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

Abstract

The present application relates to a back-illuminated image sensor and a method for preparing the same, and an electronic device, and relates to the field of integrated circuit technology, including providing a substrate, wherein the substrate includes an isolation layer, and a plurality of first isolation structures arranged at intervals along a first direction parallel to the substrate surface. A first isolation portion is formed in the substrate, which is arranged one-to-one with the first isolation structure and extends to the isolation layer via the back of the substrate. The substrate between adjacent first isolation portions is removed to obtain a sidewall semiconductor layer located on the side surface of the first isolation portion, and a first groove between adjacent sidewall semiconductor layers; the size of the sidewall semiconductor layer gradually increases in the direction approaching the isolation layer. A bottom photosensitive layer is formed in the first groove, and a top photosensitive layer is epitaxially grown on the bottom photosensitive layer. A second isolation portion connected to the first isolation portion is formed in the gap between adjacent top photosensitive layers to improve the 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 a first aspect, the present application provides a method for preparing a back-illuminated image sensor, comprising: providing a substrate, the substrate comprising an isolation layer extending in a first direction parallel to the front side of the substrate, and a plurality of first isolation structures extending from the front side of the substrate toward the inside of the substrate to the isolation layer and arranged at intervals along the first direction. A plurality of first isolation portions arranged one-to-one with the plurality of first isolation structures are formed in the substrate, and the plurality of first isolation portions extend to the isolation layer via the back side of the substrate. The substrate between adjacent first isolation portions is removed to obtain a sidewall semiconductor layer located on the side surface of the first isolation portion, and a first groove located between adjacent sidewall semiconductor layers; the size of the sidewall semiconductor layer gradually increases in a direction approaching the isolation layer. A bottom photosensitive layer is formed in the first groove, and a top photosensitive layer is epitaxially grown on the bottom photosensitive layer. A second isolation portion connected to the first isolation portion is formed in the gap between adjacent top photosensitive layers.

[0006] 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 presence of the sidewall semiconductor layer allows the depletion region to extend toward the side where the photon is incident, and the signal electrons are more easily collected by the strong electric field in the depletion region, thereby improving the quantum efficiency of medium and short wavelengths. At the same time, the photodiode structure in which photosensitive layers doped with different VA group elements are stacked in sequence produces a concentration gradient after light excitation, and this difference is used to optimize the transmission path of photogenerated carriers, thereby reducing the recombination rate during the diffusion process. And because the atomic mass of VA group elements is higher than that of silicon, their mobility in epitaxial growth is lower than that of silicon, resulting in uneven doping concentration in the grown single doped layer. Growing differently doped VA group elements in multiple times can improve the uniformity of doping concentration in the pixel area.

[0007] Furthermore, by forming spaced isolation portions and isolation structures in the pixel area, a semi-surrounding isolation portion is formed to 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 light and / or charge crosstalk on imaging quality.

[0008] In some embodiments, a plurality of first trenches are formed in the substrate, opening at the back side of the substrate and exposing a portion of the isolation layer; the plurality of first trenches are arranged one-to-one with the plurality of first isolation structures; and a plurality of first isolation portions are formed in the plurality of first trenches.

[0009] In some embodiments, the substrate between adjacent first isolation portions is dry-etched, and the substrate remaining on the side surfaces of the first isolation portions is used to form a sidewall semiconductor layer.

[0010] In some embodiments, the isolation layer contains boron; an epitaxial growth process is used to form a bottom photosensitive layer in the first groove, and the bottom photosensitive layer is a phosphor-containing photosensitive layer.

[0011] In some embodiments, an arsenic-containing photosensitive layer is epitaxially grown on the phosphorus-containing photosensitive layer; an antimony-containing photosensitive layer is epitaxially grown on the arsenic-containing photosensitive layer, the arsenic-containing photosensitive layer and the antimony-containing photosensitive layer are used to constitute a top photosensitive layer, and the bottom photosensitive layer and the top photosensitive layer are used to constitute a photodiode.

[0012] In some embodiments, the surface of the antimony-containing photosensitive layer facing away from the arsenic-containing photosensitive layer is a rounded arc surface.

[0013] In some embodiments, after forming the second isolation portion, a grid stack is formed on a surface of the second isolation portion facing away from the substrate, and the grid stack is disposed one-to-one with the second isolation portion.

[0014] In some embodiments, filters are formed between adjacent grid stacks.

