JP7534282B2 - Polishing composition - Google Patents

Description

The present invention relates to a polishing composition.
This application claims priority based on Japanese Patent Application No. 2019-058621 filed on March 26, 2019, the entire contents of which are incorporated herein by reference.

Precision polishing using polishing compositions is performed on the surfaces of materials such as metals, semi-metals, non-metals, and their oxides. For example, the surface of a silicon wafer used as a component of a semiconductor device is generally finished to a high-quality mirror surface through a lapping process (rough polishing process) and a polishing process (precise polishing process). The polishing process typically includes a preliminary polishing process (preliminary polishing process) and a finish polishing process (final polishing process). Patent documents 1 and 2 are cited as technical documents related to polishing compositions that are primarily used for polishing semiconductor substrates such as silicon wafers.

Japanese Patent Application Publication No. 63-272459 Japanese Patent Application Publication No. 2-158684

Polishing compositions used in finish polishing processes (particularly for finish polishing of semiconductor substrates such as silicon wafers and other substrates) are required to achieve high-quality surfaces after polishing. In addition to abrasive grains and water, polishing compositions for such applications often contain water-soluble polymers for the purposes of protecting the surface of the object to be polished and improving wettability.

By using a polyvinyl alcohol-based polymer as the water-soluble polymer, the wettability of the surface after polishing can be suitably improved. Meanwhile, in recent years, the demand for surface quality after polishing has become even higher. Therefore, the present invention aims to provide a polishing composition that contains a polyvinyl alcohol-based polymer as the water-soluble polymer and can improve the surface quality of the polished object after polishing.

The polishing composition provided by this specification contains abrasive grains, a water-soluble polymer, a basic compound, and water, and the water-soluble polymer contains a polyvinyl alcohol-based polymer and a polymer containing maleic acid-type structural units. By using the polymer containing maleic acid-type structural units, the surface quality of the object to be polished after polishing with the polishing composition containing the polyvinyl alcohol-based polymer and the polymer containing maleic acid-type structural units can be improved. For example, haze can be improved.

In this specification, "maleic acid type structural unit" (hereinafter also referred to as "MA unit") refers to a structural portion derived from maleic acid or its derivatives. As the "maleic acid type structural unit-containing polymer" (hereinafter also referred to as "MA unit-containing polymer") in the polishing composition disclosed herein, a water-soluble organic substance (typically a water-soluble polymer) containing MA units as its repeating unit is used.

In some embodiments of the polishing composition disclosed herein, the ratio of the content of the polyvinyl alcohol-based polymer to the content of the MA unit-containing polymer is preferably 50:50 to 99:1 by weight. Such a polishing composition can effectively improve the haze on the surface of the object to be polished after polishing.

The polyvinyl alcohol-based polymer to be used preferably has a weight average molecular weight (Mw1) of less than 10 × 10 ^4. The use of a polyvinyl alcohol-based polymer having such an Mw1 is preferable from the viewpoint of cleaning properties.

The MA unit-containing polymer may preferably have a weight average molecular weight (Mw2) of less than 10 × 10 ^4. The use of an MA unit-containing polymer having such an Mw2 is preferred from the viewpoint of cleaning properties.

In some embodiments of the polishing composition disclosed herein, the MA unit-containing polymer includes a polymer containing an MA unit and a polyoxyalkylene structure in one molecule. The haze-improving effect of using a polyvinyl alcohol-based polymer in combination with an MA unit-containing polymer can be more suitably exhibited in such embodiments.

In some embodiments of the polishing composition disclosed herein, the polishing composition further contains a surfactant. In such a configuration of the polishing composition, the haze on the surface of the object to be polished after polishing can be more effectively improved.

In a preferred embodiment, the polishing composition contains a surfactant containing a polyoxyalkylene structure. In this embodiment, the haze can be more effectively improved.

Silica particles are preferably used as the abrasive grains. The haze improvement effect achieved by using a combination of a polyvinyl alcohol-based polymer and a polymer containing MA units is effectively achieved in polishing using silica particles as the abrasive grains.

The polishing composition disclosed herein can be preferably used in the finish polishing process of silicon wafers. By performing finish polishing using the polishing composition, haze can be improved and a high-quality silicon wafer surface can be preferably achieved.

The following describes preferred embodiments of the present invention. Matters other than those specifically mentioned in this specification that are necessary for implementing the present invention can be understood as design matters of a person skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common technical knowledge in the relevant field.

The polishing composition disclosed herein contains abrasive grains, a water-soluble polymer, a basic compound, and water. The polishing composition contains a polyvinyl alcohol-based polymer and a polymer containing maleic acid-type structural units as the water-soluble polymer. The contents of the polishing composition disclosed herein are described below.

<Abrasive grain>
The polishing composition disclosed herein includes abrasive grains. The abrasive grains function to mechanically polish the surface of the object to be polished. The material and properties of the abrasive grains are not particularly limited, and can be appropriately selected according to the purpose and mode of use of the polishing composition. Examples of abrasive grains include inorganic particles, organic particles, and organic-inorganic composite particles. Specific examples of inorganic particles include oxide particles such as silica particles, alumina particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese dioxide particles, zinc oxide particles, and red iron oxide particles; nitride particles such as silicon nitride particles and boron nitride particles; carbide particles such as silicon carbide particles and boron carbide particles; diamond particles; carbonates such as calcium carbonate and barium carbonate, and the like. Specific examples of organic particles include polymethyl methacrylate (PMMA) particles, poly(meth)acrylic acid particles (here, (meth)acrylic acid refers to acrylic acid and methacrylic acid in a comprehensive sense), polyacrylonitrile particles, and the like. Such abrasive grains may be used alone or in combination of two or more kinds.

As the abrasive grains, inorganic particles are preferred, among which particles made of metal or semimetal oxides are preferred, and silica particles are particularly preferred. In polishing compositions that can be used for polishing objects having a surface made of silicon, such as silicon wafers described below (e.g., finish polishing), it is particularly meaningful to employ silica particles as the abrasive grains. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which the abrasive grains are substantially made of silica particles. Here, "substantially" means that 95% by weight or more (preferably 98% by weight or more, more preferably 99% by weight or more, and may be 100% by weight) of the particles constituting the abrasive grains are silica particles.

Specific examples of silica particles include colloidal silica, fumed silica, precipitated silica, etc. Silica particles can be used alone or in combination of two or more types. The use of colloidal silica is particularly preferred because it is easy to obtain a polished surface with excellent surface quality after polishing. As colloidal silica, for example, colloidal silica produced by the ion exchange method using water glass (sodium silicate) as a raw material, or alkoxide method colloidal silica (colloidal silica produced by the hydrolysis and condensation reaction of alkoxysilane) can be preferably used. Colloidal silica can be used alone or in combination of two or more types.

The true specific gravity of the abrasive grain constituent material (e.g., silica constituting silica particles) is preferably 1.5 or more, more preferably 1.6 or more, and even more preferably 1.7 or more. The upper limit of the true specific gravity of silica is not particularly limited, but is typically 2.3 or less, for example 2.2 or less. The true specific gravity of the abrasive grain (e.g., silica particles) can be measured using a liquid displacement method using ethanol as the displacement liquid.

The BET diameter (average primary particle diameter) of the abrasive grains (typically silica particles) is not particularly limited, but from the viewpoint of polishing efficiency, etc., it is preferably 5 nm or more, more preferably 10 nm or more. From the viewpoint of obtaining a higher polishing effect (e.g., effects such as reducing haze and removing defects), the BET diameter is preferably 15 nm or more, and more preferably 20 nm or more (e.g., more than 20 nm). In addition, from the viewpoint of preventing scratches, etc., the BET diameter of the abrasive grains is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 40 nm or less. From the viewpoint of making it easier to obtain a surface with lower haze, in some embodiments, the BET diameter of the abrasive grains may be 35 nm or less, may be less than 32 nm, or may be less than 30 nm.

