Back-illuminated image sensor and preparation method thereof, and electronic device

Abstract

The present application relates to a back-illuminated image sensor and a preparation method thereof, and an electronic device, and relates to the field of integrated circuit technology, and includes: a substrate, an isolation stack, and a photodiode and a target isolation structure located on a first surface of the substrate and alternately arranged in a parallel direction and extending toward the substrate; the substrate includes a plurality of trench isolation structures directly below the target isolation structures arranged one to one; the isolation stack is located directly above the target isolation structures arranged one to one; the target isolation structure includes a protrusion that is higher than the top surface of the photodiode and embedded in the isolation stack; the contact surface between the protrusion and the isolation stack is wavy, which improves the isolation structure's ability to intercept electrons and light, increases the amount of light entering the photosensitive area, and reduces the crosstalk of signals between pixels, thereby improving the photosensitivity and image quality of the BSI image.

Description

Technical Field

[0001] The present application relates to the field of integrated circuit technology, and in particular to a back-illuminated image sensor, a preparation method thereof, and an electronic device. Background Art

[0002] Image sensors are photoelectric conversion devices widely used in consumer electronics, security monitoring, automotive electronics, machine vision and many other fields. Backside illuminated (BSI) image sensors have the advantages of higher sensitivity, better wiring layout and high-speed recording, and are often used in fields that require higher pixel performance of image sensors.

[0003] However, in the traditional BSI front-end process, high-energy ion implantation (IMP) is required to prepare the diode structure to form the photosensitive area, which causes damage to the substrate surface. Uneven ion implantation can also cause signal crosstalk between different pixels, hindering the further improvement of BSI image sensor performance. Summary of the invention

[0004] Based on this, it is necessary to provide a back-illuminated image sensor and a preparation method and electronic device thereof to address the technical problems in the prior art, which can at least avoid signal crosstalk of the BSI image sensor and unnecessary damage caused by IMP.

[0005] In the first aspect, the present application provides a back-illuminated image sensor, comprising: a substrate, an isolation stack, and a photodiode and a target isolation structure located on a first surface of the substrate and alternately arranged along a first direction parallel to the first surface and extending toward the substrate; the substrate comprises a plurality of trench isolation structures extending into the substrate through the first surface and arranged at intervals along the first direction; the trench isolation structure is located directly below the target isolation structure arranged one to one; the isolation stack is located directly above the target isolation structure arranged one to one; the target isolation structure comprises a protrusion that is higher than the top surface of the photodiode and embedded in the isolation stack, wherein the contact surface between the protrusion and the isolation stack is wavy.

[0006] In the back-illuminated image sensor in the above-mentioned embodiment, a photodiode is arranged between adjacent target isolation structures, and the target isolation structure is used to isolate adjacent photodiodes, thereby avoiding signal crosstalk between adjacent photodiodes. After depositing the photosensitive material layer, a plurality of target isolation structures arranged at intervals can be formed in the photosensitive material layer to obtain photodiodes arranged in an array at intervals, thereby avoiding unnecessary damage caused by forming the photodiodes by high-energy ion implantation, reducing dark current, and helping to improve the imaging clarity of the image sensor. Since the target isolation structure includes a protrusion that is higher than the top surface of the photodiode and embedded in the isolation stack, and the contact surface between the protrusion and the isolation stack is wavy, the isolation The stack and the target isolation structure realize embedded matching connection, and together with the trench isolation structure form an effective physical isolation barrier, which can effectively prevent the free electrons of the pixels from penetrating into adjacent pixels through the interface between the isolation stack and the target isolation structure, and can effectively prevent the light from diffusing to adjacent pixels or diffusing at the back interface and merging with the incident light, thereby suppressing the adverse effects of the crosstalk effect on the clarity of the image imaging, and in the process, will not affect the front-end process, which helps to improve the performance and reliability of the back-illuminated image sensor; moreover, the protrusion with a rounded arc surface can avoid the strong electric field gradient caused by charge accumulation at the tip, and can also be embedded in the target isolation structure to intercept light energy and electrons.

[0007] In some embodiments, a bottom surface of the protrusion is located inside a top surface of the target isolation structure and inside a bottom surface of the isolation stack.

[0008] In some embodiments, the back-illuminated image sensor further includes a filter; the protrusion includes a protrusion adjacent to the filter; the filter is located between the protrusions adjacent to each other along the first direction; and the outer surface of the protrusion is a rounded arc surface.

[0009] In some embodiments, the target isolation structure includes an isolation column located below the protrusion; a dimension of the isolation column along the first direction gradually decreases in a direction toward the first surface.

[0010] In some embodiments, the isolation stack includes a dielectric layer, a first conductive layer, and a second conductive layer stacked in sequence along a direction away from the first surface; the protrusion is embedded in the dielectric layer, and the top surface of the protrusion is lower than the top surface of the dielectric layer, wherein the dielectric constant of the dielectric layer is greater than a preset value.

[0011] In some embodiments, a top surface of the trench isolation structure is located within a bottom surface of the target isolation structure.

[0012] In some embodiments, the photodiode includes an isolation layer and a photosensitive layer stacked along a second direction; the isolation layer is located between the photosensitive layer and the substrate, and the second direction is perpendicular to the first surface of the substrate.

[0013] In some embodiments, the back-illuminated image sensor further includes an etch stop layer, which is located on the second surface of the substrate, the first surface and the second surface are two main surfaces of the substrate that are opposite to each other along the second direction; the trench isolation structure penetrates the substrate along the second direction and extends to the etch stop layer.

