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

Abstract

The present disclosure relates to an aqueous suspension suitable for chemical mechanical planarization (CMP), uses of the aqueous suspension, and a method of CMP using the aqueous suspension. The suspension and method can be used for CMP of silicon carbide surfaces.

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application claims the priority and benefit of U.S. Provisional Patent Application No. 63 / 167275, filed on March 29, 2021, under the name "Suspensions for Chemical - Mechanical Planarization (CMP) and Methods Using the Same", and incorporates the same herein by reference in its entirety. This application claims the priority and benefit of U.S. Provisional Patent Application No. 63 / 180963, filed on April 28, 2021, under the name "Suspensions for Chemical - Mechanical Planarization (CMP) and Methods Using the Same", and incorporates the same herein by reference in its entirety. This application claims the priority and benefit of U.S. Provisional Patent Application No. 63 / 237644, filed on August 27, 2021, under the name "Suspensions for Chemical - Mechanical Planarization (CMP) and Methods Using the Same", and incorporates the same herein by reference in its entirety.

[0002] [Field] The present disclosure relates to an aqueous suspension suitable for chemical - mechanical planarization (CMP), the use of the aqueous suspension, and a method of CMP using the aqueous suspension.

Background Art

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

Summary of the Invention

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

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

[0006] A further object of this disclosure is to provide a method for chemically planarizing a substrate, the method comprising the steps of bringing the substrate into contact with an aqueous suspension according to this disclosure, moving the aqueous suspension toward the substrate with an abrasive pad, and polishing the substrate by abrading at least a portion of the substrate.

[0007] Using a suspension in the CMP method can accelerate the material removal rate and simultaneously lower the interface temperature during polishing. Furthermore, it can shorten the process time, increase the die yield of wafers, and minimize surface defects and scratches. Due to the composition of one or more types of calcined alumina particles, one or more types of metal salts of chloric acid, and one or more types of metal salts of perchloric acid, the material removal rate can be further increased to 25-30%, even at lower interface temperatures, compared to an aqueous suspension containing only one or more types of metal salts of permanganate, one or more types of zirconia nanoparticles, one or more types of alumina nanoparticles, and one or more types of salts of nitric acid, but without one or more types of calcined alumina particles, one or more types of metal salts of chloric acid, and one or more types of metal salts of perchloric acid. Removal rates of ≥13 μ / hr were observed on single-crystal 4H n-type SiC (Si surface) and ≥30 μ / hr on the C surface, resulting in the production of defect-free sub-angstrom substrates with high process yield. In addition, friction and motor load in temperature-limited CMP operations can be significantly reduced, and the corresponding CMP method allows process engineers to develop more aggressive process strategies to improve wafer throughput. Furthermore, no "sedimentation" of any component of the suspension is observed during product use or storage conditions, and therefore the suspension has a long shelf life even in its acidic medium. Moreover, the components of the suspension adhere to the wafer surface based on various surface charge dynamics, thereby ensuring that the suspension is uniformly distributed across the entire wafer surface. Finally, after the cleaning process between operations, little to no residue is observed on the CMP pad, extending the pad's lifespan.

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

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

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

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

[0012] In some embodiments, the present disclosure includes a method for preparing an aqueous suspension, comprising: (i) adding aluminum nitrate to an aqueous suspension containing alumina nanoparticles and zirconia nanoparticles; (ii) adding aqueous solutions of one or more metal salts of permanganate, one or more metal salts of perchlorate, and one or more metal salts of chlorate to the aqueous suspension; and (iii) adding one or more calcined alumina particles to the aqueous suspension.

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

[0014] In some embodiments, the present disclosure includes a method for preparing an aqueous suspension, comprising the steps of (i) adding aluminum nitrate to an aqueous suspension containing 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 the aqueous suspension contains less than 0.2% by weight of abrasive particles based on the total weight of the aqueous suspension. [Modes for carrying out the invention]

[0015] Other purposes and advantages of the disclosed advantages and improvements will become apparent from the following description, taken in conjunction with the accompanying drawings. Detailed embodiments of the disclosed are disclosed herein; however, it should be understood that the disclosed embodiments are merely illustrative examples of the disclosed, which may be embodied in various forms. In addition, each of the examples given with respect to the various embodiments of the disclosed is for illustrative purposes only and not limiting.

[0016] All prior patents and publications referenced herein are invoked in their entirety with proper attribution.

[0017] Throughout the specification and claims, the following terms have the meanings expressly associated herein unless the context clearly indicates otherwise. The phrases “in one embodiment,” “in one embodiment,” and “in several embodiments” as used herein may refer to the same embodiment, but not necessarily the same embodiment. Furthermore, the phrases “in another embodiment” and “in several other embodiments” as used herein may refer to different embodiments, but not necessarily different embodiments. All embodiments of this disclosure are intended to be combined without departing from the scope or spirit of this disclosure.

[0018] The percentage (by weight) and amount (in weight) of any of the components listed below present in an aqueous suspension shall, in each case, total 100% by weight based on the total weight of the suspension.

[0019] Where used herein, the term "based on" is not exclusive and may be based on additional factors not explicitly stated unless the context clearly indicates otherwise. In addition, throughout the specification, the meanings of "a," "an," and "the" include multiple references. The meaning of "in" includes "in" and "on."

[0020] As used herein, the term “between” does not necessarily require that an element be placed immediately next to another element. Generally, the term refers to a structure in which something is sandwiched between two or more other things. At the same time, the term “between” can also describe something that is immediately next to two opposing objects. Thus, in any one or more of the embodiments disclosed herein, a particular structural element placed between two other structural elements may be: A particular structural element can be positioned directly between two other structural elements such that it is in direct contact with both of the other structural elements; A particular structural element may be positioned immediately next to only one of two other structural elements such that it is in direct contact with only one of the other two structural elements; A particular structural element may be positioned indirectly next to only one of two other structural elements, such that it does not directly contact only one of the other structural elements, but rather there is another element that juxtaposes the particular structural element with one of the other structural elements; A particular structural element may be positioned indirectly between two other structural elements, without directly contacting either of them, such that other features may be positioned between them; or Any combination of those.

[0021] In this context, "embedded" means that the first material is distributed throughout the second material.

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

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

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

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

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

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

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

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

[0030] Over the past several decades, improvements in the cost, performance, and efficiency of power generation, storage, and distribution systems, along with government subsidies promoting widespread electrification of society, have accelerated the adoption of electric vehicles (EVs) and many other clean technologies.

[0031] The transition to a more electrified world is creating a demand for new electrical infrastructure—nodes and switches—that control the flow of electricity. At the heart of this new infrastructure are power devices, or solid-state transistors, that resemble computer chips in size and appearance, but possess the ability to handle large voltages and currents and manage the flow of electricity, for example, between the motor and battery of an electric vehicle, or between the solar panels and battery of a home charging system.

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

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

[0034] Compared to silicon (Si), silicon carbide (SiC), and more specifically 4H-SiC, possesses properties including an order of magnitude larger dielectric breakdown electric field, nearly three times larger energy bandgap, and nearly four times higher thermal conductivity. Therefore, it holds considerable promise for applications in power devices, high-frequency devices, high-temperature operating devices, and the like. As a result, SiC substrates are increasingly being used as substrates for semiconductor devices.

[0035] The SiC substrates described above are manufactured, for example, from bulk single-crystal ingots of SiC prepared by a highly controlled sublimation method. Typically, the outer surface of the ingot is ground to form a cylinder, then the cylinder is sliced ​​into a disc using a diamond-embedded wire saw, and then the outer surface is chamfered to a specified diameter to obtain the substrate. The diamond saw leaves large millimeter-sized gouges and scratches on the wafer surface, which are removed by various stages of surface lapping and grinding processes to eliminate irregularities and achieve surface parallelism. However, because the lapping and grinding processes rely on micron-sized diamond particles, they can leave micron-sized surface damage in the form of scratches, pits, and gouges.

[0036] Next, one or both sides of the substrate are subjected to chemical mechanical polishing, also known as CMP (chemical mechanical planarization), to achieve a mirror finish. This type of grinding and polishing of SiC substrates is performed to remove unevenness and process distortion, planarize the surface of the SiC substrate, and obtain an atomically nearly flat surface with virtually no surface defects, which is suitable for downstream epitaxy and further semiconductor manufacturing processes.

[0037] Because the CMP method is a polishing method that employs both chemical and mechanical actions, it can obtain a stable, flat surface without damaging the SiC substrate. As a result, the CMP method is widely used in the manufacturing process of SiC semiconductor devices and the like as a method to flatten roughness, unevenness, or irregularities caused by wiring on the surface of SiC substrates.

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

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

[0040] Therefore, it is necessary to provide a CMP slurry that is well-balanced, avoids damage to the substrate, and has sufficient aggressiveness to produce SiC wafers with atomically flat surfaces to the extent that the vicinal crystal structure can be identified by atomic force microscopy, using the CMP process.

