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

Abstract

The present application relates to a back-illuminated image sensor and a preparation method thereof, and an electronic device, and relates to the field of integrated circuit technology, comprising a substrate, and a photodiode and a stacked target isolation structure, which are located on a first surface of the substrate and are alternately arranged along a first direction parallel to the first surface and extend toward the substrate; the substrate comprises a plurality of trench isolation structures extending into the substrate via the first surface and arranged at intervals along the first direction; the trench isolation structure is arranged one-to-one with the stacked target isolation structure directly above it; the stacked target isolation structure comprises an isolation portion and an insulating portion alternately stacked in sequence along a second direction away from the substrate; the photodiode comprises at least two photosensitive layers stacked in sequence along the second direction and both having a "T" shape in longitudinal cross-section, wherein one photosensitive layer contacts the first surface of the substrate, which can avoid substrate damage caused by ion implantation while improving photoelectric conversion efficiency and quantum efficiency.

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 the first aspect, the present application provides a back-illuminated image sensor, comprising: a substrate, and a photodiode and a stacked target isolation structure 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 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 target isolation structure directly above it. The stacked target isolation structure includes an isolation portion and an insulating portion alternately stacked in sequence along a second direction away from the substrate. Among them, the photodiode includes at least two photosensitive layers stacked in sequence along the second direction and both of which have a "T" shape in longitudinal cross-section, wherein one photosensitive layer contacts the first surface of the substrate.

[0006] The back-illuminated image sensor in the above embodiment grows a photosensitive layer through multiple selective epitaxial growth processes to obtain photodiodes arranged in an interval array, thereby avoiding unnecessary damage caused by using high-energy ion implantation to form photodiodes, reducing dark current, and helping to improve the imaging clarity of the image sensor.

[0007] The isolation part and the insulating part alternately stacked in sequence along the second direction away from the substrate together with the trench isolation structure in the substrate form an effective physical isolation barrier, which can effectively prevent the free electrons of the pixel from penetrating into the adjacent pixels, prevent the light entering the pixel from diffusing to the adjacent pixels, and suppress the adverse effects of optical and electrical crosstalk on the clarity of image imaging; and the isolation part has P-type doping, a part of which is embedded in the photosensitive layer and contacts the photosensitive layer with N-type doping, forming a plurality of PN junctions arranged at intervals along the second direction away from the substrate, thereby improving the light absorption and charge separation efficiency, and the photosensitive layer with different donor doping elements has a concentration gradient after light excitation, which increases the diffusion length of minority carriers and improves the photoelectric conversion efficiency.

[0008] In some embodiments, the at least two photosensitive layers include a first photosensitive layer, a second photosensitive layer, and a third photosensitive layer stacked in sequence along a second direction away from the substrate.

[0009] In some embodiments, the insulating portion between adjacent first photosensitive layers is prepared simultaneously with the first photosensitive layers in the same process step.

[0010] In some embodiments, the insulating portion between adjacent second photosensitive layers is prepared simultaneously with the second photosensitive layers in the same process step.

[0011] In some embodiments, the bottom surface of the insulating portion is located inside the top surface of the isolation portion therebelow, and the top surface of the insulating portion is located inside the bottom surface of the isolation portion thereover.

[0012] In some embodiments, a surface of the trench isolation structure adjacent to the isolation portion is located within a bottom surface of the isolation portion.

[0013] In some embodiments, the isolation portion includes an acceptor element; and the photosensitive layer includes a donor element for forming a PN junction with the isolation portion.

[0014] In some embodiments, the at least two photosensitive layers include a first photosensitive layer, a second photosensitive layer, and a third photosensitive layer stacked in sequence along a second direction away from the substrate. The first photosensitive layer is SiP; the second photosensitive layer is SiAs; and the third photosensitive layer is SiSb.

[0015] In the second aspect, the present application also provides a method for preparing a back-illuminated image sensor, comprising: providing a substrate, the substrate comprising a plurality of trench isolation structures extending into the substrate through a first surface and arranged at intervals along a first direction; the trench isolation structure is arranged one-to-one with the stacked target isolation structure directly above it. A photodiode and a stacked target isolation structure are formed on the first surface of the substrate, which are alternately arranged along a first direction parallel to the first surface and extending toward the substrate; the stacked target isolation structure comprises an isolation portion and an insulating portion alternately stacked in sequence along a second direction away from the substrate; the photodiode comprises at least two photosensitive layers stacked in sequence along the second direction and both of which are "T"-shaped in longitudinal cross-section, wherein one photosensitive layer contacts the first surface of the substrate. A grid is formed on the stacked target isolation structure, and the grid is arranged one-to-one with the stacked target isolation structure.