[0014] In a second aspect, the present application further provides an electronic device, comprising: a back-illuminated image sensor as described in any embodiment of the present application.

[0015] In a third aspect, the present application further provides a method for preparing a back-illuminated image sensor, comprising:

[0016] A substrate is provided, wherein the substrate includes a plurality of trench isolation structures extending into the substrate through a first surface of the substrate and arranged at intervals along a first direction parallel to the first surface; a photodiode and a target isolation structure are formed on the first surface of the substrate, which are alternately arranged along a first direction and extend along a second direction; the second direction is perpendicular to the first surface of the substrate; the target isolation structure includes a protrusion which is higher than the top surface of the photodiode and has a wavy outer surface; an isolation stack is formed directly above the target isolation structure, and the protrusion is embedded in the isolation stack which is arranged one-to-one with the target isolation structure.

[0017] The back-illuminated image sensor and its preparation method, and the electronic device in the embodiments of the present application have the following unexpected technical effects:

[0018] By arranging photodiodes between adjacent target isolation structures, the target isolation structures are used to isolate adjacent photodiodes, thereby avoiding signal crosstalk between adjacent photodiodes; after depositing a photosensitive material layer, a plurality of target isolation structures arranged at intervals can be formed in the photosensitive material layer by an etching process to obtain photodiodes arranged in an interval array, thereby avoiding unnecessary damage caused by forming photodiodes by high-energy ion implantation, reducing dark current, and helping to improve the imaging clarity of the image sensor; since the target isolation structure includes a protrusion that is higher than the top surface of the photodiode and embedded in the isolation stack, and the contact surface between the protrusion and the isolation stack is wavy, the isolation stack and the target isolation structure are The structure realizes embedded matching connection and forms an effective physical isolation barrier together with the trench isolation structure, which can effectively prevent pixel free electrons from penetrating into adjacent pixels through the interface between the isolation stack and the target isolation structure. At the same time, it can also effectively prevent light from diffusing to adjacent pixels or diffusing at the back interface and merging with the incident light, thereby suppressing the adverse effects of crosstalk on image clarity. In addition, it will not affect the front-end process during the process, which helps to improve the performance and reliability of the back-illuminated image sensor. In addition, the protrusion with a rounded arc surface can avoid the strong electric field gradient caused by charge accumulation at the tip, and can also be embedded in the target isolation structure to intercept light energy and electrons. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 is a flow chart of a method for preparing a back-illuminated image sensor provided in an embodiment;

[0021] Figure 2 is a schematic cross-sectional view of a structure obtained after a trench isolation structure is formed in step S20 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0022] Figure 3a is a schematic cross-sectional view of a structure obtained after forming an isolation layer in step S20 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0023] Figure 3b It is a schematic cross-sectional view of a structure obtained after the substrate is thinned in step S20 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0024] Figure 4It is a schematic cross-sectional view of a structure obtained after a photosensitive layer, an oxide layer and a protective layer are formed in step S40 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0025] Figure 5 is a schematic cross-sectional view of a structure obtained after a groove is formed in step S40 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0026] Figure 6 It is a schematic cross-sectional view of a structure obtained after forming an isolation material layer in step S40 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0027] Figure 7 for Figure 6 A schematic cross-sectional view of the structure obtained after the top surface of the isolation material layer is planarized;

[0028] Figure 8 for Figure 7 A schematic cross-sectional view of the structure obtained after etching the photosensitive layer;

[0029] Fig. 9 It is a schematic cross-sectional view of a structure obtained after a protrusion having a wavy outer surface is formed in step S60 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0030] Fig.10 It is a schematic cross-sectional view of a structure obtained after a dielectric layer, a first conductive layer and a second conductive layer are formed in step S60 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0031] Fig.11 is a schematic cross-sectional view of a structure obtained after forming an isolation stack in step S60 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0032] Fig.12 It is a schematic cross-sectional view of a structure obtained after a filter is formed in a method for preparing a back-illuminated image sensor provided in an embodiment.

[0033] Description of reference numerals:

[0034] 1. Initial substrate; 10. Substrate; 12. Isolation layer; 13. Etch stop layer; 14. Interlayer dielectric layer; 15. Photosensitive layer; 16. Oxide layer; 17. Protective layer; 18. Isolation material layer; 20. Trench isolation structure; 30. Isolation trench; 40. Target isolation structure; 41. Protrusion; 50. Isolation stack; 51. Dielectric layer; 52. First conductive layer; 53. Second conductive layer; 60. Filter; 61. Grid groove. DETAILED DESCRIPTION

[0035] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0037] It should be understood that when an element or layer is referred to as being "on, adjacent to, connected to or coupled to other elements or layers, it may be directly on, adjacent to, connected to or coupled to other elements or layers, or there may be intervening elements or layers. On the contrary, when an element is referred to as being "directly on, directly adjacent to, directly connected to or directly coupled to other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers, doping types and / or parts, these elements, components, regions, layers, doping types and / or parts should not be limited by these terms. These terms are merely used to distinguish one element, component, region, layer, doping type or part from another element, component, region, layer, doping type or part. Therefore, without departing from the teachings of the present application, the first element, component, region, layer, doping type or portion discussed below may be represented as a second element, component, region, layer or portion; for example, the first doping type may be referred to as the second doping type, and similarly, the second doping type may be referred to as the first doping type; the first doping type and the second doping type are different doping types, for example, the first doping type may be P-type and the second doping type may be N-type, or the first doping type may be N-type and the second doping type may be P-type.