[0041] Furthermore, various different CMP process approaches exist. In one configuration, multiple SiC wafers are processed simultaneously with a large polishing tool. This is called a "batch process" and requires a particularly large CMP tool that uses a platen several feet in diameter and can process up to 20 or more wafers at a time. While batch processing offers some advantages in throughput, the large number of wafers and the size of the tool make process coordination complex and throughput problems more likely. For example, if the wafers loaded into a batch CMP tool are not of the same thickness, thicker wafers will protrude into the polishing pad and experience greater force, while thinner wafers will experience less force and may even slip off during processing. This can result in uneven polishing of the SiC wafers. Also, as is common in CMP, if a single wafer is shattered by strong mechanical force in a batch process, the wafer fragments from the broken wafer can cause further scratches or even damage the entire batch of wafers. Furthermore, the increased platen size and surface area make it difficult to uniformly apply the extreme downward force required for a satisfactory material removal rate with the tool; therefore, longer run times are required. Longer run times mean that wafers are exposed to aggressive conditions for longer periods, which can increase the risk of defects, scratches, and significant surface damage. This has spurred the testing and adoption of new tool sets, pads, and slurries specifically designed for batch processes.

[0042] In some configurations, to overcome these defects and throughput challenges, the SiC industry has begun to shift primarily from batch processes to single-wafer processes. Single-wafer processes allow for smaller platen sizes, higher process pressures, and a more uniform pressure distribution. Higher pressures result in faster material removal rates and thus shorter run times. Furthermore, single-wafer processes allow for the isolation of defective or damaged wafers without damaging other wafers. This shift to single-wafer CMP has facilitated the testing and adoption of new toolsets, pads, and slurries specifically designed for single-wafer processes.

[0043] Because process conditions such as tool sets, polishing pads, and down pressure differ between batch and single-wafer CMP processes, slurries are usually designed specifically for one type of CMP process. However, CMP slurries may be equally suitable for use in both batch and single-wafer CMP processes.

[0044] Accordingly, in order to solve various problems of the prior art, this disclosure provides a suspension having a stable pH, i.e., a pH drift of less than 0.1 over a period of at least 12 months, which enables a high material removal rate while reducing the surface roughness of the polished substrate when used in batch CMP or single-wafer CMP processes. This disclosure provides a suspension suitable as a CMP slurry in batch and single-wafer CMP processes, enabling process acceleration, i.e., a significantly increased material removal rate, thereby enabling higher throughput. This may require a suspension that is aggressive enough to polish and planarize wafers, even wafers made of 4H-SiC, while simultaneously avoiding scratches or other damage to the wafer surface. To ensure this, the suspension can be effective as a CMP slurry at a lower temperature at the interface between the polishing pad and the wafer compared to prior art slurries. The suspension is storage stable, and any precipitates, such as any precipitates that may form during storage, can be easily redispersed by simple stirring, such as stirring or shaking the suspension.

[0045] The object of this disclosure is to provide the use of such suspensions in wafer polishing, particularly in methods of chemical mechanical planarization.

[0046] A further object of this disclosure is to provide a correspondingly improved and milder method for chemically planarizing wafers, more specifically SiC wafers such as 4H-SiC wafers, using such a CMP slurry.

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

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

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

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

[0051] Suitable oxidizing agents include persulfates, organic peroxides, inorganic peroxides, peroxy acids, permanganates, chromates, percarbonates, chlorates, bromates, iodates, perchlorates and their salts, perbromates and their salts, periodates and their salts, hydroxylamines and their salts, ferricyanides, oxones, and combinations thereof.

[0052] In some embodiments, at least one oxidizing agent is a metal salt of permanganate, for example, an alkali metal salt of permanganate. The alkali metal salt of permanganate may be selected from lithium permanganate, potassium permanganate, sodium permanganate, and mixtures thereof, for example, potassium permanganate.

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

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

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

[0056] In some embodiments, all abrasive particles present in the suspension of this disclosure have a Mohs hardness of less than 6. Using abrasive particles with a Mohs hardness of less than 6 (i.e., "soft" abrasive particles) results in a stable aqueous suspension that maintains consistent quality throughout its storage period, while using abrasive particles with a Mohs hardness greater than 6, such as alumina particles with a Mohs hardness greater than 6, results in an unstable suspension. Furthermore, the use of aqueous suspensions containing these "soft" abrasive particles surprisingly results in improved material removal rates, lower polishing temperatures, and reduced surface roughness (i.e., improved quality of the polished substrate) in batch and single-wafer CMP processes compared to the use of aqueous slurries containing abrasive particles with a Mohs hardness greater than 6, such as silica.

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

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

[0059] In some embodiments, the abrasive particles may include (e.g., include, essentially consist of, or consist of) alumina particles having a Mohs hardness of less than 6. In some embodiments, alumina particles as defined in this disclosure are particles having a Mohs hardness of less than 6, including at least one of a mixed metal species comprising and consisting of any of the aforementioned alumina species and at least one further metal atom and / or oxide and / or hydroxide thereof, and / or metal ions. In some embodiments, the alumina particles may include (e.g., include, essentially consist of, or consist of) at least one of the aforementioned alumina species, including aluminum hydroxide, aluminum hydroxide, or a hydrate of any of the aforementioned alumina species.

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

[0061] In some embodiments, the suspension according to the Disclosure contains a total amount of abrasive grains of 0.2% by weight, 0.15% by weight, 0.1% by weight, or less than 0.05% by weight. This list is not exhaustive and includes values ​​in between, for example, less than 0.13% by weight. In some embodiments, the suspension according to the Disclosure contains the entire amount of abrasive particles in the range of 0.005% to 0.2% by weight, 0.005% to 0.15% by weight, 0.005% to 0.1% by weight, or 0.005% to 0.05% by weight, 0.005% to 0.01% by weight, 0.01% to 0.2% by weight, 0.05% to 0.2% by weight, 0.1% to 0.2% by weight, 0.15% to 0.2% by weight, 0.05% to 0.15% by weight, 0.01% to 0.15% by weight, or 0.05% to 0.1% by weight. This list of ranges is not exhaustive and includes any number in between, for example, 0.07% to 0.13% by weight.

[0062] Alumina particles can be manufactured by any method known in the art.

[0063] In some embodiments, the suspension according to the Disclosure contains less than 0.2% by weight of abrasive particles by total weight, and in some embodiments, less than 0.2% by weight of γ-AlOOH particles. Surprisingly, using less than 0.2% by weight of abrasive particles, for example, γ-AlOOH particles, provides a polished substrate with a significantly lower surface roughness compared to when a larger amount of abrasive particles is used, while still achieving an acceptable material removal rate in a batch CMP process. In addition, the use of smaller amounts of the alumina particles makes it possible to obtain an aqueous suspension with high storage stability, i.e., a pH change of 0.1 or less when stored for more than 12 months, thereby preventing, reducing, or limiting the formation of undesirable reaction products that reduce the material removal rate and increase surface roughness during the polishing process. Furthermore, the use of these small amounts of abrasive particles avoids clogging of the slurry distribution line or clogging of the pores of the polishing pad, which can lead to the polishing pad becoming too smooth and significantly reducing the material removal rate.

[0064] In some embodiments, abrasive particles, such as γ-AlOOH particles, are present in a total amount of less than 0.18% by weight, less than 0.15% by weight, or less than 0.12% by weight, based on the total weight of the aqueous suspension, respectively. For example, the total amount of abrasive particles, such as γ-AlOOH particles, may be 0.001 to 0.18% by weight, 0.01 to 0.15% by weight, or 0.08 to 0.12% by weight, based on the total weight of the aqueous suspension, respectively.

[0065] In some embodiments, the aqueous suspensions of the present disclosure contain aluminum nitrate. The use of aluminum nitrate allows for avoidance of pH drift, i.e., the pH change of the aqueous suspensions of the present disclosure is less than 0.1 when these suspensions are stored for at least 12 months. Since the material removal rate during CMP has been observed to be a function of the pH of the polishing suspension, a stable pH of the aqueous suspension during the storage period of the polishing suspension allows for a uniform material removal rate. Furthermore, the stable pH of the aqueous suspension avoids the formation of undesirable reaction products such as manganese dioxide, which are formed during pH drift to higher pH values, because these reaction products reduce the material removal rate and increase the surface roughness of the substrate, thus reducing the yield achieved in the aqueous suspension after storage. Furthermore, although not bound by this theory, it is thought that aluminum nitrate forms a flexible mesh structure that embeds the abrasive grains, thus forming a "soft" layer on the particle surface that improves surface roughness during polishing and reduces surface defects. However, surprisingly, the material removal rate does not decrease even when a "soft" layer is formed on the abrasive grains. Therefore, the aqueous suspension has a high material removal rate and provides a polished substrate with excellent yield throughout its entire storage period, i.e., with low surface roughness or a small amount of surface defects.

