Backside illuminated near-infrared response silicon avalanche four-quadrant detector and preparation method thereof

Abstract

The invention relates to a back-illuminated near-infrared response silicon avalanche four-quadrant detector and a preparation method thereof, and belongs to the field of photoelectron technology and semiconductor manufacturing process. The near-infrared detector provided by the invention adopts a back-illuminated device structure, specifically, a four-quadrant light incident surface is designed on the back surface of the device, an avalanche photodiode structure is designed on the front surface of the device, and the four-quadrant light incident surface and the avalanche photodiode are separated at the two ends of the device; according to the invention, on one hand, inter-quadrant edge breakdown of the silicon four-quadrant APD can be avoided, so that PN junction breakdown in advance and device failure can be avoided, and on the other hand, inter-quadrant distance reduction, detection blind area reduction and device noise reduction can be realized at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductors and optoelectronics, and relates to a back-illuminated near-infrared responsive silicon avalanche four-quadrant detector and a preparation method thereof. Background Art

[0002] Silicon avalanche photodiodes (APDs), as highly sensitive optoelectronic devices with intrinsic gain characteristics, are widely used in key areas such as weak light detection, fiber optic communications, laser ranging, and military guidance due to their excellent response speed, wide spectral adaptability, and high signal-to-noise ratio. Among them, the four-quadrant APD detector can achieve high-precision detection of the light spot position by dividing the photosensitive area into four independent quadrants, and plays an irreplaceable role in scenarios such as laser tracking and target positioning. However, the traditional direct-illuminated near-infrared silicon APD four-quadrant detector still has significant technical bottlenecks in structural design and performance optimization, which are specifically manifested in the following aspects:

[0003] 1. Traditional front-illuminated APD four-quadrant detectors usually integrate the photosensitive area and the avalanche multiplication area on the same surface of the device. In the reverse bias state, the edge area of ​​the PN junction will form a higher local electric field intensity due to the geometric curvature effect. This uneven distribution of the electric field can easily cause edge breakdown, causing the device to fail prematurely when it is far below the designed breakdown voltage. Although the existing technology attempts to alleviate the problem of edge electric field concentration by introducing guard ring structures (such as guard rings or cutoff rings), due to the design limitations of the physical size and doping concentration of the guard ring, it can only partially weaken the edge electric field and cannot completely eliminate the potential breakdown risk. In addition, the introduction of the guard ring requires additional device area, further compressing the effective photosensitive area and affecting the overall sensitivity of the detector.

[0004] 2. In a four-quadrant detector, the isolation design between pixels is the key to suppressing crosstalk and dark current. In order to reduce the risk of edge breakdown, the traditional front-illuminated structure usually requires a wider isolation area, but this design directly leads to the formation of a large non-sensitive area between adjacent pixels (i.e., a detection blind area). The existence of the detection blind area not only reduces the effective photosensitive area of ​​the device, but also affects the detection accuracy of the light spot position. Especially in applications that require high spatial resolution (such as laser guidance), an excessively large blind area will significantly weaken the positioning capability of the system. However, if the isolation distance is reduced in order to reduce the blind area, the electric field coupling effect between pixels will be aggravated, resulting in a further reduction in the breakdown threshold, forming a dilemma between stability and performance.

[0005] 3. The core advantage of APD lies in its avalanche multiplication effect, but this process introduces additional noise components, especially the excess noise factor (Excess Noise Factor) generated when holes participate in the multiplication. In the traditional direct-illuminated structure, photogenerated carriers (electrons and holes) may trigger the avalanche effect under a strong electric field, resulting in a significant increase in the noise level. Although noise can be partially suppressed by optimizing the material doping distribution and electric field gradient design, it is difficult to achieve low-noise output while maintaining high gain with existing technologies due to the symmetry of the device structure and process compatibility. In addition, the complex layout of the four-quadrant structure may introduce parasitic capacitance and resistance, further deteriorating the high-frequency response characteristics.