[0038] Spatially relative terms such as "under," "beneath," "below," "under," "above," "above," and the like may be used herein to describe the relationship of an element or feature shown in the figures to other elements or features. It should be understood that, in addition to the orientations shown in the figures, spatially relative terms also include different orientations of the device in use and operation. For example, if the device in the accompanying drawings is flipped, an element or feature described as "under other elements" or "under it" or "under it" will be oriented as being "above" the other elements or features. Thus, the exemplary terms "under" and "under" may include both upper and lower orientations. In addition, the device may also include additional orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptors used herein are interpreted accordingly.

[0039] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that when the terms "consisting of" and / or "comprising" are used in this specification, the presence of the features, integers, steps, operations, elements and / or parts can be determined, but the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups is not excluded. At the same time, when used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0040] Embodiments of the invention are described herein with reference to cross-sectional views which are schematic diagrams of ideal embodiments (and intermediate structures) of the present application, so that variations in the shapes shown due to, for example, manufacturing techniques and / or tolerances can be expected. Therefore, embodiments of the present application should not be limited to the specific shapes of the zones shown herein, but rather include deviations in shapes due to, for example, manufacturing techniques. For example, an implanted region shown as a rectangle typically has rounded or curved features and / or an implant concentration gradient at its edges, rather than a binary change from an implanted region to a non-implanted region. Similarly, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation is performed. Therefore, the regions shown in the figures are schematic in nature, their shapes do not represent the actual shape of the regions of the device, and do not limit the scope of the present application.

[0041] In an embodiment of the present application, the substrate may include a first surface located on the front side, and a back side opposite to the front side, i.e., a second surface. Ignoring the flatness of the first surface and the second surface, a first direction parallel to the first surface is defined, and the direction toward the substrate includes a second direction perpendicular to the first surface of the substrate. A first direction and a third direction that intersect each other (e.g., are perpendicular to each other) are defined in the top and bottom surface directions of the substrate (i.e., the plane where the substrate is located). For example, the arrangement direction of the target isolation structure is the first direction, and the plane where the substrate is located can be determined based on the first direction and the third direction. Among them, the first direction, the second direction, and the third direction can be perpendicular to each other in pairs. In an embodiment of the present application, the first direction is defined as the Y-axis direction, the second direction is defined as the Z-axis direction, and the third direction is defined as the X-axis direction.

[0042] See also Figure 1 The present application provides a method for preparing a back-illuminated image sensor, comprising: steps S20 to S60.

[0043] Step S20: providing a substrate, wherein the substrate includes a plurality of trench isolation structures extending into the substrate through a first surface of the substrate and arranged at intervals along a first direction parallel to the first surface.

[0044] As an example, the substrate can be made of semiconductor material, insulating material, conductor material or any combination thereof. The substrate can be a single-layer structure or a multi-layer structure. For example, the substrate can be a silicon (Si) substrate, a silicon germanium (SiGe) substrate, a silicon germanium carbon (SiGeC) substrate, a silicon carbide (SiC) substrate, a gallium arsenide (GaAs) substrate, an indium arsenide (InAs) substrate, an indium phosphide (InP) substrate or other III / V semiconductor substrates or II / VI semiconductor substrates. Alternatively, for example, the substrate can be a layered substrate including Si / SiGe, Si / SiC, silicon on insulator (SOI) or silicon germanium on insulator. Therefore, the type of substrate should not limit the scope of protection of the present disclosure.

[0045] Among them, the trench isolation structure is used to isolate electrons and light energy. As an example, the cross-sectional shape of the trench isolation structure along the OY direction may include a regular trapezoid, an inverted trapezoid, a rectangle, etc., or may also be a combination of regular trapezoids, inverted trapezoids, rectangles, etc. In this embodiment, the trench isolation structure only needs to be able to isolate electrons and light energy. In addition, the distance between adjacent trenches is not specifically limited in this embodiment and can be set according to actual needs.

[0046] Step S40: forming photodiodes and a target isolation structure alternately arranged along a first direction and extending along a second direction on the first surface of the substrate; the second direction is perpendicular to the first surface of the substrate; the target isolation structure includes a protrusion higher than the top surface of the photodiode and with a wavy outer surface.

[0047] Among them, a target isolation structure is included between two adjacent photodiodes. The target isolation structure is used to isolate light energy, ions, electrons, etc. The protrusion embedded in the isolation stack can effectively change the transmission path of the incident light entering the isolation stack, and can effectively prevent the free electrons of the pixel from penetrating into the adjacent pixels through the interface between the isolation stack and the target isolation structure; it can effectively prevent the light from diffusing to the adjacent pixels or diffusing and merging with the incident light at the back interface, thereby suppressing the adverse effects of the crosstalk effect on the clarity of the image; and the protrusion with a rounded arc surface can avoid the strong electric field gradient caused by charge accumulation at the tip, and can also be embedded in the target isolation structure to intercept light energy and electrons. As an example, the target isolation structure can be formed by etching processes such as photolithography and dry etching. In other embodiments, the etching process can be selected according to actual needs.

[0048] Step S60: forming an isolation stack directly above the target isolation structure, wherein the protrusion is embedded in the isolation stack arranged one-to-one with the target isolation structure.

