Silica particle dispersion liquid and production method thereof

Abstract

The silica particle dispersion contains silica particles that satisfy the requirements of (i) to (iii) below. (i) The average particle diameter (d) is 5 to 300 nm. (ii) The amount of basic substance absorbed per 1 g of particle is 2 mg or more. (iii) The Sears number (Y) exceeds 12.0.

Description

Technology Field

[0001] One aspect of the present disclosure relates to a silica particle dispersion and a method for preparing the same.

[0002] This application claims priority based on Japanese Patent Application No. 2019-180613 filed with the Japan Patent Office on September 30, 2019, the entire contents of which are incorporated herein by reference. Background Technology

[0003] A silica particle dispersion is useful for polishing substrates of metal wiring layers in semiconductor integrated circuits and silicon substrates. Conventionally, when obtaining a dispersion containing silica particles for polishing, which is a silica particle dispersion, the particles are densified and the entire particle is hardened in order to improve the physical polishing performance (mechanical polishing performance) of the particles (for example, see WO2008 / 123373, WO2010 / 035613, Japanese Patent Publication No. 2011-201719, Japanese Patent Publication No. 2012-211080, and Japanese Patent Publication No. 2013-082584).

[0004] However, it has been difficult to simultaneously achieve the formation of a good polished surface (improvement of surface smoothness and reduction of defects). Therefore, for many years, it has been required to reconcile the two objectives that are in this trade-off relationship. The problem to be solved

[0005] One objective of the present disclosure is to provide a silica particle dispersion as described below. With this silica particle dispersion, it is possible to maintain a predetermined polishing speed, improve the surface smoothness (surface quality) of a polished substrate, and reduce defects. means of solving the problem

[0006] As mentioned above, it was believed that improving the physical polishing performance of the particles was effective in order to improve the polishing speed.

[0007] Meanwhile, in the polishing of silica substrates and the like, along with the physical polishing action caused by the hardening of particles as described above, the chemical polishing action caused by the etching of basic substances incorporated in the polishing composition also contributes. However, incorporating a large amount of basic substances into the polishing composition (polishing liquid) resulted in over-etching, where the entire substrate was etched, causing the surface of the polished surface to become uneven. Consequently, since the amount of basic substances incorporated was inevitably limited, the polishing effect due to the chemical polishing action was limited.

[0008] The inventors of the present invention moved beyond the general concept that physical polishing action of particles is effective for realizing high polishing speeds and focused on improving polishing ability through chemical polishing, which had been limited in the past. As a result, they discovered that it is effective to make the particle structure of silica particles, which are polishing particles, such as a particle structure that maintains a sufficient amount of basic material while effectively expelling this basic material out of the particle during polishing. That is, by making the particle structure of the silica particles such as this, a high concentration of basic material is directly applied to the polished part from the silica particles during polishing. This allows for the improvement of chemical polishing action. Furthermore, in these silica particles, the particles themselves are relatively flexible, and unnecessary etching in parts other than the polished part in contact with the particles is suppressed. Accordingly, the formation of a good polished surface (improvement of surface smoothness and reduction of defects) can be realized simultaneously with maintaining a predetermined polishing speed.

[0009] In addition, silica particles having a predetermined OH group (silanol group) on their surface can be aggregated by optimizing the interaction between the silica particles and the water-soluble polymer. These aggregates are appropriately larger than the silica particles. Therefore, high polishing speeds can be achieved with silica particle aggregates. On the other hand, the bonding force between the particles in these aggregates is relatively weak. Therefore, if a strong force is applied to the aggregates during polishing, the aggregates easily collapse. From this, it is possible to ensure smoothness on the polishing substrate and suppress the occurrence of defects with silica particle aggregates.

[0010] The silica particle dispersion contains silica particles that satisfy the requirements of (i) to (iii) below. (i) The average particle diameter (d) is 5 to 300 nm. (ii) The amount of basic substance absorbed per 1 g of particle is 2 mg or more. (iii) The Sears number (Y) exceeds 12.0.

[0011] That is, one aspect of the present disclosure relates to a dispersion of silica particles. The silica particles included in the dispersion satisfy the requirements of (i) to (iii) below.

[0012] (i) The average particle diameter (d) is 5 to 300 nm.

[0013] (ii) The amount of basic substance absorbed per 1g of particle is 2mg or more.

[0014] (iii) The number of Sears (Y) exceeds 12.0.

[0015] In addition, one aspect of the present disclosure relates to a method for preparing a dispersion of silica particles. This method comprises the steps of: preparing a silica particle dispersion containing silica particles having an average particle diameter (d) of 5 to 300 nm by hydrolyzing and polycondensing an alkoxysilane in the presence of water, an organic solvent, and an alkali catalyst; replacing the organic solvent in the silica particle dispersion with water; heating the silica particle dispersion obtained by replacing with water at a pH of 7 or higher under atmospheric pressure to avoid the Sears number (Y) of the silica particles becoming 12.0 or lower; and concentrating the dispersion obtained by heating to a pH of less than 7. Effects of the invention

[0016] According to a silica particle dispersion in one embodiment of the present disclosure, it is possible to achieve the formation of a good polished surface (improvement of surface smoothness and reduction of defects) while maintaining a predetermined polishing speed. Brief explanation of the drawing

[0017] FIG. 1 is a drawing illustrating a method for calculating the average particle diameter in one embodiment of the present disclosure. The black painted part in FIG. 1 is an image of a particle-to-particle bonding part, and the bonding part may include a space. Figure 2 shows the particle growth curves in the dispersion preparation process. In the leftmost curve of this figure, a' = 29, and in the rightmost curve, a' = 9. Specific details for implementing the invention

[0018] In the following detailed description, many details are specifically described to provide an overall understanding of the disclosed embodiments. However, it is evident that one or more embodiments may be implemented without these specific details. In other examples, well-known structures and devices are schematically depicted to simplify the drawings.

[0019] [Silica particle dispersion]

[0020] A silica particle dispersion according to one embodiment of the present disclosure has silica particles included therein that satisfy the requirements of (i) to (iii) below.

[0021] (i) The average particle diameter (d) is 5 to 300 nm.

[0022] (ii) The amount of basic substance absorbed per 1g of particle is 2mg or more.

[0023] (iii) The number of Sears (Y) exceeds 12.0.

[0024] The average particle diameter (d) of the silica particles is 5 to 300 nm. This average particle diameter (d) is obtained by taking electron microscope images of the silica particles, measuring the longest diameter of the primary particle diameter of each particle for any 100 particles, as exemplified in FIG. 1, and obtaining the average of the longest diameters as a result of the measurement.

[0025] If the average particle diameter (d) of the silica particles is less than 5 nm, the stability of the dispersion becomes insufficient. In addition, in this case, since the primary particle diameter is too small, the polishing speed of the silica particles as a polishing composition also becomes insufficient. Conversely, if the average particle diameter (d) exceeds 300 nm, scratches occur on the polishing substrate, so the desired smoothness may not be obtained. The average particle diameter (d) is preferably 5 to 100 nm, more preferably 10 to 80 nm, even more preferably 20 to 60 nm, particularly preferably 25 to 55 nm, and most preferably 30 to 50 nm.

