A polishing composition and method for polishing lithium tantalate or lithium niobate

Abstract

The present application relates to the technical field of polishing, in particular to a polishing composition and a polishing method of lithium tantalate or lithium niobate, the polishing composition comprising the following components: a silica abrasive; phytate ions; the balance being water; the pH value of the polishing composition is 8-11, the pH value of the polishing composition is adjusted by an alkali metal hydroxide, the phytate ions are obtained by dissolving a mixture of one or a combination of several of phytic acid, sodium phytate and potassium phytate in water, and the polishing method is polishing lithium tantalate or lithium niobate by using the above-mentioned polishing composition. The present application has the effect of further improving the polishing removal rate and the colloidal stability of the polishing liquid of lithium tantalate and lithium niobate.

Description

Technical Field

[0001] This invention relates to the field of polishing technology, and in particular to a polishing composition and polishing method for lithium tantalate or lithium niobate. Background Technology

[0002] Lithium tantalate and lithium niobate are widely used in piezoelectric and optoelectronic fields such as radio frequency filters, second harmonic generators, electro-optic Q-switching elements, and laser frequency multipliers due to their excellent nonlinear optical effects, piezoelectric effects, and photorefractive effects. In particular, in the field of radio frequency filters, they are widely used as substrate materials for surface acoustic wave filters due to their excellent piezoelectric properties.

[0003] Lithium tantalate and lithium niobate substrates require crystal growth, cutting, grinding, and polishing. The final polishing step is crucial for removing the damaged layer and achieving the desired surface smoothness Ra < 0.5 nm. Tantalum and niobium belong to the same group VB, and the atoms in lithium tantalate and lithium niobate are similarly positioned in their crystal structures. Therefore, their chemical and material properties are also similar, and their performance during polishing is also similar. This is reflected in the fact that when polished with the same process and polishing solution, the removal rates of lithium tantalate and lithium niobate are on the same order of magnitude, and their Ra values ​​are also similar. More specifically, the removal rate of lithium niobate is slightly higher than that of lithium tantalate, approximately 1.2 to 2 times higher.

[0004] When only silica sol is used as the abrasive without other additives, the polishing rates of lithium tantalate and lithium niobate are significantly higher in the acidic range than in the alkaline range. Moriyama et al. reported that the removal rate of lithium tantalate at pH 4 is approximately 6 times that at pH 9. (K. Moriyama, A. Ozeki, S. Haba and M. Mori, "The effect of slurry pH and particle size on LiTaO3 polishing," 2016 International Symposium on Semiconductor Manufacturing (ISSM), Tokyo, Japan, 2016, pp. 1-3). However, typical silica sol is unstable in the acidic range, especially at pH 4, and easily gels.

[0005] Meanwhile, Japanese patent JP6481589B2 discloses a weakly alkaline polishing slurry for polishing lithium tantalate and lithium niobate. Its core technology uses citrate to increase the polishing rate, but higher concentrations of citrate can cause silica sol to gel. Patent publication CN1782014A discloses the use of aldoses such as sodium gluconate to increase the removal rate of lithium tantalate and lithium niobate in an alkaline silica sol system, and reveals that the silica sol system is stable when the sodium gluconate concentration is less than 3%. However, further improvements are needed in the polishing removal rate of lithium tantalate and lithium niobate and the colloidal stability of the polishing slurry. Summary of the Invention

[0006] To further improve the polishing removal rate and colloidal stability of lithium tantalate and lithium niobate, this invention provides a polishing composition and polishing method for lithium tantalate or lithium niobate, addressing the problems of the prior art.

[0007] In a first aspect, the present invention provides a polishing composition for lithium tantalate or lithium niobate, which adopts the following technical solution:

[0008] A polishing composition of lithium tantalate or lithium niobate, the polishing composition comprising the following components: phytate ions; silica abrasive; balance water; the pH of the polishing composition being 8-11, the pH of the polishing composition being adjusted by an alkali metal hydroxide.

