A method for polishing surface impurities of a sapphire substrate

Abstract

The application relates to the field of chemical engineering substrate processing technology, and discloses a surface impurity polishing method for sapphire substrates, which comprises the following steps in sequence: pretreatment, polishing liquid preparation, first-stage polishing, second-stage polishing and post-treatment. In the method, the surface is activated through ultraviolet ozone cleaning with specific parameters in the pretreatment; the polishing liquid is composed of an acidic complexing agent, an oxidizing etching agent, a surfactant and nanoscale composite abrasives with specific particle sizes and proportions; the polishing process is divided into two stages, the first-stage polishing is preliminarily processed under specific pressure and rotating speed by using a polyurethane polishing pad, the second-stage polishing is finely polished by using a porous composite fiber polishing pad and adopting a periodic variable rotating speed process; and the post-treatment comprises multistage ultrasonic cleaning and drying. The application improves the uniformity of the surface quality of the sapphire substrates, and improves the adaptability of the polishing process to substrates with different batches and different initial conditions and the robustness of the processing effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical substrate processing, in particular to a surface impurity polishing method of sapphire substrate. BACKGROUND

[0002] The chemical substrate mainly refers to the material matrix in the field of semiconductors, including nitride, sapphire, silicon carbide, etc., which needs to meet the indexes of lattice matching degree, thermal expansion coefficient, chemical stability, etc., and is used for manufacturing LED, integrated circuit and high-power device.

[0003] At present, in the surface impurity polishing process of sapphire substrate, due to the complex composition of the polishing liquid and the coupling effect between the components, the concentration change of the chemical active components of the polishing liquid cannot be monitored in real time during polishing. If the concentration of the key etchant and complexing agent changes due to reaction and decomposition, it will cause unstable polishing rate and chemical damage, affecting the consistency of the surface quality. At the same time, in the multi-step polishing process, the contact state and pressure uniformity of the polishing pad and the substrate surface cannot be sensed and adjusted in real time, which will cause scratches and uneven removal rate on the substrate surface due to abnormal local pressure, and it is difficult to compensate and correct online when abnormality occurs.

[0004] Therefore, the present application provides a surface impurity polishing method of sapphire substrate to solve the above problems. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a surface impurity polishing method of sapphire substrate to solve the problems of being unable to monitor the concentration change of the chemical active components of the polishing liquid in real time during polishing and being unable to sense and adjust the contact state and pressure uniformity of the polishing pad and the substrate surface in real time.

[0006] To achieve the above purpose, the present application provides the following technical solution: a surface impurity polishing method of sapphire substrate, comprising the following steps:

[0007] Step 1: pretreatment, placing the sapphire substrate in an ultraviolet ozone cleaning machine for surface activation treatment, the treatment time is 10-30 minutes, and the ultraviolet wavelength is 185nm and 254nm double-band irradiation;

[0008] Step 2: preparing the polishing liquid, the polishing liquid is composed of the following raw materials in volume percentage: 30%-40% of acidic complexing agent, 5%-10% of oxidizing etchant, 0.5%-1.5% of surfactant, 15%-25% of nano abrasive and the balance of deionized water;

[0009] Step three: primary polishing, the pretreated sapphire substrate is fixed on the polishing disc, and the polishing liquid prepared in step two is injected for primary polishing treatment under the conditions of a pressure of 0.5-1.5 kPa and a rotation speed of 30-60 r / min by using a polyurethane polishing pad;

[0010] Step four: secondary polishing, the porous composite fiber polishing pad is replaced, and the fine polishing is performed under the conditions of a pressure of 0.2-0.8 kPa and a rotation speed of 10-30 r / min by using a periodic variable rotation speed process;

[0011] Step five: post-treatment, the polished sapphire substrate is sequentially subjected to three-stage cleaning in an ultrasonic cleaning machine, and finally dried by high-pressure nitrogen and vacuum packaged;

[0012] In step two, the acid complexing agent is a mixed acid system composed of hydrofluoric acid, nitric acid and citric acid in a volume ratio of 3:1:2, and the oxidizing etchant is a composite oxidizing agent composed of hydrogen peroxide and sodium hypochlorite in a mass ratio of 2:1.

