Polishing silica particles, silica sol, polishing composition, polishing method, semiconductor wafer manufacturing method, and semiconductor device manufacturing method

Abstract

To provide silica particles with moderate hardness that attain both scratch suppression on an object to be polished and excellent polishing rate and are hard to adhere to the object to be polished.SOLUTION: Silica particles having a metal impurity content of 5 ppm or less satisfy the following formulae (1) and (2) when expressed as SiOxHy: 2.02≤x≤2.12 (1), and 0.04≤y≤0.24 (2). A silica sol contains the silica particles. A polishing composition contains the silica sol. A polishing method uses the polishing composition for polishing.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to silica particles, a silica sol, a polishing composition, a polishing method, a method for manufacturing a semiconductor wafer, and a method for manufacturing a semiconductor device. [Background technology]

[0002] Polishing methods using polishing solutions are known as methods for polishing the surfaces of materials such as metals and inorganic compounds. In particular, in chemical mechanical polishing (CMP), such as the final polishing of prime silicon wafers for semiconductors and reclaimed silicon wafers, and in the planarization of interlayer insulating films during semiconductor device manufacturing, the formation of metal plugs, and the formation of buried wiring, the surface condition of these components has a significant impact on their semiconductor characteristics, so the surfaces and edge faces of these components must be polished with extremely high precision.

[0003] In such precision polishing, polishing compositions containing silica particles are employed, and colloidal silica is widely used as the abrasive grains that are the main component thereof. Colloidal silica is known to be produced by different methods, such as by thermal decomposition of silicon tetrachloride (fumed silica, etc.), by deionization of alkali silicate such as water glass, and by hydrolysis and condensation reaction of alkoxysilane (generally referred to as the "sol-gel method").

[0004] Many studies have been conducted on methods for producing silica particles. For example, Patent Documents 1 and 2 disclose methods for producing silica particles by hydrolysis and condensation reactions of alkoxysilanes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-60232 [Patent Document 2] Japanese Patent Application Publication No. 2018-108924 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, the chemical structure of silica particles varies depending on the reaction conditions, post-treatment conditions, etc. The exact chemical formula of silica particles is SiOxHy, and their physical properties vary depending on the amount of oxygen and hydrogen atoms relative to the amount of silicon atoms. For example, silica particles with x = 2 and y = 0 have the chemical formula SiO2 and are composed only of Q4 units, making them very hard particles like α-quartz (crystal). On the other hand, silica particles with x = 2.5 and y = 1 have the chemical formula SiO 2.5 H and composed only of Q3 units. The physical properties of silica particles are SiO2 and SiO 2.5 It is determined by the mixing ratio with H.

[0007] Silica particles used in silicon wafer polishing and chemical-mechanical polishing (CMP) require particles of appropriate hardness because too soft particles result in poor polishing rates, while too hard particles can scratch the surface of the workpiece. In SiOxHy, when x is large and y is small, the silica particles' chemical structure becomes closer to SiO2, making them harder and resulting in the aforementioned problem of scratching the surface of the workpiece. Furthermore, when y is large in SiOxHy, the silica particles become softer due to the water trapped inside them. As mentioned above, this results in poor polishing rates, as well as the silica particles' strong adhesion to the workpiece, making it difficult to remove them from the workpiece after polishing.

[0008] The chemical structure of the silica particles disclosed in Patent Documents 1 and 2 is unknown, and it is unclear whether silica particles that solve the above-mentioned problems have been obtained.

[0009] The present invention has been made in view of these problems, and an object of the present invention is to provide silica particles that have a moderate hardness, that suppress scratching of the object to be polished, and that achieve an excellent polishing rate, and that are less likely to adhere to the object to be polished. [Means for solving the problem]

[0010] Conventional silica particles have not been able to control their chemical structure in detail, and have not been able to fully resolve issues such as scratches on the object to be polished, removal rate for the object to be polished, and adhesion to the object to be polished. However, as a result of extensive research, the present inventors have found that the above-mentioned issues can be resolved by controlling the amounts of oxygen atoms and hydrogen atoms in the silica particles, and have thus completed the present invention.

[0011] That is, the gist of the present invention is as follows. [1] Silica particles having a metal impurity content of 5 ppm or less, which, when expressed as SiOxHy, satisfy the following formulas (1) and (2): 2.02≦x≦2.12 (1) 0.04≦y≦0.24 (2) [2] The silica particles according to [1], further satisfying the following formula (1') and the following formula (2'): 2.06≦x≦2.11 (1') 0.12≦y≦0.22 (2') [3] Silica particles according to [1] or [2], wherein the silica particles are amorphous. [4] Silica particles according to any one of [1] to [3], which have an average primary particle diameter of 5 nm to 100 nm as measured by the BET method. [5] Silica particles according to any one of [1] to [4], which have an average secondary particle diameter measured by DLS method of 10 nm to 200 nm. [6] Silica particles according to any one of [1] to [5], which contain a tetraalkoxysilane condensate as a main component. [7] Silica particles according to [6], wherein the tetraalkoxysilane condensate includes a tetramethoxysilane condensate. [8] A silica sol containing the silica particles according to any one of [1] to [7]. [9] The silica sol according to [8], wherein the content of silica particles is 3% by mass to 50% by mass based on the total amount of the silica sol.

[10] A polishing composition comprising the silica sol according to [8] or [9].

[11] A polishing method using the polishing composition according to

[10] .

