Aqueous dispersion comprising particles of cerium oxide with adsorbed polyoxometalates species thereon, process for producing the same and use thereof in polishing

Abstract

The invention relates to an aqueous dispersion comprising particles of cerium oxide with polyoxometalates species adsorbed thereon, to a process for producing the same and to the use of the dispersion in polishing applications, advantageously in chemical mechanical polishing.

Description

[0001] AQUEOUS DISPERSION COMPRISING PARTICLES OF CERIUM OXIDE WITH ADSORBED POLYOXOMETALATES SPECIES THEREON, PROCESS FOR PRODUCING THE SAME AND USE THEREOF IN POLISHING

[0002] TECHNICAL FIELD

[0003] The present invention relates to a new aqueous dispersion comprising particles of cerium oxide with polyoxometalates species adsorbed thereon, a process for producing the same and the use thereof, notably, in the field of polishing, especially chemical mechanical polishing.

[0004] BACKGROUND ART

[0005] Ceric oxides are commonly used for polishing applications and are more particularly used as abrasive particles in liquid polishing compositions implemented in chemical mechanical polishing (CMP) processes. CMP processes are widely used in the manufacture of integrated circuits (IC), computer hard disks, optical glass, microelectromechanical systems (MEMS) and the like. CMP processes are implemented on various parts such as discs or dielectric compounds.

[0006] The CMP compositions, which are generally in the form of dispersions containing the abrasive particles and various additives in a liquid medium, must exhibit a certain number of characteristics. For example, they must offer a high degree of removal of material, which reflects their abrasive capacity. They must also imply a defectivity which is as low as possible; the term “defectivity” is intended to mean in particular the amount of scratches exhibited by the substrate once treated with the composition. They must as well remain stable over time: in other words, agglomeration of the abrasive particles in the liquid medium must be avoided. In addition, the presence of particles that are too fine in these dispersions reduces their abrasive capacities, and particles that are too large can contribute to an increase in the defectivity.

[0007] The performance of a CMP composition can also largely depend on the nature of the substrate to be polished, especially because the chemical and mechanical interactions between the surface of the abrasive particles and the substrate are different. Accordingly, there is also a need for versatile particles, especially suited as abrasive particles in a CMP composition or CMP process for a variety of substrates, such as, more particularly, SiCU and SiC. In addition, one of the issues encountered after the implementation of a CMP process is to suitably remove CMP micrometer and sub-micrometer residues and contaminants such as trace metals from the polished substrates. This problem negatively affects yield in the semiconductors industry. There is consequently also a need for particles suited as abrasive particles for CMP which ease the post CMP cleaning steps, notably by contributing to an amount or residues that is as low as possible, and / or as easy as possible to eliminate.

[0008] The document W02008 / 033276 discloses an isolated, particulate polyoxometalate complex comprising a polyoxometalate compound ionically bound to a cationic polymer wherein particles of the complex can include a metal oxide core. The particles depicted in this document are said to be capable of polishing a tungsten- containing substrate with low defectivity while maintaining suitable polishing removal rates. Abrasive particles for CMP having a silica core coated with poly(methacryloxyethyltrimethylammonium chloride) having an isopolytungstate salt ionically bound thereto, having a size ranging from 2000 to 4000 nm, are notably exemplified in this document.

[0009] However, such particles have several drawbacks. The presence of a cationic polymer coating on the abrasive particles is likely to decrease the interaction potential between the substrate to be polished and the polyoxometalates species. It renders the choice of additives in the CMP composition all the more difficult since the additives must be compatible both with the cationic polymer and with the polyoxometalates. Regarding the particles exemplified, because both the surface of the silica core particles and the isopolytungstate have negatives charges, the electrostatic repulsion therebetween prevents them from having strong interactions. Even if the poly(methacryloxyethyltrimethylammonium chloride) cationic polymer probably acts as a binding agent there between, it is very likely insufficient to get a suitable mechanical resistance of the particles during a CMP process. There is a risk of premature delamination between the core and the coating, leading ultimately to an unpredictable increase in the defectivity, a more tedious post-CMP treatment to remove the resulting residues and subsequently, a yield decrease and a cost increase for the whole semiconductor manufacturing process. Regarding the manufacturing method of the particles, incorporating this cationic polymer in the structure of the particle increases the complexity of the process, its cost and its efficiency. Additionally, given the electrostatic repulsion phenomenon and the hybrid nature of the particle, which is both organic and inorganic, reaching a homogeneous repartition of the polyoxometalate inside the coating matrix and all around the particle seems also particularly challenging. Finally, this document provides micro-scale particles. Today, notably because of the miniaturization of the electronic components, there is a need for smaller abrasive particles, typically nanoscale particles.

[0010] In this context, we believe that there is room for providing new dispersions of ceric oxide particles and polyoxometalate species, that would, notably, be suited for polishing applications like CMP, and that would be capable of solving at least one and preferably several of the above mentioned problems. There is also a need for a making process of such dispersions of particles which would be simple, economical and easy to implement at an industrial scale.

[0011] BRIEF DESCRIPTION OF THE INVENTION

[0012] These problems are at least partially and preferably totally solved by the present invention which offers inter alia a new aqueous dispersion comprising particles of cerium oxide comprising polyoxometalates species adsorbed thereon, a making process of this dispersion and the use thereof in polishing applications. In the following specification, said aqueous dispersion will be equally referred to as “the dispersion” and said particles will be denoted “cerium oxide and poly oxometalate particles”.

[0013] A first object of the invention thus relates to an aqueous dispersion comprising particles of cerium oxide with polyoxometalates species adsorbed thereon (the “cerium oxide and polyoxometalate particles”), wherein the pH of the dispersion ranges from 1.0 to 9.0 and the hydrodynamic mean diameter Dh of the cerium oxide and polyoxometalate particles, as measured by dynamic light scattering, ranges from 10 to 300 nm.

[0014] According to one embodiment, the zeta-potential of the particles in the dispersion is negative, in particular ranging from -60 to -10 mV, as measured on the dispersion at a concentration of cerium oxide and polyoxometalate particles ranging from 1 wt % to 5 wt % in weight of cerium oxide. This percentage is relative to the total weight of the dispersion.

[0015] One remarkable advantage of the dispersion according to the present invention lies in its good colloidal stability. The dispersion of the invention can remain stable, in other words can exhibit no particles agglomeration, for at least 30 days. This can be verified, for instance, by monitoring the evolution of the hydrodynamic mean diameter Dh of the particles over a certain period of time, as this value will increase in case of agglomeration.

[0016] The colloidal stability of a dispersion of the invention makes it particularly suitable and convenient to prepare a homogeneous polishing composition, even in presence of further additives therein.

[0017] Another advantage of the dispersion of the present invention lies in the good compatibility between the polyoxometalates species and the cerium oxide particles thanks to the strong interactions developed between the two. The adsorption of the polyoxometalates species onto the cerium oxide particles surface can notably be evidenced by infrared spectroscopy and / or quantified by inductively coupled plasma optical emission spectrometry (ICP-OES) measurements.

[0018] The cerium oxide and polyoxometalates particles present in the dispersion of the present invention preferably comprise or consist of cerium oxide cores to which polyoxometalates are ionically or covalently bonded.

[0019] An additional advantage of the dispersion according to the present invention lies in the homogeneous repartition of the poly oxometalates species on the cerium oxide cores of the particles present therein. The repartition of the polyoxometalates species can be highlighted by TEM pictures.

[0020] Given the various advantages of the dispersion according to the invention, a second object of the invention is a polishing composition, in particular a polishing composition for chemical mechanical polishing, comprising at least a dispersion of cerium oxide and polyoxometalates particles according to the present invention and optionally at least one additive.

[0021] Additives that can be added in the polishing composition of the present invention are well-known by the skilled person. The at least one additive may be more particularly selected, for instance, from abrasive particles other than cerium oxide and polyoxometalates particles depicted here, a pH regulator, a surfactant, a rheological control agent, including viscosity enhancing agents and coagulants, a polymeric additive, in particular a cationic polymer, an anionic polymer or a nonionic polymer, a starch, a silane, an oxidizer and combinations thereof.

[0022] The dispersions of the invention have the further advantage of being efficiently and easily prepared, even at industrial scale. A third object of the present invention is accordingly a process for producing an aqueous dispersion comprising particles of cerium oxide with polyoxometalates species adsorbed thereon, comprising at least the following steps:

[0023] (a) providing a dispersion of cerium oxide particles in an aqueous medium, wherein the cerium oxide particles have an hydrodynamic mean diameter Dh ranging from 8 to 298 nm, as measured by dynamic light scattering, and wherein the pH ranges from 1 to 9; providing a solution comprising at least one polyoxometalate salt in an aqueous medium, wherein the pH ranges from 1 to 8.

[0024] (b) contacting the dispersion and the solution provided in step (a) so as to form a reaction medium in which the at least one polyoxometalate is adsorbed onto the cerium oxide particles,

[0025] (c) optionally acidifying and / or washing the dispersion obtained from step (b).

[0026] According to one embodiment, before step (a), steps for producing the dispersion of cerium oxide particles according to a precipitation method, based on the precipitation of a cerium (III) salt and a cerium (IV) salt, can advantageously be implemented: such additional steps will be detailed later on in the present specification.

