CN114628424A - Single photon avalanche diode - Google Patents
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- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14601—Structural or functional details thereof
- H01L27/14625—Optical elements or arrangements associated with the device
- H01L27/14627—Microlenses
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- H01L27/144—Devices controlled by radiation
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- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
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Abstract
The invention discloses a single photon avalanche diode, which comprises a plurality of pixel units arranged in an array manner, and a shared cathode and an isolation unit which are arranged between adjacent pixel units, wherein each pixel unit comprises a diode active area, a nano moth-eye anti-reflection structure and a micro lens, the nano moth-eye anti-reflection structure is arranged on the upper surface of the diode active area, and the micro lens is arranged on the upper surface of the nano moth-eye anti-reflection structure; the shared cathode is arranged in an area surrounded by the top corners of every four adjacent pixel units; the isolation unit is arranged between two adjacent pixel units and used for optically and electrically isolating the adjacent pixel units. The nano moth-eye antireflection microstructure, the micro lens and the photoelectric detector are combined, reflection of light in a specific wave band is reduced, and the utilization rate of photons in an echo signal is increased, so that quantum efficiency is improved, and the detection efficiency of a system is improved.
Description
Technical Field
The invention belongs to the technical field of microelectronic photoelectric devices, and particularly relates to a single photon avalanche diode.
Background
In recent years, remote active imaging can provide high-resolution three-dimensional imaging of a detected target, and has wide application prospect in the fields of remote sensing and target identification. As an important means for realizing remote active imaging, the single photon laser radar obtains distance information of a target by irradiating a detection target with a laser beam and measuring a Time of Flight (ToF) of a reflected light signal, and obtains three-dimensional distance information by two-dimensionally scanning a detection object.
Single Photon Avalanche Diode (SPAD) is one of the best candidates for long-distance low-light detection because of its nearly infinite gain, high time resolution and Single Photon sensitivity. In addition, the integration of SPADs in CMOS (Complementary Metal Oxide Semiconductor) processes is of great interest due to their cost-effectiveness, mass-production capability, and ease of integration. Many advanced solutions have emerged, including the most advanced technology nodes, microlenses and 3D integration.
However, as the imaging distance increases, the return of photon signals from the target becomes more sparse. Therefore, it becomes important to improve the detection efficiency of the device, which is theoretically limited by the detection probability and the quantum efficiency, and how to improve the photon utilization rate is an urgent problem to be solved for improving the quantum efficiency.
Disclosure of Invention
In order to solve the above problems in the prior art, the present invention provides a single photon avalanche diode. The technical problem to be solved by the invention is realized by the following technical scheme:
the invention provides a single photon avalanche diode, which comprises a plurality of pixel units arranged in an array, and a shared cathode and an isolation unit arranged between the adjacent pixel units, wherein,
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;
the shared cathode is arranged in an area surrounded by the top corners of every four adjacent pixel units; the isolation unit is arranged between two adjacent pixel units and used for optically and electrically isolating the adjacent pixel units.
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,
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 antireflection structure is arranged on the upper surface of the P-type substrate layer;
the P + active layer is arranged in 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, the upper surface of the anode electrode is in contact with the lower surface of the p + active layer, and the active region photon reflection metal plate is embedded on the lower surface of the wiring layer.
In one embodiment of the invention, the P type substrate layer is a Si-based substrate doped with phosphorus or antimony, and the thickness is 3-10 μm.
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,
the shallow groove 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 groove isolation layer and is in contact with the lower surface of the N type buried layer;
the deep groove isolation region extends to the inside of the isolation N well from the upper surface of the P-type substrate layer and can be spaced from the N-type buried layer adjacent to the pixel unit.
In one embodiment of the invention, the shared cathode comprises a deep N well, an N + doped well and a cathode electrode which are sequentially stacked from top to bottom, wherein,
the deep N well and the N + doped well are arranged in the P-type epitaxial layer, the cathode electrode is located in the wiring layer, and the upper surface of the deep N well is in contact with the lower surface of the N-type buried layer.
In one embodiment of the present invention, the nano-moth-eye antireflection structure includes a moth-eye antireflection microstructure, an antireflection film, and a planarization layer, wherein,
the moth-eye antireflection microstructure comprises a plurality of nano moth-eye antireflection microstructures, wherein the heights, densities and diameters of the nano moth-eye antireflection microstructures are randomly distributed on the left and right of the average height, the average density and the average diameter respectively, and the diameters of the nano moth-eye antireflection microstructures are gradually reduced from bottom to top;
the flat layer is filled in the gaps of the nano moth-eye antireflection microstructures to form flat upper and lower surfaces, and the micro lenses are arranged above the flat layer;
the reflection-increasing film is positioned between two adjacent structures consisting of the moth-eye reflection-reducing microstructure and the flat layer.
