CN114628424A - Single photon avalanche diode - Google Patents

Abstract

The invention discloses a single-photon avalanche diode, comprising a plurality of pixel units arranged in an array, a shared cathode and an isolation unit arranged between adjacent pixel units, wherein the pixel unit includes a diode active area, a nano-moth An eye anti-reflection structure and a microlens, the nano moth-eye anti-reflection structure is arranged on the upper surface of the active region of the diode, the microlens is arranged on the upper surface of the nano moth-eye anti-reflection structure; the shared cathode The isolation unit is arranged in the area surrounded by the top corners of every four adjacent pixel units; the isolation unit is arranged between two adjacent pixel units, and is used for optically and electrically isolating the adjacent pixel units. The invention combines the nano moth-eye antireflection microstructure, the microlens and the photoelectric detection device to reduce the reflection of light in a specific wavelength band and increase the utilization rate of photons in the echo signal, thereby improving the quantum efficiency and the detection efficiency of the system.

Description

A single photon avalanche diode

technical field

The invention belongs to the technical field of microelectronic optoelectronic devices, and in particular relates to a single-photon avalanche diode.

Background technique

In recent years, long-distance active imaging can provide high-resolution 3D imaging of detected targets, and has broad application prospects in the fields of remote sensing and target recognition. As an important means to achieve long-distance active imaging, single-photon lidar detects the target by irradiating the laser beam and measures the Time of Flight (ToF) of the reflected light signal, thereby obtaining the distance information of the target. Two-dimensional scanning can obtain three-dimensional distance information.

Single-photon avalanche diodes (SPADs) have become one of the best candidates for long-range low-light detection due to their almost infinite gain, high temporal resolution, and single-photon sensitivity. In addition, the integration of SPAD in CMOS (Complementary Metal Oxide Semiconductor, Complementary Metal Oxide Semiconductor) process has attracted much attention due to its high cost-effectiveness, mass production capability, and ease of integration. Many advanced solutions have emerged, including state-of-the-art technology nodes, microlenses, and 3D integration.

However, as the imaging distance continues to increase, the photon signal returned from the target becomes rarer. Therefore, it is particularly important to improve the detection efficiency of the device. The detection efficiency is theoretically directly limited by the detection probability and quantum efficiency. How to improve the photon utilization rate is an urgent problem to be solved to improve the quantum efficiency.

SUMMARY OF THE INVENTION

In order to solve the above problems existing in the prior art, the present invention provides a single photon avalanche diode. The technical problem to be solved by the present invention is realized by the following technical solutions:

The present invention provides a single-photon avalanche diode, comprising a plurality of pixel units arranged in an array and a shared cathode and an isolation unit arranged between adjacent pixel units, wherein,

The pixel unit includes a diode active region, a nano moth-eye anti-reflection structure, and a microlens, the nano-moth-eye anti-reflection structure is arranged on the upper surface of the diode active region, and the microlens is arranged on the nano-moth eye anti-reflection structure. the upper surface of the ocular antireflection structure;

The shared cathode is arranged in the area enclosed by the top corners of every four adjacent pixel units; the isolation unit is arranged between two adjacent pixel units, and is used for optically conducting optical imaging on adjacent pixel units. and electrical isolation.

In an embodiment of the present invention, the diode active region includes a P-type substrate layer, a P-type epitaxial layer, an N-type buried layer, a p+ active layer, an active region photon reflective metal plate, an anode electrode and a wiring layer, in,

The wiring layer, the P-type epitaxial layer, the N-type buried layer and the P-type substrate layer are stacked from bottom to top, and the nano moth-eye anti-reflection structure is arranged on the P-type substrate layer surface;

the p+ active layer is arranged at the center of the lower surface of the p-type epitaxial layer;

The anode electrode is embedded on the upper surface of the wiring layer and the upper surface of the anode electrode is in contact with the lower surface of the p+ active layer, and the active region photon reflective metal plate is embedded under the wiring layer surface.

