WO2023106358A1

WO2023106358A1 - Polishing compositions for silicon carbide surfaces and methods of use thereof

Info

Publication number: WO2023106358A1
Application number: PCT/JP2022/045243
Authority: WO
Inventors: Shinya Hirano; Jeremy GARRETSON; Yusuke Yamamoto
Original assignee: Fujimi Incorporated
Priority date: 2021-12-10
Filing date: 2022-12-08
Publication date: 2023-06-15
Also published as: TW202338058A

Abstract

The present disclosure relates to chemical-mechanical polishing (CMP) compositions for polishing polycrystalline silicon carbide-containing surfaces. More particularly, the polishing compositions are in the form of a slurry with a pH of 8 or more comprising an oxidant and an abrasive.

Description

POLISHING COMPOSITIONS FOR SILICON CARBIDE SURFACES AND METHODS OF USE THEREOF

The present disclosure relates to chemical-mechanical polishing (CMP) compositions for polishing polycrystalline silicon carbide-containing surfaces. More particularly, the polishing compositions disclosed herein are in the form of a slurry with a pH of 8 or more comprising an oxidant and an abrasive.

Background

Chemical-mechanical polishing (CMP) is a process in which material is removed from a surface of a substrate (such as a semiconductor wafer), and the surface is polished (planarized) by coupling a physical process such as abrasion with a chemical process such as oxidation. In its most rudimentary form, CMP involves applying a slurry to the surface of the substrate or a polishing pad that polishes the substrate. This process achieves both the removal of unwanted material and planarization of the surface of the substrate. It is not desirable for the removal or polishing process to be purely physical or purely chemical, but rather comprise a synergistic combination of both.

CMP is used on a large variety of objects, examples of which include silicon dioxide (SiO₂) in inter-layer or buried dielectrics, metals such as aluminum (Al), copper (Cu), and tungsten (W) in wiring layers or plugs connecting to such a wiring layer, a barrier metal layer such as tantalum (Ta), tantalum nitride (TaN), and titanium (Ti), and polycrystalline silicon carbide (poly-SiC) in materials such as semiconductors.

Typically, silicon substrates are used in the manufacture of semiconductors. However, further development is limited due to the inherent characteristics of silicon. Development of the next generation of semiconductor devices has emphasized the use of materials having a greater hardness and other unique properties. For example, silicon carbide, when compared with silicon oxide, has a higher thermal conductivity, a greater tolerance for radiation, a higher dielectric strength, and is able to withstand greater temperatures. However, the use of silicon carbide has been limited by semiconductor fabrication technology.

In order to produce silicon carbide semiconductors, the surfaces of the silicon carbide substrates must be polished in such a way as to provide smooth surfaces and precise dimensions for the surfaces. To date, adaptation of CMP techniques for silicon carbide polishing has been relatively unsuccessful. Polishing compositions containing colloidal silica resulted in low silicon carbide removal rates, thus requiring a lengthy polishing cycle lasting several hours at temperatures of around 50° C., which is likely to result in damage to the silicon carbide substrate. See, e.g.: Zhou, et al., J. Electrochemical Soc., 144, p. L161-L163 (1997); Neslen, et al., J. Electronic Materials, 30, p. 1271-1275 (2001). The long polishing cycle adds considerable cost to the process and is a barrier preventing widespread use of silicon carbide within the semiconductor industry.

The silicon carbide used in semiconductors can be a single crystal or polycrystalline. Silicon carbide has many different types of crystal structures, each having its own distinct set of electronic properties. Only a small number of these polytypes, however, can be reproduced in a form acceptable for use as semiconductors. Such polytypes can be either cubic (e.g., 3C silicon carbide) or non-cubic (e.g., 4H silicon carbide, 6H silicon carbide), or a mixture of polytypes (i.e., polycrystalline).

In addition to the differences between polytypes, there are significant differences between the single crystal forms and polycrystalline silicon carbide. For example, the use of a single crystal silicon carbide substrate in the production of semiconductors results in a higher production cost of the single crystal silicon carbide substrate. Further, if a thermal process or the like is performed on the substrate, glide dislocation of the crystal may occur, causing deformation of the substrate.

In comparison to the use of a single crystal SiC substrate, a poly-SiC substrate can be produced relatively inexpensively. To construct a SiC power semiconductor device, it is necessary to form a drift layer by epitaxy on a single crystal SiC substrate and form gates, electrodes, etc. on the drift layer. The process cost of using an expensive single-crystal substrate alone is one of the major issues limiting the widespread use of single crystal SiC containing devices. The use of polySiC will reduce the process cost as: i) only a few microns of the surface layer of the single crystal SiC substrate will be used as the bulk epi junction layer of the SiC power semiconductor; and ii) the poly-SiC will be used as a support substrate for the laminated substrate (see https://www.chusho.meti.go.jp/keiei/sapoin/portal/seika/2015/2720403030h.pdf)

Further, since the poly-SiC substrate contains a large number of crystal grain boundaries, the glide of dislocation is blocked, and the deformation of the substrate is suppressed even after the thermal process is performed. For at least these reasons, poly-SiC is becoming more prevalent in the production of semiconductors.

However, when chemical-mechanical polishing (CMP) is applied to the surface of a poly-SiC-containing substrate in order to obtain a smooth surface, low removal rates and reduced smoothness of the surface is often the result. This is because in a poly-SiC substrate, polar faces and crystal orientation planes are different from each other, but mixed and exposed on the surface of the substrate, which results in differing polishing removal rates depending on the respective faces and planes. Put simply, because poly-SiC consists of different crystal plane domains or polytypes, differing removal rates are observed for each during the CMP process, making it difficult to achieve both a high removal rate and a smooth surface.

In light of the challenges surrounding polishing poly-SiC-containing substrates, it is critical to identify polishing compositions enabling a high poly-SiC removal rate while simultaneously enabling a low average roughness. These and other challenges are addressed by the subject matter disclosed herein.

Non-Patent Literature 1: Zhou et al., J. Electrochemical Soc., vol. 144, pp. L161 to L163 (1997) Non-Patent Literature 2: Neslen et al., J. Electronic Materials, vol. 30, pp. 1271 to 1275 (2001) Non-Patent Literature 3: https://www.chusho.meti.go.jp/keiei/sapoin/portal/seika/2015/2720403030 h.pdf

SUMMARY OF THE INVENTION

In accordance with the purpose(s) of the currently disclosed subject matter or problems to be solved by the invention, as embodied and broadly described herein, it is an object of the present invention to provide a composition for polishing substrates, such as substrate containing polycrystalline silicon carbide (poly-SiC), that render substrates with desirable surface morphologies (i.e., surface roughness) when using CMP. Another object of the present invention is to provide an efficient method for polishing such poly-SiC-containing substrates using the polishing compositions disclosed herein.

Accordingly, the presently disclosed subject matter in one aspect relates to a polishing composition comprising an oxidant and an abrasive, wherein the composition has a pH of 8 or more. In some embodiments, the oxidant is a composite metal oxide (e.g., potassium permanganate) and the abrasive is alumina. In some embodiments, the amount of oxidant present in the polishing composition ranges from about 1.5% to about 3.5% by weight and the amount of abrasive ranges from about 1.5% to about 3.5% by weight.

In another aspect, the subject matter described herein is directed to a method for polishing a substrate, the method comprising the steps of: 1) providing the polishing composition described herein; 2) providing a substrate, wherein the substrate comprises a polycrystalline silicon carbide layer; and 3) polishing the substrate with the polishing composition to provide a polished substrate. In some embodiments, the polishing method has a high removal rate (RR). In some embodiments, the polishing method results in a substrate with a low roughness index (Ra).

These and other aspects are disclosed in further detail below.

