Liquid dispersion and powder of cerium-based core-shell particles, method for producing same and use thereof in polishing

Abstract

To provide a dispersion of cerium-based core-shell particles having improved polishing characteristics when used in a chemical mechanical polishing process.SOLUTION: A dispersion of cerium-based core-shell particles in a liquid, each cerium-based core-shell particle having a core particle made of cerium oxide optionally doped with at least one metal (M) and a shell consisting of a plurality of nanoparticles of cerium oxide optionally doped with at least one metal (M '), said nanoparticles being formed on the surface of said core particle, wherein the ratio of the average particle size of said core-shell particles as measured by TEM to the average particle size of said core-shell particles as measured by BET is at least 1.5.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] This application claims priority from European Patent Application No. 19306524.0 filed on November 26, 2019, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to a method for producing dispersions of cerium-based core-shell particles, to dispersions and powders obtainable by such a method, and to their use in the field of polishing, in particular chemical-mechanical polishing. [Background technology]

[0003] Ceric oxide is commonly used for polishing applications, particularly chemical-mechanical polishing. The development of the electronics industry increasingly necessitates the use of compositions for polishing various workpieces, such as disks or dielectric compounds. These compositions, generally in the form of dispersions, must exhibit a certain number of characteristics. For example, they must provide a high degree of material removal, which reflects their polishing ability. They must also have as low a defectivity as possible. The term "defectivity" is intended to specifically refer to the amount of scratches exhibited by a substrate after treatment with the formulation. For reasons of stability and ease of use, these dispersions must contain particles of submicron size, i.e., generally less than 300 nm. The presence of particles that are too fine in these dispersions can reduce the polishing ability of the particles, while particles that are too large can contribute to increased defectivity.

[0004] In this regard, we believe that there is a need for cerium-based particles that have improved polishing properties when used in chemical mechanical polishing processes, as well as methods for their production that are simple and easy to implement on an industrial scale. Summary of the Invention

[0005] These problems are solved by the present invention, which provides inter alia novel cerium-based particles having a rough surface due to their particular core-shell morphology and method of manufacture.

[0006] Therefore, one object of the present invention is to provide a method for producing a pharmaceutical composition comprising the steps of: (a) providing an aqueous dispersion comprising particles of cerium oxide optionally doped with at least one metal (M); providing an aqueous solution comprising a cerium (III) salt; and optionally providing an aqueous solution comprising at least one metal (M') salt; (b) contacting the aqueous dispersion with the aqueous solution provided in step (a) under an oxidizing atmosphere while maintaining a temperature comprised between 0°C and 80°C and a pH of 11 or less to produce a dispersion of cerium-based core-shell particles. At least one of steps (a) or (b) must be carried out in the presence of nitrate ions.

[0007] The present invention also relates to cerium-based core-shell particles and dispersions thereof obtainable or obtainable by this method.

[0008] The cerium-based core-shell particles of the present invention can be described as a core particle of cerium oxide optionally doped with at least one metal (M) and a shell consisting of a plurality of nanoparticles of cerium oxide optionally doped with at least one metal (M'), said nanoparticles being formed on the surface of the core particle, wherein the ratio of the average particle size of the core-shell particles as measured by TEM to the average particle size of the core-shell particles as measured by BET is at least 1.5.

[0009] Advantageously, the specific core-shell morphology of the particles of the present invention increases their surface roughness and therefore their specific surface area compared to smooth cerium oxide particles without a shell according to the present invention. Thus, by increasing the contact area between the particles and the substrate to be polished, the polishing properties of the core-shell particles of the present invention are improved, allowing them to be used advantageously in chemical mechanical polishing processes. The core-shell particle dispersions of the present invention in particular allow for higher removal rates due to their rough surface while maintaining the same defects, due to the comparable particle size distribution compared to dispersions of smooth-surfaced cerium oxide particles without a shell according to the present invention.

[0010] As described in detail herein below, the cerium-based core-shell particle dispersions of the present invention can be used to prepare cerium-based core-shell particle powders, as well as polishing compositions.

[0011] Furthermore, one advantage of the core-shell particles of the present invention is that the nanoparticles from the shell are sufficiently attached to the core particle. It has been particularly observed that they remain attached to the core throughout the entire chemical mechanical polishing process. This is all the more important because the particle shell withstands the mechanical stresses during the chemical mechanical polishing process. If the shell nanoparticles are dislodged during polishing, these small cerium oxide particles may remain attached to the substrate even after the cleaning process, which is unacceptable to the end user. This would result in loss of substrates and unacceptable costs due to frequent polishing composition replenishment.

[0012] Another advantage of the core-shell particles of the present invention lies in the fact that they have a suitable particle size range for CMP applications and are monodisperse. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a TEM image of a dispersion of core-shell particles of the present invention obtained by the method described in Example 1, having a cerium oxide core and a cerium oxide shell. [Figure 2]TEM image of a dispersion of cerium oxide particles obtained by the method described in Counter Example 1. [Figure 3] 1 is an SEM image of a dispersion of cerium oxide particles intended to be used as core particles in the methods described in Examples 1, 2 and 4. [Figure 4] 1 is an SEM image of a dispersion of core-shell particles of the present invention obtained by the method described in Example 1, having a cerium oxide core and a cerium oxide shell. [Figure 5] 1 is an SEM image of a dispersion of core-shell particles of the present invention obtained by the method described in Example 2, having a cerium oxide core and a cerium oxide doped with a lanthanum shell. [Figure 6] 1 is an SEM image of a dispersion of core-shell particles of the present invention obtained by the method described in Example 3, having a cerium oxide core and a cerium oxide shell. [Figure 7] 1 is an SEM image of a dispersion of core-shell particles of the present invention obtained by the method described in Example 4, having a cerium oxide core and a cerium oxide shell. [Figure 8] TEM image of a dispersion of cerium oxide particles obtained by the method described in Example 2. [Figure 9] 1 is a TEM image of a dispersion of core-shell particles of the present invention obtained by the method described in Example 5, having a lanthanum-doped cerium oxide core and a cerium oxide shell. [Figure 10] 1 is an SEM image of a dispersion of core-shell particles of the present invention having a cerium oxide core and a cerium oxide shell obtained by the method described in Example 6.

[0014] Transmission electron microscope (TEM) images were collected using a JEM-1400 (JEOL) operated at 120 kV. Scanning electron microscope (SEM) images were obtained by a SEMS-5500 from Hitachi High Technologies Corporation.

[0015] definition In the present disclosure, the expression "comprises" should be understood to mean "comprises at least one."

[0016] When referring to the aqueous dispersions or solutions provided in steps (a) and (b) of the method of the present invention, the expression "comprising" encompasses embodiments in which said dispersions and solutions "consist of" the compounds described in that context.

[0017] The expression "included in" must be understood as including the limiting values.

[0018] Throughout the description, the term "cerium-based" encompasses cerium oxide and metal-doped cerium oxide. Cerium oxide typically has a purity of at least 99.8% by weight based on the weight of the oxide. Cerium oxide is typically crystalline ceric oxide. The term "cerium oxide doped with at least one metal" means that the metal ions partially substitute for the cerium ions in the CeO lattice. Therefore, it also refers to a mixed oxide of cerium and at least one metal. In some embodiments, it can also refer to a solid solution. In this case, the metal atoms are fully dispersed within the cerium oxide crystal structure. Some impurities other than the metal may be present in the oxide. These impurities may originate from raw materials or starting materials used in the preparation process of the metal-doped oxide. The total proportion of impurities is typically less than 0.2% by weight based on the metal-doped oxide. Residual nitrates are not considered impurities in this application.

[0019] The expression "dispersion" in reference to a dispersion of cerium-based particles means a system of solid particulates of submicron size stably dispersed in a liquid medium, said particles optionally containing residual amounts of bound or adsorbed ions, such as, for example, nitrate or ammonium.

[0020] The term "nanoparticles" in reference to the small particles forming the shell of the core-shell particles of the present invention means that these small particles have an average particle size comprised between 1 and 100 nm, which can be determined, inter alia, by TEM as explained below.

[0021] Different parameters can be used to characterize the particle size and particle size distribution: - all core-shell particles of the invention; - core particles, in particular by characterizing the particles provided in the dispersion of step (a) of the method of the present invention; - Nanoparticles from the shell.

