GB2403954A

GB2403954A - Polishing composition

Info

Publication number: GB2403954A
Application number: GB0414656A
Authority: GB
Inventors: Tomohide Kamiya; Noritaka Yokomichi; Toshiki Owaki
Original assignee: Fujimi Inc
Current assignee: Fujimi Inc
Priority date: 2003-07-03
Filing date: 2004-06-30
Publication date: 2005-01-19
Anticipated expiration: 2024-06-30
Also published as: MY160322A; JP2005023228A; CN1576339A; CN1576339B; MY144568A; GB0414656D0; JP4202201B2; GB2403954B

Abstract

The polishing composition contains an abrasive, a microwaviness reducing agent, an oxidizing agent, a polishing accelerator, and water. The microwaviness reducing agent is a reducing agent and contains at least one kind selected from phosphonic acid, phosphinic acid, ammonium hypophosphite, ammonium sulfite, sodium sulfite, hydroquinone, pyrogallol, erysorbic acid, sodium erysorbate acid, L-ascorbic acid, formic acid, sodium formate, amumonium formate, oxalic acid, ammonium oxalate, ammonium iodide, and gallic acid. The abrasive can contain silicon dioxide, and the oxidizing agent can contain hydrogen peroxide. The accelerator can contain e.g. phosphoric acid, glycolic acid, maleic acid or succinic acid as well as diammonium hydrogen phosphate or ammonium dilhydrogen phosphate. The polishing composition can be used in polishing a substrate for a magnetic disk.

Description

POLISHING COMPOSITION

BACKGROUND OF THE INVENTION

The present invention relates to a polishing composition to be used for polishing a substrate for a magnetic disk and the like.

With respect to a magnetic disk for use as a hard disk l0 serving as a memory device for a computer, there have been strong demands for high recording density. For this reason, a substrate for a magnetic disk is required to have good surface quality, for example, to have high surface smoothness and few scratches.

Japanese Laid-Open Patent Publication No. 2003-147331 discloses polishing composition, which is improved in order to satiety such a requirement for substrates. The polishing composition contains abrasive grains of alumina or the like, a phosphorus-cotaining inorganic acid such as phosphoric acid or a salt thereof, an inorganic acid such as nitric acid other than the phosphorus-containing inorganic acid or a salt thereof, an oxidizing agent such as hydrogen peroxide, and water. The inorganic acids have a function for improving the abrasive grain-dispersing condition to suppress the occurrence of scratches on a substrate being polished. The oxidizing agent [unctions as an etching agent to decrease the surface toughness of a subst:ratc prepared after polishing.

:50 Flowever, the substrate prepared after polishing Using tile polishing composition as described in Japanese Laid-Open Patent Publication No. 2003-147337 has a rather!ooor value of microwaviness, which is an indication of surface smoothness.

3, SUt1MARY 0 'tHf' lNVE'NTL^N

L

Accordingly, it is an objective of the present invention to provide a polishing composition more suitable for use in polishing a substrate for a magnetic disk.

To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a polishing composition is provided. The polishing composition contains an abrasive, a microwaviness reducing agent, an oxidizing agent, a polishing accelerator, and water.

The present invention also provides a method for polishing a substrate for a magnetic disk. The method includes preparing the polishing composition and polishing the surface of the substrate by using the polishing composition.

Furthermore, the present invention provides a magnetic disk. The magnetic disk is formed from a substrate prepared after polishing by using the polishing composition.

Other aspects and advantages of the invention will become apparent from the following description, illustrating by way of example the principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of the present invention will now be described.

polishing composition according to Lois e,bodirnent cor ains an abrasive, a microwaviness reducing agent, an oxidizing agent, a polishing accelerator, and water. The polistrirlg cornpositiori is used for polishinq, for example, a substrate for a magnetic iSK. This substrate may be a substrate or.r.ed by providing an electroless plating latter composed of nickel-phosphorus on a blank membe' composed of an aluminum alloy, or a substrate formed by providing a layer composed of nickel-iron on a blank member. Alternatively, the substrate may be a substrate containing boron carbide or carbon.

