JP7659703B2 - Abrasive Slurry - Google Patents

Description

The present invention relates to an abrasive slurry.

As semiconductor elements become increasingly dense and precise, the CMP (Chemical Mechanical Polishing) method was developed as a technique for flattening the surface of a thin film formed by a method such as CVD (Chemical Vapor Deposition) during the semiconductor wafer manufacturing process.

The performance of the CMP method is greatly influenced by the selection of the abrasive slurry, the selection of the polishing pad, and the like. In particular, the selection of the abrasive slurry is a factor that greatly affects the performance of the CMP method. The abrasive slurry used in the CMP method contains abrasive particles such as silicon dioxide (SiO ₂ ) and cerium (IV) oxide (CeO ₂ ). For example, Patent Document 1 discloses an abrasive composition containing cerium oxide fine particles as abrasive grains. Here, the abrasive composition disclosed in Patent Document 1 contains cerium oxide fine particles (whose average particle size (D50) is 0.01 μm to 1.0 μm) with a purity of 99 mass% or more, a chelating agent, a dispersant having a polyacrylic acid group or a polymethacrylic acid group, and elements such as Mg, Al, K, and C (whose content is 30 ppm or less).

International Publication No. 2001/080296

However, the polishing composition disclosed in Patent Document 1 had a problem in that the polishing rate decreased over time because the cerium oxide particles contained as abrasive grains were very fine. In addition, the cost of managing the polishing material increased in order to maintain the polishing rate in the polishing process.

In view of the above problems, the present invention aims to provide an abrasive slurry that can suppress the decrease in polishing rate due to changes over time, even if the abrasive grain size is fine.

The abrasive slurry of the present invention, which has been made to solve the above problems, comprises cerium oxide-based abrasive grains, magnesium hydroxide-based abrasive grains, a dispersant, and a solvent, and is characterized in that the average abrasive grain size of the cerium oxide-based abrasive grains and the magnesium hydroxide-based abrasive grains is 0.01 μm or more and 0.5 μm or less.
The abrasive slurry of the present invention contains cerium oxide-based abrasive grains, magnesium hydroxide-based abrasive grains, a dispersant, and a solvent, and therefore can suppress a decrease in the polishing rate due to changes over time even if the average abrasive grain size of the cerium oxide-based abrasive grains and the magnesium hydroxide-based abrasive grains is as fine as 0.01 μm or more and 0.5 μm or less.

As the cerium oxide-based abrasive grains, cerium oxide abrasive grains are preferred, specifically cerium oxide (IV) and cerium oxide (III), with cerium oxide (IV) being preferred from the viewpoint of material stability. The cerium oxide-based abrasive grains may be a mixture of one or more types of cerium oxide-based particles. The cerium oxide-based abrasive grains may contain other elements such as F (fluorine), Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. In particular, they may contain other elements such as F (fluorine), La, Pr, and Nd.

The abrasive slurry of the present invention contains magnesium hydroxide-based abrasive grains in addition to the above-mentioned cerium oxide-based abrasive grains. The magnesium hydroxide-based abrasive grains are presumed to function as an additive since they adsorb the polishing waste (fine powder after polishing) of the workpiece to be polished to the cerium oxide-based abrasive grains and suppress the deterioration of the polishing performance. As the magnesium hydroxide-based abrasive grains, for example, magnesium hydroxide abrasive grains are preferable. In addition, the magnesium hydroxide-based abrasive grains may be a mixture of one or more types of magnesium hydroxide-based particles. In addition, the magnesium hydroxide-based abrasive grains may contain other elements such as Ca, Si, Fe, Al, S, and B. In particular, they may contain other elements such as Ca and Si.

The abrasive slurry of the present invention contains the cerium oxide-based abrasive grains and magnesium hydroxide-based abrasive grains described above, as well as a solvent and a dispersant, which will be described later. Since fine cerium oxide-based abrasive grains tend to aggregate, the inclusion of a dispersant improves dispersibility in the solvent.

In the abrasive slurry of the present invention, the average particle size of the cerium oxide-based abrasive grains and magnesium hydroxide-based abrasive grains is preferably 0.01 μm or more and 0.5 μm or less, from the viewpoint of suppressing a decrease in the polishing rate and reducing the surface roughness Ra of the polished surface. Furthermore, the average particle size of the cerium oxide-based abrasive grains and magnesium hydroxide-based abrasive grains is more preferably 0.05 μm or more and 0.2 μm or less.

Here, the average particle size of the cerium oxide-based abrasive grains and magnesium hydroxide-based abrasive grains is the particle size (D50) measured by particle size distribution measurement using dynamic light scattering method, and can be measured as follows.

The dynamic light scattering method is a method in which a solution such as a suspension solution is irradiated with light such as a laser beam to measure the light scattering intensity from a group of particles undergoing Brownian motion, and the particle size and distribution are determined from the temporal variation of the intensity. Specifically, the particle size distribution is evaluated using a zeta potential, particle size, and molecular weight measurement system (manufactured by Otsuka Electronics Co., Ltd.: ELSZ-2000ZS) in accordance with JIS Z 8828:2019 "Particle size analysis - dynamic light scattering method". The measurement sample is a sample diluted with pure water so that the solid content concentration in the abrasive slurry of the present invention is 0.005% by mass to 0.1% by mass. The solid content concentration can be calculated as follows. First, 5 g of the abrasive slurry of the present invention is collected and heated at 180°C for 60 minutes in an air atmosphere, and the mass (Xg) of the obtained solid content is measured. Then, the solid content concentration can be calculated by calculating Xg (mass of solid content) ÷ 5 g (mass of the collected abrasive slurry of the present invention) × 100. Immediately before measurement, the measurement sample is filtered through a filter with a particle capture performance of 11 μm or more, and ultrasonically treated for 3 minutes in an ultrasonic cleaner (VS-100III, manufactured by AS ONE Corporation). Furthermore, the liquid temperature of the measurement sample is adjusted to 25° C. The particle size (D50) refers to the median size (D50) which is the particle size showing the 50% integrated value of the integrated distribution curve.

