Silica particles, silica sol, polishing composition, and polishing method

Abstract

The objective is to provide silica particles and silica sols containing silica particles, as well as polishing compositions containing silica sols, that achieve excellent polishing speeds even on objects with high mechanical strength when used as abrasive particles in polishing compositions containing silica sols. Equation: CL = 2π / ΔQ FSDP (However, ΔQ FSDP Silica particles in which the correlation length CL, calculated from the peak observed at the lowest Q end of the structure factor S(Q) obtained from X-ray total scattering measurements using 61.3 keV X-rays, is calculated by fitting the peak with a Lorentz function in the range of Q from 1.01 to 1.658, is between 11.0 Å and 14.0 Å.

Description

[Technical Field]

[0001] The present invention relates to silica particles, silica sol, polishing composition, and polishing method. [Background technology]

[0002] Silica particles are used as abrasive grains in polishing compositions used in precision polishing of semiconductor substrates, such as silicon wafers and compound semiconductors like silicon nitride, and in chemical mechanical polishing (CMP) processes for semiconductor devices. Polishing compositions generally contain a silica sol, which includes an aqueous medium such as water and silica particles, and optionally further contain alkaline compounds, acidic compounds, water-soluble polymers, chelating agents, oxidizing agents, surfactants, metal corrosion inhibitors, and the like.

[0003] Methods for producing silica particles mainly include the water glass method using alkali silicate as a raw material, the so-called sol-gel method which synthesizes silica particles by condensation in the presence of a base catalyst using alkoxysilane as a raw material, and the thermal decomposition method of silicon tetrachloride.

[0004] High polishing speed leads to improved production efficiency of silicon wafers and other materials; therefore, polishing compositions are required to achieve high polishing speeds.

[0005] For example, Patent Document 1 discloses a dispersion of irregularly shaped silica-based fine particles that, when used as a polishing composition or polishing slurry, can improve the smoothness of the substrate surface and increase the polishing speed, as well as a method for producing such a dispersion.

[0006] Furthermore, Patent Document 2 discloses a method for producing neutral colloidal silica that has numerous small protrusions on its particle surface, giving the particle as a whole a shape resembling a konpeito (Japanese sugar candy), a large BET specific surface area, high particle density (true specific gravity), and excellent polishing speed, making it suitable for use as an abrasive for CMP (Chemical Polishing).

[0007] Patent Document 3 discloses silica particles, silica sols, and abrasive compositions with excellent polishing properties and storage stability, as well as a method for producing silica particles, by optimizing the proportion of silanol groups present on the surface, calculated from the content of surface silanol groups and the content of bulk silanol groups. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] International Publication No. 2022 / 123820 [Patent Document 2] Japanese Patent Publication No. 2007-153732 [Patent Document 3] International Publication No. 2020 / 171134 [Overview of the project] [Problems that the invention aims to solve]

[0009] On the other hand, in this field, including the prior art mentioned above, silica particles are often defined solely by particle size, surface shape, specific surface area, density, and the proportion of functional groups on the surface, but there has been little discussion about the analysis of the local structure of silica particles. The present invention aims to provide silica particles and silica sols containing silica particles, as well as polishing compositions containing silica sols, that achieve excellent polishing speeds even on objects with high mechanical strength when used as abrasive particles in polishing compositions containing silica sols. [Means for solving the problem]

[0010] The inventors focused on the fact that, as a method for analyzing the local structure of silica particles, by using high-energy X-rays, scattering can be accurately obtained up to a wide wave number region, and information on the local structure can be obtained even for amorphous materials. As a result of intensive research, silica particles obtained by using a specific manufacturing method, wherein the period and / or correlation length, which are information on the local structure of the silica particles obtained from the scattering profile observed when irradiated with high-energy X-rays, are within a specific range, are used as abrasive grains, and surprisingly, an excellent polishing rate can be achieved, and the above problems can be solved. Thus, the present invention was completed.

[0011] That is, the gist of the present invention is as follows. [1] The following formula (1): CL = 2π / ΔQ FSDP (1) (However, ΔQ FSDP is the full half-value width of the peak calculated by fitting the Lorentz function in the range of Q = 1.01 to 1.658 for the peak observed on the lowest Q side among the structure factors S(Q) obtained from the X-ray total scattering measurement using X-rays of 61.3 keV for the silica particles) Silica particles in which the calculated correlation length CL is 11.0 Å or more and 14.0 Å or less. [2] The following formula (2): P = 2π / Q FSDP (2) (However, Q FSDP is the peak position calculated by fitting the Lorentz function in the range of Q = 1.01 to 1.658 for the peak observed on the lowest Q side among the structure factors S(Q) obtained from the X-ray total scattering measurement using X-rays of 61.3 keV for the silica particles) The silica particles according to [1], in which the calculated period P is 3.95 Å or more and 4.03 Å or less. [3] The following formula (3): R = P / CL (3) The silica particles according to [2], in which the ratio R of the period P to the correlation length CL calculated from the above is 0.30 or more and 0.35 or less. [4] Silica particles as described in [1], wherein the amount of silanol groups identified by the measurement method described below is 1.00 to 1.90 mmol / g. Method for measuring silanol group content: (1) A colloidal silica dispersion containing silica particles as described in [1] is brought into contact with a cation exchange resin, an anion exchange resin, and a cation exchange resin in that order, and the treated solution is ion-exchanged. The solution is then frozen at -70°C to -80°C, and the dispersion medium is removed by freeze-drying at room temperature under a pressure of 5 Pa or less to obtain silica particle powder; (2) The amount of silanol groups in the obtained silica particle powder is calculated using the following formula based on the mass loss when heated from room temperature to 700°C by thermogravimetric analysis and the molecular weight of the water molecules. Silanol group content (mmol / g) = 2 × (M2 - M1) ÷ M H2O ÷(M0-M1)×1000 (However, M0 is the mass of the silica particle powder subjected to thermogravimetric analysis before heating, M1 is the mass loss when it reaches 200°C, M2 is the mass loss when it reaches 700°C, M H2O (These represent the molecular weights of water molecules, respectively.) [5] The density determined by the following measurement method is 2.20–2.25 g / cm³ 3 The silica particles described in [1]. Method for measuring density: (1) A colloidal silica dispersion containing silica particles as described in [1] is brought into contact with a cation exchange resin, an anion exchange resin, and a cation exchange resin in that order, and the treated solution is ion-exchanged. The solution is then frozen at -70°C to -80°C, and the dispersion medium is removed by freeze-drying at room temperature under a pressure of 5 Pa or less to obtain silica particle powder; (2) The density of the obtained silica particle powder is measured by dry density measurement. [6] A silica sol comprising a solvent and the silica particles described in [1]. [7] The silica sol according to [6], wherein the solvent is water. [8] The silica sol according to [7], wherein the average primary particle diameter of the silica particles, as measured by the BET method, is 15 to 100 nm. [9] The silica sol according to [8], wherein the average secondary particle diameter of the silica particles, as measured by dynamic light scattering, is 20 to 100 nm.

[10] The silica sol according to [9], wherein the concentration of the silica particles is 20 to 45% by mass. A polishing composition comprising a silica sol as described in any one of items

[11] [6] to

[10] .

