Backside illuminated image sensor and method of making the same

Abstract

The present disclosure relates to a back-illuminated image sensor and a preparation method thereof, and relates to the technical field of integrated circuits, comprising: a P-type substrate, a plurality of photodiode structures and a grid layer, the back surface of the P-type substrate comprising a P-type epitaxial layer; a plurality of photodiode structures distributed at intervals along a first direction parallel to the back surface of the substrate, penetrating the P-type epitaxial layer along a second direction close to the substrate, and extending to the back surface of the substrate; a middle layer of a sub-light sensitive layer covering the top surface, bottom surface and side surface of the inner layer of the sub-light sensitive layer; an outer layer of a sub-light sensitive layer covering the top surface, bottom surface and side surface of the middle layer of the sub-light sensitive layer; the bottom target size of the photodiode structure gradually decreases along the second direction, the top target size of the photodiode structure gradually decreases in the direction away from the substrate, and the target size is the size along the first direction; the grid layer covers the top of the plurality of photodiode structures. At least the electron concentration of the light-sensitive area can be increased, and the light-sensing performance of the BSI image sensor can be improved.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of integrated circuits, and in particular, to a back-illuminated image sensor and a preparation method thereof. BACKGROUND

[0002] A back-illuminated (BSI) image sensor is a type of image sensor, and has better performance than a front-illuminated image sensor in low light conditions.

[0003] However, the photosensitive performance of the BSI image sensor manufactured by the existing BSI image sensor preparation method cannot meet the actual demand, and therefore, how to improve the photosensitive performance of the BSI image sensor has become one of the technical problems that need to be solved at present. SUMMARY

[0004] Therefore, it is necessary to provide a back-illuminated image sensor and a preparation method thereof to solve the technical problem of insufficient photosensitive performance of the BSI image sensor in the prior art.

[0005] In a first aspect, the present disclosure provides a back-illuminated image sensor, comprising a P-type substrate, a plurality of photodiode structures and a grid layer, the back surface of the P-type substrate comprising a P-type epitaxial layer; the plurality of photodiode structures are spaced apart along a first direction parallel to the back surface, and extend to the back surface along a second direction close to the substrate; the photodiode structure comprises an outer layer of a sub-photosensitive layer, a middle layer of a sub-photosensitive layer and an inner layer of a sub-photosensitive layer, all of which are N-type and are sequentially stacked from the outside to the inside; the middle layer of the sub-photosensitive layer covers the top surface, the bottom surface and the side surface of the inner layer of the sub-photosensitive layer; the outer layer of the sub-photosensitive layer covers the top surface, the bottom surface and the side surface of the middle layer of the sub-photosensitive layer; the bottom target size of the photodiode structure gradually decreases along the second direction, and the top target size of the photodiode structure gradually decreases in a direction away from the substrate, the target size being the size along the first direction; the grid layer covers the top of the plurality of photodiode structures.

[0006] The back-illuminated image sensor in the above embodiment, because the photodiode structure includes the outer layer sub-light sensitive layer, the middle layer sub-light sensitive layer and the inner layer sub-light sensitive layer which are all N-type and are sequentially stacked from outside to inside; the middle layer sub-light sensitive layer covers the top surface, the bottom surface and the side surface of the inner layer sub-light sensitive layer; the outer layer sub-light sensitive layer covers the top surface, the bottom surface and the side surface of the middle layer sub-light sensitive layer; the outer layer sub-light sensitive layer, the middle layer sub-light sensitive layer and the inner layer sub-light sensitive layer generate a concentration gradient in the inside thereof after being excited by light, optimize the transmission path of the photo-generated carriers, reduce the recombination rate in the diffusion process, and improve the quantum efficiency of the photodiode; the multi-layer wrapping structure from outside to inside forms a photoelectron storage container; the target size of the top of the photodiode structure gradually decreases in the direction away from the substrate, the target size is the size in the first direction, to form a light focusing effect similar to a convex lens, the incident light is transmitted to the inside of the photodiode structure, and the photoelectric conversion efficiency of the photodiode is improved; the target size of the bottom of the photodiode structure gradually decreases in the second direction, to further increase the bottom end spacing of the adjacent photodiode structures, increase the reactance between the adjacent photodiode structures, and reduce the generation probability of the leakage current.

[0007] Further, the PN junction of the photodiode can be formed between the outer layer sub-light sensitive layer of N-type and the P-type substrate. The PN junction for isolation can be formed between the P-type epitaxial layer and the outer layer sub-light sensitive layer of N-type, compared with the photodiode isolated by the dielectric material, the isolation by the PN junction can further reduce the generation probability of the current leakage channel.

[0008] Further, in the outer layer sub-light sensitive layer, the middle layer sub-light sensitive layer and the inner layer sub-light sensitive layer which are all N-type and are sequentially stacked from outside to inside, the atomic mass of the pentavalent element is higher than that of silicon, and the mobility is low in epitaxial growth, resulting in uneven doping concentration in a single doped layer. Growing the pentavalent element with different doping in multiple times can improve the uniformity of the doping concentration in the pixel area.

[0009] In some embodiments, the P-type epitaxial layer includes a first sub-epitaxial layer of P-type adjacent to the substrate; the bottom of the photodiode structure includes the bottom of the outer layer sub-light sensitive layer, the bottom of the middle layer sub-light sensitive layer and the bottom of the inner layer sub-light sensitive layer which are sequentially stacked from outside to inside. The PN junction for isolation can be formed between the bottom of the outer layer sub-light sensitive layer, the bottom of the middle layer sub-light sensitive layer and the bottom of the inner layer sub-light sensitive layer which are all N-type and the first sub-epitaxial layer of P-type, to reduce the generation probability of the current leakage channel. The target size of the bottom of the photodiode structure gradually decreases in the second direction, to further increase the bottom end spacing of the adjacent photodiode structures, increase the reactance between the adjacent photodiode structures, further reduce the generation probability of the leakage current, and provide an operable space for further improving the density of the photodiode structure per unit area.

[0010] In some embodiments, the P-type epitaxial layer includes a second sub-epitaxial layer of P-type, the second sub-epitaxial layer is located on the top surface of the first sub-epitaxial layer; the photodiode structure includes a middle part between the bottom of the photodiode structure and the top of the photodiode structure; the middle part of the photodiode structure includes, from outside to inside, a middle part of the outer layer sub-photosensitive layer, a middle part of the middle layer sub-photosensitive layer, and a middle part of the inner layer sub-photosensitive layer; the middle part of the middle layer sub-photosensitive layer circumferentially surrounds the middle part of the inner layer sub-photosensitive layer, and the middle part of the outer layer sub-photosensitive layer circumferentially surrounds the middle part of the middle layer sub-photosensitive layer; the middle part of the inner layer sub-photosensitive layer is located directly above the bottom of the inner layer sub-photosensitive layer; the middle part of the middle layer sub-photosensitive layer is located directly above the bottom of the middle layer sub-photosensitive layer; and the middle part of the outer layer sub-photosensitive layer is located directly above the bottom of the outer layer sub-photosensitive layer. The middle part of the photodiode structure, which is N-type, extends along the second direction in a columnar shape, and can provide a container for storage of photoelectric conversion. The middle part of the photodiode structure, which is N-type, and the second sub-epitaxial layer of P-type form a PN junction for isolation, reduce the probability of generation of a photoelectric current leakage channel, and can reduce the spacing between adjacent photodiode structures and improve the density of photodiode structures per unit area.

