Image sensor and manufacturing method thereof

Abstract

The invention provides an image sensor and a manufacturing method thereof. The image sensor comprises a substrate; a photodiode and a deep trench isolation structure which are arranged at intervals are arranged in the substrate; the composite dielectric stack layer is arranged on the substrate, and the composite dielectric stack layer comprises a first oxide layer, a high dielectric constant layer and a second oxide layer which are stacked; the optical gaps are arranged in the second oxide layers on the photodiodes, the optical gaps scatter incident light, and the propagation optical path of the incident light in the photodiodes is increased; the grating is arranged on the composite dielectric stack layer at the top of the deep trench isolation structure; and the light filtering structure is arranged on the composite dielectric stack layer at the top of the photodiode. According to the image sensor and the manufacturing method thereof provided by the invention, the response of the image sensor to near-infrared light can be improved, and the photoelectric conversion efficiency of the image sensor is enhanced.

Description

An image sensor and its fabrication method Technical Field

[0001] This invention belongs to the field of semiconductor device technology, and specifically relates to an image sensor and its manufacturing method. Background Technology

[0002] In semiconductor devices, CMOS image sensors (Complementary Metal Oxide Semiconductor Image Sensors, CIS) are widely used in various fields such as consumer electronics, surveillance, and industry due to their low power consumption and low cost. In specific applications, such as security and night vision in low-light scenarios, the near-infrared (NIR) response becomes crucial for the final image quality.

[0003] For silicon-based image sensors, the inherent physical properties of silicon result in relatively low conversion efficiency and response speed for near-infrared light. To improve this, techniques such as increasing the thickness of the silicon epitaxial layer or etching trenches on the silicon substrate surface can be used to increase the optical path length of near-infrared light passing through the filter and into the photodiode, thereby enhancing the image sensor's response to near-infrared light and ultimately improving its photoelectric conversion efficiency. However, increasing the thickness of the silicon epitaxial layer significantly increases the manufacturing cost of the image sensor and places higher demands on electrical design. Furthermore, etching trenches on the silicon substrate surface introduces defects, increasing dark current. Summary of the Invention

[0004] The purpose of this invention is to provide an image sensor and its manufacturing method, which can solve the problem of low photoelectric conversion efficiency of image sensors due to low conversion efficiency of near-infrared light.

[0005] To achieve the above objectives, the present invention provides an image sensor comprising at least:

[0006] A substrate in which spaced photodiodes and deep trench isolation structures are disposed;

[0007] A composite dielectric stack layer is disposed on the substrate, and the composite dielectric stack layer includes a stacked first oxide layer, a high dielectric constant layer, and a second oxide layer;

[0008] An optical gap is disposed in the second oxide layer on each of the photodiodes. The optical gap scatters the incident light and increases the optical path length of the incident light in the photodiode.

[0009] A grid is disposed on the composite dielectric stack layer atop the deep trench isolation structure; and

[0010] A filter structure is disposed on the composite dielectric stack layer on top of the photodiode.

[0011] In one embodiment of the present invention, in the second oxide layer on each of the photodiodes, the optical gap includes at least one columnar optical gap, and the radial dimension of the columnar optical gap first increases and then decreases in the thickness direction of the second oxide layer.

[0012] In one embodiment of the present invention, in the second oxide layer on each of the photodiodes, the optical gap includes at least one annular optical gap, and the radial dimension of the annular optical gap first increases and then decreases in the thickness direction of the second oxide layer.

[0013] In one embodiment of the present invention, when the second oxide layer on each photodiode includes two or more of the annular optical gaps, the annular optical gaps are concentrically arranged.

[0014] In one embodiment of the present invention, the optical gap in the second oxide layer on each photodiode includes:

[0015] A columnar optical gap, wherein the radial dimension of the columnar optical gap first increases and then decreases in the thickness direction of the second oxide layer; and

[0016] An annular optical gap surrounds the columnar optical gap, and the annular optical gap and the columnar optical gap are concentrically arranged. In the thickness direction of the second oxide layer, the radial dimension of the annular optical gap first increases and then decreases.

[0017] In one embodiment of the present invention, the image sensor further includes an isolation gap disposed in the second oxide layer on the deep trench isolation structure, and the radial dimension of the isolation gap first increases and then decreases in the thickness direction of the second oxide layer.

[0018] In one embodiment of the present invention, the image sensor is a back-illuminated image sensor or a front-illuminated image sensor. When the image sensor is a front-illuminated image sensor, a metal wiring layer is provided in the second oxide layer.