[0026] Silica particles have pores that absorb basic substances. That is, silica particles have a structure in which the pores on the particle surface and the pores inside the particle are in communication. In these silica particles, the saturated absorption amount of basic substances per gram of particle is 2 mg or more, and it is preferable that it be 2.5 mg or more. There is no specific upper limit, but for example, it is 5.0 mg. Particles with a saturated absorption amount of basic substances exceeding 5.0 mg per gram of particle are too flexible and may be unsuitable as abrasive particles.

[0027] In this way, by providing silica particles with pores that absorb basic substances (a saturated absorption capacity of 2 mg or more of basic substance per 1 g of particle), the absorbed basic substance is expelled from the particle during polishing. Consequently, a high concentration of basic substance is directly applied to the polished area. As a result, chemical polishing is effectively promoted. Basic compounds present on the surface of the particles contribute significantly to chemical polishing. Furthermore, basic substances retained inside the particles are also extruded by a pumping action caused by the pressure between the substrate and the polishing pad, thereby contributing to chemical polishing. Moreover, since these silica particles have numerous pores, they are relatively flexible. Additionally, because the excessive mixing of basic substances into the polishing composition is suppressed, unnecessary etching in areas other than the polished area is suppressed. Thus, the formation of a good polished surface (improvement of surface smoothness and reduction of defects) can be achieved simultaneously with the realization of a predetermined polishing speed.

[0028] The amount of basic substance absorbed per 1g of these silica particles (hereinafter simply referred to as “particles”) refers to the amount absorbed in a dispersion with a silica concentration of 9 mass% and a pH of 9 (equilibrium state), and specifically, it is determined as follows. On the other hand, if a large amount of basic substance is added, measurement becomes difficult because the silica particles dissolve. Therefore, in this embodiment, the following measurement method is used.

[0029] A slurry with a silica concentration of 9 mass% and a pH of 9 is prepared by adding water and water ammonia to an aqueous dispersion of silica particles (silica concentration 20 mass%, pH 6-8). After the addition of ammonia, it takes time for the pH to stabilize. For this reason, preparation is carried out over one day. The silica particles in the slurry are centrifuged. Afterward, the amount of the slurry (before centrifugation) and the amount of supernatant ammonia are quantified. The difference between these amounts is obtained as the amount of ammonia adsorbed to the particles.

[0030] Examples of basic compounds include ammonia, amines, alkali metal hydrides, alkaline earth metal hydrides, alkali metal hydroxides, alkaline earth metal hydroxides, quaternary ammonium compounds, and amine-based coupling agents. Among these, ammonia is preferred because it improves polishing performance, such as the smoothness of the substrate, is easy to clean during polishing, and is difficult to leave on the substrate. These basic compounds can be used alone or in combination.

[0031] The Sears number (Y) of the silica particles is a value exceeding 12.0. Here, the Sears number is an indicator representing the amount of OH groups (silanol groups) in the silica particles. If the Sears number (Y) exceeds 12.0, the amount of OH groups present in the particles increases. Consequently, more basic substances can be adsorbed onto the particle surface. Therefore, a Sears number (Y) exceeding 12.0 can improve the chemical polishing performance of the silica particles. Furthermore, by optimizing the interaction between the OH groups on the surface of these silica particles and the water-soluble polymers blended into the polishing composition, the silica particles can be formed into aggregates suitable for polishing. These aggregates are appropriately larger than the silica particles. For this reason, high polishing speeds can be achieved using silica particle aggregates. On the other hand, the bonding force between the particles in these aggregates is relatively weak. Consequently, if a strong force is applied to the aggregates during polishing, the aggregates easily collapse. For this reason, the aggregate of silica particles makes it possible to ensure smoothness in the polished substrate and suppress the occurrence of defects.

[0032] Here, the Sears number (Y) of the silica particles is preferably greater than 12.0 and less than or equal to 20.0, more preferably greater than 12.0 and less than or equal to 18.0, and even more preferably greater than 12.0 and less than or equal to 16.0. When the Sears number (Y) is within this range, the polishing speed can be further improved. That is, silica particles having such a Sears number (Y) possess a certain degree of hardness. For this reason, these silica particles can ensure physical polishing performance and support a greater amount of basic material on their surface. For this reason, these silica particles can ensure higher chemical polishing performance. On the other hand, the silica particles of the present embodiment, in which the Sears number (Y) exceeds 20, are relatively flexible particles and act favorably for the formation of a good polished surface rather than for improving the polishing speed. Therefore, the silica particles of the present embodiment are useful for finishing polishing.

[0033] The Sears number (Y) is measured by titration with sodium hydroxide, following the description in Analytical Chemistry 28 (1956), 12, 1981-1983 by Sears. By this measurement method, the amount of OH groups on the particle surface (outside the pores) is measured.

[0034] Specifically, 30g of sodium chloride is added to 150g of a silica particle dispersion diluted with pure water so that the silica particle concentration is 1 mass%, and the pH is adjusted to 4.0 by additionally adding hydrochloric acid. Then, a 0.1N aqueous sodium hydroxide solution is titrated into the silica particle dispersion at a rate of 0.1 ml / s. The Sears number (Y) is represented as the titration amount of aqueous sodium hydroxide solution required until the pH of the silica particle dispersion reaches 9.0.

[0035] That is, the Sears number (Y) is the titration amount of 0.1N NaOH aqueous solution required for 1.5g of silica. This Sears number (Y) can be said to take into account the behavior of the entire silica particle included in the polishing composition.

[0036] In addition, it is preferable that the density (ρ) of the silica particles be 1.00 g / cm³ or less. Since the density (ρ) of the silica particles is 1.00 g / cm³ or less, sufficient pores are formed inside the particles. Therefore, the particles can retain the desired basic compound. It is more preferable that the density (ρ) be 0.6 g / cm³ or less. The lower limit is preferably about 0.1 g / cm³, taking into account the polishing effect (strength of the particles).

[0037] Here, density (ρ) is calculated from the volume derived from the average particle diameter (d) obtained from the electron microscope image and the specific surface area (SA) based on the Sears number (Y).

[0038] The specific surface area (SA) based on the Sears number (Y) is calculated by the following Equation 1, following the description in Analytical Chemistry 28 (1956), 12, 1981-1983 by Sears.

[0039] SA = 32 * (Sears number) - 25 [Equation 1]

[0040] In addition, it is preferable that the sphericity of the silica particles be 0.80 to 1.00. The more spherical or closer the shape of the silica particles is to a perfect sphere, the smoothness of the polished surface is improved, which can suppress the occurrence of defects. For this reason, it is more preferable that the sphericity be 0.90 to 1.00, and particularly preferable that it be 1.00.

[0041] The sphericity of silica particles is obtained as follows. First, electron microscope images of silica particles are taken. Next, for any 100 particles, the ratio (DS / DL) of the maximum diameter (DL) and the minor diameter (DS) orthogonal to it is determined. In addition, the average value of the ratio (DS / DL) is calculated and obtained as the sphericity. Meanwhile, the sphericity of silica particles is calculated from unconnected particles.