[12] A method for producing a semiconductor wafer, comprising a step of polishing the semiconductor wafer using the polishing composition according to

[10] .

[13] A method for manufacturing a semiconductor device, comprising a step of polishing using the polishing composition according to

[10] . [Effects of the Invention]

[0012] The silica particles of the present invention achieve both the suppression of scratches on the object to be polished and an excellent polishing rate, and have an appropriate hardness that makes them less likely to adhere to the object to be polished. Therefore, the silica sol and polishing composition containing the silica particles of the present invention can be used to efficiently polish the object to be polished without damaging it, and the silica particles can be easily removed after polishing, making it possible to produce high-quality polished products with high productivity. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be practiced with various modifications within the scope of the gist. In this specification, when the expression "to" is used, it is used as an expression including the numerical values ​​or physical property values ​​before and after it.

[0014] (silica particles) The silica particles of the present invention are silica particles having a metal impurity content of 5 ppm or less, and when expressed as SiOxHy, satisfy the following formulas (1) and (2). 2.02≦x≦2.12 (1) 0.04≦y≦0.24 (2)

[0015] The silica particles of the present invention achieve both suppression of scratches on the object to be polished and an excellent polishing rate, are less likely to adhere to the object to be polished, and have an appropriate hardness. Therefore, when expressed as SiOxHy, they satisfy the following formula (1) and preferably the following formula (1'): 2.02≦x≦2.12 (1) 2.06≦x≦2.11 (1')

[0016] The silica particles of the present invention achieve both suppression of scratches on the object to be polished and an excellent polishing rate, are less likely to adhere to the object to be polished, and have an appropriate hardness. Therefore, when expressed as SiOxHy, they satisfy the following formula (2) and preferably the following formula (2'): 0.04≦y≦0.24 (2) 0.12≦y≦0.22 (2')

[0017] When silica particles are expressed as SiOxHy, x and y are the solid 29 It is calculated from the contents of Q3 units and Q4 units measured by Si-DD / MAS-NMR.

[0018] The x and y of the SiOxHy silica particles can be set within a desired range by controlling the production conditions of the silica particles and post-treatment such as pressurized heat treatment.

[0019] The silica particles are preferably amorphous because they can suppress scratching of the workpiece while achieving an excellent polishing rate, are less likely to adhere to the workpiece, and have an appropriate hardness. The fact that the silica particles are amorphous can be confirmed by a halo pattern in wide-angle X-ray scattering measurement.

[0020] The content of metal impurities in the silica particles is 5 ppm or less, preferably 2 ppm or less.

[0021] When polishing silicon wafers for semiconductor devices, metal impurities adhere to and contaminate the surface of the object being polished, adversely affecting the characteristics of the wafer and diffusing into the interior of the wafer, degrading its quality, resulting in a significant decrease in the performance of semiconductor devices manufactured from such wafers. Furthermore, when metal impurities are present on silica particles, coordination interactions occur between the acidic surface silanol groups and the metal impurities, which changes the chemical properties (acidity, etc.) of the surface silanol groups and the three-dimensional environment of the silica particle surface (e.g., the ease of aggregation of silica particles), thereby affecting the polishing rate.

[0022] The metal impurity content of silica particles is measured using inductively coupled plasma mass spectrometry (ICP-MS). Specifically, a silica sol containing 0.4 g of silica particles is accurately weighed, sulfuric acid and hydrofluoric acid are added, and the mixture is heated, dissolved, and evaporated. Pure water is added to the remaining sulfuric acid droplets to a total volume of exactly 10 g to create a test solution, which is then measured using an inductively coupled plasma mass spectrometer. The target metals are sodium, potassium, iron, aluminum, calcium, magnesium, zinc, cobalt, chromium, copper, manganese, lead, titanium, silver, and nickel, and the total content of these metals is the metal impurity content.

[0023] The metal impurity content of silica particles can be reduced to 5 ppm or less by obtaining silica particles through hydrolysis and condensation reactions using alkoxysilane as the main raw material. In the method of deionizing alkali silicate such as water glass, sodium and other impurities derived from the raw material remain, making it extremely difficult to reduce the metal impurity content of silica particles to 5 ppm or less.

[0024] The average primary particle diameter of the silica particles is preferably 5 nm to 100 nm, more preferably 10 nm to 60 nm. When the average primary particle diameter of the silica particles is 5 nm or more, the storage stability of the silica sol is excellent. Furthermore, when the average primary particle diameter of the silica particles is 100 nm or less, the surface roughness and scratches on the polished object, such as a silicon wafer, can be reduced, and sedimentation of the silica particles can be suppressed.

[0025] The average primary particle diameter of the silica particles is measured by the BET method. Specifically, the specific surface area of ​​the silica particles is measured using an automatic specific surface area measuring device, and the average primary particle diameter is calculated using the following formula (3). Average primary particle diameter (nm) = 6000 / (specific surface area (m 2 / g) x density (g / cm 3 )) (3)

[0026] The average primary particle size of the silica particles can be set within a desired range by adjusting the production conditions of the silica particles.

[0027] The average secondary particle diameter of the silica particles is preferably 10 nm to 200 nm, more preferably 20 nm to 100 nm. When the average secondary particle diameter of the silica particles is 10 nm or more, the removal of particles and the like during cleaning after polishing is excellent, and the storage stability of the silica sol is excellent. Furthermore, when the average secondary particle diameter of the silica particles is 200 nm or less, the surface roughness and scratches on the polished object, typified by a silicon wafer, can be reduced during polishing, the removal of particles and the like during cleaning after polishing is excellent, and sedimentation of the silica particles can be suppressed.