[0006] In summary, traditional direct-illuminated near-infrared silicon APD four-quadrant detectors still face challenges in structural design and performance optimization. Balancing breakdown suppression, blind zone reduction, noise control, and process compatibility is key to improving the overall performance of these devices. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a back-illuminated near-infrared responsive silicon avalanche four-quadrant detector and a preparation method thereof, adopting a back-illuminated device structure, and designing a four-quadrant light incident surface on the back of the device to avoid edge breakdown between quadrants of the silicon four-quadrant APD, while reducing the distance between quadrants and the detection blind area, and reducing device noise.

[0008] To achieve the above-mentioned object, the present invention provides a back-illuminated near-infrared responsive silicon avalanche four-quadrant detector, comprising:

[0009] substrate;

[0010] a unit avalanche photodiode located on the front side of the substrate;

[0011] A guard ring located on the front side of the substrate and distributed outside the avalanche photodiode;

[0012] a cutoff ring located on the front side of the substrate and distributed outside the guard ring;

[0013] a four-quadrant light incident structure located on the back side of the substrate;

[0014] an isolation ring located on the back side of the substrate and surrounding each pixel of the four-quadrant light incident structure; and

[0015] An N electrode and a P electrode are located on the front side and the back side of the substrate respectively.

[0016] Furthermore, the avalanche photodiode includes a P-avalanche region and an N+ photosensitive region located on the surface of the P-avalanche region.

[0017] Furthermore, a microstructure is included between the N+ photosensitive region and the N electrode of the avalanche photodiode. The microstructure is based on a silicon dioxide film, one side of which is etched with a honeycomb groove, and a layer of metal aluminum is deposited on the surface of the honeycomb groove.

[0018] Furthermore, in the four-quadrant light-incident structure, each quadrant includes a P+ contact region and an anti-reflection film located on the surface of the P+ contact region.

[0019] Furthermore, on the front side of the substrate, all areas except the avalanche photodiode and the N electrode are covered with an oxide layer; on the back side of the substrate, all areas except the four-quadrant light incident structure are covered with an oxide layer.

[0020] Another aspect of the present invention provides a method for preparing a back-illuminated near-infrared responsive silicon avalanche four-quadrant detector, the method comprising:

[0021] S1, obtaining a P-type single crystal substrate, and growing a first silicon dioxide film on a first surface of the single crystal substrate;

[0022] S2. Etching a cutoff ring, a guard ring, and an ion implantation window of an avalanche photodiode on the surface of the first silicon dioxide film on the first surface side of the single crystal substrate;

[0023] S3, performing ion implantation to form a cutoff ring, a guard ring, and an avalanche photodiode, respectively; wherein the guard ring 4 is distributed outside the avalanche photodiode, and the cutoff ring is distributed outside the guard ring;

[0024] S4, performing a thinning and polishing process on the second surface side of the single crystal substrate, and growing a second silicon dioxide film on the second surface;

[0025] S5, etching an isolation ring and four quadrants of ion implantation windows on the surface of the second silicon dioxide film on the second surface side of the single crystal substrate;

[0026] S6. Perform ion implantation to form an isolation ring and four quadrants of P+ contact regions, wherein each quadrant is surrounded by the isolation ring; and deposit an antireflection film on the surface of the P+ contact region in each quadrant;

[0027] S7. Form an N electrode and a P electrode on the first surface side and the second surface side respectively through a metal sputtering process, wherein the N electrode is in contact with the avalanche photodiode, and the P electrode is connected to the P+ contact region.

[0028] Furthermore, a microstructure is made between the avalanche photodiode and the N electrode. The microstructure is based on a silicon dioxide film. Honeycomb grooves are etched on one side of the silicon dioxide film, and a layer of metal aluminum is deposited on the surface of the honeycomb grooves.

