Preparation method of photoelectric detector
By employing rapid thermal oxidation and a double-layer oxide structure during the fabrication of the photodetector, combined with etching and ion implantation, the leakage current problem caused by boron diffusion was solved, thereby improving the performance of the photodetector.
Patent Information
- Application Number
- CN202511038154.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-25
- Publication Date
- 2025-11-04
AI Technical Summary
In the existing photodetector fabrication process, boron diffuses from the high-temperature furnace tube to the silicon substrate surface, causing an increase in leakage current and affecting the signal-to-noise ratio and detection sensitivity of the device.
The silicon substrate is pre-oxidized in the first furnace tube using a rapid thermal oxidation method, followed by thermal oxidation in the second furnace tube. A double oxide layer structure is formed by combining dry and wet etching, and a p-type doped region is formed by ion implantation. Finally, metal deposition is performed to fabricate a photodetector.
It effectively suppressed the diffusion of boron, reduced leakage current and dark current, and improved the position sensitivity and device performance of the photodetector.
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Figure CN120897553A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of photoelectric conversion, in particular to a preparation method of a photoelectric detector. BACKGROUND
[0002] The photoelectric detector is a kind of photoelectric sensor which converts optical signals into electrical signals and realizes accurate measurement of light spot position. The core principle is based on photoelectric effect, which divides the incident radiant energy into four independent quadrants. The light spot position information is calculated by using differential signal processing technology. The four-quadrant photoelectric detector has the characteristics of fast response speed, high sensitivity and wide detection spectral range. Dark current is one of the key performance parameters of the photoelectric detector, which directly affects the signal-to-noise ratio and detection sensitivity of the device.
[0003] However, in the prior art, the preparation process of the photoelectric detector first needs to place the silicon substrate in a high-temperature furnace tube to prepare an oxide layer. In the furnace tube heat oxidation process, the process cross contamination, heat oxidation and diffusion process are not strictly managed, resulting in boron diffusion residues caused by process chips or processing wafers doped with boron elements in the furnace tube. The residual boron elements in the high-temperature furnace tube will introduce improper doping of boron ions on the surface of the silicon substrate during the subsequent high-temperature oxidation process to generate an oxide layer, which will destroy the isolation effect, increase the leakage current of the isolation area, destroy the quadrant independence, and affect the position sensitivity of the photoelectric detector. SUMMARY
[0004] One object of the present application is to provide a preparation method of a photoelectric detector, which solves the technical problem of the prior art that the boron elements in the high-temperature furnace tube during the preparation process of the silicon substrate oxide layer are easily diffused to the surface of the silicon substrate, resulting in an increase in the leakage current.
[0005] Another object of the present application is to further improve the suppression effect of the leakage current.
[0006] According to the purpose of the present application, the present application provides a preparation method of a photoelectric detector, comprising:
[0007] performing pre-oxidation treatment of the silicon substrate in a first furnace tube by using a rapid thermal oxidation method to form a first oxide layer on the surface of the silicon substrate;
[0008] performing thermal oxidation treatment of the silicon substrate in a second furnace tube by using a tube-type thermal oxidation method to obtain a thermal oxidation silicon substrate, the thermal oxidation silicon substrate comprising the silicon substrate, the second oxide layer and the first oxide layer which are sequentially stacked from bottom to top;
[0009] performing etching treatment and ion implantation on the thermal oxidation substrate to form a p-type doped region on the thermal oxidation substrate;
[0010] The photoelectric detector is prepared by sequentially performing heat treatment and metal deposition on the thermal oxidation substrate forming the p-type doped region; wherein
[0011] The temperature of the pre-oxidation treatment is any value in the range from 1000℃ to 1200℃, the heating rate is any value in the range from 50℃ / s to 150℃ / s, the treatment time is any value in the range from 200s to 300s, and the thickness of the first oxide layer is any value in the range from 10nm to 20nm.
[0012] Optionally, the thickness of the second oxide layer is any value in the range from 20nm to 30nm.