[0028] The average secondary particle size of the silica particles is measured by the DLS method, specifically, using a dynamic light scattering particle size measuring device.

[0029] The average secondary particle size of the silica particles can be set within a desired range by adjusting the production conditions of the silica particles.

[0030] The cv value of the silica particles is preferably 10 to 50, more preferably 15 to 40, and even more preferably 20 to 35. When the cv value of the silica particles is 10 or more, the polishing rate for a workpiece such as a silicon wafer is excellent, and the productivity of the silicon wafer is excellent. Furthermore, when the cv value of the silica particles is 50 or less, the surface roughness and scratches on a workpiece such as a silicon wafer during polishing can be reduced, and the removal of particles and the like during cleaning after polishing is excellent.

[0031] The cv value of the silica particles is calculated using the following formula (4) after measuring the average secondary particle diameter of the silica particles using a dynamic light scattering particle diameter measuring device. cv value = (standard deviation (nm) / average secondary particle size (nm)) × 100 (4)

[0032] The association ratio of silica particles is preferably 1.0 to 4.0, more preferably 1.1 to 3.0. When the association ratio of silica particles is 1.0 or more, the polishing rate for a workpiece, such as a silicon wafer, is excellent, resulting in excellent silicon wafer productivity. Furthermore, when the association ratio of silica particles is 4.0 or less, the surface roughness and scratches on a workpiece, such as a silicon wafer, during polishing can be reduced, and aggregation of silica particles can be suppressed.

[0033] The association ratio of silica particles is calculated using the following formula (5) from the average primary particle diameter measured by the above-mentioned measurement method and the average secondary particle diameter measured by the above-mentioned measurement method. Association ratio=average secondary particle diameter / average primary particle diameter... (5)

[0034] The silica particles of the present invention preferably contain an alkoxysilane condensate as the main component, more preferably a tetraalkoxysilane condensate as the main component, and even more preferably a tetramethoxysilane condensate as the main component, because they have excellent mechanical strength and storage stability. The main component means that the main component accounts for 50% by mass or more of 100% by mass of all components constituting the silica particles. To obtain silica particles mainly composed of alkoxysilane condensates, it is preferable to use alkoxysilane as the main raw material. To obtain silica particles mainly composed of tetraalkoxysilane condensates, it is preferable to use tetraalkoxysilane as the main raw material. To obtain silica particles mainly composed of tetramethoxysilane condensates, it is preferable to use tetramethoxysilane as the main raw material. The main raw material means that the main raw material accounts for 50% by mass or more of the total 100% by mass of the raw materials constituting the silica particles.

[0035] (Method of producing silica particles) The silica particles of the present invention can be obtained by subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction. A preferred method involves adding a solution (B) containing tetraalkoxysilane and a solution (C) containing an alkali catalyst to a solution (A) containing water, and subjecting the tetraalkoxysilane to a hydrolysis reaction and a condensation reaction, because this method makes it easier to control the hydrolysis reaction and the condensation reaction, can increase the reaction rate of the hydrolysis reaction and the condensation reaction, prevents gelation of the silica particle dispersion, and allows silica particles with a uniform particle size to be obtained.

[0036] The solution (A) contains water.

[0037] The solution (A) preferably contains a solvent other than water, since this provides excellent dispersibility of the tetraalkoxysilane in the reaction solution. Examples of solvents other than water in solution (A) include methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used alone or in combination of two or more. Among these solvents, alcohol is preferred, more preferably methanol or ethanol, and even more preferably methanol, because it easily dissolves tetraalkoxysilane, the by-products used in the hydrolysis reaction and the condensation reaction are the same as those used in the hydrolysis reaction and the condensation reaction, and it is convenient for production.

[0038] The solution (A) preferably contains an alkali catalyst, since this can increase the reaction rates of the hydrolysis reaction and condensation reaction of the tetraalkoxysilane. Examples of alkali catalysts in solution (A) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used alone or in combination of two or more. Among these alkali catalysts, ammonia is preferred because it has excellent catalytic activity, is easy to control particle shape, can suppress the inclusion of metal impurities, is highly volatile, and is easily removable after the hydrolysis reaction and the condensation reaction.

[0039] The concentration of water in solution (A) is preferably 3% by mass to 50% by mass, and more preferably 5% by mass to 40% by mass, based on 100% by mass of solution (A). When the concentration of water in solution (A) is 3% by mass or more, the hydrolysis reaction rate of tetraalkoxysilane is easily controlled. Furthermore, when the concentration of water in solution (A) is 50% by mass or less, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and the particle shape is easily controlled.

[0040] The concentration of the alkali catalyst in solution (A) is preferably 0.5% by mass to 2.0% by mass, and more preferably 0.6% by mass to 1.5% by mass, based on 100% by mass of solution (A). When the concentration of the alkali catalyst in solution (A) is 0.5% by mass or more, aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion is excellent. Furthermore, when the concentration of the alkali catalyst in solution (A) is 2.0% by mass or less, the reaction does not proceed excessively quickly, and the reaction controllability is excellent.

[0041] The concentration of the solvent other than water in the solution (A) is preferably the balance of water and the alkali catalyst.