[0011] In some embodiments, the top of the photodiode structure includes, from outside to inside, a top of the outer layer sub-photosensitive layer, a top of the middle layer sub-photosensitive layer, and a top of the inner layer sub-photosensitive layer; the grid layer includes a top grid layer and a grid stack layer between the photodiode structures; the top surface of the grid stack layer is lower than the top surface of the outer layer sub-photosensitive layer; the top grid layer covers the top surface of the grid stack layer; the top grid layer includes trenches spaced apart along the first direction and located directly above the photodiode structures; and the trenches are used to set filters. The grid stack layer is located between the photodiode structures, which can avoid signal crosstalk. The top grid layer covers the top surface of the grid stack layer and defines trenches for setting filters, which can reduce the complexity and cost of the preparation process.

[0012] In some embodiments, the P-type substrate includes a plurality of trench isolation portions spaced apart along the first direction; and the plurality of trench isolation portions and the plurality of photodiode structures are arranged alternately along the first direction.

[0013] In some embodiments, the outer layer sub-photosensitive layer includes a SiP layer; the middle layer sub-photosensitive layer includes a SiAs layer; and the inner layer sub-photosensitive layer includes a SiSb layer; the SiAs layer is used to represent a silicon material containing As; the SiP layer is used to represent a silicon material containing P; and the SiSb layer is used to represent a silicon material containing Sb. The atomic mass of the pentavalent element is higher than that of silicon, and the mobility is lower in epitaxial growth, which causes uneven doping concentration in a single doped layer. Growing different doped pentavalent elements in multiple times can improve the uniformity of the doping concentration in the pixel area.

[0014] In a second aspect, the embodiments of the present disclosure provide a preparation method of a back-illuminated image sensor, including:

[0015] a P-type substrate is provided;

[0016] a P-type epitaxial layer is formed on the back surface of the P-type substrate, the P-type epitaxial layer includes a plurality of initial photodiode structures spaced apart along a first direction parallel to the back surface of the substrate and extending through the P-type epitaxial layer along a second direction close to the substrate and to the back surface of the substrate; a target size of the initial photodiode structure gradually decreases along the second direction; the target size is a size along the first direction;

[0017] In the process of forming the grid layer, a plurality of diode tops are formed above the plurality of initial photodiode structures, and the grid layer covers the plurality of diode tops; a target size of the plurality of diode tops gradually decreases in a direction away from the substrate; the initial photodiode structure and the diode top jointly constitute a photodiode structure; the photodiode structure includes an outer sub-photosensitive layer, a middle sub-photosensitive layer, and an inner sub-photosensitive layer, all of which are N-type and sequentially stacked from outside to inside; the middle sub-photosensitive layer covers the top surface, the bottom surface, and the side surface of the inner sub-photosensitive layer; and the outer sub-photosensitive layer covers the top surface, the bottom surface, and the side surface of the middle sub-photosensitive layer.

[0018] In some embodiments, the P-type epitaxial layer includes a first sub-epitaxial layer of P-type adjacent to the substrate; the P-type epitaxial layer formed on the back surface of the P-type substrate includes:

[0019] a first sub-epitaxial layer of P-type is formed on the back surface of the P-type substrate, and the first sub-epitaxial layer includes a plurality of grooves spaced apart along a first direction parallel to the back surface of the substrate; a target size of the groove gradually decreases along a second direction close to the substrate, and the target size is a size along the first direction;

[0020] a bottom of the photodiode structure of N-type is formed in each of the plurality of grooves, and the bottom of the photodiode structure includes, from outside to inside, a bottom of an outer sub-photosensitive layer, a bottom of a middle sub-photosensitive layer, and a bottom of an inner sub-photosensitive layer.

[0021] In some embodiments, the P-type epitaxial layer includes a second sub-epitaxial layer of P-type, and the second sub-epitaxial layer is located on the top surface of the first sub-epitaxial layer; the P-type epitaxial layer formed on the back surface of the P-type substrate includes:

[0022] the second sub-epitaxial layer is formed on the top surface of the first sub-epitaxial layer, and the second sub-epitaxial layer includes a plurality of through holes exposing the bottom of the photodiode structure;

[0023] a middle part of the photodiode structure is formed in each of the plurality of through holes, and the middle part of the photodiode structure includes, from outside to inside, a middle part of an outer sub-photosensitive layer, a middle part of a middle sub-photosensitive layer, and a middle part of an inner sub-photosensitive layer.

[0024] In some embodiments, the grid layer is formed, including:

[0025] forming an initial grid stack on a top surface of the P-type epitaxial layer, the initial grid stack comprising a plurality of first holes exposing a middle portion of a plurality of inner layer sub-photosensitive layers;

[0026] forming a top portion of the inner layer sub-photosensitive layers in the plurality of first holes;

[0027] etching the initial grid stack to obtain a plurality of second holes exposing a middle portion of a plurality of middle layer sub-photosensitive layers;

[0028] forming a top portion of the middle layer sub-photosensitive layers in the plurality of second holes, the top portion of the middle layer sub-photosensitive layers covering the top portion of the inner layer sub-photosensitive layers;

[0029] etching the initial grid stack to obtain a plurality of third holes exposing a middle portion of a plurality of outer layer sub-photosensitive layers;

[0030] forming a top portion of the outer layer sub-photosensitive layers in the plurality of third holes, the top portion of the outer layer sub-photosensitive layers covering the top portion of the middle layer sub-photosensitive layers.

[0031] The back-illuminated image sensor and the preparation method thereof in the embodiments of the present disclosure have the following unexpected technical effects:

[0032] Since the photodiode structure comprises the outer layer sub-photosensitive layers, the middle layer sub-photosensitive layers and the inner layer sub-photosensitive layers which are all N-type and are sequentially stacked from outside to inside, the middle layer sub-photosensitive layers cover the top surface, the bottom surface and the side surface of the inner layer sub-photosensitive layers, and the outer layer sub-photosensitive layers cover the top surface, the bottom surface and the side surface of the middle layer sub-photosensitive layers. After being excited by light, the outer layer sub-photosensitive layers, the middle layer sub-photosensitive layers and the inner layer sub-photosensitive layers generate a concentration gradient inside, which optimizes the transmission path of the photo-generated carriers, reduces the recombination rate in the diffusion process, and improves the quantum efficiency of the photodiode. The multilayer wrapping structure from outside to inside forms a light electron storage container. The target size of the top portion of the photodiode structure gradually decreases in the direction away from the substrate, and the target size is the size in the first direction, so as to form a light focusing effect similar to a convex lens, and the incident light is transmitted to the photodiode structure, thereby improving the photoelectric conversion efficiency of the photodiode. The target size of the bottom portion of the photodiode structure gradually decreases in the second direction, so as to further increase the distance between the bottom ends of the adjacent photodiode structures and increase the reactance between the adjacent photodiode structures, thereby reducing the probability of generating leakage current. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the following will briefly introduce the drawings needed to be used in the embodiments description. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and other drawings can also be obtained by those skilled in the art without any creative effort based on these drawings.

