Polishing slurry

Abstract

Provided is a polishing slurry that can make it possible to more efficiently obtain, at a high polishing speed, a polished surface having good surface characteristics even for objects to be polished having relatively low mechanical strength. The polishing slurry contains α-alumina as polishing particles in an aqueous medium. The α-alumina has a mean particle diameter (D50) at a 50% cumulative volume basis in particle size distribution obtained by a laser diffraction scattering method of 80-120 nm, has a specific surface area (BET) measured on the basis of the JIS-Z8830 (2013) specification of 20 m2 / g or more, and has a ratio (BET / D50) of the specific surface area (BET) to the mean particle diameter (D50) of 1.5 m / g×10-4 or more.

Description

Polishing Slurry

[0001] The present invention relates to a polishing slurry, and more particularly to a polishing slurry that can be used for precision processing of the surface of an interlayer insulating film formed on a semiconductor device such as an optical component, an electronic component, a precision instrument component, or a semiconductor package substrate mounted on these components.

[0002] In recent years, with the increasing integration and performance of semiconductor package substrates containing semiconductor integrated circuits, microfabrication techniques have been developed to achieve finer wiring and multilayering, etc. Chemical mechanical polishing (hereinafter also referred to as "CMP") is one such technique, and is a technique frequently used in the manufacturing process of semiconductor integrated circuits, particularly in the process of forming fine multilayer wiring.

[0003] However, miniaturization and multi-layering hinder the speed of semiconductor integrated circuits due to signal delays caused by increased capacitance between interconnects. Therefore, to accommodate faster processing, low-dielectric-constant insulating film materials that satisfy various properties such as low dielectric constant, low dielectric dissipation factor, and high heat resistance are being developed. The advantage of using low-dielectric-constant insulating film materials is that the smaller the dielectric constant, the faster the propagation speed. Organic insulating materials, particularly those primarily composed of polyimide resin, are known to improve transmission speeds by reducing their dielectric constant.

[0004] It is expected that by applying the CMP method to polishing the surface of a resin film such as a polyimide resin, it will be possible to form a high-quality interlayer insulating film with low surface roughness, and a process is being considered in which the CMP method is used to polish and remove excess parts of a polishing object containing resin.

[0005] Patent Document 1 discloses a polishing composition as a means for polishing a resin having high rigidity and strength at a high polishing rate, which comprises abrasive grains and a dispersion medium, and the abrasive grains have a Mohs hardness of 8 or more and a surface acid amount of 0.05 mmol / g or more as measured by an ammonia temperature-programmed desorption method (NH3-TPD method).

[0006] Patent Document 2 discloses a method for polishing an interlayer insulating material made of inorganic particles and a resin material, which includes the steps of polishing the interlayer insulating material with a first polishing slurry containing first abrasive particles having an average particle size equal to or larger than the average particle size of the inorganic particles and a dispersant, and further polishing the interlayer insulating material polished with the first polishing slurry with a second polishing slurry containing second abrasive particles having an average particle size smaller than the average particle size of the inorganic particles and a dispersant.

[0007] JP 2016-183212 A JP 2021-141213 A

[0008] However, organic interlayer insulating films made of polymeric compounds such as polyimide resins have lower mechanical strength than conventional inorganic interlayer insulating films made of SiO2 or the like. Simply using hard abrasive grains to physically process such a polishing target, which has low mechanical strength, can easily cause film defects such as cracks and scratches, and may result in insufficient polishing speed. Performing two-stage polishing to compensate for this can result in problems such as a decrease in process throughput or an increase in the size of the polishing device due to the need for separate platens.

[0009] In view of the above problems, the present invention provides a polishing slurry that can efficiently obtain a polished surface with good surface properties at a high polishing rate even on an object to be polished that has a relatively low mechanical strength.

