Single photon avalanche diode and manufacturing method thereof
By forming an inverted pyramid-like recessed light-trapping structure on the substrate surface of a single-photon avalanche diode, the problem of reduced photon detection efficiency under small pixel size is solved, and the photon detection efficiency is improved, especially showing excellent performance in the near-infrared band.
Patent Information
- Application Number
- CN202511002264.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-18
- Publication Date
- 2025-11-07
AI Technical Summary
In the prior art, as the pixel size of single-photon avalanche diodes (SPADs) shrinks, the photosensitive area decreases, leading to a significant reduction in photon detection efficiency, especially near-infrared light detection efficiency.
An inverted pyramid-like recessed light-trapping structure is formed on the substrate surface of a single-photon avalanche diode. This structure increases the effective optical path length of photons in the active region through diffraction, refraction, and reflection, thereby enhancing the photon absorption probability.
Without increasing pixel size, it significantly improves photon detection efficiency, especially near-infrared light detection efficiency, making it suitable for applications such as lidar and 3D imaging.
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Figure CN120916501A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of semiconductor technology, in particular to a single photon avalanche diode and a manufacturing method thereof. BACKGROUND
[0002] A single photon avalanche diode (SPAD) is a kind of photoelectric detector with single photon detection capability. Its basic working principle is that when an incident photon is absorbed in the depletion region of a carefully designed PN junction and generates an electron-hole pair, these carriers will gain enough energy under the action of a high electric field, and through the collision ionization process, more electron-hole pairs will be generated, thereby forming an avalanche current pulse that can be detected by an external circuit.
[0003] With the continuous progress of semiconductor process technology, the market demand for high-resolution and small-pixel-size image sensors is increasing. However, for SPAD sensors, the reduction of pixel size will lead to a decrease in photosensitive area, which in turn reduces the probability of incident photons being absorbed and utilized, directly affecting the key performance indicator of the SPAD sensor - photon detection efficiency. Especially in the near-infrared band, due to the long absorption depth of photons in semiconductor materials (such as silicon), in small-size pixels, photo-generated carriers are likely to recombine before reaching the avalanche multiplication region, resulting in a significant decrease in detection efficiency.
[0004] Therefore, how to effectively improve the photon detection efficiency of small-pixel-size SPAD sensors, especially the detection efficiency of near-infrared light, without sacrificing pixel density, has become a technical problem to be solved in the current SPAD technology field. SUMMARY
[0005] The purpose of the present application is to provide a single photon avalanche diode and a manufacturing method thereof, which aims to solve the technical problem in the prior art that as the pixel size of a single photon avalanche diode (SPAD) is continuously reduced, the photon absorption volume in its photosensitive region also decreases accordingly, resulting in a significant decrease in photon detection efficiency, especially for near-infrared light.
[0006] To achieve the above-mentioned purpose and other related purposes, the present application provides a single photon avalanche diode, comprising:
[0007] a substrate having a first surface and a second surface opposite to the first surface;
[0008] an avalanche region formed in the substrate for generating an avalanche effect in response to incident photons; and
[0009] at least one light trapping structure formed on the first surface and / or the second surface of the substrate, the light trapping structure comprising at least one inverted pyramid-shaped recess.
[0010] Preferably, the light-capturing structure comprises at least two inverted pyramidal recesses.
[0011] Preferably, the light-capturing structure is formed on the second surface of the substrate, and the second surface is a light-receiving surface.
[0012] Preferably, the at least one light-capturing structure comprises: a first light-capturing structure formed on the first surface of the substrate; and a second light-capturing structure formed on the second surface of the substrate.
[0013] Preferably, the substrate is a silicon substrate, and the silicon substrate is a (111) crystal-oriented silicon substrate.
[0014] Preferably, the inverted pyramidal recess is filled with silicon dioxide.
[0015] Preferably, the light-capturing structure is configured to improve the detection efficiency of the single-photon avalanche diode for near-infrared light.
[0016] Correspondingly, the present application also provides a manufacturing method of a single-photon avalanche diode, comprising:
[0017] Step one, providing a substrate, the substrate having a first surface and a second surface opposite to the first surface;
[0018] Step two, forming an avalanche region in the substrate for generating avalanche effect;
[0019] Step three, forming at least one light-capturing structure on the first surface and / or the second surface of the substrate, the light-capturing structure comprising at least one inverted pyramidal recess.
[0020] Preferably, in step three, the light-capturing structure is formed on the first surface of the substrate.
[0021] Preferably, in step three, the light-capturing structure is formed on the second surface of the substrate.
[0022] Preferably, in step three, the step of forming the at least one light-capturing structure comprises: forming a first light-capturing structure on the first surface of the substrate; and forming a second light-capturing structure on the second surface of the substrate.