[0019] The present invention also provides a method for manufacturing an image sensor, comprising at least the following steps:

[0020] A substrate is provided, and spaced photodiodes and deep trench isolation structures are formed in the substrate;

[0021] A composite dielectric stack layer is formed on the substrate, and the composite dielectric stack layer includes a stacked first oxide layer, a high dielectric constant layer, and a second oxide layer;

[0022] During the formation of the second oxide layer, an optical gap is formed in the second oxide layer. The optical gap scatters the incident light, thereby increasing the optical path length of the incident light in the photodiode.

[0023] A grid is formed on the second oxide layer, and the grid is located on the composite dielectric stack layer on top of the deep trench isolation structure; and

[0024] A filter structure is formed on the second oxide layer, and the filter structure is located on the composite dielectric stack layer on top of the photodiode.

[0025] In one embodiment of the present invention, forming an optical gap in the second oxide layer during the formation of the second oxide layer includes the following steps:

[0026] A first sub-oxide layer of a first thickness is deposited on the high dielectric constant layer;

[0027] Etching the first sub-oxide layer to form a gap recess; and

[0028] A second sub-oxide layer of a second thickness is deposited on the first sub-oxide layer, and the gap recess is closed to form an optical gap with a radial dimension that first increases and then decreases.

[0029] In one embodiment of the present invention, the depth-to-width ratio of the recessed gap is greater than 3:1.

[0030] In summary, the image sensor and its fabrication method provided by this invention involve setting an optical gap in the oxide layer at the top of a photodiode. The interior of the optical gap is filled with air, and the refractive index of air is much lower than that of the oxide layer. Therefore, when light converges into the optical gap, scattering occurs, increasing the optical path length of incident light in the photodiode, thereby improving the image sensor's response to near-infrared light and enhancing its photoelectric conversion efficiency. Secondly, both columnar and annular optical gaps can increase the optical path length of incident light in the photodiode. Setting only one columnar optical gap at the center of the photodiode can reduce optical crosstalk between adjacent photodiodes. Setting multiple columnar optical gaps, multiple annular optical gaps, or simultaneously setting both columnar and annular optical gaps can maximize the refractive effect of the optical gaps. Furthermore, setting the columnar and annular optical gaps with smaller radial dimensions at both ends and a larger radial dimension in the middle, essentially creating a plane, can further increase the refractive surface of the optical gaps. Moreover, the relatively small thickness of the high-dielectric-constant layer and oxide layer in this application can reduce optical crosstalk between adjacent photodiodes. By creating an isolation gap in the oxide layer at the top of the deep trench isolation structure, optical crosstalk between adjacent photodiodes can be further suppressed. Therefore, the image sensor and its fabrication method provided in this application can improve the image sensor's response to near-infrared light and enhance its photoelectric conversion efficiency while reducing optical crosstalk between adjacent light-emitting diodes. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 is a schematic diagram of the structure forming the deep trench isolation structure, photodiode, first oxide layer and high dielectric constant layer in this invention.

[0033] Figure 2 is a schematic diagram of the structure for forming the first sub-oxide layer in one embodiment of the present invention.

[0034] Figure 3 is a schematic diagram of the structure forming the columnar optical gap recess and the annular optical gap recess in one embodiment of the present invention.

[0035] Figure 4 is a top view of the columnar optical gap recess and the annular optical gap recess in Figure 3 of the present invention.

[0036] Figure 5 is a schematic diagram of the structure for forming the second sub-oxide layer in one embodiment of the present invention.

[0037] Figure 6 is a schematic diagram of the structure forming the optical gap in one embodiment of the present invention.

[0038] Figure 7 is a schematic diagram of the structure forming the grating and filter structure in one embodiment of the present invention.

[0039] Figure 8 is a schematic diagram of an image sensor with an isolation gap and an optical gap in one embodiment of the present invention.

[0040] Figure 9 is a top view of the isolation gap and optical gap formed in Figure 8 of the present invention.

[0041] Figure 10 is a schematic diagram of the structure of an image sensor with only a columnar optical gap in one embodiment of the present invention.

[0042] Figure 11 is a top view of the columnar optical gap formed in Figure 10 of the present invention.

[0043] Figure 12 is a schematic diagram of a front-illuminated image sensor with an optical gap in one embodiment of the present invention.