[12] The polishing composition according to

[11] , for use in chemical mechanical polishing (CMP) of silicon wafers, compound semiconductor substrates, or device wafers.

[13] A polishing method comprising performing chemical mechanical polishing (CMP) of a silicon wafer, a compound semiconductor substrate, or a device wafer using the polishing composition described in

[12] . [Effects of the Invention]

[0012] According to the present invention, by using high-energy X-rays, scattering can be accurately acquired over a wide wavenumber range to obtain information about the local structure of silica particles. By using silica particles as abrasive grains in which the period and / or correlation length, which are information about the local structure of silica particles obtained from the scattering profile observed when irradiated with high-energy X-rays, are within a specific range, an excellent polishing speed can be achieved. In other words, when silica particles in which the above-mentioned period and / or correlation length are within a specific range are used as abrasive grains in a polishing composition containing silica sol, it is possible to provide silica particles, silica sols containing silica particles, and polishing compositions containing silica sols that can achieve an excellent polishing speed even for polishing objects with high mechanical strength. [Brief explanation of the drawing]

[0013] [Figure 1] This figure plots the relationship between the correlation length CL and period P of silica particles obtained in the examples and comparative examples. [Modes for carrying out the invention]

[0014] Hereinafter, preferred embodiments of the present invention will be described. However, the following embodiments are examples for explaining the present invention, and the present invention is not limited to the following embodiments at all. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0015] [Silica particles] In one embodiment of the present invention, the silica particles have the following formula (1): CL = 2π / ΔQ FSDP (1) (However, ΔQ FSDP is the full half-width of the peak calculated by fitting the Lorentz function in the range of Q = 1.01 to 1.658 for the peak observed on the lowest Q side among the structure factors S(Q) obtained from the X-ray total scattering measurement using X-rays of 61.3 keV for the silica particles) means silica particles having a specific correlation length CL calculated therefrom. Considering the effects achieved by the present invention, the correlation length CL is 11.0 Å or more and 14.0 Å or less. The lower limit value is more preferably 11.5 Å, and even more preferably 12.0 Å. The upper limit value is more preferably 13.5 Å, and even more preferably 13.0 Å. When the correlation length CL is 11.0 Å or more, in silica particles composed of Si atoms and O atoms, due to the relatively high long-distance regularity of the three-dimensional network composed of Si-O-Si bonds, it has appropriate mechanical strength, can efficiently scrape the wafer surface, and can improve the polishing rate. When the correlation length CL is 14.0 Å or less, the mechanical strength of the silica particles does not become excessively high, so the occurrence of defects due to scratches generated when the silica particles are rubbed against the wafer surface during polishing can be reduced.

[0016] In one embodiment of the present invention, the silica particles have the following formula (2): P = 2π / Q FSDP (2) (However, Q FSDPThis peak position is calculated by fitting the peak observed at the lowest Q end of the structure factor S(Q) obtained from X-ray total scattering measurements using 61.3 keV X-rays to silica particles using a Lorentz function in the range of Q from 1.01 to 1.658. This refers to silica particles having a specific period P calculated from the above. Considering the effects of the present invention, the period P is 3.95 Å or more and 4.03 Å or less, with a lower limit of 3.98 Å more preferably and an upper limit of 4.02 Å more preferably. When the period P is 3.95 Å or higher, the silica particles, composed of Si and O atoms, have moderate mechanical strength due to the relatively high regularity of the three-dimensional network of Si-O-Si bonds over short distances, allowing for efficient removal of the wafer surface and improving the polishing speed. When the period P is 4.03 Å or lower, the mechanical strength of the silica particles does not become excessively high, thus reducing the occurrence of defects caused by scratches when the silica particles are rubbed against the wafer surface during polishing.

[0017] In one embodiment of the present invention, silica particles are given by the following formula (3): R = P / CL (3) The ratio R of the period P to the correlation length CL calculated from this has been determined. Considering the effects of the present invention, the ratio R is 0.30 or more and 0.35 or less, the lower limit is more preferably 0.31, and the upper limit is more preferably 0.34.

[0018] Here, we will explain the period P and correlation length CL in more detail.

[0019] The period P and correlation length CL are determined by performing high-energy X-ray total scattering measurements on silica particles. Specifically, a structure factor is extracted from the obtained high-energy X-ray scattering pattern, and its first peak is fitted. The Lorentz function is used for peak fitting. Through the above analysis, the peak position and full width at half maximum of the first peak in the structure factor are determined, and these values ​​can be used to determine the period and correlation length, respectively.

[0020] High-energy X-ray total scattering measurements can be performed, for example, using BL04B2 at the large synchrotron radiation facility SPring-8 (Super Photon ring 8GeV). The silica particles used as the sample are packed into a capillary container with a diameter of 2 mm and a wall thickness of 0.01 mm. The diffractometer and detector used are a large horizontal twin-axis X-ray diffractometer and a 7-barrel CdTe / Ge detector available at BL04B2. The X-ray energy is 61.3 keV (wavelength 0.2019 Å), the measurement range is 2θ = 0.3 to 57°, and the measurement time is approximately 90 minutes to acquire the X-ray total scattering pattern.

[0021] The scattering intensity I of the acquired total X-ray scattering pattern obs This is expressed by the following equation (A). Here, I coh This is coherent scattering, I incoh Incoherent scattering, I flu This is due to fluorescence caused by X-ray irradiation. Coherent scattering I is included in the following equation (A). coh The Faber-Ziman structure factor S(Q), normalized by the atomic scattering factor f(Q), is given by equation (B) below. Here, Q is the scattering vector (equation (C) below). However, 2θ represents the scattering angle and λ represents the wavelength of the incident X-ray.

[0022]

number

[0023]

number

[0024]

number

[0025] I required for calculating the structure factor S(Q) coh is, I obs This can be determined by subtracting the blank measurement, subtracting using a theoretical formula, and using the detector discriminator. These calculations can be performed, for example, using the software attached to BL04B2 at the large synchrotron radiation facility SPring-8 (Super Photon ring 8GeV).

[0026] The first peak of the structure factor S(Q), calculated from the acquired total X-ray scattering pattern, is curve-fitted with the Lorentz function represented by equation (D) below. Curve fitting can be performed, for example, using graphing software Igor Pro. The peak position of the Lorentz function is x0, and the full width at half maximum is expressed by equation (E) below using the symbols in equation (D) below.

[0027]

number

[0028]

number

[0029] In silica particles composed of Si and O atoms, the regularity of the three-dimensional network consisting of Si-O-Si bonds is interpreted as the origin of the first peak in the structure factor S(Q). The position of that peak is Q FSDP , the full width at half maximum is ΔQ FSDPThe period and correlation length are estimated using equations (F) and (G) below, respectively. Regarding the period and correlation length, the period represents the relatively short-range regularity of the three-dimensional network of Si-O-Si bonds in the silica particles, while the correlation length represents the relatively long-range regularity of the three-dimensional network of Si-O-Si bonds in the silica particles. Larger values ​​for the period and correlation length indicate higher regularity of the three-dimensional network of Si-O-Si bonds.