In this specification, the BET diameter refers to the particle diameter calculated from the specific surface area (BET value) measured by the BET method using the formula BET diameter (nm) = 6000/(true density (g/ ^cm3 ) x BET value ( ^m2 /g)). For example, in the case of silica particles, the BET diameter can be calculated from BET diameter (nm) = 2727/BET value ( ^m2 /g). The specific surface area can be measured using, for example, a surface area measuring device manufactured by Micromeritics, product name "Flow Sorb II 2300".

The shape (outer shape) of the abrasive grains may be spherical or non-spherical. Specific examples of non-spherical particles include peanut-shaped (i.e., peanut shell-shaped), cocoon-shaped, confetti-shaped, and rugby ball-shaped. For example, abrasive grains in which most of the particles are peanut-shaped or cocoon-shaped may be preferably used.

Although not particularly limited, the average value of the long axis/short axis ratio of the abrasive grains (average aspect ratio) is, in principle, 1.0 or more, preferably 1.05 or more, and more preferably 1.1 or more. By increasing the average aspect ratio, higher polishing efficiency can be achieved. Furthermore, from the viewpoint of reducing scratches, etc., the average aspect ratio of the abrasive grains is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.5 or less.

The shape (outer shape) and average aspect ratio of the abrasive grains can be determined, for example, by observation with an electron microscope. The specific procedure for determining the average aspect ratio is, for example, to use a scanning electron microscope (SEM) to draw the smallest rectangle circumscribing each particle image for a predetermined number (e.g., 200) of abrasive grains whose individual particle shapes can be recognized. Then, for the rectangle drawn for each particle image, the long side length (long axis value) is divided by the short side length (short axis value) to calculate the long axis/short axis ratio (aspect ratio). The average aspect ratio can be obtained by arithmetically averaging the aspect ratios of the above-mentioned predetermined number of particles.

<Water-soluble polymer>
The polishing composition disclosed herein contains a water-soluble polymer, which can be useful for protecting the surface of the object to be polished and for improving the wettability of the surface of the object to be polished after polishing.

(Polyvinyl alcohol polymer)
The polishing composition disclosed herein contains a polyvinyl alcohol-based polymer as a water-soluble polymer. As the polyvinyl alcohol-based polymer, a water-soluble organic material (typically a water-soluble polymer) containing a vinyl alcohol unit as its repeating unit is used. Here, the vinyl alcohol unit (hereinafter also referred to as "VA unit") is a structural portion represented by the following chemical formula: -CH ₂ -CH(OH)-. The polyvinyl alcohol-based polymer may contain only VA units as repeating units, or may contain repeating units other than VA units (hereinafter also referred to as "non-VA units") in addition to the VA units. The polyvinyl alcohol-based polymer may be a random copolymer containing VA units and non-VA units, or may be a block copolymer or a graft copolymer. The polyvinyl alcohol-based polymer may contain only one type of non-VA unit, or may contain two or more types of non-VA units.

The polyvinyl alcohol-based polymer used in the polishing composition disclosed herein may be unmodified polyvinyl alcohol (unmodified PVA) or modified polyvinyl alcohol (modified PVA). Here, the unmodified PVA refers to a polyvinyl alcohol-based polymer that is produced by hydrolysis (saponification) of polyvinyl acetate and does not substantially contain repeating units other than repeating units (-CH ₂ -CH(OCOCH ₃ )-) and VA units, which are vinyl polymerized structures of vinyl acetate. The degree of saponification of the unmodified PVA may be, for example, 60% or more, and from the viewpoint of water solubility, may be 70% or more, 80% or more, or 90% or more. In some embodiments, unmodified PVA having a degree of saponification of 95% or more or 98% or more may be preferably adopted as the water-soluble polymer compound.

Non-VA units that may be contained in the modified PVA include, but are not limited to, repeating units derived from N-vinyl monomers or N-(meth)acryloyl monomers described below, repeating units derived from ethylene, repeating units derived from alkyl vinyl ethers, and repeating units derived from vinyl esters of monocarboxylic acids having 3 or more carbon atoms. A suitable example of the N-vinyl monomer is N-vinylpyrrolidone. A suitable example of the N-(meth)acryloyl monomer is N-(meth)acryloylmorpholine. The alkyl vinyl ether may be, for example, a vinyl ether having an alkyl group having 1 to 10 carbon atoms, such as propyl vinyl ether, butyl vinyl ether, or 2-ethylhexyl vinyl ether. The vinyl ester of a monocarboxylic acid having 3 or more carbon atoms may be, for example, a vinyl ester of a monocarboxylic acid having 3 to 7 carbon atoms, such as vinyl propanoate, vinyl butanoate, vinyl pentanoate, or vinyl hexanoate.

The polyvinyl alcohol-based polymer may be a modified PVA containing VA units and non-VA units having at least one structure selected from oxyalkylene groups, carboxy groups, sulfo groups, amino groups, hydroxyl groups, amide groups, imide groups, nitrile groups, ether groups, ester groups, and salts thereof. The polyvinyl alcohol-based polymer may also be a modified PVA in which a portion of the VA units contained in the polyvinyl alcohol-based polymer is acetalized with an aldehyde. As the aldehyde, for example, an alkyl aldehyde can be preferably used, and an alkyl aldehyde having an alkyl group having 1 to 7 carbon atoms is preferable, and n-butyl aldehyde is particularly preferable. As the polyvinyl alcohol-based polymer, a cation-modified polyvinyl alcohol in which a cationic group such as a quaternary ammonium structure has been introduced may be used. As the cation-modified polyvinyl alcohol, for example, a cationic group derived from a monomer having a cationic group such as a diallyldialkylammonium salt or an N-(meth)acryloylaminoalkyl-N,N,N-trialkylammonium salt may be introduced.

The ratio of the number of moles of VA units to the number of moles of all repeating units constituting the polyvinyl alcohol-based polymer may be, for example, 5% or more, 10% or more, 20% or more, or 30% or more. Although not particularly limited, in some embodiments, the ratio of the number of moles of the VA units may be 50% or more, 65% or more, 75% or more, 80% or more, or 90% or more (e.g., 95% or more, or 98% or more). Substantially 100% of the repeating units constituting the polyvinyl alcohol-based polymer may be VA units. Here, "substantially 100%" means that the polyvinyl alcohol-based polymer does not contain non-VA units at least intentionally, and typically includes the case where the ratio of the number of moles of non-VA units to the number of moles of all repeating units is less than 2% (e.g., less than 1%), and 0%. In some other embodiments, the ratio of the number of moles of VA units to the number of moles of all repeating units constituting the polyvinyl alcohol-based polymer may be, for example, 95% or less, 90% or less, 80% or less, or 70% or less.

The content of VA units in the polyvinyl alcohol-based polymer (content by weight) may be, for example, 5% by weight or more, 10% by weight or more, 20% by weight or more, or 30% by weight or more. Although not particularly limited, in some embodiments, the content of the VA units may be 50% by weight or more (e.g., more than 50% by weight), 70% by weight or more, or 80% by weight or more (e.g., 90% by weight or more, 95% by weight or more, or 98% by weight or more). Substantially 100% by weight of the repeating units constituting the polyvinyl alcohol-based polymer may be VA units. Here, "substantially 100% by weight" means that at least intentionally, non-VA units are not contained as repeating units constituting the polyvinyl alcohol-based polymer, and typically the content of non-VA units in the polyvinyl alcohol-based polymer is less than 2% by weight (e.g., less than 1% by weight). In some other embodiments, the content of VA units in the polyvinyl alcohol-based polymer may be, for example, 95% by weight or less, 90% by weight or less, 80% by weight or less, or 70% by weight or less.

A polyvinyl alcohol-based polymer may contain multiple polymer chains with different VA unit contents in the same molecule. Here, a polymer chain refers to a portion (segment) that constitutes a part of a single polymer molecule. For example, a polyvinyl alcohol-based polymer may contain, in the same molecule, a polymer chain A with a VA unit content of more than 50% by weight and a polymer chain B with a VA unit content of less than 50% by weight (i.e., a non-VA unit content of more than 50% by weight).

