Silica particles, silica sol, method for producing silica particles, polishing composition, polishing method, method for manufacturing semiconductor wafer, and method for manufacturing semiconductor device

Abstract

The purpose of the present invention is to provide silica particles, a silica sol, and a polishing composition that are unlikely to cause defects in an object to be polished. The present invention relates to silica particles that satisfy formula (1) when x (mass%) is the mass ratio of alkoxy groups in the silica particles and y (mass%) is the mass ratio of silanol groups in the silica particles.　(1): y (mass%) < 8x (mass%) + 0.5

Description

Silica particles, silica sol, method for producing silica particles, polishing composition, polishing method, method for producing semiconductor wafers, and method for producing semiconductor devices.

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

[0002] Polishing methods using polishing solutions are known for polishing the surfaces of materials such as metals and inorganic compounds. In particular, in the final finishing polishing of prime silicon wafers for semiconductors and recycled silicon wafers, as well as in chemical mechanical polishing (CMP) for planarization of interlayer insulating films, formation of metal plugs, and formation of embedded wiring during semiconductor device manufacturing, the surface condition greatly affects the semiconductor properties, and therefore, the surfaces and edges of these components are required to 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 main abrasive component. Depending on the manufacturing method, colloidal silica is known to be produced by thermal decomposition of silicon tetrachloride (e.g., fumed silica), deionization of alkali silicates such as water glass, and hydrolysis and condensation reactions of alkoxysilanes (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 a method for producing silica particles by hydrolysis and condensation reactions of alkoxysilanes.

[0005] Japanese Unexamined Patent Publication No. 11-60232 Japanese Unexamined Patent Application No. 2019-89692

[0006] Currently, the composition of silica particles, specifically the amounts of silanol and alkoxy groups, cannot be said to be optimized. Using silica particles with inappropriate amounts of silanol and alkoxy groups for polishing raises concerns about defects in the polished object. Specifically, silica particles with an inappropriate amount of silanol groups may remain on the surface of the polished object or have poor stability when formed into a silica sol. Furthermore, silica particles with an inappropriate amount of alkoxy groups may cause scratches on the surface of the polished object.

[0007] This invention has been made in view of these problems, and the object of this invention is to provide silica particles, silica sol, and polishing compositions that are less likely to cause defects in the object to be polished.

[0008] As a result of diligent research, the inventors have invented silica particles in which the amounts of silanol groups and alkoxy groups within the particles are appropriately controlled.

[0009] In other words, the gist of the present invention is as follows:

[0010] One aspect of the present invention relates to silica particles that satisfy the following formula (1), where x (mass%) is the mass percentage of alkoxy groups in the silica particles and y (mass%) is the mass percentage of silanol groups in the silica particles: y (mass%) < 8x (mass%) + 0.5 ... (1)

[0011] Aspect 2 of the present invention relates to silica particles of Aspect 1 that satisfy the following formula (2): y (mass%) < 8x (mass%) + 0.1 ... (2)

[0012] Aspect 3 of the present invention relates to silica particles according to aspect 1 or 2, wherein the mass percentage of the silanol groups in the silica particles is 1.0% by mass or less.

[0013] Aspect 4 of the present invention relates to silica particles in which, in any one of the silica particles of aspects 1 to 3, the mass ratio of the alkoxy groups in the silica particles is 10% by mass or less.

[0014] Aspect 5 of the present invention relates to silica particles in which, in any one of the silica particles of aspects 1 to 4, the alkoxy group is a methoxy group.

[0015] Aspect 6 of the present invention relates to silica particles according to aspect 5, wherein the mass percentage of the methoxy group in the silica particles is 0.07% by mass or more.

[0016] Embodiment 7 of the present invention relates to silica particles in which the metal impurity content is 5 ppm by mass or less, in any one of the silica particles of Embodiments 1 to 6.

[0017] Embodiment 8 of the present invention relates to silica particles having a true specific gravity of 1.60 g / mL or more and 2.05 g / mL or less, in any one of the silica particles of Embodiments 1 to 7.

[0018] Aspect 9 of the present invention relates to silica particles having an average secondary particle diameter of 10 nm to 1000 nm, in any one of the silica particles of aspects 1 to 8.

[0019] Embodiment 10 of the present invention relates to silica particles in which the amine content is less than 5 μmol / g in any one of the silica particles of Embodiments 1 to 9.

[0020] Aspect 11 of the present invention relates to a silica sol comprising silica particles according to any one of aspects 1 to 10 and water.

[0021] Aspect 12 of the present invention relates to a silica sol in which the concentration of an alkaline substance is 1000 ppm by mass or less, as described in aspect 11.

[0022] Aspect 13 of the present invention relates to a method for producing silica particles, comprising the following steps 1 to 3, with at least one step 2 following step 3. Step 1: A step of hydrolyzing and condensing an alkoxysilane to obtain a dispersion of silica particles containing an alcohol. Step 2: A step of replacing at least a portion of the dispersion medium in the dispersion of silica particles obtained in step 1 or step 3. Step 3: A step of applying pressurized heat treatment to the dispersion of silica particles obtained in step 1 or step 2.

[0023] Aspect 14 of the present invention relates to a method for producing silica particles as described in Aspect 13, wherein in step 3, the dispersion of silica particles before pressurized heat treatment is a dispersion of silica particles having a pH of 7.5 to 10.0 and an alcohol concentration of 0.01% to 10% by mass.

[0024] Aspect 15 of the present invention relates to an abrasive composition comprising the silica sol described in Aspect 11 or 12.

[0025] Aspect 16 of the present invention relates to a polishing method using the polishing composition of Aspect 15.

[0026] Aspect 17 of the present invention relates to a method for manufacturing a semiconductor wafer, which includes a step of polishing using the polishing composition of Aspect 15.

[0027] Aspect 18 of the present invention relates to a method for manufacturing a semiconductor device, which includes a step of polishing using the polishing composition of Aspect 15.

[0028] Silica particles with an appropriate balance of silanol and alkoxy groups are less likely to cause defects in the object being polished when used for polishing.

[0029] The present invention will be described in detail below, but these are merely examples of preferred embodiments and are not limiting to these. The "~" in numerical ranges indicates a range that includes the numbers before and after it; for example, "0 mass% to 100 mass%" means a range that is 0 mass% or more and 100 mass% or less.

[0030] [Silica Particles] In this embodiment, when the mass percentage of alkoxy groups in the silica particles is x (mass%) and the mass percentage of silanol groups in the silica particles is y (mass%), the following formula (1) is satisfied: y (mass%) < 8x (mass%) + 0.5 ... (1)

[0031] When silica particles with a low mass percentage y (mass%) of silanol groups within them, satisfying formula (1) above, are used for polishing, adhesion of silica particles to the surface of the object being polished due to bonding between hydroxyl groups on the surface of the object and silanol groups within the silica particles can be avoided. Conversely, when silica particles with a high mass percentage x (mass%) of alkoxy groups, satisfying formula (1) above, i.e., silica with a low degree of condensation and internal defects, are used for polishing, their low hardness makes them less likely to scratch the object being polished.

[0032] Furthermore, the silica particles according to this embodiment are more preferably satisfied with the following formula (2) in order to reduce defects on the surface of the object to be polished: y (mass%) < 8x (mass%) + 0.1 ... (2)

[0033] The mass percentage of silanol groups within the silica particles is preferably 1.3% by mass or less, more preferably 1.0% by mass or less, even more preferably 0.8% by mass or less, and considerably more preferably 0.6% by mass or less, in order to avoid bonding between the silanol groups and the surface of the object to be polished and to reduce the adhesion of silica particles to the surface of the object to be polished. Note that if the silica particles are amorphous silica, the mass percentage of silanol groups within the silica particles is usually 0.01% by mass or more.

[0034] The mass percentage y of silanol groups in silica particles can be measured by the Sears method. Specifically, it is measured and calculated under the conditions shown below. A silica sol equivalent to 1.5 g of silica particles is taken, and pure water is added to make a volume of 90 mL. At 25°C, 0.1 mol / L hydrochloric acid aqueous solution is added until the pH reaches 3.6, then 30 g of sodium chloride is added, and pure water is gradually added to completely dissolve the sodium chloride. Finally, pure water is added until the total volume of the test solution reaches 150 mL to obtain the test solution. The obtained test solution is placed in an automatic titrator, and 0.1 mol / L sodium hydroxide aqueous solution is added dropwise to measure the titration volume A (mL) of 0.1 mol / L sodium hydroxide aqueous solution required to change the pH from 4.0 to 9.0.

[0035] Using the following formula (3), calculate the amount V (mL) of 0.1 mol / L sodium hydroxide solution required to change the pH of 1.5 g of silica particles from 4.0 to 9.0, and use the following formula (4) to calculate the mass percentage y of the silanol group. V = (A × f × 100 × 1.5) / (W × C) ... (3) A: Tit volume (mL) of 0.1 mol / L sodium hydroxide solution required to change the pH of 1.5 g of silica particles from 4.0 to 9.0 f: Titer of the 0.1 mol / L sodium hydroxide solution used C: Concentration (mass%) of silica particles in silica sol W: Amount of silica sol collected (g) y = (B × w ＯＨ ) / M × 100 ... (4) B: Amount of sodium hydroxide (mol) required to change the pH of 1.5 g of silica particles from 4.0 to 9.0 calculated from V w ＯＨ : Molecular weight of silanol group (g / mol) M: Amount of silica particles (1.5 g)

[0036] Examples of alkoxy groups whose mass percentage in the silica particles in this embodiment is x (mass%) include methoxy, ethoxy, propoxy, butoxy, and phenoxy groups. Of these, the methoxy group is preferred because it has moderately low hydrophobicity and excellent dispersibility in water.

