JP6243713B2 - Polishing liquid composition - Google Patents

Description

  The present disclosure relates to a polishing liquid composition, a method for manufacturing a substrate using the same, and a polishing method.

  In recent years, magnetic disk drives have been reduced in size and capacity, and high recording density has been demanded. In order to increase the recording density, the unit recording area is reduced, and in order to improve the detection sensitivity of the weakened magnetic signal, technological development for lowering the flying height of the magnetic head has been advanced. For magnetic disk substrates, in order to cope with low flying height of magnetic head and securing recording area, improvement of smoothness and flatness represented by reduction of surface roughness, waviness, end face sagging and scratches, protrusions, pits, etc. Demands for defect reduction represented by reduction of the level are becoming strict. In response to such a demand, a polishing liquid composition containing a copolymer having a functional group such as a polyethylene glycol (PEG) chain or a sulfonic acid group has been proposed (for example, Patent Documents 1 to 3).

  Patent Document 1 discloses a polishing liquid composition for a glass substrate containing a copolymer containing a structural unit having a PEG chain and a structural unit derived from a hydrophobic monomer. The document also discloses that the polishing rate can be improved in the polishing step using the polishing composition for glass substrate.

  Patent Document 2 discloses a polishing composition for a magnetic disk substrate containing a copolymer having a structural unit having a hydrocarbon chain and a structural unit having a sulfonic acid group. Further, this document discloses that, in the polishing step using the polishing composition for a magnetic disk substrate, in addition to scratches on the substrate surface after polishing, waviness and nanoprojection defects on the substrate surface after polishing can be reduced.

  Patent Document 3 discloses a polishing composition for a semiconductor component or the like containing a copolymer having a structural unit derived from a monomer having a sulfonic acid group or a carboxylic acid group and a structural unit derived from a monomer having a nitrogen atom. Disclose.

JP 2011-31324 A JP 2010-170648 A JP 2001-64688 A

  As the capacity of magnetic disk drives increases, the required characteristics for the surface quality of the substrate become more severe, and the development of a polishing composition that can further reduce the scratch on the surface of the substrate is required.

  Therefore, the present disclosure provides a polishing composition that can reduce scratches on the surface of a substrate after polishing without significantly impairing the polishing rate, and a method for manufacturing a magnetic disk substrate and a polishing method using the same.

[式（Ｉ）、（II）及び（III）中、Ｒ₁、Ｒ₃及びＲ₅はそれぞれ独立して水素原子又はメチル基であり、Ｘ₁及びＸ₂はそれぞれ独立して酸素原子又はＮＨ基であり、Ｒ₂は炭素数８〜１８の炭化水素鎖であり、ｐは０又は１であり、ＡＯは炭素数１以上３以下のオキシアルキレン基であり、ｎはＡＯの平均付加モル数であって１以上３０以下の数であり、Ｒ₄は水素原子又は炭素数１以上４以下のアルキル基であり、Ｒ₆はスルホン酸基を含む炭化水素基又は−Ｘ₃−Ｒ₇であり、Ｘ₃は−ＣＯＯ−又は−ＣＯＮＨ−であり、Ｒ₇はスルホン酸基を含む炭化水素基である。] In one aspect, the present disclosure is a polishing liquid composition containing silica particles, a copolymer, and water, wherein the copolymer includes a structural unit represented by the following general formula (I) and the following general formula: A copolymer having a structural unit represented by the formula (II) and a structural unit represented by the following general formula (III) or a salt thereof, and a formula ( The present invention relates to a polishing liquid composition for a magnetic disk substrate, wherein the sum of the molar ratio of the structural unit represented by II) and the molar ratio of the structural unit represented by formula (III) is 55 mol% or more.

[In the formulas (I), (II) and (III), R ₁ , R ₃ and R ₅ are each independently a hydrogen atom or a methyl group, and X ₁ and X ₂ are each independently an oxygen atom or NH R ₂ is a hydrocarbon chain having 8 to 18 carbon atoms, p is 0 or 1, AO is an oxyalkylene group having 1 to 3 carbon atoms, and n is the average added mole number of AO. Wherein R ₄ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ₆ is a hydrocarbon group containing a sulfonic acid group or —X ₃ —R ₇ . , X ₃ is —COO— or —CONH—, and R ₇ is a hydrocarbon group containing a sulfonic acid group. ]

  In another aspect of the present disclosure, the polishing composition according to the present disclosure is supplied to a surface to be polished of a substrate to be polished, the polishing pad is brought into contact with the surface to be polished, and at least one of the polishing pad and the substrate to be polished The present invention relates to a method for manufacturing a magnetic disk substrate, which includes a step of polishing by moving the head.

  In another aspect of the present disclosure, the polishing composition according to the present disclosure is supplied to a surface to be polished of a substrate to be polished, the polishing pad is brought into contact with the surface to be polished, and at least one of the polishing pad and the substrate to be polished The present invention relates to a method for polishing a substrate, which includes moving and polishing.

  According to the polishing composition according to the present disclosure, a substrate, preferably a magnetic disk substrate, more preferably a perpendicular magnetic recording type magnetic disk substrate, with reduced scratches on the surface of the substrate after polishing without impairing productivity. The effect that it can manufacture can be show | played.

  The present disclosure includes both a unit that adsorbs to a polishing pad and a unit that adsorbs to silica particles, and further uses a polishing liquid composition that includes a polymer that includes a unit that contributes to water solubility. This is based on the knowledge that scratches on the substrate surface can be reduced. In the present disclosure, “without impairing productivity” is maintained in a range in which the polishing rate is not significantly reduced in one or more embodiments as compared to the case where the composition of the present disclosure is not used. Or a significant reduction in the polishing rate is suppressed.

  That is, in one aspect, the present disclosure is a polishing liquid composition containing silica particles, a copolymer, and water, wherein the copolymer is a structural unit represented by the general formula (I). And a copolymer having the structural unit represented by the general formula (II) and the structural unit represented by the general formula (III) or a salt thereof (hereinafter also referred to as “copolymer according to the present disclosure”) Is a polishing liquid composition for a magnetic disk substrate (hereinafter also referred to as “polishing liquid composition according to the present disclosure”).

  Although details of the mechanism that can reduce scratches on the surface of the substrate after polishing without impairing productivity by the polishing composition according to the present disclosure are not clear, it is estimated as follows. That is, it is considered that the unit adsorbing to the polishing pad of the copolymer according to the present disclosure adsorbs to the entire surface of the polishing pad, reducing friction between the polishing pad and the substrate to be polished, and significantly reducing the number of scratches. Furthermore, the silica adsorption unit concentrates and holds the silica abrasive grains on the surface of the polishing pad, so that the cutting movement distance becomes longer than usual, and the scratch on the substrate surface is reduced without reducing the productivity while reducing the friction. it is conceivable that. In addition, by adding a unit that contributes to water solubility, it is possible to maintain water solubility while suppressing coagulation of the copolymer that causes clogging of the filter, further promoting maintenance of productivity and reduction of scratches. It is guessed. However, the present disclosure and the present invention are not limited to these mechanisms.

