Annealing preparation method of large-size sapphire substrate
The sapphire single crystal wafer is processed in a limited-domain container through salt etching and annealing process, which solves the problem of base step defects after annealing, and achieves uniform and low-defect step preparation, providing high-quality preparation of large-area TMDs single crystals. Stable platform.
Patent Information
- Application Number
- CN202411590984.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-08
- Publication Date
- 2025-02-18
AI Technical Summary
The prior art After the annealing of sapphire single crystal wafers, the directional growth conditions of the substrate are harsh due to step defects, making it difficult to obtain uniform and few defective steps.
Annealing process using salt etching is performed in a domain-limited container. By infiltration and drying of soluble sodium or potassium salt solutions, salt concentration is adjusted in combination with the domain-limited annealing container to achieve uniform etching of the sapphire surface.
Under low temperature and rapid annealing conditions, a more uniform and low defective sapphire base step is obtained, providing a stable platform for subsequent epitaxial growth, lithography, etching and other processes, and improving the quality of large-area TMDs single crystals.
Smart Images
Figure CN119465411A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of semiconductor materials, and in particular relates to an annealing preparation method for a large-sized sapphire substrate. Background Art
[0002] Transition metal dichalcogenides (TMDs) as two-dimensional (2D) semiconductor materials hold great potential for advanced transistor technologies beyond silicon, extending Moore's Law. The reduction of film thickness to the limit of atomic subnanometer length scales, a difficult limit for conventional semiconductors, has also pushed 2D TMDs to the forefront of non-silicon electronics and optoelectronics. Chemical vapor deposition (CVD) is an industry-standard growth method used to potentially meet some stringent requirements for large-scale grain boundary-free epitaxial growth. Indeed, controlling the orientation of domains is crucial to minimize grain boundaries and ensure smooth stitching between domains. Substrate-lattice symmetry and substrate steps directly affect the directional growth of 2D materials.
[0003] Sapphire single crystal wafers are made by cutting, grinding, polishing and other processing technologies to form circular thin slices with a certain thickness and flatness. Sapphire single crystal wafers are important basic materials for manufacturing semiconductor devices, optoelectronic devices, etc. For example, in the semiconductor industry, single crystal wafers are like the foundation of a building, providing a uniform and stable platform for subsequent epitaxial growth, photolithography, etching and other processes on its surface.
[0004] In order to obtain large-area TMDs single crystals, from the perspective of process feasibility and repeatability, it is a relatively mature technical route to anneal the single crystal wafer substrate material (such as sapphire single crystal wafer) to obtain steps, and then perform directional nucleation growth. However, this technology also has the problem that the directional growth conditions are harsh due to step defects on the substrate after annealing.
[0005] Therefore, a more optimized and simpler preparation process is needed to obtain uniform steps with fewer defects on sapphire single crystal wafers, providing a uniform and stable platform for subsequent epitaxial growth, lithography, etching and other processes on its surface, so as to prepare high-quality, large-area TMDs single crystals. Summary of the invention
[0006] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes an annealing preparation method for a large-sized sapphire substrate. The annealing preparation method provided by the present invention can obtain uniform steps with few defects on a sapphire single crystal wafer, provide a uniform and stable platform for subsequent epitaxial growth, photolithography, etching and other processes on its surface, and prepare high-quality, large-area TMDs single crystals.
[0007] The invention provides an annealing preparation method for a large-sized sapphire substrate.
[0008] Specifically, a method for preparing a large-sized sapphire substrate by annealing comprises the following steps:
[0009] The sapphire single crystal wafer is cleaned, soaked in a salt solution and dried, and then annealed in a confined container. After the annealing is completed, the temperature is lowered to obtain a large-sized sapphire substrate.
[0010] The salt solution is a soluble sodium salt solution and / or a soluble potassium salt solution;
[0011] The concentration of the salt solution is 0.01-0.5 mol / L.