Furthermore, in terms of achieving the objectives of the present application, it is preferable for the average particle size of the cerium oxide-based abrasive to be 0.01 μm or more and 0.5 μm or less, and it may also be 0.05 μm or more and 0.2 μm or less.

In addition, the average particle size of the magnesium hydroxide-based abrasive grains is preferably 0.01 μm or more and 0.5 μm or less in terms of achieving the objectives of the present application, and may be 0.05 μm or more and 0.2 μm or less.

Furthermore, the abrasive slurry of the present invention contains ZrO2 and Al2O3, which are shavings of the media used in the paint shaker and bead mill, since a paint shaker and a bead mill are used in the process of grinding the cerium oxide abrasive _grains and _the magnesium hydroxide abrasive grains in the manufacturing method of the abrasive slurry _of the present invention described later. _The content of _ZrO2 and _Al2O3 in the abrasive slurry of the present invention is not so large as to affect the polishing performance of the abrasive slurry of the present invention.

The abrasive slurry of the present invention is characterized in that it contains a solvent, and the solvent contains water.
The abrasive slurry of the present invention has high dispersibility in water, so pure water can be used as the solvent. In addition to pure water, water-soluble organic solvents such as alcohols and ketones, or mixtures thereof are preferable in terms of sufficiently increasing the polishing rate, and water is more preferable. The content of the solvent is preferably 60% by mass or more and 99.9% by mass or less, and more preferably 80% by mass or more and 90% by mass or less, when the abrasive slurry of the present invention is taken as 100% by mass. Typically, the content of the solvent may be 98% by mass or less, 97% by mass or less, or 95% by mass or less, when the abrasive slurry of the present invention is taken as 100% by mass.

The abrasive slurry of the present invention is characterized in that it contains a dispersant, and the dispersant contains at least one selected from the group consisting of organic acid alkali metal salts, phosphoric acids, and polymer dispersants.
The abrasive slurry of the present invention contains a dispersant, and the dispersant contains one or more selected from the group consisting of alkali metal salts of organic acids, phosphoric acids, and polymer dispersants, which can suppress aggregation of the cerium oxide-based abrasive grains.

The organic acid alkali metal salt preferably contains one or more selected from sodium citrate, sodium gluconate, and sodium tartrate. Examples of sodium citrate include monosodium citrate, disodium citrate, and trisodium citrate. Examples of sodium tartrate include monosodium tartrate and disodium tartrate. Sodium tartrate may be in the L-form, D-form, meso-form, or a mixture thereof. The organic acid alkali metal salt may be a hydrate.

Furthermore, it is preferable that the organic acid alkali metal salt contained in the abrasive slurry of the present invention is measured by high performance liquid chromatography. Using high performance liquid chromatography, the type and weight of the organic acid alkali metal salt can be measured by a known method. In addition, the organic acid alkali metal salt contained in the abrasive slurry of the present invention can be separated and measured.

Examples of phosphoric acids include phosphoric acid, condensed phosphoric acid, and alkali metal salts thereof. Here, examples of the alkali metal salts include one or more phosphoric acids selected from sodium phosphate, sodium hexametaphosphate, sodium pyrophosphate, sodium tetrapolyphosphate, and sodium ultrapolyphosphate.

Furthermore, it is preferable that the phosphoric acids contained in the abrasive slurry of the present invention are measured by high performance liquid chromatography. In the high performance liquid chromatography, the type and weight of phosphoric acids can be measured by a known method by using a non-suppressor method anion analysis column. For example, an example of a non-suppressor method anion analysis column is Shodex non-suppressor method anion analysis column IC I-524A (manufactured by Shoko Science Co., Ltd.), and by using this non-suppressor method anion analysis column, the phosphoric acids contained in the abrasive slurry of the present invention can be separated and measured.

Examples of the polymer dispersant include one or more water-soluble organic polymers selected from polyacrylic acid, polycarboxylic acid, polycarboxylate salts, and copolymers thereof. The polymer dispersant is particularly preferably a polyacrylate salt, and more preferably an ammonium polyacrylate salt.

The abrasive slurry of the present invention is further characterized in that, when the abrasive slurry is 100% by mass, the content of the cerium oxide-based abrasive grains is 0.5% by mass or more and 40% by mass or less, and the content of the magnesium hydroxide-based abrasive grains is 0.005% by mass or more and 20% by mass or less.

The content of the cerium oxide-based abrasive grains in the abrasive slurry of the present invention is preferably 0.5% by mass or more and 40% by mass or less from the viewpoint of realizing a good polishing rate. The content of the cerium oxide-based abrasive grains is more preferably 3.0% by mass or more and 35.0% by mass or less, even more preferably 4.0% by mass or more and 30.0% by mass or less, particularly preferably 5.0% by mass or more and 25.0% by mass or less, and most preferably 15.0% by mass or more and 25.0% by mass or less. Typically, the content of the cerium oxide-based abrasive grains in the abrasive slurry of the present invention may be 40% by mass or less, 38% by mass or less, or 36% by mass or less. The content of the cerium oxide-based abrasive grains in the abrasive slurry of the present invention is the total content of the total rare earth oxide (TREO), rare earth oxide, and F (fluorine) in the abrasive slurry of the present invention.

