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, comprising: a substrate, and photodiodes and isolation columns located on a first surface of the substrate and arranged alternately along a first direction parallel to the first surface and extending toward the substrate; the photodiode comprises a bottom photosensitive region, a middle photosensitive region, and a top photosensitive region sequentially stacked along a second direction away from the substrate; the bottom photosensitive region comprises at least two photosensitive layers of different materials stacked along the second direction; the middle photosensitive region comprises at least two photosensitive layers of different materials arranged along the first direction; and the top photosensitive region comprises at least two photosensitive layers of different materials stacked along the second direction. While avoiding substrate damage caused by ion implantation, its photoelectric conversion efficiency and quantum efficiency are improved.

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 and photodiodes and isolation columns located on a first surface of the substrate and arranged alternately along a first direction parallel to the first surface and extending toward the substrate; the photodiode comprises a bottom photosensitive area, a middle photosensitive area and a top photosensitive area stacked in sequence along a second direction away from the substrate; the bottom photosensitive area comprises at least two photosensitive layers of different materials stacked along the second direction; the middle photosensitive area comprises at least two photosensitive layers of different materials arranged along the first direction; the top photosensitive area comprises at least two photosensitive layers of different materials stacked along the second direction; 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 structures are contact-connected with the isolation columns arranged one-to-one directly above them.

[0006] In the back-illuminated image sensor in the above-mentioned embodiment, a photodiode with multiple doping concentrations and a preset regular arrangement structure is arranged between adjacent isolation columns. The vertical and horizontal arrangement of multiple N regions can effectively optimize the generation and separation process of carriers inside the photosensitive area; while fully converting the incident light, it helps to reduce the carrier recombination phenomenon, prolong the carrier life, and achieve the purpose of improving the photoelectric response efficiency. In addition, the gradient structure of different doping concentrations and / or different doping elements can guide the movement of carriers and reduce the recombination rate. By regulating the depth and concentration of different N regions, the performance of the photodiode can be customized, such as increasing the response speed, improving the quantum efficiency, etc., to meet the needs of different application scenarios.

[0007] The isolation column and the trench isolation structure in the substrate together form an effective fully isolated physical barrier, which can effectively prevent the free electrons of the pixel or the light entering the photosensitive area from propagating and penetrating into adjacent pixels, thereby suppressing the adverse effects of crosstalk on image clarity.

[0008] In some embodiments, the bottom photosensitive area includes an isolation layer, a SiP layer, a SiAs layer, and a SiSb layer stacked in sequence along the second direction, and the isolation layer is adjacent to the substrate.

[0009] In some embodiments, the middle photosensitive area includes: a first photosensitive layer, whose top surface contacts the bottom surface of the top photosensitive area and whose bottom surface contacts the top surface of the bottom photosensitive area; and a second photosensitive layer, which penetrates the first photosensitive layer along the second direction and extends to the bottom photosensitive area.

[0010] In some embodiments, the top photosensitive region includes a SiP layer and a SiAs layer sequentially stacked along the second direction, and the SiP layer is located between the SiAs layer and the middle photosensitive region.

[0011] In some embodiments, the isolation column includes a first isolation structure, a second isolation structure, and a third isolation structure stacked in sequence along a direction away from the substrate. The first isolation structure is located between the bottom photosensitive regions adjacent to each other along the first direction; the second isolation structure is located between the middle photosensitive regions adjacent to each other along the first direction; and the third isolation structure is located between the top photosensitive regions adjacent to each other along the first direction.

[0012] In some embodiments, the first isolation structure and the bottom photosensitive region are prepared simultaneously in the same process step.

[0013] In some embodiments, the third isolation structure and the top photosensitive region are prepared at the same time in the same process step.

[0014] In a second aspect, the present application further provides a method for preparing a back-illuminated image sensor, comprising: providing a substrate, wherein the substrate comprises a plurality of trench isolation structures extending into the substrate through a first surface and arranged at intervals along a first direction parallel to the first surface;

[0015] On the first surface of the substrate, photodiodes and isolation columns are alternately arranged along a first direction and extend toward the substrate; the trench isolation structure is in contact with and connected to the isolation columns arranged one-to-one directly above the trench isolation structure;

[0016] The photodiode includes a bottom photosensitive area, a middle photosensitive area and a top photosensitive area stacked in sequence along a second direction away from the substrate; the bottom photosensitive area includes at least two photosensitive layers of different materials stacked along the second direction; the middle photosensitive area includes at least two photosensitive layers of different materials arranged along the first direction; the top photosensitive area includes at least two photosensitive layers of different materials stacked along the second direction.