[0012] In some embodiments of the present invention, the sapphire single crystal wafer is a C-plane sapphire single crystal wafer or a sapphire single crystal wafer with a 1° misaligned cut angle between the C-plane and the A-plane.
[0013] In some embodiments of the present invention, the cleaning process is to use oxygen as the cleaning gas and perform vacuum plasma cleaning at a power of 30-60 W for 1-5 min. The cleaning process can enhance the hydrophilicity of the substrate surface so that the salt aqueous solution can be evenly dispersed on its surface, which is beneficial to subsequent salt etching.
[0014] In some embodiments of the present invention, the salt solution includes at least one of sodium chloride solution, sodium carbonate solution, sodium bicarbonate solution, sodium oxalate solution, potassium chloride solution, potassium carbonate solution, potassium bicarbonate solution, and potassium oxalate solution.
[0015] In some embodiments of the present invention, the concentration of the saline solution is 0.02-0.3 mol / L; preferably, the concentration of the saline solution is 0.03-0.2 mol / L.
[0016] In some embodiments of the present invention, the drying temperature is 100° C.-150° C. The drying process allows the salt in the salt solution to be evenly distributed on the surface of the sapphire single crystal wafer, so that the sapphire surface can be well etched during the subsequent annealing process, which is conducive to obtaining uniform steps with few defects.
[0017] In some embodiments of the present invention, the confined container may be a transparent quartz boat with a cover.
[0018] In some embodiments of the present invention, the temperature of the annealing treatment is 900°C-1000°C, and the time of the annealing treatment is 5min-2h. Preferably, the temperature of the annealing treatment is 950°C-980°C, and the time of the annealing treatment is 5min-2h. The annealing furnace of the annealing treatment can be a tube furnace or a muffle furnace. The annealing process is carried out in an air atmosphere.
[0019] In some embodiments of the present invention, the cooling process is a gradient cooling process, specifically: first cooling to 600°C within 5-20 minutes, and then continuing to cool to 15-40°C (normal temperature) within 20-40 minutes. Preferably, the cooling process is first cooling to 600°C within 8-15 minutes, and then continuing to cool to 15-40°C (normal temperature) within 25-35 minutes.
[0020] It should be understood that in some embodiments of the present invention, the sapphire single crystal wafer may be cut, ground, polished, etc. before and after annealing according to actual production and preparation requirements. Cutting, grinding, and polishing are all conventional techniques in the art, and the present invention does not limit this.
[0021] Compared with the prior art, the present invention has the following beneficial effects:
[0022] (1) The annealing preparation method of the large-sized sapphire substrate provided by the present invention adopts a salt etching annealing process for annealing. Compared with the previous sapphire single crystal wafer step annealing process, it has the characteristics of low temperature and high speed. Under the same annealing temperature and time, the sapphire substrate can obtain more uniform and low-defect steps.
[0023] (2) The present invention adopts a salt etching annealing process in combination with a confined annealing container, wherein the confined annealing container can effectively regulate the concentration of salt in the cavity during the annealing process, thereby regulating the etching effect of the salt on the surface of the sapphire single crystal wafer, thereby achieving annealing preparation of high repeatability and low defect sapphire single crystal wafer steps. The preparation process of the present invention is simple and efficient, and is suitable for the preparation of large-size sapphire substrates.
[0024] (3) The sapphire substrate prepared by the present invention has uniform and low-defect steps, which can provide a uniform and stable platform for subsequent epitaxial growth, photolithography, etching and other processes on its surface, and prepare high-quality, large-area TMDs single crystals. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 The surface AFM images of the C-surface sapphire single crystal wafer in Comparative Example 1 and Example 1;
[0026] Figure 2 The surface AFM images of the C-surface sapphire single crystal wafer in Comparative Example 2 and Examples 2 and 3;
[0027] Figure 3 The surface AFM images of the sapphire single crystal wafer with a C deviation of 1° to A in Comparative Example 3 and Examples 4 and 5;
[0028] Figure 4 Surface AFM images of the C-surface sapphire single crystal wafer in Comparative Example 4 and the C-biased A1° sapphire single crystal wafer in Comparative Example 5;
[0029] Figure 5 The surface AFM images of the sapphire single crystal wafer with C deviation A 1° in Comparative Examples 6 and 7;
[0030] Figure 6 Surface AFM images of sapphire single crystal wafers with C deviation of 1° to A in Comparative Examples 8 and 9. DETAILED DESCRIPTION
[0031] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.
