Photoelectric detector with near-infrared absorption enhancement structure and preparation method thereof

Abstract

The invention relates to a photoelectric detector with a near-infrared absorption enhancement structure and a preparation method of the photoelectric detector, and belongs to the field of photoelectric detectors. The photoelectric detector comprises: an absorption layer for absorbing incident light; the photosensitive area is formed in the absorption layer and is used for realizing photoelectric detection; the protection rings are positioned at two ends of the photosensitive region and used for preventing APD edge breakdown; the front concave lens microstructure substrate is formed on the front surface of the absorption layer; the front concave lens is formed on the surface of the front concave lens microstructure and is used for increasing the internal reflection angle of light which is not completely absorbed; the front reflecting mirror is formed on the surface of the front concave lens and is used for reflecting unabsorbed light back to the absorption layer; the back concave lens is formed on the back surface of the absorption layer and is used for increasing the total reflection angle of incident light in the absorption layer; and the back anti-reflection film is formed on the surface of the back concave lens and is used for improving the light inlet efficiency of the incident light. The absorption optical path of incident light is greatly improved through the double-sided concave lens, and the near-infrared light absorption efficiency of the device is greatly improved.

Description

Technical Field

[0001] The invention belongs to the field of photoelectric detection devices and relates to a photoelectric detector with a near-infrared absorption enhancement structure and a preparation method thereof. Background Art

[0002] Near-infrared silicon photodetectors (such as PIN, APD) have the advantages of high sensitivity, low dark current, high reliability, small size, low cost, simple use and maintenance, etc. They are widely used in laser ranging, three-dimensional imaging, low-light detection and other fields. With the deepening of application, higher and higher requirements are currently being put forward for the near-infrared response rate (quantum efficiency) of the detector to support the further improvement of the performance of silicon photoelectric detection and imaging systems in terms of low-light detection capability, working distance, response speed, etc.

[0003] Traditional planar silicon photodetectors (PIN, APD, etc.) can only increase the absorption rate of incident light by increasing the thickness of the absorption layer, thereby improving the near-infrared quantum efficiency (i.e., response rate). However, due to the extremely low near-infrared absorption coefficient of the silicon material itself, increasing the absorption rate by increasing the thickness of the absorption layer has little effect, and often brings about negative effects such as increased response time (the thicker the absorption layer, the longer the photogenerated carrier transit time) and increased breakdown voltage temperature coefficient, which cannot effectively improve the overall performance of the device. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a photodetector with a near-infrared absorption enhanced structure and a preparation method thereof, so as to greatly improve the absorption rate of incident light without increasing the thickness of the absorption layer, thereby greatly improving the device response rate without increasing the breakdown voltage temperature coefficient and response time, thereby effectively improving the overall performance of the device.

[0005] To achieve the above object, the present invention provides a photodetector with a near-infrared absorption enhancement structure, comprising:

[0006] an absorption layer, for absorbing incident light;

[0007] A photosensitive region, formed in the absorption layer, for realizing photoelectric detection;

[0008] Guard rings, formed in the absorption layer and located at both ends of the photosensitive region, prevent APD edge breakdown;

[0009] A front concave lens microstructure substrate formed on the front side of the absorption layer;

[0010] A front concave lens is formed on a side of the front concave lens microstructure substrate away from the absorption layer, and is used to increase the internal reflection angle of the light that is not completely absorbed;

[0011] A front reflector, formed on the surface of the front concave lens, for reflecting unabsorbed light back to the absorption layer;

[0012] A back concave lens, formed on the back of the absorption layer, for increasing the total reflection angle of incident light inside the absorption layer;

[0013] The back anti-reflection film is formed on the surface of the back concave lens to improve the efficiency of incident light entering.

[0014] Furthermore, both the front concave lens and the back concave lens are grooves with regular hexagonal openings, wherein the front concave lenses are distributed in a honeycomb shape on the surface of the front concave lens microstructure substrate, and the back concave lenses are distributed in a honeycomb shape on the back of the absorption layer.

[0015] Furthermore, the front concave lens microstructure substrate is in contact with the photosensitive area in the absorption layer and the protective layer respectively.

[0016] Furthermore, the front reflector is a Bragg reflector.

[0017] Furthermore, the photodetector also includes a first electrode and a second electrode; the first electrode is connected to the electrode contact layer through the front reflector, the front concave lens and the front concave lens microstructure substrate; the second electrode is connected to the electrode contact layer through the back anti-reflection film and the back concave lens.

