Image sensor and method of forming the same

Abstract

The application discloses a kind of image sensor and its forming method, the image sensor includes substrate, including several photosensitive regions and the isolation region between photosensitive region;Lattice structure on the isolation region;Composite structure is located on the top of the lattice structure, the composite structure includes at least two light-absorbing layers and the spacing layer between adjacent light-absorbing layers, the at least two light-absorbing layers are stacked along the direction perpendicular to substrate surface, and from the center to the edge of the composite structure, the size of the composite structure in the direction perpendicular to substrate surface is smaller.By the convergence and absorption of the composite structure to light, the light reflection on the top of the lattice structure can be weakened, so as to solve the noise problem of image sensor, and improve the imaging effect.

Description

Technical Field

[0001] This application relates to the field of semiconductor device and manufacturing technology, and in particular to an image sensor and a method for forming the same. Background Technology

[0002] An image sensor is a semiconductor device that converts light signals into electrical signals. Image sensors are divided into CMOS (Complementary Metal-Oxide-Semiconductor) image sensors and CCD (Charge-Coupled Device) image sensors. CMOS image sensors (CIS) have advantages such as simple manufacturing process, easy integration with other devices, small size, light weight, low power consumption, and low cost. Therefore, with the development of image sensing technology, CMOS image sensors are increasingly replacing CCD image sensors in various electronic products.

[0003] CMOS image sensors include front-side illumination (FSI) image sensors and back-side illumination (BSI) image sensors. In a back-side illumination image sensor, light enters from the back of the image sensor and strikes a photodiode within the sensor, thereby converting the light signal into an electrical signal.

[0004] However, with the increasing integration of devices, optical crosstalk in image sensors has become increasingly severe, becoming one of the problems that the industry urgently needs to solve. Summary of the Invention

[0005] This application provides an image sensor and a method for forming the same, which improves the absorption rate of light at a specific incident angle between pixel units, thereby at least partially mitigating the optical crosstalk problem.

[0006] To achieve the above objectives, an image sensor is provided according to the technical solution of this application, comprising: a substrate, including a plurality of photosensitive areas and an isolation area located between the plurality of photosensitive areas; a grid structure located on the isolation area; and a composite structure located on the side of the grid structure opposite to the substrate, the composite structure including a first light-absorbing layer, a second light-absorbing layer and a spacer layer stacked along a first direction perpendicular to the surface of the substrate, the spacer layer being located between the first light-absorbing layer and the second light-absorbing layer, and the thickness of the composite structure in the first direction decreasing from the center to the edge of the composite structure.

[0007] In some embodiments, the distance from the first light-absorbing layer to the grating structure is less than the distance from the second light-absorbing layer to the grating structure; the thickness of the second light-absorbing layer in the first direction decreases from the center to the edge of the composite structure.

[0008] In some embodiments, the second light-absorbing layer includes a first surface and a second surface that is closer to the lattice structure than the first surface, and the first surface protrudes in an arc shape relative to the second surface in a direction away from the substrate surface.

[0009] In some embodiments, the radius of curvature of the first surface ranges from 2 micrometers to 5 micrometers.

[0010] In some embodiments, the thickness of the first light-absorbing layer decreases in the first direction from the center to the edge of the composite structure.

[0011] In some embodiments, the first light-absorbing layer includes a third surface and a fourth surface further away from the grating structure relative to the third surface, and the third surface protrudes in an arc shape relative to the fourth surface toward the substrate surface.

[0012] In some embodiments, the radius of curvature of the third surface ranges from 2 micrometers to 5 micrometers.

[0013] In some embodiments, the composite structure further includes at least one third light-absorbing layer located between the first light-absorbing layer and the second light-absorbing layer, wherein the at least one third light-absorbing layer, the first light-absorbing layer, and the second light-absorbing layer are stacked along the first direction.

[0014] In some embodiments, the grid structure includes a first region and a second region, the grid structure of the first region having a first width, the grid structure of the second region having a second width, and the first width being greater than the second width; the composite structure is located on the side of the grid structure of the first region facing away from the substrate.

[0015] In some implementations, the first width ranges from 1 micrometer to 2 micrometers.

[0016] In some embodiments, the material of the first light-absorbing layer includes titanium, tungsten, or silicon oxynitride; the material of the second light-absorbing layer includes titanium, tungsten, or silicon oxynitride; and the material of the spacer layer includes oxides.

[0017] In some embodiments, the substrate includes opposing first and second functional surfaces, and the grid structure is located on the surface of the first functional surface; the image sensor further includes: a device layer located on the second functional surface, the device layer including logic devices; a photoelectric doped region located within the photosensitive area; a filter layer located on the first functional surface of the photosensitive area; and a lens structure located on the side of the filter layer opposite to the substrate.

[0018] Accordingly, the technical solution of this application also provides a method for forming an image sensor, the image sensor as described in any of the above claims, comprising: providing a substrate, the substrate including a plurality of photosensitive areas and an isolation area located between the plurality of photosensitive areas; forming a grid structure on the isolation area; forming a composite structure on the side of the grid structure away from the substrate, the composite structure including a first light-absorbing layer, a second light-absorbing layer and a spacer layer stacked along a first direction perpendicular to the surface of the substrate, the spacer layer being located between the first light-absorbing layer and the second light-absorbing layer, and the thickness of the composite structure in the first direction decreasing from the center to the edge of the composite structure.

[0019] In some embodiments, the method of forming a grid structure on the isolation region includes: forming an initial grid structure on the isolation region; forming a first patterned layer on the photosensitive region, the first patterned layer exposing the initial grid structure; using the first patterned layer as a mask, etching the top surface of the initial grid structure to form the grid structure, the grid structure including opposing first end faces and second end faces, the distance from the first end face to the substrate being less than the distance from the second end face to the substrate, and the second end face being arc-shaped recessed in the direction of the first end face.

[0020] In some embodiments, the method of forming the composite structure includes: forming a first light-absorbing layer on the top surface of the grating structure; forming an initial spacer layer on the first light-absorbing layer; patterning the initial spacer layer to form a spacer layer on the first light-absorbing layer; forming a second light-absorbing material layer on the surface of the spacer layer; patterning the second light-absorbing material layer to form a second light-absorbing layer on the spacer layer, wherein the thickness of the second light-absorbing layer in the first direction decreases from the center to the edge of the composite structure, the second light-absorbing layer includes a first face opposite to the first face and a second face closer to the grating structure than the first face, and the first face protrudes arcuately relative to the second face in a direction away from the substrate surface.

[0021] In the image sensor and its formation method according to embodiments of this application, by setting a composite structure on the grating structure between photosensitive areas, light incident on the side of the grating structure away from the substrate can be converged and absorbed simultaneously, thereby reducing the light reflection problem caused by the grating structure and mitigating optical crosstalk. On one hand, in a first direction perpendicular to the substrate surface, the thickness of the composite structure decreases from the center to the edge, meaning the composite structure has a convex lens structure that can converge light incident on it, effectively converging and absorbing light that is easily reflected by the grating structure but cannot be reflected to the photosensitive area. On the other hand, the composite structure includes at least two light-absorbing layers, namely a first light-absorbing layer and a second light-absorbing layer. Thus, incident light can be absorbed multiple times by the light-absorbing layers during its journey from the composite structure to the grating structure. Furthermore, light that is not completely absorbed can be reflected again by adjacent light-absorbing layers after being reflected by the top surface of the grating structure, thereby improving the light absorption efficiency of the composite structure. In summary, since the light reflection problem at the top of the grid structure can be effectively reduced by the composite structure, the problem of noise generated in part of the grid structure of the image sensor can be effectively solved, thereby improving the imaging effect of the image sensor.

