Chemical mechanical polishing composition for metal alloy, and polishing method using same

Abstract

A chemical mechanical polishing composition for a metal alloy, and a polishing method using same. The composition comprises alumina abrasive particles, an oxidant and a dispersant, wherein the dispersant is nanoclay, the nanoclay has a z-average particle size of at most 1,000 nm, and the value of the Zeta potential of the nanoclay is at least -5 mV. The composition can be used for polishing the surface of a metal alloy substrate, can achieve a high material removal rate and a longer recycling time under the condition of almost no polymer, is environmentally friendly and has higher economic benefits.

Description

Chemical mechanical polishing composition for metal alloys and polishing method thereof Technical Field

[0001] The invention belongs to the technical field of chemical engineering, and in particular relates to a chemical mechanical polishing composition for metal alloys and a polishing method. Background Art

[0002] Chemical Mechanical Polishing (CMP) is a common process for achieving global planarization in integrated circuit manufacturing and other fields. This process is primarily used to obtain a smooth surface that is both flat and free of scratches and impurities. This process polishes various target substrates through a combination of chemical and mechanical forces, and chemical mechanical polishing (CMP) compositions play a decisive role in this process. These compositions are typically aqueous solutions containing a uniform dispersion of various chemical additives and abrasive particles. CMP compositions, also known as polishing slurries, polishing solutions, or polishing compositions, are commonly used to polish the surfaces of various substrates (such as metals, metal alloys, minerals, and plastics).

[0003] There is a widespread demand for polishing metal substrates, metal alloy substrates, mineral and plastic substrates. For example, most metal parts in vehicles, ships, aircraft, pipelines, light reflectors, containers, handrails, kitchen utensils, cookware, architectural metals and jewelry require polishing. Among them, ferroalloy substrates (such as stainless steel with good corrosion resistance) are widely used in machine tools, cookware, structural materials such as surgical knives, transportation equipment, consumer electronic device parts such as smartphone and laptop casings, and metal crafts such as automobile logos. Therefore, there is also a demand for polishing stainless steel surfaces.

[0004] CMP compositions containing aluminum oxide abrasives are commonly used to polish materials containing iron alloys to obtain substrates with smooth mirror surfaces. Many applications of metal alloys require low surface roughness, high brightness and a smooth mirror effect, which can be achieved by CMP compositions containing aluminum oxide abrasives. However, aluminum oxide abrasives can easily cause pits, scratches and other surface defects on the surface of metal alloy substrates. Due to lack of oxygen and local destruction of the protective passivation film of stainless steel, such surface defects can cause corrosion problems in ferrous metal alloys such as stainless steel. And in daily use, these surface defect areas are easily contaminated by dirt, bacteria, etc. Therefore, there is still a need for a CMP composition containing aluminum oxide abrasives suitable for polishing the surface of metal alloy substrates that can achieve low surface roughness and a low number of surface defects.

[0005] To reduce manufacturing costs, waste, and environmental burdens, CMP compositions are often recycled during the polishing process of metal alloy substrates. For example, a CMP composition is used for polishing, then discharged from the polishing apparatus and collected in a tank, after which it is recycled back into the polishing apparatus for further polishing. Therefore, it is desirable to have a long recycle time for CMP compositions containing aluminum oxide abrasive particles. Recycle time refers to the time during which the composition can be reused for chemical mechanical polishing of a substrate without an overall decrease in polishing performance (e.g., material removal rate). However, during recycling, the activity of the CMP composition often decreases over time, which may be due to wear, cracking, and shrinkage of the aluminum oxide particles during the polishing process, or due to chemical changes in the aluminum oxide particles. This reduced polishing activity of the CMP composition reduces the time during which the CMP composition can be recycled for polishing, and replacing the CMP composition increases manufacturing costs and environmental burdens. Furthermore, conventional CMP compositions often contain polymers to increase the recycle time of the CMP composition, prevent aggregation of aluminum oxide particles, and reduce the number of defects in the substrate during the CMP process. Such additions often increase costs, increase environmental burdens, and reduce the material removal rate of the substrate during the CMP process. Therefore, there is still a need for a CMP composition comprising aluminum oxide abrasive grains suitable for polishing metal alloy substrate surfaces that can achieve higher removal rates, longer recycle times, low surface defect counts, and is virtually polymer-free.

[0006] Summary of the Invention

[0007] One object of the present invention is to overcome the aforementioned problems existing in the prior art. Preferably, embodiments of the present invention provide a composition suitable for chemical mechanical polishing of the surface of a metal alloy substrate, wherein the composition exhibits high material removal rates and extended recycle times, while achieving low surface roughness and a low number of surface defects. Furthermore, the composition contains virtually no polymers and is more environmentally friendly.

[0008] Specifically, the chemical mechanical polishing composition of the present invention comprises aluminum oxide abrasive particles, an oxidizing agent, and a dispersant, wherein the dispersant is nanoclay having a z-average particle size of at most 1000 nm and a zeta potential of at least -5 mV.

[0009] Preferably, the aluminum oxide abrasive grains have a zeta potential of 8 to 80 mV at a pH of 2.5 to 4 in the composition.

[0010] Preferably, the oxidizing agent is not a peroxide compound.

[0011] Preferably, the composition has a pH of 7 at most.

[0012] Preferably, the nanoclay has a D70 of at most 1600 nm as measured by dynamic light scattering.

[0013] Preferably, the composition comprises 0.0001 wt% to 15 wt% nanoclay.

[0014] Preferably, the increase ratio of the aluminum oxide D70 is at most 5.5.

[0015] Preferably, the increase ratio of the aluminum oxide D30 is at most 4.2.

[0016] Preferably, the composition is substantially free of polymers.

[0017] Another object of an embodiment of the present invention is to provide a polishing method for a metal alloy substrate, wherein the method is implemented using the above composition.

