A single photon avalanche diode

Abstract

The present invention discloses 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 comprises 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 upper surface of the nano moth-eye anti-reflection structure; the shared cathode is arranged in the area surrounded by the vertex angles of each of the four adjacent pixel units; the isolation unit is arranged between two adjacent pixel units, and is used to optically and electrically isolate the adjacent pixel units. The present invention combines the nano moth-eye anti-reflection microstructure, the microlens and the photoelectric detection device, reduces the reflection of light in a specific band, increases the utilization rate of photons in the echo signal, thereby improving the quantum efficiency, and improving the detection efficiency of the system.

Description

Technical Field

[0001] The invention belongs to the technical field of microelectronic optoelectronic devices, and in particular relates to a single-photon avalanche diode. Background Art

[0002] In recent years, long-distance active imaging can provide high-resolution three-dimensional imaging of the detected target, 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 obtains the distance information of the target by illuminating the detected target with a laser beam and measuring the flight time (ToF) of the reflected light signal. By performing a two-dimensional scan on the detected object, three-dimensional distance information can be obtained.

[0003] Single Photon Avalanche Diode (SPAD) has become one of the best candidate devices for long-distance low-light detection due to its advantages such as almost infinite gain, high time resolution and single-photon sensitivity. In addition, due to its high cost-effectiveness, mass production capability and easy integration, the integration of SPAD in CMOS (Complementary Metal Oxide Semiconductor) process has attracted much attention. Many advanced solutions have emerged, including the most advanced technology nodes, microlenses and 3D integration.

[0004] However, as the imaging distance continues to increase, the photon signals returned from the target become increasingly scarce. 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, and how to improve the utilization rate of photons is an urgent problem to be solved in order to improve quantum efficiency. Summary of the invention

[0005] 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 achieved through the following technical solutions:

[0006] 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:

[0007] The pixel unit comprises a diode active region, a nano moth-eye anti-reflection structure and a micro-lens, wherein the nano moth-eye anti-reflection structure is arranged on the upper surface of the diode active region, and the micro-lens is arranged on the upper surface of the nano moth-eye anti-reflection structure;

[0008] The shared cathode is arranged in a region enclosed by the vertex 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.

[0009] In one 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 reflection metal plate, an anode electrode and a wiring layer, wherein:

[0010] 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 upper surface of the P-type substrate layer;

[0011] The p+ active layer is arranged at the center of the lower surface of the P-type epitaxial layer;

[0012] The anode electrode is embedded in the upper surface of the wiring layer and the upper surface of the anode electrode contacts the lower surface of the p+ active layer, and the active region photon reflection metal plate is embedded in the lower surface of the wiring layer.

[0013] In one 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.

[0014] In one embodiment of the present invention, the isolation unit includes a deep trench isolation region, an isolation N well and a shallow trench isolation layer stacked sequentially from top to bottom between adjacent pixel units, wherein:

[0015] The shallow trench isolation layer is embedded in the lower surface of the P-type epitaxial layer, and the isolation N-well is arranged on the upper surface of the shallow trench isolation layer and contacts with the lower surface of the N-type buried layer;

[0016] 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 separate the N-type buried layers of adjacent pixel units.

[0017] In one embodiment of the present invention, the shared cathode comprises a deep N well, an N+ doped well and a cathode electrode stacked in sequence from top to bottom, wherein:

[0018] 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 contacts the lower surface of the N-type buried layer.

[0019] In one embodiment of the present invention, the nano moth-eye anti-reflection structure comprises a moth-eye anti-reflection microstructure, an anti-reflection film and a flat layer, wherein:

[0020] The moth-eye anti-reflection microstructure comprises a plurality of nano moth-eye anti-reflection microstructures, wherein 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;

[0021] The flat layer is filled in the gaps between the plurality of nano moth-eye anti-reflection microstructures to form flat upper and lower surfaces, and the microlens is arranged above the flat layer;

[0022] The anti-reflection film is located between two adjacent structures consisting of the moth-eye anti-reflection microstructure and the flat layer.

