and a microlens 4. A grid 5 is disposed between adjacent photodetector units to reduce crosstalk. An absorption enhancement structure 0 is disposed on a partial light incident surface of the photodetector unit. The absorption enhancement structure 0 can reduce the reflectivity and increase the effective absorption of light to improve the quantum efficiency of the photodetector. However, the existing absorption enhancement structure 0 is usually disposed in the middle region corresponding to the photodetector unit 2. After covering and filling a dielectric layer on the absorption enhancement structure 0, the grid 5 is disposed in the region between the absorption enhancement structures. Since there is a certain distance between the grid 5 and the substrate 1 in the vertical direction, this will cause a certain amount of light crosstalk between adjacent pixel units (or photodetector units 2). For example, light L passes through the end of the grid unit through the dielectric layer and enters an adjacent pixel unit from one pixel unit, which results in a reduction in the imaging quality of the image sensor due to optical crosstalk. Summary of the Invention

[0004] Based on the problems described above, the image sensor and the method for manufacturing the same provided by the present invention provide an uneven absorption enhancement structure on the surface of the substrate, and embed one end of at least part of the grid into the absorption enhancement structure. Based on the original formation processes of the absorption enhancement structure and the grid, an embedded grid can be formed without additional process flows or costs. On the one hand, it is beneficial to increase the effective area of the absorption enhancement structure and further improve the quantum efficiency of the image sensor. On the other hand, it is beneficial to reduce the optical crosstalk between adjacent pixel units.

[0005] In a first aspect, the present invention provides an image sensor, including: a substrate; a photodetector unit, wherein a plurality of photodetector units arranged in an array are disposed in the substrate; an absorption enhancement structure, which is disposed unevenly along the surface of the substrate; a grid, which is disposed on the surface of the substrate at a position between adjacent photodetector units; wherein, one end of at least part of the grid is embedded in the absorption enhancement structure.

[0006] In some embodiments, the absorption enhancement structure is formed on the entire surface of the substrate.

[0007] In some embodiments, one end of all the grids is embedded in the absorption enhancement structure.

[0008] In some embodiments, one end of the grid is embedded in the recessed portion of the absorption enhancement structure; and / or, one end of the grid is embedded in the protruding portion of the absorption enhancement structure.

[0009] In some embodiments, one end of the grid is embedded in one or more recesses and protrusions of the absorption enhancement structure.

[0010] In some embodiments, one end of the grid only covers a part of one of the protrusions of the absorption enhancement structure; and / or, one end of the grid only covers a part of one of the recesses of the absorption enhancement structure.

[0011] In some embodiments, the absorption enhancement structure is formed by protrusions and recesses of one shape among conical, pyramidal, frustum conical, frustum pyramidal, prismatic, cylindrical, or a combination of protrusions and recesses of multiple shapes.

[0012] In some embodiments, the material of the grid includes metal and / or dielectric material.

[0013] In some embodiments, the grid includes a multi-layer structure composed of a metal layer and a dielectric layer.

[0014] In some embodiments, the multi-layer structure of the grid is formed by sequentially stacking layer structures of different materials from bottom to top, and / or, the multi-layer structure of the grid is formed by covering layer structures of different materials from inside to outside.

[0015] In some embodiments, the material of the grid includes a low refractive index material, and the refractive index of the low refractive index material is less than 1.5.

[0016] In some embodiments, at least one dielectric layer is formed on the absorption enhancement structure.

[0017] In some embodiments, a first dielectric layer and a second dielectric layer that are sequentially stacked on the surface of the substrate are formed on the absorption enhancement structure.

[0018] In some embodiments, the refractive index of the at least one dielectric layer is less than the refractive index of the substrate.

[0019] In some embodiments, the refractive index of the second dielectric layer is less than the refractive index of the first dielectric layer, and the refractive index of the first dielectric layer is less than the refractive index of the substrate.

[0020] In some embodiments, a filter layer including different colors is covered on the at least one dielectric layer.

[0021] In some embodiments, the grid is located between filter layers of different colors.

[0022] In some embodiments, the image sensor further includes isolation trenches for isolating adjacent photodetector units.

[0023] In some embodiments, in the direction radiating from the central region of the image sensor towards the periphery, the grid gradually deviates from alignment with the isolation trenches, and the greater the distance from the central region, the greater the deviation.