[0013] Further, the pretreatment specifically includes: placing the sapphire substrate on the sample holder of the ultraviolet ozone cleaning machine, adjusting the rotation speed of the sample holder to 5-15 r / min, so that the substrate surface uniformly receives ultraviolet irradiation, and simultaneously introducing ozone gas into the treatment chamber at a flow rate of 0.5-1.5 L / min, and controlling the chamber temperature to be maintained at 25℃±3℃.

[0014] Further, the ultraviolet ozone cleaning machine has an ultraviolet light intensity of 10-30 mW / cm 2 , and an ozone concentration of 80-120 mg / L, and the relative humidity in the chamber is kept below 30% during the treatment process.

[0015] Further, the nanoscale abrasive is a composite abrasive composed of diamond micro powder, alumina nanoparticles and silica nanospheres in a mass ratio of 1:2:3, wherein the particle size of the diamond micro powder is 50-100 nm, the particle size of the alumina nanoparticles is 30-80 nm, and the particle size of the silica nanospheres is 20-50 nm.

[0016] Further, the preparation method of the nanoscale abrasive includes: after the above three abrasives are mixed in proportion, a dispersing agent polyethyleneimine is added to form a stable suspension in deionized water, and an ultrasonic cell disruptor is used for dispersion treatment at a power of 500-1000 W for 30-60 minutes, and finally a composite abrasive with uniform particle size distribution is obtained by centrifugal separation.

[0017] Further, in the primary polishing process of step three, the injection flow of the polishing liquid is controlled at 50-150 mL / min, the polishing temperature is maintained at 25℃±2℃ by a constant temperature system, and the polishing time is set to 30-90 minutes according to the initial roughness of the substrate surface.

[0018] Further, the secondary polishing of step four adopts a periodic variable speed process, specifically: taking 10 minutes as a cycle, maintaining the speed at 20 r / min for the first 5 minutes, linearly increasing to 30 r / min for the last 5 minutes, and thus cycling for 3-6 cycles, while pausing the injection of polishing liquid for 10-20 seconds at each cycle conversion.

[0019] Further, the tertiary cleaning of step five includes: first, ultrasonic cleaning in acetone for 5-10 minutes, then ultrasonic cleaning in anhydrous ethanol for 5-10 minutes, and finally ultrasonic cleaning in ultrapure water for 10-15 minutes, and the ultrasonic frequencies of each stage are 40 kHz, 80 kHz and 120 kHz respectively.

[0020] Further, the temperature of the cleaning liquid is maintained within the range of 20-30℃ during the ultrasonic cleaning process, and megasonic wave assisted flushing is used after each cleaning stage, with a megasonic wave frequency of 0.8-1.2 MHz and a power density of 0.5-1.0 W / cm 2 .

[0021] Further, the method further includes a quality detection step: atomic force microscope is used to detect the surface roughness after polishing, the center line average roughness Ra is required to be less than 0.2 nm, X-ray photoelectron spectrometer is used to detect the surface element content, the metal impurity element content is required to be less than 0.1 at%, and laser particle counter is used to detect the surface particle number, the particle number greater than 0.5 μm is required to be less than 10 pieces per square centimeter.

[0022] Compared with the prior art, the present application provides a surface impurity polishing method for sapphire substrates, which has the following beneficial effects:

[0023] 1. In the present application, by using a polishing liquid system composed of a specific acidic complexing agent and an oxidizing etching agent, and combining with ultraviolet ozone cleaning for pretreatment to activate the surface of the substrate, the stability of the key chemical components can be maintained during the polishing process, avoiding the fluctuation of the polishing rate caused by the decay of the chemical activity of the polishing liquid, thereby ensuring the uniformity and consistency of the material removal rate during the entire polishing process, so that the sapphire substrate surface can obtain more uniform and consistent chemical etching effect, reducing the risk of local chemical damage and improving the uniformity of the surface quality.

