Silica particle and production method therefor, silica sol, polishing composition, polishing method, method for producing semiconductor wafer, and method for producing semiconductor device

Abstract

The purpose of the present invention is to provide: a silica particle, silica sol, and polishing composition that exhibit an excellent polishing speed; and a polishing method, semiconductor wafer production method, and semiconductor device production method that exhibit an excellent productivity with regard to the object to be polished. The present invention relates to a silica particle that satisfies formulas (1a) and (1b) where x (nm) is the average secondary particle diameter and y (g / mL) is the true specific gravity.　(1a): y > -0.0018x + 2.032; (1b): x > 50

Description

Silica particles and their manufacturing method, silica sol, polishing composition, polishing method, manufacturing method of semiconductor wafer, and manufacturing method of semiconductor device

[0001] The present invention relates to silica particles and a method for producing the same, a silica sol, 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 a polishing liquid are known as methods for polishing the surfaces of materials such as metals and inorganic compounds. In particular, in the final polishing of prime silicon wafers for semiconductors and reclaimed silicon wafers, and in chemical mechanical polishing (CMP) for planarizing interlayer insulating films, forming metal plugs, forming buried wiring, and the like during semiconductor device manufacturing, the surface condition significantly affects the semiconductor characteristics, and therefore the surfaces and end faces of these components must be polished with extremely high precision.

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

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

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

[0006] Conventionally, silica particles have tended to have a lower true specific gravity as their particle size increases, and a lower true specific gravity as their particle size increases. Generally, the larger the particle size of silica particles, the faster the polishing rate. Also, the higher the true specific gravity, the faster the polishing rate. In other words, conventional silica particles have a trade-off between particle size and true specific gravity, and the polishing rate cannot be said to be sufficiently fast.

[0007] The silica particles obtained by the manufacturing methods disclosed in Patent Documents 1 and 2 do not take into consideration the true specific gravity or particle size, and the polishing rate is not necessarily sufficient.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide silica particles, a silica sol, and a polishing composition that are excellent in removal rate. Another object of the present invention is to provide a polishing method, a manufacturing method for semiconductor wafers, and a manufacturing method for semiconductor devices that are excellent in productivity of polishing objects.

[0009] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by setting the relationship between the average secondary particle diameter and the true specific gravity within a predetermined range. Furthermore, the present inventors have found that by employing a predetermined step using a salt in a method for producing silica particles, it is possible to achieve both a large average secondary particle diameter and a high true specific gravity, and have completed the present invention.

[0010] That is, the gist of the present invention is as follows.

[0011] A first aspect of the present invention relates to silica particles that satisfy the following formulas (1a) and (1b), where x (nm) is the average secondary particle diameter and y (g / mL) is the true specific gravity: y > -0.0018x + 2.032 (1a) x > 50 (1b)

[0012] A second aspect of the present invention relates to the silica particles of the first aspect, which satisfy the following formula (1c): y>−0.0018x + 2.062 (1c).

[0013] A third aspect of the present invention relates to the silica particles of the first or second aspect, which satisfy the following formula (1d): x≧55 (1d)

[0014] A fourth aspect of the present invention relates to the silica particles according to any one of the first to third aspects, wherein the content of metal impurities is 5 ppm by mass or less.

[0015] A fifth aspect of the present invention relates to the silica particles according to any one of the first to fourth aspects, which satisfy the following formula (1e): y≦2.10 (1e)

[0016] A sixth aspect of the present invention relates to the silica particles according to any one of the first to fifth aspects, wherein the refractive index is 1.380 or more.

[0017] A seventh aspect of the present invention relates to the silica particles of any one of the first to sixth aspects, wherein the average primary particle diameter is 15 nm to 700 nm.

[0018] Aspect 8 of the present invention relates to the silica particles of any one of Aspects 1 to 7, wherein the amine content is less than 5 μmol / g.

[0019] A ninth aspect of the present invention relates to a method for producing silica particles according to any one of the first to eighth aspects, comprising the step of subjecting an alkoxysilane to a hydrolysis and condensation reaction in a solution containing a salt.

[0020] A tenth aspect of the present invention relates to the method for producing silica particles according to the ninth aspect, wherein the salt is a salt that decomposes or volatilizes when heated to 100°C.

[0021] An eleventh aspect of the present invention relates to the method for producing silica particles according to the ninth or tenth aspect, wherein an alkali catalyst is used to subject an alkoxysilane to hydrolysis and condensation reaction.

[0022] A twelfth aspect of the present invention is the method for producing silica particles according to the eleventh aspect, wherein in the step of hydrolyzing and condensing the alkoxysilane in the solution containing a salt, the molar ratio of the amount of the salt to the amount of the alkali catalyst contained in the solution at the start of the reaction is 1.0 × 10 －４ ~4.5 x 10 －２ The present invention relates to a method for producing silica particles,

[0023] A thirteenth aspect of the present invention relates to a silica sol comprising the silica particles of any one of the first to eighth aspects.

[0024] A fourteenth aspect of the present invention relates to a polishing composition comprising the silica sol of the thirteenth aspect.

[0025] A fifteenth aspect of the present invention relates to a polishing method using the polishing composition of the fourteenth aspect.

[0026] A sixteenth aspect of the present invention relates to a method for producing a semiconductor wafer, comprising a step of polishing the semiconductor wafer with the polishing composition of the fourteenth aspect.

[0027] A seventeenth aspect of the present invention relates to a method for producing a semiconductor device, comprising a step of polishing with the polishing composition of the fourteenth aspect.

[0028] The silica particles, silica sol, and polishing composition of the present invention are excellent in polishing rate, and the polishing method, semiconductor wafer manufacturing method, and semiconductor device manufacturing method of the present invention are excellent in productivity of the object to be polished.

[0029] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be practiced with various modifications within the scope of the gist. In this specification, when the expression "~" is used, it is used as an expression including the numerical values ​​or physical property values ​​before and after it.

[0030] [Silica Particles] The silica particles according to this embodiment satisfy the following formulas (1a) and (1b), where x (nm) is the average secondary particle diameter and y (g / mL) is the true specific gravity: y>-0.0018x+2.032 (1a) x>50 (1b)

[0031] Silica particles that satisfy the above formulas (1a) and (1b) have an excellent polishing rate. If the silica particles do not satisfy at least one of the above formulas (1a) and (1b), the physical contact force between the silica particles and the workpiece is reduced, resulting in a poor polishing rate.

[0032] The definition of the average secondary particle size in this specification is as described below.

[0033] In this specification, the true specific gravity means the average density of silica particles, and can be measured by the ethanol substitution method.

[0034] The true specific gravity of the silica particles can be set within a desired range depending on the production conditions of the silica particles. For example, when the reaction temperature of the hydrolysis and condensation reaction of tetraalkoxysilane is high, the true specific gravity of the silica particles tends to be large, while when the reaction temperature of the reaction is low, the true specific gravity of the silica particles tends to be small.

[0035] The average secondary particle diameter x (nm) and true specific gravity y (g / mL) of the silica particles according to this embodiment are not particularly limited as long as they satisfy the above formulas (1a) and (1b), but x is greater than 50 nm, preferably 55 nm or more, more preferably 65 nm or more, even more preferably 75 nm or more, particularly preferably 100 nm or more, and most preferably 135 nm or more. Furthermore, x is preferably 1000 nm or less, more preferably 500 nm or less, even more preferably 400 nm or less, and particularly preferably 300 nm or less. On the other hand, y is preferably 1.70 g / mL or more, more preferably 1.75 g / mL or more, even more preferably 1.82 g / mL or more, and particularly preferably 1.88 g / mL or more. Furthermore, the upper limit of y is generally 2.20 g / mL or less in the case of amorphous silica. Moreover, the value of y is preferably 2.10 g / mL or less, more preferably 2.05 g / mL or less, and particularly preferably 2.00 or less, since particles that are too hard may cause scratches during polishing.

[0036] When x is greater than 50 nm, the physical contact force of silica particles to the polished object is increased, resulting in an excellent polishing rate. When x is 1000 nm or less, it is preferable because scratches on the polished object can be suppressed. On the other hand, when y is 1.70 g / mL or more, it is preferable because the physical contact force of silica particles to the polished object is increased. When y is 2.20 g / mL or less, it is preferable because scratches on the polished object can be suppressed.