[0032] Unless otherwise specified, the raw materials, reagents or devices used in the following examples and comparative examples can be obtained from conventional commercial sources or by existing known methods.
[0033] Example 1
[0034] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0035] A 2-inch C-side sapphire single crystal wafer was vacuum plasma cleaned (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), and then directly immersed in a 0.1mol / L NaCl solution for infiltration; immediately taken out after infiltration and dried at 120°C; then the dried C-side sapphire single crystal wafer was placed in a confined annealing container (a transparent quartz boat with a cover), annealed at 900°C in a muffle furnace for 5 minutes, and after the annealing was completed, the temperature was first cooled to 600°C for 10 minutes, and then the temperature was continued to be cooled to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0036] Comparative Example 1
[0037] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0038] A 2-inch C-side sapphire single crystal wafer from the same batch as Example 1 was subjected to vacuum plasma cleaning (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), and then directly placed in a confined annealing container (a transparent covered quartz boat), and annealed at 900°C in a muffle furnace for 5 minutes. After the annealing, the temperature was first cooled to 600°C for 10 minutes, and then continued to cool to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0039] The surface AFM images of the C-surface sapphire single crystal wafer in Example 1 and Comparative Example 1 are as follows: Figure 1 As shown, Figure 1 Figure a is an AFM image of the C-surface sapphire directly annealed at 900°C for 5 min in Comparative Example 1;
[0040] Figure 1 Figure b is the surface AFM image of the C-surface sapphire in Example 1 which was first infiltrated with 0.1 mol / L NaCl solution and then annealed at 900°C for 5 min. Figure 1 It can be seen that salt etching can make the steps form faster and eliminate defects in a short time. With the increase of annealing temperature and the extension of annealing time, the step edge of the single crystal wafer will become clearer and the step quality will be better. It can be seen from Example 1 of the present invention that compared with the traditional annealing method, the present invention can obtain a relatively clear step by annealing at a minimum temperature of 900°C for 5 minutes. The method provided by the present invention has the advantages of low temperature and fast speed.
[0041] Example 2
[0042] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0043] A 2-inch C-face sapphire single crystal wafer from the same batch as Example 1 was taken, and after vacuum plasma cleaning (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), it was directly immersed in a 0.1mol / L NaCl solution for infiltration; after infiltration, it was immediately taken out and dried at 120°C; then the dried C-face sapphire single crystal wafer was placed in a confined annealing container (transparent covered quartz boat), annealed at 980°C in a muffle furnace for 2 hours, and after the annealing was completed, the temperature was first cooled to 600°C for 10 minutes, and then the temperature was continued to be cooled to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0044] Example 3
[0045] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0046] Take a 2-inch C-face sapphire single crystal wafer from the same batch as Example 1, carry out vacuum plasma cleaning treatment (cleaning gas is oxygen, cleaning power is 50w, cleaning time is 2 minutes), and then directly immerse it in a 0.05mol / L K2C2O4 solution for infiltration; immediately take it out after infiltration and dry it at 120°C; then place the dried C-face sapphire single crystal wafer in a confined annealing container (transparent covered quartz boat), anneal at 980°C in a muffle furnace for 2 hours, and after the annealing is completed, cool it to 600°C for 10 minutes, and then continue to cool it to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0047] Comparative Example 2
[0048] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0049] A 2-inch C-side sapphire single crystal wafer from the same batch as Example 1 was taken for vacuum plasma cleaning (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), and then directly placed in a confined annealing container (transparent covered quartz boat), annealed at 980°C in a muffle furnace for 2 hours. After annealing, the temperature was first cooled to 600°C for 10 minutes, and then continued to cool to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0050] Figure 2 The surface AFM images of the C-surface sapphire single crystal wafer in Examples 2, 3 and Comparative Example 2 are shown. Figure 2 Figure a is an AFM image of the C-surface sapphire surface directly annealed at 980°C for 2h in Comparative Example 2; Figure 2 b is an AFM image of the C-surface sapphire surface after being infiltrated with 0.1 mol / L NaCl solution and then annealed in Example 2; Figure 2 Figure c is an AFM image of the C-surface sapphire surface after being infiltrated with 0.05 mol / L K2C2O4 solution and then annealed in Example 3. Figure 2 It can be seen that, compared with the 2-inch C-plane sapphire surface steps obtained by direct annealing treatment and salt etching treatment, the sapphire surface steps obtained by salt etching treatment are more uniform and have fewer defects.