[0049] The isolation stack can be used to form a grid for isolating light energy. The combination of the target isolation structure and the isolation stack isolates adjacent pixels from each other, thereby effectively preventing crosstalk between adjacent photoelectric sensing areas and improving the imaging quality of the image sensor.

[0050] The structure of the back-illuminated image sensor electronic device obtained after steps S20-S60 can be referred to in Fig.11 Of course, in order to facilitate the understanding of this application, Fig.11 What is given is an example of a back-illuminated image sensor prepared by the back-illuminated image sensor preparation method of the present application. There may be other suitable examples of back-illuminated image sensor electronic devices prepared by the back-illuminated image sensor preparation method of the present application, and the present application does not limit them here.

[0051] In the above embodiment, after the deposition of the photosensitive material layer, the photodiode can form a plurality of target isolation structures arranged at intervals in the photosensitive material layer to obtain a photodiode arranged in an interval array, thereby avoiding signal crosstalk between adjacent photodiodes and unnecessary damage caused by high-energy ion implantation to form the photodiode, reducing dark current in the pixel, and helping to improve the imaging clarity of the image sensor; since the prepared target isolation structure includes a protrusion that is higher than the top surface of the photodiode and embedded in the isolation stack, the isolation stack and the target isolation structure are connected in an embedded matching manner, and together with the trench isolation structure, an effective physical isolation barrier is formed, which can effectively prevent the free electrons of the pixel from penetrating into the adjacent pixel through the interface between the isolation stack and the target isolation structure. The contact surface between the protrusion and the isolation stack is wavy, which can effectively prevent the light from diffusing to the adjacent pixel or diffusing and merging with the incident light at the back interface, suppressing the adverse effects of the crosstalk effect on the image imaging clarity, and in the process, it will not affect the front-end process, which helps to improve the performance and reliability of the back-illuminated image sensor.

[0052] See also Figure 2 , Figure 3a and Figure 3b In some embodiments, step S20 includes steps S22 to S26.

[0053] Step S22 : providing an initial substrate 1 , and forming trench isolation structures 20 arranged at intervals along a first direction in the initial substrate 1 .

[0054] For example, in the front end of line (FEOL) process, a dry etching process and / or a wet etching process may be used to form first trenches (not shown) spaced apart along a first direction in the initial substrate 1, and then a deposition process may be used to form a dielectric material that at least fills the first trench, and then the top surface of the dielectric material is planarized to obtain a trench isolation structure 20 whose top surface is flush with the top surface of the initial substrate 1. The material of the trench isolation structure 20 may include, but is not limited to, silicon oxide, silicon nitride, silicon oxynitride, silicon carbide nitride, etc., or a combination thereof.

[0055] Step S24 : forming an etch stop layer 13 covering the trench isolation structure 20 on the initial substrate 1 , and then forming an interlayer dielectric layer 14 covering the etch stop layer 13 .

[0056] For example, see Figure 2, the etch stop layer 13 can be formed by a deposition process, and the etch stop layer 13 can be a single layer or multiple layers. For example, the material of the etch stop layer 13 can include but is not limited to silicon oxide, silicon nitride, silicon oxynitride, silicon carbide nitride, etc. or a combination thereof. After the etch stop layer 13 is formed, a metal can be deposited to form a partial connection structure, and on this basis, an interlayer dielectric layer 14 can be formed, and the interlayer dielectric layer 14 can be a silicon oxide layer or other low dielectric material layer.

[0057] For example, please continue to see Figure 2 , a metal layer can be formed on the interlayer dielectric layer 14, and the metal layer and part of the connection structure form a metal interconnection structure as the metal connection part of the device. Of course, this embodiment only shows one of the ways, as long as the metal interconnection structure can be reasonably formed, and the thickness of the etching stop layer 13 and the interlayer dielectric layer 14 is not limited, and can be adjusted according to specific process requirements.

[0058] Step S26 : forming an isolation layer 12 on a surface 20 a of the trench isolation structure 20 away from the interlayer dielectric layer 14 .

[0059] For example, please continue to refer to Figure 3a-Figure 3b An isolation layer 12 can be formed in the initial substrate 1 by ion implantation, wherein the isolation layer 12 covers a surface 20a of the trench isolation structure 20 that is away from the interlayer dielectric layer 14, and then the initial substrate 1 located on the side of the trench isolation structure 20 that is away from the interlayer dielectric layer 14 is thinned to expose the isolation layer 12.

[0060] For example, ionized metal plasma (IMP) implantation may be performed on the initial substrate 1, and the implanted ions may be boron ions. At least one of a dry etching process, a wet etching process, a chemical mechanical polishing process, and a push-on process may be used to thin the initial substrate 1 located on the side of the trench isolation structure 20 away from the interlayer dielectric layer 14 to expose the isolation layer 12.

[0061] In some embodiments, after the trench isolation structure 20 is fabricated, the initial substrate 1 is not thinned, and a deep trench isolation structure is directly etched on the back of the initial substrate 1, and then a photoelectric sensing region is formed by high-energy ion implantation. However, in the process of high-energy ion implantation, high-energy ions will inevitably damage the initial substrate 1, and high-energy ions may also enter the deep trench isolation structure, causing a crosstalk effect, resulting in a high dark current and blurred imaging of the prepared image sensor.

[0062] In this embodiment, since the initial substrate 1 that has undergone the ion implantation process is removed during the thinning process, the substrate damage that may be caused during the ion implantation is also removed during the thinning process, thereby avoiding the situation where excessive dark current is caused by defects in the substrate.