[0037] From the viewpoint of increasing the physical contact force of the silica particles with the workpiece to thereby increase the polishing rate, it is preferable that the silica particles according to this embodiment satisfy the following formula (1c): y>-0.0018x + 2.062 (1c) The definitions of x and y in the formula (1c) are as described above for the formulas (1a) and (1b).

[0038] From the viewpoint of increasing the physical contact force of silica particles with the workpiece to be polished and thereby increasing the polishing rate, it is preferable to simultaneously increase the true specific gravity and the average secondary particle diameter, but this can also be expressed as follows: If x > 50, it is preferable that y ≥ 1.93. If x ≥ 65, it is preferable that y ≥ 1.87. If x ≥ 85, it is preferable that y ≥ 1.81. If x ≥ 140, it is preferable that y ≥ 1.75. If x ≥ 190, it is preferable that y ≥ 1.70.

[0039] Furthermore, from the viewpoint of improving the physical contact force of the silica particles with the workpiece, it is preferable that the silica particles according to this embodiment satisfy the following formula (1d): x≧55 (1d) The definition of x in the formula (1d) is as described above for the formulas (1a) and (1b).

[0040] Furthermore, from the viewpoint of the silica particles having appropriate flexibility and preventing scratches on the workpiece during polishing, the silica particles according to this embodiment preferably satisfy the following formula (1e): y≦2.10 (1e) The definition of y in the formula (1e) is as described above for the formulas (1a) and (1b).

[0041] If the refractive index of silica particles is large, the atomic density of silica particles is high, and it is easy to maintain mechanical strength, so the refractive index of silica particles according to this embodiment is preferably 1.380 or more, more preferably 1.390 or more, and even more preferably 1.400 or more.In addition, since it is preferable that silica maintains an amorphous structure, it is preferably 1.550 or less, more preferably 1.500 or less, and even more preferably 1.450 or less.As a method for controlling the refractive index of silica particles, various methods can be considered, and for example, the refractive index of silica particles can be increased by increasing the reaction temperature.

[0042] The refractive index of the silica particles is determined by adding special-grade 2-propanol and special-grade toluene in varying ratios to a container containing the silica particles, measuring the supernatant when the silica particles in the container become transparent with an Abbe refractometer, and using this refractive index as the refractive index of the silica particles.

[0043] The silica particles according to this embodiment 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 of the object to be polished, a chemical interaction occurs between the silica particles and the object to be polished via the silanol groups, resulting in good polishing. The fact that the silica particles are amorphous can be confirmed by a halo pattern obtained by wide-angle X-ray scattering measurement.

[0044] 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. There is no particular lower limit for the metal impurity content, but it is preferable that the metal impurity content is substantially free. Substantially free means below the detection limit of the measurement method described below, in other words, 0 ppm by mass. When the metal impurity content of the silica particles is 5 ppm by mass or less, this is preferable because it reduces contamination caused by metal impurities adhering to the surface of the object to be polished and the resulting impact on wafer characteristics during polishing of silicon wafers of semiconductor devices. Furthermore, this is 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 performance degradation of semiconductor devices manufactured using such wafers.

[0045] Furthermore, when the metal impurity content of the silica particles is 5 ppm by mass or less, the influence on the polishing rate of changes in the chemical properties (acidity, etc.) of the surface silanol groups due to the occurrence of coordinate interactions between the acidic surface silanol groups and the metal impurities, and changes in the three-dimensional environment of the silica particle surfaces (ease of aggregation of silica particles, etc.) are reduced, which is preferable.

[0046] The metal impurity content of silica particles in this specification is a value measured by inductively coupled plasma mass spectrometry (ICP-MS). Specifically, a silica sol containing 0.4 g of silica particles is accurately weighed, sulfuric acid and hydrofluoric acid are added, and the mixture is heated, dissolved, and evaporated. Pure water is added to the remaining sulfuric acid droplets so that the total amount is exactly 10 g to prepare a test solution, which is then measured using an inductively coupled plasma mass spectrometer. The target metals are sodium, potassium, iron, aluminum, calcium, magnesium, zinc, cobalt, chromium, copper, manganese, lead, titanium, silver, and nickel, and the total content of these metals is taken as the metal impurity content.

[0047] The metal impurity content of silica particles can be reduced to 5 ppm by mass or less by obtaining silica particles by performing hydrolysis and condensation reactions using alkoxysilane as the main raw material. In the method of deionizing alkali silicate such as water glass, sodium and the like derived from the raw material remain, making it extremely difficult to reduce the metal impurity content of silica particles to 5 ppm by mass or less.

[0048] The average primary particle diameter of the silica particles according to this embodiment is preferably 15 nm to 700 nm, more preferably 30 nm to 400 nm, and even more preferably 45 nm to 250 nm. When the average primary particle diameter of the silica particles is 15 nm or more, the storage stability of the silica sol is excellent. Furthermore, when the average primary particle diameter of the silica particles is 700 nm or less, the surface roughness and scratches on the polished object, such as a silicon wafer, can be reduced, and sedimentation of the silica particles can be suppressed.

[0049] The average primary particle diameter of silica particles is measured by the BET method. Specifically, the specific surface area of ​​silica particles is measured using an automatic specific surface area measuring device, and the average primary particle diameter is calculated using the following formula (2): average primary particle diameter (nm) = 6000 / (specific surface area (m ２ / g) x density (g / cm ３ )) ... (2)

[0050] The average primary particle size of the silica particles can be set within a desired range by adjusting the production conditions of the silica particles.

[0051] The average secondary particle diameter of the silica particles according to this embodiment corresponds to x (nm) in the above formula (1b) and exceeds 50 nm. The average secondary particle diameter of the silica particles is preferably 55 nm to 1000 nm, more preferably 65 nm to 500 nm, even more preferably 75 nm to 400 nm, and particularly preferably 100 nm to 300 nm. When the average secondary particle diameter of the silica particles is 55 nm or more, the polishing rate of the silica particles is excellent. Furthermore, when the average secondary particle diameter of the silica particles is 1000 nm or less, the surface roughness and scratches on the polished object, such as a silicon wafer, can be reduced during polishing, the removability of particles and the like during post-polishing cleaning can be excellent, and sedimentation of the silica particles can be suppressed.

[0052] The average secondary particle size of the silica particles is measured by the DLS method, specifically, using a dynamic light scattering particle size measuring device.

[0053] The average secondary particle diameter of silica particles can be set within a desired range depending on the manufacturing conditions of silica particles.For example, when the reaction temperature of the hydrolysis and condensation reaction of tetraalkoxysilane is low, the average secondary particle diameter of silica particles tends to be large, while when the reaction temperature of the hydrolysis and condensation reaction of tetraalkoxysilane is high, the average secondary particle diameter of silica particles tends to be small.In addition, as described later, when salt is added to the reaction system, the average secondary particle diameter of silica particles tends to be large.

[0054] The cv value of the silica particles according to 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 for a workpiece, such as a silicon wafer, is excellent, resulting in excellent silicon wafer productivity. Furthermore, when the cv value of the silica particles is 50% or less, the surface roughness and scratches on a workpiece, such as a silicon wafer, during polishing can be reduced, resulting in excellent particle removal properties during post-polishing cleaning.

[0055] The cv value of the silica particles is calculated by measuring the average secondary particle diameter of the silica particles using a dynamic light scattering particle diameter measuring device and using the following formula (3): cv value = (standard deviation (nm) / average secondary particle diameter (nm)) × 100 (3)

[0056] The association ratio of the silica particles according to this embodiment is preferably 1.1 to 3.5, more preferably 1.3 to 3.0, and even more preferably 1.4 to 2.5. When the association ratio of the silica particles is 1.1 or more, the polishing rate for a workpiece, such as a silicon wafer, is excellent, and the productivity of the silicon wafer is excellent. Furthermore, when the association ratio of the silica particles is 3.5 or less, the surface roughness and scratches on a workpiece, such as a silicon wafer, during polishing can be reduced, and the aggregation of the silica particles can be suppressed.