[0023] In one 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 a Si surface, and the refractive index of the microlens material is less than the refractive index of the flat layer material and less than the refractive index of the moth-eye anti-reflection microstructure material.

[0024] In one embodiment of the present invention, the anti-reflection film is TiO2, ZrO2 or a combination thereof.

[0025] In one embodiment of the present invention, the moth-eye anti-reflection microstructure is a bullet-shaped nanostructure, a nano-truncated cone structure, a parabola-shaped nanostructure, a Gaussian surface-shaped nanostructure or a nano-cone structure.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The single-photon avalanche diode of the present invention combines nano moth-eye anti-reflection microstructures, microlenses and photoelectric detection devices. The nano moth-eye anti-reflection structure is etched or grown on the traditional photoelectric detection device, and the reflection enhancement structure is used between the pixel units to increase the reflection of useless photons, so as to maximize the use of photons irradiated on the detection chip, and the microstructure and microlens size are optimized for specific wavelengths to achieve high window transmittance in specific bands, improve quantum efficiency and thus improve detection efficiency. Efficient long-distance low-light detection is achieved.

[0028] 2. The single-photon avalanche diode of the present invention increases the effective filling rate of the device by adding a microlens structure, reduces light reflection by a nano moth-eye anti-reflection structure, and increases the utilization rate of photons in the echo signal. The n+ / P structure enables electrons to participate in avalanches in the high-field absorption region, and the electron avalanche ionization rate is relatively high, which can further improve the quantum efficiency. The detection efficiency of the device can be ultimately improved by improving the filling rate, quantum efficiency, and photon utilization.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1It is a top view of a part of a 4×4 array pixel structure of a single photon avalanche diode provided by an embodiment of the present invention;

[0031] Figure 2 is along Figure 1 The cross-sectional view taken along line AA in FIG.

[0032] Figure 3 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;

[0033] Figure 4 is a cross-sectional schematic diagram of a shared cathode provided by an embodiment of the present invention;

[0034] Figure 5 is a schematic structural diagram of a moth-eye anti-reflection microstructure with randomly distributed triangular pyramids provided by an embodiment of the present invention;

[0035] Figure 6 This 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.

[0036] Description of reference numerals:

[0037] 1-pixel unit; 11-diode active area; 111-P-type substrate layer; 112-P-type epitaxial layer; 113-N-type buried layer; 114-p+ active layer; 115-active area photon reflection metal plate; 116-anode electrode; 117-wiring layer; 12-moth-eye anti-reflection structure; 121-moth-eye anti-reflection microstructure; 122-anti-reflection film; 123-flat layer; 13-microlens; 2-shared cathode; 21-deep N well; 22-N+ doped well; 23-cathode electrode; 3-isolation unit; 31-deep trench isolation area; 32-isolation N well; 33-shallow trench isolation layer. DETAILED DESCRIPTION

[0038] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, a single photon avalanche diode proposed according to the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0039] The above and other technical contents, features and effects of the present invention are clearly presented in the following detailed description of the specific implementation modes in conjunction with the accompanying drawings. Through the description of the specific implementation modes, the technical means and effects adopted by the present invention to achieve the predetermined purpose can be more deeply and specifically understood. However, the attached drawings are only for reference and explanation purposes and are not used to limit the technical solutions of the present invention.

[0040] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants are intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements, but also other elements that are not explicitly listed. In the absence of more restrictions, the elements defined by the statement "including one..." do not exclude the existence of other identical elements in the article or device including the elements.

[0041] See also Figure 1 and Figure 2 , Figure 1 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 along Figure 1 The cross-sectional view taken along the AA line in FIG. The single-photon avalanche diode of the present embodiment includes 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, wherein the pixel unit 1 includes a diode active area 11, a nano moth-eye anti-reflection structure 12 and a microlens 13, the nano moth-eye anti-reflection structure 12 is arranged on the upper surface of the diode active area 11, and the microlens 13 is arranged 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, and is used to achieve focusing, and to gather incident light from a larger incident surface to the diode active area 11, the nano moth-eye anti-reflection structure 12 is used to reduce light reflection and increase the light transmittance of the photosensitive area, and the diode active area 11 multiplies a single photon into a photocurrent through the avalanche multiplication effect.