[0063] See also Figure 4-Figure 9 In some embodiments, step S40 includes: step S42-step S410.

[0064] Step S42 : stacking the photosensitive layer 15 , the oxide layer 16 and the protective layer 17 in sequence on the isolation layer 12 along a direction away from the isolation layer 12 (eg, an OZ direction).

[0065] For example, a deposition process may be used to form a photosensitive layer 15, an oxide layer 16, and a protective layer 17 stacked in sequence along the OZ direction, wherein the photosensitive layer 15 is adjacent to the isolation layer 12. The doping element of the photosensitive layer 15 may include one of the VA group elements, such as nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and magnesium (Mc). Specifically, the photosensitive layer 15 may be SiP. The oxide layer 16 may act as a stress buffer layer between the protective layer 17 and the photosensitive layer 15 to prevent the protective layer 17 from causing unnecessary damage to the surface of the photosensitive layer 15. The material of the protective layer 17 includes, but is not limited to, silicon nitride.

[0066] For example, one or more deposition methods including but not limited to chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD) can be used to form a photosensitive layer 15, an oxide layer 16 and a protective layer 17 stacked in sequence along the OZ direction. The deposition process can avoid problems such as crystal structure damage, temperature rise and electric field effect caused by ion implantation. In addition, the photodiode structure manufactured by this method is simple in process, low in cost, high in production efficiency, and can achieve more precise device control and consistency, improve the stability and reliability of device performance, and is conducive to large-scale production and application.

[0067] For example, in this embodiment, a selective epitaxial process in a chemical vapor deposition method is used to grow SiP on a substrate, and SiP will only form crystal nuclei on the exposed surface of the substrate.

[0068] Step S44: etching the protection layer 17, the oxide layer 16 and the photosensitive layer 15 to form a plurality of isolation trenches 30 arranged at intervals along the OY direction.

[0069] For example, please refer to Figure 5, a plurality of isolation grooves 30 spaced apart along the OY direction can be formed by combining photolithography with dry etching. The isolation grooves 30 are arranged corresponding to the trench isolation structure 20, for example, one-to-one, that is, the center lines of the isolation grooves 30 and the trench isolation structure 20 in the depth direction are located on the same straight line, and the distance between the symmetry axes of two adjacent isolation grooves 30 is 500 nanometers to 700 nanometers, for example, 500 nanometers, 550 nanometers, 600 nanometers, 650 nanometers or 700 nanometers, etc. In the above example, the larger the interval between two adjacent isolation grooves 30, the larger the photosensitive area of ​​the BSI image sensor, that is, the better the photosensitivity of the BSI image sensor, but too large an interval will result in too large pixels and reduced resolution. Therefore, by setting the distance between the symmetry axes of two adjacent isolation grooves 30 to 500 nanometers to 700 nanometers, the photosensitivity of the BSI image sensor is improved while ensuring the resolution.

[0070] For example, please continue to refer to Figure 5 After etching to form the isolation trench 30, the opening size of the isolation trench 30 can be enlarged by pullback etching, which can prevent the opening from closing prematurely during the subsequent filling process, and help to form a dense and uniform isolation material layer 18 in the isolation trench 30 to avoid filling voids or gaps.

[0071] Step S46 : forming an isolation material layer 18 that at least fills the isolation trench 30 , wherein the top surface of the isolation material layer 18 is not lower than the top surface of the protection layer 17 .

[0072] For example, please refer to Figure 6 , a deposition process can be used to form an isolation material layer 18 that at least fills the isolation groove 30. The material of the isolation material layer 18 may include an oxide. In this embodiment, a liquid dielectric formed by mixing a solvent and a silicon dioxide dielectric is applied to the isolation groove 30 by spin coating to form an isolation material layer 18 whose top surface is not lower than the top surface of the protective layer 17. The flowing liquid material has a good filling performance, which can avoid the problem that the pore corners are easily closed in advance and the void defects are generated inside in the traditional precipitation method, and is helpful to form a target isolation structure with uniform filling and no voids, so as to ensure the isolation effect between pixels and avoid signal crosstalk.

[0073] Step S48 : using the oxide layer 16 as a stop layer, planarizing the top surface of the isolation material layer 18 .

[0074] For example, please refer to Figure 7, the protective layer 17 can be silicon nitride, and the isolation material layer 18 can be silicon oxide. The isolation material layer 18 can be planarized by a CMP process, and wet cleaned with a hot phosphoric acid solution to remove the silicon nitride. Of course, this should not be limited to just one method. For example, in this embodiment, the hot phosphoric acid etching solution is composed of 85% concentrated phosphoric acid and 15% deionized water. During the etching process, phosphate ions react with silicon nitride to dissolve silicon nitride, while silicon oxide is not affected. This selective etching method can effectively remove the silicon nitride layer and retain silicon oxide.

[0075] Step S410 : removing the oxide layer 16 to expose the photosensitive layer 15 whose top surface is lower than the top surface of the isolation material layer 18 .

[0076] For example, please refer to Figure 7-Figure 9 , dry etching combined with wet etching may be used to remove the oxide layer 16 and form a target isolation structure 40 .