[0018] The CMP composition provided by the present invention not only achieves high material removal rates in chemical mechanical polishing of metal alloy substrates, but also, while being virtually polymer-free, achieves low surface defect counts and extended recycle times, making it environmentally friendly and economically efficient. Products polished with the CMP composition of the present invention exhibit low surface roughness, low surface defect counts (scratches and pits), and a satisfactory mirror finish. DETAILED DESCRIPTION

[0019] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0020] Chemical mechanical polishing compositions typically comprise abrasive particles dispersed in an aqueous carrier. The abrasive particles can aid in the removal of material from the substrate surface during the polishing process. Preferably, the abrasive particles are metal oxide abrasive particles selected from the group consisting of cerium oxide (ceria), aluminum oxide (aluminum oxide), silicon oxide (silicon dioxide), zirconium oxide (zirconium oxide), titanium oxide (titania), germanium oxide (germania), magnesium oxide (magnesium oxide), nickel oxide, gallium oxide (gallium oxide), yttrium oxide (yttrium oxide), and combinations thereof. Preferably, the abrasive particles comprise at least 67 wt% (weight percent), more preferably at least 74 wt%, more preferably at least 81 wt%, more preferably at least 88 wt%, and most preferably at least 93 wt% aluminum oxide. In particularly preferred embodiments, the abrasive particles are entirely aluminum oxide abrasive particles.

[0021] When in use, the composition preferably comprises at least 0.02 wt%, more preferably at least 0.24 wt%, more preferably at least 0.63 wt%, more preferably at least 0.82 wt%, and most preferably at least 1.0 wt% abrasive particles. As used herein, the term "when in use" refers to the moment when the composition is applied to the surface of the substrate during chemical mechanical polishing. If the concentration of abrasive particles is too high, the composition may cause undesirable surface defects such as substrate scratches during polishing. Therefore, when in use, the composition preferably comprises at most 40 wt%, more preferably at most 35 wt%, more preferably at most 30 wt%, more preferably at most 25 wt%, and most preferably at most 20 wt% abrasive particles. In a preferred embodiment, the composition comprises 0.02 wt% to 40 wt%, more preferably 0.24 wt% to 35 wt%, more preferably 0.63 wt% to 30 wt%, more preferably 0.63 wt% to 25 wt%, and most preferably 1.0 wt% to 20 wt% abrasive particles.

[0022] As known to those skilled in the art, the aluminum oxide abrasive grains may be fumed aluminum oxide or aluminum oxide with different crystalline phases, such as α-alumina, β-alumina, γ-alumina, δ-alumina, θ-alumina, σ-alumina, κ-alumina, η-alumina, χ-alumina, β-alumina, and combinations thereof. Preferably, the aluminum oxide abrasive grains are selected from α-alumina, β-alumina, γ-alumina, δ-alumina, σ-alumina, θ-alumina, and combinations thereof.

[0023] It has been shown that α-alumina can exhibit higher substrate material removal rates during chemical mechanical polishing compared to alumina abrasive grains having other crystalline phases. Therefore, the alumina abrasive grains preferably contain at least 6 wt%, more preferably at least 11 wt% of α-alumina. As known to those skilled in the art, the amount of α-alumina can be obtained by X-ray diffraction (XRD), for example, based on the integrated intensity ratio of the (113) plane using a D8 X-ray diffractometer (Bruker Corp). However, a large amount of α-alumina can lead to an increase in the number of defects such as scratches and pits on the substrate surface. The inventors have found that the composition of the present invention can exhibit a high material removal rate even when the α-alumina content is low, thereby generating a smaller number of defects on the substrate surface. Therefore, it is preferred that the alumina abrasive grains contain up to 96 wt%, more preferably up to 95 wt% of α-alumina. In a preferred embodiment, the alumina abrasive grains contain 6 wt% to 96 wt%, more preferably 11 wt% to 95 wt% of α-alumina.

[0024] Preferably, the aluminum oxide abrasive grains comprise a mixture of α-aluminum oxide and aluminum oxide having a non-α crystalline phase. The aluminum oxide having a non-α crystalline phase may be any aluminum oxide other than α-aluminum oxide, such as β-aluminum oxide, γ-aluminum oxide, δ-aluminum oxide, θ-aluminum oxide, σ-aluminum oxide, κ-aluminum oxide, η-aluminum oxide, χ-aluminum oxide, and β-aluminum oxide, or a combination thereof. Preferably, the aluminum oxide having a non-α crystalline phase is selected from β-aluminum oxide, γ-aluminum oxide, δ-aluminum oxide, σ-aluminum oxide, θ-aluminum oxide, and a combination thereof. Preferably, the aluminum oxide abrasive grains comprise at least two crystalline phases, more preferably at least three crystalline phases. The inventors have found that the aluminum oxide abrasive grains described herein can reduce the number of surface defects on the substrate and reduce the surface roughness of the substrate surface, thereby helping to improve the visual effect of mirror finishing to obtain a bright and reflective surface.

[0025] The average particle size (diameter) of the abrasive particles affects the material removal rate. As known to those skilled in the art, the average particle size of the abrasive particles can be determined by measuring the composition using laser diffraction (e.g., using an LA-960 from Horiba). The graph obtained from this measurement provides the cumulative volume percentage of particles of a certain size, from which the corresponding D10, D30, D50, D70, and D90 values ​​can be obtained. The particle size of the aluminum oxide abrasive particles mentioned herein is obtained from the particle size distribution of the aluminum oxide abrasive particles measured in the composition.

[0026] The average particle size (D50) corresponds to a value that is smaller than the particle size of 50% by volume of the particles. A smaller D50 of the aluminum oxide abrasive grains results in a reduced material removal rate. Preferably, the abrasive grains have a D50 of at least 0.09 μm, more preferably at least 0.41 μm, more preferably at least 1.28 μm, more preferably at least 1.72 μm, and most preferably at least 2.01 μm as measured by laser diffraction. However, if the D50 of the aluminum oxide abrasive grains is too large, a large number of undesirable surface defects such as scratches and pits will appear during the CMP process. Therefore, the abrasive grains preferably have a D50 of at most 15 μm, more preferably at most 12 μm, more preferably at most 10 μm, more preferably at most 8 μm, and most preferably at most 6 μm as measured by laser diffraction. In a preferred embodiment, the abrasive particles have a D50 measured by laser diffraction of 0.09 to 15 μm, more preferably 0.41 to 12 μm, more preferably 1.28 to 10 μm, more preferably 1.72 to 8 μm, more preferably 2.01 to 6 μm.