[0066] In some embodiments, aluminum nitrate is present in an amount of 0.05 to 3% by weight, 0.1 to 2% by weight, 0.2 to 1.5% by weight, or 0.3 to 1% by weight, based on the total weight of the aqueous suspension, respectively. Too little aluminum nitrate leads to undesirable pH drift of the aqueous suspension during storage, while too much aluminum nitrate causes defects such as pitting corrosion on the substrate surface and an undesirable increase in substrate / pad interface temperature. Therefore, in some embodiments, the aqueous suspension of this disclosure contains aluminum nitrate in the aforementioned amounts. This makes it possible to achieve a stable pH and high yield of the aqueous suspension during storage without adversely affecting the material removal rate.

[0067] In some embodiments, the Disclosure is an aqueous suspension having a pH value in the range of 2.0 to 5.0 and comprising one or more alkali metal permanganates, zirconia nanoparticles, alumina nanoparticles, one or more salts of nitric acid, and optionally a pH adjuster and / or pH buffer. In some embodiments, the suspension combined with a polishing pad can be an important component of the chemical mechanical planarization method claimed in the Disclosure. It is also called a chemical mechanical planarization slurry or "CMP slurry". Some components of the slurry act chemically, such as oxidizing the surface of the wafer being polished, allowing the mechanical components, such as slurry abrasion, to remove surface irregularities on the wafer more gently.

[0068] In some embodiments, the pH of the aqueous suspension of the Disclosure is in the range of 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).

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

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

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

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

[0073] Metal salts of permanganate can act as oxidizing agents to promote the oxidation of SiC bonds on the surface of a wafer being polished. In some embodiments, alkali metal permanganates such as sodium permanganate, potassium permanganate, and lithium permanganate are used as oxidizing agents. However, in some embodiments, potassium permanganate is used as the permanganate.

[0074] In some embodiments, the metal salt of permanganate is present in an amount ranging from 2.0 to 6.0% by weight, 2.6 to 5.5% by weight, 3.0 to 5.0% by weight, or 4.0 to 5.0% by weight, for example, 4.2 to 4.8% by weight, the amount being based on the total weight of the suspension according to the present disclosure.

[0075] The aforementioned scope applies regardless of whether only one metal salt of permanganate is used in the suspension according to this disclosure, or whether a mixture of metal salts of permanganate is used. In some embodiments, for example, when potassium permanganate is used as the sole metal salt of permanganate, the aforementioned scope applies to potassium permanganate.

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

[0077] In some embodiments, the aqueous suspension comprises one or more types of zirconia nanoparticles as constituent components. In some embodiments, the zirconia nanoparticles comprise ZrO2.

[0078] Zirconia nanoparticles as used in this disclosure include, but are not limited to, zirconium oxide, such as zirconium(IV) oxide, zirconium hydroxide, zirconium hydroxide oxide, hydrates of any of the aforementioned zirconia species, and nanoparticles comprising at least one of a mixed metal species comprising any of the aforementioned zirconia species and at least one further metal atom and / or its oxide and / or its hydroxide, and / or metal ion. Zirconia nanoparticles may exist in colloidal form. In some embodiments, zirconia nanoparticles are nanoparticles comprising and comprising at least one of the zirconium oxides, such as zirconium(IV) oxide.

[0079] The suspensions of this disclosure comprise zirconia nanoparticles. As described herein, zirconia nanoparticles are particles having Z-average particle sizes in the ranges of 1 nm to 1000 nm, 10 to 500 nm, 20 to 300 nm, 50 to 200 nm, and 75 to 150 nm.

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

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

[0082] The suspensions relating to this disclosure contain zirconia nanoparticles in amounts of 0.05 to 5.0% by weight, 0.1 to 2.0% by weight, 0.15 to 1.0% by weight, or 0.15 to 0.5% by weight, based on the total weight of the suspension. In some embodiments, one or more types of zirconia nanoparticles may be present in amounts ranging from 0.05 to 5.0% by weight, 0.10 to 4.0% by weight, 0.15 to 3.0% by weight, 0.15 to 2.0% by weight, or 0.25 to 1.5% by weight, based on the total weight of the aqueous suspension.

[0083] In some embodiments, if the amount of zirconia nanoparticles is too high, the solution becomes more viscous. Furthermore, the pores of the polishing pad may become "glossy" and the particles may clog, making it too smooth. In addition, the particles may settle in the solution, resulting in clogging problems in the slurry distribution line delivered by the pump. If the amount of zirconia nanoparticles is too low, the mechanical abrasive force is insufficient, reducing the material removal rate to a level that is too low to be useful. In some embodiments, within the scope of this disclosure, a balance is maintained in the material removal rate without observable settling problems or excessive viscosity. In some embodiments, the chemical and mechanical activity is balanced within a range of components of both one or more metal salts of permanganate and one or more zirconia nanoparticles to produce sub-angstrom surface quality with low rise in process temperature.

[0084] In some embodiments, the presence of zirconia nanoparticles in the suspension of the present disclosure creates a "chemical tooth" function, thereby promoting selective or catalytically enhanced oxidation of the silicon-carbon bond by a metal salt of permanganate, such as potassium permanganate.

[0085] In some embodiments, the aqueous suspension comprises one or more types of alumina nanoparticles as constituent components. In some embodiments, the alumina nanoparticles comprise colloidal alumina particles such as γ-AlOOH particles and / or γ-Al2O3 particles.

[0086] Alumina nanoparticles as used in this disclosure include, for example, at least one of a mixed metal species comprising any of the following: aluminum oxide such as aluminum(III) oxide, aluminum hydroxide, aluminum oxide hydroxide, a hydrate of any of the aforementioned alumina species, a hydrate of any of the aforementioned alumina species, and any of the aforementioned alumina species, along with at least one further metal atom and / or its oxide and / or its hydroxide, and / or metal ion. Alumina nanoparticles may exist in colloidal form or in amorphous form such as polycrystalline amorphous form. α-, β-, or theta-alumina powders can also be used as alumina nanoparticles. In some embodiments, alumina nanoparticles are nanoparticles comprising and composed of at least one of the aforementioned aluminum oxides, such as aluminum(III) oxide.

[0087] The suspensions of this disclosure include zirconia nanoparticles. As described herein, alumina nanoparticles are particles having Z-average particle sizes in the ranges of 1 nm to 1000 nm, 10 to 500 nm, 20 to 300 nm, 50 to 200 nm, and 75 to 150 nm.

[0088] Alumina nanoparticles can be manufactured by any known method in the art.

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

[0090] In some embodiments, the suspension according to the Disclosure contains alumina nanoparticles in amounts of 0.05 to 5.0% by weight, 0.1 to 2.0% by weight, 0.15 to 1.0% by weight, or 0.15 to 0.5% by weight, based on the total weight of the suspension. In some embodiments, one or more types of alumina nanoparticles may be present in amounts ranging from 0.05 to 5.0% by weight, 0.10 to 4.0% by weight, 0.15 to 3.0% by weight, or 0.15 to 2.0% by weight, based on the total weight of the aqueous suspension, respectively.

[0091] If the amount of alumina nanoparticles is too high, the viscosity of the solution becomes too high, causing the particles to settle and potentially clogging the slurry distribution line being pumped. In such cases, a smaller amount of alumina should be selected. If the amount of alumina nanoparticles is too low, the mechanical abrasive force becomes insufficient, and the removal rate becomes too low to be usable. Within the scope of this disclosure, a balance is maintained between observable settling problems, excessively high viscosity, and lack of shine on the polishing pad, while still allowing for effective material removal.

[0092] In some embodiments, the presence of alumina nanoparticles allows for a reduction in the CMP process temperature compared to a suspension without alumina nanoparticles, thus enabling an effective CMP process temperature.

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

[0094] The suspensions relating to this disclosure comprise 0.1 to 3.0% by weight of one or more salts of nitric acid, 0.2 to 2.0% by weight of one or more salts of nitric acid, or 0.5 to 1.5% by weight, for example, 0.5 to 1.0% by weight of one or more salts of nitric acid. In some embodiments, the salts of nitric acid (e.g., one or more salts of nitric acid) may be selected from metal nitrates.

[0095] In some embodiments, salts of nitrate adjust the pH value of the suspensions of the present disclosure. Therefore, salts of nitrate used in the present disclosure tend to acidify the aqueous suspensions of the present disclosure.

[0096] While salts of nitrates can be diverse, they still possess the desired effects. Suitable salts of nitrates include, for example, ammonium nitrate, alkali metal nitrates, alkaline earth metal nitrates, transition metal nitrates, and nitrates of IUPAC group 13 of the periodic table. In some embodiments of the nitrates mentioned in this disclosure, the nitrate is a metallic nitrate. Examples of suitable nitrates include, for example, calcium nitrate, magnesium nitrate, iron(III) nitrate, and copper(II) nitrate. In some embodiments, the counterion for the nitrate anion is in a highly oxidized state, for example, in the case of iron in the 3+ state (i.e., as iron(III) nitrate). This is because iron(II) nitrate is immediately oxidized by a salt of permanganate, thus forming iron(III) nitrate, but the amount of permanganate undesirably reduced in the same reaction is reduced.

[0097] In some embodiments, the presence of metal cations and nitrate counterions is beneficial in the oxidation of silicon carbide.