[0022] Other features and advantages of this application will be described in detail in the following detailed description section. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0025] Figure 1 and Figure 2 This is a schematic diagram of a back-illuminated image sensor embodiment;

[0026] Figure 3 This is a schematic flowchart illustrating the formation process of the image sensor according to an embodiment of this application;

[0027] Figures 4 to 15 This is a schematic diagram of the formation process of an image sensor according to an embodiment of this application;

[0028] Figure 16This is a schematic diagram of the structure of another image sensor according to an embodiment of this application. Detailed Implementation

[0029] As described in the background section, optical crosstalk in image sensors is becoming increasingly serious.

[0030] Figure 1 and Figure 2 This is a schematic diagram of a back-illuminated image sensor embodiment. Figure 1 yes Figure 2 A top-view structural diagram. Figure 2 yes Figure 1 A schematic diagram of the cross-sectional structure of region A along section line BB' includes: a substrate 100, including a first surface 110 and a second surface 120 opposite to each other; the substrate 100 includes a plurality of mutually independent photosensitive areas I and an isolation area II located between the photosensitive areas I; a photosensitive doped area 101 located within the photosensitive area I of the substrate 100; a grid 102 located on the first surface 110 of the isolation area II; a filter structure 103 located on the first surface 110 of the photosensitive area I, the filter structure 103 being used to allow light of a specific wavelength to pass through; a microlens 104 located on the filter structure 103; and a logic device layer 105 located on the second surface 120.

[0031] In this embodiment, incident light irradiates the first surface 110, and the light entering the photosensitive doped region 101 undergoes photoelectric conversion to generate an electrical signal. The grid 102 can reflect or absorb the light irradiated thereon, and is used to perform optical shielding between adjacent photosensitive regions I to prevent optical crosstalk between photosensitive regions I.

[0032] Specifically, the grid 102 is typically a metallic material with both light-absorbing and light-reflecting capabilities, such as tungsten. After incident light shines on the grid 102, some light rays D with a larger incident angle α can be reflected by the grid 102 into the photosensitive doped region 101. However, when the incident angle β of the light ray C hitting the top of the grid 102 is too small, for example, in the range of 0° to 45°, no matter how the material, film structure composition, or surface morphology of the grid 102 is adjusted, it is impossible to reflect the incident light C with the small incident angle β into the photosensitive doped region 101. Furthermore, the incident light C with the small incident angle β, after being reflected by the top of the grid 102, is prone to optical crosstalk, leading to image quality degradation.

[0033] In particular, when the width W of the grid 102 is relatively large in certain specific locations, the top of the grid 102 in that portion is more likely to reflect the incident light C, thereby causing a more serious optical crosstalk problem. The grid 102 is located between two adjacent photosensitive areas I, and the grid 102 and the two adjacent photosensitive areas I are arranged along a first direction E parallel to the surface of the substrate 100. The width W of the grid 102 refers to the dimension of the grid 102 in the first direction E.

[0034] To address the aforementioned problems, this application proposes an image sensor and a method for forming the same. Please refer to... Figure 3 , Figure 3 This is a schematic flowchart illustrating the formation process of the image sensor according to an embodiment of this application, including:

[0035] Step S101: Provide a substrate, the substrate including a plurality of photosensitive areas and an isolation area located between the plurality of photosensitive areas;

[0036] Step S102: A grid structure is formed on the isolation area;

[0037] Step S103: A composite structure is formed on the side of the grating structure away from the substrate. The composite structure includes a first light-absorbing layer, a second light-absorbing layer, and a spacer layer stacked along a first direction perpendicular to the substrate surface. The spacer layer is located between the first light-absorbing layer and the second light-absorbing layer, and the thickness of the composite structure in the first direction decreases from the center to the edge of the composite structure.

[0038] By setting a composite structure on the grid structure between the photosensitive areas, the light incident on the top of the grid structure can be converged and absorbed at the same time. Since the light reflection problem at the top of the grid structure can be effectively weakened by the composite structure, the problem of noise generated in part of the grid structure of the image sensor can be effectively solved, thereby improving the imaging effect of the image sensor.

[0039] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0040] Figures 4 to 15 This is a schematic diagram of the formation process of an image sensor according to an embodiment of this application.

[0041] Please refer to Figure 4 and Figure 5 , Figure 4 yes Figure 5 A top-view structural diagram. Figure 5 yes Figure 4 A cross-sectional schematic diagram of region E along the cross-section line FF'. Step S101 is performed to provide a substrate 200, which includes a plurality of photosensitive areas 201 and an isolation area 202 located between the plurality of photosensitive areas 201.

[0042] The substrate 200 is a silicon substrate, a germanium substrate, a silicon-germanium substrate, a silicon-on-insulator substrate, or a germanium-on-insulator substrate, etc. In this embodiment, the substrate 200 is a silicon substrate.

[0043] The photosensitive area 201 is used to form a photoelectric conversion device, and the isolation area 202 is used to isolate adjacent photosensitive areas 201. In this embodiment, the photosensitive areas 201 are arranged in an array along a second direction X and a third direction Y, both of which are parallel to the surface of the substrate 200 and perpendicular to each other.

[0044] The substrate 200 includes opposing first functional surfaces 204 and second functional surfaces 205.

[0045] In some embodiments, the image sensor is a back-illuminated image sensor. The first functional surface 204 is used to receive incident light, and the surface of the second functional surface 205 is also used to form a device layer. The device layer includes a logic circuit structure, which serves as the peripheral circuit of the image sensor. The device layer includes a first dielectric layer on the second functional surface 205, a device structure within the first dielectric layer, several second dielectric layers on the first dielectric layer, and an electrical interconnection structure within the second dielectric layer. The electrical interconnection structure is electrically connected to the device structure, and the device structure includes transistors, resistor structures, capacitor structures, etc.

[0046] In some embodiments, a photoelectric doped region 203 is also included within the photosensitive region 201 of the substrate 200. This photoelectric doped region 203 receives light, performs photoelectric conversion, and outputs an electrical signal. The photoelectric doped region 203 contains doped ions, causing it to be inverted relative to the substrate 200, thereby forming a photodiode in the photosensitive region 201. In some embodiments, the photoelectric doped region is doped with N-type ions, and the substrate 200 is a P-type substrate.

[0047] In the back-illuminated image sensor, since the logic circuit structure is located on the second functional surface, the first functional surface 204 is mainly used to form the optical structure. As a result, the incident light experiences less interference on the path of irradiating the first functional surface 204, and correspondingly, the incident light is more likely to be refracted or reflected on the path of entering the photosensitive area 201.

[0048] In some embodiments, step S102 is subsequently performed to form a grid structure on the isolation region 202. The formation process of the grid structure is as follows: Figures 4 to 6 As shown.

[0049] Please continue to refer to this. Figure 4 and Figure 5 An initial grid structure 210 is formed on the isolation zone 202.

[0050] The initial grid structure 210 is used to form a grid structure between photosensitive areas 201. The grid structure is used to isolate and shield optical signals between photosensitive areas 201 to prevent optical crosstalk between adjacent photosensitive areas 201.

[0051] In some embodiments, when the incident light irradiates the first functional surface 204, the initial grid structure 210 is formed on the surface of the first functional surface 204.

[0052] In some embodiments, since the photosensitive areas 201 are arranged in an array along the second direction X and the third direction Y, the initial grid structure 210 includes a plurality of grid strips extending along the second direction X and the third direction Y, and the plurality of grid strips constitute a grid structure.

