JP7545106B2 - Polishing composition for oxide-based substrates containing hydrogen peroxide - Google Patents

Description

The present invention relates to a polishing composition for oxide-based substrates such as lithium tantalate and lithium niobate.

Lithium tantalate and lithium niobate have excellent piezoelectric, pyroelectric and electro-optical effects.
Mobile phones are equipped with elements that extract electrical signals of a specific frequency band using surface acoustic wave devices, and these use lithium tantalate ( _LiTaO3 ) or lithium niobate ( _LiNbO3 ) as the piezoelectric material. For example, a signal of a specific frequency is extracted by a surface wave generated by an electrical signal of a comb-shaped electrode (Inter Digital Transducer) formed on a piezoelectric substrate such as lithium tantalate or lithium niobate.

High-speed communications such as 5G require higher frequencies (3.4 to 3.6 GHz band), wider bandwidth, and higher Q (Quality Factor: signal sensitivity at resonant frequency).
For example, lithium tantalate or lithium niobate is formed on a substrate, and the lithium tantalate or lithium niobate is polished to form a thin film, thereby improving the characteristics of the surface acoustic wave device.
Lithium tantalate and lithium niobate are hard and chemically stable, so the polishing speed is generally slow. In order to thin the film to a thickness at which it can perform well, a cyclic supply method is used in which the polishing composition is repeatedly supplied and recovered, but maintaining the polishing performance is an issue, and low productivity is an issue.

The composition disclosed in Patent Document 1 contains water, colloidal silica, and a chelating agent, and may further contain an organic acid such as formic acid or acetic acid, or a peroxide such as hydrogen peroxide, for adjusting the pH.
Patent Document 2 discloses an abrasive such as lithium tantalate or lithium niobate that contains silica having an average particle size of 10 to 200 nm, an aliphatic polycarboxylic acid, and water.
Patent Document 3 describes a colloidal silica dispersion for CMP polishing, which contains an additive selected from the group consisting of an oxidizing agent, an acid, an amine, a chelating agent, a fluorine-containing compound, a corrosion inhibitor, a biological agent, a surfactant, and a buffering agent.

JP2003-188121 Patent Publication 2011-161570 Special table 2002-528903

The present invention relates to an abrasive that polishes oxide-based substrates having high hardness, such as lithium tantalate or lithium niobate, at a high polishing rate. A circulating supply system is used in which the polishing composition is repeatedly supplied and recovered to thin the substrate until it can perform the desired function. The present invention provides a polishing composition that has sustained polishing performance, in which the polishing rate is suppressed from decreasing even during long-term polishing and the polishing rate can be maintained close to the initial polishing rate even during long-term polishing, and a polishing method using the same.

