Method for preparing back-illuminated image sensor and back-illuminated image sensor

Abstract

The present application relates to a method for preparing a back-illuminated image sensor and the back-illuminated image sensor, comprising: providing a substrate, the substrate comprising a substrate, a plurality of first isolation structures arranged at intervals on a first surface of the substrate, and a plurality of second isolation structures located in the substrate and arranged corresponding to the first isolation structures; etching the substrate based on the first isolation structures to form a plurality of grooves in the substrate between the first isolation structures; forming an isolation layer at least on the inner sidewalls and the bottom surface of the grooves; forming a photosensitive stack on the isolation layer; wherein the isolation layer surrounds the surface of the photosensitive stack in contact with the substrate, and the plane where the top surface of the photosensitive stack is located is located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located, thereby expanding the space of the photosensitive area formed by the photosensitive stack, increasing the electron concentration of the photosensitive area, and improving the photosensitivity of the BSI image sensor.

Description

Technical Field

[0001] The present application relates to the technical field of integrated circuits, and in particular to a method for preparing a back-illuminated image sensor and the back-illuminated image sensor. Background Art

[0002] Backside illumination (BSI) image sensor is a type of image sensor. In low light conditions, BSI image sensor has better performance than front-illuminated image sensor.

[0003] However, the photosensitivity of BSI image sensors manufactured by the existing BSI image sensor preparation methods cannot meet actual needs. Therefore, how to improve the photosensitivity of BSI image sensors has become one of the technical problems that urgently need to be solved. Summary of the invention

[0004] Based on this, it is necessary to provide a method for preparing a back-illuminated image sensor and a back-illuminated image sensor to address the problem of insufficient photosensitivity of BSI image sensors in the prior art.

[0005] In a first aspect, the present application provides a method for preparing a back-illuminated image sensor, comprising:

[0006] Providing a substrate, the substrate comprising a substrate, a plurality of first isolation structures arranged at intervals on a first surface of the substrate, and a plurality of second isolation structures arranged in the substrate corresponding to the first isolation structures;

[0007] Etching the substrate based on the first isolation structures to form a plurality of trenches in the substrate between the first isolation structures;

[0008] forming an isolation layer at least on the inner sidewall and bottom surface of the groove;

[0009] A photosensitive stack is formed on the isolation layer; wherein the isolation layer surrounds the surface of the photosensitive stack in contact with the substrate, and the plane where the top surface of the photosensitive stack is located is located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located.

[0010] In one embodiment, forming an isolation layer at least on the inner sidewall and bottom surface of the trench comprises:

[0011] The isolation layer is formed on the inner sidewall and bottom surface of the trench by a selective epitaxial deposition process.

[0012] In one embodiment, the photosensitive stack includes a first photosensitive layer, a second photosensitive layer and a third photosensitive layer; and forming the photosensitive stack on the isolation layer includes:

[0013] forming the first photosensitive layer on the isolation layer; the first photosensitive layer fills the remaining space of the groove, and the top surface of the first photosensitive layer is flush with the first surface of the substrate;

[0014] forming the second photosensitive layer on the first photosensitive layer and the isolation layer;

[0015] The third photosensitive layer is formed on the second photosensitive layer; wherein the plane where the top surface of the third photosensitive layer is located is located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located; the materials of the first photosensitive layer, the second photosensitive layer and the third photosensitive layer are different, and each includes one of the VA group elements.

[0016] In one embodiment, the longitudinal cross-section of the trench is rectangular; etching the substrate based on the first isolation structure to form a plurality of trenches in the substrate between the first isolation structures comprises:

[0017] Based on the first isolation structure, etching the substrate within a first preset time using carbon tetrafluoride;

[0018] The substrate etched by the carbon tetrafluoride is etched by using trifluoromethane within a second preset time to form the plurality of grooves.

[0019] In a second aspect, the present application provides a back-illuminated image sensor, comprising:

[0020] A substrate, the substrate comprising a substrate, a plurality of first isolation structures arranged at intervals on a first surface of the substrate, and a plurality of second isolation structures arranged in the substrate corresponding to the first isolation structures;

[0021] A plurality of trenches are located in the substrate between the first isolation structures;

[0022] an isolation layer, covering at least the inner sidewall and bottom surface of the groove;

[0023] A photosensitive stack is located on the isolation layer; wherein the isolation layer surrounds the surface of the photosensitive stack in contact with the substrate, and the plane where the top surface of the photosensitive stack is located is located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located.

