Core / shell particles and method for producing same

Abstract

The present invention provides: core / shell particles with which silicon oxide films can be polished so as to have reduced polished-surface roughness and which attain a sufficient rate of polishing the silicon oxide films; and a method for producing the core / shell particles.　The core / shell particles each comprise a silica particle as a core and a ceria-containing shell that covers the silica particle, and are characterized in that (1) the core / shell particles have a ceria content of 4.0-80.0 mass%, (2) the ceria has a crystallite diameter of 2.0-9.0 nm, and (3) the core / shell particles, after having undergone a disintegration treatment, have a retention of average secondary-particle diameter of 0.70-1.0.

Description

Core-shell particles and methods for producing the same

[0001] The present invention relates to core-shell particles and a method for producing the same.

[0002] Colloidal silica is a material in which silica particles are dispersed in a medium such as water. It is used as a material property modifier in fields such as paper, textiles, and steel, and is also used as an abrasive in the polishing (CMP) of semiconductor devices such as semiconductor wafers.

[0003] In the semiconductor device manufacturing process, one of the semiconductor device polishing (CMP) processes is the Charlotte wrench element separation process. In this process, ceria particles are used because they exhibit a high polishing rate against silicon oxide films. Examples have also been proposed using composite particles in which ceria is coated onto a parent particle other than ceria. Many of these particles include a calcination process during manufacturing to promote ceria crystal growth (see Patent Documents 1-3).

[0004] However, because ceria crystals have hard, sharp edges, there is a problem of increased scratch count and rougher surface finish after polishing. With the increasing miniaturization of semiconductor line widths, there is a demand for abrasive grains with higher flatness and lower defect properties.

[0005] Furthermore, although silica particles are coated with ceria under basic conditions without firing (see Non-Patent Literature 1), if unmodified silica particles are used, the adhesion of ceria to the mother particles is weak, and the ceria in the coating layer is prone to detachment. In addition, when the coating reaction is performed under basic conditions, the particles aggregate, and the aggregated particles increase scratches during polishing, resulting in a rougher polished surface.

[0006] Furthermore, as mentioned above, using abrasive grains that easily detach ceria from the coating layer presents a problem in the CMP process, where the polishing speed cannot be sufficiently increased. In the CMP process, it is necessary to polish and remove the target film type at a high speed from the perspective of improving the productivity of semiconductor devices.

[0007] Therefore, there is a need for the development of core-shell particles that can reduce the surface roughness of the silicon oxide film being polished and that allow for a sufficient polishing speed of the silicon oxide film, as well as a method for manufacturing the same.

[0008] Japanese Patent Publication No. 2017-206411, Japanese Patent Publication No. 2018-506618, Japanese Patent Publication No. 2013-133255

[0009] L. Peedikakkandy et al., “Preparation of spherical ceria coated silica nanoparticle abrasives for CMP application”, J. Applied Surface Science, 357, 2015, p1306-1312.

[0010] The present invention aims to provide core-shell particles that can reduce the surface roughness of the silicon oxide film being polished and that allow for a sufficient polishing speed of the silicon oxide film, as well as a method for producing the same.

[0011] As a result of diligent research to achieve the above objective, the inventors have found that the above objective can be achieved by using core-shell particles having a core of sulfonic acid-modified silica particles and a shell containing ceria that coats the silica particles, provided that the ceria content in the core-shell particles, the crystallite size of the ceria, and the retention rate of the average secondary particle size after disintegration treatment are within a specific range, thereby completing the present invention.

[0012] In other words, the present invention relates to the following core-shell particles and a method for producing the same: 1. Core-shell particles having a silica particle as a core and a ceria-containing shell covering the silica particle, characterized in that: (1) the ceria content in the core-shell particles is 4.0 to 80.0 mass%, (2) the crystallite size of the ceria is 2.0 to 9.0 nm, and (3) the retention rate of the average particle size after disintegration treatment is 0.70 to 1.0. 2. The core-shell particles according to item 1, wherein the primary particle size calculated from the BET specific surface area is 10.0 to 300.0 nm, and the average secondary particle size measured by dynamic scattering is 20.0 to 600.0 nm. 3. The core-shell particles according to item 1 or 2, wherein the association ratio is 1 to 10. 4. Ce detected by XPS ３＋ Originating peaks and Ce ４＋ Of the peaks of origin, Ce ３＋ 1. Core-shell particles according to any one of items 1 to 3, wherein the proportion of the peak area of ​​the originating peak is 20 to 40%. 5. Core-shell particles according to any one of items 1 to 4, wherein the isoelectric point of the aqueous dispersion of the core-shell particles is 5 to 9. 6. Core-shell particles according to any one of items 1 to 5, wherein the zeta potential of the aqueous dispersion of the core-shell particles at pH 3 is +20 to +80 mV. 7. A method for producing core-shell particles having silica particles as a core and a ceria-containing shell coating the silica particles, comprising: (1) step 1 of preparing a mother liquor containing sulfonic acid-modified silica particles and water; (2) step 2 of preparing a cerium salt aqueous solution; (3) step 3 of preparing a mixture by injecting the cerium salt aqueous solution into the mother liquor at a constant rate while maintaining a temperature of 25 to 100°C, wherein the pH of the mixture after injection of the cerium salt aqueous solution is 3.0 or less; and (4) step 4 of stirring the mixture for 1 to 24 hours while maintaining the pH and temperature of the mixture after injection of the cerium salt aqueous solution. 8. The production method according to item 7, wherein the injection time of the cerium salt aqueous solution in step 3 is 0.5 to 24 hours.

[0013] The core-shell particles of the present invention can reduce the surface roughness of the silicon oxide film being polished, and allow the polishing speed of the silicon oxide film to be sufficiently high. Furthermore, the above-mentioned core-shell particles of the present invention can be manufactured according to the manufacturing method of the present invention.

[0014] The present invention will be described in detail below. While the following descriptions of constituent elements may be based on representative embodiments and specific examples, the present invention is not limited to such embodiments.

[0015] In the numerical ranges described stepwise in this specification, the upper and lower limits of a numerical range in one step can be arbitrarily combined with the upper or lower limits of a numerical range in another step. Furthermore, in the numerical ranges described in this specification, the upper and lower limits of that range may be replaced with values ​​shown in the examples or values ​​that can be uniquely derived from the examples. Moreover, in this specification, numbers connected by "~" mean a numerical range that includes the numbers before and after "~" as the lower and upper limits.

