Abrasive particle dispersion for polishing, method for manufacturing the same, and method for polishing semiconductors.

Abstract

To provide an abrasive grain dispersion liquid for polishing, which can achieve excellent polishing speed while suppressing grain hardness of the abrasive grain within a practical range.SOLUTION: An abrasive grain dispersion liquid for polishing comprises a silica fine particle dispersed in a dispersion medium, wherein the silica fine particle meets all of the following requirements [1] to [5]: [1] an average particle diameter, as measured by dynamic light scattering method, is from 5 nm or more to 500 nm or less; [2] a ratio of short diameter / long diameter, as measured by image analysis method, is from 0.1 or more to less than 0.8; [3] a carbon content is less than 150 ppm based on the silica component; [4] a peak area ratio of Q4 / Q3 in a solid-state 29Si-NMR spectrum is from 1 or more to 10 or less; [5] a value [(P1300 / P2300) - (P1110 / P2110)] obtained by subtracting a peak ratio value of P1110 / P2110 from a peak ratio value of P1300 / P2300 is from 0.20 or more to 1 or less in FT-IR measurement using vacuum heating transmission method.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to an abrasive dispersion suitable as an abrasive used in the manufacture of various semiconductor devices. In particular, it relates to an abrasive dispersion suitable for planarizing an insulating film formed on a semiconductor substrate by chemical mechanical polishing, a method for producing the same, and a method for polishing semiconductors. [Background technology]

[0002] Semiconductor devices such as semiconductor substrates and wiring boards achieve high performance through increased density and miniaturization to meet the demands for miniaturization, increased speed, and higher functionality of the electronic devices on which they are mounted. Because the surface condition of such semiconductor devices affects their semiconductor properties, chemical-mechanical polishing (CMP) is applied in the semiconductor manufacturing process. For example, it is used to remove excess oxide in shallow trench isolation (STI), and to planarize the interlayer insulating film when forming a wiring layer on top of an interlayer insulating film covering a wiring layer. Furthermore, it is an essential technique for removing tungsten films in contact plug polishing. It is also an essential technique for removing excess Cu films in the formation process of Cu damascene wiring.

[0003] Generally, CMP abrasives consist of abrasive grains and chemical components. The chemical components promote polishing by oxidizing or corroding the target coating. On the other hand, the abrasive grains perform polishing through mechanical action, and colloidal silica, fumed silica, or ceria particles are used as abrasive grains. In the shallow trench element separation process, not only the silicon oxide film but also the silicon nitride film is polished. To facilitate element separation, it is desirable to have a high polishing rate for the silicon oxide film and a low polishing rate for the silicon nitride film, and this polishing rate ratio (selectivity ratio) is also important.

[0004] Conventionally, as a method for polishing such members, after performing a relatively rough primary polishing treatment, a precise secondary polishing treatment is performed to obtain a smooth surface or an extremely high-precision surface with few scratches or other defects. Regarding the abrasive used for such secondary polishing as finish polishing, conventionally, for example, the following methods have been proposed.

[0005] Patent Document 1 discloses a silica sol in which silica fine particles are dispersed in water, where the average secondary particle diameter of the silica fine particles is 20 to 1000 nm, the average particle diameter of the secondary particles is 1.5 to 3.0 times the average particle diameter of the primary particles, the metal impurity content is 1 ppm or less, and the silica concentration is 10 to 50% by weight. When this silica sol is applied to semiconductor polishing applications, although it meets the requirements for metal impurities, there may be cases where unreacted substances such as oligomers of silicon alkoxide that do not grow into silica particles are included, and there may also be cases where the polished substrate is contaminated. Furthermore, since the reaction progress of oligomers of silicon alkoxide and the like is insufficient, the inside of the particles is porous, the hardness of the particles is insufficient, and as a result, there is a problem that the polishing rate obtained in polishing applications is not sufficient.

[0006] On the other hand, as the conventional methods for producing colloidal silica, two methods, the water glass method and the alkoxide method, are mainstream. The water glass method involves ion-exchanging sodium silicate to prepare active silicic acid, and then adding this under heating to an aqueous solution containing seed particles whose pH is adjusted with NaOH to grow the particles (see Patent Document 2). According to this method, particles having a relatively dense structure can be obtained.

[0007] The alkoxide method, also known as the Stober method, produces silica particles by hydrolyzing alkyl silicate (tetraalkoxysilane) in the presence of a basic catalyst while simultaneously carrying out condensation and particle growth. This method makes it possible to prepare colloidal particles ranging from nanoscale to micronscale. For example, a method for producing cocoon-shaped colloidal silica has been proposed, characterized by adding methyl silicate (tetramethoxysilane) or a mixture of methyl silicate and methanol dropwise over 10 to 40 minutes under stirring in a mixed solvent consisting of water, methanol, and ammonia or ammonia and an ammonium salt, and reacting the methyl silicate with water to produce colloidal silica having a short diameter of 10 to 200 nm and a long diameter / short diameter ratio of 1.4 to 2.2 (see Patent Document 3). In addition, a method for producing cocoon-shaped colloidal silica is known, characterized by hydrolyzing a tetramethoxysilane tetramer dropwise in a mixture of methanol, water, and ammonia (see Patent Document 4). Furthermore, a method for producing silica sol in which elongated amorphous silica particles are dispersed in a liquid dispersion has been disclosed by hydrolyzing tetraethyl silicate or ethyl silicate oligomer with an acid catalyst, adding an alkaline catalyst to achieve a pH of 7 or higher, and then heating to polymerize the mixture (see Patent Document 5).

[0008] In recent years, for example, there has been a high demand for higher recording capacity in semiconductor memory. To improve the quality of silicon wafers, polishing of silicon wafers is performed in multiple stages, and in particular, finish polishing is performed with the aim of reducing surface roughness (haze) and surface defects such as scratches. However, further quality improvements are required even in the reduction of surface defects. To meet these demands, it has been proposed to add specific chemicals to reduce surface defects on the substrate to be polished. Patent document 6 discloses a polishing composition for mirror polishing of silicon semiconductor wafers, in which colloidal silica or the like is used as an abrasive grain, and a polishing liquid composition containing at least one compound having an alcoholic hydroxyl group, selected from methanol, glycerin, etc., for the purpose of reducing surface defects. Patent Document 7 discloses a polishing suspension containing a humectant such as an ethylene oxide adduct of glycerin, for use with silicon wafers as the object to be polished, with the aim of preventing the occurrence of scratches due to aggregates of abrasive grains and the residue of the polishing suspension. Patent Document 8 discloses a polishing solution composition containing an alkylene oxide adduct of a polyhydric alcohol with a hydroxyl group valency of 3 or higher, for use when the object to be polished is a silicon wafer, in order to suppress the adhesion of silica particles and aggregates of water-soluble polymer compounds to the silicon wafer surface and thereby suppress the increase of surface defects. Furthermore, in the silicon wafer polishing process, there is a constant demand for increased polishing speed, and polishing is being carried out using non-spherical (irregularly shaped) abrasive grains. For example, in the semiconductor wafer polishing method described in Patent Document 9, the short-axis / long-axis ratio is 0.3 to 0.8, indicating a high average degree of irregularity of silica particles, resulting in a high polishing speed. However, when the average degree of irregularity of silica particles is too high, scratches are likely to occur on the substrate after polishing, leading to a decrease in the smoothness of the substrate surface, which is problematic. Furthermore, the polishing method described in Patent Document 10 shows that a high polishing speed can be obtained by using irregularly shaped silica particles in which at least four primary silica particles are clustered together. However, although the polishing speed is fast because it has a clustered structure of at least four, it was found that a flocculant is used to form the cluster structure, resulting in a large amount of coarse particles, and furthermore, a large amount of small, spherical particles that are not clustered are included. As a result, it was found that polishing scratches are easily generated by the coarse particles, while the small particles, which have a high repair effect on polishing scratches and a smoothing effect, are spherical and have a slow polishing speed, so there is room for improvement in that the repair effect is small. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2005-060217 [Patent Document 2] Japanese Patent Publication No. 158810 / 1983 [Patent Document 3] Japanese Patent Application Publication No. 11-060232 [Patent Document 4] International Publication No. 2004 / 074180 [Patent Document 5] Japanese Patent Publication No. 2001-048520 [Patent Document 6] Japanese Patent Application Publication No. 11-116942 [Patent Document 7] Japanese Patent Publication No. 2002-329688 [Patent Document 8] Japanese Patent Publication No. 2014-130958 [Patent Document 9] Japanese Patent Publication No. 2001-150334 [Patent Document 10] Japanese Patent Publication No. 2015-086102 [Overview of the project] [Problems that the invention aims to solve]

[0010] Traditionally, to improve the polishing speed using silica abrasive grains, it has been considered desirable for the silica abrasive grains to be harder. One method for hardening silica abrasive grains is to promote the densification of the silica microparticles that make up the silica abrasive grains. Specifically, methods such as pressurized heating treatment or firing treatment during the preparation process of silica microparticles are known. However, hardening silica abrasive grains can cause scratches on the insulating film (film to be polished) when these silica abrasive grains are used to polish an insulating film formed on a semiconductor substrate. Furthermore, there is a limit to how much the polishing speed can be improved if the degree of hardening is such that scratches are suppressed. Another method to improve the polishing speed with silica abrasives is to use non-spherical silica abrasives (irregularly shaped silica abrasives) instead of spherical silica abrasives. While non-spherical silica abrasives certainly improve the polishing speed, it is known to cause problems such as increased scratching on the insulating film (the film being polished), similar to when hardened silica abrasives are used to polish insulating films formed on semiconductor substrates. Furthermore, adding certain chemicals, such as those containing alcoholic hydroxyl groups, to the abrasive dispersion for polishing purposes to reduce surface defects after polishing may be undesirable because the chemicals themselves may contaminate the insulating film, or the polishing speed may decrease due to the chemicals.

[0011] The present invention provides an abrasive dispersion for polishing that exhibits excellent polishing speed and can sufficiently suppress the occurrence of scratches on a substrate to be polished without using additives that reduce surface defects on the substrate to be polished. Furthermore, the invention aims to provide a method for manufacturing such an abrasive dispersion and a method for polishing semiconductors. The present invention also aims to provide an abrasive dispersion for polishing containing abrasive particles made of silica fine particles, and moreover, an abrasive dispersion containing abrasive particles made of high-purity silica fine particles. [Means for solving the problem]

[0012] According to one aspect of the present invention, an abrasive dispersion liquid for polishing is provided, comprising silica fine particles that satisfy all of the following requirements [1] to [5] dispersed in a dispersion medium. [1] The average particle diameter measured by dynamic light scattering must be between 5 nm and 500 nm. [2] The minor axis / major axis ratio measured by image analysis is 0.1 or greater and less than 0.8. [3] The carbon content is less than 150 ppm based on the silica content. [4] Solid 29When the peak area derived from Si(OSi)4 is designated as Q4 and the peak area derived from HO-Si(OSi)3 is designated as Q3 in the Si-NMR spectrum, the peak area ratio of Q4 / Q3 is 1 or more and 30 or less. (However, the chemical shift is based on tetramethylsilane as a reference substance, Q4 is a peak in the range of -110 ppm to -120 ppm, and Q3 is a peak in the range of -100 ppm to -110 ppm.) [5] In the FT-IR measurement at 300 °C using the vacuum heating transmission method, the peak near 3740 cm -1 is designated as P1 300 and the peak near 3660 cm -1 is designated as P2 300 When, in the FT-IR measurement at 110 °C, the peak near 3740 cm -1 is designated as P1 110 and the peak near 3660 cm -1 is designated as P2 110 the value obtained by subtracting the peak ratio value of P1 300 / P2 300 from the peak ratio value of P1 110 / P2 110 i.e., [(P1 300 / P2 300 )-(P1 110 / P2 110 )] is 0.20 or more and 1 or less.

