Porous silicon structure and method for manufacturing electron emitter device

Abstract

The application provides a porous silicon structure and a preparation method of an electron emission device. The method comprises the following steps: cleaning and pretreating a surface of a single crystal silicon substrate to ensure the cleanliness of the surface of the single crystal silicon substrate; forming a surface microstructure with the same material on the surface of the single crystal silicon substrate; and electrochemically corroding the single crystal silicon substrate based on the surface microstructure. In the electrochemical corrosion process, the gap between two adjacent micro-protrusions is formed as a preferential chemical reaction site, and the electrochemical corrosion solution corrodes the single crystal silicon substrate from the gap. Since the thickness of the surface microstructure is 0.05-1 microns, the distance between two adjacent micro-protrusions in the surface microstructure is 0.1-10 nanometers, and the lateral size of the micro-protrusion on the surface of the single crystal silicon substrate is 10-100 nanometers, the electrochemical corrosion can be effectively uniform, the consistency of the corrosion rate of the whole surface of the single crystal silicon substrate can be ensured, pits can be avoided, and the corrosion position of the single crystal silicon substrate can be made uniform and controllable.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device fabrication technology, and in particular to a method for fabricating a porous silicon structure and an electron emission device. Background Technology

[0002] Porous silicon was discovered by A. Uhlir in 1956 during his research on electropolishing silicon with hydrofluoric acid solution. It is a novel functional material formed by electrochemical anodizing or chemical etching of single-crystal silicon wafers, possessing a "quantum sponge"-like microstructure with nano-silicon atom clusters as its framework. In 1990, L.T. Canham et al. discovered that porous silicon can emit highly efficient visible light at room temperature and proposed a quantum confinement effect model. Subsequently, researchers from various countries have conducted extensive research on porous silicon preparation methods, explanations of its luminescence mechanism, and applications. This has led to its wide application in fields such as biological and chemical sensors, optoelectronic devices, integrated circuits, bioimaging, drug delivery solar cells, and optoelectronic communications.

[0003] Currently, the main methods for preparing porous silicon include electrochemical etching (anodic etching), hydrothermal etching, photochemical etching, electrospark etching, staining etching, and galvanic cell etching. The most widely used and simplest method is electrochemical etching. When fabricating silicon nanowire electron emission devices using electrochemical etching of single-crystal silicon, the etching liquid often concentrates in specific areas due to the surface roughness or defects of the etched single-crystal silicon. This results in uneven etching thickness in the porous silicon, forming large pits and affecting the emission performance of the electronic components. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for preparing porous silicon structures and electron emission devices, which solves the problem that when using the electrochemical etching method to manufacture silicon nanowire electron emission devices, the etching liquid often concentrates in these special areas due to the roughness or defects of the surface of the etched single crystal silicon, resulting in uneven etching thickness of porous silicon and the formation of large pits.

[0005] To achieve the above and other related objectives, the present invention provides a method for preparing a porous silicon structure, the method comprising:

[0006] A monocrystalline silicon substrate is provided, and the surface of the monocrystalline silicon substrate is pretreated to remove impurities from the surface of the monocrystalline silicon substrate;

[0007] A surface microstructure of silicon material is formed on one side of the single-crystal silicon substrate; wherein the surface microstructure is composed of a plurality of microprotrusions, and the cross-sectional size of the microprotrusions gradually decreases from the direction close to the single-crystal silicon substrate to the direction away from the single-crystal silicon substrate; the distance between two adjacent microprotrusions on the surface of the single-crystal silicon substrate is 0.1 nm to 10 nm; the lateral size of the microprotrusions on the surface of the single-crystal silicon substrate is 10 nm to 100 nm; and the thickness of the surface microstructure is 0.05 μm to 1 μm.

[0008] Electrochemical etching is performed on the monocrystalline silicon substrate based on the surface microstructure. The etching solution corrodes inward from the surface of the monocrystalline silicon substrate between two adjacent micro-protrusions to form a number of micropores of a predetermined thickness on the surface of the monocrystalline silicon substrate, thereby forming a porous silicon structure of the monocrystalline silicon substrate of the predetermined thickness.

