Polishing material slurry and polishing method of 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

Abrasive slurry and polishing method using the same

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

[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, and are therefore able to withstand 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 have a higher hardness 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 a polishing step by a so-called CMP (Chemical Mechanical Polishing) method or the like, which is a step of mirror-finishing the surface of a SiC substrate during the manufacturing process of the SiC substrate.

[0004] Patent No. 6744295

[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 to stand, the abrasive grains settle, and it takes a lot of time to peel off 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.

[0007] The abrasive slurry of the present invention, which has been made to solve the above problems, is characterized by comprising abrasive grains and nanofibers. By comprising the abrasive grains and nanofibers, the abrasive slurry of the present invention reduces frictional resistance and can be easily peeled off even if it adheres to the bottom surface of a container, etc.

[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, for example, 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. The manganese oxide particles contained in the abrasive grains are manganese oxide (II) (MnO), dimanganese trioxide (III) (Mn ２ O ３ ), manganese dioxide (IV) (MnO ２ ), trimanganese(II,III) tetroxide (Mn ３ O ４ ), and manganese dioxide (IV) (MnO ２ 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 measured by a laser diffraction / scattering particle size distribution measurement method of 0.1 μm or more from the viewpoint of having high polishing power, and preferably have a particle size of 5.0 μm or less from the viewpoint of suppressing roughness of 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 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 (D50) of the abrasive grains contained in the abrasive slurry of the present invention at 50% of the cumulative volume 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 later, and diluting the mixture with water so that the concentration of this mixture becomes about 0.01%. Then, the measurement is carried out using a laser diffraction / scattering particle size distribution measurement device (manufactured by Microtrackbell Co., Ltd.: MT3300EXII).

[0013] Furthermore, the content of abrasive grains contained in the abrasive slurry of the present invention is preferably 0.5% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 5% by mass or less, and from the viewpoint of sufficiently increasing the polishing rate of high-hardness materials 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% by mass or more and 2.5% by 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 from the viewpoint 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 in 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 on each 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 portion 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, an I-type crystalline structure. The presence or absence of the I-type 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, near 2θ = 14° to 17° and near 2θ = 22° to 23°, it can be determined that the cellulose structural units have an I-type 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 defibration treatment, or by defibration of fibers through physical stimuli such as frictional force and shear force generated in a flow field, collision, vibration, and 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. Furthermore, 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 relative to the abrasive grain content 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] The abrasive slurry of the present invention preferably further contains manganate ions in addition to the abrasive grains and nanofibers described above. ４ － ), manganate ions (MnO ４ ２－ ) and permanganate ion is preferred.

[0025] Manganate ions, when used as an oxidizing agent in combination with abrasive grains, can have a 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 viewpoint of easy availability and improving the polishing efficiency of the abrasive slurry of the present invention, alkali metal salts of manganate are preferred among the manganate salts that are the source of manganate ions, and sodium manganate (Na ２ MnO ４ ), potassium manganate (K ２ MnO ４ ), sodium permanganate (NaMnO ４ ), potassium permanganate (KMnO ４ ) is more preferred, and potassium permanganate (KMnO ４ These manganates may be used alone or in combination of two or more.

[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, from the viewpoint of sufficiently increasing the polishing rate. Furthermore, 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, from the viewpoint of preventing crystal precipitation due to increased addition amounts, ensuring safety in handling the abrasive slurry, and the tendency for the polishing rate 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 allow the abrasive grains in the abrasive slurry to settle, 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 is preferably sodium phosphate (trisodium phosphate (anhydrous) (Na ３ P.O. ４ ), CAS number: 7601-54-9; trisodium phosphate dodecahydrate (Na ３ P.O. ４ ・12H ２ O), CAS number: 10101-89-0; Sodium phosphate monobasic (NaH ２ P.O. ４), CAS number: 7558-80-7; Sodium phosphate dibasic (Na ２ HPO ４ ), CAS number: 7558-79-4) and potassium phosphate (tripotassium phosphate (anhydrous) (K ３ P.O. ４ ), CAS number: 7778-53-2; Potassium phosphate tripotassium phosphate monohydrate (K ３ P.O. ４ ・H ２ O), CAS number: 27176-10-9; Potassium phosphate dibasic trihydrate (K ２ HPO ４ ・H ２ O), CAS number: 16788-57-1; monobasic potassium phosphate (KH ２ P.O. ４ ), CAS number: 7778-77-0; dipotassium phosphate (K ２ HPO ４ ), CAS number: 7758-11-4).