[0030]

number

[0031]

number

[0032] In the structure factor S(Q) obtained from the X-ray total scattering pattern of silica particles, Q was 1.57 ± 0.03 Å. -1 A first peak exists whose peak top is located within the range, and curve fitting is performed on that peak using the above equation (D). The range of curve fitting is, for example, Q = 1.0 to 1.7 Å. -1 It can be set to the range of

[0033] <Silanol base amount> The silica particles of the present invention can have a predetermined amount of silanol groups. Specifically, the silica particle powder obtained by freeze-drying a colloidal silica dispersion containing the silica particles at room temperature under a pressure of 5 Pa or less to remove the dispersion medium can have a silanol group amount calculated by the following formula from the mass loss when heated from room temperature to 700°C and the molecular weight of the water molecules, as determined by thermogravimetric analysis, which can be, for example, 1.00 to 1.90 mmol / g, 1.20 to 1.90 mmol / g, 1.50 to 1.90 mmol / g, 1.20 to 1.80 mmol / g, 1.20 to 1.65 mmol / g, 1.20 to 1.50 mmol / g, or 1.30 to 1.60 mmol / g. Silanol group content (mmol / g) = 2 × (M2 - M1) ÷ MH2O ÷(M0-M1)×1000 However, M0 is the mass of the silica particle powder subjected to thermogravimetric analysis before heating, M1 is the mass loss when it reaches 200°C, M2 is the mass loss when it reaches 700°C, and M H2O The values ​​of each represent the molecular weight of a water molecule.

[0034] To obtain silica particle powder by the above freeze-drying method, first, a colloidal silica dispersion containing the target silica particles is brought into contact with a cation exchange resin, an anion exchange resin, and another cation exchange resin in that order to obtain an ion exchange treatment solution. This ion exchange solution is then frozen at -70°C to -80°C, and freeze-dried at room temperature under a pressure of 5 Pa or less to remove the dispersion medium, thereby obtaining the desired silica particle powder.

[0035] Silanol groups are present on the surface of silica particles, and these silanol groups readily adsorb water through hydrogen bonding. Therefore, to quantify the amount of silanol groups in silica particles from the mass loss due to heating, it is preferable to heat the particles to approximately 200°C, where the adsorbed water is removed, as described above. If the amount of silanol groups in the silica particles is, for example, 1.90 mmol / g or less, the relative long-range regularity of the three-dimensional network of Si-O-Si bonds in the silica particles, which consist of Si atoms and O atoms, is increased, and the silica particles have appropriate mechanical strength, so the wafer surface can be efficiently scraped off and the polishing speed can be improved. If the amount is, for example, 1.00 mmol / g or more, the mechanical strength of the silica particles does not become excessively high, so the occurrence of defects caused by scratches when silica particles are rubbed against the wafer surface during polishing can be reduced.

[0036] <density> The silica particles of the present invention can have a predetermined density. That is, the silica particle powder obtained by freeze-drying a colloidal silica dispersion containing the silica particles at room temperature under a pressure of 5 Pa or less to remove the dispersion medium has a density measured by dry density measurement of, for example, 2.20 to 2.25 g / cm³.3 2.21~2.25 g / cm³ 3 2.20~2.24 g / cm³ 3 , or 2.20~2.23 g / cm³ 3 It can be done this way. The procedure for obtaining silica particle powder by freeze-drying is the same as the procedure described for determining the amount of silanol groups.

[0037] The density of silica particles is as stated above, for example, 2.20 g / cm³. 3 As a result of the above, the relative long-range regularity of the three-dimensional network of Si-O-Si bonds in silica particles composed of Si and O atoms is increased, and the silica particles have appropriate mechanical strength, allowing them to efficiently remove the wafer surface and improve the polishing speed. Furthermore, if the density of the silica particles is as described above, for example 2.25 g / cm³ 3 As a result of the following, the mechanical strength of the silica particles does not become excessively high, thereby reducing the occurrence of defects caused by scratches that occur when silica particles are rubbed against the wafer surface during polishing.

[0038] The silica particles of the present invention can be obtained, for example, by the method described in the examples below, but are not necessarily limited to this, and may also be obtained by known methods. In this invention, silica particles may be referred to as colloidal silica.

[0039] [Silica sol and polishing compositions containing silica sol] In one embodiment of the present invention, the silica sol comprises a solvent and the silica particles described above. In this invention, the silica sol may also be referred to as a silica particle dispersion or a colloidal silica dispersion. The solvent may be water, an organic solvent, or a mixed solvent of water and an organic solvent.

[0040] The average primary particle size of a colloidal silica dispersion refers to the average primary particle size of the silica particles that make up the dispersed phase. In the present invention, unless otherwise specified, the average primary particle diameter of silica particles in a colloidal silica dispersion refers to the particle diameter calculated from the specific surface area obtained by the nitrogen gas adsorption method (BET method). The specific surface area diameter (average particle diameter (specific surface area diameter) D (nm)) obtained by measurement using the nitrogen gas adsorption method (BET method) is the specific surface area S (m²) measured by the nitrogen gas adsorption method. 2 From ( / g), it is given by the formula D(nm) = 2720 / S. In the present invention, the average primary particle diameter of the silica particles is, for example, 15 to 100 nm, and can also be, for example, 20 to 85 nm, 30 to 70 nm, or 35 to 60 nm. An average primary particle diameter of 15 nm or more allows for improved polishing speed when used for polishing silicon wafers, for example, because the silica particles contact both the silicon wafer and the polishing pad. Furthermore, it suppresses excessively large travel distances of silica particles due to Brownian motion, thereby reducing the frequency of contact between silica particles in the polishing composition and improving storage stability. An average primary particle diameter of 100 nm or less reduces the occurrence of defects caused by scratches when silica particles are rubbed against the silicon wafer surface when used for polishing silicon wafers, for example. Additionally, it prevents the silica particles from settling in the polishing composition and from adhering to each other at the bottom of the storage container, thus improving the storage stability of the polishing composition.

[0041] Furthermore, the silica particles in a silica particle dispersion or polishing composition can be measured by dynamic light scattering to determine their average secondary particle size and their dispersion state (whether the silica particles are dispersed or aggregated). The average secondary particle diameter represents the average value of the secondary particle diameter (dispersed particle diameter). It is said that the average secondary particle diameter in a completely dispersed state is about 1.2 to 2 times the average primary particle diameter (specific surface area diameter obtained by the nitrogen gas adsorption method (BET method) or Sears method, and represents the average value of the primary particle diameter). Furthermore, the larger the value of average secondary particle diameter / average primary particle diameter, the more aggregated the silica particles in the medium are considered to be. In this invention, the average secondary particle diameter of silica particles, i.e., colloidal silica dispersions (colloidal silica particles), measured by dynamic light scattering, can be, for example, 20 to 100 nm, 30 to 90 nm, or 40 to 85 nm. By having the average secondary particle diameter within the above range, aggregation of silica particles in the polishing composition can be suppressed. As a result, the polishing speed when used, for example, for polishing silicon wafers can be further improved, and the storage stability of the polishing composition can be improved. In this invention, the average secondary particle diameter of the silica particles measured by dynamic light scattering is measured in accordance with ISO 22412:2017 using a Zetasizer Nano (manufactured by Malvern Panalytical). Furthermore, the average secondary particle diameter refers to the Z-average particle diameter measured by dynamic light scattering.