In an embodiment of the present invention, the P-type substrate layer is a Si-based substrate doped with phosphorus or antimony, and has a thickness of 3-10 μm.

In an embodiment of the present invention, the isolation unit includes a deep trench isolation region, an isolation N-well and a shallow trench isolation layer sequentially stacked between adjacent pixel units from top to bottom, wherein,

The shallow trench isolation layer is embedded on the lower surface of the P-type epitaxial layer, and the isolation N well is disposed on the upper surface of the shallow trench isolation layer and is in contact with the lower surface of the N-type buried layer;

The deep trench isolation region extends from the upper surface of the P-type substrate layer to the interior of the isolation N-well and can space an N-type buried layer adjacent to the pixel unit.

In an embodiment of the present invention, the shared cathode includes a deep N well, an N+ doped well and a cathode electrode that are stacked in sequence from top to bottom, wherein,

The deep N well and the N+ doped well are arranged inside the P-type epitaxial layer, the cathode electrode is located inside the wiring layer, and the upper surface of the deep N well and the N-type buried layer contact with the lower surface.

In an embodiment of the present invention, the nano moth-eye anti-reflection structure includes a moth-eye anti-reflection microstructure, an anti-reflection film and a flat layer, wherein,

The moth-eye anti-reflection microstructure includes a plurality of nano moth-eye anti-reflection microstructures, and the height, density and diameter of the plurality of nano moth-eye anti-reflection microstructures are randomly distributed around the average height, average density and average diameter respectively. And the diameter gradually decreases from bottom to top;

the flat layer is filled in the gaps of the plurality of nano moth-eye anti-reflection microstructures to form flat upper and lower surfaces, and the microlenses are disposed above the flat layer;

The antireflection film is located between two adjacent structures composed of the moth-eye antireflection microstructure and the flat layer.

In an embodiment of the present invention, the moth-eye anti-reflection microstructure and the flat layer are both thin film materials that can be grown on the Si surface, and the refractive index of the microlens material<the refractive index of the flat layer material <Refractive index of the moth-eye anti-reflection microstructure material

In an embodiment of the present invention, the anti-reflection film is TiO ₂ , ZrO ₂ or a combination thereof.

In an embodiment of the present invention, the moth-eye antireflection microstructure is a bullet-shaped nanostructure, a nano-truncated cone structure, a parabolic nano-structure, a Gaussian-shaped nano-structure or a nano-pyramid structure.

Compared with the prior art, the beneficial effects of the present invention are:

1. The single-photon avalanche diode of the present invention combines nano-moth-eye anti-reflection microstructures, microlenses and photodetector devices, etches or grows nano-moth-eye anti-reflection structures on traditional photodetector devices, and places them between pixel units. Using the anti-reflection structure to increase the reflection of useless photons, maximize the use of photons irradiated on the detection chip, and optimize the size of the microstructure and microlens for specific wavelengths to achieve high window transmittance in specific wavelengths and improve quantum efficiency. Improve detection efficiency. Achieve efficient long-distance low-light detection.

2. The single-photon avalanche diode of the present invention increases the effective filling rate of the device by increasing the microlens structure, reduces the reflection of light through the nano moth-eye anti-reflection structure, and increases the utilization rate of photons in the echo signal. Through the n+/P structure In the high-field absorption region, electrons are mainly involved in avalanche, and the electron avalanche ionization rate is high, which can further improve the quantum efficiency. By improving the filling rate, quantum efficiency, and photon utilization rate, the detection efficiency of the device can be improved.

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

Description of drawings

1 is a top view of a partial 4×4 array pixel structure of a single-photon avalanche diode provided by an embodiment of the present invention;

Figure 2 is a cross-sectional view taken along line A-A in Figure 1;

3 is a schematic cross-sectional view of a pixel unit located at the edge of a device provided by an embodiment of the present invention;

4 is a schematic cross-sectional view of a shared cathode provided by an embodiment of the present invention;

5 is a schematic structural diagram of a moth-eye antireflection microstructure with randomly distributed triangular pyramids provided by an embodiment of the present invention;

6 is a reflection curve diagram of a randomly distributed moth-eye microstructure with an average diameter of 100 nm and an average height of 400 nm provided by an embodiment of the present invention.

