CN117120564A

CN117120564A - Suspension for Chemical Mechanical Planarization (CMP) and method of using the same

Info

Publication number: CN117120564A
Application number: CN202280024893.6A
Authority: CN
Inventors: S·R·阿勒蒂; M·赛夫卡; N·马哈德夫
Original assignee: Entegris Inc
Current assignee: Entegris Inc
Priority date: 2021-03-29
Filing date: 2022-03-24
Publication date: 2023-11-24

Abstract

The present disclosure relates to aqueous suspensions suitable for Chemical Mechanical Planarization (CMP), uses of the aqueous suspensions, and CMP methods using the aqueous suspensions. The suspension and the method are useful for CMP of silicon carbide surfaces.

Description

Suspension for Chemical Mechanical Planarization (CMP) and method of using the same

Cross-reference to related applications

U.S. provisional patent application No. 63/167,275, filed on patent application Ser. No. 2021/3/29 and entitled "SUSPENSION FOR Chemical Mechanical Planarization (CMP) and method of using the same (SUSPENSION FOR CHEMICAL MECHANICAL PLANARIZATION (CMP) AND METHOD EMPLOYING THE SAME), the disclosure of which is incorporated herein by reference in its entirety, claims the priority and benefits of such SUSPENSIONs. U.S. provisional patent application No. 63/180,963, filed on patent application Ser. No. 2021/4/28, and entitled "SUSPENSION FOR Chemical Mechanical Planarization (CMP) and method of using the same (SUSPENSION FOR CHEMICAL MECHANICAL PLANARIZATION (CMP) AND METHOD EMPLOYING THE SAME), is hereby incorporated by reference in its entirety. U.S. provisional patent application No. 63/237,644, filed on 8/27 of 2021, entitled "SUSPENSION FOR Chemical Mechanical Planarization (CMP) and method of using the same (suspend FOR CHEMICAL MECHANICAL PLANARIZATION (CMP) AND METHOD EMPLOYING THE SAME)", the disclosure of which is incorporated herein by reference in its entirety, claims the priority and benefits of this application.

Technical Field

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

Background

The CMP method is a polishing method having both chemical and mechanical actions.

Disclosure of Invention

The aqueous suspension as described herein and any examples thereof are labeled as suspensions according to the present disclosure. Also labeled as the chemical mechanical planarization slurry of the present disclosure or "CMP slurry of the present disclosure". Some slurry components act chemically, for example by oxidizing the surface of the substrate to be polished, allowing mechanical action on the abrasive component, for example slurry, to more gently remove any non-uniformities from the substrate surface.

Another object of the present disclosure includes the use of the suspension as a polishing composition, particularly suited for polishing silicon carbide surfaces in a chemical mechanical planarization process.

It is yet another object of the present disclosure to provide a method of chemically-mechanically planarizing a substrate that includes contacting the substrate with an aqueous suspension according to the present disclosure, moving the aqueous suspension relative to the substrate by means of a polishing pad, and abrading at least a portion of the substrate to polish the substrate.

When using a suspension in a CMP process, the rate of material removal can be accelerated and at the same time the interface temperature can be reduced during polishing. In addition, process time may be reduced, die yield of the wafer may be increased, and surface imperfections and scratches may be minimized. Due to the composition of the one or more species of calcined alumina particles, the one or more metal chlorate salts, and the one or more metal perchlorate salts, the material removal rate may be further increased by up to 25-30% even at lower interface temperatures than an aqueous suspension of the composition containing only the one or more metal permanganate salts, the one or more species of zirconia nanoparticles, the one or more species of alumina nanoparticles, the one or more nitrate salts, but not the one or more species of calcined alumina particles, the one or more metal chlorate salts, and the one or more metal perchlorate salts. A removal rate of 13. Mu.g/h or more on single crystal type 4H n SiC (Si surface) and 30. Mu.g/h or more on C surface can be observed while producing a flawless sub-angstrom substrate with high process yield. In addition, friction and motor load in temperature limited CMP operations can be substantially reduced, and the corresponding CMP methods allow process engineers room to develop more aggressive process recipes that increase wafer throughput. Furthermore, no "settling out" of any of the components of the suspension may be observed during product use or simultaneously under storage conditions, and thus the suspension has a longer shelf life, even in its acidic medium. Furthermore, based on various surface charge dynamics, the components of the suspension adhere to the wafer surface, which ensures a uniform distribution of the suspension over the wafer surface. Finally, little to no residue can be observed on the CMP pad after the inter-run cleaning process, thereby increasing pad life.

In some embodiments, the disclosure includes an aqueous suspension comprising (a) one or more metal permanganate salts, (b) zirconia nanoparticles, (c) alumina nanoparticles, and (d) one or more nitrates.

In some embodiments, the present disclosure includes a method for preparing an aqueous suspension comprising (i) adding aluminum nitrate to an aqueous suspension comprising aluminum oxide nanoparticles and zirconium oxide nanoparticles, and (ii) adding an aqueous solution of one or more metal permanganate salts to the aqueous suspension.

In some embodiments, the disclosure includes a method comprising storing an aqueous suspension having a pH in the range of 3 to 5, reducing the pH of the aqueous suspension to a pH in the range of 2 to 2.5, and using the aqueous suspension having a pH in the range of 2 to 2.5 for fourteen days.

In some embodiments, the present disclosure includes an aqueous suspension comprising (a) one or more metal salts of permanganate, (b) one or more types of zirconia nanoparticles, (c) one or more types of alumina nanoparticles, (d) one or more nitrates, (e) one or more types of calcined alumina particles, (f) one or more metal salts of chlorate, and (g) one or more metal salts of perchlorate.

In some embodiments, the present disclosure includes a method for preparing an aqueous suspension comprising (i) adding aluminum nitrate to an aqueous suspension comprising aluminum oxide nanoparticles and zirconium oxide nanoparticles, (ii) adding an aqueous solution of one or more metal permanganate salts, one or more metal perchlorate salts, and one or more metal chlorate salts to the aqueous suspension, and (iii) adding one or more types of calcined aluminum oxide particles to the aqueous suspension.

In some embodiments, the disclosure includes an aqueous suspension comprising: at least one oxidizing agent; a total amount of less than 0.2wt% abrasive particles, based on the total weight of the aqueous suspension, wherein the abrasive particles have a Mohs hardness (Mohs hardness) of less than 6; and aluminum nitrate.

In some embodiments, the present disclosure includes a method for preparing an aqueous suspension comprising (i) adding aluminum nitrate to an aqueous suspension comprising abrasive particles; and (ii) adding an aqueous solution of at least one oxidizing agent to the aqueous suspension, wherein the abrasive particles have a mohs hardness of less than 6, and wherein the aqueous suspension contains less than 0.2wt% abrasive particles, based on the total weight of the aqueous suspension.

Detailed Description

Other objects and advantages of the present disclosure will become apparent from the following description, taken in conjunction with the accompanying drawings, in which those benefits and improvements have been disclosed. Detailed embodiments of the present disclosure are disclosed herein; it is to be understood, however, that the disclosed embodiments are merely illustrative of the disclosure, which may be embodied in various forms. Moreover, the examples given with respect to the various embodiments of the present disclosure are each intended to be illustrative and not limiting.

All previous patents and publications referred to herein are incorporated by reference in their entirety.

Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. As used herein, the phrases "in one embodiment," "in an embodiment," and "in some embodiments" do not necessarily refer to the same embodiment, but they may. Furthermore, as used herein, "in another embodiment" and "in some other embodiments" do not necessarily refer to different embodiments, but they may. All embodiments of the present disclosure are intended to be combinable without departing from the scope or spirit of the disclosure.

The proportions and amounts in wt% (wt%) of any of the components present in the aqueous suspensions given below total 100wt% in each case based on the total weight of the suspension.

As used herein, unless the context clearly dictates otherwise, the term "by … …" is not exclusive and allows for additional factors not described. In addition, throughout the specification, the meaning of "a/an" and "the" includes plural references. The meaning of "in … … (in)" includes "in … … (in)" and "on … … (on)".

As used herein, the term "between … …" does not necessarily need to be disposed immediately adjacent to other components. In general, this term means a configuration in which something is sandwiched by two or more other things. Meanwhile, the term "between … …" may describe something directly next to two opposite things. Thus, in any one or more of the embodiments disclosed herein, a particular structural component disposed between two other structural components may:

disposed directly between two other structural components such that a particular structural component is in direct contact with both of the two other structural components;

Is disposed immediately adjacent to only one of the two other structural components such that a particular structural component is in direct contact with only one of the two other structural components;

is disposed indirectly immediately adjacent to only one of the two other structural components such that the particular structural component is not in direct contact with only one of the two other structural components and there is another component that juxtaposes the particular structural component and one of the two other structural components;

indirectly disposed between two other structural components such that a particular structural component is not in direct contact with both other structural components, and other features may be disposed therebetween; or any combination thereof.

As used herein, "embedded" means that the first material is distributed throughout the second material.

As used herein, the grammatical articles "a" and "an" are intended to include "at least one" or "one or more" unless otherwise indicated, even if "at least one" or "one or more" are expressly used in certain instances. Thus, as used in this specification, the articles refer to one or more than one (i.e., "at least one") of the grammatical object of the article. By way of example and not limitation, "component" means one or more components, and thus more than one component may be considered, and may be employed or used in implementation of the described embodiments. In addition, the use of a singular noun includes the plural and plural noun use includes the singular unless the context of use requires otherwise.

As used herein, the terms "include," "have," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition or method comprising a series 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.

As used herein, and unless expressly stated to the contrary, "or" means an inclusive or and not a non-exclusive or. For example, either one of the following satisfies the condition a or B: 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).

As used herein, the term "nanoparticle" in the context of zirconia and alumina means particles having a Z-average particle size in the range of 1nm to 1000nm, as determined via dynamic light scattering (dynamic light scattering; DLS) (also known as quasi-elastic light scattering (quasi-elastic light scattering; QELS)). The Z-average particle size, also known as the weighted harmonic mean particle size of the scattered light intensity, is generated from a data analysis algorithm known as the cumulant method. The Z-average particle size can be determined according to ISO22412:2017 (en), for example by using Malvern Zetasizer Nano (Mo Erwen instruments Inc. (Malvern Instruments Ltd.), UK Mo Erwen (Malvern, UK)).

The term "suspension" refers to a heterogeneous mixture in which solute particles are not dissolved but suspended in a majority of a solvent, remaining approximately free floating in a medium.

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., the water fraction of the suspension is at least 80wt%, at least 85wt%, at least 90wt%, or at least 92, 93, or 94wt%, based in each case on the total amount of solvents present (i.e., water and organic solvents, if present). In some embodiments, the aqueous suspension has a water number of 40 to 100wt%, 60 to 100wt%, or 80 to 100wt%, based in each case on the total amount of solvent present. The water employed in the suspension of the present disclosure may be deionized water. In some embodiments, the aqueous suspension of the present disclosure does not contain any organic solvent, i.e., the total amount of organic solvent is 0wt% based on the total amount of solvent present.

As used herein, the term "oxidizing agent" is a compound dissolved in an aqueous carrier of a suspension and having an oxidation potential suitable for chemical reaction with the substrate surface. In some embodiments, the oxidation potential of the oxidizing agent is 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 may not exceed 2.8V, or not exceed 2.5V, or not exceed 2.0V. The oxidation potential is the value measured relative to a standard hydrogen electrode at a temperature of 25 ℃, a pressure of 1 atmosphere, at a concentration of 1mol/L of test oxidant in water, and measured in volts (V).

"mohs hardness" refers to a qualitative sequential scale in the range of 1 to 10, and characterizes scratch resistance of various ores via the ability of harder materials to scratch softer materials. Diamond on top of the scale, the hardest naturally occurring substance known when designing the scale, has a mohs hardness of 10. The hardness of a material is measured relative to the scale by finding the hardest material that a given material can scratch or the softest material that a given material can scratch. "scratching" the material for the purpose of the Morse scale means creating dislocations visible to the naked eye. Frequently, lower materials on the mohs scale can produce microscopic inelastic dislocations on materials with higher mohs numbers. While these microscopic dislocations are permanent and sometimes detrimental to the structural integrity for harder materials, they are not considered "scratches" for determining mohs scale.

Improvements in the cost, performance, and efficiency of power generation, storage, and distribution systems, as well as government subsidies encouraging widespread social electrification, have accelerated the adoption of Electric Vehicles (EVs) and a number of other cleaning technologies over the past decades.

The transition to the more electrified world has created a need for new electrical infrastructure for nodes and switches to regulate power flow. At the heart of this new infrastructure is a power component-solid state transistor, similar in size and appearance to the computer chip powering computers and telephones, but with the ability to handle larger voltages and currents, and the functionality to manage the flow of power between, for example, the motor and battery in an electric vehicle, or the solar cell and battery in a household charging system.

A new generation of power components composed of silicon carbide (SiC) has proven to be significantly superior to older conventional silicon-based devices. Individual SiC power components (a few millimeters in size) are fabricated on SiC wafer slices (uniform substrates of crystalline SiC, which may be 4 "or 6" in diameter).

SiC is a material in which different crystal structures, which may be referred to as polytypes, exist. The order of the crystal stack of Si and C atoms (which characterizes each polytype) also determines its basic electrical characteristics. Although SiC has more than 200 known polytypes, a few are commercially available, namely 3C-SiC, 4H-SiC and 6H-SiC. Currently, 4H-SiC is a widely used SiC polytype for power component fabrication due to its excellent electrical characteristics. These characteristics enable the power component to have a high breakdown voltage, a high power density, a high switching frequency, improved thermal conductivity, and improved overall device efficiency. In addition to its use in EV motor control systems and charging stations, 4H-SiC power components have enabled improved performance in 5G wireless networks, military radars, satellite communications, power inverters of renewable power sources, and unmanned aerial vehicles, while at the same time making these devices smaller, lighter, and more robust to environmental conditions (such as vibration and radiation).

Silicon carbide (SiC), and more particularly 4H-SiC, has characteristics compared to silicon (Si) including: an insulating breaking electric field of an order of magnitude larger, an energy band gap of almost 3 times larger, and a thermal conductivity of almost 4 times higher, and thus has a considerable prospect for application to power components, high-frequency devices, high-temperature operating devices, and the like. Therefore, siC substrates are increasingly used as substrates for semiconductor devices.