[0023] Preferably, in step three, the step of forming the inverted pyramidal recess comprises: defining a region to be etched on the surface of the substrate by using a photolithography process; performing a first etching on the region to be etched to form an inverted trapezoidal recess in the substrate; and performing an anisotropic wet etching on the inverted trapezoidal recess to form the inverted pyramidal recess.
[0024] Preferably, in step three, the anisotropic wet etching process uses potassium hydroxide solution as an etchant.
[0025] Preferably, the method further comprises: filling a dielectric material with a refractive index different from that of the substrate in the inverted pyramidal recess.
[0026] Preferably, the dielectric material is silicon dioxide.
[0027] As described above, the single-photon avalanche diode and the manufacturing method thereof according to the present application have the following beneficial effects:
[0028] The present application can effectively diffract, refract and / or reflect the incident light by forming the light-capturing structure composed of the inverted pyramidal recess on one side or both sides of the substrate, significantly increasing the effective propagation distance of photons in the active region of the substrate. This greatly improves the probability of photons being absorbed and generating photo-generated carriers, thereby significantly improving the photon detection efficiency of the single-photon avalanche diode without increasing the size of the pixel. BRIEF DESCRIPTION OF DRAWINGS
[0029] Figure 1 A flowchart showing a single-photon avalanche diode manufacturing method provided by an embodiment of the present application;
[0030] Figure 2 A structural schematic diagram showing a substrate provided in an embodiment of the present application;
[0031] Figure 3 A structural schematic diagram showing a structure after forming a photoresist pattern in an embodiment of the present application;
[0032] Figure 4 A structural schematic diagram showing a structure after forming an inverted trapezoidal recess in an embodiment of the present application;
[0033] Figure 5 A structural schematic diagram showing a structure after forming an inverted pyramidal recess in an embodiment of the present application;
[0034] Figure 6 A structural schematic diagram showing a structure after filling a dielectric material in a recess in an embodiment of the present application;
[0035] Figure 7Fig. 1 shows a schematic diagram of an overall structure of a single photon avalanche diode according to an embodiment of the present application;
[0036] Figure 8 Fig. 2 shows a schematic diagram of a structure of a single photon avalanche diode according to another embodiment of the present application. DETAILED DESCRIPTION
[0037] Other advantages and effects of the present application can be easily understood by those skilled in the art from the above description. The present application can also be implemented or applied in other different embodiments, and the details in the present description can be modified or changed based on different views and applications without departing from the spirit of the present application.
[0038] Referring to Figure 7 An embodiment of the present application provides a single photon avalanche diode, comprising:
[0039] a substrate 101, an avalanche region 105, and at least one light trapping structure 104.
[0040] The substrate 101 has a first surface and a second surface opposite to the first surface.
[0041] The avalanche region 105 is formed in the substrate 101 and is configured to generate avalanche effect in response to incident photons.
[0042] The at least one light trapping structure is formed on the first surface and / or the second surface of the substrate 101, and the light trapping structure 104 comprises at least one inverted pyramidal recess 103. Referring to Figure 8 This structure design provides great design flexibility, and the propagation path of incident light can be effectively controlled by integrating the light trapping structure 104 on one side or both sides of the device. The effective optical path of incident light in the active region can be significantly increased through diffraction, refraction or reflection, thereby greatly improving the probability of photon absorption and ultimately improving the photon detection efficiency of the single photon avalanche diode.
[0043] In some embodiments, the light trapping structure 104 is formed on the first surface of the substrate 101. This configuration corresponds to a modified front-illuminated (FSI) single photon avalanche diode. By directly structuring the substrate 101 above the active region of the device, for example, between the P+ implantation region and the anode, the light coupling and trapping can be enhanced without changing the traditional optical path, which is an effective way to improve performance.
[0044] In some embodiments, the light-trapping structure 104 is formed on the second surface of the substrate 101, which is the light-receiving surface. This is a typical back-side illumination (BSI) structure, in which light is incident from the back surface of the thinned substrate 101. By placing the light-trapping structure 104 on the light-receiving surface, the incident light can be maximally utilized, completely avoiding the obstruction of the front-side metal wiring layer, thereby achieving an extremely high fill factor and photon detection efficiency.
[0045] In some embodiments, the at least one light-trapping structure 104 includes a first light-trapping structure 104 formed on the first surface of the substrate 101 and a second light-trapping structure 104 formed on the second surface of the substrate 101. This is a preferred embodiment of the present application, in which the light-trapping structures 104 are cooperatively arranged on both the front and back surfaces of the substrate 101. The structure on the back surface is mainly responsible for efficiently trapping and diffracting the incident light, while the structure on the front surface can reflect and reuse the light that has passed through the active region, forming an effect similar to an optical microcavity, thereby improving the photon detection efficiency to a new level and achieving the ultimate utilization of photons.