[0017] The method for preparing the back-illuminated image sensor in the above-mentioned embodiment improves the preparation process of the photodiode in the back-illuminated image sensor, and adopts a selective epitaxial growth method to obtain a stacked photosensitive layer to form a photodiode with multiple concentrations and structures. Compared with the traditional ion implantation process, the selective epitaxial growth process can effectively avoid the damage to the substrate caused by high-energy implanted ions, thereby reducing the number of defects in the photosensitive area and significantly reducing the dark current based on this. In addition, the vertical and horizontal arrangement of the N region design can optimize the generation and separation process of carriers, achieve more efficient photoelectric conversion, reduce the recombination rate during the conversion process, and improve the photoelectric response efficiency.

[0018] Since the isolation column and the photodiode are prepared simultaneously, the preparation method can also avoid unnecessary damage to the isolation column during high-energy ion implantation, ensuring its isolation effect. The preparation method provides a more reliable technical basis for improving the performance and device stability of back-illuminated image sensors.

[0019] In some embodiments, the isolation column includes a first isolation structure, a second isolation structure, and a third isolation structure sequentially stacked in a direction away from the substrate.

[0020] In some embodiments, forming an intermediate photosensitive area includes: forming a first photosensitive material layer on the top surface of the bottom photosensitive area; forming a second isolation structure that penetrates the first photosensitive material layer; forming a first groove in the first photosensitive material layer, and the remaining first photosensitive material layer is used to constitute the first photosensitive layer; the first groove penetrates the first photosensitive layer along a second direction and extends to the bottom photosensitive area; and forming a second photosensitive layer in the first groove.

[0021] In a third aspect, the present application further provides an electronic device, comprising a back-illuminated image sensor according to any of the above embodiments; or a back-illuminated image sensor prepared by the back-illuminated image sensor preparation method according to any of the above embodiments.

[0022] Electronic devices equipped with back-illuminated image sensors made using the improved preparation method can achieve higher photoelectric conversion efficiency and sensitivity, reduce the probability of dark current generation, and improve their image quality and resolution performance. The stability and reliability of the device are ensured, providing new ideas and directions for improving the performance of electronic devices based on back-illuminated image sensors.

[0023] The back-illuminated image sensor and its manufacturing method, and the electronic device in the embodiments of the present application have the following unexpected technical effects:

[0024] By setting up photodiodes with multiple doping concentrations and preset regular arrangement structures between adjacent isolation columns, the generation and separation process of carriers is optimized, effectively extending the life of photogenerated carriers, thereby improving the photoelectric conversion efficiency of photodiodes. The gradient structure is used to guide carriers to move toward the electrode to optimize their charge collection efficiency. The performance of customized photodiodes can be appropriately modified according to the needs of increasing response speed and improving quantum efficiency. At the same time, the isolation column and the trench structure in the substrate form an effective fully isolated physical barrier, which effectively suppresses the adverse effects of crosstalk on image clarity.

[0025] The improved preparation process uses a selective epitaxial growth method to stack the photosensitive layer. Compared with the traditional ion implantation process, the selective epitaxial growth process can effectively avoid the damage to the substrate caused by high-energy implanted ions when preparing photodiodes, thereby reducing the number of defects in the photosensitive area and significantly reducing the probability of dark current generation based on this. It can also avoid unnecessary damage to the isolation column caused by high-energy ion implantation, ensure its isolation effect, and provide a more reliable technical foundation for the performance improvement and device stability of back-illuminated image sensors.

[0026] In summary, through these innovative designs and preparation methods, back-illuminated image sensors have made significant progress in improving photoelectric conversion efficiency, improving image quality, and optimizing device stability. Electronic devices based on this have shown great development potential in terms of performance improvement and user experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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.