[0042] The shared cathode 2 is arranged in the area surrounded by the top corners of each of four adjacent pixel units 1, and is used to supply power to the diode active area 11. The isolation unit 3 is arranged between two adjacent pixel units 1, and is used to optically and electrically isolate the adjacent pixel units 1.

[0043] Furthermore, the diode active area 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 area photon reflection metal plate 115, an anode electrode 116 and a 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 arranged on the upper surface of the P-type substrate layer 111. The N-type buried layer 113 forms a multiplied main junction with the P-type epitaxial layer 112 to form a strong electric field to sense the arrival of photons. During the preparation process, before growing the P-type epitaxial layer 112, doping is performed on the P-type substrate layer 111 to form the N-type buried layer 113, which is a high-concentration doping. Preferably, the doping element of the N-type buried layer 113 is a group III element 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 to 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 It should be noted that the P-type doping in this embodiment is doping with group V elements, such as boron, aluminum, etc., and the N-type doping is doping with group III elements, such as phosphorus, antimony, etc. Since the doping concentration of the P-type epitaxial layer 112 is low and the depletion region width is wide, it is helpful to improve the device detection probability and spectral response range.

[0044] In this embodiment, the N-type buried layer 113 is shared by all pixel units to form an entire continuous area.

[0045] The avalanche multiplication region composed of the N-type buried layer 113 and the P-type epitaxial layer 112 has a main depletion width extending 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 high-field absorption region, electrons mainly participate in the avalanche, and the electron avalanche ionization rate is relatively high, which can further improve the quantum efficiency.

[0046] The p+ active layer 114 is arranged 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 a 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 .

[0047] The anode electrode 116 is embedded in the upper surface of the wiring layer 117 and the upper surface of the anode electrode 116 contacts the lower surface of the p+ active layer 114, and the active region photon reflection metal plate 115 is embedded in the lower surface of the wiring layer 117. Further, the active region photon reflection metal plate 115 is located directly below the p+ active layer 114, and can reflect the photons irradiated thereon back into the device to increase the utilization rate of the photons, and can enhance the device detection probability at a longer wavelength.

[0048] The anode electrode 116 is located at the center of the lower surface of the P+ active layer 114. It is a floating potential and is connected to the subsequent circuit. The large current generated by the avalanche multiplication effect causes the subsequent circuit to produce a potential change at the fixed node, thereby reflecting the arrival of the photon. Further, in order to avoid the anode electrode 116 connecting to a large load capacitor, the anode electrode 116 and the active region photon reflection metal plate 115 are electrically isolated by the dielectric in the wiring layer 117, and the anode electrode 116 is connected to the circuit of the lower chip through the horizontal and vertical wiring in the wiring layer 117, and the active region photon reflection metal plate 115 is in a floating state.

[0049] Furthermore, the isolation unit 3 includes a deep trench isolation region 31, an isolation N well 32 and a shallow trench isolation layer 33 stacked in sequence from top to bottom between adjacent pixel units 1, wherein the shallow trench isolation layer 33 is embedded in 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 contacts 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 interior of the isolation N well 32.

[0050] The isolation N-well 32 isolates two adjacent pixel units and forms a reverse biased PN junction structure with the P-type epitaxial layer 102 to avoid crosstalk between adjacent pixel units caused by carrier drift or tunneling.

[0051] 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. The isolation N-well 32 is connected to the N-type buried layer 113 in the vertical direction, serving as a protection ring for the multiplied main junction formed by the N-type buried layer 113 and the P-type epitaxial layer 112, leaving a sufficient safety distance to prevent traps caused by the etching and filling processes from having a negative impact on the dark count rate and after pulses.

