Abrasive slurry and polishing method using the same

Abstract

This polishing material slurry has abrasive grains and nanofibers. The abrasive grains preferably contain manganese oxide particles. The nanofibers preferably contain one or more selected from the group consisting of polysaccharide nanofibers, polymer nanofibers, and carbon nanofibers, and more preferably contain the polysaccharide nanofibers. More preferably, the polysaccharide nanofibers include cellulose nanofibers and / or lignocellulose nanofibers. This polishing material slurry preferably further contains manganate ions and phosphates. This polishing material slurry polishing method includes polishing using this polishing material slurry. This SiC wafer is polished using this polishing material slurry.

Description

[Technical Field]

[0001] The present invention relates to an abrasive slurry and a polishing method using the same. [Background technology]

[0002] Among semiconductor devices, power semiconductor elements known as power devices are being required to withstand higher voltages and currents by using silicon carbide (SiC), gallium nitride, diamond, etc. instead of the silicon that has traditionally been used as a substrate. Substrates made of these materials have a larger band gap than conventional silicon substrates, making them capable of withstanding higher voltages.

[0003] Among these, substrates made of silicon carbide (hereinafter referred to as SiC substrates) are excellent not only in hardness, heat resistance, and chemical stability, but also in cost. On the other hand, since SiC substrates are harder than conventional silicon substrates, abrasive slurries containing manganese oxide particles as abrasive grains have been developed as disclosed in Patent Document 1, for example, as abrasive slurries used in polishing processes such as a CMP (Chemical Mechanical Polishing) method, which is a process for mirror-finishing the surface of SiC substrates during the manufacturing process of SiC substrates. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6744295 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is a concern that the abrasive slurry containing manganese oxide particles as abrasive grains as disclosed in Patent Document 1 has high friction resistance against the workpiece during polishing. On the other hand, when the abrasive slurry is left standing, the abrasive grains settle, and it takes a lot of time to remove the abrasive slurry that has adhered to the bottom or wall of the container.

[0006] In view of the above problems, the present invention provides an abrasive slurry and a polishing method that reduce frictional resistance and can be easily removed even when it adheres to the bottom surface of a container or the like. [Means for solving the problem]

[0007] The abrasive slurry of the present invention, which has been made to solve the above problems, is characterized by having abrasive grains and nanofibers. The abrasive slurry of the present invention contains abrasive grains and nanofibers, thereby reducing frictional resistance and enabling easy removal even when it adheres to the bottom surface of a container or the like.

[0008] The abrasive particles contained in the abrasive slurry of the present invention include manganese oxide particles, alumina particles, silica particles, cerium oxide particles, zirconium oxide particles, titanium oxide particles, chromium oxide particles, iron oxide particles, magnesium hydroxide particles, cerium hydroxide particles, silicon carbide particles, boron carbide particles, and diamond particles, so long as the effect of preventing warpage and cracking due to the Twyman effect on the object to be polished, such as a SiC substrate, is not impaired. These particles can be used alone or in combination of two or more types, and for example, a mixture of manganese oxide particles and silica particles may be used, or a mixture of manganese oxide particles, silica particles, and alumina particles may be used.

[0009] The abrasive grains contained in the abrasive slurry of the present invention preferably contain manganese oxide particles. Examples of the manganese oxide particles contained in the abrasive grains include manganese oxide (II) (MnO), dimanganese trioxide (III) (Mn2O3), manganese dioxide (IV) (MnO2), and trimanganese tetroxide (II, III) (Mn3O4), with manganese dioxide (IV) (MnO2) being more preferred. The manganese oxide particles contained in the abrasive grains may be composited with abrasive grains other than manganese oxide particles, for example, manganese oxide particles may be surface-coated with abrasive grains other than manganese oxide particles, or manganese oxide particles may coat the surfaces of abrasive grains other than manganese oxide particles.

[0010] Furthermore, the content of abrasive grains contained in the abrasive slurry of the present invention can be determined by filtering, washing, and drying the abrasive slurry, and measuring the weight of the abrasive grains obtained. The composition of the abrasive grains contained in the abrasive slurry of the present invention can be measured by energy dispersive X-ray spectroscopy (SEM-EDX), electron probe microanalyzer (EPMA), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), etc.

[0011] Furthermore, the abrasive grains contained in the abrasive slurry of the present invention preferably have a particle size (D50) at 50% of the cumulative volume as measured by a laser diffraction / scattering particle size distribution measurement method of 0.1 μm or more in terms of having high polishing power, and preferably have a particle size (D50) of 5.0 μm or less in terms of suppressing roughness on the surface of the workpiece to be polished, such as a SiC substrate. Therefore, the abrasive grains preferably have a particle size (D50) at 50% of the cumulative volume as measured by a laser diffraction / scattering particle size distribution measurement method of 0.15 μm or more and 4.5 μm or less, and even more preferably 0.2 μm or more and 4.0 μm or less.

[0012] Here, the particle size at 50% cumulative volume (D50) of the abrasive grains contained in the abrasive slurry of the present invention, as measured by the laser diffraction / scattering particle size distribution measurement method, is prepared by preparing a sample by pulverizing the abrasive grains with beads in the method for producing an abrasive slurry of the present invention described below, and diluting the mixture with water to a concentration of about 0.01%. Then, the measurement is carried out using a laser diffraction / scattering particle size distribution measurement device (MT3300EXII, manufactured by Microtrackbell Corporation).