[0098] In some embodiments, the aqueous suspension comprises one or more types of calcined alumina particles as components. In some embodiments, the one or more types of calcined alumina particles comprises aluminum oxide heated to a temperature above 1000°C to expel chemically bound water.

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

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

[0101] In some embodiments, one or more types of calcined alumina particles are present in amounts ranging from 0.1 to 5.0% by weight, 0.1 to 2.0% by weight, and 0.1 to 1.0% by weight, based on the total weight of the aqueous suspension.

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

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

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

[0105] In some embodiments, one or more metal salts of chloric acid are present in amounts ranging from 0.1 to 2.0% by weight, 0.1 to 1.0% by weight, 0.2 to 1.0% by weight, and 0.2 to 0.5% by weight, based on the total weight of the aqueous suspension.

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

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

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

[0109] In some embodiments, one or more metal salts of perchloric acid are present in amounts ranging from 0.1 to 2.0% by weight, 0.1 to 1.0% by weight, 0.2 to 1.0% by weight, and 0.2 to 0.5% by weight, based on the total weight of the aqueous suspension.

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

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

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

[0113] The pH of the suspensions relating to this disclosure can be achieved and / or maintained by any suitable means. More specifically, the suspensions may further include pH adjusters, pH buffers, or combinations thereof. The terms pH adjusters and pH buffers as used in this specification do not encompass the essential components of the suspensions relating to this disclosure, although these essential components may affect the pH value. Accordingly, pH adjusters and pH buffers are expressly distinct from the other components of the suspensions relating to this disclosure, which are described under other headings. Accordingly, pH adjusters and pH buffers are also particularly distinct from the nitrate salts described herein.

[0114] The pH adjuster may include any suitable pH adjusting compound (e.g., including, essentially consisting of, or comprising). In some embodiments, the nitrate salts described above already function to adjust the pH value to the desired range. However, in some cases, it may be desirable to further adjust the pH value using a different pH adjuster than a salt of nitrate. For example, the pH adjuster may be any suitable acid. In some embodiments, the pH adjuster is an inorganic acid. In some embodiments, the acid is nitric acid.

[0115] The pH buffer, if present, can be any suitable buffer, including, for example, inorganic pH buffers such as phosphates and borates. In some embodiments, no pH buffer is present in the suspension of this disclosure.

[0116] The suspension relating to this disclosure may contain any appropriate amount of pH adjuster and / or pH buffer, provided that such amount is sufficient to achieve and / or maintain the desired pH value of the suspension, for example, within the range described herein.

[0117] The suspensions of the present disclosure may further contain optional components. In some embodiments, the suspensions of the present disclosure do not contain any further components. Accordingly, the suspensions of the present disclosure may contain (for example, essentially consist of or consist of) one or more metal salts of permanganate, zirconia nanoparticles, alumina nanoparticles, one or more salts of nitric acid, water, and optionally one or more pH adjusters and / or pH buffers. Of course, undesirable and unavoidable impurities present in the aforementioned components may be present in the suspensions containing, essentially consisting of, or consisting of the aforementioned components. Such impurities are not considered here as further optional components, but as unavoidable and undesirable impurities, and may be present in amounts of less than 0.005% by weight, less than 0.002% by weight, or less than 0.001% by weight based on the weight of the suspension of the present disclosure.

[0118] In some embodiments, the suspension of the Disclosure may include further optional components. In some embodiments, the suspension of the Disclosure does not include further components. Thus, in some embodiments, the suspension of the Disclosure comprises (or essentially comprises) one or more metal salts of permanganate, one or more zirconia nanoparticles, one or more alumina nanoparticles, one or more salts of nitric acid, one or more calcined alumina particles, one or more metal salts of chlorate, and one or more metal salts of perchlorate, water, and optionally one or more pH adjusters and / or pH buffers.

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

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

[0121] Accordingly, if the suspension of the present disclosure contains further components, in some embodiments, organic compounds such as organic surfactants, organic defoamers, or organic solvents may be inorganic, as they are decomposed in an oxidation process by components such as at least one oxidizing agent, one or more metal salts of permanganate, one or more metal salts of chlorate, and / or one or more metal salts of perchlorate, and are therefore excluded from the suspension of the present disclosure in some embodiments.

[0122] In some embodiments, if further optional components are present, the further components may be inorganic components, and their amounts may be 0.005 to 1% by weight, 0.005 to 1.5% by weight, 0.005 to 1% by weight, or 0.005 to 0.5% by weight, based on the weight of the suspension of the present disclosure.

[0123] In some embodiments, the aqueous suspension does not contain certain components. For example, in some embodiments, the aqueous suspension does not contain MnO2, germanium particles, and / or ceria particles.

[0124] In some embodiments, the total components of the aqueous suspension (e.g., salts of permanganate, zirconia nanoparticles, alumina nanoparticles, and salts of nitrate) constitute at least 90% by weight, at least 95% by weight, or at least 98% by weight of all components of the suspension of the Disclosure, excluding water, pH adjusters, and pH buffers. In some embodiments, the sole components of the suspension of the Disclosure are one or more salts of permanganate, zirconia nanoparticles, alumina nanoparticles, one or more salts of nitrate, water, and pH adjusters and pH buffers, and the suspension thus consists of or is essentially composed of these components.

[0125] In some embodiments, the total components of the aqueous suspension (e.g., components including one or more metal salts of permanganate, one or more zirconia nanoparticles, one or more alumina nanoparticles, one or more salts of nitric acid, one or more calcined alumina nanoparticles, one or more metal salts of chlorate, and one or more metal salts of perchlorate) constitute at least 90% by weight, at least 95% by weight, and at least 98% by weight of all components of the suspension of the Disclosure, excluding water, pH adjusters, and pH buffers. In some embodiments, the sole components of the suspension of the Disclosure are one or more metal salts of permanganate, one or more zirconia nanoparticles, one or more alumina nanoparticles, one or more salts of nitric acid, one or more calcined alumina nanoparticles, one or more metal salts of chlorate, and one or more metal salts of perchlorate, water, and components of pH adjusters and pH buffers; thus the suspension consists of these components.

[0126] In some embodiments, the total components of the aqueous suspension (e.g., at least one oxidizing agent; abrasive particles having a Mohs hardness of less than 6, in total amount less than 0.2% by weight based on the total weight of the aqueous suspension; and aluminum nitrate) constitute at least 90% by weight, at least 95% by weight, or at least 98% by weight of all components of the suspension of the present disclosure, excluding water, pH adjusters, and pH buffers. In some embodiments, the sole components of the suspension of the present disclosure are at least one oxidizing agent; abrasive particles having a Mohs hardness of less than 6, in total amount less than 0.2% by weight based on the total weight of the aqueous suspension; and aluminum nitrate, water, and pH adjusters and pH buffers; thus the suspension consists of these components.

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

[0128] In some embodiments, the aqueous suspension may contain (for example, contain, essentially consist of, or consist of) 2.6 to 5.5 wt% of one or more metal salts of permanganate, 0.1 to 2.0 wt% of zirconia nanoparticles, 0.1 to 2.0 wt% of alumina nanoparticles, and 0.2 to 2.0 wt% of one or more salts of nitric acid, water, and an inorganic acid for adjusting the pH value, with the weight percentages being based on the total weight of the aqueous suspension.

[0129] In some embodiments, the aqueous suspension according to the Disclosure may comprise (for example, comprising, essentially comprising, or consisting of) 3.0 to 5.0 wt% of one or more metal salts of permanganate, 0.15 to 1.0 wt% of zirconia nanoparticles, 0.15 to 1.0 wt% of alumina nanoparticles, and 0.5 to 1.5 wt% of one or more salts of nitric acid, the weight percentages being based on the total weight of the aqueous suspension.

[0130] In some embodiments, the aqueous suspension according to the Disclosure may comprise (for example, comprising, essentially comprising, or consisting of) 4.0 to 5.0 wt% of one or more metal salts of permanganate, 0.15 to 0.5 wt% of zirconia nanoparticles, 0.15 to 0.5 wt% of alumina nanoparticles, and 0.5 to 1.0 wt% of one or more salts of nitric acid, the weight percentages being based on the total weight of the aqueous suspension.

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

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

[0133] In some embodiments, the aqueous suspension of the present disclosure is based on the total weight of the aqueous suspension, water, and an inorganic acid such as nitric acid, which optionally adjusts the pH value to the range of 3.0 to 5.5, 3.5 to 5.0, or 4.0 to 5.0; one or more metal salts of permanganate in amounts ranging from 7.5 to 30% by weight, 10 to 25% by weight, 12 to 22% by weight, for example 13 to 20% by weight; one or more zirconia nanoparticles in amounts ranging from 0.05 to 5.0% by weight, 0.10 to 2.0% by weight, 0.15 to 1.0% by weight, for example 0.15 to 0.5% by weight; 0.05 to 5.0% by weight, 0.10 to 2.0% by weight, 0.1 The material comprises, essentially consists of, or consists of, one or more types of alumina nanoparticles in amounts ranging from 5 to 1.0% by weight, for example, in the range of 0.15 to 0.5% by weight; one or more types of calcined alumina particles in amounts ranging from 0.1 to 5.0% by weight, 0.1 to 2.0% by weight, for example, in the range of 0.1 to 1.0% by weight; one or more types of metal salts of chloric acid in amounts ranging from 0.1 to 2.0% by weight, 0.1 to 1.0% by weight, 0.2 to 1.0% by weight, for example, in the range of 0.2 to 0.5% by weight; and one or more types of metal salts of perchloric acid in amounts ranging from 0.1 to 2.0% by weight, 0.1 to 1.0% by weight, 0.2 to 1.0% by weight, for example, in the range of 0.2 to 0.5% by weight.