[0077] For example, the top surfaces of the oxide layer 16 and the isolation material layer 18 can be treated with a planarization process to make the treated top surfaces of the oxide layer 16 and the isolation material layer 18 flush, and then a patterned photoresist layer covering the top surfaces of the oxide layer 16 and the isolation material layer 18 is formed, and the patterned photoresist layer has an opening pattern exposing the oxide layer 16, and then the patterned photoresist layer is used as a mask to dry-etch and remove the oxide layer 16 to expose the photosensitive layer 15 whose top surface is lower than the top surface of the isolation material layer 18. After removing the patterned photoresist layer, the exposed surface of the isolation material layer 18 is treated with a hydrofluoric acid solution to obtain a target isolation structure 40, and the target isolation structure 40 has a protrusion 41 higher than the top surface of the photosensitive layer 15, and the outer surface of the protrusion 41 is wavy. The photosensitive layer 15 and the isolation layer 12 are used to form a photodiode together.

[0078] For example, please refer to Fig. 9 The area where the isolation material layer 18 is higher than the top surface of the photodiode is etched to form a wavy protrusion 41, and the outer surface of the protrusion 41 is a rounded arc surface. The protrusion 41 increases the interception ability of the target isolation structure 40 to the incident light, reducing the occurrence of light diffusion and crosstalk; the rounded arc surface can avoid the high-intensity electric field gradient generated by the charge accumulation at the tip under the action of a strong electric field. In an image sensor, the accumulation of charges can cause uneven electric field distribution, resulting in signal distortion and increased noise. The design of the rounded arc surface effectively reduces the risk of charge accumulation and ensures the uniformity of the electric field distribution and the stability of signal transmission.

[0079] For example, the dry etching includes at least any one of reactive ion etching (RIE), inductively coupled plasma etching (ICP) or high concentration plasma etching (HDP). The etching solution used in the wet etching process may be a mixed solution of hydrofluoric acid and hydrogen peroxide.

[0080] See also Figure 10-11 In some embodiments, forming the isolation stack 50 directly above the target isolation structure 40 in step S60 may include:

[0081] Step S62: forming a dielectric layer 51, a first conductive layer 52 and a second conductive layer 53 stacked in sequence along the OZ direction on the target isolation structure 40, wherein the dielectric layer 51 covers the protruding portion 41 of the target isolation structure 40, and the top surface of the dielectric layer 51 is not lower than the top surface of the protruding portion 41;

[0082] Step S64 : etching the second conductive layer 53 , the first conductive layer 52 and the dielectric layer 51 to obtain the isolation stack 50 arranged at intervals along the OY direction, and the protrusion 41 of the target isolation structure 40 is embedded in the isolation stack 50 .

[0083] As an example, please refer to Fig.10 In step S62, a deposition process can be used to form a dielectric layer 51 covering multiple protrusions 41 and having a top surface higher than the top surface of the protrusions 41; after the top surface of the dielectric layer 51 is planarized, a first conductive layer 52 is formed on the top surface of the dielectric layer 51; after the top surface of the first conductive layer 52 is planarized, a second conductive layer 53 is formed on the top surface of the first conductive layer 52.

[0084] As an example, please refer to Fig.11 In step S64, a patterned photoresist layer can be used as a mask, or the position, shape and size of the isolation stack 50 can be defined by a mask plate, and then the second conductive layer 53, the first conductive layer 52 and the dielectric layer 51 can be etched by a dry etching process to obtain grid grooves 61 and isolation stacks 50 arranged alternately along the OY direction. The protrusions 41 are higher than the top surface of the photosensitive layer 15 and embedded in the isolation stack 50, which can block the light transmitted into the isolation stack 50 for a second time.

[0085] By setting a target isolation structure throughout the entire pixel area, crosstalk between light and electrons between photosensitive areas can be avoided, thereby improving the display quality of the BSI image sensor. In addition, the target isolation structure embedded in the protrusion of the isolation stack can effectively improve the reflection and refraction of light, thereby focusing the light to the photosensitive area, thereby increasing the amount of light entering the photosensitive area, increasing the electron concentration in the photosensitive area, and improving the photosensitivity of the BSI image sensor.

[0086] The outer surface of the protrusion of the target isolation structure is a rounded arc surface, which can increase the amount of light entering the photosensitive area while avoiding the problem of tip discharge. The isolation column with a trapezoidal cross section maximizes the distance between two adjacent pixels, thereby increasing the photosensitive area of ​​the pixel structure. The protrusion with a rounded arc surface cooperates with each other and works together to effectively reduce the crosstalk and noise of the image sensor and improve the imaging quality of the image sensor.

[0087] As an example, see Fig.10 The material of the dielectric layer 51 may include but is not limited to materials with a high k dielectric constant, such as one or more of aluminum oxide (Al2O3), hafnium oxide (HfO2), hafnium oxynitride (HfON), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), titanium oxide (TiO2) or strontium titanium oxide (SrTiO3), the material of the first conductive layer 52 may include but is not limited to metal materials such as cobalt (Co), nickel (Ni), titanium (Ti), tungsten (W), copper (Cu), aluminum (Al), and the material of the second conductive layer 53 may include titanium nitride (TiN). The three layers of isolation material can be set by deposition, and the thickness of each layer can be adjusted as needed without limitation. The dielectric layer 51, the first conductive layer 52 and the second conductive layer 53 together form a composite metal grid to further enhance the insulation effect.

[0088] As an example, the thickness of the dielectric layer 51 may include 30 nanometers to 50 nanometers, for example, 30 nanometers, 35 nanometers, 40 nanometers, 45 nanometers or 50 nanometers, etc. The thickness of the first conductive layer 52 may include 150 nanometers to 200 nanometers, for example, 150 nanometers, 160 nanometers, 170 nanometers, 180 nanometers, 190 nanometers or 200 nanometers, etc. The thickness of the second conductive layer 53 is 30 nanometers to 50 nanometers, for example, 30 nanometers, 35 nanometers, 40 nanometers, 45 nanometers or 50 nanometers, etc.