[0027] The numerical value corresponding to D10 is: 10% by volume of the particles have a particle size smaller than this value. Experiments have shown that a smaller D10 of the aluminum oxide abrasive can achieve a smaller surface roughness during the CMP process. The D10 of the aluminum oxide abrasive mentioned here is obtained from the particle size distribution of the aluminum oxide abrasive measured in the composition. Preferably, the abrasive has a D10 measured by laser diffraction of at most 10 μm, more preferably at most 8 μm, more preferably at most 6 μm, more preferably at most 4 μm, and most preferably at most 3 μm. However, a smaller D10 of the aluminum oxide abrasive will reduce the material removal rate. Preferably, the abrasive has a D10 measured by laser diffraction of at least 0.005 μm, more preferably at least 0.009 μm, more preferably at least 0.02 μm, more preferably at least 0.04 μm, and most preferably at least 0.08 μm. In a preferred embodiment, the abrasive particles have a D10 measured by laser diffraction of 0.005 μm to 10 μm, more preferably 0.009 μm to 8 μm, more preferably 0.02 μm to 6 μm, more preferably 0.04 μm to 4 μm, most preferably 0.08 μm to 3 μm.

[0028] The numerical value corresponding to D30 is: 30% by volume of the particles have a particle size smaller than this value. Experiments have shown that a smaller D30 of the aluminum oxide abrasive can achieve a smaller surface roughness during the CMP process. The D30 of the aluminum oxide abrasive mentioned here is obtained from the particle size distribution of the aluminum oxide abrasive measured in the composition. Preferably, the abrasive has a D30 measured by laser diffraction of at most 12.5 μm, more preferably at most 11 μm, more preferably at most 9 μm, more preferably 7 μm, and most preferably at most 5 μm. However, a smaller D30 of the aluminum oxide abrasive will reduce the material removal rate. Preferably, the abrasive has a D30 measured by laser diffraction of at least 0.009 μm, more preferably at least 0.02 μm, more preferably at least 0.05 μm, more preferably at least 0.81 μm, and most preferably at least 1.12 μm. In a preferred embodiment, the abrasive particles preferably have a D30 measured by laser diffraction of 0.009 to 12.5 μm, more preferably 0.02 to 11 μm, more preferably 0.05 to 9 μm, more preferably 0.81 to 7 μm, most preferably 1.12 to 5 μm.

[0029] D70 corresponds to a value that is less than the particle size of 70% by volume of the particles. A higher D70 of the aluminum oxide abrasive results in a higher material removal rate. The D70 of the aluminum oxide abrasive mentioned here is obtained from the particle size distribution of the aluminum oxide abrasive measured in the composition. Preferably, the abrasive has a D70 of at least 0.13 μm, more preferably at least 0.64 μm, more preferably at least 1.58 μm, more preferably at least 2.21 μm, and most preferably at least 2.68 μm as measured by laser diffraction. However, if the D70 of the aluminum oxide abrasive is too large, a large number of unfavorable surface defects such as scratches and pits will appear during the CMP process. Preferably, the abrasive has a D70 of at most 19 μm, more preferably at most 16 μm, more preferably at most 13 μm, more preferably at most 10 μm, and most preferably at most 8 μm as measured by laser diffraction. In a preferred embodiment, the abrasive particles preferably have a D70 measured by laser diffraction of 0.13 to 19 μm, more preferably 0.64 to 16 μm, more preferably 1.58 to 13 μm, more preferably 2.21 to 10 μm, most preferably 2.68 to 8 μm.

[0030] D90 corresponds to a value that is smaller than the particle size of 90% by volume of the particles. A higher D90 of the abrasive particles results in a higher material removal rate. The D90 of the alumina abrasive particles mentioned here is obtained from the particle size distribution of the alumina abrasive particles measured in the composition. Preferably, the abrasive particles have a D90 of at least 0.16 μm, more preferably at least 1.58 μm, more preferably at least 2.15 μm, more preferably at least 3.26 μm, and most preferably at least 4.42 μm as measured by laser diffraction. However, if the D90 is too large, a large number of unfavorable surface defects such as scratches and pits will appear during the CMP process. Preferably, the abrasive particles have a D90 of at most 25 μm, more preferably at most 21 μm, more preferably at most 18 μm, more preferably at most 15 μm, and most preferably at most 12 μm as measured by laser diffraction. In a preferred embodiment, the abrasive particles have a D90 measured by laser diffraction of 0.16 μm to 25 μm, more preferably 1.58 μm to 21 μm, more preferably 2.15 μm to 18 μm, more preferably 3.26 μm to 15 μm, most preferably 4.42 μm to 12 μm.

[0031] The abrasive particles should have a suitable BET surface area. The BET surface area can be measured by a person skilled in the art using the Brunauer-Emmett-Teller method by adsorbing nitrogen on the abrasive particle surface. A larger surface area of ​​the particle can increase the contact area between the particle and the substrate, thereby improving the material removal rate. Therefore, the abrasive particles preferably have a surface area of ​​at least 2.1 m 2 / g, more preferably at least 6.4m 2 / g, more preferably at least 10.1m 2 / g, most preferably at least 16.3m2 The abrasive particles preferably have a BET surface area of ​​at most 94.7 m 2 / g, more preferably up to 81.2m 2 / g, more preferably up to 72.9m 2 / g, most preferably up to 60.6m 2 / g of BET surface area.

[0032] Preferably, the abrasive particles have a positive charge. Charge refers to the zeta potential, which can be measured, for example, by a Mastersizer S (Malvern Instruments). As known to those skilled in the art, the zeta potential of the abrasive particles in a composition refers to the electrical potential at the interface between the mobile fluid within the composition and the fluid stabilizing layer attached to the abrasive particles dispersed in the composition. A higher zeta potential results in stronger electrostatic repulsion between the particles, thereby increasing the stability of the particle dispersion in the composition. Preferably, the abrasive particles have a zeta potential of at least 8 mV, more preferably at least 13 mV, more preferably at least 18 mV, and most preferably at least 26 mV in the composition at a pH of 2.5 to 4. Preferably, the abrasive particles have a zeta potential of at most 80 mV, more preferably at most 75 mV, more preferably at most 70 mV, and most preferably at most 60 mV in the composition at a pH of 2 to 5. Preferably, the abrasive particles have a zeta potential of 8 to 80 mV, more preferably 13 to 75 mV, more preferably 18 to 70 mV, more preferably 26 to 60 mV at a pH of 2.5 to 4 in the composition.

