Suspension for chemical mechanical planarization (CMP) and method employing the same

Abstract

To provide aqueous suspensions suitable for chemical mechanical planarization (CMP), and methods for preparing the aqueous suspensions.SOLUTION: An aqueous suspension includes (a) one or more kinds of metal salts of permanganic acid; (b) zirconia nanoparticles; (c) alumina nanoparticles; and (d) one or more kinds of salts of nitric acid. A method for preparing the aqueous suspension includes (i) a step of adding aluminum nitrate to an aqueous suspension containing alumina nanoparticles and zirconia nanoparticles; and (ii) a step of adding an aqueous solution of one or more kinds of metal salts of permanganic acid to the aqueous suspension.SELECTED DRAWING: None

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application claims the priority and benefit of U.S. Provisional Patent Application No. 63 / 167,275, filed on March 29, 2021, under the name "Suspensions for Chemical Mechanical Planarization (CMP) and Methods of Using the Same", and incorporates the same herein by reference in its entirety. This application claims the priority and benefit of U.S. Provisional Patent Application No. 63 / 180,963, filed on April 28, 2021, under the name "Suspensions for Chemical Mechanical Planarization (CMP) and Methods of Using the Same", and incorporates the same herein by reference in its entirety. This application claims the priority and benefit of U.S. Provisional Patent Application No. 63 / 237,644, filed on August 27, 2021, under the name "Suspensions for Chemical Mechanical Planarization (CMP) and Methods of Using the Same", and incorporates the same herein by reference in its entirety.

[0002] [Field] The present disclosure relates to aqueous suspensions suitable for chemical mechanical planarization (CMP), the use of aqueous suspensions, and methods of CMP using aqueous suspensions.

Background Art

[0003] The CMP method is a polishing method that combines both chemical and mechanical actions.

Summary of the Invention

[0004] The aqueous suspensions described herein and any embodiments thereof mean the suspensions according to the present disclosure. It also means the chemical mechanical planarization slurry of the present disclosure or "the CMP slurry of the present disclosure". Some of the components of the slurry act chemically, such as oxidizing the surface of the substrate to be polished, enabling the abrasive grain component of the slurry that acts mechanically to remove unevenness from the substrate surface more gently.

[0005] A further object of the present disclosure includes the use of a suspension as a polishing composition, particularly suitable for polishing silicon carbide surfaces in a chemical mechanical planarization method.

[0006] Yet another object of the present disclosure is to provide a method for chemical mechanical planarization of a substrate, the method comprising contacting the substrate with an aqueous suspension according to the present disclosure, moving the aqueous suspension relative to the substrate by a polishing pad, and abrading at least a portion of the substrate to polish the substrate.

[0007] When a suspension is used in the CMP process, the material removal rate can be accelerated, and at the same time, the interfacial temperature during polishing can be reduced. Further, the process time can be shortened, the die yield of the wafer can be increased, and surface defects and scratches can be minimized. Due to the components of one or more kinds of calcined alumina particles, one or more kinds of metal salts of chloric acid, and one or more kinds of metal salts of perchloric acid, the material removal rate is only composed of one or more kinds of metal salts of permanganic acid, one or more kinds of zirconia nanoparticles, one or more kinds of alumina nanoparticles, and one or more kinds of salts of nitric acid, and does not include one or more kinds of calcined alumina particles, one or more kinds of metal salts of chloric acid, and one or more kinds of metal salts of perchloric acid. Compared with an aqueous suspension, it can be further increased by 25% to 30% even at a lower interfacial temperature. Removal rates of ≧13 μ / hr on single crystal 4H n-type SiC (Si face) and ≧30 μ / hr on the C face are observed, and sub-angstrom substrates without defects are produced with a high process yield. In addition, the friction and motor load in CMP operations with temperature limitations can be significantly reduced, and the corresponding CMP method allows process engineers to develop more aggressive process strategies to improve the wafer throughput. Further, no "settling" of any component of the suspension can be observed during product use or storage conditions, so the suspension has a long shelf life even in its acidic medium. Further, the components of the suspension adhere to the wafer surface based on various surface charge dynamics, thereby ensuring uniform distribution of the suspension over the entire wafer surface. Finally, after the cleaning process between runs, almost no or no residue can be observed on the CMP pad, and the life of the pad can be extended.

[0008] In some embodiments, the present disclosure includes an aqueous suspension comprising (a) one or more metal salts of permanganic acid, (b) zirconia nanoparticles, (c) alumina nanoparticles, and (d) one or more salts of nitric acid.

[0009] In some embodiments, the present disclosure includes a method for preparing an aqueous suspension, the method comprising the steps of: (i) adding aluminum nitrate to an aqueous suspension comprising alumina nanoparticles and zirconia nanoparticles; and (ii) adding an aqueous solution of one or more metal salts of permanganic acid to the aqueous suspension.

[0010] In some embodiments, the present disclosure includes a method comprising the steps of: storing an aqueous suspension having a pH in the range of 3 to 5; lowering the pH of the aqueous suspension to a range of 2 to 2.5; and using the aqueous suspension having a pH in the range of 2 to 2.5 within 14 days.

[0011] In some embodiments, the present disclosure includes an aqueous suspension comprising (a) one or more metal salts of permanganic acid, (b) one or more zirconia nanoparticles, (c) one or more alumina nanoparticles, (d) one or more salts of nitric acid, (e) one or more calcined alumina particles, (f) one or more metal salts of chloric acid, and (g) one or more metal salts of perchloric acid.

[0012] In some embodiments, the present disclosure includes a method for preparing an aqueous suspension, the method comprising the steps of: (i) adding aluminum nitrate to an aqueous suspension comprising alumina nanoparticles and zirconia nanoparticles; (ii) adding an aqueous solution of one or more metal salts of permanganic acid, one or more metal salts of perchloric acid, and one or more metal salts of chloric acid to the aqueous suspension; and (iii) adding one or more calcined alumina particles to the aqueous suspension.

[0013] In some embodiments, the present disclosure includes an aqueous suspension comprising at least one oxidizing agent, abrasive grains having a total amount of less than 0.2% by weight based on the total weight of the aqueous suspension and having a Mohs hardness of less than 6, and aluminum nitrate.

[0014] In some embodiments, the present disclosure is a method for preparing an aqueous suspension, comprising: (i) adding aluminum nitrate to an aqueous suspension containing abrasive grains; and (ii) adding an aqueous solution of at least one oxidizing agent to the aqueous suspension, wherein the abrasive grains have a Mohs hardness of less than 6 and the aqueous suspension contains less than 0.2% by weight of abrasive grains based on the total weight of the aqueous suspension.

Best Mode for Carrying Out the Invention

[0015] Among the disclosed advantages and improvements, other objects and advantages of the present disclosure will become apparent from the following description when considered in conjunction with the accompanying drawings. Specific embodiments of the present disclosure are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the present disclosure, which may be embodied in various forms. In addition, each of the examples provided with respect to the various embodiments of the present disclosure is for illustrative purposes only and not limiting.

[0016] All prior patents and publications referred to herein are hereby incorporated by reference in their entirety.

[0017] Throughout the specification and the claims, the following terms have the meanings explicitly associated herewith unless the context clearly indicates otherwise. As used herein, the phrases "in one embodiment," "in an embodiment," and "in some embodiments" may refer to the same embodiment, but not necessarily. Further, as used herein, the phrases "in another embodiment" and "in some other embodiments" may refer to different embodiments, but not necessarily. It is intended that all embodiments of the present disclosure can be combined without departing from the scope or spirit of the present disclosure.

[0018] The percentages and amounts, by weight % (percent by weight), of any of the components given below that are present in the aqueous suspension, in each case total 100 weight % based on the total weight of the suspension.

[0019] As used herein, the term "based on" is not exclusive and allows for being based on additional factors not recited, unless the context clearly indicates a different meaning. Additionally, throughout the specification, the meanings of "a", "an", and "the" include plural references. The meaning of "in" includes "in" and "on".

[0020] As used herein, the term "between" does not necessarily require being disposed immediately adjacent to other elements. Generally, this term means a structure where something is sandwiched between two or more other things. At the same time, the term "between" may also describe something that is immediately adjacent to two opposing things. Thus, in any one or more of the embodiments disclosed herein, a particular structural component disposed between two other structural elements can be as follows: It can be disposed directly between both of the two other structural elements such that the particular structural component is in direct contact with both of the two other structural elements; It can be disposed immediately adjacent to only one of the two other structural elements such that the particular structural component is in direct contact with only one of the two other structural elements; It can be disposed indirectly adjacent to only one of the two other structural elements such that the particular structural component is not in direct contact with only one of the two other structural elements and there is another element juxtaposing the particular structural element and one of the two other structural elements; It can be disposed indirectly between both of the two other structural elements such that the particular structural component is not in direct contact with both of the two other structural elements and other features can be disposed between them; or Any combination thereof.

[0021] As used herein, "embedded" means that the first material is dispersed throughout the second material.

[0022] As used herein, unless the context clearly indicates otherwise, the grammatical articles "a," "an," and "the" are intended to include "at least one" or "one or more," even if "at least one" or "one or more" is explicitly used in a given case. Thus, these articles are used herein to refer to one or more (i.e., "at least one") of the grammatical objects of the article. By way of example, and not limitation, "a component" means one or more components, such that in some cases, more than one component is contemplated and may be used or employed in the practice of the described embodiments. Further, unless the context requires otherwise, the use of singular nouns includes pluralities, and the use of plural nouns includes singulars.

[0023] As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," or any other variations thereof are intended to cover non-exclusive inclusion. For example, a composition or method that includes a list of features is not necessarily limited to only those features, but may include other features not expressly listed or inherent to such composition or method.

[0024] As used herein, unless expressly stated to the contrary, "or" refers to inclusive "or" and not exclusive "or." For example, condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or absent), A is false (or absent) and B is true (or present), and both A and B are true (or present).

[0025] As used herein in the context of zirconia and alumina, the term "nanoparticle" is quantified by dynamic light scattering (DLS), also known as quasi-elastic light scattering (QELS), and means particles having a Z-average particle size in the range of 1 nm to 1000 nm. The Z-average particle size is also referred to as the scattered light intensity weighted harmonic mean particle size obtained from a data analysis algorithm known as the cumulant method. The Z-average particle size can be quantified, for example, in accordance with ISO 22412:2017(en) by using a Malvern Zetasizer Nano (Malvern Instruments Ltd., Malvern, UK).

[0026] The term "suspension" refers to a heterogeneous mixture in which solute particles do not dissolve and are suspended throughout most of the solvent, remaining freely suspended in the medium.

[0027] As used herein, the term "aqueous suspension" refers to a suspension in which the major fraction of the liquid carrier of the suspension is water, i.e., in each case, based on the total amount of solvent (i.e., water and, if any, organic solvent) present, the water fraction of the suspension is at least 80 wt%, at least 85 wt%, at least 90 wt%, or at least 92, 93, or 94 wt%. In some embodiments, the water fraction of the aqueous suspension is 40 to 100 wt%, 60 to 100 wt%, or 80 to 100 wt% in each case based on the total amount of solvent present. The water used in the suspensions of the present disclosure can be deionized water. In some embodiments, the aqueous suspensions of the present disclosure do not contain any organic solvent, i.e., the total amount of organic solvent is 0 wt% based on the total amount of solvent present.

[0028] As used herein, the term "oxidizing agent" is a compound that dissolves in the aqueous carrier of the suspension and has an appropriate oxidation potential to chemically react with the surface of the substrate. In some embodiments, the oxidizing agent has an oxidation potential of at least 0.26V, or at least 0.4V, or at least 0.5V, or at least 1.0V, or at least 1.5V. In some embodiments, the oxidation potential can be 2.8V or less, or 2.5V or less, or 2.0V or less. The oxidation potential is a measured value relative to the standard hydrogen electrode, measured in volts (V), at a temperature of 25°C, a pressure of 1 atmosphere, and a concentration in water of 1 mol / L of the test oxidizing agent.

[0029] "Mohs hardness" refers to a qualitative ordinal scale ranging from 1 to 10, characterizing the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. When the scale was designed, diamond was at the top of the scale with a Mohs hardness of 10 as the hardest naturally occurring substance known at that time. The hardness of a material is measured against the scale by finding the hardest material that a given material can scratch, or the softest material that can scratch a given material. "Scratching" a material for the purpose of the Mohs scale means creating a non-elastic dislocation visible to the naked eye. Often, in materials with a low Mohs scale, fine non-elastic dislocations may occur on a material with a high Mohs number. These fine dislocations are permanent and may be detrimental to the structural integrity of the harder material, but are not considered "scratches" for the purpose of determining the Mohs scale number.

[0030] Over the past few decades, the introduction of electric vehicles (EVs) and many other clean technologies has been accelerated by improvements in the cost, performance, and efficiency of power generation, storage, and distribution systems, as well as government subsidies that promote the electrification of a wide society.

[0031] The shift to a more electrified world has created a need for a new electrical infrastructure of nodes and switches that control the flow of power. At the core of this new infrastructure are power devices, namely solid-state transistors, that are similar in size and appearance to computer chips that power computers and phones but have the ability to handle large voltages and currents and manage the flow of electricity, for example, between the motor and battery of an electric vehicle or between the solar cells and battery of a home charging system.

[0032] A new generation of power devices composed of silicon carbide (SiC) has been demonstrated to be dramatically superior to older, conventional silicon-based devices. Individual SiC power devices on the order of a few millimeters in size are fabricated on SiC wafers, which are uniform substrates thinly sliced from crystalline SiC that can be 4 inches or 6 inches in diameter.

[0033] SiC is a material that can exist in different crystal structures known as polytypes. The crystal stacking order of Si and C atoms that characterizes each polytype also determines its fundamental electrical properties. There are over 200 known polytypes of SiC, but only a few, namely 3C-SiC, 4H-SiC, and 6H-SiC, are commercially available. Currently, 4H-SiC is the SiC polytype most widely used in the manufacture of power devices due to its superior electrical properties. These properties enable power devices with high breakdown voltages, high power densities, high switching frequencies, improved thermal conductivities, and improved overall device efficiencies. 4H-SiC power devices enable performance improvements in 5G wireless networks, military radars, satellite communications, power converters for renewable power sources, and drones, beyond their use in EV motor control systems and charging stations, while at the same time making these devices smaller, lighter, and more robust against environmental conditions such as vibration and radiation.

[0034] Compared with silicon (Si), silicon carbide (SiC), more specifically 4H-SiC, has properties including a breakdown electric field one order of magnitude larger, an energy bandgap approximately three times larger, and a thermal conductivity approximately four times higher. Therefore, there is considerable promise for applications in power devices, high-frequency devices, high-temperature operating devices, etc. As a result, the use of SiC substrates for semiconductor devices is increasing.

[0035] The above-mentioned SiC substrates are manufactured, for example, from bulk single-crystal ingots of SiC prepared by highly controlled sublimation methods, etc. Usually, after grinding the outer peripheral surface of the ingot to process it into a cylindrical shape, it is sliced into wafers using a wire saw embedded with diamond, etc., and then the outer peripheral surface is chamfered to a specified diameter to obtain the substrate. The diamond saw leaves large mm-sized gouges and scratches on the wafer surface, but these are removed by various stages of surface lapping and grinding processes in order to remove unevenness and achieve surface flatness. However, since the lapping and grinding processes rely on micron-sized diamond particles, there is a possibility of leaving micron-sized surface damage in the form of scratches, pits, and gouges.

[0036] Subsequently, mirror finishing is achieved by performing chemical-mechanical polishing, also known as CMP (Chemical Mechanical Planarization), on one or both sides of the substrate. This type of grinding and polishing of SiC substrates is carried out for purposes such as removing undulations and process strain, flattening the surface of the SiC substrate to obtain an atomically almost flat surface with substantially no surface defects, which is suitable for downstream epitaxy and further semiconductor manufacturing processes.