[0009] Optionally, the surface microstructure is prepared by a self-assembly method or an atmospheric pressure chemical vapor deposition method.

[0010] Furthermore, the process temperature for preparing the surface microstructure by atmospheric pressure chemical vapor deposition is 600℃~1200℃.

[0011] Optionally, the etching solution used in the self-assembly method to prepare the surface microstructure is an acidic etching solution or an alkaline etching solution.

[0012] Furthermore, the acidic corrosive liquid includes a mixture of hydrofluoric acid and nitric acid; the alkaline corrosive liquid includes a mixture of ammonia and hydrogen peroxide.

[0013] Furthermore, when the surface microstructure is prepared using the acidic etching solution, the volume ratio of the acidic etching solution is hydrofluoric acid: nitric acid: water = (6-8): (0.5-1.5): (1.5-2.5), and the etching temperature is room temperature; when the surface microstructure is prepared using the alkaline etching solution, the volume ratio of the alkaline etching solution is 28% ammonia: 30% hydrogen peroxide: water = (0.5-1.5): (0.5-1.5): (4-6), and the etching temperature is 65℃-75℃.

[0014] Optionally, the monocrystalline silicon substrate is a P-type monocrystalline silicon substrate or an N-type monocrystalline silicon substrate; photoelectrochemical etching is used when electrochemically etching the monocrystalline silicon substrate.

[0015] Furthermore, the process parameters for the photoelectrochemical etching are as follows: volume ratio of 49% hydrofluoric acid solution to 99.8% ethanol = (0.5–1.5):(0.5–1.5), constant current voltage of 25V–35V, and current density of 7mA / cm². 2 ~13mA / cm 2The substrate is irradiated with a halogen light source at a distance of 18cm to 22cm from the monocrystalline silicon substrate.

[0016] Optionally, the impurities include organic residues and oxide residues; the monocrystalline silicon substrate is pretreated with sulfuric acid solution to remove the organic residues; and the monocrystalline silicon substrate is pretreated with DHF solution to remove the oxide residues.

[0017] The present invention also provides a method for fabricating an electron emission device, the method comprising:

[0018] A single-crystal silicon substrate having a porous silicon structure is provided, wherein the porous silicon structure is formed on the single-crystal silicon substrate, and the porous silicon structure is prepared by any of the above methods for preparing porous silicon structures.

[0019] A thin film of silicon oxide layer is formed on the surface of the nano-silicon grains in the porous silicon structure.

[0020] An emission electrode is formed on the surface of the oxidized porous silicon structure, and an acceleration electrode is formed on the bottom surface of the single-crystal silicon substrate.

[0021] As described above, the method for fabricating the porous silicon structure and electron emission device of the present invention first pre-treats the surface of a single-crystal silicon substrate by cleaning to ensure the cleanliness of the single-crystal silicon substrate surface. Then, a surface microstructure of the same material is formed on the surface of the single-crystal silicon substrate, and electrochemical etching is performed on the single-crystal silicon substrate based on the surface microstructure. During electrochemical etching, the gap between two adjacent micro-protrusions will form a preferential chemical reaction site. The electrochemical etching solution will etch into the single-crystal silicon substrate from the gap as the starting point. Since the thickness range of the surface microstructure is set to 0.05μm to 1μm, the distance between two adjacent micro-protrusions in the surface microstructure is 0.1nm to 10nm, and the lateral dimension of the micro-protrusions on the surface of the single-crystal silicon substrate is 10nm to 100nm, the non-uniformity of electrochemical etching can be effectively avoided during the electrochemical etching process, ensuring the consistency of the etching rate of the entire single-crystal silicon substrate surface, avoiding pits, and making the etching position of the single-crystal silicon substrate uniform and controllable. Attached Figure Description

[0022] Figures 1 to 3 The diagram shows cross-sectional structural schematics of each step in the preparation method of the porous silicon structure of the present invention.

[0023] Figure 4 Displayed as Figure 3 Enlarged diagram of point A in the middle.

[0024] Figure 5The diagram shows a three-dimensional structure of an example of forming a surface microstructure on the surface of a single-crystal silicon substrate in the method for preparing a porous silicon structure according to the present invention.