[0042] The concentration (mass percentage) of silica particles in the silica sol or abrasive composition can be 20-45% by mass, 25-40% by mass, or 30-40% by mass.

[0043] <Additives> The polishing composition of the present invention may further contain, in addition to silica particles as abrasive grains and water as an aqueous medium, at least one additive selected from the group consisting of acidic compounds, basic compounds, water-soluble compounds, chelating agents, oxidizing agents, and metal corrosion inhibitors. The silica particle dispersion of the present invention may further contain silica particles and water or an organic solvent, or a mixed solvent of water and an organic solvent, as well as at least one additive selected from the group consisting of acidic compounds and basic compounds. By setting the solid content of the polishing composition, excluding the aqueous medium, to 0.01% by mass or more, excessive dissolution of the silica particle surface by hydroxyl groups can be suppressed. By setting the solid content of the polishing composition, excluding the aqueous medium, to 40% by mass or less, an increase in the number of silica particles in the polishing composition and a decrease in the amount of solvent can be prevented, thereby suppressing aggregation. Furthermore, excessive viscosity of the polishing composition can be suppressed, making it easier to handle. As a result, the storage stability of the polishing composition is improved, making storage and transportation easier. The amount of solids in the polishing composition or silica particle dispersion can be measured, for example, by heating the composition in an electric furnace at 1000°C for 1 hour and weighing the residue.

[0044] Examples of the aforementioned acidic compounds include mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid, and organic acids such as formic acid, oxalic acid, citric acid, acetic acid, lactic acid, malic acid, malonic acid, succinic acid, tartaric acid, butyric acid, fumaric acid, benzoic acid, glycolic acid, propionic acid, or ascorbic acid. One of these acidic compounds may be used alone, or two or more may be used in combination.

[0045] Examples of the basic compounds include alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates, and nitrogen-containing basic compounds. One basic compound selected from these may be used alone, or two or more may be used in combination. Of the basic compounds mentioned above, sodium hydroxide or potassium hydroxide is preferred as the alkali metal hydroxide. Sodium bicarbonate or potassium bicarbonate is preferred as the alkali metal bicarbonate. Sodium carbonate or potassium carbonate is preferred as the alkali metal carbonate. Ammonia or a quaternary ammonium salt is preferred as the nitrogen-containing basic compound, and a quaternary ammonium compound is more preferred from the viewpoint of achieving a high polishing rate. As quaternary ammonium compounds, tetramethylammonium hydroxide, ethyltrimethylammonium hydroxide, diethyldimethylammonium hydroxide, tetraethylammonium hydroxide, or tetramethylammonium hydroxide or salts thereof can be used. Among these, tetraethylammonium hydroxide or a salt thereof is preferred, and tetramethylammonium hydroxide or a salt thereof is more preferred. The above basic compound can be incorporated into the polishing composition in proportions of, for example, 0.1 to 50% by mass, 0.1 to 30% by mass, 0.1 to 10% by mass, 1 to 50% by mass, 1 to 30% by mass, or 1 to 10% by mass relative to the silica particles. By setting the amount of the above basic compound within these ranges, it is possible to prevent the pH of the polishing composition from increasing or decreasing excessively, thereby improving the stability of the polishing composition.

[0046] By adding these acidic or basic compounds, the pH of the polishing composition according to the present invention can be adjusted to the range of 1-12, 1-6, 3-6, 7-12, 7-10, 8-11, or 10-12. By setting the pH of the polishing composition within the above range, when the polishing composition is used, for example, to polish a silicon wafer, the Si bonds on the silicon wafer surface are broken by the acid or base, making it easier for the silicon wafer surface to be abraded by silica particles, thereby improving the polishing speed. Furthermore, by adding these acidic or basic compounds, the pH of the silica particle dispersion according to the present invention can be adjusted to the range of 8-11, 8-10, or 9-10. By setting the pH within the above range, the dispersibility of the silica particles is improved, and aggregation of silica particles in the solvent can be suppressed.

[0047] Any water-soluble compound can be used as the aforementioned water-soluble compound. For example, monomers having a carboxylic acid group such as acrylic acid, methacrylic acid, and maleic acid, and polymers thereof such as polyacrylic acid and polymethacrylic acid, and salts thereof such as ammonium polyacrylate, potassium polyacrylate, polyammonium polymethacrylate, and polypotassium methacrylate. In addition, alginic acid, pectic acid, carboxymethylcellulose, polyaspartic acid, polyglutamic acid, polyamic acid, ammonium polyamic acid, polyvinylpyrrolidone, hydroxyethylcellulose, hydroxypropylcellulose, glycerin, polyglycerin, polyvinyl alcohol, polyacrylamide and its derivatives, polymethacrylamide and its derivatives, or carboxyl group or sulfonic acid group-modified polyvinyl alcohol can be used. The above-mentioned water-soluble compound can be incorporated into the polishing composition in proportions of, for example, 0.01 to 10% by mass, 0.01 to 5% by mass, 0.01 to 3% by mass, 0.05 to 10% by mass, 0.1 to 10% by mass, or 0.05 to 5% by mass relative to the silica particles. By setting the amount of the water-soluble compound within the above range, the dispersion stability of the silica particles contained in the polishing composition can be improved, while simultaneously improving the flatness of the silicon wafer by protecting areas other than the convex parts of the silicon wafer surface that adhere to the silicon wafer and concentrate the load during polishing, for example.

[0048] As the chelating agent, an aminocarboxylic acid-based chelating agent or a phosphonic acid-based chelating agent can be used. Examples of the aminocarboxylic acid-based chelating agents include ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, triethylenetetraminehexaacetic acid, 1,3-propanediaminetetraacetic acid, 1,3-diamine-2-hydroxypropanetetraacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, glycol etherdiaminetetraacetic acid, dicarboxymethylglutamic acid, and ethylenediamine-N,N'-disuccinic acid. Examples of phosphonic acid-based chelating agents include hydroxyethylidenediphosphonic acid, nitrilotris(methylenephosphonic acid), phosphonovutanetricarboxylic acid, and ethylenediaminetetra(methylenephosphonic acid). The above-mentioned chelating agent can be incorporated into the polishing composition in proportions of, for example, 0.01 to 10% by mass, 0.01 to 5% by mass, 0.01 to 3% by mass, 0.05 to 10% by mass, 0.1 to 10% by mass, or 0.05 to 5% by mass relative to the silica particles. By setting the amount of chelating agent within the above ranges, contamination of the object to be polished by metal impurities can be reduced while improving the dispersion stability of the silica particles contained in the polishing composition.

[0049] Examples of the oxidizing agent include hydrogen peroxide, potassium permanganate, potassium periodate, hypochlorous acid, and ozonated water. The above-mentioned oxidizing agent can be incorporated into the polishing composition in proportions of, for example, 0.01 to 10% by mass, 0.01 to 5% by mass, 0.01 to 3% by mass, 0.05 to 10% by mass, 0.1 to 10% by mass, or 0.05 to 5% by mass relative to the silica particles. By setting the amount of oxidizing agent within the above ranges, for example, when the polishing composition is used to polish a silicon wafer, the silicon wafer surface is oxidized, making it easier to remove with silica particles and improving the polishing speed.