[0028] Figure 1 is a flow chart of a method for preparing a back-illuminated image sensor provided in an embodiment;

[0029] Figure 2ais a schematic cross-sectional view of a structure obtained after a trench isolation structure is formed in step S202 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0030] Figure 2b is a schematic cross-sectional view of a structure obtained after an isolation layer is formed in step S206 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0031] Figure 3 It is a schematic cross-sectional view of a structure obtained after forming multiple photosensitive layers in the bottom photosensitive area in step S402 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0032] Figure 4 is a schematic cross-sectional view of a structure obtained after the first isolation structure is formed in step S404 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0033] Figure 5 is a schematic cross-sectional view of a structure obtained after forming a first photosensitive material layer in step S4062 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0034] Figure 6 is a schematic cross-sectional view of a structure obtained after the second isolation structure is formed in step S4064 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0035] Figure 7 is a schematic cross-sectional view of a structure obtained after the first photosensitive layer is formed in step S4066 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0036] Figure 8 is a schematic cross-sectional view of a structure obtained after forming a second photosensitive layer in step S4068 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0037] Fig. 9 It is a schematic cross-sectional view of a structure obtained after forming multiple photosensitive layers in the top photosensitive area in step S408 in the method for preparing a back-illuminated image sensor provided in one embodiment;

[0038] Fig.10 is a schematic cross-sectional view of a structure obtained after the third isolation structure is formed in step S410 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0039] Fig.11 A schematic cross-sectional view of a structure obtained after a grid is formed in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0040] Fig.12It 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.

[0041] Description of reference numerals:

[0042] 1. Substrate; 2. Etch stop layer; 3. Interlayer dielectric layer; 10. Trench isolation structure; 20. Isolation column; 21. First isolation structure; 22. Second isolation structure; 23. Third isolation structure; 30. Bottom photosensitive area; 31. Isolation layer; 32. First SiP layer; 33. First SiAs layer; 34. SiSb layer; 40. Middle photosensitive area; 411. First photosensitive material layer; 41. First photosensitive layer; 421. First groove; 42. Second photosensitive layer; 50. Top photosensitive area; 51. Second SiP layer; 52. Second SiAs layer; 60. Grid; 61. First grid; 62. Second grid; 63. Third grid; 70. Filter. DETAILED DESCRIPTION

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] See also Figure 1 The present application provides a method for preparing a back-illuminated image sensor, comprising: steps S20 to S40.

[0051] 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.

[0052] For example, the substrate can be made of semiconductor material, insulating material, conductor material or any combination thereof. For example, the substrate can be any of the following materials: silicon (Si) substrate, silicon germanium (SiGe) substrate, silicon germanium carbon (SiGeC) substrate, silicon carbide (SiC) substrate, gallium arsenide (GaAs) substrate, indium arsenide (InAs) substrate, indium phosphide (InP) substrate or other III / V semiconductor substrate or II / VI semiconductor substrate. Or, 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 and thickness of the substrate should not limit the scope of protection of the present disclosure.

[0053] For example, the trench isolation structure material may include, but is not limited to, other high dielectric constant materials, insulating materials, or combinations thereof. For example, the trench isolation structure material may be any of the following materials: silicon oxide (SiO2), silicon nitride (Si3N4), silicon oxynitride (Si2N2O), and the like. 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, and the like, or may also be a combination of regular trapezoids, inverted trapezoids, rectangles, and the like. In addition, the aspect ratio of the trench isolation structure is not specifically limited in this embodiment and may be set according to actual needs.

[0054] Step S40: forming photodiodes and isolation columns alternately arranged along a first direction and extending toward the substrate on the first surface of the substrate; the trench isolation structure is in contact and connected with the isolation columns arranged one-to-one directly above it; the photodiode includes a bottom photosensitive area, a middle photosensitive area and a top photosensitive area stacked in sequence along a second direction away from the substrate; the bottom photosensitive area includes at least two photosensitive layers of different materials stacked along the second direction; the middle photosensitive area includes at least two photosensitive layers of different materials arranged along the first direction; the top photosensitive area includes at least two photosensitive layers of different materials stacked along the second direction.

[0055] For example, the material of the isolation column is similar to that of the trench isolation structure, and may include but is not limited to other insulating materials such as silicon oxide (SiO2), silicon nitride (Si3N4), silicon oxynitride (Si2N2O), or a combination thereof. Similarly, the isolation column is used to isolate light energy and electrons. The trench isolation structure is in contact with the isolation column arranged one-to-one directly above it to form an effective physical isolation barrier, which can effectively prevent light diffusion or charge from entering the adjacent photosensitive area or suppress the adverse effects of optical and / or electrical crosstalk on image clarity.