[0033] The composition may further comprise an oxidizing agent. Depending on the substrate, the oxidizing agent may react with the substrate surface and promote material removal during the polishing process. Preferably, the oxidizing agent is a nitrate compound. Examples of nitrate compounds include ferric nitrate, barium nitrate, neodymium praseodymium nitrate, nickel nitrite, potassium nitrate, aluminum nitrate, sodium nitrate, uranyl nitrate, ammonium nitrate, cerium nitrate, and combinations thereof. Experiments have shown that compared to other oxidizing agents (e.g., inorganic or organic peroxide compounds), nitrate compounds can reduce defects on the substrate surface during the polishing process, and some nitrate compounds have both oxidizing effects and pH regulating effects, which can help the composition achieve a suitable pH. Furthermore, nitrate compounds are more stable in the composition than peroxide compounds. Therefore, in a particularly preferred embodiment, the oxidizing agent is not a peroxide compound. Unsuitable percompounds include, for example, hydrogen peroxide, percarbonates, organic peroxides (e.g., benzoyl peroxide), peracetic acid, di-tert-butyl peroxide, monopersulfates, dipersulfates, sodium peroxide, urea peroxide, persulfates, periodic acid, periodates, perbromic acid, perbromates, perchloric acid, perchlorates, perboric acid, permanganates, perchlorates, perborates, and combinations thereof. Preferably, when used, the composition comprises at least 0.05 wt%, more preferably at least 0.3 wt%, more preferably at least 0.84 wt%, more preferably at least 1.56 wt%, and most preferably at least 3.0 wt% of the oxidizing agent. Preferably, when used, the composition comprises at most 25 wt%, more preferably at most 20 wt%, more preferably at most 15 wt%, more preferably at most 10 wt%, and most preferably at most 8 wt% of the oxidizing agent. In a preferred embodiment, the composition comprises 0.05 wt% to 25 wt%, more preferably 0.3 wt% to 20 wt%, more preferably 0.84 wt% to 15 wt%, more preferably 1.56 wt% to 10 wt%, more preferably 3.0 wt% to 8 wt% of the oxidizing agent.

[0034] The composition comprises an aqueous carrier. The abrasive and chemical additives are suspended in the aqueous carrier. The aqueous carrier enables the abrasive and chemical additives to come into contact with the substrate and polishing pad during the CMP process. The aqueous carrier can be any component suitable for suspending the abrasive and the oxidizing agent. Examples of the aqueous carrier include water, ethers (such as dioxane and tetrahydrofuran), alcohols (such as methanol and ethanol), and combinations thereof. Preferably, the aqueous carrier contains at least 50 wt %, more preferably at least 70 wt %, more preferably at least 90 wt %, more preferably at least 95 wt %, and most preferably at least 99 wt % water. Preferably, the water is deionized water.

[0035] The pH of the composition affects the removal rate of the substrate during CMP treatment. Alkaline pH has been found to result in lower material removal rates. Therefore, the composition preferably has a pH of at most 7.0, more preferably at most 6.5, more preferably at most 6.0, more preferably at most 5.5, more preferably at most 5.0, and most preferably at most 4.5 when used.

[0036] The composition further comprises a dispersant, which helps to disperse the aluminum oxide abrasive particles and stabilize them in solution, thereby improving shelf life. The dispersant is preferably a nanoclay, polyacrylic acid, sodium dodecylbenzene sulfonate, tetrasodium pyrophosphate, sodium hexametaphosphate, or a combination thereof. In a particularly preferred embodiment, the dispersant is a nanoclay. As used herein, the term "nanoclay" refers to a clay having a z-average particle size of at most 1000 nm. The nanoclay can be any type of clay, such as natural clay, synthetic clay, modified clay, or a combination thereof. Examples of nanoclays include kaolin (e.g., kaolin, dickite, halloysite, and nacrite), montmorillonite (e.g., saponite, hectorite, laponite, nontronite, beidellite, magnesite, bentonite, andalusite, kyanite, sillimanite, kaolinite, metakaolin, mullite, aluminum silicate, dihydrate aluminum silicate, potassium aluminum silicate, sodium aluminum silicate, calcium aluminum silicate, aluminum oxide silicate, magnesium aluminum silicate, and boroaluminum silicate), illite (e.g., micas such as phlogopite, biotite, lepidolite, muscovite, and glauconite), chlorite, palygorskite, sepiolite, vermiculite, talc, pyrophyllite, modifications of such clays, and combinations thereof. In a preferred embodiment, the clay is montmorillonite. In a particularly preferred embodiment, the clay is selected from bentonite, laponite, magnesium aluminum silicate, kaolinite, or combinations thereof.

[0037] For example, nanoclay can be purchased from Shengxinxin Chemical Technology Co., Ltd. (Guangzhou, China).

[0038] The nanoclay-containing compositions of the present invention have been found to extend the shelf life of the compositions. The nanoclays of the present invention have also been found to reduce the drop in material removal rate during recycling.

[0039] Preferably, when used for polishing, the composition comprises at least 0.0001 wt%, more preferably at least 0.001 wt%, more preferably at least 0.01 wt%, more preferably at least 0.03 wt%, and most preferably at least 0.05 wt% of nanoclay. However, the amount of nanoclay should not be too high, as it can hinder the interaction of the abrasive particles with the substrate surface, thereby reducing the material removal rate during the CMP process. Therefore, when used, the composition preferably comprises at most 15 wt%, more preferably at most 13 wt%, more preferably at most 12 wt%, more preferably at most 11 wt%, and most preferably at most 10 wt% of nanoclay. In a preferred embodiment, the composition comprises from 0.0001 wt% to 15 wt%, more preferably from 0.001 to 13 wt%, more preferably from 0.01 wt% to 12 wt%, more preferably from 0.03 wt% to 11 wt%, and most preferably from 0.05 wt% to 10 wt% of nanoclay.

[0040] The composition should have a high viscosity. Viscosity can be measured in mPa*s (milliPascal seconds) at 25°C using an NDJ-8S viscometer (Shanghai Lichen Instrument Technology Co., Ltd.). The high viscosity of the composition can be achieved, for example, by the nanoclay of the present invention. It has been found that the viscosity of the present invention can reduce the aggregation and agglomeration of abrasive particles and achieve fewer defects on the substrate surface. Preferably, the composition has a viscosity of at least 2 mPa*s, more preferably at least 5 mPa*s, and most preferably at least 8 mPa*s when measured as a 2% solution at 25°C; preferably, the composition has a viscosity of at most 90 mPa*s, more preferably at most 80 mPa*s, and most preferably at most 70 mPa*s when measured as a 2% solution at 25°C.

[0041] Preferably, the nanoclay is negatively charged. The greater the absolute value of the negative zeta potential of the nanoclay, the more stable the dispersion. Preferably, the zeta potential of the nanoclay is at least -5 mV, preferably at least -10 mV, more preferably at least -15 mV, more preferably at least -20 mV, and most preferably at least -22 mV.

