Cleaning method for double-side polishing of lithium niobate wafer

Abstract

This invention belongs to the field of lithium niobate manufacturing technology, specifically relating to a cleaning method for double-sided polishing of lithium niobate wafers. This invention employs a multi-step, targeted cleaning process: from immersion in hydrofluoric acid aqueous solution to remove residual silica polishing solution, to ultrasonic cleaning with organic solvents to remove some organic matter, metal ions, and stubborn contaminants, and then to combined cleaning with brushes and chemical reagents. This comprehensive and deep cleaning of the double-sided polished lithium niobate wafer surface, along with single-sided fine brushing, further removes residual chemical reagents, reducing surface contaminant residue to an extremely low level, meeting the stringent cleanliness requirements of high-end optoelectronic devices. The alkaline cleaning agent prepared by this invention exhibits excellent cleaning performance and low residue. The cleaning method of this invention has a clear process flow, is relatively simple to operate, improves production efficiency, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of lithium niobate manufacturing technology, specifically relating to a cleaning method for double-sided polishing of lithium niobate wafers. Background Technology

[0002] Lithium niobate (LiNbO3), as an important functional crystal material, possesses excellent piezoelectric, electro-optic, acousto-optic, and nonlinear optical properties, and is widely used in optical communication, optical signal processing, and microwave devices. In these applications, the surface cleanliness of double-sided polished lithium niobate wafers is crucial, directly affecting the performance and reliability of the devices. During the processing of double-sided polished lithium niobate wafers, a large amount of polishing slurry, such as silica polishing slurry, remains on the wafer surface after polishing, and various particulate impurities, organic matter, and metal ions are also adsorbed. Traditional cleaning methods often fail to completely remove these contaminants. Pure water rinsing and simple ultrasonic cleaning are insufficient to effectively remove stubborn organic contaminants and metal ions; while using a single chemical reagent for cleaning may corrode or damage the lithium niobate wafer surface, affecting its optical and electrical properties and resulting in substandard surface cleanliness. With the development of optoelectronic devices towards high performance and miniaturization, higher requirements are placed on the surface quality and cleanliness of double-sided polished lithium niobate wafers, and existing cleaning methods can no longer meet these demands. Therefore, developing a high-efficiency, gentle cleaning method for lithium niobate double-sided polished wafers that can ensure uniform cleaning is of great practical significance.

[0003] Chinese invention patent CN114472341B discloses a cleaning method for a single-sided polished lithium niobate wafer. The method includes: immersing the lithium niobate wafer in ammonium bifluoride for cleaning; ultrasonically cleaning the wafer with an organic solvent cleaning solution; rinsing the wafer with deionized water; brushing the wafer with a double-sided brush; and brushing the wafer with a single-sided brush, ultimately yielding a lithium niobate wafer with low fragmentation and high cleanliness. However, the existing technology suffers from problems such as incomplete cleaning, easy damage to the wafer surface, and uneven cleaning. Summary of the Invention

[0004] The purpose of this invention is to provide a cleaning method for double-sided polishing of lithium niobate wafers, which solves the technical problems of incomplete cleaning, easy damage to the wafer surface, and uneven cleaning in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A cleaning method for double-sided polishing of lithium niobate wafers includes the following steps:

[0007] S1. Pre-cleaning: Immerse the lithium niobate double-sided polishing sheet in hydrofluoric acid aqueous solution to remove the oxide layer and polishing liquid residue, and rinse with deionized water.

[0008] S2. Organic solvent ultrasonic cleaning: The lithium niobate double-sided polishing sheet is placed in an organic solvent cleaning solution and ultrasonically cleaned to remove organic matter and some metal ion contaminants from the surface of the polishing sheet.

[0009] S3. Deionized water spray rinsing: Spray the lithium niobate double-sided polishing sheet with deionized water, then fill the sheet with deionized water to submerge it and let it overflow. Quickly drain the deionized water and repeat the operation 5 to 7 times.