The abrasive plays a role for polishing an object mechanically. The abrasive preferably contains at least one kind selected from aluminum oxide, silicon oxide, cerium oxide, zirconium oxide, titanium oxide, silicon carbide, and silicon nitride, and more preferably contains silicon dioxide.

Silicon dioxide has less risk of inducing occurrence of scratches on an object being polished because it has relatively low hardness.

Silicon dioxide contained in the abrasive is preferably colloidal silica, fumed silica, or precipitated silica, and is more preferably colloidal silica. Colloidal silica has particularly little risk of inducing occurrence of scratches on an object being polished. Colloidal silica is composed of amorphous silica particles the surface of which is charged, and is dispersed in a colloidal state in water. Colloidal silica may be obtained by a method in which ultra-fine colloidal silica from which sodium silicate and potassium silicate are removed through ion exchange, and is subjected t:o a particle-growing process. Alternatively, colloidal s lice may be obtained by a method in which alkoxysilare is subjected to hydrolysis by using an acid or alkali, or a method in which ar. organic silicon compound is heated and decomposed in a wet system. Fumecl silica is in a chain state and contains fror several to several tcos of particles, which are aggregated three-dimensionally. the abrasive may contain trio or more kinds of silicon dioxides.

[he average particle ciiarreter of the acrasiv-e deterriin-:i from the specific surface area of the abrasive measured by a BET method is preferably no less than 0.005 urn and no more than 0.5 m, and is more preferably no less than 0.01 Am and no more than 0.3 m. If the average particle size of the abrasive is less than 0.005 m, the polishing composition may not nave the ability to polish an object at high speed. In other words, the polishing rate of the polishing composition might be reduced. In addition, precise polishing might become difficult because vibrations are generated in the polishing machine due to large polishing resistance. If the average particle size of the abrasive is more than 0.5 am, precipitate might be generated in the polishing composition, and as a result, many scratches might be generated on an object being polished or the surface of the object prepared after polishing might become rough.

The content of the abrasive contained in the polishing composition is preferably no less than 0.01% by mass and no more than 40! by mass, and is more preferably no less than 0.1% by mass and no more than 10i by mass. If tile content of the abrasive is less than 0.01% by mass, the polishing rate of the polishing composition might be reduced and moreover, precise polishing might become difficult because vibrations are generated in the polishing machine due to large polishing resistance. If the content of the abrasive is more than 4C0- by mass, the abrasive might become agglomerated, and as a result, storage stability of the polishing composition might be deteriorated and many scratches might be generated on an object being polished dir to the agglomerated abrasive In :'0 addiLicn, a polishing oomposi'ion containing a large amount of abrasive flight be disadvantageous in terms of cost.

The microwaviness reducing agent is a reductant and ha< a function for redlcirg microwaviness of an object Prepared :: after polishing. It is presumed that the rnicrowiness reducing agent regulates the functions of the oxidizing agent and the polishing accelerator contained in the polishing composition and thereby suppresses excess etching to reduce microwaviness.

The microwavi.ness reducing agent preferably contains at least one kind selected from phosphoric acid (sometimes called phosphorous acid), phosphinic acid (sometimes called hypophosphorous acid), ammonium hypophosphite, ammonium lO sulfite, sodium sulfite, hydroquinone, pyrogallol (sometimes called pyrogallic acid), erysorbic acid, sodium erysorbate acid, L-ascorbic acid, formic acid, sodium formats, ammonium formate, oxalic acid, ammonium oxalate, ammonium iodide, and garlic acid (sometimes called 3,9,5-trihydroxybenzoic acid), more preferably contains at least one kind selected from phosphinic acid, pyrogallol, and garlic acid, and most- preferably contains garlic acid. Phosphonic acid, phosphlnic acid, ammonium phosphinate, ammonium sulfite, sodium sulfite, hydroquirone, pyrogallol, erysorbic acid, sodium erysorbate, L-ascorbic acid, formic acid, sodium formate, amrnoniurr.

formate, oxalic acid, ammonium oxalate, ammonium iodide, and garlic acid each have a high capabll.ity for reducing microwaviness. Among them, phosphinic acid, pyrogallol, and garlic acid each have a particularly high capability for reducing microwaviness, and further, garlic acid has the highest capability for reducing microwaviness.