[0013] Furthermore, the content of abrasive grains contained in the abrasive slurry of the present invention is preferably 0.5 mass% or more and 10 mass% or less, more preferably 0.5 mass% or more and 5 mass% or less, and from the viewpoint of sufficiently increasing the polishing rate of high-hardness material such as silicon carbide, ensuring the suitable fluidity of abrasive grains in the abrasive slurry, and preventing aggregation, based on the total amount of the abrasive slurry of the present invention, and from the viewpoint of sufficiently increasing polishing rate, more preferably 1.0 mass% or more and 2.5 mass% or less.In addition, in this specification, the content in the abrasive slurry of the present invention is the content in the abrasive slurry before starting polishing, unless otherwise specified.

[0014] The abrasive slurry of the present invention contains nanofibers, which reduces frictional resistance and allows the abrasive slurry to be easily removed even when it adheres to the bottom of a container or the like.

[0015] The nanofibers contained in the abrasive slurry of the present invention preferably contain one or more types selected from the group consisting of polysaccharide nanofibers, polymer nanofibers, and carbon nanofibers in terms of reducing frictional resistance. The nanofibers may also be a mixture of one type or two or more types of nanofibers.

[0016] Furthermore, the nanofibers contained in the abrasive slurry of the present invention preferably have an average fiber diameter of 2000 nm or less. The lower limit of the average fiber diameter of the nanofibers is not particularly limited, but can be, for example, 0.1 nm or more, or may be 1 nm or more. On the other hand, the average fiber diameter of the nanofibers is preferably 1000 nm or less, and may be 500 nm or less, 300 nm or less, 200 nm or less, or 100 nm or less.

[0017] The average fiber diameter of the nanofibers contained in the abrasive slurry of the present invention can be measured as follows. First, the abrasive slurry of the present invention is diluted with pure water and filtered to collect the nanofibers contained in the filtrate. Next, the collected filtrate is separated using preparative gel permeation chromatography (preparative GPC) to prepare a nanofiber dispersion. Furthermore, the dispersion is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for observation with a transmission electron microscope (TEM). Note that if the dispersion contains fibers with a large fiber diameter (100 nm or more), a scanning electron microscope (SEM) image of the surface cast onto a glass plate may be observed.

[0018] The dispersion is then observed using an electron microscope at a magnification of 5,000x, 10,000x, or 50,000x, depending on the size of the fibers constituting the nanofibers. An arbitrary vertical or horizontal axis (hereinafter referred to as the reference axis) is assumed within the image obtained using this electron microscope, and the sample and observation conditions (magnification) are adjusted so that 20 or more fibers intersect with the reference axis. Next, two random vertical and two random horizontal axes (hereinafter referred to as the measurement axes) are drawn per image adjusted in this way, and the fiber diameters of the fibers intersecting the two measurement axes are measured, for example, using a vernier caliper. In this way, at least three non-overlapping images of the surface of the nanofibers are taken with the electron microscope, and the fiber diameters of the fibers intersecting each of the two measurement axes are measured. Finally, fiber diameter information is obtained for a minimum of 20 (number of fibers) x 2 x 3 (number of images) = 120 fibers, and the average fiber diameter of the nanofibers in the dispersion is calculated from the obtained fiber diameter data. That is, the average fiber diameter of the nanofibers in this specification means the number average fiber diameter of the nanofibers.

[0019] In the nanofibers contained in the abrasive slurry of the present invention, the crystalline structure formed by the cellulose structural units is not particularly limited, and is preferably, for example, a type I crystalline structure. The presence or absence of the type I crystalline structure in the cellulose structural units can be determined, for example, by wide-angle X-ray diffraction image measurement. Specifically, if the diffraction profile obtained by wide-angle X-ray diffraction measurement has typical peaks at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°, it can be determined that the cellulose structural units have a type I crystalline structure.

[0020] The nanofibers contained in the abrasive slurry of the present invention preferably include polysaccharide nanofibers. Specific examples of polysaccharide nanofibers include lignocellulose nanofibers, cellulose nanofibers, chitin nanofibers, and chitosan nanofibers. Here, lignocellulose nanofibers and cellulose nanofibers are produced by introducing dissociative groups (ionic functional groups) onto the surface of cellulose microfibrils from raw pulp such as wood through a chemical reaction (oxidation or esterification), followed by a minor fiber defibration treatment, or by fiber defibration caused by physical stimuli such as frictional force or shear force generated in a flow field, collision, vibration, or pressure difference.

[0021] Furthermore, it is more preferable that the polysaccharide nanofibers contained in the abrasive slurry of the present invention include cellulose nanofibers and / or lignocellulose nanofibers, since this further improves the low friction and reslurry properties of the abrasive slurry of the present invention.

[0022] The content of nanofibers contained in the abrasive slurry of the present invention is preferably 0.0025% by mass or more from the viewpoint of friction, and 0.2% by mass or less from the viewpoint of pot life, based on the total amount of the abrasive slurry of the present invention. Moreover, the content of the nanofibers is more preferably 0.005% by mass or more and 0.1% by mass or less, and even more preferably 0.005% by mass or more and 0.05% by mass or less. Typically, the content of the nanofibers may be 0.005% by mass or more and 0.015% by mass or less, or may be 0.035% by mass or more and 0.05% by mass or less.

[0023] Furthermore, the content of nanofibers contained in the abrasive slurry of the present invention, expressed as a mass ratio to the content of abrasive grains in the abrasive slurry of the present invention, is preferably 0.125% to 10% inclusive, more preferably 0.25% to 5% inclusive, and even more preferably 0.25% to 2.5% inclusive. Typically, the mass ratio may be 0.25% to 0.75% inclusive, or 1.75% to 2.5% inclusive.

[0024] Furthermore, the abrasive slurry of the present invention preferably further contains manganate ions in addition to the abrasive grains and nanofibers described above. Here, the manganate ions include permanganate ions (MnO4 - ), manganate ions (MnO4 2- ) and permanganate ion is preferred.