In one embodiment of the present invention, the moth-eye antireflection microstructure and the planarization 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 planarization layer material < the refractive index of the moth-eye antireflection microstructure material
In one embodiment of the invention, the antireflective film is TiO2、ZrO2Or a combination thereof.
In one embodiment of the present invention, the moth-eye antireflection microstructure is a bullet-shaped nanostructure, a nanocomplat structure, a parabolic nanostructure, a gaussian nanostructure, or a nanocolumnar structure.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the single photon avalanche diode, the nano moth-eye antireflection microstructure, the micro lens and the photoelectric detector are combined, the nano moth-eye antireflection structure is etched or grown on the traditional photoelectric detector, reflection of useless photons is increased by using the antireflection structure among pixel units, photons irradiated on a detection chip are utilized to the maximum extent, the sizes of the microstructure and the micro lens are optimized according to specific wavelength, high window transmissivity of a specific waveband is realized, and quantum efficiency is improved, so that detection efficiency is improved. And high-efficiency remote low-light detection is realized.
2. The single photon avalanche diode increases the effective filling rate of the device by adding the micro-lens structure, reduces the reflection of light by the nano moth-eye antireflection structure, increases the utilization rate of photons in echo signals, enables electrons to participate in avalanche within the range of a high-field absorption region through the n +/P structure, has high electron avalanche ionization rate, can further improve the quantum efficiency, and finally can improve the detection efficiency of the device by improving the filling rate, the quantum efficiency and the photon utilization rate.
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Drawings
Figure 1 is a top view of a partial 4 x 4 array pixel structure for a single photon avalanche diode according to an embodiment of the present invention;
FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1;
FIG. 3 is a schematic cross-sectional view of a pixel cell at the edge of a device according to an embodiment of the present invention;
FIG. 4 is a schematic cross-sectional view of a shared cathode according to an embodiment of the present invention;
fig. 5 is a schematic structural diagram of a moth-eye anti-reflective microstructure with randomly distributed triangular pyramids according to an embodiment of the present invention;
FIG. 6 is a reflection graph of a random moth-eye microstructure with an average diameter of 100nm and an average height of 400nm according to an embodiment of the present invention.
Description of reference numerals:
1-pixel unit; 11-diode active region; a 111-P type underlayer; 112-P type epitaxial layer; 113-N type buried layer; 114-p + active layer; 115-active region photon reflective metal plate; 116-an anode electrode; 117-routing layer; 12-moth eye antireflection structure; 121-moth eye antireflective microstructure; 122-a reflection increasing film; 123-a planarization layer; 13-a microlens; 2-a shared cathode; 21-deep N-well; a 22-N + doped well; 23-a cathode electrode; 3-an isolation unit; 31-deep trench isolation regions; 32-isolated N-wells; 33-shallow trench isolation.
Detailed Description
To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, a single photon avalanche diode according to the present invention will be described in detail with reference to the accompanying drawings and the detailed description.
The foregoing and other technical matters, features and effects of the present invention will be apparent from the following detailed description of the embodiments, which is to be read in connection with the accompanying drawings. The technical means and effects of the present invention adopted to achieve the predetermined purpose can be more deeply and specifically understood through the description of the specific embodiments, however, the attached drawings are provided for reference and description only and are not used for limiting the technical scheme of the present invention.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or device that comprises a list of elements does not include only those elements but may include other elements not expressly listed. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of additional like elements in the article or device comprising the element.
Referring to fig. 1 and 2, fig. 1 is a top view of a portion of a 4 × 4 array 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 of fig. 1. 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 disposed between adjacent pixel units 1, where the pixel units 1 include a diode active region 11, a nano moth-eye anti-reflection structure 12, and a microlens 13, the nano moth-eye anti-reflection structure 12 is disposed on an upper surface of the diode active region 11, and the microlens 13 is disposed on an 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 for focusing and collecting incident light with a large incident surface to the diode active region 11, the nano moth-eye antireflection structure 12 is used for reducing reflection of light and increasing the light transmission amount of the photosensitive area, and the diode active region 11 multiplies a single photon into a photo-generated current by an avalanche multiplication effect.