[0022] In relation to particle dispersions: - the average particle size of n (>100) particles can be determined using photographs of their dispersions obtained by transmission electron microscopy (TEM); The standard deviation referred to in this application is also determined by the TEM method. It has its usual mathematical meaning: it is the square root of the variance and is expressed by the formula:

number

number

[0023] For particles in powder form (dry particles): The average particle size of the particles can be determined by X-ray diffraction (XRD) techniques. The value measured by XRD corresponds to the size of the coherent range calculated based on the width of the two most intense diffraction lines and using the Scherrer model. - The specific surface area can be determined on powders by nitrogen adsorption according to the Brunauer-Emmett-Teller method (BET method). This method is described in the standard ASTM D3663-03 (reapproved in 2015). This method is also described in the periodical "The Journal of the American Chemical Society, 60, 309 (1938)". The specific surface area can be determined automatically on a Micromeritics TriStar 3000 instrument, following the manufacturer's guidelines. Prior to the measurement, the powdered sample is degassed in static air by heating at temperatures up to 210°C to remove adsorbed species. - The average particle size estimated by BET is the theoretical average particle size obtained from the specific surface area measured by the BET method, assuming that the particles are non-porous spherical particles of cerium oxide with a density of 7.2.

[0024] The particle size distribution can be characterized by various parameters, which are based on distribution by volume rather than by number. - The hydrodynamic mean diameter Dh, which is equal to the particle median diameter D50, can be determined by dynamic light scattering (DLS). This technique allows the measurement of the hydrodynamic mean diameter Dh of solid materials, the value of which is affected by the presence of particle agglomerates. Therefore, measurements are usually carried out on aqueous dispersions of particles. Dh is determined using a Malvern Zetasizer Nano-ZS instrument, following the manufacturer's guidelines. Samples usually need to be diluted with deionized water. A dilution factor of 30,000 can be applied. Laser diffraction can also be used to determine particle size distribution. A laser particle size analyzer such as the Horiba LA-910 can be used according to the manufacturer's guidelines. A relative refractive index of 1.7 can be used for the measurement. From the volume distribution obtained by laser diffraction, various parameters commonly used in statistics can be subtracted, such as D10, D50, D90, and dispersion index. D10 is the diameter determined from a distribution obtained by laser diffraction in which 10% of the particles have a diameter smaller than D10. D50 is the median diameter determined from the distribution obtained by laser diffraction. D90 is the diameter determined from a distribution obtained by laser diffraction in which 90% of the particles have a diameter smaller than D90. The "dispersion index" is defined by the formula σ / m=(D90-D10) / 2D50. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention relates to a method for producing a method for manufacturing a semiconductor device comprising the steps of: (a) providing an aqueous dispersion comprising particles of cerium oxide optionally doped with at least one metal (M); providing an aqueous solution comprising a cerium (III) salt; and optionally providing an aqueous solution comprising at least one metal (M') salt; (b) contacting the aqueous dispersion with the aqueous solution provided in step (a) under an oxidizing atmosphere while maintaining a temperature comprised between 0°C and 80°C and a pH of not more than 11, to produce a dispersion of cerium-based core-shell particles, At least one of steps (a) or (b) is carried out in the presence of nitrate ions.

[0026] The aqueous dispersion provided in step (a) Particles of cerium oxide, optionally doped with at least one metal (M), are provided to serve as core particles for the cerium-based core-shell particles produced by the method of the present invention.

[0027] In the following detailed description of step (a), these particles will be referred to as "cerium-based particles" unless otherwise specified.

[0028] The starting dispersion used in step (a) can be prepared by dispersing a commercially available powder of cerium-based particles in water. Alternatively, commercially available dispersions of cerium-based particles can be used. If necessary, these dispersions can be concentrated or diluted and / or transferred from their original organic phase to water for carrying out step (a) by methods known per se.

[0029] The dispersion used in step (a) can contain at least 3 wt. %, particularly at least 5 wt. %, at least 10 wt. %, at least 15 wt. %, and even more particularly at least 20 wt. % of cerium-based particles, based on the total weight of the dispersion. The reaction yield is further improved. The dispersion used in step (a) can contain less than 50 wt. %, particularly less than 40 wt. %, and more particularly less than 35 wt. % of cerium-based particles, based on the total weight of the dispersion.

[0030] According to one embodiment, the cerium-based particles used in step (a) are cerium oxide particles, in particular ceria particles, which can be advantageously produced by one of the methods described by the applicant in WO 2008 / 043703, WO 2010 / 020466 and WO 2015 / 091495.

[0031] Such cerium oxide particles (and therefore core particles) may exhibit: an average particle size, measured by TEM, of at most 250 nm, in particular at most 200 nm, more particularly at most 170 nm; an average particle size, measured by TEM, of at least 30 nm, in particular at least 40 nm, more particularly at least 50 nm, the standard deviation of said average particle size values ​​may be at most 30%, in particular at most 20%, more particularly at most 15%; and / or an average particle size, calculated from BET surface measurements, of at most 120 nm, in particular at most 110 nm; an average particle size, calculated from BET surface measurements, of at least 15 nm, in particular at least 19 nm, in particular at least 30 nm, in particular at least 40 nm; and / or a median diameter D50 determined from the distribution obtained by laser diffraction, which is comprised between 60 nm and 170 nm, in particular between 70 nm and 160 nm, more particularly between 80 nm and 150 nm, and even more particularly between 90 nm and 150 nm, and / or - a dispersion index determined from the distribution obtained by laser diffraction of at most 0.5, in particular at most 0.4, more particularly at most 0.3.

[0032] According to another embodiment, the cerium-based particles used in step (a) are cerium oxide particles doped with at least one metal (M). Such particles can advantageously be produced by one of the methods described by the applicant in WO 2015 / 197656 and WO 2018 / 229005.

[0033] According to this embodiment, the metal (M) may more particularly be selected from the group consisting of alkali metal elements, alkaline earth metal elements, rare earth elements, actinide elements, transition metal elements and post-transition metal elements from the periodic table.

[0034] The expression "rare earth" is understood to mean an element from the group consisting of yttrium and the elements of the periodic table having atomic numbers from 57 to 71 inclusive. Transition metal elements are defined as any element of the d-block of the periodic table, including groups 3 to 12 of the periodic table. Post-transition metal elements, also known as impoverished metals, are defined as metallic elements of the p-block of the periodic table, including aluminum, gallium, indium, thallium, tin, lead, bismuth and polonium, among others.

[0035] Preferably, the at least one metal (M) is selected from the group consisting of transition metal elements such as Zr; post-transition metal elements such as Al; rare earth elements such as La, Pr, Nd, and Y; and alkaline earth metal elements such as Sr. More preferably, the at least one metal (M) is selected from the group consisting of lanthanum, praseodymium, neodymium, and zirconium. Even more preferably, the at least one metal (M) is selected from the group consisting of lanthanum, praseodymium, and neodymium. Even more preferably, the at least one metal (M) is lanthanum.

[0036] Further according to this embodiment, the molar ratio M / M+Ce in the metal (M)-doped cerium oxide particles used in step (a) may be comprised between 0.01 and 0.15, more particularly between 0.01 and 0.13, in particular between 0.01 and 0.12.

[0037] Such metal (M) doped cerium oxide particles can exhibit the following: an average particle size, measured by TEM, of at most 250 nm, in particular at most 200 nm, more particularly at most 170 nm; an average particle size, measured by TEM, of at least 30 nm, in particular at least 40 nm, more particularly at least 50 nm, the standard deviation of said average particle size values ​​may be at most 30%, in particular at most 20%, more particularly at most 15%; and / or - an average particle size, calculated from BET surface measurements, of at most 120 nm, in particular at most 110 nm; an average particle size, calculated from BET surface measurements, of at least 15 nm, in particular at least 19 nm, at least 30 nm, in particular at least 40 nm; and / or a median diameter D50 of 60 nm to 700 nm, in particular 70 nm to 200 nm, determined from a distribution obtained by laser diffraction; and / or - a dispersion index of at most 0.6, in particular at most 0.4, more particularly at most 0.3, determined from the distribution obtained by laser diffraction.

[0038] According to one subembodiment, the cerium-based particles used in step (a) are lanthanum-doped cerium oxide particles. Such particles may exhibit: a mean hydrodynamic diameter Dh, determined by the distribution obtained by DLS, comprised between 100 nm and 1000 nm, more particularly between 100 nm and 500 nm, even more particularly between 100 nm and 250 nm, and even more particularly between 150 nm and 250 nm, and / or a median diameter D50 determined from the distribution obtained by laser diffraction, comprised between 100 nm and 700 nm, in particular between 100 nm and 200 nm, and / or It may exhibit a dispersion index, determined from a distribution obtained by laser diffraction, of at most 0.6, in particular at most 0.4, more particularly at most 0.3. Such particles can in particular be produced as described in WO 2018 / 229005.

[0039] The temperature of the cerium-based particle dispersion provided in step (a) can be set before step (b) to a value comprised between 0°C and 80°C, preferably between 10°C and 60°C, more preferably between 15°C and 45°C, particularly between 20°C and 40°C, more specifically between 25°C and 35°C, and even more specifically between 30°C and 35°C. It is preferable to set the required temperature while stirring the dispersion. Stirring can be started before adjusting the temperature.