[0010] In order to solve the above problems, in one aspect, the polishing slurry according to the present invention contains α-alumina as abrasive particles in an aqueous medium, and the α-alumina has an average particle diameter (D50) at 50% of the volume-based integrated value in the particle size distribution determined by a laser diffraction scattering method of 80 to 120 nm, and a specific surface area (BET) measured in accordance with the provisions of JIS-Z8830 (2013) of 20 m 2 / g or more, and the ratio (BET / D50) of the specific surface area (BET) to the average particle diameter (D50) is 1.5 m / g×10 -4 The above is the polishing slurry.

[0011] In one embodiment, the polishing slurry according to the present invention has a ratio (TBD / LBD) of loose bulk density (LBD) to tight bulk density (TBD) measured in accordance with JIS-R9301-2-3 (1999) of 1.5 or less.

[0012] In another embodiment, the polishing slurry according to the present invention has a specific surface area (BET) of 25 m 2 / g or more, and the ratio (BET / D50) of the specific surface area (BET) to the average particle diameter (D50) is 2.0 m / g×10 -4 That's all.

[0013] In yet another embodiment of the polishing slurry according to the present invention, the content of abrasive particles is 0.01 to 10 mass %, and the polishing slurry contains 0.0001 to 1 mass % of nitric acid as a dispersant.

[0014] In yet another embodiment, the polishing slurry according to the present invention is a free abrasive polishing slurry used for polishing insulating materials containing polyimide resin.

[0015] According to the present invention, it is possible to provide a polishing slurry that can efficiently obtain a polished surface with good surface properties at a high polishing rate even on an object to be polished that has a relatively low mechanical strength.

[0016] The present invention is not limited to any particular object to be polished, but the polishing slurry according to the present invention is suitable for free abrasive polishing of insulating films (particularly interlayer insulating films) formed in semiconductor devices, etc.

[0017] Interlayer insulating films are used to fill and insulate fine wiring made of copper, aluminum, or the like, and to form multilayer circuit patterns. To form multilayer circuit patterns, the interlayer insulating film formed on a semiconductor substrate is planarized by CMP, and then new wiring is optically exposed on top of it by photolithography to form a circuit. This process is repeated to form a desired circuit. Specifically, a conductive layer is formed as a circuit on the surface of a base substrate (e.g., a Bakelite substrate, a glass epoxy substrate, a resin substrate such as an epoxy or polyester substrate, or a composite substrate of these), and an interlayer insulating film is then laminated on top of this. The interlayer insulating film on the substrate is then polished to planarize the substrate surface, exposing the conductive layer.

[0018] Suitable materials for such interlayer insulating films include, for example, polyimide resins, polyester resins, and epoxy resins. In particular, in this embodiment, a polyimide film containing polyimide resin as the main component (50 wt % or more) is suitable for processing. Polyimide films are generally composed primarily of aromatic polyimides obtained by imidizing (dehydrating and cyclizing) polyamic acid through high-temperature heating. Polyimide films may also be those containing fluorine atoms or alicyclic groups as substituents to reduce the dielectric constant, those made nanoporous to reduce film density, those physically containing low-dielectric additives, those with increased linearity of the main chain to reduce the thermal expansion coefficient, or those containing low-expansion fibers, whiskers, or particles.

[0019] The polyimide film used as such an interlayer insulating material has a relatively low mechanical strength compared to SiO2 films, etc., but the polishing slurry according to the embodiment of the present invention can obtain a polished surface with good surface characteristics at a higher polishing rate even for such materials with low mechanical strength.

[0020] Although not limited to the following, the interlayer insulating film that can be polished using the polishing slurry according to the embodiment of the present invention preferably has a Young's modulus of 0.1 to 20.0 GPa, more preferably 1.0 to 10.0 GPa, and even more preferably 3.0 to 8.0 GPa. The Young's modulus can be evaluated based on JIS-Z2255 (2003).