[0024] 2. In the present application, by setting the first polishing and the second polishing steps containing different pressure, rotating speed parameters and using different material polishing pads, and introducing the periodic variable rotating speed process in the second polishing, the contact state and stress distribution of the polishing pad and the substrate surface can be dynamically optimized, the scratch and uneven removal caused by local pressure concentration are relieved, the uniformity and stability of the polishing interface action are ensured, thereby improving the overall flatness of the sapphire substrate surface while removing surface impurities and reducing subsurface damage.

[0025] 3. In the present application, through the synergistic design of the pretreatment, the first polishing, the second polishing and the post-treatment multi-step process parameters, and combined with the multi-stage cleaning in the post-treatment and the final quality detection, the polishing method can adapt to sapphire substrates with different initial states, realize the targeted removal of surface impurities and micro-damage, and through the control and verification of the final surface state, the adaptability of the polishing process to different batches and different initial condition substrates and the robustness of the processing effect are improved, thereby ensuring the high quality and high yield of the final product. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0027] Embodiment 1: A surface impurity polishing method of sapphire substrate, comprising the following steps:

[0028] Step one: pretreatment, placing the sapphire substrate in an ultraviolet ozone cleaning machine for surface activation treatment, the treatment time is 10 minutes, and the ultraviolet wavelength is 185 nm and 254 nm double waveband irradiation;

[0029] Step two: preparing a polishing liquid, the polishing liquid is composed of the following volume percentage of raw materials: acid complexing agent 30%, oxidizing etchant 5%, surfactant 0.5%, nanoscale abrasive 15% and deionized water balance;

[0030] Step three: first polishing, fixing the pretreated sapphire substrate on the polishing disc, using a polyurethane polishing pad, under the conditions of pressure 0.5 kPa and rotating speed 30 r / min, injecting the polishing liquid prepared in step two for preliminary polishing treatment;

[0031] Step four: second polishing, replacing the porous composite fiber polishing pad, under the conditions of pressure 0.2 kPa and rotating speed 10 r / min, using the periodic variable rotating speed process for fine polishing;

[0032] Step five: post-treatment, the polished sapphire substrate is sequentially cleaned in a three-stage ultrasonic cleaner, and finally dried with high-pressure nitrogen and vacuum packaged;

[0033] In step two, the acid complexing agent is a mixed acid system composed of hydrofluoric acid, nitric acid and citric acid in a volume ratio of 3:1:2, and the oxidative etchant is a composite oxidizing agent composed of hydrogen peroxide and sodium hypochlorite in a mass ratio of 2:1.

[0034] The pretreatment specifically includes: placing the sapphire substrate on the sample holder of the ultraviolet ozone cleaner, adjusting the sample holder speed to 5 r / min, so that the substrate surface uniformly receives ultraviolet irradiation, and at the same time, ozone gas with a flow rate of 0.5 L / min is introduced into the treatment chamber, and the chamber temperature is controlled to maintain at 22℃.

[0035] The ultraviolet intensity of the ultraviolet ozone cleaner is 10 mW / cm 2 , the ozone concentration is 80 mg / L, and the relative humidity in the chamber is kept below 30% during the treatment process.

[0036] The nanoscale abrasive is a composite abrasive composed of diamond powder, aluminum oxide nanoparticles and silica nanospheres in a mass ratio of 1:2:3, wherein the particle size of the diamond powder is 50 nm, the particle size of the aluminum oxide nanoparticles is 30 nm, and the particle size of the silica nanospheres is 20 nm.

[0037] The preparation method of the nanoscale abrasive includes: mixing the above three abrasives in proportion, adding a dispersing agent polyethyleneimine, and forming a stable suspension in deionized water, dispersing and treating with an ultrasonic cell crusher at a power of 500 W for 30 minutes, and finally obtaining a composite abrasive with uniform particle size distribution through centrifugal separation.