[0053] In some embodiments, according to the design requirements of the image sensor, the initial grid structure 210 includes a first region and a second region. The first region of the initial grid structure 210 has a first width W1, and the second region of the initial grid structure 210 has a second width W2, wherein the first width W1 is greater than the second width W2.

[0054] In some embodiments, the first region of the initial grid structure 210 and the adjacent photosensitive areas 201 on both sides are arranged along a third direction Y, then the first width W1 is the dimension of the first region of the initial grid structure 210 in the third direction Y. And the second region of the initial grid structure 210 and the adjacent photosensitive areas 201 on both sides are arranged along a third direction Y, then the second width W2 is the dimension of the second region of the initial grid structure 210 in the third direction Y.

[0055] Because the first width W1 is relatively large, the incident light is unlikely to avoid the first region of the subsequently formed grating structure. That is, the first region of the subsequently formed grating structure is more prone to reflecting light. Therefore, in some embodiments, a composite structure needs to be formed at least on the first region of the grating structure to reduce the reflection problem of the incident light. In other embodiments, composite structures are formed on both the first and second regions of the grating structure. In some embodiments, the first width W1 ranges from 1 micrometer to 2 micrometers, for example, any value or a range of any two of 1 micrometer, 1.1 micrometer, 1.2 micrometer, 1.3 micrometer, 1.4 micrometer, 1.5 micrometer, 1.6 micrometer, 1.7 micrometer, 1.8 micrometer, 1.9 micrometer, and 2.0 micrometer.

[0056] In some embodiments, the method for forming the initial grid structure includes: forming a grid material layer on a first functional surface 204 of the substrate 200; forming a patterned mask layer on the grid material layer, the patterned mask layer exposing the grid material layer on the photosensitive area 201; and etching the grid material layer using the patterned mask layer as a mask to form the initial grid structure 210.

[0057] The initial grid structure 210 is made of tungsten, aluminum, or copper. In some embodiments, the initial grid structure 210 is made of tungsten.

[0058] In some embodiments, prior to forming the initial grid structure 210, a pad layer is also formed on the substrate surface, the initial grid structure 210 being located on the pad layer, the pad layer serving to improve the interface state between the initial grid structure 210 and the substrate 200 and enhance the interface bonding strength. The pad layer is made of one or more of silicon oxide, silicon nitride, and silicon oxynitride.

[0059] In some embodiments, an adhesion layer 206 is also formed between the initial grid structure 210 and the substrate 200, or between the initial grid structure 210 and the padding layer. The adhesion layer 206 is used to improve the bonding strength between the initial grid structure 210 and the substrate 200, and at the same time improve the interface state between the initial grid structure 210 and the substrate 200. The material of the adhesion layer 206 includes one or more of titanium nitride, tantalum nitride, titanium, and tantalum in a stacked combination.

[0060] In some embodiments, after forming the initial grid structure 210, a protective sidewall is further formed on the sidewall surface of the initial grid structure 210. The method for forming the protective sidewall includes: forming a protective material layer on the substrate 200, on the sidewall of the initial grid structure 210, and on a side facing away from the substrate 200; and etching back the protective material layer until the side of the initial grid structure facing away from the substrate 200 is exposed, thereby forming the protective sidewall. The material of the protective sidewall includes one or more of silicon oxide, silicon nitride, and silicon oxynitride stacked together.

[0061] Please refer to Figure 6 A first patterning layer 214 is formed on the photosensitive area, the first patterning layer 214 exposing the initial grid structure 210 (e.g., Figure 4 and Figure 5 (As shown); using the first patterning layer 214 as a mask, the surface of the initial grid structure 210 facing away from the substrate 200 is etched to form the grid structure 211. The grid structure 211 includes a first end face 212 and a second end face 213 facing each other. The distance from the first end face 212 to the substrate 200 is less than the distance from the second end face 213 to the substrate 200, and the second end face 213 is recessed in the direction of the first end face 212.

[0062] In this embodiment, the subsequently formed composite structure is a double-sided convex-through structure. The second end face 213 is used to contact and match the protruding arc surface of the composite structure. Therefore, the shape of the second end face 213 determines the convex shape of the subsequently formed composite structure.

[0063] When the subsequently formed composite structure is a double-sided convex structure, and the incident light is not completely absorbed after passing through the composite structure, the surface of the composite structure that contacts the recessed second end face 213 can reflect and converge the unabsorbed light back into the composite structure, thereby facilitating the re-absorption of the light within the composite structure and improving the absorption efficiency of the composite structure.

[0064] In other embodiments, the subsequently formed composite structure can also be a single-sided convex structure, wherein the surface of the composite structure facing the incident light is an arc-shaped convex surface, and the second end face is a plane.

[0065] In some embodiments, the first patterned layer 214 is a patterned photoresist layer. Using the patterned photoresist layer as the first patterned layer 214 simplifies the formation process of the first patterned layer 214, and the mask for forming the patterned photoresist layer can be the same as the mask for forming the initial grid structure 210. Since there is no need to form an additional patterned mask, the manufacturing cost can be reduced.

[0066] In some embodiments, since the second end face 213 is an arc surface recessed towards the first end face 212, the etching process for the surface of the initial grid structure 210 facing away from the substrate 200 is an isotropic etching process, such as an isotropic dry etching process or a wet etching process. Since the etching rate is the same or similar in all directions in an isotropic etching process, the formed second end face 213 can be a recessed arc surface.

[0067] In some embodiments, the pad layer is also formed on the substrate 200, and the initial grid structure 210 is also provided with protective sidewalls, with the first patterned layer 214 located on the surfaces of the pad layer and the protective sidewalls. The pad layer and the protective sidewalls protect the substrate 200 and the grid structure 211 during the formation of the first patterned layer and its subsequent removal.

[0068] In some embodiments, the first patterning layer is removed after etching the surface of the initial grid structure 210 on the side opposite to the substrate 200.

[0069] In some embodiments, the grid structure 211 includes a first region and a second region, the grid structure 211 of the first region has a first width W1, the grid structure 211 of the second region has a second width W2, and the first width W1 is greater than the second width W2.

[0070] In some embodiments, a composite structure needs to be formed subsequently at least on the first region of the grid structure 211 to mitigate the reflection problem of incident light. In other embodiments, composite structures are formed on both the first and second regions of the grid structure 211.

[0071] In some embodiments, the first width W1 ranges from 1 micrometer to 2 micrometers, for example, 1.5 micrometers. When the first width W1 is in the range of 1 micrometer to 2 micrometers, light is more likely to be reflected on the side of the grating structure 211 away from the substrate 200. Therefore, it is necessary to form a composite structure on the side of the grating structure 211 away from the substrate 200 to absorb incident light at the easily reflected angle.

[0072] In some embodiments, step S103 is subsequently performed to form a composite structure on the side of the grating structure 211 away from the substrate 200. The composite structure includes at least two light-absorbing layers and a spacer layer located between adjacent light-absorbing layers. The at least two light-absorbing layers are stacked in a direction perpendicular to the substrate surface, and the size of the composite structure decreases in the direction perpendicular to the substrate surface from the center to the edge.

[0073] In this embodiment, the at least two light-absorbing layers include a first light-absorbing layer and a second light-absorbing layer, and the distance from the first light-absorbing layer to the grating structure 211 is less than the distance from the second light-absorbing layer to the grating structure 211. The formation process of the composite structure is as follows: Figures 7 to 12 As shown.

[0074] Please refer to Figure 7 A first light-absorbing layer 221 is formed on the second end face 213 of the grid structure 211.

[0075] The method for forming the first light-absorbing layer 221 includes: forming a first light-absorbing material film on the substrate, the sidewall of the grating structure, and the second end face 213; and performing planarization treatment on a portion of the first light-absorbing film located on the second end face 213 to form the first light-absorbing layer 221.