[0013] According to one aspect of the present invention, there is provided a semiconductor polishing method including a step of polishing a semiconductor using the polishing abrasive grain dispersion liquid according to one aspect of the present invention described above.

[0014] According to one aspect of the present invention, there is provided a method for producing a polishing abrasive grain dispersion liquid according to one aspect of the present invention described above, the method including the following steps [1] to [5]. Step [1] A step of preparing a preparation liquid by adding a silicon fine particle suspension to an aqueous alkali hydroxide solution at an addition rate of 0.05 g / min·L or more and 5 g / min·L or less. Step [2] As soon as the temperature of the preparation liquid obtained in Step [1] reaches 60°C due to the dissolution reaction of silicon nanoparticles, a further silicon nanoparticle suspension is added to this preparation liquid at an addition rate of 0.05 g / min·L to 5 g / min·L, and then the liquid is held at a temperature of 60°C to 90°C for a period of 4 to 24 hours to obtain an alkali silicate solution. Step [3] A step to obtain a purified acidic silica solution by dealkalizing and demetallic ionizing the alkali silica solution obtained in step [2]. Step [4]: ​​A portion of the purified acidic silicic acid solution obtained in step [3] is added to an aqueous alkali hydroxide solution, heated at a temperature of 75°C to 98°C, maintained at a temperature of 75°C to 98°C for 30 minutes or more, and then a portion of the purified acidic silicic acid solution obtained in step [3] is added at an addition rate of 1 g / min·g to 200 g / min·g, and the temperature of 75°C to 98°C is maintained at a temperature of 30 minutes to 9 hours, after which it is cooled to room temperature to obtain a silica nanoparticle precursor dispersion. Step [5]: The silica nanoparticle precursor dispersion obtained in Step [4] is heated to a temperature of 75°C to 98°C, maintained at a temperature of 75°C to 98°C for 30 minutes or more, and then a portion of the purified acidic silicic acid solution obtained in Step [3] is added at an addition rate of 1 g / min·g to 300 g / min·g, and the temperature of 75°C to 98°C is maintained at a temperature of 30 minutes to 9 hours, after which it is cooled to room temperature. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide an abrasive particle dispersion for polishing that exhibits a superior polishing speed compared to abrasive particle dispersions for polishing containing harder abrasive particles, a method for producing the same, and a method for polishing semiconductors. Furthermore, the abrasive particle dispersion of the present invention has a relatively low hardness of abrasive particles, making it less likely to cause scratches, and is an abrasive particle dispersion with excellent practicality. [Modes for carrying out the invention]

[0016] [Abrasive particle dispersion for polishing] First, the abrasive dispersion liquid for polishing according to this embodiment will be described. The abrasive dispersion according to this embodiment comprises silica fine particles dispersed in a dispersion medium as abrasive particles. Furthermore, the silica fine particles must satisfy all of the following requirements [1] to [5]. In this specification, the abrasive dispersion liquid for polishing according to this embodiment will also be simply referred to as "the silica fine particle dispersion liquid of the present invention."

[0017] [Short axis / long axis ratio and average particle diameter] The external characteristics of the silica fine particles used as abrasive grains in this embodiment are non-spherical, and specifically satisfy the requirements of [1] and [2] below. [1] The average particle diameter measured by dynamic light scattering must be between 5 nm and 500 nm. If the average particle size of the silica microparticles is within this range, excellent polishing speed is achieved, and scratch generation on the substrate being polished is suppressed. However, if the average particle size of the silica microparticles is less than 5 nm, sufficient polishing speed may not be obtained. Furthermore, if the average particle size of the silica microparticles exceeds 500 nm, depending on the particle size distribution of the silica microparticles, it may easily lead to the generation of undulation or scratches on the substrate being polished. The average particle size of the silica fine particles (measured by dynamic light scattering) is more preferably 8 nm to 500 nm, and particularly preferably 10 nm to 300 nm. [2] The minor axis / major axis ratio measured by image analysis is 0.1 or greater and less than 0.8. Conventionally, non-spherical abrasive grains have been used, for example, to improve polishing speed, and have contributed to increasing the polishing speed. A particle with a short-axis / long-axis ratio of 0.1 or more and less than 0.8 indicates a shape in which the long axis is long. Compared to perfectly spherical abrasive grains, such irregularly shaped abrasive grains exhibit a higher polishing speed because the contact area with the polishing substrate increases in the direction of the long axis of the abrasive grain, and the area where adhesive wear occurs also increases. On the other hand, the inventors hypothesize that the increase in contact area has a pressure dispersion effect on the polishing, which alleviates localized stress concentration, and as a result the substrate surface is polished uniformly, making it easier to achieve surface smoothness. Furthermore, this minor axis / major axis ratio is preferably 0.2 or more and less than 0.8, and more preferably 0.3 or more and less than 0.8.

[0018] [Carbon content] The silica fine particles used as abrasive grains in this embodiment are, by their origin, virtually carbon-free, and specifically satisfy the requirements of [3] below. [3] The carbon content is less than 150 ppm based on the silica content. The abrasive dispersion for polishing according to this embodiment can be applied to applications where contamination is undesirable, such as polishing silicon wafers. The carbon content is preferably less than 130 ppm, and more preferably less than 120 ppm, based on the silica component. Furthermore, the abrasive particles used for polishing can be confirmed to be silica fine particles by using existing known methods, such as ICP analysis or SEM-EDS analysis.

[0019] [solid 29 [Si-NMR spectrum] The silica fine particles used as abrasive grains according to this embodiment do not need to be harder than conventional silica fine particles for polishing, due to the mechanism of action described later. They can exhibit a superior polishing speed compared to conventional silica fine particles with the same or lower hardness. In other words, they satisfy the requirements of [4] below. [4] Solid 29 In the Si-NMR spectrum, when the peak area originating from Si(OSi)4 is denoted as Q4 and the peak area originating from HO-Si(OSi)3 is denoted as Q3, the peak area ratio of Q4 / Q3 must be between 1 and 30. (However, the chemical shift is based on tetramethylsilane as the reference substance, with Q4 being a peak in the range of -110 ppm to -120 ppm and Q3 being a peak in the range of -100 ppm to -110 ppm.) In this embodiment, the hardness of the silica nanoparticles is measured using solid 29In the Si-NMR spectrum, the peak area originating from Si(OSi)4 is denoted as Q4, and the peak area originating from HO-Si(OSi)3 is denoted as Q3. The peak area ratio of Q4 / Q3 is defined as the ratio of Q4 to Q3. In this embodiment, the Q4 / Q3 peak area ratio of silica fine particles used as polishing abrasives must be between 1 and 30. If this peak area ratio is within this range, excellent polishing performance can be achieved through the mechanism of action described later. If the Q4 / Q3 peak area ratio is less than 1, the low hardness of the silica fine particles may affect the performance, and a sufficient polishing speed may not be obtained. On the other hand, if the Q4 / Q3 peak area ratio exceeds 30, a polishing speed can be obtained, but there is a strong tendency for scratches to occur on the substrate being polished. More preferably, a range of 6 to 25 is recommended for the Q4 / Q3 peak area ratio, and even more preferably, a range of 8 to 23 is recommended.

[0020] [FT-IR using vacuum heating transmission method] The silica fine particles used as abrasive grains according to this embodiment satisfy the requirements of [5] below. [5] 3740 cm using vacuum heating permeation method -1 The nearby peak is designated as the isolated silanol group peak P1, and P1 at 300°C is P1 300 Let's assume it's 3660cm. -1 The nearby peak is designated as the peak P2 of the hydrogen-bonded silanol group, and P2 at 300°C is designated as P2. 300 This is the case. 3740 cm in FT-IR measurement at 110°C. -1 The nearby peak is similarly P1 110 Toshi, 3660cm -1 Nearby peak is P2 110 In that case, P1 300 / P2 300 From the peak ratio value, P1 110 / P2 110 The value obtained by subtracting the peak ratio value [(P1 300 / P2 300 )-(P1 110 / P2 110 The value of ) must be between 0.20 and 1.