[0089] See also Figure 11-Figure 12 In some embodiments, after step S60 , the method further includes: forming a filter 60 in the grid groove 61 .

[0090] For example, see Fig.11 , the filter 60 includes but is not limited to a red filter, a yellow filter, a blue filter, etc., and the three filters are arranged adjacent to each other as a pixel group. The color filter maintains a high transmittance in a specific band, wherein the red filter transmits red light waves, the yellow filter transmits yellow light waves, and the blue filter transmits blue light waves. In addition, the top of the filter is in a rounded arc shape, which is conducive to the convergence of light. Other microlens structures can also be used to meet the focusing requirements, and this application does not make specific restrictions.

[0091] It should be understood that although Figure 1The steps in the flowchart are shown in sequence as indicated by the arrows, but the steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of the steps, and the steps can be executed in other orders. Moreover, Figure 1 At least part of the steps may include multiple steps or multiple stages. These steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the steps or stages in other steps.

[0092] See also Fig.12 The present application provides a back-illuminated image sensor, comprising: a substrate 10, an isolation stack 50, and a photodiode and a target isolation structure 40 located on a first surface of the substrate 10 and alternately arranged along a first direction parallel to the first surface and extending toward the substrate 10; the substrate 10 comprises a plurality of trench isolation structures 20 extending into the substrate 10 via the first surface and arranged at intervals along the first direction; the trench isolation structure 20 is located directly below the target isolation structure 40 arranged one-to-one; the isolation stack 50 is located directly above the target isolation structure 40 arranged one-to-one; the target isolation structure 40 comprises a protrusion 41 that is higher than the top surface of the photodiode and embedded in the isolation stack 50, wherein the contact surface between the protrusion 41 and the isolation stack 50 is wavy.

[0093] For example, please continue to see Fig.12By arranging photodiodes between adjacent target isolation structures 40, the target isolation structures 40 are used to isolate adjacent photodiodes, thereby avoiding signal crosstalk between adjacent photodiodes; since the photodiodes can form a plurality of target isolation structures 40 arranged at intervals in the photosensitive material layer after the photosensitive material layer is deposited, so as to obtain photodiodes arranged in an array at intervals, unnecessary damage caused by forming photodiodes by high-energy ion implantation can be avoided, dark current can be reduced, and the imaging clarity of the image sensor can be improved; since the target isolation structure 40 includes a protrusion 41 that is higher than the top surface of the photodiode and embedded in the isolation stack 50, and the contact surface between the protrusion 41 and the isolation stack 50 is wavy, the isolation stack 50 and the target isolation structure 40 are in contact with each other, so that the isolation stack 50 and the target isolation structure 40 are in contact with each other ... The target isolation structure 40 realizes an embedded matching connection and forms an effective physical isolation barrier together with the trench isolation structure 20, which can effectively prevent the free electrons of the pixels from penetrating into adjacent pixels through the interface between the isolation stack 50 and the target isolation structure 40, and can effectively prevent the light from diffusing into adjacent pixels or diffusing at the back interface and merging with the incident light, thereby suppressing the adverse effects of the crosstalk effect on the clarity of the image, and in the process, will not affect the front-end process, which helps to improve the performance and reliability of the back-illuminated image sensor; moreover, the protrusion 41 with a rounded arc surface can avoid the strong electric field gradient caused by charge accumulation at the tip, and can also be embedded in the target isolation structure 40 to intercept light energy and electrons.

[0094] Please continue reading Fig.12 In some embodiments, the bottom surface of the protrusion 41 is located inside the top surface of the target isolation structure 40 and inside the bottom surface of the isolation stack 50, so that the protrusion 41 is completely embedded in the isolation stack 50. The protrusion 41 increases the interception capability of the target isolation structure 40 for incident light and reduces the occurrence of light diffusion and crosstalk; the rounded arc surface can avoid the high-intensity electric field gradient generated by the charge accumulation at the tip under the action of a strong electric field.

[0095] Please continue reading Fig.12 In some embodiments, the back-illuminated image sensor further includes a filter 60; the protrusion 41 includes a protrusion (not shown) adjacent to the filter 60; the filter 60 is located between the protrusions adjacent to each other along the first direction; the outer surface of the protrusion is a rounded arc surface, and the protrusion is used to intercept light to avoid crosstalk between adjacent pixels.

[0096] Please continue reading Fig.12In some embodiments, the target isolation structure 40 includes an isolation column located below the protrusion 41; the size of the isolation column along the first direction gradually decreases in the direction toward the first surface, so that the size of the photodiode between adjacent target isolation structures 40 along the first direction gradually increases in the direction toward the first surface, thereby facilitating improving the photosensitivity of the image sensor to incident light.

[0097] In some embodiments, the isolation stack 50 includes a dielectric layer 51, a first conductive layer 52, and a second conductive layer 53 stacked in sequence in a direction away from the first surface; the protrusion 41 is embedded in the dielectric layer 51, and the top surface of the protrusion 41 is lower than the top surface of the dielectric layer 51, wherein the dielectric constant of the dielectric layer 51 is greater than a preset value. The dielectric layer 51, the first conductive layer 52, and the second conductive layer 53 together form a composite metal grid to further enhance the insulation effect.