[0021] (Polishing Slurry) The polishing slurry according to an embodiment of the present invention contains α-alumina as abrasive particles (abrasive grains) in an aqueous medium. The aqueous medium is not particularly limited as long as it is capable of dispersing abrasive particles, but impurity-free water is preferred. Examples include pure water, ultrapure water, and distilled water. The α-alumina dispersed in the aqueous medium preferably has an average particle diameter (D50) of 80 to 120 nm at 50% of the volume-based integrated value in the particle size distribution determined by laser diffraction scattering. For example, organic interlayer insulating films such as polyimide resins have lower mechanical strength than conventional inorganic interlayer insulating films such as SiO2. Therefore, simply using α-alumina, which has high hardness, as an abrasive grain is likely to cause film defects such as cracks and scratches. By adjusting the average particle diameter (D50) of the α-alumina dispersed in the aqueous medium to a relatively small particle size of 80 to 120 nm, it is possible to improve the polishing rate while reducing film defects, even on polished objects with low mechanical strength. The average particle size (D50) of α-alumina is more preferably 90 to 120 nm, and even more preferably 95 to 110 nm.

[0022] When polishing resin materials with low mechanical strength, such as organic interlayer insulating films made of polyimide resin, simply using α-alumina abrasives with a small average particle size (D50) and a large specific surface area (BET) may not provide a sufficient polishing rate or a polished surface with good surface properties. By increasing the specific surface area within an appropriate particle size range that is less likely to cause film damage, a polished surface with good surface properties can be obtained at a high polishing rate.

[0023] In this embodiment, the specific surface area (BET) of α-alumina is 20 m 2 / g or more, and2 / g or more is more preferable, and 30m 2 If the specific surface area (BET) of α-alumina is too high, dispersion becomes difficult, which may increase the load of the dispersion step, cause undispersed matter, and ultimately cause scratches on the object to be polished. 2 / g or less, and 2 / g or less is more preferable, and 50m 2 The specific surface area (BET) can be measured based on the specifications of JIS-Z8830 (2013).

[0024] Furthermore, by adjusting the ratio (BET / D50) of the specific surface area (BET) to the average particle diameter (D50) of α-alumina used as abrasive particles to an appropriate range, it is possible to suitably polish resin materials with low mechanical strength, such as organic interlayer insulating films using polyimide resin. BET / D50 is 1.5 m / g×10 -4 It is preferable that the viscosity is 2.0 m / g×10 or more. -4 More preferably, it is 2.5 m / g×10 or more. -4 In order to ensure an appropriate surface roughness and a sufficient polishing rate, BET / D50 is 15.0 m / g×10 -4 It is preferable that the saturation rate is 10.0 m / g × 10 -4 More preferably, it is 6.3 m / g×10 or less. -4 Even more preferably, the following:

[0025] If the light bulk density (LBD) of α-alumina is too high, the proportion of large primary particles increases, causing deterioration of the surface properties after polishing, while if it is too low, the proportion of alumina with a low α conversion rate increases, which may cause a decrease in the polishing rate. 3 It is preferable that the density is 0.7 g / cm or more. 3 More preferably, it is 0.8 g / cm or more. 3 The upper limit of the LBD is not particularly limited, but is preferably 1.7 g / cm. 3It is preferable that the density is 1.3 g / cm or less. 3 More preferably, it is:

[0026] Furthermore, if the packed bulk density (TBD) of α-alumina is too high, the proportion of large primary particles increases, which can cause deterioration of the surface properties after polishing, and if it is too low, the proportion of alumina with a low α conversion rate increases, which can cause a decrease in the polishing rate. 3 It is preferable that the density is 0.9 g / cm or more. 3 More preferably, it is 1.0 g / cm or more. 3 The upper limit of the TBD is not particularly limited, but is preferably 2.0 g / cm 3 It is preferable that the density is 1.5 g / cm or less. 3 It is more preferable that the light packed bulk density (LBD) and the heavy packed bulk density (TBD) are measured in accordance with JIS-R9301-2-3 (1999).