[0021] [Mechanism of action] Generally, it is known that harder particles are effective in improving the polishing speed as a particle property. When the particles are silica nanoparticles, solid 29 In the Si-NMR spectrum, Q4 (the peak area originating from Si(OSi)4) indicates that siloxane bonds are formed through all oxygen atoms bonded to a given Si. On the other hand, Q3 (the peak area originating from HO-Si(OSi)3) indicates the presence of oxygen atoms that do not form siloxane bonds. In other words, a higher Q4 indicates that polymerization reactions are progressing within the particle, and the particle is harder. Therefore, satisfying the Q4 / Q3 requirement in [4] is necessary to exhibit excellent polishing performance. However, as mentioned above, if the particles are too hard, the occurrence of scratches on the substrate to be polished increases, which is undesirable. Furthermore, it is generally known that at the contact point between the abrasive grains and the workpiece, the surfaces of the abrasive grains and the workpiece interact, and the subsequent shearing causes internal fracture of the workpiece (adhesive wear). Although the details of the adhesive wear mechanism are not clear, the inventors speculate that in the relationship between silica fine abrasive grains and the oxide film substrate as the workpiece, adhesive wear progresses due to a dehydration condensation reaction between the silanol groups on the surface of the abrasive grains and the silanol groups on the surface of the oxide film substrate. They also speculate that adhesive wear is accelerated by the frictional heat generated during polishing. [5] FT-IR measurement [(P1 300 / P2 300 )-(P1 110 / P2 110 The requirement of ) indicates the quantitative change of silanol groups due to frictional heat associated with polishing. Generally, P1 is called an isolated silanol group because it is far from adjacent silanol groups and does not form hydrogen bonds with them. On the other hand, P2 is called a hydrogen-bonding silanol because it is hydrogen-bonded to adjacent silanol groups. P1 / P2 indicates the ratio of isolated silanol groups to hydrogen-bonding silanol groups, and a larger P1 / P2 ratio indicates a higher proportion of isolated silanol groups. Generally, as the temperature increases, silanol groups undergo dehydration condensation with adjacent silanol groups, and siloxane bonding progresses. In this case, it is known that isolated silanol groups are less likely to undergo siloxane bonding than hydrogen-bonding silanol groups. Furthermore, in polishing, it is known that the contact area between the abrasive grains and the substrate becomes extremely high pressure and high temperature due to friction, and it is presumed that the requirement of [5] indicates the degree to which the adhesion process progresses due to the generation of frictional heat. The change in P1 / P2 with temperature indicates that the quantitative relationship between isolated silanol groups and hydrogen-bonded silanol groups has changed. In other words, FT-IR measurement [(P1 300 / P2 300 )-(P1 110 / P2 110 A positive value for ) indicates a greater decrease in hydrogen-bonding silanol groups compared to isolated silanol groups at 300°C. Hydrogen-bonding silanol groups represent hydrogen bonds between adjacent silanol groups or states where water molecules are adsorbed onto a silanol group. Compared to isolated silanol groups, hydrogen-bonding silanol groups are stabilized by hydrogen bonding, resulting in lower chemical reactivity and making them less susceptible to adhesive wear. In other words, the present inventors [(P1 300 / P2 300 )-(P1 110 / P2 110 It was thought that a high value of [(P1) would accelerate the progression of adhesive wear and result in a superior polishing speed when used as an abrasive grain. However, [(P1 300 / P2 300 )-(P1 110 / P2 110 If the value of )] is too large, excessive frictional heat is generated, which may lead to excessive adhesive wear and an increase in scratches, which is undesirable. As described above, the abrasive grains in this embodiment have a peak area ratio of Q4 / Q3 in the range of 1 to 30, and are not particularly hard compared to conventional abrasive grains, but [(P1 300 / P2 300 )-(P1 110 / P2 110The abrasive grain exhibits excellent adhesion, with a value of ) ranging from 0.20 to 1, and can suppress scratch generation while exhibiting excellent polishing speed. 300 / P2 300 )-(P1 110 / P2 110 The value of ) is more preferably in the range of 0.25 to 0.8, and even more preferably in the range of 0.28 to 0.6.

[0022] [Particle size distribution] In the polishing abrasive grains according to this embodiment, when the particle size distribution obtained by image analysis is defined as follows, with the cumulative frequency particle size at 10% being D10, the cumulative frequency particle size at 50% being D50, and the cumulative frequency particle size at 90% being D90, it is preferable that the conditions expressed by the following formula (F1) are satisfied. 1.0≦[(D10+D90) / 2] / D50≦1.4···(F1) By satisfying the conditions of formula (F1), the filling rate can be increased in the mechanism in which polishing proceeds after the abrasive grains fill the gap between the polishing substrate and the pad. It is estimated that as a result of increasing the filling rate, the polishing speed and surface accuracy can be obtained at a suitable level. If the value of [(D10+D90) / 2] / D50 is less than 1.0, the aforementioned effect is insufficient. Values ​​exceeding 1.4 tend to decrease surface accuracy, possibly due to the inclusion of larger particles, and are therefore undesirable. Thus, excellent polishing speed or surface accuracy can be achieved within the range that satisfies the conditions of formula (F1). During polishing, abrasive grains move in the space created between the substrate to be polished and the polishing pad, along with the solvent, while in contact with both the substrate and the polishing pad. However, there is a difference in the movement speed between relatively large abrasive grains and relatively small abrasive grains, resulting in uneven contact between the abrasive grains and the substrate per unit time. Specifically, there are areas on the substrate where relatively large abrasive grains actively make contact and areas where relatively small abrasive grains actively make contact. This is the cause of the deterioration of the surface roughness of the substrate after polishing, and it is presumed that a narrow particle size distribution can improve the unevenness of the abrasive grain movement, thereby obtaining a suitable level of polishing speed and surface accuracy. Specifically, if the value of formula (F1) is less than 1.0, D10 may be too small or D50 may be too large, resulting in insufficient effects as described above. If it is greater than 1.4, D90 may be too large or D50 may be too small, and the surface accuracy tends to decrease, possibly due to an excessively wide distribution, which is undesirable. Therefore, within the range that satisfies the conditions of formula (F1), excellent polishing speed or surface accuracy can be achieved. As mentioned above, the value of [(D10+D90) / 2] / D50 is preferably between 1.0 and 1.4, and more preferably between 1.03 and 1.3.

[0023] [Solid content concentration] In this embodiment, the solid content concentration in the abrasive dispersion is preferably 0.3% by mass or more and 50% by mass or less. If the solid content concentration is lower than 0.3% by mass, it may not be possible to reach the desired polishing speed. Conversely, if the solid content concentration exceeds 50% by mass, the stability of the abrasive particles becomes insufficient, preventing further improvement in polishing speed and efficiency. Furthermore, dried material may form and adhere during the process of supplying the dispersion for polishing, potentially causing scratches. Note that the solid content concentration in the abrasive dispersion refers to the concentration of silica fine particles. From a similar viewpoint, it is more preferable that the solid content concentration is 1% by mass or more and 30% by mass or less.

[0024] [purity] As described above, the silica fine particles used as abrasive grains in this embodiment can be suitably used, for example, for polishing silicon wafers, provided that their carbon content is less than 1 ppm (based on silica content). Furthermore, when applied to applications requiring high purity, it is preferable that the Al concentration in the silica solid content of the abrasive grain dispersion is 20 ppm or less, the Ca, Ni, and Na concentrations are each 10 ppm or less, and the Mg, Ti, Cr, Fe, Cu, Zn, Ag, and Pb concentrations are each 5 ppm or less.

[0025] [Various components in the dispersion] The abrasive dispersion according to this embodiment contains at least one of water and an organic solvent as a dispersion medium. It is preferable to use water such as pure water, ultrapure water, and ion-exchanged water as the dispersion medium. Furthermore, the abrasive dispersion according to this embodiment can be suitably used as an abrasive composition (abrasive slurry) by adding one or more additives selected from the group consisting of abrasive accelerators, surfactants, heterocyclic compounds, pH adjusters, pH buffers, and sedimentation inhibitors as additives to control abrasive performance.

[0026] [Dispersion medium] Examples of dispersion media other than water include alcohols (methanol, ethanol, isopropanol, n-butanol, and methylisocarbinol, etc.), ketones (acetone, 2-butanone, ethylamyl ketone, diacetone alcohol, isophorone, and cyclohexanone, etc.), ethers (N,N-dimethylformamide, N,N-dimethylacetamide, diethyl ether, isopropyl ether, tetrahydrofuran, 1,4-dioxane, and 3,4-dihydro-2H-pyran, etc.), glycol ethers (2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, and ethylene glycol dimethyl ether, etc.), and glycol ether acetone. Examples include tetes (such as 2-methoxyethyl acetate, 2-ethoxyethyl acetate, and 2-butoxyethyl acetate), esters (such as methyl acetate, ethyl acetate, isobutyl acetate, amyl acetate, ethyl lactate, and ethylene carbonate), aromatic hydrocarbons (such as benzene, toluene, and xylene), aliphatic hydrocarbons (such as hexane, heptane, isooctane, and cyclohexane), halogenated hydrocarbons (such as methylene chloride, 1,2-dichloroethane, dichloropropane, and chlorobenzene), sulfoxides (such as dimethyl sulfoxide), and pyrrolidones (such as N-methyl-2-pyrrolidone and N-octyl-2-pyrrolidone). These may also be used mixed with water.

[0027] [Polishing accelerator] The abrasive dispersion liquid for polishing according to this embodiment may contain conventionally known polishing accelerators, depending on the type of material to be polished. Examples of such polishing accelerators include hydrogen peroxide, peracetic acid, and urea peroxide. These may be used individually or in combination of two or more. When using an abrasive composition containing such a polishing accelerator as hydrogen peroxide, the polishing speed can be effectively improved when the material to be polished is metal.

[0028] Other examples of polishing accelerators include acids such as sulfuric acid, nitric acid, phosphoric acid, oxalic acid, or hydrofluoric acid, or sodium, potassium, or ammonium salts of these acids, as well as mixtures thereof. In polishing compositions containing these polishing accelerators, when polishing a material made of complex components, a flat polished surface can be ultimately obtained by accelerating the polishing rate for specific components of the material to be polished. If the abrasive dispersion according to this embodiment contains a polishing accelerator, the content of the accelerator is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less.

[0029] [Surfactant, hydrophilic compound] In this embodiment, abrasive particle dispersions may contain cationic, anionic, nonionic, or amphoteric surfactants or hydrophilic compounds to improve dispersibility and stability. At least one of the surfactant and hydrophilic compound has the effect of reducing the contact angle with the surface to be polished and promoting uniform polishing. As at least one of the surfactant and hydrophilic compound, for example, those selected from the following group can be used. These may be used individually or in combination of two or more.

[0030] Examples of anionic surfactants include carboxylates, sulfonates, sulfate esters, and phosphate esters. Examples of carboxylates include soaps, N-acyl amino acid salts, polyoxyethylene or polyoxypropylene alkyl ether carboxylates, and acylated peptides. Examples of sulfonates include alkyl sulfonates, alkylbenzene and alkylnaphthalene sulfonates, naphthalene sulfonates, sulfosuccinates, α-olefin sulfonates, and N-acyl sulfonates. Examples of sulfate esters include sulfated oils, alkyl sulfates, alkyl ether sulfates, polyoxyethylene or polyoxypropylene alkyl allyl ether sulfates, and alkylamide sulfates. Examples of phosphate esters include alkyl phosphates and polyoxyethylene or polyoxypropylene alkyl allyl ether phosphates.

[0031] Examples of cationic surfactants include aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium chloride salts, benzethonium chloride, pyridinium salts, and imidazolinium salts. Examples of amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate salts, imidazolinium betaine, lecithin, and alkylamine oxides.

[0032] Nonionic surfactants include ether-type, ether-ester-type, ester-type, and nitrogen-containing types. Ether-type surfactants include polyoxyethylene alkyl and alkylphenyl ethers, alkylallylformaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropylene block polymers, and polyoxyethylene polyoxypropylene alkyl ethers. Ether-ester-type surfactants include polyoxyethylene ethers of glycerin esters, polyoxyethylene ethers of sorbitan esters, and polyoxyethylene ethers of sorbitol esters. Ester-type surfactants include polyethylene glycol fatty acid esters, glycerin esters, polyglycerin esters, sorbitan esters, propylene glycol esters, and sucrose esters. Nitrogen-containing surfactants include fatty acid alkanolamides, polyoxyethylene fatty acid amides, and polyoxyethylene alkylamides. Other nonionic surfactants include fluorine-based surfactants.

[0033] As the surfactant, anionic surfactants or nonionic surfactants are preferred. As the salt, examples include ammonium salts, potassium salts, and sodium salts, with ammonium salts and potassium salts being particularly preferred.