FIG. 1 is a graph showing surface morphologies Ra/Rz as a function of pH. The graph relates to the test wafer 1. FIG. 2 is a graph showing the removal rate and surface morphology Ra as a function of the concentration of potassium permanganate (KMnO₄). The graph relates to the test wafer 1. FIG. 3 is a graph showing the removal rate and surface morphology Ra as a function of the concentration of an alumina powder. The graph relates to the test wafer 1. FIG. 4 is a graph showing surface morphologies Ra/Rz as a function of pH. The graph relates to the test wafer 2. FIG. 5 is a graph showing the removal rate and surface morphology Ra as a function of the concentration of potassium permanganate (KMnO₄). The graph relates to the test wafer 2. FIG. 6 is a graph showing the removal rate and surface morphology Ra as a function of the concentration of an alumina powder. The graph relates to the test wafer 2. FIG. 7 is a graph showing the relationship between the oxidation-reduction potential ORP and the pH of a polishing composition.

DETAILED DESCRIPTION

The present invention can be understood more readily by reference to the following detailed description of the invention and the Examples included therein.

Before the present compounds, compositions, articles, systems, devices, and/or methods are disclosed and described, it is to be understood that they are not limited to specific synthetic methods unless otherwise specified, or to particular components unless otherwise specified, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, example methods and materials are now described.

As described herein, in embodiments are polishing compositions comprising an oxidant and an abrasive, wherein the composition has a pH of 8 or higher. These polishing compositions are intended for polishing poly-SiC-containing substrates. The polishing compositions exhibit at least one benefit such as: 1) a high removal rate; 2) a smooth surface with a low Ra; 3) high efficiency and planarization capability; 4) a CMP process that does not need to use a fine lapping and/or grinding process; and 5) a lower cost of production.

The polishing compositions described herein have uses such as, but not limited to, the chemical-mechanical polishing of poly-SiC-containing semiconductor wafers.
A. DEFINITIONS

Listed below are definitions of various terms used to describe this invention. These definitions apply to the terms as they are used throughout this specification, unless otherwise limited in specific instances, either individually or as part of a larger group.

As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “an abrasive” or “a pH adjusting agent” includes mixtures of two or more such abrasives or pH adjusting agents.

Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. For example, if the value “about 10” is disclosed, then “10” is also disclosed. It is also understood that each unit between two particular units is also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed. As used herein, when there is a description of about X (X is a numerical value), about X is X ± 10%.

A weight percent (wt%) of a component, unless specifically stated to the contrary, is based on the total weight of the vehicle or composition in which the component is included.

As used herein, the terms “optional” and “optionally” mean that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

As used herein, the term “removal rate” (RR) refers to the amount of material removed per time, e.g., μm per hour (μm/h). The more material removed per hour, the higher the material removal rate. More specifically, the RR can be calculated by using the weight loss before and after CMP and the crystal density.

As used herein, the term “roughness index” (Ra) is a calculated value that characterizes the degree of roughness of a surface, i.e., the texture of a surface that is not smooth but is irregular and uneven. The lower the value, the smoother the surface.

As used herein, the term “particular average roughness depth” (Rz) is the mean value calculated from all of the heights and depths present on a surface thereby further characterizing the texture of the surface.
Ra and Rz can be calculated according to JIS B 0601-2001 or ISO 13565-1:1996. The roughness curves as the basis of Ra and Rz can be measured by an apparatus (atomic force microscope (AFM)) used in examples described later.
B. POLISHING COMPOSITION

The fundamental mechanism of chemical-mechanical polishing (CMP) is to soften a surface layer by chemical reaction and then remove the softened layer by mechanical force with abrasive particles. However, the role of CMP is not only material removal, but also planarization, surface smoothening, uniformity control, defect reduction and more. Semiconductor yield enhancement is thus influenced by CMP processing. Surface scratching, which can be generated by CMP, is an extremely detrimental defect in semiconductor manufacturing. Hence, to achieve proper CMP performance without surface scratching, development of polishing compositions is crucially important. Requirements for CMP can include planarized surfaces with a planarity < 13 nm, roughness-free surfaces with a surface roughness < 1.2 nm, and defect-free surfaces with scratch and pit counts of 0 counts per wafer. In some embodiments, planarization is performed at a high removal rate of the desired material to be removed, with no contamination and with high productivity. Here, the planarized surface can be evaluated by an index of Rz, and the roughness-free surface can be evaluated by an index of Ra.

CMP is often employed as being part of a polishing process to polish poly-SiC-containing surfaces. Due to its high level of hardness and remarkable chemical inertness, the polishing of poly-SiC-containing surfaces can be difficult. Typically, in order to prepare poly-SiC wafers, multiple polishing steps have to be carried out which require particles that are even harder than poly-SiC itself in order to achieve reasonable polishing rates. However, using such hard particles often results in a high degree of damage to the surface, such as scratches and dislocations, which generally develop both at the surface and subsurface of the wafer. Thus, CMP slurries and/or methods for polishing poly-SiC that would be able to decrease the damage and increase the polishing rate of poly-SiC-containing materials would be highly desirable.

Thus, in this regard, the current disclosure is directed towards polishing compositions having a pH of 8 or higher containing a composite metal oxide as an oxidant and alumina as an abrasive. These polishing compositions have been found to provide high polishing rates and desirable surface morphologies, indicating a decrease in damage compared to that typically observed with conventional polishing methods. These polishing compositions and methods of use thereof are disclosed in more detail below.
1. OXIDANT

The polishing compositions disclosed herein contain an oxidant. The oxidant can cause an oxidation reaction with the surface of the object to be polished thereby aiding in the polishing process of various surfaces.

For example, in some embodiments the oxidant present in the polishing compositions comprises permanganic acids such as permanganic acid and salts thereof including sodium permanganate and potassium permanganate; a peroxide such as hydrogen peroxide; nitrate compounds such as nitric acid, salts thereof including iron nitrate, silver nitrate, aluminum nitrate, and complexes thereof including cerium ammonium nitrate; persulfate compounds such as persulfuric acid including peroxomonosulfuric acid, peroxodisulfuric acid and the like, and salts thereof including persulfate ammonium, persulfate potassium and the like; chlorine-containing compounds such as chloric acid and salt thereof, perchloric acid and salt there of including potassium perchlorate; bromine-containing compounds such as bromic acid and salt thereof including potassium bromate; iodine-containing compounds such as iodic acid and salts thereof including ammonium iodate, and periodic acid and salts thereof including sodium periodate and potassium periodate; ferric acids such as ferric acid and salts thereof including potassium ferrate; chromic acids such as chromic acid and salts thereof including potassium chromate and potassium dichromate; vanadic acids such as vanadic acid and salts thereof including ammonium vanadate, sodium vanadate, and potassium vanadate; ruthenic acids such as perruthenic acid and salts thereof; molybdic acids such as molybdic acid and salts thereof including ammonium molybdate and disodium molybdate; rhenium acids such as perrhenic acid and salts thereof; and tungstic acids such as tungstic acid and salts thereof including disodium tungstate. These may be used singly or in combination of two or more types appropriately.

In some embodiments, the oxidant present in the polishing composition comprises a composite metal oxide. Examples of composite metal oxides include, but are not limited to, nitrate metal salts, ferric acids, permanganic acids, chromic acids, vanadic acids, ruthenic acids, molybdic acids, rhenium acids, and tungstic acids. Among them, ferric acids, permanganic acids, and chromic acids are more preferable, and permanganic acids are even more preferable.

In some embodiments, a composite metal oxide comprises a monovalent or divalent metal element other than transition metal elements, and a transition metal element in the fourth period in the periodic table is used as the composite metal oxide. Preferred examples of the monovalent or divalent metal element include Na, K, Mg, and Ca. Among them, Na and K are more preferable. Preferred examples of the transition metal element in the fourth period in the periodic table include Fe, Mn, Cr, V, and Ti. Among them, Fe, Mn, and Cr are more preferable, and Mn is even more preferable. The composite metal oxide can effectively reduce the hardness of the surface and cause embrittlement in the surface of a material having a high hardness such as poly-SiC.