The shared cathode 2 is arranged in the region enclosed by the top corners of every adjacent four pixel units 1 and is used for supplying power to the diode active region 11. The isolation unit 3 is disposed between two adjacent pixel units 1, and is used 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 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 antireflection structure 12 is disposed on an upper surface of the P-type substrate layer 111. The buried N-type layer 113 and the epitaxial P-type layer 112 form a multiplied main junction to form a strong electric field to sense the arrival of photons. In the preparation process, before the P-type epitaxial layer 112 is grown, doping is carried out on the P-type substrate layer 111 to form an N-type buried layer 113, and the N-type buried layer is doped at high concentration. Preferably, the doping element of the N-type buried layer 113 is a group III element such as phosphorus, antimony, etc., with a doping concentration of about 5e18cm-3. The P-type substrate layer 111 is a Si-based substrate doped with phosphorus or antimony, has a thickness of 3-10 μm and a doping concentration of about 5e15cm-3(ii) a The doping concentration of the P-type epitaxial layer 112 is about 1e15cm-3It should be noted that the P-type doping in this embodiment is doped with a group v element, for example: boron, aluminum, etc., N-type doped with group III elements, such as: phosphorus, antimony, and the like. Due to the fact that the doping concentration of the P-type epitaxial layer 112 is low, the width of a depletion region is wide, and the device detection probability and the spectral response range are improved.
In the present embodiment, the N-type buried layer 113 is shared by all pixel units, forming a whole continuous region.
The avalanche multiplication region formed by the N-type buried layer 113 and the P-type epitaxial layer 112 mainly has the depletion width extending in the P-type epitaxial layer 112, the electric field points from the P-type epitaxial layer 112 to the N-type buried layer 113, electrons mainly participate in avalanche in the high-field absorption region range, the electron avalanche ionization rate is high, and the quantum efficiency can be further improved.
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 a single pixel, and is formed by doping in the P-type epitaxial layer 112 during the preparation process. Preferably, the p + active layer 114 is doped with phosphorus or antimony at a doping concentration of 1e19cm-3-5e20cm-3。
The anode electrode 116 is located at the center of the lower surface of the P + active layer 114, is at a floating potential, and is connected to a subsequent circuit, and a large current generated by an avalanche multiplication effect causes a potential change at a node fixed by the subsequent circuit, thereby reflecting the arrival of photons. Further, to avoid the anode electrode 116 connecting a large load capacitance, the anode electrode 116 is electrically isolated from the active region photon reflection metal plate 115 by the medium in the wiring layer 117, and the anode electrode 116 is connected to the circuit of the lower chip through horizontal and vertical wirings in the wiring layer 117, and the active region photon reflection metal plate 115 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 region 33 stacked in sequence from top to bottom between adjacent pixel units 1, wherein the shallow trench isolation region 33 is embedded in the lower surface of the P-type epitaxial layer 112, and the isolation N-well 32 is disposed on the upper surface of the shallow trench isolation region 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 inside of the isolation N-well 32.
The isolation N-well 32 isolates two adjacent pixel cells, and avoids crosstalk between adjacent pixel cells caused by carrier drift or tunneling by forming a reverse-biased PN junction structure with the P-type epitaxial layer 102.
The deep groove isolation region 31 is located between the two pixel units and used for isolating the adjacent pixel units, the width of the deep groove isolation region 31 is smaller than that of the isolation N well 32, the isolation N well 32 is vertically connected with the N-type buried layer 113 and serves as a protection ring of a multiplication main junction formed by the N-type buried layer 113 and the P-type epitaxial layer 112, and a sufficient safety distance is reserved to prevent traps caused by etching and filling processes from generating negative influences on a dark count rate and a rear pulse.
Referring to fig. 3, fig. 3 is a schematic cross-sectional view of a pixel unit located at an edge of a device according to an embodiment of the invention. As described above, the single photon avalanche diode of the present embodiment includes the plurality of pixel units 1 arranged in an array, and for the pixel units located at the edge of the device, the size of the 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, and meanwhile, the lower surface of the edge of the N-type buried layer 113 is sequentially provided with the isolated N-well 32 and the shallow trench isolation layer 33. Similarly, an isolated N-well 32 and a shallow trench isolation 33 are spaced apart from the P + active layer 114 and wrapped inside the P-type epitaxial layer 112.
