Backside illuminated image sensor, preparation method thereof and electronic equipment

Abstract

The invention relates to a backside illuminated image sensor and a preparation method thereof, and electronic equipment, and relates to the technical field of integrated circuits, the backside illuminated image sensor comprises a substrate, and photodiodes and laminated isolation structures which are located on the substrate, are alternately arranged along a first direction parallel to the surface of the substrate, and extend along the direction towards the substrate. The photodiode comprises an isolation layer, a first photosensitive layer, a second photosensitive layer and a third photosensitive layer which are sequentially stacked in the direction away from the substrate. The first photosensitive layer internally comprises a plurality of first SiP layers arranged at intervals in the first direction, and the first SiP layers penetrate through the first photosensitive layer in the second direction and extend to the isolation layer. And the third photosensitive layer internally comprises a plurality of second SiP layers which are arranged at intervals along the first direction, and the plurality of second SiP layers penetrate through the third photosensitive layer along the second direction and extend to the second photosensitive layer, so that the number of photon-generated carriers can be increased, and the quantum efficiency of the device can be 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. According to the placement of metal lines and light receiving layers, they are divided into front-illuminated and back-illuminated types. Among them, back-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 today's deep submicron technology, the traditional BSI front-end process requires high-energy ion implantation (IMP) to prepare the diode structure to form the photosensitive area, which may cause damage to the substrate surface. Uneven ion implantation can also cause signal crosstalk between different pixels, thus 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 unnecessary damage to the back-illuminated image sensor caused by IMP during the preparation of the photodiode.

[0005] In a first aspect, the present application provides a back-illuminated image sensor, comprising: a substrate and a photodiode and a stacked isolation structure located on a first surface of the substrate and arranged alternately along a first direction parallel to the first surface and extending along a second direction toward the substrate; the photodiode comprises an isolation layer, a first photosensitive layer, a second photosensitive layer and a third photosensitive layer stacked in sequence along a direction away from the substrate; the first photosensitive layer comprises a plurality of first SiP layers arranged at intervals along the first direction, the plurality of first SiP layers penetrate the first photosensitive layer along the second direction and extend to the isolation layer; the third photosensitive layer comprises a plurality of second SiP layers arranged at intervals along the first direction, the plurality of second SiP layers penetrate the third photosensitive layer along the second direction and extend to the second photosensitive layer; the first photosensitive layer contains As, the second photosensitive layer contains P, and the third photosensitive layer contains Sb.

[0006] In the back-illuminated image sensor in the above embodiment, the dual photodiode structure formed by the N region and the P region doped with double VA group elements moderately increases the width of the depletion layer while maintaining the response speed compared to the single doping, thereby increasing the number of photogenerated carriers in the device and improving the photoelectric conversion efficiency of the device. The photodiode structure in which the photosensitive layers doped with different VA group elements are stacked and arranged alternately will generate a conductivity gradient inside after light excitation, and the difference is used to optimize the transmission path of the photogenerated carriers, reduce the recombination rate in the diffusion process, and improve the quantum efficiency of the photodiode based on this structure as a whole.

[0007] In addition, multiple stacked isolation structures arranged at intervals in the pixel area and the grid together constitute a physical isolation barrier to prevent photogenerated carriers from penetrating each other in adjacent pixel areas and light from diffusing to adjacent pixels, thereby suppressing the adverse effects of light and / or charge crosstalk on imaging quality by improving the internal structure of the pixel area.

[0008] In some embodiments, bottom surfaces of the plurality of first SiP layers are lower than a top surface of the isolation layer.

[0009] In some embodiments, bottom surfaces of the plurality of second SiP layers are lower than a top surface of the second photosensitive layer.

[0010] In some embodiments, a plurality of first SiP layers and a plurality of second SiP layers are arranged one to one, and a second SiP layer is located directly above a first SiP layer.

[0011] In some embodiments, the stacked isolation structure 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 extends along the second direction and penetrates the first photosensitive layer; the second isolation structure extends along the second direction and penetrates the second photosensitive layer; and the third isolation structure extends along the second direction and penetrates the third photosensitive layer.

[0012] In some embodiments, the substrate includes a plurality of trench isolation structures extending into the substrate through the first surface and arranged at intervals along a first direction; the trench isolation structure is arranged one-to-one with the stacked isolation structure directly above it.