[式（Ｉ）、（II）及び（III）中、Ｒ₁、Ｒ₃及びＲ₅はそれぞれ独立して水素原子又はメチル基であり、Ｘ₁及びＸ₂はそれぞれ独立して酸素原子又はＮＨ基であり、Ｒ₂は炭素数８以上１８以下の炭化水素鎖であり、ｐは０又は１であり、ＡＯは炭素数１以上３以下のオキシアルキレン基であり、ｎはＡＯの平均付加モル数であって１以上３０以下の数であり、Ｒ₄は水素原子又は炭素数１以上４以下のアルキル基であり、Ｒ₆はスルホン酸基を含む炭化水素基又は−Ｘ₃−Ｒ₇であり、Ｘ₃は−ＣＯＯ−又は−ＣＯＮＨ−であり、Ｒ₇はスルホン酸基を含む炭化水素基である。] [Constitutional unit of copolymer]
The copolymer according to the present disclosure has a structural unit represented by the following general formula (I), a structural unit represented by the following general formula (II), and a structural unit represented by the following general formula (III). It is a copolymer or a salt thereof. In one or a plurality of embodiments, the copolymer of the present disclosure preferably does not contain polymerized crosslinked particles such as polystyrene, and is more preferably a water-soluble copolymer. The term “water-soluble” as used herein means that, in one or a plurality of embodiments, the solubility in 100 g of water at 20 ° C. and pH 1.5 is 0.1 g or more.

[In the formulas (I), (II) and (III), R ₁ , R ₃ and R ₅ are each independently a hydrogen atom or a methyl group, and X ₁ and X ₂ are each independently an oxygen atom or NH R ₂ is a hydrocarbon chain having 8 to 18 carbon atoms, p is 0 or 1, AO is an oxyalkylene group having 1 to 3 carbon atoms, and n is an average added mole of AO. R ₄ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ₆ is a hydrocarbon group containing a sulfonic acid group or —X ₃ —R ₇ . X ₃ is —COO— or —CONH—, and R ₇ is a hydrocarbon group containing a sulfonic acid group. ]

[Structural unit of formula (I)]
The structural unit of the general formula (I) is a unit that adsorbs to the polishing pad in one or more embodiments. In Formula (I), X ₁ is preferably an oxygen atom from the viewpoint of reducing scratches on the substrate surface after polishing without impairing productivity in one or a plurality of embodiments. In one or a plurality of embodiments, the number of carbon atoms in the hydrocarbon chain of R ₂ is 8 or more, preferably 10 or more, from the viewpoint of reducing scratches on the substrate surface after polishing without impairing productivity. The above is more preferable. In one or a plurality of embodiments, the number of carbon atoms in the hydrocarbon chain of R ₂ is 18 or less, preferably 16 or less, and more preferably 14 or less, from the same viewpoint.

  In one or a plurality of embodiments, the monomer that gives the structural unit of the general formula (I) is octyl acrylate, octyl methacrylate, nonyl acrylate, nonyl methacrylate, decyl acrylate, decyl methacrylate, undecyl acrylate, undecyl methacrylate, lauryl. Acrylate (LA), lauryl methacrylate (LM), tridecyl acrylate, tridecyl methacrylate, myristyl acrylate, myristyl methacrylate, pentadodecyl acrylate, pentadodecyl methacrylate, cetri acrylate, cetyl methacrylate, palmityl acrylate, parimityl methacrylate, stearyl acrylate, Stearyl methacrylate, oleyl acrylate, oleyl methacrylate Etc.

  The molar ratio of the structural unit represented by the formula (I) in all the structural units constituting the copolymer according to the present disclosure is the substrate surface after polishing without impairing the productivity in one or a plurality of embodiments. From the viewpoint of reducing the scratch, the amount is preferably 20 mol% or more, more preferably 23 mol% or more, still more preferably 27 mol% or more, and even more preferably 30 mol% or more. The molar ratio of the structural unit represented by the formula (I) in all the structural units constituting the copolymer according to the present disclosure is the same as that in one or a plurality of embodiments, and the water solubility of the copolymer is determined. From the viewpoint of maintenance, it is preferably 45 mol% or less, more preferably 43 mol% or less, still more preferably 40 mol% or less, and even more preferably 36 mol% or less.

[Structural unit of formula (II)]
The structural unit of the general formula (II) is a unit that adsorbs to silica particles in one or a plurality of embodiments. In the formula (II), AO is an oxyalkylene group having 1 to 3 carbon atoms, and in one or a plurality of embodiments, from the viewpoint of reducing scratches on the surface of the substrate after polishing without impairing productivity, Two oxyethylene (EO) groups are preferred. n is an average added mole number of AO and is a number of 1 or more and 30 or less, and in one or a plurality of embodiments, from the viewpoint of reducing scratches on the surface of the substrate after polishing without impairing productivity, 25 or less is Preferably, it is 20 or less, more preferably 15 or less, still more preferably 10 or less, and even more preferably 5 or less. In one or a plurality of embodiments, n is 1 or more and preferably 2 or more from the viewpoint of reducing scratches on the substrate surface after polishing without impairing productivity.

In formula (II), X ₂ is preferably an oxygen atom from the viewpoint of reducing scratches on the substrate surface after polishing without impairing productivity in one or more embodiments. In one or a plurality of embodiments, R ₃ and R ₄ are preferably hydrogen atoms from the viewpoint of reducing scratches on the substrate surface after polishing without impairing productivity.

  As the monomer that gives the structural unit of the general formula (II), in one or a plurality of embodiments, when p = 1, as the monomer, polyethylene glycol methacrylate (PEGMA), polyethylene glycol acrylate (PEGAA), diethylene glycol acrylate (DEGAA) When p = 0, the monomer includes polyethylene glycol allyl ether.

  The molar ratio of the structural unit represented by the formula (II) in all the structural units constituting the copolymer according to the present disclosure is the substrate surface after polishing without impairing productivity in one or a plurality of embodiments. From the viewpoint of reducing the scratch, the amount is preferably 10 mol% or more, more preferably 15 mol% or more, still more preferably 27 mol% or more, and even more preferably 30 mol% or more. The molar ratio of the structural unit represented by the formula (II) in all the structural units constituting the copolymer according to the present disclosure is the same in one or a plurality of embodiments, and suppresses aggregation of the copolymer. Therefore, it is preferably 60 mol% or less, more preferably 52 mol% or less, still more preferably 40 mol% or less, and even more preferably 36 mol% or less.