[0042] It is preferable that the coefficient of variation (CV value) of the particle diameter of the silica particles be 10% or less. If the CV value exceeds 10%, scratches may occur on the polished substrate, and thus the desired smoothness may not be obtained. In the silica particles of the polishing composition, if the particle diameter is uniform, it is possible to improve the smoothness of the polished surface and suppress the occurrence of defects. For this reason, it is preferable that the CV value be 8% or less, and more preferable that it be 6% or less.

[0043] The dispersion according to the present embodiment may include connecting particles in which two or more silica particles are connected. In particular, it is preferable that the connecting particles in which two silica particles are connected constitute at least 10% of the total number of silica particles, as they are expected to have only a small effect on the surface of the polishing substrate while increasing the polishing speed. When the aggregates of these two connecting particles collapse during polishing, they tend to be arranged horizontally so that the connecting particles come into contact with the polishing substrate. For this reason, it is difficult for defects to occur on the polishing substrate, and since the contact area with the polishing substrate increases, the polishing speed is improved. It is more preferable that the content ratio of these two connecting particles be at least 20%.

[0044] The content ratio of connected particles is obtained as follows. First, electron microscope images of silica particles are taken. Next, for any 100 particles, the presence or absence of connection is checked, and the particles are divided into unconnected particles, connected particles with two connections, and connected particles with three or more connections, the number of each is counted, and the ratio to the total number of particles for each is calculated.

[0045] In addition, regarding the silica particles, it is preferable that the respective contents of alkali metals, alkaline earth metals, Fe, Ti, Zn, Pd, Ag, Mn, Co, Mo, Sn, Al, and Zr are less than 0.1 ppm, the respective contents of Cu, Ni, and Cr are less than 1 ppb, and the respective contents of U and Th are less than 0.3 ppb. These metal elements are impurities and it is preferable that they are not included in the dispersion solution. If an abrasive containing a dispersion solution with more of these elements than the amounts described above is used, the elements may remain on the substrate. In this case, an increase in the impedance of the metal wiring, a delay in response speed, and an increase in power consumption may occur. Furthermore, since these element ions migrate (diffuse), problems as described above may occur when usage conditions are harsh or when usage is prolonged. In particular, since U and Th generate radiation, there is a possibility that even trace amounts remaining may cause semiconductor malfunction. Meanwhile, alkali metals include Li, Na, K, Rb, Cs, and Fr. Alkaline earth metals include Be, Mg, Ca, Sr, Ba, and Ra.

[0046] The concentration of silica particles in the dispersion is, for example, 12 mass% or more, preferably 15 mass% or more, and more preferably 20 mass% or more. The upper limit of the silica particle concentration is not particularly limited, but is, for example, 40 mass%.

[0047] It is preferable that the amount of “silicon-containing compounds” (unreacted material) other than silica particles present in the dispersion be 200 ppm or less. The lower the amount of this “silicon-containing compound,” the more the adhesion to the substrate can be suppressed. In addition, when the amount of this “silicon-containing compound” is low, the adsorption of various chemicals added to the abrasive and the reaction with the various chemicals are suppressed, so the effects of the various chemicals can be exerted.

[0048] Meanwhile, “components containing silicon” include those in which the reaction has not progressed to the silica particles intended for manufacturing. Examples include unreacted raw material alkoxysilanes and their low molecular weight hydrolysates (oligomers, microgels).

[0049] [Abrasive composition (abrasive)]

[0050] The silica particle dispersion according to the above-described embodiment may be used as a polishing composition by adding other components, such as water-soluble polymers, or by appropriately preparing it using silica particles in the dispersion. In addition to silica particles and water-soluble polymers, the polishing composition may include other additives such as basic compounds, pH adjusters, surfactants, and chelating agents.

[0051] The polishing action of the silica particles is enhanced by their interaction with a water-soluble polymer within the polishing composition. The silica particles used in this embodiment have a high Sears number (Y) and exhibit significant interaction with the water-soluble polymer. For this reason, it is preferable that the amount of the added water-soluble polymer be smaller than the conventional amount.

[0052] The optimal range for the amount of water-soluble polymer varies depending on the type of water-soluble polymer compound, but it is preferable to have an amount of 0.0005 to 5 mass% relative to the total amount of the polishing composition. Additionally, it is preferable that this range be 0.005 to 40 mass% relative to the silica particles. When the amount of water-soluble polymer is within this range, the exchange of the polishing composition within the polishing pad is carried out more smoothly, making it easier to achieve a high polishing speed and the formation of a good polished surface. Furthermore, suitable aggregates can be formed through the appropriate interaction between the OH groups of the silica particles and the water-soluble polymer. It is more preferable that the amount of this water-soluble polymer be 0.0005 to 2 mass% relative to the total amount of the polishing composition, and more preferable that it be 0.05 to 10 mass% relative to the silica particles.

[0053] Examples of water-soluble polymers include water-soluble cellulose, water-soluble vinyl polymers, and polyhydric alcohol polymers. Specifically, examples of water-soluble cellulose include hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, and carboxymethylethylcellulose. Additionally, examples of water-soluble vinyl polymers include polyvinyl alcohol, polyvinylpyrrolidone, and carboxyvinyl polymers. Among these, hydroxyethylcellulose and polyvinylpyrrolidone are preferred. Examples of polyhydric alcohol polymers include polyvinyl alcohol, poly(2-propenol), poly(ethylene-1,2-diol), poly(propylene-1,2-diol), poly(propylene-1,3-diol), poly(butadiene-1,4-diol), poly(butadiene-1,3-diol), and poly(butadiene-2,3-diol). These may be used individually or in combination.

[0054] In the polishing composition, the concentration of silica particles is preferably 0.1 to 50 mass%. If the concentration of silica particles is less than 0.1 mass%, the polishing speed may be slow depending on the type of substrate and insulating film. Conversely, if the concentration of silica particles exceeds 50 mass%, the stability of the polishing composition becomes insufficient. Consequently, it becomes difficult to further improve the polishing speed and polishing efficiency. Furthermore, in this case, a dried material may be generated and adhered during the process of supplying the polishing composition for polishing treatment. The adhered dried material may cause scratches. The concentration of silica particles is more preferably 0.2 to 30 mass%.

[0055] [Method for preparing a silica particle dispersion]

[0056] A method for preparing a silica particle dispersion of the present embodiment is described.

[0057] First, a silica particle dispersion containing silica particles of a predetermined size is prepared by hydrolyzing and polycondensing an alkoxysilane in the presence of water, an organic solvent, and an alkaline catalyst (silica particle dispersion preparation process). Next, the organic solvent in this silica particle dispersion is replaced with water (water substitution process). Furthermore, the silica particle dispersion obtained by this water substitution is heated at a pH of 7 or higher under atmospheric pressure to avoid the Sears number (Y) of the silica particles becoming 12.0 or lower (particle surface conditioning process). Subsequently, the dispersion obtained from this particle surface conditioning process is concentrated to a pH of less than 7 (concentration process).