[0025] Figure 6 , Figure 8 and Figure 9 The diagram shows a cross-sectional view of each step in the fabrication method of the electron emission device of the present invention.

[0026] Figure 7 Displayed as Figure 6 Enlarged diagram of point B in the middle.

[0027] Component designation explanation

[0028] 10 Single-crystal silicon substrate

[0029] 11 Surface microstructure

[0030] 110 micro-protrusions

[0031] 12 Porous Silicon Structure

[0032] 120 micropores

[0033] 121 nanometer silicon grains

[0034] 13. Oxidized porous silicon structure

[0035] 130 silicon oxide thin film

[0036] 14 Emitting Electrode

[0037] 15 Accelerating Electrodes Detailed Implementation

[0038] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0039] Please see Figures 1 to 9 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0040] This invention provides a method for preparing a porous silicon structure, the method comprising the following steps:

[0041] A monocrystalline silicon substrate is provided, and the surface of the monocrystalline silicon substrate is pretreated to remove impurities from the surface of the monocrystalline silicon substrate;

[0042] A surface microstructure of silicon material is formed on one side of the single-crystal silicon substrate; wherein the surface microstructure is composed of a plurality of microprotrusions, and the cross-sectional size of the microprotrusions gradually decreases from the direction close to the single-crystal silicon substrate to the direction away from the single-crystal silicon substrate; the distance between two adjacent microprotrusions on the surface of the single-crystal silicon substrate is 0.1 nm to 10 nm; the lateral size of the microprotrusions on the surface of the single-crystal silicon substrate is 10 nm to 100 nm; and the thickness of the surface microstructure is 0.05 μm to 1 μm.

[0043] Electrochemical etching is performed on the monocrystalline silicon substrate based on the surface microstructure. The etching solution corrodes inward from the surface of the monocrystalline silicon substrate between two adjacent micro-protrusions to form a number of micropores of a predetermined thickness on the surface of the monocrystalline silicon substrate, thereby forming a porous silicon structure of the monocrystalline silicon substrate of the predetermined thickness.

[0044] The method for preparing the porous silicon structure of the present invention first pre-treats the surface of a monocrystalline silicon substrate by cleaning to ensure the cleanliness of the monocrystalline silicon substrate surface. Then, a surface microstructure of the same material is formed on the surface of the monocrystalline silicon substrate, and electrochemical etching is performed on the monocrystalline silicon substrate based on the surface microstructure. During electrochemical etching, the gap between two adjacent micro-protrusions will form a preferential chemical reaction site. The electrochemical etching solution will etch into the monocrystalline silicon substrate from the gap as the starting point. Since the thickness range of the surface microstructure is set to 0.05μm to 1μm, the distance between two adjacent micro-protrusions in the surface microstructure is 0.1nm to 10nm, and the lateral dimension of the micro-protrusions on the surface of the monocrystalline silicon substrate is 10nm to 100nm, the non-uniformity of electrochemical etching can be effectively avoided during the electrochemical etching process, ensuring the consistency of the etching rate of the entire monocrystalline silicon substrate surface, avoiding pits, and making the etching position of the monocrystalline silicon substrate uniform and controllable.

[0045] The method for preparing the porous silicon structure of the present invention will be described in detail below with reference to the specific accompanying drawings.

[0046] like Figure 1 As shown, step S1 is performed first, a monocrystalline silicon substrate 10 is provided, and the surface of the monocrystalline silicon substrate 10 is pretreated to remove impurities from the surface of the monocrystalline silicon substrate 10.

[0047] As an example, the single-crystal silicon substrate 10 can be selected from single-crystal silicon with a resistivity of 0.1 Ω·cm to 10 Ω·cm and a crystal orientation of

[100] . Depending on the requirements of subsequent device fabrication, the single-crystal silicon substrate 10 can be a doped or undoped single-crystal silicon material. The doped single-crystal silicon can be P-type doped or N-type doped. P-type doping is achieved using commonly used boron ion doping, and N-type doping is achieved using commonly used phosphorus ion doping, but this is not limited to these methods; other P-type and N-type ions can also be used, and no excessive restrictions are imposed here. Furthermore, the thickness of the single-crystal silicon substrate 10 is selected according to actual needs.