[0050] Examples of the metal corrosion inhibitors include triazole compounds, pyridine compounds, pyrazole compounds, pyrimidine compounds, imidazole compounds, guanidine compounds, thiazole compounds, tetrazole compounds, triazine compounds, and hexamethylenetetramine.

[0051] The aforementioned triazole compounds include 1,2,3-triazole, 1,2,4-triazole, 3-amino-1H-1,2,4-triazole, benzotriazole (BTA), 1-hydroxybenzotriazole, 1-hydroxypropylbenzotriazole, 2,3-dicarboxypropylbenzotriazole, 4-hydroxybenzotriazole, 4-carboxy-1H-benzotriazole, 4-carboxy-1H-benzotriazole methyl ester (1H-benzotriazole-4-carboxylate methyl), 4-carboxy-1H-benzotriazole butyl ester (1H-benzotriazole-4-carboxylate butyl), 4-carboxy-1H-benzotriazole octyl ester (1H-benzotriazole-4-carboxylate octyl), 5-hexylbenzotriazole, (1,2,3-benzotriazolyl-1-methyl)(1,2,4-tri Azolyl-1-methyl)(2-ethylhexyl)amine, tolyltriazol, naphthotriazol, bis[(1-benzotriazolyl)methyl]phosphonic acid, 3H-1,2,3-triazolo[4,5-b]pyridine-3-ol, 1H-1,2,3-triazolo[4,5-b]pyridine, 1-acetyl-1H-1,2,3-triazolo[4,5-b]pyridine, 3-hydroxypyridine, 1,2,4-triazolo[1,5-a]pyridine Examples include limidine, 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, 2-methyl-5,7-diphenyl-[1,2,4]triazolo[1,5-a]pyrimidine, 2-methylsulfanyl-5,7-diphenyl-[1,2,4]triazolo[1,5-a]pyrimidine, and 2-methylsulfanyl-5,7-diphenyl-4,7-dihydro-[1,2,4]triazolo[1,5-a]pyrimidine.

[0052] Examples of the aforementioned pyridine compounds include pyridine, 8-hydroxyquinoline, prothionamide, 2-nitropyridine-3-ol, pyridoxamine, nicotinamide, iproniazid, isonicotinic acid, benzo[f]quinoline, 2,5-pyridinedicarboxylic acid, 4-styrylpyridine, anabasine, 4-nitropyridine-1-oxide, pyridine-3-ethyl acetate, quinoline, 2-ethylpyridine, quinolinic acid, arecoline, citradilic acid, pyridine-3-methanol, 2-methyl-5-ethylpyridine, 2-fluoropyridine, pentafluoropyridine, 6-methylpyridine-3-ol, and pyridine-2-ethyl acetate.

[0053] Examples of the aforementioned pyrazole compounds include pyrazole, 1-allyl-3,5-dimethylpyrazole, 3,5-di(2-pyridyl)pyrazole, 3,5-diisopropylpyrazole, 3,5-dimethyl-1-hydroxymethylpyrazole, 3,5-dimethyl-1-phenylpyrazole, 3,5-dimethylpyrazole, 3-amino-5-hydroxypyrazole, 4-methylpyrazole, N-methylpyrazole, 3-aminopyrazole, and 3-aminopyrazole.

[0054] Examples of the aforementioned pyrimidine compounds include pyrimidine, 1,3-diphenyl-pyrimidine-2,4,6-trione, 1,4,5,6-tetrahydropyrimidine, 2,4,5,6-tetraaminopyrimidine sulfate, 2,4,5-trihydroxypyrimidine, 2,4,6-triaminopyrimidine, 2,4,6-trichloropyrimidine, 2,4,6-trimethoxypyrimidine, 2,4,6-triphenylpyrimidine, 2,4-diamino-6-hydroxylpyrimidine, 2,4-diaminopyrimidine, 2-acetamidopyrimidine, 2-aminopyrimidine, and 4-aminopyrazolo[3,4-d]pyrimidine.

[0055] Examples of the imidazole compounds include imidazole, 1,1'-carbonylbis-1H-imidazole, 1,1'-oxalyldiimidazole, 1,2,4,5-tetramethylimidazole, 1,2-dimethyl-5-nitroimidazole, 1,2-dimethylimidazole, 1-(3-aminopropyl)imidazole, 1-butylimidazole, 1-ethylimidazole, 1-methylimidazole, and benzimidazole.

[0056] Examples of the guanidine compounds include guanidine, 1,1,3,3-tetramethylguanidine, 1,2,3-triphenylguanidine, 1,3-di-o-tolylguanidine, and 1,3-diphenylguanidine.

[0057] Examples of the thiazole compounds include thiazole, 2-mercaptobenzothiazole, and 2,4-dimethylthiazole.

[0058] Examples of the tetrazole compounds include tetrazole, 5-methyltetrazole, 5-amino-1H-tetrazole, and 1-(2-dimethylaminoethyl)-5-mercaptotetrazole.

[0059] Examples of the aforementioned triazine compound include triazine and 3,4-dihydro-3-hydroxy-4-oxo-1,2,4-triazine.

[0060] The above-mentioned metal corrosion inhibitor can be incorporated into the polishing composition in a ratio of, for example, 0.0001 to 10% by mass relative to the silica particles. By setting the amount of the metal corrosion inhibitor within this range, the stability of the polishing composition can be improved while maintaining the corrosion-preventive effect.

[0061] (Application) The silica particle dispersion of the present invention can be suitably used in polishing compositions. The polishing composition of the present invention can be used for polishing silicon wafers, compound semiconductor substrates, or device wafers. Polishing apparatuses include single-sided polishing and double-sided polishing methods, and the polishing composition of the present invention can be used in either apparatus. The polishing process for silicon wafers and compound semiconductor substrates usually consists of multiple polishing stages, including primary polishing performed at the beginning of the polishing process and finish polishing performed after this primary polishing stage. Note that primary polishing and finish polishing may each be performed in two stages. The polishing composition of the present invention may be used in both primary polishing and finish polishing, or it may be used in only one of the primary polishing or finish polishing. The polishing composition of the present invention may be circulated within the polishing apparatus during each polishing stage, or it may be used in a single-use flow method. In addition, the polishing composition of the present invention can also be used in the CMP process for device wafers. [Examples]

[0062] The effects of the present invention will be described in more detail below based on the examples. However, the present invention is not limited to these examples.

[0063] 1) Synthesis of silica sol During the synthesis of silica sol, the pH and electrical conductivity were measured as follows.

[0064] (pH measurement) This shows the values ​​obtained from pH measurement results, measured using a pH meter (Toa DKK Multi Water Quality Meter MM-60R, pH electrode GST-5741C).

[0065] (Electrical conductivity measurement) The measurements were taken using an electrical conductivity meter (manufactured by Toa DKK Corporation, model number: CM-30R) and an electrical conductivity cell (manufactured by Toa DKK Corporation, model number: CT57101B).