[0042] The solution (B) contains a tetraalkoxysilane.

[0043] Examples of tetraalkoxysilanes in solution (B) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. These tetraalkoxysilanes may be used alone or in combination of two or more. Among these tetraalkoxysilanes, tetramethoxysilane and tetraethoxysilane are preferred, with tetramethoxysilane being more preferred, because they undergo a fast hydrolysis reaction, are less likely to leave unreacted substances, are highly productive, and allow stable silica sol to be easily obtained.

[0044] The raw materials for the silica particles may be raw materials other than tetraalkoxysilane, such as low condensates of tetraalkoxysilane. However, due to their excellent reactivity, it is preferable that, out of 100% by mass of all raw materials constituting the silica particles, tetraalkoxysilane accounts for 50% by mass or more and raw materials other than tetraalkoxysilane accounts for 50% by mass or less, and it is more preferable that tetraalkoxysilane accounts for 90% by mass or more and raw materials other than tetraalkoxysilane accounts for 10% by mass or less.

[0045] The solution (B) may contain only tetraalkoxysilane without containing a solvent, but it is preferable that the solution (B) contains a solvent, as this improves the dispersibility of the tetraalkoxysilane in the reaction liquid. Examples of the solvent in solution (B) include methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used alone or in combination of two or more. Among these solvents, alcohol is preferred, more preferably methanol or ethanol, and even more preferably methanol, because the solvents used in the hydrolysis reaction and the condensation reaction and the by-products are the same, and therefore the production is easy.

[0046] The concentration of the tetraalkoxysilane in solution (B) is preferably 60% by mass to 95% by mass, and more preferably 70% by mass to 90% by mass, based on 100% by mass of solution (B). When the concentration of the tetraalkoxysilane in solution (B) is 60% by mass or more, the reaction solution tends to become homogeneous. Furthermore, when the concentration of the tetraalkoxysilane in solution (B) is 95% by mass or less, the formation of a gel-like substance can be suppressed.

[0047] The concentration of the solvent in solution (B) is preferably 5% by mass to 40% by mass, more preferably 10% by mass to 30% by mass, based on 100% by mass of solution (B). When the concentration of the solvent in solution (B) is 5% by mass or more, the formation of a gel-like substance can be suppressed. Furthermore, when the concentration of the solvent in solution (B) is 40% by mass or less, the reaction solution tends to become homogeneous.

[0048] The addition rate of solution (B) per hour relative to the volume of solution (A) is preferably 0.05 kg / hour / L to 1.3 kg / hour / L, and more preferably 0.1 kg / hour / L to 0.8 kg / hour / L. When the addition rate of solution (B) is 0.05 kg / hour / L or more, excellent productivity of silica particles is achieved. Furthermore, when the addition rate of solution (B) is 1.3 kg / hour / L or less, the formation of a gel-like substance can be suppressed.

[0049] The solution (C) contains an alkali catalyst.

[0050] Examples of alkali catalysts in solution (C) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used alone or in combination of two or more. Among these alkali catalysts, ammonia is preferred because it has excellent catalytic activity, is easy to control particle shape, can suppress the inclusion of metal impurities, is highly volatile, and is easily removable after the hydrolysis reaction and the condensation reaction.

[0051] The solution (C) preferably contains a solvent, since this can reduce fluctuations in the concentration of the alkali catalyst in the reaction liquid. Examples of the solvent in solution (C) include water, methanol, ethanol, propanol, isopropanol, ethylene glycol, etc. These solvents may be used alone or in combination of two or more. Among these solvents, water and alcohol are preferred, and water is more preferred, because the solvents used in the hydrolysis reaction and the condensation reaction and the by-products are the same, and they are convenient for production.

[0052] The concentration of the alkali catalyst in solution (C) is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 6% by mass, based on 100% by mass of solution (C). When the concentration of the alkali catalyst in solution (C) is 0.5% by mass or more, it is easy to adjust the concentration of the alkali catalyst in the reaction solution from the start to the end of the reaction. Furthermore, when the concentration of the alkali catalyst in solution (C) is 10% by mass or less, fluctuations in the concentration of the alkali catalyst in the reaction solution can be reduced.

[0053] The concentration of the solvent in solution (C) is preferably 90% by mass to 99.5% by mass, more preferably 94% by mass to 99% by mass, based on 100% by mass of solution (C). When the concentration of the solvent in solution (C) is 90% by mass or more, fluctuations in the concentration of the alkali catalyst in the reaction solution can be reduced. Furthermore, when the concentration of the solvent in solution (C) is 99.5% by mass or less, the concentration of the alkali catalyst in the reaction solution can be easily adjusted from the start to the end of the reaction.

[0054] The addition rate of solution (C) per hour relative to the volume of solution (A) is preferably 0.02 kg / hour / L to 0.5 kg / hour / L, and more preferably 0.04 kg / hour / L to 0.3 kg / hour / L. When the addition rate of solution (C) is 0.02 kg / hour / L or more, excellent productivity of silica particles is achieved. Furthermore, when the addition rate of solution (C) is 0.5 kg / hour / L or less, the formation of a gel-like substance can be suppressed.