[0048] As an example, the impurities on the surface of the monocrystalline silicon substrate 10 are generally mostly organic residues and oxide residues. Preferably, for organic residues, the monocrystalline silicon substrate 10 can be pretreated with sulfuric acid solution to remove them; for oxide residues, the monocrystalline silicon substrate 10 can be pretreated with DHF solution (DHF solution is a mixture of hydrofluoric acid and water) to remove them. Surface pretreatment of the monocrystalline silicon substrate 10 can improve the cleanliness of the surface of the monocrystalline silicon substrate 10, laying the foundation for the subsequent formation of surface microstructures with controllable surface morphology.

[0049] like Figure 2 and Figure 5 As shown, step S2 is then performed to form a surface microstructure 11 of silicon material on one side of the single-crystal silicon substrate 10; wherein the surface microstructure 11 is composed of a plurality of micro-protrusions 110, and the cross-sectional size of the micro-protrusions 110 gradually decreases from the direction close to the single-crystal silicon substrate 10 to the direction away from the single-crystal silicon substrate 10 (e.g., Figure 2 and Figure 5 The micro-bumps 110 described herein are pyramid-shaped. The distance D between two adjacent micro-bumps on the surface of the single-crystal silicon substrate 10 is 0.1 nm to 10 nm. The lateral dimension L of the micro-bumps on the surface of the single-crystal silicon substrate 10 is 10 nm to 100 nm. The thickness of the surface microstructure 11 is 0.05 μm to 1 μm. Figure 5 As shown, the lateral dimension L of the micro-bump 110 on the surface of the monocrystalline silicon substrate 10 actually refers to the length of the micro-bump 110 in various directions on the surface of the monocrystalline silicon substrate 10. For ease of understanding... Figure 5 The diagram only shows the length of the micro-bump 110 in one direction on the surface of the single-crystal silicon substrate 10.

[0050] It should be noted that in this embodiment, the number of micro-protrusions 110 is determined by the area of ​​the porous silicon structure to be formed, and they can be formed on the entire surface of the single-crystal silicon substrate or on a portion of the single-crystal silicon substrate surface. For ease of processing, the surface microstructures 11 are generally formed on the entire surface of the single-crystal silicon substrate 10.

[0051] As a preferred example, the surface microstructure 11 can be formed using either a self-assembly method or an atmospheric pressure chemical vapor deposition (APCVD) method. The difference between the two methods is that the self-assembly method forms the surface microstructure 11 by micro-etching the surface of the monocrystalline silicon substrate 10; while APCVD deposits a layer of the surface microstructure 11 on the surface of the monocrystalline silicon substrate 10 through a deposition process.

[0052] Preferably, when APCVD is used to prepare the surface microstructure 11, the process temperature is selected to be 600℃~1200℃, for example, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, etc. The surface microstructure formed in this temperature range has better thickness uniformity.

[0053] Preferably, when the surface microstructure 11 is prepared using a self-assembly method, the etching solution can be either an acidic or alkaline solution. Preferably, the acidic etching solution is a mixture of hydrofluoric acid and nitric acid, with a volume ratio of hydrofluoric acid:nitric acid:water = (6-8):(0.5-1.5):(1.5-2.5). The surface microstructure 11 prepared at room temperature exhibits optimal thickness uniformity. Preferably, the alkaline etching solution is a mixture of ammonia and hydrogen peroxide, with a volume ratio of 28% ammonia:30% hydrogen peroxide:water = (0.5-1.5):(0.5-1.5):(4-6). The surface microstructure 11 prepared at a temperature of 65°C-75°C exhibits optimal thickness uniformity.

[0054] like Figure 3 and Figure 4 As shown, step S3 is performed last, where the monocrystalline silicon substrate 10 is electrochemically etched based on the surface microstructure 11. The electrochemical etching solution etches inward from the surface of the monocrystalline silicon substrate 10 between two adjacent micro-protrusions 110 to form a number of micropores 120 of a predetermined thickness on the surface of the monocrystalline silicon substrate 10, thereby forming a porous silicon structure 12 of the monocrystalline silicon substrate 10 of the predetermined thickness.