[0027] In this embodiment, the ratio (TBD / LBD) of the loose bulk density (LBD) to the loaded bulk density (TBD) measured according to JIS-R9301-2-3 (1999) is preferably 1.5 or less. A small difference between the TBD and LBD values ​​means that there is no significant change in porosity after tapping, and that the bulk density of individual secondary particles (aggregated particles) contained in the average particle size (D50) of α-alumina is high, i.e., the cohesive strength of the secondary particles is high. The presence of many particles that maintain the agglomerated particle form even after dispersion to an appropriate particle size allows for a polished surface with good surface properties to be obtained at a high polishing rate within a relatively small, appropriate particle size range. It is more preferable that TBD / LBD is 1.00 to 1.50, and even more preferably 1.00 to 1.35.

[0028] The content of the abrasive particles in the aqueous medium can be set as desired depending on the application. Although not particularly limited, in order to obtain a sufficient polishing rate while maintaining good surface properties, the content is preferably 0.01 to 10 mass %, more preferably 0.05 to 5 mass %, and even more preferably 0.1 to 1 mass %.

[0029] The α-alumina abrasive grains may have an α-conversion rate of, but not limited to, 40 to 65%, preferably 45 to 60%, from the viewpoint of polishing a material with relatively poor mechanical properties at a sufficient polishing rate. The α-alumina abrasive grains may have an α-conversion rate of, for example, 40 to 65%, more preferably 45 to 60%. The α-alumina abrasive grains may be determined from the integrated intensity ratio of the (113) plane diffraction line by X-ray diffraction measurement.

[0030] The polishing slurry is preferably prepared to contain abrasive particles and a dispersant. The inclusion of a dispersant in the polishing slurry efficiently disperses the abrasive particles, enabling them to be rapidly delivered into the interlayer insulating film. Known dispersants can be used, such as those that utilize the steric hindrance of the molecular chains in surfactants or those that improve dispersion by electrical repulsion of the particle surface potential. In particular, in this embodiment, α-alumina, a highly polar oxide, is used as the abrasive particles, and therefore ionic polymer surfactants such as polyacrylates and polystyrene sulfonates, and acids such as hydrochloric acid, nitric acid, citric acid, and acetic acid can be used. From the perspectives of avoiding surface contamination of semiconductor package substrates and the like (ease of cleaning) and achieving adequate corrosion resistance to the resin materials contained in the interlayer insulating material, it is preferable to use an acid as a dispersant. In particular, nitric acid is preferably used as a dispersant for organic interlayer insulating films using polyimide resins. The content of nitric acid is not particularly limited, but can be, for example, 0.0001 to 1 mass %, preferably 0.001 to 0.1 mass %, and more preferably 0.002 to 0.05 mass %.

[0031] The polishing slurry is preferably prepared so as to further contain a thickener. In one embodiment, α-alumina having a TBD / LBD ratio of 1.5 or less is preferably used, and the bulk density of the individual secondary particles (agglomerated particles) contained in the abrasive particles is high. Therefore, by further containing a thickener in the polishing slurry, it is possible to prevent the precipitation of the agglomerated particles of α-alumina, which have a high bulk density, and to improve the dispersion stability of the abrasive particles.

[0032] Examples of thickeners include surfactants and water-soluble polymers. In particular, water-soluble polymers are suitable for preventing precipitation of aggregated α-alumina particles and improving dispersion stability.

[0033] As the water-soluble polymer, a polycarboxylic acid-based water-soluble polymer can be used as an anionic (negative) polymer, for example, a polyacrylic acid-based water-soluble polymer such as polyacrylic acid or its salt, an acrylic acid-(meth)acrylic acid ester copolymer or its salt, alginate, cellulose derivatives such as carboxymethyl cellulose, etc. Examples of nonionic (non-ionic) polymers include cellulose derivatives such as hydroxyethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, and polyacrylamide. Examples of cationic (cationic) water-soluble polymers include polyethyleneimine.

[0034] In this embodiment, a nonionic water-soluble polymer can be suitably used from the viewpoint that the thickener prevents the precipitation of aggregated particles of α-alumina as abrasive particles, enhances dispersion stability, and ensures the function of suppressing polishing inhibition such as a decrease in the polishing speed of the object to be polished due to an excessive increase in viscosity. The content of the water-soluble polymer is suitably 0.01 to 1 mass %, preferably 0.1 to 0.9 mass %, based on the total polishing slurry.