[0034] Figure 1A flowchart of a method for manufacturing a back-illuminated image sensor according to an embodiment;

[0035] Figure 2 A longitudinal sectional view of a semiconductor structure after forming a sacrificial layer on the substrate in step S10 of a method for manufacturing a back-illuminated image sensor according to an embodiment;

[0036] Figure 3 A longitudinal sectional view of a semiconductor structure after forming a groove on the substrate in step S20 of a method for manufacturing a back-illuminated image sensor according to an embodiment;

[0037] Figure 4 A longitudinal sectional view of a semiconductor structure after forming a bottom of a photodiode structure on the substrate in step S20 of a method for manufacturing a back-illuminated image sensor according to an embodiment;

[0038] Figure 5 A longitudinal sectional view of a semiconductor structure after forming a sacrificial material layer in step S20 of a method for manufacturing a back-illuminated image sensor according to an embodiment;

[0039] Figure 6 A longitudinal sectional view of a semiconductor structure after forming a via in step S20 of a method for manufacturing a back-illuminated image sensor according to an embodiment;

[0040] Figure 7 A longitudinal sectional view of a semiconductor structure after forming a middle of a photodiode structure in step S20 of a method for manufacturing a back-illuminated image sensor according to an embodiment;

[0041] Figure 8 A longitudinal sectional view of a semiconductor structure after forming an initial grid stack in step S30 of a method for manufacturing a back-illuminated image sensor according to an embodiment;

[0042] Figure 9 A longitudinal sectional view of a semiconductor structure after forming a top of an inner sub-photosensitive layer in step S30 of a method for manufacturing a back-illuminated image sensor according to an embodiment;

[0043] Figure 10 A longitudinal sectional view of a semiconductor structure after forming a top grid layer in a method for manufacturing a back-illuminated image sensor according to an embodiment;

[0044] Figure 11 A longitudinal sectional view of a semiconductor structure after forming a filter in a method for manufacturing a back-illuminated image sensor according to an embodiment.

[0045] BRIEF DESCRIPTION OF REFERENCE NUMERALS:

[0046] 10, substrate; 10a, back surface of substrate; 101, trench isolation; 102, etching stop layer; 103, interlayer dielectric layer; 20, epitaxial layer; 201, sacrificial layer; 211, first sub-epitaxial material layer; 21, first sub-epitaxial layer; 221, second sub-epitaxial material layer; 202, sacrificial material layer; 22, second sub-epitaxial layer; 30, bottom of photodiode structure; 301, recess; 302, via; 303, first hole; 31, bottom of outer sub-photosensitive layer; 32, bottom of middle sub-photosensitive layer; 33, bottom of inner sub-photosensitive layer; 41, middle of outer sub-photosensitive layer; 42, middle of middle sub-photosensitive layer; 43, middle of inner sub-photosensitive layer; 40, middle of photodiode structure; 60, grid layer; 60', initial grid stack; 612, grid stack; 61, first sub-grid layer; 62, second sub-grid layer; 63, top grid layer; 631, sacrificial grid material layer; 50, top of photodiode structure; 51, top of outer sub-photosensitive layer; 52, top of middle sub-photosensitive layer; 53, top of inner sub-photosensitive layer; 200, photodiode structure; 70, optical filter; 701, trench. DETAILED DESCRIPTION

[0047] For the purpose of promoting an understanding of the disclosure, the disclosure will now be described more fully with reference to the associated drawings. Specific embodiments of the disclosure are illustrated in the accompanying drawings. However, the disclosure can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the disclosure to those skilled in the art.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used in the description of the disclosure herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure.

[0049] It will be understood that when an element or layer is referred to as being "on" or "connected to" another element or layer, it can be directly on or connected to the other element or layer or intervening elements or layers can be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" another element or layer, there are no intervening elements or layers present. It will also be understood that, although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section; for example, a first doped type could be termed a second doped type; and similarly, a second doped type could be termed a first doped type; a first doped type and a second doped type are different doped types, for example, a first doped type can be P-type and a second doped type can be N-type, or a first doped type can be N-type and a second doped type can be P-type.

[0050] Spatially relative terms, such as "beneath", "below", "lower", "under", "above", "upper" and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use and / or operation in addition to the orientations depicted in the figures. For example, if a device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. The device can also be oriented in the other directions (for example, rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0051] As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. It will be further understood that the terms "comprises" and / or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0052] Embodiments of the application are described herein with reference to cross-sectional illustrations of idealized embodiments (and intermediate structures) of the present disclosure as schematic illustrations. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and / or tolerances, are to be expected. Thus, embodiments of the present disclosure should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and / or a gradient of implant concentration at its edges rather than a binary change between implanted and non-implanted regions. Similarly, a buried region formed by implantation can result in some implantation in a region between the buried region and a surface through which the implant was performed. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the present disclosure.

[0053] In embodiments of the present disclosure, a direction parallel to the substrate surface, for example, a first direction, and a direction away from the substrate surface, for example, a second direction, are considered in the absence of substrate surface flatness. In embodiments of the present disclosure, the first direction can be an ox direction and the second direction can be an oz direction. A "cross-section" in embodiments of the present disclosure is parallel to the back surface of the substrate. A "longitudinal section" in embodiments of the present disclosure is perpendicular to the back surface of the substrate.

[0054] Reference is made to Figure 1 In some embodiments, a back-illuminated image sensor manufacturing method is provided, comprising:

[0055] Step S10: providing a P-type substrate;

[0056] Step S20: forming a P-type epitaxial layer on the back surface of the P-type substrate, the P-type epitaxial layer comprising a plurality of initial photodiode structures spaced apart along a first direction parallel to the back surface of the substrate and extending through the P-type epitaxial layer along a second direction close to the substrate and reaching the back surface of the substrate; the target size of the bottom of the initial photodiode structure gradually decreases along the second direction, and the target size is a size along the first direction;

[0057] Step S30: forming a plurality of diode tops above the plurality of initial photodiode structures in the process of forming a grid layer, the grid layer covering the plurality of diode tops; the target size of the plurality of diode tops gradually decreases along a direction away from the substrate; the initial photodiode structure and the diode top jointly constitute a photodiode structure; the photodiode structure comprises an outer sub-photosensitive layer, a middle sub-photosensitive layer, and an inner sub-photosensitive layer, all of which are N-type and sequentially stacked from the outside to the inside; the middle sub-photosensitive layer covers the top surface, the bottom surface, and the side surface of the inner sub-photosensitive layer; and the outer sub-photosensitive layer covers the top surface, the bottom surface, and the side surface of the middle sub-photosensitive layer.