A first aspect of the present invention is a polishing composition for oxide-based substrates, comprising silica particles, a chelating agent having an aminocarboxylic acid structure, hydrogen peroxide, and water, the polishing composition comprising 14 to 30 mass % of silica particles having an average primary particle size of 30 to 120 nm as measured by a nitrogen gas adsorption method, 8 to 130 mmol/L of a chelating agent having an aminocarboxylic acid structure, and 0.5 to 10 mass % of hydrogen peroxide, and having a pH of 4 to 7.5;
As a second aspect, the polishing composition according to the first aspect, wherein the average particle size of silica particles in the polishing composition is 70 to 200 nm as measured by a dynamic light scattering method.
As a third aspect, the polishing composition according to the first aspect or the second aspect, in which the chelating agent having an aminocarboxylic acid structure is ethylenediaminetetraacetic acid or a salt thereof.
As a fourth aspect, the polishing composition according to any one of the first to third aspects, further comprising an organic acid or a salt thereof;
As a fifth aspect, the polishing composition according to the fourth aspect, wherein the organic acid is a compound having a polyvalent carboxylic acid or a phosphoric acid structure.
As a sixth aspect, the polishing composition according to the fifth aspect, wherein the polyvalent carboxylic acid is citric acid or oxalic acid.
As a seventh aspect, the polishing composition according to the fifth aspect, wherein the compound having a phosphoric acid structure is phosphoric acid, hydroxyethylidenediphosphonic acid, nitrilotris(methylenephosphonic acid), phosphonobutanetricarboxylic acid, or a salt thereof;
As an eighth aspect, the polishing composition according to any one of the first to seventh aspects, further containing ammonia or an alkali metal hydroxide as a base.
As a ninth aspect, the polishing composition according to any one of the first to eighth aspects, wherein the oxide-based substrate is a lithium tantalate substrate or a lithium niobate substrate, or a composite substrate in which a part or an entirety of one side of a substrate is bonded to lithium tantalate or lithium niobate;
As a tenth aspect, a method for producing the polishing composition according to any one of the first to ninth aspects, comprising a step of mixing an acidic or alkaline aqueous silica sol having silica particles having an average primary particle diameter of 30 to 120 nm as measured by a nitrogen gas adsorption method, a chelating agent, and hydrogen peroxide solution simultaneously or in multiple stages;
As an eleventh aspect, the method includes the following steps (A) and (B):
Step (A): A step (A) of producing an aqueous silica dispersion containing an acidic or alkaline aqueous silica sol having silica particles having an average primary particle diameter of 30 to 120 nm as measured by a nitrogen gas adsorption method, and a chelating agent;
A method for producing a polishing composition according to the tenth aspect, comprising the steps of: (B) adding an aqueous hydrogen peroxide solution to an aqueous silica dispersion;
As a twelfth aspect, the method for producing a polishing composition according to the tenth or eleventh aspect, further comprising adding a base composed of ammonium or an alkali metal hydroxide together with the addition of the chelating agent;
As a thirteenth aspect, there is provided a method for polishing an oxide-based substrate by using the polishing composition according to any one of the first to ninth aspects, in which a polishing rate in a seventh and eighth polishing steps (last 2/8 steps) is 50 to 80% of a polishing rate in a first polishing step (first 1/8 step) of first to eighth polishing steps obtained by dividing a total polishing step into eight equal parts;
As a fourteenth aspect, there is provided the polishing method according to the thirteenth aspect, in which an aqueous hydrogen peroxide solution is added immediately before polishing so that the ratio of hydrogen peroxide in the polishing composition is 0.5 to 10 mass %. As a fifteenth aspect, there is provided the polishing method according to the thirteenth aspect, in which an aqueous hydrogen peroxide solution is added during the polishing step so that the ratio of the hydrogen peroxide in the polishing composition is 0.5 to 10 mass %.

Oxide materials such as lithium tantalate and lithium niobate are considered to be useful as substrate materials for surface acoustic wave devices. These oxide materials require precision polishing, and it is necessary to polish them without causing surface irregularities on the workpiece or atomic-level defects in the compounds.
Since oxides such as lithium tantalate and lithium niobate have high hardness, a circulating supply system is used in which the polishing composition is repeatedly supplied and recovered in order to thin it down until it can perform the desired function. However, when the polishing composition is used for long periods of polishing, the polishing rate decreases, posing a problem of reduced productivity.

The present invention has discovered that a combination of a chelating agent having an aminocarboxylic acid structure and hydrogen peroxide can improve the initial removal rate of the oxide-based material and suppress a decrease in the removal rate during the entire polishing process.
Hydrogen peroxide can be contained in the initial polishing composition, or hydrogen peroxide can be added as aqueous hydrogen peroxide during the polishing process to maintain the polishing rate within a specified range while circulating the polishing composition.
In addition, the polishing composition of the present invention is expected to have improved effects by further adding an organic acid to the chelating agent having an aminocarboxylic acid structure.

The present invention is a polishing composition for oxide-based substrates that contains silica particles, a chelating agent having an aminocarboxylic acid structure, hydrogen peroxide, and water. The polishing composition contains 14 to 30 mass % silica particles having an average primary particle size of 40 to 120 nm as measured by nitrogen gas adsorption method, 8 to 130 mmol/L of a chelating agent having an aminocarboxylic acid structure, and 0.5 to 10 mass % of hydrogen peroxide, and has a pH of 4 to 7.5. The remainder of the polishing composition other than the solid matter is water.