[0098] In some embodiments, the top surface of the trench isolation structure 20 is located within the bottom surface of the target isolation structure 40 , so as to facilitate the connection of the trench isolation structure 20 and the target isolation structure 40 in the OZ direction and form an effective physical isolation barrier between adjacent photodiodes.

[0099] In some embodiments, the photodiode includes an isolation layer 12 and a photosensitive layer 15 stacked along a second direction; the isolation layer 12 is located between the photosensitive layer 15 and the substrate 10 , and the second direction is perpendicular to the first surface of the substrate 10 .

[0100] In some embodiments, the back-illuminated image sensor further includes an etch stop layer 13, which is located on the second surface of the substrate 10. The first surface and the second surface are two main surfaces of the substrate 10 that are separated from each other along the second direction. The trench isolation structure 20 penetrates the substrate 10 along the second direction and extends to the etch stop layer 13. Metal can be deposited after the etch stop layer 13 is formed to form a partial connection structure, and an interlayer dielectric layer 14 is formed on this basis. The interlayer dielectric layer 14 can be a silicon oxide layer or other low-dielectric material layer.

[0101] In some embodiments, an electronic device is provided, comprising: the back-illuminated image sensor in any embodiment of the present application.

[0102] In the above embodiments, the unexpected technical effects that can be produced are:

[0103] Compared with the traditional method of manufacturing photodiodes by high-energy ion implantation, photodiodes prepared by deposition eliminate unnecessary damage and effectively reduce dark current.

[0104] The protrusions and wavy contact surfaces of the target isolation structure form an embedded matching connection with the isolation stack, building an efficient physical isolation barrier, effectively isolating adjacent photodiodes, and achieving mutual independence between pixels. This structure effectively prevents the penetration of free electrons in pixels and the diffusion of light, suppressing the adverse effects of crosstalk on image clarity. At the same time, the rounded arc design further avoids the strong electric field gradient caused by charge accumulation at the tip, ensuring the stability and accuracy of signal transmission.

[0105] Overall, this new target isolation structure technology not only improves the imaging quality and stability of the image sensor, but also optimizes the signal transmission and isolation effect between devices, enhances its reliability and applicability, and enables it to perform well in various application scenarios. With the combined effect of the above features, the performance of the back-illuminated image sensor is improved.

[0106] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features of the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0107] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A back-illuminated image sensor, characterized in that: It includes a substrate, an isolation stack, and a photodiode and a target isolation structure which are located on a first surface of the substrate and are alternately arranged along a first direction parallel to the first surface and extend toward the substrate; The substrate includes a plurality of trench isolation structures extending into the substrate through the first surface and arranged at intervals along the first direction; the trench isolation structures are located directly below the target isolation structures arranged one by one; The isolation stack is located directly above the target isolation structure arranged one-to-one; The target isolation structure includes a protrusion that is higher than the top surface of the photodiode and embedded in the isolation stack, wherein a contact surface between the protrusion and the isolation stack is wavy.

2. The back-illuminated image sensor according to claim 1, wherein: The bottom surface of the protrusion is located inside the top surface of the target isolation structure and inside the bottom surface of the isolation stack.

3. The back-illuminated image sensor according to claim 1, wherein: Also includes filters; The protrusion includes a protrusion adjacent to the filter; The filter is located between the protrusions adjacent to each other along the first direction; The outer surface of the protrusion is a rounded arc surface.

4. The back-illuminated image sensor according to claim 1, wherein: The target isolation structure includes an isolation column located below the protrusion; A dimension of the isolation column along the first direction gradually decreases in a direction toward the first surface.

5. The back-illuminated image sensor according to any one of claims 1 to 4, characterized in that: The isolation stack includes a dielectric layer, a first conductive layer, and a second conductive layer stacked in sequence in a direction away from the first surface; The protrusion is embedded in the dielectric layer, and a top surface of the protrusion is lower than a top surface of the dielectric layer, wherein a dielectric constant of the dielectric layer is greater than a preset value.

6. The back-illuminated image sensor according to any one of claims 1 to 4, characterized in that: A top surface of the trench isolation structure is located within a bottom surface of the target isolation structure.

7. The back-illuminated image sensor according to any one of claims 1 to 4, characterized in that: The photodiode includes an isolation layer and a photosensitive layer stacked along a second direction; The isolation layer is located between the photosensitive layer and the substrate; the second direction is perpendicular to the first surface.

8. The back-illuminated image sensor according to any one of claims 1 to 4, characterized in that: Also includes: an etch stop layer, located on a second surface of the substrate, wherein the first surface and the second surface are two main surfaces of the substrate that are away from each other along a second direction; The second direction is perpendicular to the first surface; The trench isolation structure penetrates the substrate along the second direction and extends to the etch stop layer.

9. An electronic device, characterized in that: include: A back-illuminated image sensor as claimed in any one of claims 1 to 8.

10. A method for preparing a back-illuminated image sensor, characterized in that: include: Providing a substrate, wherein the substrate includes a plurality of trench isolation structures extending into the substrate through a first surface of the substrate and arranged at intervals along a first direction parallel to the first surface; Forming photodiodes and target isolation structures on the first surface, which are alternately arranged along the first direction and extend along the second direction; The second direction is perpendicular to the first surface; the target isolation structure includes a protrusion that is higher than the top surface of the photodiode and has a wavy outer surface; An isolation stack is formed directly above the target isolation structure, and the protrusion is embedded in the isolation stack that is arranged one-to-one with the target isolation structure.

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