Lithium tantalate or lithium niobate polishing composition and polishing method

Abstract

The invention relates to the technical field of polishing, in particular to a polishing composition and a polishing method of lithium tantalate or lithium niobate. Phytate ions; and the balance of water. The pH value of the polishing composition is 8-11, the pH value of the polishing composition is adjusted by alkali metal hydroxide, the phytate radical ions are obtained by dissolving a mixture of one or more of phytic acid, sodium phytate and potassium phytate in water, and the polishing method comprises the step of polishing lithium tantalate or lithium niobate by using the polishing composition. The lithium tantalate and lithium niobate polishing solution has the effects of further improving the polishing removal rate of lithium tantalate and lithium niobate and the colloid stability of the polishing solution.

Description

Technical Field

[0001] The present invention relates to the technical field of polishing, in particular to a polishing composition and a polishing method of lithium tantalate or lithium niobate. Background Art

[0002] Lithium tantalate and lithium niobate are widely used in piezoelectric and optoelectronic fields such as RF filters, second harmonic generators, electro-optical Q-switched elements, and laser frequency multipliers due to their excellent nonlinear optical effects, piezoelectric effects, and photorefractive effects. Especially in the field of RF 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 undergo crystal growth, cutting, grinding, and polishing. The final polishing step is crucial for removing the damaged layer and achieving the desired surface flatness (Ra < 0.5 nm). Tantalum and niobium are both in the VB group, and the atoms of lithium tantalate and lithium niobate are similar in their crystal structures. Consequently, their chemical and material properties are similar, and their polishing performance is also similar. When polished using the same process and polishing fluid, the removal rates of lithium tantalate and lithium niobate are on the same order of magnitude, and their Ra values ​​are similar. More specifically, the removal rate of lithium niobate is slightly higher than that of lithium tantalate, ranging from approximately 1.2 to 2 times.

[0004] When silica sol is used as the abrasive alone without any 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 a pH of 4 is approximately six times that at a pH of 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, conventional silica sols are unstable in the acidic range, especially at pH 4, and are prone to gelling.

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

[0006] In order to further improve the polishing removal rate of lithium tantalate and lithium niobate and the colloidal stability of the polishing liquid, the present invention provides a polishing composition and a polishing method of lithium tantalate or lithium niobate to address 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 for lithium tantalate or lithium niobate, comprising the following components: phytate ions; silicon dioxide abrasive; and the balance being water. The pH value of the polishing composition is 8-11, and the pH of the polishing composition is adjusted by an alkali metal hydroxide.

[0009] Preferably, the polishing composition comprises the following components: phytate ions; 10-40% by weight of silica abrasive; and the balance is water; the weight percentage of the phytate ions is not less than 0.2% and less than 2%, 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.

[0010] Preferably, the phytate ion is 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 obtained from 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% by weight of the polishing composition.

[0013] In a second aspect, the present invention provides a polishing method for lithium tantalate or lithium niobate, which adopts the following technical solution:

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

[0015] S1: dissolving phytic acid or phytate in water to dissociate to obtain phytate ions, adjusting the pH to alkaline using an alkali metal hydroxide, then adding silica abrasive and stirring uniformly to obtain a polishing composition, wherein the pH of the polishing solution is 8-11;

[0016] S2: providing a lithium tantalate or lithium niobate surface to be polished, introducing the polishing composition described in S1 between the lithium tantalate or lithium niobate surface and the polishing surface of the polishing tool, and making 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 the phytate ion is not less than 0.2% and less than 2%, the weight percentage of the 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 ion is 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 obtained from 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% by weight of the polishing composition.

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

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

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

[0024] As used herein, unless otherwise expressly stated, "or" refers to an inclusive "or" rather than an exclusive "or." For example, any of the following conditions may 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 the following examples.

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

[0026] The invention discloses a polishing composition of lithium tantalate or lithium niobate and a polishing method. The polishing composition comprises phytate ions, silicon dioxide abrasive and water.

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

[0028] pH: The pH of the polishing composition must be adjusted with an alkali metal hydroxide. Using an organic base for adjustment can cause the silica sol to gel, while using an alkaline earth metal hydroxide can cause the alkaline earth metal ions to react with phytate ions to form a precipitate. Sodium hydroxide or potassium hydroxide are preferred alkali metal hydroxides. The pH is preferably between 8 and 11. A low pH can easily cause the silica sol to gel, while a high pH can slow the removal rate of lithium tantalate or lithium niobate.