[0076] The formation process of the first light-absorbing material film includes chemical vapor deposition, physical vapor deposition, or atomic layer deposition. The planarization process includes an etch-back process, which can be an anisotropic dry etching process.

[0077] In some embodiments, the first light-absorbing layer 221 is also located on the substrate 200 and the sidewall of the grid structure 211. Furthermore, in some embodiments, the substrate 200 also has a padding layer, and the sidewall of the grid structure also has protective sidewalls; in this case, the first light-absorbing layer 221 is also located on the surface of the padding layer and the surface of the protective sidewall.

[0078] The first light-absorbing layer 221 is used to reabsorb light that has not been completely absorbed by the composite structure and has been reflected by the second end face 213.

[0079] In some embodiments, the size of the first light-absorbing layer 221 in the direction perpendicular to the surface of the substrate 200 decreases from the center to the edge of the composite structure 220, that is, the first light-absorbing layer 221 is in the form of a convex lens. Thus, the first light-absorbing layer 221 can also converge the light reflected by the second end face 213, thereby improving the light absorption efficiency of the composite structure.

[0080] In other embodiments, the first light-absorbing layer may also be a conformal film layer located on the surface of the second end face.

[0081] In other embodiments, the first light-absorbing layer may also be a planar film layer with uniform thickness, and a spacer layer may be formed between the first light-absorbing layer and the second end face for isolation and light convergence.

[0082] In some embodiments, the first light-absorbing layer 221 includes opposing third and fourth surfaces, the distance from the third surface to the grid structure 211 being less than the distance from the fourth surface to the grid structure 211, and the third surface protruding in a direction toward the substrate 200. Since the third surface is in contact with the second end face 213, light reflected from the second end face 213 enters the first light-absorbing layer 221 through the third surface; therefore, the protrusion of the third surface facilitates light convergence.

[0083] In some embodiments, the third surface is an arc surface, and the radius of curvature of the third surface ranges from 2 micrometers to 5 micrometers, that is, the radius of curvature of the third surface can be any value among 2 micrometers, 2.5 micrometers, 3 micrometers, 3.5 micrometers, 4 micrometers, 4.5 micrometers, and 5 micrometers, or any combination thereof. When the radius of curvature is within the range of 2 micrometers to 5 micrometers, light rays with a small incident angle (e.g., an incident angle within the range of 0° to 45°) and reflected by the second end surface 213 can be converged. Since when the incident angle is small, it is difficult for the light rays to be reflected into the photosensitive area through optical path adjustment, that is, light rays with an excessively small incident angle are prone to unavoidable optical crosstalk, it is necessary to converge and reabsorb the light rays with small incident angles.

[0084] In some embodiments, the fourth surface is planar. In other embodiments, the fourth surface can also protrude away from the substrate 200, in which case the first light-absorbing layer is biconvex, which is beneficial for further focusing light.

[0085] In some embodiments, the material of the first light-absorbing layer 221 includes titanium. The titanium has an absorption rate of about 40% to 50% and a reflectivity of about 50% to 60% for light in the wavelength range of 400 nm to 760 nm (visible light wavelength range), and has an absorption rate of about 30% to 40% and a reflectivity of about 60% to 70% for light in the wavelength range greater than 760 nm (infrared light wavelength range).

[0086] Furthermore, in some embodiments, the spacer layer subsequently formed between the light-absorbing layers is an oxide. When the oxide is combined with titanium, it reduces the reflectivity of the light-absorbing layer and increases its light absorption rate. Specifically, for titanium materials with oxides on their surface, they have an absorption rate of approximately 60% and a reflectivity of approximately 38% for light in the wavelength range of 400nm to 760nm (visible light wavelength range), and an absorption rate of approximately 45% and a reflectivity of approximately 54% for light in the wavelength range greater than 760nm (infrared light wavelength range).

[0087] In some embodiments, the first light-absorbing layer 221 is made of tungsten. Tungsten has a slightly higher absorption rate for visible light than titanium, a slightly lower absorption rate for infrared light than titanium, a lower reflectivity for visible light than titanium, and a higher reflectivity for infrared light than titanium, thus allowing selection of the light-absorbing layer material within adjacent composite structures based on the function of the photosensitive area 201. Specifically, tungsten has an absorption rate of approximately 40% to 60% and a reflectivity of approximately 40% to 60% for light in the 400nm to 760nm wavelength band (visible light wavelength range), and an absorption rate of approximately 20% to 30% and a reflectivity of approximately 70% to 85% for light in the wavelength band greater than 760nm (infrared light wavelength range).

[0088] Furthermore, in some embodiments, the spacer layer subsequently formed between the light-absorbing layers is an oxide. When the oxide is combined with tungsten, it reduces the reflectivity of the light-absorbing layer and increases its light absorption rate. Specifically, for tungsten materials with oxides on their surface, they have an absorption rate of approximately 75% and a reflectivity of approximately 18% for light in the wavelength range of 400nm to 760nm (visible light wavelength range), and an absorption rate of approximately 40% and a reflectivity of approximately 58% for light in the wavelength range greater than 760nm (infrared light wavelength range).

[0089] In some other embodiments, the material of the first light-absorbing layer 221 includes silicon oxynitride. With silicon oxynitride, the light absorption rate and light reflectivity of the material layer can be adjusted by adjusting the ratio of nitrogen and oxygen in the material. Specifically, the higher the nitrogen content in silicon oxynitride, the higher its absorption rate and reflectivity for visible or infrared light.

[0090] Please refer to Figure 8 An initial spacer layer 222 is formed on the first light-absorbing layer 221.

[0091] The initial spacer layer 222 is used to form a spacer layer in the composite structure, and the spacer layer is located between adjacent light-absorbing layers.

[0092] In some embodiments, the material of the initial spacer layer 222 includes an oxide, and the oxide includes silicon oxide; when the material of the initial spacer layer 222 is silicon oxide, the formation process of the initial spacer layer 222 includes chemical vapor deposition, physical vapor deposition or atomic layer deposition.

[0093] In some embodiments, the initial spacer layer 222 is also located on the surface of the first light-absorbing layer 221 on the substrate 200 and on the surface of the first light-absorbing layer 221 on the sidewall of the grating structure 211.

[0094] Please refer to Figure 9For the initial spacer layer 222 (e.g. Figure 8 (As shown) The pattern is processed to form a spacer layer 223 on the first light-absorbing layer 221.

[0095] The patterning process includes: forming a second patterned layer 250 on the initial spacer layer 222, wherein the second patterned layer 250 is located at least on the grid structure 211 of the first region; using the second patterned layer 250 as a mask, etching the initial spacer layer 222 until the first light-absorbing layer 221 is exposed, thereby forming the spacer layer 223.

[0096] The second patterned layer 250 includes a patterned photoresist layer. The etching process of the initial spacer layer 222 includes anisotropic dry etching or wet etching. In some embodiments, the etching process of the initial spacer layer 222 removes the initial spacer layer 222 located on the substrate 200 and the sidewalls of the gate structure 211.

[0097] Please refer to Figure 10 In the initial spacing layer 222 (e.g. Figure 8 After the patterning process is performed (as shown), the first light-absorbing layer 221 on the photosensitive area 201 of the first light-absorbing layer and the sidewall of the grid structure 211 is removed; after removing the first light-absorbing layer 221 on the photosensitive area 201 of the first light-absorbing layer and the sidewall of the grid structure 211, an oxide layer is formed on the photosensitive area 201, the sidewall of the grid structure 211, the sidewall of the first light-absorbing layer 221 and the surface of the spacer layer 223.