[0016] In this specification, the expressions “contains” and “includes” include the concepts of “contains,” “includes,” “substantially consists of,” and “consistes of only.”

[0017] The core-shell particles of the present invention are core-shell particles having a silica particle as the core and a ceria-containing shell covering the silica particle, characterized in that (1) the ceria content in the core-shell particles is 4.0 to 80.0% by mass, (2) the crystallite size of the ceria is 2.0 to 9.0 nm, and (3) the retention rate of the average particle size when disintegrated is 0.70 to 1.0.

[0018] The core-shell particles of the present invention have a silica particle as the core and a ceria-containing shell that coats the silica particle. As such, the ceria has excellent adhesion strength, and the ceria in the coating layer is difficult to detach, thus reducing the roughness of the polished surface. Furthermore, because the core-shell particles of the present invention have the configurations (1) to (3) described above, the polishing speed of the silicon oxide film can be set to a sufficient speed. Such core-shell particles of the present invention can be used very suitably as polishing agents for the polishing (CMP) of semiconductor devices.

[0019] Furthermore, the method for producing core-shell particles of the present invention comprises: (1) step 1 of preparing a mother liquor containing sulfonic acid-modified silica particles and water; (2) step 2 of preparing a cerium salt aqueous solution; (3) step 3 of preparing a mixture by injecting the cerium salt aqueous solution into the mother liquor at a constant rate while maintaining a temperature of 25 to 100°C, and ensuring that the pH of the mixture after injection of the cerium salt aqueous solution is 3.0 or less; and (4) step 4 of stirring the mixture for 1 to 24 hours while maintaining the pH and temperature of the mixture after injection of the cerium salt aqueous solution. Because the production method of the present invention comprises the above steps 1 to 4, it is possible to easily produce core-shell particles of the present invention that can reduce the surface roughness of the silicon oxide film being polished and allow the polishing speed of the silicon oxide film to be sufficiently fast.

[0020] The core-shell particles of the present invention and their manufacturing method will be described in detail below.

[0021] 1. Core-shell particles The core-shell particles of the present invention are core-shell particles having a silica particle as the core and a ceria-containing shell covering the silica particle, wherein (1) the ceria content in the core-shell particles is 4.0 to 80.0% by mass, (2) the crystallite size of the ceria is 2.0 to 9.0 nm, and (3) the retention rate of the average particle size when disintegration treatment is 0.70 to 1.0.

[0022] The core-shell particles of the present invention have silica particles as the core. In the core-shell particles of the present invention, the silica particles used as the core are preferably silica particles modified with sulfonic acid. Sulfonic acid-modified silica particles remain negatively charged even under acidic conditions and play a role in attracting positively charged ceria. Furthermore, it is thought that the sulfo group chelates cerium ions in the solution, making it easier for ceria to bind to the particles. In this specification, the state in which silica particles are modified with sulfonic acid groups means a state in which sulfonic acid groups have been introduced to the surface of the silica particles by sulfonic acid modification.

[0023] Furthermore, the core-shell particles of the present invention are core-shell particles having the above-mentioned silica particles as a core and a ceria-containing shell that coats the above-mentioned silica particles.

[0024] The fact that silica particles are coated with a ceria-containing shell can be confirmed by the TEM-EDS confirmation method described in the examples below.

[0025] The ceria content in the core-shell particles of the present invention is 4.0 to 80.0% by mass. If the ceria content is less than 4.0% by mass, the polishing rate of the silicon oxide film is insufficient. If the ceria content exceeds 80.0% by mass, the polished surface roughness of the silicon oxide film becomes excessive. The ceria content is preferably 4.5 to 70.0% by mass, and more preferably 5.0 to 65.0% by mass.

[0026] In this specification, the ceria content in the core-shell particles is measured by the measurement method described in the examples below.

[0027] The crystallite size of the ceria in the core-shell particles of the present invention is 2.0 to 9.0 nm. If the crystallite size of the ceria is less than 2.0 nm, the polishing rate of the silicon oxide film is insufficient. If the crystallite size of the ceria exceeds 9.0 nm, the surface roughness of the polished silicon oxide film becomes large. The crystallite size of the ceria is preferably 2.5 to 6.0 nm, and more preferably 3.0 to 4.8 nm.

[0028] In this specification, the crystallite size of the ceria of the core-shell particles is measured by the measurement method described in the examples below.

[0029] The core-shell particles of the present invention have an average secondary particle diameter retention rate of 0.70 to 1.00 after disintegration treatment. If the average secondary particle diameter retention rate is less than 0.70, the polishing speed of the silicon oxide film is insufficient, and the polished surface roughness of the silicon oxide film becomes large. The average secondary particle diameter retention rate is preferably 0.75 or higher, more preferably 0.80 or higher, and even more preferably 0.90 or higher. Furthermore, the upper limit of the average secondary particle diameter retention rate is not particularly limited and may be 0.99 or lower, 0.96 or lower, etc.

[0030] In this specification, the retention rate of the average secondary particle diameter when the above-mentioned core-shell particles are subjected to disintegration treatment is measured according to the measurement method described in the examples.

[0031] The average secondary particle diameter measured by the dynamic scattering method of core-shell particles of the present invention is preferably 20.0 to 600.0 nm. An average secondary particle diameter of 20.0 nm or more improves the polishing speed of the silicon oxide film. Furthermore, an average secondary particle diameter of less than 600.0 nm can reduce the surface roughness of the polished silicon oxide film. The average secondary particle diameter is more preferably 30.0 to 500.0 nm, even more preferably 40.0 to 400.0 nm, particularly preferably 50.0 to 300.0 nm, and most preferably 60.0 to 200.0 nm.

[0032] The average secondary particle diameter measured by the dynamic scattering method of core-shell particles of the present invention is measured according to the measurement method described in the examples below.