[0052] See also Figure 3 , Figure 3It is a cross-sectional schematic diagram of a pixel unit located at the edge of a device provided by an embodiment of the present invention. As described 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 its N-type buried layer 113 is slightly smaller than the P-type substrate layer 111 and the P-type epitaxial 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. Similarly, the isolation N well 32 and the shallow trench isolation layer 33 are separated from the p+ active layer 114 and wrapped inside the P-type epitaxial layer 112.

[0053] For further information, see Figure 4 , Figure 4 1 is a cross-sectional schematic diagram of a shared cathode provided by an embodiment of the present invention. The shared cathode 2 of this embodiment includes a deep N well 21, an N+ doped well 22 and a cathode electrode 23 stacked in sequence from top to bottom, 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 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.

[0054] The cathode electrode 23 forms an 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 area 1. In order to avoid the potential inconsistency caused by the lateral resistance loss of the N-well buried layer 113, each shared cathode 2 provides a bias voltage for the adjacent four pixels.

[0055] Furthermore, 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 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, such as Figure 5 As shown; the flat layer 123 is filled in the gaps between the multiple nano moth-eye anti-reflection microstructures to form flat upper and lower surfaces, which is conducive to the production and stability of the microlens. The microlens 13 is arranged above the flat layer 123; the anti-reflection film 122 is located between two adjacent structures composed of the moth-eye anti-reflection microstructure 121 and the flat layer 123. The microlens 13 is arranged above the flat layer 123, covering the entire pixel photosensitive area, and focusing photons to the p+ active layer 114 through refraction.

[0056] Preferably, the moth-eye anti-reflection microstructure 121 and the flat layer 123 of this embodiment are both thin film materials that can be grown on the surface of Si. Furthermore, 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, a Gaussian surface nanostructure or a nano-cone structure. The refractive index of the microlens 13 is less than the refractive index of the flat layer 123, and the refractive index of the moth-eye anti-reflection microstructure 121 is less than the refractive index of Si. The flat layer 123 can be SiO2, and the moth-eye anti-reflection microstructure can be 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.

[0057] It should be noted that the height, density and diameter of the random array nano moth-eye anti-reflection microstructure 121 are randomly distributed around the average height, average density and average diameter, respectively. Compared with the periodic nanostructure, it has better anti-reflection characteristics, and the specific distribution is optimized for different wavelengths, which can make the photoelectric detection device have a window anti-reflection effect. Figure 6 This is a reflection curve diagram of a randomly distributed moth-eye microstructure with an average diameter of 100nm and an average height of 400nm provided by an embodiment of the present invention. It can be seen that its reflectivity is very low at 550nm and its transmittance is good. Further, the manufacturing process of the moth-eye anti-reflection microstructure 121 can be binary lithography technology, laser direct writing technology, electron beam lithography, reactive ion etching, etc.

[0058] The anti-reflection film 122 can reflect the photons that cannot be used in the avalanche multiplication zone to avoid side breakdown and dark counts. The anti-reflection film 122 is a thin film with low laser damage resistance and high refractive index, which can be titanium dioxide (TiO2)\zirconia (ZrO2) or a combination thereof. The thickness is optimized in the optical simulation software according to the laser wavelength to obtain the optimal value.

[0059] The microlens 13 has different curvatures for different wavelengths, and gathers all the light rays irradiating the surface of the photosensitive device into the avalanche multiplication region, thereby improving the photon utilization rate.

[0060] Furthermore, the single-photon avalanche diode of this embodiment is often used in the receiving end of a laser radar, and the specific working process is as follows: the photodetector receives the target echo reflected from the target, and the target echo first contacts the microlens, which realizes the focusing effect and focuses the light irradiated on the surface of the diode onto 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 light transmittance of the photosensitive area. At the same time, the device is biased to a reverse bias 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 pulse current. The current flows through the anode electrode to the subsequent circuit, and the subsequent circuit predicts the arrival of the photon by sensing the pulse current.