[0029] Silica abrasive: Silica abrasive is a dispersion of nanoscale silica particles in water, also known as silica sol. Silica sol can be prepared by methods such as ion exchange, silica powder, silane hydrolysis, and precipitation. It can also be prepared by a vapor phase method, where nano-silica powder is prepared and 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 in the silica sol can be no larger than 150 nm, preferably no larger than 120 nm. The silica abrasive particle size can be no smaller than 50 nm, preferably no smaller 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. The silica abrasive can be mixed with one or more abrasives having a z-average particle size between 50 nm and 150 nm.

[0030] Water: There is no special requirement for water. Tap water, distilled water, deionized water, or water purified by other methods can be used according to the application.

[0031] Polishing method: Introduce the above-mentioned polishing liquid between the surface of lithium tantalate or lithium niobate to be polished and the polishing pad, and make the surface to be polished contact with the polishing pad and move relative to each other. The polishing pad is preferably a medium hardness polishing pad with a Shore hardness of 60-90C, and more preferably a polyurethane impregnated non-woven polishing pad with a Shore hardness of 80-90C. If the hardness of the polishing pad is too low, the removal rate will be low, and if it is too high, there is a risk of scratching. The polishing pressure is preferably 100g / cm 2 Up to 400g / cm 2 Between, the better one is 150g / cm 2Up to 300g / cm 2 If the pressure is too low, the removal rate will be too low, while if the pressure is too high, the friction will be too high, resulting in abnormal noise during the polishing process and instability of the machine.

[0032] The polishing method for the following examples and comparative examples is as follows: polishing is performed using a single-sided polishing machine with a 380mm diameter plate and a polyurethane-impregnated non-woven polishing pad with a Shore hardness of 85-88C. The polishing pad has XY grooves, each grid is approximately 10mm x 10mm, the intervals are approximately 2mm wide, and the groove depth is approximately 0.8mm. Each polishing is performed on a 4-inch lithium tantalate or lithium niobate substrate at a pressure of 191g / cm 2 , the disk rotation speed is 100 rpm, the polishing liquid flow rate is 60 ml / min, the polishing time is 5 minutes, and the removal amount is measured using an electronic balance with an accuracy of 0.1 mg.

[0033] Example

[0034] Example 1

[0035] 20 grams of a 50% by weight phytic acid solution was mixed with 480 grams of deionized water, the pH adjusted to 8.57 with potassium hydroxide, and 500 grams of a 40% solids silica sol with a z-average particle size of 100 nanometers as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 9.16, a phytate ion content of 1% by weight, and a silica abrasive content of 20% by weight. 27.2 mg of lithium tantalate was removed during polishing. The polishing solution was placed in a 45°C oven for 30 days and exhibited good fluidity and no gelling.

[0036] Example 2

[0037] A 50% by weight phytic acid solution was adjusted to a pH of 8.5 with potassium hydroxide. Four grams of the solution was then added to 996 grams of a 40% solids silica sol with a z-average particle size of 50 nanometers as measured by dynamic light scattering. The resulting polishing solution had a pH of 9.76, a phytate ion content of 0.2% by weight, and a silica abrasive content of approximately 40% by weight. 25.9 mg of lithium tantalate was removed during polishing. The polishing solution was placed in a 45°C oven for 30 days and exhibited good fluidity and no gelling.

[0038] Example 3

[0039] 20 grams of a 50% by weight phytic acid solution was mixed with 730 grams of deionized water, the pH adjusted to 8.51 with potassium hydroxide, and 250 grams of a 40% solids silica sol with a z-average particle size of 150 nanometers as measured by dynamic light scattering was added. The resulting polishing solution had a pH of 8.82, a phytate ion content of 1% by weight, and a silica abrasive content of 10% by weight. 19.6 mg of lithium tantalate was removed by polishing. The polishing solution was placed in a 45°C oven for 30 days and showed good fluidity and no gelling.

[0040] Example 4

[0041] 20 grams of a 50% by weight phytic acid solution was mixed with 480 grams of deionized water, the pH adjusted to 12.5 with sodium hydroxide, and 500 grams of a 40% solids silica sol with a z-average particle size of 120 nanometers (as measured by dynamic light scattering) was added. The resulting polishing solution had a pH of 10.98, a phytate ion content of 1% by weight, and a silica abrasive content of 20% by weight. 24.7 mg of lithium tantalate was removed by polishing. The polishing solution was placed in a 45°C oven for 30 days and exhibited good fluidity and no gelling.