In addition, it is preferable that the content of magnesium hydroxide-based abrasive grains in the abrasive slurry of the present invention is 0.005% by mass or more and 20% by mass or less from the viewpoint of suppressing the decrease in the polishing rate. In addition, the content of magnesium hydroxide-based abrasive grains is more preferably 0.05% by mass or more and 5% by mass or less, even more preferably 0.1% by mass or more and 5% by mass or less, and particularly preferably 0.5% by mass or more and 3% by mass or less. Typically, the content of magnesium hydroxide-based abrasive grains in the abrasive slurry of the present invention may be 20% by mass or less, 18% by mass or less, or 16% by mass or less. The content of magnesium hydroxide-based abrasive grains in the abrasive slurry of the present invention is the Mg content in the abrasive slurry of the present invention.

Here, the total rare earth oxide (TREO) and rare earth oxide content is measured using an ICP-OES (inductively coupled plasma optical emission spectroscopy) device or an ICP-MS (inductively coupled plasma mass spectroscopy) device, and the F (fluorine) content is measured by the fluoride ion electrode method. Furthermore, the Mg content in the magnesium hydroxide-based abrasive grains is measured using an ICP-OES device or an ICP-MS device.

Specifically, 100 ml of the abrasive slurry of the present invention is placed in a glass beaker and dried by heating at 120°C for 24 hours to obtain a dried abrasive of the present invention. The dried abrasive of the present invention is used to measure the content of each component. The total rare earth oxide (TREO) content is measured by the oxalate precipitation-calcination-gravimetric method (units: solid: mass%, liquid: g/L). As a pretreatment, the dried abrasive of the present invention is dissolved in nitric acid, perchloric acid, and hydrogen peroxide, and boiled to prepare a measurement sample. Furthermore, if the measurement target is a liquid, it is not necessary to dissolve it in nitric acid or the like, and it may be boiled as is.

In addition, the F (fluorine) content can be calculated by turning the solid (abrasive) to be measured into a solution by alkali melting and hot water extraction, and measuring the F concentration in the solution using the fluoride ion electrode method, thereby calculating the F content (mass%) in the solid.

Furthermore, the Mg content can be determined as follows. Nitric acid, perchloric acid, and hydrogen peroxide are added to the dried abrasive of the present invention, which is then decomposed by heating to form a solution, and the Mg concentration can be measured using an ICP-OES device. The magnesium hydroxide content added can be estimated by multiplying this by the hydroxide coefficient. The hydroxide coefficient is Mg(OH) ₂ /Mg={24.3+(16.0+1.01)×2}/24.3≈2.40.

Furthermore, it is preferable that the content of the dispersant in the abrasive slurry of the present invention is 0.001% by mass or more and 15% by mass or less from the viewpoint of improving dispersibility. Moreover, the content of the dispersant is more preferably 0.001% by mass or more and 10% by mass or less, even more preferably 0.005% by mass or more and 5% by mass or less, and particularly preferably 0.5% by mass or more and 3% by mass or less. Typically, the content of the dispersant in the abrasive slurry of the present invention may be 15% by mass or less, 13% by mass or less, or 11% by mass or less.

Here, the content of dispersant in the abrasive slurry of the present invention is measured by gel permeation chromatography (GPC), liquid chromatography (LC), or liquid chromatography-mass spectrometry (LC-MS).

In this specification, the respective contents of cerium oxide-based abrasive grains, magnesium hydroxide-based abrasive grains, and dispersant in the abrasive slurry of the present invention are the respective contents in the abrasive slurry before polishing begins, unless otherwise specified.

The abrasive slurry of the present invention is characterized in that the weight ratio of the magnesium hydroxide abrasive grains to the cerium oxide abrasive grains is 1.25×10 ⁻⁴ or more and 40 or less.
It is preferable that the weight ratio of the magnesium hydroxide abrasive grains to the cerium oxide abrasive grains contained in the abrasive slurry of the present invention is 1.25×10 ⁻⁴ or more and 40 or less, from the viewpoint of suppressing a decrease in the polishing rate.

Furthermore, it is more preferable that the weight ratio of the weight of the magnesium hydroxide-based abrasive grains to the weight of the cerium oxide-based abrasive grains is 0.001 or more and 1 or less, and it is even more preferable that the weight ratio is 0.01 or more and 0.1 or less.

Here, the weight of the cerium oxide-based abrasive grains in the abrasive slurry of the present invention is the total content of total rare earth oxides (TREO), rare earth oxides, and F (fluorine) as described above. The weight of the magnesium hydroxide-based abrasive grains in the abrasive slurry of the present invention is the Mg hydroxide content as described above. This allows the weight ratio of the weight of the magnesium hydroxide-based abrasive grains to the weight of the cerium oxide-based abrasive grains to be determined. In addition, when Mg is contained in the cerium oxide-based abrasive grains by SEM-EDX analysis of the cerium oxide-based abrasive grains, the average weight ratio of Mg to Ce in 20 particles of cerium oxide-based abrasive grains is calculated from the results of semi-quantitative analysis. The weight of the magnesium hydroxide-based abrasive grains can be calculated by subtracting the weight of Mg contained in the cerium oxide-based abrasive grains from the Mg content contained in the entire abrasive slurry of the present invention.