[0098] In some embodiments, the substrate 200 and the sidewalls of the lattice structure 211 also have a first light-absorbing layer 221. After removing a portion of the initial spacer layer 222, the first light-absorbing layer 221 is etched using the second patterned layer 250 as a mask until the padding layer and protective sidewalls are exposed. After etching the first light-absorbing layer, the second patterned layer 250 is removed.

[0099] The process of continuing to etch the first light-absorbing layer 221 using the second patterned layer 250 as a mask includes a dry etching process or a wet etching process. The dry etching process can be an anisotropic dry etching process or an isotropic dry etching process.

[0100] The oxide layer formed on the photosensitive area 201, the sidewall of the grid structure 211, the sidewall of the first light-absorbing layer 221, and the surface of the spacer layer 223 can provide a protective layer for the surface of the first light-absorbing layer 221 located on the side of the grid structure 211 facing away from the substrate 200.

[0101] The oxide layer formation process includes chemical vapor deposition, physical vapor deposition, and atomic layer deposition.

[0102] Please refer to Figure 11 After the oxidation treatment, a second light-absorbing material layer 224 is formed on the surface of the spacer layer 223.

[0103] The formation process of the second light-absorbing material layer 224 includes chemical vapor deposition, physical vapor deposition, or atomic layer deposition. The material of the second light-absorbing material layer 224 can be the same as or different from the first light-absorbing layer 221.

[0104] In some embodiments, the material of the second light-absorbing material layer 224 includes a metallic material, such as titanium or tungsten; in other embodiments, the material of the second light-absorbing material layer 224 includes a non-metallic material, such as silicon oxynitride.

[0105] In some embodiments, the second light-absorbing material layer 224 includes a first portion located on the side of the grating structure 211 opposite to the substrate 200, and a second portion located on the substrate 200 and on the sidewall of the grating structure 211. Furthermore, in some embodiments, the substrate 200, the sidewall of the grating structure, the sidewall of the first light-absorbing layer 221, and the sidewall of the spacer layer 223 also have an oxide layer, in which case the second light-absorbing material layer 224 is also located on the surface of the oxide layer.

[0106] The first part of the second light-absorbing material layer 224 includes a central region and an edge region along a direction parallel to the surface of the substrate 200, and the edge region surrounds the central region.

[0107] Please refer to Figure 12 For the second light-absorbing material layer 224 (such as...) Figure 11 (As shown) The pattern is processed to form a second light-absorbing layer 225 on the spacer layer 223.

[0108] In some embodiments, the size of the second light-absorbing layer 225 in the direction perpendicular to the surface of the substrate 200 decreases from the center to the edge of the composite structure 220, that is, the second light-absorbing layer 225 is in the form of a convex lens. The second light-absorbing layer 225 can converge and absorb incident light toward the side of the grating structure 211 away from the substrate 200, thereby improving the light absorption efficiency of the composite structure.

[0109] In some embodiments, the second light-absorbing layer 225 includes opposing first and second surfaces, the second surface being at a smaller distance from the grating structure 211 than the first surface is at a smaller distance from the grating structure 211, and the first surface protruding in a direction away from the surface of the substrate 200. Since the first surface faces the direction of incident light illumination, its protrusion facilitates the focusing of the incident light. In other embodiments, the second surface is planar.

[0110] In some embodiments, the first surface is an arc surface, and the radius of curvature of the first surface ranges from 2 micrometers to 5 micrometers, that is, the radius of curvature of the first surface can be any value among 2 micrometers, 2.5 micrometers, 3 micrometers, 3.5 micrometers, 4 micrometers, 4.5 micrometers, and 5 micrometers, or any combination thereof. When the radius of curvature is within the range of 2 micrometers to 5 micrometers, light with a small angle of incidence can be focused, for example, incident light with an angle of incidence ranging from 0° to 45°. Since when the angle of incidence is small, it is difficult for the light to be reflected into the photosensitive area through the shape adjustment or material adjustment of the grating structure 211, that is, light with an excessively small angle of incidence is prone to unavoidable optical crosstalk, it is necessary to focus and absorb the light with a small angle of incidence.

[0111] The method for patterning the second light-absorbing material layer 224 includes: forming a third patterned layer 251 on the central region of the second light-absorbing material layer 224, wherein the third patterned layer 251 exposes the surface of the edge region of the second light-absorbing material layer 224; and using the third patterned layer 251 as a mask, etching the second light-absorbing material layer 224 to form the second light-absorbing layer 225.

[0112] In some embodiments, the third patterning layer 251 is a patterned photoresist layer, and the third patterning layer 251 is patterned using the same photomask as the first patterning layer 214 and the second patterning layer 250. Since the same photomask process is used, it is beneficial to save the cost of the patterning process.

[0113] Specifically, the third patterned layer 251 and the second patterned layer 250 are photoresists of the same type, for example, both are positive photoresists or both are negative photoresists; the third patterned layer 251 or the second patterned layer 250 are inverses of the first patterned layer 214, for example, when the first patterned layer 214 is a positive photoresist, the third patterned layer 251 or the second patterned layer 250 is a negative photoresist, and when the first patterned layer 214 is a negative photoresist, the third patterned layer 251 or the second patterned layer 250 is a positive photoresist.

[0114] In some embodiments, the etching process for the second light-absorbing material layer 224 is a dry etching process. This dry etching process has a first etching rate in the direction perpendicular to the surface of the substrate 200 and a second etching rate in both directions parallel to the surface of the substrate 200. By adjusting the relationship between the first and second etching rates, and in conjunction with the distance from the sidewall of the third patterned layer 251 to the first sidewall of the second light-absorbing material layer 224, the arcuate morphology of the formed first surface can be adjusted. In some embodiments, the first and second etching rates are the same.

[0115] In some embodiments, the dry etching process can be a plasma etching process. By increasing the plasma source power and reducing the bias power and bias voltage, the free path of the plasma in the direction parallel to the substrate surface can be increased, thereby increasing the etching rate in the direction parallel to the substrate surface.

[0116] In some embodiments, since the dry etching process has etching rates in both directions perpendicular to and parallel to the surface of the substrate 200, the dry etching process can also remove a second portion of the second light-absorbing material layer 224.

[0117] In other embodiments, the second surface can also protrude toward the substrate 200, in which case the second light-absorbing layer is a double-sided convex-transparent type.

[0118] In this embodiment, after the second light-absorbing layer 225 is formed, the composite structure 220 is formed. The composite structure 220 includes the first light-absorbing layer 221, the spacer layer 223, and the second light-absorbing layer 225.

[0119] In some embodiments, after etching the second light-absorbing material layer 224, the third patterned layer 251 is removed; after removing the third patterned layer 251, the second light-absorbing layer 225 undergoes surface treatment, which is used to repair damage to the first surface caused by the preceding process, so that the first surface of the second light-absorbing layer 225 is an arc surface. The surface treatment can be an isotropic dry etching process or an isotropic wet etching process.

[0120] Please refer to Figure 13 After surface treatment of the second light-absorbing layer 225, a protective layer 230 is formed on the substrate 200, the surface of the lattice structure 211, and the surface of the composite structure 220.

[0121] The protective layer 230 is used to protect the grid structure 211 and the composite structure in subsequent processes and to improve the bonding ability between the structures. The material of the protective layer 230 includes one or more of silicon oxide, silicon nitride, and silicon oxynitride.

[0122] Please refer to Figure 14 and Figure 15 , Figure 15 yes Figure 14 A top-view structural diagram. Figure 14 yes Figure 15 A cross-sectional schematic diagram of region E along the cross-section line FF', wherein a filter layer 240 is formed on the first functional surface 204 of the photosensitive region 201; and a lens structure 241 is formed on the side of the filter layer 240 opposite to the substrate 200.