The average primary particle size of the silica particles can be expressed as a sphere-equivalent particle size calculated from the surface area by the nitrogen gas adsorption method (BET method), and can be in the range of 30 to 120 nm, 40 to 120 nm, or 40 to 80 nm. The silica particles can be used in the polishing composition in the range of 14 to 30 mass %, or 15 to 25 mass %.
The secondary particle diameter of the silica particles used in the present invention can be measured by dynamic light scattering, and the average particle diameter is 70 to 200 nm.

The above silica particles can be prepared as a polishing composition based on an aqueous silica sol. For example, it can be obtained by growing particles of activated silicic acid obtained by cation exchange of water glass under heating. For example, the product name Snowtex manufactured by Nissan Chemical Industries, Ltd. can be used as the silica sol.
A polishing composition can be prepared by adding an alkali component, a water-soluble resin, and a chelate resin to this silica sol.

The alkaline component may be sodium hydroxide, potassium hydroxide, ammonia, primary ammonium hydroxide, secondary ammonium hydroxide, tertiary ammonium hydroxide, quaternary ammonium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, or potassium hydrogen carbonate.
The polishing composition containing these silica sols can be adjusted to a pH of 4 to 7.5, or 4 to 7, or 6 to 7, by adding an organic acid or an alkali component. By using a polishing composition in the neutral range, a high polishing accuracy can be obtained for the surface to be polished.

The chelating agent having an amino carboxylic acid structure used in the present invention is a compound having an amino group and a carboxyl group in the molecule, and may have a structure having a plurality of amino carboxylic acid moieties in the molecule. The amino carboxylic acid structure may be an iminodiacetic acid structure. For example, ethylenediaminetetraacetic acid and its salts having a plurality of iminodiacetic acid structures may be exemplified. Ethylenediaminetetraacetic acid may be used as an alkali metal salt such as a sodium salt or a potassium salt, an ammonium salt, or an amine salt in order to improve solubility. These chelating agents having an amino carboxylic acid structure may be used in the polishing composition in a range of 8 to 130 mmol/L, 10 to 80 mmol/L, or 10 to 40 mmol/L.

In the present invention, the chelating agent having an aminocarboxylic acid structure may further contain an organic acid.
The organic acid may be a compound having a polycarboxylic acid or phosphoric acid structure.
These compounds having a polyvalent carboxylic acid or phosphoric acid structure have the same function as a chelating agent as a chelating agent having an aminocarboxylic acid structure.

The compound having a polyvalent carboxylic acid or phosphoric acid structure can be used in the polishing composition in an amount within the range of 8 to 130 mmol/L, or 10 to 80 mmol/L, or 10 to 40 mmol/L.
The polyvalent carboxylic acid is preferably a saturated aliphatic carboxylic acid having two or more valences, and more preferably a di- to tetra-valent carboxylic acid. These carboxylic acids may have a hydroxyl group as a functional group in addition to a carboxyl group.
Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, and maleic acid.
Examples of hydroxycarboxylic acids include lactic acid, malic acid, and citric acid.
These polycarboxylic acids can be used in the form of alkali metal salts such as sodium salts and potassium salts, ammonium salts, or amine salts.

The compound having a phosphate structure is preferably a compound having one or more phosphate groups in the molecule, such as a compound having 2 to 4 phosphate groups. These compounds having a phosphate group may also have a hydroxyl group.
Examples of the compound having the phosphoric acid structure include phosphoric acid, hydroxyethylidene diphosphonic acid, nitrilotris(methylene phosphonic acid), phosphonobutane tricarboxylic acid, etc. These phosphoric acid compounds can also be used as phosphates. As the phosphates, water-soluble phosphates such as sodium salts and potassium salts are preferred.
The above chelating agent is available from Chelesto Co., Ltd.