[0013] In a second aspect, the present application also provides a method for preparing a back-illuminated image sensor, comprising:

[0014] 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; the first surface includes an isolation layer; and the first direction is parallel to the first surface;

[0015] A first photosensitive layer is formed on the isolation layer, and a plurality of first isolation structures are extended along a second direction close to the substrate and penetrate the second photosensitive layer; the first photosensitive layer includes a plurality of first SiP layers arranged at intervals along the first direction, and the plurality of first SiP layers penetrate the first photosensitive layer along the second direction close to the substrate and extend to the isolation layer; the first photosensitive layer contains As;

[0016] A second photosensitive layer and a plurality of second isolation structures extending along a second direction and penetrating the second photosensitive layer are formed on the first photosensitive layer; the second photosensitive layer comprises P;

[0017] A third photosensitive layer is formed on the second photosensitive layer, as well as a plurality of third isolation structures extending along the second direction and penetrating the third photosensitive layer; the third photosensitive layer includes a plurality of second SiP layers arranged at intervals along the first direction, the plurality of second SiP layers penetrate the third photosensitive layer along the second direction and extend to the second photosensitive layer, and the third photosensitive layer contains Sb; the first isolation structure, the second isolation structure and the third isolation structure stacked in sequence are used to constitute a stacked isolation structure; the stacked isolation structure is located directly above the one-to-one trench isolation structure.

[0018] The method for preparing a back-illuminated image sensor in the above embodiment avoids unnecessary damage to the substrate caused by high-energy ion implantation in the traditional process of preparing photodiodes. The photodiode structure obtained by multiple growth methods can reduce the number of defects in the pixel area, thereby achieving the purpose of reducing the dark current in the image sensor and improving the image clarity. The contact-connected stacked isolation structure and the trench isolation structure form a physical isolation barrier in the photosensitive area and the substrate, blocking the mutual penetration of photogenerated carriers between adjacent pixel areas, reducing the probability of light diffusion to adjacent pixels, and effectively suppressing the negative impact of the crosstalk effect on image clarity, providing a guarantee for obtaining high-quality images.

[0019] In some embodiments, a first photosensitive layer is formed on the isolation layer, the first photosensitive layer comprising As; a plurality of first trenches spaced apart along a first direction are formed in the first photosensitive layer; a first isolation structure is formed in the first trench directly above the trench isolation structure; and a first SiP layer is formed in the first trench between the first isolation structures.

[0020] In some embodiments, a second photosensitive layer is formed covering the first isolation structure, the first SiP layer, and the first photosensitive layer; a plurality of second grooves are formed in the second photosensitive layer in a one-to-one arrangement with the first isolation structure, the second grooves exposing the first isolation structure directly thereunder; and a second isolation structure is formed in the second grooves.

[0021] In some embodiments, after forming the third photosensitive layer and the third isolation structure, a laser annealing process is used to treat and activate ions in the photodiode.

[0022] In a third aspect, the present application also provides an electronic device, comprising a back-illuminated image sensor in any one of the embodiments of the present application.

[0023] In a fourth aspect, the present application further provides an electronic device, comprising: a back-illuminated image sensor prepared by using any back-illuminated image sensor preparation method in any embodiment of the present application.

[0024] The electronic device in the above embodiment is equipped with a back-illuminated image sensor with higher photoelectric conversion efficiency and lower dark current, which can provide clearer and more realistic images, show richer details and colors, and perform better in low-light environments. It can meet the user's demand for image quality in different scenarios, improve the shooting experience, increase user satisfaction and product attractiveness.

[0025] 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:

[0026] The photodiode structure obtained by multiple growth methods can reduce the number of defects in the pixel area and avoid unnecessary damage to the substrate caused by high-energy ion implantation in the traditional process of preparing photodiodes, thereby reducing the dark current in the image sensor and improving image clarity. Compared with single doping, the double photodiode structure composed of the N region and the P region doped with double VA elements moderately increases the width of the depletion layer while maintaining the response speed, thereby increasing the number of photogenerated carriers in the device and improving the photoelectric conversion efficiency of the device. By stacking photosensitive layers doped with different VA elements in sequence and alternatingly arranging the photodiode structure, the conductivity gradient generated after light excitation optimizes the transmission path of photogenerated carriers and reduces the recombination rate in the diffusion process. Under the joint action of the two, the quantum efficiency of the photodiode based on this structure is effectively improved.

[0027] Furthermore, the physical isolation barrier formed by the spaced stacked isolation structure and the trench isolation structure in the photosensitive area and the substrate can block the mutual penetration of photogenerated carriers between adjacent pixel areas, reduce the probability of light diffusion to adjacent pixels, and effectively suppress the adverse effects of optical or electrical crosstalk on image clarity, laying the foundation for obtaining high-quality images.

[0028] In summary, by optimizing the internal structure of the back-illuminated image sensor and improving the overall performance of the device, a solid technical foundation and guarantee is provided for the acquisition of high-quality images. In future research and applications, further optimizing the preparation method of the device structure will bring broader prospects and application potential for the development of back-illuminated image sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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.