[0015] In a second aspect, the present application also provides a back-illuminated image sensor, comprising: a substrate, a plurality of first isolation portions, a sidewall semiconductor layer, a bottom photosensitive layer, a top photosensitive layer and a second isolation portion; the substrate comprises an isolation layer extending in a first direction parallel to the front side of the substrate, and a plurality of first isolation structures extending from the front side of the substrate toward the inside of the substrate to the isolation layer and arranged at intervals along the first direction. The plurality of first isolation portions are located on the same side of the isolation layer away from the substrate, the plurality of first isolation structures are arranged one to one, the side surface of the first isolation portion comprises a sidewall semiconductor layer, and the size of the sidewall semiconductor layer gradually increases in a direction close to the isolation layer. The bottom photosensitive layer is located between adjacent sidewall semiconductor layers. The top photosensitive layer is epitaxially grown on the bottom photosensitive layer. The second isolation portion is located between adjacent top photosensitive layers and is connected to the first isolation portion.

[0016] The back-illuminated image sensor in the above embodiment adopts a photodiode structure obtained by multiple growth methods, which can reduce the number of defects in the pixel area caused by substrate damage, thereby reducing the dark current in the image sensor and improving the image clarity. The existence of the sidewall semiconductor layer allows the depletion region to extend toward the photon incident side, and the signal electrons are more easily collected by the strong electric field in the depletion region. At the same time, the photodiode structure in which the photosensitive layers doped with different VA group elements are stacked in sequence will also generate a concentration gradient inside after light excitation. The difference is used to optimize the transmission path of the photogenerated carriers, reducing the recombination rate in the diffusion process. The combination of the two improves the quantum efficiency of the BSI image sensor. By combining the stacked isolation structure and the trench isolation structure arranged at intervals, a physical isolation barrier is formed 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, effectively suppressing the crosstalk effect, and providing a guarantee for obtaining high-quality images.

[0017] In some embodiments, the isolation layer includes boron.

[0018] In some embodiments, the bottom photosensitive layer is a phosphor-containing photosensitive layer.

[0019] In some embodiments, the top photosensitive layer includes an arsenic-containing photosensitive layer epitaxially grown on the phosphorus-containing photosensitive layer, and an antimony-containing photosensitive layer epitaxially grown on the arsenic-containing photosensitive layer.

[0020] In a third 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.

[0021] In a fourth 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.

[0022] The electronic device in the above embodiment improves the quantum efficiency of the BSI image sensor and reduces the dark current, which can significantly improve the imaging performance of the device equipped with the sensor, bringing higher sensitivity, wider dynamic range and higher signal-to-noise ratio. Therefore, the electronic device can capture clearer and more accurate images in low light conditions or high contrast scenes, thereby expanding its application in professional photography, scientific imaging and security monitoring.

[0023] 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:

[0024] It is proposed to use multiple epitaxial growth to prepare BSI image sensor photodiodes, which avoids the substrate damage introduced by the photodiode preparation method of high-energy ion implantation in the traditional process.

[0025] The presence of the sidewall semiconductor layer allows the depletion region to extend toward the photon incident side, making it easier for signal electrons to be collected by the strong electric field in the depletion region, thereby improving the quantum efficiency of medium and short wavelengths. At the same time, the photodiode structure in which photosensitive layers doped with different VA group elements are stacked in sequence will also produce a concentration gradient inside after light excitation. This difference is used to optimize the transmission path of photogenerated carriers and reduce the recombination rate during the diffusion process. Since the atomic mass of VA group elements is greater than that of silicon and their mobility in epitaxial growth is lower than that of silicon, growing differently doped VA group elements in multiple times can avoid uneven doping concentrations in the photosensitive region.

[0026] In addition, by optimizing the geometric configuration of the isolation area and constructing a semi-circular isolation part around the photodiode, the incident light can be effectively confined within the pixel area, preventing some unabsorbed light from reflecting and escaping the pixel area, so that it can be fully absorbed and converted into an effective electrical signal, thereby improving the photoelectric conversion efficiency. The isolation part, the isolation structure in the substrate and the grid stack together constitute a strict physical isolation barrier. Among them, the grid stack increases the amount of light entering, while the isolation area and the isolation structure hinder the mutual penetration of photogenerated carriers between adjacent pixel areas and reduce the probability of light diffusing to adjacent pixels. The synergistic effect of these three enhances the isolation effect and effectively suppresses the crosstalk effect.

[0027] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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.

