A self-reflection-reducing SiC-based ultraviolet photodiode and its fabrication method

Abstract

This invention discloses a self-reflection-lowering SiC-based ultraviolet photodiode and its fabrication method, relating to the field of semiconductor technology. The device comprises: a cathode, an ohmic contact layer, a substrate, an epitaxial layer, and a passivation layer stacked sequentially; an isolation layer including multiple isolation units arranged in an array on the upper surface of the passivation layer, the isolation units exhibiting a bulging shape; a Schottky contact layer located on the upper surface of the passivation layer and between adjacent isolation units; an anode located on the upper surface of the Schottky contact layer; and a protective layer located on the upper surface of a portion of the anode and on the upper surface of the exposed isolation units. This invention can improve the photoelectric detection performance of the device.

Description

Technical Field

[0001] This invention belongs to the field of microelectronics technology, specifically relating to a self-reflection-reducing SiC-based ultraviolet photodiode and its fabrication method. Background Technology

[0002] Wide bandgap semiconductor materials such as silicon carbide (SiC), gallium nitride (GaN), and diamond (C) can detect ultraviolet light in the 200–380 nm wavelength range against strong visible and infrared backgrounds due to their wide bandgap. They also possess characteristics of high temperature resistance, high efficiency, and high reliability, making them ideal materials for fabricating ultraviolet photodetectors. Silicon carbide (SiC), as a novel third-generation semiconductor material, exhibits excellent properties such as a large bandgap, high electron drift velocity, high critical breakdown field strength, high thermal conductivity, and high chemical stability, giving it great application potential in high-temperature, high-power, optoelectronic, and radiation-resistant applications.

[0003] As an important type of semiconductor optoelectronic device, improving light utilization significantly enhances its performance. Therefore, various anti-reflection and anti-reflection coatings are used in optoelectronic semiconductor devices. However, limited by materials, equipment, and semiconductor processes, traditional anti-reflection and anti-reflection coating designs often use planar thin films, controlling the anti-reflection effect through film thickness, and supplementing them with transparent electrodes and specular reflective layers to reuse light energy. However, the growth cycle for anti-reflection and anti-reflection coatings is long, the quality improvement is limited, and the additional optical management processes incur additional costs.

[0004] Therefore, there is an urgent need to provide a photodiode to overcome the difficulty in generating antireflective and anti-reflective coatings from a material perspective. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a self-reflection-lowering SiC-based ultraviolet photodiode and its fabrication method. The technical problem to be solved by this invention is achieved through the following technical solution:

[0006] In a first aspect, the present invention provides a self-reflection-lowering SiC-based ultraviolet photodiode, comprising:

[0007] A cathode, an ohmic contact layer, a substrate, an epitaxial layer, and a passivation layer are stacked sequentially.

[0008] The isolation layer includes multiple isolation units arranged in an array on the upper surface of the passivation layer, and the isolation units are bulging in shape;

[0009] The Schottky contact layer is located on the upper surface of the passivation layer and between adjacent isolation cells;

[0010] The anode is located on the upper surface of the Schottky contact layer;

[0011] A protective layer is located on the upper surface of the partial anode and on the upper surface of the exposed isolation unit.

[0012] Secondly, the present invention also provides a method for fabricating a self-reflection-lowering SiC-based ultraviolet photodiode, for fabricating the aforementioned self-reflection-lowering SiC-based ultraviolet photodiode, comprising:

[0013] Provide a substrate;

[0014] An epitaxial layer is grown on the upper surface of the substrate;

[0015] The upper surface of the epitaxial layer is treated with plasma to obtain a passivation layer;

[0016] An isolation layer is deposited on the upper surface of the passivation layer, and windows are made in the isolation layer to obtain multiple rectangular structures arranged in an array on the upper surface of the passivation layer.

[0017] A first metal is deposited on the surface exposed by the rectangular structure and passivation layer, and a second metal is deposited on the surface of the substrate away from the epitaxial layer.

[0018] Annealing the first metal and the second metal causes the first metal to form a Schottky contact layer and the second metal to form an ohmic contact layer. Reflowing the rectangular structure forms an isolation unit, which appears bulging. The ohmic contact layer is made transparent using a specific solution, and the first metal remaining on the isolation unit is cleaned.