[0038] In the first polishing process of step three, the polishing liquid injection flow rate is controlled at 50 mL / min, the polishing temperature is maintained at 23℃ through a constant temperature system, and the polishing time is set to 30 minutes according to the initial roughness of the substrate surface.

[0039] The second polishing of step four adopts a periodic variable speed process, specifically: taking 10 minutes as a cycle, maintaining the speed at 20 r / min for the first 5 minutes, and linearly increasing to 30 r / min for the last 5 minutes, and so on for 3 cycles, while pausing the injection of polishing liquid for 10 seconds at each cycle conversion.

[0040] The third cleaning of step five includes: first ultrasonic cleaning in acetone for 5 minutes, then ultrasonic cleaning in anhydrous ethanol for 5 minutes, and finally ultrasonic cleaning in ultrapure water for 10 minutes, and the ultrasonic frequencies of each stage are 40 kHz, 80 kHz and 120 kHz respectively.

[0041] During ultrasonic cleaning, the cleaning fluid temperature was maintained within 20℃. After each cleaning stage, a megason-assisted rinse was performed. The megason frequency was 0.8MHz, and the power density was 0.5W / cm³. 2 .

[0042] The method also includes quality inspection steps: using an atomic force microscope to detect the surface roughness after polishing, requiring the average roughness Ra of the centerline to be less than 0.2 nm; using an X-ray photoelectron spectroscopy to detect the surface element content, requiring the content of metallic impurity elements to be less than 0.1 at%; and using a laser particle counter to detect the number of surface particles, requiring the number of particles larger than 0.5 μm to be less than 10 per square centimeter.

[0043] Example 2: A method for polishing surface impurities on a sapphire substrate, comprising the following steps:

[0044] Step 1: Pretreatment. The sapphire substrate is placed in an ultraviolet ozone cleaner for surface activation treatment for 20 minutes. The ultraviolet wavelength is 185nm and 254nm dual-band irradiation.

[0045] Step 2: Prepare the polishing slurry, which consists of the following raw materials by volume percentage: 35% acidic complexing agent, 7.5% oxidizing etchant, 1.0% surfactant, 20% nano-abrasive, and the balance deionized water;

[0046] Step 3: Primary polishing. The pretreated sapphire substrate is fixed on the polishing pad. Using a polyurethane polishing pad, the polishing liquid prepared in Step 2 is injected under the conditions of 1.0 kPa pressure and 45 r / min rotation speed for preliminary polishing.

[0047] Step 4: Secondary polishing, replacing the pad with a porous composite fiber polishing pad, and performing fine polishing using a periodic variable speed process under a pressure of 0.5 kPa and a rotation speed of 20 r / min;

[0048] Step 5: Post-processing. The polished sapphire substrate is sequentially subjected to three-stage cleaning in an ultrasonic cleaner, and finally dried with high-pressure nitrogen and vacuum packaged.

[0049] In step two, the acidic complexing agent is a mixed acid system composed of hydrofluoric acid, nitric acid and citric acid in a volume ratio of 3:1:2, and the oxidizing etching agent is a composite oxidizing agent composed of hydrogen peroxide and sodium hypochlorite in a mass ratio of 2:1.

[0050] The pretreatment specifically includes: placing the sapphire substrate on the sample holder of the ultraviolet ozone cleaner, adjusting the sample holder speed to 10 r / min to ensure that the substrate surface is uniformly irradiated with ultraviolet light, and simultaneously introducing ozone gas with a flow rate of 1.0 L / min into the treatment chamber to control the chamber temperature to be maintained at 25°C.

[0051] The UV light intensity of the UV ozone cleaner is 20mW / cm². 2 The ozone concentration is 100 mg / L, and the relative humidity of the chamber is kept below 30% during the treatment process.