[0029] Figure 1 is a flow chart of a method for preparing a back-illuminated image sensor provided in an embodiment;

[0030] Figure 2 is a schematic cross-sectional view of a structure obtained after an isolation layer is formed in step S1024 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0031] Figure 3 is a schematic cross-sectional view of a structure obtained after the initial substrate is planarized in step S1042 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0032] Figure 4 is a schematic cross-sectional view of a structure obtained after forming a first groove in step S1044 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0033] Figure 5 is a schematic cross-sectional view of a structure obtained after forming a first isolation portion in step S1046 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0034] Figure 6 It is a schematic cross-sectional view of a structure obtained after a sidewall semiconductor layer is formed in step S106 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0035] Figure 7 is a schematic cross-sectional view of a structure obtained after forming a bottom photosensitive layer in step S1082 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0036] Figure 8 It is a schematic cross-sectional view of a structure obtained after forming an arsenic-containing photosensitive layer in step S1084 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0037] Fig. 9 It is a schematic cross-sectional view of a structure obtained after forming an antimony-containing photosensitive layer in step S1086 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0038] Fig.10 It is a schematic cross-sectional view of a structure obtained after forming a second isolation portion in step S110 in a method for preparing a back-illuminated image sensor provided in an embodiment;

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

[0040] Fig.12 is a schematic cross-sectional view of a structure obtained after a grid stack is formed in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0041] Fig.13 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] 101. Initial substrate; 10. Substrate; 11. Etch stop layer; 12. Interlayer dielectric layer; 13. Isolation layer; 14. Sidewall semiconductor layer; 151. First groove; 15. Bottom photosensitive layer; 16a. Arsenic-containing photosensitive layer; 16b. Antimony-containing photosensitive layer; 16. Top photosensitive layer; 20. First isolation structure; 30. Isolation part; 31. First isolation part; 311. First groove; 32. Second isolation part; 321. Second groove; 40. Grid stack; 41. First grid layer; 42. Second grid layer; 43. Third grid layer; 50. 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 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.

[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 " / 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.

[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, 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.

[0051] See also Figure 1 In some embodiments, a method for preparing a back-illuminated image sensor is provided, comprising: steps S102 to S110.

[0052] Step S102: providing a substrate, wherein the substrate comprises an isolation layer extending along a first direction parallel to a front surface of the substrate, and a plurality of first isolation structures extending from the front surface of the substrate toward the isolation layer and arranged in isolation along the first direction.

[0053] Among them, the substrate can provide mechanical support and electrical performance, and the longitudinal cross-sectional shape of the first 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 first isolation structure only needs to be able to isolate electrons and light energy. In addition, this embodiment does not specifically limit the distance between adjacent first isolation structures, and can be set according to actual needs.

[0054] Step S104: forming a plurality of first isolation portions in the substrate, which are arranged one-to-one with the plurality of first isolation structures, and the plurality of first isolation portions extend to the isolation layer through the back side of the substrate.

[0055] Among them, a first isolation part is included between the adjacent bottom photosensitive layers along the OY direction. The first isolation part extending into the isolation layer 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 effect on image clarity.

[0056] Step S106: removing the substrate between adjacent first isolation parts to obtain a sidewall semiconductor layer located on the side surface of the first isolation part and a first groove located between adjacent sidewall semiconductor layers; the size of the sidewall semiconductor layer gradually increases in a direction approaching the isolation layer.

[0057] Among them, the existence of the sidewall semiconductor layer allows the depletion region to extend toward the photon incident side, and the medium and short wave signal electrons with poor penetration ability are more easily collected by the strong electric field of the depletion region, thereby improving the quantum efficiency of the medium and short wavelengths.

[0058] Step S108: forming a bottom photosensitive layer in the first groove, and epitaxially growing a top photosensitive layer on the bottom photosensitive layer.

[0059] Among them, stacking photosensitive layers doped with different VA group elements in sequence can optimize the diffusion path of photogenerated carriers, and the physical isolation barrier formed by the spaced isolation parts and isolation structures in the photosensitive area and the substrate further enhances the isolation effect, effectively isolating adjacent pixel areas, and providing a guarantee for obtaining high-quality images. Multiple growth can also avoid substrate damage introduced by high-energy ion implantation in traditional processes and avoid uneven doping concentration in pixel areas.

[0060] Step S110: forming a second isolation portion connected to the first isolation portion in a gap between adjacent top photosensitive layers.