[0058] According to this manufacturing method, a dispersion containing silica particles capable of adsorbing basic substances and containing a desired amount of OH groups in a high concentration can be easily prepared. That is, a dispersion containing silica particles satisfying requirements (i) to (iii) described above can be prepared. In addition, the present manufacturing method may have other processes. Unless otherwise noted, pH is the value when converted to 25°C.

[0059] Below, each process is explained in detail.

[0060] [Dispersion Preparation Process]

[0061] Here, silica particles are formed by hydrolyzing and polycondensing the alkoxysilane of the raw material in the presence of water, an organic solvent, and an alkali catalyst, and a silica particle dispersion containing silica particles having an average particle diameter (d) of 5 to 300 nm is prepared.

[0062] The alkoxysilane may be one type of alkoxysilane represented by Formula 2 below, or two or more types.

[0063] XnSi(OR) 4－n … [Equation 2]

[0064] Here, X represents a hydrogen atom, a fluorine atom, or a carbon-1 to carbon-8 alkyl group, aryl group, or vinyl group. R represents a hydrogen atom, or a carbon-1 to carbon-8 alkyl group, aryl group, or vinyl group. n is an integer from 0 to 3.

[0065] The alkoxysilanes represented by Formula 2 above include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetraoctoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, octyltrimethoxysilane, octyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, trimethoxysilane, triethoxysilane, triisopropoxysilane, fluorotrimethoxysilane, fluorotriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, Examples include dimethoxysilane, diethoxysilane, difluorodimethoxysilane, difluorodiethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, trimethylisopropoxysilane, trimethylbutoxysilane, trifluoromethyltrimethoxysilane, and trifluoromethyltriethoxysilane.

[0066] Here, as the alkoxysilane, it is preferable to use alkoxysilanes with short alkyl chains, such as tetramethoxysilane (TMOS) and tetraethoxysilane (TEOS). These have a fast hydrolysis rate and grow three-dimensionally. For this reason, using them makes it easy to obtain low-density particles.

[0067] As a method for preparing a dispersion of silica particles by hydrolysis of an alkoxysilane, the following two methods can be exemplified.

[0068] (Method I) A method of adding a mixed solution of an alkoxysilane and an organic solvent to a liquid in a container comprising water, an organic solvent, and a catalyst.

[0069] (Method II) A method of adding liquid A containing an alkoxysilane and liquid B containing a catalyst and water to a liquid in a container, which is substantially composed of an organic solvent.

[0070] Here, liquid A in Method II may contain an organic solvent. Furthermore, “substantially composed of an organic solvent” means that impurities, etc., which are inevitably included during the manufacturing process of the organic solvent, may be included, but nothing else is included. For example, the concentration of the organic solvent in the liquid substantially composed of an organic solvent is 99 mass% or more, and preferably 99.5 mass% or more.

[0071] Hydrolysis of alkoxysilanes is typically carried out at a temperature below the boiling point of the solvent used under atmospheric pressure. Meanwhile, both methods may also employ the so-called seed method, in which pre-prepared seed particles are added to the liquid in the container.

[0072] In this embodiment, in order to finally obtain particles capable of absorbing a large amount of basic substances, it is preferable to prepare low-density particles during the dispersion preparation process. To achieve this, it is preferable to prepare the particles at a low temperature for a short period of time (rapidly growing the particles). By doing so, porous particles having a large number of Sears can be obtained, along with pores capable of absorbing sufficient basic substances.

[0073] Specifically, for example, the reaction temperature is preferably less than 20°C, and more preferably 18°C ​​or lower. In addition, the time for particle growth is preferably within 60 minutes, and more preferably within 30 minutes.

[0074] In addition, in this process, it is desirable to prepare the particles by considering the particle growth rate in order to obtain particles capable of absorbing a large amount of basic substances.

[0075] (Particle growth rate)

[0076] By optimizing the conditions of the dispersion preparation process, the generation of new nucleation particles during the process can be suppressed. Consequently, growth proceeds only on the surface of the particles formed initially, using them as nucleations. For this reason, the volume of the resulting particles is proportional to the amount of alkoxysilane added.

[0077] Therefore, the relationship between the amount of alkoxysilane added and the average particle diameter (d) is as follows. Meanwhile, a is the coefficient of the particle growth curve.

[0078] Average particle diameter (d) = a * (amount of alkoxysilane added) 1 / 3 … [Equation 3]

[0079] When the addition rate of alkoxysilane during the particle growth phase is constant, (amount of alkoxysilane added) can be substituted for (addition time) and can be expressed as follows. Meanwhile, a' is the coefficient of the particle growth curve.

[0080] Average particle diameter (d) = a' * (time of alkoxysilane addition) 1 / 3 … [Equation 4]

[0081] In the above equation, the faster the particle growth, the larger the value of the coefficient a'. A specific particle growth curve based on Equation 4 is shown in Fig. 2.

[0082] It is thought that when the number of nuclear particles is the same, the faster the particle growth rate, the sparser the internal network of the particle becomes, and thus the particle can absorb more basic substances.

[0083] Therefore, in order to obtain a particle capable of absorbing a large amount of the basic substance, which is the target particle of this invention, for example, in the case of a particle with d = 50 nm, it is preferable that the coefficient a' in Equation 4 be 15 or higher, more preferable that it be 20 or higher, and even more preferable that it be 25 or higher. In the case of d = 30 nm, it is preferable that the coefficient a' be 9 or higher, more preferable that it be 12 or higher, and even more preferable that it be 15 or higher.

[0084] As such, the desirable coefficient a' varies depending on the average particle diameter (d). Therefore, if we denote the value obtained by dividing the coefficient a' by the average particle diameter (d) as b, then for the average particle diameter (d) in the range of 5 to 300 nm, it is easy to obtain the desired particle if b = 0.3 to 0.6.

[0085] The Sears number (Y) of silica particles tends to decrease in subsequent processes. Therefore, in this process, silica particles having a Sears number (Y) greater than the Sears number (Y) of the silica particles as a final product are prepared. It is preferable that the Sears number (Y) of the silica particles prepared in this process be 40 or higher. This allows the silica particles as a final product to be adjusted so that their Sears number (Y) exceeds 12.0, even when post-treatments necessary for use, such as solvent substitution with water and concentration adjustment, are performed. It is more preferable that the Sears number (Y) of the silica particles prepared in this process be 60 or higher, even more preferable that it be 70 or higher, and particularly preferable that it be 80 or higher.

[0086] Examples of organic solvents include alcohols, ketones, ethers, and esters. More specifically, examples include alcohols such as methanol, ethanol, propanol, and butanol; ketones such as methyl ethyl ketone and methyl isobutyl ketone; glycol ethers such as methyl cellosolve, ethyl cellosolve, and propylene glycol monopropyl ether; glycols such as ethylene glycol, propylene glycol, and hexylene glycol; and esters such as methyl acetate, ethyl acetate, methyl lactate, and ethyl lactate. Among these, methanol or ethanol is more preferred, and methanol is particularly preferred. These organic solvents may be used alone or in a mixture of two or more.