[0044] Figure 13 is a top view of the optical gap formed in Figure 12 of this invention. Detailed Implementation

[0045] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0046] 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 application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0047] In the description of this invention, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," and "right," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0048] A CMOS image sensor is a typical solid-state imaging sensor, typically comprising a pixel array, row drivers, column drivers, timing control logic, and an analog-to-digital converter (AD converter). These semiconductor devices are usually integrated onto a single silicon chip and are isolated from each other. The pixel array contains multiple photodiodes arranged in an array, each forming a pixel unit. When an image is focused onto the pixel array by an imaging lens, the photodiodes convert light signals from their surfaces into electrical signals. These electrical signals are then processed by the row drivers, column drivers, timing control logic, and AD converter, converting them into digital signals for readout.

[0049] CMOS image sensors have advantages such as small size, low power consumption, low price, and mass production, and hold a large market share in the image sensor field. This invention provides an image sensor and its fabrication method, which can increase the optical path length of incident light within a photodiode, enhance near-infrared response and photoelectric conversion efficiency, and solve the problem of poor near-infrared light response in photodiodes. Furthermore, the fabrication method of the image sensor provided by this invention can be applied to CMOS image sensors with different structures, including back-side illuminated (BSI) CMOS image sensors and front-side illuminated (FSI) CMOS image sensors.

[0050] Referring to Figures 7 to 13, the image sensor provided in this application includes a substrate 100, in which spaced photodiodes 101 and deep trench isolation structures 102 are disposed. A composite dielectric stack layer comprising a first oxide layer 103, a high dielectric constant layer 104, and a second oxide layer 105 is disposed on the substrate 100. An optical gap is also disposed in the second oxide layer 105, which scatters incident light, increasing the optical path length of the incident light in the photodiodes 101. A grid 107 and a filter structure are disposed on the second oxide layer 105, wherein the grid 107 is located on the composite dielectric stack layer on top of the deep trench isolation structure 102, and the filter structure is located on the composite dielectric stack layer on top of the photodiodes 101.

[0051] Specifically, as shown in Figure 1, in one embodiment of the present invention, the substrate 100 provided by the present invention can be any suitable silicon substrate, specifically monocrystalline silicon, polycrystalline silicon, silicon-on-insulator (SiI), silicon-on-insulator (SiI), silicon-germanium-on-insulator (SGE), silicon-germanium-on-insulator (SGE), etc. The material of the substrate 100 can be selected according to the fabrication requirements of the image sensor. In this embodiment, the substrate 100 is, for example, a monocrystalline silicon substrate, and specifically, an undoped monocrystalline silicon substrate.

[0052] Referring to Figure 1, in one embodiment of the present invention, a substrate 100 is provided with spaced photodiodes 101 and a deep trench isolation structure 102. The photodiodes 101 are disposed in the substrate 100, and each photodiode 101 extends from the surface of the substrate 100 into the substrate 100, converting optical signals into electrical signals. The deep trench isolation structure 102 is disposed between adjacent photodiodes 101, isolating adjacent photodiodes 101 and preventing visible light crosstalk between adjacent photodiodes 101. In some embodiments, the photodiodes 101 and the deep trench isolation structure 102 are spaced apart. In other embodiments, the edges of the photodiodes 101 and the edges of the deep trench isolation structure 102 are attached.

[0053] Please refer to Figure 1. This application does not limit the formation order of the photodiode 101 and the deep trench isolation structure. The photodiode 101 can be formed in the substrate 100 first and then the deep trench isolation structure 102 can be formed, or the deep trench isolation structure 102 can be formed first and then the photodiode 101 can be formed.

[0054] Referring to Figure 1, in one embodiment of the present invention, a substrate 100 is first etched to form multiple deep trenches (not shown in the figure). After forming the deep trenches, an isolation medium is deposited within the deep trenches to form multiple deep trench isolation structures 102. Specifically, photoresist can be coated on the surface of the substrate 100, and a patterned photoresist layer (not shown in the figure) can be formed through processes such as exposure and development. This patterned photoresist layer defines the location of the deep trenches. Then, using this patterned photoresist layer as a mask, a portion of the substrate 100 located under the patterned photoresist layer is quantitatively removed using etching methods such as dry etching, wet etching, or a combination of dry and wet etching to obtain the deep trenches. After forming the deep trenches, an isolation medium, such as silicon oxide or other insulating material, is deposited within the deep trenches. A planarization process, such as chemical mechanical polishing (CMP), is then used to flatten the top of the isolation medium, thereby forming multiple deep trench isolation structures 102.