The content of the microwaviness reducing agent containers in the polishing composition is preferably no less than O.Oli by mass and no more than 2% by mass, and is more preferably no less than 0.05% by mass and no more than 1% by mass. If the content of the rr.icrowa/ir.ess reduc nG agent is less than 0.01 ; by Grass, rn-cro'a- ness of ari object prepared after polisni!-g may not be remarkably reduced. Ir the contest i'; of the m7cr:owavirless reduc.ng agent. is more thari 2 by masts, the cost-effectiveness might be poor and it might be uneconomical to use the rnicrowaviness reducing agent in such - an amount.

The oxidizing agent accelerates mechanical polishing with the abrasive by oxidizing an object being polished. The oxidizing agent preferably contains at least one kind selected from hydrogen peroxide, nitric acid, potassium permanganate, and persulfate, and more preferably contains hydrogen peroxide. Hydrogen peroxide has a high oxidation power and decomposes to acid and water so that it is gentle to the environment and is relatively inexpensive. Hydrogen peroxide may be added to the polishing composition in an aqueous - solution state containing from 30% to 35% by mass of hydrogen peroxide.

The content of the oxidizing agent contained in the polishing composition is preferably no less than 0.16 by mass - and no more than 15% by mass, and is more preferably no less than 0 5% by mass and no more than 10% by mass. If: the content of the oxidizing agent is less than 0.1% by mass, the polishing rate of the polishing composition might be reduced or many scratches might occur on an object being Abolished. If the content of the oxidizing agent is more than 15% by mass, the cost-effectiveness might be poor and it might be - uneconomical to use the oxidizing agent in such an amount.

The polishing accelerator accelerates polishing ar object by cherubically polishing the object. The polishing accelerator preferab y contains at least one kind selec ed from phosphoric acid, phosphate, and an organic acic-l, exciusi7e of formic acid, oxalic acid, and garlic a id, and more E,referably contains phosphate and at leas one K' nc o phosphoric acid and the organic acid. Phosphoric ac_.i, s5 phosphate, anti one organ c ac d have a high capab 'c: For chemically polishing an object. Among them, phosphate not only accelerates polishing an object but also forms a protective film on the surface of the object being polished to suppress the occurrence of scratches on the object being polished.

The organic acid contained in the polishing accelerator preferably contains at least one kind selected from citric acid, maleic acid, maleic anhydride, malic acid, glycolic acid, succinic acid, itaconic acid, malonic acid, iminodiacetic acid, gluconic acid, lactic acid, mandelic acid, tartaric acid, crotonic acid, nicotinic acid, acetic acid, and adipic acid, and more preferably contains at least one kind selected from citric acid, maleic acid, maleic anhydride, glycolic acid, and succinic acid. Citric acid, maleic acid, rnaleic anhydride, malic acid, glycolic acid, succinic acid, itaconic acid, malonic acid, i.inodiacetic acid, gluconic acid, lactic acid, mandelic acid, tartaric acid, crotonic acid, nicotinic. acid, acetic acid, and adipic acid each have a high capability for chemically polishing an object. Arnoncs them, citric acid, maleic acid, rr.aleic anhydride, glycolic acid, and succinic acid each have a particularly high capability for chemically polisIinq an object.