[0016] The method for preparing a back-illuminated image sensor in the above-mentioned embodiment proposes to prepare a BSI image sensor photodiode by multiple epitaxial growths, thereby avoiding the substrate damage introduced by the photodiode preparation method of high-energy ion implantation in the traditional process. The stacked target isolation structure in the pixel area is optimized so that it can suppress the adverse effects of light and / or charge crosstalk on the imaging quality while contacting with the photosensitive layer with N-type doping to form multiple PN junctions arranged at intervals along the second direction away from the substrate, thereby improving light absorption and charge separation efficiency. The photosensitive layer with different donor doping elements generates a concentration gradient after light excitation, and the difference is used to optimize the transmission path of the photogenerated carriers, thereby reducing the recombination rate during the diffusion process.

[0017] The grid arranged one-to-one with the laminated target isolation structure can also effectively improve the reflection and refraction of light, thereby focusing the light to the photosensitive area and increasing the amount of light entering the pixel area.

[0018] In some embodiments, the step of forming the stacked target isolation structure includes: forming an isolation layer on the first surface of the substrate. Etching the isolation layer to obtain a plurality of isolation portions spaced apart along the first direction; the surface of the trench isolation structure close to the isolation portion is located within the bottom surface of the isolation portion. Forming a photosensitive material layer covering the plurality of isolation portions. Forming a plurality of insulating portions that penetrate the photosensitive material layer along the second direction and are spaced apart along the first direction, and the remaining photosensitive material layer is used to constitute the photosensitive layer.

[0019] In some embodiments, the step of forming the insulating portion includes: forming a plurality of insulating grooves penetrating the photosensitive material layer along the second direction and arranged at intervals along the first direction, and forming the insulating portion in the plurality of insulating grooves using a spin-on-glass method.

[0020] In a third aspect, the present application further provides an electronic device, comprising a back-illuminated image sensor prepared by a preparation method in any of the embodiments of the present application, or a back-illuminated image sensor in any of the embodiments of the present application.

[0021] Electronic devices based on this new back-illuminated image sensor will have lower dark current and higher photoelectric conversion efficiency, thereby achieving clearer and more accurate image acquisition and processing, and enhancing the competitiveness of products in consumer electronics, smart phones, smart home appliances, security, industrial control, automotive electronics and other fields.

[0022] 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:

[0023] The photodiode structure obtained by multiple growth methods avoids the defects caused by substrate damage after high-energy ion implantation in the traditional process, thereby achieving the purpose of reducing the dark current in the image sensor and improving image clarity.

[0024] The stacked isolation structure is formed by arranging the insulating part and the isolation part at intervals. In addition to forming a physical isolation barrier with the trench isolation structure in the substrate, blocking the mutual penetration of photogenerated carriers between adjacent pixel areas, reducing the probability of light diffusion to adjacent pixels, and suppressing the crosstalk effect, the isolation part constituting the stacked target isolation structure has P-type doping, a part of which is embedded in the photosensitive layer and contacts the photosensitive layer with N-type doping, forming multiple PN junctions arranged at intervals along the second direction away from the substrate, improving light absorption and charge separation efficiency. The photosensitive layer with different donor doping elements generates a concentration gradient after light excitation, and the difference is used to optimize the transmission path of photogenerated carriers, reducing the recombination rate in the diffusion process. The combination of the two improves the quantum efficiency of the BSI image sensor as a whole.

[0025] In summary, by optimizing the preparation method and internal structure of back-illuminated image sensors, the overall performance of the device is improved, providing a solid technical foundation and guarantee 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. In addition, improving the quantum efficiency of BSI image sensors and reducing dark current can significantly improve the imaging performance of devices equipped with this sensor, bringing higher sensitivity, wider dynamic range and higher signal-to-noise ratio, thereby enhancing the competitiveness of products in consumer electronics, smart phones, smart home appliances, security, industrial control, automotive electronics and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] Figure 1is a flow chart of a method for preparing a back-illuminated image sensor provided in an embodiment;

[0028] Figure 2 is a schematic cross-sectional view of a structure obtained after forming a first isolation layer in step S4022 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0029] Figure 3 is a schematic cross-sectional view of a structure obtained after the substrate is thinned in step S4022 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0030] Figure 4 is a schematic cross-sectional view of a structure obtained after forming a first isolation portion in step S4024 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0031] Figure 5 It is a schematic cross-sectional view of a structure obtained after forming a first photosensitive material layer in step S4026 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0032] Figure 6 is a schematic cross-sectional view of a structure obtained after forming an insulating trench in step S4028 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0033] Figure 7 is a schematic cross-sectional view of a structure obtained after forming a first insulating portion in step S4028 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0034] Figure 8 is a schematic cross-sectional view of a structure obtained after forming a second isolation portion in step S4044 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0035] Fig. 9 is a schematic cross-sectional view of a structure obtained after forming a second photosensitive material layer in step S4046 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0036] Fig.10 It is a schematic cross-sectional view of a structure obtained after forming a second insulating portion in step S4048 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0037] Fig.11 It is a schematic cross-sectional view of a structure obtained after forming a third isolation portion in step S4064 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0038] Fig.12It is a schematic cross-sectional view of a structure obtained after forming a third photosensitive material layer in step S4066 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0039] Fig.13 It is a schematic cross-sectional view of a structure obtained after forming a third insulating portion in step S4068 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0040] Fig.14 It is a schematic cross-sectional view of a structure obtained after forming a first grid layer in step S60 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0041] Fig.15 It is a schematic cross-sectional view of a structure obtained after a grid is formed in step S60 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0042] Fig.16 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.