[0013] Optionally, the oxidation temperature of the tube type thermal oxidation method is any value in the range from 1000℃ to 1200℃.
[0014] Optionally, the energy of the ion implantation is any value in the range from 20keV to 50keV, and the ion dose is any value in the range from 2.0×10 15 cm -2 -3.0×10 15 cm -2 .
[0015] Optionally, the etching treatment comprises the following steps:
[0016] The first oxide layer and the second oxide layer are etched by using dry etching and wet etching in sequence.
[0017] Optionally, the dry etching adopts a reactive ion etching process, C4F8 and O2 are used as etching gases, the etching power is any value in the range from 600W to 700W, the etching pressure is any value in the range from 20mTorr to 40mTorr, and the etching time is any value in the range from 30s to 150s, so as to remove the first oxide layer and part of the second oxide layer.
[0018] Optionally, the wet etching adopts a buffered hydrofluoric acid solution to etch for 5s to 60s at 20℃ to 25℃, so as to remove all or part of the second oxide layer.
[0019] Optionally, the buffered hydrofluoric acid solution is a mixed solution of hydrofluoric acid and ammonium fluoride with a volume ratio of 1:5 to 1:10.
[0020] The present application forms a silicon substrate by using a rapid thermal treatment method for pre-oxidation treatment of the silicon substrate, so as to form a first oxide layer with a thickness of The first oxide layer, with any value in the given information, is then transferred to a second furnace tube for thermal oxidation to form a thermally oxidized silicon substrate comprising a silicon substrate, a second oxide layer, and a first oxide layer stacked sequentially from bottom to top. This not only effectively suppresses the uncontrolled diffusion of boron in the silicon substrate during ion implantation but also prevents residual boron in the second furnace tube from diffusing to the surface of the silicon substrate during direct thermal oxidation of the silicon substrate. It also prevents improper doping of boron during oxide layer preparation, thereby preventing lateral diffusion of charge carriers and crosstalk of photogenerated current in the photodetector, preventing damage to the isolation effect of the oxide layer, reducing leakage current and dark current in the isolation region, and thus preventing damage to quadrant independence, thereby improving the position sensitivity of the photodetector.
[0021] Furthermore, the present invention limits the thickness of the second oxide layer to... While ensuring sufficient isolation and withstand voltage, it also takes into account stress, flatness and optical gain, achieving significant suppression of leakage current, reduction of dark current and improvement of quantum efficiency.
[0022] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description
[0023] The following sections will describe some specific embodiments of the invention in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:
[0024] Figure 1 This is a schematic flowchart of a method for fabricating a photodetector according to an embodiment of the present invention;
[0025] Figure 2 This is a schematic structural diagram of a photodetector according to an embodiment of the present invention.
[0026] Figure label:
[0027] 100 - Photodetector, 10 - Silicon substrate, 20 - First oxide layer, 30 - Second oxide layer, 40 - Thermally oxidized silicon substrate, 50 - p-type doped region. Detailed Implementation
[0028] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.
[0029] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.
[0030] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.
[0031] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.
[0032] Figure 1 This is a schematic flowchart illustrating a method for fabricating a photodetector according to an embodiment of the present invention. Figure 2 This is a schematic structural diagram of a photodetector according to an embodiment of the present invention.
[0033] like Figure 1 As shown, the present invention provides a method for fabricating a photodetector 100, comprising:
[0034] Step S100: The silicon substrate 10 is pre-oxidized in the first furnace tube using a rapid thermal oxidation method to form a first oxide layer 20 on the surface of the silicon substrate 10.
[0035] Step S200: The silicon substrate 10 is thermally oxidized in the second furnace tube using a tubular thermal oxidation method to prepare a thermally oxidized silicon substrate 40. The thermally oxidized silicon substrate 40 includes a silicon substrate 10, a second oxide layer 30 and a first oxide layer 20 arranged sequentially from bottom to top.