For example, the SiC substrate described above is prepared from a bulk SiC single crystal ingot prepared by a highly controlled sublimation method or the like. Typically, the outer periphery of the ingot is ground and processed into a cylindrical shape, then the cylindrical shape is cut into circular disks using a diamond-embedded wire saw or the like, and then the outer Zhou Xieqie is cut into a prescribed diameter to obtain a substrate. Diamond saws introduce larger millimeter-sized grooves and scratches into the wafer surface that are removed by various stages of the surface lapping and grinding process to remove surface non-uniformities and achieve parallelism. However, lapping and grinding processes rely on micron-sized diamond particles, which may leave micron-sized surface damage in the form of scratches, pits, and grooves.

Subsequently, one surface or both surfaces of the substrate are provided with mirror finish (CMP) by subjecting the surfaces to chemical mechanical polishing (also referred to as chemical mechanical planarization). This type of grinding and polishing of SiC substrates is performed for the purpose of, for example: removing the undulations and process distortions, and planarizing the SiC substrate surface, resulting in a nearly atomic level planar surface with little surface imperfections suitable for downstream epitaxy and other semiconductor fabrication processes.

The CMP method is a polishing method that has both chemical and mechanical actions, and thus can obtain a planar surface in a stable manner without damaging the SiC substrate. Therefore, the CMP method is widely used in the production process of SiC semiconductor devices and the like as a method for planarizing roughness or undulation generated on the surface of the SiC substrate or planarizing unevenness due to wiring and the like.

In a CMP process, a 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 from a soft porous polymer that provides a mechanical surface for rubbing against the substrate surface, as well as grooves and pores that can facilitate slurry flow and capture removed debris, oxidized surface material that is removed as part of the CMP process. The CMP slurry may be a composite liquid suspension comprising oxidizing agents, additives, and particles, and is typically acidic or basic depending on the nature of the application. In the CMP process, chemical attack of the slurry (oxidizer, additive and pH) is supplemented by mechanical (frictional) forces generated by contact between the pad, particles and substrate. In view of the large number of chemical and mechanical process variables, developing CMP slurries requires a deep understanding of the process and the interactions between the pad and particles, particle and wafer, and wafer and pad. For example, CMP processes for different materials (e.g., si, siC, sapphire, gaN, inP, etc.) all require specific processing conditions, parameters, and consumables that are unique to the technology and application requirements of each substrate.

On the one hand, in the case of SiC wafers, in particular 4H-SiC wafers, mechanical hardness and chemical inertness require highly aggressive CMP conditions (i.e. aggressive CMP suspension/slurry) and aggressive CMP parameters (high pressure, rapid polishing rates, etc.) to effectively remove SiC. On the other hand, these aggressive conditions may introduce surface scratches, pits, debris and subsurface damage.

It is therefore desirable to provide a CMP slurry that is sufficiently balanced to avoid damage to the substrate, but is aggressive enough to create a SiC wafer in the CMP process that has an atomically flat surface to the extent that nearby crystal structures can be identified via atomic force microscopy.

In addition, there are a number of different CMP processes. In one configuration, multiple SiC wafers are processed at once in a larger polishing tool. This is known as a "batch process" and requires a particularly large CMP tool that uses a platen having a diameter of a few feet and is capable of processing up to more than twenty wafers at a time. While batch processing produces some throughput advantages, the large number of wafers and large tool sizes makes process adjustments complex and prone to throughput problems. For example, if the wafer thickness loaded into a batch CMP tool is not the same, the thicker wafer will protrude into the polishing pad and thus experience a greater force, while at the same time the thinner wafer will receive a smaller force and may even slip out during processing. This can result in unevenly polished SiC wafers. And if one wafer in a batch process breaks into pieces under strong mechanical forces (common to CMP), wafer debris from the broken wafer can create further scratches or break the entire batch of wafers. Furthermore, with larger platen sizes creating larger surface areas, it is difficult for the tool to uniformly apply the extreme downward force required for satisfactory material removal rates; thus requiring a longer run time. Longer run times may mean that the wafer is exposed to aggressive conditions longer, increasing the risk of introducing flaws, scratches and significant surface damage. This motivates testing and adoption of new kits, pads and slurries specifically designed for batch-type processes.

In some configurations, to overcome these defectivity and throughput challenges, the SiC industry has begun to convert from bulk batch processes to single wafer processes. In single wafer processes, smaller platen sizes allow for higher process pressures and more uniform pressure distribution. With higher pressures, faster material removal rates occur, and thus shorter run times. In addition, in a single wafer process, any defective or broken wafers may be separated without damaging other wafers. This translates into single wafer CMP that has driven testing and adoption of new kits, pads and slurries specifically designed for single wafer processing.

Due to different process conditions, such as tool boxes, polishing pads, downforce pressures, etc., used during batch and single CMP processes, slurries are typically designed specifically for one CMP process type. However, the CMP slurry may be suitable for use in both batch CMP processes and similar single wafer CMP processes.

Accordingly, in order to solve the various problems of the prior art, the present disclosure provides a suspension having a stable pH, i.e., a pH variation of less than 0.1 over a period of at least 12 months, and allowing for a high material removal rate while providing a polished substrate of low surface roughness when used in a batch CMP or single wafer CMP process. The present disclosure provides a suspension suitable for use as a CMP slurry in a batch CMP process as well as in a single wafer CMP process that allows for an accelerated process, i.e., by significantly increasing the material removal rate to allow for higher throughput. This may require that the suspension be aggressive enough to polish and planarize the wafer (even if made of 4H-SiC) while avoiding scratches or other damage to the wafer surface. To ensure this, the suspension can be effective as a CMP slurry at the interface between the polishing pad and the wafer at lower temperatures than current state-of-the-art slurries. The suspension is storage stable and the sediment (e.g., any sediment that may form during storage) can be easily redispersed by simple agitation (e.g., stirring or shaking of the suspension).

It is an object of the present disclosure to provide a use of such a suspension in a polishing method, in particular in chemical mechanical planarization of a wafer.

It is another object of the present disclosure to provide a gentle method of chemical mechanical planarization of wafers, more particularly SiC wafers, such as 4H-SiC wafers, using such CMP slurries, which is thus improved.

In some embodiments, the disclosure is an aqueous suspension having a pH in the range of 2 to 5 and comprising: (a) one or more metal permanganates; (b) zirconia nanoparticles; (c) alumina nanoparticles; and (d) one or more nitrates. In some embodiments, the present disclosure optionally includes one or more agents selected from the group of pH adjusting agents and pH buffering agents. In some embodiments, the pH is measured from a temperature range of 20 ℃ to 30 ℃, such as 23 ℃. In some embodiments, the aqueous suspension contains particles having a mohs hardness of greater than 1, greater than 2, greater than 3, and greater than 4.

In some embodiments, the present disclosure is an aqueous suspension comprising (a) one or more metal permanganate salts; (b) one or more kinds of zirconia nanoparticles; (c) one or more types of alumina nanoparticles; (d) one or more nitrates; (e) one or more types of calcined alumina particles; (f) one or more metal chlorate salts; and (g) one or more metal perchlorate salts. In some embodiments, the present disclosure optionally includes one or more agents selected from the group of pH adjusting agents and pH buffering agents. In some embodiments, the pH of the aqueous suspension is in the range of 2 to 5. In some embodiments, the pH of the aqueous suspension is measured at a temperature ranging from 15 ℃ to 40 ℃, e.g., 23 ℃. In some embodiments, the aqueous suspension contains particles having a mohs hardness of greater than 1, greater than 2, greater than 3, and greater than 4.

In some embodiments, the disclosure is an aqueous suspension having a pH of 2 to 5 at 23 ℃ and comprising at least one oxidizing agent, less than 0.2wt% total abrasive particles, aluminum nitrate. In some embodiments, the present disclosure optionally includes one or more agents selected from the group of pH adjusting agents and pH buffering agents. In some embodiments, the mohs hardness of all abrasive particles present in the aqueous suspension is less than 6 to avoid scratching the substrate surface during the polishing process. In some embodiments, the pH is measured from a temperature range of 15 ℃ to 40 ℃, e.g., 23 ℃. In some embodiments, the disclosure includes providing an aqueous suspension having a pH of 2 to 5 at 23 ℃ and comprising at least one oxidizing agent, based on the total weight of the aqueous suspension; abrasive particles in a total amount of less than 0.2 wt%; aluminum nitrate; and optionally at least one pH adjustor and/or at least one pH buffering agent, wherein the mohs hardness of all abrasive particles present in the aqueous suspension is less than 6. In some embodiments, the present disclosure includes a method for preparing an aqueous suspension (aqueous suspension; AS) having a pH of 2 to 5 at 23 ℃, the method comprising providing an aqueous suspension of abrasive particles (ASP), wherein all abrasive particles 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 an 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 adjusting agent, wherein the Aqueous Suspension (AS) obtained by the method contains less than 0.2 wt.% abrasive particles, based on the total weight of the aqueous suspension.

The at least one oxidizing agent can be any suitable oxidizing agent that oxidizes chemical bonds (e.g., si-C bonds) on the surface of a substrate (e.g., a silicon carbide substrate) to be polished.

Suitable oxidizing agents include persulfates, organic peroxides, inorganic peroxides, peroxyacids, permanganates, chromates, percarbonates, chlorates, bromates, iodates, perchloric acid and salts thereof, perbromic acid and salts thereof, periodic acid and salts thereof, hydroxylamine and salts thereof, ferricyanide, potassium hydrogen persulfate (oxone), and combinations thereof.

In some embodiments, the at least one oxidizing agent is a metal permanganate salt, such as an alkali metal permanganate salt. The alkali metal permanganate may be selected from lithium permanganate, potassium permanganate, sodium permanganate and mixtures thereof, for example mixtures of potassium permanganate.

In some embodiments, the at least one oxidizing agent is potassium permanganate.

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

If the amount of the at least one oxidizing agent is too low, the material removal rate of the suspension in the CMP process may also be too low; and if the amount of the at least one oxidizing agent is too high, the oxidizing ability may be too strong, thus generating surface defects mainly due to etching-type mechanisms. A balance of properties and efficiency in the CMP process can be achieved if the amount of the at least one oxidizing agent is in each case 0.1 to 10 wt.%, or 3 to 5.5 wt.%, or 4 to 5 wt.%, based on the total weight of the aqueous suspension.

In some embodiments, all of the abrasive particles present in the suspension of the present disclosure have a mohs hardness of less than 6. The use of abrasive particles having a mohs hardness of less than 6 (i.e., "soft" abrasive particles) results in the formation of an aqueous suspension of: is storage stable and thus shows a constant mass during its shelf life; whereas the use of abrasive particles having a mohs hardness higher than 6 (e.g. alumina particles having a mohs hardness higher than 6) results in the formation of an unstable suspension. Furthermore, the use of aqueous suspensions comprising these "soft" abrasive particles unexpectedly results in higher material removal rates, lower polishing temperatures, and lower surface roughness (i.e., higher quality polished substrates) in batch and single CMP processes than the use of aqueous slurries comprising abrasive particles (e.g., colloidal silica) having a mohs hardness in excess of 6.

In some embodiments, the Z-average particle size of the abrasive particles is from 1nm to 1000nm, from 10 to 500nm, from 20 to 300nm, from 50 to 200nm, or from 75 to 150nm. Thus, the abrasive particles may be abrasive nanoparticles. The Z-average particle size, also known as the weighted harmonic mean particle size of the scattered light intensity, is generated from a data analysis algorithm known as the cumulant method. The Z-average particle size may be determined according to ISO 22412:2017 (en), for example by using Malvern Zetasizer Nano (Mo Erwen instruments, inc., UK Mo Erwen).

In some embodiments, the abrasive particles have a mohs hardness of less than 5.5, less than 5, or 3 to 4. The abrasive particles can include (e.g., comprise, consist essentially of, or consist of) one or more metal oxides having a mohs hardness of less than 6, e.g., 3 to 4, as described above. The metal oxide may be selected from the group consisting of aluminum oxide, titanium dioxide, zirconium oxide, cerium oxide, germanium oxide, magnesium oxide, and combinations thereof, having a mohs hardness of less than 6. The aqueous suspension may contain only one type of abrasive particles or may contain a mixture of different types of abrasive particles.

In some embodiments, the abrasive particles can include (e.g., comprise, 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 are particles containing at least one of the following: alumina, such as aluminum hydroxide, aluminum oxide hydroxide, hydrates of any of the foregoing alumina species; and a mixed metal species comprising and consisting of any of the foregoing alumina species and at least one other metal atom and/or oxide and/or hydroxide thereof and/or metal ion, and having a mohs hardness of less than 6. In some embodiments, the alumina particles can include (e.g., comprise, consist essentially of, or consist of) at least one of the following: aluminum hydroxide, aluminum oxide hydroxide, or a hydrate of any of the foregoing aluminum oxide species.

The alumina particles may exist in colloidal form or in amorphous form (e.g., polycrystalline amorphous form). In some embodiments, the abrasive particles can include (e.g., comprise, consist essentially of, or consist of) particles of boehmite (hereinafter labeled gamma-AlOOH) and/or gamma-Al ₂ O ₃ Particles, and may be in colloidal form. For example, waterThe sexual suspension may include gamma-AlOOH particles and/or gamma-Al ₂ O ₃ Colloidal alumina particles of the particles. In some embodiments, the aqueous suspension includes 0 wt.% of other abrasive particles, in addition to the alumina particles having a mohs hardness of less than 6 (e.g., gamma-AlOOH particles), based on the total weight of the aqueous suspension. The use of boehmite in combination with aluminum nitrate as a single abrasive results in better stability of the aqueous suspension, while the use of other aluminas (e.g., alpha-alumina) or the use of other nitrates (e.g., ferric nitrate, cerium nitrate, and manganese nitrate) results in reduced storage stability of the aqueous suspension due to the formation of unstable suspensions or the formation of undesired reaction products. Furthermore, the use of boehmite as a single abrasive causes less scratching of the substrate surface and lower polishing temperatures for a given downforce during the polishing process, thus allowing for improved surface quality and reduced substrate damage, and thus improved quality (or yield) of the CMP process.