[0055] The addition of solutions (B) and (C) is preferably carried out into solution (A). Adding solutions (B) and (C) into solution (A) improves the miscibility of the components in the reaction solution, suppresses abnormal reactions in the air, and makes it easier to control the particle shape when using a highly volatile alkaline catalyst, such as ammonia, and when conducting hydrolysis and condensation reactions at high reaction temperatures. "Adding into the solution" refers to adding below the liquid level. By positioning the supply outlet for solution (B) and the supply outlet for solution (C) below the liquid level of solution (A), solutions (B) and (C) can be added into solution (A).

[0056] The timing of adding solution (B) and solution (C) to solution (A) may be the same or may be different, such as alternately, but it is preferable that they are the same, as this reduces fluctuations in the reaction composition and makes the operation less complicated.

[0057] The reaction temperature for the hydrolysis reaction and the condensation reaction is preferably 15° C. to 50° C., more preferably 20° C. to 45° C. When the reaction temperature is 15° C. or higher, the reaction does not proceed too slowly, and controllability is excellent. On the other hand, when the reaction temperature is 50° C. or lower, a good balance between the hydrolysis reaction rate and the condensation reaction rate is achieved.

[0058] The water concentration in the reaction system for the hydrolysis and condensation reactions is preferably maintained at 3% to 30% by mass, and more preferably 5% to 25% by mass, based on the total amount (100% by mass) of the reaction system. When the water concentration in the reaction system is 3% by mass or more, it is easy to control the hydrolysis reaction rate of the tetraalkoxysilane. Furthermore, when the water concentration in the reaction system is 50% by mass or less, the reaction balance between the hydrolysis and condensation reactions is good, and it is easy to control the particle shape.

[0059] The concentration of the alkali catalyst in the reaction system for the hydrolysis reaction and condensation reaction is preferably maintained at 0.5% to 2.0% by mass, and more preferably at 0.6% to 1.5% by mass, based on the total amount (100% by mass) of the reaction system. When the concentration of the alkali catalyst in the reaction system is 0.5% by mass or more, aggregation of silica particles is suppressed, resulting in excellent dispersion stability of the silica particles in the dispersion. Furthermore, when the concentration of the alkali catalyst in the reaction system is 2.0% by mass or less, the reaction does not proceed excessively quickly, resulting in excellent reaction controllability.

[0060] The method for producing silica particles preferably further includes the following step (1), since it is possible to remove unnecessary components and add necessary components. Step (1): Concentrating the obtained dispersion of silica particles and adding a dispersion medium

[0061] In step (1), the concentration of the dispersion of silica particles and the addition of the dispersion medium may be carried out in any order.

[0062] The method for concentrating the dispersion of silica particles is not particularly limited, and examples thereof include a heat concentration method and a membrane concentration method. To concentrate the dispersion of silica particles by the heat concentration method, the dispersion may be heated and concentrated under normal pressure or reduced pressure. To concentrate a dispersion of silica particles by membrane concentration, membrane separation by ultrafiltration is preferred. The molecular weight cutoff of the ultrafiltration membrane used here should be selected so that it can filter and separate and remove impurities in accordance with the impurities in the dispersion. Examples of materials for the ultrafiltration membrane include polysulfone, polyacrylonitrile, sintered metal, ceramic, carbon, etc. Examples of the form of the ultrafiltration membrane include spiral, tubular, and hollow fiber types.

[0063] Examples of the dispersion medium to be added to the dispersion liquid of silica particles include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. These dispersion media may be used alone or in combination of two or more. Among these dispersion media, water and alcohol are preferred, and water is more preferred, because they have excellent affinity with silica particles.

[0064] The method for producing silica particles preferably further includes the following step (2), since this can increase the degree of condensation of the silica particles. Step (2): A step of subjecting the dispersion of silica particles obtained in step (1) to a pressure and heat treatment.

[0065] The pressure of the heat-pressure treatment is preferably 0.10 MPa to 2.3 MPa, more preferably 0.14 MPa to 1.9 MPa. When the heat-pressure treatment pressure is 0.10 MPa or more, the degree of condensation of the silica particles can be increased. When the heat-pressure treatment pressure is 2.3 MPa or less, silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, or association ratio, and the dispersion stability of the silica sol is excellent.

[0066] Pressurization can be achieved by heating the silica particle dispersion in a sealed state to a temperature above the boiling point of the dispersion medium. When the silica particle aqueous dispersion is heated to 100°C or higher in a sealed state, the pressure becomes the saturated water vapor pressure at that temperature.

[0067] The temperature for the pressure and heat treatment is preferably 100°C to 220°C, more preferably 110°C to 210°C. When the temperature for the pressure and heat treatment is 100°C or higher, the degree of condensation of the silica particles can be increased. When the temperature for the pressure and heat treatment is 220°C or lower, silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, or association ratio, and the dispersion stability of the silica sol is excellent.

[0068] The time for the pressure and heat treatment is preferably 0.25 to 10 hours, more preferably 0.5 to 8 hours. When the time for the pressure and heat treatment is 0.25 hours or more, the degree of condensation of the silica particles can be increased. When the time for the pressure and heat treatment is 10 hours or less, silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0069] The pressure and heat treatment is preferably carried out in an aqueous dispersion, since it can increase the degree of condensation of silica particles without significantly changing the average primary particle size, average secondary particle size, cv value, or association ratio.

[0070] The pH when the pressure and heat treatment is carried out in the aqueous dispersion is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pressure and heat treatment is carried out in the aqueous dispersion at a pH of 6.0 or higher, gelation of the silica sol can be suppressed. Furthermore, when the pressure and heat treatment is carried out in the aqueous dispersion at a pH of 8.0 or lower, the degree of condensation of the silica particles can be increased without significantly changing the average primary particle size, average secondary particle size, cv value, or association ratio.