[Structural unit of formula (III)]
The structural unit of the general formula (III) is a unit that imparts water solubility in one or more embodiments. In formula (III), in one or a plurality of embodiments, R ₆ is a hydrocarbon group containing a sulfonic acid group, or —X ₃ from the viewpoint of reducing scratches on the substrate surface after polishing without impairing productivity. is -R _7, X ₃ is -COO- or -CONH-, it is preferred that R ₇ is a hydrocarbon group containing a sulfonic acid group. In one or a plurality of embodiments, the number of carbon atoms of the hydrocarbon group of R ₆ is one or more in one or a plurality of embodiments from the viewpoint of reducing scratches on the substrate surface after polishing without impairing productivity. 2 or more is preferable, and 3 or more is more preferable. In one or a plurality of embodiments, the number of carbon atoms of the hydrocarbon group of R ₆ is 8 or less, preferably 6 or less, and more preferably 4 or less from the same viewpoint. In one or a plurality of embodiments, R ₆ is preferably —CONH—C (CH ₃ ) ₂ —CH ₂ —SO ₃ H from the viewpoint of reducing scratches on the substrate surface after polishing without impairing productivity.

  In one or a plurality of embodiments, the monomer giving the structural unit of the general formula (III) may be isoprenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid (AMPS), styrenesulfonic acid, methallyl. Examples include sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, isoamylene sulfonic acid, naphthalene sulfonic acid, etc., and 2- (meth) acrylamido-2-methylpropanesulfone from the viewpoint of maintaining polishing speed, reducing scratches and polymerizing properties. Acid and styrene sulfonic acid are preferred, and 2- (meth) acrylamide-2-methylpropane sulfonic acid is more preferred.

  The molar ratio of the structural unit represented by the formula (III) in all the structural units constituting the copolymer according to the present disclosure is the substrate surface after polishing without impairing the productivity in one or a plurality of embodiments. From the viewpoint of reducing the scratch, the amount is preferably 20 mol% or more, more preferably 23 mol% or more, still more preferably 27 mol% or more, and even more preferably 30 mol% or more. In one or more embodiments, the molar ratio of the structural unit represented by the formula (III) in all the structural units constituting the copolymer according to the present disclosure is preferably 45 mol% or less from the same viewpoint. More preferably, it is 43 mol% or less, More preferably, it is 40 mol% or less, More preferably, it is 36 mol% or less.

  In the present disclosure, the content (mol%) of a certain structural unit occupying in all the structural units constituting the copolymer is charged into the reaction vessel in all steps of the copolymer synthesis depending on the synthesis conditions. The amount of the compound (mol%) for introducing the structural unit charged in the reaction vessel occupied in the compound for introducing all the structural units may be used. Further, in the present specification, as a constituent ratio (molar ratio) of two structural units constituting the copolymer, depending on synthesis conditions, the copolymer charged in the reaction vessel in all steps of the copolymer synthesis. A compound amount ratio (molar ratio) for introducing two structural units may be used. In addition, the ratio of each structural unit can also be analyzed by 1H-NMR or HPLC.

  The sum of the molar ratio of the structural unit represented by the formula (II) and the molar ratio of the structural unit represented by the formula (III) in all the structural units constituting the copolymer according to the present disclosure is one or more. In the embodiment, from the viewpoint of reducing scratches on the substrate surface after polishing without impairing productivity and maintaining water solubility of the copolymer, it is 55 mol% or more, preferably 60 mol% or more, and more. Preferably it is 65 mol% or more.

  In one or a plurality of embodiments, the copolymer according to the present disclosure includes a molar ratio of the structural unit represented by the formula (I) from the viewpoint of reducing scratches on the substrate surface after polishing without impairing productivity. The molar ratio of the structural unit represented by the formula (II) and the structural unit represented by the formula (III) is preferably 1: 1: 1 or a ratio close thereto.

  The copolymer according to the present disclosure may be in the form of a salt. Although the counter ion for forming a salt is not specifically limited, 1 or more types chosen from alkali metal ions, such as sodium and potassium, ammonium ion, alkylammonium ion, etc. can be used.

[Other structural units]
The copolymer may have other structural units not included in the formula (III). From the viewpoint of reducing scratches on the surface of the substrate after polishing without impairing productivity, the content of other structural units in all the structural units constituting the copolymer is 0 mol% or more and 30 mol% or less. Preferably, it is 0 mol% or more and 20 mol% or less, more preferably 0 mol% or more and 10 mol% or less, still more preferably 0 mol% or more and 5 mol% or less, and even more preferably substantially 0 mol%. is there.

[Weight average molecular weight of copolymer]
The weight average molecular weight of the copolymer is preferably from 1,000 to 1,000,000, more preferably from 1,000 to 50,000, and even more preferably from the viewpoint of reducing scratches and waviness on the polished substrate surface without impairing productivity. It is 40000 or less, still more preferably 3000 or more and 30000 or less, still more preferably 5000 or more and 20000 or less, and even more preferably 7000 or more and 20000 or less. The weight average molecular weight is a value measured under the conditions described in Examples using gel permeation chromatography (GPC).

[Content of copolymer]
The content of the copolymer in the polishing liquid composition according to the present disclosure is preferably 30 ppm to 5000 ppm, more preferably 50 ppm to 1500 ppm, and still more preferably 100 ppm or more from the viewpoint of reducing scratches on the substrate surface after polishing. 700 ppm or less, still more preferably 200 ppm or more and 400 ppm or less. From the viewpoint of productivity, it is preferably 5000 ppm or less, more preferably 1500 ppm or less, still more preferably 700 ppm or less, even more preferably 400 ppm or less, and even more preferably 200 ppm or less. In addition, in this indication, "content of the content component in polishing liquid composition" means content of the said component at the time of using polishing liquid composition for grinding | polishing. Therefore, when the polishing liquid composition according to the present disclosure is prepared as a concentrate, the content of the component can be increased by the concentration.

[Silica particles]
In one or a plurality of embodiments, the silica particles used in the polishing composition according to the present disclosure include colloidal silica and fumed silica from the viewpoint of reducing scratches on the substrate surface after polishing without impairing productivity. Is preferred, and colloidal silica is more preferred.

[Average particle diameter of silica particles]
The “average particle diameter of the abrasive” in the present disclosure refers to an average particle diameter based on a scattering intensity distribution measured at a detection angle of 90 ° in the dynamic light scattering method (hereinafter referred to as “scattering intensity distribution” unless otherwise specified). Also referred to as “average particle size based on”). The average particle size of the abrasive is preferably from 1 nm to 40 nm, more preferably from 5 nm to 37 nm, and even more preferably from 10 nm to 35 nm, from the viewpoint of reducing scratches on the substrate surface after polishing. The average particle size of the abrasive can be specifically obtained by the method described in the examples.

  The content of the abrasive in the polishing composition according to the present disclosure is preferably 0.5% by mass or more, more preferably 1% by mass or more, further preferably 3% by mass or more, from the viewpoint of improving the polishing rate. Even more preferably, it is 4% by mass or more. Further, from the viewpoint of reducing scratches on the substrate surface after polishing, it is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 13% by mass or less, and even more preferably 10% by mass or less. That is, the content of the abrasive is preferably 0.5% by mass or more and 20% by mass or less, more preferably 1% by mass or more and 15% by mass or less, still more preferably 3% by mass or more and 13% by mass or less, and still more preferably. It is 4 mass% or more and 10 mass% or less.