[0037] Since the CMP method is a polishing method with both chemical and mechanical actions, a flat surface can be obtained in a stable form without damaging the SiC substrate. As a result, the CMP method is widely used in the manufacturing process of SiC semiconductor devices, etc., as a method for flattening the roughness or undulations generated on the surface of the SiC substrate, or the unevenness caused by wiring, etc.

[0038] In the CMP process, the wafer surface is pressed against a polishing pad with a controlled force in the presence of a CMP slurry and rotated at a controlled rotational speed, pressure, and duration. The polishing pad can be made of a soft, porous polymer, which provides a mechanical surface for rubbing against the substrate surface, as well as grooves and pores that can promote the flow of the slurry and capture the removed debris, which is the oxidized surface material removed as part of the CMP process. The CMP slurry can be a composite suspension containing an oxidizing agent, additives, and particles, and is usually acidic or alkaline depending on the nature of the application. In the CMP process, the chemical attack (oxidizing agent, additives, and pH) of the slurry is complemented by the mechanical (frictional) force generated by the contact between the pad, particles, and substrate. Considering a number of chemical and mechanical process variables, the development of a CMP slurry requires a deep understanding of the process and the interactions between the pad, particles, particles and wafer, and wafer and pad. For example, the CMP processes for various materials such as Si, SiC, sapphire, GaN, InP, etc. all require specific processing conditions, parameters, and consumables that are unique to the technical and application requirements of each substrate.

[0039] On the one hand, in the case of SiC wafers, especially 4H-SiC wafers, due to their mechanical hardness and chemical inertness, very aggressive CMP conditions, namely, an aggressive CMP suspension / slurry and aggressive CMP parameters (high pressure, high polishing speed, etc.) are required to effectively remove SiC. On the other hand, these aggressive conditions can cause surface scratching, pitting, debris, and subsurface damage.

[0040] Therefore, it is necessary to provide a CMP slurry that is well-balanced and has sufficient aggressiveness to produce a SiC wafer with an atomically flat surface up to a level where the vicinal crystal structure can be identified by atomic force microscopy observation while avoiding damage to the substrate.

[0041] Furthermore, there are various different CMP process approaches. In one configuration, multiple SiC wafers are processed at once on a large polishing tool. This is called a "batch process" and requires a particularly large CMP tool that uses a platen several feet in diameter and can process up to 20 or more wafers at a time. Batch processing offers some throughput advantages, but due to the large number of wafers and the large tool size, process adjustment becomes complex and throughput problems are likely to occur. For example, if the wafers loaded into a batch CMP tool are not the same thickness, the thicker wafers will protrude into the polishing pad and thus require more force, while the thinner wafers will receive less force and may even slip off during processing. This can result in non-uniform polishing of the SiC wafers. Also, as is common in CMP, if one wafer in a batch process is broken apart by strong mechanical forces, wafer fragments from the broken wafer can cause further scratches or even damage the entire batch of wafers. Additionally, as the platen size and surface area increase, it becomes difficult for the tool to apply the extreme downward force necessary for a satisfactory material removal rate uniformly; thus, longer run times are required. Longer run times mean that the wafers are exposed to aggressive conditions for longer periods, increasing the risk of defects, scratches, and significant surface damage. This has spurred the testing and adoption of new tool sets, pads, and slurries designed specifically for batch processes.

[0042] In some configurations, to overcome these defects and throughput issues, the SiC industry has primarily started to shift from batch processes to single-wafer processes. In single-wafer processes, smaller platen sizes enable higher process pressures and more uniform pressure distributions. Higher pressures result in faster material removal rates and thus shorter execution times. Additionally, in single-wafer processes, defective or damaged wafers can be separated without damaging other wafers. This shift to single-wafer CMP has facilitated the testing and adoption of new tool sets, pads, and slurries designed specifically for single-wafer processes.

[0043] Since the process conditions such as tool sets, polishing pads, and down pressure used during batch and single-wafer CMP processes are different, slurries are typically designed specifically for one type of CMP process. However, CMP slurries may be equally suitable for use in both batch and single-wafer CMP processes.

[0044] Accordingly, to solve various problems of the prior art, the present disclosure provides a suspension having a stable pH, i.e., a pH drift of less than 0.1 over a period of at least 12 months, which enables a high material removal rate while reducing the surface roughness of the polished substrate when used in a batch CMP or single-wafer CMP process. The present disclosure provides a suspension suitable as a CMP slurry in a batch CMP process as well as a single-wafer CMP process, which enables speeding up of the process, i.e., enables higher throughput by significantly increasing the material removal rate. For this, even for a wafer made of 4H-SiC, there may be a need for a suspension that is aggressive enough to polish and planarize the wafer while simultaneously avoiding scratches or other damage to the wafer surface. To ensure this, the suspension may be more effective as a CMP slurry at a lower temperature at the interface between the polishing pad and the wafer as compared to prior art slurries. The suspension has storage stability, and precipitates, if any, formed during storage are readily redispersible by simple agitation such as stirring or shaking the suspension.

[0045] An object of the present disclosure is to provide the use of such a suspension in a method for polishing a wafer, particularly chemical mechanical planarization.

[0046] A further object of the present disclosure is to provide a correspondingly improved gentle method for chemically mechanically planarizing a wafer, more particularly a SiC wafer such as a 4H-SiC wafer, using such a CMP slurry.

[0047] In some embodiments, the present disclosure is an aqueous suspension having a pH value in the range of 2 to 5 and comprising (a) one or more salts of permanganic acid; (b) zirconia nanoparticles; (c) alumina nanoparticles; and (d) one or more salts of nitric acid. In some embodiments, the present disclosure optionally comprises one or more agents selected from the group consisting of a pH adjuster and a pH buffer. In some embodiments, the pH value is measured at a temperature range of 20°C to 30°C, for example 23°C. In some embodiments, the aqueous suspension comprises particles having a Mohs hardness greater than 1, greater than 2, greater than 3, and greater than 4.

[0048] In some embodiments, the present disclosure is an aqueous suspension comprising (a) one or more metal salts of permanganic acid; (b) one or more zirconia nanoparticles; (c) one or more alumina nanoparticles; (d) one or more salts of nitric acid; (e) one or more calcined alumina particles; (f) one or more metal salts of chloric acid; and (g) one or more metal salts of perchloric acid. In some embodiments, the present disclosure optionally comprises one or more agents selected from the group consisting of a pH adjuster and a pH buffer. In some embodiments, the aqueous suspension has a pH value in the range of 2 to 5. In some embodiments, the pH value of the aqueous suspension is measured at a temperature range of 15°C to 40°C, for example, 23°C. In some embodiments, the aqueous suspension comprises particles having a Mohs hardness greater than 1, greater than 2, greater than 3, and greater than 4.

[0049] In some embodiments, the present disclosure is an aqueous suspension having a pH value of 2 to 5 at 23°C, containing at least one oxidizing agent, abrasive grains in an amount of less than 0.2% by weight in total, and aluminum nitrate. In some embodiments, the present disclosure optionally includes one or more agents selected from the group consisting of a pH adjuster and a pH buffer. In some embodiments, all of the abrasive grains present in the aqueous suspension have a Mohs hardness of less than 6 in order to avoid scratching the surface of the substrate during the polishing process. In some embodiments, the pH value is measured in a temperature range of 15°C to 40°C, for example, at 23°C. In some embodiments, the present disclosure provides an aqueous suspension having a pH value of 2 to 5 at 23°C, (based on the total weight of the aqueous suspension) at least one oxidizing agent, abrasive grains with a total amount of less than 0.2% by weight; aluminum nitrate; and optionally at least one pH adjuster and / or at least one pH buffer, wherein all of the abrasive grains present in the aqueous suspension have a Mohs hardness of less than 6. In some embodiments, the present disclosure includes providing an aqueous suspension of abrasive grains (ASP) wherein all of the abrasive grains present in the aqueous suspension have a Mohs hardness of less than 6, adding aluminum nitrate to the aqueous suspension (ASP) provided in the step of providing the aqueous suspension, adding an aqueous solution of at least one oxidizing agent to the aqueous suspension obtained after the step of adding aluminum nitrate, and optionally adjusting the pH of the aqueous suspension obtained after the step of adding the aqueous solution with at least one pH adjuster, to prepare a suspension (AS) having a pH value of 2 to 5 at 23°C, and the aqueous suspension (AS) obtained from the method contains abrasive grains of less than 0.2% by weight based on the total weight of the aqueous suspension.

[0050] The at least one oxidizing agent can be any suitable oxidizing agent that oxidizes chemical bonds such as Si-C bonds on the surface of a substrate such as a silicon carbide substrate to be polished.

[0051] Suitable oxidizing agents include persulfates, organic peroxides, inorganic peroxides, peroxyacids, permanganates, chromates, percarbonates, chlorates, bromates, iodates, perchloric acid and its salts, perbromic acid and its salts, periodic acid and its salts, hydroxylamine and its salts, ferricyanides, oxones, and combinations thereof.

[0052] In some embodiments, at least one oxidizing agent is a metal salt of permanganic acid, such as an alkali metal salt of permanganic acid. The alkali metal salts of permanganic acid can be selected from lithium permanganate, potassium permanganate, sodium permanganate, and mixtures thereof, such as potassium permanganate.

[0053] In some embodiments, at least one oxidizing agent is potassium permanganate.

[0054] In some embodiments, at least one oxidizing agent can be present in an amount of 0.1 to 10 wt%, 1 to 8 wt%, 2 to 6 wt%, 3 to 5.5 wt%, or 4 to 5 wt% in each case based on the total weight of the aqueous suspension. In some embodiments, the aforementioned ranges apply regardless of whether only one type of oxidizing agent is used or a mixture of different oxidizing agents is used in the suspension according to the present disclosure. In some embodiments, for example, when potassium permanganate is used as the sole oxidizing agent, the aforementioned ranges apply to potassium permanganate.

[0055] If the amount of at least one oxidizing agent is too low, the material removal rate of the suspension in the CMP process may also be too low; if the amount of at least one oxidizing agent is too high, the oxidizing power may be too strong, and thus surface defects may occur mainly by mechanisms such as etching. If the amount of at least one oxidizing agent is 0.1 to 10 wt%, or 3 to 5.5 wt%, or 4 to 5 wt% in each case based on the total weight of the aqueous suspension, a balance between the characteristics and efficiency in the CMP process can be achieved.

[0056] In some embodiments, all abrasive grains present in the suspension of the present disclosure have a Mohs hardness of less than 6. When using abrasive grains having a Mohs hardness of less than 6 (i.e., "soft" abrasive grains), there is storage stability, and thus an aqueous suspension that exhibits a certain quality during its storage period is formed. On the other hand, when using abrasive grains having a Mohs hardness exceeding 6, for example, alumina particles having a Mohs hardness exceeding 6, an unstable suspension is formed. Furthermore, the use of an aqueous suspension containing these "soft" abrasive grains surprisingly results in an improvement in material removal rate, a decrease in polishing temperature, and a decrease in surface roughness (i.e., an improvement in the quality of the polished substrate) in batch and single-wafer CMP processes compared to the use of an aqueous slurry containing abrasive grains having a Mohs hardness exceeding 6, such as silica.

[0057] In some embodiments, the abrasive grains have a Z-average particle size of from 1 nm to 1000 nm, from 10 to 500 nm, from 20 to 300 nm, from 50 to 200 nm, or from 75 to 150 nm. Thus, the abrasive grains can be nano-abrasive grains. The Z-average particle size is also referred to as the scattered light intensity-weighted harmonic mean particle size obtained from a data analysis algorithm known as the cumulant method. The Z-average particle size can be quantified in accordance with ISO 22412:2017(en), for example, by using a Malvern Zetasizer Nano (Malvern Instruments Ltd., Malvern, UK).

[0058] In some embodiments, the abrasive grains have a Mohs hardness of less than 5.5, less than 5, or from 3 to 4. The abrasive grains can include (e.g., include, consist essentially of, or consist of) one or more metal oxides having a Mohs hardness of less than 6 as described above, for example, from 3 to 4. The metal oxide can be selected from metal oxides of alumina, titania, zirconia, ceria, germanium oxide, magnesia, and combinations thereof having a Mohs hardness of less than 6. The aqueous suspension may contain only one type of abrasive grain or a mixture of different types of abrasive grains.

[0059] In some embodiments, the abrasive grains can include (e.g., include, consist essentially of, or consist of) alumina particles having a Mohs hardness of less than 6. In some embodiments, alumina particles in the sense of the present disclosure include aluminum oxide, such as aluminum hydroxide, aluminum oxyhydroxide, hydrates of any of the foregoing alumina species, and at least one of any of the foregoing alumina species and at least one additional metal atom and / or its oxide and / or hydroxide, and / or metal ions, and are particles having a Mohs hardness of less than 6. In some embodiments, the alumina particles can include (e.g., include, consist essentially of, or consist of) at least one of aluminum hydroxide, aluminum oxyhydroxide, or hydrates of any of the foregoing alumina species.

[0060] The alumina particles can be present in an amorphous form such as a colloidal form or a polycrystalline amorphous form. In some embodiments, the abrasive grains can include (e.g., include, consist essentially of, or consist of) boehmite (hereinafter referred to as γ-AlOOH) particles and / or γ-Al2O3 particles, and can be in a colloidal form. For example, the aqueous suspension can include colloidal alumina particles of γ-AlOOH particles and / or γ-Al2O3 particles. In some embodiments, the aqueous suspension includes 0 wt% of additional abrasive grains based on the total weight of the aqueous suspension (separate from, e.g., alumina particles having a Mohs hardness of less than 6, such as γ-AlOOH particles). Using boehmite as a single abrasive grain improves the stability of the aqueous suspension (in combination with aluminum nitrate), but using other aluminas such as alpha alumina, or other nitrates such as ferric nitrate, cerium nitrate, and manganese nitrate results in a decrease in the storage stability of the aqueous suspension due to the formation of an unstable suspension or an undesirable reaction product. Further, using boehmite as a single abrasive grain reduces scratches on the surface of the substrate during the polishing process, lowers the polishing temperature for a given down pressure, thus improving the surface quality and reducing substrate damage, and thus improving the quality (or yield) of the CMP process.

[0061] In some embodiments, the suspension according to the present disclosure contains less than 0.2 wt%, 0.15 wt%, 0.1 wt%, or 0.05 wt% of the total amount of abrasive grains. This list of ranges is not exhaustive and includes values in between, such as less than 0.13 wt%. In some embodiments, the suspension according to the present disclosure contains from 0.005 wt% to 0.2 wt%, from 0.005 wt% to 0.15 wt%, from 0.005 wt% to 0.1 wt%, or from 0.005 wt% to 0.05 wt%, from 0.005 wt% to 0.01 wt%, from 0.01 wt% to 0.2 wt%, from 0.05 wt% to 0.2 wt%, from 0.1 wt% to 0.2 wt%, from 0.15 wt% to 0.2 wt%, from 0.05 wt% to 0.15 wt%, from 0.01 wt% to 0.15 wt%, or from 0.05 wt% to 0.1 wt% of the total amount of abrasive grains. This list of ranges is not exhaustive and includes any value in between, for example, from 0.07 wt% to 0.13 wt%.

[0062] The alumina particles can be produced by any method known in the art.

[0063] In some embodiments, the suspension according to the present disclosure contains less than 0.2 wt% of abrasive grains in total based on the total weight of the suspension, and in some embodiments, contains less than 0.2 wt% of γ-AlOOH particles. When using less than 0.2 wt% of abrasive grains, for example, γ-AlOOH particles, surprisingly, an acceptable material removal rate can be obtained in a batch CMP process, but a polished substrate with a significantly lower surface roughness is provided compared to the case of using a larger amount of abrasive grains. In addition, the use of a smaller amount of the alumina particles makes it possible to obtain an aqueous suspension with high storage stability, that is, the change in pH when stored for more than 12 months is 0.1 or less. Therefore, it is possible to prevent, reduce, or limit the formation of undesirable reaction products that reduce the material removal rate and increase the surface roughness during the polishing process. Furthermore, the use of these small amounts of abrasive grains avoids clogging of the slurry distribution line or clogging of the pores of the polishing pad such that the polishing pad becomes too smooth and the material removal rate is significantly reduced.