[0046] In some embodiments, the substrate 101 is a silicon substrate 101, and the silicon substrate 101 is a (111) crystal-oriented silicon substrate 101. Using silicon as the substrate 101 material not only is compatible with the existing mature complementary metal-oxide-semiconductor (CMOS) process, facilitating large-scale and low-cost manufacturing, but also has good photoelectric conversion characteristics in the visible and near-infrared wavelength bands. Selecting a (111) crystal-oriented silicon substrate 101 is the key to preparing regular inverted pyramid structures, because anisotropic wet etching can form smooth (111) crystal planes with a certain inclination on the silicon wafer of this crystal orientation, thereby ensuring the precise topography and excellent optical performance of the light-trapping structure 104.
[0047] In some embodiments, the inverted pyramidal recesses 103 are filled with silicon dioxide. Since silicon dioxide (SiO2) has a lower refractive index than silicon, filling it into the recesses can form an effective total internal reflection condition or refraction effect at the silicon-silicon dioxide interface. This helps to guide the light that would otherwise penetrate the substrate 101 back into the active region of the silicon, which is equivalent to folding the optical path, thereby greatly improving the absorption efficiency of long-wavelength light such as near-infrared light. In addition, as an excellent dielectric material, silicon dioxide also plays a role in passivating the silicon surface and providing electrical isolation.
[0048] In some embodiments, the light-capturing structure 104 is configured to improve the detection efficiency of single-photon avalanche diodes for near-infrared light. Conventional small-pixel SPADs have low quantum efficiency in the near-infrared band, and the present application significantly improves this problem by introducing an inverted pyramid light-capturing structure 104, so that the device can perform excellent performance in applications such as laser radar and three-dimensional imaging that require detection of near-infrared light without increasing the pixel size.
[0049] Referring to Figure 1 The present application also provides a manufacturing method of a single-photon avalanche diode, which comprises the following steps:
[0050] Step one, referring to Figure 2 A substrate 101 is provided, which has a first surface and a second surface opposite to the first surface.
[0051] Step two, an avalanche region 105 for generating avalanche effect is formed in the substrate 101. For example, a series of ion implantation and annealing processes can be used to form P+ implantation region, N- implantation region and P ring on the first surface side of the substrate 101, which together with the N epitaxial layer in the substrate 101 form an avalanche region 105 capable of working under high reverse bias.
[0052] Step three, at least one light-capturing structure 104 is formed on the first surface and / or the second surface of the substrate 101, and the light-capturing structure 104 comprises at least one inverted pyramid-shaped recess 103.
[0053] In some embodiments, the light-capturing structure 104 is formed on the first surface of the substrate 101 in step three. This method corresponds to the manufacturing of front-illuminated devices, and the processing of the light-capturing structure 104 is performed on the first surface after the related implantation layer of the avalanche region 105 is formed.
[0054] In some embodiments, the light-capturing structure 104 is formed on the second surface of the substrate 101 in step three. This method corresponds to the manufacturing of back-illuminated devices, and the processing of the light-capturing structure 104 is performed on the thinned second surface after processes such as wafer bonding and substrate 101 thinning.
[0055] In some embodiments, the step of forming at least one light-capturing structure 104 in step three comprises: forming a first light-capturing structure 104 on the first surface of the substrate 101; and forming a second light-capturing structure 104 on the second surface of the substrate 101. This method can adopt the order of "front first, back second" or "back first, front second" by performing the structuring process on the front and back surfaces respectively, and finally obtains a double-side enhanced device, which is compatible with the advanced CMOS image sensor manufacturing technology.
[0056] In some embodiments, in step three, the step of forming the inverted pyramidal recess 103 comprises: defining a region to be etched on the surface of the substrate 101 using a lithography process, forming a structure as shown in Figure 3 ; performing a first etching on the region to be etched to form a trapezoidal recess 102 in the substrate 101, forming a structure as shown in Figure 4 ; and performing an anisotropic wet etching on the trapezoidal recess 102 to form the trapezoidal recess 102 into an inverted pyramidal recess 103, forming a structure as shown in Figure 5 . This two-step etching method can precisely control the morphology of the final structure. The first etching (e.g. reactive ion etching) can quickly form the rudiment of the recess, and the wet etching in the second step can serve as a finishing touch to form the pyramidal structure.