[0037] The presence of an alkoxy group within the silica particles of the present embodiment indicates that it exists as an alkoxy group (Si-OR group) without forming a siloxane bond (Si-O-Si) in that portion. Therefore, the presence of an alkoxy group within the silica particles reduces the degree of condensation of silica, creating voids at the molecular level within the silica particles. Also, since an alkoxy group has higher hydrophobicity than a silanol group (Si-OH group), the hydrophobic effect can suppress the localization of water molecules into the voids at the molecular level. From the above viewpoints, the mass ratio of the alkoxy group within the silica particles is preferably 0.07% by mass or more, more preferably 0.11% by mass or more, still more preferably 0.13% by mass or more. When the mass ratio of the alkoxy group within the silica particles is within the above range, the degree of condensation of silica becomes moderately low, making the silica particles softer and less likely to contain water molecules, thus reducing the weight of the silica particles. Therefore, when using such silica particles for polishing, the possibility of damaging the object to be polished can be reduced. Also, the mass ratio of the alkoxy group within the silica particles is preferably 10% by mass or less, more preferably 7.0% by mass or less, still more preferably 2.0% by mass or less, particularly preferably 1.0% by mass or less, and most preferably 0.70% by mass or less. When the mass ratio of the alkoxy group within the silica particles is within the above range, the degree of condensation of silica can be moderately increased, preventing the particles from being crushed during polishing. As described later, it is preferable that the silica particles mainly consist of a condensate of alkoxysilane. In that case, the mass ratio of the alkoxy group within the silica particles is usually 0.01% by mass or more.

[0038] The mass ratio x (% by mass) of the alkoxy group within the silica particles can be quantified, for example, by measuring a solution obtained by dissolving the silica particles in an alkali using gas chromatography.

[0039] The mass ratios of the alkoxy group and the silanol group within the silica particles can be set within a desired range by adjusting the process of applying heat to the silica particles, for example, the conditions of Process 3 described later.

[0040] The process of applying heat to silica particles, such as pressurized heat treatment, reduces both functional groups through hydrolysis of alkoxy groups and condensation reactions between silanol groups present in the silica particles. Control parameters for pressurized heat treatment include, for example, temperature, pressure, pH, and liquid composition. By appropriately controlling these parameters, the concentration of alkoxy groups inside the silica particles can be adjusted.

[0041] The metal impurity content of the silica particles according to this embodiment is preferably 5 ppm by mass or less, more preferably 1 ppm by mass or less, and even more preferably 0.5 ppm by mass or less. When the metal impurity content of the silica particles is 5 ppm by mass or less, it is preferable because it reduces contamination caused by metal impurities adhering to the surface of the object to be polished during the polishing of silicon wafers for semiconductor devices, and the resulting impact on wafer characteristics. It is also preferable because it reduces quality degradation caused by metal impurities adhering to the surface of the object to be polished diffusing into the wafer, and reduces the decrease in performance of semiconductor devices manufactured using such wafers. It is preferable that the metal impurity content of the silica particles is 0 ppm by mass, that is, substantially none.

[0042] Furthermore, when the metal impurity content of the silica particles is 5 ppm by mass or less, it is preferable because the influence on the polishing rate due to changes in the chemical properties (acidity, etc.) of the surface silanol groups and changes in the steric environment of the silica particle surface (ease of aggregation of silica particles, etc.) caused by coordination interactions between the acidic surface silanol groups and the metal impurities is reduced.

[0043] The metal impurity content of the silica particles in this specification is a value measured by high-frequency inductively coupled plasma mass spectrometry (ICP-MS). Specifically, an accurate amount of a silica sol containing 0.4 g of silica particles is weighed, sulfuric acid and hydrofluoric acid are added, heated, dissolved, and evaporated, and pure water is added to the remaining sulfuric acid droplets so that the total amount is exactly 10 g to prepare a test solution, which is then measured using a high-frequency 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 defined as the metal impurity content.

[0044] To make the metal impurity content of the silica particles 5 mass ppm or less, for example, a method of obtaining silica particles by performing a hydrolysis reaction and a condensation reaction using alkoxysilane as the main raw material can be mentioned. In the method of deionizing alkali silicate such as water glass, since sodium or the like derived from the raw material remains, it is extremely difficult to make the metal impurity content of the silica particles 5 mass ppm or less.

[0045] The average primary particle diameter of the silica particles according to this embodiment is preferably 5 nm to 500 nm, more preferably 10 nm to 200 nm, and even more preferably 20 nm to 160 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. Further, when the average primary particle diameter of the silica particles is 500 nm or less, the surface roughness and scratches of the polished object typified by a silicon wafer can be reduced, and the sedimentation of the silica particles can be suppressed.

[0046] 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 a specific surface area automatic measuring device, and the average primary particle diameter is calculated using the following formula (5). Average primary particle diameter (nm) = 6000 / (specific surface area (m ２ / g) × density (g / cm ３ )) ··· (5)

[0047] The average primary particle diameter of the silica particles can be set within a desired range according to the manufacturing conditions of the silica particles.

[0048] In this embodiment, the average secondary particle diameter of the silica particles is preferably 10 nm to 1000 nm, more preferably 20 nm to 300 nm, and even more preferably 40 nm to 250 nm. When the average secondary particle diameter of the silica particles is 10 nm or more, the removal of particles and other debris 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 1000 nm or less, the surface roughness and scratches of the workpiece, such as silicon wafers, during polishing can be reduced, the removal of particles and other debris during cleaning after polishing is excellent, and the sedimentation of silica particles can be suppressed.

[0049] The average secondary particle diameter of silica particles is measured by the DLS method. Specifically, it is measured using a dynamic light scattering particle diameter analyzer.

[0050] The average secondary particle diameter of silica particles can be set to a desired range depending on the manufacturing conditions of the silica particles. For example, when the reaction temperature during the synthesis of silica particles is low, the average secondary particle diameter of the silica particles tends to be large, while when the reaction temperature during the synthesis of silica particles is high, the average secondary particle diameter of the silica particles tends to be small.

[0051] The CV value of the silica particles in this embodiment is preferably 10% to 50%, more preferably 15% to 40%, and even more preferably 20% to 30%. When the CV value of the silica particles is 10% or more, the polishing rate on the workpiece, such as silicon wafers, is excellent, and the productivity of silicon wafers is excellent. Furthermore, when the CV value of the silica particles is 50% or less, the surface roughness and scratches on the workpiece, such as silicon wafers, during polishing can be reduced, and the removal of particles and other contaminants during cleaning after polishing is excellent.

[0052] The CV value of silica particles is calculated by measuring the average secondary particle diameter of the silica particles using a dynamic light scattering particle diameter analyzer and using the following formula (6): CV value = (standard deviation (nm) / average secondary particle diameter (nm)) × 100 ... (6)

[0053] In this embodiment, the association ratio of silica particles is preferably 1.0 to 4.0, more preferably 1.1 to 2.5, and even more preferably 1.2 to 2.2. When the association ratio of silica particles is 1.0 or higher, the polishing rate for the workpiece, such as a silicon wafer, is excellent, and the productivity of silicon wafers is excellent. Furthermore, when the association ratio of silica particles is 4.0 or lower, the surface roughness and scratches of the workpiece, such as a silicon wafer, during polishing can be reduced, and the aggregation of silica particles can be suppressed.

[0054] The association ratio of silica particles is calculated using the following formula (7) from the average primary particle diameter and the average secondary particle diameter measured using the aforementioned measurement method. Association ratio = Average secondary particle diameter / Average primary particle diameter ... (7)

[0055] The amine content of the silica particles according to this embodiment is preferably less than 5 μmol / g, more preferably 3 μmol / g or less, and even more preferably 1 μmol / g or less. There is no particular lower limit to the amine content of the silica particles, but for example, it can be 0.001 μmol / g or more. Alternatively, the content can be reduced to zero by not using amines in the production of the silica particles. In one embodiment, the silica particles according to this embodiment can have an amine content of 0.001 μmol / g or more and less than 5 μmol / g. Amines refer to primary amines, secondary amines, and tertiary amines, and are specifically represented by the following general formula (X). NRaRbRc ... (X) (wherein Ra, Rb, and Rc represent substituted alkyl groups having 1 to 12 carbon atoms, or hydrogen atoms. However, not all of Ra, Rb, and Rc are hydrogen atoms; that is, ammonia is excluded from the amines represented by the general formula (X). Ra, Rb, and Rc may be the same or different from each other. When Ra, Rb, and Rc are alkyl groups, they may be linear, branched, or cyclic alkyl groups. When Ra, Rb, and Rc are substituted alkyl groups, examples of substituents include alkoxy groups, amino groups, alkyl-substituted primary amino groups, alkyl-disubstituted amino groups, and hydroxyl groups.)

[0056] A silica particle amine content of less than 5 μmol / g is preferable because it prevents corrosion of the object being polished and the equipment used for polishing. The amine content of silica particles is measured by ion chromatography. Specifically, after separating the silica particles from other components by centrifugation or the like, the silica is dissolved in an aqueous sodium hydroxide solution, and the amine in the solution is quantified by ion chromatography.

[0057] In this embodiment, the silica particles are preferably amorphous. In this case, a moderate amount of silanol groups are present on the surface of the silica particles, and during the polishing process, chemical interactions occur between the silica particles and the workpiece via the silanol groups, allowing the polishing to proceed smoothly. The amorphous nature of the silica particles can be confirmed by the halo pattern obtained from wide-angle X-ray scattering measurements.

[0058] Examples of silica particle shapes include spherical, chain-like, cocoon-like (also referred to as knob-like or peanut-like), and irregular shapes (e.g., warty, bent, branched, etc.). Among these silica particle shapes, spherical is preferred when it is desired to reduce the surface roughness and scratches of the workpiece, such as silicon wafers, during polishing, while irregular shapes are preferred when it is desired to further increase the polishing rate of the workpiece, such as silicon wafers.

[0059] Due to the trace amounts of residual alkoxy groups within the particles, the silica particles of this embodiment possess both appropriate mechanical strength and flexibility, and exhibit excellent mechanical strength and storage stability. Therefore, it is preferable that the silica particles of this embodiment mainly consist of alkoxysilane condensates, more preferably tetraalkoxysilane condensates, and even more preferably tetramethoxysilane condensates. The main component refers to a component that accounts for 50% or more by mass of 100% by mass of all components constituting the silica particles.

[0060] Examples of tetraalkoxysilane condensates include condensates of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. These tetraalkoxysilane condensates may be used individually or in combination of two or more. Among these tetraalkoxysilane condensates, tetramethoxysilane condensates and tetraethoxysilane condensates are preferred, and tetramethoxysilane condensates are more preferred, because they undergo rapid hydrolysis, leave little unreacted residue, have excellent productivity, and allow for easy acquisition of stable silica sols.