[0018] On the other hand, the present invention provides a method for preparing a photodetector having a near-infrared absorption enhancement structure, the method comprising:

[0019] Obtaining a high-resistance single-crystal silicon material as an absorption layer;

[0020] Doping in the absorption layer to form a photosensitive region and a guard ring, wherein the guard ring is distributed at both ends of the photosensitive region;

[0021] A layer of material that does not absorb near-infrared light is grown on the front side of the absorption layer using a PECVD process as a front concave lens microstructure substrate;

[0022] A front concave lens etching pattern is formed on a side of the front concave lens microstructure substrate away from the absorption layer by using a photolithography process, and the etching pattern is arranged periodically in a regular triangle; at each etching pattern, a front concave lens with an opening of a regular hexagon is formed on the surface of the front concave lens microstructure substrate by using an isotropic RIE etching process or a wet etching process, and the formed plurality of front concave lenses are distributed in a honeycomb shape on the surface of the front concave lens microstructure substrate;

[0023] A front reflector is formed on the surface of the front concave lens;

[0024] A front electrode hole is etched on the front concave lens microstructure substrate and the front reflector by using an etching process, and then a first electrode is manufactured by using a thin film deposition and etching process;

[0025] The thickness of the back side of the absorption layer is reduced, and a back side concave lens etching pattern is formed on the back side of the absorption layer by using a photolithography process, and the etching pattern is arranged periodically in a regular triangle; at each etching pattern, an isotropic RIE etching process or a wet etching process is used to form a back side concave lens with an opening of a regular hexagon on the back side of the absorption layer, and the formed back side concave lenses are distributed in a honeycomb shape on the back side of the absorption layer;

[0026] forming a back antireflection film on the surface of the back concave lens;

[0027] The back electrode hole is etched on the absorption layer and the back anti-reflection film by using an etching process, and then the second electrode is manufactured by using a thin film deposition and etching process.

[0028] The front reflector is formed into a Bragg reflector by stacking two different optical materials.

[0029] The beneficial effect of the present invention is that the present invention greatly increases the absorption optical path of the incident light through the double-sided concave lens, thereby greatly improving the near-infrared light absorption efficiency of the device, thereby improving the sensitivity of the device. The present invention improves the near-infrared light absorption efficiency without relying on the increase of the thickness of the absorption layer, so it will not cause the increase of the breakdown voltage temperature coefficient and response time of the detector; in addition, the additional effect achieved by the present invention is that the breakdown voltage temperature coefficient of the device can be reduced by further reducing the thickness of the absorption layer, while improving the device response speed, thereby greatly improving the comprehensive performance of near-infrared silicon PIN and APD photodetectors.

[0030] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] 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 in conjunction with the accompanying drawings, wherein:

[0032] Figure 1 A schematic cross-sectional view of a photodetector with a near-infrared absorption enhancement structure provided by an embodiment of the present invention;

[0033] Figure 2 This is the concave lens etching process layout from a top-down perspective;

[0034] Figure 3 This is the SEM image of concave lenses with regular hexagonal honeycomb distribution.

[0035] Figure markings: 1-absorption layer; 2-protection ring; 3-photosensitive area; 4-front concave lens microstructure substrate; 5-front concave lens; 6-front reflector; 7-front contact hole; 8-first electrode; 9-back concave lens; 10-back anti-reflection film; 11-back contact hole; 12-second electrode. DETAILED DESCRIPTION

[0036] The following describes the embodiments of the present invention by 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 only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0037] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0038] 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 the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position 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.

[0039] In order to improve the near-infrared response rate of silicon-based PIN and APD photodetectors, and solve the contradiction between the response rate and response time, and the response rate and breakdown voltage temperature coefficient of traditional structure devices (improving the response rate will increase the breakdown voltage temperature coefficient and response time), an embodiment of the present invention provides a photodetector with a near-infrared absorption enhancement structure and a preparation method thereof. The near-infrared absorption enhancement structure is formed by a combination of a front concave lens, a front reflector, and a back concave lens. The incident light entering the absorption enhancement structure will be reflected back and forth between the front concave lens and the back concave lens for many times until it is completely absorbed by the absorption area, and only a very small number of photons escape from the absorption area. The front and back concave lenses are arranged in a hexagonal honeycomb structure to increase the duty cycle. The hexagonal honeycomb structure is made by RIE isotropic etching, ion beam assisted sputtering and other processes compatible with silicon CMOS, which is suitable for mass production and can greatly improve the yield and reduce costs.