[0030] Figure 1 is a flow chart of a method for preparing a back-illuminated image sensor provided in an embodiment;

[0031] Figure 2a is a schematic cross-sectional view of a structure obtained after an isolation layer is formed in step S202 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0032] Figure 2b is a schematic cross-sectional view of a structure obtained after the substrate is thinned in step S204 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0033] Figure 3 is a schematic cross-sectional view of a structure obtained after the first photosensitive layer is formed in step S402 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0034] Figure 4 is a schematic cross-sectional view of a structure obtained after forming a first groove in step S404 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0035] Figure 5 is a schematic cross-sectional view of a structure obtained after the first isolation structure is formed in step S406 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0036] Figure 6 is a schematic cross-sectional view of a structure obtained after the first SiP layer is formed in step S408 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0037] Figure 7 is a schematic cross-sectional view of a structure obtained after forming a second isolation structure in step S606 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0038] Figure 8 is a schematic cross-sectional view of a structure obtained after forming a second SiP layer in step S808 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0039] Fig. 9 It is a schematic cross-sectional view of a structure obtained after a grid material layer is formed in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0040] Fig.10 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;

[0041] Fig.11 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.

[0042] Description of reference numerals:

[0043] 1. Initial substrate; 10. Substrate; 11. Etch stop layer; 12. Interlayer dielectric layer; 13. Isolation layer; 14. First photosensitive layer; 15. First SiP layer; 16. Second photosensitive layer; 17. Third photosensitive layer; 18. Second SiP layer; 20. Trench isolation structure; 30. Stacked isolation structure; 31. First isolation structure; 311. First trench; 32. Second isolation structure; 321. Second trench; 33. Third isolation structure; 331. Third trench; 40. Grid; 41. First grid layer; 42. Second grid layer; 43. Third grid layer; 50. Grid groove; 60. Filter. DETAILED DESCRIPTION

[0044] 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.

[0045] 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.

[0046] 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 may be 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.

[0047] 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.

[0048] 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.

[0049] 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 regions shown herein, but rather include shape deviations 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 region of the device, and do not limit the scope of the present application.

[0050] 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.

[0051] See also Figure 1 In some embodiments, a method for preparing a back-illuminated image sensor is provided, comprising: steps S20 to S80.

[0052] 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; the first surface includes an isolation layer; and the first direction is parallel to the first surface.

[0053] Among them, the substrate can provide mechanical support and electrical performance, and the longitudinal cross-sectional shape of the trench isolation structure along the OY direction can include a regular trapezoid, an inverted trapezoid, a rectangle, etc., or can also be a combination of these shapes, which is used to isolate electrons and light energy and improve the leakage problem of adjacent devices. In the embodiment of the present application, the trench isolation structure only needs to be able to isolate electrons and light energy. In addition, this embodiment does not make specific restrictions on the distance between adjacent trench isolation structures, and can be set according to actual needs.

[0054] Step S40: forming a first photosensitive layer on the isolation layer, and a plurality of first isolation junctions extending along a second direction close to the substrate and penetrating the second photosensitive layer; the second photosensitive layer includes a plurality of first SiP layers arranged at intervals along the first direction, and the plurality of first SiP layers penetrate the first photosensitive layer along the second direction close to the substrate and extend to the isolation layer; the first photosensitive layer includes As.

[0055] Among them, an isolation structure is included between the adjacent photosensitive layers along the OY direction. The isolation structure is also used to isolate light energy, ions, electrons, etc., which can block the mutual penetration of photogenerated carriers between adjacent pixel areas, reduce the probability of light diffusion to adjacent pixels, and suppress the adverse effects of crosstalk on image clarity; the N region and P region doped with double VA group elements constitute a double photodiode structure. Compared with single doping, the depletion layer width is moderately increased while maintaining the response speed, so as to increase the number of photogenerated carriers in the device and improve the photoelectric conversion efficiency of the device.

[0056] Step S60: forming a second photosensitive layer on the first photosensitive layer, and a plurality of second isolation structures extending in a second direction and penetrating the second photosensitive layer; the second photosensitive layer includes P.

[0057] Among them, due to the different doping elements contained, the ionization energy of the impurity energy level in the first photosensitive layer and the second photosensitive layer changes. Therefore, the difference in conductivity generated after light excitation naturally forms an electron transmission path and reduces the recombination rate during the diffusion process.

[0058] Step S80: forming a third photosensitive layer on the second photosensitive layer, and a plurality of third isolation structures extending along the second direction and penetrating the third photosensitive layer; the third photosensitive layer includes a plurality of second SiP layers arranged at intervals along the first direction, the plurality of second SiP layers penetrate the third photosensitive layer along the second direction and extend to the second photosensitive layer, and the third photosensitive layer contains Sb. The first isolation structure, the second isolation structure and the third isolation structure stacked in sequence are used to form a stacked isolation structure; the stacked isolation structure is located directly above the one-to-one trench isolation structure.