[0025] When used in combination with abrasive grains as an oxidizing agent, manganate ions can provide high polishing power for high-hardness materials such as silicon carbide. Here, manganate salts are preferred as the source of manganate ions. Examples of manganate salts include alkali metal salts of manganate and alkaline earth metal salts of manganate. Furthermore, from the viewpoints of easy availability and improving the polishing efficiency of the abrasive slurry of the present invention, among the manganate salts serving as the source of manganate ions, alkali metal salts of manganate are preferred, with sodium manganate (NaMnO), potassium manganate (KMnO), sodium permanganate (NaMnO), and potassium permanganate (KMnO) being more preferred, and potassium permanganate (KMnO) being even more preferred. These manganate salts may be used alone or in combination.

[0026] The manganate ion content of the abrasive slurry of the present invention is preferably 0.5% by mass or more relative to the total amount of the abrasive slurry of the present invention in order to sufficiently increase the polishing rate. The manganate ion content of the abrasive slurry of the present invention is preferably 3.2% by mass or less relative to the total amount of the abrasive slurry of the present invention in order to prevent crystal precipitation due to increased addition amounts, ensure safe handling of the abrasive slurry, and because the polishing rate tends to saturate even when increased addition amounts are used. That is, the manganate ion content is preferably 0.5% by mass or more and 3.2% by mass or less, more preferably 1.0% by mass or more and 2.5% by mass or less, and even more preferably 1.0% by mass or more and 2.1% by mass or less relative to the total amount of the abrasive slurry of the present invention. Typically, the manganate ion content may be 1.0% by mass or more and 1.2% by mass or less, or 1.7% by mass or more and 2.1% by mass or less. The manganate ion content can be determined by centrifuging the abrasive slurry of the present invention to settle the abrasive grains in the abrasive slurry, collecting the supernatant, diluting the supernatant, and measuring the absorbance (intensity of the absorption peak appearing at a wavelength of 525 nm) of the diluted solution by absorptiometry.

[0027] Furthermore, the abrasive slurry of the present invention preferably further contains, in addition to the abrasive grains, nanofibers, and manganate ions, a phosphoric acid compound. The phosphoric acid compound, when used in combination with the abrasive grains and manganate ions, can improve the dispersibility of the abrasive slurry of the present invention.

[0028] The phosphoric acid compound contained in the abrasive slurry of the present invention is preferably, for example, an inorganic phosphorus compound. Specifically, the phosphoric acid compound may be sodium phosphate (trisodium phosphate (anhydrous) (Na3PO4), CAS number: 7601-54-9; trisodium phosphate dodecahydrate (Na3PO4 12H2O), CAS number: 10101-89-0; sodium phosphate monobasic (NaH2PO4), CAS number: 7558-80-7; sodium phosphate dibasic (Na2HPO4), CAS number: 7558-79-4), potassium phosphate (phosphorus Potassium phosphate tripotassium phosphate (anhydrous) (K3PO4), CAS number: 7778-53-2; potassium phosphate tripotassium phosphate monohydrate (K3PO4·H2O), CAS number: 27176-10-9; potassium phosphate dibasic trihydrate (K2HPO4·H2O), CAS number: 16788-57-1; potassium phosphate monobasic (KH2PO4), CAS number: 7778-77-0; and potassium phosphate dibasic (K2HPO4), CAS number: 7758-11-4).

[0029] In addition, as a metaphosphate compound, sodium metaphosphate (NaPO3) n , CAS number: 35270-09-8) and potassium metaphosphate (KPO3) n , CAS number: 7790-53-6.

[0030] Hexametaphosphate compounds include sodium hexametaphosphate (NaHPO 18 ), CAS number: 10124-56-8.

[0031] Pyrophosphate compounds include sodium pyrophosphate (Sodium pyrophosphate (anhydrous) (Na4P2O7), CAS number: 7722-88-5; Sodium pyrophosphate decahydrate (Na4P2O7·10H2O), CAS number: 13472-36-1; Sodium acid pyrophosphate (Na2H2P2O7), CAS number: 7758-16-9) and potassium pyrophosphate (K4P2O7), CAS number: 7320-34-5.

[0032] As a polyphosphate compound, sodium polyphosphate (Na3P3O 10 X2), CAS number: 68915-31-1; potassium polyphosphate (K3P3O 10 X2), CAS number: 68956-75-2.

[0033] As a tripolyphosphate compound, sodium tripolyphosphate (Na5P3O 10 ), CAS number: 7758-29-4, potassium tripolyphosphate (K5P3O 10 ), CAS number: 13845-36-8.

[0034] Further examples include salts and hydrates thereof. In the case of these salts, alkali metal salts and alkaline earth metal salts are preferred, and sodium salts and potassium salts are particularly preferred. In particular, in the abrasive slurry of the present invention, from the viewpoint of effective high dispersibility even with a small amount and from the viewpoint of sufficiently increasing the polishing rate, metaphosphate compounds, hexametaphosphate compounds, pyrophosphate compounds (sodium pyrophosphate and potassium pyrophosphate), polyphosphate compounds (sodium polyphosphate and potassium polyphosphate), and tripolyphosphate compounds are more preferred. These phosphoric acids may be used alone or in combination of two or more.

[0035] Furthermore, among the inorganic phosphorus compounds described above, pyrophosphate compounds are preferred from the viewpoints of high dispersibility and sufficiently increasing the polishing rate. Among the pyrophosphate compounds, alkali metal salts of pyrophosphate and alkaline earth metal salts of pyrophosphate are more preferred, and sodium pyrophosphate and potassium pyrophosphate are particularly preferred.