[0056] For example, in this embodiment, the photosensitive layers of different materials represent silicon layers containing different donor doping elements, such as SiP layers, SiAs layers, SiSb layers, etc. Of course, the silicon material here can also be replaced by other semiconductor materials, and the type of doping elements should not be limited to the examples given in this embodiment. Therefore, the type of substrate should not limit the protection scope of the present disclosure.

[0057] The structure of the back-illuminated image sensor electronic device obtained after steps S20-S40 can be referred to in Fig.10 Of course, in order to facilitate the understanding of this application, Fig.10 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.

[0058] In the above embodiment, a novel method for preparing a back-illuminated image sensor is proposed, and a photodiode having a photosensitive layer arranged vertically and horizontally is obtained by selective epitaxial growth. Compared with conventional ion implantation to prepare photodiodes, the selective epitaxial growth technology can effectively avoid the damage of high-energy ions to the substrate, reduce the number of defects in the photosensitive area, and thus reduce the dark current of the device caused by defect recombination.

[0059] On this basis, the N-region structure arranged in the vertical-horizontal direction is used to optimize the generation and separation of photogenerated carriers, improve the efficient conversion of photogenerated electrons and holes, reduce the recombination probability of photogenerated electrons and holes, and appropriately extend the life of photogenerated carriers. This method can also effectively prevent the damage of the isolation column structure by high-energy ion injection, ensuring the isolation effect.

[0060] See also Figure 2a and Figure 2b In some embodiments, step S20 includes steps S202 to S206.

[0061] Step S202 : providing a substrate 1 , and forming trench isolation structures 10 (not shown) arranged at intervals along a first direction in the substrate 1 .

[0062] For example, in the front end of line (FEOL) process, a dry etching process and / or a wet etching process can be used to first form grooves arranged at intervals along a first direction in the initial substrate 1, and then an isolation material that at least fills the grooves is formed, and then the top surface of the isolation material is planarized to obtain a trench isolation structure 10 whose top surface is flush with the top surface of the initial substrate 1.

[0063] Step S204 : forming an etch stop layer 2 covering the trench isolation structure 10 on the substrate 1 , and then forming an interlayer dielectric layer 3 (not shown) covering the etch stop layer 2 .

[0064] For example, the etch stop layer 2 can be formed by any method in the deposition process, and the etch stop layer 2 can be a single layer or a multilayer. For example, the material of the etch stop layer 2 can include but is not limited to silicon oxide, silicon nitride, silicon oxynitride, silicon carbide nitride, etc. or a combination thereof. Then, an interlayer dielectric layer 3 covering the etch stop layer 2 is formed. After the etch stop layer 2 is formed, a metal can be deposited to form a partial connection structure, and on this basis, an interlayer dielectric layer 3 is formed, and the interlayer dielectric layer 3 can be a low-dielectric material layer. In addition, a metal interconnect structure can also be formed on the interlayer dielectric layer 3 as a metal connection part of the device. For the thickness of the etch stop layer 2 and the interlayer dielectric layer 3, no specific restrictions are made in this embodiment, and they can be adjusted according to specific process requirements.

[0065] Step S206 : forming an isolation layer 31 on the surface 10 a of the trench isolation structure 10 away from the interlayer dielectric layer 3 .

[0066] For example, please continue to refer to Figure 2a-2b An isolation layer 31 can be formed in the substrate 1 by ion implantation, wherein the isolation layer 31 covers the surface 10a of the trench isolation structure 10 away from the interlayer dielectric layer 3, and then the substrate 1 located on the side of the trench isolation structure 10 away from the interlayer dielectric layer 3 is thinned to expose the surface 31a of the isolation layer 31.

[0067] For example, ionized metal plasma (IMP) implantation may be performed on the 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 substrate 1 located on the side of the trench isolation structure 10 away from the interlayer dielectric layer 3, exposing the surface 31a of the isolation layer 31.

[0068] In this embodiment, since the 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.

[0069] See also Figure 3-Figure 11 In some embodiments, step S40 includes: step S402-step S410.