[0058] By way of example, reference is made to Figure 2The substrate 10 can be made of a semiconductor material, an insulating material, a conductive material, or any combination thereof. The substrate 10 can be doped with boron (B) to form a P-type substrate, and a PN junction of a photodiode can be formed between the P-type substrate and an N-type photodiode structure. The substrate 10 can be a single layer structure or a multi-layer structure. For example, the substrate 10 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 substrate, or a II / VI semiconductor substrate. Alternatively, for example, the substrate 10 can be a layered substrate including, for example, Si / SiGe, Si / SiC, silicon-on-insulator (SOI), or silicon-on-silicon germanium. Thus, the type of substrate should not limit the scope of protection of the present disclosure.

[0059] Please continue to refer to Figure 2 In some embodiments, the front surface of the trench isolation portion 101 is a surface facing away from the substrate back surface 10a, and the front surface of the trench isolation portion 101 is covered with the etching stop layer 102, and the side of the etching stop layer 102 facing away from the trench isolation portion 101 includes the interlayer dielectric layer 103.

[0060] For example, please continue to refer to Figure 2 After the etching stop layer 102 is formed, metal is deposited to form a partial connection structure, and the interlayer dielectric layer 103 is formed thereon. When the etching stop layer 102 is a multi-layer, it can avoid other process problems caused by cracks in a single layer, and / or metal connection structure failure problems. The interlayer dielectric layer 103 can be a silicon oxide layer or other dielectric material layer. In addition, a metal interconnection structure can also be formed on the interlayer dielectric layer 103 as a metal connection part of the device.

[0061] Of course, the present embodiment only represents one of the ways, as long as the metal interconnection structure can be reasonably formed, and the thickness of the etching stop layer 102 and the interlayer dielectric layer 103 is not specifically limited, and can be adjusted according to the specific process requirements.

[0062] Please continue to refer to Figure 2 In some embodiments, the substrate 10 provided includes a plurality of trench isolation portions 101 spaced apart along a first direction parallel to the substrate back surface 10a, for example, the ox direction. The material of the trench isolation portion 101 can include, but is not limited to, silicon oxide (SiO2), silicon nitride (Si3N4), silicon oxynitride (Si2N2O), or a combination thereof.

[0063] For example, please continue to refer to Figure 2The trench isolation portion 101 can be used to isolate electrons and light energy. The shape of the longitudinal section (a section parallel to the zox plane) of the trench isolation portion 101 can include a right trapezoid, an inverted trapezoid, a rectangle, etc., or can also be a combination of a right trapezoid, an inverted trapezoid, a rectangle, etc. The present disclosure does not make specific limitations on the shape, material, and size of the trench isolation portion 101, and can isolate electrons, light energy, doping ions, etc. In addition, the present embodiment does not make specific limitations on the spacing between adjacent trench isolation portions 101, and can be set according to actual needs.

[0064] Please continue to refer to Figure 2 In some embodiments, after the shallow trench isolation (STI) is formed in the substrate 10, the trench isolation portion 101 can be formed after the STI is filled with dielectric material. Then, the substrate 10 can be flipped, and the back surface 10a of the substrate can be thinned and planarized to expose the back surface of the trench isolation portion 101.

[0065] For example, please continue to refer to Figure 2 A first sub-epitaxial material layer 211 can be epitaxially grown on the top surface of the substrate back surface 10a. The thickness of the first sub-epitaxial material layer 211 can be 50-60 nm. For example, the thickness of the first sub-epitaxial material layer 211 can be 50 nm, 55 nm, or 60 nm, etc. The first sub-epitaxial material layer 211 can include a SiGa layer, which is used to characterize a silicon material doped with gallium (Ga). A deposition process can be used to form a sacrificial layer 201 on the top surface of the first sub-epitaxial material layer 211. The material of the sacrificial layer 201 can include silicon oxide. The thickness of the sacrificial layer 201 can be 1-2 nm, for example, the thickness of the sacrificial layer 201 can be 1 nm, 1.5 nm, or 2 nm, etc.

[0066] Please refer to Figure 1 , Figures 3-4 In some embodiments, the P-type epitaxial layer includes a first sub-epitaxial layer 21 of P-type adjacent to the substrate 10; in step S20, the P-type epitaxial layer is formed on the P-type substrate back surface 10a, including:

[0067] Step S21: forming a first sub-epitaxial layer 21 of P-type on the P-type substrate back surface 10a, the first sub-epitaxial layer 21 including a plurality of grooves 301 spaced apart along a first direction parallel to the substrate back surface 10a; the target size of the groove 301 gradually decreases along a second direction close to the substrate 10, and the target size is the size along the first direction;

[0068] Step S22: Forming a bottom of the N-type photodiode structure 200 in the plurality of recesses 301, the bottom of the N-type photodiode structure 200 comprising, from outside to inside, a bottom 31 of an outer sub-photosensitive layer, a bottom 32 of a middle sub-photosensitive layer, and a bottom 33 of an inner sub-photosensitive layer.

[0069] Please continue to refer to Figure 3 In step S21, a dry etching and / or wet etching process can be used to form a plurality of recesses 301 spaced apart along the first direction in the first sub-epitaxial material layer 211. The target size of the recess 301 gradually decreases along the second direction close to the substrate 10, and the target size is the size along the first direction. The sacrificial layer 201 can protect the first sub-epitaxial material layer 211 during etching of the first sub-epitaxial material layer 211 to avoid unnecessary etching damage. The remaining first sub-epitaxial material layer 211 is used to form the first sub-epitaxial layer 21.

[0070] Please continue to refer to Figures 3-4 In some embodiments, in step S22, a deposition process can be used to form the bottom 31 of the outer sub-photosensitive layer on the inner surface of the plurality of recesses 301 and the top surface of the sacrificial layer 201. Then, a deposition process is used to form the bottom 32 of the middle sub-photosensitive layer covering the bottom 31 of the outer sub-photosensitive layer. Then, a deposition process is used to form the bottom 33 of the inner sub-photosensitive layer covering the bottom 32 of the middle sub-photosensitive layer. The bottom 33 of the inner sub-photosensitive layer at least fills the recess 301. Finally, the top surface of the first sub-epitaxial layer 21 is used as an etching stop layer, and a planarization process is used to remove the sacrificial layer 201, and the bottom 31 of the outer sub-photosensitive layer, the bottom 32 of the middle sub-photosensitive layer, and the bottom 33 of the inner sub-photosensitive layer are obtained. The top surfaces are flush. The bottom 31 of the outer sub-photosensitive layer, the bottom 32 of the middle sub-photosensitive layer, and the bottom 33 of the inner sub-photosensitive layer are used to form the bottom 30 of the photodiode structure.