[0009] Preferably, the polishing composition comprises the following components: phytate ions; 10-40% by weight of silica abrasive; the balance being water; the phytate ions having a weight percentage of not less than 0.2% and less than 2%; the polishing composition having a pH value of 8-11; and the pH value of the polishing composition being adjusted by sodium hydroxide or potassium hydroxide.

[0010] Preferably, the phytate ions are obtained by dissolving a mixture of one or more of phytic acid, sodium phytate, and potassium phytate in water.

[0011] Preferably, the silica abrasive is provided by silica sol, and the z-average particle size of the silica abrasive is in the range of 50-150 nm.

[0012] Preferably, the silica abrasive accounts for 20% of the weight percentage of the polishing composition.

[0013] Secondly, the present invention provides a polishing method for lithium tantalate or lithium niobate, employing the following technical solution:

[0014] A polishing method for lithium tantalate or lithium niobate includes the following steps:

[0015] S1: Phytic acid or phytate is dissolved in water to dissociate and obtain phytate ions. The pH is adjusted to alkaline using alkali metal hydroxide. Then, silica abrasive is added and stirred evenly to obtain a polishing composition. The pH of the polishing solution is 8-11.

[0016] S2: Provide a lithium tantalate or lithium niobate surface to be polished, introduce the polishing composition described in S1 between the lithium tantalate or lithium niobate surface and the polishing surface of the polishing tool, and make the lithium tantalate or lithium niobate surface contact and move relative to the polishing surface of the polishing tool.

[0017] Preferably, in the polishing composition, the weight percentage of phytate ions is not less than 0.2% and less than 2%, the weight percentage of silica abrasive is 10-40%, the pH value of the polishing composition is 8-11, and the pH value of the polishing composition is adjusted by sodium hydroxide or potassium hydroxide.

[0018] Preferably, the phytate ions are obtained by dissolving a mixture of one or more of phytic acid, sodium phytate, and potassium phytate in water.

[0019] Preferably, the silica abrasive is provided by silica sol, and the z-average particle size of the silica abrasive is in the range of 50-150 nm.

[0020] Preferably, the silica abrasive accounts for 20% of the weight percentage of the polishing composition.

[0021] In summary, the present invention has the following beneficial technical effects:

[0022] The polishing slurry containing phytic acid and silica sol has a significantly higher polishing removal rate for lithium tantalate than the polishing slurry containing sodium gluconate and silica sol. Furthermore, the polishing slurry of the present invention has good stability and does not gel. Detailed Implementation

[0023] As used herein, the terms “consisting of,” “including,” “comprising,” “having,” “having,” or any other variation thereof are intended to cover the meaning of non-exclusive inclusion. For example, a process, method, article, or apparatus that includes a list of features is not necessarily limited to the respective features, but may include other features not expressly listed or inherent to such a process, method, article, or apparatus.

[0024] As used herein, unless otherwise expressly stated, "or" means inclusive "or" rather than exclusive "or". For example, any of the following can satisfy condition A or B: A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and both A and B are true (or exist). The present application will be further described in detail below with reference to embodiments.

[0025] The present application will be further described in detail below with reference to the embodiments.

[0026] This invention discloses a polishing composition and polishing method for lithium tantalate or lithium niobate. The polishing composition includes phytate ions, silica abrasive, and water.

[0027] Phytate ions: can be obtained by dissolving phytic acid, sodium phytate or potassium phytate in water. The preferred concentration is between 0.2% and 2% by weight. If the concentration is too low, the effect of phytate on the removal rate of lithium tantalate or lithium niobate will not be obvious, and if the concentration is too high, there is a risk of gelation.

[0028] pH: The pH of the polishing composition needs to be adjusted using an alkali metal hydroxide. If an organic base is used for adjustment, the silica sol will gel. If an alkaline earth metal hydroxide is used, the alkaline earth metal ions may react with phytate ions to form a precipitate. Sodium hydroxide or potassium hydroxide is preferred as the alkali metal hydroxide. The pH is preferably between 8 and 11. If the pH is too low, the silica sol is prone to gelation, and if the pH is too high, the removal rate of lithium tantalate or lithium niobate will be too low.