[0055] Referring to Figure 1, in one embodiment of the present invention, after forming the substrate 100, ions are implanted in the substrate 100 between the deep trench isolation structures 102 to form a photodiode 101. This application does not limit the type of implanted ions; any desired device can be formed. In some embodiments, N-type ions, such as phosphorus ions or arsenic ions, can be implanted into the substrate 100 to form an N-type photodiode 101. In other embodiments, P-type ions, such as boron ions, can also be implanted into the substrate 100 to form a P-type photodiode 101. During the formation of the photodiode 101, to ensure the quality and shape of the photodiode 101 formed after ion implantation, multiple ion implantations at different angles can be performed to form a photodiode 101 conforming to a preset pattern.

[0056] Referring to Figures 1 and 2, in one embodiment of the present invention, a composite dielectric stack layer is disposed on a substrate 100, and the composite dielectric stack layer includes a first oxide layer 103, a high dielectric constant layer 104, and a second oxide layer 105. The first oxide layer 103 is disposed on the substrate 100 and covers the deep trench isolation structure 102 and the photodiode 101. The high dielectric constant layer 104 is disposed on the first oxide layer 103 and covers the first oxide layer 103. The second oxide layer 105 is disposed on the high dielectric constant layer 104 and covers the high dielectric constant layer 104. The first oxide layer 103 disposed on the substrate 100 can optimize the interface compatibility between the photodiode 101 and subsequent film layers and reduce defects. The high dielectric constant layer 104 has high dielectric constant and low leakage current characteristics, which can balance capacitance performance and power consumption. The second oxide layer 105 can be adapted to the subsequent filter structure fabrication process, providing a flat substrate and enhancing the adhesion of the filter structure.

[0057] Referring to Figures 1 and 2, in one embodiment of the present invention, the first oxide layer 103 is, for example, a silicon oxide layer, and the thickness of the first oxide layer 103 is, for example, 2 nm to 10 nm, specifically, for example, 3 nm, 5 nm, or 6 nm. Specifically, after forming the deep trench isolation structure 102 and the photodiode 101, a silicon oxide layer can be deposited on the surface of the substrate 100 as the first oxide layer 103 using a chemical vapor deposition method with tetraethoxysilane (TEOS) or silane as a precursor.

[0058] Referring to Figures 1 and 2, in one embodiment of the present invention, the high dielectric constant layer 104 is, for example, a composite dielectric layer of hafnium oxide (HfO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3), or a linear combination of HfO2-SiO2, and the thickness of the high dielectric constant layer 104 is, for example, 5 nm to 20 nm, specifically, 8 nm, 10 nm, 12 nm, or 15 nm. Specifically, after forming the first oxide layer 103, an atomic layer deposition (ALD) method can be used to deposit a layer of hafnium oxide (HfO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3), or HfO2-SiO2 stack on the first oxide layer 103 as the high dielectric constant layer 104.

[0059] Referring to Figures 2 and 6, in one embodiment of the present invention, the second oxide layer 105 is, for example, a silicon oxide layer, and the thickness of the second oxide layer 105 is, for example, 100 nm to 150 nm, specifically, for example, 120 nm, 130 nm, or 140 nm. An optical gap is provided in the second oxide layer 105 on each photodiode 101. The optical gap scatters incident light, increasing the optical path length of the incident light in the photodiode 101. In this application, the optical gap on each photodiode 101 includes one or both of a columnar optical gap 1053 and an annular optical gap 1054. Specifically, in the thickness direction of the second oxide layer 105, the columnar optical gap 1053 first increases and then decreases, while the radial dimension of the annular optical gap 1054 first increases and then decreases. Setting the radial dimension of the optical gap to first increase and then decrease causes the sidewalls of the optical gap to protrude, thereby increasing the scattering of incident light.

[0060] Referring to Figures 10 and 11, in one embodiment of the present invention, at least one columnar optical gap 1053 is provided in the second oxide layer 105 on each photodiode 101, that is, one, two, or more columnar optical gaps 1053 are provided in the second oxide layer 105 on each photodiode 101. When one columnar optical gap 1053 is provided in the second silicon oxide layer on each photodiode 101, the columnar optical gap 1053 is provided in the second oxide layer 105 at the center of the photodiode 101. That is, the orthogonal projection of the center of the columnar optical gap 1053 on the substrate 100 is located at the center of the photodiode 101. When two or more columnar optical gaps 1053 are provided in the second oxide layer 105 on each photodiode 101, the two or more columnar optical gaps 1053 are uniformly distributed in the second oxide layer 105 on each photodiode 101. In the thickness direction of the second oxide layer 105, the radial dimension of each columnar optical gap 1053 first increases and then decreases. Referring to Figure 10, in a cross-section perpendicular to the surface of the substrate 100, the shape of the columnar optical gap 1053 is, for example, elliptical. Referring to Figure 11, in a cross-section parallel to the surface of the substrate 100, the shape of the columnar optical gap 1053 is, for example, a circle with various radii.