The polymer chain A may contain only VA units as repeating units, or may contain non-VA units in addition to VA units. The content of VA units in the polymer chain A may be 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more. In some embodiments, the content of VA units in the polymer chain A may be 95% by weight or more, or 98% by weight or more. Substantially 100% by weight of the repeating units constituting the polymer chain A may be VA units.

The polymer chain B may contain only non-VA units as repeat units, or may contain VA units in addition to non-VA units. The content of non-VA units in the polymer chain B may be 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more. In some embodiments, the content of non-VA units in the polymer chain B may be 95% by weight or more, or 98% by weight or more. Substantially 100% by weight of the repeat units constituting the polymer chain B may be non-VA units.

Examples of polyvinyl alcohol-based polymers containing polymer chain A and polymer chain B in the same molecule include block copolymers and graft copolymers containing these polymer chains. The graft copolymer may be a graft copolymer having a structure in which polymer chain B (side chain) is grafted to polymer chain A (main chain), or a graft copolymer having a structure in which polymer chain A (side chain) is grafted to polymer chain B (main chain). In one embodiment, a polyvinyl alcohol-based polymer having a structure in which polymer chain B is grafted to polymer chain A can be used.

Examples of polymer chain B include polymer chains whose main repeating units are repeating units derived from N-vinyl type monomers, polymer chains whose main repeating units are repeating units derived from N-(meth)acryloyl type monomers, and polymer chains whose main repeating units are oxyalkylene units. In this specification, the term "main repeating unit" refers to a repeating unit that is contained in an amount of more than 50% by weight, unless otherwise specified.

A suitable example of polymer chain B is a polymer chain having an N-vinyl type monomer as the main repeating unit, i.e., an N-vinyl polymer chain. The content of repeating units derived from N-vinyl type monomers in the N-vinyl polymer chain is typically more than 50% by weight, and may be 70% by weight or more, 85% by weight or more, or 95% by weight or more. Substantially all of polymer chain B may be repeating units derived from N-vinyl type monomers.

In this specification, examples of N-vinyl type monomers include monomers having a nitrogen-containing heterocycle (e.g., lactam ring) and N-vinyl chain amides. Specific examples of N-vinyl lactam type monomers include N-vinyl pyrrolidone, N-vinyl piperidone, N-vinyl morpholinone, N-vinyl caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, and the like. Specific examples of N-vinyl chain amides include N-vinyl acetamide, N-vinyl propionic acid amide, N-vinyl butyric acid amide, and the like. The polymer chain B may be, for example, an N-vinyl polymer chain in which more than 50% by weight (e.g., 70% by weight or more, 85% by weight or more, or 95% by weight or more) of its repeating units are N-vinyl pyrrolidone units. Substantially all of the repeating units constituting the polymer chain B may be N-vinyl pyrrolidone units.

Other examples of polymer chain B include polymer chains whose main repeating units are repeating units derived from N-(meth)acryloyl-type monomers, i.e., N-(meth)acryloyl-based polymer chains. The content of repeating units derived from N-(meth)acryloyl-type monomers in the N-(meth)acryloyl-based polymer chains is typically more than 50% by weight, and may be 70% by weight or more, 85% by weight or more, or 95% by weight or more. Substantially all of polymer chain B may be repeating units derived from N-(meth)acryloyl-type monomers.

In this specification, examples of N-(meth)acryloyl type monomers include linear amides having an N-(meth)acryloyl group and cyclic amides having an N-(meth)acryloyl group. Examples of linear amides having an N-(meth)acryloyl group include (meth)acrylamide; N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide, and N-n-butyl(meth)acrylamide; and N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, and N,N-di(n-butyl)(meth)acrylamide. Examples of cyclic amides having an N-(meth)acryloyl group include N-(meth)acryloylmorpholine and N-(meth)acryloylpyrrolidine.

Other examples of polymer chain B include polymer chains containing oxyalkylene units as the main repeating units, i.e., oxyalkylene-based polymer chains. The content of oxyalkylene units in the oxyalkylene-based polymer chains is typically more than 50% by weight, and may be 70% by weight or more, 85% by weight or more, or 95% by weight or more. Substantially all of the repeating units contained in polymer chain B may be oxyalkylene units.

Examples of oxyalkylene units include oxyethylene units, oxypropylene units, oxybutylene units, etc. Each of these oxyalkylene units may be a repeating unit derived from the corresponding alkylene oxide. The oxyalkylene units contained in the oxyalkylene polymer chain may be one type, or two or more types. For example, the oxyalkylene polymer chain may contain a combination of oxyethylene units and oxypropylene units. In an oxyalkylene polymer chain containing two or more types of oxyalkylene units, the oxyalkylene units may be a random copolymer of the corresponding alkylene oxide, or may be a block copolymer or a graft copolymer.

Further examples of polymer chain B include polymer chains containing repeating units derived from alkyl vinyl ethers (e.g., vinyl ethers having an alkyl group with 1 to 10 carbon atoms), polymer chains containing repeating units derived from monocarboxylic acid vinyl esters (e.g., vinyl esters of monocarboxylic acids with 3 or more carbon atoms), polymer chains in which some of the VA units have been acetalized with an aldehyde (e.g., an alkyl aldehyde having an alkyl group with 1 to 7 carbon atoms), and polymer chains into which a cationic group (e.g., a cationic group having a quaternary ammonium structure) has been introduced.

As the polyvinyl alcohol-based polymer in the polishing composition disclosed herein, non-modified PVA may be used, modified PVA may be used, or non-modified PVA and modified PVA may be used in combination. In an embodiment in which non-modified PVA and modified PVA are used in combination, the amount of modified PVA used relative to the total amount of polyvinyl alcohol-based polymer contained in the polishing composition may be, for example, less than 95% by weight, 90% by weight or less, 75% by weight or less, 50% by weight or less, 30% by weight or less, 10% by weight or less, 5% by weight or less, or 1% by weight or less. The polishing composition disclosed herein may be preferably implemented, for example, in an embodiment in which only one or more types of non-modified PVA are used as the polyvinyl alcohol-based polymer.

The weight average molecular weight (Mw1) of the polyvinyl alcohol-based polymer used in the polishing composition disclosed herein is not particularly limited. The Mw1 of the polyvinyl alcohol-based polymer is usually 100×10 ⁴ or less, preferably 30×10 ⁴ or less, and may be 20×10 ⁴ or less. From the viewpoint of cleaning properties, in some embodiments, the Mw1 of the polyvinyl alcohol-based polymer may be 15×10 ⁴ or less, or 10×10 ⁴ or less (for example, less than 10×10 ⁴ ). In addition, the Mw1 of the polyvinyl alcohol-based polymer is usually 2×10 ³ or more, may be 5×10 ³ or more, or may be 1×10 ⁴ or more. As the Mw1 of the polyvinyl alcohol-based polymer increases, the effect of protecting the polished object and improving wettability tends to increase. From such a viewpoint, Mw1 of the polyvinyl alcohol-based polymer used in the polishing composition disclosed herein is preferably 5 × 10 ³ or more, more preferably 1 × 10 ⁴ or more, may be 2 × 10 ⁴ or more, may be 5 × 10 ⁴ or more, may be 6 × 10 ⁴ or more, or may be 6.5 × 10 ⁴ or more.

In this specification, the weight average molecular weight (Mws) of the water-soluble polymer and the surfactant described later can be a value based on aqueous gel permeation chromatography (GPC) (aqueous, polyethylene oxide equivalent). As the GPC measuring device, it is preferable to use a model named "HLC-8320GPC" manufactured by Tosoh Corporation. The measurement can be performed, for example, under the following conditions. The same method is also used in the examples described later.
[GPC measurement conditions]
Sample concentration: 0.1% by weight
Column: TSKgel GMPWXL
Detector: differential refractometer Eluent: 100 mM sodium nitrate aqueous solution/acetonitrile = 10-8/0-2
Flow rate: 1mL/min Measurement temperature: 40℃
Sample injection volume: 200 μL

The content of the polyvinyl alcohol-based polymer in the polishing composition (the total amount of two or more polyvinyl alcohol-based polymers when two or more types of polyvinyl alcohol-based polymers are included) is not particularly limited. From the viewpoint of improving polishing performance and surface quality, in some embodiments, the content may be, for example, 0.0001% by weight or more, and is usually 0.00025% by weight or more, preferably 0.0004% by weight or more, for example 0.0005% by weight or more. The upper limit of the content of the polyvinyl alcohol-based polymer is not particularly limited, and can be, for example, 0.05% by weight or less. From the viewpoint of stability at the concentrated liquid stage, polishing rate, cleanability, etc., in some embodiments, the content of the polyvinyl alcohol-based polymer is preferably 0.035% by weight or less, more preferably 0.025% by weight or less, even more preferably 0.02% by weight or less, particularly preferably 0.015% by weight or less, for example 0.0125% by weight or less, typically 0.01% by weight or less.