In addition, the abrasive slurry of the present invention is characterized in that, when the cerium oxide-based abrasive grains are taken as 100% by mass, the Ce content is 100% by mass or less in terms of _CeO2 , the La content is 40% by _{mass or less in terms of La2O3 ,} the F content is 10% by mass or less in terms of F, the Pr content is 10% _by mass or less in terms of _Pr6O11 , and the Nd content is 10% _by mass or less in terms of _Nd2O3 .
The cerium oxide-based abrasive grains used as the abrasive grains are preferably such that the higher the purity of the cerium oxide, the higher the polishing rate. On the other hand, when the cerium oxide particles contain impurities, it is also preferable in terms of improving the polishing rate that the ratio of rare earth elements other than cerium as the impurities is as low as possible. When the ratio of lanthanum (La) and praseodymium (Pr) among the rare earth elements other than cerium is low, the polishing rate is further improved.

The Ce content in the cerium oxide-based abrasive grains of the present invention is preferably 100% by mass or less in terms of _CeO2 conversion, from the viewpoint of realizing a good polishing rate. Moreover, the Ce content is more preferably 50% by mass or more and 100% by mass or less, even more preferably 60% by mass or more and 100% by mass or less, particularly preferably 70% by mass or more and 100% by mass or less, more particularly preferably 80% by mass or more and 100% by mass or less, and particularly preferably 90% by mass or more and 100% by mass or less. Typically, the Ce content may be 100% by mass or less, 98% by mass or less, or 96% by mass or less.

The La content in the cerium oxide- _based abrasive grains of the present invention may be 40% by mass or less in terms of _La2O3 . The La content may be 0% by mass or more and 40% by mass or less, 0.1% by mass or more and 40% by mass or less, or 20% by mass or more and 40% by mass or less. Typically, the La content may be 40% by mass or less, 38% by mass or less, or 36% by mass or less.

The F content in the cerium oxide-based abrasive grains of the present invention may be 10% by mass or less, calculated as F. The F content may be 0% by mass or more and 10% by mass or less, or 2% by mass or more and 8% by mass or less. Typically, the F content may be 10% by mass or less, 8% by mass or less, or 6% by mass or less.

The Pr content in the cerium oxide-based abrasive grains of the present invention may be 10% by mass or less in terms of Pr ₆ O _11. The Pr content may be 0% by mass or more and 10% by mass or less, 0.1% by mass or more and 10% by mass or less, or 2% by mass or more and 8% by mass or less. Typically, the Pr content may be 10% by mass or less, 8% by mass or less, or 6% by mass or less.

The Nd content in the cerium oxide- _based abrasive grains of the present invention may be 10% by mass or less in terms of _Nd2O3 . The Nd content may be 0% by mass or more and 10% by mass or less, 0.1% by mass or more and 10% by mass or less, or 0.1% by mass or more and 5% by mass or less. Typically, the Nd content may be 10% by mass or less, 8% by mass or less, or 6% by mass or less.

The content of each element in the cerium oxide abrasive grains of the present invention can be determined as follows. Specifically, CeO ₂ /TREO can be calculated by dissolving the measurement sample obtained by the above-mentioned total rare earth oxide (TREO) measurement with perchloric acid and hydrogen peroxide, and measuring it by ICP-OES method. Similarly, the contents of La ₂ O ₃ /TREO, Pr ₆ O ₁₁ /TREO, and Nd ₂ O ₃ /TREO can be calculated.

Furthermore, the abrasive slurry of the present invention may contain any additive other than the above-mentioned cerium oxide-based abrasive grains, magnesium hydroxide-based abrasive grains, dispersant, and solvent. Here, the optional additives include dispersants, pH adjusters, viscosity adjusters, chelating agents, oxidizing agents, surfactants, and rust inhibitors. The content of the optional additives is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, when the abrasive slurry of the present invention is taken as 100% by mass. Typically, the content of the optional additives may be 10% by mass or less, 8% by mass or less, or 6% by mass or less.

The polishing method for polishing an object to be polished using the above-mentioned abrasive slurry of the present invention is described below.

The polishing method includes supplying the abrasive slurry of the present invention to a polishing pad, contacting the polished surface of the object to be polished with the polishing pad, and polishing by the relative movement between the two. Here, the method may be a method of pouring the abrasive slurry of the present invention, or a method of circulating the abrasive slurry of the present invention, in which the abrasive slurry of the present invention supplied to the polishing pad and used for polishing is recovered, and the recovered abrasive slurry of the present invention is supplied to the polishing pad again by repeatedly performing the operation. Since the abrasive slurry of the present invention can be circulated and repeatedly polished to the object to be polished, the amount of use can be reduced. Here, the polishing pad can be, for example, a pad made of nonwoven fabric that has been used conventionally, a pad made by impregnating it with resin such as polyurethane or epoxy, and a suede material. The polishing pressure is preferably 5 kPa or more and 1.0 x 10 ² kPa or less, particularly 5 kPa or more and 5.0 x 10 kPa or less, in terms of the polishing force and ease of handling of the polishing jig. The supply rate of the abrasive slurry is preferably 10 mL/min or more and 2000 mL/min or less, and more preferably 50 mL/min or more and 800 mL/min or less.

Examples of the material to be polished with the abrasive slurry of the present invention include glass, quartz, silicon oxide, silicon (such as silicon wafers), and high-hardness materials with a Mohs hardness of 8 or more. Furthermore, the abrasive slurry of the present invention is expected to perform chemical mechanical polishing (CMP) due to the chemical reaction of the material to be polished caused by cerium oxide. In addition, by adding an oxidizing agent such as potassium permanganate or hydrogen peroxide to the abrasive slurry of the present invention, a CMP process that accelerates the chemical reaction more effectively is possible. The material to be polished in the CMP process is, for example, a high-hardness material with a Mohs hardness of 8 or more. Here, Mohs hardness is a numerical value of hardness based on how a standard material is scratched, and can be measured by a conventional method using a Mohs hardness meter. Standard materials are designated on the Mohs hardness scale from 1 to 10, in order from softest to softest, and specific standard materials are talc with a Mohs hardness of 1, gypsum with a Mohs hardness of 2, calcite with a Mohs hardness of 3, fluorite with a Mohs hardness of 4, apatite with a Mohs hardness of 5, orthoclase with a Mohs hardness of 6, quartz with a Mohs hardness of 7, topaz with a Mohs hardness of 9, corundum with a Mohs hardness of 9, and diamond with a Mohs hardness of 10. High hardness materials with a Mohs hardness of 8 or more include, for example, silicon carbide (Mohs hardness of about 9), gallium nitride (Mohs hardness of about 9), diamond, etc.