[water]
Water in the polishing composition according to the present disclosure is used as a medium, and examples thereof include distilled water, ion exchange water, and ultrapure water. From the viewpoint of the surface cleanliness of the substrate to be polished, ion exchange water and ultrapure water are preferable, and ultrapure water is more preferable. 60 mass% or more and 99.4 mass% or less are preferable, and, as for content of the water in polishing liquid composition, 70 mass% or more and 98.9 mass% or less are more preferable. Moreover, you may mix | blend organic solvents, such as alcohol, suitably in the range which does not inhibit the effect of this indication.

[acid]
The polishing composition according to the present disclosure preferably contains an acid from the viewpoint of improving the polishing rate. In the present disclosure, the use of an acid includes the use of an acid and / or a salt thereof. Examples of the acid used in the polishing liquid composition according to the present disclosure include nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, tripolyphosphoric acid, and amidosulfuric acid. Inorganic acid, 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid), ethane-1,1 , -Diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2- Dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid , 1-phosphonobutane-2,3,4-tricarboxylic acid, organic phosphonic acid such as α-methylphosphonosuccinic acid, aminocarboxylic acid such as glutamic acid, picolinic acid, aspartic acid, citric acid, tartaric acid, oxalic acid, nitroacetic acid And carboxylic acids such as maleic acid and oxaloacetic acid. Among these, inorganic acids and organic phosphonic acids are preferable from the viewpoint of reducing scratches and undulations on the substrate surface, improving the stability of the oxidizing agent, and improving the waste liquid treatment property. Among inorganic acids, nitric acid, sulfuric acid, hydrochloric acid, perchloric acid, and phosphoric acid are preferable, and phosphoric acid and sulfuric acid are more preferable. Among organic phosphonic acids, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid), and salts thereof are preferred. Hydroxyethylidene-1,1-diphosphonic acid and aminotri (methylenephosphonic acid) are more preferred.

  The acids may be used alone or in admixture of two or more. However, from the viewpoint of improving the polishing rate and improving the cleaning property of the substrate, it is preferable to use a mixture of two or more, reducing scratches, oxidizing agents. From the viewpoint of improving the stability of the liquid and improving the waste liquid treatment, it is further possible to use a mixture of two or more acids selected from the group consisting of phosphoric acid, sulfuric acid, and 1-hydroxyethylidene-1,1-diphosphonic acid preferable.

  The salt in the case of using the acid salt is not particularly limited, and specific examples thereof include metals, ammonium, alkylammonium and the like. Specific examples of the metal include metals belonging to the periodic table (long-period type) 1A, 1B, 2A, 2B, 3A, 3B, 4A, 6A, 7A, or Group 8. Among these, a salt with a metal belonging to Group 1A or ammonium is preferable from the viewpoint of reducing scratches on the substrate surface after polishing.

  The content of the acid and its salt in the polishing composition is preferably 0.001% by mass or more and 5.0% by mass or less, more preferably from the viewpoint of improving the polishing rate and reducing scratches on the substrate surface after polishing. Is 0.01% by mass or more and 4.0% by mass or less, more preferably 0.05% by mass or more and 3.0% by mass or less, still more preferably 0.1% by mass or more and 2.0% by mass or less, and still more preferably. Is 0.4 mass% or more and 1.0 mass% or less.

[Oxidant]
The polishing composition according to the present disclosure preferably contains an oxidizer from the viewpoints of improving the polishing rate, scratching the substrate surface, and reducing waviness. Examples of the oxidizing agent that can be used in the polishing composition according to the present disclosure include peroxide, permanganic acid or a salt thereof, chromic acid or a salt thereof, peroxo acid or a salt thereof, oxygen acid or a salt thereof, metal salt, nitric acid And sulfuric acids.

  Examples of the peroxide include hydrogen peroxide, sodium peroxide, barium peroxide, etc., examples of the permanganic acid or salt thereof include potassium permanganate, and examples of the chromic acid or salt thereof include chromium. Acid metal salts, metal dichromates, and the like. Peroxoacids or salts thereof include peroxodisulfuric acid, ammonium peroxodisulfate, metal peroxodisulfate, peroxophosphoric acid, peroxosulfuric acid, sodium peroxoborate, and performic acid. Peroxyacetic acid, perbenzoic acid, perphthalic acid, etc., and oxygen acids or salts thereof include hypochlorous acid, hypobromite, hypoiodous acid, chloric acid, bromic acid, iodic acid, hypochlorous acid. Examples include sodium chlorate, calcium hypochlorite, and metal salts include iron (III) chloride, iron (III) nitrate, iron (III) sulfate, and iron citrate. III), ammonium iron (III), and the like.

  Preferred oxidizing agents from the viewpoint of reducing scratches on the substrate surface after polishing and substrate surface waviness include hydrogen peroxide, iron (III) nitrate, peracetic acid, ammonium peroxodisulfate, iron (III) sulfate, and iron iron (III) ammonium sulfate. Etc. As a more preferable oxidizing agent, hydrogen peroxide is mentioned from the viewpoint that metal ions do not adhere to the surface and are generally used and inexpensive. These oxidizing agents may be used alone or in admixture of two or more.

  The content of the oxidizing agent in the polishing liquid composition is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and further preferably 0.1% by mass or more from the viewpoint of improving the polishing rate. Yes, from the viewpoint of reducing scratches on the substrate surface after polishing and substrate surface waviness, it is preferably 4% by mass or less, more preferably 2% by mass or less, and further preferably 1% by mass or less. Therefore, in order to improve the polishing rate while maintaining the surface quality, the content is preferably 0.01% by mass to 4% by mass, more preferably 0.05% by mass to 2% by mass, and still more preferably. Is 0.1 mass% or more and 1 mass% or less.

[Other ingredients]
In the polishing composition according to the present disclosure, other components can be blended as necessary. Examples of other components include a thickener, a dispersant, a rust inhibitor, a basic substance, and a surfactant. The content of these other optional components in the polishing liquid composition is preferably 0% by mass or more and 10% by mass or less, and more preferably 0% by mass or more and 5% by mass or less. However, the polishing liquid composition according to the present disclosure can exhibit the effect of reducing scratches and waviness on the substrate surface without containing other components, particularly surfactants. Furthermore, the polishing composition according to the present disclosure can contain alumina abrasive grains, and can also be used in a rough polishing step prior to the final polishing step.