[0066] (Example 1) As the raw material, a sodium silicate aqueous solution conforming to JIS No. 3 was prepared. In this sodium silicate aqueous solution, the main components other than water were SiO2 concentration at 28.8% by mass and Na2O concentration at 9.47% by mass.

[0067] The above sodium silicate aqueous solution was diluted with pure water to prepare a sodium silicate aqueous solution (a) with an SiO2 concentration of 4% by mass. Next, the sodium silicate aqueous solution (a) was passed through a column packed with a hydrogen-type strong acid cation exchange resin (product name) Amberlite IR-120B at a space velocity of 4.5 per hour to remove cations and prepare an activated silicate aqueous solution.

[0068] A solution adjusted to pH=13.1 and electrical conductivity 29.1 mS / cm using a 10% by mass potassium hydroxide aqueous solution and pure water was introduced into a reaction apparatus equipped with a stirrer, heating device, etc., in a 3 L stainless steel pressure-resistant container, and the temperature of the liquid inside the container was adjusted to 100-120°C. After the temperature inside the container reached 100-120°C, activated silica aqueous solution was continuously supplied while maintaining the temperature inside the container at 100-120°C until the pH of the reaction solution reached 10.3 and the electrical conductivity reached 0.6 mS / cm. After the supply, the reaction solution was obtained by further heating for 6 hours while maintaining the temperature inside the container at 100-120°C.

[0069] The resulting reaction solution was concentrated to a SiO2 concentration of 32% by mass at room temperature using a commercially available ultrafiltration apparatus equipped with a polysulfone ultrafiltration membrane with a molecular weight cutoff of 200,000 (product name Q2000 150E, manufactured by Advantech Co., Ltd.).

[0070] Furthermore, the above concentrated solution was passed through a column packed with Amberlite IR-120B, a type of strong acid cation exchange resin (product name), at a space velocity of 3.5 per hour. Then, pure water was added to adjust the SiO2 concentration to 25.5% by mass, and the pH was adjusted to 10.3 using a 10% potassium hydroxide aqueous solution to obtain silica sol.

[0071] (Example 2) A solution prepared using a 10% by mass potassium hydroxide aqueous solution and pure water, adjusted to a pH of 11.1 and an electrical conductivity of 11.7 mS / cm, was placed in a 3 L stainless steel pressure-resistant container equipped with a stirrer, heating device, etc., and the temperature of the liquid inside the container was adjusted to 100-120°C. After the temperature inside the container reached 100-120°C, while maintaining the temperature inside the container at 100-120°C, an activated silicic acid aqueous solution prepared in the same manner as in Example 1 was continuously supplied until the pH of the reaction solution reached 11.0 and the electrical conductivity reached 3.3 mS / cm. After supplying, the reaction solution was obtained by further heating for 1 hour while maintaining the temperature inside the container at 100-120°C.

[0072] The resulting reaction solution was concentrated to a silica sol at room temperature until the SiO2 concentration reached 40% by mass, using a commercially available ultrafiltration apparatus equipped with a polysulfone ultrafiltration membrane with a molecular weight cutoff of 200,000 (product name Q2000 150E, manufactured by Advantech Co., Ltd.).

[0073] (Example 3) Colloidal silica (product name Snowtex O) manufactured by Nissan Chemical Corporation was mixed with a 10% by mass potassium hydroxide aqueous solution and pure water to adjust the pH to 11.0 and the electrical conductivity to 3.2 mS / cm. The reaction was then carried out in a 3 L SUS pressure-resistant container equipped with a stirrer, heating device, etc., and the temperature inside the container was adjusted to 100-120°C. After the temperature inside the container reached 100-120°C, a 10% by mass potassium hydroxide aqueous solution and an activated silicic acid aqueous solution obtained by the same procedure as in Example 1 were continuously supplied while maintaining the temperature inside the container at 100-120°C until the pH of the reaction solution reached 10.7 and the electrical conductivity reached 1.5 mS / cm. After supplying, the reaction solution was obtained by heating for a further 1 hour while maintaining the temperature inside the container at 100-120°C.

[0074] The resulting reaction solution was concentrated to a silica sol at room temperature until the SiO2 concentration reached 40% by mass, using a commercially available ultrafiltration apparatus equipped with a polysulfone ultrafiltration membrane with a fractional molecular weight of 200,000 (product name Q2000 150E, manufactured by Advantech Co., Ltd.).

[0075] (Example 4) A solution prepared using an activated silicic acid aqueous solution obtained by the same procedure as in Example 1, a 10% by mass potassium hydroxide aqueous solution, and pure water was adjusted to a pH of 11.1 and an electrical conductivity of 14.8 mS / cm. This solution was then placed in a 3 L stainless steel pressure-resistant container equipped with a stirrer, heating device, etc., and the temperature of the liquid inside the container was adjusted to 100-120°C. After the temperature inside the container reached 100-120°C, the activated silicic acid aqueous solution obtained by the same procedure as in Synthesis Example 1 was continuously supplied while maintaining the temperature inside the container at 100-120°C until the pH of the reaction solution reached 11.0 and the electrical conductivity reached 3.6 mS / cm. After supplying, the reaction solution was obtained by heating for a further 1 hour while maintaining the temperature inside the container at 100-120°C.

[0076] The resulting reaction solution was concentrated to a silica sol at room temperature until the SiO2 concentration reached 40% by mass, using a commercially available ultrafiltration apparatus equipped with a polysulfone ultrafiltration membrane with a fractional molecular weight of 200,000 (product name Q2000 150E, manufactured by Advantech Co., Ltd.).

[0077] (Example 5) An aqueous solution of activated silicic acid obtained by the same procedure as in Example 1 above was adjusted to a pH of 3 or less by adding 8% by mass of sulfuric acid to the aqueous solution of activated silicic acid obtained by the same procedure as in Example 1 above, thereby obtaining an aqueous solution of activated silicic acid stabilized with sulfuric acid. After adding pure water to the aqueous solution of activated silicic acid stabilized with sulfuric acid obtained above under stirring, an aqueous solution of potassium hydroxide by 10% by mass was added to adjust the SiO2 concentration to 3.2% by mass and the pH to 12.0. Then, the temperature of the liquid inside the container was adjusted to 100-110°C using a reaction apparatus equipped with a stirrer, heating device, etc. in a 3L stainless steel pressure-resistant container. After the temperature inside the container reached 100-110°C, the aqueous solution of activated silicic acid stabilized with sulfuric acid obtained above was continuously supplied as the feed solution until the pH of the reaction solution reached 11.4, while maintaining the temperature inside the container at 100-110°C. After supplying an aqueous solution of activated silicic acid stabilized with sulfuric acid, the temperature inside the container was maintained at 110°C and the reaction was allowed to proceed for 1 hour. Then, an aqueous solution of activated silicic acid stabilized with sulfuric acid was continuously supplied as the feed solution until the pH of the reaction solution reached 11.1. After supplying the aqueous solution of activated silicic acid stabilized with sulfuric acid, the reaction solution was obtained by heating the container for a further 2 hours while maintaining the temperature inside the container at 110-130°C.