In addition, the object to be polished with the abrasive slurry of the present invention is preferably a silicon wafer having a silicon oxide layer on the surface, and may be a multi-layer structure or a composite material made by compounding a plurality of materials. In particular, in the case of silicon, the abrasive slurry of the present invention can be used in the formation of an STI (shallow trench isolation) structure, the planarization of a premetal insulating material or an interlayer insulating material, the formation of a plug or embedded metal wiring, etc., in the manufacturing process of a semiconductor element having a substrate (wafer).

Next, a method for producing the above-mentioned abrasive slurry of the present invention will be described below. Examples of the method for producing the abrasive slurry of the present invention include a method for producing the slurry by wet grinding and a method for producing the slurry by dry grinding.

In the manufacturing method by wet grinding or the manufacturing method by dry grinding described later, the particle size of the raw material cerium oxide (abrasive grains, _CeO2 ) or magnesium hydroxide (additive, abrasive grains, Mg(OH) ₂ ) used as the raw material is the particle size at a cumulative volumetric fraction of 50% (D50) measured by a laser diffraction/scattering particle size distribution measurement method. Specifically, a measurement sample is prepared by diluting the raw material with water so that the concentration of the raw material becomes about 0.01%. Then, the particle size at a cumulative volumetric fraction of 50% (D50) is measured using a laser diffraction/scattering particle size distribution measurement device (MT3300EXII manufactured by Microtrackbell Co., Ltd.).

First, the method for producing the abrasive slurry of the present invention by wet grinding will be described below.

Pure water, cerium oxide (abrasive grains, CeO ₂ ), magnesium hydroxide (additive, abrasive grains, Mg(OH) ₂ ), and a dispersant (e.g., trisodium citrate) are placed in a container, and the container is set in a paint shaker (60 Hz) and rotated at high speed to turn the mixture into a slurry. Note that a bead mill may be used instead of the paint shaker.

Beads (zirconia, φ0.1 mm) are placed in the container and the slurried mixture is wet-pulverized to pulverize the cerium oxide in the mixture.

The mixture containing the mixed and ground cerium oxide in the container is filtered using a filter to separate it from the beads and collect the slurry.

The solids concentration in the collected supernatant, i.e., the concentration of cerium oxide-based abrasive grains, is then measured using a heated moisture meter, and pure water is added to reach a predetermined concentration, and the abrasive slurry of the present invention is obtained by mixing.

Next, the method for producing the abrasive slurry of the present invention by dry grinding will be described below.

Cerium oxide (abrasive grains, CeO ₂ ) and beads (zirconia, φ0.4 mm) are placed in a container, the container is set on a paint shaker (60 Hz), and the container is rotated at high speed to dry-pulverize the cerium oxide.

The mixture containing the dry-ground cerium oxide in the container is separated from the beads using a filter, and the mixture containing the dry-ground cerium oxide is collected.

Then, pure water, dry-ground cerium oxide (abrasive grains, CeO ₂ ), magnesium hydroxide (additive, abrasive grains, Mg(OH) ₂ ), and a dispersant (e.g., trisodium citrate) are added to the container, and the container is placed on a paint shaker (60 Hz) and rotated at high speed to turn the mixture into a slurry.

The collected slurry is then filtered through a filter having particle capture capability (e.g., particle capture capability of 2 μm or more), and the solids concentration in the supernatant, i.e., the concentration of cerium oxide-based abrasive grains, is measured using a heated moisture meter. Pure water is then added to reach the desired concentration, and the mixture is mixed to obtain the abrasive slurry of the present invention.

In this specification, when "X to Y" (X and Y are any numbers) is expressed, unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as "preferably greater than X" or "preferably smaller than Y". Furthermore, when "X or more" (X is any number) or "Y or less" (Y is any number), it also includes the meaning of "preferably greater than X" or "preferably less than Y".

The abrasive slurry of the present invention can suppress the decrease in polishing rate due to changes over time, even if the abrasive grain size is fine.

1 is a table showing the physical properties and measurement results of the abrasive slurries of Examples 1 to 9 and Comparative Examples 1 to 5.

The abrasive slurry according to the embodiment of the present invention will be further described below with reference to the following examples. However, the present invention is not limited to the following examples.

Example 1
First, pure water, cerium oxide ( _CeO2 , raw material particle size 22.2 μm) as cerium oxide-based abrasive grains, magnesium hydroxide (Mg(OH) ₂ , raw material particle size 3.5 μm) as additive and magnesium hydroxide-based abrasive grains, and trisodium citrate as a dispersant were placed in a container and mixed to obtain a mixture slurry containing cerium oxide. Here, when the abrasive slurry of Example 1 was taken as 100% by mass, the amount of magnesium hydroxide added was 0.78% by mass. Furthermore, when the abrasive slurry of Example 1 was taken as 100% by mass, the amount of trisodium citrate added was 0.6% by mass.

Next, the container was set on a paint shaker (60 Hz) and rotated at high speed to wet-grind the cerium oxide (CeO ₂ ) and magnesium hydroxide (Mg(OH) ₂ ) so that the final average abrasive grain size was 0.1 μm.