[0055] During the electrochemical corrosion process, the gaps between two adjacent micro-protrusions 110 become preferential chemical reaction sites. These sites form micro-depressions, which generate an enhanced electric field, leading to a sharp increase in current density and solubility. This triggers the growth of porous structures within the micro-depressions, thereby improving the uniformity of the grown silicon nanocrystals 121 and causing them to arrange themselves in a columnar pattern (e.g., ...). Figure 4 (As shown) more uniform.

[0056] As a preferred example, photoelectrochemical etching is used when electrochemically etching the single-crystal silicon substrate 10. Increasing the illumination can further improve the etching rate. Especially for the N-type single-crystal silicon substrate 10, photoelectrochemical etching can effectively ensure the etching rate and improve the uniformity of the nano-silicon grains 121. Further, the process parameters for the photoelectrochemical etching can be selected as follows: a volume ratio of 49% hydrofluoric acid solution to 99.8% ethanol = (0.5–1.5):(0.5–1.5), a constant current voltage of 25V–35V, and a current density of 7mA / cm². 2 ~13mA / cm 2 The substrate is irradiated with a halogen light source at a distance of 18cm to 22cm from the monocrystalline silicon substrate.

[0057] The present invention also provides a method for fabricating an electron emission device, the method comprising the following steps:

[0058] like Figure 3 and Figure 4 As shown, a single-crystal silicon substrate 10 with a porous silicon structure 12 is first provided. The porous silicon structure 12 is formed on the single-crystal silicon substrate 10, and the porous silicon structure 12 is prepared by the porous silicon structure preparation method described above.

[0059] like Figure 6 and Figure 7 As shown, a silicon oxide layer film 130 is then formed on the surface of the nano-silicon grains 121 in the porous silicon structure 12, thereby obtaining the oxidized porous silicon structure 13.

[0060] As a specific example, the method for forming the silicon oxide thin film 130 can be electrochemical oxidation or rapid thermal oxidation. Preferably, when using rapid thermal oxidation, the temperature is selected to be 850°C to 950°C, and the thermal oxidation time is selected to be 20 min to 30 min.

[0061] As another specific example, after forming the silicon oxide layer film 130, the surface microstructure 11 can be removed or retained. Figure 8 As shown, to selectively remove the surface microstructure 11, CMP polishing is used to remove the surface microstructure 11.

[0062] like Figure 9 As shown, an emission electrode 14 is finally formed on the surface of the oxidized porous silicon structure 13, and an acceleration electrode 15 is formed on the bottom surface of the single crystal silicon substrate 10, thereby obtaining the electron emission device.

[0063] Electron emission devices are fabricated based on porous silicon structures obtained by the above-described fabrication method. Since the porous silicon structure effectively avoids pits and has a uniform and controllable thickness, the emission performance of the electron emission devices is improved.

[0064] As an example, the emitting electrode 14 and the accelerating electrode 15 can be fabricated using a sputtering process. The emitting electrode 14 can be a stacked structure of titanium and gold layers. The accelerating electrode can be an aluminum layer, a gold layer, a copper layer, etc.

[0065] The following specific examples illustrate the fabrication method of the electron emission device of the present invention. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0066] Example 1:

[0067] A method for fabricating an electron emitting device includes the following steps:

[0068] Step S1: Prepare a monocrystalline silicon substrate with a resistivity of 0.1 Ω·cm to 10 Ω·cm and perform surface pretreatment. Specifically, this includes: selecting a solution with a volume ratio of H2SO4:H2O2 = 3:1, immersing the monocrystalline silicon substrate until the bubbles disappear, and cleaning the organic residue on the surface of the monocrystalline silicon substrate; after completion, immerse the monocrystalline silicon substrate in DHF solution to remove its surface natural oxide layer (i.e., oxide residue), thus completing the surface pretreatment of the monocrystalline silicon substrate.

[0069] Step S2: Form a surface microstructure of silicon material on one side of the single-crystal silicon substrate. Either of the following two methods can be used to prepare the surface microstructure.