[0087] Basic substances are used as alkali catalysts. Examples of basic substances include ammonia, amines, alkali metal hydrides, alkaline earth metal hydrides, alkali metal hydroxides, alkaline earth metal hydroxides, quaternary ammonium compounds, and amine-based coupling agents. These catalysts may be used alone or in combination. Ammonia is preferred, although this depends on the usage conditions and amount used.

[0088] Ammonia does not contain organic groups in its structure. For this reason, when ammonia is processed into a polishing composition, it is difficult for organic groups to coat the OH groups on the surface of the particles. Consequently, ammonia is less likely to interfere with the interaction between the particles and the additives. Furthermore, ammonia is easy to handle during manufacturing, and excess ammonia can be easily discharged out of the system by heating, etc. For this reason, it is also easy to control the residual amount of ammonia in the dispersion. In addition, unlike alkali metal hydrides, alkaline earth metal hydrides, alkali metal hydroxides, and alkaline earth metal hydroxides, ammonia is also desirable in that it does not contain metal elements that may affect the insulation properties of the circuits on the polished substrate.

[0089] It is preferable that the amount of catalyst used for hydrolysis be 0.005 to 2.0 moles per mole of alkoxysilane. If the amount of catalyst is less than 0.005 moles, hydrolysis is difficult to occur, and there is a risk that the particle size distribution will become wider. Conversely, if the amount of catalyst exceeds 2.0 moles, the hydrolysis rate becomes significantly faster. Consequently, it is difficult to form particles, and there is a risk that a gel-like substance will form. It is more preferable that the amount of catalyst added be 0.01 to 1.5 moles per mole of alkoxysilane.

[0090] The amount of water used for hydrolysis is preferably 0.5 to 10 moles per mole of Si-OR groups constituting the alkoxysilane, and more preferably 1 to 5 moles.

[0091] The silica particle concentration of the dispersion is preferably less than 10 mass%, more preferably less than 8 mass%, and even more preferably less than 5 mass%.

[0092] When hydrolysis is carried out under the conditions described above, the polycondensation of alkoxysilane proceeds in three dimensions.

[0093] The average particle diameter (d) of the silica particles obtained in this process is 5 to 300 nm. The average particle diameter (d) of the silica particles is preferably 5 to 100 nm, more preferably 10 to 80 nm, even more preferably 20 to 60 nm, particularly preferably 25 to 55 nm, and most preferably 30 to 50 nm. Meanwhile, the average particle diameter of the silica particles as a final product is equivalent to the average particle diameter of the silica particles produced in this process.

[0094] [Water Substitution Process]

[0095] In the water substitution process, the organic solvent in the silica particle dispersion is replaced with water (pure water). This process can be carried out at an appropriate stage after the dispersion preparation process. In particular, it is preferable to carry out this process before the particle surface conditioning process.

[0096] The method of water substitution is not particularly limited as long as it is a method capable of replacing the organic solvent with water (pure water). Examples of such methods include thermal substitution, vacuum substitution, and membrane substitution. Among these, thermal substitution is preferred because it allows for the subsequent continuous implementation of a particle surface conditioning process. In this method, for example, the organic solvent is evaporated by heating the dispersion while the organic solvent is replaced with water while maintaining a constant liquid volume through the addition of water. For operational purposes, this method is preferably carried out at atmospheric pressure. On the other hand, it is also possible for this process to serve as a concentration process by replacing the organic solvent with water while concentrating the dispersion without maintaining a constant liquid volume.

[0097] When heating the dispersion at atmospheric pressure, water exchange may be completed when the liquid temperature substantially reaches the boiling point of water (100°C). However, in order to suppress the occurrence of microgels, it is desirable to control the liquid temperature so that it does not reach 100°C (so that it does not boil). In this method, for example, water exchange is completed when the dispersion is heated for a predetermined time while maintaining the liquid temperature at approximately 90 to 96°C.

[0098] [Particle Surface Adjustment Process]

[0099] In the particle surface adjustment process, the OH group content of the silica particles is adjusted by heating the silica particle dispersion formed in the dispersion preparation process at a pH of 7 or higher. Here, adjustment is performed to avoid the Sears number (Y) of the silica particles falling below 12.0. To adjust the Sears number (Y) of the silica particles to a desired value, the pH and holding time are adjusted according to the surface condition of the silica particles prepared in the dispersion preparation process. That is, to make the Sears number (Y) smaller, the silica particle dispersion is heated at a high pH for a long time. On the other hand, when heating the silica particle dispersion at a pH below 7, the OH group content of the silica particles is difficult to change. This pH is preferably 7.5 or higher, and more preferably 8 or higher. The upper limit of the pH is not particularly restricted, but is, for example, around 10.

[0100] Meanwhile, to achieve a desired pH, alkali may be added before or during heating. However, if a desired pH has already been achieved, alkali does not need to be added. As the alkali, the catalyst used in the dispersion preparation process described above may be used. It is preferable that this alkali species be ammonia. The reasons for this are that using ammonia facilitates pH adjustment and that ammonia does not contain organic groups or metal elements. Organic groups may modify silica particles, potentially degrading polishing performance and the stability of the dispersion. Metal elements may affect the insulation properties of the circuits on the polished substrate.

[0101] Here, in order to satisfy both the realization of a high polishing speed and the formation of a good polished surface, it is desirable to adjust the Sears number (Y) of the silica particles to be greater than 12.0 and less than or equal to 20.0.

[0102] In this process, heating is preferably performed under atmospheric pressure at a temperature below the boiling point of the dispersion medium so that the silica particle dispersion does not boil. This is because, by performing heating under conditions where the silica particle dispersion does not boil, it is possible to suppress the formation of microgels, furthermore, to improve filterability and suppress the occurrence of defects on the polished substrate. For example, the silica particle dispersion can be heated under atmospheric pressure or under pressure at a temperature below the boiling point of the dispersion medium. Specifically, heating at less than 100°C under atmospheric pressure is preferred, and heating at 90 to 96°C is more preferred.

[0103] In addition, this process may be carried out in a closed system or an open system. If this process is carried out in a closed system, the discharge of alkali to the outside of the system can be suppressed, so the adjustment of OH groups can be performed while maintaining the pH within the system. On the other hand, if this process is carried out in an open system, when ammonia or amine is used as the alkali, the alkali is discharged to the outside of the system along with the evaporation of the solvent due to heating. For this reason, it is preferable to carry out this process in a closed system where maintaining the pH is easy and more precise adjustment of OH groups is possible.

[0104] [Concentration Process]

[0105] In the concentration process, the dispersion obtained from the particle surface conditioning process is concentrated to a pH of less than 7. The lower limit of the pH is approximately 6.0. In this process, the dispersion is concentrated so as not to alter the amount of OH groups adjusted in the particle surface conditioning process. Meanwhile, this concentration process is performed after the particle surface conditioning process. However, a preliminary concentration process may be performed at an appropriate stage prior to particle surface conditioning (e.g., before the water substitution process). Meanwhile, pH adjustment may be performed by ion exchange or ultramembrane treatment in addition to the distillation removal of alkali by heating, and these methods may be used in combination. It is preferable that this pH be 6.9 or lower, and more preferable that it be 6.7 or lower.