[0027] A fourth object of the present invention is a method for removing a portion of a substrate, the method comprising polishing the substrate with a polishing composition according to the invention. In the full description the term “method” is synonymous with the term “process”. The method of the present invention can advantageously be implemented in the technical field of chemical mechanical polishing.

[0028] A fifth object of the present invention is the use for polishing, in particular for chemical mechanical polishing, of a dispersion of cerium oxide and polyoxometalates particles according to the invention, including one obtained from the making process depicted in the present specification and claims. In accordance with such a usage, the cerium oxide and polyoxometalates particles comprised in the dispersion can advantageously be used as abrasive particles.

[0029] Accordingly, the invention also relates to the use of the particles of the invention as abrasive particles. In this framework, the particles of the invention comprise (or consist of) particles of cerium oxide with polyoxometalates species adsorbed thereon, said particles having an hydrodynamic mean diameter Dh ranging from 10 to 300 nm, in particular from 10 nm to 200 nm, in particular from 10 nm to 100 nm, even more particularly from 10 nm to 65 nm, as measured by dynamic light scattering. More particularly, for their usage as abrasive particles the particles of the invention may comprise or consist of cerium oxide cores to which polyoxometalates are ionically or covalently bonded. Such abrasive particles may be used or available in the form of dispersions like the one described in the present application or in the form of powders. The powders of the abrasive particles of the invention can undergo further treatments. They can undergo at least one deagglomeration treatment. They can be subjected to at least one calcination treatment. They can be redispersed in a liquid medium, in which optionally at least one additive can be introduced. Depending on the targeted polishing application, the choice of the suitable additive(s), to modulate the abrasive effect of the particles for instance, is well known by the skilled person.

[0030] The surface finish of a substrate that has been polished with the particles of the present invention shall advantageously present less defects, notably in terms of number and size (depth, length and / or width) of scratches, and / or less residues, compared to the substrates that have been polished with conventional abrasive particles.

[0031] FIGURES

[0032] Figure 1 represents the 12 regions locations which were examined on each sample used in the examples for the residue level evaluation.

[0033] DEFINITIONS

[0034] In the present disclosure, the expression “comprising” should be understood as meaning “comprising at least one”. The expression “a” should be understood as meaning “at least one”.

[0035] An expression such as “Object P comprises at least the elements pi, p2...pi” should also be understood as explicitly encompassing the embodiment wherein Object P consists essentially of the elements pi, p2 ...pi. “Essentially” in this context means that some impurities, undesired species, unintentional compounds or the like could be present in Object P without impacting its targeted function and effect in the framework of the present invention.

[0036] The expression “comprised between ... and ...” or “ranging from... to” and the like should be understood as including the limits.

[0037] In the whole description, the term “cerium oxide” designates cerium oxide which has, generally, a purity degree of at least 99.8% by weight with respect to the dry weight of the oxide. Cerium oxide is generally crystalline ceric oxide (cerium (IV) oxide). Some impurities can be present in the oxide. The impurities may stem from the raw materials or starting materials used in the process of preparation of the oxide. The total proportion of the impurities is generally lower than 0.2% by weight with respect to the oxide. Residual nitrates, carbonates and / or ammonium are not considered as impurities in the present description.

[0038] The expression “aqueous dispersion” denotes a system consisting of solid fine particles of submicronic dimensions, stably dispersed in a liquid aqueous medium, it being possible for said particles to also optionally contain residual amounts of bound or adsorbed ions such as, for example, nitrates, carbonates or ammoniums, independently from the polyoxometalates.

[0039] In the framework of the present invention, the expression “dispersion with good colloidal stability” is used to refer to a dispersion of particles which are characterized by an initial value of Dh in the range of 10 to 300 nm and which, after a time “t”, are still characterized by a Dh value in the range of 10 to 300 nm. Time “t” is at least 7 days. Advantageously, the dispersions of the inventions remain stable up to 20 days, even up to 30 days.

[0040] In the framework of the invention, the aqueous dispersion comprises particles of cerium oxide with polyoxometalates species adsorbed thereon. In other words, such particles comprise or consist, preferably consist, of cerium oxide core particles having polyoxometalates species ionically or covalently bonded to the cerium oxide core particles.

[0041] The expression “polyoxometalate” or “POM” has its usual meaning in the art. It designates accordingly a polyatomic anion, also referred to as “polyanionic cluster”, that consists of three or more metal atoms, linked together by shared oxygen atoms to form closed 3 -dimensional frameworks. The metal atom of the POM, denoted M, may be selected from:

[0042] - group 6 of the Periodic Table of Elements, particularly from Mo, W;

[0043] - from group 5, particularly from V, Nb, Ta;

[0044] - from transition metals, particularly Tc;

[0045] - and combinations thereof. The metal atom M may be more particularly selected from the metal of groups 5 and 6 as detailed above, even more particularly from W, Mo and V. The metal atoms may be in their highest oxidation state.

[0046] The term “polyoxometalate species” as used herein encompasses any recombination species of the polyoxometalate specie. “Recombination species” denotes, in the context of the invention, any species resulting from the polyoxometalates speciation in the aqueous dispersion. The speciation denotes the evolution of the polyoxometalate species in the aqueous dispersion as a result of a variation of at least one of the following parameters: pH, temperature, concentration, ionic strength, countercations, aging time, ionic interactions and covalent bonding on surfaces.

[0047] In addition to the poly oxometalates species that are adsorbed onto the surface of the cerium oxide particles, the aqueous dispersion of the invention may comprise “free” polyoxometalates species, that is to say polyoxometalates species which are not bounded to the cerium oxide particles.

[0048] The adsorption of the polyoxometalates species on the cerium oxide particles can notably be verified by infrared spectroscopy and / or quantified by inductively coupled plasma optical emission spectroscopy. The protocols depicted in the examples section can advantageously be used.

[0049] The following methodology can be followed for the quantification of elemental concentrations by ICP-OES in the dispersions of the invention.

[0050] Quantification of [Cel

[0051] An aliquot of the dispersion is taken and diluted to 1 / 15000 (wt / wt) with nitric acid acidified water (2% vol / vol); the concentration of elemental Ce therein is quantified (in g / L) by inductively coupled plasma optical emission spectroscopy (ICP-OES) using wavelengths at 413.765 and 418.660. This concentration [Ce] is related to the total concentration of cerium oxide present in the dispersion.

[0052] Quantification of [M]totai

[0053] An aliquot of the dispersion is diluted to 1 / 15000 (wt / wt) with nitric acid acidified water (2% vol / vol); the concentration of elemental metal M deriving from the polyoxometalalte species is quantified by inductively coupled plasma optical emission spectroscopy (ICP-OES). This concentration [M]totai is related to the total concentration of the elemental metal M deriving from the polyoxometalate species present in the dispersion, adsorbed and not adsorbed. Quantification of [M]not adsorbed

[0054] The dispersion is centrifuged at 10,000 rpm during 15 minutes. The top of supernatant is recovered, diluted to 1 / 1500 (wt / wt) with nitric acid acidified water (2% vol / vol); the concentration of elemental metal M stemming from the POM is quantified by ICP-OES. This concentration [M]not adsorbed is related to the concentration of the metal M deriving from the polyoxometalate species which are not adsorbed on the cerium oxide particles.

[0055] Ratios calculations

[0056] Based on the quantifications of elemental metal M deriving from the POM and elemental cerium in the dispersions, the following calculations can be made:

[0057] Ratio of non-adsorbed elemental M relative to the total elemental M in the dispersion: wherein:

[0058] [M]totai is the concentration of elemental M deriving from the POM quantified by ICP-

[0059] OES (g / L) in the dispersion before centrifugation.

[0060] [M]not adsorbed is the concentration of elemental M deriving from the POM quantified by ICP-OES (g / L) in the supernatant retrieved after centrifugation of the dispersion.

[0061] Ratio of adsorbed elemental M relative to the total elemental Min the dispersion: wherein:

[0062] [M]totai and [M]not adsorbed are as defined above.

[0063] Molar ratio of elemental Ce relative to the total elemental M in the dispersion: wherein:

[0064] [Ce] is the concentration of cerium oxide quantified by ICP-OES (g / L) in the dispersion (before centrifugation),

[0065] Mce is the molar mass of cerium, [M]totai is the concentration of elemental M deriving from the POM quantified by ICP- OES (g / L) in the dispersion (before centrifugation),

[0066] MM is the molar mass of metal(s) M stemming from the POM.

[0067] Molar ratio of elemental Ce relative to the adsorbed elemental M in the dispersion: wherein:

[0068] [Ce], [M]totai Mce, MM and Ratio Madsorbed are as defined above. n: 100 wherein: ddispersion denotes the density of the dispersion; it can be measured as described in ISO- 758-1976 “Liquid chemical products for industrial use - Determination of density at 20°C”,

[0069] Mce is the molar mass of cerium,

[0070] MceO2 is the molar mass of cerium oxide.

[0071] In the calculations above, when more than one polyoxometalate species is adsorbed on cerium oxide particles or more than one metal M is contained in the polyoxometalate species, the content of each metal M is quantified using ICP-OES and [M]total is the sum of the concentration of all metals M deriving from the POM.