[0036] The presence or absence of phosphoric acid contained in the abrasive slurry of the present invention and its content can be determined by high performance liquid chromatography (HPLC), phosphorus-31 nuclear magnetic resonance (NMR) analysis, 31The measurement can be carried out by peak separation using the DOSY (Diffusion Ordered NMR Spectroscopy) method in P-NMR. In this case, if necessary, the abrasive slurry of the present invention may be diluted with pure water and filtered, and the phosphoric acid may be analyzed as being contained in the filtrate.

[0037] Furthermore, the measurement of the phosphoric acid compounds contained in the abrasive slurry of the present invention is preferably performed by high performance liquid chromatography. In high performance liquid chromatography, the type and weight of phosphoric acid compounds can be measured by a known method by using a non-suppressor anion analysis column. For example, an example of a non-suppressor anion analysis column is Shodex non-suppressor anion analysis column IC I-524A (manufactured by Shoko Science Co., Ltd.). By using this non-suppressor anion analysis column, the phosphoric acid compounds contained in the abrasive slurry of the present invention can be separated and measured.

[0038] Furthermore, from the viewpoint of frictional resistance, the content of phosphoric acid contained in the abrasive slurry of the present invention is preferably 0.001% by mass or more relative to the total amount of the abrasive slurry of the present invention. Furthermore, since the polishing rate tends to saturate even when the added amount is increased, the content of phosphoric acid contained in the abrasive slurry of the present invention is preferably 0.2% by mass or less relative to the total amount of the abrasive slurry of the present invention. That is, the content of phosphoric acid is preferably 0.001% by mass or more and 0.2% by mass or less relative to the total amount of the abrasive slurry of the present invention, more preferably 0.002% by mass or more from the viewpoint of frictional resistance, and more preferably 0.1% by mass or less from the viewpoint of sufficiently increasing the polishing rate. The content of phosphoric acid is more preferably 0.002% by mass or more and 0.05% by mass or less. Typically, the content of phosphoric acid may be 0.002% by mass or more and 0.02% by mass or less. In this specification, the content of phosphoric acid refers to the total amount of phosphoric acid classified as phosphoric acid unless otherwise specified.

[0039] Furthermore, the content of phosphoric acid contained in the abrasive slurry of the present invention, expressed as a mass ratio to the abrasive grain content in the abrasive slurry of the present invention, is preferably 0.05% or more and 10.0% or less. It is more preferably 0.1% or more and 5.0% or less, and even more preferably 0.1% or more and 2.5% or less. Typically, the mass ratio may be 0.1% or more and 1.0% or less.

[0040] Furthermore, the abrasive slurry of the present invention may contain, in addition to the above-mentioned abrasive grains, nanofibers, manganate ions, and phosphoric acids, a polymer additive containing one or more water-soluble organic polymers selected from the group consisting of polycarboxylic acids, polycarboxylates, salts of naphthalenesulfonic acid-formalin condensates, polyvinyl alcohols, polyethylene glycols, polyvinylpyrrolidone, and copolymers thereof. By containing the above-mentioned polymer additives, the pot life of the abrasive slurry of the present invention can be extended.

[0041] Furthermore, in the abrasive slurry of the present invention, it is more preferable that the polymer additive is one or more water-soluble organic polymers selected from polycarboxylic acids, polycarboxylates, and copolymers thereof, it is even more preferable that the polymer additive is one or more water-soluble organic polymers selected from polyacrylic acid, polymaleic acid, polyacrylates, polymaleates, and copolymers thereof, it is particularly preferable that the polymer additive is a polyacrylate, and it is even more particularly preferable that the polymer additive is an ammonium polyacrylate.

[0042] Furthermore, the content of the polymer additive contained in the abrasive slurry of the present invention is preferably 0.006% by mass or more relative to the total amount of the abrasive slurry of the present invention from the viewpoint of dispersibility. Furthermore, the content of the polymer additive in the abrasive slurry of the present invention is preferably 0.05% by mass or less relative to the total amount of the abrasive slurry of the present invention from the viewpoint of sufficiently increasing the polishing rate. That is, the content of the polymer additive is preferably 0.006% by mass or more and 0.05% by mass or less, more preferably 0.01% by mass or more and 0.03% by mass or less, and even more preferably 0.01% by mass or more and 0.02% by mass or less relative to the total amount of the abrasive slurry of the present invention. Typically, the content of the polymer additive may be 0.01% by mass or more and 0.015% by mass or less. In this specification, the content of the polymer additive is the total amount of those classified as the above-mentioned polymer additives, unless otherwise specified.

[0043] Furthermore, the content of the polymer additive in the abrasive slurry of the present invention, expressed as a mass ratio to the content of abrasive grains contained in the abrasive slurry of the present invention, is preferably 0.3% to 2.5%, more preferably 0.5% to 1.5%, and even more preferably 0.5% to 1.0%. Typically, the mass ratio may be 0.5% to 0.75%.

[0044] The abrasive slurry of the present invention contains a dispersion medium for dissolving or dispersing the abrasive grains, nanofibers, manganate ions, and phosphates. The dispersion medium is preferably water, a water-soluble organic solvent such as an alcohol or a ketone, or a mixture thereof, in order to sufficiently increase the polishing rate, and more preferably water. The content of the dispersion medium is preferably 60% by mass or more and 99.9% by mass or less, and more preferably 80% by mass or more and 99.9% by mass or less, based on the total amount of the abrasive slurry of the present invention. The content of the dispersion medium may be 99% by mass or less, 98% by mass or less, 97% by mass or less, 95% by mass or less, or 90% by mass or less, based on the total amount of the abrasive slurry of the present invention.