[0106] The concentration method is not particularly limited as long as it is a method capable of increasing the silica concentration of the dispersion. Examples of concentration methods include heating concentration, vacuum concentration, and membrane concentration. Among these, heating concentration is preferred because it can be performed continuously from the previous process. In this method, for example, the dispersion is concentrated by heating the dispersion while adding a silica particle dispersion as needed, thereby evaporating the organic solvent and water.

[0107] In the heating concentration method, if the pH is 7 or higher, the number of Sears (Y) (amount of OH groups) of the silica particles changes easily. For this reason, pH management within the above range is important. In addition, it is preferable that heating be performed under conditions where the dispersion medium of the dispersion does not boil. This is because heating the dispersion under non-boiling conditions makes it possible to suppress the formation of microgels, furthermore, to improve filtration efficiency and suppress the occurrence of defects on the polished substrate. That is, it is preferable to heat the dispersion to a temperature below the boiling point of the dispersion medium under atmospheric pressure. Specifically, when the dispersion medium is water, it is preferable to heat the dispersion to less than 100°C under atmospheric pressure, and it is more preferable to heat it to 90 to 96°C.

[0108] However, in the particle surface adjustment process, the viscosity of the dispersion obtained from the dispersion preparation process (converted to a silica concentration of 20 mass%) initially rises to, for example, 60 mPa·s or higher. However, in the process from the particle surface adjustment process to the concentration process, the pH of the dispersion is lowered to less than 7, thereby reducing the viscosity of the dispersion. Thus, the dispersion that undergoes a process to reduce viscosity after the viscosity has initially risen to 60 mPa·s or higher is likely to be free of unreacted substances. This is thought to be because, during the process in which the viscosity of the dispersion changes, the surfaces of the particles within the dispersion interact with each other, leading to densification. In this way, by undergoing the particle surface adjustment process and the concentration process, the “silicon-containing compound” (unreacted substance) can be reduced to 200 ppm or less.

[0109] Examples

[0110] Hereinafter, embodiments relating to the present embodiment will be described in detail.

[0111] <Silica Particle Dispersion>

[0112] [Synthesized Example 1]

[0113] (Dispersion preparation process)

[0114] A raw material solution was prepared by mixing 432.0 g of tetramethoxysilane (manufactured by Tama Chemical Industry Co., Ltd. (hereinafter the same)) with 144.0 g of methanol. In advance, 5,400 g of a solvent mixture of methanol, water, and ammonia was prepared in a reaction vessel. The concentration of water in this mixed solvent was 15 mass%, and the concentration of ammonia was 1 mass%. While controlling the liquid temperature to maintain the reaction solvent temperature at 15°C, the raw material solution was added dropwise to the reaction vessel at a uniform rate for 20 minutes. As a result, a silica particle dispersion with a silica particle concentration of 2.9 mass% was obtained.

[0115] (Preliminary concentration process)

[0116] The dispersion (silica particle concentration 2.9 mass%) obtained from the dispersion preparation process was concentrated by a heating concentration method. Specifically, the dispersion obtained from the dispersion preparation process was heated under atmospheric pressure to evaporate the organic solvent and water, and a pre-prepared silica particle dispersion (silica particle concentration 2.9 mass%) was added to maintain a constant liquid volume. In this way, the dispersion was concentrated.

[0117] (Water substitution process)

[0118] While adding water to the concentrated dispersion, water substitution was performed on the dispersion by the heating substitution method at atmospheric pressure. The water substitution process was terminated when the liquid temperature reached 96°C.

[0119] (Particle surface adjustment process)

[0120] After the water exchange process was completed, heat treatment was performed on the dispersion for 25 hours at a pH of 7 or higher while maintaining the liquid temperature at 96°C under atmospheric pressure. In this process as well, water was added in an amount equal to the amount of liquid removed by distillation, and heating was continued while maintaining a constant silica concentration in the system. In this way, the silica particles were adjusted to have a target number of Sears.

[0121] (Concentration process)

[0122] It was confirmed that the pH was below 7, and the addition of water was stopped. Afterwards, the dispersion was concentrated at 96°C under atmospheric pressure until the silica particle concentration reached 20 mass%. In this way, silica particle dispersion A was prepared.

[0123] Table 1 shows the number of Sears (Y), particle density (ρ), average particle diameter (d), particle variation coefficient (CV value), ratio of two or more connected particles, amount of unreacted material, and amount of basic substance adsorbed of the dispersion at the end of the concentration process (the same applies to the synthesis examples and comparative synthesis examples below). Meanwhile, various parameters were measured by the following method.

[0124] ≪Silica Particle Concentration in Dispersion≫

[0125] 5g of the sample was dried at 150°C for 1 hour. The solid content concentration was calculated from the mass of the sample after drying. From this solid content concentration, the silica particle concentration was calculated by subtracting the unreacted amount from the value obtained by converting the metal element content of the silica particles described below into oxides.

[0126] ≪Average particle diameter (d) of silica particles≫

[0127] Electron microscope images of silica particles were taken. In addition, for 100 randomly selected particles, the longest diameter of the primary particle diameter of each particle was measured, as exemplified in Fig. 1. The average value of the measurement results was obtained as the average particle diameter (d) of the silica particles.

[0128] ≪Seers number (Y) of silica particles≫

[0129] The Sears number (Y) was measured by titration using sodium hydroxide, following the description in Analytical Chemistry 28 (1956), 12, 1981-1983 by Sears.

[0130] Specifically, 30g of sodium chloride was added to 150g of a sample diluted with pure water to achieve a silica particle concentration of 1 mass%, and the pH was adjusted to 4.0 with hydrochloric acid. Subsequently, the sample was titrated with a 0.1N aqueous sodium hydroxide solution. The amount of sodium hydroxide solution required to titrate the sample until its pH reached 9.0 was expressed as the Sears number (Y) (i.e., the Sears number (Y) is the amount of 0.1N aqueous sodium hydroxide solution titrated for 1.5g of silica). Meanwhile, the titration with the 0.1N aqueous sodium hydroxide solution was performed using an automatic titration device with the titration rate fixed at 0.1 ml / second.

[0131] Density of Silica Particles

[0132] The particle density (ρ) is obtained from the specific surface area (SA = 32 * (Sears number) - 25) based on the average particle diameter (d) and the Sears number (Y).

[0133] From the particle diameter (d) [nm], the surface area (S) per particle and the volume (V) per particle are calculated as follows.

[0134] Surface area per particle (S) = 4π(d / 2) 2 =πd 2 [nm 2 / dog]

[0135] Volume per particle (V)

[0136] = (4 / 3)π(d / 2) 3 = (πd 3 ) / 6[nm 3 / dog]

[0137] If the particle density is ρ [g / cm³], the specific surface area (SA) is calculated as follows.

[0138] SA[㎡ / g]=1000·S / ρV=(1000 / ρ)·(6 / d)=6000 / ρd

[0139] thus,

[0140] ρ[g / cm³] is calculated from SA[m² / g] and d[nm] using the following formula.