[0072] The hydrodynamic mean diameter Dh of the particles may be determined by dynamic light scattering (DLS). This technique allows measurement of the hydrodynamic mean diameter Dh of solid objects, the value of which is affected by the presence of aggregates of particles. Therefore, the measurement is usually performed on a dispersion of the particles in water. Dh may be for instance determined with the appliance Zetasizer Nano-ZS of Malvern following the guidelines of the constructor. The sample usually needs to be diluted in deionized or ultrapure water.

[0073] The zeta potential of particles in an aqueous dispersion may be determined using any suitable instrument known by the person skilled in the art using standar procedures. As an example, the zeta potential may be determined using a Zetameter DT-300 from Dispersion Technology. The following protocol may be applied. A volume of 50 mL of the aqueous dispersion of particles, wherein the amount of particles has been adjusted at a value between 1 wt% and 5 wt% in weight, by addition of deionized water if needed, is poured into a container under magnetic stirring. The pHmeter and zetameter probes are calibrated following the constructor’s guidelines (referring to the ISO 13099-3:2014 Colloidal systems - Methods for zeta potential determination - Part 3: Acoustic methods). After cleaning with deionized water and drying with a tissue the pH and zeta potential probes, the pH and zeta potential of the agitated aqueous dispersion are measured with the Zetameter.

[0074] DESCRIPTION OF THE INVENTION

[0075] Variations and embodiments of the present invention will now be described in more details.

[0076] Dispersion of cerium oxide and polyoxometalates particles

[0077] According to a first of its aspects, the invention relates to an aqueous dispersion comprising particles of cerium oxide with polyoxometalates species adsorbed thereon, (the “cerium oxide and polyoxometalate particles”), wherein the pH of the dispersion ranges from 1 to 9, and the hydrodynamic mean diameter Dh of the cerium oxide and poly oxometalate particles as measured by dynamic light scattering ranges from 10 to 300 nm.

[0078] According to one embodiment, the zeta-potential of the dispersion is negative, in particular ranging from -60 mV to -10 mV, as measured on the aqueous dispersion at a concentration in cerium oxide and polyoxometalates particles ranging from 1 to 5 wt% in weight of cerium oxide.

[0079] A dispersion according to the invention has notably the advantage of exhibiting a good colloidal stability, which makes it very useful to prepare polishing compositions in which the abrasive particles are well dispersed therein and remain stable over time. As a result, polishing compositions prepared with the dispersions of the invention can advantageously be expected to generate less defects and / or less residues on the substrate to be polished therewith. The colloidal stability of the dispersion over time can notably be monitored by the method explained in more details in the examples section. According to one embodiment, the cerium oxide and polyoxometalates particles are inorganic particles. It notably enables a better compatibility of the particles with the other additives likely to be present in a polishing composition prepared with the dispersion.

[0080] According to one embodiment, the cerium oxide and polyoxometalates particles comprise or consist, preferably consist, of cerium oxide core particles to which polyoxometalates are ionically or covalently bonded. This particles configuration enables strong interactions between the cerium oxide and the polyoxometalates. It makes the dispersions of the invention well suited to be used in polishing, especially chemical mechanical polishing, for which it is required to use abrasive particles which are hard enough to endure a high mechanical stress while enabling good interactions with the substrate.

[0081] Advantageously, at least 40%, in particular at least 50%, more particularly at least 60%, of the elemental metal(s) M present in the dispersion in the form of POM are adsorbed onto the cerium oxide particles. The methodology based on ICP-OES quantification described in the definition section can notably be used.

[0082] One type of polyoxometalate or a combination of different types of polyoxometalates can be used to prepare the cerium oxide and polyoxometalates particles in the framework of the present invention.

[0083] As defined above, the expression “polyoxometalate” or “POM” has its usual meaning in the art. It designates a polyatomic ion, typically a polyatomic anion, also referred to as “polyanionic cluster”, that consists of three or more metal atoms linked together by shared oxygen atoms to form closed 3 -dimensional frameworks. The metal atom of the poly oxometalate species, denoted M, may be selected from: group 6 of the Periodic Table of the Elements, particularly from Mo, W; from group 5, particularly from V, Nb, Ta; from transition metals, particularly Tc; and combinations thereof.

[0084] The metal atom M may be more particularly selected from the metals of groups 5 and 6 as detailed above. Metal atom M may be preferably selected from the group consisting of W, Mo and V.

[0085] The metal atoms may be in their highest oxidation state. The polyoxometalates species may be advantageously selected from the group consisting of the so-called Keggin, Wells-Dawson, Anderson and Lindqvist polyoxometalates.

[0086] The poly oxometalates species may be selected from the group consisting of: compounds of formula [HhXxMnCUo]11', compounds of formula [Y2M18O62]11', compounds of formula [HhXxMeO24]n', compounds of formula [MeOw]11'

[0087] - mixtures of any of the above and recombination species thereof, wherein h is 0 or 2, X is Si or P and x = 0 when h=2 and x=l when h=0; Y is selected from Si or P; M is selected from W, Mo or V and n is an integer different from 0 denoting the number of charges of the compound. The number n typically ranges from 2 to 12.

[0088] Recombination species in the meaning of the present invention are compounds resulting from the possible POM speciation in the aqueous dispersion and are such as defined earlier in the definitions section.

[0089] The polyoxometalate can be more particularly selected from compounds of formula [HhXxMi204o]n‘, mixtures thereof and recombinations thereof, wherein h is 0 or 2, X is Si or P and x = 0 when h=2 and x=l when h=0; Y is selected from Si or P. The number n typically ranges from 2 to 10.

[0090] The polyoxometalate can be even more particularly selected from compounds of formula [HhXxMnC o]11', mixtures thereof and recombinations thereof, wherein: when M=W and h=2 and x=0, n is 6, 8 or 12; when M= W, X=P, h=0, x=l and n=3; when M= W, X=Si, h=0, x=l and n=4.

[0091] According to one particular embodiment, the polyoxometalate is a metatungstate of formula [TfcWnCUo]6' [TfcWnC o]8' or [TbWnCUo]12' or a recombination species thereof. According to another particular embodiment, the polyoxometalate is a phosphotungstate of formula [PWnCUo]3' or a recombination species therof. According to another particular embodiment, the polyoxometalate is a silicotungstate of formula [SiWi204o]4'or a recombination species thereof.

[0092] The dispersion may comprise cations selected from sodium, ammonium, potassium, phosphonium, H+ and mixtures thereof, in particular selected from sodium and / or ammonium, and more particularly ammonium. The amount of such cations is generally minimized.

[0093] The hydrodynamic mean diameter Dh of the cerium oxide and polyoxometalates particles ranges from 10 to 300 nm, in particular from 10 nm to 200 nm, in particular from 10 nm to 100 nm, even more particularly from 10 nm to 65 nm, as measured by dynamic light scattering. This sizes range contributes to the good stability of the dispersion according to the invention. It is also advantageous for a usage of the dispersion in the technical field of polishing, especially in chemical mechanical polishing. It notably contributes to keep the abrasive particles well dispersed in the polishing composition. It also helps to limit the number and the size of the scratches on the substrates. It additionally contributes to reach the desired level of material removal rate during the polishing.

[0094] The ratio of adsorbed elemental M (g / L) stemming from the adsorbed polyoxometalate species relative to the total elemental M (g / L) stemming from the polyoxometalate species in the dispersion may range from 0.40 to 1.00, in particular from 0.50 to 1.00, more particularly from 0.70 to 1.00, for example from 0.75 to 0.95. This ratio may be noted Ratio Madsorbedin the present specification. It may be based on a determination of the content of elemental M by ICP-OES. It may be notably calculated as explained in the definition section.

[0095] The content of polyoxometalates species in the dispersion may be expressed as a molar ratio Ce / Mtotai. wherein Ce denotes the total molar amount of cerium present in the dispersion, Mtotai denotes the total molar amount of metal stemming from the POM present in the dispersion, said metal being preferably selected from W, Mo and V. The molar ratio Ce Mtotai may range from 2 to 250, in particular from 3 to 200, more preferably from 5 to 150. This content can be confirmed by using ICP-OES analysis by quantification of the elemental Ce and elemental metal M stemming from the POM present in the dispersion. The methodology explained in the definition section or the example section can notably be used for the determination of this parameter.

[0096] The content of adsorbed polyoxometalates species in the dispersion may be expressed as a molar ratio Ce / Madsorbed. Accordingly, Ce denotes the total molar amount of cerium present in the dispersion and Madsorbed denotes the molar amount of metal stemming from the adsorbed polyoxometalate species present in the dispersion, said metal being preferably selected from W, Mo and V. The molar ratio Ce / Madsorbed may range from 2 to 625, in particular from 3 to 500, more preferably from 5 to 375. This content can be confirmed by using ICP-OES analysis by quantification of the elemental Ce and elemental metal M stemming from the adsorbed POM present in the dispersion. The methodology explained in the definition section or the example section can notably be used for the determination of this parameter.

[0097] The pH of the dispersion of the invention ranges from 1.0 to 9.0. It may ranges from 1.0 to 7.0, in particular from 1.0 to 6.0, more particularly from 2.0 to 6.0. This pH range contributes to the good stability of the dispersion. It also eases the preparation of a polishing composition therewith for keeping the ingredients thereof homogeneously dispersed.