[0042] The zeta potential, particle size distribution and z-average particle size of the nanoclay can be measured by ultrasonically treating a 0.1 wt.% aqueous dispersion of the nanoclay at 25°C for 30 minutes. The zeta potential, particle size distribution and z-average particle size of the nanoclay are measured for the clay in the aqueous dispersion, not the clay in the composition. The zeta potential of the nanoclay can be measured by a Mastersizer S (Malvern Instruments Ltd., UK); the particle size distribution and z-average particle size can be measured by dynamic light scattering, for example, using a Zetasizer Nano ZSE (Malvern Instruments Ltd.); the z-average particle size refers to the intensity-weighted average hydrodynamic size of the particle ensemble measured by dynamic light scattering (for example, using a Zetasizer Nano ZSE (Malvern Instruments Ltd.). The D10, D30, D50, D70 and D90 of the nanoclay can be obtained from the particle size distribution measured as described above.

[0043] The inventors have found that nanoclays with a smaller z-average particle size can improve the dispersibility of aluminum oxide particles, extend the shelf life of the composition, reduce the number of pits on the substrate surface, and reduce surface roughness. It was found that nanoclays with a larger z-average particle size can cause aggregation and agglomeration of aluminum oxide abrasive particles, resulting in a greater increase in the D10, D30, D50, D70, and D90 of aluminum oxide measured in the composition, and the increase caused by this increase in surface roughness and surface defects (such as pits). The inventors have also found that nanoclays with nanometer size can improve the surface morphology of stainless steel, while nanoclays with micrometer size can deteriorate the apparent morphology of stainless steel. The nanoclay should have a suitable z-average particle size. Preferably, the nanoclay has a z-average particle size of at most 1100 nm, preferably at most 1050 nm, preferably at most 1000 nm, preferably at most 990 nm, preferably at most 980 nm, and more preferably at most 970 nm as measured by dynamic light scattering. However, if the z-average particle size of the clay is too small, it will affect the viscosity of the composition, resulting in an adverse effect. Preferably, the nanoclay has a z-average particle size of at least 1 nm, preferably at least 2 nm, preferably at least 5 nm, preferably at least 10 nm, preferably at least 15 nm, and more preferably at least 20 nm as measured by dynamic light scattering. In a preferred embodiment, the nanoclay preferably has a z-average particle size of 1 nm to 1100 nm, preferably 2 nm to 1050 nm, preferably 5 nm to 1000 nm, preferably 10 nm to 990 nm, preferably 15 nm to 980 nm, and more preferably 20 nm to 970 nm as measured by dynamic light scattering.

[0044] Experiments have shown that nanoclays with smaller D10 can achieve smaller surface roughness during CMP processing. Preferably, the nanoclay has a D10 of at most 600 nm, more preferably at most 550 nm, more preferably at most 500 nm, more preferably at most 450 nm, and most preferably at most 400 nm, as measured by dynamic light scattering. However, if the D10 of the nanoclay is too small, the material removal rate will be reduced. Preferably, the nanoclay has a D10 of at least 0.01 nm, more preferably at least 0.05 nm, more preferably at least 0.1 nm, more preferably at least 0.5 nm, and most preferably at least 1 nm, as measured by dynamic light scattering. In preferred embodiments, the nanoclay has a D10 of 0.01 nm to 600 nm, 0.05 nm to 550 nm, 0.1 nm to 500 nm, more preferably 0.5 nm to 450 nm, and more preferably 1 nm to 400 nm, as measured by dynamic light scattering.

[0045] Experiments have shown that nanoclays with a smaller D30 can achieve smaller surface roughness during CMP processing. Preferably, the nanoclay has a D30 of at most 1100 nm, more preferably at most 1050 nm, more preferably at most 1000 nm, more preferably at most 950 nm, and most preferably at most 900 nm, as measured by dynamic light scattering. However, a smaller D30 of the nanoclay can reduce the material removal rate. Preferably, the nanoclay has a D30 of at least 0.05 nm, more preferably at least 0.1 nm, more preferably at least 0.5 nm, more preferably at least 1 nm, and most preferably at least 1.3 nm, as measured by dynamic light scattering. In a preferred embodiment, the nanoclay has a D30 of 0.05 nm to 1100 nm, more preferably 0.1 nm to 1050 nm, more preferably 0.5 nm to 1000 nm, more preferably 1 nm to 950 nm, and most preferably 1.3 nm to 900 nm, as measured by dynamic light scattering.

[0046] Experiments have shown that nanoclays with a smaller D50 can achieve smaller surface roughness during CMP processing. Preferably, the nanoclay has a D50 of at most 1300nm, more preferably at most 1200nm, more preferably at most 1100nm, more preferably at most 1000nm, and more preferably at most 950nm as measured by dynamic light scattering. However, a smaller D50 of the nanoclay will reduce the material removal rate. Preferably, the nanoclay has a D50 of at least 0.1nm, more preferably at least 0.5nm, more preferably at least 1nm, more preferably at least 1.3nm, and most preferably at least 1.5nm as measured by dynamic light scattering. In a preferred embodiment, the nanoclay has a D50 of 0.1nm to 1300nm, more preferably 0.5nm to 1200nm, more preferably 1nm to 1100nm, more preferably 1.3nm to 1000nm, and most preferably 1.5nm to 950nm as measured by dynamic light scattering.

[0047] Experiments have shown that nanoclays with a smaller D70 can achieve smaller surface roughness during CMP processing. Preferably, the nanoclay has a D70 of at most 1600 nm, more preferably at most 1550 nm, more preferably at most 1500 nm, more preferably at most 1450 nm, and most preferably at most 1400 nm, as measured by dynamic light scattering. However, a smaller D70 of the nanoclay can reduce the material removal rate. Preferably, the nanoclay has a D70 of at least 0.5 nm, more preferably at least 1 nm, more preferably at least 1.4 nm, more preferably at least 1.8 nm, and most preferably at least 2 nm, as measured by dynamic light scattering. In a preferred embodiment, the nanoclay has a D70 of 0.5 nm to 1600 nm, more preferably 1 nm to 1550 nm, more preferably 1.4 nm to 1500 nm, more preferably 1.8 nm to 1450 nm, and most preferably 2 nm to 1400 nm, as measured by dynamic light scattering.