[PH of polishing composition]
The pH of the polishing composition according to the present disclosure is preferably 4.0 or less, more preferably 3.5 or less, still more preferably 3.0 or less, and even more preferably 2.5 or less, from the viewpoint of improving the polishing rate. It is. Moreover, 0.5 or more is preferable from a viewpoint of surface roughness reduction, More preferably, it is 0.8 or more, More preferably, it is 1.0 or more, More preferably, it is 1.2 or more. Therefore, the pH of the polishing composition is preferably 0.5 or more and 4.0 or less, more preferably 0.8 or more and 3.5 or less, still more preferably 1.0 or more and 3.0 or less, and even more preferably 1. .2 or more and 2.5 or less.

[Method for preparing polishing liquid composition]
The polishing composition according to the present disclosure includes, for example, water, silica particles, a copolymer, and, if desired, an acid and / or a salt thereof, an oxidizing agent, and other components mixed by a known method. Can be prepared. At this time, the silica particles may be mixed in a concentrated slurry state, or may be mixed after being diluted with water or the like. The content and concentration of each component in the polishing liquid composition according to the present disclosure are in the above-described ranges, but as another aspect, the polishing liquid composition according to the present disclosure may be prepared as a concentrate.

[Substrate manufacturing method]
As another aspect, the present disclosure relates to a substrate manufacturing method (hereinafter, also referred to as “the manufacturing method of the present disclosure”). The manufacturing method according to the present disclosure includes a step of polishing the substrate to be polished while bringing the above-described polishing liquid composition into contact with the polishing pad (hereinafter, also referred to as “polishing step using the polishing liquid composition according to the present disclosure”). The manufacturing method of the board | substrate containing. Thereby, in addition to scratches on the substrate surface after polishing, it is possible to provide a substrate in which waviness on the substrate surface after polishing is reduced. The manufacturing method of the present disclosure is suitable for a method of manufacturing a magnetic disk substrate, and particularly suitable for a method of manufacturing a magnetic disk substrate for a perpendicular magnetic recording system. Therefore, as another aspect, the manufacturing method of the present disclosure is a method of manufacturing a substrate including a polishing step using the polishing composition according to the present disclosure, preferably a method of manufacturing a magnetic disk substrate, more preferably This is a method of manufacturing a magnetic disk substrate for perpendicular magnetic recording.

  In one or a plurality of embodiments, the polishing step using the polishing liquid composition according to the present disclosure is performed by supplying the polishing liquid composition according to the present disclosure to the surface to be polished of the substrate to be polished, and polishing pad on the surface to be polished And polishing the substrate by moving at least one of the polishing pad and the substrate to be polished, or the substrate to be polished with a surface plate to which a polishing pad such as a non-woven organic polymer polishing cloth is attached. The step of polishing the substrate to be polished by moving the surface plate or the substrate to be polished while sandwiching and supplying the polishing composition according to the present disclosure to the polishing machine.

  When the polishing process of the substrate to be polished is performed in multiple stages, the polishing process using the polishing composition according to the present disclosure is preferably performed in the second stage or later, and is performed in the final polishing process or the final polishing process. Is more preferable. At that time, in order to avoid mixing of the polishing material and polishing liquid composition in the previous process, different polishing machines may be used, and in the case of using different polishing machines, polishing is performed for each polishing process. It is preferable to clean the substrate. In addition, the polishing composition according to the present disclosure can also be used in cyclic polishing in which the used polishing liquid is reused. The polishing machine is not particularly limited, and a known polishing machine for substrate polishing can be used.

[Polishing pad]
The polishing pad used in the present disclosure is not particularly limited, and a suede type, a nonwoven fabric type, a polyurethane closed-cell foam type, or a two-layer type laminated with these can be used. From the viewpoint, a suede type polishing pad is preferable.

  The average hole diameter of the surface member of the polishing pad is preferably 50 μm or less, more preferably 45 μm or less, still more preferably 40 μm or less, and even more preferably 35 μm or less, from the viewpoint of scratch reduction and pad life. From the viewpoint of holding the polishing liquid of the pad, the average opening diameter is preferably 0.01 μm or more, more preferably 0.1 μm or more, and still more preferably in order to keep the polishing liquid in the opening and prevent the liquid from running out. Is 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more. Further, the maximum value of the opening diameter of the polishing pad is preferably 100 μm or less, more preferably 70 μm or less, further preferably 60 μm or less, and particularly preferably 50 μm or less from the viewpoint of maintaining the polishing rate.

[Polishing load]
The polishing load in the polishing step using the polishing composition according to the present disclosure is preferably 5.9 kPa or more, more preferably 6.9 kPa or more, and further preferably 7.5 kPa or more. Thereby, since the fall of a grinding | polishing speed | rate can be suppressed, productivity can be improved. In the manufacturing method of the present disclosure, the polishing load refers to the pressure of the surface plate applied to the polishing surface of the substrate to be polished during polishing. In the polishing step using the polishing composition according to the present disclosure, the polishing load is preferably 20 kPa or less, more preferably 18 kPa or less, still more preferably 16 kPa or less, and even more preferably 12 kPa or less. Thereby, generation | occurrence | production of a scratch can be suppressed. Therefore, in the polishing process using the polishing liquid composition according to the present disclosure, the polishing pressure is preferably 5.9 kPa to 20 kPa, more preferably 6.9 kPa to 18 kPa, and even more preferably 7.5 kPa to 16 kPa. The polishing load can be adjusted by applying air pressure or weight to at least one of the surface plate and the substrate to be polished.

[Supply of polishing liquid composition]
The supply rate of the polishing composition according to the present disclosure in the polishing step using the polishing composition according to the present disclosure is preferably 0.05 mL / min or more and 15 mL / min per 1 cm ^{2 of the} substrate to be polished from the viewpoint of reducing scratches. Min. Or less, more preferably 0.06 mL / min to 10 mL / min, even more preferably 0.07 mL / min to 1 mL / min, even more preferably 0.07 mL / min to 0.5 mL / min. is there.

  As a method of supplying the polishing composition according to the present disclosure to a polishing machine, for example, a method of continuously supplying using a pump or the like can be mentioned. When supplying the polishing composition to the polishing machine, in addition to the method of supplying one component containing all the components, considering the stability of the polishing composition, etc., it is divided into a plurality of compounding component liquids, Two or more liquids can be supplied. In the latter case, for example, the plurality of compounding component liquids are mixed in the supply pipe or on the substrate to be polished to obtain the polishing liquid composition according to the present disclosure.

[Polished substrate]
Examples of the material of the substrate to be polished preferably used in the present disclosure include metals, metalloids such as silicon, aluminum, nickel, tungsten, copper, tantalum, and titanium, or alloys thereof, glass, glassy carbon, and amorphous. Examples thereof include glassy substances such as carbon, ceramic materials such as alumina, silicon dioxide, silicon nitride, tantalum nitride, and titanium carbide, and resins such as polyimide resin. Among them, a polished substrate or a glass substrate containing a metal such as aluminum, nickel, tungsten, or copper, or an alloy containing these metals as a main component is preferable. Among them, a Ni—P plated aluminum alloy substrate or an aluminosilicate glass substrate is suitable, and a Ni—P plated aluminum alloy substrate is more suitable. Aluminosilicate glass substrates include those having a crystal structure and those subjected to chemical strengthening treatment. You may perform a chemical strengthening process after grinding | polishing.