[0034] Furthermore, other surfactants or hydrophilic compounds include esters (such as glycerin esters, sorbitan esters, and alanine ethyl esters), ethers (such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyethylene glycol alkyl ether, polyethylene glycol alkenyl ether, alkyl polyethylene glycol, alkyl polyethylene glycol alkyl ether, alkyl polyethylene glycol alkenyl ether, alkenyl polyethylene glycol, alkenyl polyethylene glycol alkyl ether, alkenyl polyethylene glycol alkenyl ether, polypropylene glycol alkyl ether, polypropylene glycol alkenyl ether, alkyl polypropylene glycol, alkyl polypropylene glycol alkyl ether, alkyl polypropylene glycol alkenyl ether, and alkenyl polypropylene glycol), polysaccharides (such as alginic acid, pectinic acid, carboxymethylcellulose, curdlan, and pullulan), and amino acid salts (such as glycine ammonium salts and glycine). (Sodium salts, etc.), polycarboxylic acids and their salts (polyaspartic acid, polyglutamic acid, polylysine, polymalic acid, polymethacrylic acid, polyammonium methacrylate, polymethacrylate sodium salt, polyamic acid, polymaleic acid, polyitaconic acid, polyfumaric acid, poly(p-styrene carboxylic acid), polyacrylic acid, polyacrylamide, aminopolyacrylamide, polyammonium acrylate, polyacrylate sodium salt, polyamic acid, polyamic acid ammonium salt, polyamic acid sodium salt, and polyglyoxylic acid. (etc.), vinyl polymers (such as polyvinyl alcohol, polyvinylpyrrolidone, and polyacrolein), sulfonic acids and their salts (such as ammonium methyltaurate, sodium methyltaurate, sodium methyl sulfate, ethylammonium sulfate, butylammonium sulfate, sodium vinylsulfonate, sodium 1-allylsulfonate, sodium 2-allylsulfonate, sodium methoxymethylsulfonate, ammonium ethoxymethylsulfonate, and sodium 3-ethoxypropylsulfonate), andExamples include amides (propionamide, acrylamide, methylurea, nicotinamide, succinamide, and sulfanilamide, etc.).

[0035] Furthermore, if the substrate to be polished is a glass substrate or the like, any surfactant can be suitably used. However, in the case of silicon substrates for semiconductor integrated circuits, etc., where contamination by alkali metals, alkaline earth metals, or halides is undesirable, it is desirable to use an acid or an ammonium salt-based surfactant.

[0036] If the abrasive dispersion according to this embodiment contains at least one of a surfactant and a hydrophilic compound, the total amount is preferably 0.001 g to 10 g, more preferably 0.01 g to 5 g, and particularly preferably 0.1 g to 3 g per liter of the abrasive dispersion. If the content of at least one of the surfactant and the hydrophilic compound is above the lower limit, a sufficient effect can be obtained, while if it is below the upper limit, a decrease in polishing speed can be prevented.

[0037] [Heterocyclic compounds] In the polishing abrasive dispersion according to this embodiment, when the substrate to be polished contains metal, a heterocyclic compound may be included for the purpose of forming a passivation layer or dissolution-inhibiting layer on the metal to suppress erosion of the substrate to be polished. Here, "heterocyclic compound" refers to a compound having a heterocycle containing one or more heteroatoms. A heteroatom means an atom other than a carbon atom or a hydrogen atom. A heterocycle means a cyclic compound having at least one heteroatom. A heteroatom refers only to an atom that forms a component of the ring system of a heterocycle, and does not refer to an atom that is located outside the ring system, separated from the ring system by at least one non-conjugated single bond, or is part of a further substituent of the ring system. Preferred heteroatoms include, but are not limited to, nitrogen, sulfur, oxygen, selenium, tellurium, phosphorus, silicon, and boron atoms. Examples of heterocyclic compounds include imidazole, benzotriazole, benzothiazole, and tetrazole. More specifically, examples include, but are not limited to, 1,2,3,4-tetrazole, 5-amino-1,2,3,4-tetrazole, 5-methyl-1,2,3,4-tetrazole, 1,2,3-triazole, 4-amino-1,2,3-triazole, 4,5-diamino-1,2,3-triazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, and 3,5-diamino-1,2,4-triazole. These may be used individually or in combination of two or more.

[0038] [pH adjuster] The abrasive dispersion liquid for polishing according to this embodiment can have its pH adjusted by adding an acid or base and their salt compounds (hereinafter also referred to as a pH adjuster) as needed to enhance the effects of the above-mentioned additives. When adjusting the pH of the abrasive dispersion according to this embodiment to 7 or higher, an alkaline pH adjusting agent is used. Examples of such pH adjusting agents include sodium hydroxide, aqueous ammonia, ammonium carbonate, and amines (such as ethylamine, methylamine, triethylamine, and tetramethylamine). These may be used individually or in combination of two or more. When adjusting the pH of the abrasive dispersion according to this embodiment to less than 7, an acidic pH adjusting agent is used. Examples of such pH adjusting agents include hydroxy acids (acetic acid, lactic acid, citric acid, malic acid, tartaric acid, and glyceric acid, etc.) and mineral acids (hydrochloric acid and nitric acid, etc.). These may be used individually or in combination of two or more.

[0039] [pH buffering agent] To maintain a constant pH value in the abrasive dispersion according to this embodiment, a pH buffering agent may be used. Examples of pH buffering agents include phosphates (ammonium dihydrogen phosphate and diammonium hydrogen phosphate), borates (such as ammonium tetraborate tetrahydrate), and organic acid salts. These may be used individually or in combination of two or more.

[0040] [Settling inhibitor] In this embodiment, a settling inhibitor may be added to the abrasive dispersion to suppress settling and, if settling occurs, to facilitate dispersion. While there are no particular restrictions on the settling inhibitors, examples include polycarboxylic acid surfactants, anionic polymer surfactants, cationic surfactants, sodium polyacrylate, sodium carboxylic acid copolymer salts, ammonium carboxylic acid copolymer salts, ammonium polyacrylate, polyacrylic acid, sodium sulfonic acid copolymer salts, fatty acid salts, α-sulfo fatty acid ester salts, alkylbenzene sulfonates, alkyl sulfates, alkyl ether sulfate esters, alkyl sulfate triethanolamine, fatty acid diethanolamide, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, alkyltrimethylammonium salts, dialkyldimethylammonium chloride, alkylpyridium chloride, alkylcarboxybetaine, styrene-maleic anhydride copolymer, formalin-bound naphthalene sulfonates, carboxymethylcellulose, olefin-maleic anhydride copolymer, sodium alginate, polyvinyl alcohol, polyalkylene polyamine, polyacrylamide, polyoxypropylene-polyoxyethylene block, polymer starch, polyethyleneimine, aminoalkyl acrylate copolymer, polyvinylimidasolin, and satkinsan. When a settling inhibitor is added to the abrasive dispersion according to this embodiment, the total amount is preferably 0.001g to 10g per liter of abrasive dispersion, more preferably 0.01g to 5g, and particularly preferably 0.1g to 3g. If the amount is above the lower limit, a sufficient effect can be obtained, while if it is below the upper limit, a decrease in polishing speed can be prevented.

[0041] [Method for manufacturing abrasive particle dispersion] Next, a method for producing an abrasive dispersion according to this embodiment will be described. Conventionally, one known method for producing silica fine particle dispersions (silica sols) involves adding an acidic silicic acid solution to a core particle dispersion to promote particle growth of the core particles. Here, there are no particular restrictions on the core particle dispersion as long as it functions as a core particle; conventionally known silica fine particle dispersions can be used. Furthermore, acidic silica solution can be obtained by dealkalizing alkali silicate. Here, known methods for producing alkali silicate include, for example, (1) a method for producing an aqueous alkali silicate solution by dissolving alkali silicate glass cullet, as disclosed in Japanese Patent Publication No. 9-110416, in water in the presence of a seed crystal made of calcium silicate to obtain an aqueous alkali silicate solution, and then filtering this aqueous alkali silicate solution; (2) a method for producing an aqueous alkali silicate solution having the composition A2O·nSiO2 by adding an aqueous alkali hydroxide (AOH; A: alkali metal) solution to soft silica to dissolve the silica in the silica to produce an aqueous alkali silicate solution, as disclosed in Japanese Patent Publication No. 6-171924, characterized by adding hydrogen peroxide to the aqueous solution to oxidize reducing substances derived from the soft silica; and (3) a method for producing solid alkali silicate by reacting fine silica-containing by-products discharged from the electrothermal metallurgy industry, such as metallic silicon, with liquid caustic alkali, as disclosed in Japanese Patent Publication No. 59-1216.

[0042] In contrast, in the method for producing an abrasive dispersion according to this embodiment, a reaction solution is prepared by adding a silicon microparticle suspension to an aqueous alkali hydroxide solution at an addition rate of 0.05 g / min·L to 5.0 g / min·L. As soon as the temperature of the reaction solution obtained in the previous step reaches 60°C due to the dissolution reaction of the silicon microparticles, a further silicon microparticle suspension is added to this reaction solution at an addition rate of 0.05 g / min·L to 5.0 g / min·L. Subsequently, the solution is held at a liquid temperature of 60°C to 90°C for 4 to 24 hours, and the resulting alkali silicate solution is used as the raw material. The alkali silicate solution obtained in this way has a molar ratio of SiO2 / alkali of 1 to 4 and a molecular weight of alkali silicate of 30000 or less. Furthermore, in the method for producing the abrasive dispersion according to this embodiment, a purified acidic silica solution is prepared by dealkalizing and demetallic ionizing the alkali silica solution, and the abrasive dispersion according to this embodiment is obtained by reacting this purified acidic silica solution with an aqueous alkali hydroxide solution under predetermined conditions.

[0043] The method for producing the abrasive dispersion according to this embodiment is a method for producing the abrasive dispersion according to the above embodiment, and includes the following steps [1] to [5]. Step [1] A step of preparing a compound solution by adding a silicon microparticle suspension to an alkali hydroxide aqueous solution at an addition rate of 0.05 g / min·L or more and 5 g / min·L or less. Step [2] As soon as the temperature of the preparation liquid obtained in Step [1] reaches 60°C due to the dissolution reaction of silicon nanoparticles, a further silicon nanoparticle suspension is added to this preparation liquid at an addition rate of 0.05 g / min·L to 5 g / min·L, and then the liquid is held at a temperature of 60°C to 90°C for a period of 4 to 24 hours to obtain an alkali silicate solution. Step [3] A step to obtain a purified acidic silica solution by dealkalizing and demetallic ionizing the alkali silica solution obtained in step [2]. Step [4]: ​​A portion of the purified acidic silicic acid solution obtained in step [3] is added to an aqueous alkali hydroxide solution, heated at a temperature of 75°C to 98°C, maintained at a temperature of 75°C to 98°C for 30 minutes or more, and then a portion of the purified acidic silicic acid solution obtained in step [3] is added at an addition rate of 0.005 g / min·g to 0.1 g / min·g, and the temperature of 75°C to 98°C is maintained for 30 minutes to 9 hours, after which it is cooled to room temperature to obtain a silica nanoparticle precursor dispersion. Step [5]: The silica nanoparticle precursor dispersion obtained in Step [4] is heated to a temperature of 75°C to 98°C, maintained at a temperature of 75°C to 98°C for 30 minutes or more, and then a portion of the purified acidic silicic acid solution obtained in Step [3] is added at an addition rate of 0.005 g / min·g to 0.1 g / min·g, and the temperature of 75°C to 98°C is maintained at a temperature of 30 minutes to 9 hours, after which it is cooled to room temperature.