[0052] The nanoscale abrasive is a composite abrasive composed of diamond micro powder, alumina nanoparticles and silica nanospheres in a mass ratio of 1:2:3, wherein the diamond micro powder has a particle size of 75 nm, the alumina nanoparticles have a particle size of 55 nm, and the silica nanospheres have a particle size of 35 nm.

[0053] The preparation method of nano-sized abrasives includes: mixing the above three abrasives in proportion, adding the dispersant polyethyleneimine to form a stable suspension in deionized water, dispersing the suspension for 45 minutes using an ultrasonic cell disruptor at a power of 750W, and finally obtaining composite abrasives with uniform particle size distribution by centrifugation.

[0054] In the first-stage polishing process of step three, the polishing slurry injection flow rate is controlled at 100 mL / min, the polishing temperature is maintained at 25℃ by a constant temperature system, and the polishing time is set to 60 minutes according to the initial roughness of the substrate surface.

[0055] The secondary polishing in step four adopts a periodic variable speed process, specifically: with a cycle of 10 minutes, the speed is kept at 20 r / min for the first 5 minutes, and then linearly increased to 30 r / min for the next 5 minutes. This cycle is repeated for 4.5 cycles, while pausing the injection of polishing fluid for 15 seconds at the transition between each cycle.

[0056] Step 5, the three-stage cleaning process, includes: first, ultrasonic cleaning in acetone for 7.5 minutes, then ultrasonic cleaning in anhydrous ethanol for 7.5 minutes, and finally ultrasonic cleaning in ultrapure water for 12.5 minutes. The ultrasonic frequencies for each stage are 40 kHz, 80 kHz, and 120 kHz, respectively.

[0057] During ultrasonic cleaning, the cleaning fluid temperature was maintained within 25℃. After each cleaning stage, megason-assisted rinsing was performed. The megason frequency was 1.0MHz, and the power density was 0.75W / cm³. 2 .

[0058] The method also includes quality inspection steps: using an atomic force microscope to detect the surface roughness after polishing, requiring the average roughness Ra of the centerline to be less than 0.2 nm; using an X-ray photoelectron spectroscopy to detect the surface element content, requiring the content of metallic impurity elements to be less than 0.1 at%; and using a laser particle counter to detect the number of surface particles, requiring the number of particles larger than 0.5 μm to be less than 10 per square centimeter.

[0059] Example 3: A method for polishing surface impurities on a sapphire substrate, comprising the following steps:

[0060] Step 1: Pretreatment. The sapphire substrate is placed in an ultraviolet ozone cleaner for surface activation treatment for 30 minutes. The ultraviolet wavelength is 185nm and 254nm dual-band irradiation.

[0061] Step 2: Prepare the polishing slurry, which consists of the following raw materials by volume percentage: 40% acidic complexing agent, 10% oxidizing etchant, 1.5% surfactant, 25% nano-abrasive, and the balance deionized water;

[0062] Step 3: Primary polishing. The pretreated sapphire substrate is fixed on the polishing pad. Using a polyurethane polishing pad, the polishing liquid prepared in Step 2 is injected under a pressure of 1.5 kPa and a rotation speed of 60 r / min for preliminary polishing.

[0063] Step 4: Secondary polishing, replacing the pad with a porous composite fiber polishing pad, and performing fine polishing using a periodic variable speed process under a pressure of 0.8 kPa and a speed of 30 r / min.

[0064] Step 5: Post-processing. The polished sapphire substrate is sequentially subjected to three-stage cleaning in an ultrasonic cleaner, and finally dried with high-pressure nitrogen and vacuum packaged.

[0065] In step two, the acidic complexing agent is a mixed acid system composed of hydrofluoric acid, nitric acid and citric acid in a volume ratio of 3:1:2, and the oxidizing etching agent is a composite oxidizing agent composed of hydrogen peroxide and sodium hypochlorite in a mass ratio of 2:1.