[0042] Example 5

[0043] 20 grams of a 50% phytic acid solution was mixed with 480 grams of deionized water, the pH adjusted to 12.5 with sodium hydroxide, and 500 grams of a 40% solids silica sol with a z-average particle size of 120 nanometers (as measured by dynamic light scattering) was added. The resulting polishing solution had a pH of 10.98, a phytate ion content of 1% by weight, and a silica abrasive content of 20% by weight. 37.3 mg of lithium niobate was removed by polishing. The polishing solution was placed in a 45°C oven for 30 days and exhibited good fluidity and no gelling.

[0044] Comparative Example

[0045] Comparative Example 1

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

[0047] Comparative Example 2

[0048] 10 g of sodium gluconate was dissolved in 490 g of deionized water, and 500 g of a silica sol with a solids 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%. 21.0 mg of lithium tantalate was removed by polishing.

[0049] Comparative Example 3

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

[0051] Comparative Example 4

[0052] 17 grams of a 60% by weight aqueous solution of hydroxyethylene diphosphonic acid was added to 483 grams of deionized water. The pH was adjusted to 8.50 with potassium hydroxide. Then, 500 grams of a 40% solids silica sol with a z-average particle size of 100 nanometers (as measured by dynamic light scattering) was added. The resulting polishing solution had a pH of 9.15, a hydroxyethylene diphosphonate content of 1% by weight, and a silica abrasive content of 20% by weight. 27.4 mg of lithium tantalate was removed by polishing. The polishing solution was placed in a 45°C oven and gelled within 7 days.

[0053] Comparative Example 5

[0054] Dissolve 10 g of EDTA in 490 g of deionized water, adjust the pH to 8.51 with potassium hydroxide, and then add 500 g of a 40% solids silica sol containing a z-average particle size of 100 nm as measured by dynamic light scattering. The resulting polishing solution has a pH of 9.23, an EDTA content of 1 wt%, and a silica abrasive content of 20 wt%. Polishing removes 26.4 mg of lithium tantalate. Place the polishing solution in a 45°C oven and allow it to gel within 7 days.

[0055] Comparative Example 6

[0056] 20 grams of a 50% by weight aqueous solution of diethylenetriamine penta (methylenephosphonic acid) was added to 480 grams of deionized water. The pH was adjusted to 8.49 with potassium hydroxide. 500 grams of a 40% solids silica sol with a z-average particle size of 100 nanometers (as measured by dynamic light scattering) was then added. The resulting polishing solution had a pH of 9.09, a diethylenetriamine penta (methylenephosphonic acid) content of 1% by weight, and a silica abrasive content of 20% by weight. 27.1 mg of lithium tantalate was removed by polishing. The polishing solution was placed in a 45°C oven and allowed to gel within 7 days.

[0057] Comparative Example 7

[0058] 20 grams of a 50% phytic acid solution was mixed with 448 grams of deionized water, and the pH was adjusted to 8.50 with potassium hydroxide. 500 grams of a 40% solids silica sol with a z-average particle size of 100 nanometers (as measured by dynamic light scattering) was then added. The resulting polishing solution had a pH of 9.08. 32 grams of a 31.5% hydrogen peroxide solution was then added. The polishing solution now contained 1% phytic acid ions, 20% silica abrasive, and 1% hydrogen peroxide. 20.5 mg of lithium tantalate was removed by polishing.

[0059] Comparative Example 8

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

[0061] Comparative Example 9

[0062] Dissolve 10 grams of sodium citrate in 490 grams of deionized water. Add 500 grams of silica sol with a solids 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 a 45°C oven and allow it to gel for one day.

[0063] Comparative Example 10

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

[0065] Comparative Example 11

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

[0067] Comparative Example 12

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

[0069] Comparative Example 13

[0070] Mix 40 grams of a 50% phytic acid solution with 460 grams of deionized water, adjust the pH to approximately 8.5 with sodium hydroxide, and then add 500 grams of a 40% solids silica sol containing a z-average particle size of 100 nanometers (as measured by dynamic light scattering). The resulting polishing solution has a pH of 8.94, a phytic acid ion content of 2% by weight, and a silica abrasive content of 20% by weight. Place the polishing solution in a 45°C oven and it gels after two days. This example illustrates the need for a phytic acid concentration of less than 2%.