The content of the polyvinyl alcohol-based polymer (the total amount of two or more polyvinyl alcohol-based polymers when two or more types of polyvinyl alcohol-based polymers are included) can also be specified by the relative relationship with the abrasive grains. Although not particularly limited, in some embodiments, the content of the polyvinyl alcohol-based polymer per 100 parts by weight of the abrasive grains can be, for example, 0.01 parts by weight or more, and from the viewpoint of haze reduction, etc., it is appropriate to set it to 0.1 parts by weight or more, preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, and even more preferably 3 parts by weight or more. In addition, the content of the polyvinyl alcohol-based polymer per 100 parts by weight of the abrasive grains may be, for example, 50 parts by weight or less, or may be 30 parts by weight or less. From the viewpoint of dispersion stability of the polishing composition, etc., in some embodiments, the content of the polyvinyl alcohol-based polymer per 100 parts by weight of the abrasive grains is appropriate to be 15 parts by weight or less, preferably 10 parts by weight or less, more preferably 8 parts by weight or less, and may be 7 parts by weight or less.

(Polymer containing maleic acid type structural unit)
The polishing composition disclosed herein contains a MA unit-containing polymer as a water-soluble polymer. The MA unit-containing polymer may contain only one type of MA unit as its repeating unit, or may contain two or more types of MA units. In addition to the MA unit, it may contain a non-MA unit as its repeating unit. As the MA unit-containing polymer in the polishing composition disclosed herein, a copolymer containing MA units and non-MA units is typically used. The MA unit-containing polymer may be a random copolymer containing MA units and non-MA units, or may be a block copolymer or a graft copolymer. In this case, it may contain only one type of non-MA unit, or may contain two or more types of non-MA units.

The non-MA units referred to here are selected from the group consisting of, for example, styrene-type structural units, olefin-type structural units, acrylic acid-type structural units, methacrylic acid-type structural units, and vinyl acetate-type structural units. Specific examples of water-soluble polymers of copolymers containing MA units and non-MA units include styrene-maleic acid copolymers or salts thereof, styrene-maleic anhydride copolymers, styrene sulfonic acid-maleic acid copolymers or salts thereof, copolymers of styrene sulfonate and maleic acid, styrene-N-phenylmaleimide copolymers, maleic acid-vinyl acetate copolymers or salts thereof, maleic anhydride-vinyl acetate copolymers, N-phenylmaleimide-vinyl acetate copolymers, maleic acid-isobutylene copolymers or salts thereof, maleic anhydride-isobutylene copolymers, N-phenylmaleimide-isobutylene copolymers, acrylic acid-maleic acid copolymers or salts thereof, methyl vinyl ether-maleic anhydride copolymers, etc. For example, styrene-maleic anhydride copolymers, ammonium salts of styrene-water maleic acid copolymers, sodium salts of maleic acid-isobutylene copolymers, etc. can be preferably used. The water-soluble polymer of the copolymer is easy to act on the object to be polished because the hydrophobic group and the hydrophilic group are independent, and is suitable for protecting the object to be polished. The water-soluble polymer of the copolymer can be produced, for example, by radical copolymerization of maleic acid or its derivative with other monomers. When using the copolymer, the copolymerization ratio of MA units and non-MA units in the copolymer is not particularly limited, but from the viewpoint of protecting the object to be polished and improving wettability, it is preferably 10:1 or less, more preferably 5:1 or less, and particularly preferably 1:1 or less. In addition, the copolymerization ratio is not particularly limited, but from the viewpoint of hydrophilicity, it is preferably 1:10 or more, more preferably 1:5 or more, and particularly preferably 1:3 or more.

The polishing composition disclosed herein may contain, as the MA unit-containing polymer, a polymer containing MA units and a polyoxyalkylene structure in one molecule. The polyoxyalkylene structure is a structural moiety represented by the following formula: (AO) _n (wherein n is an integer of 2 or more (typically 2 to 100), and A is an alkylene group having 2 to 4 carbon atoms (preferably 2 to 3), preferably an ethylene group). The position of the (AO) _n structure in the polymer containing a maleic acid type structural unit and a polyoxyalkylene structure in one molecule is not particularly limited. The polymer containing a maleic acid type structural unit and a polyoxyalkylene structure in one molecule may have, for example, a side chain containing an (AO) _n structure, or may have an (AO) _n chain in the main chain or side chain, the end of which may be, for example, a hydroxyl group or an amino group. When the MA unit-containing polymer used in combination with a polyvinyl alcohol-based polymer contains a polyalkylene oxide structure, the haze improving effect can be more suitably exhibited.

The MA unit-containing polymer may also include a polymer in which a portion of the maleic anhydride has been modified with, for example, a polyalkylene glycol having a terminal hydroxyl group or a polyalkylene glycol having a terminal amino group. In the polyalkylene glycol, the molar ratio of the polyethylene glycol chain to the polypropylene glycol chain is not particularly limited, but may be, for example, 6/4 to 8/1. The weight average molecular weight (Mwo) of the polyalkylene glycol is not particularly limited, but may be, for example, 500 to 3000.

The weight average molecular weight (Mw2) of the MA unit-containing polymer used in the polishing composition disclosed herein is not particularly limited. The Mw2 of the MA unit-containing polymer is usually 100×10 ⁴ or less, preferably 30×10 ⁴ or less, and may be 20×10 ⁴ or less. From the viewpoint of cleaning properties, in some embodiments, the Mw2 of the MA unit-containing polymer may be 10×10 ⁴ or less (e.g., less than 10×10 ⁴ ), 5×10 ⁴ or less, or 3×10 ⁴ or less. In addition, the Mw2 of the MA unit-containing polymer is usually 5×10 ² or more, may be 1×10 ³ or more, or may be 2×10 ³ or more.

The weight average molecular weight (Mw2) of the MA unit-containing polymer can also be specified by its relative relationship with (Mw1) of the polyvinyl alcohol-based polymer. Although not particularly limited, Mw1 is usually 100 times or less than Mw2, and may be 50 times or less. When Mw2 is smaller than Mw1, the effect of protecting the polished object and improving wettability tends to increase. From this viewpoint, in some embodiments, Mw1 is preferably 30 times or less than Mw2, and more preferably 25 times or less. Moreover, Mw1 is usually 0.5 times or more than Mw2, and may be 1 time or more, or may be 2 times or more.

The content of the MA unit-containing polymer in the polishing composition is not particularly limited. From the viewpoint of protecting the polished object in the presence of the polyvinyl alcohol-based polymer and improving wettability, in some embodiments, the content may be, for example, 0.00005% by weight or more, and is usually 0.00025% by weight or more, preferably 0.0005% by weight or more, for example 0.0007% by weight or more. The upper limit of the content of the MA unit-containing polymer is not particularly limited, and can be, for example, 0.005% by weight or less. From the viewpoint of stability, polishing rate, cleanability, etc. at the concentrated liquid stage, in some embodiments, the content of the MA unit-containing polymer is preferably 0.0035% by weight or less, more preferably 0.0025% by weight or less, even more preferably 0.002% by weight or less, and particularly preferably 0.0015% by weight or less.