[0070] Step S402 : stacking a first SiP layer 32 , a first SiAs layer 33 and a SiSb layer 34 in sequence on the isolation layer 31 along the OZ direction.

[0071] For example, see Figure 3 , one or more deposition methods including but not limited to chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc. can be used. In this embodiment, a selective epitaxial process in the chemical vapor deposition method is selected to form a first SiP layer 32, a first SiAs layer 33 and a SiSb layer 34 stacked in sequence along the OZ direction.

[0072] Among them, the selective epitaxial growth process can avoid the problems of crystal structure damage, temperature rise and electric field effect caused by ion implantation. In addition, the photodiode structure manufactured by this method is simple, low-cost, high-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.

[0073] Step S404 : forming a first isolation structure 21 penetrating the first SiP layer 32 , the first SiAs layer 33 , the SiSb layer 34 and the isolation layer 31 and arranged in intervals along the OY direction; the remaining first SiP layer 32 , the first SiAs layer 33 and the SiSb layer 34 are used to form the bottom photosensitive area 30 .

[0074] For example, please refer to Figure 4 , similar to the preparation process of the trench isolation structure 10 in the substrate 1, firstly, a plurality of isolation trenches spaced apart along the OY direction can be formed by combining photolithography and etching. Then, a liquid dielectric formed by mixing a solvent and a silicon dioxide dielectric is applied to the isolation trench by spin coating to form a first isolation structure 21 whose top surface is flush with the top surface of the SiSb layer 34. The first isolation structure 21 is arranged corresponding to the trench isolation structure 10.

[0075] The liquid material used in the spin coating has good filling performance, which can avoid the problem of premature closure of the corners of the pores in the isolation groove during filling, resulting in internal void defects. It helps 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.

[0076] At this time, the remaining first SiP layer 32, first SiAs layer 33, SiSb layer 34 and isolation layer 31 are used to form the bottom photosensitive area. The isolation layer 31 has P-type doping and can form a PN junction with the above-mentioned N-type doped photosensitive layer to participate in photoelectric conversion.

[0077] Step S406: forming a middle photosensitive region 40 on the bottom photosensitive region.

[0078] See also Figure 5-Figure 8 In some embodiments, step S406 includes:

[0079] Step S4062 : forming a first photosensitive material layer 411 on the top surface of the bottom photosensitive region 30 .

[0080] For example, see Figure 5 , the first photosensitive material layer 411 is also formed by a selective epitaxial process. In this embodiment, the material in the first photosensitive material layer 411 is SiP.

[0081] Step S4064: forming a second isolation structure 22 penetrating the first photosensitive material layer 411;

[0082] For example, see Figure 6 , a second isolation structure 22 penetrating the first photosensitive material layer 411 along the OZ direction is formed in the first photosensitive material layer 411 using the process flow for preparing the first isolation structure 21. The bottom surface of the second isolation structure 22 is within the top surface of the first isolation structure 21, and the center lines of the first isolation structure 21, the second isolation structure 22 and the trench isolation structure 10 in the OZ direction are located on the same straight line.

[0083] Step S4066 : forming a first groove 421 in the first photosensitive material layer 411 , and the remaining first photosensitive material layer 411 is used to form the first photosensitive layer 41 ; wherein the first groove 421 penetrates the first photosensitive layer 41 along the second direction and extends to the bottom photosensitive region 30 .

[0084] For example, see Figure 7 A first groove 421 can be formed in the first photosensitive material layer 411 by using a method of photolithography combined with etching, and the remaining first photosensitive material layer 411 is used to constitute the first photosensitive layer 41; wherein the first groove 421 penetrates the first photosensitive layer 41 along the OZ direction and extends into the SiSb layer 34, and the first photosensitive layer 41, the top surface contacts the bottom surface of the top photosensitive area 50, and the bottom surface contacts the top surface of the bottom photosensitive area 30.

[0085] The first groove 421 can be formed by etching once or multiple times, and the longitudinal cross-sectional shape along the OY direction can include a regular trapezoid, an inverted trapezoid, a rectangle, etc., or can also be a combination of regular trapezoid, an inverted trapezoid, a rectangle, etc. In this embodiment, the cross-sectional shape of the first groove 421 along the OY direction is a rectangle. Of course, this embodiment only shows one of the ways, as long as the first groove 421 can be reasonably formed.