[0071] For example, please continue to refer to Figure 4 The bottom 31 of the outer sub-photosensitive layer of the N-type contains SiP, the bottom 32 of the middle sub-photosensitive layer of the N-type contains SiAs, and the bottom 33 of the inner sub-photosensitive layer of the N-type contains SiSb. The SiAs layer is used to characterize a silicon material containing As; the SiP layer is used to characterize a silicon material containing P; and the SiSb layer is used to characterize a silicon material containing Sb. The bottom 31 of the outer sub-photosensitive layer, the bottom 32 of the middle sub-photosensitive layer, and the bottom 33 of the inner sub-photosensitive layer can contain a small amount of B.

[0072] Please refer to Figures 5-6 In some embodiments, the P-type epitaxial layer includes a second sub-epitaxial layer 22 of the P-type, and the second sub-epitaxial layer 22 is located on the top surface of the first sub-epitaxial layer 21. In step S20, the P-type epitaxial layer is formed on the back surface 10a of the P-type substrate, which includes:

[0073] Step S23: forming a second sub-epitaxial layer 22 on the top surface of the first sub-epitaxial layer 21, the second sub-epitaxial layer 22 including a plurality of through holes 302 exposing the bottom of the photodiode structure 200;

[0074] Step S24: forming a middle part of the photodiode structure 200 in each of the plurality of through holes 302, the middle part of the photodiode structure 200 including, from outside to inside, a middle part 41 of the outer sub-photosensitive layer, a middle part 42 of the middle sub-photosensitive layer, and a middle part 43 of the inner sub-photosensitive layer.

[0075] Please continue to refer to Figure 5 In some embodiments, in step S23, a selective epitaxial growth process can be used to form a second sub-epitaxial material layer 221 on the top surface of the first sub-epitaxial layer 21, and then a sacrificial material layer 202 is formed on the top surface of the second sub-epitaxial material layer 221. The thickness of the second sub-epitaxial material layer 221 can be 50-60 nanometers. For example, the thickness of the second sub-epitaxial material layer 221 can be 50 nanometers, 55 nanometers, or 60 nanometers, etc. The second sub-epitaxial material layer 221 can include a SiGa layer, which is used to characterize a silicon material doped with gallium (Ga). The material of the sacrificial material layer 202 can include silicon oxide. The thickness of the sacrificial material layer 202 can be 1-2 nanometers, for example, the thickness of the sacrificial material layer 202 can be 1 nanometer, 1.5 nanometers, or 2 nanometers, etc.

[0076] Please continue to refer to Figures 5-6 In some embodiments, in step S23, a dry and / or wet etching process can be used to form a plurality of through holes 302 spaced apart along the first direction in the second sub-epitaxial material layer 221, the plurality of through holes 302 exposing the bottom 30 of the plurality of photodiode structures. The remaining second sub-epitaxial material layer 221 is used to constitute the second sub-epitaxial layer 22. The sacrificial material layer 202 can protect the second sub-epitaxial material layer 221 during the etching of the second sub-epitaxial material layer 221, avoiding unnecessary etching damage. The first sub-epitaxial layer 21 and the second sub-epitaxial layer 22, both of which are P-type, are used to jointly constitute the P-type epitaxial layer 20.

[0077] Please continue to refer to Figures 6-7In some embodiments, in step S24, a deposition process is used to form an outer layer of sub-photosensitive material layer (not shown) covering the inner surface of the via 302 and the bottom 30 of the photodiode structure, and then an etching process is used to remove the outer layer of sub-photosensitive material layer on the top surface of the middle layer of sub-photosensitive layer 32 and the top surface of the inner layer of sub-photosensitive layer 33, to form a middle groove (not shown). A deposition process is used to form a middle layer of sub-photosensitive material layer (not shown) covering the inner surface of the middle groove and the bottom 30 of the photodiode structure, and then an etching process is used to remove the middle layer of sub-photosensitive material layer on the top surface of the inner layer of sub-photosensitive layer 33, to form an inner groove (not shown). Finally, a deposition process is used to form an inner layer of sub-photosensitive material layer (not shown) to fill the inner groove. The second sub-epitaxial layer 22 is used as an etching stop layer, and a planarization process is used to planarize the top surface of the inner layer of sub-photosensitive material layer, the top surface of the middle layer of sub-photosensitive material layer, and the top surface of the outer layer of sub-photosensitive material layer. The remaining outer layer of sub-photosensitive material layer is used to form the middle portion 41 of the outer layer of sub-photosensitive layer, the remaining middle layer of sub-photosensitive material layer is used to form the middle portion 42 of the middle layer of sub-photosensitive layer, and the remaining inner layer of sub-photosensitive material layer is used to form the middle portion 43 of the inner layer of sub-photosensitive layer. The middle portion 41 of the outer layer of sub-photosensitive layer, the middle portion 42 of the middle layer of sub-photosensitive layer, and the middle portion 43 of the inner layer of sub-photosensitive layer are used to form the middle portion 40 of the photodiode structure.

[0078] For reference Figures 7-11 In some embodiments, in step S30, the grid layer 60 is formed, including steps S31-S36.

[0079] Step S31: Form an initial grid stack 60' on the top surface of the P-type epitaxial layer, and the initial grid stack 60' includes a plurality of first holes 303 exposing the middle portions 43 of the plurality of inner layer of sub-photosensitive layers.

[0080] For example, please continue to refer to Figures 7-8 A deposition process is used to form a first grid material layer (not shown) covering the top surface of the P-type epitaxial layer, and then a second grid material layer (not shown) is formed on the top surface of the first grid material layer, and then a third grid material layer (not shown) is formed on the top surface of the second grid material layer. An etching process is used to etch the third grid material layer, the second grid material layer, and the first grid material layer, to form a plurality of first holes 303 exposing the middle portions 43 of the plurality of inner layer of sub-photosensitive layers. The remaining first grid material layer is used to form the first sub-grid layer 61, the remaining second grid material layer is used to form the second sub-grid layer 62, and the remaining third grid material layer is used to form the sacrificial grid material layer 631. The first sub-grid layer 61, the second sub-grid layer 62, and the sacrificial grid material layer 631 are stacked to form the initial grid stack 60'.

[0081] Step S32: Form the top portion 53 of the inner layer of sub-photosensitive layer in the plurality of first holes 303.

[0082] For example, please continue to refer to Figures 8-9 The top part 53 of the inner layer sub-light sensitive layer, the middle part 43 of the inner layer sub-light sensitive layer and the bottom part 33 of the inner layer sub-light sensitive layer are used to jointly constitute the inner layer sub-light sensitive layer of the photodiode structure. The top part 53 of the inner layer sub-light sensitive layer, the middle part 43 of the inner layer sub-light sensitive layer and the bottom part 33 of the inner layer sub-light sensitive layer all include SiSb, and SiSb is used to represent a silicon material containing Sb.

[0083] Step S33: etching the initial grid stack 60' to obtain a plurality of second holes exposing the middle parts 42 of the plurality of middle layer sub-light sensitive layers.

[0084] For example, please continue to refer to Figures 9-10 After forming the top part 53 of the inner layer sub-light sensitive layer, the initial grid stack 60' can be etched to increase the spacing of the remaining adjacent initial grid stacks 60', to obtain second holes (not shown) exposing the middle parts 42 of the middle layer sub-light sensitive layers.