[0057] The association ratio of silica particles is calculated from the average primary particle diameter measured by the above-mentioned measurement method and the average secondary particle diameter measured by the above-mentioned measurement method using the following formula (4): Association ratio = average secondary particle diameter / average primary particle diameter (4)

[0058] The major axis / minor axis ratio of the silica particles according to this embodiment is preferably 1.01 to 1.39, more preferably 1.06 to 1.25, and even more preferably 1.09 to 1.18. When the major axis / minor axis ratio is 1.01 or more, frictional force is applied between the silica particles and the object to be polished due to the rotation of the silica particles during polishing, resulting in an excellent polishing rate. Furthermore, when the major axis / minor axis ratio is 1.39 or less, the rotation of the silica particles during polishing prevents the silica particles from periodically coming into excessive contact with the object to be polished, resulting in an excellent smooth polishing process. The major axis / minor axis ratio of the silica particles is calculated by observing the silica particles with a scanning electron microscope, calculating the average major axis and average minor axis of the silica particles, and then dividing the average major axis by the average minor axis. The average major axis and average minor axis are calculated by calculating the major axis and minor axis of at least 100 silica particles, and then averaging these values. Here, the major axis is the long side of the rectangle circumscribing the electron microscope image of the particle with the smallest area, and the minor axis is the minor side of the rectangle circumscribing the electron microscope image of the particle with the smallest area.

[0059] The number of fine particles contained in the silica particles according to this embodiment is preferably 10 or less per 100 main particles, more preferably 5 or less per 100 main particles, even more preferably 1 or less per 100 main particles, and particularly preferably none are detectable. Fine particles refer to particles with a major axis of 20 nm or less, and main particles refer to particles with a major axis within ±50% of the average major axis. The number of fine particles and main particles can be counted by observing the silica particles with a scanning electron microscope. Having 10 or less fine particles contained in the silica particles per 100 main particles is preferred from the viewpoint of easily cleaning and removing silica particles adhering to the polishing target after polishing. The number of fine particles contained in the silica particles can be set within a desired range depending on the manufacturing conditions of the silica particles. For example, the number of fine particles decreases when the reaction temperature of the hydrolysis and condensation reaction of tetraalkoxysilane is high.

[0060] The silica particles according to this embodiment have a low content of metal impurities and, due to the trace amounts of residual alkoxy groups inside the particles, possess both adequate mechanical strength and flexibility. Therefore, it is preferable that the main component be an alkoxysilane condensate, more preferably a tetraalkoxysilane condensate, and even more preferably a tetramethoxysilane condensate. The main component refers to a component that accounts for 50% by mass or more of the total 100% by mass of all components constituting the silica particles. To obtain silica particles containing an alkoxysilane condensate as the main component, it is preferable to use an alkoxysilane as the main raw material. To obtain silica particles containing a tetraalkoxysilane condensate as the main component, it is preferable to use a tetraalkoxysilane as the main raw material. To obtain silica particles containing a tetramethoxysilane condensate as the main component, it is preferable to use tetramethoxysilane as the main raw material. The main raw material refers to a raw material that accounts for 50% by mass or more of the total 100% by mass of all raw materials constituting the silica particles.

[0061] The amount of silanol groups in the silica particles according to this embodiment is preferably 0.4 wt% to 2.5 wt%, more preferably 1.15 wt% to 1.55 wt%, and even more preferably 1.2 wt% to 1.45 wt%, based on the weight of the silica particles. When the amount of silanol groups in the silica particles is 0.4 wt% or more, the silica particles have appropriate surface repulsion due to the electric charge generated by ionization of the silanol groups and the water layer hydrated by the silanol groups, resulting in excellent dispersion stability of the silica sol. Furthermore, when the amount of silanol groups in the silica particles is 2.5 wt% or less, the repulsion between the silica particles and the object to be polished due to the hydration water is appropriately suppressed, resulting in excellent polishing speed.

[0062] The amount of silanol groups in silica particles is 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 collected, and pure water is added to make the liquid volume 90 mL. In an environment of 25°C, a 0.1 mol / L hydrochloric acid aqueous solution is added until the pH reaches 3.6, 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 liquid is 150 mL, thereby obtaining a test liquid. The obtained test liquid is placed in an automatic titrator, and a 0.1 mol / L sodium hydroxide aqueous solution is added dropwise. The titration amount A (mL) of the 0.1 mol / L sodium hydroxide aqueous solution required to change the pH from 4.0 to 9.0 is measured.

[0063] The amount V (mL) of 0.1 mol / L aqueous sodium hydroxide solution consumed per 1.5 g of silica particles required to change the pH from 4.0 to 9.0 is calculated using the following formula (5), and the mass proportion of silanol groups is calculated using the following formula (6). The mass proportion of silanol groups calculated in this manner is also referred to as the amount of silanol groups in the silica particles in this specification. V = (A x f x 100 x 1.5) / (W x C) (5) A: Titration amount (mL) of 0.1 mol / L aqueous sodium hydroxide solution required to change the pH per 1.5 g of silica particles from 4.0 to 9.0 f: Titration titer of 0.1 mol / L aqueous sodium hydroxide solution used C: Concentration of silica particles in the silica sol (% by mass) W: Amount of silica sol collected (g) s = (B x w ＯＨ) / M×100 (6) B: The amount (mol) of sodium hydroxide required to change the pH per 1.5 g of silica particles from 4.0 to 9.0 calculated from V. ＯＨ : formula weight of silanol group (17 g / mol) M: amount of silica particles (1.5 g) s: mass ratio of silanol group of silica particles

[0064] The amine content of the silica particles according to this embodiment is preferably less than 5 μmol / g, more preferably less than 3 μmol / g, and even more preferably less than 1 μmol / g. When the amine content of the silica particles is less than 5 μmol / g, corrosion of the object to be polished and the equipment used for polishing can be avoided when the silica particles are used for polishing, which is preferable. There is no particular limit on the lower limit of the amine content of the silica particles, but it can be, for example, 0.001 μmol / g or more. Alternatively, the content can be zero by not using amines in the production of the silica particles. The term "amine" refers to primary amines, secondary amines, and tertiary amines, and is specifically represented by the following general formula (X): NRaRbRc (X) (In the formula, Ra, Rb, and Rc represent an alkyl group having 1 to 12 carbon atoms which may be substituted, or a hydrogen atom. However, Ra, Rb, and Rc cannot all be hydrogen atoms; in other words, ammonia is excluded from the amine represented by general formula (X). Ra, Rb, and Rc may be the same or different. When Ra, Rb, and Rc are alkyl groups, they may be any of linear, branched, and cyclic alkyl groups. Furthermore, when Ra, Rb, and Rc are substituted alkyl groups, examples of the substituent include an alkoxy group, an amino group, a primary amino group substituted with an alkyl group, an amino group di-substituted with an alkyl group, and a hydroxy group.)

[0065] The amine content of silica particles is measured by ion chromatography analysis. Specifically, the silica particles are separated from other components by centrifugation or the like, the silica is dissolved in an aqueous solution such as sodium hydroxide, and the amine content in the solution is quantified by ion chromatography.

[0066] [Method for producing silica particles] The silica particles according to this embodiment can be produced by a production method comprising the step of hydrolyzing and condensing alkoxysilane in a solution containing salt.By the production method comprising such a step, silica particles that satisfy the above formula (1a) and (1b) can be obtained.The reason is unclear, but it is thought that when silica particles are grown in a state where salt is dissolved in the solution and ionic strength is increased, the repulsion caused by surface charge between silica particles is weakened, and aggregation is promoted, so that the number of particles decreases, and the particle diameter increases while maintaining the true specific gravity of particles.

[0067] The salt used in the method for producing silica particles according to this embodiment is not particularly limited, and examples thereof 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 adipate, 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, ammonium dihydrogen phosphate, and ammonium citrate. Examples of salts that can be used include sodium citric acid, ammonium citrate, ammonium nitrate, ammonium chloride, 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, and sodium bicarbonate. These salts may be used alone or in combination of two or more. 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 upon addition and do not change the reaction rate of the tetraalkoxysilane. Furthermore, as the salt, a salt that decomposes or volatilizes when heated up to 100° C. is preferred, as this can avoid contamination of the finally obtained silica particles and silica sol and broaden the industrial application range of the silica particles and silica sol. These salts do not need to completely decompose or volatilize when the temperature reaches 100° C., as long as they start to decompose or volatilize at 100° C.Specifically, the salt is preferably ammonium carbamate, ammonium carbonate, or ammonium hydrogen carbonate, and more preferably ammonium hydrogen carbonate.

[0068] In the method for producing silica particles according to the present embodiment, it is preferable to use an alkali catalyst to cause the hydrolysis and condensation reaction of the alkoxysilane. The reason why the alkali catalyst is preferably used and its preferred embodiments are as described below with respect to the solutions (A) and (C).