[0123] The filter layer 240 is used to allow incident light of a specific wavelength band to pass through and enter the photosensitive area 201, such as the green light band, red light band, or blue light band. The lens structure 241 is used to converge the incident light to enter the photosensitive area 201.

[0124] In other embodiments, please refer to Figure 16 , Figure 16 This is a schematic diagram of another image sensor structure according to an embodiment of this application. This embodiment is similar to... Figures 4 to 15 The difference in the embodiment is that: the at least two light-absorbing layers further include at least one third light-absorbing layer 300, which is located between the first light-absorbing layer 221 and the second light-absorbing layer 225; the at least one third light-absorbing layer 300, the first light-absorbing layer 221, and the second light-absorbing layer 225 are stacked along the first direction; the spacer layer 223 is also present between adjacent third light-absorbing layers 300, between the third light-absorbing layer 300 and the first light-absorbing layer 221, and between the third light-absorbing layer 300 and the second light-absorbing layer 225; the material selection range of the third light-absorbing layer 300 is the same as that of the first light-absorbing layer 221 or the second light-absorbing layer 225, and the materials between the third light-absorbing layers 300, between the third light-absorbing layer 300 and the first light-absorbing layer 221, and between the third light-absorbing layer 300 and the second light-absorbing layer 225 are the same or different; the third light-absorbing layer 300 can be a conformal film layer located on the surface of the spacer layer 223.

[0125] By adding the third light-absorbing layer 300, the incident light entering the composite structure 220 and the light reflected by the grating structure 211 can be further absorbed, thereby further improving the light absorption efficiency of the composite structure 220 and further suppressing optical crosstalk.

[0126] In summary, by forming a composite structure 220 on the grating structure 211 between the photosensitive areas 201, light incident on the side of the grating structure 211 away from the substrate 200 can be converged and absorbed simultaneously, thereby effectively reducing the problem of light reflection from the side of the grating structure 211 away from the substrate 200. In some embodiments, the dimensions of the composite structure 220 gradually decrease from the center to the edge in a direction perpendicular to the surface of the substrate 200, i.e., the composite structure 220 has a convex lens shape. This shape can effectively converge incident light, especially light that is easily reflected by the side of the grating structure 211 away from the substrate 200 and cannot be reflected to the photosensitive area, thereby achieving effective convergence and absorption. Furthermore, the composite structure 220 includes at least two light-absorbing layers. As incident light passes through the composite structure 220 and reaches the grating structure 211, it is absorbed multiple times by these light-absorbing layers. Even if some light is not completely absorbed, it can still be absorbed again by the adjacent light-absorbing layers after being reflected by the side of the grating structure 211 away from the substrate 200, thereby improving the light absorption efficiency of the composite structure 220. Therefore, since the composite structure 220 can effectively reduce the light reflection problem on the side of the grating structure 211 away from the substrate 200, it can effectively solve the problem of noise generated in part of the grating structure 211 of the image sensor, thereby improving the imaging effect of the image sensor.

[0127] Accordingly, this application also provides an image sensor formed using the above method. Please continue to refer to... Figure 14 and Figure 15 The system includes: a substrate 200, including a plurality of photosensitive areas 201 and an isolation area 202 located between the plurality of photosensitive areas 201; a grid structure 211 located on the isolation area 202; and a composite structure 220 located on the side of the grid structure 211 facing away from the substrate 200. The composite structure 220 includes a first light-absorbing layer 221, a second light-absorbing layer 225, and a spacer layer 223 stacked along a first direction perpendicular to the surface of the substrate 200. The spacer layer 223 is located between the first light-absorbing layer and the second light-absorbing layer, and the thickness of the composite structure 220 in the first direction decreases from the center to the edge of the composite structure 220.

[0128] The following will be described in detail with reference to the accompanying drawings.

[0129] The substrate 200 is a silicon substrate, a germanium substrate, a silicon-germanium substrate, a silicon-on-insulator substrate, or a germanium-on-insulator substrate, etc. In this embodiment, the substrate 200 is a silicon substrate.

[0130] In this embodiment, the photosensitive areas 201 are arranged in an array along the second direction X and the third direction Y, and the second direction X and the third direction Y are both parallel to the surface of the substrate 200 and perpendicular to each other.

[0131] The substrate 200 includes a first functional surface 204 and a second functional surface 205 opposite to each other. In some embodiments, the image sensor is a back-illuminated image sensor, the first functional surface 204 is used to receive incident light, and the surface of the second functional surface 205 also has a device layer, the device layer including a logic circuit structure, the logic circuit structure being used as peripheral circuitry of the image sensor.

[0132] The device layer includes a first dielectric layer on the second functional surface 205, a device structure within the first dielectric layer, several second dielectric layers on the first dielectric layer, and an electrical interconnection structure within the second dielectric layer. The electrical interconnection structure is electrically connected to the device structure, and the device structure includes transistors, resistor structures, capacitor structures, etc.

[0133] In some embodiments, the photosensitive area 201 includes a photoelectric doped region 203, which receives light, performs photoelectric conversion, and outputs an electrical signal. The photoelectric doped region 203 contains doped ions, causing it to be inverted relative to the substrate 200, thereby forming a photodiode in the photosensitive area 201. In some embodiments, the photoelectric doped region is doped with N-type ions, and the substrate 200 is a P-type substrate.

[0134] In some embodiments, since the photosensitive areas 201 are arranged in an array along the second direction X and the third direction Y, the grid structure 211 includes a plurality of grid strips extending along the second direction X and the third direction Y, and the plurality of grid strips constitute a grid structure.

[0135] In some embodiments, the grid structure 211 includes a first region and a second region, the grid structure 211 in the first region has a first width W1, the grid structure 211 in the second region has a second width W2, and the first width W1 is greater than the second width W2; the composite structure 220 is located on the side of the grid structure 211 in the first region that is away from the substrate 200.

[0136] In some embodiments, the first region of the grid structure 211 extends along the second direction X, and the first width W1 is the dimension of the first region of the grid structure 211 in the third direction Y. The second width W2 is the dimension of the second region of the grid structure 211 perpendicular to its extension direction.

[0137] In some embodiments, the first width W1 ranges from 1 micrometer to 2 micrometers, for example, 1.5 micrometers. Because the first width W1 is relatively large, the incident light is unlikely to avoid the first region of the subsequently formed grating structure 211; that is, the first region is more prone to reflecting light. Therefore, the composite structure is needed to mitigate the reflection problem of the incident light. In other embodiments, a composite structure is present on both the first and second regions of the grating structure.

[0138] The grid structure 211 is made of tungsten, aluminum, or copper. In some embodiments, the grid structure 211 is made of tungsten.

[0139] In some embodiments, the substrate 200 surface further has a pad layer, on which the grid structure 211 is located. The pad layer is made of one or more of silicon oxide, silicon nitride, and silicon oxynitride.

[0140] In some embodiments, an adhesion layer 206 is provided between the grid structure 211 and the substrate 200, or between the grid structure 211 and the padding layer. The material of the adhesion layer 206 includes one or more of titanium nitride, tantalum nitride, titanium, and tantalum in a laminated combination.

[0141] In some embodiments, the sidewall surface of the grid structure 211 further has protective sidewalls. The material of the protective sidewalls includes one or more of silicon oxide, silicon nitride, and silicon oxynitride laminated together.

[0142] In this embodiment, the grid structure 211 includes a first end face 212 and a second end face 213 facing each other. The distance from the first end face 212 to the substrate 200 is less than the distance from the second end face 213 to the substrate 200, and the second end face 213 is recessed towards the first end face 212. The composite structure is a double-sided convex-permeable structure, and the second end face 213 contacts and matches the protruding arc surface of the composite structure.