The content of the MA unit-containing polymer can also be specified by its relative relationship with the abrasive grains. Although not particularly limited, in some embodiments, the content of the MA unit-containing polymer per 100 parts by weight of the abrasive grains can be, for example, 0.01 parts by weight or more, and from the viewpoint of haze reduction, etc., it is appropriate to set it to 0.1 parts by weight or more, preferably 0.2 parts by weight or more, more preferably 0.5 parts by weight or more. In addition, the content of the MA unit-containing polymer per 100 parts by weight of the abrasive grains may be, for example, 30 parts by weight or less, or may be 10 parts by weight or less. From the viewpoint of dispersion stability of the polishing composition, etc., in some embodiments, the content of the MA unit-containing polymer per 100 parts by weight of the abrasive grains is appropriate to be 5 parts by weight or less, preferably 3 parts by weight or less, and may be 1 part by weight or less.

The content of the MA unit-containing polymer can also be specified by its relative relationship with the polyvinyl alcohol-based polymer. Although not particularly limited, in some embodiments, the ratio of the content of the polyvinyl alcohol-based polymer to the content of the MA unit-containing polymer in the polishing composition is preferably 10:90 or more by weight, more preferably 15:85 or more, and particularly preferably 50:50 or more, from the viewpoint of hydrophilicity. In addition, the ratio of the content of the polyvinyl alcohol-based polymer to the content of the MA unit-containing polymer is not particularly limited, but is preferably 99:1 or less by weight, more preferably 95:5 or less, and particularly preferably 90:10 or less, from the viewpoint of haze improvement effect.

(Other water-soluble polymers)
The polishing composition disclosed herein may further contain other water-soluble polymers, i.e., water-soluble polymers other than polyvinyl alcohol-based polymers and MA unit-containing polymers, as necessary, within the scope that does not significantly impede the effect of the present invention.Other water-soluble polymers can be appropriately selected from water-soluble polymers known in the field of polishing compositions.Examples of other water-soluble polymers include synthetic polymers such as polymers containing oxyalkylene units and polymers containing nitrogen atoms; polymers derived from natural products such as cellulose derivatives and starch derivatives; etc.

Examples of the polymer containing an oxyalkylene unit include polyethylene oxide (PEO), block copolymers of ethylene oxide (EO) and propylene oxide (PO) or butylene oxide (BO), and random copolymers of EO and PO or BO. Among these, block copolymers of EO and PO or random copolymers of EO and PO are preferred. The block copolymers of EO and PO may be diblock copolymers or triblock copolymers containing a PEO block and a polypropylene oxide (PPO) block. Examples of the triblock copolymers include PEO-PPO-PEO type triblock copolymers and PPO-PEO-PPO type triblock copolymers. Among these, PEO-PPO-PEO type triblock copolymers are more preferred.
In a block copolymer or random copolymer of EO and PO, the molar ratio of EO to PO (EO/PO) constituting the copolymer is preferably greater than 1, more preferably 2 or more, and even more preferably 3 or more (e.g., 5 or more), from the viewpoints of solubility in water, washability, etc.

As the nitrogen atom-containing polymer, both a polymer containing a nitrogen atom in the main chain and a polymer having a nitrogen atom in a side chain functional group (pendant group) can be used. Examples of the polymer containing a nitrogen atom in the main chain include homopolymers and copolymers of N-acyl alkylene imine type monomers. Specific examples of N-acyl alkylene imine type monomers include N-acetyl ethylene imine and N-propionyl ethylene imine. Examples of the polymer having a nitrogen atom in the pendant group include polymers containing N-vinyl type monomer units. For example, homopolymers and copolymers of N-vinyl pyrrolidone can be used.

Cellulose derivatives are polymers that contain β-glucose units as the main repeating unit, such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose (HEC), methylhydroxyethyl cellulose, etc. Starch derivatives are polymers that contain α-glucose units as the main repeating unit, such as pregelatinized starch, pullulan, carboxymethyl starch, cyclodextrin, etc.

In the technology disclosed herein, the molecular weight of the other water-soluble polymer is not particularly limited. The weight average molecular weight (Mw3) of the other water-soluble polymer may be, for example, 100×10 ⁴ or less, and from the viewpoint of cleaning properties, etc., it is usually appropriate to be 60×10 ⁴ or less, and may be 40×10 ⁴ or less, preferably 20×10 ⁴ or less, for example, 10×10 ⁴ or less, typically 8×10 ⁴ or less. In addition, from the viewpoint of protection of the polishing object, the Mw3 of the other water-soluble polymer may be, for example, 2000 or more, and usually preferably 5000 or more. In some embodiments, Mw3 is appropriately 1.0×10 ⁴ or more, preferably 1.5×10 ⁴ or more, more preferably 2×10 ⁴ or more, even more preferably 3×10 ⁴ or more, for example 4×10 ⁴ or more, typically 5×10 ⁴ or more.

The other water-soluble polymers can be used alone or in combination of two or more. Although not particularly limited, the relationship between the total amount of the polyvinyl alcohol-based polymer and the MA unit-containing polymer in the polishing composition and the amount of the other water-soluble polymer used may be, for example, 5:95 to 95:5, 10:90 to 90:10, or 25:75 to 75:25 by weight. In some embodiments, the weight ratio (total content of the polyvinyl alcohol-based polymer and the MA unit-containing polymer: content of the other water-soluble polymer) may be, for example, 50:50 to 100:0, 80:20 to 100:0, or 90:10 to 100:0.

From the viewpoint of reducing aggregates and improving washability, etc., a nonionic polymer may be preferably used as the other water-soluble polymer. Also, from the viewpoint of ease of control of chemical structure and purity, a synthetic polymer may be preferably used as the other water-soluble polymer. The polishing composition disclosed herein may be preferably implemented in an embodiment in which a polymer derived from a natural product is not substantially used as the other water-soluble polymer. Also, the polishing composition disclosed herein may be preferably implemented in an embodiment in which a water-soluble polymer other than a polyvinyl alcohol-based polymer and an MA unit-containing polymer is not substantially used. Here, "substantially not used" means that the amount used per 100 parts by weight of the polyvinyl alcohol-based polymer is typically 3 parts by weight or less, preferably 1 part by weight or less, and includes 0 parts by weight or below the detection limit.

(Water-soluble polymer content)
The content of the water-soluble polymer in the polishing composition (the total amount when two or more kinds are included) is not particularly limited. From the viewpoint of polishing performance and surface quality improvement, in some embodiments, the content may be, for example, 0.0005 wt% or more, and is usually 0.0025 wt% or more, preferably 0.005 wt% or more, for example 0.0075 wt% or more. The upper limit of the content of the water-soluble polymer is not particularly limited, and can be, for example, 0.05 wt% or less. From the viewpoint of stability, polishing rate, cleanability, etc. at the concentrated liquid stage, in some embodiments, the content of the water-soluble polymer is preferably 0.035 wt% or less, more preferably 0.025 wt% or less, even more preferably 0.02 wt% or less, particularly preferably 0.015 wt% or less, for example 0.0125 wt% or less, typically 0.01 wt% or less.

The content of the water-soluble polymer (the total amount when two or more kinds are included) can also be specified by the relative relationship with the abrasive grains. Although not particularly limited, in some embodiments, the content of the water-soluble polymer per 100 parts by weight of the abrasive grains can be, for example, 0.01 parts by weight or more, and from the viewpoint of haze reduction, etc., it is appropriate to set it to 0.1 parts by weight or more, preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, and even more preferably 3 parts by weight or more. In addition, the content of the water-soluble polymer per 100 parts by weight of the abrasive grains may be, for example, 50 parts by weight or less, or may be 30 parts by weight or less. From the viewpoint of dispersion stability of the polishing composition, etc., in some embodiments, the content of the water-soluble polymer per 100 parts by weight of the abrasive grains is appropriate to be 20 parts by weight or less, preferably 15 parts by weight or less, more preferably 13 parts by weight or less, and may be 12 parts by weight or less.

<Basic Compound>
The polishing composition disclosed herein contains a basic compound. In this specification, the basic compound refers to a compound that dissolves in water and has the function of increasing the pH of the aqueous solution. As the basic compound, an organic or inorganic basic compound containing nitrogen, a basic compound containing phosphorus, an alkali metal hydroxide, an alkaline earth metal hydroxide, various carbonates and hydrogen carbonates, etc. can be used. Examples of the basic compound containing nitrogen include quaternary ammonium compounds, ammonia, amines (preferably water-soluble amines), etc. Examples of the basic compound containing phosphorus include quaternary phosphonium compounds. Such basic compounds can be used alone or in combination of two or more.