[0059] Among them, the photosensitive layers doped with different VA group elements stacked in sequence or arranged alternately can optimize the diffusion path of photogenerated carriers, and the physical isolation barrier formed by the staggered stacked isolation structure and the trench isolation structure in the photosensitive area and the substrate further enhances the isolation effect and effectively isolates adjacent pixel areas, providing a guarantee for obtaining high-quality images.

[0060] The structure of the back-illuminated image sensor obtained after steps S20-S80 can be referred to in Fig.10 Of course, in order to facilitate the understanding of this application, Fig.10An example of a back-illuminated image sensor prepared by the back-illuminated image sensor preparation method of the present application is given. There may be other suitable examples of back-illuminated image sensors prepared by the back-illuminated image sensor preparation method of the present application, and the present application does not limit them here.

[0061] The photodiode structure obtained by multiple growth methods can reduce the number of defects in the pixel area and avoid unnecessary damage to the substrate caused by high-energy ion implantation in the traditional process of preparing photodiodes, thereby reducing the dark current in the image sensor and improving image clarity. Compared with single doping, the double photodiode structure composed of the N region and the P region doped with double VA elements can moderately increase the depletion layer width while maintaining the response speed, thereby increasing the number of photogenerated carriers in the device and improving the photoelectric conversion efficiency of the device. The photodiode structure in which photosensitive layers doped with different VA elements are stacked or alternately arranged optimizes the transmission path of photogenerated carriers through the conductivity gradient generated after light excitation, reduces the recombination rate in the diffusion process, and the quantum efficiency of the photodiode based on this structure is effectively improved under the joint action of the two.

[0062] The physical isolation barrier formed by the spaced stacked isolation structure and the trench isolation structure in the photosensitive area and the substrate can block the mutual penetration of photogenerated carriers between adjacent pixel areas, reduce the probability of light diffusion to adjacent pixels, and effectively suppress the adverse effects of optical or electrical crosstalk on image clarity, laying the foundation for obtaining high-quality images.

[0063] In summary, by combining the new photodiode structure and the stacked isolation structure, the damage to the device itself caused by high-energy ion implantation is effectively avoided, the dark current caused by defects is reduced, and the imaging clarity and photoelectric performance are improved, which is of great significance for promoting the advancement and widespread application of back-illuminated image sensors.

[0064] See also Figure 2a-2b In some embodiments, step S20 includes steps S202 to S204.

[0065] Step S202 : forming an isolation layer 13 on a surface 20 a of the trench isolation structure 20 in the initial substrate 1 away from the interlayer dielectric layer 12 .

[0066] For example, see Figure 2aThe initial substrate 1 can be made of semiconductor material, insulating material, conductor material or any combination thereof. 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. 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.

[0067] For example, the trench isolation structure 20 can be prepared by combining an etching process and a deposition process in the front end of line (FEOL). Of course, it can also be prepared by other methods known to those skilled in the art. The material may include but is not limited to silicon oxide (SiO2), silicon nitride (Si3N4), silicon oxynitride (Si2N2O), etc. or a combination thereof.

[0068] The front-end process also includes forming an etch stop layer 11 covering the trench isolation structure 20 on the initial substrate 1, depositing metal after forming the etch stop layer 11 to form a partial connection structure, and forming an interlayer dielectric layer 12 on this basis, and the interlayer dielectric layer 12 can be a low-dielectric material layer. A metal interconnect structure can also be formed on the interlayer dielectric layer 12 as a metal connection part of the device.

[0069] Of course, this embodiment only shows one of the methods. As long as the metal interconnection structure can be reasonably formed, there is no restriction on the thickness of the etch stop layer 11 and the interlayer dielectric layer 12, which can be adjusted according to specific process requirements.

[0070] Step S204 : thinning the initial substrate 1 on the side of the trench isolation structure 20 away from the interlayer dielectric layer 12 to expose the isolation layer 13 .

[0071] For example, see Figure 2b At least one of a dry etching process, a wet etching process, a chemical mechanical polishing process and a push-on process can be used to thin the initial substrate 1 located on the side of the trench isolation structure 20 away from the interlayer dielectric layer 12 to expose the isolation layer 13.

[0072] For example, chemical mechanical polishing is mainly achieved by mechanical polishing and chemical reaction. Dry etching includes at least one of reactive ion etching (RIE) or plasma etching. The etching solution of the wet etching process can be a mixed solution of hydrofluoric acid and nitric acid. The three processes have their own advantages and disadvantages, and the specific selection should be made according to different processing objects, requirements and actual conditions.

[0073] In this embodiment, the isolation layer 13 can be used as a push-off stop layer during the thinning process. Thinning removes substrate damage that may be caused during ion implantation and avoids the occurrence of excessive dark current due to defects in the substrate.

[0074] See also Figure 3-Figure 6 In some embodiments, step S40 includes: step S402-step S408.