[0061] The first isolation part and the second isolation part form a semi-circular barrier structure around the photodiode, which can effectively limit the incident light within the pixel area, prevent part of the unabsorbed light from reflecting and escaping the pixel area, so that it can be fully absorbed and converted into an effective electrical signal, thereby improving the photoelectric conversion efficiency. The isolation part and the isolation structure in the substrate play a role in preventing the mutual penetration of photogenerated carriers between adjacent pixel areas, reducing the probability of light diffusing to adjacent pixels.

[0062] The structure of the back-illuminated image sensor obtained after steps S102-S110 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.

[0063] For example, please continue to refer to Figure 1 , multiple epitaxial growths are used to prepare the photodiodes in the BSI image sensor, avoiding the substrate damage introduced by the photodiode preparation method of high-energy ion implantation in the traditional process. The presence of the sidewall semiconductor layer allows the depletion region to extend toward the side where the photons are incident, making it easier for the signal electrons to be collected by the strong electric field in the depletion region, thereby improving the quantum efficiency of medium and short wavelengths. At the same time, the photodiode structure in which the photosensitive layers doped with different VA group elements are stacked in sequence will also produce a concentration gradient inside after light excitation. This difference is used to optimize the transmission path of the photogenerated carriers and reduce the recombination rate during the diffusion process. Under the combined effect of the two, the quantum efficiency of the photodiode based on this structure is effectively improved. In addition, since the atomic mass of the VA group elements is higher than that of silicon, the mobility is low during epitaxial growth, resulting in uneven doping concentration in a single doping layer. Growing VA group elements with different dopings in multiple times can improve the uniformity of doping concentration in the pixel area.

[0064] By forming spaced isolation parts and isolation structures in the pixel area, the internal structure of the pixel area is improved, the mutual penetration of photogenerated carriers between adjacent pixel areas is blocked, the probability of light diffusion to adjacent pixels is reduced, and the adverse effects of light and / or charge crosstalk on imaging quality are suppressed.

[0065] See also Figure 2 In some embodiments, step S102 also includes: step S1022-step S1104.

[0066] Step S1022 : forming an etch stop layer 11 covering the surface of the initial substrate 101 and the first isolation structure 20 , and forming an interlayer dielectric layer 12 covering the surface of the etch stop layer 11 .

[0067] For example, the material used for the initial substrate 101 can be any suitable semiconductor material, insulating material, conductor material or any combination thereof known in the art, including a multilayer structure composed of these materials. 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 or silicon germanium on insulator. Therefore, the type of substrate should not limit the scope of protection of the present disclosure.

[0068] For example, the depth of the first isolation structure 20 is less than the thickness of the initial substrate 101, and it is prepared by any method of the prior art such as etching process, deposition process, etc. The material of the first isolation structure 20 may include but is not limited to silicon oxide (SiO2), silicon nitride (Si3N4), silicon oxynitride (Si2N2O), etc. or a combination thereof.

[0069] For example, after forming the etch stop layer 11, metal is deposited to form a partial connection structure, and an interlayer dielectric layer 12 is formed on this basis. When the etch stop layer is multi-layer, other process problems and / or failure of the metal connection structure caused by cracks in a single layer can be avoided. The interlayer dielectric layer 12 can be a silicon oxide or other low-dielectric material layer. In addition, a metal interconnect structure can be formed on the interlayer dielectric layer 12 as a metal connection part of the device.

[0070] 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.

[0071] Step S1024 : forming an isolation layer 13 on a surface 20 a of the first isolation structure 20 facing away from the interlayer dielectric layer 12 in the initial substrate 101 .

[0072] For example, please refer to Figure 2 The isolation layer 13 may be formed in the initial substrate 101 by ion implantation, and the implanted ions may be boron ions.

[0073] See also Figure 3-Figure 5 In some embodiments, step S104 includes: step S1042-step S1046.

[0074] Step S1042 : planarizing and removing a portion of the initial substrate 101 , and the remaining initial substrate 101 obtained after thinning constitutes the substrate 10 .

[0075] For example, see Figure 3 , at least one of dry etching, chemical mechanical polishing, wet etching or flat push process can be used to remove part of the initial substrate 101. The three processes have their own advantages and disadvantages. The specific selection should be made according to different processing objects, requirements and actual conditions. In this embodiment, the thickness of the thinned substrate 10 can be 200 nanometers. The initial substrate 101 after ion implantation is thinned to reduce defects caused by damage to the substrate 10 in subsequent photodiodes and reduce dark current. Of course, the thinned substrate 10 can also have other thickness values, which can be set according to specific circumstances and are not limited here.