[0024] In one of the embodiments, the back-illuminated image sensor includes at least one of the following features:

[0025] The shape of the longitudinal section of the first isolation structure is a regular trapezoid;

[0026] The depth of the groove is between 2 microns and 2.5 microns;

[0027] The material of the isolation layer includes one of the elements of Group IIIA;

[0028] The thickness of the isolation layer is in the range of 5 nanometers to 10 nanometers.

[0029] In one embodiment, the photosensitive stack comprises:

[0030] a first photosensitive layer, located on the isolation layer; the first photosensitive layer fills the remaining space of the groove, and the top surface of the first photosensitive layer is flush with the first surface of the substrate;

[0031] a second photosensitive layer, located on the first photosensitive layer and the isolation layer;

[0032] A third photosensitive layer is located on the second photosensitive layer; wherein the plane where the top surface of the third photosensitive layer is located is located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located; the materials of the first photosensitive layer, the second photosensitive layer and the third photosensitive layer are different, and each includes one of the VA group elements.

[0033] In one of the embodiments, the back-illuminated image sensor includes at least one of the following features:

[0034] The thickness of the second photosensitive layer is comprised between 60 nanometers and 80 nanometers;

[0035] The thickness of the third photosensitive layer is in a range of 30 nanometers to 40 nanometers.

[0036] In one embodiment, the first isolation structure includes a first isolation layer, a second isolation layer, and a third isolation layer sequentially stacked along a direction perpendicular to the first surface.

[0037] In one of the embodiments, the back-illuminated image sensor includes at least one of the following features:

[0038] The material of the first isolation layer includes tantalum pentoxide;

[0039] The material of the second isolation layer includes aluminum;

[0040] The material of the third isolation layer includes titanium nitride;

[0041] The thickness of the first isolation layer is 30 nanometers to 50 nanometers;

[0042] The thickness of the second isolation layer is 150 nanometers to 200 nanometers;

[0043] The thickness of the third isolation layer is 30 nanometers to 50 nanometers.

[0044] The method for preparing the back-illuminated image sensor and the back-illuminated image sensor of the present application have the following unexpected effects:

[0045] The preparation method of a back-illuminated image sensor and the back-illuminated image sensor of the present application include: providing a substrate, the substrate including a substrate, a plurality of first isolation structures arranged at intervals on a first surface of the substrate, and a plurality of second isolation structures located in the substrate and arranged corresponding to the first isolation structures; etching the substrate based on the first isolation structures to form a plurality of grooves in the substrate between the first isolation structures; forming an isolation layer at least on the inner sidewalls and bottom surfaces of the grooves; forming a photosensitive stack on the isolation layer; wherein the isolation layer surrounds the surface of the photosensitive stack in contact with the substrate, and the plane where the top surface of the photosensitive stack is located is located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located. Compared with the method of forming a photosensitive stack by ion implantation, the present application provides a substrate, then etches the substrate based on the first isolation structure in the substrate, forms a plurality of grooves in the substrate, and then forms an isolation layer and a photosensitive stack in the grooves, thereby avoiding damage to the substrate caused by ion implantation, and by making the isolation layer surround the surface where the photosensitive stack contacts the substrate, electron crosstalk between the photosensitive areas is avoided, thereby improving the display quality of the BSI image sensor. In addition, the photosensitive stack not only fills the remaining space in the groove, but the plane where the top surface of the photosensitive stack is located is also located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located, thereby expanding the space of the photosensitive area formed by the photosensitive stack, increasing the electron concentration in the photosensitive area, and improving the photosensitivity of the BSI image sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] 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.

[0047] Figure 1 is a flow chart of a method for preparing a back-illuminated image sensor provided in an embodiment;

[0048] Figure 2 is a specific flow chart of step S102 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0049] Figure 3a is a schematic cross-sectional view of a structure obtained in step S102 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0050] Figure 3bis a schematic cross-sectional view of a structure obtained in step S102 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0051] Figure 4 is a schematic cross-sectional view of a structure obtained in step S104 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0052] Figure 5 is a schematic cross-sectional view of a structure obtained in step S108 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0053] Figure 6 is a specific flow chart of step S108 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0054] Figure 7 FIG. 4 is a schematic diagram of the structure of a back-illuminated image sensor provided in an embodiment.