[0044] In step [1], a preparation solution is made by adding a silicon microparticle suspension to an alkali hydroxide aqueous solution at room temperature at an addition rate of 0.05 g / min·L or more and 5 g / min·L or less. In this specification, the addition of the silicon microparticle suspension in step [1] is also referred to as the "first stage addition of silicon microparticle suspension". The unit of addition rate "g / min·L" means the mass of silicon microparticle suspension (in terms of silica solids) added per minute per unit volume (1 L) of alkali hydroxide aqueous solution. Here, the unit "g / min·L" can also be expressed as "g / (min·L)". A silicon nanoparticle suspension can be obtained, for example, by dispersing silicon nanoparticles (metallic silicon powder) in ultrapure water. The average particle size of the silicon nanoparticles (measured by dynamic light scattering) is not particularly limited, but is usually between 0.03 μm and 10,000 μm, and more preferably between 0.03 μm and 500 μm. The method for producing silicon nanoparticles is not particularly limited, but the Siemens method or metallurgical method is preferred because it is easier to obtain high-purity silicon nanoparticles. Specifically, a silicon microparticle suspension can be prepared by adding silicon microparticles to ultrapure water and stirring it using, for example, a commonly known agitator. In practical terms, the silicon solid content of the silicon fine particle dispersion is preferably 1% by mass or more and 50% by mass or less, and more preferably 5% by mass or more and 40% by mass or less, considering its reaction with the alkali hydroxide aqueous solution. Furthermore, considering the required performance of the final silica microparticle dispersion for semiconductor polishing applications, the purity of the silicon microparticles is preferably such that the Al and Ni concentrations relative to the silicon solid content are each 1% or less. In this specification, the silicon microparticle suspension may be referred to as "Solution B".

[0045] The alkali hydroxide aqueous solution is selected from aqueous solutions of sodium hydroxide and potassium hydroxide, among others. The concentration of the alkali hydroxide aqueous solution is not particularly limited, as long as the properties of the aqueous solution are maintained. However, the concentration of the alkali hydroxide aqueous solution is preferably 1% by mass or more and 48% by mass or less at room temperature. In this specification, an aqueous solution of alkali hydroxide may be referred to as "Solution A".

[0046] Specifically, an aqueous alkali hydroxide solution is poured into a reaction vessel, and while stirring, a suspension of silicon microparticles is added at an addition rate of 0.05 g / min·L to 5 g / min·L to obtain the prepared solution. In the prepared solution, it is presumed that the metallic silicon nanoparticles dissolve in the alkali hydroxide aqueous solution, and that the reaction shown in the following equation occurs, in which case alkali silicate begins to be formed. Note that in the following equation, NaOH is used as the alkali hydroxide. Si+2NaOH+H2O→Na2SiO3+2H2↑ In this specification, "compound solution" refers to a solution in which silicon nanoparticles are present in an aqueous solution of alkali hydroxide, and a reaction between the alkali hydroxide and silicon is also occurring. The addition rate of the silicon nanoparticle suspension is preferable because, if the addition rate is within the aforementioned range, the exothermic reaction associated with the dissolution of silicon nanoparticles in alkali hydroxide easily raises the temperature of the preparation solution to around 60°C, facilitating the dissolution of silicon nanoparticles and the formation of alkali silicate. If the addition rate is less than 0.05 g / min·L, the exothermic reaction is weak and may require external heating, which is undesirable. On the other hand, if the addition rate exceeds 5.0 g / min·L, the exothermic reaction may proceed rapidly while generating hydrogen gas, making temperature control difficult and posing a safety risk to the operation, which is also undesirable. The addition rate range for the silicon fine particle suspension in step [1] is more preferably 0.1 g / min·L to 4.0 g / min·L, and even more preferably 0.2 g / min·L to 3.0 g / min·L.

[0047] When adding a suspension of silicon nanoparticles, it is desirable to blow an inert gas such as nitrogen gas into the alkali hydroxide aqueous solution or preparation solution in the reaction vessel via a tube or the like to bring the inside of the reaction vessel outside the explosive limit range.

[0048] In step [2], as soon as the temperature of the preparation obtained in step [1] reaches 60°C due to the dissolution reaction of silicon nanoparticles, a silicon nanoparticle suspension is added to this preparation at an addition rate of 0.05 g / min·L to 5 g / min·L, and then the preparation is held at a liquid temperature of 60°C to 90°C for a period of 4 to 24 hours. In this specification, the addition of the silicon nanoparticle suspension in step [2] is also referred to as the "second stage addition of silicon nanoparticle suspension". The unit of addition rate "g / min·L" means the mass of silicon nanoparticle suspension (in terms of silica solids) added per minute to the preparation obtained in step [1] (1 L). Here, the unit "g / min·L" can also be expressed as "g / (min·L)".

[0049] The temperature of this mixture rises due to the exothermic reaction that occurs when the silicon nanoparticles dissolve in alkali hydroxide. As soon as the reaction solution reaches 60°C, an additional suspension of silicon nanoparticles is added rapidly at an addition rate of 0.05 g / min·L to 5 g / min·L. The addition of the silicon nanoparticle suspension in step [2] is intended to maintain the temperature of the preparation solution, which has reached 60°C, above 60°C. Maintaining a temperature above 60°C promotes the dissolution of the metallic silicon nanoparticles and generates alkali silicate. If the addition rate is within the above range, the exothermic reaction associated with the dissolution of metallic silicon fine particles in alkali hydroxide easily raises the temperature of the preparation solution to around 60°C, which is preferable because it facilitates the dissolution of metallic silicon fine particles and the formation of alkali silicate. Here, the temperature of the preparation solution is preferably between 60°C and 90°C. Addition rates below 0.05 g / min·L are undesirable because the exothermic reaction is weak and external heating may be necessary. On the other hand, if the addition rate exceeds 5 g / min·L, the reaction may proceed rapidly while generating hydrogen gas, making it difficult to control and potentially dangerous to operate. Normally, it is preferable to maintain the temperature of the prepared solution between 60°C and 90°C for a period of 4 to 24 hours. Within this range, the formation of alkali silicate proceeds sufficiently. In practical terms, however, it is preferable to end the maintenance of the temperature range after confirming that the hydrogen gas concentration in the prepared solution has fallen to 100 ppm or less. Furthermore, the addition rate range of the silicon microparticle suspension in step [2] is more preferably in the range of 0.1 g / min·L to 4.0 g / min·L, and even more preferably in the range of 0.2 g / min·L to 3.0 g / min·L.

[0050] The alkali silicate aqueous solution obtained in step [2] preferably has a molar ratio of SiO2 / alkali of 1 or more and more preferably 2 or more and more and more than 4. If this molar ratio is within the above range, it is also advantageous in terms of removing metal ions. It is preferable that the molecular weight of the alkali silicate in the alkali silicate aqueous solution obtained in step [2] is 30,000 or less. If the molecular weight of the alkali silicate is within the above range, it is advantageous as the removal of metal components in the subsequent purification step proceeds more easily.

[0051] In step [3], the alkaline silicate aqueous solution obtained in step [2] is subjected to dealkalization and demetallication ion treatment to prepare a purified acidic silicate solution. In this specification, dealkalization and demetallic ion removal treatment refers to a treatment that simultaneously lowers the pH of an alkaline silicate aqueous solution and reduces the amount of metal ions. Typically, dealkalization and demetallic ion removal can be performed by cation exchange treatment. It is preferable to perform the cation exchange treatment two or more times, and chelate ion exchange treatment may also be used in combination. In the first cation exchange treatment, it is preferable to lower the pH value by 7 or more. That is, it is preferable that the difference in pH value before and after the first cation exchange is 7 or more. Lowering the pH by 7 or more is desirable because it allows for sufficient demetallic ion removal, resulting in a purified acidic silicate solution with excellent storage stability.

[0052] Preferably, the purified acidic silicic acid solution has an Al concentration of 20 ppm or less relative to its silica solid content, Ca, Ni, and Na concentrations of 10 ppm or less each, and Mg, Ti, Cr, Fe, Cu, Zn, Ag, and Pb concentrations of 5 ppm or less each. When a silica fine particle dispersion is prepared using a purified acidic silicic acid solution satisfying these conditions as a raw material, the silica fine particles tend to contain many silanol groups, possibly because the metal ion components do not provide a catalytic effect on silicic acid polymerization, and the hardness of the abrasive grains is not particularly high. However, although the details are not clear, perhaps because the thermal reactivity of the silanol groups is high, when such silica fine particles are used as polishing abrasive grains, the aforementioned adhesive wear is more likely to occur at the contact point between the abrasive grains and the workpiece, making it possible to exhibit an excellent polishing speed.

[0053] The purified acidic silicic acid solution preferably has a silica concentration of 1% by mass or more and 6% by mass or less. If the silica concentration is less than 1% by mass, a large amount of purified silicic acid solution needs to be added, which is economically undesirable. On the other hand, if it exceeds 6% by mass, the stability of the acidic silicic acid solution decreases and aggregation may occur, which is undesirable.