In the present invention, the pH can be adjusted to a range of 4 to 7.5, or 4 to 7. The pH can be adjusted by adding ammonia or an alkali metal hydroxide as a base. The alkali metal hydroxide that can be used includes sodium hydroxide, potassium hydroxide, etc.
The solubility of the above-mentioned chelating agents and organic acids is improved by converting them into salts, so that the above-mentioned bases can be added for neutralization and pH adjustment to convert them into chelate salts or organic acid salts.

The hydrogen peroxide used in the present invention can be used in the polishing composition in the range of 0.5 to 10% by mass. By adjusting the hydrogen peroxide content within this range, a high removal rate can be obtained.
The polishing composition can be prepared by adding hydrogen peroxide in an amount of 35 mass % or less, 30 mass % or less, or 28 mass % or less.
Hydrogen peroxide can be added to the polishing composition in advance to prepare the polishing composition, or can be added to the polishing composition just before polishing to prepare it. When polishing is performed by a circulating supply method in which the polishing composition is repeatedly supplied and recovered, the polishing rate can be maintained or improved by increasing the concentration of hydrogen peroxide in the recovered polishing composition within a predetermined concentration range.

A method for producing the polishing composition includes a process of simultaneously mixing a chelating agent and aqueous hydrogen peroxide with an acidic or alkaline aqueous silica sol containing the above-mentioned silica particles having an average primary particle diameter of 30 to 120 nm as measured by a nitrogen gas adsorption method.
In addition, when mixing is performed in a plurality of stages (steps), there is a production method including steps (A) and (B), in which step (A) is a step of producing an aqueous silica dispersion by adding a chelating agent to an acidic or alkaline aqueous silica sol having silica particles with an average primary particle size of 30 to 120 nm as measured by a nitrogen gas adsorption method, and step (B) is a production method of a polishing composition by adding a hydrogen peroxide solution to the aqueous silica dispersion.
Furthermore, there is also a method for producing a polishing composition in which a base made of ammonium or alkali metal hydroxide is added in addition to the chelating agent.

In the present invention, the oxide-based substrate contains lithium tantalate or lithium niobate on at least one surface, i.e., the oxide-based substrate is a lithium tantalate substrate or a lithium niobate substrate, or a composite substrate in which a part or the whole of one surface of the substrate is bonded to lithium tantalate or lithium niobate.
The substrate may be made of lithium tantalate or lithium niobate alone, or may have lithium tantalate or lithium niobate bonded to the entire surface or part of one side of the substrate.
Examples of the substrate to be bonded to the lithium tantalate or lithium niobate include silicon, sapphire, glass, quartz, crystal, and ceramics.
The lithium tantalate or lithium niobate of the present invention is preferably a single crystal, and preferably does not substantially contain metallic tantalum or metallic niobium.
The polishing composition of the present invention can maintain a high polishing rate throughout the entire polishing process. When the entire polishing process is 8/8, the polishing rate during the last 2/8 steps is 50 to 80%, 50 to 70%, or 50 to 60% of the polishing rate during the first 1/8 steps of the polishing composition set in the polishing device.

In such a long-term polishing process, the polishing can be performed at a high polishing rate throughout the entire polishing process without replacing the polishing composition, so that even substrates with high hardness can be polished efficiently. In addition, since hydrogen peroxide is a component that easily decomposes, hydrogen peroxide can be added during the polishing process to maintain the desired concentration.
In the present invention, by containing hydrogen peroxide, a high polishing rate can be obtained even if the content of the chelating agent is relatively low. Therefore, the electrolyte concentration derived from the chelating agent is also low, and gelation of silica particles in the polishing composition can be reduced. The polishing composition of the present invention has a conductivity of 20,000 μS/cm or less, or 15,000 μS/cm or less, or 10,000 μS/cm or less, or 8,000 μS/cm or less, and can be set to, for example, 3,000 to 20,000 μS/cm, or 3,000 to 15,000 μS/cm, or 3,000 to 10,000 μS/cm, or 3,000 to 8,000 μS/cm.