[0055] Description of reference numerals:

[0056] 10. Substrate; 201. First material layer; 210. First isolation structure; 211. First isolation layer; 203. Second material layer; 213. Second isolation layer; 205. Third material layer; 215. Third isolation layer; 30. Second isolation structure; 40. Groove; 50. Isolation layer; 60. Photosensitive stack; 61. First photosensitive layer; 62. Second photosensitive layer; 63. Third photosensitive layer; 70. Filter; 80. Etch stop layer; 90. Interlayer dielectric layer. DETAILED DESCRIPTION

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that when the terms "consisting of" and / or "comprising" are used in this specification, the presence of the features, integers, steps, operations, elements and / or parts can be determined, but the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups is not excluded. At the same time, when used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0062] 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.

[0063] In an embodiment of the present application, the substrate may include a first surface located on the front side and a second surface located on the back side opposite to the front side. Ignoring the flatness of the top and bottom surfaces, the direction perpendicular to the top and bottom surfaces of the substrate (the thickness direction of the substrate) is defined as a third direction. A first direction and a second direction that intersect each other (e.g., are perpendicular to each other) are defined in the directions of the top and bottom surfaces of the substrate (i.e., the plane where the substrate is located). For example, the arrangement direction of the first isolation structure is the first direction, and the plane where the substrate is located can be determined based on the first direction and the second direction. Among them, the first direction, the second direction, and the third direction may be perpendicular to each other. In an embodiment of the present application, the first direction is defined as the Y-axis direction, the second direction is defined as the X-axis direction, and the third direction is defined as the Z-axis direction.

[0064] Please refer to Figure 1 The present application provides a method for preparing a back-illuminated image sensor, comprising: step S102 to step S108.

[0065] Step S102: providing a substrate, the substrate comprising a substrate, a plurality of first isolation structures arranged at intervals on a first surface of the substrate, and a plurality of second isolation structures arranged in the substrate corresponding to the first isolation structures.

[0066] As an example, the substrate can be made of semiconductor material, insulating material, conductor material or any combination thereof. The substrate can be a single-layer structure or a multi-layer structure. 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. Alternatively, for example, the substrate can be a layered substrate including Si / SiGe, Si / SiC, silicon on insulator (SOI) or silicon germanium on insulator. Therefore, the type of substrate should not limit the scope of protection of the present disclosure.

[0067] Among them, the first isolation structure is used to isolate electrons and light energy, and the second isolation structure is used to isolate doped ions, electrons, etc. As an example, the shape of the longitudinal section of the first isolation structure (the section parallel to the ZOY plane) may include a regular trapezoid, an inverted trapezoid, a rectangle, etc., or it may also be a combination of a regular trapezoid, an inverted trapezoid, a rectangle, etc. The shape of the longitudinal section of the second isolation structure may include a regular trapezoid, an inverted trapezoid, a rectangle, etc., or it may also be a combination of a regular trapezoid, an inverted trapezoid, a rectangle, etc. This application does not impose specific restrictions on the shape, material, and size of the first isolation structure and the second isolation structure, as long as they can isolate electrons, light energy, and doped ions. In addition, this embodiment does not impose specific restrictions on the distance between adjacent first isolation structures, and can be set according to actual needs.

[0068] Step S104: etching the substrate based on the first isolation structures to form a plurality of trenches in the substrate between the first isolation structures.

[0069] Wherein, a trench is included in the substrate between two adjacent first isolation structures. As an example, the substrate can be etched by using an etching process such as dry etching or wet etching. In other embodiments, the etching process can be selected according to actual needs, as long as the selective etching of the substrate and the first isolation structure can be ensured.

[0070] As an example, the shape of the longitudinal section of the groove may include a regular trapezoid, an inverted trapezoid, a rectangle, etc., or may also be a combination of the regular trapezoid, the inverted trapezoid, the rectangle, etc. In other embodiments, it can be set according to actual needs.

[0071] Step S106: forming an isolation layer at least on the inner sidewall and bottom surface of the trench.

[0072] Among them, the isolation layer is used to isolate light energy and electrons.

[0073] Step S108: forming a photosensitive stack on the isolation layer; wherein the isolation layer surrounds the surface of the photosensitive stack in contact with the substrate, and the plane where the top surface of the photosensitive stack is located is located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located.

[0074] The structure of the back-illuminated image sensor obtained after steps S102-S108 can be found in Figure 5 Of course, in order to facilitate the understanding of this application, Figure 5 An example of a back-illuminated image sensor prepared by the method for preparing a back-illuminated image sensor of the present application is given. There may be other suitable examples of a back-illuminated image sensor prepared by the method for preparing a back-illuminated image sensor of the present application, and the present application does not limit them herein.