[0078] The resulting reaction solution was concentrated to a silica sol at room temperature until the SiO2 concentration reached 40% by mass, using a commercially available ultrafiltration apparatus equipped with a polysulfone ultrafiltration membrane with a fractional molecular weight of 200,000 (product name Q2000 150E, manufactured by Advantech Co., Ltd.).

[0079] (Comparative Example 1) A commercially available silica sol (manufactured by Fuso Chemical Industries, Ltd., product name PL-3) containing silica particles produced by the sol-gel method using alkoxysilane as a raw material was used as is.

[0080] (Comparative Example 2) 2400g of commercially available silica sol (manufactured by Fuso Chemical Industry Co., Ltd., product name PL-3), containing silica particles produced by the sol-gel method using alkoxysilane as a raw material, was placed in a reaction vessel equipped with a stirrer, heating device, etc., in a 3L stainless steel pressure-resistant container, and the temperature was adjusted to 190-210°C. After the temperature inside the container reached 190-210°C, the silica sol was obtained by hydrothermal treatment for 1 hour while maintaining the temperature inside the container at 190-210°C.

[0081] (Comparative Example 3) Silica sol was obtained using the same procedure as in Comparative Example 2, except that the hydrothermal treatment time was set to 5 hours while maintaining the temperature inside the container at 190-210°C.

[0082] 2) Analysis of silica particles and results The silica particles obtained in Examples 1-5 and Comparative Examples 1-3 were subjected to the following analyses.

[0083] 2-1) Measurement of period and correlation length of silica particles Samples were prepared by adding pure water to each silica sol to adjust the SiO2 concentration to 10% by mass. Next, 20 mL of the hydrogen-type strong acid cation exchange resin Amberlite (product name) IR-120B was added to 100 g of the obtained sample and stirred for 30 minutes to remove cations. After removing the cation exchange resin by filtering the obtained sample through a nylon mesh, 20 mL of the hydroxyl-type strong basic anion exchange resin Amberlite (product name) IRA-410 was added and stirred for 30 minutes to remove anions. After removing the anion exchange resin by filtering the obtained sample through a nylon mesh, 20 mL of the hydrogen-type strong acid cation exchange resin Amberlite (product name) IR-120B was added again and stirred for 30 minutes to remove cations. The cation exchange resin was removed from the obtained sample through a nylon mesh to obtain a dispersion from which cations and anions had been removed. A dispersion from which the above ions had been removed was placed in a 300 mL round-bottom flask. The round-bottom flask containing the dispersion was immersed for 10 minutes in ethanol cooled to -70°C to -80°C by adding dry ice to obtain a frozen dispersion. The frozen dispersion was allowed to stand at room temperature under a vacuum of 5 Pa or less using a freeze-drying apparatus (product name FDU-2100, manufactured by Tokyo Rikakikai Co., Ltd.) to sublimate the frozen water and obtain a freeze-dried sample. The freeze-dried sample was ground in an agate mortar for 10 minutes to obtain a freeze-dried powder sample for measurement.

[0084] X-ray total scattering measurements were performed on the sample obtained above at SPring-8 BL04B2 (incident X-ray: 61.4 keV, wavelength: 0.2019 Å). The sample was filled into a 2 mmφ borosilicate capillary to a height of approximately 1.5 cm from the bottom. The measurement range was 2θ = 0.3 to 57°, with each step being 0.1°. The scattering intensity was measured by integrating for 60 seconds at each step. The structure factor S(Q) was determined from the X-ray total scattering pattern obtained within the above measurement range using the software attached to BL04B2, as described above. For the obtained S(Q), we used the graphing software Igor Pro to calculate Q = 1.54~1.60 Å.-1 For peaks observed within this range, Q = 1.01~1.658 Å -1 Fitting was performed using the Lorentz function represented by equation (D) above within the specified range to determine the peak position and full width at half maximum (F / HMAX). The obtained peak position and F / HMAX were applied to equations (F) and (G) above to calculate the correlation length CL and period P for each silica particle.

[0085] 2-2) Measurement of average primary particle diameter using the BET method Samples were prepared by adding pure water to each silica sol to adjust the SiO2 concentration to 10% by mass. Next, 10 mL of the hydrogen-type strong acid cation exchange resin Amberlite (product name) IR-120B was added to 5 g of the obtained sample and stirred for 30 minutes to obtain a sample from which cations had been removed. The obtained sample was filtered through a nylon mesh to remove the cation exchange resin, and then heated in an electric furnace (product name DX302, manufactured by Yamato Scientific Co., Ltd.) at 290°C for 1 hour under an atmospheric atmosphere to remove the solvent and obtain a dried product. The dried product was then ground in an agate mortar for 10 minutes to obtain a heat-dried powder. The above heat-dried powder was used as the measurement sample, and the specific surface area value S based on nitrogen gas was measured using the nitrogen gas adsorption method (BET method) with a specific surface area analyzer (product name) Monosorb (manufactured by Quantachrome Instruments Japan LLC). N2 (m 2 The particle size ( / g) was measured, and the average primary particle diameter (nm) was determined from the obtained specific surface area value. That is, the average primary particle diameter is: Average primary particle diameter = 2720 / S N2 It is given by the formula.

[0086] 2-3) Measurement of average secondary particle diameter by dynamic light scattering method The average secondary particle diameter of silica particles was measured using a Zetasizer Nano (manufactured by Malvern Panalytical) by dynamic light scattering (DLS) as follows: 0.1 g of each silica sol was placed in a polystyrene cell with a path length of 10 mm, and a 0.15 mass% sodium chloride aqueous solution was added to obtain a silica sol with a silica concentration adjusted so that the count rate was 200-400 kcps when the attenuator was set to 7. The amount of the prepared silica sol added to the cell was adjusted so that the liquid level was approximately 1 cm from the bottom of the cell, and the average secondary particle diameter of the silica was measured under conditions of attenuator 7 and temperature of 22.0°C.

[0087] 2-4) Method for determining the amount of silanol group For the freeze-dried powder sample obtained in the same manner as in 2-1), the mass loss was measured when the freeze-dried powder was heated from room temperature to 700°C using a thermogravimetric differential thermal analyzer (product name TG-DTA2000SA, manufactured by Bruker). In detail, 5 to 10 mg of the above freeze-dried powder was placed in a platinum container, and this was defined as the initial sample mass M0. The platinum container containing the freeze-dried powder was placed in a thermogravimetric differential thermal analyzer and heated from room temperature to 700°C in a nitrogen gas atmosphere at a heating rate of 10°C / min. The nitrogen gas flow rate was 100 cc / min. The mass loss M1 when the instrument temperature reached 200°C was considered to be the mass loss due to the removal of water adsorbed on the surface of the silica particles contained in the freeze-dried powder. The mass loss M2 when the instrument temperature reached 700°C was subtracted from M1 to determine the mass loss due to the removal of water produced by the dehydration condensation of silanol groups. The amount of silanol groups in the silica particles was calculated using the following formula. Silanol group content (mmol / g) = 2 × (M2 - M1) ÷ 18 ÷ (M0 - M1) × 1000

[0088] 2-5) Method for measuring dry density For the freeze-dried powder sample obtained in the same manner as in 2-1), a dry automatic density analyzer (product name AccuPyc II TEC, manufactured by Micromerities) was used to measure the sample by 1 cm. 3 The silica particles were filled to 80% capacity in an aluminum cell, and the dry density was measured by gas displacement using He gas at 25°C.