[0085] Step S34: forming a top part 52 of the middle layer sub-light sensitive layer in the plurality of second holes, the top part 52 of the middle layer sub-light sensitive layer covering the top part 53 of the inner layer sub-light sensitive layer.

[0086] For example, please continue to refer to Figures 9-10 In the plurality of second holes, the top part 52 of the middle layer sub-light sensitive layer is epitaxially grown to cover the top part 53 of the inner layer sub-light sensitive layer. The top part 52 of the middle layer sub-light sensitive layer, the middle part 42 of the middle layer sub-light sensitive layer and the bottom part 32 of the middle layer sub-light sensitive layer are used to jointly constitute the middle layer sub-light sensitive layer of the photodiode structure. The top part 52 of the middle layer sub-light sensitive layer, the middle part 42 of the middle layer sub-light sensitive layer and the bottom part 32 of the middle layer sub-light sensitive layer all include SiAs, and SiAs is used to represent a silicon material containing As.

[0087] Step S35: etching the initial grid stack 60' to obtain a plurality of third holes exposing the middle parts 41 of the plurality of outer layer sub-light sensitive layers.

[0088] For example, please continue to refer to Figures 9-10 After forming the top part 52 of the middle layer sub-light sensitive layer, the initial grid stack 60' can be etched to increase the spacing of the remaining adjacent initial grid stacks 60', to obtain third holes (not shown) exposing the middle parts 41 of the outer layer sub-light sensitive layers.

[0089] Step S36: forming a top part 51 of the outer layer sub-light sensitive layer in the plurality of third holes, the top part 51 of the outer layer sub-light sensitive layer covering the top part 52 of the middle layer sub-light sensitive layer.

[0090] For example, please continue to refer to Figures 9-10, in the plurality of third holes, epitaxially growing a top portion 51 of an outer layer sub-photosensitive layer covering a top portion 52 of the middle layer sub-photosensitive layer. The top portion 51 of the outer layer sub-photosensitive layer, the middle portion 41 of the outer layer sub-photosensitive layer, and the bottom portion 31 of the outer layer sub-photosensitive layer are collectively configured to form an outer layer sub-photosensitive layer of the photodiode structure. The top portion 51 of the outer layer sub-photosensitive layer, the middle portion 41 of the outer layer sub-photosensitive layer, and the bottom portion 31 of the outer layer sub-photosensitive layer each include SiP, which is used to represent a P-containing silicon material.

[0091] Reference is made to Figures 10-11 In some embodiments, after forming the top portion 51 of the outer layer sub-photosensitive layer, the sacrificial grid material layer 631 can be removed, and then a deposition process is used to form a top grid layer 63 covering the grid stack 612 and the photodiode structure 200. After planarizing the top surface of the top grid layer 63, an etching process is used to form trenches 701 in the top grid layer 63, which are located directly above the photodiode structure 200, and the trenches 701 are used to form the optical filter 70.

[0092] In some embodiments, reference is made to Figure 11 A back-illuminated image sensor is provided, including a P-type substrate 10, a plurality of photodiode structures 200, and a grid layer 60. The P-type substrate 10 includes a P-type epitaxial layer 20. The plurality of photodiode structures 200 are spaced apart along a first direction parallel to the back surface 10a of the substrate 10, extend through the P-type epitaxial layer 20 along a second direction close to the substrate 10, and extend to the back surface 10a of the P-type substrate 10. The photodiode structure 200 includes an outer layer sub-photosensitive layer, a middle layer sub-photosensitive layer, and an inner layer sub-photosensitive layer, all of which are N-type and are sequentially stacked from the outside to the inside. The middle layer sub-photosensitive layer covers the top surface, the bottom surface, and the side surface of the inner layer sub-photosensitive layer. The outer layer sub-photosensitive layer covers the top surface, the bottom surface, and the side surface of the middle layer sub-photosensitive layer. The target size of the bottom portion 30 of the photodiode structure gradually decreases along the second direction, and the target size of the top portion 50 of the photodiode structure gradually decreases along a direction away from the substrate 10. The target size is the size along the first direction. The grid layer 60 covers the top portions of the plurality of photodiode structures 200.

[0093] For example, reference is made to Figure 11As the photodiode structure 200 includes the outer layer sub-photosensitive layer, the middle layer sub-photosensitive layer and the inner layer sub-photosensitive layer which are all N-type and are sequentially stacked from outside to inside; the middle layer sub-photosensitive layer covers the top surface, the bottom surface and the side surface of the inner layer sub-photosensitive layer; the outer layer sub-photosensitive layer covers the top surface, the bottom surface and the side surface of the middle layer sub-photosensitive layer; the outer layer sub-photosensitive layer, the middle layer sub-photosensitive layer and the inner layer sub-photosensitive layer generate a concentration gradient inside after being excited by light, optimize the transmission path of photo-generated carriers, reduce the recombination rate in the diffusion process, and improve the quantum efficiency of the photodiode; the multilayer wrapping structure from outside to inside forms a light electron storage container; the target size of the top 50 of the photodiode structure gradually decreases in the direction away from the substrate 10, the target size is the size in the first direction, to form a light focusing effect similar to a convex lens, the incident light is converged and transmitted into the photodiode structure 200, improving the photoelectric conversion efficiency of the photodiode; the target size of the bottom 30 of the photodiode structure gradually decreases in the second direction, to further increase the distance between the bottom ends of adjacent photodiode structures 200, increase the mutual inductance between adjacent photodiode structures 200, and reduce the probability of generating leakage current.

[0094] For example, please continue to refer to Figure 11 The N-type outer layer sub-photosensitive layer and the P-type substrate 10 can form a PN junction of the photodiode. The P-type epitaxial layer 20 and the N-type outer layer sub-photosensitive layer can form a PN junction for isolation. Compared with the conventional photodiode using dielectric material for isolation, the use of PN junction isolation can further reduce the probability of generating current leakage channels.

[0095] For example, please continue to refer to Figure 11 As the outer layer sub-photosensitive layer, the middle layer sub-photosensitive layer and the inner layer sub-photosensitive layer which are all N-type and are sequentially stacked from outside to inside, the atomic mass of the pentavalent element is higher than that of silicon, and the mobility is low in epitaxial growth, resulting in uneven doping concentration in a single doped layer. Growing different doped pentavalent elements in multiple times can improve the uniformity of the doping concentration in the pixel area.

[0096] Please continue to refer to Figure 11In some embodiments, the P-type epitaxial layer 20 comprises a first sub-epitaxial layer 21 of P-type adjacent to the substrate 10; the bottom of the photodiode structure 200 comprises, from outside to inside, a bottom 31 of an outer sub-photosensitive layer, a bottom 32 of a middle sub-photosensitive layer, and a bottom 33 of an inner sub-photosensitive layer. Since the bottom 31 of the outer sub-photosensitive layer, the bottom 32 of the middle sub-photosensitive layer, and the bottom 33 of the inner sub-photosensitive layer are all of N-type, and form PN junctions with the first sub-epitaxial layer 21 of P-type for isolation, the probability of current leakage channel generation can be reduced. The target size of the bottom 30 of the photodiode structure gradually decreases along the second direction, so as to further increase the distance between the bottom ends of adjacent photodiode structures 200, increase the reactance between adjacent photodiode structures 200, and further reduce the probability of leakage current generation, thereby providing operational space for further increasing the density of the photodiode structures 200 in a unit area.