[0075] In the above embodiment, a substrate is provided, the substrate includes a substrate, a plurality of first isolation structures arranged at intervals on a first surface of the substrate, and a plurality of second isolation structures located in the substrate and arranged corresponding to the first isolation structures; the substrate is etched based on the first isolation structures to form a plurality of grooves in the substrate between the first isolation structures; an isolation layer is formed at least on the inner sidewalls and the bottom surface of the grooves; a photosensitive stack is formed on the isolation layer; wherein the isolation layer surrounds the surface of the photosensitive stack in contact with the substrate, and the top surface of the photosensitive stack is located between the first surface of the substrate and the top surface of the first isolation structure. Compared with forming the photosensitive stack by ion implantation, the present embodiment provides a substrate and then The substrate is then etched based on the first isolation structure in the base to form a plurality of grooves in the substrate, and then an isolation layer and a photosensitive stack are formed in the grooves to avoid damage to the substrate caused by ion implantation. The isolation layer surrounds the surface where the photosensitive stack contacts the substrate to avoid crosstalk between electrons in each photosensitive area, thereby improving the display quality of the BSI image sensor. In addition, the photosensitive stack not only fills the remaining space in the groove, but the height of the top surface of the photosensitive stack is also between the first surface of the substrate and the top surface of the first isolation structure, thereby expanding the space of the photosensitive area formed by the photosensitive stack, increasing the electron concentration in the photosensitive area, and improving the photosensitivity of the BSI image sensor.

[0076] Please refer to Figure 2 In one embodiment, step S102, providing a substrate, includes: steps S202-S210.

[0077] Step S202: providing a substrate.

[0078] As an example, the thickness of the substrate ranges from 2.8 microns to 3.2 microns, such as 2.8 microns, 2.9 microns, 3.0 microns, 3.1 microns, 3.2 microns, etc.

[0079] Step S204: forming a first material layer, a second material layer and a third material layer stacked in sequence on the first surface along a direction perpendicular to the first surface of the substrate.

[0080] Please refer to Figure 3a , wherein the first material layer 201 is used to isolate electrons to prevent them from migrating to adjacent photosensitive areas, and the second material layer 203 and the third material layer 205 are used to isolate electrons and improve light reflection and refraction, thereby focusing light to the photosensitive area. As an example, the material of the first material layer 201 may include tantalum oxide (Ta2O5), the material of the second material layer 203 may include a metal material, such as aluminum (Al), and the material of the third material layer 205 may include titanium nitride (TiN).

[0081] As an example, the thickness of the first material layer 201 may include 30 nanometers to 50 nanometers, for example: 30 nanometers, 35 nanometers, 40 nanometers, 45 nanometers, 50 nanometers, etc. The thickness of the second material layer 203 may include 150 nanometers to 200 nanometers, for example: 150 nanometers, 160 nanometers, 170 nanometers, 180 nanometers, 190 nanometers, 200 nanometers, etc. The thickness of the third material layer 205 is 30 nanometers to 50 nanometers, for example: 30 nanometers, 35 nanometers, 40 nanometers, 45 nanometers, 50 nanometers, etc.

[0082] Step S206: etching the first material layer, the second material layer and the third material layer to form a plurality of first isolation structures arranged at intervals.

[0083] Please refer to Figure 3b As an example, the first material layer, the second material layer and the third material layer can be etched by combining photolithography and dry etching to form a plurality of first isolation structures 210. The shape of the longitudinal section of the first isolation structure 210 can be a regular trapezoid, and the distance between the symmetry axes of two adjacent first isolation structures 210 is 500 nanometers to 700 nanometers, such as 500 nanometers, 550 nanometers, 600 nanometers, 650 nanometers, 700 nanometers, etc. In the above example, the larger the interval between two adjacent first isolation structures 210, the larger the photosensitive area of ​​the BSI image sensor, that is, the better the photosensitivity of the BSI image sensor, but too large an interval will result in too large pixels and reduced resolution. By setting the distance between the symmetry axes of two adjacent first isolation structures 210 to 500 nanometers to 700 nanometers, when the thickness of the substrate 10 and the thickness of the first isolation structure 210 are within the range of this embodiment, the photosensitivity of the BSI image sensor can be improved while ensuring the resolution.

[0084] Step S208: etching the second surface of the substrate to form a plurality of isolation grooves; the plurality of isolation grooves are arranged corresponding to the first isolation structure.