[0029] Silica abrasives: Silica abrasives are dispersions of nano-sized silica particles in water, i.e., silica sol. Silica sol can be prepared by methods such as ion exchange, silica powder method, silane hydrolysis method, and precipitation method. Alternatively, it can be prepared by gas-phase method to produce nano-silica powder, which is then mechanically dispersed in water to form silica sol. The z-average particle size of the silica abrasive in the silica sol is measured by dynamic light scattering. The abrasive particle size of the silica sol is preferably not greater than 150 nm, and more preferably not greater than 120 nm. The particle size is preferably not less than 50 nm, and more preferably not less than 100 nm. If the silica abrasive particle size is too small, the removal rate of lithium tantalate or lithium niobate will be insufficient; if the particle size is too large, the colloid will be unstable, and the removal rate of lithium tantalate or lithium niobate will decrease. Silica abrasives can be a mixture of one or more abrasives with a z-average particle size between 50 nm and 150 nm.

[0030] Water: There are no special requirements for water. Tap water, distilled water, deionized water, or water purified by other methods can be used depending on the application.

[0031] Polishing method: The polishing solution described above is introduced between the surface of the lithium tantalate or lithium niobate to be polished and the polishing pad, allowing the surface to come into contact with the polishing pad and move relative to it. The polishing pad is preferably a medium-hardness polishing pad with a Shore hardness of 60-90C, and more preferably a polyurethane-impregnated nonwoven polishing pad with a Shore hardness of 80-90C. If the polishing pad hardness is too low, the removal rate will be low; if it is too high, there is a risk of scratching. The polishing pressure is preferably 100 g / cm². 2 Up to 400g / cm 2 Between these, the better one is at 150g / cm³. 2Up to 300g / cm 2 If the pressure is too low, the removal rate will be too low; if it is too high, the friction will be too great, resulting in abnormal noise and machine instability during the polishing process.

[0032] The polishing methods in the following examples and comparative cases are as follows: A single-sided polishing machine with a large disc diameter of 380 mm is used. The polishing pad is a polyurethane-impregnated non-woven fabric polishing pad with a Shore hardness of 85-88 C. The polishing pad has XY grooves, with each square approximately 10 mm x 10 mm, a groove width of approximately 2 mm, and a groove depth of approximately 0.8 mm. One 4-inch lithium tantalate or lithium niobate substrate is polished at a pressure of 191 g / cm³. 2 The large disc rotated at 100 rpm, the polishing fluid flow rate was 60 ml / min, the polishing time was 5 minutes, and the amount removed was measured using an electronic balance with an accuracy of 0.1 mg.

[0033] Example

[0034] Example 1

[0035] 20 g of a 50% phytic acid solution was mixed with 480 g of deionized water, and the pH was adjusted to 8.57 with potassium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 9.16, a phytate ion content of 1 wt%, and a silica abrasive content of 20 wt%. The polishing removed 27.2 mg of lithium tantalate. The polishing solution was placed in a 45°C oven for 30 days; the solution showed good fluidity and did not gel.

[0036] Example 2

[0037] A 50% phytic acid solution was adjusted to pH 8.5 with potassium hydroxide. 4g of this solution was added to 996g of a 40% solids silica sol containing silica abrasive with a z-average particle size of 50 nm as measured by dynamic light scattering. The resulting polishing solution had a pH of 9.76, a phytate ion content of 0.2 wt%, and a silica abrasive content of approximately 40 wt%. The polishing removed 25.9 mg of lithium tantalate. The polishing solution was then placed in a 45°C oven for 30 days; it exhibited good fluidity and did not gel.