[0036] Step S300: Etch and ion implant the thermally oxidized substrate to form a p-type doped region 50 on the thermally oxidized substrate;
[0037] Step S400: The thermally oxidized substrate forming the p-type doped region 50 is subjected to heat treatment and metal deposition in sequence to prepare the photodetector 100.
[0038] The pre-oxidation treatment temperature is any value between 1000℃ and 1200℃, the heating rate is any value between 50℃ / s and 150℃ / s, the treatment time is any value between 200s and 300s, and the thickness of the first oxide layer 20 is... Any value among them.
[0039] like Figure 2 As shown, in this embodiment, the method for fabricating the photodetector 100 firstly uses a rapid thermal oxidation method to pre-oxidize the silicon substrate 10 in a first furnace tube to form a first oxide layer 20 on the surface of the silicon substrate 10. Then, the silicon substrate 10 with the first oxide layer 20 formed on its surface is transferred to a second furnace tube, and the silicon substrate 10 is thermally oxidized in the second furnace tube using a tubular thermal oxidation method to prepare a thermally oxidized silicon substrate 40 with a second oxide layer 30. That is, the thermally oxidized silicon substrate 40 includes a silicon substrate 10, a second oxide layer 30 and a first oxide layer 20 arranged sequentially from bottom to top. Then, the thermally oxidized substrate is etched and ion implanted to form a p-type doped region 50 on the thermally oxidized substrate. Finally, the thermally oxidized substrate with the p-type doped region 50 is heat-treated and metal deposited sequentially to prepare the photodetector 100. Here, the pre-oxidation treatment temperature is any value between 1000℃ and 1200℃, that is, the pre-oxidation treatment temperature can be 1000℃, 1050℃, 1100℃, 1150℃, or 1200℃, or any other value between 1000℃ and 1200℃. The heating rate is any value between 50℃ / s and 150℃ / s, that is, the heating rate can be 50℃ / s, 60℃ / s, 80℃ / s, 100℃ / s, 1200℃ / s, or any other value between 1000℃ and 1200℃. The temperature / s can be 0℃ / s or 150℃ / s, or any other value between 50℃ / s and 150℃ / s. The processing time can be any value between 200s and 300s, meaning the pre-oxidation treatment time can be 200s, 210s, 220s, 230s, 240s, 250s, 260s, 270s, 280s, or 300s, or any other value between 200s and 300s. The thickness of the first oxide layer 20 is... Any value in the range, that is, the thickness of the oxide layer after pre-oxidation treatment, can be... or It could also be Any other value in it.
[0040] In this embodiment, a rapid thermal processing method is used to perform a pre-oxidation treatment on the silicon substrate 10 to form a layer with a thickness of [thickness missing] on the surface of the silicon substrate 10. The first oxide layer 20, which has any value, is then transferred to the second furnace tube for thermal oxidation treatment to form a thermally oxidized silicon substrate 40, which includes a silicon substrate 10, a second oxide layer 30, and a first oxide layer 20 arranged sequentially from bottom to top. This not only effectively suppresses the uncontrolled diffusion of boron in the silicon substrate 10 during ion implantation, but also prevents the diffusion of residual boron in the second furnace tube to the surface of the silicon substrate 10 when the silicon substrate 10 is directly thermally oxidized. It also prevents improper doping of boron during the oxide layer preparation process, thereby preventing lateral diffusion of charge carriers and crosstalk of photogenerated current in the photodetector 100, preventing damage to the isolation effect of the oxide layer, reducing leakage current and dark current in the isolation region, and thus preventing damage to quadrant independence, thereby improving the position sensitivity of the photodetector 100.
[0041] In a further embodiment, the thickness of the second oxide layer 30 is Any value in the range, i.e., the thickness of the oxide layer formed by thermal oxidation treatment is or It could also be Any other value among them. In this embodiment, the thickness of the second oxide layer 30 is limited to [the specified value]. While ensuring sufficient isolation and withstand voltage, it also takes into account stress, flatness and optical gain, achieving leakage current suppression, dark current reduction and quantum efficiency improvement.