[0010] S4. Combined cleaning with brush and chemical reagents: The lithium niobate double-sided polishing sheet is brushed in an alkaline cleaning solution using a double-sided drive roller brush. After brushing, it is brushed in deionized water using the same double-sided drive roller brush and sprayed to rinse away residual alkaline cleaning agent. Then it is spun dry.

[0011] S5. Single-sided fine brushing: Use a gyroscope-type brush to brush the double-sided lithium niobate polishing sheet back and forth between the center and the edge of the polishing sheet, while simultaneously spraying with two fluids. After brushing, rinse with deionized water, spin dry, and the polishing sheet is clean.

[0012] Preferably, the hydrofluoric acid aqueous solution in S1 is prepared by mixing hydrofluoric acid and deionized water at a volume ratio of 1:20-30. The lithium niobate double-sided polishing sheet is immersed in the hydrofluoric acid aqueous solution at 30-33°C for 20-30 minutes and rinsed with deionized water at 30-35°C for 5-6 minutes.

[0013] Preferably, the organic solvent cleaning solution in S2 is prepared by mixing isopropanol, ethanol and deionized water in a volume ratio of 3:2:5-8. The frequency of the ultrasonic cleaning equipment is set to 45-55kHz, and ultrasonic cleaning is performed at a temperature of 55-65℃ for 15-25 minutes. The organic solvent cleaning solution can be recycled 2-4 times after filtration and precipitation.

[0014] Preferably, in step S3, the spraying pressure is controlled between 0.2 and 0.3 MPa, the spraying time is 60 to 90 seconds, deionized water is injected until the polishing sheet is submerged, and the overflow state is maintained for 25 to 35 seconds.

[0015] Preferably, in step S4, the roller brush is made of PVA material, the roller brush speed is set to 8-12 rpm, the pressing distance between the upper and lower roller brushes is controlled between 1100-1400 μm, the brushing time is 4-6 min, the same double-sided brush is used to brush in deionized water for 3-5 min, and then sprayed and rinsed for 15-25 s. The lithium niobate double-sided polishing sheet is then spun dry at a speed of 1300-1600 rpm for 18-22 s.

[0016] Preferably, the gyro-type brush in S5 is made of PVA material, the brush pressing distance is set to 1000-1300μm, the brush rotation speed is 1200-1600rpm, the brush translation speed is 18-22mm / s, it pauses at the center of the lithium niobate double-sided polishing sheet for 0.8-1.2s, and at the edge of the lithium niobate double-sided polishing sheet for 4-6s, and brushes back and forth 4-6 times. The liquid medium of the two fluids consists of deionized water and 0.5-1% of fatty alcohol polyoxyethylene ether by volume of deionized water, the gas medium is high-purity nitrogen, the cleaning gas pressure of the two fluids is 0.3-0.5MPa, the spray angle is 45-60°, after brushing, it is rinsed with deionized water for 6-10s, and then the lithium niobate double-sided polishing sheet is spun dry at a speed of 3200-4200rpm for 28-32s.

[0017] Preferably, the method for preparing the alkaline cleaning solution in S4 includes the following steps:

[0018] S11. An alkaline cleaning agent is prepared by mixing 1-2 parts by weight of polyvinylpyrrolidone, 1-2 parts by weight of anionic surfactant, 1-2 parts by weight of nonionic surfactant, 1-2 parts by weight of organic base, 2-5 parts by weight of inorganic base, 0.5-1.5 parts by weight of complexing agent, 0.5-2 parts by weight of composite corrosion inhibitor and 0.5-1 parts by weight of defoamer.

[0019] S12. Prepare an alkaline cleaning solution by mixing alkaline cleaning agent and deionized water at a volume ratio of 1:40-50.

[0020] Preferably, the anionic surfactant is either sodium dodecylbenzenesulfonate or sodium dodecyl sulfate.

[0021] Preferably, the nonionic surfactant is any one or a combination of pentadecyl glycoside, dodecyl alcohol polyoxyethylene ether, polyethylene glycol, and Tween-80.