Specific examples of alkali metal hydroxides include potassium hydroxide and sodium hydroxide. Specific examples of carbonates or bicarbonates include ammonium bicarbonate, ammonium carbonate, potassium bicarbonate, potassium carbonate, sodium bicarbonate, and sodium carbonate. Specific examples of amines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N-(β-aminoethyl)ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, anhydrous piperazine, piperazine hexahydrate, 1-(2-aminoethyl)piperazine, N-methylpiperazine, guanidine, and azoles such as imidazole and triazole. Specific examples of quaternary phosphonium compounds include quaternary phosphonium hydroxides such as tetramethylphosphonium hydroxide and tetraethylphosphonium hydroxide.

As the quaternary ammonium compound, quaternary ammonium salts (typically strong bases) such as tetraalkylammonium salts and hydroxyalkyltrialkylammonium salts can be preferably used. The anion component in such quaternary ammonium salts can be, for example, OH ^- , F ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , BH ₄ ^- , etc. Among them, preferred examples include quaternary ammonium salts whose anion is OH ^-, that is, quaternary ammonium hydroxides. Specific examples of quaternary ammonium hydroxides include tetraalkylammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapentylammonium hydroxide, and tetrahexylammonium hydroxide; hydroxyalkyltrialkylammonium hydroxides such as 2-hydroxyethyltrimethylammonium hydroxide (also called choline); and the like.

Among these basic compounds, at least one basic compound selected from, for example, alkali metal hydroxides, quaternary ammonium hydroxides, and ammonia can be preferably used. Among these, tetraalkylammonium hydroxides (e.g., tetramethylammonium hydroxide) and ammonia are more preferred, and ammonia is particularly preferred.

<Surfactant>
The polishing composition disclosed herein may contain a surfactant as necessary. By adding a surfactant to the polishing composition, the haze on the surface of the object to be polished after polishing can be better reduced. Any of anionic, cationic, nonionic, and amphoteric surfactants can be used as the surfactant. Usually, anionic or nonionic surfactants can be preferably used. From the viewpoint of low foaming and ease of pH adjustment, nonionic surfactants are more preferable. For example, nonionic surfactants include oxyalkylene polymers such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; polyoxyalkylene derivatives such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkylamines, polyoxyethylene fatty acid esters, polyoxyethylene glyceryl ether fatty acid esters, and polyoxyethylene sorbitan fatty acid esters (e.g., polyoxyalkylene adducts); and copolymers of multiple types of oxyalkylenes (e.g., diblock copolymers, triblock copolymers, random copolymers, and alternating copolymers). The surfactant preferably contains a surfactant containing a polyoxyalkylene structure. The surfactants can be used alone or in combination of two or more.

Specific examples of nonionic surfactants containing a polyoxyalkylene structure include block copolymers of ethylene oxide (EO) and propylene oxide (PO) (diblock copolymers, PEO (polyethylene oxide)-PPO (polypropylene oxide)-PEO type triblock copolymers, PPO-PEO-PPO type triblock copolymers, etc.), random copolymers of EO and PO, polyoxyethylene glycol, polyoxyethylene propyl ether, polyoxyethylene butyl ether, polyoxyethylene pentyl ether, polyoxyethylene hexyl ether, polyoxyethylene octyl ether, polyoxyethylene-2-ethylhexyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene isodecyl ether, polyoxyethylene tridecyl ether, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene isostearyl ether, polyoxyethylene tetra ... Examples of the polyoxyethylene oleyl ether include polyoxyethylene phenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene styrenated phenyl ether, polyoxyethylene laurylamine, polyoxyethylene stearylamine, polyoxyethylene oleylamine, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene distearate, polyoxyethylene monooleate, polyoxyethylene dioleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitoate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan tetraoleate, polyoxyethylene castor oil, and polyoxyethylene hydrogenated castor oil. Among these, preferred surfactants include block copolymers of EO and PO (particularly, triblock copolymers of PEO-PPO-PEO type), random copolymers of EO and PO, and polyoxyethylene alkyl ethers (for example, polyoxyethylene decyl ether).

The weight average molecular weight (Mws) of the surfactant is typically less than 2000, and is preferably 1900 or less (e.g., less than 1800) from the viewpoint of filterability and washability. In addition, the Mws of the surfactant is usually appropriate to be 200 or more from the viewpoint of surface activity, and is preferably 250 or more (e.g., 300 or more) from the viewpoint of haze reduction effect. A more preferable range of the Mws of the surfactant may vary depending on the type of the surfactant. For example, when a polyoxyethylene alkyl ether is used as the surfactant, the Mws is preferably 1500 or less, and may be 1000 or less (e.g., 500 or less). In addition, when a PEO-PPO-PEO type triblock copolymer is used as the surfactant, the Mws may be, for example, 500 or more, 1000 or more, or even 1200 or more.

When the polishing composition disclosed herein contains a surfactant, the content is not particularly limited as long as it is within a range that does not significantly impair the effects of the present invention. Normally, from the viewpoint of cleaning properties, etc., it is appropriate to set the content of the surfactant to 20 parts by weight or less per 100 parts by weight of the abrasive grains, preferably 15 parts by weight or less, and more preferably 10 parts by weight or less (for example, 6 parts by weight or less). From the viewpoint of better exerting the effect of using the surfactant, the content of the surfactant to 100 parts by weight of the abrasive grains is appropriate to be 0.001 parts by weight or more, preferably 0.005 parts by weight or more, and may be 0.01 parts by weight or more or 0.05 parts by weight or more.

When the polishing composition disclosed herein contains a surfactant, the weight ratio (w1/ws) of the content w1 of the polyvinyl alcohol-based polymer to the content ws of the surfactant is not particularly limited, and can be, for example, in the range of 0.01 to 200, usually preferably in the range of 0.05 to 100, and more preferably in the range of 0.1 to 70. The weight ratio (w2/ws) of the content w2 of the MA unit-containing polymer to the content ws of the surfactant is not particularly limited, and can be, for example, in the range of 0.01 to 100, usually preferably in the range of 0.05 to 50, and more preferably in the range of 0.1 to 20. Furthermore, the weight ratio (wt/ws) of the total content wt of the polyvinyl alcohol-based polymer and the MA unit-containing polymer to the content ws of the surfactant is not particularly limited, and can be, for example, in the range of 0.01 to 200, usually preferably in the range of 0.05 to 100, and more preferably in the range of 0.1 to 70.
Alternatively, from the viewpoint of simplifying the composition, etc., the polishing composition disclosed herein can also be preferably implemented in an embodiment that is substantially free of a surfactant.

<Water>
As the water contained in the polishing composition disclosed herein, ion-exchanged water (deionized water), pure water, ultrapure water, distilled water, etc. can be preferably used. In order to prevent the action of other components contained in the polishing composition from being hindered as much as possible, the water used preferably has a total transition metal ion content of, for example, 100 ppb or less. For example, the purity of water can be increased by removing impurity ions with ion exchange resin, removing foreign matter with a filter, distillation, etc.

<Other ingredients>
The polishing composition disclosed herein may further contain, as necessary, known additives that can be used in polishing compositions (typically polishing compositions used in the finish polishing process of silicon wafers), such as organic acids, organic acid salts, inorganic acids, inorganic acid salts, preservatives, and fungicides, as long as the effects of the present invention are not significantly hindered. Examples of organic acids include fatty acids such as formic acid, acetic acid, and propionic acid, aromatic carboxylic acids such as benzoic acid and phthalic acid, citric acid, oxalic acid, tartaric acid, malic acid, maleic acid, fumaric acid, succinic acid, organic sulfonic acids, and organic phosphonic acids. Examples of organic acid salts include alkali metal salts (sodium salts, potassium salts, etc.) and ammonium salts of organic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, and carbonic acid. Examples of inorganic acid salts include alkali metal salts (sodium salts, potassium salts, etc.) and ammonium salts of inorganic acids. Organic acids and their salts, and inorganic acids and their salts can be used alone or in combination of two or more. Examples of the preservatives and antifungal agents include isothiazolinone compounds, paraoxybenzoic acid esters, phenoxyethanol, and the like.