[0098] The concentration of the cerium oxide in the dispersion of the invention may range from 0.5 wt% to 40 wt%, preferably from 1 wt% to 35 wt%. This content can be confirmed by using ICP-OES analysis by quantification of the elemental Ce present in the dispersion. The methodology explained in the definition section or the example section can notably be used.

[0099] The zeta potential of the cerium oxide and polyoxometalate particles in the dispersion is advantageously negative, as measured on the aqueous dispersion thereof at a concentration of said particles ranging from 1 wt % to 5 wt% in terms of cerium oxide. The protocol for measuring the zeta potential described in the definitions section may notably be implemented. The potential zeta of the cerium oxide and polyoxometalate particles in the dispersion may be advantageously below -10 mV, in particular below than -20 mV, more particularly below -25 mV, even below -30 mV. The cerium oxide and poly oxometalate particles may notably exhibit a zeta-potential ranging from -60 to -10 mV, as measured on the aqueous dispersion thereof at a concentration of particles ranging from 1 wt % to 5 wt% in terms of cerium oxide. This negative potential zeta participates to the colloidal stability of the dispersion.

[0100] As previously mentioned, the term “aqueous” when referring to the “aqueous dispersion” in accordance with the invention means that the particles are dispersed in a liquid aqueous medium. The aqueous medium may be water or a mixture of water and a water-miscible organic liquid. The water-miscible organic liquid should preferably not make the particles precipitate or agglomerate. The water-miscible organic liquid may for instance be an alcohol like isopropyl alcohol, ethanol, 1 -propanol, methanol, 1 -hexanol; a ketone like acetone, diacetone alcohol, methyl ethyl ketone; an ester like ethyl formate, propyl formate, ethyl acetate, methyl acetate, methyl lactate, butyl lactate, ethyl lactate. The proportion of water relative to said organic liquid may be between 80 / 20 to 99 / 1 (wt / wt). In some embodiments, the liquid medium comprises water, alcohols or a water / alcoholic mixture. Good results were obtained with aqueous compositions comprising cerium oxide and poly oxometalate particles dispersed in 1 -propanol, 2- propanol or mixtures thereof. According to one particular embodiment, the aqueous medium consists of water.

[0101] The cerium oxide and polyoxometalate particles used in the framework of the present invention may further exhibit one or several of the following features: an average particle size, as measured by TEM ranging from 1 to 200 nm; Said average size of n (>100) particles may be measured using a photograph of dispersions thereof obtained by transmission electron microscopy (TEM); when measuring the size of a particle on a photograph (by TEM or any other microscopy technique), the largest dimension thereof on the photograph is taken.

[0102] The standard deviation of the value of said average particles size may be of at most 20-30%; The standard deviation may also be determined from the TEM method. It has its usual mathematical meaning. It is the square root of the variance and is expressed by the formula: n being the number of particles taken into account in the measurement, (>100) xi being the size of a particle i, being the average value of the size of the particles (1 / n ixi). a specific surface area, determined by BET, comprised between 9 m2 / g to 835 m2 / g; The specific surface area may be determined on a powder by adsorption of nitrogen by the Brunauer-Emmett-Teller method (BET method). The method is disclosed in standard ASTM D 3663-03 (reapproved 2015). The method is also described in the periodical “The Journal of the American Chemical Society, 60, 309 (1938)”. The specific surface area may be determined automatically with an appliance TriStar 3000 of Micromeritics according to the guidelines of the constructor. Prior to the measurement, the samples in the form of powders shall be degassed under static air by heating at a temperature of at most 210°C to remove the adsorbed species. an average crystallite size, as determined by XRD, comprised between 3 nm to 80 nm. The average crystallite size measured by XRD can be calculated from the FWHM of diffraction peaks range from 2Theta = 50° and 2Theta = 140° by applying the Scherrer model with a Scherrer constant equal to 0.9.

[0103] Uses of the the dispersion of cerium oxide and polyoxometalates particles

[0104] The dispersion of the invention may be used to prepare a polishing composition, more particularly a CMP composition. In this context, the cerium oxide and polyoxometalates particles may be used as abrasive particles in the polishing composition, more particularly the CMP composition.

[0105] A CMP composition is a polishing composition used for the selective removal of material from the surface of a substrate. It is used in the field of integrated circuits and other electronic devices. Indeed, in the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting, and dielectric materials are deposited onto or removed from the surface of a substrate. As layers of materials are sequentially deposited onto and removed from the substrate, the uppermost surface of the substrate may become non-planar and require planarization. Planarizing a surface (or "polishing") the surface, is a process where material is removed from the surface of the substrate to form a generally even, planar surface. Planarization is useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials. Planarization also is useful in forming features on a substrate by removing excess deposited material used to fill the features and to provide an even surface for subsequent levels of metallization and processing.

[0106] The substrate that can be polished with a polishing composition or a CMP composition may be for instance a silicon dioxide-type substrate, a silicon carbide-type substrate, glass, a semiconductor or a wafer.

[0107] A polishing composition in accordance with the present invention, in particular for chemical mechanical polishing, comprises at least a dispersion as described above or obtained from the making process described in the present specification and claims, and optionally at least one additive, preferably selected from:

[0108] -abrasive particles other than cerium oxide and polyoxometalates particles,

[0109] - a pH regulator,

[0110] - a surfactant, - a rheological control agent, including viscosity enhancing agents and coagulants;

[0111] - a polymeric additive, in particular a cationic polymer, an anionic polymer or a nonionic polymer;

[0112] - a starch,

[0113] - a silane,

[0114] -an oxidizer,

[0115] -combinations thereof.

[0116] The pH of the polishing composition may be comprised between 1 and 9, it is generally comprised between 1 and 6. Typically, the polishing composition has a pH of 3.0 or greater. Also, the pH of the polishing composition typically is 6.0 or less. The pH depends notably on the substrate nature.

[0117] The dispersions of the present invention may notably be incorporated in the polishing compositions disclosed in the following documents: WO 2013 / 067696; WO 2016 / 140968; WO 2016 / 141259; WO 2016 / 141260; WO 2016 / 047725; WO

[0118] 2016 / 006553; WO 2021 / 081176; WO 2021 / 081171; WO 2021 / 081162; WO

[0119] 2021 / 081148; WO 2021 / 081153; WO 2021 / 081145.

[0120] The invention also relates to a method of removing a portion of a substrate, the method comprising polishing the substrate with the polishing composition described above.

[0121] The invention finally relates to the use of a dispersion as described above or obtained from the making process described in the present specification and claims, for polishing, in particular for chemical mechanical polishing, according to which the cerium oxide and polyoxometalates particles comprised in the dispersion are preferably used as abrasive particles. Such usage can include the preparation of a polishing composition with the dispersion of the invention. It can include the use of this polishing composition in a polishing process, notably to polish a substrate, but also possibly to get low residue on the polished substrate and / or for oxidizing compatibility.

[0122] Accordingly, the invention relates to a method for removing a portion of a substrate, the method comprising polishing the substrate with a polishing composition as described above. This method can comprise subsequently a step of removal of the residues from the substrate resulting from the polishing. In accordance with the present invention, the amount of residues can be advantageously decreased compared to the amount of residues resulting from the use of conventional polishing compositions which do not contain the cerium and polyoxometalates particles of the invention.

[0123] Manufacturing process

[0124] The present invention also relates to a process for producing an aqueous dispersion comprising particles of cerium oxide with polyoxometalates species adsorbed thereon, comprising at least the following steps:

[0125] (a) providing a dispersion of cerium oxide particles in an aqueous medium, wherein the cerium oxide particles have an hydrodynamic mean diameter Dh ranging from 8 to 298 nm, as measured by dynamic light scattering, and wherein the pH ranges from 1.0 to 9.0; providing a solution comprising at least one polyoxometalate salt in an aqueous medium, wherein the pH ranges from 1.0 to 8.0.

[0126] (b) contacting the dispersion and the solution provided in step (a) so as to form a reaction medium in which the at least one polyoxometalate is adsorbed onto the cerium oxide particles,

[0127] (c) optionally acidifying and / or washing the dispersion obtained from step (b).

[0128] A dispersion in accordance with the invention may be obtained from step (b) or (c)-

[0129] Dispersion of cerium oxide particles provided in step (a)

[0130] According to one embodiment, the dispersion of cerium oxide particles provided in step (a) (starting dispersion) can be prepared by dispersing, in an aqueous medium, a powder of cerium oxide particles having an hydrodynamic mean diameter Dh comprised between 8 to 298 nm and by adjusting the pH of the obtained dispersion to the required value. Nitric acid or aqueous ammonia can notably be used.

[0131] According to another embodiment, a dispersion of cerium oxide particles having the required hydrodynamic mean diameter Dh can be used and the pH thereof can be adjusted if necessary to the required value. Nitric acid or aqueous ammonia can notably be used. If applicable, these dispersions may be concentrated or diluted, and / or transferred from their original organic phase to an aqueous medium in order to implement step (a), by methods known per se.