[0045] Furthermore, the abrasive slurry of the present invention may contain optional additives other than the above-mentioned abrasive grains, nanofibers, manganate ions, phosphates, and dispersion medium. Here, the optional additives include dispersants, pH adjusters, viscosity adjusters, chelating agents, and rust inhibitors. The content of the optional additives is preferably 40% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, based on the total amount of the abrasive slurry of the present invention.

[0046] The abrasive slurry of the present invention can be prepared by appropriately mixing the above-mentioned abrasive grains, nanofibers, manganate ions, phosphates, dispersion medium, and any additives, and may be prepared as a kit in which these components are divided into two or more components. The kit may be configured in any form so long as the abrasive slurry of the present invention can fully exhibit its polishing ability when prepared.

[0047] The dispersibility of the abrasive slurry of the present invention can be evaluated by the following method. A measurement sample is prepared by diluting the abrasive slurry of the present invention with water to a concentration of about 0.01% by mass. Then, a laser diffraction / scattering particle size distribution analyzer (MT3300EXII, manufactured by Microtrackbell Corporation) is used to measure the particle size (D50) at a volume-based cumulative fraction of 50%. The measured particle size (D50) can be evaluated to evaluate the dispersibility of the abrasive slurry of the present invention.

[0048] A polishing method for polishing an object to be polished using the above-described abrasive slurry of the present invention will be described below.

[0049] Examples of polishing methods include supplying the abrasive slurry of the present invention to a polishing pad, contacting the polished surface of the workpiece with the polishing pad, and polishing by relative movement between the two. Here, the abrasive slurry of the present invention may be poured over, or may be circulated by repeatedly recovering the abrasive slurry of the present invention supplied to the polishing pad and used for polishing, and then supplying the recovered abrasive slurry of the present invention to the polishing pad again. Since the abrasive slurry of the present invention can be circulated and repeatedly used to polish the workpiece, the amount used can be reduced. Here, the polishing pad can be, for example, a conventionally used nonwoven fabric, a pad impregnated with a resin such as polyurethane or epoxy, or a suede material. The polishing pressure is 0.5 × 10 4 Pa or more 1.0×10 5 Pa or less, especially 1.0 × 10 4 Pa or more 5.0×10 4 It is preferable that the pressure is not more than Pa in terms of the polishing force and ease of handling of the polishing jig, etc. The supply rate of the abrasive slurry is preferably 10 mL / min to 500 mL / min, and more preferably 50 mL / min to 250 mL / min.

[0050] The object to be polished with the abrasive slurry of the present invention is a high-hardness material, for example, with a Mohs hardness of 8 or more. Here, Mohs hardness is a numerical value that represents hardness based on the degree of scratching relative to a standard material, and can be measured by a standard method using a Mohs hardness scale. Standard materials are designated on the Mohs hardness scale, ranging from 1 to 10, in order of softest to softest. Specific standard materials are: talc (Mohs hardness 1), gypsum (Mohs hardness 2), calcite (Mohs hardness 3), fluorite (Mohs hardness 4), apatite (Mohs hardness 5), orthoclase (Mohs hardness 6), quartz (Mohs hardness 7), topaz (Mohs hardness 8), and diamond (Mohs hardness 10). Examples of high-hardness materials with a Mohs hardness of 8 or more include silicon carbide (Mohs hardness approximately 9), gallium nitride (Mohs hardness approximately 9), and diamond.

[0051] The abrasive slurry of the present invention can be used in a finishing CMP (Chemical Mechanical Polishing) process after lapping of a substrate made of a high-hardness material. In particular, the abrasive slurry of the present invention can be used to polish a substrate made of silicon carbide (SiC), i.e., a SiC substrate, and can sufficiently increase the polishing rate and effectively prevent warping and cracking due to the Twyman effect. Single-crystal silicon carbide substrates are usually used for SiC substrates, and their crystal systems are usually hexagonal or rhombohedral. The hexagonal crystal is preferred in terms of demonstrating the effect of the abrasive slurry, which can prevent warping and cracking due to the Twyman effect. Polymorphs of hexagonal crystals include 2H, 4H, 6H, 8H, and 10H. Polymorphs of rhombohedral crystals include 15R.

[0052] Next, a method for producing the above-mentioned abrasive slurry of the present invention will be described below.

[0053] First, pure water, manganese dioxide (abrasive grains, MnO2), phosphoric acid (e.g., sodium pyrophosphate), and beads (zirconia, φ0.4 mm) are placed in a container, and the container is set on a paint shaker (60 Hz). The container is rotated at high speed to mix and grind the manganese dioxide (abrasive grains, MnO2).

[0054] The mixture containing the mixed and crushed manganese dioxide (abrasive grains, MnO2) in the container is separated from the beads using a centrifuge (Hitachi Koki Himac CT 6E) or the like, and the supernatant is collected.

[0055] The solids concentration in the collected supernatant, ie, the manganese oxide abrasive grain concentration, is measured using a heating moisture meter, and pure water is added to the supernatant to reach a predetermined concentration, thereby obtaining an intermediate abrasive slurry.

[0056] Nanofibers are added to the obtained abrasive slurry intermediate and mixed in. The abrasive slurry intermediate to which the nanofibers have been added is referred to as Liquid A, which is used in the reslurry evaluation described below.

[0057] The abrasive slurry of the present invention is obtained by mixing the abrasive slurry intermediate containing nanofibers with potassium permanganate (KMnO4). The potassium permanganate (KMnO4) added to the abrasive slurry intermediate containing nanofibers is referred to as Liquid B.