[0024] In a second aspect, the present invention provides a method for manufacturing the image sensor according to any one of the foregoing embodiments, including the following steps: S1: Provide a substrate, and fabricate a plurality of photodetector units arranged in an array on the substrate; S2: Form an absorption enhancement structure on the substrate; S3: Form the grid on the absorption enhancement structure.

[0025] In some embodiments, the method further includes the step of forming isolation trenches after the absorption enhancement structure is formed and before the grid is formed.

[0026] In some embodiments, step S2 specifically includes: S21: Etch the surface of the substrate to form an absorption enhancement structure; S22: Cover at least one dielectric layer on the surface of the absorption enhancement structure.

[0027] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: An uneven absorption enhancement structure is provided on the surface of the substrate, and one end of at least part of the grid is embedded in the absorption enhancement structure. Based on the original formation processes of the absorption enhancement structure and the grid, an embedded grid can be formed without additional process flows or costs. On the one hand, it is beneficial to increase the effective area of the absorption enhancement structure and further improve the quantum efficiency of the image sensor. On the other hand, it is beneficial to reduce the optical crosstalk between adjacent pixel units. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings of the present invention form a part of this specification and are used to further understand the present invention. The drawings illustrate embodiments of the present invention and, together with the description, are used to explain the principles of the present invention.

[0029] Figure 1 It is a schematic diagram of an existing image sensor.

[0030] Figure 2 It is a schematic diagram of an image sensor according to an embodiment of the present invention.

[0031] Figure 3 Schematic diagram of an image sensor according to another embodiment of the present invention.

[0032] Figure 4 Schematic diagram of an alternative embodiment of the grid-embedded absorption enhancement structure of the present invention.

[0033] Figure 5 Schematic diagram of the distribution of the grid on the substrate surface of the present invention.

[0034] Figure 6 is a schematic diagram of another embodiment of the grid-embedded absorption enhancement structure of the present invention.

[0035] Figure 7 Schematic diagram of an embodiment of the grid structure of the present invention. Detailed implementation manners

[0036] The following detailed descriptions are all exemplary and are intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0037] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention.

[0038] As Figure 2 shown, it is a schematic diagram of an image sensor according to an embodiment of the present invention. The image sensor can be a CMOS image sensor (CIS). The image sensor includes a substrate 11, and the substrate 11 can be, for example, a silicon substrate or a substrate formed of other III-V group materials. A photodetection unit 12, and the photodetection unit 12 can include, for example, a photodiode, an avalanche photodiode (APD), a single photon avalanche diode (SPAD), or other suitable photodetectors. A plurality of photodetection units 12 are arranged in an array in the substrate 11; an absorption enhancement structure 10 is arranged to be uneven along the surface of the substrate 11, as Figure 2As shown, the absorption enhancement structure 10 is not only disposed in the central region corresponding to the photoelectric detection unit 12, but also in the region between adjacent photoelectric detection units 12; the grid 15 is disposed on the surface of the substrate 11 and is located between adjacent photodetector units 12. By disposing the absorption enhancement structure 10 in the region between adjacent photoelectric detection units 12, one end of at least part of the grid 15 can be embedded in the absorption enhancement structure 10. In this way, on the one hand, it is beneficial to increase the effective area of the absorption enhancement structure and further improve the quantum efficiency of the image sensor. On the other hand, it is beneficial to reduce the optical crosstalk between adjacent pixel units. A filter layer 13 is disposed in the opening of the grid 15, and the filter layers 13 of different pixel units can be respectively configured with materials that allow light of a specific wavelength to pass through. For example, the filter layers 13 of different pixel units can include material layers that allow red, green, or blue light to pass through. A plurality of microlenses 14 are arranged on the filter layer 13. Each of the plurality of microlenses 14 corresponds one-to-one to each of the filter layers 13, and the microlenses 14 are used to focus the incident light into the photodetector. In other embodiments, one microlens 14 can also correspond to a plurality of filter layers, and this embodiment is not limited thereto.