[0069] In the step of hydrolyzing and condensing alkoxysilane in a solution containing a salt, the molar ratio of the amount of salt to the amount of alkali catalyst contained in the solution at the start of the reaction is not particularly limited, but is preferably 1.0 × 10 －４ ~4.5 x 10 －２ is preferred, and 1.0 × 10 －３ ~3.0 x 10 －２ More preferably, 2.5 × 10 －３ ~2.0 x 10 －２ is more preferably 4.5 × 10 －３ ~1.0 x 10 －２ The molar ratio is particularly preferably calculated by the following formula: (molar ratio) = (amount of salt used (mol)) / (amount of alkali catalyst used (mol)). When the molar ratio is 1.0 × 10 －４ If the particle size is 4.5×10 or more, the particle size can be effectively adjusted to a large size. －２ When the content is equal to or less than this, aggregation and precipitation of the silica particles can be suppressed.

[0070] Furthermore, since the hydrolysis reaction and condensation reaction are easily controlled, the reaction rates of the hydrolysis reaction and condensation reaction can be increased, gelation of the silica particle dispersion can be prevented, and silica particles with a uniform particle size can be obtained, the method for producing silica particles according to this embodiment preferably includes a step of adding a solution (B) containing tetraalkoxysilane and, if necessary, a solution (C) to a solution (A) containing water, and subjecting the tetraalkoxysilane to hydrolysis and condensation reaction. Since the purpose is to promote the aggregation of particles generated at the beginning of the reaction, when the above-mentioned solution (A), solution (B), and, if necessary, solution (C) are used in the method for producing silica particles according to this embodiment, it is preferable that the above-mentioned salt is contained in solution (A).

[0071] The solution (A) contains water.

[0072] Solution (A) preferably contains a solvent other than water, since this provides excellent dispersibility of the tetraalkoxysilane in the reaction solution. Examples of the solvent other than water in solution (A) include methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used alone or in combination of two or more. Among these solvents, alcohol is preferred, more preferably methanol or ethanol, and even more preferably methanol, because it easily dissolves the tetraalkoxysilane, the solvent used in the hydrolysis reaction and the condensation reaction are the same as the by-product, and this provides excellent manufacturing convenience.

[0073] The solution (A) preferably contains an alkali catalyst, since this can increase the reaction rates of the hydrolysis reaction and condensation reaction of the tetraalkoxysilane.

[0074] Examples of alkali catalysts in solution (A) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used alone or in combination of two or more. Among these alkali catalysts, ammonia is preferred because it has excellent catalytic activity, is easy to control the particle shape, can suppress the inclusion of metal impurities, is highly volatile, and is easily removable after the hydrolysis reaction and the condensation reaction.

[0075] The concentration of water in solution (A) is preferably 3% by mass to 90% by mass, and more preferably 5% by mass to 50% by mass, based on 100% by mass of solution (A). When the concentration of water in solution (A) is 3% by mass or more, the hydrolysis reaction rate of tetraalkoxysilane is easily controlled. Furthermore, when the concentration of water in solution (A) is 90% by mass or less, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and the particle shape is easily controlled.

[0076] The concentration of the alkali catalyst in solution (A) is preferably 0.5% by mass to 3.0% by mass, and more preferably 1.3% by mass to 2.5% by mass, based on 100% by mass of solution (A). When the concentration of the alkali catalyst in solution (A) is 0.5% by mass or more, aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion is excellent. Furthermore, when the concentration of the alkali catalyst in solution (A) is 3.0% by mass or less, the reaction does not proceed excessively rapidly, and excellent reaction controllability is achieved. Furthermore, this is advantageous in that the alkali catalyst can be easily removed by evaporation in step (1) described below.

[0077] When the solution (A) contains a solvent other than water, the concentration of the solvent other than water is preferably the balance of water, the alkali catalyst, and the above-mentioned salt.

[0078] The solution (B) contains a tetraalkoxysilane.

[0079] Examples of tetraalkoxysilanes in solution (B) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. These tetraalkoxysilanes may be used alone or in combination of two or more. Among these tetraalkoxysilanes, tetramethoxysilane and tetraethoxysilane are preferred, and tetramethoxysilane is more preferred, because they undergo a fast hydrolysis reaction, are less likely to leave unreacted substances, are highly productive, and allow stable silica sol to be easily obtained.

[0080] As the raw material for the silica particles, raw materials other than tetraalkoxysilane, such as a low condensate of tetraalkoxysilane, may be used. However, due to their excellent reactivity, it is preferable that, out of 100% by mass of all raw materials constituting the silica particles, tetraalkoxysilane accounts for 50% by mass or more and raw materials other than tetraalkoxysilane accounts for less than 50% by mass, and it is more preferable that tetraalkoxysilane accounts for 90% by mass or more and raw materials other than tetraalkoxysilane accounts for less than 10% by mass.

[0081] Although solution (B) may contain only tetraalkoxysilane without a solvent, it is preferable to contain a solvent because this provides excellent dispersibility of the tetraalkoxysilane in the reaction solution. Examples of solvents in solution (B) include methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used alone or in combination of two or more. Among these solvents, alcohol is preferred because the solvents used in the hydrolysis reaction and the condensation reaction and the by-products are the same, and therefore are convenient for production. Methanol and ethanol are more preferred, and methanol is even more preferred.

[0082] The concentration of the tetraalkoxysilane in solution (B) is preferably 60% by mass to 95% by mass, and more preferably 70% by mass to 90% by mass, based on 100% by mass of solution (B). When the concentration of the tetraalkoxysilane in solution (B) is 60% by mass or more, the reaction solution tends to become homogeneous. Furthermore, when the concentration of the tetraalkoxysilane in solution (B) is 95% by mass or less, the formation of a gel-like substance can be suppressed.

[0083] The concentration of the solvent in solution (B) is preferably 5% by mass to 40% by mass, and more preferably 10% by mass to 30% by mass, based on 100% by mass of solution (B). When the concentration of the solvent in solution (B) is 5% by mass or more, the formation of a gel-like substance can be suppressed. Furthermore, when the concentration of the solvent in solution (B) is 40% by mass or less, the reaction solution tends to become homogeneous.

[0084] The addition rate of solution (B) per hour 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 addition rate of solution (B) is 0.02 kg / hour / L or more, excellent productivity of silica particles is achieved. Furthermore, when the addition rate of solution (B) is 1.3 kg / hour / L or less, the formation of a gel-like substance can be suppressed.

[0085] The ratio of the volume of solution (B) to the volume of solution (A) is preferably 0.120 to 4.00, more preferably 0.400 to 1.50. When the ratio is 0.120 or more, the concentration of silica contained in the liquid obtained after the reaction is high, resulting in excellent yield. When the ratio is 4.00 or less, the concentration of silica particles in the reaction liquid is kept appropriately low, resulting in excellent dispersibility of the silica particles.

[0086] The solution (C) is a solution containing water, and preferably further contains an alkali catalyst.

[0087] Examples of alkali catalysts that can be contained in solution (C) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used alone or in combination of two or more. Among these alkali catalysts, ammonia is preferred because it has excellent catalytic activity, is easy to control the particle shape, can suppress the inclusion of metal impurities, is highly volatile, and is easily removable after the hydrolysis reaction and the condensation reaction.

[0088] Solution (C) contains water as a solvent, and examples of solvents other than water include methanol, ethanol, propanol, isopropanol, and ethylene glycol. The solvents other than water may be used alone or in combination of two or more. Among the solvents for solution (C), water alone or a combination of water and an alcohol is preferred, and water alone is more preferred, since the solvents used in the hydrolysis reaction and the condensation reaction and the by-products are the same, providing excellent manufacturing convenience.

[0089] The concentration of the alkali catalyst in solution (C) is preferably 0% by mass to 10% by mass, based on 100% by mass of solution (C). The alkali catalyst in solution (C) may be 0% by mass, i.e., it may not be contained. However, if an alkali catalyst is contained, its concentration is preferably 0.5% by mass or more, more preferably 3% by mass or more, and even more preferably 4% by mass or more. When the concentration of the alkali catalyst in solution (C) is 0.5% by mass or more, it is easy to adjust the concentration of the alkali catalyst in the reaction solution from the start to the end of the reaction. Furthermore, from the viewpoint of minimizing fluctuations in the alkali catalyst concentration in the reaction solution, the concentration of the alkali catalyst in solution (C) is preferably 10% by mass or less, more preferably 7% by mass or less.