Description of reference numbers:

1-pixel unit; 11-diode active region; 111-P-type substrate layer; 112-P-type epitaxial layer; 113-N-type buried layer; 114-p+active layer; 115-active region photon reflective metal plate; 116-anode electrode; 117-wiring layer; 12-moth-eye anti-reflection structure; 121-moth-eye anti-reflection microstructure; 122-reflection enhancement film; 123-flat layer; 13-microlens; 2-shared cathode; 21- 22-N+ doped well; 23-cathode electrode; 3-isolation unit; 31-deep trench isolation region; 32-isolated N-well; 33-shallow trench isolation layer.

Detailed ways

In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, a single photon avalanche diode according to the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

The foregoing and other technical contents, features and effects of the present invention can be clearly presented in the following detailed description of the specific implementation with the accompanying drawings. Through the description of the specific embodiments, the technical means and effects adopted by the present invention to achieve the predetermined purpose can be more deeply and specifically understood. However, the accompanying drawings are only for reference and description, and are not used for the technical description of the present invention. program is restricted.

It should be noted that, in this document, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any relationship between these entities or operations. any such actual relationship or sequence exists. Moreover, the terms "comprising", "comprising" or any other variation are intended to encompass a non-exclusive inclusion, whereby an article or device comprising a list of elements includes not only those elements, but also other elements not expressly listed. Without further limitation, an element qualified by the phrase "comprising a..." does not preclude the presence of additional identical elements in the article or device that includes the element.

Please refer to FIGS. 1 and 2 . FIG. 1 is a top view of a partial 4×4 pixel structure of a single photon avalanche diode according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1 . The single-photon avalanche diode of this embodiment includes a plurality of pixel units 1 arranged in an array, a shared cathode 2 and an isolation unit 3 disposed between adjacent pixel units 1, wherein the pixel unit 1 includes a diode active area 11, a nanometer The moth-eye anti-reflection structure 12 and the microlens 13 , the nano moth-eye anti-reflection structure 12 is disposed on the upper surface of the diode active region 11 , and the microlens 13 is disposed on the upper surface of the nano moth-eye anti-reflection structure 12 . Specifically, the microlens 13 covers the entire pixel photosensitive area of the pixel unit 1 for focusing, and the incident light on the larger incident surface is concentrated to the diode active area 11, and the nano moth-eye anti-reflection structure 12 is used to reduce the reflection of light , increasing the light transmittance of the photosensitive region, and the diode active region 11 multiplies a single photon into a photo-generated current through the avalanche multiplication effect.

The shared cathode 2 is arranged in the area enclosed by the top corners of every adjacent four pixel units 1 , and is used for supplying power to the diode active area 11 . The isolation unit 3 is disposed between two adjacent pixel units 1 for optically and electrically isolating the adjacent pixel units 1 .