[0022] Preferably, the organic base is any one of triethanolamine, tetramethylammonium hydroxide, or glucosamine, and the inorganic base is any one or a combination of sodium hydroxide and potassium hydroxide.

[0023] Preferably, the complexing agent is any one or a combination of ethylenediaminetetraacetic acid, sodium citrate, and hypozoxytriacetic acid.

[0024] The defoamer is either MX-9014 or DF-691.

[0025] Preferably, the preparation method of the composite corrosion inhibitor includes the following steps:

[0026] S21. According to the mass parts, 19-20 parts of 4-chloro-6,8-dimethyl-quinazoline and 20-50 parts of N,N'-dimethylformamide solvent are added to the reaction vessel, stirred evenly, and then 12-13 parts of 1-hydroxymethylbenzimidazole and 0.05-0.3 parts of potassium carbonate catalyst are added. The temperature is raised to react. After the reaction is completed, the mixture is filtered and washed to obtain the corrosion inhibitor.

[0027] S22. A composite corrosion inhibitor is prepared by mixing 5-10 parts by weight of corrosion inhibitor and 5-8 parts by weight of benzotriazole.

[0028] Preferably, the reaction principle of the corrosion inhibitor is as follows:

[0029]

[0030] The corrosion inhibitor was analyzed by mass spectrometry, and the results are as follows: m / z: 304.13 (100.0%), 305.14 (19.7%), 306.14 (2.0%), 305.13 (1.5%).

[0031] Preferably, the molar ratio of 4-chloro-6,8-dimethylquinazoline and 1-hydroxymethylbenzimidazole in S21 is 1:1.1 to 1.3.

[0032] Preferably, in step S21, the temperature is raised to 75-80°C and refluxed for 4-6 hours. After the reaction is completed, the pH of the reaction solution is adjusted to 3-4 with hydrochloric acid and then filtered. The solution is then washed with anhydrous ethanol and recrystallized for purification.

[0033] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0034] 1. This invention employs a multi-step, targeted cleaning process, from soaking in hydrofluoric acid aqueous solution to remove residual silicon dioxide polishing liquid, to ultrasonic cleaning with organic solvents to remove some organic matter, metal ions, and stubborn contaminants, to combined cleaning with brushes and chemical reagents to comprehensively and deeply clean the surface of lithium niobate double-sided polished wafers. Furthermore, single-sided fine brushing and two-fluid spraying can further remove residual chemical reagents from the polishing wafers, reducing the amount of surface contaminants to an extremely low level, thus meeting the stringent requirements of high-end optoelectronic devices for wafer surface cleanliness.

[0035] 2. This invention produces an alkaline cleaning agent by mixing polyvinylpyrrolidone, anionic surfactants, nonionic surfactants, organic bases, inorganic bases, complexing agents, composite corrosion inhibitors, and defoamers. The complexing agent can complex metal ions, while polyvinylpyrrolidone can disperse contaminants and reduce residue on the polishing surface. The combined anionic and nonionic surfactants work synergistically to remove contaminants, enhancing the cleaning ability of the alkaline cleaning agent. The composite corrosion inhibitor reduces excessive corrosion of the polishing sheet by the cleaning solution, and the combined use of organic and inorganic bases further reduces corrosion. The alkaline cleaning agent prepared by this invention exhibits excellent cleaning and anti-corrosion properties.

[0036] 3. This invention prepares a corrosion inhibitor by reacting 4-chloro-6,8-dimethyl-quinazoline and 1-hydroxymethylbenzimidazole under alkaline conditions. The quinazoline and benzimidazole groups of the corrosion inhibitor have nitrogen elements and aromatic rings, resulting in a large number of adsorption sites. They can combine with the surface of lithium niobate to form a protective film, reducing the corrosion of the lithium niobate surface by the cleaning agent. Furthermore, they can adsorb and complex metal ions through nitrogen-containing heterocyclic groups to prevent impurity deposition. The composite corrosion inhibitor prepared by mixing the corrosion inhibitor and benzotriazole has excellent corrosion inhibition performance.