[0064] In some embodiments, the abrasive grains, e.g., γ-AlOOH particles, are present in each case in a total amount of less than 0.18 wt%, less than 0.15 wt%, or less than 0.12 wt% based on the total weight of the aqueous suspension. For example, the total amount of abrasive grains, e.g., γ-AlOOH particles, can be from 0.001 to 0.18 wt%, from 0.01 to 0.15 wt%, or from 0.08 to 0.12 wt% based on the total weight of the aqueous suspension in each case.

[0065] In some embodiments, the aqueous suspension of the present disclosure contains aluminum nitrate. The use of aluminum nitrate makes it possible to avoid pH drift, i.e., the change in the pH of the aqueous suspension of the present disclosure is less than 0.1 when these suspensions are stored for at least 12 months. Since the material removal rate during CMP has been observed to be a function of the pH of the polishing suspension, a stable pH of the aqueous suspension during the storage period of the polishing suspension enables a uniform material removal rate. Further, since the pH of the aqueous suspension is stable, the formation of undesirable reaction products such as manganese dioxide formed during pH drift to a higher pH value is avoided, because these reaction products reduce the material removal rate and increase the surface roughness of the substrate, thus reducing the yield achieved with the aqueous suspension after storage. Further, without being bound by this theory, it is believed that aluminum nitrate forms a flexible network structure that embeds the abrasive grains, thus forming a "soft" layer on the particle surface that improves the surface roughness during polishing and reduces surface defects. However, surprisingly, even when a "soft" layer is formed on the abrasive grains, the material removal rate does not decrease. Thus, the aqueous suspension has a high material removal rate and provides a polished substrate with excellent yield over its entire storage period, i.e., low surface roughness or a low amount of surface defects.

[0066] In some embodiments, aluminum nitrate is present in each case in an amount of from 0.05 to 3 wt%, from 0.1 to 2 wt%, from 0.2 to 1.5 wt%, or from 0.3 to 1 wt% based on the total weight of the aqueous suspension. If the amount of aluminum nitrate is too low, an undesirable pH drift of the aqueous suspension is observed during storage, while if the amount of aluminum nitrate is too high, defects such as pitting corrosion occur on the substrate surface and an undesirable increase in the substrate / pad interface temperature occurs. Accordingly, in some embodiments, the aqueous suspension of the present disclosure contains aluminum nitrate in the aforementioned amounts. This makes it possible to achieve a stable pH and high yield of the aqueous suspension during the storage period without adversely affecting the material removal rate.

[0067] In some embodiments, the present disclosure is an aqueous suspension having a pH value in the range of 2.0 to 5.0 and containing one or more alkali metal permanganates, zirconia nanoparticles, alumina nanoparticles, one or more salts of nitric acid, and optionally a pH adjuster and / or a pH buffer. In some embodiments, the suspension in combination with a polishing pad can be an important component of the chemical mechanical planarization method described in the claims of the present disclosure. It is also referred to as a chemical mechanical polishing slurry or "CMP slurry". Some of the components of the slurry act chemically, such as oxidizing the surface of the wafer being polished, enabling mechanical acting components such as the wear of the slurry to more gently remove the unevenness on the wafer surface.

[0068] In some embodiments, the pH of the aqueous suspension of the present disclosure is in the range of from about 2 to about 5, from about 2.5 to about 5, from about 3 to about 5, from about 3.5 to about 5, from about 4 to about 5, from about 4.5 to about 5, from about 2 to about 4.5, from about 2 to about 4, from about 2 to about 3.5, from about 2 to about 3, from about 2 to about 2.5, from about 2.5 to about 3.5, from about 3 to about 4.5, or any intermediate value (e.g., about 4.3) or range (e.g., from about 2.6 to about 4.8).

[0069] In some embodiments, the aqueous suspension contains, as a constituent, one or more metal salts of permanganic acid. In some embodiments, the one or more metal salts of permanganic acid include, for example, LiMnO4, KMnO4, and / or NaMnO4.

[0070] In some embodiments, the one or more metal salts of permanganic acid are selected from alkali metal salts of permanganic acid consisting of lithium permanganate, sodium permanganate, potassium permanganate, and mixtures thereof, or may be selected from the group consisting of sodium permanganate, potassium permanganate, and mixtures thereof.

[0071] In some embodiments, there are at least two different metal salts of permanganic acid selected from the group consisting of sodium permanganate and potassium permanganate, the amount of sodium permanganate exceeds the amount of potassium permanganate, and the weight ratio of sodium permanganate to potassium permanganate is in the range of 7:1 to 1.5:1, or in the range of 6:1 to 1.7:1, for example, 5.5:1 to 1.9:1.

[0072] In some embodiments, the one or more metal salts of permanganic acid are present in an amount in the range of 7.5 to 30% by weight, in the range of 10 to 25% by weight, in the range of 12 to 22% by weight, or in the range of 13 to 20% by weight, based on the total weight of the aqueous suspension in each case. In some embodiments, there are at least two different metal salts of permanganic acid, for example, selected from the group consisting of sodium permanganate and potassium permanganate.

[0073] The metal salt of permanganic acid can function as an oxidizing agent that promotes the oxidation of SiC bonds on the surface of the wafer to be polished. In some embodiments, alkali metal permanganates such as sodium permanganate, potassium permanganate, and lithium permanganate are used as the oxidizing agent. However, in some embodiments, potassium permanganate is used as the permanganate.

[0074] In some embodiments, the metal salt of permanganic acid is present in an amount in the range of 2.0 to 6.0 wt%, 2.6 to 5.5 wt%, 3.0 to 5.0 wt%, or 4.0 to 5.0 wt%, for example 4.2 to 4.8 wt%, and the amount is based on the total weight of the suspension according to the present disclosure.

[0075] The above ranges apply regardless of whether only one metal salt of permanganic acid or a mixture of metal salts of permanganic acid is used in the suspension according to the present disclosure. In some embodiments, for example, when potassium permanganate is used as the only metal salt of permanganic acid, the above ranges apply to potassium permanganate.

[0076] In some embodiments, if the amount of the metal salt of permanganic acid is less than 2.0 wt%, the material removal rate of the suspension in the CMP method is too low; if the amount of the metal salt of permanganic acid exceeds 6.0 wt%, the oxidizing power is too strong, and surface defects mainly occur due to mechanisms such as etching. When the amount of the metal salt of permanganic acid is in the range of 3.0 to 5.0 wt%, more preferably 4.0 to 5.0 wt%, a balance between the characteristics and efficiency in the CMP method can be achieved. All of the above amounts are based on the total weight of the suspension according to the present disclosure.

[0077] In some embodiments, the aqueous suspension contains one or more types of zirconia nanoparticles as a constituent. In some embodiments, the zirconia nanoparticles contain ZrO2.

[0078] Zirconia nanoparticles in the meaning of the present disclosure include zirconium oxide, such as zirconium(IV) oxide, zirconium hydroxide, zirconium hydroxide oxide, hydrates of any of the aforementioned zirconia species, and any of the aforementioned zirconia species and at least one additional metal atom and / or its oxide and / or its hydroxide, and / or metal ions, and include at least one of the mixed metal species composed of them and are nanoparticles composed of them. Zirconia nanoparticles can exist in a colloidal form. In some embodiments, the zirconia nanoparticles are nanoparticles containing at least one zirconium oxide such as zirconium(IV) oxide and composed of it.

[0079] The suspension of the present disclosure contains zirconia nanoparticles. As described herein, the zirconia nanoparticles are particles having a Z-average particle size in the range of 1 nm to 1000 nm, in the range of 10 to 500 nm, in the range of 20 to 300 nm, in the range of 50 to 200 nm, and in the range of 75 to 150 nm.

[0080] Zirconia nanoparticles can be produced by any known method in the art. The aforementioned patent application documents describe the production of zirconia nanoparticles by using a hydrothermal process to generate a zirconia sol. The nanoparticles in such a sol are aggregates of zirconia subunits, and the determined Z-average particle size is the particle size of the aggregates.

[0081] Zirconia particles can be used in the suspension of the present disclosure in the form of a more concentrated colloidal composition to achieve the desired concentration required for the suspension of the present disclosure.

[0082] The suspension according to the present disclosure contains 0.05 to 5.0 wt%, 0.1 to 2.0 wt%, 0.15 to 1.0 wt%, or 0.15 to 0.5 wt% of zirconia nanoparticles based on the total weight of the suspension. In some embodiments, one or more types of zirconia nanoparticles may each be present in an amount in the range of 0.05 to 5.0 wt%, 0.10 to 4.0 wt%, 0.15 to 3.0 wt%, 0.15 to 2.0 wt%, or 0.25 to 1.5 wt% based on the total weight of the aqueous suspension.

[0083] In some embodiments, if the amount of zirconia nanoparticles is too high, the solution becomes more viscous. Furthermore, the pores of the polishing pad may become "glossy" and the particles may clog and become too smooth. Additionally, the particles may settle in the solution, resulting in clogging problems in the slurry distribution line pumped by the pump. If the amount of zirconia nanoparticles is too low, the mechanical wear force becomes insufficient, reducing the material removal rate to a level that is too low to be useful. In some embodiments, within the scope of the present disclosure, the balance of the material removal rate is maintained without observable sedimentation problems or overly high viscosity. In some embodiments, within the range of both components of one or more metal salts of permanganic acid and one or more types of zirconia nanoparticles, the increase in process temperature produces a surface quality of sub-angstrom with a balanced chemical and mechanical activity.

[0084] In some embodiments, the presence of zirconia nanoparticles in the suspension of the present disclosure creates a "chemical tooth" function, whereby the zirconia nanoparticles promote selective or catalytically enhanced oxidation by metal salts of permanganic acid with silicon-carbon bonds, such as potassium permanganate.

[0085] In some embodiments, the aqueous suspension contains one or more types of alumina nanoparticles as a component. In some embodiments, the alumina nanoparticles include colloidal alumina particles such as γ-AlOOH particles and / or γ-Al2O3 particles.

[0086] Alumina nanoparticles in the context of the present disclosure can include aluminum oxides such as aluminum(III) oxide, aluminum hydroxides, aluminum oxide hydroxides, hydrates of any of the foregoing alumina species, hydrates of any of the foregoing alumina species, and any of the foregoing alumina species and at least one additional metal atom and / or its oxide and / or its hydroxide, and / or metal ions, including, for example, at least one of the mixed metal species composed of them, and can be nanoparticles composed of them. The alumina nanoparticles may exist in colloidal form or in amorphous form such as polycrystalline amorphous form. α-, β-, or theta-alumina powders can also be used as alumina nanoparticles. In some embodiments, the alumina nanoparticles include at least one aluminum oxide such as aluminum(III) oxide and are nanoparticles composed of it.

[0087] The suspension of the present disclosure contains zirconia nanoparticles. As described herein, the alumina nanoparticles are particles having a Z-average particle size in the range of 1 nm to 1000 nm, in the range of 10 to 500 nm, in the range of 20 to 300 nm, in the range of 50 to 200 nm, and in the range of 75 to 150 nm.

[0088] The alumina nanoparticles can be produced by any known method in the art.

[0089] The alumina particles can be used in the suspension of the present disclosure in the form of a more concentrated composition to achieve the desired concentration required for the suspension of the present disclosure.

[0090] In some embodiments, the suspension according to the present disclosure contains alumina nanoparticles in an amount of 0.05 to 5.0 wt%, 0.1 to 2.0 wt%, 0.15 to 1.0 wt%, or 0.15 to 0.5 wt% based on the total weight of the suspension. In some embodiments, one or more types of alumina nanoparticles can be present in an amount in the range of 0.05 to 5.0 wt%, 0.10 to 4.0 wt%, 0.15 to 3.0 wt%, or 0.15 to 2.0 wt% in each case based on the total weight of the aqueous suspension.

[0091] If the amount of alumina nanoparticles is too large, the viscosity of the solution becomes too high, the particles settle, and there may be a problem of clogging in the slurry distribution line to be pumped. In such a case, it is necessary to select a smaller amount of alumina. If the amount of alumina nanoparticles is too small, the mechanical wear force becomes insufficient, the removal rate decreases too much, and it becomes unusable. At the levels within the scope of the present disclosure, there are no observable sedimentation problems, overly high viscosities, and no gloss on the polishing pad, and the balance of material removal is maintained.

[0092] In some embodiments, the presence of alumina nanoparticles enables a reduction in the CMP process temperature compared to a suspension without alumina nanoparticles, and thus an effective CMP process temperature becomes possible.

[0093] In some embodiments, the aqueous suspension contains one or more salts of nitric acid as a constituent. In some embodiments, one or more salts of nitric acid include Al(NO3)3.

[0094] The suspension according to the present disclosure contains one or more salts of nitric acid in an amount of 0.1 to 3.0 wt%, 0.2 to 2.0 wt%, or 0.5 to 1.5 wt%, for example 0.5 to 1.0 wt%. In some embodiments, the salt of nitric acid (for example, one or more salts of nitric acid) can be selected from metal nitrates.

[0095] In some embodiments, the nitrate salt adjusts the pH value of the suspension of the present disclosure. Thus, the nitrate salt used in the present disclosure is such that it is easy to acidify the aqueous suspension of the present disclosure.

[0096] The nitrate salts can be diverse and still have the desired effect. Suitable salts of nitric acid are, for example, ammonium nitrate, alkali metal nitrates, alkaline earth metal nitrates, transition metal nitrates and nitrates of IUPAC group 13 of the periodic table. Among the nitrates mentioned in the present disclosure, in some embodiments, the nitrate is a metal nitrate. Examples of suitable nitrates are, for example, calcium nitrate, magnesium nitrate, iron(III) nitrate and copper(II) nitrate. In some embodiments, the counterion to the nitrate anion is, for example, in a high oxidation state in the case of iron in the 3+ state (i.e., as iron(III) nitrate). This is because iron(II) nitrate is immediately oxidized by the salt of permanganic acid, thus forming iron(III) nitrate, but the amount of permanganate that is undesirably reduced in the same reaction is decreased.

[0097] In some embodiments, the presence of the metal cation and nitrate counterion provides an advantage in the oxidation of silicon carbide.

[0098] In some embodiments, the aqueous suspension contains one or more kinds of calcined alumina particles as a constituent. In some embodiments, the one or more kinds of calcined alumina particles contain aluminum oxide heated at a temperature exceeding 1000 °C to drive out chemically bound water.

[0099] Calcined alumina is alumina that has been heated at a temperature exceeding 1000 °C to remove chemically bound water, particularly aluminum oxide such as aluminum(III) oxide. This term is known to those skilled in the art. Calcined alumina particles are present to further enhance the mechanical wear of surfaces such as the chemically oxidized SiC surface.

[0100] In some embodiments, alpha-alumina particles are used. In some embodiments, the calcined alumina particles have a particle size that is larger than the particle sizes of the constituent particles including zirconia nanoparticles and alumina nanoparticles, for example, in the range of 0.5 μm to 5 μm. The particle size in this regard is the average particle size and is quantified by laser diffraction in accordance with ISO 13320:2020-01.

[0101] In some embodiments, one or more types of calcined alumina particles are present in an amount in the range of 0.1 to 5.0 wt%, 0.1 to 2.0 wt%, 0.1 to 1.0 wt% based on the total weight of the aqueous suspension in each case.

[0102] In some embodiments, if the amount of the calcined alumina particles is too large, the particles may aggregate and destabilize the slurry. In some embodiments, if the amount of the calcined alumina particles is too small, the suspension may not provide sufficient mechanical wear.