Further, the diode active region 11 of each pixel unit 1 includes a P-type substrate layer 111, a P-type epitaxial layer 112, an N-type buried layer 113, a p+ active layer 114, an active region photon reflective metal plate 115, an anode The electrode 116 and the wiring layer 117, wherein the wiring layer 117, the P-type epitaxial layer 112, the N-type buried layer 113 and the P-type substrate layer 111 are stacked from bottom to top, and the nano moth-eye anti-reflection structure 12 is provided on the P-type substrate layer 111's upper surface. The N-type buried layer 113 and the P-type epitaxial layer 112 form a multiplication main junction to form a strong electric field to sense the arrival of photons. In the preparation process, before growing the P-type epitaxial layer 112, doping is performed on the P-type substrate layer 111 to form an N-type buried layer 113, which is a high-concentration doping. Preferably, the doping elements of the N-type buried layer 113 are group III elements such as phosphorus and antimony, and the doping concentration is about 5e ¹⁸ cm ⁻³ . The P-type substrate layer 111 is a Si-based substrate doped with phosphorus or antimony, with a thickness of 3-10 μm and a doping concentration of about 5e ¹⁵ cm ⁻³ ; the doping concentration of the P-type epitaxial layer 112 is about 1e ¹⁵ cm ^{−3 3.} It should be noted that the P-type doping in this embodiment is doped with Group V elements, such as boron, aluminum, etc., and the N-type doping is doped with Group III elements, such as phosphorus, antimony, and the like. Since the doping concentration of the P-type epitaxial layer 112 is low, the width of the depletion region is wide, which helps to improve the detection probability and spectral response range of the device.

In this embodiment, the N-type buried layer 113 is shared by all pixel units and forms an entire continuous area.

The main depletion width of the avalanche multiplication region formed by the N-type buried layer 113 and the P-type epitaxial layer 112 extends in the P-type epitaxial layer 112, and the electric field is directed from the P-type epitaxial layer 112 to the N-type buried layer 113, within the range of the high-field absorption region , mainly by electrons participating in avalanche, the electron avalanche ionization rate is higher, which can further improve the quantum efficiency.

The p+ active layer 114 is disposed at the center of the lower surface of the P-type epitaxial layer 112, that is, the P+ active layer 114 of a single pixel unit is located at the center of the single pixel, and is formed by doping the P-type epitaxial layer 112 during the preparation process. Preferably, the p+ active layer 114 is doped with phosphorus or antimony, and the doping concentration is 1e ¹⁹ cm ^-3 -5e ²⁰ cm ^-3 .

The anode electrode 116 is embedded on the upper surface of the wiring layer 117 and the upper surface of the anode electrode 116 is in contact with the lower surface of the p+ active layer 114 . Further, the photon reflective metal plate 115 in the active region is located directly under the p+ active layer 114, which can reflect the photons irradiated on it back to the inside of the device, so as to increase the utilization rate of photons and enhance the detection of the device at longer wavelengths. probability.

The anode electrode 116 is located in the center of the lower surface of the P+ active layer 114, which is a floating potential and is connected to the subsequent circuit. The large current generated by the avalanche multiplication effect makes the subsequent circuit re-fix the node to generate a potential change, thereby reflecting the arrival of photons . Further, in order to prevent the anode electrode 116 from being connected to a large load capacitance, the anode electrode 116 and the photon reflective metal plate 115 in the active region are electrically isolated by the medium in the wiring layer 117, and the anode electrode 116 is connected to the wiring layer 117 through horizontal and vertical wirings. The circuits of the underlying chips are connected, and the photon reflecting metal plate 115 in the active region is in a floating state.

Further, the isolation unit 3 includes a deep trench isolation region 31 , an isolation N well 32 and a shallow trench isolation layer 33 that are sequentially stacked between adjacent pixel units 1 from top to bottom, wherein the shallow trench isolation layer 33 is embedded in the P-type isolation layer 33 . On the lower surface of the epitaxial layer 112, the isolation N well 32 is arranged on the upper surface of the shallow trench isolation layer 33 and is in contact with the lower surface of the N-type buried layer 113; the deep trench isolation region 31 extends from the upper surface of the P-type substrate layer 111 to the isolation Inside the N well 32 .

The isolation N well 32 isolates two adjacent pixel units, and by forming a reverse biased PN junction structure with the P-type epitaxial layer 102 , crosstalk between adjacent pixel units caused by carrier drift or tunneling is avoided.

The deep trench isolation region 31 is located between two pixel units and is used to isolate adjacent pixel units. The width of the deep trench isolation region 31 is smaller than the width of the isolation N well 32, which isolates the N well 32 from the N-type buried layer 113 in the vertical direction. Adhere to, as the guard ring of the multiplication main junction formed by the N-type buried layer 113 and the P-type epitaxial layer 112, leaving a sufficient safety distance to prevent the traps caused by the etching and filling process from negatively affecting the dark count rate and post-pulse .