[0042] In a further embodiment, the oxidation temperature of the tubular thermal oxidation method is any value between 1000℃ and 1200℃. That is, the oxidation temperature for preparing the second oxide layer 30 by thermal oxidation is 1000℃, 1100℃, 1120℃, 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, or 1200℃, or any other value between 1000℃ and 1200℃. In this embodiment, by controlling the thermal oxidation temperature within the range of 1000℃ to 1200℃, not only can the thickness of the second oxide layer 30 be precisely controlled to ensure the density and uniformity of the oxide layer, but it can also effectively cooperate with the pre-oxidation process to control the lateral diffusion of boron ions, improve the isolation performance of the device, and reduce dark current and leakage current.
[0043] In a further embodiment, the ion implantation energy is any value between 20 keV and 50 keV, that is, the ion implantation energy can be 20 keV, 23 keV, 30 keV, 40 keV, or 50 keV, or any other value between 20 keV and 50 keV, and the ion dose is 2.0 × 10⁻⁶. 15 cm -2 -3.0×10 15 cm -2 Any value in the range, i.e., the ion dose can be 2.0 × 10⁻⁶. 15 cm -22.1×10 15 cm -2 2.2×10 15 cm -2 2.3×10 15 cm -2 2.4×10 15 cm -2 2.5×10 15 cm -2 2.6×10 15 cm -2 2.7×10 15 cm -2 2.8×10 15 cm -2 2.9×10 15 cm -2 Or 3.0×10 15 cm -2 It can also be 2.0×10 15 cm -2 -3.0×10 15 cm -2 Any other value. In this embodiment, 20keV and 2.0×10¹⁵cm are used. -2 The boron ion implantation dose-energy window, with a thickness of The first oxide layer 20 and its thickness are The synergistic effect of the bilayer oxide structure of the second oxide layer 30 allows for the simultaneous attainment of excellent characteristics such as shallow junction, low chip resistance, low leakage current, and high bandwidth without increasing the thermal budget.
[0044] In a further embodiment, the etching process includes the following steps:
[0045] The first oxide layer 20 and the second oxide layer 30 are etched sequentially using dry etching and wet etching.
[0046] In this embodiment, during the etching process of the first oxide layer 20 and the second oxide layer 30 of the thermally oxidized silicon substrate 40 for ion implantation windows, a combination of dry etching and wet etching is used. This can maintain the verticality of the etching profile and the accuracy of the opening while further removing residual oxides and defects generated during the dry etching process, thereby achieving cleanliness and fine control of the implantation window. Ultimately, this helps to improve the consistency of subsequent ion implantation and the device performance of the photodetector 100.
[0047] In a further embodiment, the dry etching employs a reactive ion etching process, using C4F8 and O2 as etching gases. The etching power is any value between 600W and 700W, i.e., 600W, 610W, 620W, 650W, or 700W, or any other value between 600W and 700W. The etching pressure is any value between 20mTorr and 40mTorr, i.e., the etching pressure can be 20mTorr, 30mTorr, 35mTorr, 36mTorr, 37mTorr, or 40mTorr. The etching time can be any value between 20 mTorr and 40 mTorr, and any value between 30 s and 150 s. That is, the etching time can be 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s, or 150 s, or any other value between 30 s and 150 s, to completely remove the first oxide layer 20 and part of the second oxide layer 30. It can also suppress lateral corrosion, improve the etching quality and consistency with the ion implantation window, and further enhance the structural integrity and device reliability of the photodetector 100. Here, dry etching can selectively remove the entire thickness of the first oxide layer 20 and part of the thickness of the second oxide layer 30 at the position corresponding to the ion implantation window.