[0076] Step S1044 : forming a plurality of first trenches 311 in the substrate 10 , which are opened at the back side of the substrate 10 and expose a portion of the isolation layer 13 . The plurality of first trenches 311 and the plurality of first isolation structures 20 are arranged one-to-one.

[0077] For example, see Figure 4 , the first groove 311 can be prepared 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. The pattern 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. Among them, multiple first grooves 311 are set one-to-one with the first isolation structure 20, that is, the center lines of the first grooves 311 and the first isolation structure 20 in the depth direction are located on the same straight line.

[0078] Step S1046 : forming a plurality of first isolation portions 31 in the plurality of first trenches 311 .

[0079] For example, see Figure 5 The first isolation portion 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. Since the flowing liquid material has good filling performance, the problem of internal voids formed by premature closure of the corners of the pores during filling is avoided, thereby ensuring the isolation effect between pixels.

[0080] See also Figure 6 In some embodiments, step S106 further includes: dry etching the substrate 10 between adjacent first isolation portions 31, the substrate 10 retained on the side surface of the first isolation portion 31 is used to form a sidewall semiconductor layer 14, and a first groove 151 is formed between adjacent sidewall semiconductor layers 14. The size of the sidewall semiconductor layer 14 gradually increases in the direction close to the isolation layer 13.

[0081] For example, dry etching is used to remove the substrate 10 between the first isolation parts 31. Dry etching is generally divided into three types: plasma etching (PE), sputtering etching, and reactive ion etching (RIE). During the etching process, the angle between the side wall of the groove and the OY direction can be adjusted by the gas ratio in the dry etching. Reducing the content of chemical etching gases such as fluorine, chlorine or hydrogen bromide helps to generate sidewall polymers, passivate the sidewalls, and make them smoother, that is, the angle between the side wall of the groove and the OY direction becomes smaller; conversely, increasing the content of chemical etching gases such as fluorine, chlorine or hydrogen bromide can increase the angle and make the sidewalls steeper, close to 90 degrees. Thus, the gas content in the main etching process is changed to adjust the angle between the side wall of the groove and the OY direction. The presence of the sidewall semiconductor layer 14 allows the depletion region to extend toward the side where the photons are incident, and medium and short wave signals with weak transmission ability are more easily absorbed by the depletion region. Electrons are collected by the strong electric field, thereby improving the quantum efficiency of medium and short wavelengths.

[0082] See also Figure 7-Figure 9 In some embodiments, step S108 also includes: step S1082-step S1086.

[0083] Step S1082 : forming a bottom photosensitive layer 15 in the first groove 151 by using an epitaxial growth process, wherein the bottom photosensitive layer 15 is a phosphor-containing photosensitive layer.

[0084] For example, see Figure 7 , the bottom photosensitive layer 15 can be formed by epitaxial processes such as liquid phase epitaxy (Liquid Phase Epitaxy, LPE), vapor phase epitaxy (Vapour Phase Epitaxy, VPE), and molecular beam epitaxy (Molecular Beam Epitaxy, MBE). In other embodiments, the process can be selected according to actual needs. The epitaxial process can avoid problems such as crystal structure damage, temperature increase, and electric field effect caused by ion implantation. In addition, the photodiode prepared by the epitaxial process has a low defect density, a long carrier lifetime, and the interface quality between the N region and the P region is excellent, with few defects and a low carrier recombination rate, which is beneficial to improving the conversion efficiency and stability of the photodiode.

[0085] Step S1084 : epitaxially grow an arsenic-containing photosensitive layer 16 a on the bottom photosensitive layer 15 .

[0086] For example, see Figure 8 , an epitaxial growth method similar to step S1082 is used to obtain an arsenic-containing photosensitive layer.

[0087] Step S1086: epitaxially grow an antimony-containing photosensitive layer 16b on the arsenic-containing photosensitive layer 16a, and the surface of the antimony-containing photosensitive layer 16b that is away from the arsenic-containing photosensitive layer 16a is a rounded arc surface. The arsenic-containing photosensitive layer 16a and the antimony-containing photosensitive layer 16b are used to form the top photosensitive layer 16, and the bottom photosensitive layer 15 and the top photosensitive layer 16 are used to form a photodiode.

[0088] For example, see Fig. 9 , similar to the epitaxial growth method in step S1082, the antimony-containing photosensitive layer is obtained. The photodiode structure in which the photosensitive layers doped with different VA group elements are stacked in sequence generates a concentration gradient after light excitation. The gradient is used to optimize the transmission path of the photogenerated carriers and reduce the recombination rate in the diffusion process. At the same time, since the atomic mass of the VA group elements is higher than that of silicon, the mobility is lower in epitaxial growth, resulting in uneven doping concentration in the single doped layer obtained by the growth. Growing VA group elements with different doping multiple times can improve the uniformity of doping concentration in the pixel area.