Please refer to FIG. 3 , which is a schematic cross-sectional view of a pixel unit located at an edge of a device provided by an embodiment of the present invention. As mentioned above, the single-photon avalanche diode of this embodiment includes a plurality of pixel units 1 arranged in an array. For the pixel unit located at the edge of the device, the size of the N-type buried layer 113 is slightly smaller than that of the P-type substrate layer 111 and the P-type epitaxy Layer 112, that is, the edge of the N-type buried layer 113 is wrapped inside the P-type substrate layer 111 and the P-type epitaxial layer 112. At the same time, the lower surface of the edge of the N-type buried layer 113 is sequentially provided with an isolation N well 32 and a shallow trench isolation layer 33. . Likewise, there are isolated N-wells 32 and shallow trench isolation layers 33 spaced apart from the p+ active layer 114 and wrapped inside the P-type epitaxial layer 112 .

Further, please refer to FIG. 4 , which is a schematic cross-sectional view of a shared cathode provided by an embodiment of the present invention. The shared cathode 2 in this embodiment includes a deep N well 21 , an N+ doped well 22 and a cathode electrode 23 that are stacked in sequence from top to bottom, wherein the deep N well 21 and the N+ doped well 22 are arranged on the P-type epitaxial layer 112 Inside, the cathode electrode 23 is located inside the wiring layer 117 , and the upper surface of the deep N well 21 is in contact with the lower surface of the N-type buried layer 113 .

The cathode electrode 23 forms electrical contact with the N-type buried layer 113 through the N+ doped well 22 and the deep N-well 21 , and provides a reverse bias voltage for the N-type buried layer 113 in the adjacent diode active region 1 . In order to avoid potential inconsistency caused by the lateral resistance loss of the N-well buried layer 113, each shared cathode 2 provides a bias voltage for adjacent four pixels.

Further, the moth-eye anti-reflection structure 12 includes a moth-eye anti-reflection microstructure 121, an anti-reflection film 122 and a flat layer 123, wherein the moth-eye anti-reflection microstructure 121 includes a plurality of nano moth-eye anti-reflection The height, density and diameter of the moth-eye anti-reflection microstructure are randomly distributed around the average height, average density and average diameter, respectively, and the diameter gradually decreases from bottom to top, as shown in FIG. 5 ; the flat layer 123 is filled with a plurality of nanometers. In the gap between the moth-eye anti-reflection microstructures, to form flat upper and lower surfaces, which is beneficial to the fabrication and stability of the microlenses, the microlenses 13 are arranged above the flat layer 123; between the structure composed of the structure 121 and the flat layer 123 . The microlens 13 is disposed above the flat layer 123 , covers the entire pixel photosensitive area, and collects photons to the p+ active layer 114 through refraction.

Preferably, the moth-eye anti-reflection microstructure 121 and the flat layer 123 in this embodiment are both thin film materials that can be grown on the Si surface. Further, the diameter of the moth-eye anti-reflection microstructure 121 gradually decreases from bottom to top. Preferably, the moth-eye anti-reflection microstructure 121 is a bullet-shaped nanostructure, a nano-truncated cone structure, a parabolic nanostructure, and a Gaussian surface nanostructure. or nanocone structure. Refractive index of microlens 13 <refractive index of flat layer 123 <refractive index of moth-eye anti-reflection microstructure 121 <refractive index of Si. The flat layer 123 can be selected from SiO ₂ , and the moth-eye anti-reflection microstructure can be selected from SiN. The moth-eye anti-reflection microstructure 121 can absorb most of the incident light, and the refractive index changes continuously from top to bottom without reflection, thereby improving the photon utilization rate.