[0061] 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 refers to a raw material that accounts for 50% or more by mass of the total raw materials constituting the silica particles (100% by mass).

[0062] The fact that alkoxysilane condensates are the main component can be confirmed by examining the presence of alkoxy groups in silica particles. While there are no specific restrictions on the method used to examine the presence of alkoxy groups, for example, regarding silica particles... １３ Methods such as measuring 13C solid NMR and measuring the alcohol content in an alkaline solution containing dissolved silica particles can be used.

[0063] The true specific gravity of the silica particles according to this embodiment is preferably 1.60 g / mL or more and 2.05 g / mL or less, more preferably 1.70 g / mL or more and 2.00 g / mL or less, and even more preferably 1.80 g / mL or more and less than 1.95 g / mL. When the true specific gravity is 1.60 g / mL or more, the inside of the particles is moderately densely packed, resulting in excellent mechanical strength and preventing the silica particles from breaking when used for polishing. When the true specific gravity is 2.05 g / mL or less, the inside of the particles is moderately sparse, the particles are highly flexible, and preventing scratches on the surface of the object being polished when the silica particles are used for polishing. In another embodiment, it is preferable that the true specific gravity of the silica particles be less than 2.07 g / mL. For example, the true specific gravity of the silica particles can be 1.60 g / mL or more and less than 2.07 g / mL.

[0064] The true specific gravity of silica particles can be set to a desired range depending on the manufacturing conditions of the silica particles. For example, when the reaction temperature during the synthesis of silica particles is low, the true specific gravity of the silica particles tends to be low, while when the reaction temperature during the synthesis of silica particles is high, the true specific gravity of the silica particles tends to be high.

[0065] The true specific gravity of silica particles can be measured by the ethanol substitution method. It can be calculated using the difference between the mass of a container of known volume filled with silica particles and ethanol and the mass of the same container filled with ethanol alone, the volume of the container, and the density of ethanol.

[0066] [Silica Sol] The silica sol according to this embodiment contains silica particles according to this embodiment and water.

[0067] The silica sol may be prepared by using the silica particle dispersion according to this embodiment as is, or by removing unnecessary components and adding necessary components from the silica particle dispersion according to this embodiment.

[0068] The silica sol according to this embodiment 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. One of these dispersion mediums in the silica sol may be used alone, or two or more may be used in combination. Among these dispersion mediums in the silica sol, water and alcohol are preferred, and water is more preferred, because they have excellent affinity with silica particles.

[0069] The silica particle content in the silica sol is preferably 3% to 50% by mass, more preferably 4% to 40% by mass, and even more preferably 5% to 30% by mass, based on 100% by mass of the total silica sol. When the silica particle content in the silica sol is 3% by mass or more, the polishing rate for the workpiece, such as silicon wafers, is excellent. Furthermore, when the silica particle content in the silica sol is 50% by mass or less, aggregation of silica particles in the silica sol and polishing composition can be suppressed, resulting in excellent storage stability for the silica sol and polishing composition.

[0070] The content of the dispersion medium in the silica sol is preferably 50% to 97% by mass, more preferably 60% to 96% by mass, and even more preferably 70% to 95% by mass, based on 100% by mass of the total amount of silica sol. 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 and polishing composition can be suppressed, resulting in excellent storage stability of the silica sol and polishing composition. Furthermore, when the content of the dispersion medium in the silica sol is 97% by mass or less, the polishing rate for the workpiece, such as silicon wafers, is excellent.

[0071] The alcohol content in the silica sol is preferably 0.100% by mass or less, more preferably 0.050% by mass or less, and even more preferably 0.030% by mass or less, based on 100% by mass of the total silica sol. Having an alcohol content of 0.100% by mass or less has the advantage of preventing unexpected side reactions between the alkali and other components when preparing an abrasive composition using the silica sol, such as the oxidation reaction of alcohol by an oxidizing agent, thus avoiding contamination of the object to be polished. The alcohol content in the silica sol is preferably 0.0001% by mass or more, more preferably 0.0005% by mass or more, and even more preferably 0.001% by mass or more, based on 100% by mass of the total silica sol. Having an alcohol content of 0.0001% by mass or more is preferable because it suppresses and stabilizes the hydrolysis of the alkoxy groups of the silica particles in the silica sol.

[0072] The content of silica particles and dispersion medium in the silica sol can be set to a desired range by removing unnecessary components and adding necessary components from the components of the resulting silica particle dispersion.

[0073] In this embodiment, the silica sol preferably has an alkaline substance concentration of 1000 ppm by mass or less, more preferably 500 ppm by mass or less, and even more preferably 100 ppm by mass or less. By having an alkaline substance concentration of 1000 ppm by mass or less, it is possible to prevent unexpected side reactions between the alkaline substance and the object to be polished when using silica sol, such as corrosion of the object to be polished by the alkaline substance. Furthermore, from the viewpoint of maintaining the pH of the silica sol at an appropriate basic level and improving the dispersibility of silica particles, the concentration of the alkaline substance is preferably 10 ppm by mass or more, and more preferably 30 ppm by mass or more.

[0074] Examples of alkaline substances include ammonia, amines, and quaternary ammonium salts.

[0075] The concentration of alkaline substances in silica sol can be kept low by using a volatile alkaline substance as a catalyst in step 1 of the manufacturing process for silica particles and silica sol described later. Specifically, it is preferable to use an alkaline substance with a boiling point of 100°C or lower, and it is even more preferable to use ammonia.

[0076] In addition to silica particles and a dispersion medium, silica sol may contain other components as needed, such as oxidizing agents, preservatives, fungicides, pH adjusters, pH buffers, surfactants, chelating agents, and antimicrobial biocides, to the extent that it does not impair its performance. In particular, it is preferable to include antimicrobial biocides in silica sol because it has excellent storage stability.

[0077] Examples of antimicrobial biocides include hydrogen peroxide, ammonia, quaternary ammonium hydroxide, quaternary ammonium salts, ethylenediamine, glutaraldehyde, methyl p-hydroxybenzoate, and sodium chlorite. These antimicrobial biocides may be used individually or in combination of two or more. Among these antimicrobial biocides, hydrogen peroxide is preferred due to its excellent affinity for silica sol. Antimicrobial biocides also include those generally known as disinfectants.

[0078] The content of the antimicrobial biocide in the silica sol is preferably 0.0001% to 10% by mass, and more preferably 0.001% to 1% by mass, based on 100% by mass of the total silica sol. When the content of the antimicrobial biocide in the silica sol is 0.0001% by mass or more, the silica sol has excellent storage stability. When the content of the antimicrobial biocide in the silica sol is 10% by mass or less, the original performance of the silica sol is not impaired.

[0079] The pH of the silica sol is preferably 6.0 to 8.5, and more preferably 6.5 to 8.2. A pH of 6.0 or higher provides excellent dispersion stability and suppresses the aggregation of silica particles. Furthermore, a pH of 8.5 or lower prevents the dissolution of silica particles and provides excellent long-term storage stability. The pH of the silica sol can be set to a desired range by adding a pH adjusting agent.

[0080] [Method for producing silica particles, method for producing silica sol] The silica particles according to this embodiment can be produced by a method comprising the following steps 1 to 3, and at least one step 2 after step 3. Step 1: A step of hydrolyzing and condensing an alkoxysilane to obtain a dispersion of silica particles containing an alcohol. Step 2: A step of replacing at least a portion of the dispersion medium in the dispersion of silica particles obtained in step 1 or step 3. Step 3: A step of applying pressurized heat treatment to the dispersion of silica particles obtained in step 1 or step 2.

[0081] In the silica particle manufacturing method of this embodiment, step 2 is usually performed at least once after step 1, but it is not required. However, another step may be performed between step 1 and step 2, for example, a step to concentrate the silica particle dispersion, a step to add another component to the silica particle dispersion, a step to modify the silica particles by reacting them with some chemical substance, or a step to remove a specific component from the silica particle dispersion. By performing step 2 after step 3, both the amount of silanol groups and alkoxy groups in the silica particles and the alcohol content in the silica sol can be controlled simultaneously. In the silica particle manufacturing method of this embodiment, step 2 is performed once after step 3. Alternatively, steps 2 and 3 may be repeated multiple times.

[0082] (Step 1) Step 1 is a step in which an alkoxysilane is subjected to a hydrolysis reaction and a condensation reaction to obtain a dispersion of silica particles containing an alcohol.

[0083] As the alkoxysilane used in step 1, tetraalkoxysilane is preferred because it can reduce the metal impurity content and allows for easy control of the silica particle shape. Examples of tetraalkoxysilanes include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. These tetraalkoxysilanes may be used individually or in combination of two or more. Among these tetraalkoxysilanes, tetramethoxysilane and tetraethoxysilane are preferred, and tetramethoxysilane is preferred, because they undergo a rapid hydrolysis reaction, leave little unreacted residue, have excellent productivity, and allow for easy acquisition of a stable silica sol.

[0084] The raw materials for silica particles may include raw materials other than tetraalkoxysilane, such as low condensates of tetraalkoxysilane. However, due to their excellent reactivity, it is preferable that tetraalkoxysilane accounts for 50% or more by mass and other raw materials account for 50% or less by mass of the total raw materials constituting the silica particles, and more preferably that tetraalkoxysilane accounts for 90% or more by mass and other raw materials account for 10% or less by mass.

[0085] Examples of solvents or dispersion media used in hydrolysis and condensation reactions include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents or dispersion media may be used individually or in combination of two or more. Among these solvents or dispersion media, water and alcohols are preferred, and water and methanol are more preferred, because the by-products used in the hydrolysis and condensation reactions are the same, and they offer excellent manufacturing convenience.

[0086] In step 1, the concentration of water in the reaction system for the hydrolysis and condensation reactions is preferably maintained at 3% to 90% by mass, more preferably at 4% to 30% by mass, and even more preferably at 5% to 25% by mass, out of 100% by mass of the total amount in the reaction system. When the concentration of water in the reaction system is 3% by mass or more, it is easy to control the hydrolysis reaction rate of the alkoxysilane. Furthermore, when the concentration of water in the reaction system is 90% by mass or less, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and it is easy to control the particle shape.