[0086] Step S4068 : forming a second photosensitive layer 42 in the first groove 421 .

[0087] For example, see Figure 8 , the selective epitaxial growth process is still used to form the second photosensitive layer 42 in the first groove 421, and the second photosensitive layer 42 is partially embedded in the SiSb layer 34. The first photosensitive layer 41 and the second photosensitive layer 42.

[0088] Step S408 : forming a top photosensitive region 50 on the middle photosensitive region 40 .

[0089] For example, see Fig. 9 The steps of forming the top photosensitive region 50 are similar to the steps of forming the bottom photosensitive region 30 , and a second SiP layer 51 and a second SiAs layer 52 covering the middle photosensitive region 40 are sequentially formed by selective epitaxial growth.

[0090] Step S410 : forming a third isolation structure 23 penetrating the top photosensitive region 50 .

[0091] For example, see Fig.10 , repeat the process of preparing the first isolation structure 21 and the second isolation structure 22, that is, etching the second SiP layer 51 and the second SiAs layer 52, and then forming the third isolation structure 23 by spin coating. At this time, the remaining second SiP layer 51 and the second SiAs layer 52 are used to form the top photosensitive area 50. The third isolation structure 23, the second isolation structure 22 and the first isolation structure 21 together constitute an isolation column arranged one-to-one directly above the trench isolation structure 10.

[0092] The distance between the isolation columns 20 is not specifically set in this embodiment. The larger the interval between two adjacent isolation columns 20, the larger the photosensitive area of ​​the pixel, that is, the better the photosensitivity. However, if the interval is too large, the pixel will be too large and the resolution will be reduced. Therefore, it is necessary to set the corresponding interval according to actual needs, taking into account both resolution and photosensitivity.

[0093] Please refer to Fig.11 In some embodiments, step S40 may further include forming a grid 60 .

[0094] The steps of forming the grid 60 include: forming a first grid 61, a second grid 62 and a third grid 63 stacked in sequence along the OZ direction on the isolation column 20; firstly using a patterned photoresist layer as a mask, or defining the position, shape and size of the grid 60 through a mask plate, and then etching the first grid 61, the second grid 62 and the third grid 63 to obtain grids 60 arranged at intervals along the OY direction, and grid grooves located between adjacent grids 60; wherein the grid grooves do not penetrate the first grid 61, so that the remaining first grid 61 covers the top photosensitive area 50, thereby playing a role in etching protection.

[0095] For example, the material of the first grid 61 includes, but is not limited to, insulating materials with high dielectric constants such as aluminum oxide (Al2O3), hafnium oxide (HfO2), tantalum pentoxide (Ta2O5), zirconium oxide (ZrO2), etc.; the material of the second grid 62 includes, but is not limited to, metal materials such as cobalt (Co), nickel (Ni), titanium (Ti), etc.; the material of the third grid includes titanium nitride (TiN). The thickness of each layer can be adjusted as needed without limitation. The first grid 61, the second grid 62, and the third grid 63 together constitute the grid 60, which is used to isolate light energy, converge light, and further enhance the insulation effect between different photodiodes.

[0096] See also Fig.12 In some embodiments, after step S40, the method further includes: forming a filter 70 in the grid groove.

[0097] For example, see Fig.11 , the filter 70 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.

[0098] It should be understood that although Figure 1 The 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.

[0099] See also Fig.12The present application provides a back-illuminated image sensor, comprising: a substrate 1, and photodiodes and isolation columns 20 located on a first surface of the substrate 1 and arranged alternately along a first direction parallel to the first surface and extending toward the substrate 1; the photodiode comprises a bottom photosensitive area 30, a middle photosensitive area 40 and a top photosensitive area 50 stacked in sequence along a second direction away from the substrate; the bottom photosensitive area 30 comprises at least two photosensitive layers of different materials stacked along the second direction; the middle photosensitive area 40 comprises at least two photosensitive layers of different materials arranged along the first direction; the top photosensitive area 50 comprises at least two photosensitive layers of different materials stacked along the second direction; the substrate 1 comprises a plurality of trench isolation structures 10 extending into the substrate via the first surface and arranged at intervals along the first direction; the trench isolation structures are in contact and connected with the isolation columns 20 arranged one-to-one directly above them.