[0035] The polishing slurry according to the embodiment of the present invention is preferably used for polishing an interlayer insulating material mainly composed of polyimide resin, but when polishing an interlayer insulating material, it may be necessary to planarize metal wiring made of copper, aluminum, etc. together with the interlayer insulating film by CMP. In this case, an oxidizing agent, a complexing agent, an antioxidant, a pH adjuster, etc. may be appropriately added as needed.

[0036] The oxidizing agent has the function of moderately oxidizing and ionizing a metal film such as copper, and the complexing agent promotes the ionization of the metal film such as copper. The antioxidant can suppress excessive etching of the metal film by the oxidizing agent or complexing agent, and adjusting the concentrations of these agents can adjust the polishing rate for the metal film within a suitable range.

[0037] Examples of oxidizing agents that can be used include peroxides such as H2O2, Na2O2, Ba2O2, and (C6H5C)2O2, as well as organic peroxides such as hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, peracetic acid, and nitrobenzene. Among these, hydrogen peroxide (H2O2) is preferred because it does not contain metal components and does not generate harmful by-products. The content of the oxidizing agent in the polishing slurry is 0.01 to 15 mass %, preferably 0.1 to 10 mass %, based on the total mass of the polishing slurry.

[0038] The complexing agent may be a known organic acid such as a carboxylic acid or an amino acid. Examples of the organic acid include glycine, alanine, valine, serine, threonine, cysteine, phenylalanine, proline, asparagine, aspartic acid, lysine, histidine, arginine, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citric acid, and lactic acid, as well as salts thereof such as ammonium salts and alkali metal salts, and mixtures thereof. Among them, glycine, an amino acid having both an amino group and a carboxyl group, is suitable for dissolving metals that are difficult to dissolve. The content of the complexing agent is 0.01 to 5 mass %, preferably 0.05 to 3 mass %, and more preferably 0.1 to 1 mass %, based on the total polishing slurry.

[0039] Examples of antioxidants that can be used include benzotriazole, 1,2,3-triazole, 1,2,4-triazole, benzofuroxan, 2,1,3-benzothiazole, o-phenylenediamine, m-phenylenediamine, catechol, o-aminophenol, 2-mercaptobenzothiazole, 2-mercaptobenzimidazole, 2-mercaptobenzoxazole, melamine, and derivatives thereof. The content of the antioxidant is 0.001 to 1 mass %, preferably 0.01 to 0.1 mass %, based on the total polishing slurry.

[0040] The pH of the polishing slurry is suitably 3 to 8, preferably 4 to 7, from the viewpoint of polishing speed, slurry viscosity, dispersion stability of abrasive particles, etc. The pH of the polishing slurry can be adjusted by a known method, and when nitric acid is used as the dispersant of the polishing slurry, it is preferable to use an alkali, and alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali metal carbonates such as sodium carbonate and potassium carbonate, ammonia, amines, etc. can be used, and among them, it is suitable to add ammonia to adjust the pH to a suitable range.

[0041] (Method for producing abrasive slurry) The method for producing abrasive slurry according to the embodiment of the present invention can be, for example, by stirring and mixing abrasive particles and dispersant in aqueous medium, and then diluting.For example, water and dispersant such as nitric acid are added to abrasive particles, and then by using a bead mill or the like, stirring and mixing the average particle diameter (D50) of abrasive particles to 80-120nm, then diluting with water so that the content of abrasive particles is 0.01-10 mass%, and then adjusting pH, can produce abrasive slurry (free abrasive grain abrasive slurry) suitable for polishing insulating materials including polyimide resin.