[0087] The water concentration in the reaction system refers to the ratio of the total amount of water to the total amount of liquid and dissolved substances in the reaction system during hydrolysis and condensation reactions. As described later, when solutions (A), (B), and (C) are used in step 1, the total amount of liquid and dissolved substances in the reaction system is initially only solution (A), and during the reaction it becomes the total amount of solution (A), solution (B), solution (C), and the alcohol produced by the reaction. Silica particles dispersed in the liquid are not included in the definition of liquid and dissolved substances in the reaction system.

[0088] Hydrolysis and condensation reactions may be carried out in the presence or absence of a catalyst, but the presence of a catalyst is preferred because it can accelerate the hydrolysis and condensation reactions.

[0089] In the method for producing silica particles of this embodiment, examples of catalysts that may be used in step 1 include acid catalysts such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, formic acid, and citric acid, and alkaline catalysts such as ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. Among these catalysts, alkaline catalysts are preferred because they exhibit excellent catalytic activity and allow for easy control of particle shape.

[0090] In the method for producing silica particles of this embodiment, examples of alkali catalysts that may be used in step 1 include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used individually or in combination of two or more. Among these alkali catalysts, ammonia is preferred because it exhibits excellent catalytic activity, allows for easy control of particle shape, suppresses the inclusion of metal impurities, and has high volatility, resulting in excellent removal after hydrolysis and condensation reactions. Furthermore, even if some alkali catalyst remains in the silica sol, ammonia is preferred because it exhibits low corrosiveness to the object being polished when the silica sol is used for polishing.

[0091] The concentration of the alkaline catalyst in the reaction system for hydrolysis and condensation reactions is preferably maintained at 0.5% to 5.5% by mass, more preferably at 1.0% to 5.0% by mass, and even more preferably at 1.2% to 4.5% by mass, based on 100% by mass of the total amount in the reaction system. When the concentration of the alkaline catalyst in the reaction system is 0.5% by mass or higher, the aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion is excellent. Furthermore, when the concentration of the alkaline catalyst in the reaction system is 5.5% by mass or lower, the reaction does not proceed excessively quickly, and the reaction is well controllable.

[0092] The concentration of the alkaline catalyst in the reaction system refers to the total amount of alkaline catalyst in the total amount of liquid and substances dissolved in the liquid in the reaction system during hydrolysis and condensation reactions.

[0093] In step 1, the solution used for the hydrolysis and condensation reactions of the alkoxysilane may contain a salt.

[0094] In the method for producing silica particles of this embodiment, there are no particular restrictions on the salts that may be used in step 1, and examples include ammonium acetate, ammonium tartrate, ammonium citrate, ammonium acetate, ammonium benzoate, ammonium malate, ammonium butyrate, ammonium propionate, ammonium oxalate, ammonium maleate, ammonium succinate, ammonium glutarate, ammonium fumarate, ammonium adipicate, ammonium sorbate, ammonium palmitate, ammonium laurate, ammonium sebacate, ammonium pimarate, ammonium stearate, sodium acetate, ammonium acetate, sodium carbonate, sodium hydrogen phosphate, ammonium hydrogen phosphate, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate. Examples include sodium citrate, ammonium citrate, ammonium nitrate, sodium sulfate, ammonium sulfate, sodium borate, ammonium borate, sodium butyrate, ammonium butyrate, sodium propionate, ammonium carbamate, ammonium sulfamate, ammonium lactate, ammonium oxalate, tetramethoxyammonium acetate, tetraethoxyammonium acetate, tetrapropoxyammonium acetate, tetrabutoxyammonium acetate, ammonium trifluoroacetate, tetramethoxyammonium benzoate, tetraethoxyammonium benzoate, tetrapropoxyammonium benzoate, tetrabutoxyammonium benzoate, tetraethylammonium bicarbonate, ammonium carbonate, sodium bicarbonate, and ammonium bicarbonate. These salts may be used individually or in combination of two or more. As for the salts, neutral salts, i.e., salts of a weak acid and a weak base or a strong acid and a strong base, are preferred because they minimize the change in pH of the reaction solution due to the addition and do not alter the reaction rate of the alkoxysilane.

[0095] Furthermore, as the salt, salts that decompose and volatilize when heated are preferred, and salts that decompose or volatilize when heated to 100°C are more preferred, as they help avoid contamination of the final silica particles and silica sol and broaden the industrial application range of the silica particles and silica sol. These salts do not need to decompose or volatilize completely when they reach 100°C; it is sufficient if decomposition or volatilization begins at 100°C. Specifically, ammonium nitrate, ammonium carbamate, ammonium carbonate, and ammonium bicarbonate are preferred, and ammonium bicarbonate is more preferred.

[0096] In step 1, the molar ratio of the amount of salt used to the amount of alkali catalyst used in the reaction system of the hydrolysis reaction and the condensation reaction is preferably 0.0001 to 0.0450, more preferably 0.0010 to 0.0200, and even more preferably 0.0045 to 0.0100. The molar ratio can be determined in detail by the following formula: (Molar ratio) = (Amount of salt used (moles)) / (Amount of alkali catalyst used (moles)). When the molar ratio of the amounts used is 0.0001 or higher, the particle size can be effectively adjusted to be larger. When it is 0.0450 or lower, the aggregation and precipitation of silica particles can be suppressed.

[0097] The pH in the reaction system for the hydrolysis and condensation reactions in step 1 is preferably 8.0 to 14, more preferably 8.2 to 13, and even more preferably 8.5 to 12. When the pH is 8.0 or higher, the reaction rate of the hydrolysis and condensation reactions is excellent, and the aggregation of silica particles can be suppressed. When the pH is 14 or lower, the shape of the silica particles is easier to control, and the smoothness of the silica particle surface is excellent.

[0098] The reaction temperature for the hydrolysis and condensation reactions in step 1 is preferably 20°C to 50°C, preferably 30°C or higher, more preferably 40°C or higher, even more preferably 44°C or higher, and preferably 50°C or lower. When the reaction temperature is 20°C or higher, the balance between the hydrolysis reaction rate and the condensation reaction rate is excellent, and the particle size and shape of the silica particles can be easily controlled. Furthermore, when the reaction temperature is 50°C or lower, the controllability of the reaction temperature is excellent, and the reaction can proceed stably.

[0099] Step 1 preferably includes adding a solution (B) containing alkoxysilane to a solution (A) containing a catalyst. Such an addition makes it easier to control the hydrolysis and condensation reactions, increases the reaction rates of the hydrolysis and condensation reactions, prevents gelation of the silica particle dispersion, and makes it easier to obtain silica particles of uniform size.

[0100] Solution (A) containing the catalyst preferably contains water, and more preferably contains water and a solvent other than water, because it exhibits excellent dispersibility in the reaction solution of alkoxysilane. Examples of solvents other than water in solution (A) include those other than water that were exemplified as solvents or dispersion media during the hydrolysis and condensation reactions in step 1.

[0101] The inclusion of a catalyst in solution (A) can increase the reaction rates of the hydrolysis and condensation reactions of alkoxysilanes.

[0102] When solution (A) contains water, the concentration of water is preferably 3% to 90% by mass, and more preferably 5% to 50% by mass, of 100% by mass of solution (A). When the concentration of water in solution (A) is 3% by mass or more, it is easier to control the hydrolysis reaction rate of the alkoxysilane. Furthermore, when the concentration of water in solution (A) is 90% by mass or less, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and it is easier to control the particle shape.

[0103] The concentration of the catalyst in solution (A) is preferably 0.5% to 5.5% by mass, more preferably 1.0% to 5.0% by mass, and even more preferably 1.2% to 4.5% by mass, based on 100% by mass of solution (A). When the concentration of the catalyst in solution (A) is 0.5% by mass or higher, aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion is excellent. Furthermore, when the concentration of the catalyst in solution (A) is 5.5% by mass or lower, the reaction does not proceed excessively quickly, and the reaction is well controllable.

[0104] Solution (A) may contain salt. When solution (A) contains salt, there are no particular restrictions on the amount of salt used, but the molar ratio of the amount of salt to the amount of alkali catalyst used is preferably 0.0005 to 0.045, more preferably 0.00125 to 0.02, and even more preferably 0.0025 to 0.01. The molar ratio can be determined in detail by the following formula: (Molar ratio) = (Amount of salt used (moles)) / (Amount of alkali catalyst used (moles)). When the molar ratio of the amounts used is 0.0005 or higher, the particle size can be effectively adjusted to be larger. When it is 0.045 or lower, the aggregation and precipitation of silica particles can be suppressed.

[0105] When solution (A) contains a solvent other than water, the concentration of the solvent other than water is preferably the remainder of the water, alkaline catalyst, and the salt described above.

[0106] Solution (B) containing alkoxysilane may contain only alkoxysilane without a solvent, but it is preferable to include a solvent because it provides excellent dispersibility of the alkoxysilane in the reaction solution.

[0107] Examples of solvents in solution (B) include methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used individually or in combination of two or more. Among these solvents, alcohols are preferred, methanol and ethanol are more preferred, and methanol is even more preferred, because the by-products used in the hydrolysis and condensation reactions are the same, and they offer excellent manufacturing convenience.

[0108] The concentration of alkoxysilane in solution (B) is preferably 60% to 95% by mass, and more preferably 70% to 90% by mass, based on 100% by mass of solution (B). When the concentration of alkoxysilane in solution (B) is 60% by mass or higher, the reaction solution tends to become more homogeneous. Furthermore, when the concentration of alkoxysilane in solution (B) is 95% by mass or lower, the formation of gel-like substances can be suppressed.

[0109] The concentration of the solvent in solution (B) is preferably 5% to 40% by mass, and more preferably 10% 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 gel-like substances can be suppressed. Also, when the concentration of the solvent in solution (B) is 40% by mass or less, the reaction solution tends to become more homogeneous.