It should be noted that the height, density and diameter of the aforementioned random array nano moth-eye antireflection microstructures 121 are randomly distributed around the average height, average density and average diameter, respectively. Compared with periodic nanostructures, it has better antireflection properties, and the specific distribution is optimized for different wavelengths, which can enable the photodetection device to have a window antireflection effect. 6 is a reflection curve diagram of a randomly distributed moth-eye microstructure with an average diameter of 100 nm and an average height of 400 nm provided by an embodiment of the present invention. It can be seen that the reflectivity is very low at 550 nm and the light transmittance is good. Further, the fabrication process of the moth-eye anti-reflection microstructure 121 may be binary lithography technology, laser direct writing technology, electron beam lithography, reactive ion etching and the like.

The anti-reflection film 122 can reflect the photons that cannot be used in the avalanche multiplication region to avoid side breakdown and dark counting. The anti-reflection film 122 is a film with low laser damage resistance and high refractive index, which can be titanium dioxide (TiO ₂ ) \ zirconium oxide (ZrO ₂ ), etc. or a combination thereof. The thickness is optimized according to the laser wavelength in the optical simulation software. value.

The microlens 13 has different curvatures for different wavelengths, and it gathers all the light irradiated on the surface of the photosensitive device into the avalanche multiplication area, thereby improving the photon utilization rate.

Further, the single-photon avalanche diode of this embodiment is often used at the receiving end of the lidar, and the specific working process is as follows: the photodetector receives the target echo reflected from the target, the target echo first contacts the microlens, and the microlens realizes the convergence. The effect of light is to focus the light irradiated on the surface of the diode to the surface of the moth-eye anti-reflection structure above the avalanche multiplication area. The moth-eye anti-reflection structure reduces the reflection of light and increases the amount of light transmission in the photosensitive area. At the same time, the device is biased to a reverse-biased state with a high breakdown voltage through the cathode shared electrode. When the device absorbs a photon, the avalanche multiplication effect of the carriers in the active region of the diode absorbs a single photon and amplifies it into a single photon. A pulsed current, which flows through the anode electrode to a subsequent circuit, which predicts the arrival of photons by inducing the pulsed current.

To sum up, the single-photon avalanche diode of this embodiment combines nano-moth-eye anti-reflection microstructures, microlenses and photodetection devices, and etches or grows nano-moth-eye anti-reflection structures on traditional photodetector devices. The enhancement and reflection structure is used between the units to increase the reflection of useless photons, maximize the use of photons irradiated on the detection chip, and optimize the microstructure and microlens size for specific wavelengths to achieve high window transmittance in specific wavelength bands and improve quantum efficiency to improve detection efficiency. Achieve efficient long-distance low-light detection. In addition, the single-photon avalanche diode increases the effective filling rate of the device by increasing the micro-lens structure, reduces the reflection of light through the nano moth-eye anti-reflection structure, and increases the utilization rate of photons in the echo signal. In the high-field absorption region, electrons are mainly involved in avalanche, and the electron avalanche ionization rate is high, which can further improve the quantum efficiency.

The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deductions or substitutions can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (9)