The polishing composition disclosed herein is preferably substantially free of oxidizing agents. If an oxidizing agent is contained in the polishing composition, for example, in polishing a silicon wafer, the surface of the silicon wafer is oxidized to form an oxide film, which increases the required polishing time. Specific examples of the oxidizing agent include hydrogen peroxide (H ₂ O ₂ ), sodium persulfate, ammonium persulfate, and sodium dichloroisocyanurate. The polishing composition being substantially free of oxidizing agents means that the oxidizing agent is not intentionally contained at least. Therefore, a polishing composition that inevitably contains a small amount of oxidizing agent (for example, the molar concentration of the oxidizing agent in the polishing composition is 0.0005 mol/L or less, preferably 0.0001 mol/L or less, more preferably 0.00001 mol/L or less, particularly preferably 0.000001 mol/L or less) due to raw materials, manufacturing method, etc., can be included in the concept of a polishing composition that does not substantially contain an oxidizing agent.

<pH>
The pH of the polishing composition disclosed herein is typically 8.0 or more, preferably 8.5 or more, more preferably 9.0 or more.When the pH of the polishing composition is high, the polishing efficiency tends to improve.On the other hand, from the viewpoint of preventing dissolution of abrasive grains (e.g., silica particles) and suppressing the decrease in mechanical polishing action, the pH of the polishing composition is usually appropriate to be 12.0 or less, preferably 11.0 or less, more preferably 10.8 or less, and even more preferably 10.5 or less.

The pH can be determined by using a pH meter (for example, a glass electrode type hydrogen ion concentration indicator (model number F-23) manufactured by Horiba, Ltd.) and performing three-point calibration using standard buffer solutions (phthalate pH buffer, pH: 4.01 (25°C), neutral phosphate pH buffer, pH: 6.86 (25°C), carbonate pH buffer, pH: 10.01 (25°C)), then placing the glass electrode in the composition to be measured and measuring the value after it has stabilized for at least two minutes.

<Polishing solution>
The polishing composition disclosed herein is typically supplied to the surface of an object to be polished in the form of a polishing liquid containing the polishing composition, and is used to polish the object to be polished. The polishing liquid may be prepared, for example, by diluting any of the polishing compositions disclosed herein (typically diluting with water). Alternatively, the polishing composition may be used as a polishing liquid as it is. That is, the concept of the polishing composition in the technology disclosed herein includes both the polishing liquid (working slurry) that is supplied to an object to be polished and used to polish the object to be polished, and the concentrated liquid (original polishing liquid) that is diluted and used as a polishing liquid.

<Concentrate>
The polishing composition disclosed herein may be in a concentrated form (i.e., in the form of a concentrated polishing liquid) before being supplied to an object to be polished. Such a concentrated polishing composition is advantageous from the viewpoints of convenience and cost reduction during production, distribution, storage, etc. The concentration ratio is not particularly limited, and can be, for example, about 2 to 100 times in volume terms, and is usually about 5 to 50 times (for example, about 10 to 40 times).
Such a concentrated solution can be used in such a manner that it is diluted at a desired timing to prepare a polishing solution (working slurry) and the polishing solution is supplied to an object to be polished. The dilution can be performed, for example, by adding water to the concentrated solution and mixing it.

The content of the abrasive grains in the concentrated liquid can be, for example, 25% by weight or less. From the viewpoint of the dispersion stability and filterability of the polishing composition, the content is usually preferably 20% by weight or less, more preferably 15% by weight or less. In a preferred embodiment, the content of the abrasive grains may be 10% by weight or less, or may be 5% by weight or less. In addition, from the viewpoint of convenience and cost reduction during production, distribution, storage, etc., the content of the abrasive grains in the concentrated liquid can be, for example, 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 0.7% by weight or more, and even more preferably 1% by weight or more.

<Preparation of Polishing Composition>
The polishing composition used in the technology disclosed herein may be a one-component type or a multi-component type including a two-component type. For example, the polishing composition may be configured to prepare a polishing liquid by mixing a part A containing at least abrasive grains and a part B containing at least a part of the remaining components, and mixing and diluting them at an appropriate timing as necessary.

The method for preparing the polishing composition is not particularly limited. For example, the components constituting the polishing composition may be mixed using a well-known mixing device such as a blade stirrer, ultrasonic disperser, or homomixer. The manner in which these components are mixed is not particularly limited, and for example, all the components may be mixed at once or in an appropriately set order.

<Applications>
The polishing composition disclosed herein can be applied to polishing objects having various materials and shapes.The material of the object to be polished can be, for example, metal or semimetal such as silicon, aluminum, nickel, tungsten, copper, tantalum, titanium, stainless steel, or their alloys; glassy materials such as quartz glass, aluminosilicate glass, glassy carbon; ceramic materials such as alumina, silica, sapphire, silicon nitride, tantalum nitride, titanium carbide; compound semiconductor substrate materials such as silicon carbide, gallium nitride, gallium arsenide; resin materials such as polyimide resin; etc.The object to be polished can be made of a plurality of these materials.

The polishing composition disclosed herein can be particularly preferably used for polishing a surface made of silicon (typically, polishing a silicon wafer). A typical example of a silicon wafer is a silicon single crystal wafer, for example, a silicon single crystal wafer obtained by slicing a silicon single crystal ingot.

The polishing composition disclosed herein can be preferably applied to a polishing process of an object to be polished (e.g., a silicon wafer). Prior to the polishing process with the polishing composition disclosed herein, the object to be polished may be subjected to a general treatment that can be applied to an object to be polished in a process upstream of the polishing process, such as lapping or etching.

The polishing composition disclosed herein is effective when used in the finishing step of an object to be polished (e.g., a silicon wafer) or in the polishing step immediately preceding the finishing step, and is particularly preferably used in the finishing polishing step. Here, the finishing polishing step refers to the final polishing step in the manufacturing process of the object (i.e., a step after which no further polishing is performed).

<Polishing>
The polishing composition disclosed herein can be used for polishing an object to be polished, for example, in an embodiment including the following operations. A preferred embodiment of a method for polishing an object to be polished (e.g., a silicon wafer) using the polishing composition disclosed herein is described below.
That is, a polishing liquid containing any one of the polishing compositions disclosed herein is prepared. The preparation of the polishing liquid may include adjusting the concentration (e.g., diluting), adjusting the pH, etc., of the polishing composition to prepare the polishing liquid. Alternatively, the polishing composition may be used as it is as the polishing liquid.

The polishing liquid is then supplied to the object to be polished, and the object is polished in the usual manner. For example, when performing finish polishing of silicon wafers, typically, the silicon wafer that has been through the lapping process is set in a general polishing device, and the polishing liquid is supplied to the surface of the silicon wafer to be polished through the polishing pad of the polishing device. Typically, while the polishing liquid is continuously supplied, the polishing pad is pressed against the surface of the silicon wafer to be polished, and the two are moved relative to one another (e.g., rotated). Through this polishing process, the polishing of the object to be polished is completed.

The polishing pad used in the above polishing process is not particularly limited. For example, polishing pads of a polyurethane foam type, a nonwoven fabric type, a suede type, etc. can be used. Each polishing pad may or may not contain abrasive grains. Usually, a polishing pad that does not contain abrasive grains is preferably used.

The object to be polished that has been polished using the polishing composition disclosed herein is typically washed. The washing can be performed using an appropriate washing liquid. The washing liquid to be used is not particularly limited, and for example, an SC-1 washing liquid (a mixture of ammonium hydroxide (NH ₄ OH), hydrogen peroxide (H ₂ O ₂ ), and water (H 2 O)) that is common in the field of semiconductors, etc., an SC-2 washing liquid (a mixture of hydrochloric acid (HCl), H ₂ O ₂ , and H ₂ O), etc. can be used. The temperature of the washing liquid can be, for example, in the range of room temperature (typically about 15° C. to ₂₅ ° C.) or higher, up to about 90° C. From the viewpoint of improving the washing effect, a washing liquid of about 50° C. to 85° C. can be preferably used.