[0058] The SiC wafer of the present invention is characterized by being polished using the above-mentioned abrasive slurry of the present invention. The SiC wafer of the present invention is polished using the above-mentioned abrasive slurry of the present invention, and therefore does not have warpage or cracks due to the Twyman effect. Also, the SiC wafer of the present invention is polished by the above-mentioned polishing method using the abrasive slurry of the present invention.

[0059] In this specification, when "X to Y" (X and Y are any numbers) is expressed, unless otherwise specified, it means "X or more and Y or less," and also includes the meaning "preferably larger 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 "preferably larger than X" or "preferably smaller than Y." [Effects of the Invention]

[0060] The abrasive slurry of the present invention reduces frictional resistance and can be easily peeled off even when it adheres to the bottom surface of a container or the like. [Brief explanation of the drawings]

[0061] [Figure 1] 1 is a table showing the physical property values ​​and measurement results of abrasive slurries according to Examples 1 to 6 and Comparative Example 1. BEST MODE FOR CARRYING OUT THE INVENTION

[0062] The abrasive slurry according to the embodiment of the present invention will be further described below with reference to the following examples, although the present invention is not limited to these examples.

[0063] Example 1 A container was charged with pure water, manganese dioxide (MnO2) as abrasive grains, sodium pyrophosphate as a phosphate (specifically, sodium pyrophosphate decahydrate (Na4P2O7·10H2O), CAS number: 13472-36-1), ammonium polyacrylate as a polymer additive, and beads (zirconia, φ0.4 mm). The container was then placed on a paint shaker (60 Hz) and rotated at high speed to mix and grind the manganese dioxide.

[0064] The mixture containing the mixed and pulverized manganese dioxide in the container was separated from the beads using a centrifuge (Hitachi Koki Himac CT 6E) or the like, and the supernatant was collected. The solid concentration in the collected supernatant, i.e., the manganese oxide abrasive grain concentration, was measured using a heating moisture meter, and pure water was added to reach a predetermined concentration, thereby obtaining an abrasive slurry intermediate.

[0065] Cellulose nanofibers (product name: ELLEX-S(A) manufactured by Daio Paper Co., Ltd.) were added as nanofibers to the abrasive slurry intermediate and mixed in. The abrasive slurry intermediate to which the nanofibers were added was designated as Liquid A, which was used in the reslurry evaluation described below.

[0066] Then, the abrasive slurry according to Example 1 was obtained by mixing the abrasive slurry intermediate to which the nanofibers had been added with an aqueous potassium permanganate (KMnO4) solution having a KMnO4 mass % concentration of 3.2 mass %.

[0067] The content of each component relative to the total amount of the abrasive slurry in Example 1 described above was as follows: total abrasive grain content 2.0 mass%, total permanganate ion content 1.2 mass%, total phosphoric acid content 0.002 mass%, total nanofiber content 0.005 mass%, and total polymer additive content 0.01 mass%.

[0068] In addition, the mass ratio of the content of each component to the total content of the abrasive grains in Example 1 was 0.1% for the total content of phosphoric acids, 0.25% for the total content of nanofibers, and 0.5% for the total content of polymer additives.

[0069] Example 2 In Example 2, the same manufacturing method as in Example 1 was carried out, except that the content of the nanofibers used in Example 1 was adjusted to be 0.025 mass% relative to the total amount of the abrasive slurry of Example 2, and the abrasive slurry of Example 2 was obtained.

[0070] The content of each component relative to the total amount of the abrasive slurry in Example 2 described above was as follows: total abrasive grain content 2.0 mass%, total permanganate ion content 1.2 mass%, total phosphoric acid content 0.002 mass%, total nanofiber content 0.025 mass%, and total polymer additive content 0.01 mass%.

[0071] In addition, the mass ratio of the content of each component to the total content of the abrasive grains in Example 2 was 0.1% for the total content of phosphoric acids, 1.25% for the total content of nanofibers, and 0.5% for the total content of polymer additives.

[0072] Example 3 In Example 3, the abrasive slurry of Example 3 was obtained by carrying out the same manufacturing method as in Example 1, except that lignocellulose nanofibers (manufactured by Daio Paper Co., Ltd., product name: ELLEX-S(C)) were added instead of the nanofibers used in Example 1, and the content of the nanofibers of Example 3 was adjusted to be 0.005 mass% relative to the total amount of the abrasive slurry of Example 3.

[0073] The content of each component relative to the total amount of the abrasive slurry in Example 3 described above was as follows: total abrasive grain content 2.0 mass%, total permanganate ion content 1.2 mass%, total phosphoric acid content 0.002 mass%, total nanofiber content 0.005 mass%, and total polymer additive content 0.01 mass%.

[0074] In addition, the mass ratio of the content of each component to the total content of the abrasive grains in Example 3 was 0.1% for the total content of phosphoric acids, 0.25% for the total content of nanofibers, and 0.5% for the total content of polymer additives.

[0075] Example 4 In Example 4, the abrasive slurry of Example 4 was obtained by carrying out the same manufacturing method as in Example 1, except that lignocellulose nanofibers (manufactured by Daio Paper Co., Ltd., product name: ELLEX-S(C)) were added instead of the nanofibers used in Example 1, and the content of the nanofibers of Example 4 was adjusted to be 0.025 mass% relative to the total amount of the abrasive slurry of Example 4.

[0076] The content of each component relative to the total amount of the abrasive slurry in Example 4 described above was as follows: total abrasive grain content 2.0 mass%, total permanganate ion content 1.2 mass%, total phosphate content 0.002 mass%, total nanofiber content 0.025 mass%, and total polymer additive content 0.01 mass%.

[0077] In addition, the mass ratio of the content of each component to the total content of the abrasive grains in Example 4 was 0.1% for the total content of phosphoric acids, 1.25% for the total content of nanofibers, and 0.5% for the total content of polymer additives.