[0033] The average primary particle diameter calculated from the BET specific surface area of ​​the core-shell particles of the present invention is preferably 10.0 to 300.0 nm. An average primary particle diameter of 10.0 nm or more further improves the polishing speed of the silicon oxide film. Furthermore, an average primary particle diameter of 300.0 nm or less can further reduce the surface roughness of the polished silicon oxide film. An average primary particle diameter of 20.0 to 250.0 nm is more preferable, and 30.0 to 200.0 nm is even more preferable.

[0034] The measurement of the average primary particle diameter calculated from the BET specific surface area of the core-shell particles of the present invention is carried out by the measurement method described in the examples below.

[0035] The aggregation ratio of the core-shell particles of the present invention is preferably from 1 to 10. When the aggregation ratio is 10 or less, the polishing surface roughness of the silicon oxide film to be polished can be made smaller. The aggregation ratio is preferably from 1.2 to 8, more preferably from 1.5 to 7.

[0036] The aggregation ratio of the core-shell particles of the present invention is calculated by the method described in the examples below.

[0037] The core-shell particles of the present invention are Ce detected by XPS ３＋ derived peak and Ce ４＋ Among the derived peaks, the ratio of the peak area of the Ce ３＋ peak is preferably 20 to 40%. When the ratio of the peak area of the peak derived from Ce ３＋ is 20% or more, the polishing rate of the silicon oxide film becomes more sufficient. When the ratio of the peak area of the peak of Ce ３＋ is 40% or less, over-polishing of the oxide film is suppressed, and the polishing surface roughness of the silicon oxide film can be made smaller. The ratio of the peak area of the peak of Ce ３＋ is preferably from 21 to 38%, more preferably from 22 to 35%.

[0038] The ratio of the peak area of the Ce ３＋ peak of the core-shell particles of the present invention is calculated by the method described in the examples below.

[0039] The isoelectric point of the aqueous dispersion of the core-shell particles of the present invention is preferably from 5 to 9. When the isoelectric point is 5 or more, the polishing rate is further improved by the electrostatic action with the silicon oxide film. When the isoelectric point is 9 or less, the electrostatic action with the silicon oxide film to be polished can be appropriately adjusted so as not to become too strong, and the polishing surface roughness can be made smaller. The isoelectric point is more preferably from 5.5 to 8.5, still more preferably from 6.0 to 8.0.

[0040] The isoelectric point of the core-shell particles of the present invention is calculated by the isoelectric point measurement method described in the examples below.

[0041] The zeta potential of the aqueous dispersion of core-shell particles of the present invention at pH 3 is preferably 20 to 80 mV. When the zeta potential at pH 3 is 20 mV or higher, the electrostatic attraction with the silicon oxide film increases, further improving the polishing speed. When the zeta potential at pH 3 is 80 mV or lower, the electrostatic effect with the silicon oxide film being polished can be appropriately adjusted so that it does not become too strong, and the surface roughness of the polished surface can be reduced. The zeta potential at pH 3 is preferably 25 to 70 mV, and more preferably 30 to 60 mV.

[0042] The zeta potential of the aqueous dispersion of the core-shell particles of the present invention at pH 3 is measured by the zeta potential measurement method described in the examples below.

[0043] Since the core-shell particles of the present invention have the above-described structure, they can be usefully used as polishing agents (CMP) for semiconductor devices such as semiconductor wafers.

[0044] 2. Method for Producing Core-Shell Particles The method for producing core-shell particles of the present invention is a method for producing core-shell particles having silica particles as a core and a ceria-containing shell coating the silica particles, and is characterized by comprising: (1) step 1 of preparing a mother liquor containing sulfonic acid-modified silica particles and water; (2) step 2 of preparing a cerium salt aqueous solution; (3) step 3 of preparing a mixed solution by injecting the cerium salt aqueous solution into the mother liquor at a constant rate while maintaining a temperature of 25 to 100°C, wherein the pH of the mixed solution after injection of the cerium salt aqueous solution is 3.0 or less; and (4) step 4 of stirring the mixed solution for 1 to 24 hours while maintaining the pH and temperature of the mixed solution after injection of the cerium salt aqueous solution. The method for producing core-shell particles of the present invention can suitably produce the above-described core-shell particles of the present invention.

[0045] The manufacturing method of the present invention will be described in detail below, step by step.

[0046] (Step 1) Step 1 is a step of preparing a mother liquor containing sulfonic acid-modified silica particles and water.

[0047] Sulfonic acid-modified silica particles are not particularly limited as long as they are silica particles on which sulfonic acid groups have been introduced to the surface of the silica particles by sulfonic acid modification or the like. Examples of such silica particles include silica particles obtained by a modification treatment in which a silane coupling agent having mercapto groups is added to colloidal silica containing silica particles to convert the mercapto groups into sulfonic acid groups.

[0048] The colloidal silica used as a raw material preferably has silanol groups on its surface. Considering that the semiconductor should not contain diffusible metal impurities or corrosive ions such as chlorine, it is more preferable to use a hydrolyzable silicon compound (e.g., alkoxysilane or its derivative) as a raw material and obtain colloidal silica by hydrolysis and condensation. One or more of these silicon compounds can be used.

[0049] In this invention, the silicon compound is preferably an alkoxysilane represented by the following general formula (1) or a derivative thereof. Si(OR) ４ (1) [In the formula, R is an alkyl group, preferably a lower alkyl group having 1 to 8 carbon atoms, and more preferably a lower alkyl group having 1 to 4 carbon atoms.]

[0050] Examples of R include methyl, ethyl, propyl, isopropyl, butyl, pentyl, and hexyl groups, with tetramethoxysilane (where R is a methyl group), tetraethoxysilane (where R is an ethyl group), and tetraisopropoxysilane (where R is an isopropyl group) being preferred. Furthermore, low-condensate products obtained by partially hydrolyzing alkoxysilane can also be cited as derivatives of alkoxysilane. In this invention, tetramethoxysilane is preferred because it allows for easy control of the hydrolysis rate, readily obtains single-nm fine silica particles, and leaves little unreacted residue.

[0051] The silicon compounds described above are hydrolyzed and condensed in the reaction solvent to form colloidal silica. Water or an organic solvent containing water is used as the reaction solvent.

[0052] Examples of organic solvents include alcohols such as methanol, ethanol, isopropanol, n-butanol, t-butanol, pentanol, ethylene glycol, propylene glycol, and 1,4-butanediol, as well as hydrophilic organic solvents such as ketones such as acetone and methyl ethyl ketone.