[0075] Step S402 : forming a first photosensitive layer 14 on the isolation layer 13 , wherein the first photosensitive layer 14 comprises As.

[0076] For example, see Figure 3 The first photosensitive layer 14 can be formed by any deposition method such as chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc., but not limited to. The deposition process can avoid problems such as crystal structure damage, temperature rise and electric field effect caused by ion implantation. In this embodiment, the first photosensitive layer 14 can be formed on the isolation layer 13 by chemical vapor deposition.

[0077] Step S404 : forming a plurality of first trenches 311 spaced apart along the first direction in the first photosensitive layer 14 ; a first trench 311 is located directly above a trench isolation structure 20 .

[0078] For example, see Figure 4 The first groove 311 can be formed by combining photolithography and dry etching. In this embodiment, photolithography uses a light source to selectively irradiate the photoresist layer to change its chemical properties, and then develops and removes the corresponding photoresist to obtain a corresponding pattern, which is used as a mask to further selectively etch the position exposed by the photolithography to obtain the first groove 311. In other embodiments, the process can be selected according to actual needs.

[0079] Step S406 : forming a first isolation structure 31 in the first trench 311 directly above the trench isolation structure 20 .

[0080] For example, see Figure 5 The first isolation structure 31 can be prepared by processes such as spin-on glass (SOG), flowable chemical vapor deposition (FCVD), and high aspect ratio filling process (HARP). In this embodiment, a liquid dielectric formed by mixing a solvent and a silicon dioxide dielectric is applied to the first groove 311 used to form the first isolation structure 31 by spin coating to form a first isolation structure 31 with a top surface not lower than the top surface of the first photosensitive layer 14. Since the flowing liquid material has a good filling performance, it can avoid the problem that the corners of the pores are easily closed in advance during the traditional precipitation method, and the problems such as the generation of void defects inside can be avoided, thereby ensuring the isolation effect between pixels and avoiding the crosstalk effect.

[0081] Step S408 : forming a first SiP layer 15 in the first trenches 311 between the first isolation structures 31 .

[0082] For example, see Figure 6 After the first SiP layer 15 is formed by deposition, chemical mechanical polishing is performed until the top surface of the first SiP layer 15 is flush with the top surface of the first isolation structure 31. At this time, the first photosensitive layer 14 containing As and the first SiP layer 15 form a double VA group element doped N region, which contacts the P region to form a dual photodiode structure.

[0083] Since SiP has a smaller impurity ionization energy, the PN junction formed by SiP and P-type silicon has a wider depletion layer than the PN junction of SiAs. Therefore, compared with single doping, photodiodes with double VA group elements can absorb more photons and generate electron-hole pairs, thereby increasing the number of photogenerated carriers in the device and improving the photoelectric conversion efficiency of the device.

[0084] See also Figure 7 In some embodiments, step S60 also includes: step S602-step S606.

[0085] Step S602: forming a second photosensitive layer 16 covering the first isolation structure 31, the first SiP layer 15, and the first photosensitive layer 14;

[0086] Step S604: forming a plurality of second trenches 321 in the second photosensitive layer 16 and arranged one-to-one with the first isolation structure 31 , wherein the second trenches 321 expose the first isolation structure 31 directly thereunder;

[0087] Step S606 : forming a second isolation structure 32 in the second trench 321 .

[0088] For example, see Figure 7 In this embodiment, steps S602 to S606 are consistent with the previous steps S402 to S406, that is, steps S402 to S406 are repeated to etch the deposited second photosensitive layer 16, and then the second isolation structure 32 is prepared by the spin-on-glass method, and the second photosensitive layer 16 and the second isolation structure 32 are alternately spaced along the OY direction. Among them, the second isolation structure 32 is arranged in contact with the first isolation structure 31 in a one-to-one manner, that is, the center lines of the second isolation structure 32 and the first isolation structure 31 in the depth direction are located on the same straight line.

[0089] See also Figure 8 In some embodiments, step S80 also includes: step S802-step S810.

[0090] Step S802: forming a third photosensitive layer 17 covering the second isolation structure 32 and the second photosensitive layer 16;

[0091] Step S804: forming a plurality of third trenches 331 spaced apart from each other along the first direction in the third photosensitive layer 17 to expose the second isolation structure 32 directly thereunder;

[0092] Step S806: forming a third isolation structure 33 in the first trench 331 directly above the second isolation structure 32;

[0093] Step S808 : forming a second SiP layer 18 in the first trench 331 between the third isolation structures 33 , wherein a plurality of second SiP layers 18 penetrate the third photosensitive layer 17 along the second direction and extend to the second photosensitive layer 16 .