[0043] Description of reference numerals:

[0044] 101. Initial substrate; 10. Substrate; 11. Etch stop layer; 12. Interlayer dielectric layer; 131. First isolation layer; 141. First photosensitive material layer; 14. First photosensitive layer; 151. Second photosensitive material layer; 15. Second photosensitive layer; 161. Third photosensitive material layer; 16. Third photosensitive layer; 20. Trench isolation structure; 30. Stacked target isolation structure; 31. First target isolation structure; 31a. First isolation portion; 31b. First insulating portion; 311. Insulating trench; 32. Second target isolation structure; 32a. Second isolation portion; 32b. Second insulating portion; 33. Third target isolation structure; 33a. Third isolation portion; 33b. Third insulating portion; 40. Grid; 41. First grid layer; 42. Second grid layer; 43. Third grid layer; 50. Filter. DETAILED DESCRIPTION

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] When used herein, the singular forms "a", "an" and " / the" may also include the 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 features, integers, steps, operations, elements and / or components can be determined, but the presence or addition of one or more other features, integers, steps, operations, elements, components 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.

[0050] 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.

[0051] 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, and the surface on the side along the OZ reverse direction is defined as the front side of the substrate, and the surface on the side along the OZ positive direction is defined as the back side of the substrate.

[0052] See also Figure 1 In some embodiments, a method for preparing a back-illuminated image sensor is provided, comprising: steps S20 to S60.

[0053] Step S20: providing a substrate, wherein 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 structures are arranged one-to-one with the stacked target isolation structures directly above them.

[0054] 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.

[0055] By way of example, the material of the trench isolation structure may include, but is not limited to, silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), silicon oxynitride (Si 2 N 2 O), or other insulating materials or a combination thereof.

[0056] Among them, the trench isolation structure in the substrate is used to isolate electrons and light energy, and the cross-sectional shape of the trench isolation structure along the OY direction may include a regular trapezoid, an inverted trapezoid, a rectangle, etc., or may also be a combination of regular trapezoids, inverted trapezoids, rectangles, etc. In the embodiment of the present application, the trench isolation structure only needs to be able to isolate electrons and light energy, and the depth does not exceed the initial substrate thickness. In addition, the distance between adjacent trench isolation structures and the aspect ratio of the trench isolation structure are not specifically limited in this embodiment, and can be set according to actual needs.

[0057] Step S40: forming photodiodes and a stacked target isolation structure on the first surface of the substrate, which are alternately arranged along a first direction parallel to the first surface and extend toward the substrate; the stacked target isolation structure includes isolation parts and insulating parts alternately stacked in sequence along a second direction away from the substrate; the photodiode includes at least two photosensitive layers stacked in sequence along the second direction and both of which have a "T" shape in longitudinal cross-section, wherein one photosensitive layer contacts the first surface.

[0058] For example, the material of the insulating portion is similar to the trench isolation structure in the substrate, and may include but is not limited to silicon oxide (SiO2), silicon nitride (Si3N4), silicon oxynitride (Si2N2O), and other insulating materials or a combination thereof.

[0059] Illustratively, the spacer material contains an acceptor doping element and the photoactive layer contains a donor doping element.

[0060] Among them, the isolation part and the insulating part alternately stacked in sequence along the second direction away from the substrate together with the trench isolation structure in the substrate form an effective physical isolation barrier, which can effectively prevent the free electrons of the pixel from penetrating into the adjacent pixels, prevent the light entering the pixel from diffusing to the adjacent pixels, and suppress the adverse effects of optical and electrical crosstalk effects on the clarity of image imaging; and, the isolation part has P-type doping, a part of which is embedded in the photosensitive layer and contacts with the photosensitive layer with N-type doping, forming a plurality of PN junctions arranged at intervals along the second direction away from the substrate, thereby improving light absorption and charge separation efficiency.

[0061] Step S60: forming a grid on the laminated target isolation structure, wherein the grid is arranged one-to-one with the laminated target isolation structure.