[0110] The rate at which solution (B) is added per unit time relative to the volume of solution (A) is preferably 0.02 kg / hour / L to 1.3 kg / hour / L, and more preferably 0.05 kg / hour / L to 0.8 kg / hour / L. When the rate at which solution (B) is added is 0.02 kg / hour / L or higher, the productivity of silica particles is excellent. Furthermore, when the rate at which solution (B) is added is 1.3 kg / hour / L or lower, the formation of gel-like substances can be suppressed.

[0111] In another embodiment, step 1 may include adding a solution (B) containing an alkoxysilane and a solution (C) containing water to a solution (A) containing a catalyst. Preferably, the solution (C) containing water further contains a catalyst.

[0112] Solution (C) contains water as a solvent. Other solvents include those other than water, as exemplified for use as solvents or dispersion media during hydrolysis and condensation reactions. Among the solvents in solution (C), water alone or a combination of water and alcohol is preferred, and water alone is more preferred, because the by-products are the same as those used in the hydrolysis and condensation reactions, and it offers excellent manufacturing convenience.

[0113] The concentration of the catalyst in solution (C) is preferably 0% to 10% by mass, based on 100% by mass of solution (C). The catalyst in solution (C) may be 0% by mass, i.e., not present at all. However, if a catalyst is present, its concentration is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 1.5% by mass or more. When the concentration of the catalyst in solution (C) is 0.5% by mass or more, it is easy to adjust the concentration of the catalyst in the reaction solution from the start to the end of the reaction. Furthermore, from the viewpoint of minimizing fluctuations in the concentration of the catalyst in the reaction solution, the concentration of the catalyst in solution (C) is preferably 10% by mass or less, and more preferably 6% by mass or less.

[0114] The concentration of water in solution (C) is preferably 90% to 100% by mass of solution (C) as a percentage of 100% by mass. While solution (C) may consist solely of water at 100% by mass, if other components are present, the water concentration is preferably 99.5% by mass or less, and more preferably 99% by mass or less. From the viewpoint of minimizing fluctuations in the concentration of the alkaline catalyst in the reaction solution, the water concentration in solution (C) is preferably 90% by mass or more, and more preferably 94% by mass or more. Furthermore, if the water concentration in solution (C) is 99.5% by mass or less, it is easier to adjust the concentration of the alkaline catalyst in the reaction solution from the start to the end of the reaction.

[0115] The concentration of the solvent other than water in solution (C) is preferably equal to the concentration of the remainder of the water, or the remainder of the water and alkaline catalyst.

[0116] It is preferable to add solution (B), or solutions (B) and (C), to solution (A) while it is still in the solution (A). This improves the mixability of the components in the reaction solution, which is useful when using a highly volatile alkaline catalyst such as ammonia, and when you want to proceed with the hydrolysis and condensation reactions at high reaction temperatures. This suppresses abnormal reactions in the air and makes it easier to control the particle shape. Adding to the solution means adding it below the liquid level. By setting the supply outlet for solution (B), or the supply outlets for both solution (B) and solution (C), below the liquid level of solution (A), solution (B), or solutions (B) and (C) can be added to solution (A).

[0117] When adding solution (B) and solution (C) to solution (A), the timing of adding solution (B) and solution (C) to solution (A) may be the same or alternate, but it is preferable that the timing be the same because it minimizes variation in the reaction composition and does not complicate the procedure.

[0118] The dispersion of silica particles obtained in step 1 contains alcohol. Preferred alcohols include, for example, methanol, ethanol, propanol, isopropanol, and ethylene glycol. The dispersion of silica particles may contain one of the above alcohols, or two or more. Since it is easily removed by boiling in step 2, methanol or ethanol is more preferred as the alcohol, and methanol is even more preferred.

[0119] In the dispersion of silica particles obtained in step 1, the amount of alcohol is preferably 1% to 95% by mass, more preferably 50% to 90% by mass, and even more preferably 70% to 85% by mass.

[0120] In the silica particle dispersion obtained in step 1, the amount of silica particles is preferably 1% to 40% by mass, more preferably 7% to 20% by mass.

[0121] (Step 2) Step 2 is a step of replacing at least a portion of the dispersion medium in the silica particle dispersion obtained in Step 1 or Step 3.

[0122] The step of replacing the dispersion medium in step 2 preferably includes a step of removing alcohol and adding water, and more preferably includes a step of removing alcohol and alkaline catalyst and adding water.

[0123] In step 2, for example, the dispersion of silica particles obtained in step 1 or 3 can be heated while adding water to remove the alcohol-containing solution and add water.

[0124] The heating temperature should be the boiling point of the dispersion medium in the silica particle dispersion, preferably 50°C to 100°C. Alternatively, the boiling point of the dispersion medium can be lowered by performing step 2 under reduced pressure.

[0125] Furthermore, in step 2, it is preferable to maintain the ratio of the volume of dispersion medium distilled off per unit time to the volume of water added at 4:6 to 6:4, and more preferably at 4.5:5.5 to 5.5:4.5. When this ratio is within the above range, variations in the viscosity of the silica sol and aggregation of silica particles can be suppressed.

[0126] In step 2, it is sufficient to replace at least a portion of the dispersion medium. When step 3 is performed after step 2, from the viewpoint of easily adjusting the amount of silanol groups and alkoxy groups in the silica particles to a preferred range, it is preferable that the amount of alcohol contained in the dispersion medium of the silica particle dispersion before pressurized heat treatment in step 3 be 0.01% to 10% by mass, more preferably 0.1% to 5% by mass, and even more preferably 0.5% to 2% by mass. From a similar viewpoint, the pH of the silica particle dispersion obtained in step 2 is preferably 7.5 to 10.0, more preferably 7.7 to 9.5, and even more preferably 8.0 to 9.0.

[0127] If step 3 is not performed after step 2, i.e., if silica sol is obtained by this step 2, it is preferable that the amount of alcohol contained in the dispersion medium of the silica particle dispersion obtained in step 2 be 0.100% by mass or less, more preferably 0.050% by mass or less, and even more preferably 0.030% by mass or less. Furthermore, when silica sol is obtained by this step 2, it is preferable that the amount of alcohol contained in the dispersion medium of the silica particle dispersion obtained in step 2 be 0% by mass, i.e., substantially absent. On the other hand, the pH of the silica particle dispersion obtained in step 2 is preferably 6.0 to 8.5, and more preferably 6.5 to 8.2. If the pH of the silica sol is 6.0 or higher, it has excellent dispersion stability and can suppress the aggregation of silica particles. Furthermore, if the pH of the silica sol is 8.5 or lower, it prevents the dissolution of silica particles and has excellent long-term storage stability. The amount of alcohol contained in the dispersion medium of the silica particle dispersion obtained in step 2 and the pH can be controlled by the pressure and boiling point at the end of step 2. Furthermore, the process can also be controlled by adjusting the length of time in step 2 and the ratio of the added dispersion medium to the dispersion medium removed in step 2.

[0128] (Step 3) Step 3 is a process of applying pressure and heat treatment to the dispersion of silica particles obtained in Step 1 or Step 2. Step 3 can increase the degree of condensation of the silica particles.

[0129] The pressure for the pressurized heat treatment in step 3 is preferably 0.10 MPa to 2.3 MPa, more preferably 0.12 MPa to 1.8 MPa, and even more preferably 0.15 MPa to 0.5 MPa. When the pressurized heat treatment pressure is 0.10 MPa or higher, the degree of condensation of silica particles can be increased. Furthermore, when the pressurized heat treatment pressure is 2.3 MPa or lower, silica particles can be produced without significantly changing the average primary particle diameter, average secondary particle diameter, cv value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0130] Pressurization can be achieved by heating the silica particle dispersion to above the boiling point of the dispersion medium while it is sealed. When a silica particle aqueous dispersion is heated to above 100°C while sealed, the pressure will be the sum of the increase in pressure due to the saturated water vapor pressure at that temperature and the expansion of the gas contained within the sealed container due to the temperature rise.

[0131] The temperature for the pressurized heat treatment is preferably 100°C to 220°C, more preferably 110°C to 200°C, and even more preferably 115°C to 150°C. If the pressurized heat treatment temperature is 100°C or higher, the degree of condensation of silica particles can be increased, and the mass ratio of silanol groups can be reduced. In addition, the true specific gravity of the silica particles can be reduced. If the pressurized heat treatment temperature is 220°C or lower, silica particles can be produced without significantly changing the average primary particle diameter, average secondary particle diameter, CV value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0132] The pressurized heat treatment time is preferably 0.25 to 15 hours, more preferably 0.5 to 12 hours, and even more preferably 1 to 10 hours. If the pressurized heat treatment time is 0.25 hours or longer, the condensation of silanol groups can be promoted. If the pressurized heat treatment time is 15 hours or less, silica particles can be produced without significantly changing the average primary particle diameter, average secondary particle diameter, CV value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0133] Pressurized heat treatment is more preferably performed in an aqueous dispersion because it can reduce the amount of silanol groups in silica particles without significantly changing the average primary particle diameter, average secondary particle diameter, CV value, or association ratio.

[0134] The pH of the silica particle dispersion before pressurized heat treatment is preferably 7.5 to 10.0, more preferably 7.7 to 9.5, and even more preferably 8.0 to 9.0. If the pH of the silica particle dispersion before pressurized heat treatment is 7.5 or higher, the amount of silanol groups in the silica particles can be efficiently condensed and reduced. If the pH of the silica particle dispersion before pressurized heat treatment is 10.0 or lower, the dissolution of silica particles and condensation of silica particles can be prevented, and the amount of silanol groups in the silica particles can be reduced while avoiding aggregation of silica particles and changes in the average secondary particle size of silica particles.

[0135] The alcohol concentration of the silica particle dispersion before pressurized heat treatment is preferably 0.01% to 10% by mass, more preferably 0.1% to 8% by mass, and even more preferably 0.7% to 5% by mass. If the alcohol concentration of the silica particle dispersion before pressurized heat treatment is 10% by mass or less, aggregation of silica particles can be prevented. If the alcohol concentration of the silica particle dispersion before pressurized heat treatment is 0.01% by mass or more, the hydrolysis reaction of alkoxy groups during pressurized heat treatment can be suppressed, and the amount of alkoxy groups in the silica particles can be increased.