[0078] Example 5 In Example 5, the abrasive slurry of Example 5 was obtained by carrying out the same manufacturing method as in Example 1, except that cellulose nanofibers (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., product name: Leocrysta i-2SX) were added instead of the nanofibers used in Example 1, and the content of the nanofibers of Example 5 was adjusted to be 0.005 mass% relative to the total amount of the abrasive slurry of Example 5.

[0079] The content of each component relative to the total amount of the abrasive slurry of Example 5 described above was as follows: total abrasive grain content 2.0 mass%, total permanganate ion content 1.2 mass%, total phosphate content 0.002 mass%, total nanofiber content 0.005 mass%, and total polymer additive content 0.01 mass%.

[0080] In addition, the mass ratio of the content of each component to the total content of the abrasive grains in Example 5 was 0.1% for the total content of phosphoric acids, 0.25% for the total content of nanofibers, and 0.5% for the total content of polymer additives. Example 6 In Example 6, the abrasive slurry of Example 6 was obtained by carrying out the same manufacturing method as in Example 1, except that cellulose nanofibers (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., product name: Leocrysta i-2SX) were added instead of the nanofibers used in Example 1, and the content of the nanofibers of Example 6 was adjusted to be 0.025 mass% relative to the total amount of the abrasive slurry of Example 6.

[0081] The content of each component relative to the total amount of the abrasive slurry of Example 6 described above was as follows: total abrasive grain content 2.0 mass%, total permanganate ion content 1.2 mass%, total phosphate content 0.002 mass%, total nanofiber content 0.025 mass%, and total polymer additive content 0.01 mass%.

[0082] In addition, the mass ratio of the content of each component to the total content of the abrasive grains in Example 6 was 0.1% for the total content of phosphoric acids, 1.25% for the total content of nanofibers, and 0.5% for the total content of polymer additives.

[0083] (Comparative Example 1) In Comparative Example 1, the same manufacturing method as in Example 1 was carried out except that nanofibers were not added, and an abrasive slurry according to Comparative Example 1 was obtained.

[0084] The content of each component relative to the total amount of the abrasive slurry in Comparative Example 1 described above was as follows: total abrasive grain content 2.0 mass%, total permanganate ion content 1.2 mass%, total phosphoric acid content 0.002 mass%, total nanofiber content 0.0 mass%, and total polymer additive content 0.01 mass%.

[0085] In addition, the mass ratio of the content of each component to the total content of the abrasive grains in Comparative Example 1 was 0.1% for the total content of phosphoric acids, 0.0% for the total content of nanofibers, and 0.5% for the total content of polymer additives.

[0086] The following physical properties were measured for the abrasive slurries of Examples 1 to 6 and Comparative Example 1. The measured physical properties and the methods for measuring the physical properties are shown below, and the measurement results are shown in Figure 1. The compositions of the abrasive slurries of Examples 1 to 6 and Comparative Example 1 shown in Figure 1 are the compositions of the final products.

[0087] <Friction characteristic evaluation> The friction characteristics of the abrasive slurries of Examples 1 to 6 and Comparative Example 1 were evaluated as follows. A polishing pad (IC1000 manufactured by Nitta DuPont) was attached and fixed to the platen of a polishing machine, and 1 L of the abrasive slurries of Examples 1 to 6 and Comparative Example 1 was supplied to the polishing pad at a rate of 200 mL / min in a circulating manner. A workpiece was placed on the polishing pad as the object to be polished. A spring balance was then hooked onto the workpiece, and the platen of the polishing machine was rotated, while the workpiece was rotated in the same direction as the platen by a forced drive unit. The forced drive unit had a rotating roller that could contact the workpiece, and the workpiece was rotated by rotating the rotating roller. The spring balance was then pulled in a direction that separated the workpiece from the forced drive unit, and the rotation of the workpiece was stopped by the forced drive unit separating the rotating roller from the workpiece. The digital display value (i.e., pulling force) displayed on the spring balance was measured 30 seconds after the rotation of the workpiece had stopped. The tensile force measured in this manner was divided by the load of the workpiece to determine the coefficient of friction of the abrasive slurries according to Examples 1 to 6 and Comparative Example 1. If the coefficient of friction was 0.41 or less, it was evaluated as "〇〇 (VERY GOOD)", if the coefficient of friction was more than 0.41 and less than 0.42, it was evaluated as "〇 (GOOD)", and if the coefficient of friction was more than 0.42, it was evaluated as "× (BAD)".

[0088] <Re-Rally Evaluation> 2000 g of the slurry of Liquid A according to Examples 1 to 6 and Comparative Example 1 was placed in a container (wide-mouth bottle, Eye Boy 2L, manufactured by AS ONE Corporation) and allowed to stand at room temperature (25°C) for one week. After standing for one week, the container containing each Liquid A was placed in a shaker (manufactured by Yamato Scientific Co., Ltd., model: SA300) and shaken for 30 seconds. After 30 seconds of shaking, the container was inverted, and the tester visually confirmed the state of adhesion of each slurry to the container. If each slurry adhered to the bottom or other surface of the container, the container was placed in the shaker again and shaken for 30 seconds, after which the container was inverted, and the tester visually confirmed the state of adhesion of each slurry to the container. The total shaking time required for each slurry to no longer adhere to the bottom or other surface of the container was used to evaluate the results as follows. If the total shaking time was 150 seconds or less, it was rated as "〇〇 (VERY GOOD)", if the total shaking time was more than 150 seconds but less than 200 seconds, it was rated as "〇 (GOOD)", and if the total shaking time was more than 200 seconds, it was rated as "× (BAD)".