The mixture slurry containing the wet-ground cerium oxide in the container was filtered using a filter to separate it from the beads, and the mixture slurry was collected.

The collected mixture slurry was measured using a heated moisture meter, and pure water was added so that the solids concentration in the supernatant liquid, i.e., the cerium oxide-based abrasive grain concentration, was 10% by mass when the abrasive slurry of Example 1 was taken as 100% by mass, thereby obtaining the abrasive slurry of Example 1.

Example 2
In Example 2, the same manufacturing method as in Example 1 was carried out, except that the particle size of the raw material magnesium hydroxide (Mg(OH) ₂ ) was 6 μm, to obtain an abrasive slurry according to Example 2.

Example 3
In Example 3, the same manufacturing method as in Example 1 was carried out, except that the particle diameter of the raw material magnesium hydroxide (Mg(OH) ₂ ) was 0.15 μm, to obtain an abrasive slurry according to Example 3.

Example 4
In Example 4, the same manufacturing method as in Example 1 was carried out except that the amount of magnesium hydroxide (Mg(OH) ₂ ) added was 0.1 mass %, to obtain an abrasive slurry according to Example 4.

Example 5
In Example 5, the same production method as in Example 1 was carried out except that the dispersant was changed from trisodium citrate to trisodium gluconate, to obtain an abrasive slurry according to Example 5.

Example 6
In Example 6, the same manufacturing method as in Example 1 was carried out, except that the dispersant was changed from trisodium citrate to disodium (L)-tartrate dihydrate, to obtain an abrasive slurry according to Example 6.

(Example 7)
In Example 7, the same manufacturing method as in Example 1 was carried out except that the amount of magnesium hydroxide (Mg(OH) ₂ ) added was 0.01 mass %, to obtain an abrasive slurry according to Example 7.

(Example 8)
In Example 8, the same manufacturing method as in Example 1 was carried out except that the amount of magnesium hydroxide (Mg(OH) ₂ ) added was 10 mass %, to obtain an abrasive slurry according to Example 8.

(Example 9)
In Example 9, the same manufacturing method as in Example 1 was carried out to obtain an abrasive slurry according to Example 9, except that wet grinding was carried out so that the final average particle size of the abrasive grains, cerium oxide (CeO ₂ ), which is a cerium oxide-based abrasive grain, and magnesium hydroxide (Mg(OH) ₂ ), which is a magnesium hydroxide-based abrasive grain, was 0.3 μm.

(Comparative Example 1)
In Comparative Example 1, the additive was changed from magnesium hydroxide (Mg(OH) ₂ , raw material particle size 3.5 μm) to calcium hydroxide (Ca(OH) ₂ , raw material particle size 26.9 μm), but the same manufacturing method as in Example 1 was carried out to obtain the abrasive slurry of Comparative Example 1.

(Comparative Example 2)
In Comparative Example 2, the additive was changed from magnesium hydroxide (Mg(OH) ₂ , raw material particle size 3.5 μm) to aluminum hydroxide (Al(OH) ₃ , raw material particle size 70.1 μm), and the same manufacturing method as in Example 1 was carried out to obtain an abrasive slurry according to Comparative Example 2.

(Comparative Example 3)
In Comparative Example 3, the same manufacturing method as in Example 1 was carried out except that no additive was added, to obtain an abrasive slurry according to Comparative Example 3.

(Comparative Example 4)
In Comparative Example 4, the same manufacturing method as in Example 1 was carried out, except that the average particle size of the cerium oxide (CeO ₂ ) abrasive grains, which are cerium oxide-based abrasive grains, and the magnesium hydroxide (Mg(OH) ₂ ) abrasive grains, which are magnesium hydroxide-based abrasive grains, was set to 0.7 μm, to obtain an abrasive slurry according to Comparative Example 4.

(Comparative Example 5)
In Comparative Example 5, the same manufacturing method as in Example 1 was carried out, except that no additive was added and the average grain size of the cerium oxide (CeO ₂ ) abrasive grains was set to 0.7 μm, to obtain an abrasive slurry according to Comparative Example 5.

The following physical properties were measured for the abrasive slurries of Examples 1 to 9 and Comparative Examples 1 to 5. The measured physical properties and the methods for measuring the physical properties are shown below, and the measurement results are shown in Figure 1.

<Component Analysis>
Among the contents of the cerium oxide-based abrasive grains used in the abrasive slurries according to Examples 1 to 9 and Comparative Examples 1 to 5, the total rare earth oxide (TREO) was measured by the oxalate precipitation-calcination-gravimetric method (unit: solid: mass %, liquid: g/L). As a pretreatment for the measurement, if the measurement object was a solid (abrasive raw material or abrasive), it was dissolved with nitric acid, perchloric acid, and hydrogen peroxide, and boiled. If the measurement object was a liquid, it was boiled as it was. Specifically, 100 ml of the abrasive slurries according to Examples 1 to 9 and Comparative Examples 1 to 5 were placed in a glass beaker, and heated and dried at 120° C. for 24 hours to make them into a dry powder state, and then dissolved by adding 5 mL of 60% nitric acid, 5 mL of 60% perchloric acid, and 1 mL of 35% hydrogen peroxide water, and then boiled to obtain the measurement samples according to Examples 1 to 9 and Comparative Examples 1 to 5. The total rare earth oxide (TREO) content of the measurement samples according to Examples 1 to 9 and Comparative Examples 1 to 5 was measured by the oxalate precipitation-calcination-gravimetry method. CeO ₂ /TREO was calculated by dissolving the measurement sample obtained by the above-mentioned total rare earth oxide (TREO) measurement by adding 5 mL of 60% nitric acid, 5 mL of 60% perchloric acid, and 1 mL of 35% hydrogen peroxide solution, and measuring it by the ICP-OES method. Similarly, La ₂ O ₃ /TREO, Pr ₆ O ₁₁ /TREO, and Nd ₂ O ₃ /TREO were calculated. The fluorine (F) content was calculated by dissolving the measurement sample by alkali fusion and hot water extraction, and measuring the F concentration in the solution by the fluoride ion electrode method, thereby calculating the F content (mass%) in the measurement sample.