[0143] When the composite structure is a double-sided convex structure, and the incident light is not completely absorbed after passing through the composite structure, the surface of the composite structure that contacts the recessed second end face 213 can reflect the unabsorbed light and converge it back into the composite structure, thereby facilitating the absorption of the light again within the composite structure and improving the absorption efficiency of the composite structure.

[0144] In other embodiments, the composite structure can also be a single-sided convex structure, wherein the surface of the composite structure facing the incident light is an arc-shaped convex surface, and the second end face is a plane.

[0145] In some embodiments, the at least two light-absorbing layers include a first light-absorbing layer 221 and a second light-absorbing layer 225, wherein the distance from the first light-absorbing layer 221 to the grating structure 211 is less than the distance from the second light-absorbing layer 225 to the grating structure 211. The first light-absorbing layer 221 is used to reabsorb light that has not been completely absorbed by the composite structure and has been reflected by the second end face 213.

[0146] In some embodiments, the thickness of the first light-absorbing layer 221 decreases in the direction from the center to the edge of the composite structure 220 in the first direction, that is, the first light-absorbing layer 221 is in the form of a convex lens. Thus, the first light-absorbing layer 221 can also converge the light reflected by the second end face 213, thereby improving the light absorption efficiency of the composite structure.

[0147] In other embodiments, the first light-absorbing layer may also be a conformal film layer located on the surface of the second end face.

[0148] In other embodiments, the first light-absorbing layer may also be a planar film layer with uniform thickness, and the first light-absorbing layer and the second end face may be isolated by a spacer layer and light converged.

[0149] In some embodiments, the first light-absorbing layer 221 includes opposing third and fourth surfaces, the distance from the third surface to the grid structure 211 being less than the distance from the fourth surface to the grid structure 211, and the third surface protruding towards the substrate 200. Since the third surface is in contact with the second end face 213, light reflected from the second end face 213 enters the first light-absorbing layer 221 through the third surface; therefore, the protrusion of the third surface facilitates light convergence.

[0150] In some embodiments, the third surface is an arc surface, and the radius of curvature of the third surface ranges from 2 micrometers to 5 micrometers, that is, the radius of curvature of the third surface can be any value or a range of any two of 2 micrometers, 2.5 micrometers, 3 micrometers, 3.5 micrometers, 4 micrometers, 4.5 micrometers, and 5 micrometers. When the radius of curvature is within the range of 2 micrometers to 5 micrometers, light rays with a small incident angle (e.g., an incident angle within the range of 0° to 45°) reflected by the second end surface 213 can be converged. Since the incident angle is small, it is difficult for the light rays to be reflected into the photosensitive area through optical path adjustment. That is, light rays with an excessively small incident angle are prone to unavoidable optical crosstalk. Therefore, it is necessary to converge and reabsorb light rays with a small incident angle.

[0151] In other embodiments, the fourth surface can also protrude in a direction away from the substrate 200, so that the first light-absorbing layer is double-sided convex and transparent, which is beneficial for further converging light.

[0152] In some embodiments, the size of the second light-absorbing layer 225 in the direction perpendicular to the surface of the substrate 200 decreases from the center to the edge of the composite structure 220, that is, the second light-absorbing layer 225 is in the form of a convex lens. The second light-absorbing layer 225 can converge and absorb incident light toward the side of the grating structure 211 away from the substrate 200, thereby improving the light absorption efficiency of the composite structure.

[0153] In some embodiments, the second light-absorbing layer 225 includes a first surface opposite to the first surface and a second surface closer to the lattice structure 211, and the first surface protrudes in an arc shape relative to the second surface in a direction away from the surface of the substrate 200. Since the first surface faces the direction of incident light illumination, the protrusion of the first surface facilitates the focusing of the incident light.

[0154] In some embodiments, the first surface is an arc surface, and the radius of curvature of the first surface ranges from 2 micrometers to 5 micrometers, that is, the radius of curvature of the first surface can be any value among 2 micrometers, 2.5 micrometers, 3 micrometers, 3.5 micrometers, 4 micrometers, 4.5 micrometers, and 5 micrometers, or any combination thereof. When the radius of curvature is within the range of 2 micrometers to 5 micrometers, light with a small angle of incidence can be focused, for example, light with an angle of incidence ranging from 0° to 45°. Because when the angle of incidence is small, it is difficult for the light to be reflected into the photosensitive area through the shape adjustment or material adjustment of the grating structure 211, that is, light with an excessively small angle of incidence is prone to unavoidable optical crosstalk, therefore, it is necessary to focus and absorb light with a small angle of incidence.

[0155] In other embodiments, the second surface can also protrude toward the substrate 200, in which case the second light-absorbing layer is a double-sided convex-transparent type.

[0156] The material of the first light-absorbing layer 221 includes titanium, tungsten, or silicon oxynitride; the material of the second light-absorbing layer 225 includes titanium, tungsten, or silicon oxynitride; the materials of the first light-absorbing layer 221 and the second light-absorbing layer 225 may be the same or different.

[0157] In some embodiments, the material of the first light-absorbing layer 221 or the second light-absorbing layer 225 includes titanium. The titanium has an absorption rate of about 40% to 50% and a reflectivity of about 50% to 60% for light in the wavelength range of 400 nm to 760 nm (visible light wavelength range), and has an absorption rate of about 30% to 40% and a reflectivity of about 60% to 70% for light in the wavelength range greater than 760 nm (infrared light wavelength range).

[0158] In some embodiments, the spacer layer 223 located between the first light-absorbing layer 221 and the second light-absorbing layer 225 is an oxide. When the oxide is combined with titanium, it reduces the reflectivity of the light-absorbing layer and increases the light absorption rate of the light-absorbing layer. Specifically, for titanium materials with oxide on their surface, they have an absorption rate of approximately 60% and a reflectivity of approximately 38% for light in the wavelength range of 400nm to 760nm (visible light wavelength range), and an absorption rate of approximately 45% and a reflectivity of approximately 54% for light in the wavelength range greater than 760nm (infrared light wavelength range).

[0159] In some embodiments, the material of the first light-absorbing layer 221 or the second light-absorbing layer 225 includes tungsten. The tungsten has a slightly higher absorption rate for visible light than titanium, a slightly lower absorption rate for infrared light than titanium, a lower reflectivity for visible light than titanium, and a higher reflectivity for infrared light than titanium, thereby allowing selection of the light-absorbing layer material within adjacent composite structures based on the function of the photosensitive area 201. Specifically, tungsten has an absorption rate of approximately 40% to 60% and a reflectivity of approximately 40% to 60% for light in the wavelength range of 400 nm to 760 nm (visible light wavelength range), and an absorption rate of approximately 20% to 30% and a reflectivity of approximately 70% to 85% for light in the wavelength range greater than 760 nm (infrared light wavelength range).

[0160] In some embodiments, the spacer layer 223 located between the first light-absorbing layer 221 and the second light-absorbing layer 225 is an oxide. When the oxide is combined with tungsten, it reduces the reflectivity of the light-absorbing layer and increases its light absorption rate. Specifically, for tungsten materials with oxides on their surface, they have an absorption rate of approximately 75% and a reflectivity of approximately 18% for light in the wavelength range of 400nm to 760nm (visible light wavelength range), and an absorption rate of approximately 40% and a reflectivity of approximately 58% for light in the wavelength range greater than 760nm (infrared light wavelength range).