[0062] The grid may include a first grid layer, a second grid layer and a third grid layer stacked in sequence along the second direction, and the first grid layer is located between the second grid layer and the stacked target isolation structure. The material of the first grid layer may include but is not limited to a material with a high-k dielectric constant, such as one or more of aluminum oxide (Al2O3), hafnium oxide (HfO2), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), titanium oxide (TiO2) or strontium titanium oxide (SrTiO3); the material of the second grid layer may include but is not limited to metal materials such as cobalt (Co), nickel (Ni), titanium (Ti), aluminum (Al); the material of the third grid layer may include but is not limited to titanium nitride (TiN). The first grid layer, the second grid layer and the third grid layer may be formed in sequence by deposition, and the thickness of each layer may be adjusted as needed without limitation.

[0063] The grid can be used to isolate light energy, isolating adjacent pixels from each other, thereby effectively preventing light from entering adjacent pixels and causing crosstalk, improving the imaging quality of the image sensor. In addition, the grid also focuses light onto the photosensitive area, increasing the amount of light entering the photosensitive area, thereby increasing the electron concentration in the photosensitive area and improving the photosensitivity of the BSI image sensor.

[0064] The structure of the back-illuminated image sensor obtained after steps S20-S60 can be referred to in Fig.15 Of course, in order to facilitate the understanding of this application, Fig.15 An 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.

[0065] See also Figure 2 In some embodiments, step S20 further includes: preparing a trench isolation structure 20 in the initial substrate 101 .

[0066] For example, see Figure 2 In the front end of line (FEOL) process, a trench isolation structure 20 can be prepared in the initial substrate 101 by combining an etching process and a deposition process, and an etch stop layer 11 covering the trench isolation structure 20 is formed, and then an interlayer dielectric layer 12 covering the etch stop layer 11 is formed. After forming the etch stop layer 11, metal can be deposited to form a partial connection structure, and on this basis, an interlayer dielectric layer 12 is formed, and the interlayer dielectric layer 12 can be a low dielectric material layer. In addition, a metal interconnect structure can also be formed on the interlayer dielectric layer 12 as a metal connection part of the device.

[0067] Of course, this embodiment only shows one of the methods, as long as the metal interconnection structure can be reasonably formed, and the thickness of the etch stop layer 11 and the interlayer dielectric layer 12 is not limited, and can be adjusted according to specific process requirements.

[0068] See also Figure 2-Figure 15 In some embodiments, step S40 includes: step S402-step S406.

[0069] Step S402: forming a first target isolation structure 31 .

[0070] See also Figure 2-Figure 7 In some embodiments, step S402 includes: step S4022-step S4028.

[0071] Step S4022 : forming a first isolation layer 131 on the first surface 10 a of the substrate 10 .

[0072] For example, see Figure 2 A first isolation layer 131 is formed on a surface 20a of the trench isolation structure 20 in the initial substrate 101 away from the interlayer dielectric layer 12. The first isolation layer 131 may be formed by ion implantation from the back side.

[0073] For example, see Figure 3 At least one of a dry etching process, a wet etching process, a chemical mechanical polishing process and a flat push process can be used to thin the initial substrate 101 located on the side of the trench isolation structure 20 away from the interlayer dielectric layer 12 to expose the first isolation layer 131. At this time, the plane where the surface 20a of the trench isolation structure 20 is located is the first surface 10a of the substrate 10, and the remaining initial substrate 101 constitutes the substrate 10. 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.

[0074] In this embodiment, the initial substrate 101 is thinned using a chemical mechanical polishing process, wherein the thinning process removes substrate damage that may be caused during ion implantation, thereby avoiding the occurrence of excessive dark current due to defects in the substrate.

[0075] Step S4024: etching the first isolation layer 131 to obtain a plurality of first isolation portions 31 a arranged at intervals along the first direction, and the surface of the trench isolation structure 20 close to the first isolation portion 31 a is located within the bottom surface of the first isolation portion 31 a.

[0076] For example, see Figure 4 , photolithography combined with dry etching is used to obtain a plurality of first isolation portions 31a spaced apart along the first direction. Among them, dry etching includes at least any one of reactive ion etching (RIE), inductively coupled plasma etching (ICP) or high concentration plasma etching (HDP). Photoresist can transfer the pattern on the mask to the photoresist layer on the top layer of the wafer surface, and the patterned photoresist layer is realized by coating the photoresist and a series of steps such as exposure and development to define the position of the first isolation portion 31a.

[0077] The first isolation portion 31 a is connected to and in contact with the trench isolation structure 20 , and a surface of the trench isolation structure 20 close to the first isolation portion 31 a is located within the bottom surface of the first isolation portion 31 a .

[0078] Step S4026: forming a first photosensitive material layer 141 covering the plurality of first isolation portions 31 a.