In some embodiments, the amount of oxidant has an effect on the properties of the polishing composition, such as RR, Ra, and Rz. The amount of oxidant in the polishing compositions ranges from about 0.01 wt% to about 5.0 wt%, about 0.05 wt% to about 4.5 wt%, from about 0.1 wt% to about 4.0 wt%, from about 0.5 wt% to about 3.5 wt%, from about 1.0 wt% to about 3.5 wt%, from about 1.5 wt% to about 3.5 wt%, from about 1.5 wt% to about 3.0 wt%, or from about 2.0 wt% to about 3.0 wt%. Alternatively, or in addition, the amount of oxidant present in the polishing composition is less than about 5.0 wt%, less than about 4.5 wt%, less than about 4.0 wt%, less than about 3.5 wt%, less than about 3.0 wt%, less than about 2.5 wt%, less than about 2.0 wt%, less than about 1.5 wt%, or less than about 1 wt%. In some embodiments, the amount of oxidant is about 1.5 wt%, about 2.0 wt%, about 2.5 wt%, about 2.95 wt%, about 3.0 wt%, or about 3.5 wt%. The percentage of oxidizer is measured with respect to the entire composition. In some embodiments, the amount of oxidant may range from 1.5 wt% to 3.5 wt% in the polishing composition. In some embodiments, the amount of permanganate may range from 1.5 wt% to 3.5 wt% in the polishing composition.

In an embodiment, the polishing composition has an oxidation-reduction potential ORPx higher by 100 mV or more than the oxidation-reduction potential ORPy of the material to be polished. In some embodiments, the polishing composition has an oxidation-reduction potential ORPx higher by about 150 mV, 200 mV, 250 mV, 300 mV, 350 mV, 400 mV, 450 mV, 500 mV, 550 mV, or about 600 mV. In some embodiments, the polishing composition has an oxidation-reduction potential ORPx higher than the oxidation-reduction potential ORPy of the material to be polished by about 150 mV or more, 200 mV or more, 250 mV or more, 300 mV or more, 350 mV or more, 400 mV or more, 450 mV or more, 500 mV or more, 550 mV or more, or about 600 mV or more. In an embodiment, the polishing composition has an oxidation-reduction potential ORPx ranging from about 100 mV to about 1500 mV, about 200 mV to about 1400 mV, about 300 mV to about 1300 mV, about 400 mV to about 1200 mV, about 400 mV to about 1100 mV, about 400 mV to about 1000 mV, about 400 mV to about 900 mV, about 400 mV to about 800 mV, about 450 mV to about 800 mV, about 500 mV to about 1200 mV, about 600 mV to about 1200 mV, about 700 mV to about 1200 mV, about 800 mV to about 1100 mV, or about 800 mV to about 1,000 mV. That is, the relation of ORPx (mV) and ORPy (mV) satisfies the formula (1) below: ORPx - ORPy ≧100 mV (1). In an embodiment, the oxidation-reduction potential ORPx of the polishing composition may be about 800 mV or less, about 750 mV or less, about 650 mV or less, about 600 mV or less, or about 550 mV or less. In an embodiment, the oxidation-reduction potential ORPy of the material to be polished may be about 460 mV at pH 8.0, about 400 mV at pH 9.0, about 330 mV at pH 10.0, about 300 mV at pH 11.0, about 220 mV at pH 12.0, about 190 mV at pH 13.0, and about 150 mV at pH 14.0.

The oxidation-reduction potentials of the polishing composition and the material to be polished referred to herein indicate the oxidation-reduction potential values versus standard hydrogen electrode that are determined at a liquid temperature of 25° C. The oxidation-reduction potential can be measured by using Horiba Laqua Act PC110 as the main body of the measuring device and Horiba Laqua 9300-10D as the electrode.
2. ABRASIVE

The polishing compositions described herein contain an abrasive. The abrasive is typically a metal oxide abrasive preferably selected from the group consisting of silica, alumina, titania, zirconia, germania, ceria and mixtures thereof. In some embodiments, the abrasive is alumina. In a further embodiment, the abrasive contains alpha-alumina.

The abrasive disclosed herein exhibits a suitable isoelectric point. For example, a suitable isoelectric point would be an isoelectric point ranging from about 3 to about 8.5, from about 3.5 to about 8.0, from about 4 to about 7.5, from about 4.5 to about 7.0, from about 5 to about 7, or from about 5.5 to about 6.5. In some embodiments, the abrasive exhibits an isoelectric point of less than about 9.0, less than about 8.5, less than about 8.0, less than about 7.5, less than about 7.0, less than about 6.5, less than about 6, or less than about 5. In some embodiments, the isoelectric point is about 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, or 8.0. Note that the isoelectric point of the abrasive in examples described later was about 5 to 7. In some embodiments, the isoelectric point can be calculated by measuring the zeta potential. The zeta potential [mV] may be calculated, for example, by subjecting an object for which the zeta potential is to be measured to ELS-Z2 manufactured by Otsuka Electronics Co., Ltd., measuring the zeta potential by a laser Doppler method (electrophoretic light scattering measurement method) using a flow cell at a measurement temperature of 25°C, and analyzing the obtained data by the Smoluchowski equation.

The abrasive can have any suitable particle size. The abrasive can have an average secondary particle size of about 10 nm or more, about 25 nm or more, 50 nm or more, about 100 nm or more, or about 500 nm or more. In some embodiments, the abrasive can have an average secondary particle size of about 100 nm or more, about 200 nm or more, about 250 nm or more, about 300 nm or more, about 350 nm or more, or about 380 nm or more. Alternatively, or in addition, the abrasive can have an average secondary particle size of about 1,000 nm or less, about 500 nm or less, about 200 nm or less, about 150 nm or less, about 100 nm or less, about 50 nm or less, or about 25 nm or less. In some embodiments, the abrasive can have an average secondary particle size of about 900 nm or less, about 800 nm or less, about 700 nm or less, about 650 nm or less, or about 600 nm or less. For example, in embodiments, the abrasive can have an average secondary particle size in a range from about 10 nm to about 500 nm, from about 20 nm to about 100 nm, or from about 30 nm to about 50 nm. For example, in embodiments, the abrasive can have an average secondary particle size in a range from about 100 nm to about 500 nm, from about 200 nm to about 500 nm, or from about 300 nm to about 500 nm. In some embodiments, the average secondary particle size is about 10 nm, about 15 nm, about 20 nm, about 25 nm, about 30 nm, about 35 nm, about 40 nm, about 45 nm, about 50 nm, about 75 nm, or about 100 nm. In some embodiments, the average secondary particle size is about 200 nm, about 300 nm, about 400 nm, or about 500 nm. The average particle size of the abrasive can be measured by a particle size analyzer (HORIBA Particle Size Distribution tool). Here, the average particle size means an average secondary particle size.

In addition, the abrasive may be further characterized in terms of specific surface area, which may be obtained using BET techniques. In some embodiments, the abrasive comprises a specific surface area ranging from about 10 m²/g to about 250 m²/g, from about 25 m²/g to about 200 m²/g, from about 50 m²/g to about 175 m²/g, from about 75 m²/g to about 150 m²/g, or from about 100 m²/g to about 150 m²/g. In some embodiments, the abrasive comprises a specific surface area of at least about 25 m²/g, at least about 50 m²/g, at least about 75 m²/g, at least about 100 m²/g, at least about 125 m²/g, at least about 150 m²/g, at least about 175 m²/g, at least about 200 m²/g, or at least about 225 m²/g.

In addition, the abrasive can be found to have an average density ranging from about 0.5 to about 5 g/cm³. In some embodiments, the abrasive has an average density of at least about 1 g/cm³, at least about 1.5 g/cm³, at least about 2 g/cm³, at least about 2.5 g/cm³, at least about 3.0 g/cm³, at least about 3.5 g/cm³, at least about 4 g/cm³, or at least about 5 g/cm³.