[0090] The water concentration in solution (C) is preferably 90% by mass to 100% by mass, based on 100% by mass of solution (C). The water concentration in solution (C) may be 100% by mass, i.e., solution (C) may be composed only of water, but when other components are contained, the water concentration is preferably 99.5% by mass or less, more preferably 99% by mass or less. From the viewpoint of minimizing fluctuations in the alkali catalyst concentration in the reaction solution, the water concentration in solution (C) is preferably 90% by mass or more, more preferably 94% by mass or more. Furthermore, when the water concentration in solution (C) is 99.5% by mass or less, it is easy to adjust the alkali catalyst concentration in the reaction solution from the start to the end of the reaction.

[0091] The concentration of the solvent other than water in the solution (C) is preferably the balance of water, or the balance of water and the alkali catalyst.

[0092] The addition of solution (B), or solution (B) and solution (C), is preferably carried out into solution (A). By adding solution (B), or solution (B) and solution (C) into solution (A), when using a highly volatile alkaline catalyst such as ammonia and when proceeding with a hydrolysis reaction and a condensation reaction at a high reaction temperature, the miscibility of the components in the reaction solution is improved, abnormal reactions in the air can be suppressed, and the particle shape can be easily controlled. "Adding into the liquid" means adding below the liquid level. By setting the supply outlet for solution (B), or the supply outlet for solution (B) and the supply outlet for solution (C) below the liquid level of solution (A), solution (B), or solution (B) and solution (C) can be added into solution (A).

[0093] When adding solution (B) and solution (C), the timing of adding solution (B) and solution (C) to solution (A) may be the same or may be different, such as alternately, but it is preferable that they are the same, as this reduces fluctuations in the reaction composition and makes the operation less complicated.

[0094] The pH in the step of subjecting tetraalkoxysilane to hydrolysis and condensation reactions is 8.0 to 14, preferably 8.2 to 13, and more preferably 8.5 to 12. When the pH in this step is 8.0 or higher, the reaction rates of the hydrolysis and condensation reactions are excellent and aggregation of silica particles can be suppressed. Furthermore, when the pH in this step is 14 or lower, the shape of the silica particles can be easily controlled and the smoothness of the silica particle surfaces can be excellent.

[0095] The method for producing silica particles according to this embodiment preferably includes a step of carrying out the hydrolysis reaction and condensation reaction of alkoxysilane at 40°C or higher, more preferably at 46°C or higher. When the reaction temperature is 40°C or higher, the reaction rate of the hydrolysis reaction and condensation reaction of alkoxysilane is appropriately improved, and the four bonds of the silicon atom can form a siloxane bond before particle growth proceeds. This makes it possible to reduce the size of the micropores present in the particles. As a result, the true specific gravity of the particles can be increased, which is preferable. Furthermore, the reaction temperature is preferably less than 70°C, more preferably 60°C or lower, and even more preferably 50°C or lower. When the reaction temperature is less than 70°C, the balance between the hydrolysis reaction rate and the condensation reaction rate is excellent.

[0096] The concentration of water in the reaction system for the hydrolysis reaction and condensation reaction is preferably maintained at 3% to 90% by mass, more preferably 5% to 30% by mass, and even more preferably 6% to 25% by mass, based on 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 tetraalkoxysilane. 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.

[0097] The concentration of the alkali catalyst in the reaction system for the hydrolysis reaction and the condensation reaction is preferably 0.5% by mass to 3.0% by mass, and more preferably 1.3% by mass to 2.5% by mass, based on 100% by mass of the total amount in the reaction system. When the concentration of the alkali catalyst in the reaction system is 0.5% by mass or more, aggregation of silica particles is suppressed, and the dispersion stability of the silica particles in the dispersion is excellent. Furthermore, when the concentration of the alkali catalyst in the reaction system is 3.0% by mass or less, the reaction does not proceed excessively quickly, and the reaction controllability is excellent.

[0098] The silica particle concentration in the dispersion of silica particles obtained by the step of hydrolyzing and condensing the alkoxysilane is preferably 5.0% by mass to 30.0% by mass, and more preferably 12.0% by mass to 20% by mass. When the silica particle concentration in the dispersion of silica particles is 5.0% by mass or more, the yield of the silica particles is excellent. When the silica particle concentration in the dispersion of silica particles is 30.0% by mass or less, the dispersibility of the silica particles is excellent.

[0099] Since the method for producing silica particles according to this embodiment can remove unnecessary components and add necessary components, it is preferable that the method further includes the following step (1): Step (1): Removing the dispersion medium from the obtained dispersion of silica particles and adding the dispersion medium to the dispersion of silica particles.

[0100] In step (1), the removal of the dispersion medium from the dispersion of silica particles and the addition of the dispersion medium may be performed in either order, or they may be performed simultaneously. When only the concentration of the dispersion medium is performed, the dispersion of silica particles is concentrated.

[0101] The method for concentrating the dispersion of silica particles is not particularly limited, and examples thereof include a heat concentration method, a membrane concentration method, etc. To concentrate the dispersion of silica particles by the heat concentration method, the dispersion may be heated and concentrated under normal pressure or reduced pressure.

[0102] To concentrate a dispersion of silica particles using a membrane concentration method, membrane separation by ultrafiltration is preferred. Here, the main purpose of ultrafiltration is to remove unnecessary components, such as intermediate products. The molecular weight cutoff of the ultrafiltration membrane used here is selected to match the intermediate products in the dispersion and to filter and remove the intermediate products. Examples of materials for the ultrafiltration membrane include polysulfone, polyacrylonitrile, sintered metal, ceramic, and carbon. Examples of the ultrafiltration membrane configuration include spiral, tubular, and hollow fiber types.

[0103] Examples of the dispersion medium to be added to the dispersion liquid of silica particles include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. These dispersion media may be used alone or in combination of two or more. Among these dispersion media, water and alcohol are preferred, and water is more preferred, because they have excellent affinity with silica particles.

[0104] When the dispersion medium is simultaneously removed and added to the dispersion of silica particles, the dispersion medium is replaced, which is preferable because the dispersion medium can be replaced without significantly changing the amount of silica particles contained in a unit volume of the dispersion of silica particles.

[0105] The method for producing silica particles according to this embodiment preferably further includes the following step (2) because the degree of condensation of the silica particles can be increased. Step (2): A step of subjecting the dispersion of silica particles obtained in step (1) to a pressure and heat treatment.

[0106] The pressure of the pressure and heat treatment is preferably 0.10 MPa to 2.3 MPa, and more preferably 0.12 MPa to 2.0 MPa. When the pressure of the pressure and heat treatment is 0.10 MPa or more, the degree of condensation of the silica particles can be increased. Furthermore, when the pressure of the pressure and heat treatment is 2.3 MPa or less, silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0107] The pressure can be applied by heating the silica particle dispersion in a sealed state to a temperature equal to or higher than the boiling point of the dispersion medium. When the silica particle aqueous dispersion is heated to 100°C or higher in a sealed state, the pressure becomes the saturated water vapor pressure at that temperature.

[0108] The temperature of the pressure and heat treatment is preferably 100°C to 220°C, more preferably 110°C to 180°C. When the temperature of the pressure and heat treatment is 100°C or higher, the degree of condensation of the silica particles can be increased. When the temperature of the pressure and heat treatment is 220°C or lower, silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0109] The time for the pressure and heat treatment is preferably 0.25 to 10 hours, more preferably 0.5 to 8 hours. When the time for the pressure and heat treatment is 0.25 hours or more, the degree of condensation of the silica particles can be increased. When the time for the pressure and heat treatment is 10 hours or less, silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0110] The pressure and heat treatment is preferably carried out in an aqueous dispersion because it can increase the degree of condensation of silica particles without significantly changing the average primary particle size, average secondary particle size, cv value, or association ratio.

[0111] The pH when the pressure and heat treatment is carried out in the aqueous dispersion is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pressure and heat treatment is carried out in the aqueous dispersion at a pH of 6.0 or higher, gelation of the silica sol can be suppressed. Furthermore, when the pressure and heat treatment is carried out in the aqueous dispersion at a pH of 8.0 or lower, the degree of condensation of the silica particles can be increased without significantly changing the average primary particle size, average secondary particle size, cv value, or association ratio.

[0112] [Silica Sol] The silica sol according to this embodiment contains the silica particles according to this embodiment.