[0042] (Polishing Method) Using the polishing slurry according to the embodiment of the present invention, a free-abrasive polishing process can be suitably performed on an insulating film containing a polyimide resin formed on a semiconductor device substrate. The polishing apparatus is not particularly limited, and various common polishing apparatuses can be used, including single-sided and double-sided polishing apparatuses. For example, when using a single-sided polishing apparatus, the semiconductor substrate is held by a holder such as a carrier, and the polishing slurry according to the embodiment of the present invention is applied to the surface of the insulating film containing a polyimide resin formed on the semiconductor substrate. Then, a platen with a predetermined polishing pad attached thereto is pressed against the object to be polished and rotated, thereby polishing the surface of the insulating film at a predetermined polishing rate or higher.

[0043] According to the polishing method using the polishing slurry of the embodiment of the present invention, even for materials with relatively low mechanical strength, such as insulating materials containing polyimide resin, a polished surface with good surface properties can be obtained at a high polishing rate by a single polishing process without repeating polishing processes step by step, thereby realizing an efficient polishing process.

[0044] According to the polishing method of the present invention, the polishing rate can be set to 200 nm / min or more, further 300 nm / min or more, and even 350 nm / min or more. While the recommended upper limit of the polishing rate is not particularly specified, if the polishing rate is set too high, it may be difficult to adjust the desired removal amount. Therefore, it is typically set to 3000 nm / min or less, and even 1500 nm / min or less. Although not limited to the following, the polishing load applied to the insulating film containing polyimide resin can be, for example, 0.1 to 10.0 psi, and preferably 1.0 to 5.0 psi. By performing such a process, the surface of the insulating film can be made to have a surface roughness (center line average roughness Ra) according to Appendix JB of JIS-B0601 (2013). 75 ) is 10 nm or less, further 5.0 nm or less, and further 2.0 nm or less, and a polished surface having good flatness characteristics can be obtained.

[0045] Examples of the present invention are given below, but these examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0046] <Polishing Slurry> Using various abrasive particles shown in Table 1, 0.2% by mass of nitric acid was added to the abrasive particle / water mixture with an abrasive particle content of 30% by mass, and dispersed by a bead mill, followed by dilution with water to prepare abrasive slurries with an abrasive particle content (abrasive particle concentration) of 0.5% by mass and an average particle diameter (D50) of abrasive particles shown in Table 1. The pH of the abrasive slurry was adjusted to pH=6 by adding ammonia.

[0047] <Measurement of particle size> The particle size of the abrasive particles contained in the polishing slurry is measured using a laser diffraction / scattering particle size distribution measuring device (LA-960, manufactured by Horiba, Ltd.). The particle size value is the average particle size (D50) at 50% of the volume-based integrated value in the particle size distribution obtained by laser diffraction / scattering method.

[0048] <Object to be Polished> A silicon wafer having a diameter of 200 mm was coated with polyimide (photosensitive positive type manufactured by Advanced Materials Technology Co., Ltd.) using a spin coater, and the coated silicon wafer was thermally cured to form a polyimide film having a thickness of 10 μm on the silicon wafer.

[0049] <Polishing Conditions> A Mirra CMP device manufactured by Applied Materials was used as the polishing device, and polishing was performed under the following conditions: A polishing pad (IC1400 manufactured by Nitta DuPont Co., Ltd.) was attached to the platen of the polishing device. Down Force = 2.0 psi, Head Speed ​​ / Platen Speed ​​= 120 / 117 rpm, Slurry Flow = 200 ml / min, Polish Time = 30 sec

[0050] <Measurement of Polishing Rate> The polishing rate was measured by measuring the change in film thickness of the object to be polished (polyimide film) before and after polishing using FilmTec 1000 manufactured by SCI, measuring the amount of film thickness reduction per polishing time, and calculating the polishing rate.

[0051] <Measurement of Surface Roughness> The surface roughness was measured using a scanning probe microscope (Nanoscope V, manufactured by Bruker Japan Co., Ltd.). The surface roughness value was the centerline average roughness Ra defined in Appendix JB of JIS-B0601 (2013). 75 was used.