[0070] Method 1: The cleaned single-crystal silicon substrate is placed in the heating system of an APCVD device and heated to the temperature required for epitaxial growth, typically between 600°C and 1200°C. Then, a gas containing a silicon source, such as SiH4, and other necessary reactive gases, such as H2 and O2, are introduced into the deposition chamber, causing a chemical reaction on the surface of the single-crystal silicon substrate to form an epitaxial layer. Because the surface of this epitaxial layer is uneven and the grain size is not too large, it can function similarly to a surface microstructure on the single-crystal silicon substrate surface. Therefore, this epitaxial layer forms the surface microstructure described in this invention.

[0071] Method 2: Immerse the surface of the monocrystalline silicon substrate to be formed with an acidic or alkaline solution, and perform self-assembly on the monocrystalline silicon substrate surface to form a nanoscale textured structure. Commonly used acidic solutions include mixed acids such as HF and HNO3; commonly used alkaline solutions include alkaline solutions such as NaOH or NH3·H2O. During the self-assembly process, the etching rate and surface roughness are adjusted by controlling the solution concentration, temperature, and time. In this embodiment, the acidic solution selected is a mixed solution of HF and HNO3, with a volume ratio of HF:HNO3:H2O = 7:1:2, the temperature is room temperature, and the reaction time is 60 s to complete the fabrication of the nanoscale surface microstructure. The alkaline solution selected in this embodiment is ammonia water, with a volume ratio of NH3 (28%):H2O2 (30%):H2O = 1:1:5, the temperature is 70℃, and the reaction time does not exceed 2 min to complete the fabrication of the nanoscale surface microstructure.

[0072] Step S3: The monocrystalline silicon substrate with surface microstructures is subjected to photoelectrochemical etching under constant current conditions. The etching solution is a hydrofluoric acid mixture, specifically a 1:1 mixture of 49% HF acid solution and 99.8% ethanol, at 30V and a current density of 10mA / cm². 2 Under the condition that the halogen light source is 20cm away from the sample, photoelectrochemical etching is performed for 60s. During the etching process, the etching proceeds along the concave points between the micro-protrusions in the surface microstructure, thereby forming the desired porous silicon structure.

[0073] Step S4: After photoelectrochemical etching, the columnar porous silicon structure containing nano-silicon grains is oxidized using a rapid thermal oxidation process. The rapid thermal oxidation temperature is 900℃ and the time is 25min. A silicon oxide layer film is formed on the outer surface of the silicon nano-grains, resulting in the oxidized porous silicon structure.

[0074] Step S5: Remove the surface microstructure using CMP polishing process.

[0075] Step S6: After CMP polishing, a Ti / Au metal layer for the emitter electrode is sputtered onto the oxidized porous silicon structure surface. Specific parameters are: gas flow rate of 50 sccm, RF power of 300 W, and sputtering thickness of approximately [thickness value missing] at a pressure of 7.52 mTorr. A Ti layer; sputtered at a pressure of 7.50 mTorr with a thickness of approximately An Au layer is formed. A metal electrode, made of Al, Au, or Cu, is sputtered onto the bottom surface of a single-crystal silicon substrate as an accelerating electrode. The final electron emission device is obtained.