1. a single photon avalanche diode, is characterized in that, comprises a plurality of pixel units (1) arranged in an array and a shared cathode (2) and an isolation unit (3) arranged between adjacent pixel units (1), in, The pixel unit (1) includes a diode active region (11), a nano moth-eye anti-reflection structure (12) and a microlens (13), and the nano-moth-eye anti-reflection structure (12) is arranged on the diode active area. the upper surface of the area (11), the microlenses (13) are arranged on the upper surface of the nano moth-eye anti-reflection structure (12); The shared cathode (2) is arranged in the area enclosed by the top corners of every four adjacent pixel units (1); the isolation unit (3) is arranged in two adjacent pixel units (1) between the adjacent pixel units (1) for optical and electrical isolation. 2. The single-photon avalanche diode according to claim 1, wherein the diode active region (11) comprises a P-type substrate layer (111), a P-type epitaxial layer (112), and an N-type buried layer (113) ), p+ active layer (114), active region photon reflective metal plate (115), anode electrode (116) and wiring layer (117), wherein, The wiring layer (117), the P-type epitaxial layer (112), the N-type buried layer (113), and the P-type substrate layer (111) are stacked from bottom to top, and the nano-moth-eye reduction An inverse structure (12) is arranged on the upper surface of the P-type substrate layer (111); the p+ active layer (114) is arranged in the center of the lower surface of the p-type epitaxial layer (112); The anode electrode (116) is embedded on the upper surface of the wiring layer (117) and the upper surface of the anode electrode (116) is in contact with the lower surface of the p+ active layer (116), the active region A photon reflective metal plate (115) is embedded on the lower surface of the wiring layer (117). 3 . The single-photon avalanche diode according to claim 2 , wherein the P-type substrate layer ( 111 ) is a Si-based substrate doped with phosphorus or antimony, and has a thickness of 3-10 μm. 4 . 4 . The single-photon avalanche diode according to claim 2 , wherein the isolation unit ( 3 ) comprises deep trench isolation regions ( 4 ) sequentially stacked between adjacent pixel units ( 1 ) from top to bottom. 31), isolating the N well (32) and the shallow trench isolation layer (33), wherein, The shallow trench isolation layer (33) is embedded on the lower surface of the P-type epitaxial layer (112), and the isolation N well (32) is arranged on the upper surface of the shallow trench isolation layer (33) and is connected to the P-type epitaxial layer (112). The lower surface of the N-type buried layer (113) contacts; The deep trench isolation region (31) extends from the upper surface of the P-type substrate layer (111) to the interior of the isolation N-well (32) and can separate the N-type buried regions of the adjacent pixel units (1). layer (113). 5 . The single-photon avalanche diode according to claim 1 , wherein the shared cathode ( 2 ) comprises a deep N well ( 21 ), an N+ doped well ( 22 ) and a cathode that are stacked in sequence from top to bottom. 6 . electrode (23), wherein, The deep N well (21) and the N+ doped well (22) are arranged inside the P-type epitaxial layer (112), the cathode electrode (23) is inside the wiring layer (117), and the The upper surface of the deep N well (21) is in contact with the lower surface of the N-type buried layer (113). 6 . The single-photon avalanche diode according to claim 1 , wherein the nano moth-eye anti-reflection structure ( 12 ) comprises a moth-eye anti-reflection microstructure ( 121 ), a reflection enhancement film ( 122 ) and a flat layer ( 6 . 123), where, The moth-eye anti-reflection microstructure (121) includes a plurality of nano moth-eye anti-reflection microstructures, and the height, density and diameter of the plurality of nano moth-eye anti-reflection microstructures are respectively about the average height, average density and average diameter It is randomly distributed and the diameter gradually decreases from bottom to top; The flat layer (123) is filled in the gaps of the plurality of nano moth-eye anti-reflection microstructures to form flat upper and lower surfaces, and the microlenses (13) are arranged above the flat layer (123); The antireflection film (122) is located between two adjacent structures composed of the moth-eye antireflection microstructure (121) and the flat layer (123). 7 . The single-photon avalanche diode according to claim 6 , wherein the moth-eye antireflection microstructure ( 121 ) and the flat layer ( 123 ) are both thin-film materials that can grow on the surface of Si, and the The refractive index of the material of the microlens (13) < the refractive index of the material of the flat layer (123) < the refractive index of the material of the moth-eye anti-reflection microstructure (121). 8 . The single-photon avalanche diode according to claim 6 , wherein the reflection enhancement film ( 122 ) is TiO ₂ , ZrO ₂ or a combination thereof. 9 . 9. The single-photon avalanche diode according to any one of claims 6 to 8, wherein the moth-eye antireflection microstructure (121) is a bullet-shaped nanostructure, a nano-truncated cone structure, a parabolic nano-structure, Gaussian planar nanostructures or nanocone structures.

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