[0038] Example 3

[0039] 20 g of a 50% phytic acid solution was mixed with 730 g of deionized water, and the pH was adjusted to 8.51 with potassium hydroxide. Then, 250 g of silica sol with a solid content of 40% and a z-average particle size of 150 nm as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 8.82, a phytate ion content of 1 wt%, and a silica abrasive content of 10 wt%. The polishing removed 19.6 mg of lithium tantalate. The polishing solution was placed in a 45°C oven for 30 days; the solution showed good fluidity and did not gel.

[0040] Example 4

[0041] 20 g of a 50% phytic acid solution was mixed with 480 g of deionized water, and the pH was adjusted to 12.5 with sodium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 120 nm as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 10.98, a phytate ion content of 1 wt%, and a silica abrasive content of 20 wt%. The polishing removed 24.7 mg of lithium tantalate. The polishing solution was placed in a 45°C oven for 30 days; the solution showed good fluidity and did not gel.

[0042] Example 5

[0043] 20 g of a 50% phytic acid solution was mixed with 480 g of deionized water, and the pH was adjusted to 12.5 with sodium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 120 nm as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 10.98, a phytate ion content of 1 wt%, and a silica abrasive content of 20 wt%. The polishing removed 37.3 mg of lithium niobate. The polishing solution was placed in a 45°C oven for 30 days; it showed good fluidity and did not gel.

[0044] Comparative Example

[0045] Comparative Example 1

[0046] 500g of deionized water was added to 500g of silica sol with a solid content of 40% and a z-average particle size of 100nm for silica abrasives as measured by dynamic light scattering. The pH was adjusted to 9.21 with nitric acid. The resulting polishing solution contained 20wt% silica abrasives. The weight of lithium tantalate removed by polishing was 17.4mg.

[0047] Comparative Example 2

[0048] 10 g of sodium gluconate was dissolved in 490 g of deionized water, and then 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 9.22, a sodium gluconate content of 1 wt%, and a silica abrasive content of 20 wt%. The weight of lithium tantalate removed by polishing was 21.0 mg.

[0049] Comparative Example 3

[0050] 20 g of a 50% (w / w) aqueous solution of aminotrimethylenephosphonic acid was added to 480 g of deionized water. The pH was adjusted to 8.55 with potassium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm (measured by dynamic light scattering) was added. The resulting polishing solution had a pH of 9.30, an aminotrimethylenephosphonic acid content of 1 wt%, and a silica abrasive content of 20 wt%. The polishing removed 28.1 mg of lithium tantalate. The polishing solution was then placed in a 45°C oven and allowed to gel for 7 days.

[0051] Comparative Example 4

[0052] 17 g of a 60% (w / w) aqueous solution of hydroxyethylidene diphosphonic acid was added to 483 g of deionized water. The pH was adjusted to 8.50 with potassium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm (measured by dynamic light scattering) was added. The resulting polishing solution had a pH of 9.15, a hydroxyethylidene diphosphonate content of 1 wt%, and a silica abrasive content of 20 wt%. The polishing removed 27.4 mg of lithium tantalate. The polishing solution was then placed in a 45°C oven and allowed to gel for 7 days.

[0053] Comparative Example 5

[0054] 10 g of ethylenediaminetetramethylenephosphonic acid (EDTA) was dissolved in 490 g of deionized water, and the pH was adjusted to 8.51 with potassium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm (measured by dynamic light scattering) was added. The resulting polishing solution had a pH of 9.23, an EDTA content of 1 wt%, and a silica abrasive content of 20 wt%. The polishing removed 26.4 mg of lithium tantalate. The polishing solution was then placed in a 45°C oven and allowed to gel within 7 days.

[0055] Comparative Example 6

[0056] 20 g of a 50% (w / w) aqueous solution of diethylenetriaminepentamethylenephosphonic acid was added to 480 g of deionized water. The pH was adjusted to 8.49 with potassium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm (measured by dynamic light scattering) was added. The resulting polishing solution had a pH of 9.09, a diethylenetriaminepentamethylenephosphonic acid (DTA) content of 1 wt%, and a silica abrasive content of 20 wt%. The polishing removed 27.1 mg of lithium tantalate. The polishing solution was then placed in a 45°C oven and allowed to gel for 7 days.