[0113] The silica sol may be produced by using the dispersion liquid of silica particles according to this embodiment as it is, or by removing unnecessary components from the dispersion liquid of silica particles according to this embodiment and adding necessary components.

[0114] 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. These dispersion mediums in the silica sol may be used alone or in combination of two or more. 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.

[0115] The content of silica particles in the silica sol is preferably 3% by mass to 50% by mass, more preferably 4% by mass to 40% by mass, and even more preferably 5% by mass to 30% by mass, based on 100% by mass of the total amount of silica sol. When the content of silica particles in the silica sol is 3% by mass or more, the polishing rate for a workpiece such as a silicon wafer is excellent. Furthermore, when the content of silica particles in the silica sol is 50% by mass or less, aggregation of silica particles in the silica sol or polishing composition can be suppressed, and the storage stability of the silica sol or polishing composition is excellent.

[0116] The content of the dispersion medium in the silica sol is preferably 50% by mass to 97% by mass, more preferably 60% by mass to 96% by mass, and even more preferably 70% by mass to 95% by mass, based on 100% by mass of the total amount of the 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 or polishing composition can be suppressed, and the storage stability of the silica sol or polishing composition is excellent. Furthermore, when the content of the dispersion medium in the silica sol is 97% by mass or less, the polishing rate for a workpiece, typically a silicon wafer, is excellent.

[0117] The content of the basic substance in the silica sol is preferably 1 ppm to 1000 ppm, more preferably 10 ppm to 500 ppm, even more preferably 45 ppm to 150 ppm, and particularly preferably 50 ppm to 100 ppm, per weight of the silica sol. When the content of the basic substance in the silica sol is 1 ppm or more, the pH of the silica sol can be maintained at a moderately neutral level, resulting in excellent storage stability. Furthermore, when the silica sol is used for polishing, corrosion of the object to be polished and the equipment used for polishing can be avoided, which is preferable. Furthermore, when the silica sol is used to prepare a polishing composition, pH adjustment is facilitated, which is preferable. Here, the term "basic substance" refers collectively to substances that exhibit basicity, such as nitrogenous basic substances such as ammonia and amines, and inorganic hydroxides.

[0118] The content of the basic substance in the silica sol can be adjusted by appropriately selecting the type of alkali catalyst used in the process of producing silica particles and then appropriately removing it. When ammonia is used as the alkali catalyst, the ammonia content in the silica sol can be appropriately reduced by removing the dispersion medium for an appropriate length of time in the above-mentioned step (1). In this case, it is preferable to heat the dispersion of silica particles to remove the dispersion medium, as this improves the efficiency of ammonia removal.

[0119] The method for measuring the content of basic substances in silica sol may be selected depending on the type of basic substance to be measured. For example, in the case of amines, sodium hydroxide is added to silica sol to dissolve silica particles, and the resulting liquid is measured by ion chromatography to quantify the amines. In the case of ammonia, sodium hydroxide is added to silica sol to convert all the ammonia into ammonia molecules (NH ３ The ammonia content in the silica sol can be quantified by separating the ammonia from the silica particles in the form of ammonia and measuring it with an ammonia electrode.

[0120] The content of silica particles and dispersion medium in the silica sol can be set within a desired range by removing unnecessary components from the components in the obtained dispersion of silica particles and adding necessary components.

[0121] In addition to the silica particles and the dispersion medium, the silica sol may contain other components such as an oxidizing agent, an antiseptic, an antifungal agent, a pH adjuster, a pH buffer, a surfactant, a chelating agent, an antibacterial biocide, etc., as needed, within the range that does not impair the performance of the silica sol. In particular, it is preferable to include an antibacterial biocide in the silica sol, as this provides excellent storage stability of the silica sol.

[0122] Examples of antibacterial biocides include hydrogen peroxide, ammonia, quaternary ammonium hydroxides, quaternary ammonium salts, ethylenediamine, glutaraldehyde, methyl p-hydroxybenzoate, and sodium chlorite. These antibacterial biocides may be used alone or in combination of two or more. Among these antibacterial biocides, hydrogen peroxide is preferred because of its excellent affinity with silica sol. Antibacterial biocides also include those generally known as disinfectants.

[0123] The content of the antibacterial biocide in the silica sol is preferably 0.0001% by mass to 10% by mass, and more preferably 0.001% by mass to 1% by mass, based on 100% by mass of the total amount of the silica sol. When the content of the antibacterial biocide in the silica sol is 0.0001% by mass or more, the storage stability of the silica sol is excellent. When the content of the antibacterial biocide in the silica sol is 10% by mass or less, the inherent performance of the silica sol is not impaired.

[0124] The pH of the silica sol is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pH of the silica sol is 6.0 or higher, the dispersion stability is excellent and aggregation of silica particles can be suppressed. Furthermore, when the pH of the silica sol is 8.0 or lower, dissolution of the silica particles is prevented and long-term storage stability is excellent. The pH of the silica sol can be adjusted by adjusting the content of the basic substance in the silica sol to an appropriate range. Furthermore, the pH can be set to a desired range by adding a pH adjuster.

[0125] [Polishing Composition] The polishing composition according to this embodiment contains the silica sol according to this embodiment. The polishing composition according to this embodiment preferably contains a water-soluble polymer in addition to the silica sol according to this embodiment.

[0126] The water-soluble polymer enhances the wettability of the polishing composition to the object to be polished, such as a silicon wafer. The water-soluble polymer is preferably a polymer having a functional group with high water affinity, and this functional group with high water affinity has a high affinity with the surface silanol groups of the silica particles, so that the silica particles and the water-soluble polymer are stably dispersed in close proximity in the polishing composition. Therefore, when polishing an object to be polished, such as a silicon wafer, the effects of the silica particles and the water-soluble polymer function synergistically.

[0127] Examples of water-soluble polymers include cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, copolymers having a polyvinylpyrrolidone skeleton, and polymers having a polyoxyalkylene structure.

[0128] Examples of cellulose derivatives include hydroxyethyl cellulose, hydrolyzed hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, and carboxymethyl cellulose.

[0129] Examples of copolymers having a polyvinylpyrrolidone skeleton include graft copolymers of polyvinyl alcohol and polyvinylpyrrolidone.

[0130] Examples of polymers having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, and copolymers of ethylene oxide and propylene oxide.

[0131] These water-soluble polymers may be used alone or in combination of two or more. Among these water-soluble polymers, cellulose derivatives are preferred, and hydroxyethyl cellulose is more preferred, because they have high affinity with the surface silanol groups of silica particles and act synergistically to impart good hydrophilicity to the surface of the object to be polished.

[0132] The mass-average molecular weight of the water-soluble polymer is preferably 1,000 to 3,000,000, more preferably 5,000 to 2,000,000, and even more preferably 10,000 to 1,000,000. When the mass-average molecular weight of the water-soluble polymer is 1,000 or more, the hydrophilicity of the polishing composition is improved. Furthermore, when the mass-average molecular weight of the water-soluble polymer is 3,000,000 or less, the affinity with silica sol is excellent and the polishing rate for the object to be polished, typified by a silicon wafer, is excellent.

[0133] The mass average molecular weight of the water-soluble polymer is measured by size exclusion chromatography using a 0.1 mol / L NaCl solution as the mobile phase, in terms of polyethylene oxide.

[0134] The content of the water-soluble polymer in the polishing composition is preferably 0.02% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass, based on 100% by mass of the total amount of the polishing composition. When the content of the water-soluble polymer in the polishing composition is 0.02% by mass or more, the hydrophilicity of the polishing composition is improved. Furthermore, when the content of the water-soluble polymer in the polishing composition is 10% by mass or less, aggregation of silica particles during preparation of the polishing composition can be suppressed.

[0135] In addition to the silica sol and the water-soluble polymer, the polishing composition according to this embodiment may contain other components, such as a basic compound, a polishing accelerator, a surfactant, a hydrophilic compound, a preservative, an antifungal agent, a pH adjuster, a pH buffer, a surfactant, a chelating agent, an antibacterial biocide, etc., as needed, provided that the performance of the polishing composition is not impaired. In particular, it is preferable to include a basic compound in the polishing composition, since this can chemically act on the surface of a polished object, such as a silicon wafer, to perform chemical polishing (chemical etching), and can improve the polishing rate of a polished object, such as a silicon wafer, due to a synergistic effect with the surface silanol groups of the silica particles.