[0019] A third metal is deposited on the exposed upper surface of the Schottky contact layer and the isolation unit, and part of the third metal on the upper surface of the isolation unit is removed, with the remaining third metal on the upper surface of the Schottky contact layer forming the anode;

[0020] A protective layer is deposited on the exposed upper surfaces of the anode and isolation units;

[0021] A fourth metal is deposited on the surface of the ohmic contact layer away from the substrate to form a cathode.

[0022] The beneficial effects of this invention are:

[0023] This invention provides a self-antireflection SiC-based ultraviolet photodiode and its fabrication method, which can simultaneously form Schottky contacts and ohmic contacts; in addition, the isolation units set in the isolation layer have good antireflection and anti-transmission functions, which is beneficial to improving the photoelectric detection performance of the device.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1This is a schematic diagram of a self-reflection-reducing SiC-based ultraviolet photodiode provided in an embodiment of the present invention;

[0026] Figure 2 This is a flowchart of a method for fabricating a self-reflection-reducing SiC-based ultraviolet photodiode according to an embodiment of the present invention;

[0027] Figures 3a-3i This is a schematic diagram of a method for fabricating a self-reflection-reducing SiC-based ultraviolet photodiode provided in an embodiment of the present invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0029] Please see Figure 1 , Figure 1 This is a schematic diagram of a self-reflection-attenuating SiC-based ultraviolet photodiode provided in an embodiment of the present invention. The self-reflection-attenuating SiC-based ultraviolet photodiode provided by the present invention includes:

[0030] A cathode 9, an ohmic contact layer 6, a substrate 1, an epitaxial layer 2, and a passivation layer 3 are stacked sequentially.

[0031] The isolation layer includes multiple isolation units 4 arranged in an array on the upper surface of the passivation layer 3, and the isolation units 4 are bulging in shape;

[0032] Schottky contact layer 5 is located on the upper surface of passivation layer 3 and between adjacent isolation units 4;

[0033] Anode 7 is located on the upper surface of Schottky contact layer 5;

[0034] The protective layer 8 is located on the upper surface of the partial anode 7 and on the upper surface of the exposed isolation unit 4.

[0035] For details, please continue to see Figure 1 The device provided in this embodiment can simultaneously form Schottky contacts and ohmic contacts; in addition, the isolation unit 4 provided in the isolation layer has good anti-reflection and anti-transmission functions, which is beneficial to improving the photoelectric detection performance of the device.

[0036] In an optional embodiment of the invention, the material of the isolation unit 4 includes alkaline earth-doped silicon oxide.

[0037] Specifically, in this embodiment, the isolation unit 4 is made of alkaline earth doped silicon oxide, which allows for the use of one-step annealing and chemical etching processes to realize Schottky contacts and ohmic contacts when implementing the device structure. At the same time, the matrix structure is annealed and reflowed to form a bulging array, thereby obtaining the function of light anti-reflection and anti-transmission, and improving the photoelectric detection performance of the device.

[0038] In an optional embodiment of the present invention, the spacing between adjacent isolation units 4 is 500-800 nm;

[0039] Optionally, the spacing between adjacent isolation units 4 is 600 nm or 700 nm.

[0040] In an optional embodiment of the invention, the protective layer 8 includes a SiyNx antireflective surface.

[0041] Based on the same inventive concept, please refer to Figure 2 , Figure 2 This is a flowchart illustrating a method for fabricating a self-reflection-lowering SiC-based ultraviolet photodiode according to an embodiment of the present invention. The present invention also provides a method for fabricating a self-reflection-lowering SiC-based ultraviolet photodiode, used to fabricate the self-reflection-lowering SiC-based ultraviolet photodiode provided in the above embodiments. Examples of the diode are described above and will not be repeated here. The fabrication method includes:

[0042] S101, Provide a substrate 1;

[0043] S102, An epitaxial layer 2 is grown on the upper surface of substrate 1;

[0044] S103. The upper surface of the epitaxial layer 2 is treated with plasma to obtain the passivation layer 3;

[0045] Specifically, the upper surface of the epitaxial layer 2 is treated with oxygen or oxygen-hydrogen mixed plasma to obtain the passivation layer 3.