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

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

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

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

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

[0139] Furthermore, in some embodiments, the pH value of the suspension is in the range of 3 to 4, for example, 3.4 to 4.

[0140] In several embodiments, exemplary embodiments of the aqueous suspensions of this disclosure exhibit excellent pH stability during storage, i.e., pH drift is less than 0.1 for a period of at least 12 months, and exhibit high material removal rates and excellent surface roughness of the polished substrate despite the small amount of abrasive particles. Furthermore, small amounts of abrasive particles can be stably suspended in an aqueous carrier without the use of surfactants or dispersants, thus avoiding the adverse effects of such surfactants or dispersants on the polishing process. If sedimentation occurs, the abrasive particles can be easily resuspended by shaking or stirring the suspension before use, thereby preventing, mitigating, or limiting clogging problems in the circulation line and ensuring a uniform suspension and material removal rate during polishing.

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

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

[0143] Suitable substrates to be polished include ceramic materials, metals, metal alloys, or diamond. In some embodiments, the substrate may be a group III-V compound, such as gallium nitride, aluminum nitride, indium 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 suitable for chemomechanical polishing of a substrate comprising at least one layer of silicon carbide. The silicon carbide may be single-crystal or polycrystalline. In some embodiments, the substrate comprises at least one layer of single-crystal silicon carbide, such as single-crystal 4H silicon carbide (i.e., 4H-SiC).

[0144] In some embodiments, the aqueous suspension of the present disclosure can be adapted to polish a substrate, such as silicon carbide, at a material removal rate of at least 1.5 μm / hr, at least 2 μm / hr, 2.5 to 12 μm / hr, or 2.5 to 9 μm / hr. Generally, higher material removal rates can be achieved in single-wafer CMP processes compared to batch CMP processes, because the polishing conditions described above vary in batch CMP processes. The material removal rate can be determined by the change in mass of the substrate before and after polishing using the following formula: TIFF0007888599000001.tif14170 Here, Δm is the change in mass of the substrate before and after polishing. ρ substrate This is the density of the substrate, r is the radius of the substrate, t is the polishing time.

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

[0146] In some embodiments, the surface roughness after polishing a substrate, such as a silicon carbide substrate, using the aqueous suspension of the present disclosure is less than 0.6 nm, e.g., ≤0.3 nm. The roughness can be calculated as RMS roughness by AFM measurement (5x5 scans, 1 Hz scan speed). This level of roughness is generally considered desirable and acceptable for downstream substrate processing involving surface epitaxy, such as chemical vapor deposition (CVD). While we do not wish to be bound by this theory, the low surface roughness achieved using the aqueous suspension of the present disclosure is thought to be due to the use of aluminum nitrate, which results in the formation of a mesh structure that embeds the abrasive particles. The embedding creates a "soft" layer on the particle surface, which prevents, mitigates, or limits damage to the substrate surface during polishing without adversely affecting the high material removal rate.

[0147] The suspensions relating to this disclosure can be supplied as a single-component system comprising water, at least one oxidizing agent, less than 0.2% by weight of abrasive particles based on the total weight of the suspension, aluminum nitrate, and optionally other aforementioned components. Such a single-component system is a ready-to-use suspension. In some embodiments, the suspensions of this disclosure are provided in the form of a single-component system because such suspensions have high storage stability, i.e., do not exhibit pH drift and abrasive particle sedimentation, and can be used immediately without requiring further mixing and / or dilution steps. The preparation of such a single-component system can be carried out as described in relation to the preparation of aqueous suspensions.

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

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

[0150] However, the aqueous suspensions of this disclosure already have a high degree of storage stability under typical storage conditions because the use of aluminum nitrate prevents, reduces, or limits pH drift during storage, and thus prevents, reduces, or limits the formation of undesirable reaction products such as manganese dioxide, which would result in a reduced removal rate of the material and increased surface roughness. Even if a small precipitate of solid particles occurs after storage for several weeks or months, such precipitates can be easily redispersed by stirring, such as by agitation and / or shaking. Accordingly, in some embodiments, the aqueous suspensions of this disclosure are supplied as the aforementioned one-component system.

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

[0152] In some embodiments, the suspensions of the present disclosure may be supplied as a one-package system comprising water, one or more salts of permanganate, alumina nanoparticles, zirconia nanoparticles, one or more salts of nitric acid, and optionally other aforementioned components. Such a one-package system is a ready-to-use suspension. In some embodiments, the suspensions of the present disclosure may be in the form of a one-package system because such compositions are storage-stable and ready to use without further mixing and / or dilution steps. Thus, in some embodiments, it may be appropriate to first dissolve one or more salts of permanganate and then supplement the solution with the other components to obtain a one-package system.

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

[0154] However, the ready-to-use suspensions of this disclosure already possess high storage stability under typical storage conditions. Even if a small precipitate of solid particles occurs after storage for several weeks or months, such precipitates can be easily redispersed by stirring and / or shaking. Therefore, customers do not need to mix the components immediately before use.

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

[0156] In some embodiments, a method for preparing an aqueous suspension includes the steps of (i) adding aluminum nitrate to the aqueous suspension and (ii) adding an aqueous solution of one or more metal salts of permanganate to the aqueous suspension, wherein the aqueous suspension contains alumina nanoparticles and zirconia particles in water. In some embodiments, the method includes filtering the aqueous suspension before adding aluminum nitrate. In some embodiments, the method includes filtering the aqueous solution of one or more metal salts of permanganate before adding the aqueous solution. In some embodiments, MnO2 is absent from the aqueous suspension. In some embodiments, the aqueous suspension has a pH value in the range of 2 to 5 at 23°C. In some embodiments, the steps of adding aluminum nitrate (i) and adding the aqueous solution (ii) are carried out sequentially. The steps of the method of this disclosure can be rearranged, and the order of the steps can be changed. For example, the first step may be step (ii), or the aqueous solution may be added to the aqueous suspension first. This is not an exhaustive list of the order of the steps of the method. The steps can be rearranged in any order.

[0157] In some embodiments, a method for preparing an aqueous suspension includes the steps of (i) adding aluminum nitrate to the aqueous suspension; (ii) adding aqueous solutions of one or more metal salts of permanganate, one or more metal salts of perchlorate, and one or more metal salts of chlorate to the aqueous suspension; and (iii) adding one or more 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 before adding aluminum nitrate. In some embodiments, the method includes filtering the aqueous solution before adding the aqueous solution. In some embodiments, MnO2 is absent in the aqueous suspension. In some embodiments, the aqueous suspension has a pH value in the range of 2 to 5 at 23°C. In some embodiments, the steps of adding aluminum nitrate (i), adding aqueous solutions (ii), and adding one or more calcined alumina particles (iii) are carried out sequentially. The steps of the method disclosed herein can be rearranged, and the order of the steps can be changed. For example, the first step may be step (ii), in which case the aqueous solution is first added to the aqueous suspension, followed by step (iii), and then step (i). In some examples, step (iii) may be followed by step (ii), and then step (i). This is not an exhaustive list of the order of the steps of the method. The steps can be rearranged in any order (e.g., step (iii), step (i), then step (ii)).

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

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

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

[0161] Process (A):

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

[0163] The aqueous suspension provided in step (A) may, in any case, contain abrasive particles in an amount of 0.1 to 3% by weight, for example, 0.2 to 1% by weight, based on the total amount of aqueous suspension obtained in step (A).

[0164] Process (B):

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

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

[0167] Process (C):

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

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

[0170] Optional process (D):

[0171] In an optional step (D), the pH of the aqueous suspension obtained from step (C) is adjusted using at least one pH adjusting agent. In some embodiments, an aqueous suspension with the desired pH is already obtained after step (C) by using an appropriate amount of aluminum nitrate, and the optional step (D) is not required or used.

[0172] Further steps (E):

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

[0174] The statements relating to aqueous suspensions, and in particular to the components of aqueous suspensions, in this disclosure shall apply mutatis mutandis to further embodiments of methods for preparing aqueous suspensions.

[0175] The suspension of this disclosure is useful as an abrasive composition suitable for polishing silicon carbide surfaces, for example, in chemical mechanical planarization.

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

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

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

[0179] The CMP method described herein can be used in combination with chemical mechanical polishing (CMP) equipment / tools / devices. Any of the commonly known CMP equipment in the industry, including equipment from suppliers such as Applied Materials, Revasum, Axus, Lapmaster Wolters, and Ibarra, can be used in the CMP method described herein.

