Sapphire polishing solution and preparation method thereof

Abstract

According to the sapphire polishing solution and the preparation method thereof, the main raw materials of the polishing solution adopt a raw material structure with aluminum oxide powder as a main material and silicon dioxide as an auxiliary material, the polishing solution can be widely applied to the field of C-oriented sapphire materials through compound grinding, scientific proportioning and combination, the raw material cost is relatively low, and the polishing solution is suitable for industrial production. The comprehensive efficiency is improved on the whole, the polishing time is saved, the polishing comprehensive cost of customers can be reduced by about 15%, and C-direction machining can completely meet various requirements of the customers.

Description

Technical Field

[0001] This invention relates to the field of sapphire polishing technology, and in particular, to a polishing fluid for sapphire polishing and its preparation method. Background Technology

[0002] Sapphire is the general term for corundum gemstones of all colors except red ruby. Its main component is aluminum oxide (Al₂O₃), and it has a Mohs hardness of 9, second only to diamond. It possesses excellent optical, physical, and chemical properties. Its high hardness, high melting point, good light transmittance, excellent thermal conductivity and electrical insulation, good mechanical properties, good wear resistance, and stable corrosion resistance make it widely used in optoelectronics, communications, and defense industries.

[0003] With the continuous development of science and technology, sapphire workpieces are required to have very high surface quality, thus demanding increasingly higher surface processing precision and surface integrity from sapphire crystals. CMP (Chemical Mechanical Polishing) technology is currently the only technology capable of achieving global planarization, combining the advantages of chemical, mechanical, and fluid dynamics. Applying CMP technology can achieve both high polishing rates and smooth, flat surfaces. However, due to the high hardness, strong chemical stability, and brittleness of sapphire crystals, machining is difficult. The processing of sapphire workpieces generally suffers from low polishing efficiency, high wafer surface roughness, and excessively rapid wear of auxiliary materials, limiting large-scale industrial applications in the sapphire industry.

[0004] In the chemical mechanical polishing (CMP) process of sapphire crystals, the polishing slurry is crucial in determining the polishing quality and efficiency. The type, particle size, and content of the abrasive significantly influence polishing efficiency and wafer surface roughness. Currently, the abrasives used in sapphire polishing slurries mainly include diamond powder, silica sol, and alumina (Al2O3). While diamond's high hardness ensures high polishing efficiency, the surface roughness may not meet requirements, and diamond is also expensive. Therefore, diamond polishing slurries are currently mainly used for rough polishing or grinding of sapphire. Silica sol polishing slurries are most widely used in the precision polishing process of sapphire. They produce high-quality sapphire wafer surfaces, offer good suspension effects, are easy to use, and are inexpensive. However, the biggest drawback of silica sol polishing slurries is their low polishing efficiency. Furthermore, silica sol polishing slurries are prone to gelling when heated during polishing and easily dry on the sapphire wafer surface, which is detrimental to subsequent cleaning.

[0005] Al₂O₃ nanoparticles have a hardness comparable to sapphire crystals and can be used for sapphire crystal polishing. Sapphire crystal polishing is generally carried out under alkaline conditions. Al₂O₃ is more stable than silica sol under alkaline conditions, can withstand higher temperatures without deterioration, and polishing slurries using Al₂O₃ as an abrasive can be adjusted over a wider pH range compared to silica sol, resulting in higher polishing efficiency and lower cost, which is conducive to industrial application. However, Al₂O₃ particles tend to agglomerate during preparation, and these agglomerates are hard and dense, making them difficult to disperse effectively in the polishing slurry, thus scratching the sapphire wafers. Furthermore, Al₂O₃ tends to settle in the polishing slurry, which limits its application to some extent.

[0006] Patent application CN104356950A discloses a sapphire wafer polishing slurry, which is composed of the following components: 20-30 wt% silica sol with a solid content of 30-40 wt%; 10-20 wt% alumina with a diameter of 80-200 nm; 0.1-4 wt% organic base; 0.1-3 wt% dispersant, wherein the dispersant is sodium hexametaphosphate, pyridine, or polyethylene glycol; 0.3-1 wt% nonylphenol polyoxyethylene ether; and the balance being deionized water.