[0046] S104. An isolation layer is deposited on the upper surface of the passivation layer 3, and windows are made in the isolation layer to obtain a rectangular structure with multiple arrays arranged on the upper surface of the passivation layer 3.

[0047] Specifically, the isolation layer is windowed using photolithography and etching processes to obtain a rectangular structure; wherein the spacing between adjacent rectangular structures is 500-800 nm, and the width of the window is 500-800 nm.

[0048] S105. A first metal is deposited on the surface exposed by the rectangular structure and the passivation layer 3, and a second metal is deposited on the surface of the substrate 1 away from the epitaxial layer 2.

[0049] Specifically, tungsten metal is deposited on the surface exposed by the rectangular structure and passivation layer 3 using electron beam evaporation or magnetron sputtering, and nickel metal is deposited on the surface of the substrate 1 away from the epitaxial layer 2; wherein the thickness of the tungsten metal and the nickel metal is 60-70 nm.

[0050] S106. Anneal the first metal and the second metal to form a Schottky contact layer 5 and an ohmic contact layer 6, and reflow the rectangular structure to form an isolation unit 4, which is bulging in shape. Use a mixing solution to make the ohmic contact layer 6 transparent, and clean the first metal remaining on the isolation unit 4.

[0051] Specifically, a rapid thermal annealing process is used to anneal the first metal and the second metal. The annealing conditions include an inert gas atmosphere, a temperature of 900–1100°C, and an annealing time of 160–190 s.

[0052] Specifically, the solution includes nitric acid, buffer oxide etching solution, and deionized water, with a volume ratio of 1:1:5.

[0053] Compared to traditional device fabrication methods, in this embodiment, alkaline earth-doped silicon oxide is used as the material for the isolation unit 4. This allows the device to simultaneously perform functions such as a contact image mask located on the rectangular structure, the reflow of the rectangular structure to form the isolation unit 4 (passivation isolation), and the optical management structure after a one-step annealing process and a mixing solution cleaning process. This greatly simplifies the process, and all processes are standard processes with strong universality.

[0054] S107. A third metal is deposited on the exposed upper surface of the Schottky contact layer 5 and the isolation unit 4, and part of the third metal on the upper surface of the isolation unit 4 is removed, with the remaining third metal on the upper surface of the Schottky contact layer 5 forming the anode 7.

[0055] S108. A protective layer 8 is deposited on the upper surface exposed by the anode 7 and the isolation unit 4;

[0056] S109. A fourth metal is deposited on the surface of the ohmic contact layer 6 away from the substrate 1 to form the cathode 9.

[0057] In an optional embodiment of the present invention, the self-reflection-reducing SiC-based ultraviolet photodiode is fabricated through the following process:

[0058] S1, Provide substrate 1.

[0059] Specifically, substrate 1 is an n+ type SiC substrate 1, with a thickness of 350 μm and a doping concentration of 5e18 cm⁻¹. -3 .

[0060] S2, Prepare epitaxial layer 2, such as Figure 3a As shown.

[0061] Specifically, an epitaxial layer 2 is formed on the upper surface of substrate 1. Epitaxial layer 2 is an n-type epitaxial layer with a thickness of 1.5–2 μm and a doping concentration of 1e16–2e16 cm⁻¹. -3 .

[0062] S3. Prepare passivation layer 3, such as Figure 3b As shown.

[0063] Specifically, the surface of the n-type SiC epitaxial layer 2 is treated with oxygen or oxygen-hydrogen mixed plasma to form a passivation layer 3; the upper surface of the epitaxial layer 2 is treated with plasma, which can reduce the surface states and dangling bonds of the n-type SiC epitaxial layer 2.

[0064] Optionally, the thickness of passivation layer 3 is about 5 nm.

[0065] S4. Prepare the isolation layer, such as Figure 3c As shown.

[0066] Specifically, an alkaline earth-doped silicon oxide passivation isolation layer is deposited on the upper surface of passivation layer 3 using a low-pressure chemical vapor deposition (LPCVD) process. The isolation layer also serves as a passivation protection layer.

[0067] Optionally, the thickness of the isolation layer is 500–1000 nm, and 800 nm is selected in this embodiment.