[0057] Comparative Example 7

[0058] 20 g of a 50% phytic acid solution was mixed with 448 g of deionized water, and the pH was adjusted to 8.50 with potassium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm (measured by dynamic light scattering) was added. The resulting polishing solution had a pH of 9.08. Finally, 32 g of a 31.5% hydrogen peroxide solution was added. At this point, the polishing solution contained 1 wt% phytate ions, 20 wt% silica abrasive, and 1 wt% hydrogen peroxide. The weight of lithium tantalate removed during polishing was 20.5 mg.

[0059] Comparative Example 8

[0060] 20 g of a 50% phytic acid solution was mixed with 480 g of deionized water, and the pH was adjusted to 8.49 with sodium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 25 nm as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 9.10, a phytate ion content of 1 wt%, and a silica abrasive content of 20 wt%. The weight of lithium tantalate removed by polishing was 14.3 mg.

[0061] Comparative Example 9

[0062] Dissolve 10 grams of sodium citrate in 490 grams of deionized water, then add 500 grams of silica sol with a solid content of 40% and a z-average particle size of 100 nanometers as measured by dynamic light scattering. Adjust the pH to 8.56 with nitric acid. Place the polishing solution in an oven at 45°C and allow it to gel for 1 day.

[0063] Comparative Example 10

[0064] 20 g of a 50% phytic acid solution was mixed with 480 g of deionized water, and the pH was adjusted to approximately 8.5 with tetramethylammonium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 9.24, a phytate ion content of 1 wt%, and a silica abrasive content of 20 wt%. The polishing solution was placed in an oven at 45°C and allowed to gel for 2 days.

[0065] Comparative Example 11

[0066] 20 g of a 50% phytic acid solution was mixed with 480 g of deionized water, and the pH was adjusted to approximately 8.5 with triethanolamine. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 8.54, a phytate ion content of 1 wt%, and a silica abrasive content of 20 wt%. The polishing solution was placed in a 45°C oven. After 4 days, gelation was visible at the bottom, and after 9 days, complete gelation was achieved.

[0067] Comparative Example 12

[0068] 20 g of a 50% phytic acid solution was mixed with 480 g of deionized water, and the pH was adjusted to approximately 8.5 with 1,1,3,3-tetramethylguanidine. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 9.17, a phytate ion content of 1 wt%, and a silica abrasive content of 20 wt%. The polishing solution was placed in an oven at 45°C and gelled after 2 days.

[0069] Comparative Example 13

[0070] 40 g of a 50% phytic acid solution was mixed with 460 g of deionized water, and the pH was adjusted to approximately 8.5 with sodium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm (measured by dynamic light scattering) was added. The resulting polishing solution had a pH of 8.94, a phytate ion content of 2 wt%, and a silica abrasive content of 20 wt%. The polishing solution was placed in a 45°C oven and gelled after 2 days. This example illustrates that the phytic acid concentration should be less than 2%.

[0071] Comparative Example 14

[0072] 20 g of a 50% phytic acid solution was mixed with 480 g of deionized water, and the pH was adjusted to approximately 5.5 with sodium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 5.89, a phytate ion content of 1 wt%, and a silica abrasive content of 20 wt%. The polishing solution was placed in an oven at 45°C and gelled after 1 day.

[0073] Comparative Example 15

[0074] 20 g of a 50% phytic acid solution was mixed with 480 g of deionized water, and the pH was adjusted to approximately 3.5 with sodium hydroxide. Then, 500 g of silica sol with a solid content of 40% and a z-average particle size of 100 nm as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 3.97, a phytate ion content of 1 wt%, and a silica abrasive content of 20 wt%. The polishing solution was placed in an oven at 45°C and gelled after 2 days.

[0075] Polishing Test Data Recording Sheet

[0076] Table 1. Component content and test data of Examples 1-4 and Comparative Examples 1-15

[0077]

[0078]

[0079] As can be seen from Example 1 and Comparative Example 1, phytate ions can significantly increase the polishing removal rate of lithium tantalate, and the polishing solution is colloidal and does not exhibit gelation after heating at 45°C for 30 days.