[0057] In some embodiments, in the anisotropic wet etching, a potassium hydroxide (KOH) solution is used as the etchant. KOH is a classic anisotropic etchant, which has significantly different etching rates for different crystal orientations of silicon, and can automatically stop at the (111) plane on a (111) crystal silicon substrate 101, thereby precisely trimming the initial trapezoidal structure into an inverted pyramidal structure with smooth sidewalls and precise angles, ensuring the repeatability of the process and the consistency of the device performance.
[0058] In some embodiments, the method further comprises: filling a dielectric material with a refractive index different from that of the substrate 101 in the inverted pyramidal recess 103, forming a structure as shown in Figure 6 .
[0059] In some embodiments, the dielectric material is silicon dioxide. Filling silicon dioxide can be achieved by a chemical vapor deposition (CVD) process or the like, which not only achieves the aforementioned optical enhancement effect, but also planarizes the structure formed by etching, providing a flat surface for subsequent wafer bonding or device integration, improving the manufacturability of the process.
[0060] It should be noted that the diagrams provided in the present embodiment only illustrate the basic concept of the present application in a schematic manner, and only show the components related to the present application in the diagrams, rather than being drawn according to the number, shape and size of the components in actual implementation. The actual implementation of each component can be arbitrarily changed in terms of shape, number and proportion, and the layout pattern of the components can be more complex.
[0061] The above embodiments are only illustrative of the principles of the present application and its efficacy, and are not intended to limit the present application. Any modification or change made by any person skilled in the art without departing from the spirit and scope of the present application shall be covered by the claims of the present application.
Claims
1. A single-photon avalanche diode, characterized in that, include: A substrate having a first surface and a second surface opposite to the first surface; Avalanche regions, formed within the substrate, are used to generate an avalanche effect in response to incident photons; as well as At least one light-catching structure is formed on the first surface and / or the second surface of the substrate, the light-catching structure including at least one inverted pyramid-like recess.
2. The single-photon avalanche diode according to claim 1, characterized in that: The light-catching structure includes at least two of the inverted pyramid-like recesses.
3. The single-photon avalanche diode according to claim 1, characterized in that: The light-harvesting structure is formed on the second surface of the substrate, and the second surface is a light-receiving surface.
4. The single-photon avalanche diode according to claim 1, characterized in that: The at least one light-trapping structure includes: a first light-trapping structure formed on the first surface of the substrate; and a second light-trapping structure formed on the second surface of the substrate.
5. The single-photon avalanche diode according to claim 1, characterized in that: The substrate is a silicon substrate, and the silicon substrate is a silicon substrate with a (111) crystal orientation.
6. The single-photon avalanche diode according to claim 5, characterized in that: The inverted pyramid-like depression is filled with silicon dioxide.
7. The single-photon avalanche diode according to any one of claims 1 to 6, characterized in that: The light-trapping structure is configured to improve the detection efficiency of the single-photon avalanche diode for near-infrared light.
8. A method for manufacturing a single-photon avalanche diode, characterized in that, include: Step 1: Provide a substrate having a first surface and a second surface opposite to the first surface; Step 2: Form an avalanche zone within the substrate to generate the avalanche effect; Step 3: Form at least one light-catching structure on the first surface and / or the second surface of the substrate, the light-catching structure including at least one inverted pyramid-like recess.
9. The method for manufacturing a single-photon avalanche diode according to claim 8, characterized in that: In step three, the light-trapping structure is formed on the first surface of the substrate.
10. The method for manufacturing a single-photon avalanche diode according to claim 8, characterized in that: In step three, the light-trapping structure is formed on the second surface of the substrate.
11. The method for manufacturing a single-photon avalanche diode according to claim 8, characterized in that: In step three, the step of forming the at least one light-trapping structure includes: forming a first light-trapping structure on the first surface of the substrate; and forming a second light-trapping structure on the second surface of the substrate.
12. The method for manufacturing a single-photon avalanche diode according to claim 8, characterized in that: In step three, the step of forming the inverted pyramid-like depression includes: defining an area to be etched on the surface of the substrate using a photolithography process; performing a first etching on the area to be etched to form an inverted trapezoidal depression in the substrate; and performing anisotropic wet etching on the inverted trapezoidal depression to form the inverted trapezoidal depression into the inverted pyramid-like depression.
13. The method for manufacturing a single-photon avalanche diode according to claim 12, characterized in that: In step three, the anisotropic wet etching process uses potassium hydroxide solution as the etching agent.
14. The method for manufacturing a single-photon avalanche diode according to claim 8, characterized in that: The method further includes filling the inverted pyramid-like depression with a dielectric material having a different refractive index than the substrate.
15. The method for manufacturing a single-photon avalanche diode according to claim 14, characterized in that: The dielectric material is silicon dioxide.