Furthermore, the abrasive can include crystals having an average crystallite size of no greater than about 1 micron. Reference herein to crystallite size may be the same as reference to a grain size, or the average size of the smallest single crystal structure within a grit of the abrasive particulate material. In other instances, the average crystallite size can be less, such as not greater than about 800 nanometers, not greater than about 500 nanometers, such as not greater than about 300 nanometers or even not greater than about 200 nanometers. In some embodiments, the average crystallite size can be not greater than about 175 nanometers, not greater than about 160 nanometers or even not greater than about 150 nanometers. In some embodiments, the abrasive is in the form of alumina crystals, which have an average crystallite size of at least about 0.1 nanometers, at least about 1 nanometer, at least about 5 nanometers, at least about 10 nanometers, at least about 20 nanometers, at least about 30 nanometers, at least about 40 nanometers, at least about 50 nanometers, or even at least about 80 nanometers. It will be appreciated that the abrasive can be made of alumina crystals having an average crystallite size within a range between any of the minimum and maximum values noted above.

In certain other instances, the abrasive can have a finer grit size, including, for example, an average particle size of no greater than about 1.5 millimeters, no greater than about 1 millimeter, no greater than about 500 microns, no greater than about 300 microns, no greater than about 100 microns, no greater than about 50 microns, no greater than about 10 microns, no greater than about 1 micron, no greater than about 0.8 microns, or even no greater than about 0.6 microns. In some embodiments, the finer grit size of the abrasive ranges from about 0.5 microns to about 2 millimeters, from about 1 micron to about 1 millimeter, or from about 1 micron to about 500 microns.

In some embodiments, the amount of abrasive in the polishing composition is about 0.01 wt% or more, about 0.05 wt% or more, about 0.1 wt% or more, about 0.2 wt% or more, about 0.25 wt% or more, about 0.5 wt% or more, about 0.75 w% or more, about 1 wt% or more, about 2 wt% or more, or about 3 wt% or more. Alternatively, or in addition, the amount of abrasive in the polishing composition can be about 3 wt% or less, about 2.5 wt% or less, about 2 wt% or less, about 1 wt% or less, about 0.75 wt% or less, about 0.5 wt% or less, or about 0.1 wt% or less. In some embodiments, the amount of abrasive in the polishing composition can be in a range from about 0.01 wt% to about 5 wt%, about 0.01 wt% to about 4.5 wt%, from about 0.1 wt% to about 4.0 wt%, from about 1.0 wt% to about 3.5 wt%, from about 1.5 wt% to about 3.0 wt%, or from about 2.0 wt% to about 3.0 wt%. In some embodiments, the amount of abrasive is about 0.1 wt%, about 0.25 wt%, about 0.5 wt%, about 0.75 wt%, about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%, about 3.5 wt%, about 4 wt%, about 4.5 wt%, or about 5 wt%. In some embodiments, the amount of abrasive in the polishing composition can be in a range from 1.5 wt% to 3.5 wt%. In some embodiments, the amount of alumina in the polishing composition can be in a range from 1.5 wt% to 3.5 wt%.

In some embodiments, the alumina abrasive has an alpha conversion rate. As used herein, the term “alpha conversion” refers to conversion of an alpha aluminum precursor into alpha alumina. In some embodiments, the alpha alumina conversion rate may vary. In some embodiments, the alumina abrasive has an alpha alumina conversion rate in the range from about 50% to about 100%, from about 55% to about 95%, from about 60% to about 90%, from about 65% to about 85%, or from about 70% to about 80%. In some embodiments, the alpha conversion rate of the abrasive is less than about 100%, less than about 90%, or is less than about 80%. In some embodiments, the alpha conversion rate of the abrasive is at least about 50%, about 55%, about 60%, about 65%, or is at least about 70%.
In the present specification, the alpha conversion rate is also referred to as an alphatization rate. As the alphatization rate, a value obtained from the integrated intensity of a diffraction line peak (2θ = 57.5°) peculiar to α-alumina in the X-ray diffraction spectrum can be adopted. More specifically, the alphatization rate and the crystallite size of alumina can be determined by X-ray diffraction measurement under the following measurement conditions;
Apparatus: Powder X-ray diffractometer UltimaIV manufactured by Rigaku Corporation
X-ray generation voltage: 40 kV
Radiation: Cu-Kα1 ray
Current: 10 mA
Scan speed: 10°/min
Measurement step: 0.01°
The alphatization rate can be calculated based on the integrated intensity of a diffraction line peak (2θ = 57.5°) peculiar to α-alumina. In addition, the crystallite size can be calculated using powder X-ray diffraction pattern comprehensive analysis software JADE (automatic calculation by the Scherrer equation, manufactured by MDI).
3. PH ADJUSTING AGENT

The polishing composition may contain at least one pH adjusting agent to control the pH. In some embodiments, the pH adjusting agent is a basic compound (basic pH adjusting agent). The basic compound may be appropriately selected from various basic compounds that have a function of raising the pH of polishing compositions in which the compounds are dissolved. For example, an inorganic basic compound such as an alkali metal hydroxide, an alkaline earth metal hydroxide, various carbonates, bicarbonates and the like may be used. Such basic compounds may be used singly or in combination of two or more types thereof.

Specific examples of the alkali metal hydroxide include potassium hydroxide, sodium hydroxide, ammonium hydroxide, and the like. Specific examples of the carbonate and bicarbonate include ammonium hydrogen carbonate, ammonium carbonate, potassium hydrogen carbonate, potassium carbonate, sodium hydrogen carbonate, sodium carbonate and the like.

In alternate embodiments, the pH adjusting agent may be a mixture of an acidic agent and basic agent (such as a buffer). In such embodiments, the choice of acid is not particularly limited provided that the strength of the acid is sufficient to modulate the pH of the polishing composition of the present invention. In some embodiments, the acidic agent may be an inorganic acid or an organic acid. For example, and without limitation, such inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, boric acid, carbonic acid, hypophosphorous acid, phosphorous acid, and phosphoric acid.

For example, and without limitation, such organic acids include formic acid, acetic acid, chloroacetic acid, propionic acid, butanoic acid, valeric acid, 2-methylbutyric acid, N-hexanoic acid, 3,3-dimethylbutanoic acid, 2-ethylbutanoic acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methyl hexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citrate, citric acid, lactic acid, diglycolic acid, 2-furancarboxylic acid, 3-furancarboxylic acid, 2-tetrahydrofurancarboxylic acid, methoxyacetic acid, methoxyphenylacetic acid, and phenoxyacetic acid. Such organic acids also include, without limitation, organic sulfonic acid, such as methanesulfonic acid, ethanesulfonic acid, and isethionic acid.

In an alternate embodiment, the pH adjusting agent may be a buffer containing phosphates, acetates, borated, sulfonates, carboxylates, and the like.

The amount of pH adjusting agent can vary and is typically an amount sufficient to achieve and/or maintain the desired pH of the polishing composition, e.g., within the ranges set forth herein.

In an embodiment, the pH of the polishing composition is adjusted to a range that is from about 8.0 to about 13.0, from about 8.5 to about 13.0, from about 9.0 to about 13.0, from about 9.5 to about 13.0, from about 10 to about 13.0, from about 10.5 to about 13, from about 11.0 to about 13.0, from about 11.5 to about 13.0, from about 12.0 to about 13.0, or from about 12.5 to about 13.0. In an embodiment, the pH of the polishing composition may be adjusted to a range that is from 9 to 10.

In an embodiment, the pH of the polishing composition is adjusted to greater than about 8.0, greater than about 8.5, greater than about 9.0, greater than about 9.5, greater than about 10.0, greater than about 10.5, greater than about 11.0, greater than about 11.5, greater than about 12, or greater than about 12.5. In other words, the pH of the polishing vehicle or polishing composition can be about 8 or more, about 9 or more, about 10 or more, about 11 or more, about 12 or more, or about 13 or more.

In some embodiments, the pH of the polishing composition is adjusted to about 13 or less, about 12 or less, about 11 or less, about 10 or less, or about 9 or less, wherein the pH is no less than about 8. In some embodiments, the pH of the polishing composition has a pH greater than 8.