  There is no restriction | limiting in particular in the shape of the said to-be-polished substrate, For example, what is necessary is just the shape which has planar parts, such as a disk shape, plate shape, slab shape, prism shape, and the shape which has curved surface parts, such as a lens. Of these, a disk-shaped substrate to be polished is suitable. In the case of a disk-shaped substrate to be polished, the outer diameter is, for example, about 2 mm to 95 mm, and the thickness is, for example, about 0.5 mm to 2 mm.

  Further, according to the present disclosure, in addition to scratching of the substrate surface after polishing, a substrate with reduced waviness of the substrate surface after polishing can be provided, so that a magnetic disk substrate that requires high surface smoothness, especially It can be suitably used for polishing a perpendicular magnetic recording type magnetic disk substrate.

[Polishing method]
As another aspect, the present disclosure relates to a method for polishing a substrate to be polished, which includes polishing the substrate to be polished using the polishing composition according to the present disclosure. By using the polishing method of the present disclosure, in addition to scratching of the substrate surface after polishing, a substrate with reduced waviness of the substrate surface after polishing is provided. Examples of the substrate to be polished in the polishing method of the present disclosure include those used for manufacturing a magnetic disk substrate as described above, and among them, a substrate used for manufacturing a magnetic disk substrate for a perpendicular magnetic recording system is preferable. The specific polishing method and conditions can be as described above.

  Polishing a substrate to be polished using the polishing liquid composition according to the present disclosure includes supplying the polishing liquid composition according to the present disclosure to a surface to be polished of the substrate to be polished in one or a plurality of embodiments, and polishing the polishing substrate. A surface plate in which a polishing pad is brought into contact with a target surface and polishing is performed by moving at least one of the polishing pad and the substrate to be polished, or a polishing pad such as a non-woven organic polymer polishing cloth is attached. In this case, the substrate to be polished is sandwiched and the surface plate or the substrate to be polished is moved to polish the substrate to be polished while supplying the polishing composition according to the present disclosure to the polishing machine.

  Regarding the above-described embodiment, the present disclosure further discloses a composition, a production method, or an application according to one or more of the following embodiments.

[式（Ｉ）、（II）及び（III）中、Ｒ₁、Ｒ₃及びＲ₅はそれぞれ独立して水素原子又はメチル基であり、Ｘ₁及びＸ₂はそれぞれ独立して酸素原子又はＮＨ基であり、Ｒ₂は炭素数８以上１８以下の炭化水素鎖であり、ｐは０又は１であり、ＡＯは炭素数１以上３以下のオキシアルキレン基であり、ｎはＡＯの平均付加モル数であって１以上３０以下の数であり、Ｒ₄は水素原子又は炭素数１以上４以下のアルキル基であり、Ｒ₆はスルホン酸基を含む炭化水素基又は−Ｘ₃−Ｒ₇であり、Ｘ₃は−ＣＯＯ−又は−ＣＯＮＨ−であり、Ｒ₇はスルホン酸基を含む炭化水素基である。] <1> A polishing composition comprising silica particles, a copolymer, and water,
The copolymer has a structural unit represented by the following general formula (I), a structural unit represented by the following general formula (II), and a structural unit represented by the following general formula (III) or The sum of the molar ratio of the structural unit represented by the formula (II) and the molar ratio of the structural unit represented by the formula (III) occupying all the structural units constituting the copolymer is 55. A polishing composition for a magnetic disk substrate, comprising at least mol%, preferably at least 60 mol%, more preferably at least 65 mol%.

[In the formulas (I), (II) and (III), R ₁ , R ₃ and R ₅ are each independently a hydrogen atom or a methyl group, and X ₁ and X ₂ are each independently an oxygen atom or NH R ₂ is a hydrocarbon chain having 8 to 18 carbon atoms, p is 0 or 1, AO is an oxyalkylene group having 1 to 3 carbon atoms, and n is an average added mole of AO. R ₄ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ₆ is a hydrocarbon group containing a sulfonic acid group or —X ₃ —R ₇ . X ₃ is —COO— or —CONH—, and R ₇ is a hydrocarbon group containing a sulfonic acid group. ]

<2> The weight average molecular weight of the copolymer is preferably 1000 or more and 1000000 or less, more preferably 1000 or more and 50000 or less, further preferably 1500 or more and 40000 or less, still more preferably 3000 or more and 30000 or less, and even more preferably 5000. The polishing composition for a magnetic disk substrate according to <1>, which is 20,000 or more and 20,000 or less, more preferably 7,000 or more and 20,000 or less.
<3> The molar ratio of the structural unit represented by the formula (II) in all the structural units constituting the copolymer is preferably 60 mol% or less, more preferably 52 mol% or less, and still more preferably 40 mol. % Or less, still more preferably 36 mol% or less, and preferably 10 mol% or more, more preferably 15 mol% or more, still more preferably 27 mol% or more, even more preferably 30 mol% or more, p is 1, X ₂ is an oxygen atom, AO is an oxyethylene group, and the average added mole number n is preferably 1 or more, more preferably 2 or more, preferably 25 or less, more preferably 20 Or less, more preferably 15 or less, even more preferably 10 or less, and even more preferably 5 or less, the magnetic disk substrate polishing liquid set according to <1> or <2> Thing.
<4> The molar ratios of the structural units represented by the formula (I) and the formula (III) in all the structural units constituting the copolymer are each independently, preferably 20 mol% or more, more preferably Is at least 23 mol%, more preferably at least 27 mol%, even more preferably at least 30 mol%, preferably at most 45 mol%, more preferably at most 43 mol%, even more preferably at most 40 mol%, even more. The polishing composition for a magnetic disk substrate according to any one of <1> to <3>, preferably 36 mol% or less.
<5> The polishing composition for a magnetic disk substrate according to any one of <1> to <4>, further comprising an acid and an oxidizing agent.
<6> The pH is preferably 0.5 or more and 4.0 or less, more preferably 0.8 or more and 3.5 or less, further preferably 1.0 or more and 3.0 or less, and still more preferably 1.2 or more and 2 or less. The polishing composition for a magnetic disk substrate according to any one of <1> to <5>, which is .5 or less.
<7> The polishing composition for a magnetic disk substrate according to any one of <1> to <6>, wherein the magnetic disk substrate is an alumina substrate having a Ni—P-containing layer.
<8> The polishing composition according to any one of <1> to <7> is supplied to a surface to be polished of a substrate to be polished, a polishing pad is brought into contact with the surface to be polished, and the polishing pad and the object to be polished A method for manufacturing a magnetic disk substrate, comprising a step of polishing by moving at least one of the substrates.
<9> The polishing composition according to any one of <1> to <7> is supplied to a surface to be polished of a substrate to be polished, a polishing pad is brought into contact with the surface to be polished, and the polishing pad and the object to be polished A method for polishing a substrate, comprising polishing by moving at least one of the substrates.