[0071] (silica sol) The silica sol of the present invention contains the silica particles of the present invention.

[0072] The silica sol may be produced by using the dispersion of silica particles of the present invention as is, or by removing unnecessary components from the dispersion of silica particles of the present invention and adding necessary components.

[0073] The silica sol of the present invention preferably contains silica particles and a dispersion medium. Examples of the dispersion medium in the silica sol include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. These dispersion media in the silica sol may be used alone or in combination of two or more. Among these dispersion media in the silica sol, water and alcohol are preferred, and water is more preferred, because they have excellent affinity with silica particles.

[0074] The content of silica particles in the silica sol is preferably 3% by mass to 50% by mass, more preferably 4% by mass to 40% by mass, and even more preferably 5% by mass to 30% by mass, based on 100% by mass of the total amount of silica sol. When the content of silica particles in the silica sol is 3% by mass or more, the polishing rate for a workpiece such as a silicon wafer is excellent. Furthermore, when the content of silica particles in the silica sol is 50% by mass or less, aggregation of silica particles in the silica sol or polishing composition can be suppressed, and the storage stability of the silica sol or polishing composition is excellent.

[0075] The content of the dispersion medium in the silica sol is preferably 50% by mass to 97% by mass, more preferably 60% by mass to 96% by mass, and even more preferably 70% by mass to 95% by mass, based on the total amount of the silica sol (100% by mass). When the content of the dispersion medium in the silica sol is 50% by mass or more, aggregation of silica particles in the silica sol or polishing composition can be suppressed, resulting in excellent storage stability of the silica sol or polishing composition. Furthermore, when the content of the dispersion medium in the silica sol is 97% by mass or less, the polishing rate for a workpiece, typically a silicon wafer, is excellent.

[0076] The content of silica particles and dispersion medium in the silica sol can be set within a desired range by removing unnecessary components from the components in the obtained dispersion of silica particles and adding necessary components.

[0077] In addition to silica particles and a dispersion medium, the silica sol may contain other components such as an oxidizing agent, an antiseptic, an antifungal agent, a pH adjuster, a pH buffer, a surfactant, a chelating agent, and an antibacterial / biocide, as needed, within a range that does not impair the performance of the silica sol. In particular, it is preferable to include an antibacterial biocide in the silica sol, since this gives the silica sol excellent storage stability.

[0078] Examples of antibacterial biocides include hydrogen peroxide, ammonia, quaternary ammonium hydroxides, quaternary ammonium salts, ethylenediamine, glutaraldehyde, methyl p-hydroxybenzoate, and sodium chlorite. These antibacterial biocides may be used alone or in combination of two or more. Among these antibacterial biocides, hydrogen peroxide is preferred because of its excellent affinity with silica sol. Antimicrobial biocides also include those commonly referred to as disinfectants.

[0079] The content of the antibacterial biocide in the silica sol is preferably 0.0001% by mass to 10% by mass, and more preferably 0.001% by mass to 1% by mass, based on the total amount of the silica sol (100% by mass). When the content of the antibacterial biocide in the silica sol is 0.0001% by mass or more, the storage stability of the silica sol is excellent. When the content of the antibacterial biocide in the silica sol is 10% by mass or less, the original performance of the silica sol is not impaired.

[0080] The pH of the silica sol is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pH of the silica sol is 6.0 or higher, the dispersion stability is excellent and aggregation of the silica particles can be suppressed. Furthermore, when the pH of the silica sol is 8.0 or lower, dissolution of the silica particles is prevented and long-term storage stability is excellent. The pH of the silica sol can be adjusted to a desired range by adding a pH adjuster.

[0081] (polishing composition) The polishing composition of the present invention comprises the silica sol of the present invention. The polishing composition of the present invention preferably contains a water-soluble polymer in addition to the silica sol of the present invention.

[0082] The water-soluble polymer enhances the wettability of the polishing composition to the object to be polished, such as a silicon wafer. The water-soluble polymer is preferably a polymer having a functional group with high water affinity, and this functional group with high water affinity has a high affinity with the surface silanol groups of the silica particles, so that the silica particles and the water-soluble polymer are stably dispersed in close proximity in the polishing composition. Therefore, when polishing an object to be polished, such as a silicon wafer, the effects of the silica particles and the water-soluble polymer function synergistically.

[0083] Examples of water-soluble polymers include cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, copolymers having a polyvinylpyrrolidone skeleton, and polymers having a polyoxyalkylene structure.

[0084] Examples of cellulose derivatives include hydroxyethyl cellulose, hydrolyzed hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, and carboxymethyl cellulose. Examples of copolymers having a polyvinylpyrrolidone skeleton include graft copolymers of polyvinyl alcohol and polyvinylpyrrolidone. Examples of polymers having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, and copolymers of ethylene oxide and propylene oxide.

[0085] These water-soluble polymers may be used alone or in combination of two or more. Among these water-soluble polymers, cellulose derivatives are preferred, and hydroxyethyl cellulose is more preferred, because they have high affinity with the surface silanol groups of silica particles and act synergistically to impart good hydrophilicity to the surface of the object to be polished.