[0054] In step [4], a portion of the purified acidic silicic acid solution obtained in step [3] is added to an aqueous alkali hydroxide solution, heated at a temperature of 75°C to 98°C, and maintained at a temperature of 75°C to 98°C for 30 minutes or more. Another portion of the purified acidic silicic acid solution obtained in step [3] is then added at an addition rate of 1 g / min·g to 200 g / min·g, and the temperature of 75°C to 98°C is maintained for 30 minutes to 9 hours. After that, it is cooled to room temperature to obtain a silica nanoparticle precursor dispersion. In this specification, "a portion of the purified acidic silicic acid solution obtained in step [3]" may be referred to as "seed solution," and "another portion of the purified acidic silicic acid solution obtained in step [3]" may be referred to as "feed solution," "first feed solution," "second feed solution," or "third feed solution." In step [4], the concentration of the aqueous alkali hydroxide solution when the purified acidic silica solution is first added to the alkali hydroxide is preferably 0.5% by mass or more and 10% by mass or less. Furthermore, the amount of aqueous alkali hydroxide solution per 100 parts by mass of purified acidic silica solution is preferably 1 part by mass or more and 100 parts by mass or less. If the amount of aqueous alkali hydroxide solution is less than the lower limit, the reaction between the added purified acidic silica solution, the alkali hydroxide, and the silica component in the reaction solution will not proceed sufficiently, which is undesirable. If it exceeds the upper limit, the solubility of the silica contained in the added purified acidic silica solution will be excessive, and it will not be possible to obtain the silica fine particle dispersion of the present invention that ultimately exhibits the desired physical properties, which is undesirable. If the amount of aqueous alkali hydroxide solution is within the above range, the physical properties of the ultimately obtained silica fine particle dispersion can be stably obtained within the desired range. First, the purified acidic silica solution is added to the alkali hydroxide, heated to a temperature between 75°C and 98°C, and held for at least 30 minutes. Then, a portion of the purified acidic silica solution is added at an addition rate of 1 g / min·g to 200 g / min·g. If the heating temperature after adding the purified acidic silicic acid solution to the alkali hydroxide aqueous solution is within the range (75°C to 98°C), the polymerization reaction of the purified acidic silicic acid solution in subsequent steps proceeds stably, which is preferable. If the heating temperature is below the lower limit (75°C), the reaction between the added purified acidic silicic acid solution, alkali hydroxide, and silica components in the reaction solution does not proceed sufficiently, which is undesirable. On the other hand, if the heating temperature exceeds the upper limit (98°C), it becomes difficult to control the reaction between the added purified acidic silicic acid solution, alkali hydroxide, and silica components in the reaction solution, and even after going through the subsequent step [5], it becomes impossible to obtain the silica fine particle dispersion of the present invention that exhibits the predetermined physical properties, which is undesirable. Adding purified acidic silicic acid solution to an aqueous alkali hydroxide solution and holding it for 30 minutes or more after heating is preferable because the reaction between the purified acidic silicic acid solution and the alkali hydroxide proceeds sufficiently, and the physical properties of the resulting silica fine particle dispersion can be stably obtained within the desired range. Holding it for less than 30 minutes is undesirable because the reaction between the purified acidic silicic acid solution and the alkali hydroxide is insufficient. If the rate at which the purified acidic silicic acid solution is added to the aqueous alkali hydroxide solution and the mixture after heating is within the range described above (1 g / min·g or more and 200 g / min·g or less), the reaction between the added purified acidic silicic acid solution, the alkali hydroxide, and the silica component in the reaction solution proceeds sufficiently. Furthermore, the relatively fast rate at which the purified acidic silicic acid solution is added makes it easier to obtain a silica nanoparticle precursor dispersion suitable for obtaining silica nanoparticles with a shape within the range specified by the present invention (short diameter / long diameter ratio in the range of 0.1 or more and less than 0.8) through the subsequent step [5]. If the rate at which the purified acidic silicic acid solution is added is below the lower limit (1 g / min·g), it is difficult to produce silica nanoparticles within the range specified by the present invention (short diameter / long diameter ratio in the range of 0.1 or more and less than 0.8) as silica nanoparticles obtained through step [5], and the addition time of the purified acidic silicic acid solution becomes longer, which is economically undesirable. On the other hand, if the addition rate exceeds the upper limit (200 g / min·g), aggregated particles are likely to occur at the stage of the silica microparticle precursor dispersion obtained in step [4], and the proportion of aggregated particles in the silica microparticles obtained through step [5] also increases, which is undesirable. Regarding the addition rate of the purified acidic silica solution, a range of 1 g / min·g to 150 g / min·g is more preferably recommended, and a range of 2 g / min·g to 100 g / min·g is even more preferably recommended. The unit "g / min·g" for the addition rate represents the rate at which silica solids in the purified acidic silicic acid solution are added relative to the silica solids in the seed solution. Here, the unit "g / min·g" can also be expressed as "g / (min·g)". Following the addition of the purified acidic silicic acid solution at the aforementioned rate, the temperature is further maintained at 75°C to 98°C for 30 minutes to 9 hours, and then cooled to room temperature to obtain a silica microparticle precursor dispersion. By maintaining the temperature at 75°C to 98°C for 30 minutes to 9 hours, a silica microparticle precursor in which the reaction of the silanol group has proceeded sufficiently can be obtained, making it suitable to obtain a silica microparticle dispersion of the predetermined particle size range of the present invention via step [5].

[0055] In step [4], as described above, first the purified acidic silicic acid solution is added to the alkali hydroxide, heated to a temperature of 75°C to 98°C, held for 30 minutes or more, and then a portion of the purified acidic silicic acid solution is added at an addition rate of 1 g / min·g to 200 g / min·g. However, this addition of the purified acidic silicic acid solution may be carried out in multiple steps.

[0056] In step [5], the silica nanoparticle precursor dispersion obtained in step [4] is heated to a temperature of 75°C to 98°C, maintained at a temperature of 75°C to 98°C for 30 minutes or more, and then a portion of the purified acidic silicic acid solution obtained in step [3] is added at an addition rate of 1 g / min·g to 300 g / min·g, and the temperature of 75°C to 98°C is maintained at a temperature of 30 minutes to 9 hours, after which it is cooled to room temperature. In step [5], water may be added to the silica nanoparticle precursor dispersion obtained in step [4] as needed to adjust the silica concentration. Subsequently, the silica nanoparticle precursor dispersion is heated to a temperature of 75°C to 98°C and held for 30 minutes or more, and then a portion of the purified acidic silicic acid solution obtained in step [3] is added at an addition rate of 1 g / min·g to 300 g / min·g. Here, it is preferable that the heating temperature of the silica microparticle precursor dispersion is within the temperature range (75°C to 98°C) because this allows the polymerization reaction of the purified acidic silicic acid solution in the latter half of this process to proceed stably. It is undesirable if the heating temperature of the silica microparticle precursor dispersion is below the lower limit (75°C) because the reaction between the added purified acidic silicic acid solution, alkali hydroxide, and silica components in the reaction solution does not proceed sufficiently. It is undesirable if the heating temperature of the silica microparticle precursor dispersion exceeds the upper limit (98°C) because although the reaction between the added purified acidic silicic acid solution, alkali hydroxide, and silica components in the reaction solution proceeds, it becomes difficult to control, and the generation of coarse particles increases, ultimately making it impossible to obtain the silica microparticle dispersion of the present invention that exhibits the desired physical properties. If the holding time after heating the silica nanoparticle precursor dispersion at 75°C to 98°C is 30 minutes or more, it is preferable because the reaction between the silanol groups of the silica nanoparticle precursor proceeds sufficiently. If the holding time is less than 30 minutes, the reaction between the silanol groups of the silica nanoparticle precursor will be insufficient, and for example, the particle size of the ultimately obtained silica nanoparticles may not reach the range of silica nanoparticles of the present invention, which is undesirable. If the addition rate of the purified acidic silicic acid solution to the silica nanoparticle precursor dispersion is within the range (1 g / min·g or more and 300 g / min·g or less), the reaction between the silanol groups of the silica nanoparticle precursor proceeds sufficiently, which is preferable. If the addition rate is below the lower limit (1 g / min·g), the reaction between the silanol groups of the silica nanoparticle precursor becomes insufficient, and for example, the particle size of the ultimately obtained silica nanoparticles may not reach the range of silica nanoparticles of the present invention, which is undesirable. If the addition rate exceeds the lower limit (300 g / min·g), it is likely to cause the generation of aggregated particles, and the silica fine particle dispersion obtained through step [5] may contain a large amount of coarse particles, which is undesirable. Regarding the rate of addition of the purified acidic silica solution, a range of 1 g / min·g to 200 g / min·g is more preferably recommended, and a range of 5 g / min·g to 200 g / min·g is even more preferably recommended. Furthermore, if the holding time after the addition of the purified acidic silicic acid solution is within the aforementioned range (30 minutes to 9 hours), the silica nanoparticles obtained by the manufacturing method of the present invention can exhibit sufficient polishing performance. This is presumed to be due to the sufficient reaction between the silanol groups present in the silica nanoparticle precursor, resulting in densification.

[0057] Furthermore, in the manufacturing method of the present invention, instead of the seed solution (purified acidic silicic acid solution) used in steps [4] and [5], a silica fine particle dispersion prepared separately in advance by the manufacturing method of the present invention may be used as the seed solution. Also, instead of the feed solution (purified acidic silicic acid solution) used in steps [4] and [5], a silica fine particle dispersion prepared separately in advance by the manufacturing method of the present invention may be used as the feed solution. [Examples]

[0058] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited in any way by these examples. Furthermore, unless otherwise specified, the methods for measuring the various properties of silica fine particles or silica fine particle dispersions in the examples and comparative examples were carried out by the methods described below.

[0059] (1) Average particle diameter of silica nanoparticles measured by dynamic light scattering method As the particle size measuring device (laser particle analyzer), we used the "Zeta Potential / Particle Size Measurement System ELSZ-1000" manufactured by Otsuka Electronics Co., Ltd. (measurement principle: dynamic light scattering method, light source wavelength: 665.70 nm, cell: 10 mm square plastic cell). Specifically, a silica fine particle dispersion was diluted with 0.58% ammonia water to adjust the silica concentration to 1% by mass, and then measured using the laser particle analyzer.

[0060] (2) Short diameter / long diameter ratio and particle size distribution of silica nanoparticles measured by image analysis method 1) Short diameter / long diameter ratio of silica nanoparticles Using a scanning electron microscope (magnification 200,000x), 500 silica microparticles contained in a silica microparticle dispersion were examined. For 100 randomly selected silica microparticles in images or photographs containing 100 or more silica microparticles within the same field of view, their short and long axes were measured. The short axis / long axis ratio (DS / DL) was then calculated for each of the 500 silica microparticles. This process was repeated for 5 randomly selected fields of view. The numerical average of the short axis / long axis ratios for all 500 silica microparticles was then calculated and defined as the short axis / long axis ratio of the silica microparticles. In this specification, a high-resolution field emission scanning electron microscope S-5500 (manufactured by Hitachi High-Technologies Corporation) was used. The specific measurement method for silica nanoparticles involved defining the longest diameter of the projected silica nanoparticle image as the major axis, measuring its length, and defining this value as the major axis (DL). Furthermore, a point was determined that bisects the major axis, and two points where a line perpendicular to these points intersects the outer edge of the silica nanoparticle image were identified. The distance between these two points was measured and defined as the minor axis (DS), and the minor axis / major axis ratio (DS / DL) was calculated.

[0061] 2) Particle size distribution For 500 silica nanoparticles obtained using the short-axis / long-axis ratio measurement method, the arithmetic mean of the short-axis and long-axis of each particle was taken as the average particle diameter of the silica nanoparticles, and the cumulative frequency particle distribution (horizontal axis: particle diameter, vertical axis: cumulative frequency) was calculated. Then, the particle diameters at 10% cumulative frequency (D10), 50% cumulative frequency (D50), and 90% cumulative frequency (D90) were determined, and the value of [(D10+D90) / 2] / D50 was calculated. Furthermore, if the short-axis / long-axis ratio of the silica nanoparticles is 0.9 or higher, the cumulative frequency particle distribution may be determined by scanning an image obtained with a scanning electron microscope (magnification 200,000x) and scanning it, then using an image analysis device and particle analysis software. An example of an image analysis device is the IP-1000 image analysis device (manufactured by Asahi Kasei Corporation).