[0066] The pretreatment specifically includes: placing the sapphire substrate on the sample holder of the ultraviolet ozone cleaner, adjusting the sample holder speed to 15 r / min to ensure that the substrate surface is uniformly irradiated with ultraviolet light, and simultaneously introducing ozone gas at a flow rate of 1.5 L / min into the treatment chamber to control the chamber temperature to be maintained at 28°C.

[0067] The UV light intensity of the UV ozone cleaner is 30mW / cm². 2 The ozone concentration was 120 mg / L, and the relative humidity of the chamber was kept below 30% during the treatment process.

[0068] The nanoscale abrasive is a composite abrasive composed of diamond micro powder, alumina nanoparticles and silica nanospheres in a mass ratio of 1:2:3, wherein the diamond micro powder has a particle size of 100 nm, the alumina nanoparticles have a particle size of 80 nm, and the silica nanospheres have a particle size of 50 nm.

[0069] The preparation method of nano-sized abrasives includes: mixing the above three abrasives in proportion, adding the dispersant polyethyleneimine to form a stable suspension in deionized water, dispersing the suspension for 60 minutes using an ultrasonic cell disruptor at a power of 1000W, and finally obtaining composite abrasives with uniform particle size distribution by centrifugation.

[0070] In the first-stage polishing process of step three, the polishing slurry injection flow rate is controlled at 150 mL / min, the polishing temperature is maintained at 27℃ by a constant temperature system, and the polishing time is set to 90 minutes according to the initial roughness of the substrate surface.

[0071] The secondary polishing in step four adopts a periodic variable speed process, specifically: with a cycle of 10 minutes, the speed is kept at 20 r / min for the first 5 minutes, and then linearly increased to 30 r / min for the next 5 minutes. This cycle is repeated for 6 cycles, and the injection of polishing fluid is paused for 20 seconds at the transition between each cycle.

[0072] Step five, the three-stage cleaning process, includes: first, ultrasonic cleaning in acetone for 10 minutes, then ultrasonic cleaning in anhydrous ethanol for 10 minutes, and finally ultrasonic cleaning in ultrapure water for 15 minutes, with ultrasonic frequencies of 40kHz, 80kHz, and 120kHz for each stage.

[0073] During ultrasonic cleaning, the cleaning fluid temperature was maintained within 30℃. After each cleaning stage, megason-assisted rinsing was performed. The megason frequency was 1.2MHz, and the power density was 1.0W / cm³. 2 .

[0074] The method also includes quality inspection steps: using an atomic force microscope to detect the surface roughness after polishing, requiring the average roughness Ra of the centerline to be less than 0.2 nm; using an X-ray photoelectron spectroscopy to detect the surface element content, requiring the content of metallic impurity elements to be less than 0.1 at%; and using a laser particle counter to detect the number of surface particles, requiring the number of particles larger than 0.5 μm to be less than 10 per square centimeter.

[0075] Comparative Example 1: The difference between this comparative example and Example 1 is that no oxidizing etchant was added when preparing the polishing slurry in this comparative example.

[0076] Comparative Example 2 differs from Example 2 in that the comparative example does not use a periodic variable speed process in the secondary polishing process, but keeps the speed constant at 20 r / min.

[0077] Comparative Example 3 differs from Example 3 in that: this comparative example did not undergo ultraviolet ozone cleaning in the pretreatment stage, but only used conventional organic solvent cleaning.

[0078] Comparative Example 4 differs from Example 3 in that: in the preparation of the polishing slurry, this comparative example uses alumina abrasive with a single particle size instead of composite nano-sized abrasive.

[0079] The surface impurity polishing methods for sapphire substrates in Examples 1-3 and Comparative Examples 1-4 were tested for performance. The test items and methods are as follows:

[0080] Surface roughness test: The average roughness Ra value of the centerline was measured using an atomic force microscope within a scanning range of 5μm×5μm.