[0040] Similarly, the pH of the dispersion of cerium-based particles provided in step (a) can be set to a value of 11 or less, preferably between 3 and 11, preferably between 4 and 11, preferably between 8 and 11, more preferably between 8 and 10, particularly between 8 and 9, more particularly about 9, before step (b). A pH adjuster can be used in this regard. Depending on the initial pH of the dispersion, the pH adjuster can be an acid or a base. Suitable acids include nitric acid, hydrochloric acid, sulfonic acid, carbonic acid, picolinic acid, propionic acid, and mixtures thereof, with nitric acid being preferred. Suitable bases include alkali metal or alkaline earth metal hydroxides and aqueous ammonia. Secondary, tertiary, or quaternary amines can also be used. Aqueous ammonia is preferred. According to a preferred embodiment, the pH adjuster is a base, preferably aqueous ammonia.

[0041] Preparation of the core particles provided in step (a) According to one embodiment, the cerium-based particles used in step (a) are prepared by a method based on the precipitation of cerium(III) and cerium(IV) salts, comprising the following steps: (a') Under an inert atmosphere, an aqueous solution of a base and NO3 - with an aqueous solution containing Ce(III), Ce(IV) and optionally at least one metal (M); (b') heat-treating the mixture obtained in step (a') under an inert atmosphere; (c') the mixture obtained at the end of step (b') may optionally be acidified; (d') the solid material obtained at the end of step (b') or step (c') may optionally be washed with water; (e') The solid material obtained at the end of step (d') can optionally be subjected to a mechanical treatment to deagglomerate the particles.

[0042] The Ce(IV) / total Ce molar ratio in step (a') can be comprised between 1 / 500,000 and 1 / 4,000. It may usually be between 1 / 90,000 and 1 / 100,000.

[0043] If at least one metal (M) is provided in step (a'), its suitable amount is determined in order to obtain a molar ratio M / M+Ce of the metal (M)-doped cerium oxide particles produced according to this embodiment comprised between 0.01 and 0.15, more particularly between 0.01 and 0.12.

[0044] When present in the aqueous solution of step (a'), the metal (M) is provided by a salt which may be a metal (M) nitrate, chloride, sulfate, phosphate, acetate or carbonate, as well as a mixture of these salts, such as a mixed nitrate / chloride. It is preferably a metal (M) nitrate. The metal (M) is as defined above in the description relating to step (a) of the process of the present invention.

[0045] No. 3 - The amount of nitrate ions in the aqueous solution used in step (a'), expressed in terms of the molar ratio of nitrate ions to Ce(III), is usually 1 / 3 to 5 / 1.

[0046] The acidity of the aqueous solution used in step (a') is chosen so that the cerium(III) is completely in solution, it is preferably comprised between 0.8N and 12.0N.

[0047] Cerium (IV) can be provided in step (a') by a salt, which can be cerium (IV) nitrate, sulfate, ammonium cerium nitrate, or ammonium cerium sulfate. It is preferably cerium (IV) nitrate. The cerium nitrate solution can be advantageously obtained by the method of electrochemical oxidation of a cerium nitrate solution as disclosed in French Patent No. 2570087. The cerium nitrate solution obtained according to the teachings of French Patent No. 2570087 can exhibit an acidity of approximately 0.6N.

[0048] Cerium(III) can be provided in step (a') by a salt which can be cerium(III) nitrate, chloride, sulfate, phosphate, acetate or carbonate, as well as mixtures of these salts such as mixed nitrate / chloride, and is preferably cerium(III) nitrate.

[0049] The amount of free oxygen in the starting solution in step (a') should be carefully controlled and minimized. For this purpose, the starting solution may be degassed by bubbling with an inert gas. The term "inert gas" or "inert atmosphere" is intended to mean an atmosphere or gas that does not contain oxygen, and the gas can be, for example, nitrogen or argon.

[0050] As the base used in step (a'), hydroxide-type products can be used in particular. Mention may be made of alkali metal or alkaline earth metal hydroxides and aqueous ammonia. Secondary, tertiary, or quaternary amines can also be used. The aqueous solution of the base can be degassed beforehand by bubbling with an inert gas. The amount of base used in step (a'), expressed as the molar ratio base / (Ce + optional M), is preferably comprised between 8.0 and 30.0. This ratio can preferably be greater than 9.0.

[0051] Step (a') is usually carried out at a temperature comprised between 5°C and 50°C. This temperature may be between 20 and 25°C.

[0052] Step (b') is the thermal treatment of the reaction medium obtained at the end of the previous step. It consists of (i) a heating substep and (ii) an ageing substep. The heating substep (i) consists of heating the medium at a temperature usually comprised between 75°C and 95°C, more particularly between 80°C and 90°C, and even more particularly between 85°C and 90°C.

[0053] The aging substep (ii) consists of maintaining the medium at a temperature between 75°C and 95°C, more specifically between 80°C and 90°C, and even more specifically between 85°C and 90°C. The duration of the aging substep (ii) is between 2 hours and 20 hours. The higher the temperature of the aging step, the shorter the time of the aging substep. For example, when the temperature of the aging substep is between 85°C and 90°C, e.g., 88°C, the duration of the aging substep may be between 2 hours and 15 hours, more specifically, between 4 hours and 15 hours. When the temperature of the aging substep is between 75°C and 85°C, e.g., 80°C, the duration of the aging substep may be between 15 hours and 30 hours.

[0054] During step (b'), oxidation of Ce(III) to Ce(IV) occurs. This step may be carried out under an inert atmosphere. The comments regarding the atmosphere for step (a') are applicable here.

[0055] In step (c'), the mixture obtained at the end of step (b') may optionally be acidified. This step (c') can be carried out by using nitric acid. The reaction mixture may be acidified with HNO3 to a pH below 3.0, more specifically to a pH comprised between 1.5 and 2.5.

[0056] In step (d'), the solid material obtained at the end of step (b') or step (c') is washed with water, preferably deionized water. This operation reduces the amount of residual anions, particularly nitrates, in the dispersion and allows the target conductivity to be achieved. This step can be carried out by filtering the solid from the mixture and redispersing the solid in water. If necessary, the filtering and redispersion can be carried out multiple times.

[0057] In step (e'), the solid material obtained at the end of step (d) can be subjected to a mechanical treatment to deagglomerate the particles. This step may be carried out by double-jet processing or ultrasonic deagglomeration. This step typically results in a sharp particle size distribution and a reduced number of large agglomerated particles. According to one embodiment, the cerium-based particles have been subjected to a mechanical deagglomeration treatment. According to another embodiment, the cerium-based particles have not been subjected to a mechanical deagglomeration treatment.

[0058] After step (e'), the solid material can be dried to obtain the cerium-based particles provided in step (a) in powder form. After step (e'), water can also be added to directly obtain an aqueous dispersion of the cerium-based particles provided in step (a).

[0059] The aqueous solution provided in step (a) The purpose of the aqueous solution containing a cerium (III) salt and the optional aqueous solution containing at least one metal (M') salt is to form the nanoparticles of the shell of the cerium-based core-shell particles that are produced.

[0060] The cerium(III) salt may be cerium(III) nitrate, chloride, sulfate, phosphate or carbonate and also mixtures of these salts, such as mixed nitrate / chloride salts. It is preferably cerium(III) nitrate.

[0061] Nitrate ions can be provided in either step (a) or (b). - The amount of nitrate ions, expressed as / Ce(III), is generally 1 / 3 to 5 / 1.

[0062] The acidity of the aqueous solution containing the cerium (III) salt provided in step (a) is selected so that the cerium (III) is completely in solution, and is preferably comprised between 0.8 N and 12.0 N. In this respect, suitable acids such as nitric acid, hydrochloric acid, sulfonic acid, carbonic acid, picolinic acid, propionic acid and mixtures thereof can be used, and preferably nitric acid.

[0063] It is advantageous to use salts and ingredients of high purity, the purity of the salt may be at least 99.5% by weight, more particularly at least 99.9% by weight.