[0053] The amount of water added to the organic solvent is not particularly limited; it should be sufficient to provide the amount required for the hydrolysis of the silicon compound, with a preference of about 2 to 200 moles per mole of silicon compound.

[0054] It is preferable to adjust the reaction solvent to be alkaline by adding a basic catalyst. This adjusts the reaction solvent to a pH of preferably 8 to 11, more preferably 8.5 to 10.5, allowing for the rapid formation of colloidal silica. The type of basic catalyst is not particularly limited. As a basic catalyst, an organic basic catalyst that does not contain metal components is preferred in order to avoid contamination with metal impurities, and among these, an organic basic catalyst containing nitrogen is preferred. Examples of such organic basic catalysts include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, tetramethylammonium hydroxide (TMAH), tetramethylguanidine, 3-ethoxypropylamine, dipropylamine, and triethylamine. These can be used individually or in combination of two or more. Ammonia is preferred because it has excellent catalytic activity and is highly volatile, making it easy to remove in subsequent processes. From the viewpoint of increasing the true specific gravity of silica particles, it is preferable to select an organic base catalyst with a boiling point of 90°C or higher so that it does not volatilize easily even when the reaction temperature is high, and at least one selected from tetramethylammonium hydroxide and 3-ethoxypropylamine is more preferable.

[0055] By adding a silane coupling agent having mercapto groups that can be chemically converted to sulfonic acid groups to the above-mentioned colloidal silica, and then converting the mercapto groups to sulfonic acid groups, the silica particles in the colloidal silica can be modified with sulfonic acid.

[0056] Examples of silane coupling agents having a mercapto group include 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane.

[0057] The silane coupling agents having the above-mentioned mercapto group can be used individually or in combination of two or more.

[0058] When adding a coupling agent to colloidal silica, it is preferable to include a hydrophilic organic solvent in the colloidal silica, considering the solubility of the coupling agent. In this regard, when colloidal silica is obtained by the Stöber process, in which alkoxysilane is hydrolyzed and condensed in an alcohol-water solvent using a basic catalyst, alcohol is already present in the reaction solution, so it is not necessary to add a hydrophilic organic solvent further. In this case, it is more preferable that the hydrophilic organic solvent be 5% by mass or more relative to the water in the colloidal silica, so this can be adjusted by concentrating the reaction solution as needed.

[0059] On the other hand, when adding a silane coupling agent to water-dispersed colloidal silica, a hydrophilic solvent may be added to the extent that the silane coupling agent dissolves. Examples of hydrophilic organic solvents include isopropyl alcohol, ethanol, and methanol. Among these, it is preferable to use an alcohol of the same type as the alcohol produced by the hydrolysis of the silicon compound. This is because using an alcohol of the same type as the alcohol produced by the hydrolysis of the silicon compound facilitates the recovery and reuse of the solvent.

[0060] By adding an oxidizing agent such as hydrogen peroxide to colloidal silica to which the above-mentioned silane coupling agent has been added, the mercapto groups on the surface of the silica particles can be oxidized and converted to sulfo groups. Since hydrogen peroxide acts as an oxidizing agent, the mercapto groups modified on the colloidal silica are oxidized. This allows for the preparation of sulfonic acid-modified silica particles.

[0061] In step 1, a mother liquor containing the sulfonic acid-modified silica particles and water is prepared. The method for preparing the mother liquor is not particularly limited, and for example, it can be prepared by adding colloidal silica containing the sulfonic acid-modified silica particles to water.

[0062] The type of water used is not particularly limited; tap water, industrial water, ultrapure water, etc., can be used, and among these, ultrapure water is preferably used.

[0063] The silica particle content in the mother liquor is preferably 5 to 100 parts by mass, and more preferably 10 to 50 parts by mass, based on 100 parts by mass of water. In step 1, the above sulfone-modified silica particles and water are mixed to prepare the mother liquor.

[0064] Step 1, as described above, prepares sulfonic acid-modified silica particles and a mother liquor containing water.

[0065] (Step 2) Step 2 is the step of preparing an aqueous solution of cerium salt.

[0066] The cerium salt is not particularly limited as long as it is water-soluble; for example, cerium nitrate, ammonium cerium nitrate, cerium chloride, cerium acetate, etc., can be used. Among these, ammonium cerium nitrate is preferred because it is more water-soluble and has excellent reactivity under acidic conditions.

[0067] The water used to prepare the cerium salt aqueous solution is not particularly limited and can be tap water, industrial water, ultrapure water, etc., and among these, ultrapure water is preferably used.

[0068] The cerium content in the aqueous cerium salt solution is preferably 10 to 200 parts by mass, more preferably 20 to 180 parts by mass, even more preferably 30 to 150 parts by mass, and particularly preferably 50 to 120 parts by mass, based on 100 parts by mass of water.

[0069] A cerium salt aqueous solution is prepared by the process described in step 2 above.

[0070] (Step 3) Step 3 is a process in which a cerium salt aqueous solution is injected at a constant rate into the mother liquor while maintaining a temperature of 25 to 100°C to prepare a mixed solution, and the pH of the mixed solution after the injection of the cerium salt aqueous solution is 3.0 or less.

[0071] The holding temperature of the mixture is 25 to 100°C. By maintaining the temperature of the mixture within the specified range, the crystallite size of ceria and the proportion of Ce3+ can be adjusted. If the holding temperature is below 25°C, a sufficient ceria-containing shell cannot be formed on the surface of the silica particles. If the holding temperature exceeds 100°C, the solvent in the mixture evaporates, making it difficult to form a ceria-containing shell on the surface of the silica particles. In addition, the crystal growth of ceria is promoted, making it easier to cause scratches. The above holding temperature is preferably 30 to 98°C.

[0072] In step 3, it is sufficient that the temperature of the mixture prepared by injecting the cerium salt aqueous solution into the mother liquor is maintained within the above temperature range. However, from the viewpoint of making it easier to adjust the temperature of the mixture within the above range, it is preferable that the temperatures of both the cerium salt aqueous solution and the mother liquor are maintained within the above temperature range.