[0094] For example, see Figure 8 In this embodiment, steps S802 to S808 are basically the same as the previous steps S402 to S408, that is, steps S402 to S408 are repeated to etch the deposited third photosensitive layer 17; the third isolation structure 33 is prepared by the spin-on-glass method, and the second SiP layer 18 is deposited and planarized. The third photosensitive layer 17, the second SiP layer 18, and the third isolation structure 33 are alternately spaced along the OY direction. Among them, multiple second SiP layers 18 penetrate the third photosensitive layer 17 along the second direction and extend to the second photosensitive layer 16.

[0095] For example, in this embodiment, the ionization energy of the impurity energy levels of SiSb, SiP, and SiAs increases in sequence, so SiSb, SiP, and SiAs generate conductivity gradients inside them after light excitation. This gradient is used to construct an electron transmission path in the photodiode, quickly transfer the photogenerated carriers, optimize the migration path of the photogenerated carriers in the N region, and reduce their recombination rate.

[0096] For example, the distance between the symmetry axes of two adjacent stacked isolation structures 30 is 500 nanometers to 700 nanometers. In the above example, the larger the interval between the two adjacent stacked isolation structures 30, the larger the photosensitive area of ​​the pixel, that is, the better the photosensitivity, but too large an interval will cause the pixel to be too large and the resolution to decrease. Therefore, by setting the distance between the symmetry axes of two adjacent stacked isolation structures 30 to 500 nanometers to 700 nanometers, the photosensitivity of the device can be improved while ensuring the resolution.

[0097] The first isolation structure, the second isolation structure and the third isolation structure stacked in sequence are used to form a stacked isolation structure, and the stacked isolation structure is located directly above the trench isolation structure arranged one by one. Multiple stacked isolation structures arranged at intervals in the pixel area and the grid together form a physical isolation barrier to prevent photogenerated carriers from penetrating each other in adjacent pixel areas and light from diffusing to adjacent pixels, and to suppress the adverse effects of light and / or charge crosstalk on imaging quality by improving the internal structure of the pixel area.

[0098] Step S810: After forming the third photosensitive layer 17 and the third isolation structure 33, a laser annealing process is used to treat and activate ions in the photodiode.

[0099] For example, a laser pulse with an energy of 700-800 mJ is used to process the photodiode to activate the internal ions. Common ions include but are not limited to doped impurity ions and oxide ions. In this embodiment, the doping elements are P, As, and Sb, and the oxide ions are derived from the oxidation of the material, and their presence will affect the structure and performance of the material. The laser annealing process can better activate and fix the ions in the device, reduce the impact of external environmental factors on the performance of the device, and promote the ions to better participate in the charge transfer and photoelectric conversion process, thereby improving the performance of the device.

[0100] See also Figure 9-10 In some embodiments, after step S80 , the method further includes: forming a one-to-one grid 40 directly above the stacked isolation structure 30 , wherein the bottom surface of the grid 40 is smaller than the top surface of the stacked isolation structure 30 .

[0101] For example, see Fig. 9, a first grid layer 41, a second grid layer 42, and a third grid layer 43 covering the third isolation structure 33, the third photosensitive layer 17, and the top surface of the second SiP layer 18 are obtained by a deposition method. The material of the second grid layer 42 may include but is not limited to metal materials such as cobalt (Co), nickel (Ni), titanium (Ti), and aluminum (Al); the material of the third grid layer 43 may include but is not limited to titanium nitride (TiN); the material of the first grid layer 41 may include but is not limited to aluminum oxide (Al2O3), hafnium oxide (HfO2), hafnium oxynitride (HfON), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), or strontium titanium oxide (SrTiO3), etc.

[0102] For example, see Fig.10 , a patterned photoresist layer can be used as a mask, or the position of the grid 40 can be defined by a mask plate, and then any etching method can be used to form the grid 40. A narrower grid can increase the amount of light entering and effectively reflect the light into the corresponding pixel area. By combining the stacked trench isolation structure with the grid, the light is prevented from propagating in the pixel area, and part of the light is prevented from entering adjacent pixels to form optical crosstalk, thereby improving the display quality of the BSI image sensor.

[0103] See also Fig.11 In some embodiments, after step S80 , the method further includes: adding a filter 60 into the grille groove 50 .

[0104] For example, see Fig.11 , the colors of the filter 60 include but are not limited to red, yellow and blue, and three different color filters are arranged adjacent to form a pixel group. The color filter maintains high transmittance in a specific band. For example, 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.

[0105] 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.