Further, referring to fig. 4, fig. 4 is a schematic cross-sectional view of a shared cathode according to an embodiment of the present invention. The shared cathode 2 of the present embodiment includes a deep N well 21, an N + doped well 22, and a cathode electrode 23 sequentially stacked from top to bottom, where the deep N well 21 and the N + doped well 22 are disposed inside the P-type epitaxial layer 112, the cathode electrode 23 is located inside the wiring layer 117, and an upper surface of the deep N well 21 is in contact with a lower surface of the N-type buried layer 113.
The cathode electrode 23 is electrically contacted with the N-type buried layer 113 through the N + doped well 22 and the deep N-well 21 to provide a reverse bias voltage to the N-type buried layer 113 in the adjacent diode active region 1. In order to avoid potential inconsistency caused by lateral resistive loss of the N-well buried layer 113, each shared cathode 2 supplies bias voltages to adjacent 4 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 microstructures, and heights, densities and diameters 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 gradually decrease from bottom to top in diameter, as shown in fig. 5; the flat layer 123 is filled in the gaps of the nano moth-eye antireflection microstructures to form flat upper and lower surfaces, which is beneficial to the manufacturing and stability of the micro lens, and the micro lens 13 is arranged above the flat layer 123; the antireflection film 122 is located between two adjacent structures consisting of the moth-eye antireflection microstructure 121 and the planarization layer 123. The microlens 13 is disposed over the planarization layer 123, covering the entire pixel photosensitive area, and focuses photons by refraction to the p + active layer 114.
Preferably, the moth eye anti-reflective microstructure 121 and the planarization layer 123 of the present embodiment are both thin film materials that can be grown on a Si surface. Further, the diameter of the moth-eye antireflection microstructure 121 gradually decreases from bottom to top, and preferably, the moth-eye antireflection microstructure 121 is a bullet-shaped nanostructure, a nanocone structure, a parabolic nanostructure, a gaussian nanostructure, or a nanocone structure. The refractive index of the microlens 13 < the refractive index of the flattening layer 123 < the refractive index of the moth-eye antireflection microstructure 121 < the refractive index of Si. The planarization layer 123 may be SiO2The moth-eye antireflection microstructure may be SiN. The moth-eye antireflection microstructure 121 can absorb most of incident light, and the refractive index continuously changes from top to bottom without reflection, thereby improving the photon utilization rate.
The heights, densities, and diameters of the random array nano-moth-eye antireflection microstructures 121 are randomly distributed around the average height, average density, and average diameter, respectively. Compared with a periodic nano structure, the light-emitting diode has better antireflection property, the specific distribution is optimized aiming at different wavelengths, and the photoelectric detector has a window antireflection function. Fig. 6 is a reflection curve diagram of a moth-eye microstructure with an average diameter of 100nm and an average height of 400nm, which shows that the reflectance is very low at 550nm and the transmittance is good. Further, the fabrication process of the moth-eye antireflection microstructure 121 may be a binary lithography technique, a laser direct writing technique, an electron beam lithography, a reactive ion etching, or the like.
The reflection increasing film 122 can reflect photons which cannot be utilized by the avalanche multiplication region, so as to avoid side breakdown and dark counting. The reflection enhancing film 122 is a thin film with small laser damage resistance and high refractive index, and can be titanium dioxide (TiO)2) Zirconium oxide (ZrO)2) And the like or a combination thereof, and the thickness is optimized in an optical simulation software according to the laser wavelength in a simulation mode to obtain an optimal value.
The micro lens 13 has different curvatures aiming at different wavelengths, and gathers all light rays irradiated on the surface of the photosensitive device to an avalanche multiplication region, so that the photon utilization rate is improved.
Further, the single photon avalanche diode of this embodiment is commonly used for the receiving end of the laser radar, and the specific working process is as follows: the photoelectric detector receives a target echo reflected from a target, the target echo firstly contacts the micro lens, the micro lens realizes a light condensation effect, light irradiated on the surface of the diode is focused on the surface of the moth-eye antireflection structure above the avalanche multiplication region, the moth-eye antireflection structure reduces reflection of the light, and the light transmission quantity of the photosensitive region is increased. Meanwhile, the device is biased to a reverse bias state of high breakdown voltage through the cathode shared electrode, when the device absorbs a photon, the avalanche multiplication effect of the current carrier in the active region of the diode absorbs a single photon and amplifies the single photon into a pulse current, the current flows to a subsequent circuit through the anode electrode, and the subsequent circuit predicts the arrival of the photon through the induction of the pulse current.