[0048] In a further embodiment, wet etching is performed using a buffered hydrofluoric acid solution at 20°C-25°C for 5s-60s. That is, the processing temperature for wet etching can be 20°C, 21°C, 22°C, 23°C, 24°C, or 25°C, or any other value within the 20°C-25°C range. The wet etching time can be 5s, 10s, 20s, 30s, 40s, 50s, or 60s, or any other value within the 5s-60s range, to remove the remaining thickness of the second oxide layer 30. In other words, using a buffered hydrofluoric acid solution to perform wet etching of the oxide layer within a set temperature range allows for precise removal of the second oxide layer 30, avoiding overshoot and improving the edge quality and cleanliness of the implantation window. This contributes to the uniformity of subsequent ion implantation and the control of device leakage current. Here, the wet etching process can selectively remove the remaining thickness of the second oxide layer 30 at the position corresponding to the ion implantation etching window of the dry etching process.
[0049] In a further embodiment, the buffer hydrofluoric acid solution is a mixed solution of hydrofluoric acid and ammonium fluoride in a volume ratio of 1:5 to 1:10. That is, the volume ratio of hydrofluoric acid to ammonium fluoride in the buffer hydrofluoric acid solution can be 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10, or any other value within the range of 1:5 to 1:10. In this embodiment, the 1:5 volume ratio of hydrofluoric acid and ammonium fluoride forms a stable buffer system, effectively controlling the activity of HF, i.e., the NH4 released by ammonium fluoride. + and F -Ions can adjust the solution pH, suppress the free concentration change of HF, improve the uniformity and repeatability of etching, and stably achieve precise removal of the first oxide layer 20 or the second oxide layer 30, improve the quality of the etching window, reduce edge roughness and size drift, and significantly reduce the etching rate. This is beneficial for fine control of shallow or microstructures. Furthermore, the uniform and slow etching process can produce a smooth and clean interface, providing a clean and flat surface foundation for subsequent processes such as ion implantation, heat treatment, and metal deposition.
[0050] The present application will now be described in further detail with reference to specific embodiments.
[0051] In some embodiments, in the fabrication method of the photodetector 100, the silicon substrate 10 is first pre-oxidized in a first furnace tube using a rapid thermal oxidation method at a temperature of 1000°C.
[0052] The temperature range is any value between -1200℃ and 1200℃, the heating rate is any value between 50℃ / s and 150℃ / s, and the processing time is any value between 200s and 300s, to form a thickness of [thickness value missing] on the surface of the silicon substrate 10. A first oxide layer 20 is formed at any value within the specified range. Subsequently, the silicon substrate 10 undergoes thermal oxidation in a second furnace tube using a tubular thermal oxidation method. The oxidation temperature of the tubular thermal oxidation method is any value between 1000℃ and 1200℃. The thickness of the second oxide layer 30 is... A thermally oxidized silicon substrate 40 is prepared by using any of the following values to form a second oxide layer 30 at the bottom of the first oxide layer 20. The thermally oxidized substrate is then sequentially etched using dry etching and wet etching, followed by ion implantation. The ion implantation energy is any value between 20keV and 50keV, and the ion dose is 2.0 × 10⁻⁶. 15 cm -2 -3.0×10 15 cm -2 Any value is used to form a p-type doped region 50 on a thermally oxidized substrate. Finally, the thermally oxidized substrate with the p-type doped region 50 is subjected to heat treatment and metal deposition in sequence to prepare a photodetector 100.
[0053] Example 1
[0054] In the fabrication method of the photodetector 100, the silicon substrate 10 is first pre-oxidized in a first furnace tube using a rapid thermal oxidation method. The pre-oxidation temperature is 1100℃, the heating rate is 50℃ / s, and the processing time is 250s, so as to form a thickness of [missing information] on the surface of the silicon substrate 10. The first oxide layer 20 is formed, followed by thermal oxidation of the silicon substrate 10 in a second furnace tube using a tubular thermal oxidation method at an oxidation temperature of 1100℃, to obtain a thermally oxidized silicon substrate 40, thereby forming a second oxide layer 30 at the bottom of the first oxide layer 20. The thickness of the second oxide layer 30 is... Next, the thermally oxidized substrate was etched using both dry and wet etching methods, followed by ion implantation. The ion implantation energy was any value within 20 keV, and the ion dose was 2.0 × 10⁻⁶. 15 cm -2 A p-type doped region 50 is formed on a thermally oxidized substrate. Finally, the thermally oxidized substrate with the p-type doped region 50 is subjected to heat treatment and metal deposition in sequence to prepare a photodetector 100.