In some embodiments, the pH of the polishing composition is about 8, about 8.5, about 9, about 9.5, about 10, about 10.5, about 11, about 11.5, about 12, about 12.5, or about 13.

The pH adjusting agent may be present at a specific concentration range, regardless of pH. For example, in some embodiments, the amount of the pH adjusting agent is in a range from about 0.0001 wt% to about 1 wt%, from about 0.005 wt% to about 0.5 wt%, or from about 0.001 wt% to about 0.1 wt%. In alternate embodiments, the amount of pH adjusting agent is in a range from about 0.0001 wt% to about 0.0010 wt%, from about 0.0003 wt% to about 0.0009 wt%, or from about 0.0005 wt% to about 0.0008 wt%. In alternate embodiments, the amount of pH adjusting agent is in a range from about 0.0009 wt% to about 0.0040 wt% or from about 0.0010 wt% to about 0.0030 wt%. In still alternate embodiments, the pH adjusting agent is in a range from about 0.001 wt% to about 0.01 wt%. In some embodiments, the amount of pH adjusting agent is present in an amount of at least about 0.0001 wt%, at least about 0.0005 wt%, at least about 0.001 wt%, at least about 0.005 wt%, at least about 0.01 wt%, at least about 0.025 wt%, at least about 0.05 wt%, at least about 0.075 wt%, or at least about 0.1 wt%. In some embodiments, the pH adjusting agent is present in an amount of less than about 0.01 wt%, less than about 0.005 wt%, less than about 0.001 wt%, or less than about 0.0005 wt%. In some embodiments, the pH adjusting agent is present in an amount that is about 0.0001 wt%, about 0.00025 wt%, about 0.0005 wt%, about 0.0006 wt%, about 0.0007 wt%, about 0.0008 wt%, about 0.0009 wt%, about 0.001 wt%, about 0.005 wt%, about 0.0075 wt%, about 0.01 wt%, about 0.025 wt%, or about 0.05 wt%.

However, the polishing compositions cannot use too much pH adjusting agent, as the amount of ions will have a negative effect on the selectivity ratio. This limits the type of pH adjusting agent as well.
4. WATER

In some embodiments, the polishing compositions disclosed herein contain a carrier, medium, or vehicle. In an embodiment, the carrier, medium, or vehicle is water. Ion exchanged water (deionized water), pure water, ultrapure water, distilled water and the like may be used as the water. In order to reduce the amount of unwanted components present in the water, the purity of water may be increased by operations such as removal of impurity ions with an ion exchange resin, removal of contaminants with a filter, and/or distillation.

In some embodiments, the water is relatively free of impurities. In some embodiments, the water contains less than about 10% w/w, less than about 9% w/w, less than about 8% w/w, less than about 7% w/w, less than about 6% w/w, less than about 5% w/w, less than about 4% w/w, less than about 3% w/w, less than about 2% w/w, less than about 1% w/w, less than about 0.9% w/w, less than about 0.8% w/w, less than about 0.7% w/w, less than about 0.6% w/w, less than about 0.5% w/w, less than about 0.4% w/w, less than about 0.3% w/w, or less than about 0.1% w/w impurities based on the total weight of the water.

The amount of water in the polishing composition can vary. In some embodiments, water is present in an amount of at least about 50 wt%, at least about 60 wt%, at least about 70 wt%, at least about 80 wt%, at least about 90 wt%, at least about 92 wt%, at least about 94 wt%, at least about 96 wt%, or at least about 98 wt%.

Polishing compositions comprising any of the above-mentioned carrier, medium, or vehicle would be in the form of a slurry or dispersion.
In an embodiment, the temperature of the polishing composition may be adjusted to 5 to 30°C, 6 to 20°C, or 7 to 13°C.
5. ADDITIONAL COMPONENTS

In an embodiment, the polishing compositions disclosed herein may contain additional components such as corrosion inhibitors, carbohydrates, chelating agents, biocides, surfactants, or co-solvents. Additionally or alternatively, the compositions disclosed herein can include other additives as will be understood by those skilled in the art.

In another embodiment, the additional component may include a corrosion inhibitor. Non-limiting examples of the corrosion inhibitor may include 2-methyl-3-butyn-2-ol, 3-methyl-2pyrazolin-5-one, 8-hydroxyquinoline, and dicyandiamide, benzotriazole and its derivatives, pyrazole and its derivatives, imidazole and its derivatives, benzimidazole and its derivatives, isocyanurate and its derivatives, and mixtures thereof. The amount of the corrosion inhibitor in the polishing composition may range from about 0.0005 wt% to 0.25 wt%, preferably from 0.0025 wt% to 0.15 wt%, and more preferably from 0.05 wt% to 0.1 wt%.

In an alternative embodiment, the polishing composition is corrosion inhibitor agent free. The term “corrosion inhibitor agent free” as used herein means that the polishing composition does not contain compounds known in the art to be used as corrosion inhibitors.

In one embodiment, the additional component may include a carbohydrate. Carbohydrates include sugar, and in some embodiments, the sugar is a polysaccharide known as pullulan. The polysaccharide pullulan is comprised of maltotriose units consisting of three α-1,4-linked glucose molecules are further linked by α-1,6-bonds.

In an alternative embodiment, the polishing composition is carbohydrate free. The term “carbohydrate free” as used herein means that the polishing composition does not contain compounds known in the art as carbohydrates.

In another embodiment, the additional component may include a chelating agent. The term chelating agent is intended to mean any substance that in the presence of an aqueous solution chelates metals, such as copper. Non-limiting examples of chelating agents include inorganic acids, organic acids, amines, and amino acids such as glycine, alanine, citric acid, acetic acid, maleic acid, oxalic acid, malonic acid, phthalic acid, succinic acid, nitrilotriacetic acid, iminodiacetic acid, ethylenediamine, CDTA, and EDTA.

In an alternative embodiment, the polishing composition is chelating agent free. The term “chelating agent free” as used herein means that the polishing composition does not contain compounds known in the art as chelating agents. Non-limiting examples of chelating agents include compounds such as glycine, alanine, citric acid, acetic acid, maleic acid, oxalic acid, malonic acid, phthalic acid, succinic acid, nitrilotriacetic acid, iminodiacetic acid, ethylenediamine, CDTA, and EDTA.

In an embodiment, the additional component may be a biocide. Non-limiting examples of biocides include hydrogen peroxide, quaternary ammonium compounds, and chlorine compounds. More specific examples of the quaternary ammonium compounds include, but are not limited to, methylisothiazolinone, tetramethylammonium chloride, tetraethylammonium chloride, tetrapropylammonium chloride, alkylbenzyldimethylammonium chloride, and alkylbenzyldimethylammonium hydroxide, wherein the alkyl chain ranges from 1 to about 20 carbon atoms. More specific examples of the chlorine compounds include, but are not limited to, sodium chlorite and sodium hypochlorite. Additional examples of the biocides include biguanide, aldehydes, ethylene oxide, isothiazolinone, iodophor, KATHON (trademark) and NEOLENE (trademark) product families that are commercially available from Dow Chemicals, and the Preventol (trademark) family available from Lanxess. The amount of biocide used in the polishing composition may range from about 0.0001 wt% to 0.10 wt%, from 0.0001 wt% to 0.005 wt%, or from 0.0002 wt% to 0.0025 wt%.

In another embodiment, the additional component may include a surfactant. The surfactants may be anionic, cationic, nonionic, or zwitterionic and may increase lubricity of the vehicle or compositions. Non-limiting examples of the surfactants are dodecyl sulfates, sodium salts or potassium salts, lauryl sulfates, secondary alkane sulfonates, alcohol ethoxylate, acetylenic diol surfactant, quaternary ammonium-based surfactants, amphoteric surfactants, such as betaines and amino acid derivatives-based surfactants, and any combination thereof. Examples of suitable commercially available surfactants include TRITON^TM, Tergitol^TM, DOWFAX^TM family of surfactants manufactured by Dow Chemicals and various surfactants in SURFYNOL^TM, DYNOL^TM, Zetasperse^TM, Nonidet^TM, and Tomadol^TM surfactant families, manufactured by Air Products and Chemicals. Suitable surfactants of surfactants may also include polymers comprising ethylene oxide (EO) and propylene oxide (PO) groups. An example of EO-PO polymer is Tetronic^TM 90R4 from BASF Chemicals. An example of acetylenic diol surfactant is Dynol^TM 607 from Air Products and Chemicals. The amount of surfactant used in the polishing composition may range from about 0.0005 wt% to 0.15 wt%, from 0.001 wt% to 0.05 wt%, or from 0.0025 wt% to 0.025 wt%.