[0081] Material removal rate test: The difference in substrate mass before and after polishing is measured by a precision balance, and the amount of material removed per unit time is calculated in combination with the polishing time.

[0082] Surface defect detection: The density of microscopic defects such as scratches and pits on the surface is detected using a laser confocal microscope, and the number of defects per unit area is counted.

[0083] Surface cleanliness test: X-ray photoelectron spectroscopy was used to detect the content of metallic impurities on the surface, with a detection limit of 0.1 at%.

[0084] The test data of the surface impurity polishing method for sapphire substrates in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below:

[0085]

[0086] By comparing and analyzing the data in the table, it can be seen that the surface impurity polishing method for sapphire substrates in Examples 1-3 performs better than the surface impurity polishing method for sapphire substrates in Comparative Examples 1-4. This indicates that by using a polishing slurry system composed of a specific acidic complexing agent and an oxidizing etchant, and combining it with UV ozone cleaning for pretreatment to activate the substrate surface, the stable activity of key chemical components can be maintained during the polishing process. This avoids fluctuations in the polishing rate caused by the decay of the chemical activity of the polishing slurry, thereby ensuring the uniformity and consistency of the material removal rate throughout the polishing process. This results in a more uniform chemical etching effect on the sapphire substrate surface, reduces the risk of local chemical damage, and improves the uniformity of surface quality. By setting up primary and secondary polishing steps with different pressure, rotation speed parameters, and polishing pads of different materials, and... The introduction of a periodic variable speed process in the two-stage polishing stage dynamically optimizes the contact state and stress distribution between the polishing pad and the substrate surface. This alleviates scratches and uneven removal caused by localized pressure concentration, ensuring the uniformity and stability of the polishing interface. Consequently, while removing surface impurities, it improves the overall flatness of the sapphire substrate surface and reduces subsurface damage. Through the coordinated design of process parameters across multiple steps—pretreatment, primary polishing, secondary polishing, and post-treatment—and combined with multi-stage cleaning and final quality inspection in post-treatment, this polishing method can adapt to sapphire substrates in different initial states. It achieves targeted removal of surface impurities and microscopic damage. Furthermore, by controlling and verifying the final surface state, the adaptability and robustness of the polishing process to different batches and substrates with different initial conditions are improved, thus ensuring high quality and high yield of the final product.

[0087] By comparing and analyzing the relevant data in the table, it can be seen that the surface impurity polishing method for sapphire substrates of the present invention has superior overall performance.

[0088] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0089] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for polishing surface impurities on a sapphire substrate, characterized in that, Includes the following steps: Step 1: Pretreatment. Place the sapphire substrate in an ultraviolet ozone cleaner for surface activation treatment. The treatment time is 10-30 minutes, and the ultraviolet wavelength is irradiated in two bands: 185nm and 254nm. Step 2: Prepare the polishing slurry, which is composed of the following raw materials by volume percentage: 30%-40% acidic complexing agent, 5%-10% oxidizing etchant, 0.5%-1.5% surfactant, 15%-25% nano-abrasive, and the balance being deionized water; Step 3: Primary polishing. The pretreated sapphire substrate is fixed on the polishing pad. A polyurethane polishing pad is used. Under the conditions of pressure 0.5-1.5 kPa and rotation speed 30-60 r / min, the polishing liquid prepared in step 2 is injected for preliminary polishing. Step 4: Secondary polishing, replacing the pad with a porous composite fiber polishing pad, and performing fine polishing using a periodic variable speed process under a pressure of 0.2-0.8 kPa and a speed of 10-30 r / min. Step 5: Post-processing. The polished sapphire substrate is sequentially subjected to three-stage cleaning in an ultrasonic cleaner, and finally dried with high-pressure nitrogen and vacuum packaged. In step two, the acidic complexing agent is a mixed acid system composed of hydrofluoric acid, nitric acid and citric acid in a volume ratio of 3:1:2, and the oxidizing etching agent is a composite oxidizing agent composed of hydrogen peroxide and sodium hypochlorite in a mass ratio of 2:

1.