[0103] In some embodiments, the aqueous suspension contains one or more metal salts of chloric acid as a constituent. In some embodiments, one or more metal salts of chloric acid include NaClO3.

[0104] In some embodiments, one or more metal salts of chloric acid are selected from the group consisting of alkali metal salts of chloric acid and non-transition metal salts of chloric acid, for example, from the group consisting of lithium chlorate, sodium chlorate, potassium chlorate, aluminum chlorate and mixtures thereof, for example, from the group consisting of sodium chlorate, potassium chlorate, aluminum chlorate and mixtures thereof.

[0105] In some embodiments, one or more metal salts of chloric acid are present in an amount in the range of 0.1 to 2.0 wt%, 0.1 to 1.0 wt%, 0.2 to 1.0 wt%, 0.2 to 0.5 wt% based on the total weight of the aqueous suspension in each case.

[0106] In some embodiments, if the amount of one or more metal salts of chloric acid is too high, the material removal rate may decrease and the slurry may become unstable. In some embodiments, if the amount of one or more metal salts of chloric acid is too low, the suspension may not provide a sufficient material removal rate.

[0107] The aqueous suspension contains one or more metal salts of perchloric acid as a constituent. In some embodiments, the one or more metal salts of perchloric acid include Al(ClO4)3.

[0108] In some embodiments, the one or more metal salts of perchloric acid are selected from alkali metal salts of perchloric acid and non-transition metal salts of perchloric acid, for example, selected from the group consisting of lithium perchlorate, sodium perchlorate, potassium perchlorate, aluminum perchlorate, and mixtures thereof, for example, selected from the group consisting of sodium perchlorate, potassium perchlorate, aluminum perchlorate, and mixtures thereof.

[0109] In some embodiments, the one or more metal salts of perchloric acid are present in an amount in the range of 0.1 to 2.0 wt%, 0.1 to 1.0 wt%, 0.2 to 1.0 wt%, 0.2 to 0.5 wt% based on the total weight of the aqueous suspension in each case.

[0110] In some embodiments, if the amount of one or more metal salts of perchloric acid is too high, the material removal rate may decrease and the slurry may become unstable. In some embodiments, if the amount of one or more metal salts of perchloric acid is too low, the suspension may not provide a sufficient material removal rate.

[0111] The suspension according to the present disclosure is "aqueous". An aqueous suspension contains water, such as deionized water, as its main liquid carrier medium. In some embodiments, based on the total weight of the suspension, the amount of water is at least 60 wt%, at least 65 wt%, at least 70 wt%, at least 75 wt%, at least 80 wt%, at least 85 wt%, at least 90 wt%, at least 92, 93, or 94 wt%, and less than 97.5 wt%, less than 97 wt%, less than 96.5 wt%, or less than 95.5 wt%. Any of the above lower limits can be combined with any of the above upper limits, but the range of the amount of water contained in the suspension according to the present disclosure is from 60 to 97 wt%, from 80 to 97 wt%, from 65 to 96.5 wt%, from 85 to 96.5 wt%, from 70 to 96 wt% (e.g., from 75 to 95.5 wt% or from 80 to 95 wt%), or from 90 to 96 wt% (e.g., from 92 to 95.5 wt% or from 93 to 95 wt% or from 94 to 95 wt%). The water used in the suspension of the present disclosure can be deionized water.

[0112] In some embodiments, the aqueous suspension of the present disclosure has a pH value in the range of 2.0 to 5.0, in the range of 2.5 to 4.5, or in the range of 3.0 to 4.0, for example, in the range of 3.2 to 3.8 at 23°C. In some embodiments, the aqueous suspension of the present disclosure can have a pH value in the range of 3.0 to 5.5, in the range of 3.5 to 5.0, or in the range of 4.0 to 5.0 at 23°C. In some embodiments, the aqueous suspension of the present disclosure has a pH value of 2 to 5, 3 to 4, or 3.4 to 4 at 23°C.

[0113] The pH of the suspension according to the present disclosure can be achieved and / or maintained by any suitable means. More specifically, the suspension can further contain a pH adjuster, a pH buffer, or a combination thereof. The terms pH adjuster and pH buffer as used in this specification do not include essential components of the suspension of the present disclosure, although essential components may affect the pH value. Thus, the pH adjuster and the pH buffer are explicitly different from the other components of the suspension of the present disclosure described under other headings. Thus, the pH adjuster and the pH buffer are also particularly different from the salts of nitric acid described herein.

[0114] The pH adjuster can include (e.g., include, consist essentially of, or consist of) any suitable pH adjusting compound. In some embodiments, the nitrate described above is already functioning to adjust the pH value to the desired range. However, in some cases, it may be desirable to further adjust the pH value using another pH adjuster different from the nitrate of nitric acid. For example, the pH adjuster can be any suitable acid. In some embodiments, the pH adjuster is an inorganic acid. In some embodiments, the acid is nitric acid.

[0115] The pH buffer, if present at all, can be any suitable buffer including inorganic pH buffers such as phosphates, borates, etc. In some embodiments, there is no pH buffer in the suspension of the present disclosure.

[0116] The suspension according to the present disclosure can include any suitable amount of a pH adjuster and / or a pH buffer, provided that such amount is sufficient to achieve and / or maintain the desired pH value of the suspension, for example, within the ranges described herein.

[0117] The suspension of the present disclosure can further include optional components. In some embodiments, the suspension of the present disclosure does not include further components. Accordingly, the suspension of the present disclosure can include (e.g., consist essentially of, or consist of) one or more metal salts of permanganic acid, zirconia nanoparticles, alumina nanoparticles, one or more salts of nitric acid, water, and optionally one or more pH adjusters and / or pH buffers. Of course, unavoidable undesirable impurities present in the foregoing components may be present in a suspension including, consisting essentially of, or consisting of the foregoing components. Such impurities are not considered further optional components here but are considered unavoidable undesirable impurities and can be included in an amount less than 0.005 wt%, less than 0.002 wt%, or less than 0.001 wt% based on the weight of the suspension of the present disclosure.

[0118] In some embodiments, the suspension of the present disclosure may include further optional components (optional components). In some embodiments, the suspension of the present disclosure does not include further components. Thus, in some embodiments, the suspension of the present disclosure consists of (or consists essentially of) one or more metal salts of permanganic acid, one or more zirconia nanoparticles, one or more alumina nanoparticles, one or more salts of nitric acid, one or more calcined alumina particles, one or more metal salts of chloric acid, and one or more metal salts of perchloric acid, water, and optionally one or more pH adjusters and / or pH buffers.

[0119] In some embodiments, the suspension of the present disclosure may include at least one oxidizing agent, abrasive grains with a total amount of less than 0.2 wt%, aluminum nitrate, water, and optionally at least one pH adjuster and / or at least one pH buffer (e.g., including them, consisting essentially of them, or consisting of them). All the abrasive grains present in the suspension of the present disclosure have a Mohs hardness of less than 6. Of course, the undesirable inevitable impurities present in the aforementioned components may be present in the suspension including, consisting essentially of, or consisting of the aforementioned components. Such impurities are not considered here as further optional components but as inevitable undesirable impurities and may be included in an amount of less than 0.005 wt%, less than 0.002 wt%, or less than 0.001 wt% based on the weight of the suspension of the present disclosure.

[0120] However, it is also possible to consciously add further components to the aforementioned suspension. In some embodiments, such further components need to be inert, i.e., non-reactive with the reactive components of the suspension, such as one or more metal salts of permanganic acid in the suspension.

[0121] Accordingly, when additional components are included in the suspension of the present disclosure, in some embodiments, organic compounds such as organic surfactants, organic defoamers, or organic solvents are decomposed in the oxidation process by components such as at least one oxidizing agent, one or more metal salts of permanganic acid, one or more metal salts of chloric acid, and / or one or more metal salts of perchloric acid, and thus are excluded from the suspension of the present disclosure in some embodiments, so such components can be inorganic.

[0122] In some embodiments, when additional optional components are present, the additional components can be inorganic components, and their amounts can be from 0.005 to 1 wt%, from 0.005 to 1.5 wt%, from 0.005 to 1 wt%, or from 0.005 to 0.5 wt% based on the weight of the suspension of the present disclosure.

[0123] In some embodiments, a given component is not present in the aqueous suspension. For example, in some embodiments, MnO2, germanium particles, and / or ceria particles are not present in the aqueous suspension.

[0124] In some embodiments, the total of the components of the aqueous suspension (e.g., salts of permanganic acid, zirconia nanoparticles, alumina nanoparticles, and salts of nitric acid) constitutes at least 90 wt%, at least 95 wt%, or at least 98 wt% of all the components of the suspension of the present disclosure excluding water, pH adjusters, and pH buffers. In some embodiments, the only components of the suspension of the present disclosure are one or more salts of permanganic acid, zirconia nanoparticles, alumina nanoparticles, one or more salts of nitric acid, water, and pH adjusters and pH buffers, and thus the suspension consists of or consists essentially of these components.

[0125] In some embodiments, the total of the components of the aqueous suspension (e.g., one or more metal salts of permanganic acid, one or more zirconia nanoparticles, one or more alumina nanoparticles, one or more salts of nitric acid, one or more calcined alumina nanoparticles, one or more metal salts of chloric acid, and one or more metal salts of perchloric acid, the components including these) constitutes at least 90 wt%, at least 95 wt%, and at least 98 wt% of all the components of the suspension of the present disclosure excluding water, pH adjuster, and pH buffer. In some embodiments, the only components of the suspension of the present disclosure are one or more metal salts of permanganic acid, one or more zirconia nanoparticles, one or more alumina nanoparticles, one or more salts of nitric acid, one or more calcined alumina nanoparticles, one or more metal salts of chloric acid, and one or more metal salts of perchloric acid, water, and the components of the pH adjuster and pH buffer; thus, the suspension consists of these components.

[0126] In some embodiments, the total of the components of the aqueous suspension (e.g., at least one oxidizing agent; abrasive grains with a total amount of less than 0.2 wt% based on the total weight of the aqueous suspension and having a Mohs hardness of less than 6; and aluminum nitrate) constitutes at least 90 wt%, at least 95 wt%, or at least 98 wt% of all the components of the suspension of the present disclosure excluding water, pH adjuster, and pH buffer. In some embodiments, the only components of the suspension of the present disclosure are at least one oxidizing agent; abrasive grains with a total amount of less than 0.2 wt% based on the total weight of the aqueous suspension and having a Mohs hardness of less than 6; and aluminum nitrate, water, and the pH adjuster and pH buffer; thus, the suspension consists of these components.

[0127] In some embodiments, the aqueous suspension may include (e.g., include, consist essentially of, or consist of) 2.0 to 6.0 wt% of one or more metal salts of permanganic acid, 0.05 to 5.0 wt% of zirconia nanoparticles, 0.05 to 5.0 wt% of alumina nanoparticles, and 0.1 to 3.0 wt% of one or more salts of nitric acid, water, and an inorganic acid for adjusting the pH value, and the weight percentages are based on the total weight of the aqueous suspension.

[0128] In some embodiments, the aqueous suspension can include (e.g., include, consist essentially of, or consist of) one or more metal salts of permanganic acid at 2.6 to 5.5 wt%, zirconia nanoparticles at 0.1 to 2.0 wt%, alumina nanoparticles at 0.1 to 2.0 wt%, and one or more salts of nitric acid at 0.2 to 2.0 wt%, water, and an inorganic acid for adjusting the pH value, and the weight percentages are based on the total weight of the aqueous suspension.

[0129] In some embodiments, the aqueous suspension according to the present disclosure can include (e.g., include, consist essentially of, or consist of) one or more metal salts of permanganic acid at 3.0 to 5.0 wt%, zirconia nanoparticles at 0.15 to 1.0 wt%, alumina nanoparticles at 0.15 to 1.0 wt%, and one or more salts of nitric acid at 0.5 to 1.5 wt%, and the weight percentages are based on the total weight of the aqueous suspension.

[0130] In some embodiments, the aqueous suspension according to the present disclosure can include (e.g., include, consist essentially of, or consist of) one or more metal salts of permanganic acid at 4.0 to 5.0 wt%, zirconia nanoparticles at 0.15 to 0.5 wt%, alumina nanoparticles at 0.15 to 0.5 wt%, and one or more salts of nitric acid at 0.5 to 1.0 wt%, and the weight percentages are based on the total weight of the aqueous suspension.

[0131] In some embodiments, one or more metal salts of permanganic acid are, for example, potassium permanganate, and / or the inorganic acid for adjusting the pH value is nitric acid.

[0132] Furthermore, in some embodiments, the pH value of the suspension ranges from 3.0 to 4.0, for example, from 3.2 to 3.8.

[0133] In some embodiments, the aqueous suspension of the present disclosure, in each case, based on the total weight of the aqueous suspension, water, and optionally an inorganic acid such as nitric acid that adjusts the pH value to a range of 3.0 to 5.5, 3.5 to 5.0, or 4.0 to 5.0; one or more metal salts of permanganic acid in an amount ranging from 7.5 to 30 wt%, 10 to 25 wt%, 12 to 22 wt%, for example 13 to 20 wt%; one or more zirconia nanoparticles in an amount ranging from 0.05 to 5.0 wt%, 0.10 to 2.0 wt%, 0.15 to 1.0 wt%, for example 0.15 to 0.5 wt%; one or more alumina nanoparticles in an amount ranging from 0.05 to 5.0 wt%, 0.10 to 2.0 wt%, 0.15 to 1.0 wt%, for example 0.15 to 0.5 wt%; one or more calcined alumina particles in an amount ranging from 0.1 to 5.0 wt%, 0.1 to 2.0 wt%, for example 0.1 to 1.0 wt%; one or more metal salts of chloric acid in an amount ranging from 0.1 to 2.0 wt%, 0.1 to 1.0 wt%, 0.2 to 1.0 wt%, for example 0.2 to 0.5 wt%; one or more metal salts of perchloric acid in an amount ranging from 0.1 to 2.0 wt%, 0.1 to 1.0 wt%, 0.2 to 1.0 wt%, for example 0.2 to 0.5 wt%, contains, consists essentially of, or consists of them.

[0134] In some embodiments, the aqueous suspension can contain (e.g., contain, consist essentially of, or consist of) 1 to 8 wt% of at least one oxidizing agent, 0.001 to 0.18 wt% of alumina particles, 0.05 to 3 wt% of aluminum nitrate, water, and optionally an inorganic acid for adjusting the pH value, and the weight percentages are based on the total weight of the aqueous suspension, and the particles present in the suspension (e.g., total particles) have a Mohs hardness of less than 6.

[0135] In some embodiments, the aqueous suspension may contain (e.g., include, consist essentially of, or consist of) at least one oxidizing agent of 2 to 6% by weight, 0.01 to 0.15% by weight of alumina particles, and 0.1 to 2% by weight of aluminum nitrate, water, and optionally an inorganic acid for adjusting the pH value. The weight percentages are based on the total weight of the aqueous suspension, and the particles present in the suspension (e.g., all particles) have a Mohs hardness of less than 6.

[0136] In some embodiments, the aqueous suspension may contain (e.g., include, consist essentially of, or consist of) at least one oxidizing agent of 3 to 5.5% by weight, 0.08 to 0.12% by weight of alumina particles, and 0.2 to 1.5% by weight of aluminum nitrate. The weight percentages are based on the total weight of the aqueous suspension, and the particles present in the suspension (e.g., all particles) have a Mohs hardness of less than 6.

[0137] In some embodiments, the aqueous suspension may contain (e.g., include, consist essentially of, or consist of) at least one oxidizing agent of 4 to 5% by weight, 0.1% by weight of alumina particles, and 0.3 to 1.0% by weight of aluminum nitrate. The weight percentages are based on the total weight of the aqueous suspension, and the particles present in the suspension (e.g., all particles) have a Mohs hardness of less than 6.