[0089] 2-6) Analysis results (physical properties of silica particles) Table 1 shows the physical properties of the silica particles obtained in Examples 1-5 and Comparative Examples 1-3. Figure 1 shows the relationship between the correlation length CL and period P of each silica particle. In Figure 1, the black-filled plots represent the values ​​of the silica particles in the examples, and the white-out plots represent the values ​​of the silica particles in the comparative examples. [Table 1]

[0090] 3) Preparation of polishing composition Using the silica sols obtained in Examples 1-5 and Comparative Examples 1-3, pure water and a 10% by mass aqueous solution of potassium hydroxide or an 8% by mass aqueous solution of sulfuric acid were added to each to prepare polishing compositions containing 10.0% by mass of silica particles and a pH of 10.0.

[0091] 4) Polishing test Polishing tests were conducted using the above-mentioned polishing composition under the polishing conditions shown below. The wafers to be polished were single-crystal silicon wafers equipped with an orientation flat (orifura), with a diameter of 100 mm, a conduction type of P, a crystal orientation of Miller index <100>, and a resistivity of 0.01 to 0.02 Ω·cm. The polishing composition was supplied by a flow method, and the liquid temperature was 18 to 22°C. The polishing time was 10 minutes per batch.

[0092] (polishing conditions) Polishing machine: Lappmaster Co., Ltd. Product name: Single-sided polishing machine LM-18 Polishing pad: Manufactured by JH-RHODES Corporation, product name LP-57, groove width 2mm, groove pitch 20mm Polishing load: 200g / cm 2 Spindle speed: 60 rpm Plate rotation speed: 60 rpm Supply rate of polishing composition: 140 mL / min Polishing time: 10min

[0093] (Evaluation conditions for polished wafers) The polishing speed is determined by measuring the weight of the wafer before and after polishing, subtracting the weight of the wafer after polishing from the weight of the wafer before polishing, and calculating the density of single-crystal silicon (2.35 g / cm³). 3 The polishing amount was calculated from the wafer diameter and then divided by the polishing time. However, the effect of the orientation flat was ignored when calculating the polishing amount, and the calculation was performed assuming a perfect circle.

[0094] Table 2 shows the results of the polishing test. [Table 2]

[0095] As shown in Table 2, the polishing speeds for the silica sol polishing compositions of Examples 1 to 5 were 0.163 to 0.200 μm / min, while the polishing speeds for the silica sol polishing compositions of Comparative Examples 1 to 3 were 0.121 to 0.127 μm / min. The silica sol used in the Examples yielded better results. This is thought to be because silica particles with a correlation length CL of 11.0 Å to 14.0 Å possess moderate mechanical strength due to the relatively high regularity of the three-dimensional network composed of Si-O-Si bonds over long distances, allowing them to efficiently remove the wafer surface and achieve a good polishing speed. On the other hand, silica particles with a correlation length CL of less than 11.0 Å exhibited lower mechanical strength and a weaker wafer surface abrasion effect, resulting in a lower polishing speed, likely due to the relatively low long-range regularity of the three-dimensional network composed of Si-O-Si bonds. [Industrial applicability]

[0096] The present invention provides silica particles that can achieve a high polishing speed when used, for example, as abrasive grains in an abrasive composition.

Claims

1. The following equation (1): CL=2π / ΔQ ＦＳＤＰ (1) (However, ΔQ ＦＳＤＰ This is the full width at half maximum of the peak calculated by fitting the peak observed at the lowest Q end of the structure factor S(Q) obtained from X-ray total scattering measurements using 61.3 keV X-rays to silica particles using a Lorentz function in the range of Q from 1.01 to 1.

658. Silica particles whose calculated correlation length CL is between 11.0 Å and 14.0 Å.

2. The following equation (2): P=2π / Q ＦＳＤＰ (2) (However, Q ＦＳＤＰ This peak position is calculated by fitting the peak observed at the lowest Q end of the structure factor S(Q) obtained from X-ray total scattering measurements using 61.3 keV X-rays to silica particles using a Lorentz function in the range of Q 1.01 to 1.

658. The silica particles according to claim 1, wherein the period P calculated from the results is 3.95 Å or more and 4.03 Å or less.

3. The following equation (3): R = P / CL (3) The silica particles according to claim 2, wherein the ratio R of the period P to the correlation length CL calculated from the above is 0.30 or more and 0.35 or less.

4. Silica particles according to claim 1, wherein the amount of silanol groups identified by the measurement method described below is 1.00 to 1.90 mmol / g. Method for measuring silanol group content: (1) A colloidal silica dispersion containing silica particles as described in claim 1 is brought into contact with a cation exchange resin, an anion exchange resin, and a cation exchange resin in that order to perform ion exchange. The treated solution is then frozen at -70°C to -80°C, and the dispersion medium is removed by freeze-drying at room temperature under a pressure of 5 Pa or less to obtain silica particle powder; (2) The amount of silanol groups in the obtained silica particle powder is calculated using the following formula based on the mass loss when heated from room temperature to 700°C by thermogravimetric analysis and the molecular weight of the water molecules. Amount of silanol groups (mmol / g) = 2 × (M ２ − M １ ) ÷ M Ｈ２Ｏ ÷ (M ０ − M １ ) × 1000 (However, M ０ The mass of the silica particle powder subjected to thermogravimetric analysis before heating is M. １ M is the amount of mass loss when the temperature reaches 200°C. ２ M is the amount of mass loss when the temperature reaches 700°C. Ｈ２Ｏ (These represent the molecular weights of water molecules, respectively.)

5. The density determined by the measurement method described below is 2.20–2.25 g / cm³. ３ The silica particles according to claim 1. Method for measuring density: (1) A colloidal silica dispersion containing silica particles as described in claim 1 is brought into contact with a cation exchange resin, an anion exchange resin, and a cation exchange resin in that order to perform ion exchange. The treated solution is then frozen at -70°C to -80°C, and the dispersion medium is removed by freeze-drying at room temperature under a pressure of 5 Pa or less to obtain silica particle powder; (2) The density of the obtained silica particle powder is measured by dry density measurement.

6. A silica sol comprising a solvent and silica particles according to claim 1.

7. The silica sol according to claim 6, wherein the solvent is water.

8. The silica sol according to claim 7, wherein the average primary particle diameter of the silica particles, as measured by the BET method, is 15 to 100 nm.

9. The silica sol according to claim 8, wherein the average secondary particle diameter of the silica particles, as measured by dynamic light scattering, is 20 to 100 nm.

10. The silica sol according to claim 9, wherein the concentration of the silica particles is 20 to 45% by mass.

11. A polishing composition comprising the silica sol described in any one of claims 6 to 10.

12. The polishing composition according to claim 11, for use in chemical mechanical polishing (CMP) of silicon wafers, compound semiconductor substrates, or device wafers.

13. A polishing method for performing chemical mechanical polishing (CMP) of a silicon wafer, a compound semiconductor substrate, or a device wafer using the polishing composition described in claim 12.

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