2. The surface impurity polishing method for a sapphire substrate according to claim 1, characterized in that, The pretreatment specifically includes: placing the sapphire substrate on the sample holder of the ultraviolet ozone cleaner, adjusting the rotation speed of the sample holder to 5-15 r / min to ensure that the substrate surface is uniformly irradiated with ultraviolet light, and simultaneously introducing ozone gas with a flow rate of 0.5-1.5 L / min into the treatment chamber, and controlling the chamber temperature to be maintained at 25℃±3℃.

3. The surface impurity polishing method for a sapphire substrate according to claim 1, characterized in that, The ultraviolet light intensity of the ultraviolet ozone cleaner is 10-30 mW / cm². 2 The ozone concentration is 80-120 mg / L, and the relative humidity of the chamber is kept below 30% during the treatment process.

4. The surface impurity polishing method for a sapphire substrate according to claim 1, characterized in that, The nanoscale abrasive is a composite abrasive composed of diamond micro powder, alumina nanoparticles and silica nanospheres in a mass ratio of 1:2:3, wherein the particle size of the diamond micro powder is 50-100nm, the particle size of the alumina nanoparticles is 30-80nm, and the particle size of the silica nanospheres is 20-50nm.

5. The surface impurity polishing method for a sapphire substrate according to claim 4, characterized in that, The preparation method of the nanoscale abrasive includes: mixing the above-mentioned diamond micro powder, alumina nanoparticles and silica nanospheres in a certain proportion, adding the dispersant polyethyleneimine to form a stable suspension in deionized water, dispersing it for 30-60 minutes using an ultrasonic cell disruptor at a power of 500-1000W, and finally obtaining a composite abrasive with uniform particle size distribution by centrifugation.

6. The surface impurity polishing method for a sapphire substrate according to claim 1, characterized in that, In the first-stage polishing process of step three, the flow rate of the polishing slurry is controlled at 50-150 mL / min, the polishing temperature is maintained at 25℃±2℃ by a constant temperature system, and the polishing time is set to 30-90 minutes according to the initial roughness of the substrate surface.

7. The surface impurity polishing method for a sapphire substrate according to claim 1, characterized in that, The secondary polishing in step four adopts a periodic variable speed process, specifically: with a cycle of 10 minutes, the speed is maintained at 20 r / min for the first 5 minutes, and then linearly increased to 30 r / min for the next 5 minutes. This cycle is repeated for 3-6 cycles, while pausing the injection of polishing fluid for 10-20 seconds at the transition between each cycle.

8. The surface impurity polishing method for a sapphire substrate according to claim 1, characterized in that, The three-stage cleaning in step five includes: first, ultrasonic cleaning in acetone for 5-10 minutes, then ultrasonic cleaning in anhydrous ethanol for 5-10 minutes, and finally ultrasonic cleaning in ultrapure water for 10-15 minutes, with ultrasonic frequencies of 40kHz, 80kHz and 120kHz respectively.

9. The surface impurity polishing method for a sapphire substrate according to claim 8, characterized in that, During the ultrasonic cleaning process, the cleaning fluid temperature is maintained within the range of 20-30℃. After each stage of cleaning, megasonite-assisted rinsing is performed, with a megasonite frequency of 0.8MHz-1.2MHz and a power density of 0.5-1.0W / cm³. 2 .

10. The surface impurity polishing method for a sapphire substrate according to claim 1, characterized in that, The method also includes a quality inspection step: using an atomic force microscope to inspect the surface roughness after polishing, requiring the average roughness Ra of the centerline to be less than 0.2 nm; using an X-ray photoelectron spectroscopy to inspect the surface element content, requiring the content of metallic impurity elements to be less than 0.1 at%; and using a laser particle counter to inspect the number of surface particles, requiring the number of particles larger than 0.5 μm to be less than 10 per square centimeter.

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