[0048] Experiments have shown that nanoclays with a smaller D90 can achieve smaller surface roughness during CMP processing. Preferably, the nanoclay has a D90 of at most 2000 nm, more preferably at most 1950 nm, more preferably at most 1900 nm, more preferably at most 1800 nm, and most preferably at most 1700 nm, as measured by dynamic light scattering. However, a smaller D90 of the nanoclay can reduce the material removal rate. Preferably, the nanoclay has a D90 of at least 1 nm, more preferably at least 2 nm, more preferably at least 3 nm, more preferably at least 3.5 nm, and most preferably at least 4 nm, as measured by dynamic light scattering. In a preferred embodiment, the nanoclay has a D90 of 1 nm to 2000 nm, more preferably 2 nm to 1950 nm, more preferably 3 nm to 1900 nm, more preferably 3.5 nm to 1800 nm, and most preferably 4 nm to 1700 nm, as measured by dynamic light scattering.

[0049] The increase in the D10, D30, D50, D70, and D90 of the alumina particles refers to the ratio of the particle size of the alumina particles in the composition to the particle size of the alumina particles in the aqueous dispersion (regardless of the composition's composition composition), specifically obtained by laser diffraction measurement, and specifically refers to the ratio of the alumina particle size measured in the composition to the corresponding alumina particle size measured in an alumina dispersion having an alumina concentration of 15 wt.% (85 wt.% water). The inventors have found that a smaller increase ratio is associated with a reduction in the number of pits and a reduction in surface roughness. The inventors have found that the nanoclay of the present invention can reduce the increase ratio of the D10, D30, D50, D70, and D90 of the alumina particles. Preferably, the increase ratio of the D10 of the alumina in the composition to the D10 of the alumina measured in an alumina dispersion having an alumina concentration of 15 wt.% (85 wt.% water) is at most 3.5, more preferably at most 3, more preferably at most 2.5, and most preferably at most 2. Preferably, the ratio of the increase in D30 of the aluminum oxide in the composition to the D30 of the aluminum oxide measured in an aluminum oxide dispersion having an aluminum oxide concentration of 15 wt.% (85 wt.% water) is at most 4.2, preferably at most 3.5, more preferably at most 3, and more preferably at most 2.5. Preferably, the ratio of the increase in D50 of the aluminum oxide in the composition to the D50 of the aluminum oxide measured in an aluminum oxide dispersion having an aluminum oxide concentration of 15 wt.% (85 wt.% water) is at most 5.5, preferably at most 5, more preferably at most 4.5, and even more preferably at most 4. Preferably, the ratio of the increase in D70 of the aluminum oxide in the composition to the D70 of the aluminum oxide measured in an aluminum oxide dispersion having an aluminum oxide concentration of 15 wt.% (85 wt.% water) is at most 5.5, preferably at most 5, more preferably at most 4.5, and even more preferably at most 4. Preferably, the increased ratio of the D90 of alumina in the composition to the D90 of alumina measured in an alumina dispersion having an alumina concentration of 15 wt.% (85 wt.% water) is at most 5.5, preferably at most 5, further preferably at most 4.5, and most preferably at most 4.

[0050] Preferably, the composition is substantially free of polymers. The polymer can be any polymer. Typically, polymers are used in CMP compositions containing aluminum oxide to improve the dispersibility of the aluminum oxide particles, thereby increasing the shelf life of the composition, and to prevent particle aggregation, which can lead to defects on the substrate surface. However, during the CMP polishing process, polymers typically reduce the material removal rate of the substrate. Surprisingly, it was found that the composition according to the present invention caused fewer defects in the substrate surface, even in the absence of polymers.

[0051] As used herein, the term "substantially free of component X" refers to a composition that does not substantially contain the component X, ie, such component may at most be present in the composition as an impurity or contaminant but is not added to the composition as a separate component.

[0052] Optionally, the composition includes a pH adjusting agent. The pH adjusting agent can help the composition achieve a suitable pH. The pH adjusting agent can be an acid or a salt thereof. The acid or salt thereof can be an organic acid, an inorganic acid, or a combination thereof.

[0053] Examples of organic acids are formic acid, acetic acid, propionic acid, butyric acid, valeric acid, methylbutyric acid, hexanoic acid, dimethylbutyric acid, ethylbutyric acid, methylvaleric acid, heptanoic acid, methylhexanoic acid, octanoic acid, ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, malic acid, phthalic acid, tartaric acid, citric acid, lactic acid, diglycolic acid, furancarboxylic acid, tetrahydrofuranic acid, methoxyacetic acid, methoxyphenylacetic acid, phenoxyacetic acid, methanesulfonic acid, ethanesulfonic acid, sulfosuccinic acid, benzenesulfonic acid, toluenesulfonic acid, phenylphosphonic acid, hydroxyethyldiphosphonic acid, and combinations thereof.

[0054] Examples of inorganic acids are hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, boric acid, carbonic acid, hypophosphorous acid, phosphorous acid, phosphoric acid, and combinations thereof.

[0055] The composition also optionally includes one or more preservatives. The preservative can be any suitable compound that prevents, inhibits, reduces growth, inhibits activity, or eliminates unwanted microorganisms. Examples of suitable preservatives include sodium hypochlorite, methylisothiazolinone, benzisothiazolinone, chloromethylisothiazolinone, and combinations thereof. Preferably, the composition includes at least 0.6ppm by weight, more preferably at least 1.6ppm by weight, more preferably at least 2.7ppm by weight, more preferably at least 3.8, most preferably at least 4.6ppm by weight of preservative. High concentrations of preservatives can cause undesirable interactions between the preservative and other components of the composition and the substrate. Therefore, the composition preferably includes at most 98ppm by weight, more preferably at most 83ppm by weight, more preferably at most 74ppm by weight, most preferably at most 69ppm by weight of preservative. Ppm used herein refers to ppm by weight.

[0056] The present invention also provides a method for chemical mechanical polishing of a substrate, comprising the following steps: (a) providing a chemical mechanical polishing composition; (b) contacting the substrate with the chemical mechanical polishing composition and a polishing pad; (c) moving the polishing pad relative to the substrate with the chemical mechanical polishing composition positioned therebetween; and (d) removing at least a portion of the substrate. The CMP composition provided in step (a) is a composition of the present invention. The method may optionally include other steps.

[0057] The composition can be prepared using suitable techniques known to those skilled in the art. The abrasive particles, nanoclay, and other chemical additives described above can be added to the aqueous carrier in any order and in appropriate amounts to achieve the desired concentration. The abrasive particles, nanoclay, and other chemical additives can be mixed and stirred in the aqueous carrier. The pH value can be adjusted using the pH regulators and pH buffers described above to achieve and maintain the desired pH. The abrasive particles, nanoclay, and other chemical additives can be added at any time prior to use or during the CMP process.