[0132] According to another embodiment, the dispersion of cerium oxide particles provided in step (a) is manufactured by one of the processes described by the Applicant in WO 2008 / 043703, WO 2010 / 020466 and WO 2015 / 091495, which are incorporated by reference. The cerium oxide particles of such dispersions may exhibit: an average particles size measured by TEM of at most 250 nm, in particular at most 200 nm more particularly at most 170 nm; an average particles size measured by TEM of at least 10 nm, in particular at least 30 nm, more particularly at least 50 nm. The standard deviation of the value of said average particles size may be of at most 30%, particularly of at most 20%, more particularly of at most 15%; and / or an average particles size calculated from BET surface measurement of at most 120 nm, particularly of at most 110 nm; an average particles size calculated from BET surface measurement of at least 5 nm, in particular of at least 19 nm, in particular of at least 30 nm, in particular of at least 40 nm; and / or a median diameter D50, determined from a distribution obtained by laser diffraction, comprised between 60 nm and 170 nm, particularly between 70 nm and 160 nm, more particularly between 80 nm and 150 nm, even more particularly between 90 nm and 150 nm; a laser particle sizer like Horiba LA-910 may be used following the guidelines of the constructor. For the measurement, a relative refractive index of 1.7 may be used, and / or a dispersion index, determined from a distribution obtained by laser diffraction, of at most 0.5, particularly of at most 0.4, more particularly of at most 0.3. The “dispersion index” is defined by the following formula o / m = (D90-D10) / 2D50. D10 is the diameter determined from a distribution obtained by laser diffraction for which 10% of the particles have a diameter of less than D10. D50 is, as specified above, the median diameter determined from a distribution obtained by laser diffraction. D90 is the diameter determined from a distribution obtained by laser diffraction for which 90% of the particles have a diameter of less than D90.

[0133] According to another embodiment, the dispersion of cerium oxide particles used in step (a) is prepared by a method based on the precipitation of a cerium (III) salt and a cerium (IV) salt. This method comprises the following steps:

[0134] (a’) contacting under an inert atmosphere, an aqueous solution of a base and an aqueous solution comprising NCh', Ce(III), Ce(IV);

[0135] (b’) subjecting the mixture obtained in step (a’) to a thermal treatment;

[0136] (c’) the mixture obtained at the end of step (b’) may optionally be acidified;

[0137] (d’) the solid material contained in the mixture 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’) may optionally be subjected to a mechanical treatment of deagglomeration; so as to obtain a dispersion of cerium oxide particles in an aqueous medium.

[0138] The Ce(IV) / total Ce molar ratio in step (a’) may be comprised between 1 / 500 000 and 1 / 50. It may generally be between 1 / 90 000 and 1 / 100.

[0139] The amount of nitrate ions in the aqueous solution used in step (a’), expressed by the NOs' / Ce II) molar ratio is generally between 1 / 3 and 5 / 1.

[0140] The acidity of the aqueous solution used in step (a’) is chosen so as to have the cerium (III) entirely present in solution. It is preferably comprised between 0.8 N and 12.0 N.

[0141] Cerium (IV) may be provided in step (a’) by a salt which may be cerium (IV) nitrate, sulfate, cerium ammonium nitrate, cerium ammonium sulfate. It is preferably cerium (IV) nitrate. A ceric nitrate solution can advantageously be obtained according to the method of electrolytic oxidation of a cerous nitrate solution as disclosed in FR 2570087. A solution of ceric nitrate obtained according to the teaching of FR 2570087 may exhibit an acidity of around 0.6 N.

[0142] Cerium (III) may be provided in step (a’) by a salt which may be cerium (III) nitrate, chloride, sulfate, phosphate, acetate or carbonate, and also mixtures of these salts, such as mixed nitrates / chlorides. It is preferably cerium (III) nitrate.

[0143] The amount of free oxygen in the starting solution in step (a’) should be carefully controlled and minimized. To this end, 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 a gas free of oxygen, it being possible for the gas to be, for example, nitrogen or argon.

[0144] As base used in step (a’), products of the hydroxide type can in particular be used. 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 also be degassed beforehand by bubbling with an inert gas. The amount of the base used in step (a’), expressed by the molar ratio base / Ce, is preferably comprised between 5.0 and 30.0, in particular between 5.0 and 10.0.

[0145] Step (a’) may be generally carried out at a temperature comprised between 5°C and 50°C. This temperature may be 20-25°C. Step (b’) is a thermal treatment of the reaction medium obtained at the end of the preceding step. It may consist in (i) an heating sub step and (ii) in an aging sub step. The heating sub step (i) may consist in heating the medium at a temperature which is generally comprised between 75°C and 95°C, more particularly between 80°C and 90°C, even more particularly between 85°C and 90°C.

[0146] The aging sub step (ii) may consist in maintaining the medium at a temperature comprised between 75°C and 95°C, more particularly between 80°C and 90°C, even more particularly between 85°C and 90°C. The duration of the aging substep (ii) is between 2 hours to 20 hours. The higher the temperature of the aging step, the lower the duration of the aging substep. For instance, when the temperature of the aging substep is between 85°C and 90°C, eg. 88°C, the duration of the aging sub step may be between 2 hours and 15 hours, more particularly between 4 hours and 15 hours. When the temperature of the aging substep is between 75°C and 85°C, eg. 80°C, the duration of the aging substep may be between 15 hours and 30 hours.

[0147] During step (b’), the oxidation of Ce (III) to Ce (IV) occurs. This step may also be carried out under an inert atmosphere. The description with respect to the atmosphere for step (a’) applies herein.

[0148] In step (c’), the mixture obtained at the end of step (b’) may optionally be acidified. This step (c’) may be performed by using nitric acid. The reaction mixture may be acidified by HNO3 to a pH lower than 3.0, more particularly comprised between 1.5 and 2.5.

[0149] In step (d’), the solid material obtained at the end of step (b’) or step (c’) may be washed with water, preferably deionized water. This operation makes it possible to decrease the amount of residual anions, especially nitrates, in the dispersion and to obtain the targeted conductivity. This step may be carried out by filtering the solid from the mixture and redispersing the solid in water. Filtration and redispersion may be performed several times if necessary.

[0150] In step (e’), the solid material obtained at the end of step (d) may be subjected to a mechanical treatment to deagglomerate the particles. The step may be carried out by a double jet treatment or ultrasonic deagglomeration. This step usually leads to a sharp particle size distribution and to a reduction of the number of large agglomerated particles. According to an embodiment, the cerium based particles are subjected to the mechanical treatment of deagglomeration. According to another embodiment, the cerium based particles are not subjected to the mechanical treatment of deagglomeration.

[0151] After carrying out such a process, a dispersion of cerium oxide particles, suitable to be provided in step (a), is obtained.

[0152] The aqueous medium in the dispersion of cerium oxide provided in step (a) can be water or a water-miscible organic liquid. If a water-miscible organic liquid is chosen, it is preferably selected among the list described earlier in connection with the final dispersion of cerium oxide and polyoxometalate particles. According to one preferred embodiment, the aqueous medium is water.

[0153] The pH of the dispersion of cerium oxide particles provided in step (a) is to be set up at a value comprised between 1 and 9, in particular it can be comprised between 1 and 8, more particularly between 1 and 7, more particularly between 1 and 6, even more particularly between 1 and 5. A basic or acidic pH adjuster can be used to this end. As suitable acid, mention can be made of nitric acid, hydrochloric acid, sulfonic acid, carbonic acid, picolinic acid, propionic acid, and mixtures thereof, being preferably nitric acid. As suitable base, mention can be made of alkali metal and alkaline earth metal hydroxides and aqueous ammonia. Secondary, tertiary or quaternary amines can also be used. Aqueous ammonia is preferred.

[0154] The dispersion of cerium oxide particles provided in step (a) may comprise from 0.5 wt% to 40 wt%, preferably from 1 wt% to 35 wt%. of cerium oxide particles relative to the total weight of the dispersion.

[0155] According to one embodiment, the hydrodynamic mean diameter Dh of the cerium oxide particles ranges from 8 to 298 nm, in particular from 8 nm to 198 nm, in particular from 8 nm to 198 nm, even more particularly from 8 nm to 63 nm, as measured by dynamic light scattering.

[0156] Solution comprising polyoxometalate salt provided in step (a)

[0157] For the avoidance of doubt the expression “poly oxometalate salt” refers to compounds comprising a polyoxometalate species as defined above and suitable counterions to achieve charge neutrality.

[0158] The counterion in the polyoxometalate salt can be selected from the group consisting of alkali metal ions, such as sodium and potassium, ammonium, phosphonium, H+; the counterion is preferably selected from the group consisting of sodium and ammonium, more preferably ammonium ions. The polyoxometalate can be selected from the compounds detailed earlier in connection with the final cerium oxide and polyoxometalates particles.

[0159] The aqueous medium can be water or a water-miscible organic liquid. If a water- miscible organic liquid is chosen, it is preferably selected among the list described earlier in connection with the final dispersion of cerium oxide and polyoxometalate particles. According to one preferred embodiment, the aqueous medium is water.

[0160] The pH of the solution comprising the polyoxometalate salt provided in step (a) is to be set up at a value comprised between 1 and 8, in particular it can be comprised between 1 and 7, more particularly between 1 and 6, even more particularly between 1 and 5. A basic or acidic pH adjuster can be used to this end, notably one selected among the compounds detailed earlier in connection with the cerium oxide dispersion.