[Examples 1 to 12, Reference Example 1 and Comparative Examples 1 to 11]
The polishing liquid compositions of Examples 1 to 12, Reference Example 1 and Comparative Examples 1 to 11 were prepared to polish the substrate to be polished, and washed with pure water to obtain a substrate for evaluation. The dispersibility of each polishing liquid composition, the polishing rate, and the number of scratches on the surface of the evaluation substrate were evaluated. The copolymer used, the method for preparing the polishing composition, the method for measuring each parameter, the polishing conditions (polishing method) and the evaluation method are as follows.

1. Preparation of Copolymers A to T Copolymers A to T (Table 1) were prepared or purchased as follows. About each prepared copolymer, water-soluble evaluation and the measurement of the weight average molecular weight were performed. The results are shown in Table 1.
[Preparation of Copolymer A]
First, in a 500 mL four-necked flask, N, N-dimethylformamide (DMF) 235 g (manufactured by Wako Pure Chemical Industries), lauryl acrylate 23 g (manufactured by Wako Pure Chemical Industries), diethylene glycol acrylate 15 g (trade name “AE”) -90 ", manufactured by NOF Corporation), and 20 g of 2-acrylamido-2-methylpropanesulfonic acid (manufactured by Wako Pure Chemical Industries, Ltd.) were added to obtain a mixed solution. Then, the temperature of the mixed solution in the flask was raised to 65 ± 2 ° C., and 1.8 g of 2,2′-azobis (2,4-dimethylvaleronitrile) as a reaction initiator (trade name “V-65”). (Manufactured by Wako Pure Chemical Industries, Ltd.) and 0.77 g of thioglycerol as a chain transfer agent were added dropwise over 2 hours, and then aging was performed for 3 hours. Thereafter, the mixture in the flask was neutralized with an aqueous sodium hydroxide solution, and then the solvent was removed under reduced pressure to obtain a white polymer LA / DEGAA / AMPS copolymer sodium salt (hereinafter referred to as copolymer). A).
[Preparation of Copolymers B to E, I, K to O]
It was prepared in the same manner as the copolymer A except that the contents of the structural units (I) to (III) were prepared as shown in Table 1.
[Preparation of copolymers F to H]
Copolymer F was prepared in the same manner as Copolymer A, except that the structural unit of formula (I) was changed to that derived from lauryl methacrylate.
Copolymer G was prepared in the same manner as Copolymer A, except that the average added mole number of EO of the structural unit of formula (II) was changed to 4-5.
Copolymer H was prepared in the same manner as Copolymer A, except that the average added mole number of EO of the structural unit of formula (II) was changed to 10.

[Copolymer J, PT]
The following copolymers were used as the copolymers J and P to T.
Copolymer J: acrylic acid (AA) / acrylamidomethylpropanesulfonic acid (AMPS) copolymer, polymerization molar ratio 60/40, weight average molecular weight 25000
Copolymer P: styrene (St) / sodium styrenesulfonate (NaSS) copolymer, polymerization molar ratio 66/34, weight average molecular weight 6000
Copolymer Q: Methacrylic acid (MAA) / Sodium styrenesulfonate (NaSS) copolymer, polymerization molar ratio 70/30, weight average molecular weight 15000
Copolymer R: acrylic acid (AA) / polyethylene glycol (EO = 2 mol) acrylate (PEGAA (EO = 2 mol) / acrylamidomethylpropanesulfonic acid (AMPS) copolymer, polymerization molar ratio 66/17/17) Weight average molecular weight 15000
Copolymer S: Styrene (St) / polyethylene glycol (EO = 9 mol) methacrylate (PEGMA (EO = 9 mol) copolymer, polymerization molar ratio 30/70, weight average molecular weight 57000
Copolymer T: Styrene (St) / polyethylene glycol (EO = 23 mol) methacrylate (PEGMA (EO = 23 mol) copolymer, polymerization molar ratio 30/70, weight average molecular weight 55000

[Evaluation of water solubility of copolymer]
Here, the water solubility of the copolymer was evaluated as follows. That is, the above copolymers A to T are dissolved in ion-exchanged water adjusted to pH = 1.5 with sulfuric acid at a concentration of 300 ppm, and it is visually confirmed whether or not the aqueous solution is transparent. The water solubility of the coalesced was evaluated. In Table 2 described later, “+” is indicated when the aqueous solution is colorless and transparent, “±” when the aqueous solution is translucent, and “−” when the aqueous solution is cloudy.

[Measurement of molecular weight of copolymer]
The weight average molecular weights of the copolymers A to T were measured under the following conditions.
Column: TSKgel α-M + TSKgel α-M (manufactured by Tosoh Corporation)
Eluent: 60 mmol / L; phosphoric acid, 50 mmol / L; LiBr / DMF
Temperature: 40 ° C
Flow rate: 1.0 mL / min Sample size: 5 mg / mL
Detector: RI (manufactured by Tosoh Corporation)
Standard material: polystyrene (Molecular weight 3600, 30000: manufactured by Nishio Kogyo Co., Ltd., 96,44,000, 820,000: manufactured by Tosoh Corp., 92.9000: manufactured by chemco Corp.)

2. Preparation of Polishing Liquid Composition Abrasive material (colloidal silica), a copolymer, an acid, and hydrogen peroxide solution (concentration: 35% by mass) were added to ion-exchanged water and stirred to obtain Example 1. -12, the polishing composition of Reference Example 1 and Comparative Examples 1-11 was prepared (pH 1.5).
As the colloidal silica, spherical silica having an average particle diameter of 22 nm was used in an addition amount of 5% by mass.
As the acid, either 0.5% by mass of sulfuric acid, 1.0% by mass of HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, manufactured by Sorcia Japan) or 1.0% by mass of phosphoric acid was used.
Hydrogen peroxide was used in an addition amount of 0.4% by mass.
As the copolymer, copolymers A to T shown in Table 1 were used in Table 2 in an addition amount (50 to 300 ppm). The weight average molecular weight was measured by the gel permeation chromatography (GPC) method under the following conditions.

[Average particle size of colloidal silica]
Colloidal silica, sulfuric acid, HEDP, and hydrogen peroxide used for the preparation of the polishing composition were added to ion-exchanged water and stirred to prepare a standard sample (pH 1.5). The contents of colloidal silica, sulfuric acid, HEDP, and hydrogen peroxide in the standard sample were 5% by mass, 0.5% by mass, 0.1% by mass, and 0.4% by mass, respectively. Scattering intensity obtained by the cumulant method at a detection angle of 90 ° when this standard sample is accumulated 200 times with a dynamic light scattering device (“DLS-6500” manufactured by Otsuka Electronics Co., Ltd.) according to the instructions attached by the same manufacturer. The particle size at which the area of distribution was 50% of the total was determined and used as the average particle size of colloidal silica.