[0037] 4. This invention effectively cleans while precisely controlling operating parameters, ensuring uniform cleaning on the polished wafer surface. This minimizes corrosion and damage to the lithium niobate wafer surface, ensuring the wafer's optical and electrical properties remain unaffected, and improving product performance stability and reliability. The cleaning method of this invention has a clear process flow, is relatively simple to operate, and has tight connections between each step, enabling the cleaning process to be completed in a short time, improving production efficiency and making it suitable for large-scale industrial production. Detailed Implementation

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1: A cleaning method for double-sided polishing of lithium niobate wafers according to this example includes the following steps:

[0040] S1. Pre-cleaning: Place the lithium niobate double-sided polishing sheet into a hydrofluoric acid aqueous solution prepared by mixing hydrofluoric acid and deionized water at a volume ratio of 1:25, soak at 30°C for 20 minutes to remove the oxide layer and polishing liquid residue, and rinse with deionized water at 32°C for 6 minutes.

[0041] S2. Organic solvent ultrasonic cleaning: The lithium niobate double-sided polishing sheet is placed in an organic solvent cleaning solution prepared by mixing isopropanol, ethanol and deionized water in a volume ratio of 3:2:6. The frequency of the ultrasonic cleaning equipment is set to 50kHz, and ultrasonic cleaning is performed at 60℃ for 20 minutes to remove organic matter and some metal ion contaminants from the surface of the polishing sheet.

[0042] S3. Deionized water spray rinsing: Spray the lithium niobate double-sided polished sheet with deionized water. The spray pressure is controlled at 0.25MPa and the spray time is 75s. After the lithium niobate double-sided polished sheet is submerged in deionized water, it overflows for 30s. After quickly draining the deionized water, repeat the operation 6 times.

[0043] S4. Combined cleaning with brush and chemical reagents: The lithium niobate double-sided polishing sheet is brushed in an alkaline cleaning solution using a double-sided drive roller brush. The roller brush material is PVA material, the roller brush speed is set to 10 rpm, the pressing distance between the upper and lower roller brushes is controlled to 1200 μm, and the brushing time is 5 min. After brushing, it is brushed and rinsed in deionized water using the same double-sided drive roller brush method for 4 min, and then spun dry at a speed of 1400 rpm for 20 s.

[0044] S5. Single-sided fine brushing: The lithium niobate double-sided polishing wafer is brushed with a gyro-type brush made of PVA material. The brush pressure distance is set to 1000μm, the brush rotation speed is 1400rpm, and the brush translation speed is 20mm / s. The brush stops for 1s at the center of the wafer and 5s at the edge of the wafer. The brushing is repeated 5 times. At the same time, a two-fluid spray is performed. The liquid medium of the two fluids consists of deionized water and 1% dodecyl alcohol polyoxyethylene ether by volume of deionized water. The gas medium is high-purity nitrogen. The cleaning gas pressure of the two fluids is 0.4MPa, and the spray angle is 45°. After brushing, the wafer is rinsed with deionized water for 8s and then spun dry at 3500rpm for 30s. The resulting polishing wafer is clean.

[0045] The method for preparing the alkaline cleaning solution in this embodiment includes the following steps:

[0046] S11. An alkaline cleaning agent is prepared by mixing 20g of polyvinylpyrrolidone, 15g of sodium dodecylbenzenesulfonate anionic surfactant, 15g of pentadecyl glycoside, dodecyl alcohol polyoxyethylene ether and Tween-80 in a mass ratio of 1:2:1 to obtain a nonionic surfactant, 13g of triethanolamine and tetramethylammonium hydroxide in a mass ratio of 1:2 to obtain an organic base, 30g of sodium hydroxide, 10g of composite corrosion inhibitor, 12g of ethylenediaminetetraacetic acid complexing agent and 5g of defoamer of type MX-9014.

[0047] S12. Prepare an alkaline cleaning solution by mixing 50 mL of alkaline cleaning agent with 2 L of deionized water.