[0089] <Polishing test> The polishing rates of the abrasive slurries of Examples 1 to 6 and Comparative Example 1 were evaluated by the following procedure. The object to be polished was a 4H-SiC substrate with a diameter of 4 inches and an off angle of 4° after CMP processing. The polishing test was carried out on the Si surface of the substrate. The polishing device used was a single-side polisher BC-15 manufactured by MAT Corporation. The polishing pad attached to the surface plate was an IC1000 manufactured by Nitta DuPont. The surface plate rotation speed was set to 60 rpm, and the peripheral speed was set to 7,136 cm / min. The carrier rotation speed was also set to 60 rpm, and the peripheral speed was set to 961 cm / min. Furthermore, the load during polishing was 2.8 psi (approximately 1.96 × 10 4 The polishing rate was calculated from the difference in the mass of the substrate before and after polishing, after which the polishing rate was calculated. If the polishing rate was 0.10 μm / h or higher, it was evaluated as "Good", and if the polishing rate was less than 0.10 μm / h, it was evaluated as "Bad".

[0090] <Pot life evaluation> The pot life of Examples 1 to 6 and Comparative Example 1 was evaluated as follows. The abrasive slurries of Examples 1 to 6 and Comparative Example 1 were left standing at room temperature (25°C) for 3 days. The MnO4 - The concentration was measured by the MnO4 - Compared with the concentration, MnO4 - The retention rate of the concentration was calculated. - Concentration vs. MnO4 after 3 days of standing - If the concentration retention rate is 50% or more, it is evaluated as "Good". - Concentration vs. MnO4 after 3 days of standing - If the concentration retention rate was less than 50%, it was evaluated as "BAD (bad)". - The concentration was evaluated as follows. First, the abrasive slurry was centrifuged (4,000 rpm x 20 min) to allow the manganese oxide abrasive grains in the abrasive slurry to settle. Next, 1.0 g of the supernatant was taken and diluted with 109 g of pure water to prepare a diluted solution. Then, using a spectrophotometer (UH-4150 manufactured by Hitachi High-Tech Science Corporation), the MnO4 - The absorbance (intensity of the absorption peak appearing at a wavelength of 525 nm) of MnO4 was measured and calculated using a calibration curve prepared in advance. - The concentration was calculated.

[0091] <Crystallization test> Abrasive slurry samples according to Examples 1 to 6 and Comparative Example 1 were prepared. Each prepared sample was stored in a refrigerator set at 10°C for 24 hours. Thereafter, each sample was removed from the refrigerator, and the solids concentration in each sample, i.e., the sum of the abrasive grain concentration and the potassium permanganate concentration, was determined using a heating moisture meter. If the solids concentration after storage maintained 90% or more of the solids concentration before storage, the sample was evaluated as "Good (◯)." If the solids concentration after storage maintained less than 90% of the solids concentration before storage, the sample was evaluated as "Bad (×)."

[0092] As shown in FIG. 1, the abrasive slurries according to Examples 1 to 6 had a friction coefficient of 0.41 or less, and therefore achieved low friction.

[0093] The abrasive slurries of Examples 1 to 6 had very good adhesion, as the total shaking time required for each abrasive slurry to become free from adhesion to the bottom surface of the container was 150 seconds or less.

[0094] The abrasive slurries according to Examples 1 to 6 exhibited high polishing rates, with polishing rates of 0.10 μm / h or more.

[0095] The abrasive slurries of Examples 1 to 6 were stored in a refrigerator set at 10°C for 24 hours, and the solid content concentration after storage maintained 90% or more of the solid content concentration before storage, indicating that no crystals precipitated.

[0096] The abrasive slurries according to Examples 1 to 6 were left standing at room temperature (25°C) for 3 days, and the MnO4 - The retention rate of the concentration was 50% or more, which extended the pot life.

[0097] The inventions disclosed in this specification include, in addition to the configurations of each invention and embodiment, those specified by changing these partial configurations to other configurations disclosed in this specification, to the extent applicable, or those specified by adding other configurations disclosed in this specification to these configurations, or those specified as higher-level concepts specified by deleting these partial configurations to the extent that partial effects can be obtained. [Industrial Applicability]

[0098] The abrasive slurry of the present invention reduces frictional resistance and can be easily peeled off even when it adheres to the bottom of a container, making it suitable as an abrasive for polishing objects made of high-hardness materials. Furthermore, the abrasive slurry of the present invention has excellent dispersibility, making it easy to clean the objects to be polished, such as SiC substrates and polishing pads, and thus reduces the amount of cleaning water used, shortens cleaning time, and reduces the amount of wastewater to be treated, thereby reducing the environmental impact. Furthermore, the abrasive slurry of the present invention exhibits a high polishing rate, thereby shortening the polishing process time.

Claims

1. an abrasive grain containing manganese oxide particles; one type of nanofiber selected from lignocellulose nanofibers and chitin nanofibers; manganate ions, An abrasive slurry comprising:

2. Abrasive grains and one type of nanofiber selected from lignocellulose nanofibers and chitin nanofibers; manganate ions, Phosphates, and The abrasive slurry is characterized in that the phosphoric acid compound is at least one selected from metaphosphate compounds, hexametaphosphate compounds, pyrophosphate compounds, polyphosphate compounds, tripolyphosphate compounds, and salts or hydrates thereof.

3. 2. The abrasive slurry according to claim 1, further comprising a phosphoric acid.

4. 3. The abrasive slurry according to claim 1, wherein the solvent is water.

5. 3. A polishing method comprising polishing using the abrasive slurry according to claim 1.

6. A SiC wafer polished with the abrasive slurry according to claim 1 or 2.

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