[0062] (3) Carbon content 30 g of silica microparticle dispersion was dried at 110°C, and 0.1 g of the dried sample was taken. The carbon concentration in the silica microparticles was measured using a carbon-sulfur analyzer (LECO CS-844).

[0063] (4)Solid 29 Si-NMR 29 0.6 mL of silica microparticle dispersion was injected into a Si-NMR glass cell, and a 5 wt% tetramethylsilane deuterated chloroform solution was used as the reference material, with the peak position set to 0 ppm. An NMR spectrometer (JEOL Ltd., ECZ-400R) was used, employing the reverse-gate decoupling method. 29 Si-NMR spectra were obtained. The pulse flip angle was 30°, the pulse repetition time was 10 seconds, and the number of integrations was 5000. The total area (ST) of peaks in the chemical shift range of -73.0 ppm to -120.0 ppm of the obtained NMR spectrum was defined as the peak area of ​​the siloxane structure (Q0 structure to Q4 structure), the peak area in the chemical shift range of -110.0 ppm to -120.0 ppm was defined as the peak area of ​​the Q4 structure (S4), and the peak area in the chemical shift range of -100.0 ppm to -110.0 ppm was defined as the peak area of ​​the Q3 structure (S3). The peak areas of the Q4 structure (S4 / ST) and the peak areas of the Q3 structure (S3 / ST) were then calculated. Finally, the peak area ratio of the two structures (Q4 / Q3) was calculated.

[0064] (5) FT-IR measurement using vacuum heating transmission method The measurement device used was a JASCO FT / IR-6100. The measurement sample consisted of a 20 mg silica fine particle dispersion dried at 110°C for over 12 hours, which was then molded into a disc. The disc was placed in a transmission cell and subjected to vacuum heating at the target temperature using a vacuum pretreatment device. After heating, the cell was allowed to cool to room temperature and sealed. The cell was then measured using the transmission method with the aforementioned measurement device. The measurement conditions were a TGS detector with 100 integration cycles and a resolution of 4 cm. -1 The aperture was set to 5 mm. For data processing, Spectrum Manager was used as the analysis software, and baseline correction and 1870 cm⁻¹ were performed. -1 (1100cm -1 Normalization was performed using the harmonics of the siloxane peak.

[0065] (6)Component analysis The content of each element shall be measured by the following method. (Measurement of SiO2 content) Regarding the SiO2 content in silica microparticle dispersions, when sodium silicate was used as the raw material, the silica microparticle dispersion was subjected to loss on heat at 1000°C and weighed. The content was then determined by assuming that all of the obtained material was SiO2. (Measurement of Na and K content) First, take approximately 1 g of the sample (adjusted to 20% solid content by mass) consisting of silica fine particle dispersion into a platinum dish. Add 3 mL of phosphoric acid, 5 mL of nitric acid, and 10 mL of hydrofluoric acid, and heat on a sand bath. Once dry, add a small amount of water and 50 mL of nitric acid to dissolve, transfer to a 100 mL volumetric flask, and add water to make a total volume of 100 mL. In this solution, the Na and K content is measured using an atomic absorption spectrometer (e.g., Hitachi Z-2310). (Measurement of Cr, Cu, Ni, Fe, etc. content) The procedure of taking 10 mL of the separatory solution from a 100 mL volumetric solution and transferring it to a 20 mL volumetric flask is repeated five times to obtain five 10 mL separatory samples. These samples are then used to measure Al, Ag, Ca, Cr, Cu, Fe, Mg, Ni, Ti, Zn, U, and Th using an ICP plasma emission spectrometer (e.g., SII SPS5520) with the standard addition method. A blank sample is also measured in the same manner, and the results are adjusted by subtracting the blank sample to obtain the measured values ​​for each element. Then, based on the mass of SiO2 obtained by the method described above, the content of each component relative to the amount of silica was determined.

[0066] (7) Polishing test method (Preparation of abrasive dispersion) The silica fine particle dispersions obtained in each of the examples and comparative examples were diluted with deionized water to adjust the solid content concentration to 1.0% by mass. Then, a 5% aqueous nitric acid solution was added to adjust the pH to 6.0 to prepare abrasive particle dispersions. (Polishing test method) A SiO2 insulating film substrate (1 μm thick) fabricated by thermal oxidation was prepared as the substrate to be polished. This substrate was set in a polishing device (NF300, manufactured by Nanofactor Co., Ltd.), and polishing was performed using a polishing pad (IC-1000 / SUBA400 concentric type, manufactured by Nitta Haas Co., Ltd.) with a substrate load of 0.04 MPa and a table rotation speed of 90 rpm, by supplying abrasive dispersion liquid at a rate of 200 mL / min for 1 minute. The polishing rate (nm / min) was calculated by determining the weight change of the substrate before and after polishing. Furthermore, the surface smoothness (surface roughness [Ra]) of the polished substrate was measured using an atomic force microscope (AFM, Hitachi High-Tech Science Corporation). Since smoothness and surface roughness are generally proportional, the surface roughness is listed in Table 1.

[0067] [Example 1] Sodium hydroxide (48% by mass) was added to ultrapure water to obtain 1276 g of a 19% by mass sodium hydroxide aqueous solution (hereinafter referred to as Solution A). Next, metallic silicon powder (average particle size = 0.08 μm) was added to ultrapure water and stirred to disperse it, thereby obtaining 2728 g of silicon fine particle suspension with a silicon solid content of 25% by mass (hereinafter also referred to as solution B). Next, while stirring solution A, and while blowing nitrogen gas into the reaction vessel at 10 L / min, solution B was added at room temperature for 0.5 hours at an addition rate of 1.2 g / min·L for the first stage of silicon nanoparticle suspension addition. During this time, the reaction heat from the dissolution of metallic silicon by sodium hydroxide caused the liquid temperature to rise, and when it reached 60°C, the addition rate of the silicon nanoparticle suspension for the second stage of addition was changed to 0.4 g / min·L and added for 5.5 hours. After the addition of solution B was completed, an external heat source was used to maintain the liquid temperature at 60°C for 8 hours, and the maintenance at 60°C was terminated after confirming that the hydrogen gas concentration in the reaction vessel was below 100 ppm. Next, the solution was cooled to room temperature to obtain 5949 g of an alkali silicate solution with a solid SiO2 content of 24.1% by mass. The SiO2 / alkali (molar ratio) of this alkali silicate was 3.03, and its molecular weight was 227. Here, the average molecular weight is the value obtained by filtering a high-purity alkali silicate solution using a Millipore 0.22 μm filter MILLEX-GV, filling it into a plastic cell, measuring it in auto mode using a nanoSAQLA manufactured by Otsuka Electronics, and converting the resulting average particle size to the average molecular weight according to the calculation formula below. Average molecular weight={22×π×(average particle diameter) 3} / 6 The above calculations were performed using the formula described on page 68 of "The Science of New Industrial Materials B Series 8: Silica and Alumina" published by Kinbara Publishing. The average molecular weight in the following examples and comparative examples was calculated in the same manner as in Example 1.

[0068] (Preparation of purified acidic silica solution) Ultrapure water was added to the alkali silicate solution obtained as described above to obtain 12,020 g of alkali silicate solution with an SiO2 concentration of 5%. This solution was then poured into 6 L of strongly acidic cation exchange resin (Duolite C255LFH, manufactured by Rohm & Haas) at a space velocity of 2.75 h. -1The solution was passed through a siphon to obtain 11,280 g of acidic silicic acid solution with a pH of 2.7. The SiO2 concentration of the obtained acidic silicic acid solution was 4.7% by mass. Next, the entire volume of the acidic silica solution is transferred to 6 L of chelate ion exchange resin (CR-11, manufactured by Mitsubishi Chemical Corporation) at a space velocity of 2.75 h. -1 The solution was passed through a filter to obtain 9,660 g of purified acidic silicic acid solution with a pH of 2.7. The SiO2 concentration of the obtained purified silicic acid solution was 4.5% by mass. Furthermore, the entire volume of the purified acidic silica solution is transferred to a separate 6L of strongly acidic cation exchange resin (Duolite C255LFH, manufactured by Rohm & Haas) at a space velocity of 2.75h. -1 The solution was passed through a filter to obtain 8,720 g of purified acidic silicic acid solution with a pH of 2.7. The SiO2 concentration of the obtained purified acidic silicic acid solution was 4.2% by mass.

[0069] (Preparation of silica microparticle dispersion) As described above, 14.51 kg of the purified acidic silica solution was taken as the seed solution, another 20.91 kg of the purified acidic silica solution was taken as the first feed solution, and another 143.42 kg of the purified acidic silica solution was taken as the second feed solution. Next, 1.238 kg of 48% by mass potassium hydroxide aqueous solution was added to 1.624 kg of ultrapure water, and then 14.51 kg of the seed solution was added and heated. After reaching 75°C, the temperature was maintained for 30 minutes, and while maintaining this temperature, 20.91 kg of the first feed solution was added at an addition rate of 70 g / min·g over 5 hours. The temperature was then raised to 98°C, maintained at this temperature for 7 hours, and then cooled to room temperature to obtain a silica nanoparticle precursor dispersion. To 16.5 kg of the obtained silica nanoparticle precursor dispersion, 0.865 kg of ultrapure water was added and heated. After reaching 98°C, the temperature was maintained for 120 minutes. While maintaining this temperature, 143.42 kg of the second feed solution was added at an addition rate of 159.4 g / min·g over 15 hours, and then the temperature was maintained for 1 hour before cooling to room temperature. The obtained solution was concentrated to 12% by mass using an ultrafiltration membrane (SIP-1013, manufactured by Asahi Kasei Chemicals), and then concentrated to 40% by mass using a rotary evaporator. The concentration of metal impurities in the obtained silica fine particle dispersion was then measured using the method described above, and the concentrations of each metal impurity relative to the silica solid content are shown in Table 1. The conditions used in the preparation of the silica fine particle dispersion in Example 1 are shown in Table 2.