[0064] According to one embodiment in which it is desired to obtain a metal (M')-doped cerium oxide shell, an aqueous solution containing at least one metal (M') salt is also provided in step (a). The metal (M') salt can be a metal (M') nitrate, chloride, sulfate, phosphate, acetate, or carbonate, as well as a mixture of these salts, such as a mixed nitrate / chloride salt. It is preferably a metal (M') nitrate. When it is desired to produce cerium-based core-shell particles in which both the core and the shell are doped, the metal (M') can be the same as or different from the metal (M) described above. More specifically, the metal (M') can be selected from the group consisting of alkali metal elements, alkaline earth metal elements, rare earth elements, actinide elements, transition metal elements, and post-transition metal elements from the periodic table. The definitions of these groups of elements indicated in association with the metal (M) apply equally. Preferably, the at least one metal (M') is selected from the group consisting of transition metal elements such as Zr; post-transition metal elements such as Al; rare earth elements such as La, Pr, Nd, and Y; and alkaline earth metal elements such as Sr. More preferably, the at least one metal (M') is selected from the group consisting of lanthanum, praseodymium, neodymium, and zirconium. Even more preferably, the at least one metal (M') is selected from the group consisting of lanthanum, praseodymium, and neodymium. Even more preferably, the at least one metal (M') is lanthanum.

[0065] According to this embodiment, the amount of salt of metal (M') can be determined to obtain a molar ratio M' / M'+Ce in the shell of the core-shell particle comprised between 0.01 and 0.15, more particularly between 0.01 and 0.12.

[0066] Step (b) Step (b) consists in reacting, under an oxidizing atmosphere, an aqueous dispersion comprising particles of cerium oxide optionally doped with at least one metal (M), an aqueous solution comprising a cerium (III) salt and, optionally, an aqueous solution comprising at least one metal (M') salt provided in step (a), while maintaining a temperature comprised between 0°C and 80°C and a pH less than or equal to 11, to produce a dispersion of cerium-based core-shell particles.

[0067] The aqueous dispersion and the aqueous solution can be contacted simultaneously or sequentially, in any order, or in any combination. When both are provided, the aqueous solution containing a cerium (III) salt and the aqueous solution containing at least one metal (M') salt can particularly be contacted with each other prior to step (b) to form an aqueous solution containing a cerium (III) salt and at least one metal (M') salt. The resulting solution can then be contacted in step (b) with a dispersion containing cerium oxide particles optionally doped with at least one metal (M).

[0068] "Oxidizing atmosphere" means an atmosphere containing free oxygen. It can be air or any oxygen-containing atmosphere, such as a molecular oxygen-rich atmosphere.

[0069] The contacting step (b) may comprise a contacting substep (i) followed by an aging substep (ii). During the contacting substep (i), the dispersion and the solution are brought into contact with each other while maintaining the required temperature and pH. During the aging substep (ii), the medium resulting from the contacting substep (i) is maintained at the required temperature and pH for a specific time.

[0070] The contacting substep (i) can be carried out by introducing the solution into the dispersion provided in step (a), preferably slowly.

[0071] The molar ratio of cerium oxide / cerium(III) before starting step (c) may be comprised between 1 / 1 and 100 / 1, in particular between 3 / 1 and 30 / 1, more particularly between 5 / 1 and 15 / 1.

[0072] The duration of the ageing substep (ii) may be between 2 hours and 24 hours, in particular between 2 hours and 10 hours, more particularly between 2 hours and 5 hours.

[0073] The temperature of the medium is maintained during step (b) at a value comprised between 0°C and 80°C, preferably between 10°C and 60°C, more preferably between 15°C and 45°C, in particular between 20°C and 40°C, more particularly between 25°C and 35°C, and even more particularly between 30°C and 35°C. Very notably, the process can be operated at lower temperatures, thus achieving energy savings.

[0074] The pH of the medium is maintained at a value of 11 or less during step (b), preferably 3 to 11, preferably 4 to 11, preferably 8 to 11, more preferably 8 to 10, particularly 8 to 9, and more particularly about 8. Depending on the initial pH of the medium, the pH adjuster can be an acid or a base. Suitable acids include nitric acid, hydrochloric acid, sulfonic acid, carbonic acid, picolinic acid, propionic acid, and mixtures thereof, preferably nitric acid. Suitable bases include alkali metal and alkaline earth metal hydroxides and aqueous ammonia. Secondary, tertiary, or quaternary amines can also be used. Aqueous ammonia is preferred. According to a preferred embodiment, the pH adjuster is a base, preferably aqueous ammonia.

[0075] Step (b) may advantageously be carried out at atmospheric pressure (ie at about 1,013.25 mbar).

[0076] Agitation of the medium may be carried out for the duration of step (b).

[0077] According to one embodiment, no Ce(IV) salt is introduced in either step (a) or (b). In conventional cerium precipitation methods, cerium(IV) ions are used as crystal seeds to promote nucleation in the solution. However, in the method of the present invention, the cerium-based particles provided from the dispersion in step (a) and intended to be core particles already fulfill this role. The presence of additional Ce(IV) salts may result in the formation of small cerium oxide particles independent of the core-shell particles, thus increasing the dispersion index of the resulting particle dispersion, which is undesirable for the target polishing application.

[0078] Optional step (c) In step (c), the mixture obtained at the end of step (b) or step (d), which will be described in detail later, may optionally be acidified. This step (c) can be carried out using a suitable acid such as nitric acid, picolinic acid, propionic acid, hydrochloric acid, sulfonic acid, carbonic acid, and mixtures thereof, preferably nitric acid. The reaction mixture can be acidified to a pH below 3.0, more particularly to a pH comprised between 1.5 and 2.5.

[0079] Optional step (d) In step (d), the solid material obtained at the end of step (b) or step (c) can be washed with water, preferably deionized water. When both steps are performed, steps (c) and (d) can be performed in any order. This operation reduces the amount of residual anions, particularly nitrates, in the dispersion and allows the target conductivity to be achieved. This step can be performed by filtering the solid from the mixture and redispersing the solid in water. Filtration and redispersion can be performed multiple times if necessary.

[0080] Optional Step (e) In step (e), the solid material obtained at the end of steps (b), (c), or (d) can be subjected to a mechanical treatment to deagglomerate the core-shell particles. This step may be carried out by double-jet processing or ultrasonic deagglomeration. This step usually results in a sharp particle size distribution and a reduction in the number of large agglomerated particles. According to one embodiment, the cerium-based core-shell particles are subjected to a mechanical deagglomeration treatment. According to another embodiment, the cerium-based core-shell particles are not subjected to a mechanical deagglomeration treatment.

[0081] After step (e), the solid material can be dried in step (f) to obtain the cerium-based core-shell particles of the present invention in powder form. After step (e), water can also be added to obtain an aqueous dispersion of the cerium-based core-shell particles of the present invention. Liquids other than water can be used to prepare the dispersion of the present invention, such as water / water-miscible or compatible solvent mixtures or organic solvents. Such dispersions can be prepared from the aqueous dispersion obtained by the method of the present invention by methods known per se. The pH of the dispersion can also be adjusted to a value typically between 4 and 6.

[0082] According to one embodiment, cerium-based core-shell particles having a cerium oxide core and a shell consisting of nanoparticles of La-doped cerium oxide are produced by carrying out the method described above, in which an aqueous dispersion of cerium oxide particles, an aqueous solution containing a cerium(III) salt, preferably cerium(III) nitrate, and an aqueous solution containing a lanthanum salt, preferably lanthanum nitrate, are provided in step (a).

[0083] According to another embodiment, cerium oxide core-shell particles having a cerium oxide core and a shell consisting of cerium oxide nanoparticles are produced by carrying out the method described above, in step (a) of which an aqueous dispersion of cerium oxide particles and an aqueous solution of a cerium(III) salt, preferably cerium(III) nitrate, are provided.

[0084] particle The present invention relates to cerium-based core-shell particles obtainable or obtained by the process described above.

[0085] The present invention particularly relates to cerium-based core-shell particles, each cerium-based core-shell particle having a core particle made from cerium oxide optionally doped with at least one metal (M) and a shell consisting of a plurality of nanoparticles of cerium oxide optionally doped with at least one metal (M'), said nanoparticles being formed on the surface of the core particle, and wherein the ratio of the average particle size of the core-shell particles as measured by TEM to the average particle size of the core-shell particles as measured by BET is at least 1.5.