[0085] The first surface and the second surface of the substrate are arranged opposite to each other along the thickness direction of the substrate.

[0086] Step S210 : forming an isolation material in a plurality of isolation trenches to form a plurality of second isolation structures.

[0087] Please continue to refer to Figure 3bAs an example, the shape of the longitudinal section of the second isolation structure 30 may be a right trapezoid, the bottom surface of the right trapezoid is flush with the second surface of the substrate 10, and the material of the second isolation structure 30 may include oxide. In addition, the method for preparing the back-illuminated image sensor also includes: forming an etch stop layer 80 and an interlayer dielectric layer 90 on the second surface of the substrate 10; wherein the etch stop layer 80 is used to avoid damaging the substrate 10 when etching the through hole, and the interlayer dielectric layer 90 covers the etch stop layer 80 and is used to isolate the substrate 10 and the subsequently formed metal interconnect layer (not shown).

[0088] In one embodiment, the shape of the longitudinal cross-section of the groove is a rectangle; step S104, etching the substrate based on the first isolation structure to form a plurality of grooves in the substrate between each first isolation structure, including: based on the first isolation structure, using carbon tetrafluoride to etch the substrate within a first preset time, and using trifluoromethane to etch the substrate after carbon tetrafluoride etching within a second preset time to form a plurality of grooves.

[0089] As an example, the first preset time may include 30S-40S, for example, 30S, 33S, 35S, 37S, 40S, etc., and the second preset time may include 35S-45S, for example, 35S, 37S, 40S, 43S, 45S, etc. A carrier gas, for example, an inert gas such as nitrogen, may be introduced into the reaction chamber including the back-illuminated image sensor, and then carbon tetrafluoride is introduced into the reaction chamber, and the gas flow rate of carbon tetrafluoride may include 100 standard cubic centimeter per minute (SCCM). After 35S, the introduction of carbon tetrafluoride is stopped, and then trifluoromethane is introduced into the reaction chamber, and the gas flow rate of trifluoromethane may include 60SCCM. After 40S, the introduction of trifluoromethane is stopped to form a groove.

[0090] Please refer to Figure 4 , wherein the longitudinal section is a section parallel to the ZOY plane. As an example, the depth of the groove 40 may include 2 micrometers to 2.5 micrometers, such as 2.1 micrometers, 2.2 micrometers, 2.3 micrometers, 2.4 micrometers, 2.5 micrometers, etc.

[0091] In the above embodiment, by first using carbon tetrafluoride to etch the substrate within a first preset time, and then using trifluoromethane to etch the substrate after carbon tetrafluoride etching within a second preset time, the verticality of the side wall of the groove can be improved, so that the shape of the longitudinal section of the groove is rectangular, thereby increasing the area of ​​the photosensitive region while ensuring that the thickness of the substrate between two adjacent photosensitive regions is greater than a certain thickness, thereby avoiding mutual interference between electrons in the two photosensitive regions.

[0092] In one embodiment, step S106, forming an isolation layer at least on the inner sidewall and bottom surface of the trench, includes: forming the isolation layer on the inner sidewall and bottom surface of the trench using a selective epitaxial deposition process.

[0093] Please refer to Figure 5 As an example, the material of the isolation layer 50 may include one of the elements of Group IIIA, such as boron, and the isolation layer 50 may be SiB. The thickness of the isolation layer 50 may include 5 nanometers to 10 nanometers, such as 5 nanometers, 6 nanometers, 7 nanometers, 8 nanometers, 9 nanometers, 10 nanometers, etc. When SiB is deposited by a selective epitaxial deposition process, SiB will only form a crystal nucleus on the exposed surface of the substrate, that is, SiB will only be formed on the inner sidewall and bottom surface of the groove 40.

[0094] In the above embodiment, compared with the process of forming an isolation layer in the substrate on the side wall and the bottom of the groove respectively, a selective epitaxial deposition process is used to directly form an integrally formed isolation layer 50 on the inner side wall and the bottom of the groove, and the isolation layer 50 surrounds the surface where the photosensitive stack 60 contacts the substrate 10, which can improve the isolation effect and save a process step, thereby simplifying the process of the isolation layer 50.

[0095] Please refer to Figure 6 In one embodiment, the photosensitive stack includes a first photosensitive layer, a second photosensitive layer and a third photosensitive layer; the materials of the first photosensitive layer, the second photosensitive layer and the third photosensitive layer are different, and each includes one of the VA group elements; step S108, forming a photosensitive stack on the isolation layer, including: steps S602-step S606.