[0029] Furthermore, as the metaphosphate compound, sodium metaphosphate (NaPO ３ ) ｎ , CAS number: 35270-09-8) and potassium metaphosphate (KPO ３ ) ｎ , CAS number: 7790-53-6.

[0030] As a hexametaphosphate compound, sodium hexametaphosphate (NaH ７ P ６ O １８ ), CAS number: 10124-56-8.

[0031] As the pyrophosphate compound, sodium pyrophosphate (sodium pyrophosphate (anhydrous) (Na ４ P ２ O ７ ), CAS number: 7722-88-5; Sodium pyrophosphate decahydrate (Na ４ P ２ O ７ ・10H ２ O), CAS number: 13472-36-1; Sodium acid pyrophosphate (Na ２ H ２ P２ O ７ ), CAS number: 7758-16-9) and potassium pyrophosphate (K ４ P ２ O ７ ), CAS number: 7320-34-5.

[0032] As the polyphosphate compound, sodium polyphosphate (Na ３ P ３ O １０ X ２ ), CAS number: 68915-31-1; potassium polyphosphate (K ３ P ３ O １０ X ２ ), CAS number: 68956-75-2.

[0033] As a tripolyphosphate compound, sodium tripolyphosphate (Na ５ P ３ O １０ ), CAS number: 7758-29-4, potassium tripolyphosphate (K ５ P ３ O 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 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 ( ３１ The measurement can be carried out by peak separation using the DOSY (Diffusion Ordered NMR Spectroscopy) method in P-NMR. In this case, the abrasive slurry of the present invention may be diluted with pure water and filtered, if necessary, to analyze the phosphoric acid contained in the filtrate.

[0037] Furthermore, the measurement of the phosphoric acids contained in the abrasive slurry of the present invention is preferably performed by high performance liquid chromatography. In high performance liquid chromatography, by using a non-suppressor anion analysis column, the type and weight of phosphoric acids can be measured by a known method. 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 acids 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 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 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 mass% or more and 0.2 mass% or less relative to the total amount of the abrasive slurry of the present invention, and from the viewpoint of frictional resistance, it is more preferably 0.002 mass% or more, and from the viewpoint of sufficiently increasing the polishing rate, it is more preferably 0.1 mass% or less. The content of phosphoric acid is more preferably 0.002 mass% or more and 0.05 mass% or less. Typically, the content of phosphoric acid may be 0.002 mass% or more and 0.02 mass% or less. In this specification, the content of phosphoric acid is the total amount of those 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 relative to the abrasive grain content in the abrasive slurry of the present invention, is preferably 0.05% or more and 10.0% or less. More preferably, it is 0.1% or more and 5.0% or less, and even more preferably, it is 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 relative to the abrasive grain content 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 in a form in which the above-mentioned abrasive grains, nanofibers, manganate ions, phosphates, dispersion medium, and optional additives are appropriately mixed, and for example, these components may be divided into two or more components to form a kit. The kit may be configured in any form so that 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. The abrasive slurry of the present invention is diluted with water so that the concentration becomes about 0.01% by mass, and a measurement sample is prepared. Then, using a laser diffraction / scattering particle size distribution analyzer (manufactured by Microtrackbell Co., Ltd.: MT3300EXII), the particle size (D50) at a volume-based cumulative fraction of 50% is measured, and 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] The polishing method includes 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 the relative movement between them. Here, the abrasive slurry of the present invention may be a method of pouring the abrasive slurry, 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 repeatedly supplied to the polishing pad. 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 pad made of 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 abrasive pressure is 100 Pa or less in terms of 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 500 mL / min or less, and more preferably 50 mL / min or more and 250 mL / min or less.