[0039] In a specific embodiment, the absorption enhancement structure 10 can be formed on the entire surface of the substrate 11, or can be disposed only on a partial surface of the substrate 11. The case of being disposed only on a partial surface of the substrate 11 can be for regions with relatively severe optical crosstalk. For example, only in that part of the region with relatively severe optical crosstalk, an uneven absorption enhancement structure 10 is disposed to completely cover the region, and one end of the grid 15 in this region is embedded in the absorption enhancement structure 10. When the absorption enhancement structure 10 can be formed on the entire surface of the substrate 11, it is convenient for one end of the grid 15 at all positions to be embedded in the absorption enhancement structure 10, ensuring that one end of the grid 15 at every place of the entire image sensor is embedded in the absorption enhancement structure 10, improving the optical crosstalk of the image sensor, and increasing the quantum efficiency.

[0040] In a specific embodiment, one end of at least part of the grid 15 is embedded in the absorption enhancement structure 10. As Figure 2 shown, one end of the grid 15 is embedded in a raised region of the absorption enhancement structure 10. Since one end of the grid 15 can partially cover the raised region of the absorption enhancement structure 10, the probability of incident light entering adjacent pixel units is significantly reduced. For example, the light L originally corresponding to one pixel unit is blocked by the grid and cannot enter the adjacent pixel unit, thereby reducing the optical crosstalk.

[0041] In addition to one end of the grid 15 being embedded in the protruding part of the absorption enhancement structure 10; one end of the grid 15 can also be embedded in the recessed part of the absorption enhancement structure 10. As Figure 3As shown, one end of the grid 15 is embedded in a recessed area of the absorption enhancement structure 10. Since one end of the grid 15 can extend deep into the recessed area, the probability of incident light entering adjacent pixel units is significantly reduced. For example, the light L originally corresponding to one pixel unit is blocked by the grid and cannot enter the adjacent pixel unit, thereby reducing optical crosstalk.

[0042] Optionally, in an image sensor, one end of the grid 15 can be embedded only in the recessed part of the absorption enhancement structure 10, or only in the protruding part of the absorption enhancement structure 10, or it can be both embedded in the recessed part of the absorption enhancement structure 10 and embedded in the protruding part of the absorption enhancement structure 10.

[0043] In a specific embodiment, one end of the grid 15 can be embedded in one or more recesses and protrusions of the absorption enhancement structure 10, as Figure 4 shown, which exemplifies the optional cases of the grid being embedded in the absorption enhancement structure. Preferably, one end of the grid 15 completely covers all of one of the recesses of the absorption enhancement structure 10, as Figure 4 shown in (a); one end of the grid 15 can also only partially cover one of the recesses of the absorption enhancement structure 10, as Figure 4 shown in (b); one end of the grid 15 can also partially cover two of the recesses of the absorption enhancement structure 10 and completely cover one of the protrusions, as Figure 4 shown in (c); one end of the grid 15 can also partially cover one of the recesses of the absorption enhancement structure 10 and completely cover one of the protrusions, as Figure 4 shown in (d); one end of the grid 15 can only cover a part of one of the protrusions and a part of one of the recesses of the absorption enhancement structure 10, as Figure 4 shown in (e); or it can be partially or completely cover multiple protrusions and one or more recesses of the absorption enhancement structure 10, as Figure 4 shown in (f) to (h).

[0044] In a specific embodiment, as Figure 5 shown, in an image sensor, the grid 15 includes portions extending in the mutually perpendicular X and Y directions, and the portions extending in the X and Y directions intersect to form the grid 15. Among them, the embedding forms of the portion of the grid 15 extending in the X direction and the portion extending in the Y direction can be the same or different. For example, one end of the grid portion extending in the X direction is only embedded in one of the protrusions of the absorption enhancement structure, and one end of the grid portion extending in the Y direction is embedded in multiple protrusions of the absorption enhancement structure.

[0045] Optionally, on the premise that one end of the grid 15 is embedded in one or more recesses and protrusions of the absorption enhancement structure 10, the other end of the grid 15 can be flat-topped or pointed-topped; attachedFigures 2 - 4 illustrates a grid 15 with a flat top, such as Figure 2 shown. After one end of the grid 15 is embedded in the absorption enhancement structure 10, the distance between the two side edges of the cross-section of the grid 15 remains unchanged. Its cross-section is a rectangle including a triangular notch, and the other end is flat-topped. However, the shape of the grid 15 in the embodiments of the present invention is not limited to this, and the grid 15 can be formed into any form of dam shape. As shown in FIG. 6, the distance between the two side edges of the cross-section of the grid 15 can gradually decrease from the embedded end to the top end. For example, the grid 15 can have a trapezoidal cross-section. The distance between the two side edges of the cross-section of the grid 15 can also gradually decrease and even intersect from the embedded end to the top end, that is, a pointed top end is formed.