[0138] In some embodiments, at least one oxidizing agent is a metal salt of permanganic acid, such as potassium permanganate, and / or the inorganic acid for adjusting the pH value is nitric acid, and / or the aluminum particles may have a Z-average particle size of 75 to 150 nm, and / or the alumina particles are γ-AlOOH particles, and / or the Mohs hardness of the particles present in the suspension (e.g., all particles) is 3 to 4.

[0139] Furthermore, in some embodiments, the pH value of the suspension ranges from 3 to 4, e.g., from 3.4 to 4.

[0140] In some embodiments, exemplary embodiments of the aqueous suspensions of the present disclosure exhibit excellent pH stability during the storage period, i.e., the pH drift is less than 0.1 over a period of at least 12 months, and exhibit a high material removal rate and excellent surface roughness of the polished substrate despite the small amount of abrasive grains. Further, since a small amount of abrasive grains can be stably suspended in an aqueous carrier without using a surfactant or a dispersant, the adverse effects of such surfactants or dispersants on the polishing process are avoided. When sedimented, the abrasive grains can be easily resuspended by shaking or stirring the suspension before use, thus preventing, reducing, or limiting the problem of clogging in the circulation line and ensuring a uniform suspension and material removal rate during polishing.

[0141] In some embodiments, the pot life of the aqueous suspension exceeds 7 days, exceeds 10 days, exceeds 12 days, or exceeds 14 days.

[0142] The aqueous suspensions of the present disclosure can be chemical mechanical polishing suspensions. In some embodiments, the aqueous suspensions of the present disclosure can be chemical mechanical polishing suspensions adapted for batch and / or single wafer chemical mechanical polishing processes. Surprisingly, the suspensions of the present disclosure provide a high material removal rate and excellent surface roughness of the polished substrate in both batch and single wafer CMP processes, despite the different process conditions used in these processes.

[0143] Suitable substrates to be polished include ceramic materials, metals, metal alloys, or diamond. In some embodiments, the substrate can be a Group III-V compound, such as gallium nitride, aluminum nitride, indium nitride, aluminum indium nitride, thallium nitride, gallium arsenide, indium gallium arsenide, gallium phosphide, indium antimonide, indium arsenide, boron arsenide, or aluminum arsenide. In some embodiments, the substrate can be a Group IV-IV compound, such as silicon germanium, silicon tin, diamond, graphene, germanium tin, or silicon carbide. In some embodiments, the aqueous suspension of the present disclosure is compatible with chemical mechanical polishing of a substrate comprising at least one layer of silicon carbide. The silicon carbide can be single crystal or polycrystalline. In some embodiments, the substrate comprises at least one layer of single crystal silicon carbide, such as single crystal 4H silicon carbide (i.e., 4H-SiC).

[0144] In some embodiments, the aqueous suspension of the present disclosure can be adapted to polish a substrate, such as silicon carbide, at a material removal rate of at least 1.5 μm / hr, at least 2 μm / hr, from 2.5 to 12 μm / hr, or from 2.5 to 9 μm / hr. Generally, higher material removal rates are achieved in a single-wafer CMP process compared to a batch CMP process because the polishing conditions described above vary in the batch CMP process. The material removal rate can be determined by the change in mass of the substrate before and after polishing using the following formula: TIFF2025097974000001.tif14170where Δm is the change in mass of the substrate before and after polishing, ρ substrate is the density of the substrate, r is the radius of the substrate, t is the polishing time.

[0145] The material removal rate is calculated by dividing the change in mass of the substrate before and after by the time required for polishing. The mass of the substrate can be measured using a desktop scale.

[0146] In some embodiments, the surface roughness after polishing a substrate such as a silicon carbide substrate using the aqueous suspension of the present disclosure is less than 0.6 nm, for example, ≤ 0.3 nm. The roughness can be calculated as the RMS roughness by AFM measurement method (5×5 scan, 1 Hz scan speed). This level of roughness is generally desirable and acceptable for downstream substrate processing involving surface epitaxy such as chemical vapor deposition (CVD). Although not wishing to be bound by this theory, the low surface roughness achieved using the aqueous suspension of the present disclosure is thought to be due to the use of aluminum nitrate which results in the formation of a mesh structure that embeds the abrasive grains. The embedding forms a "soft" layer on the particle surface, which prevents, reduces, or limits damage to the substrate surface during polishing without adversely affecting the high material removal rate.

[0147] The suspension according to the present disclosure can be supplied as a single-component system containing water, at least one oxidizing agent, abrasive grains less than 0.2 wt% based on the total weight of the suspension, aluminum nitrate, and optionally other of the aforementioned components. Such a single-component system is a suspension that can be used immediately. In some embodiments, the suspension of the present disclosure is provided in the form of a single-component system because such a suspension has high storage stability, that is, it shows no pH drift and no sedimentation of the abrasive grains and can be used immediately without the need for further mixing and / or dilution steps. The preparation of such a single-component system can be carried out as described in connection with the present disclosure for preparing an aqueous suspension.

[0148] Alternatively, some of the components such as at least one oxidizing agent can be supplied in a dry form or as an aqueous solution in a first container, and the abrasive grains and the remaining components such as aluminum nitrate can be supplied in a second container or a plurality of other containers. Other combinations of two or more containers of the components of the suspension according to the present disclosure are within the knowledge of those skilled in the art. Solid components such as abrasive grains can be placed in one or more containers in a dry state or as a colloidal solution. Further, it may be appropriate for the components in the first, second, or other containers to have different pH values, or to have substantially similar or equal pH values. The components of the suspension according to the present disclosure can be supplied partially or entirely separately from each other, and can be combined, for example, by the end user immediately before use (e.g., within one week before use, within one day before use, within one hour before use, within ten minutes before use, or within one minute before use).

[0149] The suspension according to the present disclosure can also be provided as a concentrate that can be diluted with an appropriate amount of water before use. In such an embodiment, the suspension concentrate contains water, at least one oxidizing agent, abrasive grains, aluminum nitrate, and optionally other components contemplated in the present disclosure, such that when the concentrate is diluted with an appropriate amount of water, each component will be present in the desired suspension in an amount within the appropriate range for each component, as described herein, for example. For example, each component can be present in the concentrate in an amount about 1.5 times, for example about 2 times or more, the concentration listed above for each component in the aqueous suspension. When the concentrate is diluted with an appropriate amount of water, each component will be present in the resulting aqueous suspension in an amount within the range described above for each component. Further, as will be understood by those skilled in the art, the concentrate can contain an appropriate proportion of water present in the final suspension to ensure that the other components of the suspension are at least partially or completely dissolved or suspended in the concentrate. The concentrate can be prepared as described herein in connection with the present disclosure for preparing an aqueous suspension by using a larger amount of each component.

[0150] However, the aqueous suspensions of the present disclosure have a high degree of storage stability under typical storage conditions because the use of aluminum nitrate prevents, reduces, or limits pH drift during storage, thus preventing, reducing, or limiting the formation of undesirable reaction products such as manganese dioxide that would result in a decreased material removal rate and an increased surface roughness. Even if slight precipitation of solid particles occurs after storage for several weeks or months, such precipitates can be easily redispersed by agitation such as stirring and / or shaking. Accordingly, in some embodiments, the aqueous suspensions of the present disclosure are provided as the one-component system described above.

[0151] It may be beneficial to lower the pH of the aqueous suspension from 2 to 2.5 (quantified at 23° C.) using nitric acid immediately before use to enhance the oxidizing power of at least one oxidizing agent and ensure a high material removal rate during polishing.

[0152] In some embodiments, the suspensions of the present disclosure can be provided as a one-package system that includes water, one or more salts of permanganic acid, alumina nanoparticles, zirconia nanoparticles, and one or more salts of nitric acid, and optionally other components described above. Such a one-pack system is a suspension that can be used immediately. In some embodiments, the suspensions of the present disclosure can be in the form of a one-pack system because such compositions are storage stable and can be used immediately without further mixing and / or dilution steps. Thus, in some embodiments, it may be appropriate to first dissolve one or more salts of permanganic acid and then supplement the solution with other components to obtain the one-pack system.

[0153] In some embodiments, alternatively or additionally, some of the components, such as one or more salts of permanganic acid, can be supplied in a dry form or in water in a first container, and the remaining components, such as alumina nanoparticles, zirconia nanoparticles, and one or more salts of nitric acid, can be supplied in a second container or a plurality of other containers. Combinations of two or more than two other containers of the components of the suspension are part of the present disclosure. Solid components such as alumina nanoparticles and zirconia nanoparticles can be placed in one or more containers in a dry state or as a colloidal solution. Further, it may be appropriate for the components in the first, second, or other containers to have different pH values, or to have substantially similar or equal pH values. The components of the suspension can be supplied partially or wholly separately from each other and can be combined, for example, by an end user immediately before use (e.g., within one week before use, within one day before use, within one hour before use, within ten minutes before use, or within one minute before use).

[0154] However, the ready-to-use suspension of the present disclosure already has a high storage stability under typical storage conditions. Even if slight precipitation of solid particles occurs after storage for several weeks or months, such precipitates can be easily redispersed by agitation such as stirring and / or shaking. Therefore, there is no need for the customer to mix the components immediately before use.

[0155] In some embodiments, the suspension of the present disclosure can also be provided as a concentrate intended to be diluted with an appropriate amount of water before use. The suspension concentrate, when diluted with an appropriate amount of water, can contain water and optionally other components in an amount such that each component is present in the desired suspension within the appropriate range of amounts described above for each component. For example, each component can be present in the concentrate in an amount that is about 1.5 times, such as about 2 times or more, greater than the concentration listed above for each component in the polishing composition. Thus, when the concentrate is diluted with an appropriate volume of water, each component will be present in the final suspension within the range of amounts described above for each component. Further, as will be understood by those skilled in the art, the concentrate can contain an appropriate proportion of water present in the final suspension to ensure that other components of the suspension are at least partially or completely dissolved or suspended in the concentrate.

[0156] In some embodiments, a method for preparing an aqueous suspension comprises: (i) adding aluminum nitrate to the aqueous suspension; and (ii) adding an aqueous solution of one or more metal salts of permanganic acid to the aqueous suspension, wherein the aqueous suspension contains alumina nanoparticles and zirconia particles in water. In some embodiments, before adding the aluminum nitrate, the method comprises filtering the aqueous suspension. In some embodiments, before adding the aqueous solution, the method comprises filtering the aqueous solution of one or more metal salts of permanganic acid. In some embodiments, no MnO2 is present in the aqueous suspension. In some embodiments, the aqueous suspension has a pH value in the range of 2 to 5 at 23°C. In some embodiments, step (i) of adding the aluminum nitrate and step (ii) of adding the aqueous solution are performed sequentially. The steps of the method of the present disclosure can be rearranged and the order of the steps can be changed. For example, the first step can be step (ii), and the aqueous solution can be added to the aqueous suspension first. This is not an exhaustive list of the order of the steps of the method. The steps can be rearranged in any order.

[0157] In some embodiments, a method for preparing an aqueous suspension comprises: (i) adding aluminum nitrate to the aqueous suspension; (ii) adding an aqueous solution of one or more metal salts of permanganic acid, one or more metal salts of perchloric acid, and one or more metal salts of chloric acid to the aqueous suspension; and (iii) adding one or more calcined alumina particles to the aqueous suspension, wherein the aqueous suspension contains alumina nanoparticles and zirconia particles. In some embodiments, prior to adding the aluminum nitrate, the method comprises filtering the aqueous suspension. In some embodiments, prior to adding the aqueous solution, the method comprises filtering the aqueous solution. In some embodiments, no MnO2 is present in the aqueous suspension. In some embodiments, the aqueous suspension has a pH value in the range of 2 to 5 at 23 °C. In some embodiments, step (i) of adding the aluminum nitrate, step (ii) of adding the aqueous solution, and step (iii) of adding one or more calcined alumina particles are performed sequentially. The steps of the method of the present disclosure can be rearranged and the order of the steps can be changed. For example, the first step may be step (ii), in which case the aqueous solution is first added to the aqueous suspension, followed by step (iii) and then step (i). In some examples, step (ii) may follow step (iii) first, and then step (i). This is not an exhaustive list of the order of the steps of the method. The steps can be rearranged in any order (e.g., step (iii), step (i), then step (ii)).

[0158] In some embodiments, the present disclosure includes a method for preparing an aqueous suspension, comprising: (i) adding aluminum nitrate to an aqueous suspension; and (ii) adding an aqueous solution of at least one oxidizing agent to the resulting aqueous suspension. In some embodiments, the aqueous suspension contains abrasive grains. In some embodiments, the abrasive grains have a Mohs hardness of less than 6. In some embodiments, the aqueous suspension contains less than 0.2 wt% abrasive grains based on the total weight of the aqueous suspension. In some embodiments, prior to adding aluminum nitrate, the method includes filtering the aqueous suspension. In some embodiments, prior to adding the aqueous solution, the method includes filtering the aqueous solution. In some embodiments, MnO2 is not present in the aqueous suspension. In some embodiments, the aqueous suspension has a pH value in the range of 2 to 5 at 23 °C. In some embodiments, step (i) of adding aluminum nitrate and step (ii) of adding the aqueous solution are performed sequentially. The steps of the method of the present disclosure can be rearranged and the order of the steps can be changed. For example, the first step may be step (ii), in which case the aqueous solution is first added to the aqueous suspension, followed by step (i). This is not an exhaustive list of the order of the steps of the method. The steps can be rearranged in any order.

[0159] A further object of the present disclosure is a method for preparing an aqueous suspension (AS) having a pH value in the range of 2 to 5 at 23 °C, comprising: (A) providing an aqueous suspension (ASP) of abrasive grains, wherein all the abrasive grains present in the aqueous suspension (ASP) have a Mohs hardness of less than 6; (B) adding aluminum nitrate to the aqueous suspension (ASP) provided in step (A); (C) adding an aqueous solution of at least one oxidizing agent to the aqueous suspension obtained after step (B); and (D) optionally, adjusting the pH of the aqueous suspension (AS) obtained after step (C) with at least one pH adjuster. The method comprises.

[0160] In some embodiments, the aqueous suspension (AS) obtained from the present disclosure contains less than 0.2 wt% abrasive grains based on the total weight of the aqueous suspension. Accordingly, the amount of abrasive grains present in the aqueous suspension provided in step (A) is selected such that the aqueous suspension obtained from the method of the present disclosure contains less than 0.2 wt% abrasive grains. This can be achieved by considering the amount of water present in the aqueous oxidizing agent solution used in step (C), or by diluting the aqueous suspension obtained from step (C) or (D) with water as described herein.

[0161] Step (A):

[0162] In step (A) of the present disclosure, an aqueous suspension of abrasive grains is provided. This can include preparing an aqueous suspension by mixing a dry powder of abrasive grains with an appropriate amount of water, diluting a commercially available aqueous suspension of abrasive grains with an appropriate amount of water, or using a commercially available suspension of abrasive grains. The suspension can be filtered prior to step (B) to avoid the presence of larger aggregates, as these aggregates can scratch the substrate during polishing, thus increasing the surface roughness and therefore degrading the quality of the polished product. In some embodiments, step (A) includes providing an aqueous suspension of colloidal alumina nanoparticles (i.e., alumina particles having a Z-average particle size of 1 to 1000 nm) by mixing dry alumina powder with water and filtering the resulting suspension. Suitable abrasive grains that can be used in step (A) of the method of the present disclosure include the abrasive grains described herein in connection with the aqueous suspensions of the present disclosure.

[0163] The aqueous suspension provided in step (A) can contain abrasive grains in an amount of 0.1 to 3 wt%, such as 0.2 to 1 wt%, in total based on the total amount of the aqueous suspension obtained in step (A) in any case.