[0050] The object to be polished with the abrasive slurry of the present invention is a high-hardness material, for example, having 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 conventional 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: Mohs hardness 1: talc, 2: gypsum, 3: calcite, 4: fluorite, 5: apatite, 6: orthoclase, 7: quartz, 8: topaz, 9: corundum, and 10: diamond. 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. Hexagonal crystals are 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, put pure water and manganese dioxide (abrasive grains, MnO ２ ), phosphoric acid (e.g., sodium salt of pyrophosphate), and beads (zirconia, φ0.4 mm) were placed in the container, which was then placed on a paint shaker (60 Hz). The container was rotated at high speed, and manganese dioxide (abrasive grains, MnO ２ ) are mixed and ground.

[0054] The mixed and crushed manganese dioxide (abrasive grains, MnO ２ The mixture containing the beads is separated from the beads using a centrifuge (himac CT 6E manufactured by Hitachi Koki Co., Ltd.) 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] The 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] Then, the abrasive slurry intermediate to which the nanofibers were added and potassium permanganate (KMnO ４ The abrasive slurry of the present invention can be obtained by mixing the abrasive slurry intermediate with the nanofibers. ４ ) is called solution B.

[0058] The SiC wafer of the present invention is characterized by being polished using the above-described abrasive slurry of the present invention. The SiC wafer of the present invention is free from warpage and cracking due to the Twyman effect because it has been polished using the above-described abrasive slurry of the present invention. The SiC wafer of the present invention is also polished by the above-described 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 means "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 means "preferably larger than X" or "preferably smaller than Y".

[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.

[0061] 1 is a table showing the physical properties and measurement results of the abrasive slurries according to Examples 1 to 6 and Comparative Example 1.

[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 and manganese dioxide (MnO ２ ), as a phosphoric acid, sodium pyrophosphate (specifically, sodium pyrophosphate decahydrate (Na ４ P ２ O ７ ・10H ２0), CAS number: 13472-36-1), ammonium polyacrylate as a polymer additive, and beads (zirconia, φ0.4 mm) were placed in the container, and the container was set on a paint shaker (60 Hz). The container was 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 (himac CT 6E manufactured by Hitachi Koki Co., Ltd.) or the like, and the supernatant was collected. The solids 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 intermediate to which the nanofibers were added and KMnO ４ Potassium permanganate (KMnO) with a mass % concentration of 3.2 mass % ４ ) aqueous solution to obtain an abrasive slurry according to Example 1.

[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 phosphate 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 0.025 mass% relative to the total amount of the abrasive slurry of Example 2, and an 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 phosphate 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 Corporation, 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% with respect 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 phosphate 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% with respect 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: Rheocrysta 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 % with respect 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] Furthermore, the mass ratio of the content of each component relative to the total content of the abrasive grains according to 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, an abrasive slurry according to Example 6 was obtained by carrying out the same production method as in Example 1, except that cellulose nanofibers (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., product name: Rheocrysta i-2SX) were added instead of the nanofibers used in Example 1, and the content of the nanofibers according to Example 6 was adjusted to 0.025% by mass relative to the total amount of the abrasive slurry according to Example 6.

[0081] The content of each component relative to the total amount of the abrasive slurry in 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, to obtain an abrasive slurry according to Comparative Example 1.

[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 phosphate 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 Property Evaluation> The friction properties of the abrasive slurries according to 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 according to Examples 1 to 6 and Comparative Example 1 was supplied to the polishing pad at a supply rate of 200 mL / min in a circulating manner. A workpiece was placed on the polishing pad as the object to be polished. Furthermore, with a spring balance hooked onto the workpiece, the platen of the polishing machine was rotated, and the workpiece was rotated in the same direction as the platen by a forced drive unit. Here, the forced drive unit was provided with 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 moved the workpiece away from the forced drive unit, and the forced drive unit separated the rotating roller from the workpiece, thereby stopping the rotation of the workpiece. The digital display value (i.e., tensile 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 friction coefficient of the abrasive slurries of Examples 1 to 6 and Comparative Example 1. If the friction coefficient was 0.41 or less, it was evaluated as "〇〇 (VERY GOOD)", if the friction coefficient was more than 0.41 and less than 0.42, it was evaluated as "〇 (GOOD)", and if the friction coefficient was more than 0.42, it was evaluated as "× (BAD)".