[0086] Such cerium-based core-shell particles may further exhibit: - an average core-shell particle size, measured by TEM, of at most 200 nm, in particular at most 190 nm; it may also be at most 180 nm, in particular at most 150 nm, at most 140 nm, at most 130 nm, or even at most 120 nm. The cerium oxide particles may exhibit an average particle size, measured by TEM, of at least 30 nm, in particular at least 40 nm, more particularly at least 50 nm. The standard deviation of the average particle size value may be at most 30%, in particular at most 25%, in particular at most 20%, more particularly at most 15%; and / or - an average core-shell particle size, calculated from BET surface measurements, of at most 120 nm, in particular at most 100 nm, in particular at most 85 nm. The cerium oxide particles may exhibit an average particle size, calculated from BET surface measurements, of at least 15 nm, in particular at least 19 nm, in particular at least 20 nm, in particular at least 30 nm; and / or - the ratio of the average particle size of the core-shell particles, as determined by TEM, to the average particle size of the core-shell particles, as determined by BET, is in particular at least 1.7, at least 1.9, more in particular at least 2.0; and / or a hydrodynamic mean diameter Dh, determined by DLS, comprised between 50 nm and 300 nm, in particular between 70 nm and 280 nm, in particular between 80 nm and 250 nm, in particular between 90 nm and 230 nm. a median diameter D50 of 30 nm to 180 nm, in particular 60 nm to 160 nm, more particularly 80 nm to 150 nm, even more particularly 90 nm to 145 nm, determined from a distribution obtained by laser diffraction; and / or a median diameter D10 of 10 nm to 160 nm, in particular 40 nm to 130 nm, more particularly 60 nm to 120 nm, even more particularly 70 nm to 110 nm, determined from a distribution obtained by laser diffraction; and / or a median diameter D90 of 45 nm to 250 nm, in particular 90 nm to 220 nm, more particularly 100 nm to 210 nm, even more particularly 110 nm to 200 nm, determined from a distribution obtained by laser diffraction; and / or a dispersion index of at most 0.5, in particular at most 0.4, at most 0.3, determined from a distribution obtained by laser diffraction; and / or - the ratio of the average particle size of the nanoparticles from the shell, measured by TEM, to the average particle size of the core particles, measured by TEM, is at most 1 / 2, in particular at most 1 / 3, in particular at most 1 / 4; and / or - 8-60m, determined by BET 2 / g, especially 8-45m 2 / g, especially 8-30m 2 / g, especially 10-28m 2 / g, especially 14-25m 2 / g, more specifically 15-22m 2 / g specific surface area; and / or - average crystallite size comprised between 60 and 120 nm, in particular between 60 and 80 nm, calculated from the FWHM of the (111) plane by applying the Scherrer model with a Scherrer constant equal to 0.94.

[0087] In the examples of the present patent application, the minimum values ​​of D10, D50, and D90 may be selected, respectively. In the examples of the present patent application, the maximum values ​​of D10, D50, and D90 may be selected, respectively.

[0088] The metals (M) and / or (M') optionally present in the core-shell particles of the invention can be chosen from among the metals described above in connection with the manufacturing process.

[0089] When the core particle is doped with at least one metal (M), the molar ratio M / M+Ce in the core particle may be comprised between 0.01 and 0.15, more particularly between 0.01 and 0.13, in particular between 0.01 and 0.12.

[0090] When the shell nanoparticles are doped with at least one metal (M'), the molar ratio M' / M'+Ce in the shell particles may be comprised between 0.01 and 0.15, more particularly between 0.01 and 0.13, in particular between 0.01 and 0.12.

[0091] According to a particular embodiment of the present invention: - both the core and shell particles are made from cerium oxide; or - the core particles are made of cerium oxide and the shell particles are made of lanthanum-doped cerium oxide; or - the core particles are made from lanthanum-doped cerium oxide and the shell particles are made from cerium oxide; or The core particles are made from lanthanum-doped cerium oxide and the shell particles are made from lanthanum-doped cerium oxide.

[0092] dispersion liquid The present invention also relates to a dispersion of the cerium-based core-shell particles of the present invention in a liquid medium.

[0093] The zeta potential of the cerium-based core-shell particles contained in the dispersion of the present invention is advantageously positive. It can be measured at a pH value of the dispersion between 4 and 9.5. The zeta potential can be measured for a 1% by weight dispersion using a zetameter DT300 from Quantachrome.

[0094] The dispersions of the present invention may advantageously exhibit a conductivity of less than 600 μS / cm, less than 300 μS / cm, more particularly less than 150 μS / cm, and even more particularly less than 100 μS / cm.

[0095] The liquid medium may be water or a mixture of water and a water-miscible organic liquid. The water-miscible organic liquid must not cause the particles to precipitate or aggregate. The water-miscible organic liquid may be, for example, an alcohol such as isopropyl alcohol, ethanol, 1-propanol, methanol, or 1-hexanol; a ketone such as acetone, diacetone alcohol, or methyl ethyl ketone; or an ester such as ethyl formate, propyl formate, ethyl acetate, methyl acetate, methyl lactate, butyl lactate, or ethyl lactate. The water / organic liquid ratio may be 80 / 20 to 99 / 1 (wt / wt).

[0096] The proportion of cerium-based core-shell particles in the dispersion may be comprised between 0.5% and 40.0% by weight, expressed as the weight of cerium-based core-shell particles relative to the total weight of the dispersion, and may be comprised between 10.0% and 35.0% by weight.

[0097] Use of cerium-based core-shell particles or dispersions The cerium-based core-shell particles of the present invention or the dispersion of the present invention can be used to prepare a polishing composition, more specifically a CMP composition, and are used as components of the polishing composition, more specifically a CMP composition.

[0098] A CMP composition (or chemical-mechanical polishing composition) is a polishing composition used to selectively remove material from the surface of a substrate. It is used in the field of integrated circuits and other electronic devices. In practice, in the fabrication of integrated circuits and other electronic devices, multiple layers of conductive, semiconductive, and dielectric materials are deposited or removed from the surface of a substrate. As layers of material are sequentially deposited on and removed from a substrate, the top surface of the substrate may become non-planar and require planarization. Surface planarization (or "polishing") is the process of removing material from the surface of a substrate to generally form a smooth, flat surface. Planarization is useful for removing undesirable surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials. Planarization is also useful for forming features on a substrate by removing excess deposited material used to fill the features and providing a uniform, horizontal surface for subsequent metallization and processing.

[0099] The substrate that can be polished with the polishing or CMP composition can be, for example, a silicon dioxide type substrate, glass, semiconductor, or wafer.

[0100] The polishing or CMP composition typically contains different components other than the cerium-based core-shell particles. The polishing composition may include one or more of the following components: abrasive particles other than cerium-based particles (referred to herein as "additional abrasive particles"); and / or pH adjusters; and / or surfactants; and / or - rheology modifiers such as viscosity improvers and coagulants; and / or - anionic copolymers of carboxylic acid, sulfonated or phosphonated monomers with acrylates, polyvinylpyrrolidone or polyvinyl alcohol (e.g. copolymers of 2-hydroxyethyl methacrylate and methacrylic acid); nonionic polymers which are polyvinylpyrrolidone or polyethylene glycol; silanes which are aminosilanes, ureidosilanes or glycidylsilanes; functionalized pyridine N-oxides (e.g. picolinic acid N-oxide); starch; cyclodextrins (e.g. alpha-cyclodextrin or beta-cyclodextrin); and combinations thereof.

[0101] The pH of the polishing composition is usually within the range of 1 to 6. Typically, the polishing composition has a pH of 3.0 or higher. The pH of the polishing composition is typically 6.0 or lower.

[0102] The cerium-based core-shell particles of the present invention can be used in the polishing compositions disclosed in the following documents: WO 2013 / 067696; WO 2016 / 140968; WO 2016 / 141259; WO 2016 / 141260; WO 2016 / 047725; and WO 2016 / 006553.

[0103] The present invention also relates to a method for removing a portion of a substrate, comprising polishing the substrate with a polishing composition prepared from a dispersion containing cerium-based core-shell particles according to the present invention.

[0104] The invention finally relates to a semiconductor containing substrate polished by this method.

[0105] To the extent that the disclosure of any patents, patent applications, and publications incorporated herein by reference contradicts the statements of this application to the extent that the term may be unclear, the statements of this application shall control. [Example]

[0106] The present invention is further illustrated by the following examples, which are not intended to limit the invention.

[0107] Example 1: Particle core CeO2 (60 nm) shell CeO2 - concentration 5 wt% A 5 wt% aqueous dispersion of cerium oxide particles is prepared by adding 233 g of 30 wt% Zenus® aqueous cerium oxide dispersion (commercially available from Solvay) (average primary particle size calculated by BET measurement = 60 nm) to 1167 g of deionized water. A diluted ammonia solution is prepared by adding 42 g of 28% aqueous ammonia to 208 g of deionized water. A solution of cerium nitrate is prepared by adding 25.5 g of 2.87 M trivalent cerium nitrate solution to 87.5 g of deionized water.