[0061] Referring to Figures 4, 6, and 7, in another embodiment of the present invention, at least one annular optical gap 1054 is provided in the second oxide layer 105 of each photodiode 101, that is, one, two, or more annular optical gaps 1054 are provided in the second silicon oxide layer of each photodiode 101. When one annular optical gap 1054 is provided in the second oxide layer 105 of each photodiode 101, the annular optical gap 1054 is located in the second oxide layer 105 at the center of the photodiode 101. That is, the orthogonal projection of the center of the annular optical gap 1054 onto the substrate 100 is located at the center of the photodiode 101. When two or more annular optical gaps 1054 are provided in the second silicon oxide layer of each photodiode 101, the two or more annular optical gaps 1054 are concentrically arranged, and the orthogonal projection of the center of the annular optical gap 1054 onto the substrate 100 is located at the center of the photodiode 101. Furthermore, the spacing between adjacent annular optical gaps 1054 is set to be equal. Specifically, in the thickness direction of the second oxide layer 105, the radial dimension of each annular optical gap 1054 first increases and then decreases. Referring to Figure 4, in a cross-section parallel to the surface of the substrate 100, the shape of the annular optical gap 1054 is, for example, a ring of various ring widths. Referring to Figure 7, in a cross-section perpendicular to the surface of the substrate 100, the shape of the annular optical gap 1054 includes, for example, two ellipses, and the two ellipses are symmetrical about the center of the annular optical gap 1054.

[0062] Referring to Figures 4, 6, and 7, in another embodiment of the present invention, columnar optical gaps 1053 and annular optical gaps 1054 are provided in the second oxide layer 105 on each photodiode 101. Each photodiode 101 has one columnar optical gap 1053 and one, two, or more annular optical gaps 1054 in the second oxide layer 105. In this case, one columnar optical gap 1053 is disposed in the second oxide layer 105 at the center of the photodiode 101, and the annular optical gaps 1054 surround the columnar optical gap 1053, and are concentrically arranged with the columnar optical gaps 1053. Further, the spacing between the annular optical gaps 1054 and the columnar optical gaps 1053, as well as the spacing between adjacent annular optical gaps 1054, is set to be equal. In the thickness direction of the second oxide layer 105, the radial dimension of each columnar optical gap 1053 first increases and then decreases, and the radial dimension of each annular optical gap 1054 first increases and then decreases. Referring to Figure 4, in a cross-section parallel to the surface of the substrate 100, the columnar optical gap 1053 is, for example, a circle of various radii, and the annular optical gap 1054 is, for example, an annulus of various ring widths. Referring to Figure 7, in a cross-section perpendicular to the surface of the substrate 100, the columnar optical gap 1053 is, for example, an ellipse, and the annular optical gap 1054 comprises, for example, two ellipses, and the two ellipses in the cross-section of the annular optical gap 1054 are symmetrical about the center of the columnar optical gap 1053.

[0063] Referring to Figures 8 and 9, in one embodiment of the present invention, an isolation gap 1056 is further provided in the second oxide layer 105, and the isolation gap 1056 is located in the second oxide layer 105 on the deep trench isolation structure 102. The isolation gap 1056 surrounds the photodiode 101, and the radial dimension of the isolation gap 1056 first increases and then decreases in the thickness direction of the second oxide layer 105. Referring to Figure 8, in a cross-section perpendicular to the surface of the substrate 100, the shape of the isolation gap 1056 is, for example, elliptical. Referring to Figure 9, in a cross-section parallel to the surface of the substrate 100, the shape of the isolation gap 1056 is, for example, a rectangular ring of various ring widths.

[0064] In the embodiments shown in Figures 7 to 11, the image sensor is a back-illuminated CMOS image sensor, and the metal wiring layer of the back-illuminated CMOS image sensor is disposed on the other surface of the substrate 100 away from the composite dielectric stack layer. In the embodiments shown in Figures 12 and 13, the image sensor is a front-illuminated CMOS image sensor, in which case the metal wiring layer is disposed in the second oxide layer 105, and the metal wiring layer is located in the second oxide layer 105 on the deep trench isolation structure 102, so that the metal wiring layer does not interfere with the optical gap. In this case, the isolation gap 1056 can be omitted.