[0079] For example, see Figure 5 , a selective epitaxial process can be used to grow a first photosensitive material layer 141 covering the first isolation portion 31a on the basis of the original substrate 10. In this embodiment, the first photosensitive material layer 141 is SiP. Selective epitaxial growth of the first photosensitive material layer 141 can avoid problems such as crystal structure damage, temperature rise and electric field effect caused by ion implantation. In addition, the photodiode structure manufactured in this way is simple in process, low in cost, and high in production efficiency, and can achieve more precise device control and consistency, improve the stability and reliability of device performance, and is conducive to large-scale production and application.

[0080] Step S4028 : forming a plurality of first insulating portions 31 b penetrating the first photosensitive material layer 141 along the second direction and arranged at intervals along the first direction, and the remaining first photosensitive material layer 141 is used to constitute the first photosensitive layer 14 .

[0081] For example, see Figure 6 , a photolithography and etching process can be used to form a plurality of insulating trenches 311 penetrating the first photosensitive material layer 141 along the second direction and arranged at intervals along the first direction.

[0082] For example, see Figure 7 , please use the spin-on glass method to form the first insulating part 31b in the groove. In the form of spin coating, a liquid dielectric formed by mixing a solvent and a silicon dioxide dielectric is applied to the insulating groove 311 used to form the first insulating part 31b, forming a first insulating part 31b whose top surface is not lower than the top surface of the first photosensitive layer 14. Since the flowing liquid material has 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 void defects are generated inside, thereby ensuring the isolation effect between pixels and avoiding the crosstalk effect. Among them, the first insulating part 31b and the first isolation part 31a are arranged one-to-one and contact each other to form a first target isolation structure 31. The center lines of the first target isolation structure 31 and the trench isolation structure 20 in the OZ direction are located on the same straight line, and the remaining first photosensitive material layer 141 is used to form the first photosensitive layer 14.

[0083] Among them, the first isolation part 31a doped with boron ions extends along the OY direction and is embedded in the first photosensitive layer 14, so that the longitudinal section of the first photosensitive layer 14 along the OY direction is "T"-shaped. Due to the different conductivity types, a PN junction is formed at the contact point between the two. While converting incident photons, the built-in electric field can effectively block the passage of photogenerated electrons, thereby isolating the adjacent first photosensitive layer 14.

[0084] Step S404: forming a second target isolation structure 32 .

[0085] See also Figure 8-Figure 10 In some embodiments, step S404 also includes: step S4042-step S4046.

[0086] Step S4042 : forming a second isolation layer (not shown) covering the first target isolation structure 31 and the first photosensitive layer 14 .

[0087] For example, the second isolation layer is prepared by deposition. In this embodiment, the second isolation layer may be SiB.

[0088] Step S4044: processing the second isolation layer based on photolithography and etching processes to obtain a plurality of second isolation portions 32 a arranged at intervals along the first direction.

[0089] Step S4046: forming a second photosensitive material layer 151 covering the plurality of second isolation portions 32a.

[0090] Step S4048 : forming a plurality of second insulating portions 32 b penetrating the second photosensitive material layer 151 along the second direction and arranged at intervals along the first direction, and the remaining second photosensitive material layer 151 is used to constitute the second photosensitive layer 15 .

[0091] For example, in this embodiment, steps S4044 to S4048 are consistent with previous steps S4024 to S4028, that is, steps S4024 to S4028 are repeated.

[0092] For example, see Fig. 9 , a second photosensitive material layer 151 may be grown by a selective epitaxial process, and the second photosensitive material layer 151 may be SiAs; see Fig.10 , forming a second insulating portion 32b which is arranged one-to-one with the second isolating portion 32a, at this time, the remaining second photosensitive material layer 151 is used to form the second photosensitive layer 15, and the second isolating portion 32a and the second insulating portion 32b are used to form the second target isolation structure 32. The center lines of the second target isolation structure and the first target isolation structure in the OZ direction are located on the same straight line.

[0093] The second isolation portion 32a contacts the second photosensitive layer 15 to form a PN junction. In this embodiment, the second photosensitive layer 15 is SiAs, which generates a concentration gradient with the first photosensitive layer 14 after light excitation, thereby increasing the diffusion length of minority carriers and improving the photoelectric conversion efficiency.

[0094] After step S404 , in some embodiments, the process further includes: step S406 , forming a third target isolation structure 33 .

[0095] See also Figure 11-13 In some embodiments, step S406 also includes: step S4062-step S4068.

[0096] Step S4062 : forming a third isolation layer (not shown) covering the second target isolation structure 32 and the second photosensitive layer 15 .

[0097] Step S4064: processing the third isolation layer based on photolithography and etching processes to obtain a plurality of third isolation portions 33 a arranged at intervals along the first direction.