In another embodiment, the additional component may include another solvent, termed a co-solvent. Non-limiting examples of co-solvents include, but are not limited to, alcohol (such as methanol or ethanol), ethyl acetate, tetrahydrofuran, alkanes, tetrahydrofuran, dimethylformamide, toluene, ketones (such as acetone), aldehydes, and esters. Other non-limiting examples of co-solvents include dimethyl formamide, dimethyl sulfoxide, pyridine, acetonitrile, glycols, and mixtures thereof. The co-solvent may be employed in various amounts, preferably from a lower limit of about 0.0001, 0.001, 0.01, 0.1, 0.5, 1, 5, or 10 (wt%) to an upper limit of about 0.001, 0.01, 0.1, 1, 5, 10, 15, 20, 25, or 35 (wt%).

Accordingly, as described herein, in some embodiments are polishing compositions comprising an oxidant and an abrasive, wherein the oxidant comprises a composite metal oxide, the abrasive comprises alumina, and the pH of the composition is about 8 or greater.

As in any embodiment above, a polishing composition wherein the oxidant comprises potassium permanganate.

As in any embodiment above, a polishing composition wherein the abrasive comprises alpha-alumina.

As in any embodiment above, a polishing composition wherein the abrasive has an isoelectric point ranging from about 5 to about 7.

As in any embodiment above, a polishing composition wherein the oxidant is potassium permanganate, and the abrasive is alumina.

As in any embodiment above, a polishing composition wherein the pH is adjusted with a pH adjuster, such as potassium hydroxide.

As in any embodiment above, a polishing composition wherein the oxidant is present in an amount of from about 1.5 wt% to about 3.5 wt%.

As in any embodiment above, a polishing composition wherein the abrasive is present in an amount of from about 1.5 wt% to about 3.5 wt%.

As in any above embodiment above, a polishing composition wherein the oxidant is potassium permanganate and is present in an amount of from about 1.5 wt% to about 3.5 wt%.

As in any above embodiment above, a polishing composition wherein the abrasive is alumina and is present in an amount of from about 1.5 wt% to about 3.5 wt%.

As in any above embodiment above, a polishing composition wherein the oxidant is potassium permanganate and is present in an amount of from about 1.5 wt% to about 3.5 wt% and the abrasive is alumina and is present in an amount of from about 1.5 wt% to about 3.5 wt%.

As in any above embodiment above, a polishing composition wherein the pH is at least 9.

As in any above embodiment above, a polishing composition wherein the pH is 10 or less.

As in any above embodiment above, a polishing composition further comprising a carrier (e.g., water).

As in any above embodiment above, a polishing composition is in the form of a slurry.
C. METHODS OF USING THE POLISHING COMPOSITIONS

The polishing compositions described herein are useful for polishing any suitable substrate comprising poly-SiC. In some embodiments, the substrate comprises at least one layer of poly-SiC. In some embodiments, the at least one layer comprising poly-SiC is on the surface of the substrate, i.e., top layer of the substrate. The poly-SiC-containing surface can be in the form of a wafer or can be in the form of a thin (or thick) film.

The silicon carbide used in semiconductors can be a single crystal or polycrystalline, where examples of such polytypes are cubic (e.g., 3C silicon carbide) or non-cubic (e.g., 4H silicon carbide, 6H silicon carbide), or a mixture of polytypes (i.e., poly-SiC). An advantage of using poly-SiC is a reduced cost of the substrate. Some distinguishing characteristics of poly-SiC are that it typically does not have the same polarity (Si/C surface) as a single crystal 4H-SiC, it is black in color, and it is non-transparent.

Additional characteristics of poly-SiC are that since it consists of many polytypes (such as 4H, 3C, and various other polytype crystals), there may be voids (vacancies) at the grain boundaries. The different polytypes in poly-SiC lead to challenging crystallinity, with wide variations in the poly-SiC. Further, the density of poly-SiC is smaller than 3.21 g/cm³ of 4H-SiC. The density of poly-SiC may be 3.20 g/cm³or less, 3.19 g/cm³ or less, 3.18 g/cm³ or less, 3.17 g/cm³ or less, or 3.16 g/cm³ or less. Furthermore, the density of poly-SiC may be 3.10 g/cm³ or more, 3.15 g/cm³ or more, 3.16 g/cm³or more, 3.17 g/cm³ or more, 3.18 g/cm³ or more, 3.19 g/cm³ or more, or 3.20 g/cm³ or more. Because of these and other characteristics, it is difficult to obtain a high removal rate and desired smoothness of poly-SiC during CMP, which increases time for production and the associated costs.
Accordingly, it is an object of the disclosed invention to provide a method for polishing poly-SiC which provides a high removal rate of poly-SiC, with a desired smoothness.

Polishing of poly-SiC comprising materials can be beneficial for a variety of applications such as, but not limited to, flat panel displays, integrated circuits, memory or rigid disks, metals, interlayer dielectric (ILD) devices, semiconductors, micro-electro-mechanical systems, ferro-electrics, and magnetic bands.

Thus, in some embodiments, the subject matter disclosed herein is directed to a method for polishing a poly-SiC-containing substrate with the polishing composition disclosed herein. In some embodiments, the method of polishing a poly-SiC-containing substrate comprises: (a) providing a poly-SiC-containing substrate; (b) providing a polishing composition described herein; (c) applying the polishing composition to at least a portion of the substrate; and (d) abrading at least a portion of the substrate with the polishing composition to polish the substrate,

In some embodiments, the apparatus used in the polishing methods disclosed herein is a chemical-mechanical polishing (CMP) apparatus, although the disclosed method should not be limited thereto. Typically, the apparatus comprises a platen, which, when in use, is in motion and has a velocity that results from orbital, linear, or circular motion, a polishing pad in contact with the platen and moving with the platen when in motion, and a carrier that holds a substrate to be polished by contacting and moving relative to the surface of the polishing pad. The polishing of the substrate takes place by the substrate being placed in contact with the polishing pad and the polishing composition (which generally is disposed between the substrate and the polishing pad), with the polishing pad moving relative to the substrate, so as to abrade at least a portion of the substrate to polish the substrate. The polishing end-point can then be determined by monitoring the weight of the poly-SiC-containing substrate, which is used to compute the amount poly-SiC removed from the substrate. Such techniques are well known in the art.

The polishing pad used here is not particularly limited. For example, any polishing pad of a non-woven fabric type, a suede type, a polyurethane type including a hard foamed type and a soft foamed type, a type containing an abrasive, a type containing no abrasive, and the like may be used.

Polishing refers to the removal of at least a portion of a surface to polish the surface. Polishing can be performed to provide a surface having reduced surface roughness by removing gouges, crates, pits, and the like, but polishing also can be performed to introduce or restore a surface geometry characterized by an intersection of planar segments.

The poly-SiC can be removed at any suitable rate to effect polishing of the substrate in the polishing methods disclosed herein. In some embodiments, the polishing compositions employed in the disclosed polishing methods have a removal rate (RR) ranging from about 1 μm/h to about 10 μm/h, from about 2 μm/h to about 8 μm/h, from about 3 μm/h to about 7 μm/h, from about 4 μm/h to about 7 μm/h from about 4.5 μm/h to about 6.5 μm/h, from about 5.0 μm/h to about 6.0 μm/h. In some embodiments, the RR ranges from about 6.0 μm/h to about 7.0 μm/h. In some embodiments, the RR is at least about 1.0 μm/h, about 2.0 μm/h, about 3.0 μm/h, about 4.0 μm/h, about 4.5 μm/h, about 5.0 μm/h, about 5.5 μm/h, about 6.0 μm/h, or about 7.0 μm/h. In some embodiments, the RR is less than about 10.0 μm/h, about 9.0 μm/h, about 8.0 μm/h, about 7.0 μm/h, about 6.5 μm/h, about 5.0 μm/h, about 4.5 μm/h, about 4.0 μm/h, about 3.0 μm/h, about 2.0 μm/h, or about 1.0 μm/h.