[0141] ρ[g / cm³]=6000 / SA·d

[0142] ≪Coefficient of Variation in Particle Diameter of Silica Particles≫

[0143] The coefficient of variation of the particle diameter was calculated using the following formula. Here, the values ​​obtained from the electron microscope image above were used as the individual particle diameters and the average particle diameter when calculating the coefficient of variation (CV value).

[0144]

[0145] ≪Ratio of Connected Particles≫

[0146] Electron microscope images of silica particles were taken. For 100 randomly selected particles, the presence or absence of connections was checked, and the particles were divided into unconnected particles, particles with two connections, and particles with three or more connections, and the number of each was counted. The ratio of particles with two connections to the total number of particles was calculated.

[0147] ≪Amount of unreacted material in the dispersion≫

[0148] Using a small ultracentrifuge (CS150GXL manufactured by Hitachi Air Co., Ltd.), the dispersion was centrifuged for 30 minutes at a set temperature of 30°C and 137,000 rpm (1,000,000 G). The “silicon-containing compounds” (unreacted material) other than silica particles present in the supernatant of this treated liquid were measured as Si using an ICP emission analyzer (ICPS-8100 manufactured by Shimadzu Corporation). The amount of unreacted material was obtained by converting this measured value into the SiO2 concentration in the dispersion.

[0149] ≪Evaluation of Basic Substance Adsorption Amount≫

[0150] A silica particle dispersion was prepared using 28% ammonia water and pure water to adjust the silica particle concentration to 9.0 mass% and the pH to 9.0. The dispersion was centrifuged, and the amount of ammonia in the dispersion (total) before centrifugation and the amount of ammonia in the supernatant of the dispersion after centrifugation were quantified. The difference between these amounts was obtained as the amount of ammonia adsorbed by the silica particles. By converting this amount to a value per gram of particle, the amount of ammonia adsorbed (amount of basic substance adsorbed) was obtained. For centrifugation, a small ultracentrifuge (CS150GXL manufactured by Hitachi Air Co., Ltd.) was used to centrifuge the dispersion at a set temperature of 30°C and 137,000 rpm (1,000,000 G) for 30 minutes.

[0151] Metal element content of silica particles

[0152] The content of alkali metals, alkaline earth metals, Fe, Ti, Zn, Pd, Ag, Mn, Co, Mo, Sn, Al, and Zr, the content of Cu, Ni, and Cr, and the content of U and Th in the silica particles were measured as follows. First, the silica particles were dissolved in hydrofluoric acid, and the hydrofluoric acid was removed by heating. Then, a solution was obtained by adding pure water to the dissolved silica particles as needed. The above content was measured by using an ICP-MS inductively coupled plasma mass spectrometer (Agilent 7900s) on this solution.

[0153] ≪Sphericity of Primary Particles of Silica≫

[0154] Electron microscope images were taken. In addition, for 100 randomly selected particles, the ratio (DS / DL) of the maximum diameter (DL) and the minor diameter (DS) orthogonal to it was calculated for each. Furthermore, the average value of the ratio (DS / DL) was calculated and obtained as the sphericity. Meanwhile, the sphericity was calculated from unconnected particles.

[0155] [Synthesized Example 2]

[0156] A silica particle dispersion B was prepared by the same method as in Synthesis Example 1, except that the water substitution process was performed under reduced pressure (-0.06 MPa (gauge pressure)).

[0157] [Synthesized Example 3]

[0158] (Dispersion preparation process)

[0159] A raw material solution was prepared by mixing 388.8 g of tetramethoxysilane with 129.6 g of methanol. 5,400 g of a solvent mixture of methanol, water, and ammonia was prepared in advance in a reaction vessel. The concentration of water in this mixture was 15 mass%, and the concentration of ammonia was 1 mass%. While controlling the liquid temperature to maintain the reaction solvent temperature at 13°C, the raw material solution was added dropwise to the reaction vessel at a uniform rate for 18 minutes. As a result, a silica particle dispersion with a silica particle concentration of 2.6 mass% was obtained.

[0160] (Preliminary concentration process)

[0161] The dispersion (silica particle concentration 2.6 mass%) obtained from the dispersion preparation process was concentrated by a heating concentration method. Specifically, the dispersion obtained from the dispersion preparation process was heated under atmospheric pressure to evaporate the organic solvent and water, and at the same time, a pre-prepared silica particle dispersion (silica concentration 2.6 mass%) was added to maintain a constant liquid volume. In this way, the dispersion was concentrated.

[0162] After the water substitution process, silica particle dispersion C was obtained by the same method as in Synthesis Example 1.

[0163] [Synthesized Example 4]

[0164] (Dispersion preparation process)

[0165] A raw material solution was prepared by mixing 345.6 g of tetramethoxysilane with 115.2 g of methanol. 5,400 g of a solvent mixture of methanol, water, and ammonia was prepared in advance in a reaction vessel. The concentration of water in this mixture was 15 mass%, and the concentration of ammonia was 1 mass%. While controlling the liquid temperature to maintain the reaction solvent temperature at 12.0°C, the raw material solution was added dropwise to the reaction vessel at a uniform rate for 16 minutes. As a result, a silica particle dispersion with a silica particle concentration of 2.3 mass% was obtained.

[0166] (Preliminary concentration process)

[0167] The dispersion (silica particle concentration 2.3 mass%) obtained from the dispersion preparation process was concentrated by a heating concentration method. Specifically, the dispersion obtained from the dispersion preparation process was heated under atmospheric pressure to evaporate the organic solvent and water, and at the same time, a silica particle dispersion (silica concentration 2.3 mass%) prepared in advance was added to ensure a constant liquid volume. In this way, the dispersion was concentrated.

[0168] After the water substitution process, silica particle dispersion D was obtained by the same method as in Synthesis Example 1.

[0169] Meanwhile, in any synthesis example, the respective content of alkali metals, alkaline earth metals, Fe, Ti, Zn, Pd, Ag, Mn, Co, Mo, Sn, Al, and Zr in the silica particles was less than 0.1 ppm, the respective content of Cu, Ni, and Cr was less than 1 ppb, and the respective content of U and Th was less than 0.3 ppb. In addition, the sphericity of the primary particles of the silica particles was 0.80 to 1.00.

[0170] [Synthesized Example 5]

[0171] (Dispersion preparation process)

[0172] A raw material solution was prepared by mixing 648 g of tetramethoxysilane with 216 g of methanol. 5,400 g of a solvent mixture of methanol, water, and ammonia was prepared in advance in a reaction vessel. The concentration of water in this mixture was 15 mass%, and the concentration of ammonia was 1 mass%. While controlling the liquid temperature to maintain the reaction solvent temperature at 20°C, the raw material solution was added dropwise to the reaction vessel at a uniform rate for 30 minutes. As a result, a silica particle dispersion with a silica particle concentration of 4.1 mass% was obtained.

[0173] (Preliminary concentration process)

[0174] The dispersion (silica particle concentration 4.1 mass%) obtained from the dispersion preparation process was concentrated by a heating concentration method. Specifically, the dispersion obtained from the dispersion preparation process was heated under atmospheric pressure to evaporate the organic solvent and water, and at the same time, a silica particle dispersion (silica concentration 4.1 mass%) prepared in advance was added to maintain a constant liquid volume. In this way, the dispersion was concentrated.