[0058] The composition can be provided as a one-part system, a two-part system, or a multi-part system. For example, as a two-part system, the first part can include abrasive particles and one or more chemical additives, and the second part can include nanoclay and one or more other chemical additives. The first and second parts can be mixed at any time before or during the CMP process, such as when using a polishing apparatus having multiple supply paths for the CMP composition.

[0059] The composition can be provided as a concentrate and can be diluted with a suitable amount of water before use. The concentration of the components in the composition can be any suitable concentration, for example, 2 times, 3 times, 10 times, or 25 times the above-mentioned concentrations for use. For example, the concentrate can contain the abrasive and chemical additives at concentrations such that, upon dilution with a suitable amount of water, the abrasive and chemical additives are present in the composition at the above-mentioned concentrations. If the composition is provided, for example, as a two-part system, one or both parts can be provided as a concentrate. The two parts can be provided at different concentrations, for example, the first part at a concentration of three times and the second part at a concentration of five times. The two parts can be diluted in any order before mixing.

[0060] The composition should achieve high material removal rates during CMP processing of substrates comprising ferrous metal alloys, such as stainless steel, carbon steel, leaded steel, tool steel, and cast steel. Preferably, the composition exhibits a material removal rate of at least 8 μm / h, more preferably at least 13 μm / h, more preferably at least 21 μm / h, and more preferably at least 25 μm / h of substrates comprising ferrous metal alloys during CMP processing.

[0061] The present invention also relates to uses of the compositions of the present invention. The compositions of the present invention can be used to polish a variety of materials. Preferably, the compositions of the present invention are used for chemical mechanical polishing of substrates comprising one or more materials, including metals, semi-metals, metal alloys, metal oxides, semi-metal oxides, carbides, minerals, plastics, or combinations thereof. As known to those skilled in the art, chemical mechanical polishing refers to a process in which a substrate is placed in a CMP apparatus and brought into contact with a polishing pad and a CMP composition positioned therebetween. The polishing pad and substrate are moved relative to each other to remove portions of the substrate.

[0062] For some materials such as metals, metal alloys, metal oxides, and minerals, the compositions are used in a final polishing step, while for other materials such as ceramics and plastics, the compositions are used in intermediate polishing steps.

[0063] Examples of metals, metal alloys, and metal oxides that can be polished with the compositions of the present invention include iron, iron alloys (e.g., steel), aluminum, aluminum alloys, titanium, titanium alloys, nickel, nickel alloys, copper, copper alloys, Kovar, cupronickel, Inconel, brass, niobium, bronze, nickel silver, beryllium, monel, vanadium, Hastelloy, tantalum, silver, gold, molybdenum, Nimonic alloys, Waspaloy alloys, tungsten, ceramics, and combinations thereof. The metal oxides can be in the form of single crystals, polycrystalline, sintered bodies (ceramics), or combinations thereof.

[0064] In a particularly preferred embodiment, the present invention is used for chemical mechanical polishing of a substrate comprising a metal alloy. The metal alloy may comprise a metal as its main component and at least one metal different from the main component. The number of metal species different from the main component is not limited and may be, for example, two, three or more. Preferably, the metal that is the main component of the metal alloy is selected from aluminum, titanium, magnesium, iron, nickel and copper. In a particularly preferred embodiment, the main metal species is iron. Examples of iron alloys include stainless steel, carbon steel, alloy steel, leaded steel, tool steel, cast steel, maraging steel, cast iron and combinations thereof.

[0065] The present application is described in detail below through specific embodiments.

[0066] Example 1

[0067] Compositions A1-A5 and E1-E6 were evaluated for stainless steel material removal rate, surface roughness, and surface defects. Compositions A1-A5 and E1-E6 included 15 wt% aluminum oxide abrasive grains, 5 wt% potassium nitrate, 0.5 wt% potassium citrate, and 30 ppm (by weight) of the corrosion inhibitor KATHON™ LX 150 (Dow Inc.). These compositions had a pH of 3.5. Except for A1, all other compositions also contained 1 wt% of the nanoclay listed in Table 1. All compositions were free of peroxide and polymer.

[0068] Compositions without clay were prepared by first adding the chemical additive to deionized water and stirring until the additive dissolved. Aluminum oxide abrasive particles were then added to the solution and stirred until the aluminum oxide was dispersed. Compositions containing clay were prepared by first stirring to dissolve the chemical additive, then adding the clay, and finally adding the aluminum oxide abrasive particles to the solution. The solution containing the chemical additive and clay was stirred until the clay was dispersed.

[0069] The z-average particle size of the nanoclay was measured by dynamic light scattering using a Zetasizer Nano ZSE (Malvern Instruments Ltd., UK) at 0.1 wt% aqueous dispersion. The zeta potential of the nanoclay was measured using a Mastersizer S (Malvern Instruments Ltd., UK) at 0.1 wt% aqueous dispersion. Prior to measuring the z-average particle size and zeta potential, the nanoclay aqueous dispersion was sonicated at 25°C for 30 minutes to obtain a homogenous aqueous dispersion.

[0070] As described above, before the aluminum oxide abrasive particles were added to the composition, the D30, D50, D70, and D90 of the aluminum oxide abrasive particles were obtained by laser diffraction in an 85 wt.% aqueous dispersion using a Horiba LA960. After the aluminum oxide particles were dispersed, the D30, D50, D70, and D90 of the aluminum oxide abrasive particles were measured within the composition using a Horiba LA960. As described above, the increase ratio of D30, D50, D70, and D90 was obtained by calculating the ratio of the corresponding particle size of the aluminum oxide abrasive particles dispersed in the composition to the corresponding particle size of the aluminum oxide abrasive particles dispersed in the 85 wt.% aqueous dispersion.

[0071] A stainless steel plate with an area of ​​9 cm2 and a thickness of 3 mm was polished for 4 min using a Nano-Max polishing tool (Shenzhen Nanos Precision Machinery Technology Co., Ltd.) at a platen speed of 80 rpm, a down force of 2.0 psi, and a slurry flow rate of 100 ml / min.