In summary, in the single photon avalanche diode of the embodiment, the nano moth-eye antireflection microstructure, the micro lens and the photodetector device are combined, the nano moth-eye antireflection structure is etched or grown on the conventional photodetector device, reflection of useless photons is increased by using the antireflection structure between pixel units, photons irradiated onto a detection chip are utilized to the maximum extent, the sizes of the microstructure and the micro lens are optimized for a specific wavelength, high window transmittance of a specific waveband is realized, and quantum efficiency is improved, so that detection efficiency is improved. And high-efficiency remote low-light detection is realized. 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 by the nano moth-eye antireflection structure, increases the utilization rate of photons in echo signals, enables electrons to participate in avalanche within the range of a high-field absorption region through the n +/P structure, has high electron avalanche ionization rate, can further improve the quantum efficiency, and finally can improve the detection efficiency of the device by improving the filling rate, the quantum efficiency and the photon utilization rate.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.
Claims (9)
1. A single photon avalanche diode comprising a plurality of pixel cells (1) arranged in an array and a shared cathode (2) and an isolation unit (3) arranged between adjacent pixel cells (1), wherein,
the pixel unit (1) comprises a diode active region (11), a nanometer moth-eye anti-reflection structure (12) and a micro lens (13), wherein the nanometer moth-eye anti-reflection structure (12) is arranged on the upper surface of the diode active region (11), and the micro lens (13) is arranged on the upper surface of the nanometer moth-eye anti-reflection structure (12);
the shared cathode (2) is arranged in a region surrounded by the top corners of every four adjacent pixel units (1); the isolation unit (3) is arranged between two adjacent pixel units (1) and used for optically and electrically isolating the adjacent pixel units (1).
2. The single photon avalanche diode according to claim 1, characterized in that said diode active region (11) comprises a P-type substrate layer (111), a P-type epitaxial layer (112), a N-type buried layer (113), a P + active layer (114), an active region photon reflective 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 antireflection 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 inlaid on the upper surface of the wiring layer (117), the upper surface of the anode electrode (116) is in contact with the lower surface of the p + active layer (116), and the active region photon reflection metal plate (115) is inlaid on the lower surface of the wiring layer (117).
3. The single photon avalanche diode according to claim 2, characterized in that said P-type substrate layer (111) is a Si based substrate doped with phosphorus or antimony, with a thickness of 3-10 μm.
4. The single photon avalanche diode according to claim 2, characterized in that said isolation unit (3) comprises a deep trench isolation region (31), an isolation N-well (32) and a shallow trench isolation region (33) stacked in sequence from top to bottom between adjacent said pixel cells (1), 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 in contact with the lower surface of the N-type buried layer (113);
the deep groove isolation region (31) extends from the upper surface of the P-type substrate layer (111) to the inside of the isolation N well (32) and can be used for spacing an N-type buried layer (113) adjacent to the pixel unit (1).
5. The single photon avalanche diode according to claim 1, characterized in that said shared cathode (2) comprises, in a sequence from top to bottom, a deep N well (21), an N + doped well (22) and a cathode electrode (23) in a stack, 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).
6. The single photon avalanche diode according to claim 1, characterized in that said nano-moth-eye antireflection structure (12) comprises a moth-eye antireflection microstructure (121), an antireflection film (122) and a planarization layer (123),
the moth-eye antireflection microstructure (121) comprises a plurality of nano moth-eye antireflection microstructures, wherein the heights, densities and diameters of the nano moth-eye antireflection microstructures are randomly distributed on the left and right sides of the average height, average density and average diameter respectively, and the diameters of the nano moth-eye antireflection microstructures are gradually reduced from bottom to top;
the flat layer (123) is filled in the gaps of the plurality of nano-moth-eye antireflection microstructures to form flat upper and lower surfaces, and the micro lens (13) is arranged above the flat layer (123);
the reflection-increasing film (122) is positioned between two adjacent structures consisting of the moth-eye reflection-reducing microstructure (121) and the flat layer (123).
7. The single photon avalanche diode according to claim 6, characterized in that said moth eye antireflection microstructure (121) and said flattening layer (123) are both thin film materials that can be grown on Si surface, the refractive index of the microlens (13) material < the refractive index of the flattening layer (123) material < the refractive index of the moth eye antireflection microstructure (121) material.
8. The single photon avalanche diode according to claim 6, wherein said reflection increasing film (122) is TiO2、ZrO2Or a combination thereof.
9. The single photon avalanche diode according to any of the claims 6 to 8, characterized in that the moth-eye antireflection microstructure (121) is a bullet-like nanostructure, a nanocomplature structure, a parabolic nanostructure, a gaussian nanostructure or a nanocone structure.
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