[0040] like Figure 1 As shown, the photoelectric detector with near-infrared absorption enhancement structure provided in this embodiment includes:

[0041] An absorption layer 1, used for absorbing incident light;

[0042] Guard ring 2, which prevents APD edge breakdown;

[0043] Photosensitive region 3, mainly plays the role of separating photogenerated carriers and realizing photoelectric detection;

[0044] The front concave lens microstructure substrate 4 is used to provide a basic material for manufacturing the front concave lens 5;

[0045] The front concave lens 5 mainly increases the internal reflection angle of the light that is not completely absorbed, so as to improve the absorption optical path and absorption rate of the incident light; the front concave lens 5 is made of a material that does not absorb near-infrared light, such as SiO2, Si3N4, etc., so as to improve the effective utilization rate of light energy of the device;

[0046] The front reflector 6 is used to reflect the unabsorbed light back to the absorption area for repeated absorption; it uses a stack of SiO2, TiO2 and other media to form a Bragg reflector to reduce the absorption of incident light by the reflector material, improve the utilization rate of light energy converted by photoelectric conversion, and thus improve the sensitivity of the device;

[0047] A front contact hole 7, used to connect the electrode contact layer and the first electrode 8;

[0048] The first electrode 8 is mainly used for power supply and signal output of the APD / PIN device;

[0049] The back concave lens 9 mainly increases the internal reflection angle of the light that is not completely absorbed, so as to improve the absorption optical path and absorption rate of the incident light; the back concave lens 9 is made on silicon material to increase the total reflection angle of the incident light inside the absorption layer 1, thereby improving the absorption efficiency;

[0050] The back anti-reflection film 10 is used to improve the efficiency of incident light entering the device; the back anti-reflection film 10 can be made of dielectric materials such as SiO2, Si3N4, TiO2, etc. that do not absorb visible light and near-infrared light, so as to improve the effective utilization rate of light energy of the device;

[0051] A back contact hole 11, used to connect the electrode contact layer and the second electrode;

[0052] The second electrode 12 is mainly used for power supply and signal output of the APD / PIN device.

[0053] When the first electrode 8 is an anode, the second electrode 12 is a cathode; when the first electrode 8 is a cathode, the second electrode 12 is an anode.

[0054] Another embodiment of the present invention provides a method for preparing a photodetector, which is used to prepare the photodetector with a near-infrared absorption enhancement structure described in the above embodiment. The method comprises:

[0055] 1) Using high-resistance single crystal silicon material as the absorption layer 1;

[0056] 2) forming active area structures such as a guard ring 2 and a photosensitive area 3 in the absorption layer 1 by using an ion implantation process or an impurity diffusion process;

[0057] 3) Using PECVD process to grow a 0.5 μm to 20 μm thick SiO2 layer on the absorption layer 1 (the thickness is adjusted according to the application wavelength, etching process, and pattern size) as the front concave lens microstructure substrate 4;

[0058] 4) A front concave lens etching pattern is formed on the surface of the front concave lens microstructure substrate 4 by using a photolithography process, and the pattern distribution adopts an equilateral triangle periodic arrangement mode, such as Figure 2 As shown, in order to improve the duty cycle of the concave lens after molding; using isotropic RIE etching process or wet etching process to form a front concave lens 5 with a regular hexagonal honeycomb distribution on the front concave lens microstructure substrate 4, as shown Figure 3 As shown;

[0059] 5) An ion beam assisted sputtering process is used to form a front reflector 6 on the surface of the front concave lens 5 to increase the absorption optical path of the incident light in the absorption zone; the front reflector 6 is formed by stacking SiO2, TiO2 and other media to form a Bragg reflector to reduce the absorption of the incident light by the reflector material, improve the utilization rate of light energy in photoelectric conversion, and thus improve the sensitivity of the device.