[0086] The mass-average molecular weight of the water-soluble polymer is preferably 1,000 to 3,000,000, more preferably 5,000 to 2,000,000, and even more preferably 10,000 to 1,000,000. When the mass-average molecular weight of the water-soluble polymer is 1,000 or more, the hydrophilicity of the polishing composition is improved. Furthermore, when the mass-average molecular weight of the water-soluble polymer is 3,000,000 or less, the affinity with silica sol is excellent and the polishing rate for a workpiece, such as a silicon wafer, is excellent.

[0087] The mass average molecular weight of the water-soluble polymer is measured by size exclusion chromatography using a 0.1 mol / L NaCl solution as the mobile phase, in terms of polyethylene oxide.

[0088] The content of the water-soluble polymer in the polishing composition is preferably 0.02% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass, based on 100% by mass of the total amount of the polishing composition. When the content of the water-soluble polymer in the polishing composition is 0.02% by mass or more, the hydrophilicity of the polishing composition is improved. Furthermore, when the content of the water-soluble polymer in the polishing composition is 10% by mass or less, aggregation of silica particles during preparation of the polishing composition can be suppressed.

[0089] In addition to the silica sol and the water-soluble polymer, the polishing composition of the present invention may contain other components, such as a basic compound, a polishing accelerator, a surfactant, a hydrophilic compound, a preservative, an antifungal agent, a pH adjuster, a pH buffer, a surfactant, a chelating agent, or an antibacterial / biocide, as needed, within a range that does not impair the performance of the composition. In particular, it is preferable to include a basic compound in the polishing composition, since it can exert a chemical action on the surface of the object to be polished, such as a silicon wafer, thereby performing chemical polishing (chemical etching), and the synergistic effect with the surface silanol groups of the silica particles can improve the polishing rate of the object to be polished, such as a silicon wafer.

[0090] Examples of basic compounds include organic basic compounds, alkali metal hydroxides, alkali metal hydrogencarbonates, alkali metal carbonates, and ammonia. These basic compounds may be used alone or in combination of two or more. Among these basic compounds, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium hydrogencarbonate, and ammonium carbonate are preferred because they have high water solubility and excellent affinity with silica particles and water-soluble polymers, with ammonia, tetramethylammonium hydroxide, and tetraethylammonium hydroxide being more preferred, and ammonia being even more preferred.

[0091] The content of the basic compound in the polishing composition is preferably 0.001% by mass to 5% by mass, more preferably 0.01% by mass to 3% by mass, based on 100% by mass of the total amount of the polishing composition. When the content of the basic compound in the polishing composition is 0.001% by mass or more, the polishing rate of a polished object, typically a silicon wafer, can be improved. Furthermore, when the content of the basic compound in the polishing composition is 5% by mass or less, the stability of the polishing composition is excellent.

[0092] The pH of the polishing composition is preferably 8.0 to 12.0, more preferably 9.0 to 11.0. When the pH of the polishing composition is 8.0 or higher, aggregation of silica particles in the polishing composition can be suppressed, and the polishing composition has excellent dispersion stability. When the pH of the polishing composition is 12.0 or lower, dissolution of silica particles can be suppressed, and the polishing composition has excellent stability. The pH of the polishing composition can be adjusted to a desired range by adding a pH adjuster.

[0093] The polishing composition can be obtained by mixing the silica sol of the present invention, the water-soluble polymer, and, if necessary, other components. However, in consideration of storage and transportation, the polishing composition may be prepared at a high concentration and then diluted with water or the like immediately before polishing.

[0094] (polishing method) The polishing method of the present invention is a method of polishing using a polishing composition containing the silica sol of the present invention. The polishing composition used is preferably the polishing composition described above. A specific polishing method includes, for example, a method in which the surface of a silicon wafer is pressed against a polishing pad, the polishing composition of the present invention is dropped onto the polishing pad, and the surface of the silicon wafer is polished.

[0095] (Semiconductor wafer manufacturing method) The method for producing a semiconductor wafer of the present invention includes the polishing method of the present invention, and the specific polishing method is as described above. Examples of semiconductor wafers include silicon wafers and compound semiconductor wafers.

[0096] (Method of manufacturing semiconductor devices) The method for manufacturing a semiconductor device of the present invention includes the polishing method of the present invention, and the specific polishing method is as described above.

[0097] (Application) The silica particles and silica sol of the present invention can be suitably used for polishing purposes, such as polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing (chemical mechanical polishing) in the planarization process when manufacturing integrated circuits, polishing synthetic quartz glass substrates used for photomasks and liquid crystal displays, and polishing magnetic disk substrates, and are particularly suitable for polishing silicon wafers and chemical mechanical polishing. [Example]

[0098] The present invention will be explained in more detail below using examples, but the present invention is not limited to the description of the following examples as long as it does not deviate from the gist of the invention.