['hosphoric acid contained in the polishing accelerator preferably contains at least one kind selected from orthohosphoric acid, c. iiphosphoric acid (sometimes called pyrophospnoric acid), po yphosphoric acid, and metaphosrhor- c acid. Orthophosphoric acid, diphosphoric acid, poly:'hosphoric acid, and met.aphosphoric acid each have a high capability or chemically polishing an object. Orthophosphoric acid is represented By the formula H3PO4. Diphosphoric acid is represe,tec by forr..,ila H,P2O-7. Folvrhosphor_c add is a linear polymeric phosphoric ac d produced by dehydration condensation of ortheplosp.,lari- acid and is represented by the ':orrnul. l

n+2PnO3n+,, wherein n is an integer of 2 to 4 inclusive.

Polyphosphoric acid may be a mixture of linear polymeric phosphoric acids which are different from each other in the number of n, more specifically, a mixture of at least two kinds selected from diphosphoric acid, triphosphoric acid (H5P30io), and tetraphosphoric acid (H6PO13). A condensation ratio of polyphosphoric acid, more specifically, a ratio of the mass of the orthophosphoric acid produced by hydrolysis of the polypnosphoric acid based on the mass of the polyphosphori.c acid may be 105% or 116\, or may be values other than those. Metaphosphoric acid is a cycli c: phosphoric acid produced by dehydration condensation of the orthop.hosphoric acid and is represented by the formula (HPO3)m, wherein m i s an integer of 3 to 8 inclusive.

Phosphate contained ire the polishing accelerator preferably contains at 1 east one kind selected from i triamrnoniurn phosphate ( (Nil4) COW), diarnmonium hydrogen: phosphate ( (NH)2liPO4), amrnoni.um dihydrogen phosphate (NH<H2PO9), trisodium phosphate (Na3PO4), disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate (NaH2PO4), tripotassium phosphate (K3PO4), dipotassium hydrogen phosphate (K2HPO4), and potassium dihydrogen phosphate (KH2POq), and more preferably contains diammonium hydrogen phosphate.

T riammonium phosphate, diammonium hydrogen phosphate, ammonium dibydrogen phosphate, trisodium phosphate, disodium hydrogen i phosphate, sodium clihydrogen phosphate, tripotassium phosphate, dipotassium hydrogen phosphate, and potassium ddhydecceri phosphate each have a high capability tot suppress- ng t he occurrence of scratches on an ob ject being polished. Among them, d;.amrnoni um hydrogen phosphate has a part. icular-ly high capability or suE:2ressinc tne occurrence of scratc yes O!' an cb ject oei ng pal ished.

The content or the pal sting accelerator cc rained ire the polishing composition is preferably no less than 0.01% by mass and no more than 40t by mass, and is more preferably no less than 0.1% by mass and no more than 20% by mass. If the content of the polishing accelerator is less than 0.01% by mass, the polishing rate of the polishing composition might be reduced. If the content of the polishing accelerator is more than 40 by mass, the cost-effectiveness might be poor and it might be uneconomical to use the polishing accelerator in such an amount.

When the polishing accelerator contains phosphate, the content of phosphate contained in the polishing composition is preferably no less than 0.01% by mass and no more than 30 by mass, and is more preferably no less than 0.1% by mass and no more than 10% by mass. If the phosphate o. onten is less than O.Olt by mass, the occurrence of scratches on an object being polished is not effectively suppressed. When the phosphate j content is more than 30 by mass, the cost-effectiveness might be poor and it might be uneconomical to use phosphate in such an amount.

the water contained in the polishing composition plays a role as a medium for dispersing or dissolving components other than water. It is preferred that the water conta r.s as little impurities as possible. More specifically, purified water, ultrapure welter, or distilled water is preferable. ; The E,[! of the polishing composition is preferably no less than 1 and no fore than 7, and is more preferably no less than 2 and rho more than 4. lf the pi! is less,han 1, corrosion fright be generated in an object being poli.shec;.. If the pE is more than 7, oxidization due t:c the omit zinc agent might be suppressed, ar,1 as a result, the polishing rate of the po'ishinc Co'!'.'pO',i LO on!-.igh- be reciuce.