[0161] The solution comprising polyoxometalate salt provided in step (a) preferably comprises a suitable amount of polyoxometalate to achieve a molar ratio Ce / Mtotai as defined thereafter.

[0162] Step (b)

[0163] Step (b) consists in contacting the dispersion and the solution provided in step (a) so as to form a reaction medium in which the at least one polyoxometalate is adsorbed onto the cerium oxide particles.

[0164] According to one embodiment, the dispersion of cerium oxide is added to the solution of polyoxometalate salt.

[0165] The contacting step can be conducted in a time ranging for instance from 5 minutes to 5 hours, in particular from 15 minutes to 1 hour. Stirring means can be used. The contacting step can be advantageously conducted at room temperature, being typically in the range 20°C to 25°C. The pressure can advantageously be atmospheric pressure, being typically about 1 013,25 hPa. The use of an inert atmosphere is not generally required.

[0166] The molar ratio Ce / Mtotai preferably ranges from 2 to 250, in particular from 3 to 200, more preferably from 5 to 150; Ce denotes the total molar amount of cerium introduced, Mtotai denotes the total molar amount of the metal coming from the POM introduced, being preferably selected from W, Mo and V.

[0167] Optional step (c)

[0168] In step (c), the mixture obtained at the end of step (b) may optionally be acidified and / or washed. Acidification may be performed by 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 may be acidified to a pH ranging from 0 to 7, in particular 0 to 6, more particularly 1 to 6, notably 2 to 6.

[0169] Washing may be performed with water, preferably deionized water. This step may be carried out by filtering the solid from the medium and redispersing the solid in water. Filtration and redispersion may be performed several times if necessary.

[0170] When both performed, acidification and washing may be performed in any order.

[0171] Optional step (d)

[0172] The solid material obtained at the end of step (b) or (c) may be subjected to a mechanical treatment to deagglomerate the particles. The step may be carried out by a double jet treatment or ultrasonic deagglomeration. This step usually leads to a sharp particle size distribution and to a reduction of the number of large agglomerated particles. According to an embodiment, the particles are subjected to the mechanical treatment of deagglomeration. According to another embodiment, the particles are not subjected to the mechanical treatment of deagglomeration.

[0173] Optional step (e)

[0174] In an optional step (e) a solid / liquid separation to separate the cerium oxide particles having polyoxometalates species adsorbed thereon from the reaction medium can be performed.

[0175] Optional step (f)

[0176] A subsequent step of redispersing the particles in an aqueous medium may be performed.

[0177] Optional step (g)

[0178] The solid obtained after the optional step (e) may be dried. For instance, the temperature of at least 70°C, preferably ranging from 70°C to 150°C, can be used.

[0179] The particles thus obtained comprise (or consist of) cerium oxide and polyoxometalate particles. Such particles may be used or available in the form of dispersions like the one described in the present application or in the form of powders. The powders of the particles of the invention can undergo further treatments. They can undergo at least one deagglomeration treatment. They can be redispersed in a liquid medium, in which optionally at least one additive can be introduced. Once dispersed in a liquid medium, such as water, for instance by means of sonication, said particles may be advantageously characterized by a hydrodynamic mean diameter Dh ranging from 10 to 300 nm, in particular from 10 nm to 200 nm, in particular from 10 nm to 100 nm, even more particularly from 10 nm to 65 nm, as measured by dynamic light scattering. More particularly, the cerium oxide and polyoxometalate particles may comprise or consist of cerium oxide cores to which polyoxometalates species are ionically or covalently bonded.

[0180] The disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0181] EXAMPLES

[0182] The invention will now be further described in the following examples without intending to limit it.

[0183] Materials

[0184] The aqueous dispersions of cerium oxide used as starting material in the following examples were:

[0185] - a cerium oxide particles dispersion prepared by a precipitation method as described in example 1, wherein the hydrodynamic mean diameter of the cerium oxide particles obtained is of 39 nm, as measured by dynamic light scattering (dispersion Al).

[0186] - two commercial aqueous dispersions of cerium oxide provided by Solvay SA (Zenus® range); the hydrodynamic mean diameter, as measured by dynamic light scattering, is of 87 nm for the one implemented in example 2 (dispersion A2) and of 144 nm for the one implemented in example 3 (dispersion A3).

[0187] All the other materials used were commercially available. The salts of polyoxometalate were notably supplied by Sigma Aldrich: Ammonium metatungstate hydrate (NH^eTLWnCUo.xEkO reference 463922, Phosphotungstic acid hydrate H3PW12O40.XH2O reference 455970 and Tungstosilicic acid hydrate TLSiWnCUo.xEkO reference: T2786.

[0188] Characterizations

[0189] Particles size measurements - 1 -

[0190] The DLS measurements of the particles contained in the dispersions prepared in the following examples were made using a Zetasizer Nano-ZS Malvern apparatus following the guidelines of the constructor. Samples of the dispersions to be analyzed were prepared in the following manner. A volume of 100 mL of the dispersion was magnetically stirred at 300 rpm. A droplet of the previously homogenized dispersion was introduced in 4mL of MilliQ water and re-homogenized using a pipette. A droplet of the resulting dispersion was introduced in 4mL MilliQ water one more time and rehomogenized using a pipette.

[0191] Infrared (IR) Spectroscopy

[0192] The presence of adsorbed polyoxometalate species on the cerium oxide particles of the dispersion obtained from example 1 was detected using infrared spectroscopy. The dispersion was centrifuged (10000 rpm 15 min - Sigma 6 16KS - Refrigerated benchtop centrifuge, rotor Sigma 12269) and the resulting product was flash dried for 1 hour at 160°C with a Halogene HC-103 dessicant from Mettler Toledo. The infrared spectrum of the sample (CeCh with adsorbed POM) was analyzed in Total Attenuated Reflection mode, on a Bruker Tensor 27 spectrometer equipped with the ATR Diamant accessory, with the following parameters:

[0193] Measurement range: 650 to 4000 cm’1

[0194] Resolution: 4 cm’1

[0195] No. of scans: 35

[0196] Zeta potential

[0197] The zeta potential measurements were made using a Zetameter DT-300 from Dispersion Technology. A volume of 50 mL of each of the dispersions prepared in examples 1 to 5 was poured into a container under magnetic stirring. The pHmeter and zetameter probes were calibrated following the constructor’s guidelines (referring to the ISO 13099-3:2014 Colloidal systems - Methods for zeta potential determination - Part 3: Acoustic methods). After cleaning with deionized water and drying with a tissue the pH and zeta potential probes, the pH and zeta potential of the agitated dispersions were measured with the Zetameter.

[0198] Quantification of the elemental concentrations by ICP-OES

[0199] Samples of 100 grams of the dispersions containing the cerium and polyoxometalate particles prepared in the following examples were taken.

[0200] Quantification of [Cel An aliquot of each sample was taken and diluted to 1 / 15000 (wt / wt) with nitric acid acidified water (2% vol / vol); the concentration of elemental Ce therein was quantified (in g / L) by inductively coupled plasma optical emission spectroscopy (ICP- OES) using wavelengths at 413.765 and 418.660. This concentration [Ce] was related to the total concentration of cerium oxide present in the dispersion.

[0201] Quantification of [Wltotai

[0202] An aliquot of each sample was taken and diluted to 1 / 15000 (wt / wt) with nitric acid acidified water (2% vol / vol); the concentration of elemental W therein was quantified (in g / L) by inductively coupled plasma optical emission spectroscopy (ICP- OES) using wavelengths at 207.911 and 239.709. This concentration [W]totai was related to the total concentration of the polyoxometalate species present in the dispersion, adsorbed and not adsorbed.

[0203] Quantification Of [Wlnot adsorbed

[0204] The samples were centrifuged at 10,000 rpm during 15 minutes, using a Sigma 6 16KS - Refrigerated benchtop centrifuge, rotor Sigma 12269. The top of supernatant was then carefully recovered, diluted to 1 / 1500 (wt / wt) with nitric acid acidified water (2% vol / vol); the concentration of elemental metal W therein was quantified (in g / L) by ICP- OES using wavelengths at 207.911 and 239.709. This concentration [W]not adsorbed was related to the concentration of the polyoxometalate species which were not adsorbed on the cerium particles.

[0205] Ratios calculations

[0206] Based on the quantifications of elemental tungsten and elemental cerium in the samples, the following calculations were made:

[0207] Ratio of not adsorbed elemental W relative to the total elemental W in the dispersion sample: wherein:

[0208] [W]totai is the concentration of elemental W quantified by ICP-OES (g / L) in the whole sample before centrifugation.

[0209] [W]not adsorbed is the concentration of elemental W quantified by ICP-OES (g / L) in the supernatant retrieved after centrifugation of the sample. Ratio of adsorbed elemental W relative to the total elemental W in the dispersion sample: wherein:

[0210] [W]totai and [W]not adsorbed are as defined above.