[0029] Furthermore, the thickness of the first silicon dioxide film and the second silicon dioxide film are both 200 nm to 600 nm.

[0030] The beneficial effects of the present invention are as follows: the back-illuminated near-infrared responsive silicon avalanche four-quadrant detector proposed by the present invention has the following beneficial effects:

[0031] 1) In this detector, the avalanche photodiode and the four-quadrant light-input structure are fabricated on two surfaces of the device, respectively, so that the avalanche photodiode and the four-quadrant light-input structure are separated. This can avoid the premature breakdown of the PN junction edge caused by the four-quadrant light-input structure and the PN junction being integrated on the same surface in the front-illuminated APD four-quadrant detector;

[0032] 2) By fabricating the avalanche photodiode and the four-quadrant light-entry structure on two surfaces of the device, an isolation ring can be provided to reduce the distance between the quadrants of the four-quadrant light-entry structure, thereby increasing the detection area of ​​the device.

[0033] 3) When the back-illuminated silicon APD absorbs photons, the near-infrared wavelength photons undergo an attenuation process in the silicon, and the intensity of the photons reaching the avalanche zone length decreases. The electron-hole pairs generated within the avalanche zone length also decrease, and the number of holes participating in the multiplication effect decreases, thus effectively reducing device noise. At the same time, the back-illuminated silicon APD can effectively avoid edge breakdown problems and reduce dark current and noise.

[0034] 4) The present invention designs a microstructure between the avalanche photodiode and the N electrode, which can increase the absorptivity of the avalanche photodiode to incident light, thereby enhancing the responsiveness of the device to near-infrared light.

[0035] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0037] Figure 1 Schematic diagram of the structure of a traditional positive-illuminated silicon-based avalanche four-quadrant detector;

[0038] Figure 2 A schematic structural diagram of a back-illuminated silicon-based avalanche four-quadrant detector provided in one embodiment of the present invention;

[0039] Figure 3 Schematic diagram of the integrated microstructure.

[0040] Figure numerals: 1-P-type single crystal substrate, 2-front oxide layer, 3-P+ cut-off ring, 4-N+ ​​guard ring, 5-P-avalanche region, 6-N+ photosensitive region, 7-isolation ring, 8-antireflection film, 9-P+ contact region, 10-N electrode, 11-P electrode, 12-back oxide layer. DETAILED DESCRIPTION

[0041] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0042] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0043] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0044] like Figure 1The figure shows the structure of a traditional direct-illuminated near-infrared silicon APD four-quadrant detector. It integrates a four-quadrant structure on the light-incident surface, with each quadrant featuring a PN junction consisting of a P-valve region 5 and an N+ photosensitive region 6, known as an APD. Each quadrant is designed with a double guard ring structure to prevent premature breakdown at the PN junction edge. A cutoff ring structure is designed outside the quadrant region to reduce pixel dark current. While the guard ring structure increases the distance between pixels in a traditional direct-illuminated near-infrared silicon APD four-quadrant detector, it also increases the detection blind spot of each pixel, which is detrimental to the detector's performance.

[0045] To address this issue, the present invention proposes a back-illuminated near-infrared silicon APD four-quadrant detector. This design forms a unit structure by designing the photosensitive region and avalanche region on the front side of the device, thereby forming an APD of considerable size. The back side of the device serves as the light incident surface for the detector, and the light incident surface is designed to be divided into four quadrants. This structural design, which separates the four-quadrant light incident surface from the PN junction, avoids the premature breakdown of the PN junction edge caused by the integration of the four quadrants and the PN junction in the same direction in traditional front-illuminated APD four-quadrant detectors. It also minimizes the distance between the pixels in the four quadrants of the APD, thereby reducing detection blind spots and device noise.