[0136] In the method for producing silica particles according to this embodiment, the dispersion of silica particles before pressurized heat treatment can be a dispersion of silica particles having a pH of 7.5 to 10.0 and an alcohol concentration of 0.01% to 10% by mass.

[0137] (Other steps) The method for producing silica particles according to this embodiment may include other steps in addition to steps 1 to 3. Examples of other steps include a step of concentrating the silica particle dispersion. This step may be performed after step 1 or after step 3.

[0138] Methods for concentrating a dispersion of silica particles include, for example, heating and reducing pressure.

[0139] In the process of concentrating the dispersion of silica particles, the concentration ratio is preferably 101% to 220% by mass, and more preferably 102% to 140% by mass. A concentration ratio of 101% by mass or higher results in excellent polishing rates for the workpiece, such as silicon wafers. A concentration ratio of 220% by mass or lower suppresses variations in the viscosity of the silica sol and aggregation of silica particles.

[0140] The concentration ratio can be calculated using the following formula: Concentration ratio (mass%) = (a / b) × 100 In the above formula, a represents the mass of the silica particle dispersion before concentration, and b represents the mass of the silica particle dispersion after concentration.

[0141] [Abrasive Composition] The abrasive composition according to this embodiment contains a silica sol according to this embodiment. Preferably, the abrasive composition according to this embodiment contains a water-soluble polymer in addition to the silica sol according to this embodiment.

[0142] Water-soluble polymers enhance the wettability of the polishing composition to the workpiece, such as silicon wafers. Preferably, the water-soluble polymer has functional groups with high water affinity. These water-affinity functional groups have a high affinity for the surface silanol groups of silica particles, resulting in a more stable dispersion of silica particles and water-soluble polymers in close proximity within the polishing composition. Therefore, during polishing of workpieces such as silicon wafers, the effects of silica particles and water-soluble polymers function synergistically.

[0143] Examples of water-soluble polymers include cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, copolymers having a polyvinylpyrrolidone skeleton, and polymers having a polyoxyalkylene structure.

[0144] Examples of cellulose derivatives include hydroxyethylcellulose, hydrolyzed hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, and carboxymethylcellulose.

[0145] Examples of copolymers having a polyvinylpyrrolidone skeleton include graft copolymers of polyvinyl alcohol and polyvinylpyrrolidone.

[0146] Examples of polymers having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, and copolymers of ethylene oxide and propylene oxide.

[0147] These water-soluble polymers may be used individually or in combination of two or more. Among these water-soluble polymers, cellulose derivatives are preferred, and hydroxyethylcellulose is more preferred, because they have a high affinity for the silanol groups on the surface of silica particles and act synergistically to provide good hydrophilicity to the surface of the object to be polished.

[0148] 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, it exhibits excellent affinity with silica sol and provides excellent polishing rate for materials to be polished, such as silicon wafers.

[0149] The mass-average molecular weight of water-soluble polymers is measured by size exclusion chromatography using a 0.1 mol / L NaCl solution as the mobile phase, based on polyethylene oxide.

[0150] The content of water-soluble polymers in the abrasive composition is preferably 0.02% to 10% by mass, and more preferably 0.05% to 5% by mass, based on 100% by mass of the total amount of the abrasive composition. When the content of water-soluble polymers in the abrasive composition is 0.02% by mass or more, the hydrophilicity of the abrasive composition is improved. Furthermore, when the content of water-soluble polymers in the abrasive composition is 10% by mass or less, aggregation of silica particles during the preparation of the abrasive composition can be suppressed.

[0151] In addition to silica sol and water-soluble polymer, the polishing composition according to this embodiment may optionally contain other components such as basic compounds, polishing accelerators, surfactants, hydrophilic compounds, preservatives, fungicides, pH adjusters, pH buffers, surfactants, chelating agents, and antimicrobial biocides, to the extent that it does not impair its performance. In particular, it is preferable to include basic compounds in the polishing composition because they can chemically polish (chemical etching) the surface of the object to be polished, such as a silicon wafer, by providing a chemical reaction, and the polishing speed of the object to be polished, such as a silicon wafer, can be improved by the synergistic effect with the silanol groups on the surface of the silica particles.

[0152] Examples of basic compounds include organic basic compounds, alkali metal hydroxides, alkali metal bicarbonates, alkali metal carbonates, and ammonia. These basic compounds may be used individually or in combination of two or more. Among these basic compounds, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium bicarbonate, and ammonium carbonate are preferred due to their high water solubility and excellent affinity with silica particles and water-soluble polymers. Ammonia, tetramethylammonium hydroxide, and tetraethylammonium hydroxide are more preferred, and ammonia is even more preferred.

[0153] The content of basic compounds in the polishing composition is preferably 0.001% to 5% by mass, and more preferably 0.01% to 3% by mass, based on 100% by mass of the total amount of the polishing composition. When the content of basic compounds in the polishing composition is 0.001% by mass or more, the polishing speed of the workpiece, such as silicon wafers, can be improved. Furthermore, when the content of basic compounds in the polishing composition is 5% by mass or less, the stability of the polishing composition is excellent.

[0154] The pH of the abrasive composition is preferably 8.0 to 12.0, and more preferably 9.0 to 11.0. A pH of 8.0 or higher suppresses the aggregation of silica particles in the abrasive composition, resulting in excellent dispersion stability. Furthermore, a pH of 12.0 or lower suppresses the dissolution of silica particles, resulting in excellent stability. The pH of the abrasive composition can be set to a desired range by adding a pH adjusting agent.

[0155] The polishing composition can be obtained by mixing the silica sol, water-soluble polymer, and other components as needed according to this embodiment. However, considering storage and transportation, it may be prepared at a high concentration first and then diluted with water or the like immediately before polishing.

[0156] [Polishing Method] The polishing method according to this embodiment is a method of polishing using a polishing composition containing silica sol according to this embodiment. It is preferable to use the polishing composition described above.

[0157] Specific polishing methods include, for example, pressing the surface of a bare silicon wafer, the surface of a semiconductor device having at least one of a film of another material, a transistor, and a circuit formed on the surface of a bare silicon wafer or other substrate, or the surface of a substrate in which multiple semiconductor chips are linked together via a material such as resin or glass, against a polishing pad, dropping the polishing composition according to this embodiment onto the polishing pad, and polishing the surface of the silicon wafer.

[0158] [Method for Manufacturing Semiconductor Wafers] The method for manufacturing semiconductor wafers according to this embodiment includes a step of polishing using the polishing composition according to this embodiment, and the specific polishing composition and polishing method are as described above. Examples of semiconductor wafers include silicon wafers and compound semiconductor wafers.

[0159] [Method for Manufacturing Semiconductor Devices] The method for manufacturing semiconductor devices according to this embodiment includes a step of polishing using the polishing composition according to this embodiment, and the specific polishing composition and polishing method are as described above.

[0160] [Applications] The silica particles and silica sol according to this embodiment can be suitably used for polishing applications, for example, polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing in the planarization process when manufacturing integrated circuits (chemical mechanical polishing), polishing synthetic quartz glass substrates used in photomasks and liquid crystals, polishing magnetic disk substrates, etc., and can be used particularly suitably for polishing silicon wafers and chemical mechanical polishing.

[0161] Other materials that can be polished include metals such as Si, Cu, W, Ti, Cr, Co, Zr, Hf, Mo, Ta, Ru, Au, Pt, Ag, Ni, and Al; metal compounds such as oxides, nitrides, and silicides of the aforementioned metals; and intermetallic compounds. Among these materials that can be polished, this product can be suitably used for metals and metal oxides, and is particularly suitably used for metal oxides.

[0162] The silica particles according to this embodiment have an optimized amount of silanol groups and alkoxy groups within the particles, making them less likely to cause defects in the object being polished when used for polishing. Therefore, they can be suitably used for polishing semiconductor wafers and semiconductor devices.

[0163] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention.

[0164] (Measurement of the mass percentage of methoxy groups) Silica sol was centrifuged at 215,000 G for 90 minutes, and the supernatant was discarded. The resulting solid was vacuum-dried at 60°C for 90 minutes. 0.5 g of the dried silica solid was weighed and placed in 50 mL of 1 M sodium hydroxide aqueous solution. The silica was dissolved by heating at 50°C for 24 hours with stirring. The silica solution was analyzed by gas chromatography to determine the methanol content. Reagent-grade methanol from Fujifilm Wako Pure Chemical Industries, Ltd., with a purity of 100%, was used as the standard sample and quantified using the absolute calibration curve method. The measurement was performed twice, and the average of the two measurements was taken as the measured value. The obtained methanol content was divided by the mass of the silica solid to obtain the mass percentage of methoxy groups in the silica particles.

[0165] (Measurement of the mass percentage of silanol groups) The mass percentage y (mass%) of silanol groups in silica particles was measured by the Sears method. Specifically, it was measured and calculated under the conditions shown below. A silica sol containing 1.5 g of silica particles was taken, and pure water was added to make a volume of 90 mL. At 25°C, 0.1 mol / L hydrochloric acid aqueous solution was added until the pH reached 3.6, then 30 g of sodium chloride was added, and pure water was gradually added to completely dissolve the sodium chloride. Finally, pure water was added until the total volume of the test solution reached 150 mL to obtain the test solution. The obtained test solution was placed in an automatic titrator, and 0.1 mol / L sodium hydroxide aqueous solution was added dropwise to measure the titration volume A (mL) of 0.1 mol / L sodium hydroxide aqueous solution required to raise the pH from 4.0 to 9.0.

[0166] Using the following formula (3), the amount of 0.1 mol / L sodium hydroxide solution consumed (V) (mL) to change the pH of 1.5 g of silica particles from 4.0 to 9.0 was calculated, and using the following formula (4), the mass percentage y of the silanol group was calculated. V = (A × f × 100 × 1.5) / (W × C) ... (3) A: Tit volume (mL) of 0.1 mol / L sodium hydroxide solution required to change the pH of 1.5 g of silica particles from 4.0 to 9.0 f: Titer of the 0.1 mol / L sodium hydroxide solution used C: Concentration (mass%) of silica particles in silica sol W: Amount of silica sol collected (g) y = (B × w ＯＨ) / M × 100 ··· (4) B: The amount of sodium hydroxide (mol) required for the pH per 1.5 g of silica particles calculated from V to be 4.0 to 9.0 w ＯＨ : The formula weight of the silanol group (g / mol) M: The amount of silica particles (1.5 g)

[0167] (Measurement of average secondary particle diameter) The dispersion of silica particles obtained in the examples and comparative examples was used to measure the average secondary particle diameter of silica particles using a dynamic light scattering particle size measuring device (Zetasizer Nano ZS manufactured by Malvern Panalytical).