The content of magnesium hydroxide-based abrasive grains used in the abrasive slurries of Examples 1 to 9 and Comparative Examples 1 to 5 was determined by adding 5 mL of 60% nitric acid, 5 mL of 60% perchloric acid, and 1 mL of 35% hydrogen peroxide to the above-mentioned solid (abrasive raw material or abrasive) measurement sample, decomposing it by heating to form a solution, and measuring the Mg concentration using an ICP-OES device. This was multiplied by the hydroxide coefficient to estimate the added Mg hydroxide content, which was calculated as above. The hydroxide coefficient was 2.40.

<Particle size evaluation>
The average particle diameter of the abrasive grains of cerium oxide (CeO ₂ ), magnesium hydroxide (Mg(OH) ₂ ), calcium hydroxide (Ca(OH) ₂ ), and aluminum hydroxide (Al(OH) ₃ ) in the abrasive slurries according to Examples 1 to 9 and Comparative Examples 1 to 5 is the particle diameter (D50) measured by particle diameter distribution measurement using a dynamic light scattering method. Here, the particle size distribution was evaluated using a zeta potential/particle diameter/molecular weight measurement system (manufactured by Otsuka Electronics Co., Ltd.: ELSZ-2000ZS) in accordance with JIS Z 8828:2019 "Particle diameter analysis-dynamic light scattering method", and the particle diameter (D50) at a volume-based cumulative fraction of 50% was measured. In addition, the abrasive slurries according to Examples 1 to 9 and Comparative Examples 1 to 5 were diluted with pure water as necessary so that the solid content concentration in each abrasive slurry was 0.005% by mass to 0.1% by mass, and the measurement sample was prepared. Immediately before the measurement, the measurement sample was filtered through a filter with a pore size of 11 μm and subjected to ultrasonic treatment for 3 minutes in an ultrasonic cleaner (VS-100III manufactured by AS ONE CORPORATION). Furthermore, the liquid temperature of the measurement sample was adjusted to 25° C. The particle size (D50) refers to the median size (D50) which is the particle size showing the 50% integrated value of the integrated distribution curve.

<Polishing rate measurement test>
The polishing rates of the abrasive slurries according to Examples 1 to 9 and Comparative Examples 1 to 5 were evaluated by the following procedure. The object to be polished was soda-lime glass with a diameter of 60 mm. The polishing device used was a single-sided polishing machine manufactured by MAT Corporation. The polishing pad attached to the surface plate was a polyurethane polishing pad. Furthermore, the abrasive slurries used in the measurement were those in Examples 1 to 9 and Comparative Examples 1 to 5, in which the abrasive grain concentration was adjusted to 100 g/L. The supply speed of the abrasive slurry was set to 600 mL/min, the pressure on the polished surface was set to 9.8 kPa (100 g/cm ² ), and the rotation speed of the polishing machine was set to 60 rpm. Then, a polishing process was performed, and the mass of the soda-lime glass to be polished before and after the polishing process was measured to determine the amount of reduction in the mass of the soda-lime glass due to the polishing process, and the polishing rate was calculated based on this value. The polishing rate after 20 minutes of polishing was defined as the initial rate, and the polishing rate after 6 hours of polishing was defined as the aging rate. If the initial rate was 0.45 μm/min or more, it was evaluated as "〇〇 (VERY GOOD)", if it was 0.40 μm/min or more and less than 0.45 μm/min, it was evaluated as "〇 (GOOD)", and if it was less than 0.40 μm/min, it was evaluated as "× (BAD)". If the aging rate was 80% or more of the initial rate, it was evaluated as "〇〇 (VERY GOOD)", if it was 60% or more and less than 80%, it was evaluated as "〇 (GOOD)", and if it was less than 60% of the initial rate, it was evaluated as "× (BAD)". The aging rate is preferably 0.2 μm/min or more, more preferably 0.32 μm/min or more, and particularly preferably 0.36 μm or more.

<Polishing accuracy evaluation>
The polished surface of the soda-lime glass that had been polished for 6 hours in the above-mentioned polishing rate measurement test was washed with pure water and dried in a dust-free state, and then the polishing accuracy was evaluated. The polishing accuracy was evaluated by measuring the polished surface after the polishing process in a measurement range of 10 μm×10 μm using an atomic force microscope (AFM; AFM5400L manufactured by Hitachi High-Tech Science Corporation) and calculating the surface roughness Ra of the polished surface. If the surface roughness Ra was less than 0.24 nm, it was evaluated as "〇〇 (VERY GOOD)", if it was 0.25 nm or more and less than 0.30, it was evaluated as "〇 (GOOD)", and if it was 0.30 nm or more, it was evaluated as "× (BAD)".

<pH measurement>
The pH of the abrasive slurries according to Examples 1 to 9 and Comparative Examples 1 to 5 was measured using an electrode (Standard ToupH electrode 9615S-10D, manufactured by HORIBA) of a pH meter (Glass electrode type hydrogen ion concentration indicator D-53, manufactured by HORIBA) after confirming that the liquid temperature was stabilized at 25° C. The pH measured after 20 minutes of polishing treatment was defined as the initial pH, and the pH measured after 6 hours of polishing treatment was defined as the time-dependent pH.