[0007] While the aforementioned polishing slurry addresses the issues of agglomeration and sedimentation in alumina polishing slurries to some extent, the polishing speed is significantly reduced because it requires the use of silica sol to help uniformly disperse the alumina. Furthermore, directly removing the silica sol from this solution would cause the agglomeration and sedimentation problems in the alumina polishing slurry to reappear.

[0008] Therefore, a new polishing slurry that offers excellent polishing results, improves overall efficiency, saves polishing time, and is easy to operate is in demand in the market. Summary of the Invention

[0009] The purpose of this invention is to provide an aluminum-silicon composite CMP polishing slurry for C-axis sapphire substrates, which reduces costs, improves overall efficiency, saves polishing time, and fully meets various customer needs for C-axis processing.

[0010] Therefore, the present invention provides a sapphire polishing slurry, which is an aqueous solution comprising the following components: 10-15 wt% alumina powder, 5-15 wt% silica, 1-3 wt% dispersant, 0.5-1 wt% coupling agent, 2-13 wt% pH adjuster, and 0.1-0.5 wt% cleaning agent.

[0011] In some embodiments, the particle size D50 of the alumina powder is 0.8 to 2 μm.

[0012] In some embodiments, the particle size D50 of the silica is 80–110 nm.

[0013] In some embodiments, the pH adjuster is one or more of sodium hydroxide, potassium hydroxide, sodium pyrosilicon, tetrapropylammonium hydroxide, sodium ethoxide, and ethylenediamine, adjusting the pH to 10.2–13.5.

[0014] In some embodiments, the pH adjuster is a combination of 1-3 wt% inorganic base and 1-3 wt% organic base.

[0015] In some embodiments, the dispersant is one or more of sodium dodecylbenzenesulfonate, sodium silicate, sodium pyrophosphate, xanthan gum, glyceryl monostearate, agar, sodium polyacrylate, sodium alginate, carbomer, carrageenan, and polyethylene glycol.

[0016] In some embodiments, the coupling agent is one or more of glycerol, N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC), sodium hydroxymethyl cellulose, sorbitol, mannitol, and hexyl laurate.

[0017] In some embodiments, the cleaning agent is one or more of dodecylphenol polyoxyethylene ether (OP-10), hydrogen peroxide, thiourea, sodium citrate, and citric acid.

[0018] The above method for preparing sapphire polishing fluid may include the following steps:

[0019] A. Add deionized water to the reactor, start stirring, slowly add alumina powder to form an alumina powder solution, add dispersant and coupling agent to the alumina powder solution in sequence, and stir to dissolve evenly;

[0020] B. Add silica and stir until well mixed;

[0021] C. Add a pH adjuster to the required pH value, then add a cleaning agent to obtain the finished polishing solution.

[0022] The surface quality of sapphire has a significant impact on the performance and quality of LED devices. Currently, the market demands ultra-smooth, defect-free surfaces with a surface roughness Ra of less than 0.2 nanometers. Therefore, the final polishing stage requires extremely high precision and has become a crucial manufacturing process. Due to its high hardness and brittleness, sapphire crystal is a typical example of a very difficult material to process. Existing polishing slurries on the market suffer from problems such as insufficient wafer surface roughness, low polishing efficiency, and a tendency for the slurry to agglomerate and settle.

[0023] The polishing slurry provided by this invention primarily uses alumina powder as the main raw material and silica as a secondary material. Through the scientific proportioning and combination of composite abrasives, and by appropriately controlling the particle size and uniform distribution of alumina and silica, a high removal rate is achieved during the polishing process, resulting in a good surface finish free of defects such as orange peel, pitting, pinholes, and streaks. The slurry incorporates reagents to modify and complex the powder surface, allowing the alumina and silica to complex more tightly, thus improving the cutting rate and ensuring a better surface finish and smoothness. A strong alkali is also added, with the pH value controlled between 11.5 and 13.5. The strong alkali primarily acts to form a softening layer under CMP pressure grinding. For example, potassium hydroxide reacts with sapphire to form potassium tetrahydroxyaluminate, resulting in a high surface cutting rate. When this formula is applied to C-axis sapphire substrates, the hourly cutting rate can reach 17-25 micrometers.