[0089] See also Fig.10 In some embodiments, step S110 further includes: forming a second isolation portion 32 connected to the first isolation portion 31 in a second groove 321 in a gap between adjacent top photosensitive layers.

[0090] For example, in this embodiment, spin-on glass is used to fill the gap between adjacent top photosensitive layers with silicon dioxide to form a second isolation portion 32, wherein the second isolation portion 32 covers the rounded arc surface area of ​​the antimony-containing photosensitive layer 16b, which can effectively limit the incident light within the pixel area, prevent part of the unabsorbed light from reflecting and escaping the pixel area, so that it can be fully absorbed and converted into an effective electrical signal, thereby improving the photoelectric conversion efficiency. The second isolation portion 32 and the first isolation portion 31 form an isolation portion 30 that semi-surrounds the photodiode. The semi-surrounding isolation portion can hinder the mutual penetration of photogenerated carriers between adjacent pixel areas and reduce the probability of light diffusing to adjacent pixels.

[0091] See also Figure 11-Figure 12 In some embodiments, after step S110 , the method further includes: forming a grid stack 40 on a surface of the second isolation portion 32 facing away from the substrate 10 , wherein the grid stack 40 and the second isolation portion 32 are arranged one-to-one.

[0092] For example, see Fig.11 The first grid layer 41 , the second grid layer 42 , and the third grid layer 43 may be formed by deposition methods such as but not limited to chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD).

[0093] For example, the material of the first grid layer 41 may include but is not limited to aluminum oxide (Al2O3), hafnium oxide (HfO2), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), etc. with a high-k dielectric constant. 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), tungsten (W), copper (Cu), and aluminum (Al). The material of the third grid layer 43 may include titanium nitride (TiN). The thickness of each layer can be adjusted as needed without limitation.

[0094] For example, see Fig.12 After the grid layer is formed, the position of the grid stack 40 is defined and is arranged one-to-one with the second isolation portion 32. The first grid layer 41, the second grid layer 42, and the third grid layer 43 together constitute a composite metal grid, which can effectively improve the reflection and refraction of light, thereby focusing the light to the photosensitive area. The narrower grid stack 40 increases the amount of light entering the photosensitive area, thereby improving the photosensitivity of the BSI image sensor.

[0095] See also Fig.13 In some embodiments, after step S110 , the method further includes: forming a filter 50 between adjacent grid stacks 40 .

[0096] For example, after the grid stack 40 is formed, a filter 50 is arranged between adjacent grid stacks 40. The filter 50 includes but is not limited to a red filter, a yellow filter, and a blue filter, and the three filters of different colors are arranged adjacent to each other as a pixel group. The color filter maintains high transmittance in a specific band and filters monochromatic light of different bands respectively. In addition, the top of the filter is in a rounded arc shape, which focuses the filtered light into the pixel area. Of course, other microlens structures can also be used to meet the focusing requirements, and this application does not make specific restrictions.

[0097] 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.

[0098] See also Fig.13In some embodiments, a back-illuminated image sensor is provided, comprising: a substrate 10, a plurality of first isolation portions 31, a sidewall semiconductor layer 14, a bottom photosensitive layer 15, a top photosensitive layer 16, and a second isolation portion 32; the substrate 10 includes an isolation layer 13 extending in a first direction parallel to the front surface of the substrate 10, and a plurality of first isolation structures 20 extending from the front surface of the substrate 10 toward the inside of the substrate 10 to the isolation layer 13 and arranged at intervals along the first direction. The plurality of first isolation portions 31 are located on the same side of the isolation layer 13 away from the substrate 10, and the plurality of first isolation structures 20 are arranged one by one. The side surface of the first isolation portion 31 includes a sidewall semiconductor layer 14, and the size of the sidewall semiconductor layer 14 gradually increases in the direction close to the isolation layer 13. The bottom photosensitive layer 15 is located between adjacent sidewall semiconductor layers 14. The top photosensitive layer 16 is epitaxially grown on the bottom photosensitive layer 15. The second isolation portion 32 is located between adjacent top photosensitive layers 16 and is connected to the first isolation portion 31.