[0100] In the design, multiple N regions are arranged vertically and horizontally, which optimizes the generation and separation process of carriers, helps to maximize the conversion of incident light and reduce carrier recombination, thereby extending the life of carriers. With the combined effect of multiple doping concentrations and structures in the photosensitive area, the photoelectric response efficiency of the back-illuminated image sensor is improved. In addition, the gradient structure of different concentration areas can guide carriers to move toward the electrode, improving the charge collection efficiency. By adjusting the depth and concentration of different N regions, the performance of the photodiode can be customized, such as increasing the response speed and improving the quantum efficiency, to meet the needs of different application scenarios.

[0101] Please continue reading Fig.12 In some embodiments, the bottom photosensitive area 30 includes an isolation layer 31, a first SiP layer 32, a first SiAs layer 33, and a SiSb layer 34 sequentially stacked along the second direction, and the isolation layer 31 is adjacent to the substrate 1. The isolation layer 31 and the first SiP layer 32, the first SiAs layer 33, and the SiSb layer 34 have different conductivity types and can form a PN junction to produce a photoelectric effect.

[0102] Please continue reading Fig.12 In some embodiments, the middle photosensitive region 40 includes: a first photosensitive layer 41, the top surface of which contacts the bottom surface of the top photosensitive region 50, and the bottom surface of which contacts the top surface of the bottom photosensitive region 30; and a second photosensitive layer 42, which penetrates the first photosensitive layer 41 along the second direction and extends to the bottom photosensitive region 30. The preset regularly arranged N region structure can increase the number of photoelectrons of the photodiode.

[0103] Please continue reading Fig.12In some embodiments, the top photosensitive region 50 includes a second SiP layer 51 and a second SiAs layer 52 sequentially stacked along the second direction, and the second SiP layer 51 is located between the second SiAs layer 52 and the middle photosensitive region 40. Photosensitive layers with different doping elements have different ionization energies, and after light excitation, a concentration gradient is formed inside the photodiode, thereby increasing the diffusion length of minority carriers.

[0104] Please continue reading Fig.12 In some embodiments, the isolation column 20 includes a first isolation structure 21, a second isolation structure 22, and a third isolation structure 23 that are sequentially stacked along a direction away from the substrate 1. The first isolation structure 21 is located between the bottom photosensitive regions 30 adjacent to each other along the first direction; the second isolation structure 22 is located between the middle photosensitive regions 40 adjacent to each other along the first direction; and the third isolation structure 23 is located between the top photosensitive regions 50 adjacent to each other along the first direction.

[0105] Please continue reading Fig.12 In some embodiments, the first isolation structure 21 and the bottom photosensitive region 30 are prepared at the same time in the same process step.

[0106] Please continue reading Fig.12 In some embodiments, the third isolation structure 23 and the top photosensitive region 50 are prepared at the same time in the same process step.

[0107] The present application also provides an electronic device, comprising a back-illuminated image sensor according to any one of the above embodiments; or a back-illuminated image sensor prepared by the back-illuminated image sensor preparation method according to any one of the above embodiments.

[0108] In the above embodiments, the unexpected technical effects of the present application are:

[0109] Compared with the traditional high-energy ion implantation method of manufacturing photodiodes, the improved preparation process uses a selective epitaxial growth method to stack the photosensitive layer, eliminating unnecessary damage and effectively reducing dark current. It can also avoid unnecessary damage to the isolation column caused by high-energy ion implantation, ensuring its isolation effect.

[0110] The use of multiple doping concentrations and preset regular arrangement structures optimizes the generation and separation process of carriers in the photodiode, effectively prolonging the life of photogenerated carriers, thereby improving the photoelectric conversion efficiency of the photodiode. The gradient structure is used to guide the carriers to move toward the electrode, optimizing their charge collection efficiency. At the same time, the isolation column and the trench structure in the substrate form an effective fully isolated physical barrier, effectively suppressing the adverse effects of crosstalk on image clarity.