As shown in Figure 1, the abrasive slurries of Examples 1 to 9 contained magnesium hydroxide-based abrasive grains as an additive, and thus deterioration due to changes over time was suppressed even when the average abrasive grain size of the cerium oxide-based abrasive grains and magnesium hydroxide-based abrasive grains was 0.01 μm to 0.5 μm.

The abrasive slurries of Examples 1 to 9 contained one or more dispersants selected from sodium citrate, sodium gluconate, and sodium tartrate, thereby suppressing deterioration over time.

The abrasive slurries of Examples 1 to 9 suppressed the decrease in polishing rate due to changes over time, and also had excellent surface roughness Ra. On the other hand, the abrasive slurries of Comparative Examples 1 and 2 caused excessive aggregation due to changes over time during the polishing process, making polishing impossible or causing the polishing process to be interrupted. Furthermore, the abrasive slurries of Comparative Examples 4 and 5 had a surface roughness Ra of 0.30 nm or more due to the large average particle size of the cerium oxide-based abrasive grains or magnesium hydroxide-based abrasive grains.

The abrasive slurries of Examples 1 to 9 also had reduced pH fluctuations over time.

In the abrasive slurries of Examples 1 to 9, when the abrasive slurry is taken as 100% by mass, the content of cerium oxide-based abrasive grains is 0.5% by mass or more and 40% by mass or less, and the content of magnesium hydroxide-based abrasive grains is 0.005% by mass or more and 20% by mass or less, and a good polishing rate can be achieved.

In the abrasive slurries of Examples 1 to 9, when the weight ratio of the magnesium hydroxide abrasive grains to the cerium oxide abrasive grains was 1.25×10 ⁻⁴ or more and 40 or less, the decrease in the polishing rate could be suppressed.

In the abrasive slurries of Examples 1 to 9, when the cerium oxide-based abrasive grains are taken as 100 mass%, the Ce content is 100 mass% or less in terms of _CeO2 , the La content is 40 mass% or less in terms _{of La2O3} , the F content is 10 mass% or less in terms of F, the Pr content is 10 mass% _or less in terms of _Pr6O11 , and the Nd content is 10 mass% or less in terms _{of Nd2O3} , and a good polishing rate was achieved.

The inventions disclosed in this specification include, in addition to the configurations of each invention or embodiment, to the extent applicable, those that are specified by changing these partial configurations to other configurations disclosed in this specification, or those that are specified by adding other configurations disclosed in this specification to these configurations, or those that are specified as higher-level concepts by deleting these partial configurations to the extent that partial effects are obtained.

The abrasive slurry according to the present invention is suitable as an abrasive used in the CMP method because the polishing rate is not likely to decrease with time and the pH fluctuation is suppressed. In addition, the abrasive slurry according to the present invention is not likely to decrease with time and the pH fluctuation is suppressed, so the abrasive slurry can be used for a longer period of time than before. This makes it possible to reduce the amount of the product itself and the associated waste, and also to reduce energy costs during production and waste disposal. These points make it possible to achieve the sustainable management and efficient benefits of natural resources, as well as decarbonization (carbon neutrality).

Claims (10)

Cerium oxide abrasive grains;
Magnesium hydroxide abrasive grains;
A dispersant;
A solvent;
It consists only of
The abrasive slurry is characterized in that the average particle size of the cerium oxide-based abrasive grains and the magnesium hydroxide-based abrasive grains is 0.01 μm or more and 0.5 μm or less. Cerium oxide abrasive grains;
Magnesium hydroxide abrasive grains;
A dispersant;
an abrasive slurry having a solvent,
The abrasive slurry does not contain a chelating agent,
The abrasive slurry is characterized in that the average particle size of the cerium oxide-based abrasive grains and the magnesium hydroxide-based abrasive grains is 0.01 μm or more and 0.5 μm or less. 3. The abrasive slurry according to claim 1 , wherein the solvent contains water. 3. The abrasive slurry according to claim 1 , wherein the dispersant comprises at least one selected from the group consisting of organic acid alkali metal salts, phosphoric acids, and polymer dispersants. 5. The abrasive slurry according to claim 4 , wherein the organic acid alkali metal salt comprises at least one selected from the group consisting of sodium citrate, sodium gluconate, and sodium tartrate. 3. The abrasive slurry according to claim 1 , wherein the cerium oxide-based abrasive grains are cerium oxide abrasive grains. When the abrasive slurry is 100 mass %,
The content of the cerium oxide-based abrasive grains is 0.5% by mass or more and 40% by mass or less,
3. The abrasive slurry according to claim 1 , wherein the content of the magnesium hydroxide-based abrasive grains is 0.005% by mass or more and 20% by mass or less. 3. The abrasive slurry according to claim 1 , wherein the weight ratio of the magnesium hydroxide abrasive grains to the cerium oxide abrasive grains is 1.25×10 ⁻⁴ or more and 40 or less. The cerium oxide-based abrasive grains, when the cerium oxide-based abrasive grains are taken as 100 mass %,
The Ce content is 100% by mass or less in terms of _CeO2 ,
The La content is 40% _by mass or less in terms of _La2O3 ,
The F content is 10% by mass or less in terms of F,
The Pr content is 10% _by mass or less in terms of _Pr6O11 ,
The abrasive slurry according to claim 1 or 2, characterized in that the Nd content is 10 mass % or less calculated as _{Nd2O3 .} A polishing method comprising polishing an object to be polished with the abrasive slurry according to claim 1 or 2 .

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