[0073] In step 3, a cerium salt aqueous solution is injected into the mother liquor at a constant rate to prepare the mixture. The injection rate of the cerium salt aqueous solution is not particularly limited as long as it is constant, but 1.5 ml / min to 300 ml / min is preferred. By injecting the cerium salt aqueous solution within the above range, it becomes easier to more uniformly adjust the formation of ceria-containing shells, the average particle size of core-shell particles, and the crystallite size of ceria.

[0074] In step 3, the injection time of the cerium salt aqueous solution is preferably 0.5 to 3 hours, and more preferably 0.5 to 2 hours. Having the lower limit of the injection time within this range makes it easier to form a more uniform shell containing ceria. Furthermore, having the upper limit of the injection time within this range shortens the time required for step 3, making it more industrially advantageous.

[0075] In step 3, the pH of the mixture after injection of the cerium salt aqueous solution is 3.0 or lower. If the pH exceeds 3.0, the aggregation of ceria coating the silica particles progresses, and the average secondary particle size of the core-shell particles increases significantly. The pH of the mixture is preferably 2.5 or lower, more preferably 2.0 or lower, and even more preferably 1.5 or lower. Furthermore, from the viewpoint of the reactivity of the cerium salt, the pH of the mixture is preferably 0.5 or higher, and more preferably 0.8 or higher.

[0076] The mixture is prepared by the process described in step 3 above.

[0077] (Step 4) Step 4 is a step in which the mixture is stirred for 1 to 24 hours while maintaining the pH and temperature of the mixture after injection of the cerium salt aqueous solution. By having step 4 in the manufacturing method of the present invention, a ceria-containing shell that coats the silica particles which are the core is sufficiently formed, and the core-shell particles of the present invention can be manufactured.

[0078] The pH of the mixture after injecting the cerium salt aqueous solution should be kept within the range described in step 3 above. The method for maintaining the pH within this range is not particularly limited, and examples include adding the cerium salt aqueous solution injected in step 3 and injecting it at a constant rate.

[0079] The temperature of the mixture after injecting the cerium salt aqueous solution should be kept within the range described in step 3 above. The method for maintaining the temperature within this range is not particularly limited, and examples include heating the container containing the mixture using known means such as a heater.

[0080] In step 4, the above mixture is stirred for 1 to 24 hours. If the stirring time is less than 1 hour, a ceria-containing shell that coats the silica particles, which are the core, will not be sufficiently formed. Also, if the stirring time exceeds 24 hours, the crystal growth and aggregation of ceria will progress, which is undesirable. The stirring time of the mixture is preferably 2 to 20 hours, and more preferably 3 to 10 hours.

[0081] The core-shell particles of the present invention are manufactured by step 4 as described above.

[0082] Since the method for producing core-shell particles of the present invention has the above-described configuration, the core-shell particles of the present invention can be easily produced. The core-shell particles of the present invention produced by this method can be usefully used as polishing agents (CMP) for semiconductor devices such as semiconductor wafers.

[0083] The present invention will be described in detail below with reference to examples, etc., but the present invention is not limited to these.

[0084] (Synthesis procedure for colloidal silica A1) A mother liquor was prepared by mixing 100 parts by mass of methanol, 20 parts by mass of ultrapure water, and 10 parts by mass of 28% by mass aqueous ammonia. A starting material solution was prepared by mixing 100 parts by mass of tetramethoxysilane and 50 parts by mass of methanol. An alkaline catalyst solution was prepared by mixing 50 parts by mass of ultrapure water and 20 parts by mass of 28% by mass aqueous ammonia. The starting material solution and the alkaline catalyst solution were injected at a constant rate into the mother liquor over 100 minutes while maintaining the temperature of the mother liquor at 30°C to obtain a mixture.

[0085] The mixture was concentrated while maintaining a constant volume by heating 100 parts by mass of the resulting mixture to remove the solvent by distillation, and adding 200 parts by mass of the mixture.

[0086] 100 parts by mass of the concentrated mixture was heated to 70°C, and 0.5 parts by mass of 3-mercaptopropyltrimethoxysilane and 2 parts by mass of a 30% aqueous hydrogen peroxide solution were added. Then, while heating and distilling off the solvent, 200 parts by mass of ultrapure water was added to replace the solvent component with water while maintaining a constant volume, thereby synthesizing colloidal silica A1.

[0087] (Synthesis procedure for colloidal silica A2) A mother liquor was prepared by mixing 100 parts by mass of methanol, 20 parts by mass of ultrapure water, and 10 parts by mass of 28% by mass aqueous ammonia. A starting material solution was prepared by mixing 200 parts by mass of tetramethoxysilane and 100 parts by mass of methanol. An alkaline catalyst solution was prepared by mixing 50 parts by mass of ultrapure water and 20 parts by mass of 28% by mass aqueous ammonia. Colloidal silica A2 was synthesized using the same procedure as for colloidal silica A1.

[0088] (Synthesis procedure for colloidal silica A3) A mother liquor was prepared by mixing 100 parts by mass of methanol, 20 parts by mass of ultrapure water, and 10 parts by mass of 28% by mass of aqueous ammonia. A starting material solution was prepared by mixing 40 parts by mass of tetramethoxysilane and 20 parts by mass of methanol. An alkaline catalyst solution was prepared by mixing 50 parts by mass of ultrapure water and 20 parts by mass of 28% by mass of aqueous ammonia. Colloidal silica A3 was synthesized using the same procedure as for colloidal silica A1.

[0089] (Synthesis procedure for colloidal silica B) A mother liquor was prepared by mixing 100 parts by mass methanol, 20 parts by mass ultrapure water, and 10 parts by mass 28% ammonia water. A starting material solution was prepared by mixing 400 parts by mass tetramethoxysilane and 100 parts by mass methanol. An alkaline catalyst solution was prepared by mixing 50 parts by mass ultrapure water and 20 parts by mass 28% ammonia water. Colloidal silica B was synthesized using the same procedure as for colloidal silica A1.