[0106] See also Fig.11 In some embodiments, a back-illuminated image sensor is provided, comprising: a substrate 10, and a photodiode and a stacked isolation structure 30, which are located on a first surface of the substrate 10 and arranged alternately along a first direction parallel to the first surface and extending along a second direction toward the substrate 10. The photodiode comprises an isolation layer 13, a first photosensitive layer 14, a second photosensitive layer 16, and a third photosensitive layer 17, which are stacked in sequence in a direction away from the substrate 10; the first photosensitive layer 14 comprises a plurality of first SiP layers 15 arranged at intervals along the first direction, and the plurality of first SiP layers 15 penetrate the first photosensitive layer 14 along the second direction and extend to the isolation layer 13. The third photosensitive layer 17 comprises a plurality of second SiP layers 18 arranged at intervals along the first direction, and the plurality of second SiP layers 18 penetrate the third photosensitive layer 17 along the second direction and extend to the second photosensitive layer 16; the first photosensitive layer 14 comprises As, the second photosensitive layer 16 comprises P, and the third photosensitive layer 17 comprises Sb.

[0107] The back-illuminated image sensor in the above embodiment avoids unnecessary damage to the substrate caused by high-energy ion implantation in the traditional process of preparing photodiodes. The photodiode structure obtained by multiple growth methods can reduce the number of defects in the pixel area, thereby achieving the purpose of reducing the dark current in the image sensor and improving the image clarity. Through the contact-connected stacked isolation structure and the trench isolation structure, a physical isolation barrier is formed between the photosensitive area and the substrate, blocking the mutual penetration of photogenerated carriers between adjacent pixel areas, reducing the probability of light diffusion to adjacent pixels, and effectively suppressing the negative impact of the crosstalk effect on image clarity, providing a guarantee for obtaining high-quality images.

[0108] Please continue to Fig.11 In some embodiments, the bottom surfaces of the plurality of first SiP layers 15 are lower than the top surface of the isolation layer 13. In addition to being one of the N regions doped with double VA group elements to form a dual photodiode structure with the P region, the first SiP layer 15 can also be used as a fast transmission path for photogenerated carriers.

[0109] Please continue reading Fig.11 In some embodiments, the bottom surfaces of the plurality of second SiP layers 18 are lower than the top surface of the second photosensitive layer 16. The second SiP layer 18 extending into the second photosensitive layer 16 can better optimize the function of the transmission path and reduce the recombination rate of photogenerated carriers in the diffusion process.

[0110] Please continue reading Fig.11 In some embodiments, a plurality of first SiP layers 15 and a plurality of second SiP layers 18 are arranged one to one, and a second SiP layer 18 is located directly above a first SiP layer 15. Similar to the above, such a structure can better optimize the function of the transmission path and play a role in diverting photogenerated carriers.

[0111] Please continue reading Fig.11 In some embodiments, the substrate 10 includes a plurality of trench isolation structures 20 extending into the substrate 10 through the first surface and arranged at intervals along the first direction; the trench isolation structure 20 and the stacked isolation structure 30 directly above it are arranged one-to-one. The one-to-one trench isolation structure 20 and the stacked isolation structure 30 can reduce the transmittance of light to the greatest extent, have a stronger isolation capability, and thus have a lower crosstalk value.

[0112] In some embodiments, an electronic device is provided, comprising a back-illuminated image sensor in any of the embodiments of the present application.

[0113] In some embodiments, an electronic device is provided, including: a back-illuminated image sensor prepared by using any back-illuminated image sensor preparation method in any embodiment of the present application.

[0114] 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:

[0115] The photodiode structure obtained by multiple growth methods can reduce the number of defects in the pixel area and avoid unnecessary damage to the substrate caused by high-energy ion implantation in the traditional photodiode preparation process, thereby reducing the dark current in the image sensor and improving image clarity. Compared with single doping, the double photodiode structure composed of the N region and the P region doped with double VA elements can moderately increase the depletion layer width while maintaining the response speed, thereby increasing the number of photogenerated carriers in the device and improving the photoelectric conversion efficiency of the device. The photodiode structure in which photosensitive layers doped with different VA group elements are stacked in sequence and / or arranged alternately optimizes the transmission path of photogenerated carriers through the conductivity gradient generated after light excitation, reduces the recombination rate in the diffusion process, and under the combined effect of the two, the quantum efficiency of the photodiode based on this structure is effectively improved; the spaced stacked isolation structure and the trench isolation structure form a physical isolation barrier between the photosensitive area and the substrate, which can block the mutual penetration of photogenerated carriers between adjacent pixel areas, reduce the probability of light diffusion to adjacent pixels, and effectively suppress the adverse effects of optical or electrical crosstalk on image clarity. The narrower grid can increase the amount of light entering the pixel area, laying the foundation for obtaining high-quality images.

[0116] In summary, by optimizing the internal structure of the back-illuminated image sensor to improve the overall performance of the device, a solid technical foundation and guarantee is provided for the acquisition of high-quality images. In future research and applications, further optimizing the device structure and preparation method will bring broader prospects and application potential for the development of back-illuminated image sensors.