[0046] As shown in FIG. 6(a), the cross-section of the grid 15 is wedge-shaped, and one end of it is embedded by covering a part of one of the protrusions of the absorption enhancement structure 10 (in the embodiment of FIG. 6(a), since the unevenness is triangular serrated, so here it can also be considered that one end of it is embedded by covering a part of one of the depressions of the absorption enhancement structure 10). Since one end of the grid 15 can partially cover the protrusion area of the absorption enhancement structure 10, the probability of incident light entering adjacent pixel units is significantly reduced, thereby reducing optical crosstalk. In addition, the grid 15 of this shape can also realize the difference in the incident light amount of adjacent pixel units (corresponding to adjacent filter layers 131 and 132). For the pixel unit corresponding to the filter layer 131, at least the light rays l1 and l2 irradiated on the long side of the grid 15 will be absorbed or reflected by the grid 15. However, for the pixel unit corresponding to the filter layer 132, only the light ray l2 is absorbed or reflected by the grid 15. Therefore, the shape of the grid 15 in FIG. 6(a) can be used to adjust the incident light amount requirements of different pixel units.

[0047] In addition, as shown in FIG. 6(b), different from FIG. 6(a), the grid 15 between adjacent pixel units includes a wedge shape symmetric about the z-axis. Specifically, the grid 15 straddles the protrusion (which can be one protrusion or multiple protrusions) of the absorption enhancement structure 10 to be embedded in the absorption enhancement structure 10. In the drawings, the other end of the grid 15 is pointed, but it is not limited to this, and the other end can also be flat-topped. Through this setting, the incident light amount of adjacent pixel units (corresponding to adjacent filter layers 131 and 132) can be increased to the same extent to improve the quantum efficiency of the image sensor.

[0048] In a specific embodiment, the absorption enhancement structure 10 can be formed by a combination of protrusions and depressions of one shape among a conical shape, a pyramidal shape, a frustum of a conical shape, a frustum of a pyramidal shape, a prismatic shape, a cylindrical shape, or a combination of protrusions and depressions of multiple shapes.

[0049] In a specific embodiment, the grid 15 is also disposed on at least one dielectric layer. Optionally, the grid 15 may comprise a metal (such as aluminum, cobalt, copper, silver, gold, tungsten, etc.) and / or a dielectric material (such as SiO2, SiN, etc.). Preferably, the grid 15 comprises a multi-layer structure composed of a metal layer and a dielectric layer.

[0050] In a specific embodiment, as Figure 7 shown, the multi-layer structure of the grid 15 is formed by sequentially stacking layer structures of different materials from bottom to top. By way of example, as Figure 7 (a) shown; and / or, the multi-layer structure of the grid 15 is formed by covering layer structures of different materials from inside to outside. By way of example, as Figure 7 (b) to 7(c) shown. In Figure 7 (a), the multi-layer structure of the grid 15 is sequentially stacked from bottom to top, and the thickness of the metal layer m 1 is much greater than the thickness of the dielectric material layer f 1 to f 4, so as to better avoid optical crosstalk between adjacent pixel units. In Figure 7 (b), the multi-layer structure of the grid 15 is formed by covering layer structures of different materials from inside to outside. The dielectric material forms layers f 1 to f 2, and the metal layer m 1. Since the light-blocking effect of the metal layer is the best, optical crosstalk between adjacent pixel units can be avoided. It is formed in a covering form, which can make the grid 15 more stable and prevent the grid 15 from toppling. In Figure 7 (c), the multi-layer structure of the grid 15 not only includes layer structures of different materials sequentially stacked from bottom to top, but also includes a dielectric layer structure covering the stack. The stacked layers include dielectric layers f 1 to f 4 and the metal layer m 1, and the dielectric layer f 5 covers the stacked layers; through this setting, on the one hand, the risk of the grid 15 toppling can be reduced. On the other hand, in some special cases, complete light-blocking by the grid is not conducive to image quality. The light absorption and reflection performance of the dielectric material layers f 1 to f 5 is quite different from the light absorption and reflection performance of the metal layer m 1. Therefore, forming the grid through the combination of the dielectric material layer and the metal layer can better balance requirements such as optical crosstalk and incident light amount, and can further optimize the imaging quality.