pH: Measured using a pH meter (manufactured by DKK-Toa Corporation).
Average primary particle size by nitrogen adsorption method (BET method): The aqueous silica sol was dried at 300° C. to obtain a silica solid, which was then pulverized and further dried to obtain a silica powder. The average primary particle size was calculated based on the specific surface area measured using a specific surface area measurement device, Monosorb (manufactured by Quantachrome Instruments).
Average particle size measured by dynamic light scattering (DLS average particle size): Measured using a dynamic light scattering particle size measuring device Zetasizer Nano (manufactured by the Malvern Division of Spectris Co., Ltd.). The aqueous silica sol to be measured was diluted in advance with an aqueous sodium chloride solution (concentration 0.15% by mass) to a concentration at which the scattering intensity measured by the device was 300 to 400 kcps.

(Preparation of a composition containing silica particles and a chelating agent)
Example 1
A polishing composition containing silica particles and a chelating agent was prepared by adding 10% by mass of colloidal silica (silica particles based on silica sol, manufactured by Nissan Chemical Industries, Ltd.) having an average primary particle diameter of 60 nm as determined by nitrogen adsorption method and an average secondary particle diameter of 98 nm as determined by dynamic light scattering method, 11 mmol/L of ethylenediaminetetraacetic acid (manufactured by Chelest Co., Ltd.) and 12 mmol/L of citric acid (manufactured by Kanto Chemical Industries, Ltd.) as chelating agents, and the remainder being water and ammonia, a basic compound, in an amount that makes the composition pH 6.5. A 30% by mass concentration of hydrogen peroxide water was added to the above polishing composition as a polishing accelerator so that the amount of the added hydrogen peroxide water was 1.8% by mass in the polishing composition, thereby preparing the polishing composition of Example 1. Similarly, each polishing composition was prepared as shown in the table below.

In the table, ethylenediaminetetraacetic acid is represented by EDTA, ammonia by _NH3 , and sodium hydroxide by NaOH. BET indicates the average primary particle size (nm) by the BET method, and DLS indicates the average particle size (nm) by the dynamic light scattering method. mmol/L indicates millimoles/liter. In the table below, the amount of each additive indicates the blending ratio of the polishing composition of the present invention.
[Table 1]
Table 1-1
------------------------------------------------------------------Polishing composition (Colloidal silica) (Chelating agent 1) (Chelating agent 2)
BET DLS Content Type Content Organic Acid Content
Mass % mmol/L mmol/L Example 1 60 98 18 EDTA 11 Citric acid 12
Example 2 60 98 18 EDTA 11 Citric acid 12
Example 3 60 98 18 EDTA 11 Citric acid 12
Example 4 60 98 18 EDTA 11 Citric acid 12
Example 5 60 98 17 EDTA 11 Citric acid 12
Example 6 60 98 18 EDTA 11 Citric acid 12
Example 7 60 98 18 EDTA 11 Citric acid 12
Example 8 60 98 18 EDTA 11 -- --
Example 9 60 98 18 EDTA 23 -- --
Example 10 60 98 18 EDTA 46 -- --
Example 11 60 98 18 EDTA 77 -- --
Example 12 60 98 18 EDTA 115 -- --
Example 13 60 98 27 EDTA 12 Citric acid 13
Example 14 44 77 18 EDTA 11 Citric acid 12
Example 15 79 134 18 EDTA 11 Citric acid 12
Example 16 110 190 18 EDTA 11 Citric acid 12
Example 17 60 98 18 EDTA 11 Citric acid 12
Example 18 60 98 18 EDTA 11 Citric acid 12
Example 19 60 98 18 EDTA 11 Citric acid 12
Example 20 60 98 20 EDTA 11 -- --
Example 21 60 98 20 EDTA 11 Oxalic acid 39
------------------------------------------------------------------In the table above, (--) indicates that the material is not contained.