[0117] Furthermore, electronic devices equipped with back-illuminated image sensors with higher photoelectric conversion efficiency and lower dark current can provide clearer and more realistic images, show richer details and colors, and perform better in low-light environments, meeting users' needs for image quality in different scenarios, improving shooting experience, increasing user satisfaction and product appeal.

[0118] 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.

[0119] 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: include: A substrate, and photodiodes and a stacked isolation structure located on a first surface of the substrate and alternately arranged along a first direction parallel to the first surface and extending along a second direction toward the substrate; The photodiode comprises an isolation layer, a first photosensitive layer, a second photosensitive layer and a third photosensitive layer which are sequentially stacked in a direction away from the substrate; The first photosensitive layer includes a plurality of first SiP layers arranged at intervals along the first direction, and the plurality of first SiP layers penetrate the first photosensitive layer along the second direction and extend to the isolation layer; The third photosensitive layer includes a plurality of second SiP layers arranged at intervals along the first direction, and the plurality of second SiP layers penetrate the third photosensitive layer along the second direction and extend to the second photosensitive layer; The first photosensitive layer contains As, the second photosensitive layer contains P, and the third photosensitive layer contains Sb.

2. The back-illuminated image sensor according to claim 1, characterized in that: The bottom surfaces of the plurality of first SiP layers are lower than the top surface of the isolation layer; and / or The bottom surfaces of the plurality of second SiP layers are lower than the top surface of the second photosensitive layer.

3. The back-illuminated image sensor according to claim 1, wherein: The plurality of first SiP layers and the plurality of second SiP layers are arranged one to one; The second SiP layer is located directly above the first SiP layer.

4. The back-illuminated image sensor according to any one of claims 1 to 3, characterized in that: The stacked isolation structure comprises a first isolation structure, a second isolation structure and a third isolation structure which are sequentially stacked in a direction away from the substrate; The first isolation structure extends along the second direction and penetrates the first photosensitive layer; The second isolation structure extends along the second direction and penetrates the second photosensitive layer; The third isolation structure extends along the second direction and penetrates the third photosensitive layer.

5. The back-illuminated image sensor according to any one of claims 1 to 3, characterized in that: 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 structure is arranged one-to-one with the stacked isolation structure directly above it.

6. 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; The first surface includes an isolation layer; the first direction is parallel to the first surface; A first photosensitive layer is formed on the isolation layer, and a plurality of first isolation structures are extended along a second direction close to the substrate and penetrate the second photosensitive layer; the first photosensitive layer includes a plurality of first SiP layers arranged at intervals along the first direction, and the plurality of first SiP layers penetrate the first photosensitive layer along the second direction close to the substrate and extend to the isolation layer; The first photosensitive layer comprises As; forming a second photosensitive layer on the first photosensitive layer, and a plurality of second isolation structures extending along the second direction and penetrating the second photosensitive layer; the second photosensitive layer comprises P; A third photosensitive layer is formed on the second photosensitive layer, as well as a plurality of third isolation structures extending along the second direction and penetrating the third photosensitive layer; the third photosensitive layer includes a plurality of second SiP layers arranged at intervals along the first direction, the plurality of second SiP layers penetrate the third photosensitive layer along the second direction and extend to the second photosensitive layer, and the third photosensitive layer contains Sb; the first isolation structure, the second isolation structure and the third isolation structure stacked in sequence are used to constitute a stacked isolation structure; the stacked isolation structure is located directly above the one-to-one trench isolation structure.

7. The method for preparing a back-illuminated image sensor according to claim 6, characterized in that: A first photosensitive layer and the plurality of first isolation structures are formed on the isolation layer, comprising: forming a first photosensitive layer on the isolation layer; the first photosensitive layer comprises As; A plurality of first trenches are formed in the first photosensitive layer and are arranged in a spaced relationship along the first direction; a first trench is included directly above the trench isolation structure; forming a first isolation structure in a first trench directly above the trench isolation structure; A first SiP layer is formed in the first trench between the first isolation structures.

8. The method for preparing a back-illuminated image sensor according to claim 7, characterized in that: Forming a second photosensitive layer and the plurality of second isolation structures on the first photosensitive layer, comprising: forming a second photosensitive layer covering the first isolation structure, the first SiP layer, and the first photosensitive layer; forming a plurality of second grooves in the second photosensitive layer that are arranged one-to-one with the first isolation structure, wherein the second grooves expose the first isolation structure directly thereunder; A second isolation structure is formed in the second trench.

9. The method for preparing a back-illuminated image sensor according to claim 7 or 8, characterized in that: After forming the third photosensitive layer and the third isolation structure, the method further includes: The ions in the photodiode are treated and activated by a laser annealing process.

10. An electronic device, characterized in that: A back-illuminated image sensor comprising any one of claims 1 to 5; or The back-illuminated image sensor is prepared by the method for preparing the back-illuminated image sensor according to any one of claims 6 to 9.

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