[0052] <Experimental Results> The polishing results using polishing slurries containing various abrasive particles are shown in Table 1 below.

[0053]

[0054] The abrasive particles used were α-alumina, with particle diameters in the range of 80 to 120 nm and a specific surface area (BET) of 20 m 2 / g or more, and the ratio (BET / D50) of the specific surface area (BET) to the average particle diameter (D50) is 1.5 m / g×10 -4 In Example 1, a higher polishing rate was obtained compared to Comparative Examples 1 to 4. In addition, the surface roughness of the polyimide film was 75 In Example 1, the ratio of the light packed bulk density (LBD) to the heavy packed bulk density (TBD) (TBD / LBD) was 1.5 or less.

[0055] In Comparative Examples 1 to 4, which used α-alumina as abrasive particles, the average particle diameter (D50) was adjusted to the range of 80 to 120 nm, and the surface roughness after polishing was good in all cases. However, the polishing rate was lower than in Example 1. In Comparative Example 4, the BET was 20 m 2 / g or less, BET / D50 is 1.5m / g x 10 -4 In Comparative Example 3, the BET and BET / D50 were not within the preferred ranges, and the TBD / LBD was 1.5 or less, resulting in a lower polishing rate compared to Example 1. In Comparative Example 3, the BET / D50 was 1.5 m / g×10 -4 That was all, but the bet was 20m 2 / g, and TBD / LBD was 1.5 or more, resulting in a lower polishing rate compared to Example 1. Comparative Example 2 had a small BET and a large TBD / LBD value, resulting in a lower polishing rate. Comparative Example 1 had a small BET and a BET / D50 of 1.5 m / g×10 -4The polishing rate was less than 1 / 3 of the original polishing rate, and was low. Furthermore, in Reference Examples 1 and 2, in which θ-alumina and silica were used as abrasive particles, a polishing rate higher than that of Example 1 was not obtained. From these results, it can be seen that when α-alumina is used as abrasive particles, and the α-alumina has an average particle diameter (D50) at 50% of the volume-based integrated value in the particle size distribution determined by the laser diffraction scattering method of 80 to 120 nm, and a specific surface area (BET) measured in accordance with the provisions of JIS-Z8830 (2013) of 20 m 2 / g or more, and the ratio (BET / D50) of the specific surface area (BET) to the average particle diameter (D50) is 1.5 m / g×10 -4 It has been found that when the above conditions are met, and preferably when the ratio (TBD / LBD) of the loose bulk density (LBD) to the loaded bulk density (TBD) measured in accordance with JIS-R9301-2-3 (1999) is 1.5 or less, sufficiently high speed and excellent planarization can be achieved in polishing materials with low mechanical strength used in interlayer insulating films, such as polyimide resins.

Claims

1. An aqueous medium contains α-alumina as abrasive particles, and the α-alumina has an average particle diameter (D50) of 80 to 120 nm at a volume-based integrated value of 50% in a particle size distribution determined by a laser diffraction scattering method, and a specific surface area (BET) of 20 m2 measured according to the provisions of JIS-Z8830 (2013) 2 / g or more, and the ratio (BET / D50) of the specific surface area (BET) to the average particle diameter (D50) is 1.5 m / g×10 -4 The above is the polishing slurry.

2. The polishing slurry according to claim 1, wherein the ratio (TBD / LBD) of the loose bulk density (LBD) to the loaded bulk density (TBD) measured in accordance with JIS-R9301-2-3 (1999) is 1.5 or less.

3. The specific surface area (BET) is 25 m 2 / g or more, and the ratio (BET / D50) of the specific surface area (BET) to the average particle diameter (D50) is 2.0 m / g×10 -4 The polishing slurry according to claim 1 or 2.

4. The polishing slurry according to claim 1 or 2, containing 0.01 to 10% by mass of the abrasive particles and containing 0.0001 to 1% by mass of nitric acid as a dispersant.

5. The polishing slurry according to claim 1 or 2, which is a free abrasive polishing slurry used for polishing insulating materials containing polyimide resin.

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