[0024] Existing alumina-containing formulations are prone to producing small amounts of agglomerate, forming a sludge-like substance that settles to the bottom, with some agglomerates adhering firmly to the bottom of the container. This solution effectively solves this problem by adding dispersants and coupling agents. Although the polishing slurry disclosed in this invention may also experience settling, a slight shake will resuspend the dispersed abrasive particles in the liquid. In actual CMP polishing processes, the polishing slurry is continuously stirred by an electric agitator during the dripping process and pumped to the surface of the polishing machine for CMP polishing and grinding of semiconductor materials. This achieves uniform abrasive dispersion during production and effectively solves problems such as powder agglomeration, sludge formation, and adhesion to the container.

[0025] It can be widely used in the field of C-axis sapphire materials, and the raw material cost is relatively low. Overall efficiency is improved, polishing time is saved, and the overall polishing cost for customers can be reduced by about 15%. C-axis processing can fully meet the various needs of customers. Attached Figure Description

[0026] Figure 1 Here is an electron microscope image of the alumina powder used in Example 3;

[0027] Figure 2 This is a particle size distribution diagram of the alumina powder used in Example 3. Detailed Implementation

[0028] The following describes the embodiments of the present invention in detail. It should be noted that the following embodiments are only used to illustrate the present invention and not to limit the present invention.

[0029] Example 1:

[0030] The sapphire polishing solution is composed of the following components by mass percentage: 10% alumina powder with a particle size D50 of 1 μm, 5% silica with a particle size D50 of 100 nm, 2% sodium hydroxide, 3% triethanolamine, 0.5% sodium silicate, 0.3% sodium pyrophosphate, 0.1% polyvinyl alcohol, 1% xanthan gum, 1% glycerol, 1% xylitol, 0.5% hydrogen peroxide, and the remainder is deionized water.

[0031] The steps for preparing the sapphire polishing slurry in this embodiment are as follows:

[0032] (1) Weigh each raw material component according to its mass percentage;

[0033] (2) Add deionized water to the reactor and start stirring. Then slowly add alumina powder to form an alumina powder solution. Under stirring conditions of 800 r / min, add sodium silicate, sodium pyrophosphate, xanthan gum, polyvinyl alcohol and xylitol to the alumina powder solution in sequence and stir until dissolved.

[0034] (3) Add silicon dioxide and continue stirring for about 15 minutes until the mixture is evenly mixed.

[0035] (4) Add sodium hydroxide and triethanolamine, continue stirring for 15 minutes until the mixture is uniform, adjust the pH value to 13, and then add hydrogen peroxide to obtain the sapphire polishing solution of this embodiment.

[0036] Example 2

[0037] The sapphire polishing solution, by weight percentage, consists of the following components: 12% alumina powder with a particle size D50 of 2 μm, 15% silica with a particle size D50 of 110 nm, 1.5% tetrapropylammonium hydroxide, 0.5% sodium ethoxide, 0.5% sodium dodecyl sulfate, 0.5% sodium carboxymethyl cellulose, 0.1% glyceryl monostearate, 1% gum arabic, 1% agar, 0.5% thiourea, and the remainder being deionized water.

[0038] The steps for preparing the sapphire polishing slurry in this embodiment are as follows:

[0039] (1) Weigh each raw material component according to its mass percentage;

[0040] (2) Add deionized water to the reactor and start stirring. Then slowly add alumina powder to form an alumina powder solution. Under stirring conditions of 800 r / min, add sodium hydroxymethyl cellulose, sodium dodecyl sulfate, glyceryl monostearate, gum arabic, and agar to the alumina powder solution in sequence and stir until dissolved.

[0041] (3) Add silicon dioxide and continue stirring for about 15 minutes until the mixture is evenly mixed.

[0042] (4) Add tetrapropylamine hydroxide and sodium ethoxide, continue stirring for 15 minutes until the mixture is uniform, adjust the pH value to 10.2, and then add thiourea to obtain the sapphire polishing solution of this embodiment.