[0090] (Synthesis procedure for colloidal silica C) A mother liquor was prepared by mixing 100 parts by mass of methanol, 20 parts by mass of ultrapure water, and 10 parts by mass of 28% by mass aqueous ammonia. A starting material solution was prepared by mixing 100 parts by mass of tetramethoxysilane and 50 parts by mass of methanol. An alkaline catalyst solution was prepared by mixing 50 parts by mass of ultrapure water and 20 parts by mass of 28% by mass aqueous ammonia. The starting material solution and the alkaline catalyst solution were injected at a constant rate into the mother liquor over 100 minutes while maintaining the temperature of the mother liquor at 30°C to obtain a mixture.

[0091] The mixture was concentrated while maintaining a constant volume by heating 100 parts by mass of the resulting mixture to remove the solvent by distillation, and adding 200 parts by mass of the mixture.

[0092] Colloidal silica C was synthesized by heating the concentrated mixture to remove the solvent by distillation, while adding 200 parts by mass of ultrapure water, thereby replacing the solvent component with water while maintaining a constant volume.

[0093] (Example 1) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A1 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 15 parts by mass of cerium ammonium nitrate with 15 parts by mass of ultrapure water. The mother liquor was heated to 100°C, and the cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 1.2. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 100°C and the pH at 1.2. Then, it was cooled to room temperature, and core-shell particles were produced by replacing the solvent with ultrapure water using an ultrafiltration membrane (Asahi Kasei AOP-0013) while keeping the volume constant until the electrical conductivity reached 200 μS / cm.

[0094] (Example 2) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A1 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 20 parts by mass of cerium ammonium nitrate with 20 parts by mass of ultrapure water. The mother liquor was heated to 100°C, and the cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 1.0. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 100°C and the pH at 1.0. Then, it was cooled to room temperature, and core-shell particles were produced by replacing the solvent with ultrapure water while maintaining a constant volume using an ultrafiltration membrane (Asahi Kasei AOP-0013) until the electrical conductivity reached 200 μS / cm.

[0095] (Example 3) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A1 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 2 parts by mass of cerium ammonium nitrate with 2 parts by mass of ultrapure water. The mother liquor was heated to 100°C, and the cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 1.4. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 100°C and the pH at 1.4. Then, it was cooled to room temperature, and core-shell particles were produced by replacing the solvent with ultrapure water using an ultrafiltration membrane (Asahi Kasei AOP-0013) while keeping the volume constant until the electrical conductivity reached 200 μS / cm.

[0096] (Example 4) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A1 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 15 parts by mass of cerium ammonium nitrate with 15 parts by mass of ultrapure water. The mother liquor was heated to 60°C, and the cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 1.2. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 60°C and the pH at 1.2. Then, it was cooled to room temperature, and core-shell particles were produced by replacing the solvent with ultrapure water while maintaining a constant volume using an ultrafiltration membrane (Asahi Kasei AOP-0013) until the electrical conductivity reached 200 μS / cm.

[0097] (Example 5) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A1 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 15 parts by mass of cerium ammonium nitrate with 15 parts by mass of ultrapure water. The cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring the mother liquor at 25°C. The pH at the end of the injection of the cerium salt aqueous solution was 1.2. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 25°C and the pH at 1.2. Then, core-shell particles were produced by replacing the solvent with ultrapure water using an ultrafiltration membrane (Asahi Kasei AOP-0013) while keeping the volume constant, until the electrical conductivity reached 200 μS / cm.

[0098] (Example 6) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A1 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 15 parts by mass of cerium ammonium nitrate with 15 parts by mass of ultrapure water. The mother liquor was heated to 100°C, and the cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 1.2. Next, the mixture was stirred for 23 hours while maintaining the liquid temperature at 100°C and the pH at 1.2. Then, it was cooled to room temperature, and core-shell particles were produced by replacing the solvent with ultrapure water while maintaining a constant volume using an ultrafiltration membrane (Asahi Kasei AOP-0013) until the electrical conductivity reached 200 μS / cm.

[0099] (Example 7) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A1 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 15 parts by mass of cerium ammonium nitrate with 15 parts by mass of ultrapure water. The mother liquor was heated to 100°C, and the cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 1.2. Next, the mixture was stirred for 1 hour while maintaining the liquid temperature at 100°C and the pH at 1.2. Then, it was cooled to room temperature, and core-shell particles were produced by replacing the solvent with ultrapure water using an ultrafiltration membrane (Asahi Kasei AOP-0013) while maintaining a constant volume until the electrical conductivity reached 200 μS / cm.

[0100] (Example 8) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A2 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 15 parts by mass of cerium ammonium nitrate with 15 parts by mass of ultrapure water. The mother liquor was heated to 100°C, and the cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 1.2. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 100°C and the pH at 1.2. Then, it was cooled to room temperature, and core-shell particles were produced by replacing the solvent with ultrapure water while maintaining a constant volume using an ultrafiltration membrane (Asahi Kasei AOP-0013) until the electrical conductivity reached 200 μS / cm.

[0101] (Example 9) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A3 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 15 parts by mass of cerium ammonium nitrate with 15 parts by mass of ultrapure water. The mother liquor was heated to 100°C, and the cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 1.2. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 100°C and the pH at 1.2. Then, it was cooled to room temperature, and core-shell particles were produced by replacing the solvent with ultrapure water while maintaining a constant volume using an ultrafiltration membrane (Asahi Kasei AOP-0013) until the electrical conductivity reached 200 μS / cm.

[0102] (Comparative Example 1) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A1 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 15 parts by mass of cerium ammonium nitrate with 15 parts by mass of ultrapure water. The mother liquor was heated to 100°C, and the cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 1.2. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 100°C and pH 1.2. Then, it was cooled to room temperature, and the solvent was replaced by adding ultrapure water through an ultrafiltration membrane (Asahi Kasei AOP-0013) while keeping the volume constant, until the electrical conductivity reached 200 μS / cm. The obtained dispersion was dried at 150°C for 10 hours, and then calcined in a muffle oven at 1000°C for 2 hours to obtain a powder. 1667 parts by mass of ultrapure water were added to 100 parts by mass of the obtained powder, and wet crushing and pulverization were performed using φ0.22 mm high-purity silica beads (manufactured by Daiken Chemical Industry Co., Ltd.) to prepare a crushed calcined body dispersion with a solid content concentration of 6.0% by mass.