[0051] In a specific embodiment, the material of the grid 15 may further include a low refractive index material. Preferably, the refractive index of the low refractive index material is less than 1.5. Thereby reducing the absorption of incident light by the grid and improving the quantum efficiency of the image sensor.

[0052] In a specific embodiment, as Figure 2 shown, at least one dielectric layer is formed on the absorption enhancement structure 10. Preferably, the refractive index of the at least one dielectric layer is less than the refractive index of the substrate 11. The at least one dielectric layer may include, for example, any combination of one or more of silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride, hafnium oxide, tantalum oxide. Preferably, a first dielectric layer 16 and a second dielectric layer 17 are formed on the absorption enhancement structure and are stacked in sequence on the surface of the substrate 11. Preferably, the refractive index of the second dielectric layer 17 is less than the refractive index of the first dielectric layer 16, and the refractive index of the first dielectric layer 16 is less than the refractive index of the substrate 11. By setting the refractive index, total internal reflection of incident light between layers can be avoided, and incident light can enter the substrate as much as possible and be absorbed by the photodetector.

[0053] In a specific embodiment, color filter layers 13 of different colors are provided to cover the at least one dielectric layer.

[0054] In a specific embodiment, color filter layers 13 of different colors are located in the openings of the grid 15, and adjacent color filter layers 13 respectively cover parts of the other end (top end) of the grid 15 and meet at the top end of the grid 15, as Figure 2 shown.

[0055] In a specific embodiment, the image sensor further includes isolation trenches 18 for isolating adjacent photodetector units 12, as Figure 2 shown. A number of photodetector units 12 of the image sensor are arranged regularly and in an array, and the isolation trenches 18 regularly space apart the photodetector units 12. The so-called regular spacing means that in the first and second directions, the horizontal distances between the isolation trenches 18 and the photodetector units 12 are the same. The first and second directions are two mutually perpendicular directions, for example, the row direction and the column direction of the photodetector units 12 arranged in an array.

[0056] In a specific embodiment, in the direction radiating from the central region of the image sensor to the periphery, the grid 15 gradually deviates from the isolation trench 18. Further, the greater the distance from the central region, the greater the deviation. Specifically, in the central region of the image sensor, the grid 15 is aligned with the isolation trench 18 (i.e., no deviation), and the so-called alignment means that the vertical centerlines of the grid 15 in this region and the isolation trench 18 in this region are on the same line z as Figures 2 - 3 shown; in the edge region of the image sensor, the grid 15 deviates from the isolation trench 18, and the so-called deviation means that the vertical centerlines of the grid 15 in this region and the isolation trench 18 in this region are not on the same line.

[0057] In addition, the present invention further provides a method for manufacturing the image sensor of any one of the foregoing embodiments, including the following steps: S1: Provide a substrate, and fabricate a plurality of photodetector units arranged in an array on the substrate; S2: Form an absorption enhancement structure on the substrate; S3: Form the grid on the absorption enhancement structure.

[0058] In a specific embodiment, the method further includes the step of forming isolation trenches after the absorption enhancement structure is formed and before the grid is formed.

[0059] In a specific embodiment, step S2 specifically includes: S21: Etch the surface of the substrate to form an absorption enhancement structure; S22: Cover at least one dielectric layer on the surface of the absorption enhancement structure.

[0060] The method for manufacturing the image sensor of any one of the foregoing embodiments provided by the present invention further includes steps such as fabricating a color filter layer, a microlens, etc., which will not be elaborated herein.

[0061] In summary, the present invention discloses an image sensor and a method for manufacturing the same. An uneven absorption enhancement structure is provided on the surface of the substrate, and one end of at least part of the grid is embedded in the absorption enhancement structure. Based on the original formation process of the absorption enhancement structure and the grid, an embedded grid can be formed without additional process flows or costs. On the one hand, the image sensor and the method for manufacturing the same are beneficial to increasing the effective area of the absorption enhancement structure and further improving the quantum efficiency of the image sensor. On the other hand, it is beneficial to reducing the optical crosstalk between adjacent pixel units.

[0062] The basic concepts have been described above. Obviously, for those skilled in the art, the above detailed disclosure is only an example and does not constitute a limitation to the present invention. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to the present invention. Such modifications, improvements, and corrections are proposed in the present invention, so such modifications, improvements, and corrections still fall within the spirit and scope of the exemplary embodiments of the present invention.