[0180] The apparatus may comprise a platen that operates in use and has a velocity resulting from orbital, linear, or circular motion; a polishing pad that contacts the platen and moves with the platen in operation; and a carrier that contacts the surface of the polishing pad and holds a substrate to be polished by moving relative to the surface of the polishing pad. Polishing of the substrate is performed by positioning the substrate in contact with the polishing pad and the suspension of the Disclosure (generally placed between the substrate and the polishing pad), and by the polishing pad moving relative to the substrate, thereby abrading at least a portion of the substrate and polishing and / or planarizing the substrate.

[0181] In some embodiments, the substrate is a silicon carbide substrate. In some embodiments, the polishing endpoint is determined by monitoring the weight of the silicon carbide substrate, 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 mentioned in relation to the quantification of the material removal rate. Polishing refers to removing at least a portion of a surface in order to polish the surface. Polishing may be performed to provide a surface with reduced surface roughness by removing gouge, crates, pits, etc., but polishing may also be performed to introduce or restore a surface shape characterized by the intersection of planar segments. The methods of the present disclosure can be used to polish and / or planarize any suitable substrate, for example, a substrate comprising at least one layer of silicon carbide.

[0182] In some embodiments, before contacting the substrate with the aqueous suspension, the method includes lowering the pH of the aqueous suspension to a range of 2 to 2.5. The lowering step may include adding an acid. The pot life of the aqueous suspension is the usable life of the aqueous suspension after it has been lowered to, for example, a pH range of 2 to 2.5. The storage life of the aqueous suspension may exceed one year, as described herein.

[0183] In some embodiments, the aqueous suspension is stored for up to one year and beyond, and then reduced immediately before use (e.g., by adding an acid to the aqueous suspension). After the aqueous suspension has been reduced, it has a pot life, after which it may no longer be usable for its intended purpose. The pot life of the aqueous suspension is called the pot life. In some embodiments, the pot life may be at least 5, 7, 10, 12, or 14 days. To ensure that the aqueous suspension is used during its pot life, in some embodiments, the method of the present disclosure includes contacting a substrate with the reduced aqueous suspension within a set time frame of the reduction step. For example, the method includes contacting a substrate with the reduced aqueous suspension within 5, 7, 10, 12, or 14 days of the reduction step. This ensures that the reduced aqueous suspension is in contact with the substrate for the duration of its pot life.

[0184] A suspension combined with a polishing pad is an essential component of the chemical mechanical planarization method described in the claims of this disclosure. In some embodiments, the type and material of the polishing pad used in the CMP method of this disclosure is not important to the disclosure. In fact, any conventionally used polishing pad used in a CMP method for planarizing silicon carbide wafers can be used. Suitable polishing pads include, for example, woven and nonwoven polishing pads. Furthermore, suitable polishing pads may include any suitable polymer of varying densities, hardness, thickness, compressibility, ability to rebound upon compression, and compressive modulus. Suitable polymers include, for example, polyvinyl chloride, polyvinyl fluoride, nylon, fluorocarbon, polycarbonate, polyester, polyacrylate, polyether, polyethylene, polyamide, polyurethane, polystyrene, polypropylene, adapted products thereof, and mixtures thereof. In some embodiments, polyurethane pads can be used. Conventional pads may be manufactured as a cake, one at a time, or later sliced ​​into individual pad substrates. These substrates are then machined to the final thickness, and grooves are further machined therein. Polymer or polymer / fiber circular pads can be 1 mm to 4 mm thick. The polishing pad can have any suitable structure. For example, the polishing pad may be circular and, in use, rotate around an axis perpendicular to the plane defined by the pad's surface. The polishing pad may be cylindrical, with its surface acting as the polishing surface, and in use, rotate around the central axis of the cylinder. The polishing pad can be in the form of an endless belt that moves linearly with respect to the cutting edge being polished during use. The polishing pad can have any suitable shape and, in use, reciprocate or orbital along a plane or semicircle. Many other modifications are readily apparent to those skilled in the art.

[0185] Conventional polymer-based CMP polishing pads are typically bonded to a flat, rotating circular table within the CMP apparatus using a pressure-sensitive adhesive.

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

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

[0188] The lower temperatures of the suspensions of this disclosure and the suspensions prepared according to the methods of this disclosure offer advantages in that the CMP method can be performed a) at lower temperatures, resulting in a gentler process that is less prone to surface defects and thus yields a higher process yield, or b) at higher material removal rates by increasing the pressure on the polishing pad and / or increasing the rate of CMP to levels higher than those allowed for conventional suspensions. Depending on the specific objective to be achieved, such as yield versus throughput, these temperature-related advantages are highly valuable.

[0189] However, the upper limit of the polishing temperature is limited by the material of the polishing pad, which is desirable to have little to no degradation during the CMP process. Typically, the polishing temperature does not exceed 60°C.

[0190] The flow rate at which the suspension of this disclosure is distributed onto a CMP device depends on the specific device and pad configuration used. However, the suspension of this disclosure works well at industry-standard flow rates.

[0191] The CMP method of this disclosure, using the suspension of this disclosure, can remove silicon carbide without damaging the surface at a material removal rate of approximately 3 to 15 μm / hr, typically 5 to 12 μm / hr or 6 to 10 μm / hr, thus resulting in a scratch-free silicon carbide surface, i.e., a surface that is shown to be free of CMP-related scratches, often present due to other slurries, pads, tools, etc., as measured using confocal optical microscopy techniques with automated scratch detection and characterization measurements.

[0192] In a typical CMP process, the scratch length per wafer may be expected to be less than 20 mm, although this depends heavily on the customer's process, tools, pads, wafer quality, etc. However, the suspension of this disclosure used in the CMP method of this disclosure provides a significant improvement in terms of scratch occurrence and length, and even when scratches occur, they are typically significantly lower than the above values.

[0193] The suspension of this disclosure yields a SiC wafer surface having a surface roughness of less than 1 angstrom. The roughness is calculated as RMS roughness by AFM measurement (5x5 scans, 1 Hz scan speed). This level of roughness is generally considered desirable and acceptable for downstream silicon carbide processing, including surface epitaxy, such as chemical vapor deposition (CVD).

[0194] Finally, the suspension enables very low CMP polishing temperatures. Polishing temperatures are typically lower than those used in prior art slurries. The lower temperatures of the suspensions of this disclosure offer significant advantages in that the CMP method can be performed at a) lower temperatures, resulting in a gentler process with fewer surface defects and thus higher process yield, or b) by increasing the pressure on the polishing pad and / or increasing the CMP rate to levels higher than those allowed for conventional suspensions, thereby enabling higher material removal rates. Depending on the specific objectives to be achieved, such as yield versus throughput, these temperature-related advantages are valuable.

[0195] The descriptions of aqueous suspensions in this disclosure, particularly the components of aqueous suspensions and methods for preparing aqueous suspensions, will be applied mutatis mutandis to further embodiments of methods for chemically planarizing substrates. [Examples]

[0196] The following embodiments further illustrate the present disclosure, but should not be construed as limiting its scope.

[0197] Example 1 (Comparative Example)

[0198] This example demonstrates the effect of alumina nanoparticle concentration on single-crystal SiC polishing temperature and material removal rate. Polishing temperature and removal rate were quantified for each aqueous suspension containing 4 wt% KMnO4 and 0.5 wt% nitrate at pH 2.3, and the results are shown in Table 1. TIFF0007888599000002.tif68170

[0199] Increasing the abrasive particle concentration leads to a decrease in temperature, and simultaneously reduces the silicon carbide removal rate.

[0200] Example 2 (Comparative Example)

[0201] This example demonstrates the effect of zirconia nanoparticle concentration on single-crystal SiC polishing temperature and material removal rate. Polishing temperature and removal rate were quantified for each aqueous suspension containing 4 wt% KMnO4 and 0.5 wt% nitrate at pH 2.3, and the results are shown in Table 2. TIFF0007888599000003.tif71170

[0202] The temperature and removal rates of zirconia nanoparticles showed similar trends to those of alumina nanoparticles. However, the presence of zirconia particles improved the SiC removal rate by up to approximately 20% compared to alumina nanoparticles of similar concentration.

[0203] Example 3 (Comparative Example)

[0204] This example demonstrates the effect of a combination of alumina and zirconia nanoparticles on the polishing temperature and material removal rate of single-crystal SiC. The polishing temperature and removal rate were quantified for each aqueous suspension containing 4.5 wt% KMnO4 and 0.75 wt% nitrate at pH 2.3, and the respective compositions and results are shown in Table 3. TIFF0007888599000004.tif70170

[0205] The synergistic effect of alumina and zirconia nanoparticles resulted in a remarkable increase in removal rate of approximately 11 μF / hr. Simultaneously, a significant decrease in temperature was observed.

[0206] Surface roughness (R) of single-crystal SiC (Si surface) using a mixed particle (alumina + zirconia) sample a Table 4 shows the atomic force microscope (AFM) data from the measurement data. TIFF0007888599000005.tif65170

[0207] The mixed particles provide sub-angiotensin surface roughness on high-quality SiC substrates.