[0098] Step S4066: forming a third photosensitive material layer 161 covering the plurality of third isolation portions 33 a.

[0099] Step S4068 : forming a plurality of third insulating portions 33 b penetrating the third photosensitive material layer 161 along the second direction and arranged at intervals along the first direction, and the remaining third photosensitive material layer 161 is used to constitute the third photosensitive layer 16 .

[0100] For example, in this embodiment, step S4062 to step S4068 are consistent with the previous step S4044 to step S4048, that is, step S4044 to step S4048 are repeated.

[0101] For example, see Fig.12, a selective epitaxial process may be used to grow the third photosensitive material layer 161; see Fig.13 , forming a third insulating portion 33b arranged one-to-one with the third isolation portion 33a, the remaining third photosensitive material layer 161 is used to constitute the third photosensitive layer 16, and the third isolation portion 33a and the third insulating portion 33b constitute the third target isolation structure 33.

[0102] The first target isolation structure 31 , the second target isolation structure 32 and the third target isolation structure 33 are sequentially stacked along the OZ direction to form a stacked target isolation structure 30 .

[0103] For example, the spacing between the symmetry axes of two adjacent stacked target isolation structures 30 can be 500 nanometers to 700 nanometers, for example, 500 nanometers, 550 nanometers, 600 nanometers, 650 nanometers or 700 nanometers, etc. In the above example, the larger the spacing between the two adjacent stacked target isolation structures 30, the larger the photosensitive area of ​​the pixel, that is, the better the photosensitivity, but too large a spacing will result in too large a pixel and reduced resolution. Therefore, by setting the distance between the symmetry axes of two adjacent stacked target isolation structures 30 to 500 nanometers to 700 nanometers, the photosensitivity of the device can be improved while ensuring the resolution.

[0104] The stacked target isolation structure 30 is located directly above the one-to-one trench isolation structure 20. It is a physical isolation barrier that prevents photogenerated carriers from penetrating each other in adjacent pixel areas and light from diffusing to adjacent pixels in the pixel area, and suppresses the adverse effects of light and / or charge crosstalk on imaging quality by improving the internal structure of the pixel area.

[0105] See also Figure 14-15 In some embodiments, step S60 further includes: forming a one-to-one grid 40 directly above the laminated target isolation structure 30 , wherein the first grid layer 41 covers the laminated target isolation structure 30 and the third photosensitive layer 16 .

[0106] For example, see Fig.14 , a first grid layer 41 is formed on the surface of the stacked target isolation structure 30 facing away from the substrate 10. The first grid layer 41 can be obtained by deposition.

[0107] The dielectric constant of the material of the first grid layer 41 is greater than that of other grid layer materials, and the thickness of the first grid layer 41 includes but is not limited to 150 nanometers to 200 nanometers, for example: 150 nanometers, 160 nanometers, 170 nanometers, 180 nanometers, 190 nanometers, 200 nanometers, etc. In addition to preventing the light reflected twice in the pixel from escaping the pixel area, the first grid layer 41 also serves as a protective layer for the third photosensitive layer 16 in the subsequent process of defining and etching the grid.

[0108] For example, see Fig.15 , a one-to-one grid 40 is formed directly above the laminated target isolation structure 30. After the second grid layer 42 and the third grid layer 43 are deposited, the position of the grid 40 is defined. Specifically, 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 the grid 40 can be formed by any etching method. By combining the laminated target isolation structure 30 and the grid 40, the crosstalk between light and electrons between pixels is effectively avoided, thereby improving the display quality of the BSI image sensor.

[0109] See also Fig.16 After step S60 , in some embodiments, the process further includes forming a filter 50 between adjacent grids 40 .

[0110] For example, see Fig.16 , the colors of the filter 50 include but are not limited to red, yellow and blue, and three different colored 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.

[0111] 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.

[0112] See also Fig.15In some embodiments, a back-illuminated image sensor is provided, comprising: a substrate 10, and photodiodes and a stacked target isolation structure 30 located on a first surface 10a of the substrate 10 and arranged alternately along a first direction parallel to the first surface 10a and extending toward the substrate. The substrate 10 includes a plurality of trench isolation structures 20 extending into the substrate 10 via the first surface 10a and arranged at intervals along the first direction; the trench isolation structure 20 is arranged one-to-one with the stacked target isolation structure 30 directly above it. The stacked target isolation structure 30 includes an isolation portion and an insulating portion alternately stacked in sequence along a second direction away from the substrate 10. Among them, the photodiode contacting the first surface 10a includes at least two photosensitive layers stacked in sequence along the second direction, and the longitudinal cross-sections are both "T"-shaped.