[0097] Please continue to refer to Figure 11 In some embodiments, the P-type epitaxial layer 20 comprises a second sub-epitaxial layer 22 of P-type located on the top surface of the first sub-epitaxial layer 21; the photodiode structure 200 comprises a middle part 40 of the photodiode structure located between the bottom 30 of the photodiode structure and the top 50 of the photodiode structure; the middle part 40 of the photodiode structure comprises, from outside to inside, a middle part 41 of an outer sub-photosensitive layer, a middle part 42 of a middle sub-photosensitive layer, and a middle part 43 of an inner sub-photosensitive layer; the middle part 42 of the middle sub-photosensitive layer circumferentially surrounds the middle part 43 of the inner sub-photosensitive layer, and the middle part 41 of the outer sub-photosensitive layer circumferentially surrounds the middle part 42 of the middle sub-photosensitive layer; the middle part 43 of the inner sub-photosensitive layer is located directly above the bottom 33 of the inner sub-photosensitive layer; the middle part 42 of the middle sub-photosensitive layer is located directly above the bottom 32 of the middle sub-photosensitive layer; and the middle part 41 of the outer sub-photosensitive layer is located directly above the bottom 31 of the outer sub-photosensitive layer. The middle part 40 of the photodiode structure of N-type extends along the second direction in a columnar shape, which can provide a container for storage of photoelectric conversion. The middle part 40 of the photodiode structure of N-type and the second sub-epitaxial layer 22 of P-type form a PN junction for isolation, which reduces the probability of photoelectric current leakage channel generation, reduces the distance between adjacent photodiode structures 200, and increases the density of the photodiode structures 200 in a unit area.

[0098] Please continue to refer to Figure 11In some embodiments, the top part 50 of the photodiode structure comprises, from outside to inside, a top part 51 of the outer sub-photosensitive layer, a top part 52 of the middle sub-photosensitive layer, and a top part 53 of the inner sub-photosensitive layer; the grid layer 60 comprises a top grid layer 63 and a grid stack layer 612 between the photodiode structures 200; the top surface of the grid stack layer 612 can be lower than the top surface of the outer sub-photosensitive layer; the top grid layer 63 covers the top surface of the grid stack layer 612; the top grid layer 63 comprises trenches 701 distributed along the first direction and located directly above the photodiode structures 200; the trenches 701 are used to arrange the optical filter 70. The grid stack layer is located between the photodiode structures 200, which can avoid signal crosstalk. The top grid layer 63 covers the top surface of the grid stack layer and defines the trenches 701 for arranging the optical filter 70, which can reduce the complexity and cost of the preparation process.

[0099] For example, please continue to refer to Figure 11 The optical filter 70 includes but is not limited to a red filter, a yellow filter, a blue filter, etc., and the three kinds of filters are arranged adjacent to each other as a pixel group. Among them, the red filter transmits red light waves, the yellow filter transmits yellow light waves, and the blue filter transmits blue light waves.

[0100] Please continue to refer to Figure 11 In some embodiments, the P-type substrate 10 comprises a plurality of trench isolation portions 101 distributed along the first direction; the plurality of trench isolation portions 101 and the plurality of photodiode structures 200 are arranged alternately along the first direction.

[0101] Please continue to refer to Figure 11 In some embodiments, the outer sub-photosensitive layer comprises a SiP layer; the middle sub-photosensitive layer comprises a SiAs layer; and the inner sub-photosensitive layer comprises a SiSb layer; wherein the SiAs layer is used to represent a silicon material containing As; the SiP layer is used to represent a silicon material containing P; and the SiSb layer is used to represent a silicon material containing Sb. The atomic mass of the pentavalent element is higher than that of silicon, and the mobility is lower in epitaxial growth, which causes the doping concentration to be uneven in a single doped layer. Growing different doped pentavalent elements in multiple times can improve the uniformity of the doping concentration in the pixel area.

[0102] Please continue to refer to Figure 11 The back-illuminated image sensor and the preparation method thereof in the embodiments of the present disclosure have the following unexpected technical effects:

[0103] Since the photodiode structure 200 comprises the outer layer sub-photosensitive layer, the middle layer sub-photosensitive layer and the inner layer sub-photosensitive layer which are all N-type and are sequentially stacked from outside to inside; the middle layer sub-photosensitive layer covers the top surface, the bottom surface and the side surface of the inner layer sub-photosensitive layer; the outer layer sub-photosensitive layer covers the top surface, the bottom surface and the side surface of the middle layer sub-photosensitive layer; the outer layer sub-photosensitive layer, the middle layer sub-photosensitive layer and the inner layer sub-photosensitive layer generate a concentration gradient in the interior thereof after being excited by light, optimize the transmission path of the photo-generated carriers, reduce the recombination rate in the diffusion process, and improve the quantum efficiency of the photodiode; the multi-layer wrapping structure from outside to inside forms a light electron storage container; the target size of the top 50 of the photodiode structure gradually decreases in the direction away from the substrate 10, the target size is the size in the first direction, to form a light focusing effect similar to a convex lens, the incident light is converged and transmitted into the photodiode structure 200, improving the photoelectric conversion efficiency of the photodiode; the target size of the bottom 30 of the photodiode structure gradually decreases in the second direction, to further increase the spacing between the bottom ends of adjacent photodiode structures 200, increase the mutual inductance between adjacent photodiode structures 200, and reduce the probability of generating leakage current.

[0104] It should be understood that although Figure 1 The steps in the flowchart of the method are shown in sequence according to the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, the execution of these steps is not strictly limited in sequence, and these steps can be executed in other orders. Moreover, Figure 1 At least part of the steps in the method can include multiple steps or stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily sequential, but can be alternately or alternately executed with at least part of other steps or steps or stages in other steps.

[0105] The technical features of the above-mentioned embodiments can be combined in any way. In order to make the description simple, all possible combinations of the technical features of the above-mentioned embodiments are not described, but as long as the combination of these technical features does not exist contradictory, it should be considered as the scope of the present disclosure.

[0106] The above-mentioned embodiments only express several implementation manners of the present disclosure, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the application. It should be noted that for those skilled in the art, without departing from the concept of the present disclosure, a number of modifications and improvements can be made, which are within the scope of protection of the present disclosure.