[0076] In summary, this invention provides a method for fabricating porous silicon structures and electron emission devices. First, the surface of a single-crystal silicon substrate is pre-treated by cleaning to ensure its cleanliness. Then, a surface microstructure of the same material is formed on the single-crystal silicon substrate. Based on this surface microstructure, the single-crystal silicon substrate is electrochemically etched. During electrochemical etching, the gap between adjacent micro-protrusions becomes a preferential chemical reaction site. The electrochemical etching solution etches into the single-crystal silicon substrate from this gap. Because the thickness of the surface microstructure ranges from 0.05 μm to 1 μm, the distance between adjacent micro-protrusions in the surface microstructure is 0.1 nm to 10 nm, and the lateral dimension of the micro-protrusions on the single-crystal silicon substrate surface is 10 nm to 100 nm, the non-uniformity of electrochemical etching can be effectively avoided during the electrochemical etching process, ensuring the consistency of the etching rate across the entire single-crystal silicon substrate surface, preventing pitting, and making the etching location of the single-crystal silicon substrate uniform and controllable. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0077] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a porous silicon structure, characterized in that, The preparation method includes: A monocrystalline silicon substrate is provided, and the surface of the monocrystalline silicon substrate is pretreated to remove impurities from the surface of the monocrystalline silicon substrate; A surface microstructure of silicon material is formed on one side of the single-crystal silicon substrate; wherein the surface microstructure is composed of a plurality of microprotrusions, and the cross-sectional size of the microprotrusions gradually decreases from the direction close to the single-crystal silicon substrate to the direction away from the single-crystal silicon substrate; the distance between two adjacent microprotrusions on the surface of the single-crystal silicon substrate is 0.1 nm to 10 nm; the lateral size of the microprotrusions on the surface of the single-crystal silicon substrate is 10 nm to 100 nm; and the thickness of the surface microstructure is 0.05 μm to 1 μm. Electrochemical etching is performed on the monocrystalline silicon substrate based on the surface microstructure. The etching solution corrodes inward from the surface of the monocrystalline silicon substrate between two adjacent micro-protrusions to form a number of micropores of a predetermined thickness on the surface of the monocrystalline silicon substrate, thereby forming a porous silicon structure of the monocrystalline silicon substrate of the predetermined thickness.

2. The method for preparing a porous silicon structure according to claim 1, characterized in that: The methods for preparing the surface microstructures include self-assembly or atmospheric pressure chemical vapor deposition.

3. The method for preparing a porous silicon structure according to claim 2, characterized in that: The process temperature for preparing the surface microstructure by atmospheric pressure chemical vapor deposition is 600℃~1200℃.

4. The method for preparing a porous silicon structure according to claim 2, characterized in that: The etching solution used in the self-assembly method to prepare the surface microstructure is either an acidic or alkaline etching solution.

5. The method for preparing a porous silicon structure according to claim 4, characterized in that: The acidic corrosive solution includes a mixture of hydrofluoric acid and nitric acid; the alkaline corrosive solution includes a mixture of ammonia and hydrogen peroxide.

6. The method for preparing a porous silicon structure according to claim 5, characterized in that: When preparing the surface microstructure using the acidic etching solution, the volume ratio of the acidic etching solution is hydrofluoric acid: nitric acid: water = (6-8): (0.5-1.5): (1.5~2.5), the corrosion temperature is room temperature; when the alkaline etching solution is used to prepare the surface microstructure, the volume ratio of the alkaline etching solution is 28% ammonia water: 30% hydrogen peroxide: water = (0.5~1.5): (0.5~1.5): (4~6), and the corrosion temperature is 65℃~75℃.

7. The method for preparing a porous silicon structure according to claim 1, characterized in that: The monocrystalline silicon substrate is a P-type monocrystalline silicon substrate or an N-type monocrystalline silicon substrate; photoelectrochemical etching is used when electrochemically etching the monocrystalline silicon substrate.

8. The method for preparing a porous silicon structure according to claim 7, characterized in that, The process parameters for the photoelectrochemical etching are as follows: volume ratio of 49% hydrofluoric acid solution to 99.8% ethanol = (0.5–1.5):(0.5–1.5), constant current voltage of 25V–35V, and current density of 7mA / cm². 2 ~13mA / cm 2 The substrate is irradiated with a halogen light source at a distance of 18cm to 22cm from the monocrystalline silicon substrate.

9. The method for preparing a porous silicon structure according to claim 1, characterized in that: The impurities include organic residues and oxide residues; the monocrystalline silicon substrate is pretreated with sulfuric acid solution to remove the organic residues; the monocrystalline silicon substrate is pretreated with DHF solution to remove the oxide residues.

10. A method for fabricating an electron emission device, characterized in that, The preparation method includes: A single-crystal silicon substrate having a porous silicon structure is provided, wherein the porous silicon structure is formed on the single-crystal silicon substrate, and the porous silicon structure is prepared by the method for preparing a porous silicon structure as described in any one of claims 1 to 9; A thin film of silicon oxide layer is formed on the surface of the nano-silicon grains in the porous silicon structure. An emission electrode is formed on the surface of the oxidized porous silicon structure, and an acceleration electrode is formed on the bottom surface of the single-crystal silicon substrate.

Images