[0096] Step S602: forming a first photosensitive layer on the isolation layer; the first photosensitive layer fills the remaining space of the groove, and the top surface of the first photosensitive layer is flush with the first surface of the substrate.

[0097] As an example, please refer to Figure 5 The material of the first photosensitive layer 61 may include one of the VA group elements, such as nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi) and magnesium (Mc), etc. Specifically, the first photosensitive layer 61 may be SiP. The thickness of the first photosensitive layer 61 is related to the depth of the groove and the thickness of the isolation layer 50. Therefore, the thickness of the isolation layer 50 needs to be guaranteed to meet the isolation requirements, and the thickness of the isolation layer 50 cannot be too thick to occupy the space of the first photosensitive layer 61.

[0098] Step S604: forming a second photosensitive layer on the first photosensitive layer and the isolation layer.

[0099] As an example, please refer to Figure 5The material of the second photosensitive layer 62 includes one of the VA group elements, for example, the second photosensitive layer 62 may include SiAs. The thickness of the second photosensitive layer 62 is 60 nanometers to 80 nanometers, for example, 60 nanometers, 65 nanometers, 70 nanometers, 75 nanometers, 80 nanometers, etc.

[0100] Step S606: forming a third photosensitive layer on the second photosensitive layer; wherein a top surface of the third photosensitive layer is located between the first surface of the substrate and a top surface of the first isolation structure.

[0101] As an example, please refer to Figure 5 The third photosensitive layer 63 may include SiSb. The thickness of the third photosensitive layer 63 may include 30 nanometers to 40 nanometers, for example, 30 nanometers, 33 nanometers, 35 nanometers, 37 nanometers, 38 nanometers, 40 nanometers, etc.

[0102] As an example, the first photosensitive layer 61 , the second photosensitive layer 62 and the third photosensitive layer 63 may be formed by a selective epitaxial deposition process, thereby avoiding the formation of voids in the first photosensitive layer 61 due to a large aspect ratio of the groove.

[0103] In the above embodiment, the first photosensitive layer fills the remaining space of the groove, and then the second photosensitive layer and the third photosensitive layer are sequentially formed on the first photosensitive layer and the isolation layer, and the top surface height of the third photosensitive layer is located between the first surface and the top surface of the first isolation structure, thereby expanding the area of ​​the photosensitive region, and the first isolation structure and the isolation layer can block electrons between the photosensitive regions, thereby avoiding electrical crosstalk between adjacent photosensitive regions.

[0104] In one embodiment, after step S108, the method further includes: forming a filter on the photosensitive stack.

[0105] As an example, see Figure 7 The filters 70 include but are not limited to red filters, yellow filters, blue filters, etc., and the three filters are arranged adjacent to form a pixel group. The red filter transmits red light waves, the yellow filter transmits yellow light waves, and the blue filter transmits blue light waves.

[0106] It should be understood that although Figure 1 , Figure 2 and Figure 6 The steps in the flowchart are shown in sequence as indicated by the arrows, but these 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 these steps, and these steps can be executed in other orders. Moreover, Figure 1 , Figure 2 and Figure 6At least part of the steps may include multiple steps or multiple stages. These steps or stages are not necessarily performed at the same time, but can be performed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed in turn or alternately with other steps or at least part of the steps or stages in other steps.

[0107] In one embodiment, the present application also provides a back-illuminated image sensor, comprising: a substrate, a plurality of grooves, an isolation layer and a photosensitive stack; wherein the substrate comprises a substrate, a plurality of first isolation structures arranged at intervals on a first surface of the substrate, and a plurality of second isolation structures arranged in the substrate corresponding to the first isolation structures, and the top surface of the second isolation structure is flush with the second surface of the substrate; a plurality of grooves are located in the substrate between the first isolation structures; the isolation layer at least covers the inner side walls and the bottom surface of the grooves; the photosensitive stack is located on the isolation layer; wherein the isolation layer surrounds the surface of the photosensitive stack in contact with the substrate, and the plane where the top surface of the photosensitive stack is located is between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located.

[0108] In the above embodiment, the isolation layer surrounds the surface where the photosensitive stack contacts the substrate, thereby avoiding crosstalk between electrons in each photosensitive area, thereby improving the display quality of the BSI image sensor. In addition, the photosensitive stack not only fills the remaining space of the groove, but the height of the top surface of the photosensitive stack is also between the first surface of the substrate and the top surface of the first isolation structure, thereby expanding the space of the photosensitive area formed by the photosensitive stack, increasing the electron concentration in the photosensitive area, and improving the photosensitivity of the BSI image sensor.