[0046] Example 1

[0047] like Figure 2 As shown, a back-illuminated near-infrared responsive silicon avalanche four-quadrant detector provided in this embodiment includes a P-type single crystal substrate 1, a front oxide layer 2, a P+ cutoff ring 3, an N+ guard ring 4, a P- avalanche region 5, an N+ photosensitive region 6, an isolation ring 7, an anti-reflection film 8, a P+ contact region 9, an N electrode 10, a P electrode 11, and a back oxide layer 12.

[0048] The N+ photosensitive region 6 and the P- avalanche region 5 are formed in the center of the front surface of the P-type single crystal substrate 1 using a silicon planar process. The N+ guard ring 4 is located outside the N+ photosensitive region 6 and the P- avalanche region 5, and the P+ stop ring 3 is formed outside the N+ guard ring 4. Both the N+ guard ring 4 and the P+ stop ring 3 are formed using a silicon planar process.

[0049] An N electrode 10 is formed on the surface of the N+ photosensitive region 6 , and the front surface of the detector except for the N electrode 10 is covered by a front oxide layer 2 to protect the device.

[0050] Each of the four quadrants of the light-entering surface includes a P+ contact region 9 and an antireflection film 8 coated on the surface of the P+ contact region 9. Isolation rings 7 are designed between each quadrant and on the outside of each quadrant. The isolation rings 7 are formed through photolithography, boron ion implantation, phosphorus ion implantation, and high-temperature nitrogen push-bonding.

[0051] A P electrode 11 is also formed on the back of the near-infrared responsive silicon avalanche quadrant detector. The back of the detector except for the anti-reflection film 8 is covered by a back oxide layer 12 to protect the device.

[0052] In this embodiment, a microstructure is also fabricated between the N+ photosensitive region 6 and the N electrode 10 of the near-infrared responsive silicon avalanche quadrant detector, such as Figure 3 As shown in the figure, the microstructure is made of low-temperature silicon dioxide film through photolithography and dry etching processes. A layer of metal aluminum is also made on the surface of the microstructure as a reflective film, which effectively reflects the incident light reaching the APD, increases the APD's absorption rate of the incident light, and enhances the near-infrared response.

[0053] Example 2

[0054] This embodiment provides a method for preparing the back-illuminated near-infrared responsive silicon avalanche four-quadrant detector described in Example 1, the method comprising:

[0055] S1. A silicon dioxide film of a certain thickness is grown on the surface of the P-type single crystal material by a high-temperature oxidation process. The silicon dioxide film has a surface passivation effect and a thickness of 200nm to 600nm.

[0056] S2. A near-infrared responsive silicon avalanche photodiode unit structure is fabricated on the front surface of a P-type single crystal material using a silicon planar process, including a P+ cutoff ring 3, an N+ guard ring 4, a P- avalanche region 5, and an N+ photosensitive region 6; all of these parts are fabricated using an ion implantation doping process;

[0057] S3, growing a layer of silicon dioxide film on the surface of the N+ photosensitive region 6 by a low-temperature CVD method, and then etching honeycomb grooves on the surface of the silicon dioxide film by photolithography and dry etching processes;

[0058] S4. forming a layer of metal aluminum on the surface of the honeycomb grooves of the silicon dioxide film by a metal sputtering process to serve as a light reflecting surface;

[0059] S5. Performing thinning and polishing processing on the back side of the P-type single crystal material;

[0060] S6. Using a high-temperature oxidation process, a silicon dioxide film of a certain thickness is grown on the back of the P-type single crystal material. The silicon dioxide film has a surface passivation effect and a thickness of 200 nm to 600 nm.

[0061] S7. Using a double-sided photolithography process and an ion implantation process, an isolation ring 7 and a P+ contact region 9 are formed on the back side of the P-type single crystal material. The isolation ring 7 is designed to have a width of 5 μm to 20 μm. Phosphorus and boron ions are doped in the isolation ring 7 using an ion implantation process to form a PNP structure to reduce inter-quadrant crosstalk. The P+ contact region 9 is designed to have a quadrant isolation spacing of 40 μm to 60 μm to reduce detection blind spots.