[0048] The preparation method of the composite corrosion inhibitor in this embodiment includes the following steps:

[0049] S21. Add 19.5g of 4-chloro-6,8-dimethyl-quinazoline and 20-50g of N,N'-dimethylformamide solvent to a reaction vessel, stir evenly, then add 13g of 1-hydroxymethylbenzimidazole and 0.3g of potassium carbonate catalyst, heat to 80℃ and reflux for 5h. After the reaction is completed, adjust the pH of the reaction solution to 4 with hydrochloric acid, filter, wash with anhydrous ethanol, recrystallize and purify to obtain the corrosion inhibitor.

[0050] S22. A composite corrosion inhibitor is prepared by mixing 5g of corrosion inhibitor and 5g of benzotriazole.

[0051] Example 2 differs from Example 1 in that the hydrofluoric acid aqueous solution is replaced with a volume ratio of hydrofluoric acid and deionized water of 1:20 during the pre-cleaning process.

[0052] Example 3 differs from Example 1 in that the organic solvent cleaning solution is replaced with a volume ratio of isopropanol, ethanol and deionized water of 3:2:8 in the ultrasonic cleaning process. The frequency of the ultrasonic cleaning equipment is set to 45kHz, and ultrasonic cleaning is performed at 55°C for 15 minutes.

[0053] Example 4: The difference between this example and Example 1 is that the spray pressure is controlled at 0.3 MPa and the spray time is 60 s during the deionized water spray rinsing. After the lithium niobate double-sided polishing sheet is submerged in deionized water, it overflows for 25 s. After the deionized water is quickly drained, the operation is repeated 5 times.

[0054] Example 5 differs from Example 1 in that the alkaline cleaning solution used in the combined cleaning of the brush and chemical reagents is prepared by mixing 50 mL of alkaline cleaning agent with 2.5 L of deionized water.

[0055] Example 6 differs from Example 1 in that the alkaline cleaning agent is prepared by mixing 10g of polyvinylpyrrolidone, 10g of sodium dodecylbenzenesulfonate anionic surfactant, 20g of pentadecyl glycoside, dodecyl alcohol polyoxyethylene ether and Tween-80 in a mass ratio of 1:2:1 to obtain a nonionic surfactant, 13g of triethanolamine and tetramethylammonium hydroxide in a mass ratio of 1:2 to obtain an organic base, 30g of sodium hydroxide, 5g of corrosion inhibitor and benzotriazole in a mass ratio of 2:1 to obtain a composite corrosion inhibitor, 12g of ethylenediaminetetraacetic acid complexing agent and 5g of defoamer of type DF-691.

[0056] Example 7 differs from Example 1 in that the alkaline cleaning agent is prepared by mixing 20g of polyvinylpyrrolidone, 15g of sodium dodecyl sulfate anionic surfactant, 15g of dodecyl alcohol polyoxyethylene ether, polyethylene glycol and Tween-80 in a mass ratio of 1:1:1 to obtain a nonionic surfactant, 10g of tetramethylammonium hydroxide organic base, 20g of potassium hydroxide, 5g of corrosion inhibitor and benzotriazole in a mass ratio of 5:8 to obtain a composite corrosion inhibitor, 5g of ethylenediaminetetraacetic acid and sodium citrate in a mass ratio of 1:1 to obtain a complexing agent, and 10g of defoamer of type DF-691.

[0057] Example 8 differs from Example 1 in that the alkaline cleaning agent is prepared by mixing 15g of polyvinylpyrrolidone, 20g of sodium dodecylbenzenesulfonate anionic surfactant, 10g of pentadecyl glycoside and dodecyl alcohol polyoxyethylene ether in a mass ratio of 1:2 to obtain a nonionic surfactant, 20g of triethanolamine and tetramethylammonium hydroxide in a mass ratio of 1:2 to obtain an organic base, 50g of sodium hydroxide, 20g of corrosion inhibitor and benzotriazole in a mass ratio of 2:1 to obtain a composite corrosion inhibitor, 15g of ethylenediaminetetraacetic acid and hypozoxytriacetic acid in a mass ratio of 1:1 to obtain a complexing agent, and 8g of defoamer of type MX-9014.