[0051] Example 4
[0052] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0053] A 2-inch sapphire single crystal wafer with a C bias of 1° to A was subjected to vacuum plasma cleaning (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), and then directly immersed in a 0.1mol / L NaCl solution for infiltration; immediately taken out after infiltration and dried at 120°C; then the dried sapphire single crystal wafer with a C bias of 1° to A was placed in a confined annealing container (a transparent quartz boat with a cover), annealed at 980°C in a muffle furnace for 2 hours, and after the annealing was completed, the temperature was first lowered to 600°C for 10 minutes, and then the temperature was further lowered to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0054] Example 5
[0055] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0056] A 2-inch sapphire single crystal wafer with a C deviation of 1° from the same batch as Example 4 was taken for vacuum plasma cleaning (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), and then it was directly immersed in a 0.1mol / L KCl solution for infiltration; after infiltration, it was immediately taken out and dried at 120°C; then the dried sapphire single crystal wafer with a C deviation of 1° was placed in a confined annealing container (a transparent quartz boat with a cover), annealed at 980°C in a muffle furnace for 2 hours, and after the annealing was completed, the temperature was first lowered to 600°C for 10 minutes, and then the temperature was continued to be lowered to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0057] Comparative Example 3
[0058] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0059] A 2-inch sapphire single crystal wafer with a C deviation of A1° from the same batch as Example 4 was taken for vacuum plasma cleaning (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), and then directly placed in a confined annealing container (transparent covered quartz boat), annealed at 980°C in a muffle furnace for 2 hours, cooled to 600°C 10 minutes after the annealing, and continued to cool to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0060] Figure 3 The surface AFM images of the C-surface sapphire single crystal wafer in Examples 4 and 5 and Comparative Example 3 are shown. Figure 3 a is the AFM image of the sapphire surface with a C deviation of 1° after direct annealing at 980°C for 2h in Comparative Example 3;
[0061] Figure 3 b is an AFM image of the sapphire surface with a C deviation of 1° after being infiltrated with 0.1 mol / L NaCl solution and then annealed in Example 4; Figure 3Figure c is an AFM image of the sapphire surface with a C deviation of 1° from A after being soaked in 0.1 mol / L KCl solution and then annealed in Example 5. Figure 3 It can be seen that, compared with the 2-inch sapphire surface steps with a C deviation of A1° obtained by direct annealing treatment and salt etching treatment, the sapphire surface steps etched by salt are more uniform and have fewer defects.