[0043] Example 3

[0044] By mass percentage, this sapphire polishing solution consists of the following components: 15% alumina powder with a D50 of 1 μm, 8% silicon dioxide with a particle size of 80 nm, 3% potassium hydroxide, 3% ethylenediamine, 0.8% sodium dodecylbenzenesulfonate, 0.3% sodium polyacrylate, 0.1% carbomer, 1% sorbitol, 1% mannitol, 0.5% OP-10, and the remainder is deionized water.

[0045] The steps for preparing the sapphire polishing slurry in this embodiment are as follows:

[0046] (1) Weigh each raw material component according to its mass percentage;

[0047] (2) Add deionized water to the reactor and start stirring. Then slowly add alumina powder to form an alumina powder solution. Under stirring conditions of 800 r / min, add sodium polyacrylate, sodium dodecylbenzene sulfonate, carbomer, sorbitol and mannitol to the alumina powder solution in sequence and stir until dissolved.

[0048] (3) Add silicon dioxide and continue stirring for about 15 minutes until the mixture is evenly mixed.

[0049] (4) Add potassium hydroxide and ethylenediamine, continue stirring for 15 minutes until the mixture is uniform, adjust the pH value to 13.5, and then add OP-10 to obtain the sapphire polishing solution of this embodiment.

[0050] Example 4

[0051] The sapphire polishing solution is composed of the following components by mass percentage: 10% alumina powder with a D50 of 1 μm, 8% silica with a particle size of 108 nm, 2% sodium hydroxide, 0.5% sodium pyrosilicate, 0.5% sodium carbomer, 0.3% carbomer, 1% sodium alginate, 1% hexyl laurate, 0.5% sodium citrate, and the remainder is deionized water.

[0052] The steps for preparing the sapphire polishing slurry in this embodiment are as follows:

[0053] (1) Weigh each raw material component according to its mass percentage;

[0054] (2) Add deionized water to the reactor and start stirring. Then slowly add alumina powder to form an alumina powder solution. Under stirring conditions of 800 r / min, add sodium pyrophosphate, sodium hydroxymethyl cellulose, sodium alginate, carrageenan and polyethylene glycol to the alumina powder solution in sequence and stir until dissolved.

[0055] (3) Add silicon dioxide and continue stirring for about 15 minutes until the mixture is evenly mixed.

[0056] (4) Add sodium hydroxide and continue stirring for 15 minutes until the mixture is uniform. Adjust the pH value to 12.8 and then add sodium citrate to obtain the sapphire polishing solution of this embodiment.

[0057] Example 5

[0058] The sapphire polishing solution is composed of the following components by mass percentage: 10% alumina powder with a D50 of 1 μm, 8% silica with a particle size of 108 nm, 1.5% sodium hydroxide, 1% ethylenediamine, 0.5% sodium pyrosilicate, 0.5% sodium carbomer, 0.3% carbomer, 1% sodium alginate, 1% hexyl laurate, 0.5% sodium citrate, and the remainder is deionized water.

[0059] The steps for preparing the sapphire polishing slurry in this embodiment are as follows:

[0060] (1) Weigh each raw material component according to its mass percentage;

[0061] (2) Add deionized water to the reactor and start stirring. Then slowly add alumina powder to form an alumina powder solution. Under stirring conditions of 800 r / min, add sodium pyrophosphate, sodium hydroxymethyl cellulose, sodium alginate, carrageenan and polyethylene glycol to the alumina powder solution in sequence and stir until dissolved.

[0062] (3) Add silicon dioxide and continue stirring for about 15 minutes until the mixture is evenly mixed.

[0063] (4) Add sodium hydroxide and ethylenediamine and continue stirring for 15 minutes until the mixture is uniform. Adjust the pH value to 12.8 and then add sodium citrate to obtain the sapphire polishing solution of this embodiment.

[0064] Example 6

[0065] The sapphire polishing solution, by weight percentage, consists of the following components: 15% alumina powder with a particle size D50 of 1.5 μm, 15% silica with a particle size D50 of 95 nm, 1.5% tetrapropylamine hydroxide, 1% potassium hydroxide, 0.5% sodium pyrophosphate, 0.5% sodium carboxymethyl cellulose, 0.3% sodium alginate, 1% carrageenan, polyethylene glycol, 0.5% sodium citrate, and the remainder being deionized water.