[0061] In summary, the single-photon avalanche diode of this embodiment combines the nano moth-eye anti-reflection microstructure, microlens and photoelectric detection device, etches or grows the nano moth-eye anti-reflection structure on the traditional photoelectric detection device, and uses the anti-reflection structure between the pixel 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 a specific band, improve quantum efficiency and thus improve detection efficiency. Efficient long-distance low-light detection is achieved. In addition, the single-photon avalanche diode increases the effective filling rate of the device by adding a microlens structure, reduces the reflection of light by the nano moth-eye anti-reflection structure, increases the utilization rate of photons in the echo signal, and makes the avalanche mainly participated by electrons within the high field absorption region through the n+ / P structure, 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 finally improved.

[0062] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A single photon avalanche diode, characterized in that: The invention 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), wherein the pixel unit (1) comprises a diode active region (11), a nano moth-eye anti-reflection structure (12) and a micro lens (13), the nano moth-eye anti-reflection structure (12) being arranged on the upper surface of the diode active region (11), and the micro lens (13) being arranged on the upper surface of the nano moth-eye anti-reflection structure (12); The shared cathode (2) is arranged in a region enclosed by the top corners of each of four adjacent pixel units (1); the isolation unit (3) is arranged between two adjacent pixel units (1) and is used to optically and electrically isolate adjacent pixel units (1); The diode active region (11) comprises 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 reflection metal plate (115), an anode electrode (116) and a 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 arranged on the upper surface of the P-type substrate layer (111); The p+ active layer (114) is arranged at the center of the lower surface of the P-type epitaxial layer (112); The anode electrode (116) is embedded in the upper surface of the wiring layer (117), and the upper surface of the anode electrode (116) contacts the lower surface of the p+ active layer (114), and the active region photon reflection metal plate (115) is embedded in the lower surface of the wiring layer (117); The isolation unit (3) comprises a deep trench isolation region (31), an isolation N well (32) and a shallow trench isolation layer (33) which are sequentially stacked from top to bottom between adjacent pixel units (1), wherein the shallow trench isolation layer (33) is embedded in 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 contacts 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 interior of the isolation N-well (32) and is capable of spacing the N-type buried layers (113) of adjacent pixel units (1); The shared cathode (2) comprises a deep N well (21), an N+ doped well (22) and a cathode electrode (23) which are stacked in sequence from top to bottom, 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 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).

2. The single photon avalanche diode according to claim 1, characterized in that: The P-type substrate layer (111) is a Si-based substrate doped with phosphorus or antimony and has a thickness of 3 to 10 μm.

3. The single photon avalanche diode according to claim 1, characterized in that: The nano moth-eye anti-reflection structure (12) comprises 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) comprises 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 an average height, an average density and an average diameter, respectively, and the diameters gradually decrease from bottom to top; The flat layer (123) is filled in the gaps between the plurality of nano moth-eye anti-reflection microstructures to form flat upper and lower surfaces, and the microlens (13) is arranged above the flat layer (123); The anti-reflection film (122) is located between two adjacent structures consisting of the moth-eye anti-reflection microstructure (121) and the flat layer (123).

4. The single photon avalanche diode according to claim 3, characterized in that: The moth-eye anti-reflection microstructure (121) and the flat layer (123) are both thin film materials that can be grown on a Si surface, and the refractive index of the microlens (13) material is less than the refractive index of the flat layer (123) material and less than the refractive index of the moth-eye anti-reflection microstructure (121) material.

5. The single photon avalanche diode according to claim 3, characterized in that: The anti-reflection film (122) is TiO2, ZrO2 or a combination thereof.

6. The single photon avalanche diode according to any one of claims 3 to 5, characterized in that: The moth-eye anti-reflection microstructure (121) is a bullet-shaped nanostructure, a nano-truncated cone structure, a parabola-shaped nanostructure, a Gaussian surface-shaped nanostructure or a nano-cone structure.

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