In some embodiments, the polishing method disclosed herein employs a polishing composition with a particular average roughness index (Ra). In some embodiments, the Ra of the polishing compositions ranges from about 0.01 nm to about 1.50 nm, from about 0.01 nm to about 1.20 nm, from about 0.10 nm to about 1.2 nm, from about 0.25 nm to about 1.20 nm, from about 0.50 nm to about 1.20 nm, from about 0.6 nm to about 0.90 nm, or from about 0.70 nm to about 0.90 nm. In some embodiments, the Ra of the polishing compositions employed in the disclosed polishing methods is less than about 1.20 nm, less than about 1.10 nm, less than about 1.0 nm, less than about 0.90 nm, less than about 0.80 nm, less than about 0.70 nm, less than about 0.60 nm, less than about 0.50 nm, less than about 0.40 nm, or less than about 0.30 nm.

In some embodiments, the polishing method disclosed herein employs a polishing composition with a particular average roughness depth (Rz). In some embodiments, the Rz of the polishing compositions ranges from about 1 nm to about 20 nm, from about 5 nm to about 15 nm, from about 6 nm to about 12 nm, from about 7 nm to about 10 nm, from about 8 nm to about 10 nm, or from about 9 nm to about 10 nm. In some embodiments, the Rz of the polishing composition is less than about 15 nm, about 14 nm, about 13 nm, about 12 nm, about 11 nm, about 10 nm, about 9.75 nm, about 9.50 nm, about 9.25 nm, about 9.00 nm, 8.75 nm, about 8.50 nm, about 8.25 nm, about 8.0 nm, 7.75 nm, about 7.5 nm, about 7.25 nm, about 7.00 nm, or about 6.50 nm.

In some embodiments, the polishing method disclosed herein employs any suitable head pressure. In some embodiments, the head pressure of the polishing method ranges from about 1.4 psi to about 22 psi, from about 2.9 psi to about 14.5 psi, from about 3 psi to about 12 psi, from about 4 psi to about 10 psi, from about 5 psi to about 9 psi, or from about 6 psi to about 8 psi.

In some embodiments, the polishing method disclosed herein employs any suitable platen rotation velocity. In some embodiments, the platen rotation velocity of the polishing method ranges from about 60 rpm to about 180 rpm, from about 70 rpm to about 170 rpm, from about 80 rpm to about 160 rpm, from about 90 rpm to about 150 rpm, from about 100 rpm to about 140 rpm, or from about 110 rpm to about 130 rpm.

In some embodiments, the polishing method disclosed herein employs any suitable head rotation velocity. In some embodiments, the head rotation velocity of the polishing method ranges from about 90 rpm to about 200 rpm, from about 100 rpm to about 190 rpm, from about 110 rpm to about 180 rpm, from about 120 rpm to about 170 rpm, from about 130 rpm to about 160 rpm, or from about 140 rpm to about 150 rpm.

In some embodiments, the polishing method disclosed herein employs any suitable pressure velocity (PV). In some embodiments, the PV of the polishing method ranges from about 300 psi*inch/sec to about 900 psi*inch/sec, from about 350 psi*inch/sec to about 850 psi*inch/sec, from about 400 psi*inch/sec to about 800 psi*inch/sec, or from about 450 psi*inch/sec to about 750 psi*inch/sec.

Accordingly, as described herein in some embodiments are methods of using the polishing compositions, where the methods comprise the steps of: a) providing the polishing composition as disclosed herein (e.g. of claim 1); b) providing a substrate, wherein the substrate comprises a polycrystalline silicon carbide (poly-SiC) containing layer; and c) polishing the substrate with the polishing composition to provide a polished substrate.

As in any embodiment above, wherein the substrate is a semiconductor.

As in any embodiment above, wherein the method results in a poly-SiC removal rate ranging from about 4 μm/h to about 7 μm/h.

As in any embodiment above, wherein the polished substrate has a roughness index (Ra) of less than about 1.2 nm.

As in any embodiment above, wherein the polished substrate has a particular average roughness depth (Rz) of less than about 10 nm.

As in any embodiment above, wherein the polishing composition comprises an abrasive which has an isoelectric point ranging from about 5 to about 7. The isoelectric point of the polishing composition in examples described later was in the range from about 5 to about 7.

As in any embodiment above, wherein the polishing composition comprises an abrasive which is free of transition phase alumina.

As in any embodiment above, wherein the polishing composition comprises an oxidant which is potassium permanganate.

As in any embodiment above, wherein the polishing composition further comprises a pH adjusting agent present in an amount of less than about 0.001 wt%.

As in any embodiment above, wherein the polishing composition has pH in a range from about 9 to about 10.
D. EXAMPLES

The following preparations and examples are given to enable those skilled in the art to more clearly understand and to practice the present invention. They should not be considered as limiting the scope of the invention, but merely as being illustrative and representative.

In one aspect, disclosed are methods of making the polishing compositions. In another aspect are disclosed methods of using the polishing compositions to polish materials.

Example 1 - Abrasive Evaluation

The average secondary particle size of the alumina abrasive was measured by a laser diffraction/scattering particle size distribution measuring device (LA-950 manufactured by Horiba, Ltd.) and is shown in Table 1.

Example 2: Measurements of Removal Rates (RR), Roughness Index (Ra) and Average Roughness Depth (Rz) of experimental slurries.

Table 2 below shows a general set up of the polishing equipment and polishing parameters used.

Testing conditions/parameters from Table 2:
(a) REVSUM 6EC2 was used for single side polishing of an about 22-inch diameter platen;
(b) a Rohm and Haas IC1000 k-grooved pad was selected that is a hard polyurethane polishing pad;
(c) KINIK 179B was used as a conditioner of pads and a conditioning sequence was adopted which lasted approximately 2 min before test polishing with 5 Lbs;
(d) the chiller temperature was set to 10 ^oC during polishing testing;
(e) the slurry flow rate was used 50 ml/min;
(f) the polishing conditions employed a Head pressure of 7.0 psi, and a platen and head rotation speed of 120 and 145 rpm, respectively; and
(g) the polishing time was 5 min.

Table 3 above shows the common method employed for evaluating the polishing of wafers.

Testing conditions/parameters:
(a) 6 inches of poly-SiC test wafers were used, which could be purchased from conventional suppliers;
(b) In the test wafer 1, the nominal value for a once polished mirror finish is that Ra is smaller than 7 nm, density is assuming 3.15 g/cm³, and SORI is smaller than 50 μm.
In the test wafer 2, the nominal value for a once polished mirror finish is that Ra is smaller than 7 nm, density is assuming 3.2 g/cm³, and SORI is smaller than 50 μm. Note that “once polished” means that the provider has already polished the test wafer 1 and the test wafer 2.
(c) The wafer was cleaned by 1) PVA wiping with organic acid and surfactant (i.e. Kanto chemical CMP-MO₂ diluted to 10 times with H₂O), then RCA-based cleaning, such as 2) sulfuric acid and hydrogen peroxide mixed solutions (SPM), and 3) hydrofluoric acid cleaning;
(d) RR was calculated using the weight loss and crystal density before and after CMP after cleaning the substrate; this CMP was performed using the polishing composition of Example 3 (Comparison Study) and
(e) For the surface roughness evaluations, the values of Ra and Rz were observed by the atomic force microscope (AFM). The measurement area was a 10-micron area.