[0109] In one embodiment, a longitudinal cross-section of the first isolation structure is in the shape of a regular trapezoid.

[0110] In the above embodiment, by setting the shape of the longitudinal section of the first isolation structure to a regular trapezoid, the amount of light entering the photosensitive area can be increased. In addition, since the height of the top surface of the photosensitive stack is located between the first surface and the top surface of the first isolation structure, the first isolation structure with a regular trapezoidal longitudinal section can increase the distance between two adjacent photosensitive stacks to the greatest extent while increasing the amount of light entering, thereby enhancing the isolation performance of the first isolation structure.

[0111] In one embodiment, please continue to refer to Figure 7 The first isolation structure includes a first isolation layer 211, a second isolation layer 213 and a third isolation layer 215 sequentially stacked in a direction perpendicular to the first surface.

[0112] In one embodiment, the material of the first isolation layer includes tantalum pentoxide.

[0113] In one embodiment, the material of the second isolation layer includes aluminum.

[0114] In one embodiment, the material of the third isolation layer includes titanium nitride.

[0115] In one embodiment, the thickness of the first isolation layer is 30 nanometers to 50 nanometers.

[0116] In one embodiment, the thickness of the second isolation layer is 150 nanometers to 200 nanometers.

[0117] In one embodiment, the thickness of the third isolation layer is 30 nanometers to 50 nanometers.

[0118] In one embodiment, the depth of the trenches comprises 2 microns - 2.5 microns.

[0119] In one embodiment, the material of the isolation layer includes one of the Group IIIA elements.

[0120] In one embodiment, the thickness of the isolation layer is comprised between 5 nanometers and 10 nanometers.

[0121] In one embodiment, the photosensitive stack includes: a first photosensitive layer, a second photosensitive layer and a third photosensitive layer; the first photosensitive layer is located on the isolation layer; the first photosensitive layer fills the remaining space of the groove, and the top surface of the first photosensitive layer is flush with the first surface of the substrate; the second photosensitive layer is located on the first photosensitive layer and the isolation layer; the third photosensitive layer is located on the second photosensitive layer; wherein the top surface of the third photosensitive layer is located between the first surface of the substrate and the top surface of the first isolation structure; the materials of the first photosensitive layer, the second photosensitive layer and the third photosensitive layer are different, and each includes one of the VA group elements.

[0122] In one embodiment, the thickness of the second photosensitive layer is comprised between 60 nanometers and 80 nanometers.

[0123] In one embodiment, the thickness of the third photosensitive layer is comprised between 30 nanometers and 40 nanometers.

[0124] The method for preparing the back-illuminated image sensor and the back-illuminated image sensor of the present application have the following unexpected effects:

[0125] The preparation method of a back-illuminated image sensor and the back-illuminated image sensor of the present application include: providing a substrate, the substrate including a substrate, a plurality of first isolation structures arranged at intervals on a first surface of the substrate, and a plurality of second isolation structures located in the substrate and arranged corresponding to the first isolation structures; etching the substrate based on the first isolation structures to form a plurality of grooves in the substrate between the first isolation structures; forming an isolation layer at least on the inner sidewalls and bottom surfaces of the grooves; forming a photosensitive stack on the isolation layer; wherein the isolation layer surrounds the surface of the photosensitive stack in contact with the substrate, and the plane where the top surface of the photosensitive stack is located is located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located. Compared to forming a photosensitive stack by ion implantation, the present application provides a substrate, then etches the substrate based on the first isolation structure in the substrate, forms a plurality of grooves in the substrate, and then forms an isolation layer and a photosensitive stack in the grooves, thereby avoiding damage to the substrate caused by ion implantation, and by making the isolation layer surround the surface where the photosensitive stack contacts the substrate, avoiding crosstalk between electrons in each photosensitive area, thereby improving the display quality of the BSI image sensor. In addition, the photosensitive stack not only fills the remaining space in the groove, but the height of the top surface of the photosensitive stack is also between the first surface of the substrate and the top surface of the first isolation structure, thereby expanding the space of the photosensitive area formed by the photosensitive stack, increasing the electron concentration in the photosensitive area, and improving the photosensitivity of the BSI image sensor.