In some embodiments, suspensions according to the present disclosure contain less than 0.2wt%, 0.15wt%, 0.1wt%, or 0.05wt% total abrasive particles. This list of ranges is not exhaustive and includes any intermediate values, for example less than 0.13wt%. In some embodiments, a suspension according to the present disclosure contains a total amount of abrasive particles within the following range: 0.005 to 0.2wt%, 0.005 to 0.15wt%, 0.005 to 0.1wt%, or 0.005 to 0.05wt%, 0.005 to 0.01wt%, 0.01 to 0.2wt%, 0.05 to 0.2wt%, 0.1 to 0.2wt%, 0.15 to 0.2wt%, 0.05 to 0.15wt%, 0.01 to 0.15wt% or 0.05 to 0.1wt%. This list of ranges is not exhaustive and includes any intermediate values, for example 0.07wt% to 0.13wt%.

The alumina particles may be prepared by any method known in the art.

In some embodiments, the suspensions according to the present disclosure contain less than 0.2wt% total abrasive particles, and in some embodiments, less than 0.2wt% gamma-AlOOH particles, based on the total weight of the suspension. The use of less than 0.2wt% abrasive particles (e.g., gamma-AlOOH particles) unexpectedly results in acceptable material removal rates in a batch CMP process, but provides a polished substrate with significantly reduced surface roughness compared to the use of higher amounts of abrasive particles. Furthermore, the use of lower amounts of said alumina particles allows to obtain the following aqueous suspensions: storage is highly stable, i.e., the pH changes to 0.1 or less after storage for more than 12 months, thus preventing, reducing or limiting the formation of undesirable reaction products that lead to reduced material removal rates and increased surface roughness during the polishing process. In addition, the use of these low amounts of abrasive particles avoids clogging the slurry distribution lines or filling the pores of the polishing pad, so that the polishing pad becomes too smooth, resulting in a significant reduction in the material removal rate.

In some embodiments, the abrasive particles (e.g., gamma-AlOOH particles) are present in a total amount of less than 0.18wt%, less than 0.15wt%, or less than 0.12wt%, in each case based on the total weight of the aqueous suspension. For example, the total amount of abrasive particles (e.g., gamma-AlOOH particles) may be 0.001 to 0.18wt%, 0.01 to 0.15wt%, or 0.08 to 0.12wt% in each case based on the total weight of the aqueous suspension.

In some embodiments, the aqueous suspension of the present disclosure contains aluminum nitrate. The use of aluminum nitrate allows avoiding pH variations, i.e. the pH of the aqueous suspensions of the present disclosure varies less than 0.1 after at least 12 months of storage of these suspensions. Since the material removal rate during CMP is observed to be a function of the pH of the polishing suspension, the stable pH of the aqueous suspension during the storage period of the polishing suspension allows for a uniform material removal rate. In addition, the stable pH of the aqueous suspension avoids the formation of undesirable reaction products, such as manganese dioxide, which form after pH shifts to higher pH values, because these reaction products result in reduced material removal rates and increased surface roughness of the substrate, thus reducing yields achieved with the stored aqueous suspension. Furthermore, without wishing to be bound by this theory, it is believed that aluminum nitrate forms a soft network of embedded abrasive particles, thus forming a "soft" layer on the particle surface, which results in improved surface roughness and reduced surface defects during polishing. Surprisingly, the formation of a "soft" layer on the abrasive particles does not result in a reduction in the material removal rate. Thus, the aqueous suspension has a high material removal rate and provides a polished substrate with excellent yield, i.e., low surface roughness or low surface defect levels, throughout its shelf life.

In some embodiments, the aluminum nitrate is present in a total amount of 0.05 to 3wt%, 0.1 to 2wt%, 0.2 to 1.5wt%, or 0.3 to 1wt%, based in each case on the total weight of the aqueous suspension. If the amount of aluminum nitrate is too low, undesirable pH variations of the aqueous suspension are observed after the storage time, while high amounts of aluminum nitrate result in defects (e.g., pits) on the substrate surface and undesirable increases in the substrate/pad interface temperature. Thus, in some embodiments, the aqueous suspension of the present disclosure contains aluminum nitrate in the aforementioned amounts. This allows to obtain a stable pH of the aqueous suspension during the storage time and a high yield without adversely affecting the material removal rate.

In some embodiments, the present disclosure is an aqueous suspension having a pH in the range of 2.0 to 5.0 and comprising one or more alkali metal permanganates, zirconia nanoparticles, alumina nanoparticles, one or more nitrates, and optionally a pH adjustor and/or a pH buffering agent. In some embodiments, the suspension and polishing pad can be an important component of the chemical mechanical planarization methods claimed in this disclosure. Which is also denoted as chemical mechanical planarization slurry or "CMP slurry". Some slurry components act chemically, for example by oxidizing the wafer surface to be polished, allowing mechanical action on the abrasive component, for example slurry, to more gently remove any non-uniformities from the wafer surface.

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

In some embodiments, the aqueous suspension includes one or more metal permanganate salts as a component. In some embodiments, the one or more metal permanganate salts include, for example, LiMnO ₄ 、KMnO ₄ And/or NaMnO ₄ 。

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

In some embodiments, there are at least two different metal permanganate salts selected from the group consisting of: sodium permanganate and potassium permanganate, wherein the amount of sodium permanganate exceeds the amount of potassium permanganate, wherein 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.

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

The metal permanganate can act as an oxidizing agent to promote oxidation of SiC bonds on the wafer surface 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.

In some embodiments, the metal permanganate salt is present in an amount in the range of 2.0 to 6.0wt%, 2.6 to 5.5wt%, 3.0 to 5.0wt%, or 4.0 to 5.0wt% (e.g., 4.2 to 4.8 wt%) based on the total weight of the suspension according to the present disclosure.

The aforementioned ranges apply whether only one type of metal permanganate salt or a mixture of metal permanganate salts is employed in the suspension according to the present disclosure. In some embodiments, the aforementioned ranges apply to potassium permanganate if, for example, potassium permanganate is used as the sole metal permanganate salt.

In some embodiments, if the amount of the metal permanganate is less than 2.0wt%, the material removal rate of the suspension in the CMP process is too low; and if the amount of the metal permanganate is more than 6.0wt%, the oxidizing ability is too strong, thus generating surface defects mainly due to etching-type mechanisms. If the amount of the metal permanganate is in the range of 3.0 to 5.0wt% or even more preferably 4.0 to 5.0wt%, a balance of properties and efficiency in the CMP process can be achieved. All of the aforementioned amounts are by total weight of the suspension according to the present disclosure.

In some embodiments, the aqueous suspension includes one or more types of zirconia nanoparticles as a component. In some embodiments, the zirconia nanoparticles include ZrO ₂ 。

Zirconia nanoparticles in the sense of the present disclosure are nanoparticles containing and consisting of at least one of the following: zirconia, such as zirconia (IV), zirconium hydroxide, hydrates of any of the foregoing zirconia species; and mixed metal species comprising and consisting of any of the aforementioned zirconia species and at least one other metal atom and/or oxide and/or hydroxide thereof and/or metal ion. The zirconia nanoparticles may exist in colloidal form. In some embodiments, the zirconia nanoparticle is a nanoparticle containing and consisting of at least one zirconia, such as zirconia (IV).

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

The zirconia nanoparticles can be prepared by any method known in the art. The aforementioned patent application describes the production of zirconia nanoparticles by generating zirconia sol using a hydrothermal process. The nanoparticles in such sols are aggregates of zirconia subunits and the measured Z-average particle size is the particle size of the aggregates.

Zirconia particles can be used in the suspensions of the present disclosure in more concentrated colloidal compositions to achieve the desired concentration as needed for the suspensions of the present disclosure.

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

In some embodiments, if the amount of zirconia nanoparticles is too high, the solution becomes more viscous. In addition, the pores of the polishing pad may "glaze" and become filled with particles and too smooth. In addition, particles can settle in solution, creating clogging problems in the pumped slurry distribution line. If the amount of zirconia nanoparticles is too low, there is insufficient mechanical grinding force, causing the material removal rate to drop to a level too low to be suitable. In some embodiments, within the scope of the present disclosure, there is a balance in material removal rates without observable settling problems or excessive viscosity. In some embodiments, the composition is a blend of two components: a balance of chemical and mechanical activities exists within the scope of one or more species of metal permanganate and one or more species of zirconia nanoparticles to produce sub-angstrom surface quality at low process temperature increases.

In some embodiments, the presence of zirconia nanoparticles in the suspension of the present disclosure creates "chemical tooth" functionality whereby the zirconia nanoparticles promote selective or catalytic enhancement of oxidation of silicon-carbon bonds by metal permanganate salts (e.g., potassium permanganate).

In some embodiments, the aqueous suspension includes one or more types of alumina nanoparticles as a component. In some embodiments, the alumina nanoparticles include colloidal alumina particles, such as gamma-AlOOH particles and/or gamma-Al particles ₂ O ₃ And (3) particles.

Alumina nanoparticles in the sense of the present disclosure may be nanoparticles containing and consisting of at least one of the following: alumina (e.g., alumina (III)), aluminum hydroxide, alumina hydroxide, hydrates of any of the foregoing alumina species; and mixed metal species comprising, e.g. consisting of, any of the aforementioned alumina species and at least one other metal atom and/or oxide and/or hydroxide thereof and/or metal ion. The alumina nanoparticles may exist in colloidal form or in amorphous form (e.g., polycrystalline amorphous form). Alpha-, beta-, or theta-alumina powders may also be used as alumina nanoparticles. In some embodiments, the alumina nanoparticle is a nanoparticle containing and consisting of at least one alumina, such as alumina (III).

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

The alumina nanoparticles can be prepared by any method known in the art.

The alumina particles may be used in the suspensions of the present disclosure in more concentrated compositions to achieve the desired concentration as needed for the suspensions of the present disclosure.

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

If the amount of alumina nanoparticles is too high, the solution may become too viscous and the particles may settle, creating a plugging problem in the pumped slurry distribution line. In such cases, a lower amount of alumina is selected. If the amount of alumina nanoparticles is too low, there is insufficient mechanical grinding force, causing the removal rate to drop too low to be applicable. At levels within the scope of the present disclosure, there is an equilibrium in material removal without observable settling problems, excessive viscosity, and polishing pad glazing.

In some embodiments, the presence of alumina nanoparticles allows for a reduced and thus effective CMP process temperature compared to a suspension without alumina nanoparticles.

In some embodiments, the aqueous suspension includes one or more nitrates as a component. In some embodiments, the one or more nitrates comprises Al (NO ₃ ) ₃ 。

The suspension according to the present disclosure contains 0.1 to 3.0wt% of one or more nitrates, 0.2 to 2.0wt% of one or more nitrates, or 0.5 to 1.5wt% (e.g., 0.5 to 1.0 wt%) of one or more nitrates. In some embodiments, the nitrate (e.g., one or more nitrates) may be selected from metal nitrates.

In some embodiments, the nitrate adjusts the pH of the suspension of the present disclosure. Thus, the nitrate salts to be used in the present disclosure are suitable for acidifying the aqueous suspension of the present disclosure.

Nitrates can be varied but still have the desired effect. Suitable nitrates are, for example, ammonium nitrate, alkali metal nitrates, alkaline earth metal nitrates, transition metal nitrates and nitrates of group 13 of the IUPAC periodic table of the elements. Among the nitrates mentioned in this 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 counter ion of the nitrate anion is in a high oxidation state, e.g., in the case of iron, in the 3+ state (i.e., as iron (III) nitrate). This is because iron (II) nitrate will immediately oxidize from permanganate resulting in the formation of iron (III) nitrate, but reducing the amount of permanganate that is undesirably reduced in the same reaction.

In some embodiments, the presence of metal cations and nitrate counter ions provides benefits in silicon carbide oxidation.

In some embodiments, the aqueous suspension includes one or more types of calcined alumina particles as a component. In some embodiments, the one or more types of calcined alumina particles comprise alumina that has been heated at a temperature in excess of 1000 ℃ to drive off chemically bound water.

Calcined alumina is alumina, particularly alumina such as alumina (III), which has been heated at temperatures in excess of 1000 ℃ to drive off chemically bound water. This term is known to those skilled in the art. Calcined alumina particles are present to further enhance mechanical abrasion to surfaces, such as chemically oxidized SiC surfaces.

In some embodiments, alpha alumina particles are used. In some embodiments, the calcined alumina particles have the following particle sizes: particle sizes of particles larger than the component comprising zirconia nanoparticles and alumina nanoparticles are, for example, in the range of 0.5 μm to 5 μm. In this regard, the particle size is the average particle size and is determined via laser diffraction according to ISO 13320:2020-01.

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

In some embodiments, if the amount of calcined alumina particles is too high, the particles may agglomerate and form an unstable slurry. In some embodiments, if the amount of calcined alumina particles is too low, the suspension may not provide sufficient mechanical abrasion.

In some embodiments, the aqueous suspension includes one or more metal chlorate salts as a component. In some embodiments, the one or more metal chlorate salts comprise NaClO ₃ 。

In some embodiments, the one or more metal chlorate salts are selected from alkali metal chlorate salts and non-transition metal chlorate salts, 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.

In some embodiments, the one or more metal chlorate salts are present in an amount ranging from 0.1 to 2.0 wt.%, from 0.1 to 1.0 wt.%, from 0.2 to 0.5 wt.%, based in each case on the total weight of the aqueous suspension.

In some embodiments, if the amount of one or more metal chlorate salts 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 chlorate salts is too low, the suspension may not provide a sufficient material removal rate.

The aqueous suspension comprises one or more metal perchlorate salts as a component. In some embodiments, the one or more metal perchlorate salts include Al (ClO) ₄ ) ₃ 。

In some embodiments, the one or more metal perchlorate salts are selected from alkali metal perchlorate salts and non-transition metal perchlorate salts, such as from the group consisting of lithium perchlorate, sodium perchlorate, potassium perchlorate, aluminum perchlorate, and mixtures thereof, such as from the group consisting of sodium perchlorate, potassium perchlorate, aluminum perchlorate, and mixtures thereof.

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

In some embodiments, if the amount of the one or more metal perchlorate salts 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 perchlorate salts is too low, the suspension may not provide a sufficient material removal rate.

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

In some embodiments, the aqueous suspension of the present disclosure has a pH 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, e.g., in the range of 3.2 to 3.8, at 23 ℃. In some embodiments, the aqueous suspension of the present disclosure may have a pH in the range of 3.0 to 5.5, 3.5 to 5.0, or 4.0 to 5.0 at 23 ℃. In some embodiments, the aqueous suspension of the present disclosure has a pH of 2 to 5, 3 to 4, or 3.4 to 4 at 23 ℃.