Several examples of the present invention are described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

<Preparation of Polishing Composition>
(Examples 1 to 6)
Abrasive grains, water-soluble polymer 1, water-soluble polymer 2, basic compound, surfactant and deionized water were mixed to prepare the polishing composition according to each example. Colloidal silica (average primary particle size: 25 nm) was used as the abrasive grains, and its content was set to 0.18%. Polyvinyl alcohol (non-modified PVA) with a weight average molecular weight of about 70000 and a saponification degree of 98% or more was used in the amount shown in Table 1 as the water-soluble polymer 1. Furthermore, a polymer containing MA units of the type and amount shown in Table 1 was used as the water-soluble polymer 2. Ammonia was used as the basic compound, and its content was set to 0.005%. Polyoxyethylene decyl ether (C10EO5) with 5 moles of ethylene oxide added was used as the surfactant, and its content was set to 0.00015%.

(Comparative Example 1)
A polishing composition according to this example was prepared in the same manner as in Example 1, except that the MA unit-containing polymer was omitted from the composition of Example 1.

(Comparative Examples 2 and 3)
Polishing compositions according to Comparative Examples 2 and 3 were prepared in the same manner as in Comparative Example 1 except that the surfactant was used in the amount shown in Table 1.

(Comparative Examples 4 to 7)
Polishing compositions of Comparative Examples 4 to 7 were prepared in the same manner as in Example 1, except that a water-soluble polymer of the type and amount shown in Table 1 was used as water-soluble polymer 2 instead of the MA unit-containing polymer.

(Example 7)
The polishing composition according to this example was prepared by mixing abrasive grains, a water-soluble polymer, a basic compound, and deionized water. Colloidal silica (average primary particle size: 25 nm) was used as the abrasive grains, and the content was 0.18%. As the polyvinyl alcohol-based polymer as the water-soluble polymer, polyvinyl alcohol (non-modified PVA) with a weight-average molecular weight of about 70,000 and a degree of saponification of 98% or more was used, and the content was 0.0074%. Furthermore, as the MA unit-containing polymer as the water-soluble polymer, a water-soluble polymer having a styrene-maleic anhydride resin structure, in which part of the maleic anhydride is modified by a polyalkylene glycol having a terminal hydroxyl group, and with a weight-average molecular weight of about 12,000 was used, and the content was 0.0013%. As the basic compound, ammonia was used, and the content was 0.005%.

(Comparative Example 8)
In this example, the content of the polyvinyl alcohol-based polymer as the water-soluble polymer was 0.0088%, and the MA unit-containing polymer was not used. The polishing composition according to this example was prepared in the same manner as in Example 7 in other respects.

<Polishing of silicon wafers>
As the object to be polished, a commercially available silicon single crystal wafer having a diameter of 200 mm (conductivity type: P type, crystal orientation: <100>, COP (Crystal Originated Particle)-free) that had been lapped and etched was pre-polished under the following polishing condition 1 to prepare a silicon wafer. The pre-polishing was performed using a polishing solution containing 1.0% abrasive grains (colloidal silica with a BET diameter of 35 nm) and 0.068% potassium hydroxide in deionized water.

[Polishing condition 1]
Polishing device: Single-wafer polishing device model "PNX-322" manufactured by Okamoto Machine Tools Works, Ltd.
Polishing load: 15 kPa
Rotation speed of the platen: 30 rpm
Head (carrier) rotation speed: 30 rpm
Polishing pad: Fujibo Ehime Co., Ltd. Product name "FP55"
Supply rate of preliminary polishing liquid: 550 mL/min
Temperature of preliminary polishing solution: 20°C
Temperature of cooling water for surface plate: 20°C
Polishing time: 3 min

The polishing compositions prepared in each example above were used as polishing liquids to polish the silicon wafers after the above preliminary polishing under the polishing conditions 2 below.

[Polishing condition 2]
Polishing device: Single-wafer polishing device model "PNX-322" manufactured by Okamoto Machine Tools Works, Ltd.
Polishing load: 15 kPa
Rotation speed of the platen: 30 rpm
Head (carrier) rotation speed: 30 rpm
Polishing pad: Fujibo Ehime Co., Ltd. Product name "POLYPAS27NX"
Polishing liquid supply rate: 400 mL/min
Polishing solution temperature: 20°C
Temperature of cooling water for surface plate: 20°C
Polishing time: 4 min

The polished silicon wafer was removed from the polishing apparatus and washed with a cleaning solution of NH ₄ OH (29%):H ₂ O ₂ (31%):deionized water (DIW)=1:1:12 (volume ratio) (SC-1 washing). Specifically, first and second washing tanks were prepared, and the above-mentioned cleaning solution was contained in each of these washing tanks and maintained at 60° C. The polished silicon wafer was immersed in the first washing tank for 5 minutes, passed through a rinse tank in which it was immersed in ultrapure water and subjected to ultrasonic waves, immersed in the second washing tank for 5 minutes, passed through a rinse tank in which it was immersed in ultrapure water and subjected to ultrasonic waves, and then dried using a spin dryer.

<Haze measurement>
The haze (ppm) of the silicon wafer surface after cleaning was measured in DWO mode using a wafer inspection device manufactured by KLA Tencor Corporation, product name "Surfscan SP2 ^XP ". The obtained results are shown in Table 1 as relative values (haze ratios) with the haze value of Comparative Example 2 taken as 100%, and in Table 2 as relative values (haze ratios) with the haze value of Comparative Example 8 taken as 100%. If the haze ratio is less than 100%, it can be said that the haze improvement effect can be significantly confirmed.

As shown in Table 1, in Examples 1 to 6, in which a polyvinyl alcohol-based polymer and an MA unit-containing polymer were used as the water-soluble polymer, a significant haze improvement effect was confirmed compared to Comparative Example 2. On the other hand, in Comparative Examples 1 and 3, in which only a polyvinyl alcohol-based polymer was used as the water-soluble polymer and no MA unit-containing polymer was used, no effect of improving haze was observed compared to Comparative Example 2. Furthermore, in Comparative Examples 4 to 7, in which a water-soluble polymer not having MA units was used instead of the MA unit-containing polymer as the water-soluble polymer, no effect of improving haze was observed compared to Comparative Example 2.

Furthermore, as shown in Table 2, a significant haze improvement effect was confirmed by combining a polyvinyl alcohol-based polymer and a polymer containing MA units, even in compositions that did not use a surfactant.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above.

Claims (9)

A polishing composition used in a finish polishing step of a silicon wafer, comprising:
The method includes the steps of:
The water-soluble polymer includes a polyvinyl alcohol-based polymer and a polymer containing a maleic acid type structural unit,
A polishing composition that is substantially free of an oxidizing agent . The polishing composition according to claim 1, wherein the ratio of the content of the polyvinyl alcohol-based polymer to the content of the polymer containing maleic acid-type structural units is 50:50 to 99:1 by weight. The polishing composition according to claim 1 or 2, wherein the polyvinyl alcohol-based polymer has a weight average molecular weight of less than 10 x 10 ⁴ . The polishing composition according to claim 1 , wherein the maleic acid type structural unit-containing polymer has a weight average molecular weight of less than 10×10 ⁴ . The method includes the steps of:
The polishing composition includes, as the water-soluble polymer, a polyvinyl alcohol-based polymer and a polymer containing a maleic acid type structural unit, and as the polymer containing a maleic acid type structural unit, a polymer containing a maleic acid type structural unit and a polyoxyalkylene structure in one molecule. The polishing composition according to claim 5 , which is used in a finish polishing step of a silicon wafer. The polishing composition according to claim 1 , further comprising a surfactant. The polishing composition according to claim 7 , comprising, as the surfactant, a surfactant containing a polyoxyalkylene structure. The polishing composition according to claim 1 , wherein the abrasive grains are silica grains.