[0126] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features of the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0127] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A method for preparing a back-illuminated image sensor, characterized in that: include: Providing a substrate, the substrate comprising a substrate, a plurality of first isolation structures arranged at intervals on a first surface of the substrate, and a plurality of second isolation structures arranged in the substrate corresponding to the first isolation structures; Etching the substrate based on the first isolation structures to form a plurality of trenches in the substrate between the first isolation structures; forming an isolation layer at least on the inner sidewall and bottom surface of the groove; A photosensitive stack is formed on the isolation layer; wherein the isolation layer surrounds the surface of the photosensitive stack in contact with the substrate, and the plane where the top surface of the photosensitive stack is located is located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located.

2. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The step of forming an isolation layer at least on the inner sidewall and bottom surface of the trench comprises: The isolation layer is formed on the inner sidewall and bottom surface of the trench by a selective epitaxial deposition process.

3. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The photosensitive stack includes a first photosensitive layer, a second photosensitive layer and a third photosensitive layer; the photosensitive stack is formed on the isolation layer, including: forming the first photosensitive layer on the isolation layer; the first photosensitive layer fills the remaining space of the groove, and the top surface of the first photosensitive layer is flush with the first surface of the substrate; forming the second photosensitive layer on the first photosensitive layer and the isolation layer; The third photosensitive layer is formed on the second photosensitive layer; wherein the plane where the top surface of the third photosensitive layer is located is located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located; the materials of the first photosensitive layer, the second photosensitive layer and the third photosensitive layer are different, and each includes one of the VA group elements.

4. The method for preparing a back-illuminated image sensor according to any one of claims 1 to 3, characterized in that: The longitudinal cross-section of the groove is in a rectangular shape; the etching of the substrate based on the first isolation structure to form a plurality of grooves in the substrate between the first isolation structures comprises: Based on the first isolation structure, etching the substrate within a first preset time using carbon tetrafluoride; The substrate etched by the carbon tetrafluoride is etched by using trifluoromethane within a second preset time to form the plurality of grooves.

5. A back-illuminated image sensor, characterized in that: include: A substrate, the substrate comprising a substrate, a plurality of first isolation structures arranged at intervals on a first surface of the substrate, and a plurality of second isolation structures arranged in the substrate corresponding to the first isolation structures; A plurality of trenches are located in the substrate between the first isolation structures; an isolation layer, covering at least the inner sidewall and bottom surface of the groove; A photosensitive stack is located on the isolation layer; wherein the isolation layer surrounds the surface of the photosensitive stack in contact with the substrate, and the plane where the top surface of the photosensitive stack is located is located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located.

6. The back-illuminated image sensor according to claim 5, characterized in that: The back-illuminated image sensor includes at least one of the following features; The shape of the longitudinal section of the first isolation structure is a regular trapezoid; The depth of the groove is 2 microns to 2.5 microns; The material of the isolation layer includes one of the elements of Group IIIA; The thickness of the isolation layer is 5 nanometers to 10 nanometers.

7. The back-illuminated image sensor according to claim 5, characterized in that: The photosensitive stack comprises: a first photosensitive layer, located on the isolation layer; the first photosensitive layer fills the remaining space of the groove, and the top surface of the first photosensitive layer is flush with the first surface of the substrate; a second photosensitive layer, located on the first photosensitive layer and the isolation layer; A third photosensitive layer is located on the second photosensitive layer; wherein the plane where the top surface of the third photosensitive layer is located is located between the plane where the first surface of the substrate is located and the plane where the top surface of the first isolation structure is located; the materials of the first photosensitive layer, the second photosensitive layer and the third photosensitive layer are different, and each includes one of the VA group elements.

8. The back-illuminated image sensor according to claim 7, wherein: The back-illuminated image sensor includes at least one of the following features; The thickness of the second photosensitive layer is 60 nanometers to 80 nanometers; The thickness of the third photosensitive layer is 30 nanometers to 40 nanometers.

9. The back-illuminated image sensor according to claim 5, wherein: The first isolation structure includes a first isolation layer, a second isolation layer, and a third isolation layer sequentially stacked in a direction perpendicular to the first surface.

10. The back-illuminated image sensor according to claim 9, wherein: The back-illuminated image sensor includes at least one of the following features; The material of the first isolation layer includes tantalum pentoxide; The material of the second isolation layer includes aluminum; The material of the third isolation layer includes titanium nitride; The thickness of the first isolation layer is 30 nanometers to 50 nanometers; The thickness of the second isolation layer is 150 nanometers to 200 nanometers; The thickness of the third isolation layer is 30 nanometers to 50 nanometers.

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