2. Polishing method The following to-be-polished substrate was grind | polished on the grinding | polishing conditions shown below using the polishing liquid composition of Examples 1-12, Reference Example 1 and Comparative Examples 1-11 prepared as mentioned above. Next, the polishing rate, the number of scratches, and dispersibility were measured. The results are shown in Table 2. Table 2 also shows the contents of Table 1, that is, the constituent units of copolymers A to T, water-soluble evaluation, and weight average molecular weight.

[Polished substrate]
As the substrate to be polished, a substrate obtained by rough polishing an aluminum alloy substrate plated with Ni-P in advance with a polishing composition containing an alumina abrasive was used. The substrate to be polished has a thickness of 1.27 mm, an outer diameter of 95 mm, and an inner diameter of 25 mm. The center line average roughness Ra measured by AFM (Digital Instrument NanoScope IIIa Multi Mode AFM) is 1 nm, and a long wavelength waviness ( The amplitude of the wavelength 0.4-2 mm was 2 nm, and the amplitude of the short wavelength waviness (wavelength 50-400 μm) was 2 nm.

[Polishing conditions]
Polishing tester: "Fast double-sided 9B polishing machine" manufactured by Speedfam
Polishing pad: Fujibow Suede type (thickness 0.9mm, average hole diameter 10μm)
Polishing liquid composition supply amount: 100 mL / min (supply rate per 1 cm ^{2 of} substrate to be polished: 0.076 mL / min)
Lower platen rotation speed: 32.5 rpm
Polishing load: 7.9 kPa
Polishing time: 6 minutes

[Calculation method of polishing rate]
Per unit time obtained by dividing the weight difference (g) of the substrate before and after polishing by the density of Ni—P plating (7.99 g / cm ³ ), the single-sided area of the substrate (65.97 cm ² ), and the polishing time (min). The polishing amount was calculated, and the polishing rate (μm / min) was calculated. Table 2 below shows the relative values with Comparative Example 1 as 100.

[Measurement method of the number of scratches]
Measuring instrument: “OSA7100” manufactured by Candela Instruments
Evaluation: Four substrates were randomly selected from the substrates put into the polishing tester, and each substrate was irradiated with a laser at 10,000 rpm to measure scratches. The total number of scratches (both) on each of the four substrates was divided by 8 to calculate the number of scratches per substrate surface. The results are shown in Table 2 below as relative values with Comparative Example 1 taken as 100.

[Dispersibility evaluation method]
In general, the dust and coarse particles in the polishing liquid composition are removed by a filter immediately before being put into the polishing machine. However, the clogging of the filter is suppressed, and the polishing liquid is used from the viewpoint of extending the filter life and productivity. The dispersibility of the composition is preferably good. Here, the dispersibility was evaluated as follows. That is, based on the degree of cloudiness of the polishing composition of Comparative Example 1, the dispersibility of the polishing composition of Examples 1 to 12, Reference Example 1, and Comparative Examples 2 to 11 was visually evaluated. A sample having the same degree of white turbidity as that of the polishing liquid composition of Comparative Example 1 was designated as +, a sample that became thinner and cloudy than Comparative Example 1, and a sample that became significantly cloudy than Comparative Example 1 as-.

  As shown in Table 2 above, it is shown that the polishing liquid compositions of Examples 1 to 12 effectively reduce scratches on the substrate surface as compared with the polishing liquid compositions of Reference Example 1 and Comparative Examples 1 to 11. It was done. Among them, in Examples 3 to 7, the number of scratches was further reduced while suppressing a decrease in the polishing rate as compared with Examples 1, 2, and 8 to 12.

  According to the present disclosure, for example, a magnetic disk substrate suitable for increasing the recording density can be provided.

Claims (11)

A polishing composition comprising silica particles, a copolymer, and water,
A copolymer having a structural unit represented by the following general formula (I), a structural unit represented by the following general formula (II), and a structural unit represented by the following general formula (III): Its salt,
The sum of the molar ratio of the structural unit represented by the formula (II) and the molar ratio of the structural unit represented by the formula (III) in all the structural units constituting the copolymer is 55 mol% or more. A polishing composition for a magnetic disk substrate.

[In the formulas (I), (II) and (III), R ₁ , R ₃ and R ₅ are each independently a hydrogen atom or a methyl group, and X ₁ and X ₂ are each independently an oxygen atom or NH R ₂ is a hydrocarbon chain having 8 to 18 carbon atoms, p is 0 or 1, AO is an oxyalkylene group having 1 to 3 carbon atoms, and n is an average added mole of AO. R ₄ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ₆ is a hydrocarbon group containing a sulfonic acid group or —X ₃ —R ₇ . X ₃ is —COO— or —CONH—, and R ₇ is a hydrocarbon group containing a sulfonic acid group. ] The polishing composition for a magnetic disk substrate according to claim 1, which does not contain alumina abrasive grains and is used for finish polishing. The polishing composition for a magnetic disk substrate according to claim 1 or 2 , wherein the copolymer has a weight average molecular weight of 1,000 to 1,000,000. The molar ratio of the structural unit represented by the formula (II) in all the structural units constituting the copolymer is 60 mol% or less, p is 1, X ₂ is an oxygen atom, AO is The polishing composition for a magnetic disk substrate according to any one of claims 1 to 3, which is an oxyethylene group and has an average addition mole number n of 2 or more and 10 or less. The molar ratio of the structural units represented by the formula (I) and the formula (III) in all the structural units constituting the copolymer is each independently 23 mol% or more and 45 mol% or less. Item 5. A polishing composition for a magnetic disk substrate according to any one of Items 1 to 4 . In the formula (III), R ₆ -CONH-C (CH _Three ) ₂ -CH ₂ -SO _Three The polishing composition for a magnetic disk substrate according to claim 1, wherein the polishing composition is H. The polishing composition for a magnetic disk substrate according to any one of claims 1 to 6 , further comprising an acid and an oxidizing agent. The polishing composition for a magnetic disk substrate according to any one of claims 1 to 7 , wherein the pH is 1.0 or more and 3.0 or less. The polishing composition for a magnetic disk substrate according to any one of claims 1 to 8 , wherein the magnetic disk substrate is an alumina substrate having a Ni-P-containing layer. The polishing composition according to any one of claims 1 to 9 is supplied to the polished surface of the substrate to be polished is brought into contact with the polishing pad to the polishing target surface, at least one of said polishing pad and the substrate to be polished A method of manufacturing a magnetic disk substrate, comprising a step of moving and polishing. The polishing composition according to any one of claims 1 to 9 is supplied to the polished surface of the substrate to be polished is brought into contact with the polishing pad to the polishing target surface, at least one of said polishing pad and the substrate to be polished A method for polishing a substrate, comprising moving and polishing.