[0161] In some other embodiments, the material of the first light-absorbing layer 221 or the second light-absorbing layer 225 includes silicon oxynitride. With silicon oxynitride, the light absorption rate and light reflectivity of the material layer can be adjusted by adjusting the ratio of nitrogen and oxygen in the material. Specifically, the higher the nitrogen content in silicon oxynitride, the higher its absorption rate and reflectivity for visible or infrared light.

[0162] In some embodiments, the spacer layer 223 is made of an oxide, which includes silicon oxide.

[0163] In some embodiments, such as Figure 16 As shown, the at least two light-absorbing layers further include at least one third light-absorbing layer 300, which is located between the first light-absorbing layer 221 and the second light-absorbing layer 225. The at least one third light-absorbing layer 300, the first light-absorbing layer 221 and the second light-absorbing layer 225 are stacked along the first direction. The spacer layer 223 is also present between adjacent third light-absorbing layers 300, between the third light-absorbing layer 300 and the first light-absorbing layer 221, and between the third light-absorbing layer 300 and the second light-absorbing layer 225; the material of the third light-absorbing layer 300 includes titanium, tungsten, or silicon oxynitride; the material selection range of the third light-absorbing layer 300 is the same as or different from that of the first light-absorbing layer 221 or the second light-absorbing layer 225, and the materials between the third light-absorbing layers 300, between the third light-absorbing layer 300 and the first light-absorbing layer 221, and between the third light-absorbing layer 300 and the second light-absorbing layer 225 are the same as or different; the third light-absorbing layer 300 can be a conformal film layer located on the surface of the spacer layer 223.

[0164] By adding the third light-absorbing layer, the incident light entering the composite structure 220 and the light reflected by the grating structure 211 can be further absorbed, thereby further improving the light absorption efficiency of the composite structure 220 and further suppressing optical crosstalk.

[0165] In some embodiments, the first functional surface 204 of the photosensitive area 201 further comprises a filter layer 240, and the filter layer 240 comprises a lens structure 241. The filter layer 240 is used to allow incident light of a specific wavelength band to pass through and enter the photosensitive area 201, such as the green light band, red light band, or blue light band. The lens structure 241 is used to converge the incident light to enter the photosensitive area 201.

[0166] In summary, by adding a composite structure 220 to the grating structure 211 between the photosensitive areas 201, light incident on the side of the grating structure 211 facing away from the substrate 200 can be gathered and absorbed. The composite structure 220 effectively reduces light reflection on the side of the grating structure 211 facing away from the substrate 200, thereby effectively solving the problem of noise generation in certain areas of the image sensor in the grating structure 211 and improving the imaging effect.

[0167] In the description of the embodiments of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0168] Furthermore, in the embodiments of this application, the description of a feature being located on the "surface" of another feature is used to describe the relative positional relationship between the features and should not be construed as limiting the direct contact between the features.

[0169] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0170] The embodiments, implementation methods, and related technical features of this application can be combined and substituted for each other without conflict.

[0171] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. An image sensor, characterized in that, include: The substrate includes a plurality of photosensitive areas and an isolation area located between the plurality of photosensitive areas; The grid structure located on the isolation zone; A composite structure located on the side of the grating structure facing away from the substrate, the composite structure comprising a first light-absorbing layer, a second light-absorbing layer, and a spacer layer stacked along a first direction perpendicular to the substrate surface, the spacer layer being located between the first light-absorbing layer and the second light-absorbing layer, and the thickness of the composite structure in the first direction decreasing from the center to the edge of the composite structure, the thickness of the second light-absorbing layer in the first direction decreasing from the center to the edge of the composite structure, and the distance from the first light-absorbing layer to the grating structure being less than the distance from the second light-absorbing layer to the grating structure.

2. The image sensor according to claim 1, characterized in that, The second light-absorbing layer includes a first surface and a second surface that is closer to the lattice structure than the first surface, and the first surface protrudes in an arc shape relative to the second surface in a direction away from the substrate surface.

3. The image sensor according to claim 2, characterized in that, The radius of curvature of the first surface ranges from 2 micrometers to 5 micrometers.

4. The image sensor according to claim 1, characterized in that, The thickness of the first light-absorbing layer decreases in the first direction from the center to the edge of the composite structure.

5. The image sensor according to claim 4, characterized in that, The first light-absorbing layer includes a third surface and a fourth surface further away from the grating structure relative to the third surface, and the third surface protrudes in an arc shape relative to the fourth surface toward the substrate surface.

6. The image sensor according to claim 5, characterized in that, The radius of curvature of the third surface ranges from 2 micrometers to 5 micrometers.

7. The image sensor according to claim 3, characterized in that, The composite structure further includes at least one third light-absorbing layer located between the first light-absorbing layer and the second light-absorbing layer, wherein the at least one third light-absorbing layer, the first light-absorbing layer, and the second light-absorbing layer are stacked along the first direction.

8. The image sensor according to claim 1, characterized in that, The grid structure includes a first region and a second region. The grid structure of the first region has a first width, and the grid structure of the second region has a second width, wherein the first width is greater than the second width; the composite structure is located on the side of the grid structure of the first region that is away from the substrate.

9. The image sensor according to claim 8, characterized in that, The first width ranges from 1 micrometer to 2 micrometers.

10. The image sensor according to claim 1, characterized in that, The material of the first light-absorbing layer includes titanium, tungsten, or silicon oxynitride; the material of the second light-absorbing layer includes titanium, tungsten, or silicon oxynitride; and the material of the spacer layer includes oxides.

11. The image sensor according to claim 1, characterized in that, The substrate includes a first functional surface and a second functional surface opposite to each other, and the grid structure is located on the surface of the first functional surface; the image sensor further includes: a device layer located on the second functional surface, the device layer including logic devices; a photoelectric doped region located in the photosensitive area; a filter layer located on the first functional surface of the photosensitive area; and a lens structure located on the side of the filter layer opposite to the substrate.

12. A method for forming an image sensor, the image sensor as described in any one of claims 1 to 11, characterized in that, include: A substrate is provided, the substrate including a plurality of photosensitive areas and an isolation area located between the plurality of photosensitive areas; A grid structure is formed on the isolation zone; A composite structure is formed on the side of the grating structure away from the substrate. The composite structure includes a first light-absorbing layer, a second light-absorbing layer, and a spacer layer stacked along a first direction perpendicular to the substrate surface. The spacer layer is located between the first light-absorbing layer and the second light-absorbing layer, and the thickness of the composite structure in the first direction decreases from the center to the edge of the composite structure.

13. The method for forming an image sensor according to claim 12, characterized in that, The method of forming a grid structure on the isolation region includes: forming an initial grid structure on the isolation region; forming a first patterning layer on the photosensitive region, the first patterning layer exposing the initial grid structure; using the first patterning layer as a mask, etching the top surface of the initial grid structure to form the grid structure, the grid structure including opposing first end faces and second end faces, the distance from the first end face to the substrate being less than the distance from the second end face to the substrate, and the second end face being arc-shaped recessed in the direction of the first end face.

14. The method for forming an image sensor according to claim 12, characterized in that, The method of forming the composite structure includes: forming a first light-absorbing layer on the top surface of the grating structure; forming an initial spacer layer on the first light-absorbing layer; patterning the initial spacer layer to form a spacer layer on the first light-absorbing layer; forming a second light-absorbing material layer on the surface of the spacer layer; patterning the second light-absorbing material layer to form a second light-absorbing layer on the spacer layer, wherein the thickness of the second light-absorbing layer in the first direction decreases from the center to the edge of the composite structure, the second light-absorbing layer includes a first face opposite to the first face and a second face closer to the grating structure than the first face, and the first face protrudes in an arc shape relative to the second face in a direction away from the substrate surface.

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