[0071] Comparative Example 14

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

[0073] Comparative Example 15

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

[0075] Polishing test data record sheet

[0076] Table 1 Ingredient contents and test data of Examples 1-4 and Comparative Examples 1-15

[0077]

[0078]

[0079] From Example 1 and Comparative Example 1, it can be seen that phytate ions can significantly increase the polishing removal rate of lithium tantalate, and the polishing liquid is colloidally stable, and no gelation occurs when heated at 45° C. for 30 days.

[0080] Comparative Example 2 reproduces the results of the prior art with Patent Publication No. CN1782014A. From Example 1 and Comparative Example 2, it can be seen that phytate can significantly increase the polishing removal rate of lithium tantalate compared to gluconate.

[0081] It can be seen from Example 1 and Comparative Examples 3-6 that although various organic phosphonic acids can increase the removal rate of lithium tantalate polishing, they will cause the silica sol to be unstable and gel to appear. However, the polishing solution using phytic acid does not gel, indicating that phytic acid has little effect on the stability of the silica sol.

[0082] It can be seen from Example 1 and Comparative Example 7 that the removal rate of lithium tantalate is reduced after adding an oxidant such as hydrogen peroxide.

[0083] It can be seen from Comparative Example 8 that when the particle size of the silicon dioxide abrasive is too small, the removal rate of lithium tantalate will be significantly reduced.

[0084] Comparative Example 9 reproduces the results of the prior art patent No. JP6481589B2, indicating that the use of sodium citrate will cause the polishing liquid to gel.

[0085] Comparative Examples 10-12 show that gel will appear in the polishing liquid when the pH is adjusted with an organic base.

[0086] It can be seen from Comparative Example 13 that when the phytic acid ion concentration reaches 2%, gel will appear in the polishing liquid.

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

[0088] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention is disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes by using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technology of the present invention are all within the scope of the technical solution of the present invention without departing from the content of the technical solution of the present invention.

Claims

1. A polishing composition for lithium tantalate or lithium niobate, characterized in that: The polishing composition comprises the following components: Silica abrasive; Phytate ion; The balance is water; The pH value of the polishing composition is 8-11, and the pH of the polishing composition is adjusted by an alkali metal hydroxide.

2. The polishing composition of lithium tantalate or lithium niobate according to claim 1, characterized in that: The polishing composition comprises the following components: 10-40% by weight of silica abrasive; Phytate ion; The balance is water; The weight percentage of the phytate ion is not less than 0.2% and less than 2%, 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.

3. The polishing composition of lithium tantalate or lithium niobate according to claim 1, characterized in that: The phytate ion is obtained by dissolving one or a mixture of several of phytic acid, sodium phytate and potassium phytate in water.

4. The polishing composition of lithium tantalate or lithium niobate according to claim 1, characterized in that: The silicon dioxide abrasive is obtained from silica sol, and the z-average particle size of the silicon dioxide abrasive is in the range of 50-150 nm.

5. The polishing composition of lithium tantalate or lithium niobate according to claim 1, characterized in that: The silica abrasive accounts for 20% by weight of the polishing composition.

6. A method for polishing lithium tantalate or lithium niobate, characterized in that: The following steps are involved: S1: dissolving phytic acid or phytate in water to dissociate to obtain phytate ions, adjusting the pH to alkaline using an alkali metal hydroxide, then adding silica abrasive and stirring uniformly to obtain a polishing composition, wherein the pH of the polishing solution is 8-11; S2: providing a lithium tantalate or lithium niobate surface to be polished, introducing the polishing composition described in S1 between the lithium tantalate or lithium niobate surface and the polishing surface of the polishing tool, and making the lithium tantalate or lithium niobate surface contact and move relative to the polishing surface of the polishing tool.

7. The polishing method of lithium tantalate or lithium niobate according to claim 6, characterized in that: In the polishing composition, the weight percentage of the phytate ion is not less than 0.2% and less than 2%, the weight percentage of the 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.

8. The polishing method of lithium tantalate or lithium niobate according to claim 6, characterized in that: The phytate ion is obtained by dissolving one or a mixture of several of phytic acid, sodium phytate and potassium phytate in water.

9. The polishing method of lithium tantalate or lithium niobate according to claim 6, characterized in that: The silicon dioxide abrasive is obtained from silica sol, and the z-average particle size of the silicon dioxide abrasive is in the range of 50-150 nm.

10. The polishing method of lithium tantalate or lithium niobate according to claim 6, characterized in that: The silica abrasive accounts for 20% by weight of the polishing composition.

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