The pH of the suspension according to the present disclosure may be achieved and/or maintained by any suitable means. More specifically, the suspension may further include a pH adjustor, a pH buffering agent, or a combination thereof. As used in this specification, the terms pH adjustor and pH buffering agent do not encompass the essential components of the suspension of the present disclosure, but the essential components may have an effect on pH. Thus, the pH adjuster and pH buffer are clearly different from the other components of the suspension of the present disclosure described under other headings. Thus, the pH adjustor and the pH buffering agent are also particularly different from the nitrate as described herein.

The pH adjusting agent can comprise (e.g., consist of, consist essentially of, or consist of) any suitable pH adjusting compound. In some embodiments, the above-mentioned nitrates have been used to adjust the pH to within a desired range. However, in some cases, it may be desirable to further adjust the pH by using a separate pH adjuster other than nitrate. For example, the pH adjuster may be any suitable acid. In some embodiments, the pH adjuster is a mineral acid. In some embodiments, the acid is nitric acid.

The pH buffer, if present, may be any suitable buffer, including inorganic pH buffers, such as phosphates, borates, and the like. In some embodiments, no pH buffer is present in the suspension of the present disclosure.

The suspensions according to the present disclosure may include any suitable amount of pH adjusting agent and/or pH buffering agent, provided that such amount is sufficient to achieve and/or maintain the desired pH value of the suspension, e.g., within the ranges as set forth herein.

The suspensions of the present disclosure may include other optional ingredients. In some embodiments, the suspension of the present disclosure is free of other ingredients. Thus, the suspensions of the present disclosure may include (e.g., consist essentially of or consist of) one or more metal permanganate salts, zirconia nanoparticles, alumina nanoparticles, one or more nitrates, water, and optionally one or more of a pH adjusting agent and/or a pH buffer. Of course, the undesired and unavoidable impurities present in the aforementioned ingredients may be present in a suspension comprising, consisting essentially of, or consisting of the aforementioned ingredients. Such impurities (which are not considered herein as other optional ingredients, but are considered unavoidable and undesired impurities) may be present in an amount of less than 0.005wt%, less than 0.002wt% or less than 0.001wt%, based on the weight of the suspension of the present disclosure.

In some embodiments, the suspensions of the present disclosure may include other optional components (optional ingredients). In some embodiments, the suspension of the present disclosure is free of other ingredients. Thus, in some embodiments, the suspension of the present disclosure consists of (or consists essentially of): one or more metal salts of permanganate, one or more types of zirconia nanoparticles, one or more types of alumina nanoparticles, one or more nitrates, one or more types of calcined alumina particles, one or more metal salts of chlorate and one or more metal salts of perchlorate, water, and optionally one or more of a pH adjusting agent and/or a pH buffer.

In some embodiments, the suspension of the present disclosure can include (e.g., comprise, consist essentially of, or consist of) at least one oxidizing agent, a total amount of less than 0.2wt% abrasive particles, aluminum nitrate, water, and optionally at least one pH adjustor and/or at least one pH buffering agent. The mohs hardness of all abrasive particles present in the suspension of the present disclosure is less than 6. Of course, the undesired and unavoidable impurities present in the aforementioned ingredients may be present in a suspension comprising, consisting essentially of, or consisting of the aforementioned ingredients. Such impurities (which are not considered herein as other optional ingredients, but are considered unavoidable and undesired impurities) may be present in an amount of less than 0.005wt%, less than 0.002wt% or less than 0.001wt%, based on the weight of the suspension of the present disclosure.

However, other ingredients may also be intentionally added to the suspension as previously mentioned. In some embodiments, such other ingredients may need to be inert, i.e., non-reactive with the reactive ingredients of the suspension (e.g., with the one or more metal permanganates in the suspension).

Thus, where other ingredients are contained in the suspensions of the present disclosure, in some embodiments, such ingredients may have inorganic properties, as organic compounds (e.g., organic surfactants, organic defoamers, or organic solvents) will be degraded by the ingredients (e.g., at least one oxidizing agent, one or more metal permanganate salts, one or more metal chlorate salts, and/or one or more metal perchlorate salts) in the oxidation process, and thus are excluded from the suspensions of the present disclosure in some embodiments.

In some embodiments, if other optional ingredients are present, the other ingredients may be inorganic ingredients and may be present in an amount of 0.005 to 1wt%, 0.005 to 1.5wt%, 0.005 to 1wt%, or 0.005 to 0.5wt%, based on the weight of the suspension of the present disclosure.

In some embodiments, the aqueous suspension is free of certain components. For example, in some embodiments, the aqueous suspension is absent MnO ₂ Germanium particles and/or cerium oxide particles.

In some embodiments, the sum of the components of the aqueous suspension (e.g., permanganate, zirconia nanoparticles, alumina nanoparticles, and nitrate) comprises at least 90wt%, at least 95wt%, or at least 98wt% of all components of the suspension of the present disclosure except for water, pH adjuster, and pH buffer. In some embodiments, the only components of the suspension of the present disclosure are, consist of, or consist essentially of one or more permanganates, zirconia nanoparticles, alumina nanoparticles, one or more nitrates, water, and pH adjusting agents and pH buffers.

In some embodiments, the components of the aqueous suspension (e.g., including the ingredients: one or more metal salts of permanganate, one or more types of zirconia nanoparticles, one or more types of alumina nanoparticles, one or more nitrates, one or more types of calcined alumina particles, one or more metal salts of chlorate and one or more metal salts of perchlorate) together comprise at least 90wt%, at least 95wt% and at least 98wt% of all components of the suspension of the disclosure except water, pH adjustor and pH buffering agent. In some embodiments, the only components of the suspensions of the present disclosure are the following: one or more metal salts of permanganic acid, one or more types of zirconia nanoparticles, one or more types of alumina nanoparticles, one or more nitrates, one or more types of calcined alumina particles, one or more metal salts of chloric acid and one or more metal salts of perchloric acid, water and pH adjusting agents and pH buffers; the suspension thus consists of these components.

In some embodiments, the components of the aqueous suspension (e.g., at least one oxidizing agent; a total amount of less than 0.2 wt.% abrasive particles, wherein the abrasive particles have a Mohs hardness of less than 6; and aluminum nitrate) together comprise at least 90 wt.%, at least 95 wt.%, or at least 98 wt.% of all components of the suspension of the disclosure except water, pH adjustor, and pH buffering agent, based on the total weight of the aqueous suspension. In some embodiments, the only components of the suspension of the present disclosure are: at least one oxidizing agent; less than 0.2wt% total abrasive particles, based on the total weight of the aqueous suspension, wherein the abrasive particles have a mohs hardness of less than 6; and aluminum nitrate; water; and a pH adjustor and a pH buffering agent; the suspension thus consists of these components.

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

In some embodiments, the aqueous suspension may include (e.g., comprise, consist essentially of, or consist of) 2.6 to 5.5 wt.% of one or more metal permanganate salts, 0.1 to 2.0 wt.% zirconia nanoparticles, 0.1 to 2.0 wt.% alumina nanoparticles, and 0.2 to 2.0 wt.% of one or more nitrates, water, and an inorganic acid for adjusting pH, the weight percentages being based on the total weight of the aqueous suspension.

In some embodiments, an aqueous suspension according to the present disclosure may include (e.g., comprise, consist essentially of, or consist of) 3.0 to 5.0wt% of one or more metal permanganate salts, 0.15 to 1.0wt% zirconia nanoparticles, 0.15 to 1.0wt% alumina nanoparticles, and 0.5 to 1.5wt% of one or more nitrates, the weight percentages being based on the total weight of the aqueous suspension.

In some embodiments, an aqueous suspension according to the present disclosure may include (e.g., comprise, consist essentially of, or consist of) 4.0 to 5.0wt% of one or more metal permanganate salts, 0.15 to 0.5wt% zirconia nanoparticles, 0.15 to 0.5wt% alumina nanoparticles, and 0.5 to 1.0wt% of one or more nitrates, the weight percentages being based on the total weight of the aqueous suspension.

In some embodiments, the one or more metal permanganate salts are, for example, potassium permanganate, and/or the mineral acid used to adjust the pH is nitric acid.

Furthermore, in some embodiments, the pH of the suspension is in the range of 3.0 to 4.0, such as 3.2 to 3.8.

In some embodiments, the aqueous suspension of the present disclosure comprises, consists essentially of, or consists of: one or more metal permanganate salts in an amount in the range from 7.5 to 30 wt.%, from 10 to 25 wt.%, from 12 to 22 wt.%, for example from 13 to 20 wt.%, based in each case on the total weight of the aqueous suspension; one or more kinds of zirconia nanoparticles in an amount ranging from 0.05 to 5.0wt%, from 0.10 to 2.0wt%, from 0.15 to 1.0wt%, for example from 0.15 to 0.5wt%; one or more kinds of alumina nanoparticles in an amount ranging from 0.05 to 5.0wt%, from 0.10 to 2.0wt%, from 0.15 to 1.0wt%, for example from 0.15 to 0.5wt%; one or more kinds of calcined alumina particles in an amount in the range of 0.1 to 5.0wt%, 0.1 to 2.0wt%, for example 0.1 to 1.0wt%; one or more metal chlorate salts in an amount in the range of 0.1 to 2.0wt%, 0.1 to 1.0wt%, 0.2 to 1.0wt%, e.g. 0.2 to 0.5wt%; one or more metal perchlorate salts in an amount in the range from 0.1 to 2.0 wt.%, from 0.1 to 1.0 wt.%, from 0.2 to 1.0 wt.%, for example from 0.2 to 0.5 wt.%; water; and optionally a mineral acid, such as nitric acid, for adjusting the pH to a range of 3.0 to 5.5, 3.5 to 5.0 or 4.0 to 5.0.

In some embodiments, the aqueous suspension may include (e.g., comprise, consist essentially of, or consist of) 1 to 8wt% of at least one oxidizing agent, 0.001 to 0.18wt% alumina particles, 0.05 to 3wt% aluminum nitrate, water, and optionally an inorganic acid for the pH, the weight percentages being based on the total weight of the aqueous suspension, and the particles (e.g., all particles) present in the suspension have a mohs hardness of less than 6.

In some embodiments, the aqueous suspension may include (e.g., comprise, consist essentially of, or consist of) 2 to 6 weight percent of at least one oxidizing agent, 0.01 to 0.15 weight percent alumina particles, and 0.1 to 2 weight percent aluminum nitrate, water, and optionally an inorganic acid for adjusting pH, the weight percentages being based on the total weight of the aqueous suspension, and the particles (e.g., all particles) present in the suspension having a mohs hardness of less than 6.

In some embodiments, the aqueous suspension may include (e.g., comprise, consist essentially of, or consist of) 3 to 5.5 wt.% of at least one oxidizing agent, 0.08 to 0.12 wt.% alumina particles, and 0.2 to 1.5 wt.% aluminum nitrate, the weight percentages being based on the total weight of the aqueous suspension, and the particles (e.g., all particles) present in the suspension each have a mohs hardness of less than 6.

In some embodiments, the aqueous suspension may include (e.g., comprise, consist essentially of, or consist of) 4 to 5 weight percent of at least one oxidizing agent, 0.1 weight percent alumina particles, and 0.3 to 1.0 weight percent aluminum nitrate, the weight percentages being based on the total weight of the aqueous suspension, and the particles (e.g., all particles) present in the suspension having a mohs hardness of less than 6.

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

Furthermore, in some embodiments, the pH of the suspension is in the range of 3 to 4, such as 3.4 to 4.

In some embodiments, exemplary embodiments of the aqueous suspensions of the present disclosure exhibit excellent pH stability (i.e., pH variation less than 0.1 over a period of at least 12 months) and high material removal rates, but lower amounts of abrasive particles and excellent surface roughness of the polished substrate during their shelf life. In addition, lower amounts of abrasive particles can be stably suspended in the aqueous carrier without the use of surfactants or dispersants, thus avoiding the negative impact of such surfactants or dispersants on the polishing process. In the case of sedimentation, the abrasive particles can be easily resuspended by shaking or stirring the suspension prior to use, thus preventing, reducing or limiting clogging problems in the recycle line and ensuring uniform suspension and material removal rates during polishing.

In some embodiments, the pot life of the aqueous suspension is more than seven days, more than ten days, more than twelve days, or more than fourteen days.

The aqueous suspension of the present disclosure may be a chemical mechanical polishing suspension. In some embodiments, the aqueous suspension of the present disclosure may be a chemical mechanical polishing suspension adapted for batch-type and/or single-type chemical mechanical polishing processes. Surprisingly, the suspensions of the present disclosure produce high material removal rates and excellent surface roughness of polished substrates in batch-type as well as single-type CMP processes, despite the different process conditions used in these processes.

Suitable substrates to be polished include ceramic materials, metals, metal alloys or diamond. In some embodiments, the substrate may be a group III-V compound, such as gallium nitride, aluminum nitride, indium aluminum nitride, thallium nitride, gallium arsenide, indium gallium arsenide, gallium phosphide, indium antimonide, indium arsenide, boron arsenide, or aluminum arsenide. In some embodiments, the substrate may 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 adapted for chemical mechanical polishing of a substrate comprising at least one layer of silicon carbide. Silicon carbide may be monocrystalline or polycrystalline. In some embodiments, the substrate includes at least one layer of single crystal silicon carbide, such as single crystal 4H silicon carbide (i.e., 4H-SiC).

In some embodiments, the aqueous suspension of the present disclosure may be adapted to polish a substrate (e.g., silicon carbide) at a material removal rate of at least 1.5 μm/h, at least 2 μm/h, 2.5 to 12 μm/h, or 2.5 to 9 μm/h. In general, a higher material removal rate is achieved in a single wafer CMP process compared to a batch type CMP process because the fluctuating polishing conditions that have been previously mentioned occur in a batch type CMP process. The material removal rate can be determined by the change in substrate mass before and after polishing using the following equation:

wherein the method comprises the steps of

Δm is the change in substrate mass before and after polishing,

ρ _substrate in order to achieve the density of the substrate,

r is the radius of the substrate and,

t is the polishing time.

The mass change of the substrate before and after divided by the time taken for polishing calculates the material removal rate. The mass of the substrate can be measured using a table balance.