[0164] Step (B):

[0165] In step (B) of the present disclosure, aluminum nitrate is added to the aqueous suspension of abrasive grains provided in step (A). The addition of aluminum nitrate increases the viscosity of the aqueous suspension provided in step (A), which indicates the formation of a network structure that embeds the abrasive grains.

[0166] The amount of aluminum nitrate added in step (B) can be 0.5 to 5 wt%, for example 1 to 3 wt%, in each case based on the total amount of the aqueous suspension (ASP). These amounts ensure that a sufficient amount of network structure is formed so that the abrasive grains are completely covered with the soft layer and stably suspended in the aqueous carrier. Furthermore, these amounts ensure that the pH drift during storage of the aqueous suspension prepared by the method of the present disclosure, and thus the formation of undesirable reaction products such as manganese dioxide, is prevented, reduced, or limited because the reaction products reduce the material removal rate and increase the surface roughness.

[0167] Step (C):

[0168] In step (C) of the method of the present disclosure, an aqueous solution of at least one oxidizing agent is added to the mixture obtained after step (B). This solution can be prepared by adding an appropriate amount of an oxidizing agent, for example a water-soluble oxidizing agent, to an appropriate amount of water, or by diluting a concentrated aqueous solution of the oxidizing agent with water to obtain the desired concentration of the oxidizing agent in the aqueous solution. In some embodiments, the resulting aqueous solution of the oxidizing agent may be filtered before being added to the mixture obtained in step (B) to avoid the presence of undissolved oxidizing agent particles, since these particles can scratch the substrate during polishing, thus increasing the surface roughness and therefore degrading the quality of the polished product. Suitable oxidizing agents have been described above in connection with the aqueous suspensions of the present disclosure. In some embodiments, an aqueous solution of potassium permanganate is used in step (C).

[0169] The aqueous solution added in step (C) can contain at least one oxidizing agent in an amount of 1 to 10 wt%, for example 3 to 6 wt%, in each case based on the total amount of the aqueous solution added in step (C).

[0170] Optional step (D):

[0171] In the optional step (D), the pH of the aqueous suspension obtained from step (C) is adjusted using at least one pH adjuster. In some embodiments, the use of an appropriate amount of aluminum nitrate results in an aqueous suspension having the desired pH after step (C), and the optional step (D) is not required and not used.

[0172] Further step (E):

[0173] The method of the present disclosure may include at least one further step (E). In a first alternative of this step, the aqueous suspension obtained after step (C) is diluted with water before performing step (D). In a second alternative of this step, the aqueous suspension obtained after step (D) is diluted with water. In some embodiments, the further step (E) may be beneficial to ensure that the total amount of abrasive grains in the aqueous suspension produced by the method of the present disclosure is less than 0.2% by weight based on the total weight of the resulting aqueous suspension.

[0174] What has been said about the aqueous suspension of the present disclosure, particularly the components of the aqueous suspension, is mutatis mutandis applicable to further embodiments of the method for preparing the aqueous suspension.

[0175] The suspension of the present disclosure is useful as a polishing composition suitable for polishing a silicon carbide surface, for example, in a chemical mechanical planarization process.

[0176] In some embodiments, the method of the present disclosure includes the steps of storing an aqueous suspension (e.g., the aqueous suspension of the present disclosure) having a pH in the range of 3 to 5; reducing the pH of the aqueous suspension to a range of 2 to 2.5; and using the aqueous suspension having a pH in the range of 2 to 2.5 within 14 days. In some embodiments, storing the aqueous suspension includes storing the aqueous suspension for at least one year.

[0177] In some embodiments, lowering the pH of the first aqueous suspension includes adding an acid. The acid can include nitric acid. In some embodiments, lowering the pH of the initial aqueous suspension to a range of 2 to 2.5 includes lowering the pH of the initial aqueous suspension to 2.3. In some embodiments, using the lowered aqueous suspension includes using the lowered aqueous suspension in a single-wafer chemical mechanical planarization method and / or a batch chemical mechanical planarization method.

[0178] The present disclosure further provides a method for chemically mechanically planarizing a substrate (i.e., a CMP method) that includes contacting a substrate, such as a silicon carbide surface, e.g., a silicon carbide wafer surface, with an aqueous suspension according to the present disclosure; moving the aqueous suspension relative to the substrate using a polishing pad; and abrading at least a portion of the substrate to polish and / or planarize the substrate. In some embodiments, during abrasion, the substrate does not exceed a temperature of 60°C, 59°C, 58°C, 57°C, 56°C, 55°C, 54, 53°C, 52°C, 51°C, 50°C, or any value in between (e.g., 56.3°C).

[0179] The CMP method according to the present disclosure can be used in combination with a chemical mechanical polishing (CMP) apparatus / tool / equipment. Any of the well-known CMP apparatuses in the industry, including apparatuses from suppliers such as Applied Materials, Revasum, Axus, Lapmaster Wolters, and Ibarra, can be used in the CMP method of the present disclosure.

[0180] The apparatus can include a platen that operates during use and has a speed resulting from orbital, linear, or circular motion, a polishing pad that contacts the platen and moves with the platen during operation, and a carrier that contacts the surface of the polishing pad and holds the substrate that is polished by moving relative to the surface of the polishing pad. Polishing of the substrate is performed by disposing the substrate in contact with the polishing pad and the suspension of the present disclosure (generally disposed between the substrate and the polishing pad), moving the polishing pad relative to the substrate, and abrading at least a portion of the substrate to polish and / or planarize the substrate.

[0181] In some embodiments, the substrate is a silicon carbide substrate. In some embodiments, the polishing endpoint is determined by monitoring the weight of the silicon carbide substrate, and the weight is used to calculate the amount of silicon carbide removed from the substrate. Such techniques are well known in the art. For example, the polishing endpoint is determined by monitoring the weight of the substrate, as described above in connection with quantifying the material removal rate. Polishing refers to removing at least a portion of the surface to polish the surface. Polishing can be performed to provide a surface with reduced surface roughness by removing gouges, craters, pits, etc., but polishing can also be performed to introduce or restore a surface shape characterized by the intersection of planar segments. The method of the present disclosure can be used to polish and / or planarize any suitable substrate, such as a substrate including at least one layer of silicon carbide.

[0182] In some embodiments, prior to contacting the substrate with the aqueous suspension, the method includes reducing the pH of the aqueous suspension to a range from 2 to 2.5. The reducing step can include adding an acid. The pot life of the aqueous suspension is the useful life of the aqueous suspension after reducing the aqueous suspension to a pH range of, for example, 2 to 2.5. The shelf life of the aqueous suspension can exceed one year, as described herein.

[0183] In some embodiments, after storing the aqueous suspension for up to and beyond one year, the aqueous suspension is reduced (e.g., an acid is added to the aqueous suspension) immediately prior to use. After the aqueous suspension is reduced, the aqueous suspension has a service life, after which the aqueous suspension may no longer be usable for its intended purpose. The available time of the aqueous suspension is referred to as the pot life. In some embodiments, the pot life can be at least 5, 7, 10, 12, or 14 days. To ensure that the aqueous suspension is used during its pot life, in some embodiments, the method of the present disclosure includes contacting the substrate with the reduced aqueous suspension within a set time frame of the reduction step. For example, the method includes contacting the substrate with the reduced aqueous suspension within 5, 7, 10, 12, or 14 days of the reduction step. Thereby, during its pot life, the reduced aqueous suspension is ensured to contact the substrate.

[0184] The suspension combined with the polishing pad is an essential component of the chemical mechanical planarization method described in the claims of the present disclosure. In some embodiments, the type and material of the polishing pad used in the CMP method of the present disclosure are not important for the present disclosure. In fact, any conventionally used polishing pad for the CMP method for planarizing a silicon carbide wafer can be used. Suitable polishing pads include, for example, woven and non-woven polishing pads. Further, a suitable polishing pad may include any suitable polymer of various densities, hardnesses, thicknesses, compressibilities, abilities to rebound upon compression, and compression elastic moduli. Suitable polymers include, for example, polyvinyl chloride, polyvinyl fluoride, nylon, fluorocarbon, polycarbonate, polyester, polyacrylate, polyether, polyethylene, polyamide, polyurethane, polystyrene, polypropylene, their compatible products, and mixtures thereof. In some embodiments, a polyurethane pad can be used. Conventional pads can be manufactured one at a time or as a cake that is later sliced onto individual pad substrates. These substrates are then machined to the final thickness, and grooves are further machined thereon. The polymer or polymer / fiber circular pad can be 1 mm to 4 mm thick. The polishing pad can have any suitable structure. For example, the polishing pad may be circular and, during use, will rotate about an axis perpendicular to the plane defined by the surface of the pad. The polishing pad can be cylindrical, with its surface functioning as a polishing surface and capable of rotating about the central axis of the cylinder during use. The polishing pad can be in the form of an endless belt that can move linearly with respect to the cutting edge being polished during use. The polishing pad can have any suitable shape and, during use, will perform a reciprocating or orbital motion along a plane or a semi-circle. Many other variations will be immediately apparent to those skilled in the art.

[0185] Conventional polymeric CMP polishing pads are typically adhered to a flat rotating circular table within a CMP apparatus using a pressure-sensitive adhesive.

[0186] Substrates polished using the CMP method of the present disclosure can be any suitable substrate, such as a substrate including at least one layer of silicon carbide. Suitable substrates include, but are not limited to, flat panel displays, integrated circuits, memories or rigid disks, metals, interlayer dielectric (ILD) devices, semiconductors, microelectromechanical systems, ferroelectrics, and magnetic heads. Silicon carbide can include, consist essentially of, or consist of any suitable silicon carbide, many of which are known in the art. For example, the substrate can be a silicon carbide substrate. The silicon carbide can be single crystal or polycrystalline. As already explained above, silicon carbide has many different types of crystal structures, each with its own set of electronic properties. However, only a few of these polytypes can be reproduced in a form that can be used as a semiconductor. Such polytypes can be either cubic (e.g., 3C silicon carbide) or non-cubic (e.g., 4H silicon carbide, 6H silicon carbide). The properties of these polytypes are well known in the art. In some embodiments, the substrate used in the CMP method of the present disclosure is 4H silicon carbide (i.e., 4H-SiC).

[0187] The effective polishing temperature for polishing SiC wafers using the CMP method of the present disclosure, i.e., the temperature measured on the polishing pad during polishing and typically recorded with an IR thermometer, is several degrees Celsius lower than the temperature observed for similar structures using commercially available slurries.

[0188] The lower temperatures of the suspensions of the present disclosure and suspensions prepared according to the methods of the present disclosure provide advantages in that the CMP process can be a) run at a lower temperature, thus resulting in a gentler process where surface defects are less likely to occur, thus resulting in a higher process yield, or b) run at a higher material removal rate by increasing the pressure on the polishing pad and / or increasing the CMP rate to levels higher than those allowed for conventional suspensions. Depending on the specific objectives to be achieved, such as yield versus throughput, the advantages associated with these temperatures are very valuable.

[0189] However, the upper limit of the polishing temperature is restricted by the material of the polishing pad which desirably has little or no degradation during the CMP process. Typically, the polishing temperature does not exceed 60°C.

[0190] The flow rate at which the suspension of the present disclosure is dispensed onto the CMP apparatus depends on the particular apparatus and pad structure used. However, the suspension of the present disclosure functions well at industry-standard flow rates.

[0191] In the CMP method of the present disclosure using the suspension of the present disclosure, silicon carbide can be removed at a material removal rate of about 3 to 15 μm / hr, typically 5 to 12 μm / hr or 6 to 10 μm / hr, without damaging the surface, thus resulting in a silicon carbide surface without scratches, that is, a surface measured using confocal optical microscopy technology involving automated scratch detection and characterization measurement and shown to typically have no CMP-related scratches present for other slurries, pads, tools, etc.

[0192] In a typical CMP process, the scratch length per wafer may be expected to be less than 20 mm, but this greatly depends on the customer's process, tool, pad, wafer quality, etc. However, the suspension of the present disclosure used in the CMP method of the present disclosure brings about significant improvement with respect to the occurrence and length of scratches, and even if scratches occur, they are typically significantly lower than the above values.

[0193] The suspension of the present disclosure results in a SiC wafer surface having a surface roughness of less than 1 angstrom. The roughness is calculated as the RMS roughness by AFM measurement method (5×5 scan, 1 Hz scan speed). This level of roughness is generally desirable and acceptable for downstream silicon carbide processing including surface epitaxy, for example chemical vapor deposition (CVD).

[0194] Finally, the suspension enables a very low CMP polishing temperature. The polishing temperature is routinely lower than the temperature used with prior art slurries. The lower temperature of the suspensions of the present disclosure results in a milder process in which the CMP process can be run at a) a lower temperature, thus lessening the occurrence of surface defects and thus resulting in a higher process yield, or b) can be run at a higher material removal rate by increasing the pressure on the polishing pad and / or increasing the CMP rate to levels higher than those allowed for conventional suspensions. Depending on the particular objective to be achieved, e.g., yield vs. throughput, etc., the advantages associated with these temperatures are valuable.

[0195] What has been said about the aqueous suspensions of the present disclosure, particularly the components of the aqueous suspensions and the method of preparing the aqueous suspensions, is applicable mutatis mutandis to further embodiments of the method of chemically mechanically planarizing a substrate.

Examples

[0196] The following examples further illustrate the present disclosure but, of course, should in no way be construed as limiting its scope.

[0197] Example 1 (Comparative Example)

[0198] This example demonstrates the effect of alumina nanoparticle concentration on single crystal SiC polishing temperature and material removal rate. The polishing temperature and removal rate were quantified for each aqueous suspension containing 4 wt% KMnO4 and 0.5 wt% nitrate at pH 2.3, and the results are shown in Table 1. TIFF2025097974000002.tif68170

[0199] An increase in abrasive concentration shows a decrease in temperature and simultaneously also decreases the silicon carbide removal rate.

[0200] Example 2 (Comparative Example)

[0201] This example shows the concentration effect of zirconia nanoparticles on the single-crystal SiC polishing temperature and material removal rate. The polishing temperature and removal rate were quantified for each aqueous suspension containing 4 wt% KMnO4 and 0.5 wt% nitrate at pH 2.3, and the results are shown in Table 2. TIFF2025097974000003.tif71170

[0202] The temperature and removal rate of zirconia nanoparticles showed a similar trend to that of alumina nanoparticles. However, due to the presence of zirconia particles, the SiC removal rate was improved by up to approximately 20% compared to alumina nanoparticles of the same concentration.

[0203] Example 3 (Comparative Example)

[0204] This example shows the effect of the combination of alumina and zirconia nanoparticles on the single-crystal SiC polishing temperature and material removal rate. The polishing temperature and removal rate were quantified for each aqueous suspension containing 4.5 wt% KMnO4 and 0.75 wt% nitrate at pH 2.3, and each composition and result are shown in Table 3. TIFF2025097974000004.tif70170

[0205] Due to the synergistic effect of alumina and zirconia nanoparticles, a significant increase in the removal rate of approximately 11 μ / hr was shown. At the same time, a significant decrease in temperature was observed.

[0206] Atomic force microscope (AFM) data of the measurement data of the surface roughness (R a ) of a single-crystal SiC (Si plane) using a mixed particle (alumina + zirconia) sample are shown in Table 4. TIFF2025097974000005.tif65170

[0207] The mixed particles result in a surface roughness of sub-Å on a high-quality SiC substrate.

[0208] Example 4 (Example of the Present Disclosure)

[0209] This example shows the effect of the combination of alumina and zirconia nanoparticles and calcined alumina (these components are collectively referred to as abrasive grains in Table 5) and additional components (chlorates, perchlorates, collectively referred to as additives in Table 5) on the polishing temperature and material removal rate of single-crystalline SiC (Si face). The polishing temperature and removal rate were quantified for each aqueous suspension containing 15 wt% permanganate (KMnO4, NaMnO4) and 0.75 wt% nitrate at pH 2.3, and the compositions and results are shown in Table 5. TIFF2025097974000006.tif62170

[0210] The data given in Table 5 clearly shows the importance of balancing chemical activity and mechanical wear to achieve a high material removal rate along with an acceptable process temperature. A high abrasive grain concentration (6% abrasive grains) with zero percent additives reduces the removal rate as the process temperature decreases. The synergistic effect of the abrasive grains and additives showed a significant increase in the removal rate of up to approximately 14 μ / hr at an acceptable process temperature.