[0113] The back-illuminated image sensor in the above embodiment obtains photodiodes arranged in an array by multiple depositions of a photosensitive layer, thereby avoiding unnecessary damage caused by high-energy ion implantation to form photodiodes, reducing dark current, and helping to improve the imaging clarity of the image sensor.

[0114] The isolation part and the insulating part alternately stacked in sequence along the second direction away from the substrate together with the trench isolation structure in the substrate form an effective physical isolation barrier, which can effectively prevent the free electrons of the pixel from penetrating into the adjacent pixels, prevent the light entering the pixel from diffusing to the adjacent pixels, and suppress the adverse effects of optical and electrical crosstalk on the clarity of image imaging; and the isolation part has P-type doping, a part of which is embedded in the photosensitive layer and contacts the photosensitive layer with N-type doping, forming a plurality of PN junctions arranged at intervals along the second direction away from the substrate, thereby improving light absorption and charge separation efficiency, and the photosensitive layer with different donor doping elements has a concentration gradient after light excitation, which increases the diffusion length of minority carriers and improves the photoelectric conversion efficiency.

[0115] Please continue reading Fig.15 In some embodiments, the at least two photosensitive layers include a first photosensitive layer 14 , a second photosensitive layer 15 , and a third photosensitive layer 16 stacked in sequence along a second direction away from the substrate 10 .

[0116] The first photosensitive layer 14, the second photosensitive layer 15 and the third photosensitive layer 16 are doped with VA group elements of different atomic masses. After light excitation, the concentration of photogenerated carriers generated due to different ionization energies is different, and a concentration gradient is generated inside the photodiode, thereby optimizing the diffusion path, reducing the recombination rate of photogenerated electrons during free diffusion, and improving the photoelectric conversion efficiency.

[0117] Please continue reading Fig.15 In some embodiments, the insulating portion between adjacent first photosensitive layers 14 is prepared at the same time as the first photosensitive layer 14 in the same process step.

[0118] Please continue reading Fig.15 In some embodiments, the insulating portion between adjacent second photosensitive layers 15 is prepared at the same time as the second photosensitive layer in the same process step.

[0119] Please continue reading Fig.15 In some embodiments, the bottom surface of the insulating portion is located within the top surface of the isolation portion below it, and the top surface of the insulating portion is located within the bottom surface of the isolation portion above it. The depletion layer formed by the isolation portion contacting the photosensitive layer can effectively prevent minority carriers in the pixel from penetrating into adjacent pixels via the interface between the isolation portion and the insulating portion.

[0120] Please continue reading Fig.15 In some embodiments, the surface of the trench isolation structure 20 close to the isolation portion is located within the bottom surface of the isolation portion. The trench isolation structure 20 is in contact with the stacked target isolation structure 30 to form a barrier structure that penetrates the photodiode, which can better improve the isolation effect.

[0121] Please continue reading Fig.15 In some embodiments, the isolation part includes an acceptor element; the photosensitive layer includes a donor element for forming a PN junction with the isolation part. The acceptor doping element in the isolation part includes but is not limited to boron, that is, a doping element constituting a P-type doping; the donor doping element in the photosensitive layer includes but is not limited to phosphorus, arsenic, and antimony, that is, a doping element constituting an N-type doping.

[0122] Please continue reading Fig.15 In some embodiments, the at least two photosensitive layers include a first photosensitive layer 14, a second photosensitive layer 15, and a third photosensitive layer 16 stacked in sequence along a second direction away from the substrate. The first photosensitive layer 14 is SiP; the second photosensitive layer 15 is SiAs; and the third photosensitive layer 16 is SiSb. In the industrial field, N-type doping is often performed by adding VA group elements such as phosphorus, arsenic, and antimony in silicon wafer manufacturing and applications.

[0123] In some embodiments, an electronic device is provided, comprising a back-illuminated image sensor manufactured using any back-illuminated image sensor manufacturing method in any of the embodiments of the present application.

[0124] In some embodiments, an electronic device is provided, including any back-illuminated image sensor in the embodiments of the present application. The electronic device based on the novel back-illuminated image sensor will have lower dark current and higher photoelectric conversion efficiency, thereby achieving clearer and more accurate image acquisition and processing.

[0125] 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:

[0126] The photodiode structure obtained by multiple growth methods avoids the defects caused by substrate damage after high-energy ion implantation in the traditional process, achieving the purpose of reducing the dark current in the image sensor and improving image clarity.

[0127] The stacked isolation structure is formed by arranging the insulating part and the isolation part at intervals. In addition to forming a physical isolation barrier with the trench isolation structure in the substrate, blocking the mutual penetration of photogenerated carriers between adjacent pixel areas, reducing the probability of light diffusion to adjacent pixels, and suppressing the crosstalk effect, the isolation part constituting the stacked target isolation structure has P-type doping, a part of which is embedded in the photosensitive layer and contacts the photosensitive layer with N-type doping, forming multiple PN junctions arranged at intervals along the second direction away from the substrate, improving light absorption and charge separation efficiency. The photosensitive layer with different donor doping elements generates a concentration gradient after light excitation, and the difference is used to optimize the transmission path of photogenerated carriers, reducing the recombination rate in the diffusion process. The combination of the two improves the quantum efficiency of the BSI image sensor as a whole.