In some embodiments, after polishing a substrate (e.g., a silicon carbide substrate) with an aqueous suspension of the present disclosure, the surface roughness is less than 0.6nm, e.g., 0.3nm. Roughness can be calculated as RMS roughness by AFM metrology (5 x 5 scan, 1Hz scan rate). This level of roughness is considered generally desirable and acceptable for downstream substrate processing involving surface epitaxy, such as Chemical Vapor Deposition (CVD). Without wishing to be bound by this theory, it is believed that the low surface roughness achieved with the aqueous suspension of the present disclosure is due to the use of aluminum nitrate, which causes the formation of a network of embedded abrasive particles. The embedding causes the formation of a "soft" layer on the particle surface that prevents, reduces, or limits damage to the substrate surface during polishing without adversely affecting the high material removal rate.

The suspension according to the present disclosure may be supplied as a one-component system comprising water, at least one oxidizing agent, less than 0.2 wt.% (based on the total weight of the suspension) of abrasive particles, aluminum nitrate, and optionally other ingredients previously mentioned. Such one-component systems are ready-to-use suspensions. In some embodiments, the suspensions of the present disclosure are provided in the form of a one-component system, as such suspensions are highly storage stable, i.e., they exhibit no pH fluctuations and no sedimentation of the abrasive particles, and can be readily used without further mixing and/or dilution steps. The preparation of such one-component systems may be performed as described for the preparation of aqueous suspensions in connection with the present disclosure.

Alternatively, some of the components (e.g., at least one oxidizing agent) may be supplied in a first container in dry form or in aqueous solution, and the remaining components (e.g., abrasive particles and aluminum nitrate) may be supplied in a second container or multiple other containers. Other two containers or three or more container combinations of components of a suspension according to the present disclosure are within the knowledge of one of ordinary skill in the art. The solid components (e.g., abrasive particles) may be placed in one or more containers in dry form or in the form of a colloidal solution. Furthermore, the components in the first, second or other containers may be adapted to have different pH values, or to have substantially similar or even equal pH values. The components of a suspension according to the present disclosure may be supplied partially or completely separately from each other and may be combined shortly before use (e.g., 1 week or less before use, 1 day or less before use, 1 hour or less before use, 10 minutes or less before use, or 1 minute or less before use), for example by an end user.

Suspensions according to the present disclosure may also be provided in the form of concentrates which may be diluted with an appropriate amount of water prior to use. In such embodiments, the suspension concentrate can include water, at least one oxidizing agent, abrasive particles, aluminum nitrate, and optionally other components as discussed in this disclosure, in amounts such that upon dilution of the concentrate with an appropriate amount of water, each component will be present in the desired suspension in an amount within the appropriate ranges, e.g., as described herein for each component. For example, the components may be present in the concentrate in an amount about 1.5 times, e.g., about 2 times or more, higher than the concentrations recited above for the components in the aqueous suspension. After dilution of the concentrate with an appropriate amount of water, the components will be present in the resulting aqueous suspension in amounts within the ranges set forth above for the components. Furthermore, as will be appreciated by one of ordinary skill in the art, the concentrate may contain an appropriate fraction of water present in the final suspension to ensure that the other components of the suspension are at least partially or fully dissolved or suspended in the concentrate. Concentrates may be prepared by using higher amounts of the components as described herein with respect to the present disclosure for preparing aqueous suspensions.

However, the aqueous suspensions of the present disclosure have been highly storage stable under typical storage conditions because the use of aluminum nitrate prevents, reduces or limits pH fluctuations after storage and thus prevents, reduces or limits the formation of undesirable reaction products (e.g., manganese dioxide) that lead to reduced material removal rates and increased surface roughness. Even after weeks or months of storage, slight settling of the solid particles may occur, which settling may be easily redispersed by agitation (e.g., stirring and/or shaking). Thus, in some embodiments, the aqueous suspension of the present disclosure is supplied in the form of a one-component system as previously described.

It may be beneficial to reduce the pH of the aqueous suspension to 2 to 2.5 with nitric acid shortly before its use (measured at 23 ℃) to increase the oxidizing capacity of the at least one oxidizing agent to ensure a high material removal rate during polishing.

In some embodiments, the suspensions of the present disclosure may be supplied in a single package system comprising water, one or more permanganates, alumina nanoparticles, zirconia nanoparticles, and one or more nitrates, and optionally other ingredients previously mentioned. Such single package systems are ready-to-use suspensions. In some embodiments, the suspensions of the present disclosure may be in the form of a single package system, as the compositions as such are storage stable and may be readily used without further mixing and/or dilution steps. Thus, in some embodiments, it may be appropriate to first dissolve one or more permanganates and replenish the solution with other ingredients to obtain a single package system.

In some embodiments, alternatively or additionally, some components (e.g., one or more permanganates) may be supplied in a first container in dry form or in water, and the remaining components (e.g., alumina nanoparticles, zirconia nanoparticles, and one or more nitrates) may be supplied in a second container or multiple other containers. The other two containers or three or more container combinations of components of the suspension are part of the present disclosure. The solid components (e.g., alumina nanoparticles, zirconia nanoparticles) may be placed in one or more containers in dry form or in the form of a colloidal solution. Furthermore, the components in the first, second or other containers may be adapted to have different pH values, or to have substantially similar or even equal pH values. The components of the suspension may be supplied partially or completely separately from each other and may be combined shortly before use (e.g., 1 week or less before use, 1 day or less before use, 1 hour or less before use, 10 minutes or less before use, or 1 minute or less before use), for example by the end user.

However, the instant suspensions of the present disclosure are already highly storage stable under typical storage conditions. Even after weeks or months of storage, slight settling of the solid particles may occur, which settling may be easily redispersed by agitation (e.g., stirring and/or shaking). Thus, it is not necessary for the customer to mix the components just prior to use.

In some embodiments, the suspensions of the present disclosure may also be provided in the form of a concentrate intended to be diluted with an appropriate amount of water prior to use. The suspension concentrate may include water and optionally other components in amounts such that, upon dilution of the concentrate with an appropriate amount of water, each component will be present in the desired suspension in an amount within the appropriate ranges recited above for each component. For example, the components can be present in the concentrate in an amount that is about 1.5 times, e.g., about 2 times or more, higher than the concentration recited above for the components in the polishing composition, such that when the concentrate is diluted with an appropriate volume of water, the components will be present in the final suspension in amounts within the ranges set forth above for the components. Furthermore, as will be appreciated by one of ordinary skill in the art, the concentrate may contain an appropriate fraction of water present in the final suspension in order to ensure that the other components of the suspension are at least partially or fully dissolved or suspended in the concentrate.

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 permanganate salts to the aqueous suspension, wherein the aqueous suspension comprises alumina nanoparticles and zirconia particles in water. In some embodiments, the method includes filtering the aqueous suspension prior to adding the aluminum nitrate. In some embodiments, the method includes filtering the aqueous solution of one or more metal permanganate salts prior to adding the aqueous solution. In some embodiments, the aqueous suspension is free of MnO ₂ . In some embodiments, the aqueous suspension has a pH in the range of 2 to 5 at 23 ℃. In some embodiments, step (i) of adding aluminum nitrate and step (ii) of adding an aqueous solution are performed sequentially. The method steps of the present disclosure may be rearranged and the order of the steps changed. For example, the first step may be step (ii), and the aqueous solution may be added to the aqueous suspension first. This is not an exhaustive list of the order of the method steps. The steps may be rearranged in any order.

In some embodiments, a method for preparing an aqueous suspension comprises: (i) adding aluminum nitrate to the aqueous suspension; (ii) One or more metal permanganate salts, aAdding an aqueous solution of one or more metal perchlorate salts and one or more metal chlorate salts to an aqueous suspension; and (iii) adding one or more types of calcined alumina particles to the aqueous suspension, wherein the aqueous suspension comprises alumina nanoparticles and zirconia particles. In some embodiments, the method includes filtering the aqueous suspension prior to adding the aluminum nitrate. In some embodiments, the method comprises filtering the aqueous solution prior to adding the aqueous solution. In some embodiments, the aqueous suspension is free of MnO ₂ . In some embodiments, the aqueous suspension has a pH in the range of 2 to 5 at 23 ℃. In some embodiments, step (i) of adding aluminum nitrate, step (ii) of adding an aqueous solution, and step (iii) of adding one or more kinds of calcined alumina particles are performed sequentially. The method steps of the present disclosure may be rearranged and the order of the steps changed. For example, the first step may be step (ii), wherein the aqueous solution may be added to the aqueous suspension first, followed by step (iii) and then step (i). In some examples, step (iii) may be followed by step (ii) and then step (i) first. This is not an exhaustive list of the order of the method steps. The steps (e.g., step (iii), step (i) and then step (ii)) may be rearranged in any order.

In some embodiments, the present disclosure includes a method for preparing an aqueous suspension comprising (i) adding aluminum nitrate to the 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 includes abrasive particles. In some embodiments, the abrasive particles have a mohs hardness of less than 6. In some embodiments, the aqueous suspension contains less than 0.2 wt.% abrasive particles, based on the total weight of the aqueous suspension. In some embodiments, the method includes filtering the aqueous suspension prior to adding the aluminum nitrate. In some embodiments, the method comprises filtering the aqueous solution prior to adding the aqueous solution. In some embodiments, the aqueous suspension is free of MnO ₂ . In some embodiments, the aqueous suspension has a pH in the range of 2 to 5 at 23 ℃. In some embodiments, step (i) of adding aluminum nitrate and adding water are performed sequentiallyStep (ii) of the solution. The method steps of the present disclosure may be rearranged and the order of the steps changed. For example, the first step may be step (ii), wherein an aqueous solution may first be added to the aqueous suspension; step (i) follows. This is not an exhaustive list of the order of the method steps. The steps may be rearranged in any order.

Another object of the present disclosure is a process for preparing an Aqueous Suspension (AS) having a pH value of 2 to 5 at 23 ℃, comprising:

(A) Providing an Aqueous Suspension (ASP) of abrasive particles, wherein all abrasive particles 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) produced after step (C) with at least one pH-adjusting agent

In some embodiments, the Aqueous Suspension (AS) produced by the present disclosure contains less than 0.2wt% abrasive particles, based on the total weight of the aqueous suspension. Thus, the amount of abrasive particles present in the aqueous suspension provided in step (a) is selected such that the aqueous suspension produced by the method of the present disclosure contains less than 0.2wt% abrasive particles. This may be accomplished by considering the amount of water present in the aqueous oxidant solution used in step (C), or by diluting the aqueous suspension resulting from step (C) or (D) with water as described herein.

Step (A):

in step (a) of the present disclosure, an aqueous suspension of abrasive particles is provided. This may include: the dry powder of abrasive particles is mixed with a suitable amount of water to prepare an aqueous suspension, and the commercial aqueous suspension of abrasive particles is diluted with a suitable amount of water, or the commercial suspension of abrasive particles is used. The suspension may be filtered prior to step (B) to avoid the presence of larger agglomerates, as these may lead to scratching of the substrate during polishing, thus increasing the surface roughness and thus reducing the quality of the polished product. In some embodiments, step (a) comprises 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 a dry alumina powder with water, and filtering the resulting suspension. Suitable abrasive particles useful in step (a) of the methods of the present disclosure include the abrasive particles described herein with respect to the aqueous suspensions of the present disclosure.

The aqueous suspension provided in step (a) may comprise a total amount of from 0.1 to 3 wt.% (e.g. from 0.2 to 1 wt.%) of abrasive particles, based in each case on the total amount of the aqueous suspension provided in step (a).

Step (B):

in step (B) of the present disclosure, aluminum nitrate is added to the aqueous suspension of abrasive particles provided in step (a). The addition of aluminum nitrate causes an increase in the viscosity of the aqueous suspension provided in step (a), which indicates the formation of a network of embedded abrasive particles.

The amount of aluminium nitrate added in step (B) may be in each case 0.5 to 5wt%, for example 1 to 3wt%, based on the total amount of Aqueous Suspension (ASP). These amounts ensure that a sufficient amount of network is formed so that the abrasive particles are fully covered with the soft layer and stably suspended in the aqueous carrier. Furthermore, these amounts ensure that pH fluctuations of the aqueous suspension prepared by the disclosed method after storage are prevented, reduced or limited and thus undesired reaction products (e.g., manganese dioxide) are formed, as the reaction products reduce the material removal rate and increase the surface roughness.

Step (C):

in step (C) of the disclosed method, an aqueous solution of at least one oxidizing agent is added to the mixture obtained after step (B). This solution can be prepared by: a suitable amount of an oxidizing agent (e.g., a water-soluble oxidizing agent) is added to a suitable amount of water, or by diluting a concentrated aqueous solution of the oxidizing agent with water to obtain a desired concentration of the oxidizing agent in the aqueous solution. In some embodiments, the aqueous solution of the obtained oxidizing agent may be filtered before adding the aqueous solution to the mixture obtained in step (B) to avoid the presence of undissolved oxidizing agent particles, as these particles may cause scratching of the substrate during polishing, thus increasing the surface roughness and thus reducing the quality of the polished product. Suitable oxidizing agents have been previously described with respect to the aqueous suspensions of the present disclosure. In some embodiments, an aqueous solution of potassium permanganate is used in step (C).

The aqueous solution added in step (C) may comprise a total amount of 1 to 10 wt.% (e.g. 3 to 6 wt.%) of at least one oxidizing agent, based in each case on the total amount of the aqueous solution added in step (C).

Optional step (D):

in optional step (D), the pH of the aqueous suspension resulting from step (C) is adjusted with at least one pH adjusting agent. In some embodiments, the use of an appropriate amount of aluminum nitrate already provides an aqueous suspension having the desired pH after step (C), without the need and without the use of optional step (D).

Other step (E):

the method of the present disclosure may include at least one other step (E). In a first alternative of this step, the aqueous suspension obtained after step (C) is diluted with water before carrying out step (D). In a second alternative of this step, the aqueous suspension obtained after step (D) is diluted with water. In some embodiments, the additional step (E) may be beneficial to ensure that the total amount of abrasive particles in the aqueous suspension prepared by the disclosed method is less than 0.2wt% based on the total weight of the aqueous suspension prepared.

The details of what has been described with respect to the aqueous suspensions of the present disclosure, particularly with respect to the components of the aqueous suspensions, apply mutatis mutandis to other embodiments of the method for preparing an aqueous suspension.

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

In some embodiments, the methods of the present disclosure include storing an aqueous suspension (e.g., an aqueous suspension of the present disclosure) 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 an aqueous suspension having a pH in the range of 2 to 2.5 over fourteen days. In some embodiments, storing the aqueous suspension comprises storing the aqueous suspension for at least 1 year.