[0058] Example 9 differs from Example 1 in that the brush pressing distance is set to 1300μm, the brush rotation speed is 1200rpm, the brush translation speed is 18mm / s, the brush pauses for 1.2s at the center of the wafer, pauses for 6s at the edge of the wafer, and the brushing is repeated 6 times.

[0059] Example 10 differs from Example 1 in that the liquid medium of the two fluids in the single-sided fine brushing consists of deionized water and 0.5% dodecyl alcohol polyoxyethylene ether, which accounts for 0.5% of the volume of deionized water. The gas medium is high-purity nitrogen. The cleaning gas pressure of the two fluids is 0.3 MPa, and the spray angle is 60°.

[0060] Comparative Example 1 differs from Example 1 in that the hydrofluoric acid aqueous solution is replaced with a volume ratio of hydrofluoric acid and deionized water of 1:10 during pre-cleaning.

[0061] Comparative Example 2 differs from Example 1 in that the frequency of the ultrasonic cleaning equipment in the organic solvent ultrasonic cleaning is set to 100kHz, and ultrasonic cleaning is performed at a temperature of 80°C for 20 minutes.

[0062] Comparative Example 3 differs from Example 1 in that the spray pressure is controlled at 0.8 MPa and the spray time is 60 s during the deionized water spray rinsing.

[0063] Comparative Example 4 differs from Example 1 in that it eliminates the overflow after the lithium niobate double-sided polishing sheet is submerged in injected deionized water, and the deionized water is quickly drained without repeating the operation.

[0064] Comparative Example 5 differs from Example 1 in that the alkaline cleaning solution used in the combined cleaning of the brush and chemical reagents was prepared by mixing 50 mL of alkaline cleaning agent with 1 L of deionized water.

[0065] Comparative Example 6 differs from Example 1 in that the alkaline cleaning agent is prepared by mixing 15g of dodecyl alcohol polyoxyethylene ether nonionic surfactant, 40g of sodium hydroxide and 15g of ethylenediaminetetraacetic acid complexing agent.

[0066] Comparative Example 7 differs from Example 1 in that no corrosion inhibitor is added to the composite corrosion inhibitor.

[0067] Comparative Example 8 differs from Example 1 in that the roller brush pauses for 2 seconds at the center of the wafer and 10 seconds at the edge of the wafer during single-sided fine brushing, and the brushing is repeated 6 times.

[0068] Comparative Example 9 differs from Example 1 in that it only uses ultrasonic cleaning and deionized water spray rinsing.

[0069] Performance testing

[0070] The cleaned polished sheets were prepared using the various embodiments and comparative examples. The surface roughness before and after cleaning was measured using a white light interferometer, and the number of residual contaminant particles on the surface of the polished sheets was observed using a metallographic microscope. The sheets were then sent to relevant institutions to test the product qualification rate.

[0071] The test results are shown in Table 1 below:

[0072] Table 1 Test Results

[0073]

[0074]

[0075] As shown in the table above, the surface roughness Ra of the lithium niobate double-sided polishing sheets in Examples 1-10 after cleaning is between 0.216 and 0.349 nm, and the number of residual contaminant particles on the surface is between 26 and 39, indicating that the cleaning method of the present invention has excellent cleaning performance and low residue. The product qualification rate of the lithium niobate double-sided polishing sheets in Examples 1-10 after cleaning is between 87.6% and 90.4%, indicating that the cleaning method of the present invention improves the performance stability of the polishing sheets.