[0062] Comparative Example 4
[0063] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0064] A 2-inch C-side sapphire single crystal wafer from the same batch as Example 1 was taken for vacuum plasma cleaning (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), and then it was directly immersed in a 0.1mol / L NaCl solution for infiltration; after infiltration, it was immediately taken out and dried at 120°C; then it was directly placed in a muffle furnace and annealed at 980°C for 2 hours. After the annealing was completed, the temperature was first cooled to 600°C for 10 minutes, and then the temperature was continued to be cooled to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0065] Comparative Example 5
[0066] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0067] A 2-inch sapphire single crystal wafer with a C deviation of A1° from the same batch as Example 4 was taken for vacuum plasma cleaning (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), and then it was directly immersed in a 0.1mol / L NaCl solution for infiltration; after infiltration, it was immediately taken out and dried at 120°C; then it was directly placed in a muffle furnace and annealed at 980°C for 2 hours. After the annealing was completed, the temperature was first cooled to 600°C for 10 minutes, and then the temperature was continued to be cooled to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0068] Figure 4 The surface AFM images of the C-biased A1° sapphire single crystal wafer in Comparative Example 5 and the C-surface sapphire single crystal wafer in Comparative Example 4. Figure 4 a is an AFM image of the sapphire surface with a C deviation of 1° after being soaked in 0.1 mol / L NaCl solution and then annealed in an infinite domain container in Comparative Example 5; Figure 4 Figure b is a surface AFM image of the C-surface sapphire single crystal wafer in Comparative Example 4 after being soaked in 0.1 mol / L NaCl solution and then annealed in an infinite domain container. Figure 4 It can be seen that when the sapphire single crystal wafer is annealed in an infinite domain container, the salt evaporates and diffuses at the annealing temperature, resulting in poor etching effect.
[0069] Comparative Example 6
[0070] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0071] A 2-inch sapphire single crystal wafer with a C deviation of 1° from A from the same batch as Example 3 was taken for vacuum plasma cleaning (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), and then it was directly immersed in a 1mol / L NaCl solution for infiltration. After infiltration, it was immediately taken out and dried at 120°C; then the dried sapphire single crystal wafer with a C deviation of 1° from A was placed in a confined annealing container (a transparent quartz boat with a cover), annealed at 980°C in a muffle furnace for 2 hours, and after the annealing was completed, the temperature was first lowered to 600°C for 10 minutes, and then the temperature was continued to be lowered to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0072] Comparative Example 7
[0073] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0074] A 2-inch sapphire with a C deviation of 1° from the same batch as in Example 3 was taken for vacuum plasma cleaning (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), and then it was directly immersed in a 1mol / L K2C2O4 solution for infiltration; after infiltration, it was immediately taken out and dried at 120°C; then the dried sapphire single crystal wafer with a C deviation of 1° was placed in a confined annealing container (a transparent quartz boat with a cover), annealed at 980°C in a muffle furnace for 2 hours, and after the annealing was completed, the temperature was first lowered to 600°C for 10 minutes, and then the temperature was continued to be lowered to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0075] Figure 5 Surface AFM images of sapphire single crystal wafers with C deviation of 1° to A in Comparative Examples 6 and 7.
[0076] in, Figure 5 a is an AFM image of the surface of a sapphire single crystal wafer with a C deviation of 1° after being infiltrated with 1 mol / L NaCl solution and then annealed in Comparative Example 6; Figure 5 Figure b is an AFM image of the surface of a sapphire single crystal wafer with a C deviation of 1° from A after being infiltrated with 1 mol / L K2C2O4 solution and then annealed in Comparative Example 7. Figure 5 It can be seen that when the concentration of the salt solution used during infiltration is too high, the steps will be over-etched, affecting the quality of the sapphire single crystal wafer. Therefore, controlling the concentration of the infiltration salt solution can produce more uniform steps with fewer defects.