In some embodiments, lowering the pH of the initial aqueous suspension includes adding an acid. The acid may comprise nitric acid. In some embodiments, reducing the pH of the initial aqueous suspension to a range of 2 to 2.5 comprises reducing the pH of the initial aqueous suspension to 2.3. In some embodiments, using the reduced aqueous suspension includes using the reduced aqueous suspension in a single-type chemical mechanical planarization process and/or a batch-type chemical mechanical planarization process.

The present disclosure further provides a method of chemically-mechanically planarizing a substrate (i.e., a CMP method) comprising contacting a substrate (e.g., a silicon carbide surface, such as a silicon carbide wafer surface) with an aqueous suspension according to the present disclosure; moving the aqueous suspension relative to the substrate by means of a polishing pad; and grinding at least a portion of the substrate to polish and/or planarize the substrate. In some embodiments, during polishing, the substrate does not exceed a temperature of 60 ℃, 59 ℃, 58 ℃, 57 ℃, 56 ℃, 55 ℃, 54 ℃, 53 ℃, 52 ℃, 51 ℃, 50 ℃, or any intermediate number (e.g., 56.3 ℃).

CMP methods according to the present disclosure may be used in conjunction with Chemical Mechanical Polishing (CMP) apparatus/tools/devices. Any of the commonly known CMP apparatuses, including those from suppliers such as application materials (Applied Materials), revasum Su M (Revasum), chongshuo technology (Axus), ramasto waltts (Lapmaster Wolters), and ibara (Ibarra), which are common in the industry, may be used in the CMP methods of the present disclosure.

The apparatus may include: a platen which is in motion when in use and has a velocity resulting from orbital, linear or circular motion; a polishing pad in contact with the platen and moving with the platen when in motion; and a carrier holding a substrate to be polished by contacting and moving relative to a surface of the polishing pad. Polishing of a substrate occurs by placing the substrate in contact with a polishing pad and a suspension of the present disclosure (which is typically disposed between the substrate and the polishing pad), wherein the polishing pad moves relative to the substrate to abrade at least a portion of the substrate to polish and/or planarize the substrate.

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, which 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 previously described with respect to the determination of the material removal rate. Polishing refers to removing at least a portion of the surface to polish the surface. Polishing may be performed to provide a surface with reduced surface roughness by removing grooves, crates, pits, etc., but polishing may also be performed to introduce or restore a surface geometry characterized by the intersection of flat sections. The methods of the present disclosure may be used to polish and/or planarize any suitable substrate, such as those comprising at least one layer of silicon carbide.

In some embodiments, the method includes reducing the pH of the aqueous suspension to a range of 2 to 2.5 prior to contacting the substrate with the aqueous suspension. The reducing step may include adding an acid. The pot life of an aqueous suspension is the pot life of the aqueous suspension after the aqueous suspension has been reduced to a pH range of, for example, 2 to 2.5. As may be described herein, the shelf life of the aqueous suspension may be greater than one year.

In some embodiments, the aqueous suspension will be lowered (e.g., acid added to the aqueous suspension) shortly before use after storing the aqueous suspension up to and greater than one year. After lowering the aqueous suspension, the aqueous suspension will have a working life after which the aqueous suspension may not be used for its intended purpose. The working life of an aqueous suspension is called pot life. In some embodiments, the pot life may be at least five, seven, ten, twelve, or fourteen days. To ensure that the aqueous suspension is used during the pot life, in some embodiments, the methods of the present disclosure include contacting the substrate with the lowered aqueous suspension within a set timeframe of the lowering step. For example, the method comprises contacting the substrate with the reduced aqueous suspension for five, seven, ten, twelve, or fourteen days of the reducing step. This ensures that the reduced aqueous suspension contacts the substrate during the pot life.

The suspension in combination with the polishing pad is an integral component of the chemical mechanical planarization method as claimed in this disclosure. In some embodiments, the type and materials of polishing pad to be used in the CMP methods of the present disclosure are not critical to the present disclosure. Almost any conventionally used polishing pad used in CMP methods for planarizing silicon carbide wafers may be used. Suitable polishing pads include, for example, woven and non-woven polishing pads. Further, suitable polishing pads can comprise any suitable polymer having different densities, hardness, thickness, compressibility, ability to rebound upon compression, and compression modulus. Suitable polymers include, for example, polyvinyl chloride, polyvinyl fluoride, nylon, fluorocarbon, polycarbonate, polyester, polyacrylate, polyether, polyethylene, polyamide, polyurethane, polystyrene, polypropylene, acceptable products thereof, and mixtures thereof. In some embodiments, polyurethane pads may be used. Conventional pads may be prepared one at a time or in the form of a cake (which is then diced into individual pad substrates). These substrates are then machined to a final thickness and the trenches are further machined thereto. The polymer or polymer/fiber circular pad may be 1mm to 4mm thick. The polishing pad can have any suitable configuration. For example, the polishing pad can be circular and, in use, will have rotational motion about an axis perpendicular to the plane defined by the pad surface. The polishing pad can be cylindrical with a surface that acts as a polishing surface and, in use, can have a rotational motion about the central axis of the cylinder. The polishing pad can be in the form of an endless belt that, in use, can have a linear motion relative to the cutting edge being polished. The polishing pad can have any suitable shape and, in use, has a reciprocating or orbital motion along a plane or semicircle. Many other variations will be apparent to those skilled in the art.

Conventional polymer-based CMP polishing pads typically use a pressure sensitive adhesive to adhere to a flat rotating circular table within the CMP machine.

The substrate to be polished using the CMP methods of the present disclosure can be any suitable substrate, such as those comprising at least one layer of silicon carbide. Suitable substrates include, but are not limited to, flat panel displays, integrated circuits, memory or rigid disks, metals, inter-layer dielectric (ILD) devices, semiconductors, microelectromechanical systems, ferroelectrics, and magnetic heads. The silicon carbide can comprise, consist essentially of, or consist of any suitable silicon carbide, many of which are known in the art. For example, the substrate may be a silicon carbide substrate. Silicon carbide may be monocrystalline or polycrystalline. As has been explained above, silicon carbide has many different types of crystal structures, each with its own different set of electronic properties. However, only a few of these polytypes may be reproducible in a form acceptable for use as a semiconductor. Such polytypes may be cubic (e.g., 3C silicon carbide) or non-cubic (e.g., 4H silicon carbide, 6H silicon carbide). The nature of these polytypes is well known in the art. In some embodiments, the substrate to be used in the CMP methods of the present disclosure is 4H silicon carbide (i.e., 4H-SiC).

The effective polishing temperature for polishing SiC wafers in the CMP methods of the present disclosure, i.e., the temperature measured on the polishing pad during polishing and typically recorded on an IR thermometer, is a few degrees celsius lower than that observed for similar configurations using commercially available slurries.

The lower temperature of the suspensions of the present disclosure and suspensions prepared according to the methods of the present disclosure yields benefits, including because the CMP process can be run as follows: a) Low temperature, thus resulting in a more gradual process that is less prone to surface defects and thus results in higher process yields; or b) a higher material removal rate by increasing the pressure on the polishing pad and/or increasing the rate of CMP to a higher level than is allowed by conventional suspensions. Depending on the particular goal to be achieved (e.g., yield and throughput), these temperature-related benefits are of great value.

However, the upper limit of polishing temperature is limited by the polishing pad material, which needs to degrade little or no during the CMP process. Typically, the polishing temperature does not exceed 60 ℃.

The flow rate at which the suspension of the present disclosure is dispensed onto a CMP apparatus depends on the particular apparatus and pad configuration used. However, the suspensions of the present disclosure work well at the industry standard flow rates.

Using the CMP methods of the present disclosure, silicon carbide can be removed using the suspensions of the present disclosure at a material removal rate of about 3 to 15 μm/hour, typically 5 to 12 μm/hour or 6 to 10 μm/hour without damaging the surface, and thus providing a scratch-free silicon carbide surface, i.e., a surface of: using confocal optical microscopy, measured with automated scratch detection and characterization metrology, was shown to be free of CMP-related scratches, sometimes present due to other slurries, pads, tools, etc.

In a typical CMP process, the scratch length per wafer can be expected to be <20mm, but this is highly dependent on customer process, tool, pad, wafer quality, etc. However, the suspensions of the present disclosure used in the CMP methods of the present disclosure provide significant improvements with respect to scratch occurrence and their length, which if occurring is typically significantly lower than the values mentioned above.

The suspension of the present disclosure provides a SiC wafer surface having a surface roughness of less than 1 angstrom. Roughness was calculated as RMS roughness by AFM metrology (5 x 5 scan, 1Hz scan rate). This level of roughness is considered generally desirable and acceptable for downstream silicon carbide processing involving surface epitaxy, such as Chemical Vapor Deposition (CVD).

Finally, the suspension allows for very low CMP polishing temperatures. The polishing temperature is typically lower than that used in the case of prior art slurries. The lower temperature of the suspension of the present disclosure gives great benefit because the CMP process can be run at the following: a) Lower temperatures, thus resulting in a more gradual process that is less prone to surface defects and thus results in higher process yields; or b) a higher material removal rate by increasing the pressure on the polishing pad and/or increasing the rate of CMP to a higher level than is allowed by conventional suspensions. Depending on the particular goal to be achieved (e.g., yield and throughput), these temperature-related benefits are valuable.

Other embodiments of the method for chemical mechanical planarization of a substrate have been described with respect to the aqueous suspensions of the present disclosure, particularly with respect to the components of the aqueous suspensions, and the method for preparing the aqueous suspensions, mutatis mutandis.

Examples

The following examples further illustrate the disclosure but, of course, should not be construed as in any way limiting its scope.

Example 1 (comparison)

This example demonstrates the concentration effect of alumina nanoparticles on single crystal SiC polishing temperature and material removal rate. It was determined to contain 4wt% KMnO at pH 2.3 ₄ And 0.5wt% nitrate, and the results are shown in table 1.

TABLE 1

Alumina nanoparticle concentration [ wt ]]	Polishing temperature (. Degree. C.)	Silicon carbide removal Rate (mu/h)
			0.1％	46.4	5.8
0.2％	45.2	5.2
			0.5％	41.4	4.5
1％	35.5	3.1
			5％	28.7	1.2

An increase in abrasive concentration shows a decrease in temperature and at the same time it also decreases the silicon carbide removal rate.

Example 2 (comparison)

This example shows the concentration effect of zirconia nanoparticles on single crystal SiC polishing temperature and material removal rate. It was determined to contain 4wt% KMnO at pH 2.3 ₄ And 0.5wt% nitrate, and the results are shown in table 2.

TABLE 2

The temperature and removal rate of the zirconia nanoparticles showed a trend similar to that of the alumina nanoparticles. However, the presence of zirconia particles enhances SiC removal rates by up to 20% compared to similar concentrations of alumina nanoparticles.

Example 3 (comparison)

This example shows the effect of a combination of alumina and zirconia nanoparticles on single crystal SiC polishing temperature and material removal rate. Determination of the presence of 4.5wt% KMnO at pH 2.3 ₄ And 0.75wt% nitrate, each composition and results are shown in table 3.

TABLE 3 Table 3

Nanoparticle concentration [ wt ]]	Polishing temperature (. Degree. C.)	Silicon carbide removal Rate (mu/h)
			0.1% alumina+0.1% zirconia	49.7	9.4
0.25% alumina+0.25% zirconia	46.4	10.8
			0.5% alumina+0.5% zirconia	44.8	8.7
0.2% alumina+0.8% zirconia	45.3	10.2
			1% alumina+1% zirconia	42.8	7.9

The synergistic effect of alumina and zirconia nanoparticles showed a significant increase in removal rate, up to 11 μ/h. At the same time, a considerable temperature decrease is observed.

Single crystal SiC (Si-surface) surface roughness (R) using mixed particle (alumina+zirconia) samples _a ) Atomic force microscopy (Atomic force microscopy; AFM) data are given in table 4.

TABLE 4 Table 4

Nanoparticle concentration [ wt ]]	Surface roughness R _a (nm)
		0.1% alumina+0.1% zirconia	0.23
0.25% alumina+0.25% zirconia	0.0636
		0.5% alumina+0.5% zirconia	0.17
0.2% alumina+0.8% zirconia	0.0842
		1% alumina+1% zirconia	0.23

The mixed particles create a sub-a surface roughness for the quality SiC substrate.

Example 4 (examples of the present disclosure)

This example shows the effect of the combination of alumina and zirconia nanoparticles and calcined alumina (these components together are referred to as abrasives in table 5) and other components (chlorate, perchlorate, together are referred to as additives in table 5) on single crystal SiC (Si-surface) polishing temperature and material removal rate. The polishing temperature and removal rate of each aqueous suspension containing 15 wt.% permanganate (KMnO 4, naMnO 4) and 0.75 wt.% nitrate at pH 2.3 were determined and each composition and result are shown in table 5.

TABLE 5

Concentration [ wt ]]	Polishing temperature (. Degree. C.)	Silicon carbide removal Rate (mu/h)
			6% abrasive +0% additive (comparative)	42.8	10.5
4% abrasive+1% additive	48.5	12.3
			5% abrasive +0.5% additive	47.2	13.2
6% abrasive+1.5% additive	52	14

The data presented in table 5 clearly shows the importance of balancing chemical activity and mechanical abrasion to achieve high material removal rates and acceptable process temperatures. Zero percent additive and high abrasive concentration (6% abrasive) reduce removal rate and reduce process temperature. The synergistic effect of the abrasive and additives showed a significant increase in removal rate up to-14 μ/h at acceptable process temperatures.

Single crystal SiC (Si-surface) surface roughness (R) obtained on polished SiC (Si-surface) wafers using the concentrations given above (table 5) _a ) Atomic Force Microscopy (AFM) data measured are given in table 6.

TABLE 6

Concentration [ wt ]]	Surface roughness R _a (nm)
		6% abrasive +0% additive	0.1
4% abrasive+1% additive	0.092
		5% abrasive +0.5% additive	0.0667
6% abrasive+1.5% additive	0.258

As is apparent from the data shown in table 6, this slurry provides a scratch-free, sub-a ° horizontal surface roughness (R _a ) Which enhances SiC wafer throughput. The combination of high concentrations of chemically active ions with high concentrations of particles produces an increase in the removal rate of single crystal SiC (Si-surface) material, with acceptable process temperatures and excellent surface conditioning. Thus, all of these performance benefits make these slurries useful for all SiC process applications (i.e., batch processes, single wafer processes).