[0208] Example 4 (An example of the present disclosure)

[0209] This example demonstrates the effects of combinations of alumina and zirconia nanoparticles or calcined alumina (these components are collectively referred to as abrasive grains in Table 5) and further components (chlorates, perchlorates, collectively referred to as additives in Table 5) on the polishing temperature and material removal rate of single-crystal SiC (Si surface). The polishing temperature and removal rate were quantified for each aqueous suspension containing 15 wt% permanganate (KMnO4, NaMnO4) and 0.75 wt% nitrate at pH 2.3, and the respective compositions and results are shown in Table 5. TIFF0007888599000006.tif62170

[0210] The data presented in Table 5 clearly demonstrates the importance of balancing chemical activity and mechanical wear to achieve high material removal rates along with acceptable process temperatures. High abrasive concentrations (6% abrasive) of zero-percent additives decrease the removal rate as the process temperature decreases. The synergistic effect of abrasives and additives resulted in a significant increase in removal rate of up to approximately 14 μ / hr at acceptable process temperatures.

[0211] The surface roughness (R) of a single-crystal SiC (Si surface) obtained on a polished SiC (Si surface) wafer using the concentrations given above (Table 5) is as follows: a Table 6 shows the atomic force microscopy (AFM) data from the measurements. TIFF0007888599000007.tif47170

[0212] From the data shown in Table 6, this slurry provides a scratch-free, sub-angiotensin-level surface roughness (R) that enhances the throughput of SiC wafers. a It is clear that this results in: The combination of high concentrations of chemically active ions and high concentrations of particles leads to improved single-crystal SiC (Si surface) material removal rates, along with excellent surface finish at acceptable process temperatures. Therefore, all these performance advantages make these slurries usable in all SiC process applications (i.e., batch processes, single-wafer processes).

[0213] The present disclosure will be described in more detail below using the following embodiments, but the disclosure is not limited to these embodiments. Furthermore, unless otherwise specified, “parts,” “%,” and “ratio” in the embodiments mean “parts by mass,” “% by mass,” and “ratio by mass,” respectively.

[0214] 1.Quantification method:

[0215] 1.1 Material removal rate

[0216] The material removal rate (MRR) is determined by the change in substrate mass before and after polishing, according to the formula described above. The material removal rate is calculated by dividing the change in substrate mass before and after polishing by the time required for polishing. The substrate mass is measured using a bench scale. The material removal rate is quantified for each wafer polished in a single batch polishing process and averaged over three consecutive batch polishing processes.

[0217] 1.2 Surface roughness

[0218] Surface roughness is calculated as RMS roughness using AFM measurement (5x5 scan, 1Hz scan speed) by measuring the surface roughness of each SiC substrate at three locations. If the surface roughness is repeated at these three locations, each value is given as the surface roughness.

[0219] 1.3 Storage stability

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

[0221] 2. Preparation of Examples and Comparative Aqueous Suspensions of the Disclosure

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

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

[0224] Step A1: An aqueous suspension containing alumina particles and aluminum nitrate was 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.

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

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

[0227] The amounts of alumina particles, aluminum nitrate, potassium permanganate, and water used in steps A1 and A2 are selected so that they are in the amounts shown in Table 7 after the completion of step A3.

[0228] Comparison method B (comparative example):

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

[0230] Step B2: Add the aqueous slurry of alumina particles and aluminum nitrate to the aqueous solution prepared in Step B1.

[0231] The amounts of alumina particles, aluminum nitrate, potassium permanganate, and water used in steps B1 and B2 are selected so that the amounts given in Table 7 are obtained after the completion of step B2.

[0232] Table 7 shows the final compositions of all the prepared examples and comparative aqueous suspensions of this disclosure. TIFF0007888599000008.tif130170

[0233] 3. CMP Process

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

[0235] 4.Results

[0236] 4.1 Storage stability

[0237] Storage stability was determined as described in the storage stability section (Section 1.3) above, and the results obtained are listed in Table 8. TIFF0007888599000009.tif108170

[0238] The results shown in Table 8 demonstrate that aqueous suspensions prepared according to the method of this disclosure, containing aluminum nitrate and less than 5% by weight of alumina particles (S-I1, S-C1 to S-C3), do not exhibit pH drift or color change even after 12 months of storage, thus enabling consistent polishing quality regardless of storage period. In contrast, aqueous suspension S-C4, prepared according to the method of this disclosure, containing aluminum nitrate and 5% by weight of alumina particles, lacks storage stability as it settles during storage. Aqueous suspension S-C5, containing the same amounts of aluminum nitrate, alumina particles, and potassium permanganate as aqueous suspension SS-I1 of this disclosure, but not prepared according to the method of this disclosure, is also unstable during storage. When aqueous suspensions S-C6 to S-C9 containing nitrates other than aluminum nitrate are stored, undesirable manganese dioxide is generated due to pH drift to higher pH values. However, the presence of manganese dioxide is undesirable as it increases the surface roughness of the stored suspension and reduces the material removal rate (see Tables 9 and 11 below).

[0239] 4.2 Silicon Carbide Removal Rate

[0240] The silicon carbide removal rate was quantified as described in Section 1.1 above, and the results obtained are listed in Tables 9 and 10. TIFF0007888599000010.tif80170TIFF0007888599000011.tif33170

[0241] Batch-based CMP process:

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

[0243] Single-wafer CMP process:

[0244] The aqueous suspension S-I1 of this disclosure enables high material removal rates and excellent surface roughness (see Table 12 below) even at high down pressures, resulting in an efficient and high-speed polishing process that yields high yield (i.e., substrates with high surface quality).

[0245] 4.3 Surface roughness

[0246] The surface roughness was quantified as described in Section 1.2 above, and the results obtained are listed in Tables 11 and 12. TIFF0007888599000012.tif76170TIFF0007888599000013.tif33170

[0247] Batch-based CMP process:

[0248] The aqueous suspension S-I1 of this disclosure yields excellent surface roughness of less than 3 angstroms; however, the use of a larger amount of alumina particles (see comparative suspensions S-C1 to S-C3) results in significantly higher surface roughness, thus degrading the quality of the polished SiC substrate. The use of comparative aqueous suspensions S-C6 and S-C7, which contain ferric nitrate and cerium nitrate, results in large scratches on the substrate surface, yielding polished products of unacceptable quality. The surface roughness of the comparative aqueous suspensions S-C5, S-C8, and S-C9 could not be quantified due to their low stability after preparation (see Table 12 above).

[0249] Single-wafer CMP process:

[0250] The aqueous suspension S-I1 of this disclosure enables the achievement of excellent surface roughness even at high down pressures, and thus enables a high-speed polishing process that results in excellent yield.

[0251] 5. Discussion of Results

[0252] Aqueous suspension S-I1 of the present disclosure, containing less than 0.2 wt% alumina particles and aluminum nitrate, yields high material removal rates and excellent surface roughness in batch and single-wafer CMP processes. Furthermore, these suspensions exhibit excellent storage stability exceeding 12 months, thus ensuring consistent material removal rates and surface quality in the polishing process throughout their storage period. While not bound by this specific theory, the presence of aluminum nitrate is thought to prevent or mitigate pH changes that occur during storage due to the dissolution of alumina particles in an acidic medium, and further to form a "soft" layer on the alumina particles, thereby yielding polished products with high surface quality (i.e., low surface roughness). Surprisingly, high material removal rates are achieved only when an aqueous solution of an oxidizing agent is added to the aqueous suspension containing alumina particles and aluminum nitrate; adding the aqueous suspension of alumina particles and aluminum nitrate to an aqueous solution of potassium nitrate results in a decrease in material removal rates (see comparative suspension S-C5).

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

[0254] Suspensions containing 0.2% to 1% by weight of alumina particles and aluminum nitrate (comparative suspensions S-C1 to S-C3) exhibit high storage stability and result in increased material removal rates in batch CMP processes compared to the suspensions of this disclosure. However, this increase in material removal rate is accompanied by an unacceptable increase in the surface roughness of the polished substrate, and therefore dramatically reduces the yield of the polishing process. Further increasing the amount of alumina particles to 5% by weight resulted in unstable suspensions that did not possess the required storage stability.

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

[0256] [Pattern]

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

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

[0259] Embodiment 2. The aqueous suspension of Embodiment 1, further comprising at least one pH adjusting agent and / or at least one pH buffering agent.

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

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

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

[0263] Embodiment 6. An aqueous suspension of any of the preceding embodiments, wherein one or more metal salts of permanganate are selected from the group consisting of LiMnO4, KMnO4, NaMnO4, and mixtures thereof.

[0264] Embodiment 7. An aqueous suspension of any of the preceding embodiments, wherein zirconia nanoparticles contain ZrO2.

[0265] Embodiment 8. An aqueous suspension of any of the preceding embodiments, wherein the alumina nanoparticles contain colloidal alumina particles.

[0266] Embodiment 9. An aqueous suspension of Embodiment 8, wherein the colloidal alumina particles comprise γ-AlOOH particles and / or γ-Al2O3 particles.