[0111] Overall, the structure and preparation method of this new back-illuminated image sensor not only improves the imaging quality and stability of the image sensor, but also optimizes the signal transmission and isolation effects 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. Electronic devices equipped with back-illuminated image sensors prepared by the improved preparation method can achieve higher photoelectric conversion efficiency and sensitivity, reduce the probability of dark current generation, and improve their image quality and resolution performance. The stability and reliability of the device are ensured, providing new ideas and directions for improving the performance of electronic devices based on back-illuminated image sensors.

[0112] 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.

[0113] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, 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. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A back-illuminated image sensor, characterized in that: include: A substrate, and photodiodes and isolation columns 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 photodiode comprises a bottom photosensitive region, a middle photosensitive region and a top photosensitive region stacked in sequence along a second direction away from the substrate; The bottom photosensitive area includes at least two photosensitive layers of different materials stacked along the second direction; the middle photosensitive area includes at least two photosensitive layers of different materials arranged along the first direction; the top photosensitive area includes at least two photosensitive layers of different materials stacked along the second direction; the photosensitive layers of different materials include silicon layers of different donor doping elements; 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 in contact and connected with the isolation columns arranged one by one directly above the trench isolation structures.

2. The back-illuminated image sensor according to claim 1, wherein: The bottom photosensitive area includes an isolation layer, a SiP layer, a SiAs layer, and a SiSb layer stacked in sequence along the second direction; The isolation layer is adjacent to the substrate.

3. The back-illuminated image sensor according to claim 2, wherein: The intermediate light sensing area comprises: A first photosensitive layer, a top surface of which contacts the bottom surface of the top photosensitive area, and a bottom surface of which contacts the top surface of the bottom photosensitive area; The second photosensitive layer penetrates the first photosensitive layer along the second direction and extends to the bottom photosensitive area.

4. The back-illuminated image sensor according to claim 3, wherein: The second photosensitive layer is partially embedded in the SiSb layer.

5. The back-illuminated image sensor according to any one of claims 1 to 4, characterized in that: The top photosensitive area includes a SiP layer and a SiAs layer sequentially stacked along the second direction; The SiP layer is located between the SiAs layer and the middle photosensitive area.

6. The back-illuminated image sensor according to any one of claims 2 to 4, characterized in that: The isolation column comprises a first isolation structure, a second isolation structure and a third isolation structure sequentially stacked in a direction away from the substrate; The first isolation structure is located between the bottom photosensitive areas adjacent to each other along the first direction; The second isolation structure is located between adjacent intermediate photosensitive areas along the first direction; The third isolation structure is located between the top photosensitive regions adjacent to each other along the first direction.

7. The back-illuminated image sensor according to claim 6, wherein: Includes at least one of the following features; The first isolation structure and the bottom photosensitive area are prepared at the same time in the same process step; The third isolation structure and the top photosensitive area are prepared at the same time in the same process steps.

8. 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 and arranged at intervals along a first direction parallel to the first surface; Forming photodiodes and isolation columns on the first surface of the substrate, which are alternately arranged along the first direction and extend toward the substrate; The trench isolation structure is in contact with and connected to the isolation pillars disposed one-to-one directly above it; The photodiode includes a bottom photosensitive area, a middle photosensitive area and a top photosensitive area stacked in sequence along a second direction away from the substrate; the bottom photosensitive area includes at least two photosensitive layers of different materials stacked along the second direction; the middle photosensitive area includes at least two photosensitive layers of different materials arranged along the first direction; the top photosensitive area includes at least two photosensitive layers of different materials stacked along the second direction; the photosensitive layers of different materials contain silicon layers of different donor doping elements.

9. The preparation method according to claim 8, characterized in that: The isolation column comprises a first isolation structure, a second isolation structure and a third isolation structure sequentially stacked in a direction away from the substrate; Forming the intermediate light sensing area includes: forming a first photosensitive material layer on the top surface of the bottom photosensitive area; forming the second isolation structure penetrating the first photosensitive material layer; A first groove is formed in the first photosensitive material layer, and the remaining first photosensitive material layer is used to form a first photosensitive layer; the first groove penetrates the first photosensitive layer along the second direction and extends to the bottom photosensitive area; A second photosensitive layer is formed in the first groove.

10. An electronic device, characterized in that: include: The back-illuminated image sensor according to any one of claims 1 to 7; or A back-illuminated image sensor prepared by the method for preparing a back-illuminated image sensor according to claim 8 or 9.

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