[0211] Atomic force microscope (AFM) data for the measurement of the surface roughness (R a ) of single-crystalline SiC (Si face) wafers polished using the concentrations given above (Table 5) are shown in Table 6. TIFF2025097974000007.tif47170

[0212] From the data shown in Table 6, it is clear that this slurry results in a scratch-free sub-Å level surface roughness (R a ) that enhances the throughput of SiC wafers. The combination of a high concentration of chemically active ions and a high concentration of particles results in an improvement in the material removal rate of single-crystalline SiC (Si face) with excellent surface finish at an acceptable process temperature. Therefore, due to all these performance advantages, these slurries can be used in all SiC process applications (i.e., batch processes, single-wafer processes).

[0213] The present disclosure will be described in more detail below using the following examples, but the present disclosure is in no way limited to these examples. Further, "parts", "%", and "ratio" in the examples mean "parts by mass", "% by mass", and "mass ratio", respectively, unless otherwise specified.

[0214] 1. Quantification method:

[0215] 1.1 Material removal rate

[0216] The material removal rate (MRR) is based on the change in the mass of the substrate before and after polishing according to the formula described above. The change in the mass of the substrate before and after polishing is divided by the time required for polishing to calculate the material removal rate. The mass of the substrate is measured using a tabletop scale. The material removal rate is quantified for each wafer polished in a single batch polishing process and averaged for three consecutive batch polishing processes.

[0217] 1.2 Surface roughness

[0218] The surface roughness is calculated as the RMS roughness by the AFM measurement method (5×5 scan, 1 Hz scan speed) by measuring the surface roughness of each SiC substrate at three positions. When the surface roughness is repeated at these three positions, each value is given as the surface roughness.

[0219] 1.3 Storage stability

[0220] The storage stability of the prepared suspension was determined by measuring the pH at 23°C for 12 months and also by visually evaluating the suspension at the end of the storage period.

[0221] 2. Preparation of examples of the present disclosure and comparative aqueous suspensions

[0222] The aqueous suspensions of the examples of the present disclosure and the comparative aqueous suspensions were prepared using one of the following methods:

[0223] Method A (example of the present disclosure):

[0224] Process A1: An aqueous suspension containing alumina particles and aluminum nitrate was prepared by mixing an aqueous slurry of alumina particles (alumina particles having a Mohs hardness of 3 to 4 dispersed in water, and the resulting dispersion was filtered) and aluminum nitrate.

[0225] Process A2: An aqueous solution of potassium permanganate was prepared by dissolving potassium permanganate in water.

[0226] Process A3: The aqueous solution of potassium permanganate prepared in Process A2 was added to the aqueous suspension prepared in Process A1.

[0227] The amounts of alumina particles, aluminum nitrate, potassium permanganate, and water used in Processes A1 and A2 are selected so as to be the amounts shown in Table 7 after the completion of Process A3.

[0228] Comparative Method B (Comparative Example):

[0229] Process B1: An aqueous solution of potassium permanganate was prepared by dissolving potassium permanganate in water.

[0230] Process B2: An aqueous slurry of alumina particles and aluminum nitrate was added to the aqueous solution prepared in Process B1.

[0231] The amounts of alumina particles, aluminum nitrate, potassium permanganate, and water used in Processes B1 and B2 are selected so as to be the amounts given in Table 7 after the completion of Process B2.

[0232] Table 7 shows the final compositions of all the prepared examples and comparative aqueous suspensions of the present disclosure. TIFF2025097974000008.tif130170

[0233] 3. CMP Process

[0234] The polishing characteristics of the aqueous suspension S-I1 of the present invention and the comparative aqueous suspensions S-C1 to S-C9 were each tested and compared by polishing 16 silicon carbide substrates in a batch CMP process using a batch CMP tool and in a single-wafer CMP process using a commercially available single-wafer CMP tool. The silicon carbide substrates were each 4H-type circular wafers with a diameter of 150 nm. Before polishing, the pH of each composition was lowered to 2.1 with nitric acid.

[0235] 4. Results

[0236] 4.1 Storage stability

[0237] The storage stability was determined as described in the storage stability section above (section 1.3), and the results obtained are listed in Table 8. TIFF2025097974000009.tif108170

[0238] The results shown in Table 8 demonstrate that aqueous suspensions prepared according to the method of the present disclosure and containing aluminum nitrate and less than 5 wt% alumina particles (S-I1, S-C1 to S-C3) show no pH drift or color change even after 12 months of storage, thus enabling a constant polishing quality regardless of the storage period. In contrast, the aqueous suspension S-C4 prepared according to the method of the present disclosure and containing aluminum nitrate and 5 wt% alumina particles has no storage stability because it sediments during storage. An aqueous suspension S-C5 containing the same amounts of aluminum nitrate, alumina particles, and potassium permanganate as the aqueous suspension SS-I1 of the present disclosure but not prepared according to the method of the present disclosure is also not stable during storage. When the aqueous suspensions S-C6 to S-C9 containing nitrates other than aluminum nitrate are stored, undesirable manganese dioxide is generated due to pH drift to higher pH values. However, the presence of manganese dioxide results in an increase in the surface roughness of the stored suspension and a decrease in the material removal rate (see Tables 9 and 11 below), which is thus undesirable.

[0239] 4.2 Silicon carbide removal rate

[0240] Quantify the silicon carbide removal rate as described in Section 1.1 above, and list the obtained results in Tables 9 and 10. TIFF2025097974000010.tif80170TIFF2025097974000011.tif33170

[0241] Batch CMP process:

[0242] The comparative aqueous slurry S-C5 containing 0.1 wt% alumina particles and aluminum nitrate but not prepared according to the process of the present disclosure has the same composition but a lower material removal rate in the batch CMP process than the aqueous slurry S-I1 of the present invention prepared according to the process of the present disclosure. Further, the comparative aqueous suspensions S-C6 and S-C7 containing ferric nitrate or cerium nitrate result in a lower material removal rate than the aqueous slurry S-I1 of the present disclosure containing aluminum nitrate. The material removal rates of the comparative aqueous suspensions S-C5, S-C8, and S-C9 could not be quantified due to their low stability after preparation (see Table 8 above). The comparative aqueous suspensions S-C1 to S-C3 containing a larger amount of alumina particles than the aqueous suspension S-I1 of the present invention result in a higher material removal rate. However, the increase in the material removal rate is accompanied by an undesirable significant increase in the surface roughness of the polished product (see Table 11 below). In conclusion, only the aqueous suspension S-I1 of the present disclosure shows a good balance between the material removal rate and the surface roughness, while a larger amount of alumina particles results in an unacceptable surface roughness, and the use of other nitrates results in a decrease in the material removal rate and an unacceptable surface roughness.

[0243] Single-wafer CMP process:

[0244] The aqueous suspension S-I1 of the present disclosure enables achieving a high material removal rate and excellent surface roughness even at a high down pressure (see Table 12 below), resulting in an efficient and fast polishing process that provides a high yield (i.e., a substrate with high surface quality).

[0245] 4.3 Surface roughness

[0246] Quantify the surface roughness as described in Section 1.2 above and list the resulting values in Tables 11 and 12. TIFF2025097974000012.tif76170TIFF2025097974000013.tif33170

[0247] Batch CMP process:

[0248] The aqueous suspension S-I1 of the present disclosure provides excellent surface roughness of 3 angstroms or less. However, when a larger amount of alumina particles is used (see Comparative suspensions S-C1 to S-C3), significantly higher surface roughness occurs, thus degrading the quality of the polished SiC substrate. When using Comparative aqueous suspensions S-C6 and S-C7 containing ferric nitrate and cerium nitrate, large scratches occur on the substrate surface, resulting in a polished product with unacceptable quality. The surface roughness of the aqueous suspensions S-C5, S-C8, and S-C9 of the comparative examples could not be quantified due to their low stability after preparation (see Table 12 above).

[0249] Single wafer CMP process:

[0250] The aqueous suspension S-I1 of the present disclosure enables achieving excellent surface roughness even at high down pressures, thus enabling a high-speed polishing process that provides excellent yield.

[0251] 5. Discussion of results

[0252] The aqueous suspension S-I1 of the present disclosure containing less than 0.2 wt% alumina particles and aluminum nitrate provides a high material removal rate and excellent surface roughness in batch and single-wafer CMP processes. Further, these suspensions have excellent storage stability for more than 12 months, thus guaranteeing a constant material removal rate and surface quality during their storage period in the polishing process. Without being bound by this particular theory, the presence of aluminum nitrate is thought to prevent or mitigate the pH change occurring during storage by dissolution of the alumina particles in an acidic medium and further form a "soft" layer on the alumina particles, whereby a polished product with a high surface quality (i.e., low surface roughness) can be obtained. Surprisingly, the high material removal rate is achieved only when an aqueous solution of an oxidizing agent is added to the aqueous suspension containing alumina particles and aluminum nitrate, and when the aqueous suspension of alumina particles and aluminum nitrate is added to an aqueous solution of potassium nitrate, a decrease in the material removal rate occurs (see comparative suspension S-C5).

[0253] In contrast, aqueous suspensions (comparative suspensions S-C6 to S-C9) containing less than 0.2 wt% alumina particles and other nitrates other than aluminum nitrate show significantly reduced storage stability due to the pH drift occurring during storage. This pH drift forms manganese dioxide, which reduces the material removal rate and significantly increases the surface roughness of the polished substrate.

[0254] Suspensions (comparative suspensions S-C1 to S-C3) containing 0.2 wt% to 1 wt% alumina particles and aluminum nitrate show high storage stability and result in an increase in the material removal rate in the batch CMP process compared to the suspensions of the present disclosure. However, the increase in the material removal rate is accompanied by an unacceptable increase in the surface roughness of the polished substrate, thus dramatically reducing the yield of the polishing process. Further increasing the amount of alumina particles to 5 wt% resulted in an unstable suspension without the required storage stability.

[0255] In conclusion, the aqueous suspensions of the present disclosure, which contain less than 0.2 wt% alumina particles and aluminum nitrate and are prepared by the process of the present disclosure, enable achieving a high material removal rate and excellent surface roughness (i.e., high yield) of substrates polished in batch and single-wafer CMP processes. The high material removal rate enables shortening the polishing time, thus making the polishing process more efficient. Further, the aqueous suspensions of the present disclosure have excellent storage stability and thus guarantee a consistent quality in the CMP process during their storage period.

[0256] [Aspect]

[0257] Various aspects are described below. It should be understood that any one or more of the features described in the following aspects can be combined with any one or more of the other aspects.

[0258] Aspect 1. An aqueous suspension comprising (a) one or more metal salts of permanganic acid; (b) zirconia nanoparticles; (c) alumina nanoparticles; and (d) one or more salts of nitric acid.

[0259] Aspect 2. The aqueous suspension of Aspect 1, further comprising at least one pH adjuster and / or at least one pH buffer.

[0260] Aspect 3. The aqueous suspension of Aspect 1 or 2, wherein the aqueous suspension has a pH value in the range of 2 to 5.

[0261] Aspect 4. The aqueous suspension of Aspect 3, wherein the pH value is measured at a temperature in the range of 20°C to 30°C.

[0262] Aspect 5. The aqueous suspension of Aspect 3, wherein the pH value is measured at a temperature of 23°C.

[0263] Aspect 6. The aqueous suspension of any of the preceding aspects, wherein the one or more metal salts of permanganic acid are selected from the group consisting of LiMnO4, KMnO4, NaMnO4, and mixtures thereof.

[0264] Aspect 7. An aqueous suspension according to any of the previous aspects, wherein the zirconia nanoparticles contain ZrO2.

[0265] Aspect 8. An aqueous suspension according to any of the previous aspects, wherein the alumina nanoparticles contain colloidal alumina particles.

[0266] Aspect 9. The aqueous suspension of Aspect 8, wherein the colloidal alumina particles contain γ -AlOOH particles and / or γ -Al2O3 particles.

[0267] Aspect 10. An aqueous suspension according to any of the previous aspects, wherein one or more salts of nitric acid contain Al(NO3)3.

[0268] Aspect 11. An aqueous suspension according to any of the previous aspects, wherein MnO2 is not present in the aqueous suspension.

[0269] Aspect 12. A method for chemically - mechanically planarizing a substrate, comprising: (i) a step of bringing the substrate into contact with the aqueous suspension of Aspect 1; (ii) a step of moving the aqueous suspension relative to the substrate using a polishing pad; and (iii) a step of polishing the substrate by abrading at least a part of the substrate.

[0270] Aspect 13. The method of Aspect 12, wherein the substrate is a silicon carbide substrate.

[0271] Aspect 14. The method of Aspect 12 or Aspect 13, wherein the temperature of the substrate does not exceed 60 °C during abrasion.

[0272] Aspect 15. The method according to any of Aspects 12 - 14, further comprising a step of reducing the pH of the aqueous suspension to a range of 2 to 2.5 before bringing the substrate into contact with the aqueous suspension.

[0273] Aspect 16. The method of Aspect 15, wherein the pH is reduced by adding an acid.

[0274] Aspect 17. The method of Aspect 15, wherein the substrate is brought into contact with the aqueous suspension within 14 days from the reduction of the pH.

[0275] Aspect 18. A method for preparing an aqueous suspension, comprising: (i) a step of adding aluminum nitrate to an aqueous suspension containing alumina nanoparticles and zirconia nanoparticles; and (ii) a step of adding an aqueous solution of one or more metal salts of permanganic acid to the aqueous suspension.

[0276] Aspect 19. The method of Aspect 18, further comprising a step of filtering the aqueous suspension before adding the aluminum nitrate.

[0277] Aspect 20. The method of Aspect 18 or Aspect 19, further comprising a step of filtering the aqueous solution of one or more metal salts of permanganic acid before adding the aqueous solution.

[0278] Aspect 21. The method according to any of the preceding aspects, wherein MnO2 is not present in the aqueous suspension.

[0279] Aspect 22. The method according to any of the preceding aspects, wherein the aqueous suspension has a pH value in the range of 2 to 5 at 23 °C.

[0280] Aspect 23. The method according to any of the preceding aspects, wherein steps (i) and (ii) are carried out sequentially.

[0281] Aspect 24. A method comprising: a step of storing an aqueous suspension having a pH in the range of 3 to 5; a step of lowering the pH of the aqueous suspension to a range of 2 to 2.5; and a step of using the aqueous suspension having a pH in the range of 2 to 2.5 within 14 days.

[0282] Aspect 25. The method of Aspect 24, wherein the aqueous suspension contains (a) one or more metal salts of permanganic acid; (b) zirconia nanoparticles; (c) alumina nanoparticles; and (d) one or more salts of nitric acid.

[0283] Aspect 26. The method of Aspect 24 or Aspect 25, wherein the aqueous suspension is stored for at least one year.

[0284] Aspect 27. The method according to any of the preceding aspects, wherein the pH of the aqueous suspension is lowered by adding an acid, and the acid contains nitric acid.

[0285] Aspect 28. Any of the previous methods, wherein the pH of the aqueous suspension is reduced to 2.3.

[0286] Aspect 29. Any of the previous methods, wherein an aqueous suspension having a pH in the range of 2 to 2.5 is used in a single-wafer or batch chemical mechanical planarization method.

[0287] Aspect 1. An aqueous suspension comprising: (a) one or more metal salts of permanganic acid; (b) one or more zirconia nanoparticles; (c) one or more alumina nanoparticles; (d) one or more salts of nitric acid; (e) one or more calcined alumina particles; (f) one or more metal salts of chloric acid; and (g) one or more metal salts of perchloric acid.