The present disclosure will now be explained in more detail through the use of the following working examples, but the present disclosure is by no means limited to these working examples. In addition, unless otherwise indicated, the terms "parts", "percent" and "ratio" in the examples mean "parts by mass", "mass%" and "mass ratio", respectively.

1. The measuring method comprises the following steps:

1.1 Material removal Rate

The Material Removal Rate (MRR) is the change in substrate mass before and after polishing according to the previously mentioned equation. The mass change of the substrate before and after divided by the time taken for polishing calculates the material removal rate. The mass of the substrate is measured using a table balance. The material removal rate of each wafer polished in one batch polishing process was determined and averaged over three consecutive batch polishing processes.

1.2 surface roughness

The surface roughness was measured by AFM (5 x 5 scan, 1Hz scan rate) and calculated as RMS roughness by measuring the surface roughness of each SiC substrate at three locations. If the surface roughness at these three positions is repeated, the corresponding values are given as the surface roughness.

1.3 storage stability

The storage stability of the prepared suspension was determined by measuring the pH at 23 ℃ for a period of 12 months, and by visually evaluating the suspension at the end of the storage time.

2. Examples of the present disclosure and preparation of comparative aqueous suspensions

Example aqueous suspensions and comparative aqueous suspensions of the present disclosure were prepared using one of the following methods:

method a (examples of the present disclosure):

step A1: an aqueous suspension including alumina particles and aluminum nitrate is prepared by mixing an aqueous slurry of alumina particles (prepared by dispersing alumina particles having a mohs hardness of 3 to 4 in water and filtering the resulting dispersion) with aluminum nitrate.

Step A2: an aqueous solution of potassium permanganate is prepared by dissolving potassium permanganate in water.

Step A3: the aqueous potassium permanganate solution prepared in step A2 was added to the aqueous suspension prepared in step A1.

The amounts of alumina particles, aluminum nitrate, potassium permanganate and water used in steps A1 and A2 were chosen such that the amounts given in table 7 were produced after the end of step A3.

Comparative method B (comparative):

step B1: an aqueous potassium permanganate solution is prepared by dissolving potassium permanganate in water.

Step B2: an aqueous slurry of alumina particles and aluminum nitrate was added to the aqueous solution prepared in step B1.

The amounts of alumina particles, aluminum nitrate, potassium permanganate and water used in steps B1 and B2 were chosen such that the amounts given in table 7 were produced after the end of step B2.

The final compositions of all prepared examples of the present disclosure and comparative aqueous suspensions are given in table 7.

Table 7: summary of examples of the present disclosure and comparative aqueous suspensions prepared (all amounts given in wt% based on the total weight of the corresponding aqueous suspension)

Compounds of formula (I)	S-I1*	S-C1	S-C2	S-C3	S-C4	S-C5	S-C6	S-C7	S-C8	S-C9
											Potassium permanganate	4.0	4.0	4.0	4.0	4.0	4.0	4.0	4.0	4.0	4.0
Aluminum nitrate	0.50	0.50	0.50	0.5	0.5	0.50	-	-	-	-
											Ferric nitrate	-	-	-	-	-	-	0.5	-	-	-
Cerium nitrate	-	-	-	-	-	-	-	0.5	-	-
											Ammonium cerium nitrate	-	-	-	-	-	-	-	-	0.5	-
Manganese nitrate	-	-	-	-	-	-	-	-	-	0.5
											Alumina particles ¹	0.10	0.20	0.50	1.0	5.0	0.10	0.10	0.10	0.10	0.10
Distilled water	95.4	95.3	95.0	94.5	90.5	95.4	95.4	95.4	95.4	95.4
											pH(23℃)	3.6-3.8	3.6-3.8	3.8-4.0	3.9-4.1	4.4-4.8	3.6-3.8	3.8-4.0	3.8-4.0	4.0-4.2	3-3.2
Preparation method	MA ²	MA ²	MA ²	MA ²	MA ²	MB ³	MA ²	MA ²	MA ²	MA ²

* Examples of the present disclosure

¹ Diaspore particles with Z-average particle size of 100nm (supplied by Saxol functional chemical (Sasol Performance Chemicals))

² MA is an abbreviation for method A

³ MB is an abbreviation for method B

CMP process

The polishing characteristics of the aqueous suspension S-I1 of the 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 type CMP process using a batch type CMP tool and in a single type CMP process using a commercially available single type CMP tool. The silicon carbide substrates were each 4H-type circular wafers with a diameter of 150 nm. The pH of each composition was reduced to 2.1 with nitric acid prior to polishing.

4. Results

4.1 storage stability

The storage stability was determined as described in the storage stability section above (section 1.3), and the obtained results are listed in table 8.

Table 8: results of storage stability test

^* Examples of the present disclosure

¹⁾ Not measured

The results shown in table 8 demonstrate that aqueous suspensions (S-I1, S-C1 to S-C3) prepared according to the methods of the present disclosure and comprising aluminum nitrate and less than 5wt% of aluminum oxide particles do not show pH variations and color variations after 12 months of storage, thus allowing a constant polishing quality to be obtained, independent of storage time. In contrast, an aqueous suspension S-C4 prepared according to the method of the present disclosure and comprising aluminum nitrate and 5wt% aluminum oxide particles settled after storage and was therefore storage unstable. Containing the same amounts of aluminum nitrate, aluminum oxide particles, and potassium permanganate as the aqueous suspension S-I1 of the present disclosure, but not the aqueous suspension S-C5 prepared according to the method of the present disclosure is also unstable after storage. After storage of aqueous suspensions S-C6 to S-C9 containing other nitrates in addition to aluminum nitrate, undesirable manganese dioxide is formed due to pH shift to higher pH values. However, the presence of manganese dioxide causes an increase in surface roughness and a decrease in the material removal rate of the stored suspension (see tables 9 and 11 below), and is therefore not desirable.

4.2 silicon carbide removal Rate

The silicon carbide removal rate was determined as described in section 1.1 above and the results obtained are listed in tables 9 and 10.

Table 9: results of silicon carbide removal rates of aqueous suspensions S-I1 and S-C1 to S-C9 in a batch CMP process.

Slurry liquid	Alumina particle content [ wt ]]	Nitrate salts	Silicon carbide removal Rate [ mu ] m/h]
				S-I1*	0.1	Aluminum nitrate	3
S-C1	0.2	Aluminum nitrate	3.8
				S-C2	0.5	Aluminum nitrate	4.2
S-C3	1.0	Aluminum nitrate	4.8
				S-C4	5.0	Aluminum nitrate	n.d. ¹⁾
S-C5	0.1	Aluminum nitrate	2.5
				S-C6	0.1	Ferric nitrate	2.8
S-C7	0.1	Cerium nitrate	2.1
				S-C8	0.1	Ammonium cerium nitrate	n.d ¹⁾
S-C9	0.1	Manganese nitrate	n.d ¹⁾

* Examples of the present disclosure

¹⁾ Is not determinable due to the instability of the aqueous suspensions S-C4, S-C8 and S-C9

Table 10: results of silicon carbide removal rates of aqueous slurries S-I1 of the invention for use in a single CMP process using different downforce pressures

Downward Pressure (PV) [ psi in/s ]]	Silicon carbide removal Rate [ mu ] m/h]
		972	8
675	4.9
		405	2.6

Batch CMP process:

a comparative aqueous slurry S-C5 containing 0.1wt% alumina particles and aluminum nitrate, but not prepared according to the process of the present disclosure, resulted in a lower material removal rate in a batch CMP process than an aqueous slurry S-I1 of the present invention having the same composition but prepared according to the process of the present disclosure. Furthermore, the comparative aqueous suspensions S-C6 and S-C7 containing ferric nitrate or cerium nitrate resulted in lower material removal rates than the aqueous slurries 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 were not determined due to their low stability after preparation (see Table 8 above). Comparative aqueous suspensions S-C1 to S-C3 containing higher amounts of alumina particles than the aqueous suspension S-I1 of the invention lead to higher material removal rates. However, an increase in the material removal rate was associated with an undesirable significant increase in the surface roughness of the polished product (see table 11 below). In summary, only the aqueous suspension S-I1 of the present disclosure shows a good balance between material removal rate and surface roughness, while higher amounts of alumina particles cause unacceptable surface roughness, and the use of other nitrates causes a decrease in material removal rate and unacceptable surface roughness.

Single CMP process:

the aqueous suspension S-I1 of the present disclosure allows for achieving high material removal rates and excellent surface roughness (see table 12 below), even at high downforce pressures, and thus results in an efficient and fast polishing process that provides high yields (i.e., substrates with high surface quality).

4.3 surface roughness

The surface roughness was measured as described in section 1.2 above, and the results obtained are listed in tables 11 and 12.

Table 11: results of surface roughness measurement of polished SiC-wafer in batch CMP process

* Examples of the present disclosure

1) Is not determinable due to the instability of the aqueous suspensions S-C4, S-C8 and S-C9

Table 12: results of surface roughness measurement of SiC-wafers polished using the aqueous slurry S-I1 of the present invention used in a single CMP process

Downward Pressure (PV) [ psi in/s ]]	Surface roughness R _a [nm]
		972	0.066
675	0.057
		405	0.063

Batch CMP process:

the aqueous suspensions S-I1 of the present disclosure caused excellent surface roughness of 3 angstroms or less, while the use of higher amounts of alumina particles (see comparative aqueous suspensions S-C1 to S-C3) caused significantly higher surface roughness and thus reduced the quality of polished SiC substrates. The use of comparative aqueous suspensions S-C6 and S-C7 comprising ferric nitrate and cerium nitrate causes high scratching of the substrate surface and provides a polished product with unacceptable quality. The surface roughness of the comparative aqueous suspensions S-C5, S-C8 and S-C9 could not be measured due to their low stability after preparation (see Table 12 above).

Single CMP process:

the aqueous suspension S-I1 of the present disclosure allows for achieving excellent surface roughness even at high downforce pressures and thus allows for a rapid polishing process that provides excellent yields.

5. Discussion of results

The aqueous suspension S-I1 of the present disclosure comprising less than 0.2wt% alumina particles and aluminum nitrate results in high material removal rates and excellent surface roughness in batch as well as single CMP processes. Furthermore, these suspensions have an excellent storage stability of more than 12 months, thus ensuring a constant material removal rate and surface quality during the polishing process during their shelf-life. Without wishing to be bound by this particular theory, the presence of aluminum nitrate appears to prevent or reduce pH shifts that occur during storage due to dissolution of the alumina particles in an acidic medium, and furthermore, to form a "soft" layer on the alumina particles, which allows to obtain a polished product with high surface quality (i.e. low surface roughness). Surprisingly, a high material removal rate was achieved only when an aqueous solution of an oxidizing agent was added to an aqueous suspension comprising alumina particles and aluminum nitrate, while the addition of an aqueous suspension of alumina particles and aluminum nitrate to an aqueous potassium nitrate solution caused a reduction in the material removal rate (see comparative suspension S-C5).

In contrast, aqueous suspensions (comparative suspensions S-C6 to S-C9) comprising less than 0.2wt% alumina particles and other nitrates other than aluminum nitrate showed a significant decrease in storage stability due to pH fluctuations that occurred after storage. This pH shift causes the formation of manganese dioxide, which reduces the material removal rate and significantly increases the surface roughness of the polished substrate.

Suspensions (comparative suspensions S-C1 to S-C3) comprising 0.2wt% to 1wt% of alumina particles and aluminum nitrate show high storage stability compared to the suspensions of the present disclosure, and cause an increase in material removal rate in a batch CMP process. However, an increase in the material removal rate is associated with an unacceptable increase in the surface roughness of the polished substrate, thus greatly reducing the yield of the polishing process. Further increasing the amount of alumina particles to 5wt% resulted in an unstable suspension which did not have the required storage stability.

In summary, the aqueous suspension of the present disclosure having less than 0.2wt% alumina particles and aluminum nitrate and prepared by the process of the present disclosure allows for high material removal rates and excellent surface roughness (i.e., high yield) of polished substrates in batch-type as well as single-type CMP processes. The high material removal rate makes the polishing process more efficient because it allows for reduced polishing times. Furthermore, the aqueous suspensions of the present disclosure have excellent storage stability, thus ensuring constant quality in the CMP process during their shelf life.

Aspects of the invention

Various aspects are described below. It will be appreciated that any one or more of the features recited in the following aspects may be combined with any one or more of the other aspects.

Aspect 1 an aqueous suspension comprising: (a) one or more metal permanganates; (b) zirconia nanoparticles; (c) alumina nanoparticles; and (d) one or more nitrates.

Aspect 2. The aqueous suspension according to aspect 1, further comprising at least one pH adjustor and/or at least one pH buffering agent.

Aspect 3. The aqueous suspension according to aspect 1 or 2, wherein the pH of the aqueous suspension is in the range of 2 to 5.

Aspect 4. The aqueous suspension according to aspect 3, wherein the pH is measured at a temperature in the range of 20 ℃ to 30 ℃.

Aspect 5. The aqueous suspension according to aspect 3, wherein the pH is measured at a temperature of 23 ℃.

Aspect 6 the aqueous suspension of any one of the preceding aspects, wherein the one or more metal permanganate salts are selected from the group consisting of: liMnO ₄ 、KMnO ₄ 、NaMnO ₄ And mixtures thereof.

Aspect 7 the aqueous suspension according to any one of the preceding aspects, wherein the zirconia nanoparticles comprise ZrO ₂ 。

Aspect 8 the aqueous suspension according to any one of the preceding aspects, wherein the alumina nanoparticles comprise colloidal alumina particles.

Aspect 9 the aqueous suspension according to aspect 8, wherein the colloidal alumina particles comprise gamma-AlOOH particles and/or gamma-Al ₂ O ₃ And (3) particles.

Aspect 10 the aqueous suspension according to any one of the preceding aspects, wherein the one or more nitrates comprises Al (NO ₃ ) ₃ 。

Aspect 11 the aqueous suspension according to any one of the preceding aspects, wherein the aqueous suspension is free of MnO ₂ 。

Aspect 12. A method of chemical mechanical planarization of a substrate, comprising: (i) Contacting the substrate with the aqueous suspension of aspect 1; (ii) Moving the aqueous suspension relative to the substrate with a polishing pad; and (iii) abrading at least a portion of the substrate to polish the substrate.