Since there is no polarity in poly-SiC, and both surfaces were treated as having similar properties when testing RR and Ra/Rz. The RR and Ra evaluations were done using one set on each side. First, the RR was obtained by weight loss conversion, and then the substrate was cleaned to measure AFM. In addition, one side was evaluated alternately to avoid the influence of residual stress on the polished surface.

Example 3 - Comparison Study

(Comparison Study 1)
Procedure for Preparing Polishing Composition: The alumina A was provided as the abrasive and mixed in water so that the content of the entire abrasive (powder) was set to the value shown in Table 4-1. Next, potassium permanganate as an oxidant was added to a content of the value shown in Table 4-1, followed by stirring at room temperature (25°C) for 30 minutes, thereby preparing a dispersion. While checking the pH of the dispersion with a pH meter (manufactured by Horiba, Ltd.), KOH or HNO₃ was added as the pH adjusting agent so that the pH was adjusted to the value shown in Table 4-1, and thus the polishing composition was prepared.
Test wafer 1 was used in Comparison Study 1.

According to the polishing composition according to an aspect of the present invention, when a test wafer 1 having a low density is polished, Ra and Rz can be reduced while RR is maintained high. Since there is a high possibility that pits and grains are present in a wafer having a low density, when this wafer is polished, RR tends to be high, while Ra and Rz tend to deteriorate. Therefore, a polishing composition capable of reducing Ra and Rz while maintaining RR high is useful for a wafer having a low density. On the other hand, in comparatives 1 to 6 and 8, RR is high, but Ra and Rz cannot be sufficiently reduced. Further, in comparative 7, RR is low, and Ra and Rz cannot be sufficiently reduced.

(Comparison Study 2)
Procedure for Preparing Polishing Composition: The alumina A was provided as the abrasive and mixed in water so that the content of the entire abrasive (powder) was set to the value shown in Table 4-2. Next, potassium permanganate as an oxidant was added to a content of the value shown in Table 4-2, followed by stirring at room temperature (25°C) for 30 minutes, thereby preparing a dispersion. While checking the pH of the dispersion with a pH meter (manufactured by Horiba, Ltd.), KOH or HNO₃was added as the pH adjusting agent so that the pH was adjusted to the value shown in Table 4-2, and thus the polishing composition was prepared.
Test wafer 2 was used in Comparison Study 2.

According to the polishing composition according to an aspect of the present invention, when a test wafer 2 having a high density is polished, RR can be improved while an increase in Ra and Rz is suppressed. Since a wafer having a high density is close to the performance of a single crystal wafer, when this wafer is polished, Ra and Rz are low, but RR is hardly improved. Therefore, as described above, the polishing composition capable of improving RR while suppressing an increase in Ra and Rz is useful for a wafer having a high density. On the other hand, in comparative 9 and comparative 10, RR is high, but Ra and Rz are deteriorated. In addition, in comparatives 11 to 14, Ra and Rz are suppressed to be low, but the value of RR is low.

In some embodiments, the density of poly-SiC is 3.18 g/cm³ or more. In some embodiments, the density of poly-SiC is less than 3.18 g/cm³.
In some embodiments, the contents of both the oxidant and the abrasive in the polishing composition are preferably more than 1.5 wt%.
Example 4: Relationship between oxidation-reduction potential ORP and pH of polishing composition
Each of the polishing composition of the

inventions

1, 2, 5, and 6 was prepared, and the pH was adjusted to the pH described in the following table using HNO₃in order to adjust the pH to the acidic side, and using KOH in order to adjust the pH to the alkaline side. Then, the oxidation-reduction potential ORP at each PH was measured.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. Other aspects of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
The present invention includes the following aspects and forms.
1. A polishing composition comprising an oxidant, an abrasive, and water, wherein the oxidant is a permanganate present in an amount from about 1.5 wt% to about 3.5 wt%; and the abrasive is alumina present in an amount from about 1.5 wt% to about 3.5 wt%; wherein the polishing composition has a pH greater than about 8.
2. The polishing composition according to item 1, wherein the abrasive has an isoelectric point ranging from about 5 to about 7.
3. The polishing composition according to

item

1 or 2, wherein the oxidant is potassium permanganate.
4. The polishing composition according to any one of items 1 to 3, wherein the polishing composition further comprises a pH adjusting agent present in an amount of less than about 0.001 wt%.
5. The polishing composition according to item 4, wherein the pH adjusting agent is a basic pH adjusting agent.
6. The polishing composition according to item 5, wherein the pH adjusting agent is potassium hydroxide.
7. The polishing composition according to any one of items 1 to 6, wherein the pH is in a range from about 9 to about 10.
8. The polishing composition according to any one of items 1 to 7, wherein the polishing composition has a poly-SiC removal rate of about 4 μm/h to about 7 μm/h.
9. A method for polishing a substrate containing polycrystalline silicon carbide, the method comprising the steps of: a) providing the polishing composition according to any one of items 1 to 8; b) providing a substrate, wherein the substrate comprises a polycrystalline silicon carbide (poly-SiC) containing layer; and c) polishing the substrate with the polishing composition to provide a polished substrate.
10. The method according to item 9, wherein the substrate is a semiconductor.
11. The method according to

item

9 or 10, wherein the method results in a poly-SiC removal rate ranging from about 4 μm/h to about 7 μm/h.
12. The method according to any one of items 9 to 11, wherein the polished substrate has a roughness index (Ra) of less than about 1.2 nm.
13. The method according to any one of items 9 to 12, wherein the polished substrate has a particular average roughness depth (Rz) of less than about 13 nm.
14. The method according to any one of items 9 to 13, wherein the polishing composition comprises an abrasive which has an isoelectric point ranging from about 5 to about 7.
15. The method according to any one of items 9 to 14, wherein the polishing composition comprises an oxidant which is potassium permanganate.
16. The method according to any one of items 9 to 15, wherein the polishing composition has pH in a range from about 9 to about 10.
This application is based on U.S. Provisional Patent Application No. 63/288039, filed on December 10, 2021, the disclosure of which is incorporated herein by reference in its entirety.

Claims

A polishing composition comprising an oxidant, an abrasive, and water, wherein
the oxidant is a permanganate present in an amount from about 1.5 wt% to about 3.5 wt%; and
the abrasive is alumina present in an amount from about 1.5 wt% to about 3.5 wt%; wherein the polishing composition has a pH greater than about 8.
The polishing composition of claim 1, wherein the abrasive has an isoelectric point ranging from about 5 to about 7.
The polishing composition of claim 1, wherein the oxidant is potassium permanganate.
The polishing composition of claim 1, wherein the polishing composition further comprises a pH adjusting agent present in an amount of less than about 0.001 wt%.
The polishing composition of claim 4, wherein the pH adjusting agent is a basic pH adjusting agent.
The polishing composition of claim 5, wherein the pH adjusting agent is potassium hydroxide.
The polishing composition of claim 1, wherein the pH is in a range from about 9 to about 10.
The polishing composition of claim 1, wherein the polishing composition has a poly-SiC removal rate of about 4 μm/h to about 7 μm/h.
A method for polishing a substrate comprising polycrystalline silicon carbide, the method comprising the steps of:
a) providing the polishing composition of claim 1;
b) providing a substrate, wherein the substrate comprises a polycrystalline silicon carbide (poly-SiC) containing layer; and
c) polishing the substrate with the polishing composition to provide a polished substrate.
The method of claim 9, wherein the substrate is a semiconductor.
The method of claim 9, wherein the method results in a poly-SiC removal rate ranging from about 4 μm/h to about 7 μm/h.
The method of claim 9, wherein the polished substrate has a roughness index (Ra) of less than about 1.2 nm.
The method of claim 9, wherein the polished substrate has a particular average roughness depth (Rz) of less than about 13 nm.
The method of claim 9, wherein the polishing composition comprises an abrasive which has an isoelectric point ranging from about 5 to about 7.
The method of claim 9, wherein the polishing composition comprises an oxidant which is potassium permanganate.
The method of claim 9, wherein the polishing composition has pH in a range from about 9 to about 10.