[0068] S5. Prepare a rectangular structure, such as Figure 3d As shown.

[0069] Specifically, the isolation layer is windowed using photolithography and etching processes, with a window width of 500–800 nm and a window spacing of 500–800 nm; optionally, the window width is 600 nm and the window spacing is 600 nm.

[0070] It should be noted that the window shape can be polygonal or circular. The shape of the window is chosen during the actual production process and is not limited here.

[0071] S6. Prepare the first metal and the second metal, such as Figure 3e As shown.

[0072] Specifically, metals are deposited on the front and back sides of the device using electron beam evaporation or magnetron sputtering processes. Specifically, tungsten metal is deposited on the surface exposed by the rectangular structure and passivation layer 3, and nickel metal is deposited on the surface of the substrate 1 away from the epitaxial layer 2. Optionally, the thickness of both tungsten metal and nickel metal is 60-70 nm, or optionally, the thickness of both tungsten metal and nickel metal is 65 nm.

[0073] S7. Prepare Schottky contact layer 5 and ohmic contact layer 6, such as Figure 3f As shown.

[0074] Specifically, a rapid thermal annealing process is used to anneal the first metal and the second metal to form Schottky contact metal and ohmic contact metal, respectively. After the annealing reaction, the isolation unit 4 is reflowed to form a bulging array, which simultaneously obtains the optical anti-reflection and anti-reflection function, improving the photoelectric detection performance of the device. After annealing, nitric acid, buffered oxide etchant (BOE) and deionized water are used to make the ohmic contact layer 6 transparent. At the same time, the residual first metal on the isolation unit 4 is cleaned away. After cleaning with the chemical solution, the free Ni element remaining in the alloy is cleaned away by the chemical solution, and the remaining SiNi related alloy becomes transparent.

[0075] Optionally, the annealing conditions are annealing at 1000°C for 180 seconds in an inert gas atmosphere.

[0076] S8, Prepare anode 7, such as Figure 3g As shown.

[0077] Specifically, aluminum metal is deposited on the front side of the device, i.e. the exposed upper surface of the Schottky contact layer 5 and the isolation unit 4, using electron beam evaporation or magnetron sputtering processes, with a deposition thickness of 500-1000 nm; then, photolithography and etching processes are used to etch away the remaining aluminum metal on the upper surface of the isolation unit 4, and the remaining aluminum metal on the upper surface of the Schottky contact layer 5 forms the anode 7.

[0078] S9. Prepare protective layer 8, such as Figure 3h As shown.

[0079] Specifically, a SiyNx antireflective surface passivation protective layer 8 is deposited on the front side of the device, i.e., on the upper surface exposed by the anode 7 and the isolation unit 4, using a plasma-enhanced chemical vapor deposition (PECVD) process.

[0080] S10, Prepare cathode 9, as follows Figure 3i As shown.

[0081] Specifically, an electron beam evaporation process is used to form a Ti / Ni / Ag cathode 9 on the back side of the device, i.e., on the side of the ohmic contact layer 6 away from the substrate 1; at the same time, the cathode 9 can serve as a back reflective layer to increase the light utilization of the device.

[0082] Optionally, the cathode 9 includes Ti / Ni / Ag thicknesses of 200nm / 200nm / 1000nm, respectively.

[0083] This invention proposes a novel method for fabricating SiC ultraviolet optoelectronic devices. This method uses an alkaline earth-doped silicon oxide film, which undergoes annealing and reflow to form an antireflection window. The annealing process directly forms Schottky and ohmic contacts. This method achieves high-performance devices while saving multiple process steps and reducing device fabrication costs.

[0084] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device comprising said element. Terms such as "connected" or "linked" are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect. The orientations or positional relationships indicated by terms such as "upper," "lower," "left," and "right" are based on the orientations or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0085] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0086] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A self-reflection-attenuating SiC-based ultraviolet photodiode, characterized in that, include: A cathode, an ohmic contact layer, a substrate, an epitaxial layer, and a passivation layer are stacked sequentially. The isolation layer includes multiple isolation units arranged in an array on the upper surface of the passivation layer. The isolation units are bulging in shape and have light anti-reflection and anti-reflection functions. The material of the isolation units includes alkaline earth-doped silicon oxide. A Schottky contact layer is located on the upper surface of the passivation layer and between adjacent isolation units; The anode is located on the upper surface of the Schottky contact layer; A protective layer is located on the upper surface of a portion of the anode and on the upper surface of the exposed isolation unit.