[0175] After the water substitution process, silica particle dispersion E was obtained by the same method as in Synthesis Example 2.

[0176] [Comparative Example 1 of Synthesis]

[0177] (Dispersion preparation process)

[0178] To a mixture of 440.8g of pure water, 135.0g of 28% ammonia water, and 3669.0g of methanol, a mixture of 3044.4g of tetramethoxysilane and 229.2g of methanol, and a mixture of 621.0g of pure water and 134.9g of 28% ammonia water were added over 150 minutes while maintaining the liquid temperature at 30℃. By doing so, a silica particle dispersion with a silica particle concentration of 14.5% was obtained.

[0179] (Water substitution process)

[0180] A preliminary concentration process was not performed. While adding water to the dispersion obtained from the dispersion preparation process, water substitution was performed on the dispersion by the heating substitution method at atmospheric pressure. The water substitution process was terminated when the liquid temperature reached 96°C.

[0181] Subsequently, silica particle dispersion F was obtained by the same method as in Synthesis Example 1.

[0182] [Comparative Example 2 of Synthesis]

[0183] Silica particles prepared by the water glass method (SI-45P manufactured by Nikki Catalytic Chemical Co., Ltd.) were used as Comparative Example 2.

[0184] Meanwhile, in Comparative Example 1 of synthesis, the respective contents of alkali metals, alkaline earth metals, Fe, Ti, Zn, Pd, Ag, Mn, Co, Mo, Sn, Al, and Zr in the silica particles were less than 0.1 ppm, the respective contents of Cu, Ni, and Cr were less than 1 ppb, and the respective contents of U and Th were less than 0.3 ppb. In addition, in both Comparative Examples of synthesis, the sphericity of the primary particles of the silica particles was 0.80 to 1.00.

[0185] <Abrasive Composition>

[0186] [Example 1]

[0187] A polishing composition A with a silica particle concentration of 0.45 mass% was prepared by mixing silica particle dispersion A and a water-soluble polymer (hydroxyethylcellulose (molecular weight 350,000)) in the ratio shown in Table 2. Meanwhile, 0.02 mass% of ammonia was added to the polishing composition.

[0188] [Example 2]

[0189] A polishing composition B was prepared by the same method as in Example 1, except that silica particle dispersion B was used instead of silica particle dispersion A.

[0190] [Example 3]

[0191] A polishing composition C was prepared by the same method as in Example 1, except that silica particle dispersion C was used instead of silica particle dispersion A.

[0192] [Example 4]

[0193] A polishing composition D was prepared by the same method as in Example 1, except that silica particle dispersion D was used instead of silica particle dispersion A.

[0194] [Example 5]

[0195] A polishing composition E was prepared by the same method as in Example 1, except that silica particle dispersion E was used instead of silica particle dispersion A.

[0196] [Comparative Example 1]

[0197] A polishing composition F was prepared by the same method as in Example 1, except that silica particle dispersion F was used instead of silica particle dispersion A.

[0198] Table 2 shows the determination of polishing characteristics (polishing speed, smoothness, and defects). Meanwhile, each measurement value was obtained by the following method.

[0199] <Evaluation of Abrasive Composition>

[0200] 1. Grinding speed

[0201] A polishing substrate (a single-crystal silicon wafer with a crystal structure of 1.0.0) was set in a polishing device (NF300 manufactured by Nano Factor Co., Ltd.). Polishing of the polishing substrate was performed for 5 minutes using a polishing pad Polytex P103 driven at a polishing load of 0.05 MPa, a table rotation speed of 50 rpm, and a spindle speed of 50 rpm, and the polishing composition supplied at a rate of 100 ml / min. Afterward, the substrate was washed with pure water and air-dried. The polishing speed of the substrate was evaluated according to the following criteria.

[0202] ≪Grinding Speed ​​Determination Method≫

[0203] ○: Exceeding 25 nm / min

[0204] △: 20–25 nm / min

[0205] ×: Less than 20 nm / min

[0206] 2. Condition of the polished surface

[0207] The curvature of the polished surface of the obtained polished substrate was observed using a scanning white interferometer (Zygo New View 7300) at wavelengths of 50 to 500 μm. Surface smoothness was evaluated based on the following criteria (curvature).

[0208] ≪Method for Determining Surface Smoothness≫

[0209] ○: Curvature less than 0.5 nm

[0210] △: Curvature of 0.5 nm or more and less than 1.0 nm

[0211] ×: Curvature is 1.0 nm or greater

[0212] The extent of defects, such as scratches on the polished substrate, was checked using a laser microscope (VK-X250 manufactured by Keyence Co., Ltd.). The defects were evaluated according to the following criteria.

[0213] Defect Judgment Method

[0214] ○: Almost no defects identified

[0215] △: Minor defects identified

[0216] ×: Extensive defects identified

[0217]

[0218]

[0219] The detailed description foregoing is provided for illustrative and explanatory purposes. Various modifications and variations are possible within the scope of the disclosure. The invention is not to be encompassed or limited to the specific forms disclosed above. Although the invention is described in terms of structural features and / or methodological acts, it is understood that the invention according to the appended claims is not in any way limited to the specific features or acts described above. Rather, the specific features or acts described above are disclosed as examples for practicing the appended claims.

Claims

Claim 1 A silica particle dispersion characterized by containing silica particles satisfying the requirements of (i) to (v) below: (i) an average particle diameter (d) of 5 to 300 nm; (ii) having pores that absorb ammonia, with an ammonia absorption amount of 2 mg or more per 1 g of particle; (iii) a Sears number (Y) greater than 12.0; (iv) a density (ρ) of 1.00 g / cm³ or less; (v) a particle diameter variation coefficient of 10% or less. Claim 2 A silica particle dispersion according to claim 1, characterized in that the Sears number (Y) of requirement (iii) is greater than 12.0 and less than or equal to 20.

0. Claim 3 A silica particle dispersion according to claim 1 or 2, characterized in that the silica particles have a structure in which the particle surface and the pores inside the particles are in communication. Claim 4 A silica particle dispersion according to claim 1 or 2, characterized as being for abrasive use. Claim 5 A method for preparing a silica particle dispersion, characterized by comprising: a dispersion preparation process of hydrolyzing and polycondensing an alkoxysilane in the presence of water, an organic solvent, and ammonia to prepare a dispersion containing silica particles having an average particle diameter (d) of 5 to 300 nm and a Sears number (Y) of 40 or more, within 60 minutes at a reaction temperature of less than 20°C; a water substitution process of replacing the organic solvent in the silica particle dispersion with water; a particle surface conditioning process of heating the water-substituted silica particle dispersion at a pH of 7 or higher under atmospheric pressure so that the Sears number (Y) of the silica particles does not become 12.0 or lower; and a concentration process of concentrating the dispersion obtained from the particle surface conditioning process at a pH of less than 7. Claim 6 A method for manufacturing a silica particle dispersion according to claim 5, characterized in that, in the particle surface adjustment process, the Sears number (Y) is adjusted to be greater than 12.0 and less than or equal to 20.

0. Claim 7 delete Claim 8 delete

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