[0168] (Measurement of average primary particle diameter) The dispersion of silica particles obtained in the examples and comparative examples was dried at 150 °C, and the specific surface area of silica particles was measured using a specific surface area automatic measuring device "BELSORP-MR1" (model name, Microtrac BEL Co., Ltd.). Using the following formula (5), with a density of 2.2 g / cm ３ and the average primary particle diameter was calculated. Average primary particle diameter (nm) = 6000 / (specific surface area (m ２ / g) × density (g / cm ３ )) ··· (5)

[0169] (Measurement of true specific gravity) The dispersion of silica particles obtained in the examples and comparative examples was heated and dried, and the true specific gravity was measured by the ethanol substitution method. 10 g of the powdered silica particles obtained by drying were precisely weighed into a glass specific gravity bottle, and then ethanol was filled to make the specific gravity bottle full. The volume of the filled ethanol was calculated from the difference in the weight of the specific gravity bottle before and after filling with ethanol and the specific gravity of ethanol. Furthermore, the volume of silica particles was calculated from the difference between the specific gravity bottle volume and the volume of the filled ethanol. The true specific gravity of silica was calculated by dividing the weight of silica particles by the volume.

[0170] (Measurement of Ammonia Concentration) The ammonia concentration in the silica particle dispersion was measured using an ammonia-selective electrode. Approximately 10 g of the silica particle dispersion was precisely weighed into an Erlenmeyer flask, and 90 mL of ultrapure water was added to dilute it 10-fold. Furthermore, 10 mL of an ionic strength adjuster (ISA-NH, manufactured by Toa DKK Co., Ltd.) was added to adjust the pH of the solution to 12 or higher. An ammonia-selective electrode (AE-2041, used in connection with a multi-water quality meter MM-43X, both manufactured by Toa DKK Co., Ltd.), which had been calibrated in advance, was inserted into the adjusted solution, and the ammonia concentration was measured. The mass of the silica particle dispersion and water used in the adjustment was used to convert it to the ammonia concentration in the silica particle dispersion.

[0171] (Measurement of methanol concentration in silica particle dispersion) The methanol concentration was measured by analyzing the silica particle dispersion using gas chromatography. Acetonitrile was added to the silica particle dispersion as an internal standard, and the methanol concentration was quantified using the internal standard method.

[0172] [Example 1] A silica sol containing the silica particles of Example 1 was obtained by performing the following steps 1, 2, 3, and a second step 2.

[0173] (Step 1) Solution (B) was prepared by mixing tetramethoxysilane and methanol in a 5.7:1 (mass ratio), and solution (C) was prepared by mixing a 2.3% by mass aqueous ammonia solution. Solution (A), which had been pre-mixed methanol, pure water, and aqueous ammonia in a 14.9:1.17:1 (mass ratio), was charged into a reaction vessel equipped with a thermometer, stirrer, feed pipe, and distillation line. The ammonia concentration in solution (A) was set to 1.7% by mass.

[0174] While maintaining the temperature of solution (A) at 44°C, 60.0 parts by volume of solution (B) and 18.9 parts by volume of solution (C) were added to 100 parts by volume of solution (A) at a constant rate over 143 minutes to obtain a dispersion of silica particles. Subsequently, the obtained dispersion of silica particles was heated to evaporate the dispersion medium and concentrate it to obtain a dispersion of silica particles with a silica particle concentration of 17.5% by mass and containing alcohol.

[0175] (Step 2) Water was added to the dispersion of silica particles obtained in Step 1 while heating to evaporate the dispersion medium and replace a portion of the dispersion medium in the silica particle dispersion. This operation was carried out at atmospheric pressure. The rate at which water was added was adjusted so that the liquid level reached a constant height. Step 2 was terminated when the temperature of the dispersion reached 99°C. At this time, the pH of the silica particle dispersion was 8.5 and the methanol concentration was 0.94% by mass.

[0176] (Step 3) The silica particle dispersion obtained in Step 2 was subjected to pressurized heat treatment. The silica particle dispersion was sealed in a pressure vessel and heated to raise the temperature to 130°C. The treatment was carried out for 5 hours.

[0177] (Step 2: Second time) Water was added to the dispersion of silica particles obtained in Step 3 and heated to evaporate the dispersion medium, thereby replacing the dispersion medium in the silica particle dispersion again. At the end of the replacement operation, the temperature of the dispersion was 100°C, which is the boiling point of water at atmospheric pressure. Subsequently, the dispersion medium was evaporated and the dispersion was concentrated to a silica particle concentration of 20% by mass to obtain a silica sol. The methanol concentration in the obtained silica sol was 0.01% by mass or less. The ammonia concentration was 32 ppm by mass and the pH was 7.0.

[0178] [Comparative Example 1] A silica sol containing the silica particles of Comparative Example 1 was obtained by performing the following steps 1 and 2.

[0179] (Step 1) The same procedure as in Step 1 of Example 1 was performed to obtain a dispersion of silica particles.

[0180] (Step 2) Water was added to the dispersion of silica particles obtained in Step 1 while heating to evaporate the dispersion medium and replace it. This operation was carried out at atmospheric pressure. The rate at which water was added was adjusted so that the liquid level remained at a constant height. At the end of Step 2, the temperature of the dispersion was 100°C, which is the boiling point of water at atmospheric pressure. At this time, the pH of the silica particle dispersion was 7.4, and the methanol concentration was 0.01% by mass or less. The ammonia concentration was 73 ppm by mass.

[0181] [Comparative Example 2] A silica sol containing silica particles of Comparative Example 2 was obtained by performing the following step 3 on the silica sol obtained in Comparative Example 1. (Step 3) The silica sol obtained in Comparative Example 1 was subjected to pressurized heat treatment. The dispersion of silica particles was sealed in a pressure vessel and heated to raise the temperature to 130°C. The treatment was carried out for 5 hours. The pH of the obtained silica sol was 7.4.

[0182] [Example 2] A silica sol containing the silica particles of Example 2 was obtained by performing the following steps 1, 2, 3, and a second step 2.

[0183] (Step 1) Solution (B) was prepared by mixing tetramethoxysilane and methanol in a 5.7:1 (mass ratio), and solution (C) was prepared by mixing 1.9% by mass aqueous ammonia. Solution (A), which had been pre-mixed methanol, pure water, and aqueous ammonia in a 14.6:0.498:1 (mass ratio), was charged into a reaction vessel equipped with a thermometer, stirrer, feed pipe, and distillation line. The ammonia concentration in solution (A) was set to 1.8% by mass.

[0184] While maintaining the temperature of solution (A) at 44°C, 57.9 volumes of solution (B) and 15.9 volumes of solution (C) were added to 100 volumes of solution (A) at a constant rate over 143 minutes to obtain a dispersion of silica particles. Subsequently, the obtained dispersion of silica particles was heated to evaporate the dispersion medium and concentrate it to obtain a dispersion of silica particles with a silica particle concentration of 17.5% by mass and containing alcohol.

[0185] (Step 2) Water was added to the dispersion of silica particles obtained in Step 1 while heating to evaporate the dispersion medium and replace a portion of the dispersion medium in the silica particle dispersion. This operation was carried out at atmospheric pressure. The rate at which water was added was adjusted so that the liquid level remained at a constant height. Step 2 was terminated when the temperature of the dispersion reached 99°C. At this time, the pH of the silica particle dispersion was 8.1 and the methanol concentration was 1.1% by mass.

[0186] (Step 3) The silica particle dispersion obtained in Step 2 was subjected to pressurized heat treatment. The silica particle dispersion was sealed in a pressure vessel and heated to raise the temperature to 130°C. The treatment was carried out for 5 hours.

[0187] (Step 2: Second time) Water was added to the dispersion of silica particles obtained in Step 3 and heated to evaporate the dispersion medium, thereby replacing the dispersion medium in the silica particle dispersion again. At the end of the replacement operation, the temperature of the dispersion was 100°C, which is the boiling point of water at atmospheric pressure. Subsequently, the dispersion medium was evaporated and the dispersion was concentrated to a silica particle concentration of 20% by mass to obtain a silica sol. The methanol concentration in the obtained silica sol was 0.01% by mass or less. The ammonia concentration was 41 ppm by mass and the pH was 6.9.

[0188] [Comparative Example 3] A silica sol containing silica particles of Comparative Example 3 was obtained by performing the following steps 1 and 2. (Step 1) A dispersion of silica particles was obtained by performing the same procedure as in Example 2. (Step 2) Water was added to the dispersion of silica particles obtained in Step 1 while heating to evaporate the dispersion medium and replace the dispersion medium in the silica particle dispersion. At this time, the operation was performed at atmospheric pressure. The rate at which water was added was adjusted so that the liquid level reached a constant height. At the end of Step 2, the temperature of the dispersion was 100°C, which is the boiling point of water at atmospheric pressure, the pH of the silica particle dispersion at this time was 7.1, and the methanol concentration was 0.01% by mass or less. The ammonia concentration was 82 ppm by mass.

[0189] [Comparative Example 4] A silica sol containing silica particles of Comparative Example 4 was obtained by performing the following step 3 on the silica sol obtained in Comparative Example 3. (Step 3) The silica sol obtained in Comparative Example 3 was subjected to pressurized heat treatment. The dispersion of silica particles was sealed in a pressure vessel and heated to raise the temperature to 130°C. The treatment was carried out for 5 hours. The pH of the obtained silica sol was 7.1.

[0190] [Example 3] A silica sol containing silica particles of Example 3 was obtained by performing the following steps 1, 2, 3, and a second step 2.