[Table 2]
Table 1-2
------------------------------------------------------------------Polishing composition (Colloidal silica) (Chelating agent 1) (Chelating agent 2)
BET DLS Content Type Content Organic Acid Content
Mass % mmol/L mmol/L
Comparative Example 1 60 98 19 EDTA 11 Citric acid 12
Comparative Example 2 60 98 10 EDTA 11 Citric acid 12
Comparative Example 3 60 98 19 EDTA 11 Citric acid 12
Comparative Example 4 60 98 19 EDTA 2.7 -- --
Comparative Example 5 60 98 18 EDTA 5.4 -- --
Comparative Example 6 60 98 18 EDTA 153 -- --
Comparative Example 7 60 98 10 EDTA 11 Citric acid 11
Comparative Example 8 22 34 18 EDTA 11 Citric acid 12
Comparative Example 9 60 98 18 EDTA 11 Citric acid 12
Comparative Example 10 60 98 18 EDTA 11 Citric acid 12
Comparative Example 11 60 98 18 EDTA 11 Citric acid 12
Comparative Example 12 60 98 18 -- -- Citric acid 12
Comparative Example 13 60 98 20 EDTA 11 -- --
Comparative Example 14 60 98 20 EDTA 11 Oxalic acid 39
------------------------------------------------------------------In the table above, (--) indicates that the material is not contained.

[Table 3]
Table 1-3
------------------------------------------------------------------Polishing composition Basic compound pH Hydrogen peroxide Electrical conductivity
Concentration (%) (μS/cm)
Example 1 Ammonia 6.4 1.8 5820
Example 2 Ammonia 6.5 0.5 6090
Example 3 Ammonia 6.4 1.8 5830
Example 4 Ammonia 6.4 3.0 5670
Example 5 Ammonia 6.2 4.0 5360
Example 6 Ammonia 6.1 10.0 5540
Example 7 NaOH 6.4 1.8 4680
Example 8 Ammonia 6.4 1.8 3390
Example 9 Ammonia 6.4 1.8 5650
Example 10 Ammonia 6.6 1.8 9920
Example 11 Ammonia 6.3 1.8 14740
Example 12 Ammonia 6.5 1.8 20200
Example 13 Ammonia 6.4 1.8 6370
Example 14 Ammonia 6.8 1.8 6220
Example 15 Ammonia 6.5 1.8 5600
Example 16 Ammonia 6.4 1.8 5540
Example 17 Ammonia 4.0 1.8 3610
Example 18 Ammonia 5.0 1.8 4350
Example 19 Ammonia 7.0 1.8 6020
Example 20 Ammonia 6.2 1.8 3610
Example 21 Ammonia 6.5 1.8 8260
――――――――――――――――――――――――――――――――――――

[Table 4]
Table 1-4
------------------------------------------------------------------Polishing composition Basic compound pH Hydrogen peroxide Electrical conductivity
Concentration (%) (μS/cm)
Comparative Example 1 Ammonia 6.5 -- 6170
Comparative Example 2 Ammonia 6.5 -- 5600
Comparative Example 3 Ammonia 6.5 -- 6180
Comparative Example 4 Ammonia 6.5 1.8 1523
Comparative Example 5 Ammonia 6.4 1.8 2220
Comparative Example 6 Ammonia 6.4 1.8 24600
Comparative Example 7 Ammonia 6.4 1.8 5460
Comparative Example 8 Ammonia 6.9 1.8 5170
Comparative Example 9 Ammonia 8.0 1.8 6340
Comparative Example 10 Ammonia 8.9 1.8 6870
Comparative Example 11 Ammonia 6.1 15.0 5440
Comparative Example 12 Ammonia 6.4 1.8 3720
Comparative Example 13 Ammonia 6.6 -- 2970
Comparative Example 14 Ammonia 6.5 -- 8480
------------------------------------------------------------------In the table above, (--) indicates that the material is not contained.