[0063] It should be understood that the embodiments described in the present invention are only used to illustrate the principles of the embodiments of the present invention. Other deformations may also fall within the scope of the present invention. Therefore, as an example rather than a limitation, the alternative configurations of the embodiments of the present invention can be regarded as consistent with the teachings of the present invention. Accordingly, the embodiments of the present invention are not limited to the embodiments explicitly introduced and described in the present invention.

Claims

1. An image sensor, characterized in that, Comprising, a substrate; photoelectric detector units, a plurality of photo - electric detector units arranged in an array are disposed in the substrate; an absorption enhancement structure, which is disposed in a concavo - convex manner along the surface of the substrate; a grid, which is disposed on the surface of the substrate at a position between adjacent photoelectric detector units; wherein, one end of at least part of the grid is embedded in the absorption enhancement structure.

2. The image sensor according to claim 1, characterized in that, The absorption enhancement structure is formed on the entire surface of the substrate.

3. The image sensor according to any one of claims 1 to 2, characterized in that, One end of all the grids is embedded in the absorption enhancement structure.

4. The image sensor according to any one of claims 1 to 3, characterized in that, One end of the grid is embedded in a concave part of the absorption enhancement structure; and / or, one end of the grid is embedded in a convex part of the absorption enhancement structure.

5. The image sensor according to claim 4, characterized in that, One end of the grid is embedded in one or more concave and convex parts of the absorption enhancement structure.

6. The image sensor according to claim 4, wherein, One end of the grid only covers a part of one convex of the absorption enhancement structure; and / or, one end of the grid only covers a part of one concave of the absorption enhancement structure.

7. The image sensor according to claim 1, wherein The absorption enhancement structure is formed by a combination of convex and concave parts of one shape among a conical shape, a pyramidal shape, a frustum - conical shape, a frustum - pyramidal shape, a prismatic shape, a cylindrical shape, or a combination of convex and concave parts of multiple shapes.

8. The image sensor according to claim 1, wherein The material of the grid includes metal and / or a dielectric material.

9. The image sensor according to claim 9, wherein, The grid includes a multi - layer structure composed of a metal layer and a dielectric layer.

10. The image sensor according to claim 10, characterized in that, The multi - layer structure of the grid is stacked in sequence from bottom to top by layer structures of different materials, and / or, the multi - layer structure of the grid is coated from inside to outside by layer structures of different materials.

11. The image sensor according to claim 1, characterized in that, The material of the grid includes a low - refractive - index material, and the refractive index of the low - refractive - index material is less than 1.

5.

12. The image sensor according to claim 1, wherein At least one dielectric layer is formed on the absorption enhancement structure.

13. The image sensor according to claim 14, wherein, A first dielectric layer and a second dielectric layer are formed on the absorption enhancement structure in sequence and stacked on the surface of the substrate.

14. The image sensor according to claim 14, characterized in that, The refractive index of the at least one dielectric layer is less than the refractive index of the substrate.

15. The image sensor according to claim 15, characterized in that The refractive index of the second dielectric layer is less than the refractive index of the first dielectric layer, and the refractive index of the first dielectric layer is less than the refractive index of the substrate.

16. The image sensor according to claim 14, wherein A filter layer with different colors is covered on the at least one dielectric layer.

17. The image sensor according to claim 18, wherein, The grid is located between filter layers with different colors.

18. The image sensor according to claim 1, characterized in that, The image sensor further includes isolation trenches for isolating adjacent photoelectric detector units.

19. The image sensor according to claim 12, wherein, In the direction radiating from the central region of the image sensor to the periphery, the grid gradually deviates from alignment with the isolation trenches, and the greater the distance from the central region, the greater the deviation.

20. A method for manufacturing an image sensor according to any one of claims 1 - 19, comprising the following steps: S1: Providing a substrate and fabricating a plurality of photoelectric detector units arranged in an array on the substrate; S2: Forming an absorption enhancement structure on the substrate; S3: Forming the grid on the absorption enhancement structure.

21. The method according to claim 20, characterized in that, The method further includes a step of forming isolation trenches after the absorption enhancement structure is formed and before the grid is formed.

22. The method according to claim 20, wherein Step S2 specifically includes: S21: Etching the surface of the substrate to form an absorption enhancement structure; S22: Covering at least one dielectric layer on the surface of the absorption enhancement structure.

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