[0066] The steps for preparing the sapphire polishing slurry in this embodiment are as follows:

[0067] (1) Weigh each raw material component according to its mass percentage;

[0068] (2) Add deionized water to the reactor and start stirring. Then slowly add alumina powder to form an alumina powder solution. Under stirring conditions of 800 r / min, add sodium pyrophosphate, sodium hydroxymethyl cellulose, sodium alginate, carrageenan and polyethylene glycol to the alumina powder solution in sequence and stir until dissolved.

[0069] (3) Add silicon dioxide and continue stirring for about 15 minutes until the mixture is evenly mixed.

[0070] (4) Add tetrapropylamine hydroxide and potassium hydroxide, continue stirring for 15 minutes until the mixture is uniform, adjust the pH value to 10.8, and then add sodium citrate to obtain the sapphire polishing solution of this embodiment.

[0071] Comparative Example 1: Commercially available alumina polishing slurry, Universal Corporation, USA.

[0072] Comparative Example 2: The raw material composition and preparation method are basically the same as those in Example 1, except that the particle size D50 of the alumina powder is 2.8 μm.

[0073] Comparative Example 3: The other raw material components, particle size and preparation method are the same as those in Example 2, except that the proportion of alumina powder is 8% and the proportion of silicon dioxide is 8%.

[0074] Comparative Example 4: Other raw material components, particle size, and preparation method are the same as in Example 5, except that the silicon dioxide content is 30%. Comparative Example 5: Other raw material components, particle size, and preparation method are the same as in Example 3, except that the alumina powder content is 23% and silicon dioxide is not present.

[0075] Comparative Example 6: The raw material composition is the same as that of Example 5, except that the alumina powder D50 is 0.6 μm and the silicon dioxide D50 is 150 nm.

[0076] Polishing test

[0077] The sapphire polishing slurries prepared in Examples 1-6 and Comparative Examples 1-6 were subjected to performance tests. The polishing test conditions were as follows: material: 4-inch sapphire substrate; machine: Hunan Shenggao No. 610 polishing machine; polishing pad: imported FUJIBO polishing pad; polishing time: 60 min (cycle); polishing pressure: 180 g / cm². 2 Polishing fluid flow rate: 45 mL / min.

[0078] Polishing test results of the sapphire polishing slurries in Examples 1-6 and Comparative Examples 1-6 show that the polishing speed and / or roughness of the examples are better than those of the comparative examples, and the examples all have good surface effects without defects such as orange peel, pitting, pinholes, or lines. Details are shown in Table 1 below.

[0079] Table 1. Polishing Test Results

[0080] Polishing liquid Polishing time (min) Polishing rate (μm / h) Roughness Ra (nm) Example 1 60 17.5 0.19 Example 2 60 18.5 0.18 Example 3 60 22 0.21 Example 4 60 19.3 0.17 Example 5 60 23 0.14 Example 6 60 19.4 0.15 Comparative Example 1 60 19.3 0.15 Comparative Example 2 60 17.7 0.31 Comparative Example 3 60 15.8 0.26 Comparative Example 4 60 14.1 0.18 Comparative Example 5 60 15.1 0.27 Comparative Example 6 60 14.7 0.23

[0081] The test results above show that the sapphire polishing slurries of Examples 1-5 have a slightly higher polishing rate and slightly lower surface roughness compared to the imported sapphire polishing slurry and the comparative example. Example 2 has a higher cutting rate and a more ideal surface roughness. The main difference between Example 2 and Example 1 is that the alumina particle size is increased to 2 micrometers and the silicon dioxide is increased to 110 nanometers. However, the amount of alumina powder added is increased to 12%, and the amount of silicon dioxide is increased to 15%. At the same time, the pH value is reduced to 10.2. Although the pH is reduced, the overall cutting rate is slightly improved compared to Example 1.

[0082] In Example 3, compared to Example 2, the alumina particle size was reduced to 1 micrometer and the silica particle size was reduced to 80 nanometers. At the same time, the alumina ratio was increased by 3% and the silica ratio was reduced by 7% compared to the two abrasives. The test results showed that the cutting rate was increased by 3.5%, which indicates that it is also related to the added chemical reagents. The organic amine base added in Example 3 has a positive catalytic effect on the formulation. At the same time, the dispersant and coupling agent are more conducive to the overall performance of the formulation.