[0099] The photodiode structure obtained by multiple growth methods can reduce the number of defects in the pixel area caused by substrate damage, thereby reducing the dark current in the image sensor and improving image clarity. The presence of the sidewall semiconductor layer allows the depletion region to extend toward the side where the photons are incident, and the signal electrons are more easily collected by the strong electric field in the depletion region. At the same time, the photodiode structure in which the photosensitive layers doped with different VA group elements are stacked in sequence will also produce a concentration gradient inside after light excitation. This difference is used to optimize the transmission path of the photogenerated carriers and reduce the recombination rate in the diffusion process. The combination of the two improves the quantum efficiency of the BSI image sensor. By combining the stacked isolation structure and the trench isolation structure arranged at intervals, a physical isolation barrier is formed 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, effectively suppressing the crosstalk effect, and providing a guarantee for obtaining high-quality images.

[0100] Please continue to Fig.13 In some embodiments, the isolation layer 13 includes boron. It may also include other P-type doping elements, which are not limited here.

[0101] Please continue reading Fig.13 In some embodiments, the bottom photosensitive layer 15 is a phosphorescent photosensitive layer.

[0102] Please continue reading Fig.13In some embodiments, the top photosensitive layer 16 includes an arsenic-containing photosensitive layer 16a epitaxially grown on the phosphorus-containing photosensitive layer, and an antimony-containing photosensitive layer 16b epitaxially grown on the arsenic-containing photosensitive layer 16a. Due to the difference in impurity ionization energies, the phosphorus-containing photosensitive layer, the arsenic-containing photosensitive layer 16a, and the antimony-containing photosensitive layer 16b have different concentrations of photogenerated carriers generated by light excitation, which are, from low to high, arsenic-containing photosensitive layer 16a, phosphorus-containing photosensitive layer, and antimony-containing photosensitive layer 16b. The electrons in the phosphorus-containing photosensitive layer diffuse into the arsenic-containing photosensitive layer 16a by the concentration gradient, replenishing its electron concentration, and then diffuse into the antimony-containing photosensitive layer 16b, reducing the recombination rate of the photogenerated electrons during free diffusion.

[0103] Please continue reading Fig.13 In some embodiments, an electronic device is provided, comprising a back-illuminated image sensor prepared by using any back-illuminated image sensor preparation method in any embodiment of the present application.

[0104] Please continue reading Fig.13 In some embodiments, an electronic device is provided, comprising a back-illuminated image sensor in any of the embodiments of the present application.

[0105] Electronic devices equipped with high quantum efficiency and low dark current BSI image sensors have higher sensitivity, wider dynamic range and higher signal-to-noise ratio than original devices in low light conditions and high contrast scenes, and significantly improved imaging performance. Clearer and more accurate image quality lays the foundation for expanding its application in professional photography, scientific imaging, security monitoring and other fields. 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:

[0106] It is proposed to use multiple epitaxial growth to prepare BSI image sensor photodiodes, which avoids the substrate damage introduced by the photodiode preparation method of high-energy ion implantation in the traditional process.

[0107] The presence of the sidewall semiconductor layer allows the depletion region to extend toward the photon incident side, making it easier for signal electrons to be collected by the strong electric field in the depletion region, thereby improving the quantum efficiency of medium and short wavelengths. At the same time, the photodiode structure in which photosensitive layers doped with different VA group elements are stacked in sequence will also produce a concentration gradient inside after light excitation. This difference is used to optimize the transmission path of photogenerated carriers and reduce the recombination rate during the diffusion process. Growing differently doped VA group elements in multiple times can also improve the uniformity of doping concentration in the pixel area.

[0108] In addition, by optimizing the geometric configuration of the isolation area and constructing a semi-circular isolation part around the photodiode, the incident light can be effectively confined within the pixel area, preventing some unabsorbed light from reflecting and escaping the pixel area, so that it can be fully absorbed and converted into an effective electrical signal, thereby improving the photoelectric conversion efficiency. The isolation part, the isolation structure in the substrate and the grid stack together constitute a strict physical isolation barrier. Among them, the grid stack increases the amount of light entering, while the isolation area and the isolation structure hinder the mutual penetration of photogenerated carriers between adjacent pixel areas, reducing the probability of light diffusing to adjacent pixels. The synergistic effect of these three enhances the isolation effect and effectively suppresses the crosstalk effect.