[0108] A 5 wt. % aqueous cerium oxide dispersion is introduced into a 2 L semi-closed jacketed reactor and then stirred (a stirrer with four pitched blades at 300 rpm). The reaction mixture is then heated to 35°C under the same stirring. The initial pH of the dispersion is increased to 9 by adding a 2.5 M ammonia solution. A trivalent cerium nitrate solution is then added at 5 mL / min via a peristaltic pump. During this process, the pH is maintained at 8 by controlled addition of the 2.5 M ammonia solution. After the addition is complete, the reaction mixture is maintained at the same temperature and stirring for 4 hours. The pH is maintained over this time by controlled addition of the 2.5 M ammonia solution. The reaction is then stopped, and the dispersion is washed several times by centrifugation, removal of the centrifuge supernatant, and redispersion of the cake in deionized water. Finally, the dispersion is adjusted to 10-15 wt. %, with a pH of about 5 and an ionic conductivity of 0.1 mS.cm. -1 The dispersion is deagglomerated by passing it continuously through a dual impact jet homogenizer.

[0109] The resulting dispersion is observed by TEM. It is noted that the particles are monodisperse and centered around 110 nm in size. The diameter is determined after counting 150 particles on the TEM image, which gives a mean particle size of 109 nm with a standard deviation of 16 nm (15% of the mean particle size). It is observed that the cerium salt precipitates on the Zenus® cerium oxide particles, resulting in the formation of a shell with a rough surface (Figure 1).

[0110] A portion of the dispersion is dried in an oven at 200 °C, which yields a powder for XRD analysis and BET surface measurements. The diffractogram of this powder shows the signature of crystallized CeO (record ASTM 34-394). The average crystallite size of the core-shell particles is 69 nm. The BET specific surface area, determined by nitrogen adsorption, is 13.0 m for the starting particles. 2 / g and 18m for core-shell particles 2 / g, resulting in average primary particle sizes of 64 nm and 46 nm, respectively. Secondary particle sizes are measured for the starting particles and the final core-shell particles by a laser particle size analyzer (Horiba LA-910) at a relative refractive index of 1.7 for CeO2 in water. The D10, D50, and D90 are 81, 99, and 123 nm for the starting particles, respectively. The D10, D50, and D90 are 89, 107, and 129 nm for the core-shell particles, respectively, indicating a dispersion index σ / m of 0.19. Secondary particle sizes are also measured by dynamic light scattering (DLS) at a relative refractive index of 1.7 for CeO2 in water. The hydrodynamic diameter is 169 nm for the core-shell particles. The particle morphology before and after shell formation is observed by SEM (Figures 3 and 4, respectively).

[0111] Example 2: Particle core CeO2 (60 nm) shell CeO2: La-concentration 5 wt% Example 1 is repeated, with the difference that instead of the cerium nitrate solution, a solution of cerium nitrate and lanthanum nitrate is used, which is prepared by adding 22.95 g of a 2.87 M cerium nitrate solution and 2.55 g of a 2.87 M lanthanum nitrate solution to 87.5 g of deionized water (molar ratio La / La+Ce 0.10).

[0112] The resulting dispersion is observed by TEM. It is noted that the particles are monodisperse and centered around 110 nm in size. The diameter is determined after counting 150 particles on the TEM image, which gives an average particle size of 109 nm and a standard deviation of 17 nm (16% of the average particle size). It is noted that cerium and lanthanum salts precipitate on the Zenus® cerium oxide particles, resulting in the formation of a shell with a rough surface.

[0113] A portion of the dispersion is dried in an oven at 200 °C, which yields a powder for XRD analysis and BET surface measurements. The diffractogram of this powder shows the signature of crystallized CeO (record ASTM 34-394). The average crystallite size of the core-shell particles is 68 nm. The BET specific surface area, determined by nitrogen adsorption, is 13.0 m for the starting particles. 2 / g and 16m for core-shell particles 2 / g, resulting in average primary particle sizes of 64 nm and 52 nm, respectively. Secondary particle sizes are measured for the starting particles and core-shell particles using a laser particle size analyzer (Horiba LA-910) at a relative refractive index of 1.7 for CeO2 in water. The D10, D50, and D90 are 81 nm, 99 nm, and 123 nm, respectively, for the starting particles. The D10, D50, and D90 are 82 nm, 99 nm, and 122 nm, respectively, for the core-shell particles, indicating a dispersion index σ / m of 0.20. Secondary particle sizes are also measured by dynamic light scattering (DLS) at a relative refractive index of 1.7 for CeO2 in water. The hydrodynamic diameter is 150 nm for the core-shell particles. The particle morphologies before and after shell formation are observed by SEM (Figures 3 and 5, respectively).

[0114] Example 3: Particle core CeO2 (90 nm) shell CeO2 - concentration 5 wt% A 5 wt% aqueous dispersion of cerium oxide particles is prepared by adding 180 g of 24 wt% Zenus® aqueous cerium oxide dispersion (commercially available from Solvay) (average primary particle size = 90 nm calculated by BET measurement) to 670 g of deionized water. A diluted ammonia solution is prepared by adding 42 g of 28% aqueous ammonia to 208 g of deionized water. A solution of cerium nitrate trivalent is prepared by adding 19.1 g of 2.87 M cerium nitrate solution to 76.8 g of deionized water.

[0115] A 5 wt. % aqueous cerium oxide dispersion is introduced into a 1 L semi-closed jacketed reactor and then stirred (a stirrer with four pitched blades at 300 rpm). The reaction mixture is then heated to 35°C under the same stirring. The initial pH of the dispersion is increased to 9 by adding a 2.5 M ammonia solution. A trivalent cerium nitrate solution is then added at 2.55 mL / min via a peristaltic pump. During this process, the pH is maintained at 8 by controlled addition of the 2.5 M ammonia solution. After the addition is complete, the reaction mixture is maintained at the same temperature and stirring for 6 hours. The pH is maintained over this time by controlled addition of the 2.5 M ammonia solution. The reaction is then stopped, and the dispersion is washed several times by centrifugation, removal of the centrifugation supernatant, and redispersion of the cake in deionized water. Finally, the dispersion is adjusted to 10-15 wt. %, with a pH of about 5 and an ionic conductivity of 0.1 mS.cm. -1 The dispersion is deagglomerated by passing it continuously through a dual impact jet homogenizer.

[0116] The resulting dispersion is observed by TEM. It is noted that the particles are monodisperse and centered around 110 nm in size. The diameter is determined after counting 150 particles on the TEM image, which gives a mean particle size of 185 nm with a standard deviation of 33 nm (18% of the mean particle size). It is noted that the cerium salt precipitates on the Zenus® cerium oxide particles, resulting in the formation of a shell with a rough surface.

[0117] A portion of the dispersion is dried in an oven at 200 °C, which yields a powder for XRD analysis and BET surface measurement. The diffractogram of this powder shows the signature of crystallized CeO (record ASTM 34-394). The average crystallite size of the core-shell particles is 100 nm. The BET specific surface area, determined by nitrogen adsorption, is 8.0 m for the starting particles. 2 / g and 10m for core-shell particles 2 / g, resulting in average primary particle sizes of 104 nm and 83 nm, respectively. Secondary particle sizes are measured for the starting particles and core-shell particles using a laser particle size analyzer (Horiba LA-910) at a relative refractive index of 1.7 for CeO2 in water. The D10, D50, and D90 are 106, 140, and 200 nm, respectively, for the starting particles. The D10, D50, and D90 are 107, 140, and 199 nm, respectively, for the core-shell particles, indicating a dispersion index σ / m of 0.33. Secondary particle sizes are also measured by dynamic light scattering (DLS) at a relative refractive index of 1.7 for CeO2 in water. The hydrodynamic diameter is 222 nm for the core-shell particles. The particle morphology after shell formation is observed by SEM (Figure 6).

[0118] Example 4: Particle core CeO2 (60 nm) shell CeO2 - concentration 20 wt% A 20 wt% aqueous dispersion of cerium oxide particles is prepared by adding 805.8 g of 34 wt% Zenus® aqueous cerium oxide dispersion (commercially available from Solvay) (average primary particle size calculated by BET measurement = 60 nm) to 594.2 g of deionized water. A dilute ammonia solution is prepared by adding 42 g of 28% aqueous ammonia to 208 g of deionized water. A solution of cerium nitrate trivalent is prepared by adding 153.4 g of 2.87 M cerium nitrate solution to 21.2 g of deionized water.

[0119] A 20 wt. % aqueous cerium oxide dispersion is introduced into a 2 L semi-closed jacketed reactor and then stirred (400 rpm, 4 pitched blade stirrer). The reaction mixture is then heated to 35°C under the same stirring. The initial pH of the dispersion is increased to 8 by adding a 2.5 M ammonia solution. A trivalent cerium nitrate solution is then added at 3.4 mL / min via a peristaltic pump. During this process, the pH is maintained at 8 by controlled addition of the 2.5 M ammonia solution. After the addition is complete, the reaction mixture is maintained at the same temperature and stirring for 22 hours. The pH is maintained over this time by controlled addition of the 2.5 M ammonia solution. The reaction is then stopped, and the dispersion is washed several times by centrifugation, removal of the centrifuge supernatant, and redispersion of the cake in deionized water. Finally, the dispersion is adjusted to 10-15 wt. %, with a pH of about 5 and an ionic conductivity of 0.1 mS.cm. -1 The dispersion is deagglomerated by passing it continuously through a dual impact jet homogenizer.