[0136] Examples of basic compounds include organic basic compounds, alkali metal hydroxides, alkali metal hydrogencarbonates, alkali metal carbonates, and ammonia. These basic compounds may be used alone or in combination of two or more. Among these basic compounds, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium hydrogencarbonate, and ammonium carbonate are preferred because they have high water solubility and excellent affinity with silica particles and water-soluble polymers, and ammonia, tetramethylammonium hydroxide, and tetraethylammonium hydroxide are more preferred, with ammonia being even more preferred.

[0137] The content of the basic compound in the polishing composition is preferably 0.001% by mass to 5% by mass, more preferably 0.01% by mass to 3% by mass, based on 100% by mass of the total amount of the polishing composition. When the content of the basic compound in the polishing composition is 0.001% by mass or more, the polishing rate of a polished object, such as a silicon wafer, can be improved. Furthermore, when the content of the basic compound in the polishing composition is 5% by mass or less, the stability of the polishing composition is excellent.

[0138] The pH of the polishing composition is preferably 8.0 to 12.0, more preferably 9.0 to 11.0. When the pH of the polishing composition is 8.0 or higher, aggregation of silica particles in the polishing composition can be suppressed, and the polishing composition has excellent dispersion stability. Furthermore, when the pH of the polishing composition is 12.0 or lower, dissolution of silica particles can be suppressed, and the polishing composition has excellent stability. The pH of the polishing composition can be set within a desired range by adding a pH adjuster.

[0139] The polishing composition can be obtained by mixing the silica sol according to this embodiment, the water-soluble polymer, and, if necessary, other components. However, taking into consideration storage and transportation, the polishing composition may be prepared at a high concentration first and then diluted with water or the like immediately before polishing.

[0140] [Polishing method] The polishing method according to this embodiment is a method of polishing using a polishing composition containing the silica sol according to this embodiment. The polishing composition is preferably the polishing composition described above. A specific polishing method includes, for example, pressing the surface of a silicon wafer against a polishing pad, dropping the polishing composition according to this embodiment onto the polishing pad, and polishing the surface of the silicon wafer.

[0141] [Method for manufacturing a semiconductor wafer] The method for manufacturing a semiconductor wafer 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 the semiconductor wafer include a silicon wafer, a compound semiconductor wafer, etc.

[0142] [Method for Manufacturing a Semiconductor Device] The method for manufacturing a semiconductor device according to this embodiment is a method that 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.

[0143] [Uses] The silica particles and silica sol according to this embodiment can be suitably used for polishing purposes, for example, polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing in the planarization step in manufacturing integrated circuits (chemical mechanical polishing), polishing synthetic quartz glass substrates used for photomasks and liquid crystal displays, polishing magnetic disk substrates, etc., and among these, they can be particularly suitably used for polishing silicon wafers and chemical mechanical polishing.

[0144] Other examples of the object to 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 above metals; intermetallic compounds; glass; and resins. Among these objects to be polished, the polishing agent can be suitably used for metals and metal oxides, and can be particularly suitably used for metal oxides.

[0145] The present invention will be explained in more detail below using examples, but the present invention is not limited to the description of the following examples as long as it does not deviate from the gist of the invention.

[0146] (Measurement of average secondary particle diameter) The average secondary particle diameter of the silica particles in the dispersions obtained in the examples and comparative examples was measured using a dynamic light scattering particle diameter measuring device (Zetersizer Nano ZS, manufactured by Malvern Panalytical).

[0147] (Measurement of true specific gravity) The dispersions of silica particles obtained in the examples and comparative examples were heated and dried, and the true specific gravity was measured by the ethanol substitution method. 10 g of powdered silica particles obtained by drying was precisely weighed into a glass pycnometer, and ethanol was further filled to make the pycnometer full. The volume of the filled ethanol was calculated from the difference in weight of the pycnometer before and after filling with ethanol and the specific gravity of the ethanol. Furthermore, the volume of the silica particles was calculated from the difference between the volume of the pycnometer and the volume of the filled ethanol. The true specific gravity of silica was calculated by dividing the weight of the silica particles by the volume.

[0148] (Measurement of average primary particle diameter) The dispersions of silica particles obtained in the examples and comparative examples were dried at 150°C, and the specific surface area of ​​the silica particles was measured using an automatic specific surface area measuring device "BELSORP-MR1" (model name, Microtrac BEL Co., Ltd.), and the density was calculated to be 2.2 g / cm using the following formula (2). ３ The average primary particle diameter was calculated as follows: Average primary particle diameter (nm) = 6000 / (specific surface area (m ２ / g) x density (g / cm ３ )) ... (2)

[0149] (Calculation of Association Ratio) The association ratio of the silica particles obtained in the examples and comparative examples was calculated from the average primary particle diameter measured by the above-mentioned measurement method and the average secondary particle diameter measured by the above-mentioned measurement method using the following formula (4): Association ratio = average secondary particle diameter / average primary particle diameter (4)

[0150] (Surface silanol group density) The surface silanol group density of the silica particles contained in the obtained silica sol was determined by the Sears method using an automatic titrator (GT-200, manufactured by Nitto Seiko Analytech Co., Ltd.). Specifically, a silica sol equivalent to 1.5 g of silica particles was collected, and pure water was added to make the liquid volume 90 mL. In an environment of 25°C, a 0.1 mol / L aqueous hydrochloric acid 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 liquid reached 150 mL, thereby obtaining a test liquid.

[0151] The obtained test solution was placed in the above automatic titrator, and a 0.1 mol / L aqueous solution of sodium hydroxide was added dropwise to measure the titration amount A (mL) of the 0.1 mol / L aqueous solution of sodium hydroxide required to change the pH from 4.0 to 9.0.

[0152] The amount V (mL) of 0.1 mol / L sodium hydroxide solution consumed per 1.5 g of silica particles required to change the pH from 4.0 to 9.0 was calculated using the following formula (5), and the mass proportion s of silanol groups in the silica particles was calculated using the following formula (6). The results are shown in Table 1.

[0153] The amount V (mL) of 0.1 mol / L aqueous sodium hydroxide solution required to change the pH per 1.5 g of silica particles from 4.0 to 9.0 was calculated using the following formula (5), and the mass proportion of silanol groups was calculated using the following formula (6): V = (A x f x 100 x 1.5) / (W x C) (5) A: Titration amount (mL) of 0.1 mol / L aqueous sodium hydroxide solution required to change the pH per 1.5 g of silica particles from 4.0 to 9.0 f: Titer of the 0.1 mol / L aqueous sodium hydroxide solution used C: Concentration (% by mass) of silica particles in the silica sol W: Amount (g) of silica sol s = (B x w ＯＨ ) / M×100 (6) B: The amount (mol) of sodium hydroxide required to change the pH per 1.5 g of silica particles from 4.0 to 9.0 calculated from V. ＯＨ: formula weight of silanol group (g / mol) M: amount of silica particles (1.5 g) s: mass ratio of silanol group of silica particles

[0154] The cv value of the silica particles was calculated using the following formula (3) by measuring the average secondary particle diameter of the silica particles using a dynamic light scattering particle diameter measuring device: cv value = (standard deviation (nm) / average secondary particle diameter (nm)) × 100 (3)

[0155] (Average major axis and average minor axis, and major axis / minor axis ratio of silica particles) Silica sol was diluted approximately 10,000 times with water and 1-propanol, and the resulting droplets were dried on a flat substrate. 100 or more silica particles remaining on the substrate surface were observed using a scanning electron microscope. The major axis and minor axis of each particle were determined, and then the average major axis and minor axis values ​​of all the particles observed were calculated. The average major axis was divided by the average minor axis to determine the major axis / minor axis ratio of the silica particles. Here, the major axis and minor axis were defined as the long and short sides, respectively, of a rectangle circumscribing the particle with the smallest area. The magnification used for observation using a scanning electron microscope was set so that 10 to 30 particles were included in one field of view.

[0156] (Number of Fine Particles in Silica Sol) In observing the silica particles with the above scanning electron microscope, the presence or absence of particles having a major axis of less than 20 nm was confirmed.

[0157] (Silica concentration in silica sol) Approximately 3 g of silica sol was precisely weighed and placed in a glass container, which was then heated in an oven at 150° C. to evaporate the water and dry it. The mass of the silica particles obtained after drying was accurately measured, and the silica concentration in the silica sol was calculated from the difference between the weight before and after drying.