Claims

1. A back-illuminated image sensor, characterized in that, include: A P-type substrate, the back side of which includes a P-type epitaxial layer; A plurality of photodiode structures are spaced apart along a first direction parallel to the back surface, and extend through the P-type epitaxial layer along a second direction close to the substrate, reaching the back surface. Each photodiode structure includes an outer sub-photosensitive layer, a middle sub-photosensitive layer, and an inner sub-photosensitive layer, all of which are N-type and stacked sequentially from the outside in. The middle sub-photosensitive layer covers the top, bottom, and side surfaces of the inner sub-photosensitive layer. The outer sub-photosensitive layer covers the top, bottom, and side surfaces of the middle sub-photosensitive layer. The bottom target size of the photodiode structure gradually decreases along the second direction, and the top target size of the photodiode structure gradually decreases along the direction away from the substrate. The target size is the size along the first direction. A grid layer covers the top of the plurality of photodiode structures.

2. The back-illuminated image sensor according to claim 1, characterized in that, The P-type epitaxial layer includes a first P-type sub-epitaxial layer adjacent to the substrate; The bottom of the photodiode structure comprises, from the outside to the inside, the bottom of the outer sub-photosensitive layer, the bottom of the middle sub-photosensitive layer, and the bottom of the inner sub-photosensitive layer.

3. The back-illuminated image sensor according to claim 2, characterized in that, The P-type epitaxial layer includes a second sub-epitaxial layer of the P-type, and the second sub-epitaxial layer is located on the top surface of the first sub-epitaxial layer; The photodiode structure includes a middle section located between the bottom and the top of the photodiode structure; The photodiode structure comprises, from the outside to the inside, the following layers stacked sequentially: the middle of the outer sub-photosensitive layer, the middle of the middle sub-photosensitive layer, and the middle of the inner sub-photosensitive layer; The middle sub-photosensitive layer is circumferentially surrounded by the middle part of the inner sub-photosensitive layer, and the middle part of the outer sub-photosensitive layer is circumferentially surrounded by the middle sub-photosensitive layer; The middle part of the inner sub-photosensitive layer is located directly above the bottom of the inner sub-photosensitive layer; The middle part of the intermediate sub-photosensitive layer is located directly above the bottom of the intermediate sub-photosensitive layer; The middle part of the outer sub-photosensitive layer is located directly above the bottom of the outer sub-photosensitive layer.

4. The back-illuminated image sensor according to claim 3, characterized in that, The top of the photodiode structure comprises, from the outside to the inside, the top of the outer sub-photosensitive layer, the top of the middle sub-photosensitive layer, and the top of the inner sub-photosensitive layer; The grid layer includes a top grid layer and grid stacks located between the photodiode structures; The top surface of the grid stack is lower than the top surface of the outer sub-photosensitive layer; The top grid layer covers the top surface of the grid stack; The top grid layer includes grooves spaced apart along the first direction, and the grooves are located directly above the photodiode structure; The groove is used to set the filter.

5. The back-illuminated image sensor according to any one of claims 1-4, characterized in that, The P-type substrate includes a plurality of trench isolation portions spaced apart along the first direction; The plurality of trench isolation sections and the plurality of photodiode structures are arranged alternately along the first direction.

6. The back-illuminated image sensor according to any one of claims 1-4, characterized in that, The outer sub-photosensitive layer comprises a SiP layer; the middle sub-photosensitive layer comprises a SiAs layer; and the inner sub-photosensitive layer comprises a SiSb layer. Among them, the SiAs layer is used to characterize silicon materials containing As; the SiP layer is used to characterize silicon materials containing P; and the SiSb layer is used to characterize silicon materials containing Sb.

7. A method for fabricating a back-illuminated image sensor, characterized in that, include: P-type substrates are provided; A P-type epitaxial layer is formed on the back side of the P-type substrate. The P-type epitaxial layer includes a plurality of initial photodiode structures that are spaced apart along a first direction parallel to the back side of the substrate and extend through the P-type epitaxial layer and to the back side of the substrate along a second direction close to the substrate. The bottom target size of the initial photodiode structure gradually decreases along the second direction, and the target size is the size along the first direction. During the formation of the grid layer, multiple diode tops are formed directly above the multiple initial photodiode structures, and the grid layer covers the multiple diode tops; the target size of the multiple diode tops gradually decreases in the direction away from the substrate; the initial photodiode structures and the diode tops together constitute a photodiode structure; the photodiode structure includes an outer sub-photosensitive layer, a middle sub-photosensitive layer, and an inner sub-photosensitive layer, all of which are N-type and stacked sequentially from the outside to the inside; the middle sub-photosensitive layer covers the top, bottom, and side surfaces of the inner sub-photosensitive layer; the outer sub-photosensitive layer covers the top, bottom, and side surfaces of the middle sub-photosensitive layer.

8. The method for fabricating a back-illuminated image sensor according to claim 7, characterized in that, The P-type epitaxial layer includes a first P-type sub-epitaxial layer adjacent to the substrate; A P-type epitaxial layer is formed on the back side of the P-type substrate, comprising: A first sub-epitaxial layer of P-type is formed on the back side of the P-type substrate. The first sub-epitaxial layer includes a plurality of grooves spaced apart along a first direction parallel to the back side of the substrate. The target size of the grooves gradually decreases along a second direction close to the substrate. The target size is the size along the first direction. The bottom of the photodiode structure, which is formed in an N-type pattern within each of the plurality of grooves, comprises, from the outside to the inside, the bottom of the outer sub-photosensitive layer, the bottom of the middle sub-photosensitive layer, and the bottom of the inner sub-photosensitive layer.

9. The method for fabricating a back-illuminated image sensor according to claim 8, characterized in that, The P-type epitaxial layer includes a second sub-epitaxial layer of the P-type, and the second sub-epitaxial layer is located on the top surface of the first sub-epitaxial layer; A P-type epitaxial layer is formed on the back side of the P-type substrate, comprising: A second sub-epilithography layer is formed on the top surface of the first sub-epilithography layer, and the second sub-epilithography layer includes a plurality of vias that expose the bottom of the photodiode structure; The photodiode structure is formed in the middle of each of the plurality of through holes. The middle of the photodiode structure includes, from the outside to the inside, the middle of the outer sub-photosensitive layer, the middle of the middle sub-photosensitive layer, and the middle of the inner sub-photosensitive layer.

10. The method for fabricating a back-illuminated image sensor according to claim 9, characterized in that, Forming the grid layer includes: An initial grid stack is formed on the top surface of the P-type epitaxial layer, and the initial grid stack includes a plurality of first holes that expose the middle part of a plurality of inner sub-photosensitive layers; The top of a plurality of inner sub-photosensitive layers is formed within the plurality of first holes; The initial grid stack is etched to expose multiple second holes in the middle of multiple intermediate sub-photosensitive layers; The top of the middle sub-photosensitive layer is formed within the plurality of second holes, and the top of the middle sub-photosensitive layer covers the top of the inner sub-photosensitive layer; The initial grid stack is etched to expose multiple third holes in the middle of multiple outer sub-photosensitive layers; The top of the outer sub-photosensitive layer is formed within the plurality of third holes, and the top of the outer sub-photosensitive layer covers the top of the middle sub-photosensitive layer.

Images