[0099] (Measurement of average primary particle size) The dispersions of silica particles obtained in the examples and comparative examples were dried at 150°C, and the specific surface area of ​​the silica particles was measured using an automatic specific surface area measuring device "BELSORP-MR1" (model name, Microtrack BEL Corporation). The density was calculated to be 2.2 g / cm using the following formula (3). 3The average primary particle size was calculated. Average primary particle diameter (nm) = 6000 / (specific surface area (m 2 / g) x density (g / cm 3 )) (3)

[0100] (Measurement of average secondary particle size and cv value) The dispersions of silica particles obtained in the examples and comparative examples were measured for their average secondary particle diameter using a dynamic light scattering particle size analyzer "Zetersizer Nano ZS" (model name, manufactured by Malvern Instruments), and the cv value was calculated using the following formula (4). cv value = (standard deviation (nm) / average secondary particle size (nm)) × 100 (4)

[0101] (Calculation of association ratio) The association ratio was calculated from the measured average primary particle size and average secondary particle size using the following formula (5). Association ratio=average secondary particle diameter / average primary particle diameter... (5)

[0102] (Metal content measurement) A dispersion of silica particles obtained in each of the Examples and Comparative Examples containing 0.4 g of silica particles was accurately weighed out, sulfuric acid and hydrofluoric acid were added, and the mixture was heated, dissolved, and evaporated. Pure water was added to the remaining sulfuric acid droplets so that the total amount was exactly 10 g to prepare a test solution. The content of sodium, potassium, iron, aluminum, calcium, magnesium, zinc, cobalt, chromium, copper, manganese, lead, titanium, silver, and nickel was measured using a high-frequency inductively coupled plasma mass spectrometer "ELEMENT2" (model name, manufactured by Thermo Fisher Scientific), and the total was taken as the metal content.

[0103] (Measurement of x·y of SiOxHy) The dispersions of silica particles obtained in the examples and comparative examples were freeze-dried to prepare powder samples. 29The contents of Q3 and Q4 units were measured using a Si-DD / MAS-NMR (model "AVANCEIII 400WB", manufactured by Bruker, BO = 9.4T, 4.00 mm HX VT-MAS probe), and x·y was calculated. The measurement conditions were rotor spun rate = 6 kHz, pulse length (p / 4) = 2.62 ms, recycle delay = 30 sec, number of scans = 2048, 1 H decoupling sequence: SPINAL64.

[0104] [Example 1] Solution (B) was prepared by mixing tetramethoxysilane and methanol in a volume ratio of 2.3:1, and solution (C) was prepared as a 3.5% by mass aqueous ammonia solution. A reaction vessel equipped with a thermometer, a stirrer, a supply pipe, and a distillation line was charged with solution (A), which was prepared by mixing methanol, pure water, and ammonia. The water concentration in solution (A) was 13% by mass, and the ammonia concentration in solution (A) was 1.1% by mass. While maintaining the temperature of the reaction solution at 31°C, 100% by volume of solution (B) and 32% by volume of solution (C) were added at equal rates to 194% by volume of solution (A) over 109 minutes to obtain a dispersion of silica particles. The temperature was raised to remove methanol and ammonia from the obtained dispersion of silica particles while adjusting the liquid volume by adding pure water so that the silica particle content was approximately 20% by mass, obtaining a dispersion of silica particles with a silica particle content of approximately 20% by mass. The obtained dispersion of silica particles was subjected to a pressure and heat treatment at 1.6 MPa and 200° C. for 5 hours to obtain a dispersion of silica particles with a silica particle content of approximately 20 mass %. The evaluation results of the obtained silica particles are shown in Table 1. The silica particles were confirmed to be amorphous by a halo pattern obtained by wide-angle X-ray scattering measurement.

[0105] [Comparative Example 1] A commercially available dispersion of silica particles (product name "PL-3", manufactured by Fuso Chemical Co., Ltd.) was used as is. The evaluation results of the silica particles used are shown in Table 1.

[0106] [Table 1]

[0107] As can be seen from Table 1, the silica particles obtained in Example 1 have almost the same physical properties, such as particle size, as the silica particles used in Comparative Example 1, but because both x and y are smaller, they are able to both suppress scratches on the workpiece and achieve an excellent polishing rate, and have an appropriate hardness that makes them less likely to adhere to the workpiece. [Industrial Applicability]

[0108] The silica particles and silica sol of the present invention can be suitably used for polishing purposes, such as polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing (chemical mechanical polishing) in the planarization process when manufacturing integrated circuits, polishing synthetic quartz glass substrates used for photomasks and liquid crystal displays, and polishing magnetic disk substrates, and are particularly suitable for polishing silicon wafers and chemical mechanical polishing.

Claims

1. Silica particles having a metal impurity content of 5 ppm or less, Silica particles for polishing, which, when expressed as SiOxHy, satisfy the following formula (1') and formula (2'), and contain a tetraalkoxysilane condensate as a main component. 2.06≦x≦2.11 (1′) 0.12≦y≦0.22 (2′)

2. 2. The abrasive silica particles according to claim 1, wherein the silica particles are amorphous.

3. 3. Silica particles for polishing according to claim 1, wherein the average primary particle diameter measured by the BET method is 5 nm to 100 nm.

4. 4. Silica particles for polishing according to claim 1, wherein the average secondary particle diameter measured by DLS is 10 nm to 200 nm.

5. 5. Silica particles for polishing according to claim 1, wherein the tetraalkoxysilane condensate comprises a tetramethoxysilane condensate.

6. A silica sol comprising the silica particles for polishing according to any one of claims 1 to 5.

7. A silica sol as described in claim 6, wherein the content of polishing silica particles is 3 mass% to 50 mass% of the total amount of silica sol.

8. A polishing composition comprising the silica sol according to claim 6 or 7.

9. A polishing method, comprising polishing using the polishing composition according to claim 8.

10. A method for producing a semiconductor wafer, comprising a step of polishing the semiconductor wafer with the polishing composition of claim 8.

11. A method for manufacturing a semiconductor device, comprising a step of polishing with the polishing composition of claim 8.

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