[0088] <Reslurry 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 adhesion state of each slurry to the container. If each slurry adhered to the bottom of the container, the container was placed in the shaker again, shaken for 30 seconds, and then the container was inverted. The tester visually confirmed the adhesion state of each slurry to the container. Then, the total shaking time required for each slurry to no longer adhere to the bottom of the container was used to evaluate the results as follows. If the total shaking time was 150 seconds or less, it was evaluated as "〇〇 (VERY GOOD)", if the total shaking time was more than 150 seconds and less than 200 seconds, it was evaluated as "〇 (GOOD)", and if the total shaking time was more than 200 seconds, it was evaluated as "× (BAD)".

[0089] <Polishing Test> The polishing rates of the abrasive slurries according to Examples 1 to 6 and Comparative Example 1 were evaluated by the following procedure. The object to be polished was a 4H-SiC substrate having 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 apparatus 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 rotation speed of the surface plate was set to 60 rpm, and the peripheral speed was set to 7,136 cm / min. The rotation speed of the carrier was 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 to be polished before and after polishing, with the supply rate of the abrasive slurry being 200 mL / min. The polishing rate was calculated from the difference in the mass of the substrate to be polished before and after polishing for 1 hour. If the polishing rate was 0.10 μm / h or more, it was evaluated as "Good (Good)", and if the polishing rate was less than 0.10 μm / h, it was evaluated as "Bad (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 allowed to stand at room temperature (25°C) for 3 days. The MnO content in the abrasive slurries after standing for 3 days was ４ － The concentration was measured by the MnO ４ － Compared with the concentration, MnO ４ － The retention rate of the MnO concentration was calculated. ４ － MnO after standing for 3 days versus concentration ４ － If the retention rate of the concentration was 50% or more, it was evaluated as "Good (Good)." ４ － MnO after standing for 3 days versus concentration ４ － If the concentration retention rate was less than 50%, it was evaluated as "× (BAD)". ４ － 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 MnO ４ － The absorbance (intensity of the absorption peak appearing at a wavelength of 525 nm) of MnO was measured, and the absorbance was calculated using a calibration curve prepared in advance. ４ － The concentration was calculated.

[0091] <Crystallization Test> Samples of abrasive slurries 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 of the container was 150 seconds or less.

[0094] The abrasive slurries according to Examples 1 to 6 exhibited high polishing rates, ie, 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 MnO ４ － Since the concentration was maintained at 50% or more, the pot life was extended.

[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.

[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 reduces the amount of cleaning water used, the cleaning time, and 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 slurry characterized by comprising abrasive grains and nanofibers.

2. The abrasive slurry according to claim 1, wherein the nanofibers contain one or more selected from the group consisting of polysaccharide nanofibers, polymer nanofibers, and carbon nanofibers.

3. The abrasive slurry according to claim 2, wherein the nanofibers contain the polysaccharide nanofibers.

4. The abrasive slurry according to claim 3, wherein the polysaccharide nanofibers contain cellulose nanofibers and / or lignocellulose nanofibers.

5. The abrasive slurry according to claim 1, wherein the abrasive grains contain manganese oxide particles.

6. The abrasive slurry according to claim 1, further comprising manganate ions.

7. The abrasive slurry according to claim 1, further comprising phosphoric acids.

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

9. A polishing method characterized by polishing using the abrasive slurry according to any one of claims 1 to 8.

10. A SiC wafer characterized by being polished using the abrasive slurry according to any one of claims 1 to 8.

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