[0109] In summary, by optimizing the preparation method and internal structure of the back-illuminated image sensor, 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 the sensor, resulting in higher sensitivity, wider dynamic range and higher signal-to-noise ratio. As a result, the electronic device is able to capture clearer and more accurate images under various lighting conditions, especially in low-light conditions or high-contrast scenes, thereby expanding its application in professional photography, scientific imaging and security monitoring.

[0110] 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.

[0111] 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 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 method for preparing a back-illuminated image sensor, characterized in that: include: Providing a substrate, wherein the substrate includes an isolation layer extending along a first direction parallel to the front surface of the substrate, and a plurality of first isolation structures extending from the front surface of the substrate toward the inside of the substrate to the isolation layer and arranged at intervals along the first direction; forming a plurality of first isolation parts in the substrate, which are arranged one-to-one with the plurality of first isolation structures, and the plurality of first isolation parts extend to the isolation layer through the back side of the substrate; The substrate between adjacent first isolation parts is removed to obtain a sidewall semiconductor layer located on the side surface of the first isolation part and a first groove located between adjacent sidewall semiconductor layers; the size of the sidewall semiconductor layer gradually increases in a direction close to the isolation layer; forming a bottom photosensitive layer in the first groove, and epitaxially growing a top photosensitive layer on the bottom photosensitive layer; A second isolation portion connected to the first isolation portion is formed in a gap between adjacent top photosensitive layers.

2. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: Forming the plurality of first isolation portions comprises: A plurality of first trenches are formed in the substrate, which are opened at the back side of the substrate and expose a portion of the isolation layer; the plurality of first trenches are arranged one-to-one with the plurality of first isolation structures; The first isolation portions are formed in the first trenches.

3. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: Forming the sidewall semiconductor layer comprises: The substrate between adjacent first isolation parts is dry-etched, and the substrate remaining on the side surface of the first isolation part is used to form the sidewall semiconductor layer.

4. The method for preparing a back-illuminated image sensor according to any one of claims 1 to 3, characterized in that: The isolation layer includes boron; forming a bottom photosensitive layer in the first groove includes: The bottom photosensitive layer is formed in the first groove by an epitaxial growth process, and the bottom photosensitive layer is a phosphor-containing photosensitive layer.

5. The method for preparing a back-illuminated image sensor according to claim 4, characterized in that: Forming the top photosensitive layer comprises: epitaxially growing an arsenic-containing photosensitive layer on the phosphorus-containing photosensitive layer; An antimony-containing photosensitive layer is epitaxially grown on the arsenic-containing photosensitive layer. The arsenic-containing photosensitive layer and the antimony-containing photosensitive layer are used to constitute the top photosensitive layer. The bottom photosensitive layer and the top photosensitive layer are used to constitute a photodiode.

6. The method for preparing a back-illuminated image sensor according to claim 5, characterized in that: The surface of the antimony-containing photosensitive layer facing away from the arsenic-containing photosensitive layer is a rounded arc surface.

7. The method for preparing a back-illuminated image sensor according to any one of claims 1 to 3, characterized in that: After forming the second isolation part, the method further includes: forming a grid stack on a surface of the second isolation portion facing away from the substrate, the grid stack being arranged one-to-one with the second isolation portion; and A filter is formed between adjacent grid stacks.

8. A back-illuminated image sensor, characterized in that: The back-illuminated image sensor is prepared by the method for preparing the back-illuminated image sensor according to any one of claims 1 to 7, comprising: A substrate, wherein the substrate includes an isolation layer extending along a first direction parallel to the front surface of the substrate, and a plurality of first isolation structures extending from the front surface of the substrate toward the inside of the substrate to the isolation layer and arranged at intervals along the first direction; A plurality of first isolation parts are located on the same side of the isolation layer away from the substrate and are arranged one-to-one with the plurality of first isolation structures, wherein the side surface of the first isolation part comprises a sidewall semiconductor layer, and the size of the sidewall semiconductor layer gradually increases in a direction close to the isolation layer; A bottom photosensitive layer, located between adjacent sidewall semiconductor layers; A top photosensitive layer, epitaxially grown on the bottom photosensitive layer; The second isolation portion is located between adjacent top photosensitive layers and is connected to the first isolation portion.

9. The back-illuminated image sensor according to claim 8, characterized in that: Includes at least one of the following features: The isolation layer comprises boron; The bottom photosensitive layer is a phosphorescent photosensitive layer; The top photosensitive layer includes an arsenic-containing photosensitive layer epitaxially grown on the phosphorus-containing photosensitive layer, and an antimony-containing photosensitive layer epitaxially grown on the arsenic-containing photosensitive layer.

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

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