[0070] [Example 2] 9.15 kg of the purified acidic silicic acid solution obtained in Example 1 was taken as the seed solution, 13.19 kg of another portion of the purified acidic silicic acid solution was taken as the first feed solution, 7.91 kg of another portion of the purified acidic silicic acid solution was taken as the second feed solution, and 122.21 kg of another portion of the purified acidic silicic acid solution was taken as the third feed solution. Next, 0.788 kg of 48% by mass potassium hydroxide aqueous solution was added to 1.114 kg of ultrapure water, and then 9.15 kg of the seed solution was added and heated. After reaching 75°C, the temperature was maintained for 30 minutes, and while maintaining this temperature, 13.19 kg of the first feed solution was added at an addition rate of 44 g / min·g over 5 hours. The temperature was further raised to 98°C and maintained at this temperature for 4 hours, and then, while maintaining this temperature, 7.91 kg of the second feed solution was added at an addition rate of 44 g / min·g over 3 hours. After maintaining this temperature for 1 hour, the mixture was cooled to room temperature to obtain a silica nanoparticle precursor dispersion. To 18 kg of the obtained silica nanoparticle precursor dispersion, 22.21 kg of ultrapure water was added and heated. After reaching 98°C, the temperature was maintained for 60 minutes, and while maintaining this temperature, 122.21 kg of the third feed solution was added at an addition rate of 113.2 g / min·g. After adding the silica over an 18-hour period, the mixture was held at the specified temperature for 1 hour and then cooled to room temperature to obtain a silica nanoparticle dispersion. The obtained solution was concentrated to 12% by mass using an ultrafiltration membrane (SIP-1013, manufactured by Asahi Kasei Chemicals), and then concentrated to 40% by mass using a rotary evaporator. The resulting silica fine particle dispersion was then analyzed in the same manner as in Example 1. The conditions used in the preparation of the silica microparticle dispersion in Example 2 are shown in Table 2.

[0071] [Example 3] In Example 1, 4.67 kg of purified acidic silicic acid solution similar to that used as the seed solution was prepared, 2.61 kg of purified acidic silicic acid solution similar to that used as the first feed solution was prepared, and 7.31 kg of purified acidic silicic acid solution similar to that used as the second feed solution was prepared. Next, 0.161 kg of a 48% by mass potassium hydroxide aqueous solution was added to 0.698 kg of ultrapure water, and then 4.67 kg of seed solution was added and the mixture was heated. After reaching 90°C, the mixture was held at that temperature for 2 hours. While maintaining this temperature, 2.61 kg of the first feed solution was added at an addition rate of 3.6 g / min·g over 12 hours, and then the mixture was further heated to 90°C, held at that temperature for 30 minutes, and then cooled to room temperature to obtain a silica nanoparticle precursor dispersion. To 1.32 kg of the obtained silica nanoparticle precursor dispersion, 1.429 kg of ultrapure water was added and heated. After reaching 98°C, the temperature was maintained for 1 hour. While maintaining this temperature, 7.31 kg of the second feed solution was added at an addition rate of 6.77 g / min·g over 18 hours, and the temperature was maintained for 1 hour before cooling to room temperature. The obtained solution was concentrated to 12% by mass using an ultrafiltration membrane (SIP-1013, manufactured by Asahi Kasei Chemicals), and then concentrated to 40% by mass using a rotary evaporator. The resulting silica fine particle dispersion was then analyzed in the same manner as in Example 1. The conditions used in the preparation of the silica microparticle dispersion in Example 3 are shown in Table 2.

[0072] [Comparative Example 1] A portion of the purified acidic silica solution obtained as described above (318g) was taken out as the seed solution, and another portion of the purified acidic silica solution (8,070g) was taken out as the feed solution. Next, 15 g of 48.8% by mass potassium hydroxide aqueous solution was added to 524 g of ultrapure water, and then 318 g of seed solution was added and heated. After reaching 83°C, the temperature was maintained for 30 minutes. While maintaining this temperature, 1145 g of purified acidic silicic acid solution was added as feed solution at an addition rate of 0.02 g / min·g over 3 hours. Then, the addition rate was increased by 1.5 times, and another 6869 g of purified acidic silicic acid solution was added as feed solution over 12 hours. After adding the entire amount of feed solution to the seed solution, the temperature was maintained at 83°C for 1 hour and then cooled to room temperature. The obtained solution was concentrated to 12% by mass using an ultrafiltration membrane (SIP-1013, manufactured by Asahi Kasei Chemicals), and then concentrated to 48% by mass using a rotary evaporator. [Comparative Example 2] 3581g of pure water was placed in a 10L autoclave container and stirred while 29.5g of sodium hydroxide aqueous solution (48% by mass) was added as a molar ratio adjuster. Next, sodium silicate cullet, crushed to a size of a few centimeters or less, was added to adjust the molar ratio to (SiO2 / Na2O) = 3.19. Subsequently, the temperature was raised to 151°C and held for 3 hours to dissolve. After cooling to below 40°C, the resulting water glass was filtered through quantitative filter paper (No. 5A, particle retention capacity 7μm) to obtain 5240g of alkali silicate solution with an SiO2 solid content concentration of 24.4% by mass. Then, silica sol was prepared using the obtained alkali silicate solution. The molecular weight of this alkali silicate was 16,184. (Preparation of acidic silica solution) Ultrapure water was added to the alkali silicate solution obtained as described above to obtain 12,020 g of a high-purity alkali silicate solution with an SiO2 concentration of 5%. This solution was then poured into 6 L of a strongly acidic cation exchange resin (Duolite C255LFH, manufactured by Rohm & Haas) at a space velocity of 2.75 h. -1 The solution was passed through a siphon to obtain 11,120 g of acidic silicic acid solution with a pH of 2.6. The SiO2 concentration of the obtained acidic silicic acid solution was 4.6% by mass. (Preparation of silica sol) The procedure was carried out in the same manner as in Comparative Example 1, except that the purified acidic silicic acid solution in Example 1 was replaced with the acidic silicic acid solution obtained as described above, and the addition rate was set to 0.11 g / min·g.

[0073] [Comparative Example 3] 12,090 g of ethanol and 6,363.9 g of orthosilicate were mixed to make mixture a1. Next, 6,120 g of ultrapure water and 444.9 g of 29% aqueous ammonia were mixed to form mixture b1. Next, 192.9g of ultrapure water and 444.9g of ethanol were mixed together to form the substrate. The substrate water was then stirred and adjusted to 75°C. Mixture a1 and mixture b1 were added simultaneously, with each being added over a period of 10 hours. After the addition was complete, the liquid temperature was maintained at 75°C for 3 hours to allow it to mature. The solid content concentration was then adjusted to obtain 9,646.3 g of silica sol with an SiO2 solid content concentration of 19% by mass.

[0074] [Results of various measurements] Table 1 shows the results of various measurements in the examples and comparative examples.

[0075] [Table 1]

[0076] [Table 2]

Claims

1. Abrasive dispersion liquid for polishing, comprising silica fine particles that satisfy all of the following requirements [1] to [5] dispersed in a dispersion medium. [1] The average particle diameter measured by dynamic light scattering is between 5 nm and 500 nm. [2] The minor axis / major axis ratio measured by image analysis is 0.1 or greater and less than 0.

8. [3] The carbon content is less than 150 ppm based on the silica content. [4] Solid ２９ The peak area derived from Si(OSi) in the Si-NMR spectrum ４ is defined as Q ４ and the peak area derived from HO-Si(OSi) ３ is defined as Q ３ When this is done, the peak area ratio of Q ４ / Q ３ is 1 or more and 30 or less. (However, the chemical shift is based on tetramethylsilane as a reference substance, Q ４ is a peak in the range of -110 ppm to -120 ppm, and Q ３ is a peak in the range of -100 ppm to -110 ppm.) [5] FT-IR measurement at 300°C using vacuum heating transmission method, 3740 cm －１ Nearby peak P1 ３００ Toshi, 3660cm －１ Nearby peak is P2 ３００ Furthermore, in FT-IR measurements at 110°C, 3740 cm⁻¹ －１ Nearby peak P1 １１０ Toshi, 3660cm －１ Nearby peak is P2 １１０ In that case, P1 ３００ / P2 ３００ From the peak ratio value, P1 １１０ / P2 １１０ The value obtained by subtracting the peak ratio value [(P1 ３００ / P2 ３００ ) - (P1 １１０ / P2 １１０ The value of ) must be between 0.20 and 1.

2. The abrasive dispersion liquid for polishing according to claim 1, wherein, in the particle size distribution obtained by image analysis, the particle size at a cumulative frequency of 10% is defined as D10, the particle size at a cumulative frequency of 50% is defined as D50, and the particle size at a cumulative frequency of 90% is defined as D90, the condition expressed by the following formula (F1) is satisfied. 1.0≦[(D10+D90) / 2] / D50≦1.4...(F1)

3. The abrasive dispersion according to claim 1 or claim 2, wherein the Al concentration in the silica solid content of the abrasive dispersion is 20 ppm or less, the Ca, Ni, and Na concentrations are each 10 ppm or less, and the Mg, Ti, Cr, Fe, Cu, Zn, Ag, and Pb concentrations are each 5 ppm or less.

4. A polishing abrasive dispersion according to claim 3, for use in polishing semiconductors.

5. A method for polishing a semiconductor, comprising the step of polishing the semiconductor using the polishing abrasive dispersion described in claim 4.

6. A method for producing an abrasive dispersion according to claim 1, comprising the following steps [1] to [5]. Step [1] A step of preparing a compound solution by adding a suspension of silicon fine particles to an aqueous alkali hydroxide solution at an addition rate of 0.05 g / min·L or more and 5 g / min·L or less. Step [2] As soon as the temperature of the preparation liquid obtained in Step [1] reaches 60°C due to the dissolution reaction of silicon nanoparticles, a further silicon nanoparticle suspension is added to the preparation liquid at an addition rate of 0.05 g / min·L to 5 g / min·L, and then the liquid is held at a temperature of 60°C to 90°C for a period of 4 hours to 24 hours to obtain an alkali silicate solution. Step [3] A step to obtain a purified acidic silica solution by dealkalizing and demetallic ionizing the alkali silica solution obtained in step [2]. Step [4] A portion of the purified acidic silicic acid solution obtained in step [3] is added to an aqueous alkali hydroxide solution, heated at a temperature of 75°C to 98°C, maintained at a temperature of 75°C to 98°C for 30 minutes or more, and then a portion of the purified acidic silicic acid solution obtained in step [3] is added at an addition rate of 1 g / min·g to 200 g / min·g, and the temperature of 75°C to 98°C is maintained for 30 minutes to 9 hours, after which it is cooled to room temperature to obtain a silica nanoparticle precursor dispersion. Step [5]: The silica nanoparticle precursor dispersion obtained in Step [4] is heated to a temperature of 75°C to 98°C, maintained at a temperature of 75°C to 98°C for 30 minutes or more, and then a portion of the purified acidic silicic acid solution obtained in Step [3] is added at an addition rate of 1 g / min·g to 300 g / min·g, and the temperature of 75°C to 98°C is maintained at a temperature of 30 minutes to 9 hours, after which it is cooled to room temperature.

7. The method for producing an abrasive dispersion according to claim 6, wherein the dealkalization and demetallic ion treatment in step [3] includes at least two cation exchanges, and the difference in pH value before and after the first cation exchange is 7 or more.

8. A method for producing an abrasive dispersion for polishing according to claim 6, wherein the Al concentration relative to the silica solid content of the purified acidic silicic acid solution obtained in step [3] is 20 ppm or less, the Ca, Ni, and Na concentrations are each 10 ppm or less, and the Mg, Ti, Cr, Fe, Cu, Zn, Ag, and Pb concentrations are each 5 ppm or less.

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