[0060] 6) etching a front electrode hole 7 on the front concave lens microstructure substrate 4 and the front reflector 6 by an etching process, and then manufacturing a first electrode by a thin film deposition and etching process;

[0061] 7) Using thinning and CMP processes to remove excess thickness on the back side of the absorption layer 1, using photolithography to photoetch a back side concave lens pattern on the back side of the absorption layer 1, and the pattern distribution also uses an equilateral triangle periodic arrangement mode; using isotropic RIE etching process or wet etching process to form a regular hexagonal honeycomb distribution of back side concave lenses 9 on the back side of the absorption layer 1;

[0062] 8) An ion beam assisted sputtering process is used to form a back anti-reflection film 10 on the surface of the back concave lens 9. The back anti-reflection film 10 is made of a dielectric material such as SiO2, Si3N4, TiO2, etc. that does not absorb visible light and near-infrared light, so as to improve the effective utilization rate of light energy of the device;

[0063] 9) The back electrode hole 11 is etched on the absorption layer 1 and the back antireflection film 10 by an etching process, and then the second electrode 12 is manufactured by a thin film deposition and etching process to obtain a photodetector with a near-infrared absorption enhancement structure.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. 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 solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A photodetector with a near-infrared absorption enhancement structure, characterized in that: It includes: an absorption layer, for absorbing incident light; A photosensitive region, formed in the absorption layer, for realizing photoelectric detection; A guard ring is formed in the absorption layer and is located at both ends of the photosensitive region to prevent APD edge breakdown; A front concave lens microstructure substrate, formed on the front side of the absorption layer; A front concave lens, formed on a side of the front concave lens microstructure substrate away from the absorption layer, for increasing the internal reflection angle of light that is not completely absorbed; A front reflector, formed on the surface of the front concave lens, for reflecting unabsorbed light back to the absorption layer; A back concave lens, formed on the back of the absorption layer, for increasing the total reflection angle of incident light inside the absorption layer; The back anti-reflection film is formed on the surface of the back concave lens and is used to improve the light entry efficiency of the incident light.

2. The photodetector according to claim 1, characterized in that: The front concave lens and the back concave lens are both grooves with regular hexagonal openings.

3. The photodetector according to claim 2, characterized in that: The front concave lenses are distributed in a honeycomb shape on the surface of the front concave lens microstructure substrate; and the back concave lenses are distributed in a honeycomb shape on the back of the absorption layer.

4. The photodetector according to claim 1, characterized in that: The front concave lens microstructure substrate is in contact with the photosensitive area in the absorption layer and the protective layer respectively.

5. The photodetector according to claim 1, characterized in that: The front reflector is a Bragg reflector.

6. The photodetector according to any one of claims 1 to 5, characterized in that: The photodetector also includes a first electrode and a second electrode; the first electrode is connected to the electrode contact layer through a front reflector, a front concave lens and a front concave lens microstructure substrate; the second electrode is connected to the electrode contact layer through a back antireflection film and a back concave lens.

7. A method for preparing a photodetector having a near-infrared absorption enhancement structure, characterized in that: The method includes: Obtaining a high-resistance single-crystal silicon material as an absorption layer; Doping in the absorption layer to form a photosensitive region and a guard ring, wherein the guard ring is distributed at both ends of the photosensitive region; A layer of material that does not absorb near-infrared light is grown on the front side of the absorption layer using a PECVD process as a front concave lens microstructure substrate; A front concave lens etching pattern is formed on a side of the front concave lens microstructure substrate away from the absorption layer by using a photolithography process, and the etching pattern is arranged periodically in a regular triangle; at each etching pattern, a front concave lens with an opening of a regular hexagon is formed on the surface of the front concave lens microstructure substrate by using an isotropic RIE etching process or a wet etching process, and the formed plurality of front concave lenses are distributed in a honeycomb shape on the surface of the front concave lens microstructure substrate; A front reflector is formed on the surface of the front concave lens; A front electrode hole is etched on the front concave lens microstructure substrate and the front reflector by using an etching process, and then a first electrode is manufactured by using a thin film deposition and etching process; The thickness of the back side of the absorption layer is reduced, and a back side concave lens etching pattern is formed on the back side of the absorption layer by using a photolithography process, and the etching pattern is arranged periodically in a regular triangle; at each etching pattern, an isotropic RIE etching process or a wet etching process is used to form a back side concave lens with an opening of a regular hexagon on the back side of the absorption layer, and the formed back side concave lenses are distributed in a honeycomb shape on the back side of the absorption layer; forming a back antireflection film on the surface of the back concave lens; The back electrode hole is etched on the absorption layer and the back anti-reflection film by using an etching process, and then the second electrode is manufactured by using a thin film deposition and etching process.

8. The method according to claim 7, characterized in that The front reflector is formed as a Bragg reflector by stacking two different optical materials.

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