[0072] The polished stainless steel plates were visually inspected for surface defects, and pits and scratches were counted and classified as A = no corresponding defects, B = less than 10 corresponding defects, and C = more than 10 corresponding defects. The results are shown in Table 1. The material removal rate of the stainless steel plates was measured using an electronic balance, and the weight difference before and after polishing was calculated. The material removal rate is listed in Table 1 as a percentage relative to the material removal rate of composition A1. The surface roughness (average roughness, Ra) was measured using an SJ-410 surface roughness tester (Mitutoyo Corp) at a measuring length of 25 mm and is listed in Table 1. As known to those skilled in the art, surface roughness is the arithmetic mean of the absolute value of the deviation of the profile height from the average height within the measuring length. In addition, all surface roughness values ​​below 0.02 can be considered good.

[0073] The stainless steel plates were polished and the relative removal rate, surface roughness, and pitting were measured as described above, and the results are shown in Table 1.

[0074] The shelf life of compositions A1-A5 and E1-E6 was evaluated by placing 500 mL of each composition into a 500 mL polyethylene bottle and allowing it to stand at room temperature without stirring. "Shelf life" was defined as the time from the start of standing until the composition settled and formed a hard cake that was difficult to redisperse. The results of the shelf life evaluation are shown in Table 1.

[0075] Table 1

[0076] As can be seen from Table 1, the composition of magnesium silicate, bentonite and laponite containing nanoclay with z-average particle size below 1000 nm does not cause pitting, and a larger z-average particle size is associated with a greater surface roughness.

[0077] The D30, D50, D70, and D90 values ​​of alumina in the composite increased with increasing nanoclay size. Since the D30, D50, D70, and D90 values ​​of alumina were measured in composites containing nanoclay, this suggests that nanoclay can bind to the surface of alumina particles and influence their size. Larger nanoclay particles tend to aggregate more, and aggregates can contain both alumina and nanoclay particles.

[0078] The results for A2-A5 show that nanoclays with z-average particle sizes greater than 1000 nm significantly increase the D30, D50, D70, and D90 values ​​of the alumina abrasive particles, indicating aggregation and agglomeration of the alumina abrasive particles, resulting in pitting and significantly higher surface roughness. The results for E1-E6 show that nanoclays with z-average particle sizes below 1000 nm do not significantly increase the alumina abrasive particle size and do not cause pitting.

[0079] The shelf life was determined by observing the compositions at room temperature. For composition A1, which did not contain nanoclay, the aluminum oxide settled after 5 days and formed a hard cake that was difficult to redisperse. Compositions A2-A5 and E1-E6, all containing nanoclay, were observed for up to 9 months and remained dispersed (not settled) after 9 months. No further observation of the compositions was performed after 9 months.

[0080] Example 2

[0081] Compositions A6-A8 and E7-E9 were evaluated for stainless steel material removal rate, surface roughness, and surface defects. Compositions A6-A8 and E7-E9 included 10 wt% alumina abrasive grains, 5 wt% potassium nitrate, 0.1 wt% potassium citrate, 1.4 wt% of the nanoclay listed in Table 2, and 30 ppm (by weight) of the corrosion inhibitor KATHON™ LX 150 (Dow Inc.). The pH of these compositions was 3.5. All compositions were free of peroxides and polymers. The compositions were prepared as in Example 1. Prior to polishing, the zeta potential of the alumina abrasive grains in the compositions was measured using a Mastersizer S (Malvern Instruments Ltd., UK). The D10, D30, D50, D70, and D90 values ​​of the nanoclay in the aqueous dispersion were measured using a Zetasizer Nano ZSE (Malvern Instruments Ltd., UK) under the same conditions as described in Example 1.

[0082] Stainless steel plates were polished using compositions A6-A8 and compositions E7-E9 under the same conditions as described in Example 1 for 8 hours, and the ratio of the stainless steel material removal rate of compositions A6-A8 and compositions E7-E9 relative to the removal rate of composition A1 in Example 1, surface roughness, and surface defects were evaluated under the same conditions as described in Example 1.

[0083] Table 2

[0084] As shown in Table 2, the composition containing magnesium silicate, bentonite and laponite with nanoclay D50 less than 1000 nm has a relatively higher composition zeta potential, does not cause pits, and the polished steel plate has a better surface roughness (Ra≤0.02).

[0085] Example 3

[0086] Compositions E5 and A10 were evaluated for stainless steel removal and pH during recycling. Composition E5 was the same as in Example 1, while composition A10 was a composition containing aluminum oxide purchased from Fujimi Corp. Compositions E5 and A10 were used to polish stainless steel plates under the same conditions as described in Example 1 for 8 hours.

[0087] The composition is recycled and reused during the polishing process, meaning that the spent composition is collected in a tank and reapplied to the substrate. At the start of the polishing process, 500 ml of the composition is applied to the polishing system for polishing. Every two hours, an additional 100 ml of the composition is added to the polishing system to compensate for losses of the recycled composition due to, for example, evaporation.

[0088] The pH and stainless steel removal rates of the compositions were measured hourly as described in Example 1 and are reported in Table 3, where the relative removal rates are listed as a percentage relative to the stainless steel removal rate of E5 at 0 hours.

[0089] Table 3

[0090] The results show that under substantially the same pH conditions, the removal rate of the composition of Example E5 is always higher than that of Reference Example A10, and the removal rate of the composition of E5 does not decrease in the first two hours, while that of A10 decreases slowly.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A chemical mechanical polishing composition for a metal alloy surface, comprising aluminum oxide abrasive particles, an oxidizing agent and a dispersant, wherein: The dispersant is a nanoclay having a z-average particle size of at most 1000 nm and a value of the nanoclay Zeta potential of at least -5 mV.

2. The composition according to claim 1, characterized in that The aluminum oxide abrasive particles have a zeta potential of at least 8 mV at a pH of 2.5 to 4 in the composition.

3. The composition according to claim 1, characterized in that The oxidizing agent is not a peroxide.

4. The composition according to claim 1, characterized in that The composition has a pH of 7 at most.

5. The composition according to claim 1, characterized in that The nanoclay has a D70 of at most 1600 nm as measured by dynamic light scattering.

6. The composition according to claim 1, characterized in that The composition comprises 0.0001 wt % to 15 wt % of nanoclay.

7. The composition according to claim 1, characterized in that The increase ratio of the aluminum oxide D70 is at most 5.

5.

8. The composition according to claim 1, characterized in that The increase ratio of the aluminum oxide D30 is at most 4.

2.

9. The composition according to claim 1, characterized in that The composition is substantially free of polymers.

10. A polishing method for a metal alloy substrate, the method being achieved by using the composition according to any one of claims 1 to 9.

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