[0103] (Comparative Example 2) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A1 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 15 parts by mass of cerium ammonium nitrate with 15 parts by mass of ultrapure water. The cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring the mother liquor at 5°C. The pH at the end of the injection of the cerium salt aqueous solution was 1.2. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 5°C and the pH at 1.2. Then, it was cooled to room temperature and the solvent was replaced by adding ultrapure water through an ultrafiltration membrane (Asahi Kasei AOP-0013) while keeping the volume constant, until the electrical conductivity reached 200 μS / cm.

[0104] (Comparative Example 3) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A1 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 1.0 part by mass of cerium ammonium nitrate with 1.0 part by mass of ultrapure water. The mother liquor was heated to 100°C, and the cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 1.8. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 100°C and the pH at 1.8. Then, it was cooled to room temperature, and the solvent was replaced using an ultrafiltration membrane (Asahi Kasei AOP-0013) while adding ultrapure water to maintain a constant volume until the electrical conductivity reached 200 μS / cm.

[0105] (Comparative Example 4) A mother liquor was prepared by adding 13 parts by mass of colloidal silica B to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 15 parts by mass of cerium ammonium nitrate with 15 parts by mass of ultrapure water. The mother liquor was heated to 100°C, and the cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 1.2. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 100°C and the pH at 1.2. Then, it was cooled to room temperature, and the solvent was replaced using an ultrafiltration membrane (Asahi Kasei AOP-0013) while adding ultrapure water to maintain a constant volume until the electrical conductivity reached 200 μS / cm.

[0106] (Comparative Example 5) A mother liquor was prepared by adding 13 parts by mass of colloidal silica A1 to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 15 parts by mass of cerium ammonium nitrate with 15 parts by mass of ultrapure water. The mother liquor was heated to 100°C, and the cerium salt aqueous solution and 5 parts by mass of 28% by mass ammonia aqueous solution were injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 10.0. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 100°C and the pH at 10.0. Then, it was cooled to room temperature, and the solvent was replaced using an ultrafiltration membrane (Asahi Kasei AOP-0013) while adding ultrapure water to maintain a constant volume until the electrical conductivity reached 200 μS / cm.

[0107] (Comparative Example 6) A mother liquor was prepared by adding 13 parts by mass of colloidal silica C to 100 parts by mass of ultrapure water. A cerium salt aqueous solution was prepared by mixing 15 parts by mass of cerium ammonium nitrate with 15 parts by mass of ultrapure water. The mother liquor was heated to 100°C, and the cerium salt aqueous solution was injected at a constant rate over 1 hour while stirring. The pH at the end of the injection of the cerium salt aqueous solution was 1.2. Next, the mixture was stirred for 5 hours while maintaining the liquid temperature at 100°C and the pH at 1.2. Then, it was cooled to room temperature, and the solvent was replaced using an ultrafiltration membrane (Asahi Kasei AOP-0013) while adding ultrapure water to maintain a constant volume until the electrical conductivity reached 200 μS / cm.

[0108] Evaluation Method The examples and comparative examples obtained as described above were evaluated by the following method.

[0109] (Method for confirming that silica particles are coated with ceria) An aqueous dispersion of core-shell particles was dried in a vacuum dryer (Matsuura Seisakusho, AUO-250V) at 25°C for 8 hours at a pressure of 0.1 MPa or less. The resulting powder was analyzed using TEM-EDS (TEM: JEOL Ltd., JEM-2100F; EDS: JEOL Ltd., JED-2300T). The elemental mapping images of Si, O, and Ce of the coated particles were obtained under the following observation conditions to confirm whether the silica particles were coated with ceria. [Observation conditions] Acceleration voltage: 200kV Magnification: ×500,000

[0110] (Ceria content in core-shell particles) The solid content concentration of the core-shell particle dispersion was determined by weighing after loss on ignition at 800°C for 1 hour. Next, approximately 3.3 g of the core-shell particle dispersion sample (solid content concentration 6.0 mass%) was placed in a platinum dish. 3 ml of phosphoric acid, 5 ml of nitric acid, and 10 ml of hydrofluoric acid were added, and the mixture was heated on a sand bath. After drying, a small amount of water and 50 ml of nitric acid were added to dissolve the mixture, and it was placed in a 100 ml volumetric flask, where water was added to make a total volume of 100 ml. The procedure of taking 10 ml of the separatory solution from the 100 ml solution into a 20 ml volumetric flask was repeated 5 times to obtain 5 10 ml separatory samples. Next, these samples were measured using an ICP plasma emission spectrometer (SII, SPS5520) by the standard addition method, and CeO2 (mass%) was calculated from the obtained Ce content. Next, assuming that the only component of the core-shell particles other than CeO2 is SiO2, the mass percentage of SiO2 was calculated.

[0111] (Average secondary particle diameter) A mixture prepared by diluting the solid content with ultrapure water to a solid content concentration of 0.10 mass% was used as the measurement sample. The average secondary particle diameter of core-shell particles was measured using dynamic light scattering (ELSZ-2000, manufactured by Otsuka Electronics Co., Ltd.) with this measurement sample.

[0112] (Retention rate of average secondary particle diameter after disintegration treatment) A core-shell particle aqueous dispersion (solid content concentration: 6.0 mass%) was prepared, and the average secondary particle diameter was measured using the method for measuring the average secondary particle diameter described above. Next, 40 ml of the core-shell particle aqueous dispersion (solid content concentration: 6.0 mass%) was placed in a screw-cap tube No. 6 (manufactured by Maruemu Co., Ltd.), set in an ultrasonic cleaner (ASU CLEANER, model number: ASU-100), and immersed in a bath (25°C) with an output of 240 W and a frequency of 40 kHz for 10 minutes. Next, the average secondary particle diameter after disintegration treatment was measured using the method for measuring the average particle diameter described above. The retention rate of the average secondary particle diameter was calculated by dividing the average secondary particle diameter after disintegration treatment by the average particle diameter before treatment.

[0113] (Celite size of Celia) A core-shell particle aqueous dispersion was dried at a pressure of 0.1 MPa or less for 8 hours in a vacuum dryer (Matsuura Seisakusho Co., Ltd., ASU-250V) at 25°C. The obtained powder was ground in a mortar for 5 minutes, and the X-ray diffraction pattern was measured using an X-ray diffractometer (Rigaku Corporation, SmartLab 9kW) under the following conditions.