[0062] S8. Deposit a silicon nitride antireflection film 8 on the back side using an LPCVD process; and manufacture an N electrode 10 and a P electrode 11 using a double-sided photolithography process and a metal sputtering process.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A back-illuminated near-infrared responsive silicon avalanche four-quadrant detector, characterized in that: The device includes: substrate; a unit avalanche photodiode located on the front side of the substrate; A guard ring located on the front side of the substrate and distributed outside the avalanche photodiode; a cutoff ring located on the front side of the substrate and distributed outside the guard ring; a four-quadrant light incident structure located on the back side of the substrate; an isolation ring located on the back side of the substrate and surrounding each pixel of the four-quadrant light incident structure; and An N electrode and a P electrode are located on the front side and the back side of the substrate respectively.

2. The back-illuminated near-infrared responsive silicon avalanche four-quadrant detector according to claim 1, characterized in that: The avalanche photodiode includes a P-avalanche region and an N+ photosensitive region located on the surface of the P-avalanche region.

3. The back-illuminated near-infrared responsive silicon avalanche four-quadrant detector according to claim 2, characterized in that: The invention also includes a microstructure, which is located between the N+ photosensitive region and the N electrode of the avalanche photodiode.

4. The back-illuminated near-infrared responsive silicon avalanche four-quadrant detector according to claim 3, characterized in that: The microstructure is based on a silicon dioxide film, one side of the silicon dioxide film is etched with a honeycomb groove, and a layer of metal aluminum is deposited on the surface of the honeycomb groove.

5. The back-illuminated near-infrared responsive silicon avalanche four-quadrant detector according to claim 1, characterized in that: In the four-quadrant light-entry structure, each quadrant includes a P+ contact region and an anti-reflection film located on the surface of the P+ contact region.

6. The back-illuminated near-infrared responsive silicon avalanche four-quadrant detector according to claim 1, characterized in that: On the front side of the substrate, all areas except the avalanche photodiode and the N electrode are covered with an oxide layer; On the back side of the substrate, areas other than the four-quadrant light incident structure are all covered with an oxide layer.

7. A method for preparing a back-illuminated near-infrared responsive silicon avalanche four-quadrant detector, characterized in that: The method includes: S1, obtaining a P-type single crystal substrate, and growing a first silicon dioxide film on a first surface of the single crystal substrate; S2. Etching a cutoff ring, a guard ring, and an ion implantation window of an avalanche photodiode on the surface of the first silicon dioxide film on the first surface side of the single crystal substrate; S3, performing ion implantation to form a cutoff ring, a guard ring, and an avalanche photodiode, respectively; wherein the guard ring 4 is distributed outside the avalanche photodiode, and the cutoff ring is distributed outside the guard ring; S4, performing a thinning and polishing process on the second surface side of the single crystal substrate, and growing a second silicon dioxide film on the second surface; S5, etching an isolation ring and four quadrants of ion implantation windows on the surface of the second silicon dioxide film on the second surface side of the single crystal substrate; S6. Perform ion implantation to form an isolation ring and four quadrants of P+ contact regions, wherein each quadrant is surrounded by the isolation ring; and deposit an antireflection film on the surface of the P+ contact region in each quadrant; S7. Form an N electrode and a P electrode on the first surface side and the second surface side respectively through a metal sputtering process, wherein the N electrode is in contact with the avalanche photodiode, and the P electrode is connected to the P+ contact region.

8. The method according to claim 7, characterized in that A microstructure is also made between the avalanche photodiode and the N electrode. The microstructure is based on a silicon dioxide film. Honeycomb grooves are etched on one side of the silicon dioxide film, and a layer of metal aluminum is deposited on the surface of the honeycomb grooves.

9. The method according to claim 7, characterized in that The thickness of the first silicon dioxide film and the second silicon dioxide film are both 200 nm to 600 nm.

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