Aspect 13. The method of aspect 12, wherein the substrate is a silicon carbide substrate.

Aspect 14. The method of aspect 12 or aspect 13, wherein the substrate does not exceed a temperature of 60 ℃ during grinding.

Aspect 15 the method of any one of aspects 12-14, further comprising reducing the pH of the aqueous suspension to a range of 2 to 2.5 prior to contacting the substrate with the aqueous suspension.

Aspect 16. The method of aspect 15, wherein the pH is lowered by addition of an acid.

Aspect 17. The method of aspect 15, wherein the substrate is contacted with the aqueous suspension within fourteen days of lowering the pH.

Aspect 18. A method for preparing an aqueous suspension comprising: (i) Adding aluminum nitrate to an aqueous suspension comprising aluminum oxide nanoparticles and zirconium oxide nanoparticles; and (ii) adding an aqueous solution of one or more metal permanganate salts to the aqueous suspension.

Aspect 19 the method of aspect 18, further comprising filtering the aqueous suspension prior to adding aluminum nitrate.

Aspect 20 the method of aspect 18 or aspect 19, further comprising filtering the aqueous solution of one or more metal permanganate salts prior to adding the aqueous solution.

Aspect 21 the method of any one of the preceding aspects, wherein the aqueous suspension is absent MnO ₂ 。

Aspect 22. The method of any one of the preceding aspects, wherein the aqueous suspension has a pH in the range of 2 to 5 at 23 ℃.

Aspect 23. The method according to any one of the preceding aspects, wherein step (i) and step (ii) are performed sequentially.

Aspect 24, a method comprising: 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 over fourteen days.

Aspect 25 the method of aspect 24, wherein the aqueous suspension comprises: (a) one or more metal permanganates; (b) zirconia nanoparticles; (c) alumina nanoparticles; and (d) one or more nitrates.

Aspect 26. The method of aspect 24 or aspect 25, wherein the aqueous suspension is stored for at least 1 year.

Aspect 27 the method of any one of the preceding aspects, wherein the pH of the aqueous suspension is reduced by adding an acid, and wherein the acid comprises nitric acid.

Aspect 28. The method of any one of the preceding aspects, wherein the pH of the aqueous suspension is reduced to 2.3.

Aspect 29. The method according to any one of the preceding aspects, wherein the aqueous suspension having a pH in the range of 2 to 2.5 is used in a single or batch type chemical mechanical planarization method.

Aspect 1 an aqueous suspension comprising: (a) one or more metal permanganates; (b) one or more kinds of zirconia nanoparticles; (c) one or more types of alumina nanoparticles; (d) one or more nitrates; (e) one or more types of calcined alumina particles; (f) one or more metal chlorate salts; and (g) one or more metal perchlorate salts.

Aspect 3. The aqueous suspension according to aspect 1 or aspect 2, wherein the pH of the aqueous suspension is in the range of 2 to 5.

Aspect 4. The aqueous suspension according to aspect 3, wherein the pH is measured at a temperature in the range of 15 ℃ to 40 ℃.

Aspect 7 the aqueous suspension according to any one of the preceding aspects, whereinThe one or more kinds of zirconia nanoparticles comprise ZrO ₂ 。

Aspect 8 the aqueous suspension according to any one of the preceding aspects, wherein the one or more kinds of alumina nanoparticles comprise colloidal alumina particles.

Aspect 11 the aqueous suspension according to any one of the preceding aspects, wherein the one or more species of calcined alumina particles comprise alumina that has been heated at a temperature in excess of 1000 ℃ to drive off chemically bound water.

Aspect 12 the aqueous suspension according to any one of the preceding aspects, wherein the one or more metal chlorate salts comprise NaClO ₃ 。

Aspect 13 the aqueous suspension according to any one of the preceding aspects, wherein the one or more metal perchlorate salts comprise Al (ClO ₄ ) ₃ 。

Aspect 14 the aqueous suspension according to any one of the preceding aspects, wherein the aqueous suspension is free of MnO ₂ 。

Aspect 15. A method of chemical mechanical planarization of a substrate, wherein the method comprises: (i) Contacting the substrate with the aqueous suspension of aspect 1; (ii) Moving the aqueous suspension relative to the substrate with a polishing pad; and (iii) abrading at least a portion of the substrate to polish the substrate.

Aspect 16 the method of aspect 15, wherein the substrate is a silicon carbide substrate.

Aspect 17 the method of aspect 15 or aspect 16, wherein the substrate does not exceed a temperature of 60 ℃ during grinding.

Aspect 18 the method of any one of the preceding aspects, further comprising reducing the pH of the aqueous suspension to a range of 2 to 2.5 prior to contacting the substrate with the aqueous suspension.

Aspect 19. The method of aspect 18, wherein the pH is lowered by addition of an acid.

Aspect 20. The method of aspect 18, wherein the substrate is contacted with the aqueous suspension within fourteen days of lowering the pH.

Aspect 21. A method for preparing an aqueous suspension comprising: (i) Adding aluminum nitrate to the aqueous suspension comprising aluminum oxide nanoparticles and zirconium oxide 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 chlorate to the aqueous suspension; and (iii) adding one or more types of calcined alumina particles to the aqueous suspension.

Aspect 22 the method of aspect 21, further comprising filtering the aqueous suspension prior to adding aluminum nitrate.

Aspect 23 the method of aspect 21 or aspect 22, further comprising filtering the aqueous solution prior to adding the aqueous solution.

Aspect 24 the method of any one of the preceding aspects, wherein the aqueous suspension is absent MnO ₂ 。

Aspect 25 the method according to any one of the preceding aspects, wherein the aqueous suspension has a pH in the range of 2 to 5 at 23 ℃.

Aspect 26 the method according to any one of the preceding aspects, wherein step (i), step (ii) and step (iii) are performed sequentially.

Aspect 27, a method comprising: 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 over fourteen days.

Aspect 28 the method of aspect 27, wherein the aqueous suspension comprises: (a) one or more metal permanganates; (b) one or more kinds of zirconia nanoparticles; (c) one or more types of alumina nanoparticles; (d) one or more nitrates; (e) one or more types of calcined alumina particles; (f) one or more metal chlorate salts; and (g) one or more metal perchlorate salts.

Aspect 29. The method of aspect 27 or aspect 28, wherein the aqueous suspension is stored for at least 1 year.

Aspect 30 the method of any one of the preceding aspects, wherein the pH of the aqueous suspension is reduced by adding an acid, and wherein the acid comprises nitric acid.

Aspect 31. The method of any one of the preceding aspects, wherein the pH of the aqueous suspension is reduced to 2.3.

Aspect 32. The method according to any one of the preceding aspects, wherein the aqueous suspension having a pH in the range of 2 to 2.5 is used in a single or batch type chemical mechanical planarization method.

Aspect 1 an aqueous suspension comprising: at least one oxidizing agent; a total amount of less than 0.2wt% abrasive particles, based on the total weight of the aqueous suspension, wherein the abrasive particles each have a mohs hardness of less than 6; and aluminum nitrate.

Aspect 6 the aqueous suspension according to any one of the preceding aspects, wherein the at least one oxidizing agent is selected from the group consisting of: liMnO ₄ 、KMnO ₄ 、NaMnO ₄ And mixtures thereof.

Aspect 7. According to aspect 6An aqueous suspension wherein the at least one oxidizing agent is KMnO ₄ 。

Aspect 8 the aqueous suspension according to any one of the preceding aspects, wherein the abrasive particles comprise alumina particles.

Aspect 9. The aqueous suspension of aspect 8, wherein the alumina particles comprise gamma-AlOOH particles.

Aspect 10 the aqueous suspension according to aspect 8, wherein the alumina particles are gamma-AlOOH particles.

Aspect 13. The method of aspect 12, wherein the substrate comprises at least one layer of silicon carbide.

Aspect 14. The method of aspect 13, wherein the at least one layer of silicon carbide is at least one layer of single crystal silicon carbide.

Aspect 15 the method of any one of the preceding aspects, wherein the substrate does not exceed a temperature of 60 ℃ during grinding.

Aspect 16 the method of any one of the preceding aspects, further comprising reducing the pH of the aqueous suspension to a range of 2 to 2.5 prior to contacting the substrate with the aqueous suspension.

Aspect 17. The method of aspect 16, wherein the pH of the aqueous suspension is reduced by adding an acid.

Aspect 18. The method of aspect 16, wherein the substrate is contacted with the aqueous suspension within fourteen days of lowering the pH.

Aspect 19. A method for preparing an aqueous suspension comprising: (i) Adding aluminum nitrate to the aqueous suspension comprising abrasive particles; and (ii) adding an aqueous solution of at least one oxidizing agent to the aqueous suspension, wherein the abrasive particles each have a mohs hardness of less than 6, and wherein the aqueous suspension contains less than 0.2wt% of the abrasive particles, based on the total weight of the aqueous suspension.

Aspect 20 the method of aspect 19, further comprising filtering the aqueous suspension prior to adding aluminum nitrate.

Aspect 21 the method of aspect 19 or aspect 20, further comprising filtering the aqueous solution prior to adding the aqueous solution.

Aspect 22 the method of any one of the preceding aspects, wherein the aqueous suspension is absent MnO ₂ 。

Aspect 23. The method of any one of the preceding aspects, wherein the aqueous suspension has a pH in the range of 2 to 5 at 23 ℃.

Aspect 24. The method according to any one of the preceding aspects, wherein step (i) and step (ii) are performed sequentially.

Aspect 25, a method comprising: 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 over fourteen days.

Aspect 26 the method of aspect 25, wherein the aqueous suspension comprises: at least one oxidizing agent; a total amount of less than 0.2wt% abrasive particles, based on the total weight of the aqueous suspension, wherein the abrasive particles each have a mohs hardness of less than 6; and aluminum nitrate.

Aspect 29. The method of aspect 25 or aspect 26, wherein the aqueous suspension is stored for at least 1 year.

Aspect 29. The method of any of the preceding aspects, wherein the pH of the aqueous suspension is reduced by adding an acid, and wherein the acid comprises nitric acid.

Aspect 30. The method of any one of the preceding aspects, wherein the pH of the aqueous suspension is reduced to 2.3.

Aspect 31. The method according to any one of the preceding aspects, wherein the aqueous suspension having a pH in the range of 2 to 2.5 is used in a single or batch type chemical mechanical planarization method.

Aspect 32 the method of any one of the preceding aspects, wherein using the aqueous suspension comprises using the aqueous suspension having a pH in the range of 2 to 2.5 in a batch-type chemical mechanical planarization process.

It will be appreciated that changes may be made in detail, especially in matters of construction materials employed, as well as shapes, sizes and arrangements of parts, without departing from the scope of the present disclosure. The specification and described embodiments are examples in which the true scope and spirit of the disclosure is indicated by the following claims.

Claims

1. An aqueous suspension comprising:

at least one oxidizing agent;

a total amount of less than 0.2wt% abrasive particles, based on the total weight of the aqueous suspension, wherein the abrasive particles have a mohs hardness of less than 6; and

aluminum nitrate.

2. The aqueous suspension according to claim 1, further comprising at least one pH adjustor and/or at least one pH buffering agent.

3. The aqueous suspension according to claim 1, wherein the pH of the aqueous suspension is in the range of 2 to 5.

4. The aqueous suspension according to claim 1, wherein the at least one oxidizing agent is selected from the group consisting of: liMnO ₄ 、KMnO ₄ 、NaMnO ₄ And mixtures thereof.

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

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

7. A method of chemical mechanical planarization of a substrate, comprising:

(i) Contacting the substrate with the aqueous suspension of claim 1;

(ii) Moving the aqueous suspension relative to the substrate with a polishing pad; and

(iii) At least a portion of the substrate is abraded to polish the substrate.

8. The method of claim 7, wherein the substrate does not exceed a temperature of 60 ℃ during grinding.

9. The method of claim 7, further comprising reducing the pH of the aqueous suspension to within the range of 2 to 2.5 prior to contacting the substrate with the aqueous suspension.

10. The method of claim 9, wherein the substrate is contacted with the aqueous suspension within fourteen days of lowering the pH.

11. A method for preparing an aqueous suspension comprising:

(i) Adding aluminum nitrate to the aqueous suspension comprising abrasive particles; and

(ii) Adding an aqueous solution of at least one oxidizing agent to the aqueous suspension,

wherein the abrasive particles have a Mohs hardness of less than 6 and

wherein the aqueous suspension contains less than 0.2wt% of the abrasive particles, based on the total weight of the aqueous suspension.

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

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

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

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

16. A method, comprising:

storing an aqueous suspension 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

the aqueous suspension having a pH in the range of 2 to 2.5 was used over fourteen days.

17. The method of claim 16, wherein the aqueous suspension comprises:

at least one oxidizing agent;

aluminum nitrate.

18. The method of claim 16, wherein the aqueous suspension is stored for at least 1 year.

19. The method of claim 16, wherein the pH of the aqueous suspension is reduced to 2.3.

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

21. An aqueous suspension comprising:

(a) One or more metal permanganates;

(b) Zirconia nanoparticles;

(c) Alumina nanoparticles; and

(d) One or more nitrates.

22. The aqueous suspension according to claim 21, further comprising at least one pH adjustor and/or at least one pH buffering agent.

23. The aqueous suspension according to claim 21, wherein the pH of the aqueous suspension is in the range of 2 to 5.

24. The aqueous suspension of claim 21, wherein the one or more metal permanganate salts are selected from the group consisting of: liMnO ₄ 、KMnO ₄ 、NaMnO ₄ And mixtures thereof.

25. The aqueous suspension of claim 21, wherein the zirconia nanoparticles comprise ZrO ₂ 。

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

27. The aqueous suspension according to claim 26, wherein the colloidal alumina particles comprise gamma-AlOOH particles and/or gamma-Al particles ₂ O ₃ And (3) particles.

28. The aqueous suspension of claim 21, wherein the one or more nitrates comprises Al (NO ₃ ) ₃ 。

29. A method for preparing an aqueous suspension comprising:

(i) Adding aluminum nitrate to an aqueous suspension comprising aluminum oxide nanoparticles and zirconium oxide nanoparticles; and

(ii) Adding an aqueous solution of one or more metal permanganate salts to the aqueous suspension.

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

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

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

33. The method of claim 29, wherein the steps (i) and (ii) are performed sequentially.