[0065] Please refer to Figures 7, 8, 10 and 12. An optical gap is provided in the oxide layer on the top of the photodiode 101. Compared with the optical path of the incident light when no optical gap is provided (yellow dashed line in the figure), the optical gap will scatter the incident light (purple dashed line in the figure), thereby increasing the propagation optical path of the incident light in the photodiode 101, thereby improving the response of the image sensor to near-infrared light and enhancing the photoelectric conversion efficiency of the image sensor.

[0066] Please refer to Figures 3 to 13. In one embodiment of the present invention, after forming a high dielectric constant layer 104, a second oxide layer 105 is formed on the high dielectric constant layer 104. When forming the second oxide layer 105, one or both of optical gaps and isolation gaps 1056 are formed in the second oxide layer 105.

[0067] Referring to Figure 3, in one embodiment of the present invention, after forming the high dielectric constant layer 104, a first sub-oxide layer of a first thickness is deposited on the high dielectric constant layer 104. Specifically, tetraethoxysilane or silane can be used as a precursor, and a silicon oxide layer is deposited on the surface of the high dielectric constant layer 104 as the first sub-oxide layer using chemical vapor deposition. The thickness of the first sub-oxide layer is, for example, 90 nm to 120 nm, specifically, 90 nm, 100 nm, or 110 nm.

[0068] Referring to Figure 4, in one embodiment of the present invention, after forming the first sub-oxide layer, the first sub-oxide layer is etched to form a gap recess. Specifically, a dry etching method can be used to etch the first sub-oxide layer to form the gap recess within it. The gas used for dry etching is, for example, a fluorine-containing gas such as CF4, CHF3, or SF6. Fluorine-containing gases have a high etching selectivity for the first sub-oxide layer and several high-dielectric layers, which can avoid damage to the high-dielectric-constant layer 104. The bottom wall of the gap recess can contact the high-dielectric-constant layer 104, or the bottom wall of the gap recess can have a predetermined distance from the high-dielectric-constant layer 104. The aspect ratio of the gap recess is greater than 3:1, ensuring that the gap recess opening is closed during the subsequent deposition of the second sub-oxide layer, forming an optical gap or isolation gap 1056 with a radial dimension that first increases and then decreases.

[0069] Referring to Figures 3 and 4, and in conjunction with Figures 8 and 9, in one embodiment of the present invention, the gap recess may include one, two, or three of the following: a columnar optical gap recess 1051, an annular optical gap recess 1052, and an isolation gap recess 1055. The columnar optical gap recess 1051 may have a circular cross-section, for example; the annular optical gap recess 1052 may have a circular cross-section, for example; and the isolation gap recess 1055 may have a rectangular ring cross-section, for example.

[0070] Referring to Figures 10 and 11, when the gap recess only includes the columnar optical gap recess 1051, a columnar optical gap recess 1051 is disposed in the second oxide layer 105 on the photodiode 101, and the center of the columnar optical gap recess 1051 is aligned with the center of the photodiode 101, or two or more columnar optical gap recesses 1051 are evenly distributed in the second oxide layer 105 on the photodiode 101.

[0071] Referring to Figures 3 and 4, when the gap recess only includes the annular optical gap recess 1052, one annular optical gap recess 1052 is disposed in the second oxide layer 105 on the photodiode 101, or two or more annular optical gap recesses 1052 are concentrically distributed in the second oxide layer 105 on the photodiode 101, and the center of one, two or more annular optical gap recesses 1052 is aligned with the center of the photodiode 101, and adjacent annular optical gap recesses 1052 are equally spaced.

[0072] Referring to Figures 3 and 4, when the gap recess includes a columnar optical gap recess 1051 and an annular optical gap recess 1052, the columnar optical gap recess 1051 and the annular optical gap recess 1052 are disposed in the second oxide layer 105 on the photodiode 101, and the columnar optical gap recess 1051 and the annular optical gap recess 1052 are concentrically arranged, with the center of the columnar optical gap recess 1051 and the center of the annular optical gap recess 1052 aligned with the center of the photodiode 101. Furthermore, the columnar optical gap recess 1051 and the annular optical gap recess 1052 are spaced at equal intervals, as are adjacent annular optical gap recesses 1052.

[0073] Referring to Figures 8 and 9, when the gap recess includes a columnar optical gap recess 1051, an annular optical gap recess 1052, and an isolation gap recess 1055, the optical gap recess 1051, annular optical gap recess 1052, and isolation gap recess 1055 are disposed in the second oxide layer 105 on the photodiode 101, and the columnar optical gap recess 1051, annular optical gap recess 1052, and isolation gap recess 1055 are concentrically arranged, and the center of the columnar optical gap recess 1051, the center of the annular optical gap recess 1052, and the center of the isolation gap recess 1055 are aligned with the center of the photodiode 101.