[0077] Comparative Example 8
[0078] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0079] A 2-inch sapphire single crystal wafer with a C deviation of 1° from the same batch as in Example 3 was taken for vacuum plasma cleaning (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), and then it was directly immersed in a 0.1mol / L NaCl solution for infiltration; after infiltration, it was immediately taken out and dried at 120°C; then the dried sapphire single crystal wafer with a C deviation of 1° from A was placed in a confined annealing container (a transparent quartz boat with a cover), annealed at 980°C in a muffle furnace for 8 hours, and after the annealing was completed, the temperature was first lowered to 600°C for 10 minutes, and then the temperature was continued to be lowered to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0080] Comparative Example 9
[0081] A method for preparing a large-size sapphire substrate by annealing, comprising the following steps:
[0082] A 2-inch sapphire single crystal wafer with a C deviation of 1° from the same batch as in Example 3 was taken for vacuum plasma cleaning (cleaning gas was oxygen, cleaning power was 50w, and cleaning time was 2 minutes), and then it was directly immersed in a 0.1mol / L K2C2O4 solution for infiltration; after infiltration, it was immediately taken out and dried at 120°C; then the dried sapphire single crystal wafer with a C deviation of 1° was placed in a confined annealing container (a transparent quartz boat with a cover), annealed at 980°C in a muffle furnace for 8 hours, and after the annealing was completed, the temperature was first lowered to 600°C for 10 minutes, and then the temperature was continued to be lowered to room temperature for 30 minutes to obtain a large-size sapphire substrate.
[0083] Figure 6 Surface AFM images of sapphire single crystal wafers with C deviation of 1° to A in Comparative Examples 8 and 9.
[0084] in, Figure 6 a is an AFM image of the surface of a sapphire single crystal wafer with a C deviation of 1° to A after being infiltrated with a 0.1 mol / L NaCl solution and then annealed in Comparative Example 8; Figure 6 Figure b is an AFM image of the surface of a sapphire single crystal wafer with a C deviation of 1° from A after being infiltrated with 0.05 mol / L K2C2O4 solution and then annealed in Comparative Example 9. Figure 6 It can be seen that when the annealing time is too long, the etching effect of the salt will also be prolonged. Under the continuous etching of the salt, the edge of the step will become blurred, which will seriously affect the quality of the sapphire single crystal wafer.
[0085] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.
Claims
1. A sapphire substrate annealing preparation method, characterized in that: The following steps are involved: The sapphire single crystal wafer is cleaned, soaked in a salt solution and dried, and then annealed in a confined container. After the annealing is completed, the temperature is lowered to obtain a large-sized sapphire substrate. The salt solution is a soluble sodium salt solution and / or a soluble potassium salt solution; The concentration of the salt solution is 0.01-0.5 mol / L.
2. The annealing preparation method according to claim 1, characterized in that: The sapphire single crystal wafer is a C-plane sapphire single crystal wafer or a sapphire single crystal wafer with a 1° misaligned cut angle between the C-plane and the A-plane.
3. The annealing preparation method according to claim 1 or 2, characterized in that: The cleaning process is to use oxygen as the cleaning gas and perform vacuum plasma cleaning at a power of 30-60W for 1-5min.
4. The annealing preparation method according to claim 1 or 2, characterized in that: The salt solution includes at least one of sodium chloride solution, sodium carbonate solution, sodium bicarbonate solution, sodium oxalate solution, potassium chloride solution, potassium carbonate solution, potassium bicarbonate solution, and potassium oxalate solution.
5. The annealing preparation method according to claim 4, characterized in that: The concentration of the salt solution is 0.02-0.3 mol / L.
6. The annealing preparation method according to claim 5, characterized in that: The concentration of the salt solution is 0.03-0.2 mol / L.
7. The annealing preparation method according to claim 1 or 2, characterized in that: The drying temperature is 100°C-150°C.
8. The annealing preparation method according to claim 1 or 2, characterized in that: The temperature of the annealing treatment is 900° C.-1000° C., and the time of the annealing treatment is 5 min-2 h.
9. The annealing preparation method according to claim 1 or 2, characterized in that: The cooling process is a gradient cooling process, specifically: firstly cooling to 600°C within 5-20 minutes, and then further cooling to 15-40°C within 20-40 minutes.