Commercially available lithium tantalate wafers were polished in the following manner.
Polishing Conditions (1)
Polishing machine: Hamai Sangyo double-sided polishing machine 6BN
Pressure: 100g/ ^cm2
Upper platen rotation speed: 0 rpm
Lower platen rotation speed: 40 rpm
Polishing pad: Nitta Haas SUBA600
Amount of polishing composition used: 2.5L
Supply rate of polishing composition: 1.0 L/min
Polishing time: 8 hours Wafer: 42° Y-Cut lithium tantalate, diameter 100 mm
Number of wafers: 3 Polishing conditions (2)
Polishing machine: Hamai Sangyo double-sided polishing machine 6BN
Pressure: 100g/ ^cm2
Upper platen rotation speed: 0 rpm
Lower platen rotation speed: 40 rpm
Polishing pad: Nitta Haas SUBA600
Amount of polishing composition used: 4.0 L
Supply rate of polishing composition: 1.0 L/min
Polishing time: 1 hour Wafer: 42° Y-Cut lithium tantalate, diameter 100 mm
Number of wafers: 3

(Method of Measuring Polishing Rate)
The polishing rate was calculated from the average weight loss of three wafers before and after polishing, assuming a wafer density of 7.4 g/ ^cm2 . Under the above polishing condition (1), the weight of the wafer was measured before and after polishing as well as at 1 hour and 6 hours after polishing, and the initial polishing rate (polishing rate during the first 1/8 steps of the total polishing time) was calculated from the weight loss of the wafer from before polishing to 1 hour of polishing, and the final polishing rate (polishing rate during the last 2/8 steps of the total polishing time) was calculated from the weight loss of the wafer from 6 hours of polishing to after polishing.
Table 5
Table 2-1
------------------------------------------------------------------Polishing composition Polishing conditions Initial polishing rate Final polishing rate (Final polishing rate/
(μm/hour) (μm/hour) Initial polishing rate)
(%)
Example 1 1 2.616 1.350 51.6
Example 2 2 2.626 -- --
Example 3 2 2.769 -- --
Example 4 2 2.489 -- --
Example 5 2 2.383 -- --
Example 6 2 2.299 -- --
Example 7 2 2.793 -- --
Example 8 2 2.870 -- --
Example 9 2 2.672 -- --
Example 10 2 2.533 -- --
Example 11 2 2.558 -- --
Example 12 2 2.455 -- --
Example 13 2 2.257 -- --
Example 14 2 2.300 -- --
Example 15 2 2.473 -- --
Example 16 2 2.307 -- --
Example 17 2 2.532 -- --
Example 18 2 2.691 -- --
Example 19 2 2.727 -- --
Example 20 1 2.922 1.660 56.8
Example 21 1 2.601 1.513 58.2
-----------------------------------------------------------------In the table above, (--) indicates not measured.

Table 6
Table 2-2
------------------------------------------------------------------Polishing composition Polishing conditions Initial polishing rate Final polishing rate (Final polishing rate/
(μm/hour) (μm/hour) Initial polishing rate)
(%)
Comparative Example 1 1 2.087 0.956 45.8
Comparative Example 2 1 2.077 0.816 39.3
Comparative Example 3 2 2.081 -- --
Comparative Example 4 2 1.887 -- --
Comparative Example 5 2 2.065 -- --
Comparative Example 6 2 2.027 -- --
Comparative Example 7 2 2.041 -- --
Comparative Example 8 2 0.261 -- --
Comparative Example 9 2 1.512 -- --
Comparative Example 10 2 0.951 -- --
Comparative Example 11 2 2.048 -- --
Comparative Example 12 2 2.051 -- --
Comparative Example 13 1 2.334 1.073 46.0
Comparative Example 14 1 2.102 0.891 42.4
-----------------------------------------------------------------In the table above, (--) indicates not measured.