[0211] Molar ratio of elemental Ce relative to the total elemental W in the dispersion sample: wherein:

[0212] [Ce] is the concentration of cerium oxide quantified by ICP-OES (g / L) in the whole sample (before centrifugation),

[0213] Mceis the molar mass of cerium,

[0214] [W]totai is the concentration of elemental W quantified by ICP-OES (g / L) in the whole sample (before centrifugation),

[0215] Mw is the molar mass of tungstene.

[0216] Molar ratio of elemental Ce relative to the adsorbed elemental W in the dispersion sample: wherein:

[0217] [Ce], [W]totai Mce, Mw and Wadsorbed are as defined above.

[0218] Cerium oxide weight concentration in the dispersion sample: 100 wherein: dsampie denotes the density of the whole sample, measured as described in ISO-758-1976 “Liquid chemical products for industrial use - Determination of density at 20°C” Mceis the molar mass of cerium,

[0219] Mceo2 is the molar mass of cerium oxide,

[0220] Example 1

[0221] 1.1 Preparation of the aqueous dispersion Al : A dilute cerium nitrate solution was prepared by adding 13.6 kg of a 2.9M trivalent cerium nitrate solution (density d=l .7), 2.1 kg of 68 wt% HNO3 solution, 0.48 kg of deionized water and cerium nitrate (IV) corresponding to a molar ratio Ce IV / Ce total = 1 / 100. This solution was loaded into a semi-closed 20 L vessel and then degassed with agitation and with nitrogen bubbling.

[0222] A dilute aqueous ammonia solution was prepared by adding 79 kg of deionized water and a solution of 10.1 kg of 25wt % aqueous ammonia. This solution was loaded into a semi-closed 100 L jacketed reactor and then subjected to agitation and nitrogen bubbling.

[0223] The diluted cerium nitrate solution was then added in approximately 30 min, at ambient temperature, to the dilute aqueous ammonia solution, with the same agitation and under nitrogen sweeping. The temperature of the reaction mixture was then increased to 80°C and then maintained at this temperature for 1 hour. At the end of this heat treatment, the reaction mixture was left to cool and was acidified to pH 2 by adding 68wt% HNO3.

[0224] The reaction mixture was filtrated and washed with deionized water. The washing was repeated when the conductivity of washing solution was less 0.04 mS / cm. The amount of water of the dispersion was adjusted so as to reach a CeO2 content of 25 wt% relative to the total weight of the aqueous dispersion (Dispersion Al).

[0225] The hydrodynamic mean diameter of the cerium oxide particles was of 39 nm, as measured by dynamic light scattering.

[0226] 1.2 Preparation of the dispersions of cerium and polyoxometalate particles:

[0227] An amount of 32 grams of the aqueous dispersion Al of cerium oxide particles (CeO2 content is 25 wt%) was diluted with 160 grams of water. The pH was around 4. 1,56 grams of a salt of ammonium metatungstate (NH4)6H2W12O40.xH2O was dissolved in 40 grams of water. The pH was of 4.2.

[0228] The diluted cerium oxide dispersion was added in 30 minutes under stirring to the solution of ammonium metatungstate. After addition, the mixture was stirred during 30 minutes. The pH was of 4.

[0229] The molar ratio Ce / Wtotai in the dispersion was of 7.2.

[0230] The hydrodynamic mean diameter of the cerium and polyoxometalate particles obtained was of 110 nm, as measured by DLS. The concentration in weight of CeO2 in the dispersion of cerium and poly oxometalate particles obtained was of 3.43 wt% relative to the total weight of the dispersion. The Zeta potential measured was -32 mV.

[0231] The presence of adsorbed polyoxometalate species on the cerium oxide particles was evidenced by infra-red spectroscopy in total attenuated reflection mode as a band assigned to W-0 was observed at 958 cm’1.

[0232] Using the quantification method by ICP-OES described above, it was established that the Ratio Wadsorbed is 0.75 meaning that 75% of the elemental W present in the dispersion in the form of POM were adsorbed onto the surface of cerium oxide particles. The molar ratio Ce / Wadsorbed was of 7.2 / 0.75 = 9.6.

[0233] Example 2

[0234] 26,7 grams of the aqueous dispersion of Zenus® cerium oxide particles having a size of 87 nm as measured by DLS (CeO2 content is 30 wt%) (dispersion A2) was diluted with 160 grams of water. The pH was around 3.7.

[0235] 0,48 grams of a salt of ammonium metatungstate (NH4)6H2W12O40.xH2O was dissolved in 40 grams of water. The pH was around 4.2.

[0236] The diluted cerium oxide dispersion was added in 30 minutes under stirring to the solution of ammonium metatungstate. After addition, the mixture was stirred during 30 minutes. The pH was of 4.7.

[0237] The molar ratio Ce / Wtotai in the dispersion was 23.

[0238] The hydrodynamic mean diameter of the cerium and polyoxometalate particles obtained was 146 nm as measured by DLS. The concentration in weight of CeO2 in the dispersion of cerium and poly oxometalate particles obtained was of 3.53 wt% relative to the total weight of the dispersion. The Zeta potential was -39 mV.

[0239] Using the quantification method by ICP-OES described above, it was established that the Ratio Wadsorbed is 0.56 meaning that 56% of the elemental W present in the dispersion in the form of POM were adsorbed onto the surface of cerium oxide particles. The molar ratio Ce / Wadsorbed was of 23 / 0.56 = 41.

[0240] Example 3 26.7 grams of the aqueous dispersion of Zenus® cerium oxide particles having a size of 144 nm as measured by DLS (CeO2 content is 30 wt%) (dispersion A3) was diluted with 160 grams of water. The pH was around 4.

[0241] 0.23 grams of a salt of ammonium metatungstate (NH4)6H2W12O40.xH2O was dissolved in 40 grams of water. The pH was around 4.2.

[0242] The diluted cerium oxide dispersion was added in 30 minutes under stirring to the solution of ammonium metatungstate. After addition, the mixture was stirred during 30 minutes. The pH was around 4.

[0243] The molar ratio Ce / Wtotaiin the dispersion was 49.

[0244] The hydrodynamic mean diameter of the cerium and polyoxometalate particles obtained was 167 nm as measured by DLS. The concentration in weight of CeCh in the dispersion of cerium and poly oxometalate particles obtained was of 3.53 wt% relative to the total weight of the dispersion. The Zeta potential was -45 mV.

[0245] Using the quantification method by ICP-OES described above, it was established that the Ratio Wadsorbed is 0.46 meaning that 46% of the elemental W present in the dispersion in the form of POM were adsorbed onto the surface of cerium oxide particles. The molar ratio Ce / Wadsorbed was of 49 / 0.46 = 106.

[0246] Example 4

[0247] An amount of 32 grams of the aqueous dispersion (Al) of cerium oxide particles obtained from example 1 (CeO2 content is 25 wt%) was diluted with 160 grams of water. The pH was around 4.

[0248] 1.55 grams of a salt of tungstosilicic acid H4SiW12O40.xH2O was dissolved in 40 grams of water. The pH was around 1.6.

[0249] The diluted cerium oxide dispersion was added in 30 minutes under stirring to the solution of tungstosilicic acid. After addition, the mixture was stirred during 30 minutes. The pH was around 2.1.

[0250] The molar ratio Ce / Wtotai in the dispersion was 7.2.

[0251] The hydrodynamic mean diameter of the cerium and polyoxometalate particles obtained was 190 nm as measured by DLS. The concentration in weight of CeO2 in the dispersion of cerium and poly oxometalate particles obtained was of 3.43 wt% relative to the total weight of the dispersion. The Zeta potential was -21 mV. Using the quantification method by ICP-OES described above, it was established that the Ratio Wadsorbed is 0.75 meaning that 75% of the elemental W present in the dispersion in the form of POM were adsorbed on the surface of cerium oxide particles. The molar ratio Ce / Wadsorbed was of 7.2 / 0.75 = 9.6.

[0252] Example 5

[0253] An amount of 32 grams of the aqueous dispersion (Al) of cerium oxide particles obtained from example 1 (CeO2 content is 25 wt%) was diluted with 160 grams of water. The pH was around 4.

[0254] 1,54 grams of a salt of phosphotungstic acid H3PW12O40.xH2O was dissolved in 40 grams of water. The pH was around 1.7.

[0255] The diluted cerium oxide dispersion was added in 30 minutes under stirring to the solution of phosphotungstic acid. After addition, the mixture was stirred during 30 minutes. The pH was around 2.1.

[0256] The molar ratio Ce / Wtotai in the dispersion was 7.2.

[0257] The hydrodynamic mean diameter of the cerium and polyoxometalate particles obtained was 50 nm as measured by DLS. The concentration in weight of CeO2 in the dispersion of cerium and poly oxometalate particles obtained was of 3.43 wt% relative to the total weight of the dispersion. The Zeta potential was -35 mV.

[0258] Using the quantification method by ICP-OES described above, it was established that the Ratio Wadsorbed is 0.95 meaning that 95% of the elemental W present in the dispersion in the form of POM were adsorbed on the surface of cerium oxide particles. The molar ratio Ce / Wadsorbed was of 7.2 / 0,95 = 7,6.

[0259] The following tables 1 and 2 summarize the main parameters and features of the examples.