[0076] Comparative Example 1: The hydrofluoric acid aqueous solution was replaced with a 1:10 volume ratio of hydrofluoric acid and deionized water, resulting in an excessively rapid pretreatment rate of corrosion on the polished sheet. Consequently, the surface roughness Ra after cleaning was 2.633 nm. Comparative Example 4: The lithium niobate double-sided polished sheet was submerged in deionized water, then overflowed, and the deionized water was quickly drained without repeating the process. This resulted in ineffective removal of impurities during cleaning, leading to a surface roughness Ra of 3.135 nm and 60 residual surface contaminant particles. Comparative Example 2: The ultrasonic cleaning equipment was set to a frequency of 100 kHz and ultrasonic cleaning was performed at 80°C for 20 minutes. The excessively high ultrasonic frequency increased the brittleness of the polished sheet, and the 80°C temperature caused organic solvents and organic components to easily escape, making the polished sheet more prone to breakage during cleaning. Therefore, its pass rate was 70.8%. Comparative Example 3: Spray pressure control... The spray pressure was set at 0.8 MPa, which was too high, making the samples more prone to breakage during the cleaning process, resulting in a pass rate of 88.1%. Comparative Example 6 used an alkaline cleaning agent prepared by mixing dodecyl alcohol polyoxyethylene ether nonionic surfactant, sodium hydroxide, and ethylenediaminetetraacetic acid complexing agent. The single-component nonionic surfactant had lower cleaning efficiency compared to a combination of multiple surfactants, resulting in a surface roughness Ra of 0.697 nm and 49 residual surface contaminant particles after cleaning. Comparative Example 7 did not add corrosion inhibitors, which aggravated surface corrosion of the polished sheet, leading to an increased roughness of 0.670 nm. Comparative Example 9 only used ultrasonic cleaning and deionized water spray rinsing, resulting in ineffective removal of contaminants. Therefore, its surface roughness Ra after cleaning was 7.641 nm, with 515 residual surface contaminant particles, resulting in a pass rate of only 59.7%.

[0077] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0078] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A cleaning method for double-sided polishing of lithium niobate wafers, characterized in that, Includes the following steps: S1. Pre-cleaning: Immerse the lithium niobate double-sided polishing sheet in hydrofluoric acid aqueous solution to remove the oxide layer and polishing liquid residue, and rinse with deionized water. S2. Organic solvent ultrasonic cleaning: The lithium niobate double-sided polishing sheet is placed in an organic solvent cleaning solution and ultrasonically cleaned to remove organic matter and some metal ion contaminants from the surface of the polishing sheet. S3. Deionized water spray rinsing: Spray the lithium niobate double-sided polishing sheet with deionized water, then fill the sheet with deionized water until it overflows, and quickly drain the deionized water. Repeat the operation 5-7 times. S4. Combined cleaning with brush and chemical reagents: The lithium niobate double-sided polishing sheet is brushed in an alkaline cleaning solution using a double-sided drive roller brush. After brushing, it is brushed in deionized water using the same double-sided drive roller brush and sprayed to rinse away residual alkaline cleaning agent. Then it is spun dry. S5. Single-sided fine brushing: Use a gyroscope-type brush to brush the double-sided polishing sheet of lithium niobate, brushing back and forth between the center and the edge of the polishing sheet, while simultaneously spraying with two fluids. After brushing, rinse with deionized water, spin dry, and the polishing sheet is clean. The preparation method of the alkaline cleaning solution in S4 includes the following steps: S11. An alkaline cleaning agent is prepared by mixing 1-2 parts by weight of polyvinylpyrrolidone, 1-2 parts by weight of anionic surfactant, 1-2 parts by weight of nonionic surfactant, 1-2 parts by weight of organic base, 2-5 parts by weight of inorganic base, 0.5-1.5 parts by weight of complexing agent, 0.5-2 parts by weight of composite corrosion inhibitor and 0.5-1 parts by weight of defoamer. S12. Prepare an alkaline cleaning solution by mixing alkaline cleaning agent and deionized water at a volume ratio of 1:40~50. The preparation method of the composite corrosion inhibitor includes the following steps: S21. According to the mass parts, 19-20 parts of 4-chloro-6,8-dimethyl-quinazoline and 20-50 parts of N,N'-dimethylformamide solvent are added to the reaction vessel, stirred evenly, and then 12-13 parts of 1-hydroxymethylbenzimidazole and 0.05-0.3 parts of potassium carbonate catalyst are added. The temperature is raised to react. After the reaction is completed, the mixture is filtered and washed to obtain the corrosion inhibitor. S22. A composite corrosion inhibitor is prepared by mixing 5-10 parts by weight of corrosion inhibitor and 5-8 parts by weight of benzotriazole.