[0083] In Example 4, compared to Example 3, the particle size of both alumina and silica increased, the silica addition ratio increased by 7%, the pH value increased to 10.8, and the hourly cutting rate decreased to 19.3. This is due to the change in the main materials, as well as the synergistic effect of the pH adjuster, dispersant, and coupling agent. This demonstrates that Example 4 is also a relatively ideal polishing solution.

[0084] Compared to other formulations, Examples 5 and 6 have moderate proportions of both main and auxiliary materials, and the polishing rate is also moderate.

[0085] Meanwhile, all of the above solutions have good surface finishes, with no defects such as orange peel, pitting, or lines.

[0086] Comparative Example 1: Compared with the alumina polishing slurry from Universal Scientific Industrial Co., Ltd., some embodiments showed better polishing rates, similar or better surface roughness, and reduced costs.

[0087] In Comparative Example 2, although the particle size was increased to 2.8 micrometers, the polishing rate did not increase significantly, indicating that the increase in particle size of the main material alone has a limited impact on the polishing rate.

[0088] Compared with Example 3, reducing the proportion of main material significantly reduced the cutting rate, indicating that the solid content of abrasive has a significant impact on the polishing rate.

[0089] Comparative Examples 4 and 6 show that changing the weight ratio or particle size ratio of alumina and silica will also affect the polishing rate or surface roughness.

[0090] Comparative Example 5 shows that the absence of silica reduces the polishing rate and results in a rougher surface.

[0091] In summary, to achieve an ideal polishing effect that balances improved cutting rate and good surface roughness, it requires not only the abrasive particle size but also the combination of organic amine bases within a certain concentration range, as well as the synergistic effect of dispersants and coupling agents, in order to achieve a more ideal overall effect.

Claims

1. A sapphire polishing slurry, characterized in that, The polishing solution is an aqueous solution comprising the following components: 10-15 wt% alumina powder, 5-15 wt% silica, 1-3 wt% dispersant, 0.5-1 wt% coupling agent, 2-13 wt% pH adjuster, and 0.1-0.5 wt% cleaning agent.

2. The sapphire polishing slurry as described in claim 1, characterized in that, The particle size D50 of the alumina powder is 0.8–2 μm.

3. The sapphire polishing slurry as described in claim 1 or claim 2, characterized in that, The D50 of the silica particle size is 80–110 nm.

4. The sapphire polishing slurry according to any one of claims 1 to 3, characterized in that, The pH adjuster is one or more of sodium hydroxide, potassium hydroxide, sodium pyrosilicate, tetrapropylammonium hydroxide, sodium ethoxide, and ethylenediamine, used to adjust the pH to 10.2–13.

5.

5. The sapphire polishing slurry as described in claim 4, characterized in that, The pH adjuster is a combination of the following: 1-3 wt% inorganic base and 1-3 wt% organic base.

6. The sapphire polishing slurry as described in claim 1, characterized in that, The dispersant is one or more of the following: sodium dodecylbenzenesulfonate, sodium silicate, sodium pyrophosphate, xanthan gum, glyceryl monostearate, agar, sodium polyacrylate, sodium alginate, carbomer, carrageenan, and polyethylene glycol.

7. The sapphire polishing slurry as described in claim 1, characterized in that, The coupling agent is one or more of glycerol, N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide, sodium hydroxymethyl cellulose, sorbitol, mannitol, and hexyl laurate.

8. The sapphire polishing slurry as described in claim 1, characterized in that, The cleaning agent is one or more of the following: dodecylphenol polyoxyethylene ether, hydrogen peroxide, thiourea, sodium citrate, and citric acid.

9. The sapphire polishing slurry as described in claim 1, characterized in that, Includes the following steps: A. Add deionized water to the reactor, start stirring, slowly add alumina powder to form an alumina powder solution, add dispersant and coupling agent to the alumina powder solution in sequence, and stir to dissolve evenly; B. Add silica and stir until well mixed; C. Add a pH adjuster to the required pH value, then add a cleaning agent to obtain the finished polishing solution.

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