[0128] In summary, by optimizing the preparation method and internal structure of back-illuminated image sensors, the overall performance of the device is improved, providing a solid technical foundation and guarantee 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. In addition, improving the quantum efficiency of BSI image sensors and reducing dark current can significantly improve the imaging performance of devices equipped with this sensor, bringing higher sensitivity, wider dynamic range and higher signal-to-noise ratio, thereby enhancing the competitiveness of products in consumer electronics, smart phones, smart home appliances, security, industrial control, automotive electronics and other fields.

[0129] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features of the above 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.

[0130] The above 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 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 a photodiode and a stacked target isolation structure located on a first surface of the substrate and alternately arranged along a first direction parallel to the first surface and extending toward the substrate; The substrate 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 target isolation structure directly above it; The stacked target isolation structure includes isolation parts and insulating parts alternately stacked in sequence along a second direction away from the substrate; The photodiode includes at least two photosensitive layers stacked in sequence along the second direction and both of which have a "T" shape in longitudinal cross-section, wherein one of the photosensitive layers contacts the first surface.

2. The back-illuminated image sensor according to claim 1, characterized in that: The at least two photosensitive layers include a first photosensitive layer, a second photosensitive layer, and a third photosensitive layer sequentially stacked along a second direction away from the substrate; The backside illuminated image sensor comprises at least one of the following features: The insulating portion located between adjacent first photosensitive layers is prepared in the same process step as the first photosensitive layer; The insulating portion located between adjacent second photosensitive layers is prepared in the same process step as the second photosensitive layer; The insulating portion located between adjacent third photosensitive layers is prepared simultaneously with the third photosensitive layer in the same process step.

3. The back-illuminated image sensor according to claim 1, characterized in that: The bottom surface of the insulating portion is located within the top surface of the isolation portion therebelow; and The top surface of the insulating portion is located within the bottom surface of the isolation portion thereover.

4. The back-illuminated image sensor according to claim 1, characterized in that: A surface of the trench isolation structure close to the isolation portion is located within a bottom surface of the isolation portion.

5. The back-illuminated image sensor according to claim 1, wherein: The isolation portion includes an acceptor element; The photosensitive layer includes a donor element and is used to form a PN junction with the isolation portion.

6. The back-illuminated image sensor according to any one of claims 1 to 5, characterized in that: The at least two photosensitive layers include a first photosensitive layer, a second photosensitive layer, and a third photosensitive layer sequentially stacked along a second direction away from the substrate; The first photosensitive layer is SiP; The second photosensitive layer is SiAs; The third photosensitive layer is SiSb.

7. 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; The trench isolation structure and the stacked target isolation structure directly above it are arranged one-to-one; A photodiode and a stacked target isolation structure are formed on the first surface of the substrate, which are alternately arranged along the first direction and extend toward the substrate; the stacked target isolation structure includes an isolation portion and an insulating portion alternately stacked in sequence along a second direction away from the substrate; the photodiode includes at least two photosensitive layers stacked in sequence along the second direction and both of which have a "T" shape in longitudinal cross-section, wherein one of the photosensitive layers contacts the first surface; A grid is formed on the stacked target isolation structure, and the grid is arranged one-to-one with the stacked target isolation structure.

8. The method for preparing a back-illuminated image sensor according to claim 7, characterized in that: Forming the stacked target isolation structure includes: forming an isolation layer on the first surface of the substrate; The isolation layer is etched to obtain a plurality of isolation portions spaced apart along the first direction; the surface of the trench isolation structure close to the isolation portion is located within the bottom surface of the isolation portion; forming a photosensitive material layer covering the plurality of isolation portions; A plurality of insulating portions are formed which penetrate the photosensitive material layer along the second direction and are arranged at intervals along the first direction, and the remaining photosensitive material layer is used to constitute a photosensitive layer.

9. The method for preparing a back-illuminated image sensor according to claim 8, characterized in that: Forming the plurality of insulating parts includes: forming a plurality of insulating grooves penetrating the photosensitive material layer along the second direction and arranged at intervals along the first direction; The insulating portion is formed in the insulating groove by using a spin-on-glass method.

10. An electronic device, characterized in that: A back-illuminated image sensor comprising any one of claims 1 to 6; or A back-illuminated image sensor manufactured by the method for manufacturing a back-illuminated image sensor according to any one of claims 7 to 9.

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