2. The cleaning method for double-sided polishing of lithium niobate wafers according to claim 1, characterized in that, The hydrofluoric acid aqueous solution in S1 is prepared by mixing hydrofluoric acid and deionized water at a volume ratio of 1:20~30. The lithium niobate double-sided polishing sheet is immersed in the hydrofluoric acid aqueous solution at 30~33℃ for 20~30 minutes and rinsed with deionized water at 30~35℃ for 5~6 minutes.

3. The cleaning method for double-sided polishing of lithium niobate wafers according to claim 1, characterized in that, The organic solvent cleaning solution in S2 is prepared by mixing isopropanol, ethanol and deionized water in a volume ratio of 3:2:5~8. The frequency of the ultrasonic cleaning equipment is set to 45~55kHz, and ultrasonic cleaning is performed at a temperature of 55~65℃ for 15~25min. The organic solvent cleaning solution can be recycled 2~4 times after filtration and precipitation.

4. The cleaning method for double-sided polishing of lithium niobate wafers according to claim 1, characterized in that, In step S3, the spray pressure is controlled between 0.2 and 0.3 MPa, the spray time is 60 to 90 seconds, and deionized water is injected until the polishing disc is submerged, maintaining an overflow state for 25 to 35 seconds. In step S4, the roller brush is made of PVA material, the roller brush speed is set to 8 to 12 rpm, the upper and lower roller brush pressing distance is controlled between 1100 and 1400 μm, the brushing time is 4 to 6 minutes, and the same double-sided brush is used to brush the disc in deionized water for 3 to 5 minutes, followed by a 15 to 25 second spray rinse. The polishing disc is then spun dry at a speed of 1300 to 1600 rpm for 18 to 22 seconds.

5. The cleaning method for double-sided polishing of lithium niobate wafers according to claim 1, characterized in that, The S5 gyro-type brush is made of PVA material. The brush pressing distance is set to 1000~1300μm, the brush rotation speed is 1200~1600rpm, and the brush translation speed is 18~22mm / s. It pauses for 0.8~1.2s at the center of the lithium niobate double-sided polishing sheet and for 4~6s at the edge of the lithium niobate double-sided polishing sheet, and brushes back and forth 4~6 times. The liquid medium of the two fluids consists of deionized water and 0.5~1% of fatty alcohol polyoxyethylene ether by volume of deionized water. The gas medium is high-purity nitrogen. The cleaning gas pressure of the two fluids is 0.3~0.5MPa, and the spray angle is 45~60°. After brushing, it is rinsed with deionized water for 6~10s, and then the lithium niobate double-sided polishing sheet is spun dry at a speed of 3200~4200rpm for 28~32s.

6. The cleaning method for double-sided polishing of lithium niobate wafers according to claim 1, characterized in that, The anionic surfactant is any one of sodium dodecylbenzenesulfonate and sodium dodecyl sulfate; the nonionic surfactant is any one or a combination of pentadecyl glycoside, dodecyl alcohol polyoxyethylene ether, polyethylene glycol, and Tween-80; the organic base is any one of triethanolamine, tetramethylammonium hydroxide, and glucosamine; the inorganic base is any one of sodium hydroxide and potassium hydroxide; the complexing agent is any one of ethylenediaminetetraacetic acid, sodium citrate, and hypozoxytriacetic acid; and the defoamer is any one of MX-9014 and DF-691.

7. The cleaning method for double-sided polishing of lithium niobate wafers according to claim 1, characterized in that, The molar ratio of 4-chloro-6,8-dimethylquinazoline and 1-hydroxymethylbenzimidazole in S21 is 1:1.1~1.

3. The mixture is heated to 75~80℃ and refluxed for 4~6 hours. After the reaction is completed, the pH of the reaction solution is adjusted to 3~4 with hydrochloric acid and then filtered. The solution is washed with anhydrous ethanol and recrystallized for purification.

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