2. The self-reflection-attenuating SiC-based ultraviolet photodiode according to claim 1, characterized in that, The spacing between adjacent isolation units is 500~800nm.

3. The self-reflection-attenuating SiC-based ultraviolet photodiode according to claim 1, characterized in that, The material of the protective layer includes Si. y N x The protective layer has anti-reflective properties.

4. A method for fabricating a self-reflection-lowering SiC-based ultraviolet photodiode, used to fabricate the self-reflection-lowering SiC-based ultraviolet photodiode as described in any one of claims 1 to 3, characterized in that, include: Provide a substrate; An epitaxial layer is grown on the upper surface of the substrate; The upper surface of the epitaxial layer is treated with plasma to obtain a passivation layer; An isolation layer is deposited on the upper surface of the passivation layer, and windows are made in the isolation layer to obtain a rectangular structure with multiple arrays arranged on the upper surface of the passivation layer. A first metal is deposited on the surface exposed by the rectangular structure and the passivation layer, and a second metal is deposited on the surface of the substrate opposite to the epitaxial layer. The first metal and the second metal are annealed in one step, so that the first metal forms a Schottky contact layer and the second metal forms an ohmic contact layer, and the rectangular structure is reflowed to form an isolation unit. The isolation unit is bulging and has the function of light anti-reflection and light transmission enhancement. The ohmic contact layer is made transparent using a specific solution, while the first metal remaining on the isolation unit is cleaned; wherein the material of the isolation unit includes alkaline earth-doped silicon oxide. A third metal is deposited on the exposed upper surfaces of the Schottky contact layer and the isolation unit, and a portion of the third metal on the upper surface of the isolation unit is removed, with the remaining third metal on the upper surface of the Schottky contact layer forming the anode; A protective layer is deposited on the exposed upper surfaces of the anode and the isolation unit; A fourth metal is deposited on the surface of the ohmic contact layer opposite to the substrate to form a cathode.

5. The method for fabricating a self-reflection-lowering SiC-based ultraviolet photodiode according to claim 4, characterized in that, The upper surface of the epitaxial layer is treated with plasma to obtain a passivation layer, comprising: The upper surface of the epitaxial layer is treated with oxygen or oxygen-hydrogen mixed plasma to obtain a passivation layer.

6. The method for fabricating a self-reflection-lowering SiC-based ultraviolet photodiode according to claim 4, characterized in that, By opening windows in the isolation layer, multiple rectangular structures arranged in an array on the upper surface of the passivation layer are obtained, including: The isolation layer is windowed using photolithography and etching processes to obtain the rectangular structure; wherein the spacing between adjacent rectangular structures is 500~800nm, and the width of the window is 500~800nm.

7. The method for fabricating a self-reflection-lowering SiC-based ultraviolet photodiode according to claim 4, characterized in that, A first metal is deposited on the surface exposed by the rectangular structure and the passivation layer, and a second metal is deposited on the surface of the substrate opposite to the epitaxial layer, including: Using electron beam evaporation or magnetron sputtering, tungsten metal is deposited on the surface exposed by the rectangular structure and the passivation layer, and nickel metal is deposited on the surface of the substrate opposite to the epitaxial layer; wherein the thickness of the tungsten metal and the nickel metal is 60~70nm.

8. The method for fabricating a self-reflection-lowering SiC-based ultraviolet photodiode according to claim 4, characterized in that, Annealing the first metal and the second metal includes: The first metal and the second metal were annealed using a rapid thermal annealing process. The annealing conditions included an inert gas atmosphere, a temperature of 900~1100℃, and an annealing time of 160~190s.

9. The method for fabricating a self-reflection-lowering SiC-based ultraviolet photodiode according to claim 4, characterized in that, The mixing solution includes nitric acid, buffer oxide etching solution, and deionized water, with a volume ratio of nitric acid, buffer oxide etching solution, and deionized water of 1:1:5.

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