[0267] Embodiment 10. An aqueous suspension of any of the preceding embodiments, wherein one or more salts of nitric acid contain Al(NO3)3.

[0268] Embodiment 11. An aqueous suspension of any of the preceding embodiments, wherein MnO2 is not present in the aqueous suspension.

[0269] Embodiment 12. A method for chemically and mechanically planarizing a substrate, comprising: (i) bringing the substrate into contact with the aqueous suspension of Embodiment 1; (ii) moving the aqueous suspension onto the substrate using an abrasive pad; and (iii) polishing the substrate by abrading at least a portion of it.

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

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

[0272] Embodiment 15. Any method of Embodiments 12 to 14, further comprising the step of lowering the pH of the aqueous suspension to a range of 2 to 2.5 before bringing the substrate into contact with the aqueous suspension.

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

[0274] Embodiment 17. The method of Embodiment 15, wherein the substrate is brought into contact with an aqueous suspension within 14 days of the decrease in pH.

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

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

[0277] Embodiment 20. The method of Embodiment 18 or Embodiment 19, further comprising the step of filtering an aqueous solution of one or more metal salts of permanganate before adding the aqueous solution.

[0278] Embodiment 21. Any method of the preceding embodiment, wherein MnO2 is not present in the aqueous suspension.

[0279] Embodiment 22. Any method of the preceding embodiment, wherein the aqueous suspension has a pH value in the range of 2 to 5 at 23°C.

[0280] Embodiment 23. Any method of the preceding embodiments, wherein steps (i) and (ii) are carried out sequentially.

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

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

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

[0284] Embodiment 27. Any method according to the preceding embodiment, wherein the pH of an aqueous suspension is lowered by the addition of an acid, and the acid contains nitric acid.

[0285] Aspect 28. A method according to any of the previous aspects, wherein the pH of the aqueous suspension is reduced to 2.3.

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

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

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

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

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

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

[0292] Aspect 6. The aqueous suspension according to any of the previous aspects, wherein the one or more metal salts of permanganic acid are selected from the group consisting of LiMnO4, KMnO4, NaMnO4, and mixtures thereof.

[0293] Aspect 7. The aqueous suspension according to any of the previous aspects, wherein the one or more zirconia nanoparticles contain ZrO2.

[0294] Aspect 8. The aqueous suspension according to any of the previous aspects, wherein the one or more alumina nanoparticles contain colloidal alumina particles.

[0295] Embodiment 9. An aqueous suspension of Embodiment 8, wherein the colloidal alumina particles comprise γ-AlOOH particles and / or γ-Al2O3 particles.

[0296] Embodiment 10. An aqueous suspension of any of the preceding embodiments, wherein one or more salts of nitric acid contain Al(NO3)3.

[0297] Embodiment 11. An aqueous suspension of any of the preceding embodiments, comprising aluminum oxide in which one or more calcined alumina particles are heated at a temperature exceeding 1000°C to expel chemically bound water.

[0298] Embodiment 12. An aqueous suspension of any of the preceding embodiments, wherein one or more metal salts of chloric acid contain NaClO3.

[0299] Embodiment 13. An aqueous suspension of any of the preceding embodiments, wherein one or more metal salts of perchloric acid contain Al(ClO4)3.

[0300] Embodiment 14. An aqueous suspension of any of the preceding embodiments, wherein MnO2 is not present in the aqueous suspension.

[0301] Embodiment 15. A method for chemically planarizing a substrate, comprising: (i) bringing the substrate into contact with the aqueous suspension of claim 1; (ii) moving the aqueous suspension onto the substrate using an abrasive pad; and (iii) polishing the substrate by abrading at least a portion of it.

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

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

[0304] Embodiment 18. Any method of the preceding embodiment, further comprising the step of lowering the pH of the aqueous suspension to a range of 2 to 2.5 before bringing the substrate into contact with the aqueous suspension.

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

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

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

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

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

[0310] Aspect 24. The method of any of the preceding aspects, wherein MnO2 is not present in the aqueous suspension.

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

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

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

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

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

[0316] Embodiment 30. Any method according to the preceding embodiment, wherein the pH of an aqueous suspension is lowered by the addition of an acid, and the acid contains nitric acid.

[0317] Embodiment 31. Any method according to the preceding embodiment, wherein the pH of the aqueous suspension is reduced to 2.3.

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

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

[0320] Embodiment 2. The aqueous suspension of Embodiment 1, further comprising at least one pH adjusting agent and / or at least one pH buffering agent.

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

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

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

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

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

[0326] Embodiment 8. An aqueous suspension of any of the preceding embodiments, wherein the abrasive particles contain alumina particles.

[0327] Embodiment 9. An aqueous suspension of Embodiment 8, wherein the alumina particles contain γ-AlOOH particles.

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

[0329] Embodiment 11. An aqueous suspension of any of the preceding embodiments, wherein MnO2 is not present in the aqueous suspension.

[0330] Embodiment 12. A method for chemically and mechanically planarizing a substrate, comprising: (i) bringing the substrate into contact with the aqueous suspension described in claim 1; (ii) moving the aqueous suspension onto the substrate using an abrasive pad; and (iii) polishing the substrate by abrading at least a portion of it.

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

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

[0333] Embodiment 15. Any method of the preceding embodiment, wherein the substrate temperature does not exceed 60°C during wear.

[0334] Embodiment 16. Any method of the preceding embodiment, further comprising the step of lowering the pH of the aqueous suspension to a range of 2 to 2.5 before bringing the substrate into contact with the aqueous suspension.

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

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

[0337] Embodiment 19. A method for preparing an aqueous suspension, comprising the steps of (i) adding aluminum nitrate to an aqueous suspension containing 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 the aqueous suspension contains less than 0.2% by weight of abrasive particles based on the total weight of the aqueous suspension.

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

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

[0340] Embodiment 22. Any method of the preceding embodiment, wherein MnO2 is not present in the aqueous suspension.

[0341] Embodiment 23. Any method of the preceding embodiment, wherein the aqueous suspension has a pH value in the range of 2 to 5 at 23°C.

[0342] Embodiment 24. Any method of the preceding embodiments, wherein steps (i) and (ii) are carried out sequentially.

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

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

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

[0346] Embodiment 29. Any method according to the preceding embodiment, wherein the pH of an aqueous suspension is lowered by the addition of an acid, and the acid contains nitric acid.

[0347] Embodiment 30. Any method according to the preceding embodiment, wherein the pH of the aqueous suspension is reduced to 2.3.

[0348] Embodiment 31. Any method of the preceding embodiment, wherein an aqueous suspension having a pH in the range of 2 to 2.5 is used in a single-wafer or batch-type chemical mechanical planarization process.

[0349] Embodiment 32. Any of the preceding embodiments, wherein the step of using an aqueous suspension includes the step of using an aqueous suspension having a pH in the range of 2 to 2.5 in a batch chemical mechanical flattening method.

[0350] It should be understood that modifications can be made without departing from the scope of this disclosure, particularly in detail with respect to the constituent materials used and the shape, size, and arrangement of the components. This specification and the embodiments described are illustrative, and the true scope and spirit of this disclosure are shown by the subsequent claims.

Claims

1. A method for preparing an aqueous suspension (AS), (A) A step of providing a first aqueous suspension of abrasive grains; (B) A step of adding aluminum nitrate to the first aqueous suspension to obtain a second aqueous suspension; and (C) A step of adding an aqueous solution of at least one oxidizing agent to a second aqueous suspension to obtain an aqueous suspension (AS). Includes, Here, the abrasive grains have a Mohs hardness of less than 6. The aqueous suspension (AS) contains less than 0.2% by weight of abrasive particles based on the total weight of the aqueous suspension (AS), and A method in which the abrasive grains contain γ-AlOOH particles.

2. The method according to claim 1, further comprising the step of filtering the first aqueous suspension before adding aluminum nitrate.

3. The method according to claim 1, further comprising the step of filtering the aqueous solution before adding the aqueous solution.

4. The method according to claim 1, wherein the aqueous suspension (AS) has a pH value in the range of 2 to 5 at 23°C.

5. (D) The method according to claim 1, further comprising the step of adjusting the pH of an aqueous suspension (AS) with at least one pH adjusting agent.

6. An aqueous suspension, At least one type of oxidizing agent; Abrasive grains having a total weight of less than 0.2% by weight based on the total weight of the aqueous suspension, having a Mohs hardness of less than 6, and containing γ-AlOOH particles; and Aluminum nitrate A step of storing an aqueous suspension containing and having a pH in the range of 3 to 5; A step of lowering the pH of an aqueous suspension to a range of 2 to 2.5; and A process of using an aqueous suspension having a pH in the range of 2 to 2.5 within 14 days. Methods that include...

7. The method according to claim 6, wherein the aqueous suspension is stored for at least one year.

8. The method according to claim 6, wherein the pH of the aqueous suspension is reduced to 2.

3.

9. The method according to claim 6, wherein an aqueous suspension having a pH in the range of 2 to 2.5 is used in a single-wafer or batch-type chemical mechanical planarization method.

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