[0080] Comparative Example 2 reproduced the results in the prior art with patent publication number CN1782014A. As can be seen from Example 1 and Comparative Example 2, phytate can significantly increase the polishing removal rate of lithium tantalate than gluconate.

[0081] As can be seen from Example 1 and Comparative Examples 3-6, although various organophosphonic acids can increase the removal rate of lithium tantalate polishing, they will cause instability of silica sol and gelation. However, no gelation occurred when phytic acid was used as the polishing solution, indicating that phytic acid has little effect on the stability of silica sol.

[0082] As can be seen from Example 1 and Comparative Example 7, the removal rate of lithium tantalate actually decreases after adding oxidants such as hydrogen peroxide.

[0083] As shown in Comparative Example 8, when the particle size of the silica abrasive is too small, the removal rate of lithium tantalate will be significantly reduced.

[0084] Comparative Example 9 reproduced the results of the prior art with patent number JP6481589B2, demonstrating that the use of sodium citrate causes the polishing slurry to gel.

[0085] As shown in Comparative Examples 10-12, the polishing solution will gel when the pH is adjusted with an organic base.

[0086] As shown in Comparative Example 13, when the phytate ion concentration reaches 2%, the polishing solution will gel.

[0087] As can be seen from Comparative Examples 14-15, when the polishing solution is acidic, gelation will occur.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the present invention without departing from the scope of the present invention are within the scope of the present invention.

Claims

1. A polishing composition of lithium tantalate or lithium niobate characterized in that: The polishing composition comprises the following components: Abrasive containing 10-40% silica by weight; Phytate ions; The remainder is water; The phytate ions contain a weight percentage of not less than 0.2% and less than 2%, the polishing composition has a pH value of 8-11, the pH of the polishing composition is adjusted by alkali metal hydroxide, the silica abrasive is provided by silica sol, and the z-average particle size of the silica abrasive is in the range of 50-150 nm.

2. A polishing composition for lithium tantalate or lithium niobate according to claim 1, characterized by: The pH value of the polishing composition is adjusted by sodium hydroxide or potassium hydroxide.

3. The polishing composition of claim 1, wherein: The phytate ions are obtained by dissolving one or more of phytic acid, sodium phytate, and potassium phytate in water.

4. The polishing composition of claim 1, wherein: The silica abrasive accounts for 20% of the weight of the polishing composition.

5. A method of polishing lithium tantalate or lithium niobate characterized by: Includes the following steps: S1: Phytic acid or phytate is dissolved in water and dissociated to obtain phytate ions. The pH is adjusted to alkaline using an alkali metal hydroxide. Then, silica sol containing silica abrasive is added and stirred evenly to obtain a polishing composition. The pH of the polishing solution is 8-11, and the z-average particle size range of the silica abrasive is 50-150 nm. S2: Provide a lithium tantalate or lithium niobate surface to be polished, introduce the polishing composition described in S1 between the lithium tantalate or lithium niobate surface and the polishing surface of the polishing tool, and bring the lithium tantalate or lithium niobate surface into contact with and relative to the polishing surface of the polishing tool, wherein the relative movement is at 150 g / cm². 2 Up to 300g / cm 2 The polishing is carried out under high pressure.

6. The method of claim 5 wherein: In the polishing composition, the weight percentage of phytate ions is not less than 0.2% and less than 2%, the weight percentage of silica abrasive is 10-40%, the pH value of the polishing composition is 8-11, and the pH value of the polishing composition is adjusted by sodium hydroxide or potassium hydroxide.

7. The method of claim 5, wherein the polishing composition is applied to the lithium tantalate or lithium niobate substrate at a pressure of about 0.1 psi to about 5 psi. The phytate ions are obtained by dissolving one or more of phytic acid, sodium phytate, and potassium phytate in water.

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