[0288] Aspect 2. The aqueous suspension of Aspect 1, further comprising at least one pH adjuster and / or at least one pH buffer.

[0289] Aspect 3. The aqueous suspension of Aspect 1 or Aspect 2, wherein the aqueous suspension has a pH value in the range of 2 to 5.

[0290] Aspect 4. The aqueous suspension of Aspect 3, wherein the pH value is measured at a temperature in the range of 15°C to 40°C.

[0291] Aspect 5. The aqueous suspension of Aspect 3, wherein the pH value is measured at a temperature of 23°C.

[0292] Aspect 6. Any of the previous aqueous suspensions, wherein one or more metal salts of permanganic acid are selected from the group consisting of LiMnO4, KMnO4, NaMnO4, and mixtures thereof.

[0293] Aspect 7. Any of the previous aqueous suspensions, wherein one or more zirconia nanoparticles comprise ZrO2.

[0294] Aspect 8. Any of the previous aqueous suspensions, wherein one or more alumina nanoparticles comprise colloidal alumina particles.

[0295] Aspect 9. The aqueous suspension of Aspect 8, wherein the colloidal alumina particles contain γ-AlOOH particles and / or γ-Al2O3 particles.

[0296] Aspect 10. The aqueous suspension of any of the previous aspects, wherein one or more salts of nitric acid contain Al(NO3)3.

[0297] Aspect 11. The aqueous suspension of any of the previous aspects, wherein one or more kinds of calcined alumina particles contain aluminum oxide that has been heated at a temperature exceeding 1000 °C to drive off chemically bound water.

[0298] Aspect 12. The aqueous suspension of any of the previous aspects, wherein one or more metal salts of chloric acid contain NaClO3.

[0299] Aspect 13. The aqueous suspension of any of the previous aspects, wherein one or more metal salts of perchloric acid contain Al(ClO4)3.

[0300] Aspect 14. The aqueous suspension of any of the previous aspects, wherein MnO2 is not present in the aqueous suspension.

[0301] Aspect 15. A method for chemically mechanical planarization of a substrate, comprising: (i) a step of bringing the substrate into contact with the aqueous suspension of claim 1; (ii) a step of moving the aqueous suspension relative to the substrate using a polishing pad; and (iii) a step of polishing the substrate by abrading at least a part of the substrate.

[0302] Aspect 16. The method of Aspect 15, wherein the substrate is a silicon carbide substrate.

[0303] Aspect 17. The method of Aspect 15 or Aspect 16, wherein the temperature of the substrate does not exceed 60 °C during abrasion.

[0304] Aspect 18. The method of any of the previous aspects, further comprising a step of lowering the pH of the aqueous suspension to a range of 2 to 2.5 before bringing the substrate into contact with the aqueous suspension.

[0305] Aspect 19. The method of Aspect 18, wherein the pH is lowered by adding an acid.

[0306] Aspect 20. The method of Aspect 18, wherein the substrate is contacted with the aqueous suspension within 14 days from the pH decrease.

[0307] Aspect 21. A method for preparing an aqueous suspension, comprising: (i) a step of adding aluminum nitrate to an aqueous suspension containing alumina nanoparticles and zirconia nanoparticles; (ii) a step of adding an aqueous solution of one or more metal salts of permanganic acid, one or more metal salts of perchloric acid, and one or more metal salts of chloric acid to the aqueous suspension; and (iii) a step of adding one or more kinds of calcined alumina particles to the aqueous suspension.

[0308] Aspect 22. The method of Aspect 21, further comprising a step of filtering the aqueous suspension before adding aluminum nitrate.

[0309] Aspect 23. The method of Aspect 21 or Aspect 22, further comprising a step of filtering the aqueous solution before adding the aqueous solution.

[0310] Aspect 24. The method of any of the preceding aspects, wherein no MnO2 is present in the aqueous suspension.

[0311] Aspect 25. The method of any of the preceding aspects, wherein the aqueous suspension has a pH value in the range of 2 to 5 at 23 °C.

[0312] Aspect 26. The method of any of the preceding aspects, wherein steps (i), (ii), and (iii) are carried out sequentially.

[0313] Aspect 27. A method comprising: a step of storing an aqueous suspension having a pH in the range of 3 to 5; a step of lowering the pH of the aqueous suspension to the range of 2 to 2.5; and a step of using the aqueous suspension having a pH in the range of 2 to 2.5 within 14 days.

[0314] Aspect 28. The method of Aspect 27, wherein the aqueous suspension comprises (a) one or more metal salts of permanganic acid; (b) one or more zirconia nanoparticles; (c) one or more alumina nanoparticles; (d) one or more salts of nitric acid; (e) one or more calcined alumina particles; (f) one or more metal salts of chloric acid; and (g) one or more metal salts of perchloric acid.

[0315] Aspect 29. The method of Aspect 27 or Aspect 28, wherein the aqueous suspension is stored for at least one year.

[0316] Aspect 30. The method of any of the preceding aspects, wherein the pH of the aqueous suspension is lowered by adding an acid, and the acid comprises nitric acid.

[0317] Aspect 31. The method of any of the preceding aspects, wherein the pH of the aqueous suspension is lowered to 2.3.

[0318] Aspect 32. The method of any of the preceding aspects, wherein an aqueous suspension having a pH in the range of 2 to 2.5 is used in a single-wafer or batch chemical mechanical planarization process.

[0319] Aspect 1. An aqueous suspension comprising at least one oxidizing agent; abrasive grains having a total amount of less than 0.2% by weight based on the total weight of the aqueous suspension and having a Mohs hardness of less than 6; and aluminum nitrate.

[0320] Aspect 2. The aqueous suspension of Aspect 1, further comprising at least one pH adjuster and / or at least one pH buffer.

[0321] Aspect 3. The aqueous suspension of Aspect 1 or Aspect 2, having a pH value in the range of 2 to 5.

[0322] Aspect 4. The aqueous suspension of Aspect 3, wherein the pH value is measured at a temperature in the range of 15°C to 40°C.

[0323] Aspect 5. The aqueous suspension of Aspect 3, wherein the pH value is measured at a temperature of 23°C.

[0324] Aspect 6. An aqueous suspension according to any of the preceding aspects, wherein at least one oxidizing agent is selected from the group consisting of LiMnO4, KMnO4, NaMnO4, and mixtures thereof.

[0325] Aspect 7. The aqueous suspension of Aspect 6, wherein at least one oxidizing agent is KMnO4.

[0326] Aspect 8. An aqueous suspension according to any of the preceding aspects, wherein the abrasive grains include alumina particles.

[0327] Aspect 9. The aqueous suspension of Aspect 8, wherein the alumina particles include γ-AlOOH particles.

[0328] Aspect 10. The aqueous suspension of Aspect 8, wherein the alumina particles are γ-AlOOH particles.

[0329] Aspect 11. An aqueous suspension according to any of the preceding aspects, wherein MnO2 is not present in the aqueous suspension.

[0330] Aspect 12. A method for chemically-mechanically planarizing a substrate, comprising: (i) contacting the substrate with the aqueous suspension according to claim 1; (ii) moving the aqueous suspension relative to the substrate using a polishing pad; and (iii) abrading at least a portion of the substrate to polish the substrate.

[0331] Aspect 13. The method of Aspect 12, wherein the substrate includes at least one silicon carbide layer.

[0332] Aspect 14. The method of Aspect 13, wherein at least one silicon carbide layer is at least one single-crystalline silicon carbide layer.

[0333] Aspect 15. A method according to any of the preceding aspects, wherein the temperature of the substrate does not exceed 60 °C during abrasion.

[0334] Aspect 16. A method according to any of the preceding aspects, further comprising reducing the pH of the aqueous suspension to a range of 2 to 2.5 before contacting the substrate with the aqueous suspension.

[0335] Aspect 17. The method of Aspect 16, wherein the pH of the aqueous suspension is lowered by adding an acid.

[0336] Aspect 18. The method of Aspect 16, wherein the substrate is brought into contact with the aqueous suspension within 14 days from the pH decrease.

[0337] Aspect 19. A method for preparing an aqueous suspension, comprising: (i) a step of adding aluminum nitrate to an aqueous suspension containing abrasive grains; (ii) a step of adding an aqueous solution of at least one oxidizing agent to the aqueous suspension, wherein the abrasive grains have a Mohs hardness of less than 6 and the aqueous suspension contains less than 0.2% by weight of abrasive grains based on the total weight of the aqueous suspension.

[0338] Aspect 20. The method of Aspect 19, further comprising a step of filtering the aqueous suspension before adding the aluminum nitrate.

[0339] Aspect 21. The method of Aspect 19 or Aspect 20, further comprising a step of filtering the aqueous solution before adding the aqueous solution.

[0340] Aspect 22. The method of any of the previous aspects, wherein MnO2 is not present in the aqueous suspension.

[0341] Aspect 23. The method of any of the previous aspects, wherein the aqueous suspension has a pH value in the range of 2 to 5 at 23 °C.

[0342] Aspect 24. The method of any of the previous aspects, wherein steps (i) and (ii) are carried out sequentially.

[0343] Aspect 25. A method comprising: a step of storing an aqueous suspension having a pH in the range of 3 to 5; a step of lowering the pH of the aqueous suspension to a range of 2 to 2.5; and a step of using the aqueous suspension having a pH in the range of 2 to 2.5 within 14 days.

[0344] Aspect 26. The method of Aspect 25, wherein the aqueous suspension comprises at least one oxidizing agent; abrasive grains in an amount less than 0.2% by weight based on the total weight of the aqueous suspension, the abrasive grains having a Mohs hardness of less than 6; and aluminum nitrate.

[0345] Aspect 29. The method of Aspect 25 or Aspect 26, wherein the aqueous suspension is stored for at least one year.

[0346] Aspect 29. The method of any of the preceding aspects, wherein the pH of the aqueous suspension is lowered by adding an acid, and the acid contains nitric acid.

[0347] Aspect 30. The method of any of the preceding aspects, wherein the pH of the aqueous suspension is lowered to 2.3.

[0348] Aspect 31. The method of any of the preceding aspects, wherein an aqueous suspension having a pH in the range of 2 to 2.5 is used in a single-wafer or batch chemical mechanical planarization method.

[0349] Aspect 32. The method of any of the preceding aspects, wherein the step of using the aqueous suspension includes the step of using an aqueous suspension having a pH in the range of 2 to 2.5 in a batch chemical mechanical planarization method.

[0350] It should be understood that without departing from the scope of the present disclosure, particularly, changes can be made in terms of the constituent materials used and the shape, size, and arrangement of the components. This specification and the described embodiments are examples, and the true scope and spirit of the present disclosure are indicated by the following claims.

Claims

1. 1. An aqueous suspension comprising: At least one oxidizing agent; abrasive grains in a total amount of less than 0.2 wt.%, based on the total weight of the aqueous suspension, the abrasive grains having a Mohs hardness of less than 6; and Aluminum nitrate 13. An aqueous suspension comprising:

2. 2. The aqueous suspension of claim 1, further comprising at least one pH adjuster and / or at least one pH buffer.

3. 2. The aqueous suspension of claim 1 having a pH value in the range of from 2 to 5.

4. At least one oxidizing agent is LiMnO ４ , KMnO ４ , NaMnO ４ 2. The aqueous suspension of claim 1, wherein the aqueous suspension is selected from the group consisting of:

5. 2. The aqueous suspension of claim 1, wherein the abrasive comprises alumina particles.

6. 6. The aqueous suspension of claim 5, wherein the alumina particles comprise γ-AlOOH particles.

7. 1. A method for chemically mechanically planarizing a substrate, comprising: (i) contacting a substrate with the aqueous suspension of claim 1; (ii) moving the aqueous suspension against the substrate with a polishing pad; and (iii) polishing the substrate by abrading at least a portion of the substrate. A method comprising:

8. The method of claim 7 , wherein the substrate does not exceed a temperature of 60° C. during abrasion.

9. 8. The method of claim 7, further comprising the step of lowering the pH of the aqueous suspension to a range of 2 to 2.5 prior to contacting the substrate with the aqueous suspension.

10. 10. The method of claim 9, wherein the substrate is contacted with the aqueous suspension within 14 days of the pH being reduced.

11. 1. A method for preparing an aqueous suspension comprising the steps of: (i) adding aluminum nitrate to an aqueous suspension containing abrasive grains; and (ii) adding an aqueous solution of at least one oxidizing agent to the aqueous suspension; Including, wherein the abrasive grains have a Mohs hardness of less than 6; and The method, wherein the aqueous suspension comprises less than 0.2 weight percent abrasive grains, based on the total weight of the aqueous suspension.

12. 12. The method of claim 11 further comprising filtering the aqueous suspension prior to adding aluminum nitrate.

13. 12. The method of claim 11, further comprising filtering the aqueous solution prior to adding the aqueous solution.

14. 12. The method of claim 11, wherein the aqueous suspension has a pH value in the range of 2 to 5 at 23°C.

15. The method of claim 11 , wherein steps (i) and (ii) are carried out sequentially.

16. storing the aqueous suspension having a pH in the range of 3 to 5; lowering the pH of the aqueous suspension to a range of 2 to 2.5; and using the aqueous suspension having a pH in the range of 2 to 2.5 for no more than 14 days. A method comprising:

17. The aqueous suspension is At least one oxidizing agent; abrasive grains in a total amount of less than 0.2 wt.%, based on the total weight of the aqueous suspension, the abrasive grains having a Mohs hardness of less than 6; and Aluminum nitrate 17. The method of claim 16, comprising:

18. 17. The method of claim 16, wherein the aqueous suspension is stored for at least one year.

19. 17. The method of claim 16, wherein the pH of the aqueous suspension is lowered to 2.

3.

20. 17. The method of claim 16, wherein an aqueous suspension having a pH in the range of 2 to 2.5 is used in a single-wafer or batch chemical mechanical planarization process.

21. (a) one or more metal salts of permanganic acid; (b) zirconia nanoparticles; (c) alumina nanoparticles; and (d) one or more salts of nitric acid 13. An aqueous suspension comprising:

22. 22. An aqueous suspension according to claim 21 further comprising at least one pH adjuster and / or at least one pH buffering agent.

23. 22. An aqueous suspension according to claim 21, wherein the aqueous suspension has a pH value in the range of from 2 to 5.

24. The one or more metal salts of permanganic acid are LiMnO ４ , KMnO ４ , NaMnO ４ 22. The aqueous suspension of claim 21, wherein the aqueous suspension is selected from the group consisting of:

25. Zirconia nanoparticles are ZrO ２ 22. The aqueous suspension of claim 21 comprising:

26. 22. The aqueous suspension of claim 21 , wherein the alumina nanoparticles comprise colloidal alumina particles.

27. The colloidal alumina particles are γ-AlOOH particles and / or γ-Al ２ O ３ 27. An aqueous suspension according to claim 26 comprising particles.

28. One or more salts of nitric acid are Al(NO ３ ) ３ 22. The aqueous suspension of claim 21 comprising:

29. 1. A method for preparing an aqueous suspension comprising the steps of: (i) adding aluminum nitrate to an aqueous suspension containing alumina nanoparticles and zirconia nanoparticles; and (ii) adding an aqueous solution of one or more metal salts of permanganate to the aqueous suspension; A method comprising:

30. 30. The method of claim 29, further comprising filtering the aqueous suspension prior to adding aluminum nitrate.

31. 30. The method of claim 29, further comprising the step of filtering the aqueous solution of one or more metal salts of permanganate prior to adding the aqueous solution.

32. 30. The method of claim 29, wherein the aqueous suspension has a pH value in the range of 2 to 5 at 23°C.

33. 30. The method of claim 29, wherein steps (i) and (ii) are carried out sequentially.

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