[0120] The resulting dispersion is observed by TEM. It is noted that the particles are monodisperse and centered around 110 nm in size. The diameter is determined after counting 150 particles on the TEM image, which gives an average particle size of 109 nm with a standard deviation of 16 nm (15% of the average particle size). It is noted that the cerium salt precipitates on the Zenus® cerium oxide particles, resulting in the formation of a shell with a rough surface.

[0121] A portion of the dispersion is dried in an oven at 200 °C, which yields a powder for XRD analysis and BET surface measurements. The diffractogram of this powder shows the signature of crystallized CeO (record ASTM 34-394). The average crystallite size of the core-shell particles is 71 nm. The BET specific surface area, determined by nitrogen adsorption, is 13 m for the starting particles. 2 / g and 21m for core-shell particles 2 / g, resulting in average primary particle sizes of 64 nm and 40 nm, respectively. Secondary particle sizes are measured for the starting particles and core-shell particles using a laser particle size analyzer (Horiba LA-910) at a relative refractive index of 1.7 for CeO2 in water. The D10, D50, and D90 are 81, 99, and 123 nm for the starting particles, respectively. The D10, D50, and D90 are 96, 114, and 144 nm for the core-shell particles, respectively, indicating a dispersion index σ / m of 0.21. Secondary particle sizes are also measured by dynamic light scattering (DLS) at a relative refractive index of 1.7 for CeO2 in water. The hydrodynamic diameter is 159 nm for the core-shell particles. The particle morphologies before and after shell formation are observed by SEM (Figures 3 and 7, respectively).

[0122] Example 5: Particle Core CeO2:La (212 nm) - Shell CeO2 - Concentration 20 wt% A 5 wt% aqueous dispersion of cerium oxide particles is prepared by adding 940.5 g of 29.8 wt% CeO2:La particles (average primary particle size calculated from TEM images = 212 nm, La / La + Ce molar ratio 0.025, synthesized according to Example 1 of WO 2018 / 229005) to 459.5 g of deionized water. A diluted ammonia solution is prepared by adding 42 g of 28% aqueous ammonia to 208 g of deionized water. A solution of trivalent cerium nitrate solution is prepared by adding 70.5 g of 2.87 M trivalent cerium nitrate solution to 9.7 g of deionized water. The 20 wt% doped aqueous cerium oxide dispersion is introduced into a 2 L semi-closed jacketed reactor and then stirred (a stirrer with four pitched blades at 300 rpm). The reaction mixture is then heated to 35 °C under the same stirring. The initial pH of the dispersion is increased to 8 by adding 2.5 M ammonia solution. Then, trivalent cerium nitrate solution is added at 5 mL / min by a peristaltic pump. During this step, the pH is maintained at 8 by controlled addition of 2.5 M ammonia solution.

[0123] After the addition is complete, the reaction mixture is maintained at the same temperature and stirring for 3 hours. The pH is maintained over this time by controlled addition of 2.5 M ammonia solution. The reaction is then stopped, and the dispersion is washed several times by centrifugation, removal of the centrifuge supernatant, and redispersion of the cake in deionized water. Finally, the dispersion is adjusted to 10-15 wt. % with a pH of approximately 5 and an ionic conductivity of less than 0.1 mS.cm-1. The dispersion is deagglomerated by passing it continuously through a dual impact jet homogenizer.

[0124] The resulting dispersion is observed by TEM. Note that the particles are monodisperse and centered around 130 nm in size. The diameter is determined after counting 150 particles on the TEM image, which gives a mean particle size of 131 nm with a standard deviation of 29 nm (22.1% of the mean particle size). Note that cerium salt precipitates on the lanthanum-doped cerium oxide particles, resulting in the formation of a shell with a rough surface.

[0125] A portion of the dispersion is dried in an oven at 200 °C, thereby obtaining a powder for the measurement of the BET surface area. The BET specific surface area, determined by nitrogen adsorption, is 11 m for the starting particles. 2 / g and 17m for core-shell particles 2 / g, resulting in average primary particle sizes of 75 nm and 49 nm, respectively. Secondary particle size is measured by dynamic light scattering (DLS) at a relative refractive index of 1.7 for CeO in water. The hydrodynamic diameter is 197 nm for the core-shell particles. The morphology of the particles after shell formation, as observed by TEM, can be seen in Figure 9.

[0126] Example 6: Particle Core CeO2 (30 nm) - Shell CeO2 - Concentration 20 wt% A 20 wt% aqueous dispersion of cerium oxide particles was prepared by adding 664.5 g of 30.1 wt% CeO2 particles (average primary particle size = 35 nm calculated from TEM images, commercially available from Solvay) to 335.5 g of deionized water. A diluted ammonia solution was prepared by adding 160.9 g of 28% aqueous ammonia to 839.1 g of deionized water. A solution of cerium nitrate was prepared by adding 342.5 g of 2.87 M cerium nitrate solution to 8.6 g of deionized water.

[0127] A 20 wt.% aqueous cerium oxide dispersion is introduced into a 2-L semi-closed jacketed reactor and then stirred (400 rpm, four pitched blade stirrer). The reaction mixture is then heated to 35°C under the same stirring. The initial pH of the dispersion is increased to 8 by adding 4.5% ammonia solution. Trivalent cerium nitrate solution is then added at 9.8 g / min via a peristaltic pump. During this process, the pH is maintained at 8 by controlled addition of dilute ammonia solution. After the addition is complete, the reaction mixture is maintained at the same temperature and stirring for 100 minutes. The pH is maintained over this time by controlled addition of dilute ammonia solution. The reaction is then stopped, and the dispersion is washed several times by centrifugation, removal of the centrifuge supernatant, and redispersion of the cake in deionized water. Finally, the dispersion is adjusted to 10 wt.%, with a pH of approximately 5 and an ionic conductivity of less than 0.1 mS.cm-1. The dispersion is deagglomerated by passing it continuously through a dual impact jet homogenizer.

[0128] The resulting dispersion is observed by SEM. It is noted that the particles are monodisperse and centered around 40 nm in size. The diameter is determined after counting 150 particles on the TEM image, which gives a mean particle size of 43 nm with a standard deviation of 9 nm (20.9% of the mean particle size). It is observed that the cerium salt precipitates on the cerium oxide particles, resulting in the formation of a shell with a rough surface (Figure 10).

[0129] A portion of the dispersion is dried in an oven at 200 °C, thereby obtaining a powder for the measurement of the BET surface area. The BET specific surface area, determined by nitrogen adsorption, is 28 m for the starting particles. 2 / g and 40m for core-shell particles 2 / g, resulting in average primary particle sizes of 30 nm and 20 nm, respectively. Secondary particle size is measured for the final core-shell particles by a laser particle size analyzer (Horiba LA-910) at a relative refractive index of 1.7 for CeO2 in water. D10, D50, and D90 are 67, 81, and 95 nm, respectively, for the core-shell particles, indicating a dispersion index σ / m of 0.17. Secondary particle size is also measured by dynamic light scattering (DLS) at a relative refractive index of 1.7 for CeO2 in water. The hydrodynamic diameter is 95 nm for the core-shell particles.

[0130] Comparative Example 1: The same dispersion and solution as in Example 1 are prepared. A 5% by weight aqueous cerium oxide dispersion is introduced into a 2 L semi-closed jacketed reactor and then stirred (a stirrer with four pitched blades at 300 rpm). The reaction mixture is then heated to 85°C under the same stirring. The initial pH of the dispersion is increased to 9.8 by adding a 2.5 M ammonia solution. A trivalent cerium nitrate solution is then added at 5 mL / min by a peristaltic pump. During this process, the pH is maintained at 9.8 by controlled addition of the 2.5 M ammonia solution. The reaction mixture changes from white to light purple, and particle aggregation is observed. After the addition is complete, the reaction mixture is maintained at the same temperature and stirring for 4 hours. The pH is maintained over this time by controlled addition of the 2.5 M ammonia solution.

[0131] The dispersion is observed by TEM and it is noted that the starting particles are not covered by small crystallites (no core-shell structure) and that rods of cerium hydroxide are formed (Figure 2).