The polishing composition of the present invention exhibits a high polishing rate, and as shown by the ratio of (initial polishing rate)/(final polishing rate) during the entire polishing process, the initial polishing rate can be maintained throughout the polishing process. Therefore, when polishing a substrate with high hardness, such as an oxide-based substrate, there is no need to replace the polishing composition, and polishing can be performed efficiently. In addition, the polishing composition can be regenerated by adding hydrogen peroxide water to the polishing composition.

The present invention is a polishing composition capable of polishing oxide-based substrates having high hardness, such as lithium tantalate or lithium niobate, at a high polishing rate, and is capable of maintaining a polishing rate close to the initial polishing rate even during long-term polishing. The present invention can be applied to a polishing composition and a polishing method using the same.

Claims (14)

A polishing composition for oxide-based substrates, comprising silica particles, a chelating agent having an aminocarboxylic acid structure, hydrogen peroxide, and water, the polishing composition comprising 14 to 30 mass% of silica particles having an average primary particle size of 30 to 120 nm as measured by a nitrogen gas adsorption method, 8 to 130 mmol/L of a chelating agent having an aminocarboxylic acid structure, and 0.5 to 10 mass% of hydrogen peroxide, and having a pH of 4 to 7.5;
The above polishing composition , wherein the oxide-based substrate is a lithium tantalate substrate or a lithium niobate substrate, or a composite substrate in which a part or the whole of one side of a substrate is bonded to lithium tantalate or lithium niobate. The polishing composition according to claim 1, wherein the average particle size of the silica particles in the polishing composition is 70 to 200 nm as measured by dynamic light scattering. The polishing composition according to claim 1 or 2, wherein the chelating agent having an aminocarboxylic acid structure is ethylenediaminetetraacetic acid or a salt thereof. The polishing composition according to any one of claims 1 to 3, further comprising an organic acid or a salt thereof. The polishing composition according to claim 4, wherein the organic acid is a compound having a polycarboxylic acid or phosphoric acid structure. The polishing composition according to claim 5, wherein the polycarboxylic acid is citric acid or oxalic acid. The polishing composition according to claim 5, wherein the compound having a phosphoric acid structure is phosphoric acid, hydroxyethylidene diphosphonic acid, nitrilotris(methylene phosphonic acid), phosphonobutane tricarboxylic acid, or a salt thereof. 8. The method according to claim 1, further comprising the step of:
2. The polishing composition according to claim 1 . 9. A method for producing a polishing composition according to any one of claims 1 to 8, comprising a step of mixing an acidic or alkaline aqueous silica sol having silica particles having an average primary particle diameter of 30 to 120 nm as measured by a nitrogen gas adsorption method, a chelating agent, and hydrogen peroxide solution simultaneously or in multiple stages. The following steps (A) and (B):
Step (A): A step (A) of producing an aqueous silica dispersion containing an acidic or alkaline aqueous silica sol having silica particles having an average primary particle diameter of 30 to 120 nm as measured by a nitrogen gas adsorption method, and a chelating agent;
The method for producing the polishing composition according to claim 9 , further comprising: step (B): adding an aqueous hydrogen peroxide solution to the aqueous silica dispersion. 11. The method for producing a polishing composition according to claim 9 or 10 , wherein a base made of ammonium or alkali metal hydroxide is added together with the addition of the chelating agent. A method for polishing an oxide-based substrate by using the polishing composition according to any one of claims 1 to 8 , wherein when polishing is performed without replacing the polishing composition, the polishing rate during the seventh and eighth polishing steps (the last 2/8 steps) is 50 to 80% of the polishing rate during the first polishing step (the first 1/8 step) of the first to eighth polishing steps obtained by dividing the entire polishing step into eight equal parts. 13. The polishing method according to claim 12 , wherein immediately before polishing, aqueous hydrogen peroxide is added to the polishing composition so that the ratio of hydrogen peroxide in the polishing composition is 0.5 to 10 mass %. 13. The polishing method according to claim 12 , wherein hydrogen peroxide solution is added during the polishing step so that the ratio of the hydrogen peroxide in the polishing composition is 0.5 to 10 mass %.