[0055] Comparative Example 1
[0056] The only difference between Comparative Example 1 and Example 1 is that the silicon substrate 10 is directly placed in the second furnace tube and the oxide layer is prepared by thermal oxidation using a tubular thermal oxidation method.
[0057] The photodetectors 100 prepared in Example 1 and Comparative Example 1 were subjected to photoelectric performance testing, and the photoelectric performance testing results are shown in Table 1.
[0058] Table 1. Photoelectric properties of the photodetectors prepared in Example 1 and Comparative Example 1
[0059] Dark current / nA Example 1 10 Comparative Example 1 30
[0060] As shown in Table 1, the dark current and leakage current of the photodetector 100 prepared in Example 1 are significantly lower than those of the photodetector 100 prepared in Comparative Example 1, and the photoelectric responsivity of the photodetector 100 prepared in Example 1 is higher than that of the photodetector 100 prepared in Comparative Example 1. This indicates that preparing a pre-oxidized layer using a rapid thermal oxidation method before thermal oxidation treatment can significantly reduce the dark current and leakage current of the photodetector 100, while improving its photoelectric conversion efficiency.
[0061] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0062] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.
Claims
1. A method for fabricating a photodetector, characterized in that, include: A silicon substrate is pre-oxidized in a first furnace tube using a rapid thermal oxidation method to form a first oxide layer on the surface of the silicon substrate. The silicon substrate is thermally oxidized in a second furnace tube using a tubular thermal oxidation method to prepare a thermally oxidized silicon substrate, which includes the silicon substrate, the second oxide layer, and the first oxide layer arranged in sequence from bottom to top. The thermally oxidized substrate is etched and ion implanted to form a p-type doped region on the thermally oxidized substrate; The photodetector is fabricated by sequentially heat-treating and depositing metal onto the thermally oxidized substrate forming the p-type doped region; wherein, The pre-oxidation treatment temperature is any value between 1000℃ and 1200℃, the heating rate is any value between 50℃ / s and 150℃ / s, and the treatment time is any value between 200s and 300s. The thickness of the first oxide layer is... Any value among them.
2. The preparation method according to claim 1, characterized in that, The thickness of the second oxide layer is Any value among them.
3. The preparation method according to claim 2, characterized in that, The oxidation temperature of the tubular thermal oxidation method is any value between 1000℃ and 1200℃.
4. The preparation method according to claim 3, characterized in that, The ion implantation energy is any value between 20keV and 50keV, and the ion dose is 2.0 × 10 15 cm -2 -3.0×10 15 cm -2 Any value among them.
5. The preparation method according to claim 4, characterized in that, The etching process includes the following steps: The first oxide layer and the second oxide layer are etched sequentially using dry etching and wet etching.
6. The preparation method according to claim 5, characterized in that, The dry etching process employs reactive ion etching, using C4F8 and O as etching gases, with an etching power of 600W-700W, an etching pressure of 20mTorr-40mTorr, and an etching time of 30s-150s, to remove the first oxide layer and part of the second oxide layer.
7. The preparation method according to claim 4, characterized in that, The wet etching process uses a buffered hydrofluoric acid solution to etch for 5-60 seconds at 20-25°C to remove all or part of the second oxide layer.
8. The preparation method according to claim 7, characterized in that, The buffered hydrofluoric acid solution is a mixed solution of hydrofluoric acid and ammonium fluoride in a volume ratio of 1:5 to 1:10.