[0132] Comparative Example 2: The same dispersion and solution as in Example 1 are prepared. A 5% by weight aqueous cerium oxide dispersion is introduced into a 2 L semi-closed jacketed reactor and then stirred (stirrer with four pitched blades at 300 rpm). The reaction mixture is then heated to 35°C under the same stirring. The initial pH of the dispersion is increased to 12 by adding a 2.5 M ammonia solution. A trivalent cerium nitrate solution is then added at 5 mL / min by a peristaltic pump. During this process, the pH is maintained at 12 by controlled addition of the 2.5 M ammonia solution. After the addition is complete, the reaction mixture is maintained at the same temperature and stirring for 4 hours. The pH is maintained over this time by controlled addition of the 2.5 M ammonia solution.

[0133] Observe the dispersion by TEM and note that the starting particles are aggregated and not covered by small crystallites (no core-shell structure).

[0134] Comparative Example 3: A 5 wt% aqueous dispersion of cerium oxide particles is prepared by adding 41.6 g of 30 wt% Zenus® aqueous cerium oxide dispersion (commercially available from Solvay) (average primary particle size calculated by BET measurement = 60 nm) to 208.4 g of deionized water. A 1 N ammonia solution is prepared by adding 28 g of 28% aqueous ammonia to 771 g of deionized water. A solution of cerium nitrate is prepared by adding 0.75 g of 2.87 M trivalent cerium nitrate solution to 249.25 g of deionized water.

[0135] A 5% by weight cerium oxide suspension and a trivalent cerium nitrate solution are introduced into a 2 L semi-closed jacketed reactor and then stirred (a stirrer with four pitched blades at 300 rpm). The pH of the mixture is adjusted to 11 by adding an appropriate amount of 1N ammonia solution and stirred for 2 hours. The solution is then transferred to a Teflon bottle and placed in a stainless steel autoclave at 170 °C for 12 hours.

[0136] The dispersion is observed by TEM and it is noted that the starting particles are not covered by small crystallites (no core-shell structure) (Figure 8).

[0137] Evaluation of polishing performance The polishing machine used is a Struers Tegramin. The surfaces to be polished are made of amorphous silica. The aqueous dispersions of core-shell particles were tested under the following conditions: · Pressure applied to head: 50N; Rotation speed: 150 rpm; Pads: Neoprene (MD-Chem) - new pads per order; Dispersion flow rate: 15 mL / min; Dispersion: the amount of core-shell particles is 1% by weight; The pH of the dispersion is comprised between 6.0 and 6.1 and is obtained by adding diluted NH4OH; Polishing time: 10 minutes.

[0138] As a reference, an aqueous cerium oxide dispersion of Zenus® particles (average CeO 2 primary particle size calculated by BET measurements=60 nm) commercially available from Solvay is used at 1% by weight and pH=6.0.

[0139] The order is as follows: 1) Testing a reference dispersion; 2) testing the sample; 3) Test the sample a second time.

[0140] Between each step in the sequence, the pad is cleaned with deionized water and the dispersion to be tested is introduced under a controlled flow rate onto the surface to be polished.

[0141] The weight loss of the substrate is recorded. The removal rate (RR) expressed in nm / min is then calculated as follows:

number

[0142] The removal efficiency ratio is the ratio of the average removal rate achieved with the dispersions tested for each sequence to the removal rate achieved with the reference dispersion. As can be seen from Table 1, all particles of the present invention show an improvement in removal rate compared to the standard used (removal efficiency ratio greater than 1). The best results are obtained with doped particles (Examples 2 and 5).

[0143] At the end of the polishing test, the substrate and core-shell particles are visually inspected: it is confirmed that the nanoparticles from the shell of the core-shell particles of the present invention are sufficiently immobilized and have remained attached to the core during polishing.

[0144] [Table 1]

Claims

1. 1. A method for producing a dispersion of cerium-based core-shell particles in a liquid, comprising the steps of: (a) providing an aqueous dispersion comprising particles of cerium oxide optionally doped with at least one metal (M); providing an aqueous solution comprising a cerium (III) salt; and optionally providing an aqueous solution comprising at least one metal (M') salt; (b) contacting said aqueous dispersion with the aqueous solution provided in step (a) under an oxidizing atmosphere while maintaining a temperature comprised between 0°C and 80°C and a pH of 11 or less to produce a dispersion of cerium-based core-shell particles; Including, A method wherein at least one of steps (a) and (b) is carried out in the presence of nitrate ions.

2. 2. The method according to claim 1, wherein the aqueous dispersion in step (a) comprises at least 3 wt.-%, in particular at least 5 wt.-%, in particular at least 10 wt.-%, in particular at least 15 wt.-%, more in particular at least 20 wt.-% of particles of cerium oxide optionally doped with at least one metal (M) relative to the total weight of the aqueous dispersion.

3. 3. The method of claim 1 or 2, wherein the particles provided in the aqueous dispersion in step (a) are particles of cerium oxide.

4. 3. The method of claim 1 or 2, wherein the particles provided in the aqueous dispersion in step (a) are particles of cerium oxide doped with at least one metal (M) selected from the group consisting of alkali metal elements, alkaline earth metal elements, rare earth elements, actinides, transition metal elements and post-transition metal elements from the periodic table.

5. 5. The method of claim 4, wherein the metal (M) is selected from the group consisting of Zr, Al, La, Pr, Nd, Y, and Sr.

6. 6. The method according to claim 4 or 5, wherein the molar ratio M / (M+Ce) of the particles provided in the aqueous dispersion in step (a) is comprised between 0.01 and 0.15, preferably between 0.01 and 0.

12.

7. 7. The method of any one of claims 1 to 6, wherein the aqueous solution comprising the at least one salt of metal (M') is provided in step (a), and wherein the metal (M') is selected from the group consisting of alkali metal elements, alkaline earth metal elements, rare earth elements, actinide elements, transition metal elements and post-transition metal elements from the periodic table.

8. 8. The method of claim 7, wherein the metal (M') is selected from the group consisting of Zr, Al, La, Pr, Nd, Y, and Sr.

9. The method according to claim 7 or 8, wherein the molar ratio M' / (M'+Ce) of the shell of the produced core-shell particles is comprised between 0.01 and 0.15, preferably between 0.01 and 0.

12.

10. 10. The method according to any one of claims 1 to 9, wherein the temperature in step (b) is maintained at from 10°C to 60°C, more preferably from 15°C to 45°C, in particular from 20°C to 40°C, more particularly from 25°C to 35°C, and even more particularly from 30°C to 35°C.

11. 11. The method according to any one of claims 1 to 10, wherein the pH in step (b) is maintained at 3 to 11, particularly 4 to 11, particularly 8 to 11, in particular 8 to 10, more particularly 8 to 9.

12. 12. The process according to any one of claims 1 to 11, wherein the molar ratio of cerium oxide / cerium(III) before starting step (b) is comprised between 1 / 1 and 100 / 1, preferably between 3 / 1 and 30 / 1, preferably between 5 / 1 and 15 / 1.

13. The method of any one of claims 1 to 12, further comprising, in any order, a step (c) of acidifying the dispersion of cerium-based core-shell particles and / or a step (d) of washing.

14. The method of any one of claims 1 to 13, further comprising a step (e) of deagglomeration of the cerium-based core-shell particles.

15. The method of any one of claims 1 to 14, further comprising a step (f) of drying the cerium-based core-shell particles.

16. 15. A dispersion of cerium-based core-shell particles in a liquid obtainable by the method according to any one of claims 1 to 14, wherein each cerium-based core-shell particle has a core particle made from cerium oxide optionally doped with at least one metal (M) and a shell consisting of a plurality of nanoparticles of cerium oxide optionally doped with at least one metal (M'), said nanoparticles being formed on the surface of said core particle, and wherein the ratio of the average particle size of said core-shell particles as measured by TEM to the average particle size of said core-shell particles as measured by BET is at least 1.

5.

17. 16. A cerium-based core-shell particle powder obtainable by the method of claim 15, wherein each cerium-based core-shell particle has a core particle made of cerium oxide optionally doped with at least one metal (M) and a shell consisting of a plurality of nanoparticles of cerium oxide optionally doped with at least one metal (M'), said nanoparticles being formed on the surface of the core particle, and wherein the ratio of the average particle size of the core-shell particles measured by TEM to the average particle size of the core-shell particles measured by BET is at least 1.

5.

18. 18. A polishing composition comprising the cerium-based core-shell particle dispersion liquid according to claim 16 or the cerium-based core-shell particle powder according to claim 17.

19. 18. Use of the cerium-based core-shell particle dispersion according to claim 16 or the cerium-based core-shell particle powder according to claim 17 for preparing a polishing composition, more specifically a chemical-mechanical polishing composition.

20. 18. A method for removing a portion of a substrate, comprising polishing the substrate with a polishing composition prepared from the dispersion of claim 16 or a dispersion prepared from the core-shell cerium oxide particle powder of claim 17.

21. A semiconductor comprising a substrate polished by the method of claim 20.

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