[0260] Table 2: main features of the aqueous dispersions of cerium oxide and poly oxometalate particles obtained

[0261] Evaluation of the colloidal stability of the dispersions The dispersions of cerium and polyoxometalates particles prepared in examples 2 and 3 are tested for their colloidal stability over time at room temperature (about 20°C). On day 0, 52 mL of each dispersion is magnetically stirred in a 100 mL vial at 200 rpm, then an aliquot is taken for DLS analysis. The aliquot is diluted in water (milliQ grade) and homogenized in the way explained above for DLS measurements, then characterized using a Nano-ZS Malvern apparatus to determine the hydrodynamic mean diameter Dh on day 0. The Dh measurement is repeated every day for 30 days: until a Dh value of 300 nm it can be considered that there is no agglomeration of the particles and that the dispersion is still stable. Over a Dh value of 300 nm it is considered that an agglomeration of the particles occurred. The results are reported in the table 3 below. These results confirm the great stability of the dispersions of the invention.

[0262] Evaluation of the low residue performance of the dispersions after their use in polishing

[0263] The polishing machine used is a Struers Tegramin. The surface to be polished is made of amorphous silica. The dispersions of the cerium oxide polyoxometalates particles in water were tested under the following conditions:

[0264] • pressure applied on the head: 5 ON;

[0265] • rotation speed: 150 rpm;

[0266] • pad: neoprene (MD-Chem);

[0267] • flow-rate of the dispersion: 15 mL / min;

[0268] • dispersions: the amount of particles is 1 wt% (adjusted whenever necessary with deionized water); the pH of the dispersion is comprised between 5.9 and 6.1 (adjusted whenever necessary by addition of diluted NH40H);

[0269] • polishing time: 20 minutes.

[0270] As references, the following cerium oxide aqueous dispersions were used in the same conditions:

[0271] - dispersion (Al) of cerium oxide particles synthesized in example 1 (CeCh mean particles size = 39 nm, as measured by DLS): for comparison with the dispersion of cerium oxide and metatungstate particles obtained at the end of example 1;

[0272] - dispersion (A2) of Zenus® particles commercially available from Solvay (CeO2 mean particles size = 87 nm, as measured by DLS): for comparison with the dispersion of cerium oxide and metatungstate particles obtained at the end of example 2;

[0273] - dispersion (A3) of Zenus® particles commercially available from Solvay (CeO2 mean particles size = 144 nm, as measured by DLS): for comparison with the dispersion of cerium oxide and metatungstate particles obtained at the end of example 3.

[0274] After the polishing sequence, the residue amount on the substrates polished with each dispersion was quantified by the following method. The substrate was fully submerged in a water bath with gentle magnetic stirring, ensuring the polished side faces downward. This process was conducted for 5 minutes and was repeated twice, with fresh water used for each iteration. The substrate was then dried with compressed air until no water mark was visible. The polished surface was examined using Scanning Electron Microscopy (SEM) equipped with a Field Emission Gun (FEG) source. The instrument used was an Ultra55 from Zeiss. Images with a resolution of 1024x768 pixels and a pixel size of 19.53 nm were captured using an in-lens secondary electron detector, operating at an acceleration voltage of 0.5 V and a working distance in the range of 2 - 3 mm. For each sample, 12 regions were imaged, distributed approximately evenly according to the layout shown in Figure 1.

[0275] The residue level for an imaged region was calculated as the ratio of the particle- covered surface area to the total surface area. The residue level of a sample was determined as the median of the residue levels measured across the 12 imaged regions. Low residue efficiency ratio (LR efficiency ratio) was defined as the ratio of the residue level obtained with the dispersion of the invention (Ex 1 to 3) to the residue level obtained with the reference dispersion for each (Al to A3). The results are given in Table 5 below:

[0276] Table 5: low residue efficiency ratio of dispersions of cerium oxide and polyoxometalates particles according to the invention

[0277] It is thus evidenced that the particles dispersions of the invention exhibit an outstanding low residue performance compared to dispersions of particles which are deprived of POM on their surface.

Claims

CLAIMS1. An aqueous dispersion comprising particles of cerium oxide with polyoxometalates species adsorbed thereon, denoted “cerium oxide and polyoxometalate particles”, wherein the pH of the dispersion ranges from 1.0 to 9.0 and the hydrodynamic mean diameter Dh of the cerium oxide and polyoxometalate particles, as measured by dynamic light scattering, ranges from 10 to 300 nm.

2. The dispersion of claim 1, wherein the polyoxometalates species are selected from the group consisting of: compounds of formula [HhXxMnCUo]11', compounds of formula [Y2M18O62]11', compounds of formula [HhXxM6O24]n‘, compounds of formula [MeOw]11', mixtures of any of the above and recombination species thereof, wherein h is 0 or 2, X is Si or P and x=0 when h=2 and x=l when h=0; Y is selected from Si or P; M is selected from W, Mo or V; n is an integer different from 0 denoting the number of charges of the compound, typically ranging from 2 to 12.

3. The dispersion of claim 1 or 2, exhibiting a negative zeta-potential, in particular ranging from -60 to -10 mV, as measured on the dispersion at a concentration of the cerium oxide and polyoxometalate particles comprised between 1 wt% and 5 wt% in weight of cerium oxide.

4. The dispersion of any of claims 1 to 3, wherein the pH thereof ranges from 1.0 to 7.0, in particular from 1.0 to 6.0, more particularly from 2.0 to 6.0.

5. The dispersion of any of claims 1 to 4, wherein the molar ratio Ce / Madsorbed ranges from 2 to 625, in particular from 3 to 500, more preferably from 5 to 375, wherein Ce denotes the total molar amount of cerium present in the dispersion and Madsorbedthe molar amount of metal M stemming from the adsorbed polyoxometalate species present in the dispersion.

6. The dispersion of any of claims 1 to 5, wherein the ratio of adsorbed elemental M (g / L) stemming from the adsorbed polyoxometalate species relative to the total elemental M (g / L) stemming from all the polyoxometalate species in the dispersion ranges from 0.40 to 1.00, in particular from 0.50 to 1.00, more particularly from 0.70 to 1.00, for example from 0.75 to 0.95.

7. The dispersion of any of claims 1 to 6, wherein the molar ratio Ce / Mtotai ranges from 2 to 250, in particular from 3 to 200, more preferably from 5 to 150, wherein Ce denotes the total molar amount of cerium present in the dispersion and Mtotai denotes the total molar amount of metal stemming from the polyoxometalate species present in the dispersion.

8. The dispersion of any of claims 1 to 7, wherein the cerium oxide and polyoxometalates particles exhibit an hydrodynamic mean diameter Dh, as measured by dynamic light scattering, ranging from 10 nm to 200 nm, in particular from 10 nm to 100 nm, even more particularly from 10 nm to 65 nm.

9. The dispersion of any of claims 1 to 8, wherein the concentration of cerium oxide ranges from 0.5 wt% to 40 wt%, preferably from 1 wt% to 35 wt%, relative to the total weight of the dispersion.

10. The dispersion of any of claims 1 to 9, wherein the cerium oxide and polyoxometalate particles are dispersed in an aqueous medium which is water or a mixture of water and a water-miscible organic liquid.

11. A process for producing an aqueous dispersion comprising particles of cerium oxide with polyoxometalates species adsorbed thereon, comprising at least the following steps:(a) providing a dispersion of cerium oxide particles in an aqueous medium, wherein the cerium oxide particles have an hydrodynamic mean diameter Dh ranging from 8 to 298 nm, as measured by dynamic light scattering, and whereinthe pH ranges from 1 to 9; providing a solution comprising at least one poly oxometalate salt in an aqueous medium, wherein the pH ranges from 1 to 8.(b) contacting the dispersion and the solution provided in step (a) so as to form a reaction medium in which the at least one polyoxometalate is adsorbed onto the cerium oxide particles,(c) optionally acidifying and / or washing the dispersion obtained from step (b).

12. The process of claim 11, wherein the dispersion of cerium oxide particles provided in step (a) is obtained by:(a’) contacting under an inert atmosphere, an aqueous solution of a base and an aqueous solution comprising NOs-’ Ce(III), Ce(IV);(b’) subjecting the mixture obtained in step (a’) to a thermal treatment;(c’) the mixture obtained at the end of step (b’) may optionally be acidified;(d’) the solid material contained in the mixture 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’) may optionally be subjected to a mechanical treatment of deagglomeration.

13. A polishing composition, in particular for chemical mechanical polishing, comprising at least the dispersion of any of claims 1 to 10 or the dispersion obtained from the process of claim 11 or 12, and optionally at least one additive, preferably selected from:-abrasive particles other than cerium oxide and polyoxometalates particles,- a pH regulator,- a surfactant,- a rheological control agent, including viscosity enhancing agents and coagulants;- a polymeric additive, in particular a cationic polymer, an anionic polymer or a nonionic polymer;- a starch,- a silane, an oxidizer-combinations thereof.

14. A method for removing a portion of a substrate, the method comprising polishing the substrate with the polishing composition of claim 13.

15. Use of the dispersion according to any of claims 1 to 10 or of the dispersion obtained from the process of claim 11 or 12 for polishing, in particular for chemical mechanical polishing, wherein the cerium oxide and polyoxometalates particles comprised in the dispersion are preferably abrasive particles.

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