[0074] Referring to Figures 5 and 6, in one embodiment of the present invention, after forming the gap recess, a second sub-oxide layer of a second thickness is deposited on the gap recess. During the deposition of the second sub-oxide layer, the opening of the gap recess is closed, forming an optical gap or isolation gap 1056 with a radial dimension that first increases and then decreases. Specifically, tetraethoxysilane or silane can be used as a precursor, and a silicon oxide layer is deposited on the surface of the high dielectric constant layer 104 as the second sub-oxide layer using chemical vapor deposition. The thickness of the second sub-oxide layer is, for example, 30 nm to 50 nm, specifically, 35 nm, 40 nm, 45 nm, or 50 nm.

[0075] Referring to Figures 3 to 6, when depositing silicon oxide using chemical vapor deposition, the reactant gas is adsorbed on the wafer surface due to the large depth-to-width ratio of the gap recess and diffuses into the interior of the gap recess. Because the gas at the gap recess inlet is abundant and the reactant concentration is high, the deposition rate is fast, easily forming a "bottleneck." Furthermore, as deposition progresses, the inlet gradually narrows, restricting gas diffusion to the bottom of the gap. The reactant gas needs to diffuse to the bottom of the gap recess to deposit, but as the diffusion path lengthens, the reactant concentration at the bottom is lower, resulting in slower deposition. When the gap recess inlet and bottom are deposited and sealed simultaneously, the middle region of the gap recess is trapped inside, forming a void. This results in an optical gap or isolation gap 1056 with smaller radial dimensions at both ends and a larger radial dimension in the middle within the second oxide layer 105.

[0076] Referring to Figures 7, 8, 10, and 12, in one embodiment of the present invention, a grid 107 and a filter structure are disposed on the second oxide layer 105. The grid 107 is disposed on the composite dielectric stack layer and located on top of the deep trench isolation structure 102. The filter structure is disposed on the composite dielectric stack layer and located on top of the photodiode 101.

[0077] Referring to Figures 7, 8, 10, and 12, in one embodiment of the present invention, after the deposition of the second oxide layer 105 and the formation of optical gaps and isolation gaps 1056 in the second oxide layer 105, a grid 107 is first formed on the second oxide layer 105. The orthogonal projection of the formed grid 107 on the substrate 100 is located within the deep trench isolation structure 102. The grid 107 is, for example, a metal grid. Specifically, a metal material with high light-shielding capacity, such as chromium (Cr), aluminum (Al), or copper (Cu), is deposited on the second oxide layer 105 using processes such as magnetron sputtering to form a metal layer. Then, the metal layer is etched according to the desired shape of the metal grid 107, retaining a portion of the metal layer on the deep trench isolation structure 102 to form the metal grid 107.

[0078] Referring to Figures 7, 8, 10, and 12, in one embodiment of the present invention, after forming the grid 107, a filter structure is formed on the photodiodes 101 between adjacent grids 107. The filter structure is located on the composite dielectric stack layer on top of the photodiodes 101. The filter structure includes, for example, multiple color filters 106, which together form a color filter array. Each color filter 106 corresponds to one photodiode 101. In this embodiment, the filter structure may include at least three primary color filters 106, such as a blue filter, a green filter, and a red filter, and the color filters 106 can be arranged in any suitable combination. For example, the blue, green, and red filters can be arranged alternately. Alternatively, a transparent filter can be provided, with the blue, green, and red filters and the transparent filter arranged alternately. The color filter 106 can be a polymer material, such as a negative photoresist based on an acrylic polymer, and may contain colored dyes. After the grid 107 is formed, the color filter 106 can be vacuum-deposited directly between adjacent grids 107. When light passes through the color filter 106, its color can be changed, maintaining high transmittance in a certain wavelength band (color), thereby enhancing the photoelectric conversion effect.

[0079] Please refer to Figures 7, 8, 10, and 12. In one embodiment of the present invention, the filter structure further includes a microlens 108. The microlens 108 is disposed on the color filter 106, and the top of the microlens 108 is an outwardly convex arc shape, which can focus the incident light onto the photodiode 101. The curvature of the filter structure surface can be changed according to the light-gathering requirements to improve the photosensitivity. The microlens 108 structure can be formed in any way, and the present invention does not impose any specific limitations. The number of photodiodes 101 and the filter structure can be set according to actual needs; the figures in this embodiment are only examples. When the image sensor is working, light passes through the microlens 108, the color filter 106, and the composite dielectric stack layer, and is scattered in the optical gaps in the composite dielectric stack layer before entering the photodiode 101. Increasing the amount of light scattering and diffusion can increase the optical path of the incident light, improve the near-infrared sensitivity of the image sensor, and thus improve the photoelectric conversion efficiency of the image sensor.