[0114] [Measurement Conditions] X-ray tube: Cu Kα X-ray output: 45kV, 200mA Step width: 0.01deg Scan range: 5-90deg Entrance slit: 1 / 6deg Receiving slit 1: 20mm Receiving slit 2: 20mm

[0115] Furthermore, the full width at half maximum (FWHM) of the peak on the (111) plane near 2θ = 28 degrees in the obtained X-ray diffraction pattern was measured, and the crystallite size of ceria was determined using the following Scherrer equation: L = Kλ / βcosθ L: crystallite size, nm K: Scherrer constant (0.89) λ: X-ray wavelength (0.154 nm) β: FWHM θ: diffraction angle

[0116] (Average primary particle diameter) After pre-drying the core-shell particle aqueous dispersion on a hot plate, a sample for measurement was prepared by heat treatment at 100°C for 5 hours under reduced pressure. The BET specific surface area was measured using the prepared sample. Assuming the true specific gravity of silica is 2.2, 2727 / BET specific surface area (m²) was used. 2 The value ( / g) was converted to determine the average primary particle size (nm) of the silica particles in colloidal silica.

[0117] (Association Ratio) The average secondary particle diameter and average primary particle diameter were measured as described above, and the average secondary particle diameter / average primary particle diameter was calculated to determine the association ratio of core-shell particles.

[0118] (Ce 3+ (Percentage of peak area of ​​peaks) Core-shell particle aqueous dispersion was dried in a vacuum dryer (Matsuura Seisakusho, AUO-250V) at 25°C at 0.1 MPa or less for 8 hours, and the obtained powder was analyzed using an X-ray photoelectron spectrometer (XPS, PHI5000 VersaProbe II). The range of 880-894 eV was measured, and the waveform separation of the obtained peaks was performed, and Ce 4+ The origin of the peaks at 883eV and 889eV, Ce 3+Using the area of ​​the 885eV peak from which it originates, the following formula can be used to determine Ce 3+ The ratio of the peak area of ​​the peak was calculated. (Ce 3+ Peak area of ​​the peak / Ce 4+ and Ce 3+ (Sum of peak areas of the peaks) × 100

[0119] (Zeta potential, isoelectric point) The zeta potential of the aqueous dispersion of core-shell particles was measured using an ultrasonic attenuation method after diluting the aqueous dispersion with ultrapure water to a solid content concentration of 5 wt%, adjusting the pH to 3. The pH at which the zeta potential becomes 0 was defined as the isoelectric point.

[0120] (Oxide film polishing speed, polished surface roughness RMS) A mixture containing core-shell particles was diluted with ultrapure water so that the solid content concentration of the core-shell particles was 3.0% by mass. The pH was adjusted to 4.0 using 1.0 M hydrochloric acid and 1.0 M sodium hydroxide aqueous solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to prepare a polishing composition. Using the obtained polishing composition, a 3 cm square silicon wafer with a silicon oxide film deposited on its surface was polished under the following conditions.

[0121] [Polishing Conditions] Polishing machine: NF-300CMP manufactured by Nanofactor Co., Ltd. Polishing pad: IC1000TMPad manufactured by Nitta DuPont Co., Ltd. Slurry supply rate: 50 mL / min Head rotation speed: 90 rpm Platen rotation speed: 90 rpm Polishing pressure: 4 psi Polishing time: 2 minutes The film thickness of the wafer before and after polishing was measured using an optical interferometry film thickness analyzer (Ava Spec-2048), and the polishing speed was calculated from the difference. In addition, the surface roughness RMS of the polished surface of the wafer was evaluated using an atomic force microscope under the following conditions.

[0122] [Surface Roughness Evaluation Conditions] Atomic force microscope: Shimadzu Corporation SPM-9700HT Cantilever: OLYMPUS MICRO CANTILEVER OMCL-AC240TS-R3 Observation mode: Dynamic Scanning range: 3.0 μm square Scanning speed: 1.00 Hz Number of fields of view: 5 fields were observed per polished wafer. Method of calculating surface roughness RMS: The average value of the root mean square roughness (RMS) of the 5 fields was calculated and used as the surface roughness RMS of the polished surface.

[0123] The results are shown in Table 1.

[0124]

Claims

1. Core-shell particles having a silica particle as a core and a ceria-containing shell covering the silica particle, characterized in that: (1) the ceria content in the core-shell particles is 4.0 to 80.0% by mass; (2) the crystallite size of the ceria is 2.0 to 9.0 nm; and (3) the retention rate of the average secondary particle size after disintegration treatment is 0.70 to 1.

0.

2. The core-shell particle according to claim 1, wherein the average primary particle diameter calculated from the BET specific surface area is 10.0 to 300.0 nm, and the average secondary particle diameter measured by dynamic scattering is 20.0 to 600.0 nm.

3. The core-shell particle according to claim 1, wherein the association ratio is 1 to 10.

4. Ce detected by XPS ３＋ Originating peaks and Ce ４＋ Of the peaks of origin, Ce ３＋ The core-shell particle according to claim 1, wherein the proportion of the peak area of ​​the originating peak is 20 to 40%.

5. The core-shell particle according to claim 1, wherein the isoelectric point of the aqueous dispersion of the core-shell particle is 5 to 9.

6. The core-shell particle according to claim 1, wherein the zeta potential of the aqueous dispersion of the core-shell particle at pH 3 is +20 to +80 mV.

7. A method for producing core-shell particles having a shell containing ceria that coats silica particles, comprising: (1) step 1 of preparing a mother liquor containing sulfonic acid-modified silica particles and water; (2) step 2 of preparing an aqueous cerium salt solution; (3) step 3 of preparing a mixed solution by injecting the aqueous cerium salt solution into the mother liquor at a constant rate while maintaining a temperature of 25 to 100°C, wherein the pH of the mixed solution after injection of the aqueous cerium salt solution is 3.0 or less; and (4) step 4 of stirring the mixed solution for 1 to 24 hours while maintaining the pH and temperature of the mixed solution after injection of the aqueous cerium salt solution.

8. The manufacturing method according to claim 7, wherein the injection time of the cerium salt aqueous solution in step 3 is 0.5 to 24 hours.

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