[0158] (Ammonia concentration in silica sol) The ammonia concentration in the silica particle dispersion was measured using an ammonia selective electrode. Approximately 10 g of silica sol was precisely measured into an Erlenmeyer flask, and 90 mL of ultrapure water was added to dilute the solution 10-fold. 10 mL of an ionic strength adjuster (ISA-NH, manufactured by Toa DKK Corporation) was then added to adjust the pH of the solution to 12 or higher. A pre-calibrated ammonia selective electrode (AE-2041, used in connection with a multi-purpose water quality meter MM-43X, both manufactured by Toa DKK Corporation) was inserted into the adjusted solution, and the ammonia concentration was measured. The masses of the silica particle dispersion and water used in the adjustment were used to convert the ammonia concentration in the silica particle dispersion.

[0159] (Polishing Rate) The polishing rates of the silica particles obtained in the Examples and Comparative Examples against a substrate having a metal oxide film on the surface were evaluated using the following indices: A: The polishing rate is expected to be extremely excellent. B: The polishing rate is expected to be excellent. C: The polishing rate is expected to be poor.

[0160] Example 1: Solution (B) was prepared by mixing tetramethoxysilane and methanol at a mass ratio of 5.7:1, and solution (C) was prepared as a 4.2 mass% aqueous ammonia solution. A reaction vessel equipped with a thermometer, a stirrer, a supply pipe, and a distillation line was charged with solution (A), which was prepared by mixing methanol, pure water, and aqueous ammonia at a mass ratio of 16.1:2.2:1. The ammonia concentration in solution (A) was adjusted to 2.4 mass%. Furthermore, ammonium bicarbonate was added to solution (A). The molar ratio of ammonium bicarbonate to ammonia was adjusted to 0.00125:1. While maintaining the temperature of the reaction solution at 50°C, 63.1 parts by volume of solution (B) and 23.5 parts by volume of solution (C) were added at equal rates to 100 parts by volume of solution (A) over a period of 153 minutes, thereby obtaining a dispersion of silica particles. The temperature was raised to remove methanol and ammonia while adjusting the liquid volume by adding pure water so that the silica particle content of the obtained dispersion of silica particles was about 20% by mass, and a dispersion of silica particles with a silica particle content of about 20% by mass was obtained. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0161] [Example 2] A dispersion of silica particles was obtained in the same manner as in Example 1, except that the molar ratio of ammonium bicarbonate to ammonia in solution (A) was changed to 0.00250:1. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0162] Example 3: Solution (B) was prepared by mixing tetramethoxysilane and methanol at a mass ratio of 5.7:1, and solution (C) was prepared as a 6.6 mass% aqueous ammonia solution. A reaction vessel equipped with a thermometer, a stirrer, a supply pipe, and a distillation line was charged with solution (A), which was prepared by mixing methanol, pure water, and aqueous ammonia at a mass ratio of 10.0:1.1:1. The ammonia concentration in solution (A) was adjusted to 2.4 mass%. Furthermore, ammonium bicarbonate was added to solution (A). The molar ratio of ammonium bicarbonate to ammonia was adjusted to 0.00125:1. While maintaining the temperature of the reaction solution at 50°C, 63.6 volume parts of solution (B) and 24.6 volume parts of solution (C) were added at equal rates to 100 volume parts of solution (A) over a period of 153 minutes, yielding a dispersion of silica particles. The temperature was raised to remove methanol and ammonia while adjusting the liquid volume by adding pure water so that the silica particle content of the obtained dispersion of silica particles was about 20% by mass, and a dispersion of silica particles with a silica particle content of about 20% by mass was obtained. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0163] [Example 4] A dispersion of silica particles was obtained in the same manner as in Example 3, except that the molar ratio of ammonium bicarbonate to ammonia in solution (A) was set to 0.00250: 1. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0164] [Example 5] A dispersion of silica particles was obtained in the same manner as in Example 3, except that the molar ratio of ammonium bicarbonate to ammonia in solution (A) was set to 0.00375: 1. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0165] [Example 6] A dispersion of silica particles was obtained in the same manner as in Example 3, except that the molar ratio of ammonium bicarbonate to ammonia in solution (A) was set to 0.00500: 1. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0166] [Example 7] A dispersion of silica particles was obtained in the same manner as in Example 3, except that the molar ratio of ammonium bicarbonate to ammonia in solution (A) was changed to 0.00876: 1. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0167] Comparative Example 1 A dispersion of silica particles was obtained in the same manner as in Example 1, except that ammonium bicarbonate was not added to solution (A). When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected. In Table 1, "-" indicates that data was not obtained.

[0168] Comparative Example 2 A dispersion of silica particles was obtained in the same manner as in Example 1, except that ammonium hydrogen carbonate was not added to the solution (A) and the temperature of the reaction solution was maintained at 35°C.

[0169] Comparative Example 3 As the silica particle dispersion liquid of Comparative Example 3, a silica particle dispersion liquid "PL-3" manufactured by Fuso Chemical Co., Ltd. was used.

[0170] Comparative Example 4 As the silica particle dispersion in Comparative Example 4, a silica particle dispersion "PL-7" manufactured by Fuso Chemical Co., Ltd. was used.

[0171] Comparative Example 5: An attempt was made to produce silica particles in the same manner as in Example 3, except that the molar ratio of ammonium bicarbonate to ammonia in solution (A) was set to 5:100. However, as soon as solution (B) and solution (C) were added to solution (A), the silica aggregated and production could not be continued. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0172]

[0173] As can be seen from Table 1, the silica particles of Examples 1 to 7 satisfied the above-mentioned formulas (1a) and (1b), while the silica particles of Comparative Examples 1 to 4 did not satisfy either formula (1a) or (1b). Furthermore, the silica particles of Examples 1 to 7 each had a higher true specific gravity than the silica particles of Comparative Examples 1 to 4, which had similar particle diameters. Since the ratios of the average secondary particle diameter and the true specific gravity were both within the desired ranges, it is believed that the use of the silica particles of Examples 1 to 7 in polishing will result in an excellent polishing rate.

[0174] Although various embodiments have been described above, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any manner as long as they do not deviate from the spirit of the invention.

[0175] This application is based on a Japanese patent application (Patent Application No. 2023-214121) filed on December 19, 2023, the contents of which are incorporated herein by reference.

[0176] The silica particles of the present invention can be used, for example, for 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 for photomasks and liquid crystal displays, polishing magnetic disk substrates, and the like.

Claims

1. Silica particles that satisfy the following formulas (1a) and (1b) when the average secondary particle diameter is x (nm) and the true specific gravity is y (g / mL): y>-0.0018x + 2.032 (1a) x>50 (1b) 2. The silica particles according to claim 1, which satisfy the following formula (1c): y>-0.0018x + 2.062 (1c) 3. The silica particles according to claim 1, which satisfy the following formula (1d): x≧55 (1d) 4. Silica particles according to claim 1, having a metal impurity content of 5 ppm by mass or less.

5. The silica particles according to claim 1, which satisfy the following formula (1e): y≦2.10 (1e) 6. The silica particles according to claim 1, having a refractive index of 1.380 or more.

7. The silica particles according to claim 1, having an average primary particle size of 15 nm to 700 nm.

8. The silica particles of claim 1, having an amine content of less than 5 μmol / g.

9. A method for producing silica particles according to any one of claims 1 to 8, comprising a step of subjecting an alkoxysilane to a hydrolysis and condensation reaction in a solution containing a salt.

10. The method for producing silica particles according to claim 9, wherein the salt is a salt that decomposes or volatilizes when heated to 100°C.

11. The method for producing silica particles according to claim 9, wherein an alkoxysilane is subjected to hydrolysis and condensation reaction using an alkali catalyst.

12. In a process for hydrolyzing and condensing an alkoxysilane in a solution containing a salt, the molar ratio of the amount of the salt to the amount of the alkali catalyst contained in the solution at the start of the reaction is 1.0 x 10 －４ ~4.5 x 10 －２ The method for producing silica particles according to claim 11, 13. A silica sol comprising the silica particles according to any one of claims 1 to 8.

14. A polishing composition comprising the silica sol according to claim 13.

15. A polishing method comprising polishing with the polishing composition according to claim 14.

16. A method for producing a semiconductor wafer, comprising the step of polishing the wafer with the polishing composition according to claim 14.

17. A method for manufacturing a semiconductor device, comprising the step of polishing with the polishing composition according to claim 14.