[0080] In summary, this invention provides an image sensor and its fabrication method. The image sensor includes a substrate with spaced photodiodes and a deep trench isolation structure disposed therein; a composite dielectric stack layer disposed on the substrate, comprising a stacked first oxide layer, a high dielectric constant layer, and a second oxide layer; an optical gap disposed in the second oxide layer on each photodiode, the optical gap scattering incident light and increasing the optical path length of the incident light within the photodiode; a grid disposed on the composite dielectric stack layer on top of the deep trench isolation structure; and a filter structure disposed on the composite dielectric stack layer on top of the photodiodes. This invention provides an image sensor and its fabrication method that improves the image sensor's response to near-infrared light and enhances the photoelectric conversion efficiency of the image sensor.

[0081] The embodiments of the present invention disclosed above are merely illustrative of the invention. The embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. An image sensor, characterized in that, At least including: A substrate in which spaced photodiodes and deep trench isolation structures are disposed; a composite dielectric stack layer is disposed on the substrate, and the composite dielectric stack layer includes a stacked first oxide layer, a high dielectric constant layer and a second oxide layer; an optical gap is disposed in the second oxide layer on each of the photodiodes, and the optical gap scatters incident light, increasing the optical path length of incident light in the photodiodes; A grid is disposed on the composite dielectric stack layer at the top of the deep trench isolation structure; And a filter structure is disposed on the composite dielectric stack layer on top of the photodiode.

2. An image sensor according to claim 1, characterized in that, In the second oxide layer on each of the photodiodes, the optical gap includes at least one columnar optical gap, and the radial dimension of the columnar optical gap first increases and then decreases in the thickness direction of the second oxide layer.

3. An image sensor according to claim 1, characterized in that, In the second oxide layer on each of the photodiodes, the optical gap includes at least one annular optical gap, and the radial dimension of the annular optical gap first increases and then decreases in the thickness direction of the second oxide layer.

4. An image sensor according to claim 3, characterized in that, When the second oxide layer on each of the photodiodes includes two or more of the annular optical gaps, the annular optical gaps are arranged concentrically.

5. An image sensor according to claim 1, characterized in that, In the second oxide layer on each of the photodiodes, the optical gaps include: a columnar optical gap, the radial dimension of which first increases and then decreases in the thickness direction of the second oxide layer; and an annular optical gap, surrounding the columnar optical gap and concentrically arranged with the columnar optical gap, the radial dimension of which first increases and then decreases in the thickness direction of the second oxide layer.

6. An image sensor according to claim 1, characterized in that, The image sensor also includes an isolation gap disposed in the second oxide layer on the deep trench isolation structure, and the radial dimension of the isolation gap first increases and then decreases in the thickness direction of the second oxide layer.

7. An image sensor according to claim 1, characterized in that, The image sensor is a back-illuminated image sensor or a front-illuminated image sensor. When the image sensor is a front-illuminated image sensor, a metal wiring layer is provided in the second oxide layer.

8. A method for manufacturing an image sensor, characterized in that, At least the following steps are included: A substrate is provided, and spaced photodiodes and deep trench isolation structures are formed in the substrate; a composite dielectric stack layer is formed on the substrate, and the composite dielectric stack layer includes a stacked first oxide layer, a high dielectric constant layer and a second oxide layer; when forming the second oxide layer, an optical gap is formed in the second oxide layer, and the optical gap scatters incident light, increasing the optical path of the incident light in the photodiode; A grid is formed on the second oxide layer, and the grid is located on the composite dielectric stack layer on top of the deep trench isolation structure; and a filter structure is formed on the second oxide layer, and the filter structure is located on the composite dielectric stack layer on top of the photodiode.

9. A method for manufacturing an image sensor according to claim 8, characterized in that, When forming the second oxide layer, forming an optical gap in the second oxide layer includes the following steps: depositing a first sub-oxide layer of a first thickness on the high dielectric constant layer; etching the first sub-oxide layer to form a gap recess; and depositing a second sub-oxide layer of a second thickness on the first sub-oxide layer, wherein the gap recess is closed, forming an optical gap with a radial dimension that first increases and then decreases.

10. A method for manufacturing an image sensor according to claim 9, characterized in that, The depth-to-width ratio of the recessed gap is greater than 3:1.

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