[0191] (Step 1) Solution (B) was prepared by mixing tetramethoxysilane and methanol in a 5.7:1 (mass ratio), and solution (C) was prepared by mixing 1.9% by mass aqueous ammonia. Solution (A), which had been pre-mixed methanol, pure water, and aqueous ammonia in a 17.3:0.214:1 (mass ratio), was charged into a reaction vessel equipped with a thermometer, stirrer, feed pipe, and distillation line. The ammonia concentration in solution (A) was set to 1.57% by mass.

[0192] While maintaining the temperature of solution (A) at 30°C, 82.5 volumes of solution (B) and 20.9 volumes of solution (C) were added to 100 volumes of solution (A) at a constant rate over 205 minutes to obtain a dispersion of silica particles. Subsequently, the obtained dispersion of silica particles was heated to evaporate the dispersion medium and concentrate it to obtain a dispersion of silica particles with a silica particle concentration of 17.5% by mass and containing alcohol.

[0193] (Step 2) Water was added to the dispersion of silica particles obtained in Step 1 while heating to evaporate the dispersion medium and replace a portion of the dispersion medium in the silica particle dispersion. This operation was carried out at atmospheric pressure. The rate at which water was added was adjusted so that the liquid level remained at a constant height. Step 2 was terminated when the temperature of the dispersion reached 99°C.

[0194] (Step 3) The silica particle dispersion obtained in Step 2 was subjected to pressurized heating treatment. The silica particle dispersion was sealed in a pressure vessel and heated to raise the temperature to 120°C. The treatment was carried out for 10 hours.

[0195] (Step 2: Second time) Water was added to the dispersion of silica particles obtained in Step 3 and heated to evaporate the dispersion medium, thereby replacing the dispersion medium in the silica particle dispersion again. At the end of the replacement operation, the temperature of the dispersion was 100°C, which is the boiling point of water at atmospheric pressure. Subsequently, the dispersion medium was evaporated and the dispersion was concentrated to a silica particle concentration of 20% by mass to obtain a silica sol. The methanol concentration in the obtained silica sol was 0.015% by mass. The ammonia concentration was 43 ppm by mass and the pH was 7.2.

[0196] [Example 4] A silica sol containing the silica particles of Example 4 was obtained by performing the following steps 1, 2, 3, and a second step 2.

[0197] (Step 1) The same procedure as in Example 3 was performed to obtain a dispersion of silica particles.

[0198] (Step 2) Water was added to the dispersion of silica particles obtained in Step 1 while heating to evaporate the dispersion medium and replace a portion of the dispersion medium in the silica particle dispersion. This operation was carried out at atmospheric pressure. The rate at which water was added was adjusted so that the liquid level reached a constant height. Step 2 was terminated when the temperature of the dispersion reached 95°C. At this time, the pH of the silica particle dispersion was 8.5 and the methanol concentration was 4.1% by mass.

[0199] (Step 3) The silica particle dispersion obtained in Step 2 was subjected to pressurized heating treatment. The silica particle dispersion was sealed in a pressure vessel and heated to raise the temperature to 120°C. The treatment was carried out for 10 hours.

[0200] (Step 2: Second time) Water was added to the dispersion of silica particles obtained in Step 3 and heated to evaporate the dispersion medium, thereby replacing the dispersion medium in the silica particle dispersion again. At the end of the replacement operation, the temperature of the dispersion was 100°C, which is the boiling point of water at atmospheric pressure. Subsequently, the dispersion medium was evaporated and the dispersion was concentrated to a silica particle concentration of 20% by mass to obtain a silica sol. The methanol concentration in the obtained silica sol was 0.026% by mass. The ammonia concentration was 38 ppm by mass and the pH was 6.9.

[0201] [Example 5] A silica sol containing silica particles of Example 5 was obtained by performing the following steps 1, 2, 3, and a second step 2.

[0202] (Step 1) Solution (B) was prepared by mixing tetramethoxysilane and methanol in a 5.7:1 (mass ratio), and solution (C) was prepared by mixing 0.2% by mass aqueous ammonia. Solution (A), which had been pre-mixed methanol, pure water, and aqueous ammonia in a 5.64:0.099:1 (mass ratio), was charged into a reaction vessel equipped with a thermometer, stirrer, feed pipe, and distillation line. The ammonia concentration in solution (A) was set to 4.3% by mass.

[0203] While maintaining the reaction solution temperature at 44°C, 89.4 volumes of solution (B) and 28.2 volumes of solution (C) were added to 100 volumes of solution (A) at a constant rate over 220 minutes to obtain a dispersion of silica particles. Subsequently, the obtained silica particle dispersion was heated to evaporate the dispersion medium and concentrate it to obtain a dispersion of silica particles with a silica particle concentration of 17.5% by mass and containing alcohol.

[0204] (Step 2) Water was added to the dispersion of silica particles obtained in Step 1 while heating to evaporate the dispersion medium and replace a portion of the dispersion medium in the silica particle dispersion. This operation was carried out at atmospheric pressure. The rate at which water was added was adjusted so that the liquid level remained at a constant height. Step 2 was terminated when the temperature of the dispersion reached 99°C.

[0205] (Step 3) The silica particle dispersion obtained in Step 2 was subjected to pressurized heating treatment. The silica particle dispersion was sealed in a pressure vessel and heated to raise the temperature to 120°C. The treatment was carried out for 10 hours.

[0206] (Step 2: Second time) Water was added to the dispersion of silica particles obtained in Step 3 and heated to evaporate the dispersion medium, thereby replacing the dispersion medium in the silica particle dispersion again. At the end of the replacement operation, the temperature of the dispersion was 100°C, which is the boiling point of water at atmospheric pressure. Subsequently, the dispersion medium was evaporated and the dispersion was concentrated to a silica particle concentration of 20% by mass to obtain a silica sol. The methanol concentration in the obtained silica sol was 0.001% by mass or less. The ammonia concentration was 14 ppm by mass and the pH was 8.1.

[0207] [Comparative Example 5] A silica sol containing silica particles of Comparative Example 5 was obtained by performing the following steps 1 and 2. (Step 1) A dispersion of silica particles was obtained by performing the same procedure as in Example 5. (Step 2) Water was added to the dispersion of silica particles obtained in Step 1 and heated to evaporate the dispersion medium, thereby replacing the dispersion medium in the silica particle dispersion. This operation was performed at atmospheric pressure. The rate at which water was added was adjusted so that the liquid level reached a constant height. At the end of Step 2, the temperature of the dispersion was 100°C, which is the boiling point of water at atmospheric pressure. At this time, the pH of the silica particle dispersion was 8.1, and the methanol concentration was 0.01% by mass or less. The ammonia concentration was 106 ppm by mass.

[0208] Table 1 shows the physical properties for each of the Examples 1 to 5 and Comparative Examples 1 to 5.

[0209] The silica sols obtained in the examples and comparative examples were evaluated for their impact on defects when a substrate having a metal oxide film on its surface was polished, using the following indicators. The evaluation results are shown in the "Influence on Defects" column of Table 1. A: Defects are expected to be significantly reduced. B: Defects are expected to be reduced. C: Defects are expected to occur easily.

[0210]

[0211] As shown in Table 1, Examples 1 to 5 demonstrated that the mass percentage x (mass%) of alkoxy groups and the mass percentage y (mass%) of silanol groups in the silica particles satisfied formula (1) as defined herein. On the other hand, Comparative Examples 1 to 5 did not satisfy formula (1).

[0212] Although various embodiments have been described above, it goes without saying that the present invention is not limited to these examples. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of the present invention. Furthermore, the components in the above embodiments may be combined in any way without departing from the spirit of the invention.

[0213] This application is based on a Japanese patent application (Patent Application No. 2025-009457) filed on January 22, 2025, the contents of which are incorporated herein by reference.

[0214] The silica particles of the present invention can be used for polishing semiconductor wafers and semiconductor devices.

Claims

1. A silica particle that satisfies the following equation (1), where x (mass%) is the mass percentage of alkoxy groups in the silica particle and y (mass%) is the mass percentage of silanol groups in the silica particle: y (mass%) < 8x (mass%) + 0.5 ... (1) 2. Silica particles according to claim 1, satisfying the following formula (2): y (mass%) < 8x (mass%) + 0.1 ... (2) 3. The silica particles according to claim 1, wherein the mass percentage of the silanol groups in the silica particles is 1.0% by mass or less.

4. The silica particles according to claim 1, wherein the mass percentage of the alkoxy groups in the silica particles is 10% by mass or less.

5. The silica particles according to claim 1, wherein the alkoxy group is a methoxy group.

6. The silica particles according to claim 5, wherein the mass percentage of the methoxy group in the silica particles is 0.07% by mass or more.

7. Silica particles according to claim 1, wherein the metal impurity content is 5 ppm by mass or less.

8. Silica particles according to claim 1, wherein the true specific gravity is 1.60 g / mL or more and 2.05 g / mL or less.

9. Silica particles according to claim 1, wherein the average secondary particle diameter is 10 nm to 1000 nm.

10. Silica particles according to claim 1, wherein the amine content is less than 5 μmol / g.

11. A silica sol comprising the silica particles described in claim 1 and water.

12. The silica sol according to claim 11, wherein the concentration of the alkaline substance is 1000 ppm by mass or less.

13. A method for producing silica particles, comprising the following steps 1 to 3, with at least one step 2 following step 3: Step 1: A step of hydrolyzing and condensing an alkoxysilane to obtain a dispersion of silica particles containing an alcohol. Step 2: A step of replacing at least a portion of the dispersion medium in the dispersion of silica particles obtained in step 1 or step 3. Step 3: A step of applying pressurized heat treatment to the dispersion of silica particles obtained in step 1 or step 2.

14. The method for producing silica particles according to claim 13, wherein in step 3, the dispersion of silica particles before pressurized heat treatment is a dispersion of silica particles having a pH of 7.5 to 10.0 and an alcohol concentration of 0.01% to 10% by mass.

15. An abrasive composition comprising the silica sol described in claim 11 or 12.

16. A polishing method comprising polishing using the polishing composition described in claim 15.

17. A method for manufacturing a semiconductor wafer, comprising the step of polishing using the polishing composition described in claim 15.

18. A method for manufacturing a semiconductor device, comprising the step of polishing using the polishing composition described in claim 15.

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