The polishing composition is prepared by mixing an abrasive, a microwaviness reducing agent, an oxidizing agent, a polishing accelerator, and water. During the mixing, the order in which each component is added may be in any order, or all the components may be added at the same time.

When the surface of a substrate for a magnetic disk is polished using the polishing composition, for example, the surface of the substrate is rubbed with a polishing pad while lO supplying the polishing composition to the surface of the substrate. After the polishing, the substrate is washed and dried.

A substrate for a magnetic disk is generally prepared through a plurality of polishing steps including at least first polishing step and a final polishing step. The first polishing step is generally performed to remove waviness and surface defects such as large scratches and irregularities on the substrate that might not be capable of being removed in the following polishing step. The final polishing step is generally performed to make an adjustment to a desired surface roughness of the substrate and to remove surface defects that occurred in the previous polishing step and surface defects that could not be removed in the previous polishing step. I\ polishing composition according to this embodiment is preferably used in the final polishing step.

The embodiment provides the following advantage.

polishing composition according to this embodiment contains a microwaviress reducing agent and t;herel'ore, the object and particularly the substrate for a magnetic disk prepared hi, polishing using the polishers composition ha.ve reduced rnicrowaviness. Accordingly, the polishing composition i'- is extreme_v suitable for use in polishing G srbstraLe for a ](' magnetic. disk, particularly suitable for use in final polishing step for a substrate, and contributes to improvement of the recording density of a magnetic disk.

It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms.

The polishing composition may further contain a surfactant, a thickener, or an antifoaming agent, if necessary. The surfactant may be a polycarboxylic. acid-based surfactant or a polysulfonic acid-based surfactant. More specifically, the surfactant may be sodium polystyrene slfcnate or sodium polyacrylaLe. The surfactant improves dispersibility of the abrasive contained in the polishing composition. The thickener may be water-souble cellu]oses or polyvinyl alcohols.

The polishing composition may be prepared by diluting a stock solution with water irarnediately before its use. In this case, the polishing composition thus prepared facilitates the handling and the transportation of the polishing composition.

When the oxidizing agent in the polishing composition contains hydrogen peroxide, the polishing cornposit:ion may b prepared, immediately before its use, by mixing a mixture of components other Lhan hydrogen peroxide with hydrogen peroxide. In this case, the use or the polishing compcsitior thus prepared prevents stability ot- the polishing composition from lowering caused by decomposing h\/drogen peroxide in ton polish ng composition during storage thereof.

Jr The go isning composition may be used n One polish not step other than the final polishing step. For example, the polishing composition may be used in the first polishing step for a substrate.

The polishing composition may be used in polishing an object other than a substrate for a magnetic disk.

The present invention will now be described in more detail by referring to Examples and Comparative Examples.

In each of L'xamples l to l9 and Comparative Examples l to 8, a polishing composition was prepared by mixing an abrasive, a microwaviness reducing agent, an oxidizing agent, - a polishing accelerator, and water. In each polishing 1.6 composition, the kinds and the content of the abrasive, the microwaviness reducing agent, the oxidizing agent and the polishing accelerator are shown in liable l. - Using the polishing composition prepared in each of Examples l to l9 and Comparative Examples 1 to 8, the surface ot a substrate was polished uncle' the following polishing condi'.ions.

Polishing conditions: Substrate to be polished: a substrate of q3.5 inches - (about 95 mm) provided with a nickel-phosphorus elect-roless plated layer Polishing machine: a double-sidecl polishing machine, "SFDL-9B", rnanuTactured by SPEE;DEAM Co., I.td.

Polishing pad: a suede-type polishing pad, "Belatrix N0058", rr. anufaccured by Kanebo, Ltd. Polishing load: 80 g/crr!2 Ra.e of revolution of 'rosier fixed base: /!0 rE)m Rate of supply of polishing c:ompos tior. : lOO ml/e, n 3 Pol-shing Diane: 5 r.-nutes With respect to polishing processes carried out under the above-mentioned conditions, the polishing rate was calculated based on the following formula. The polishing rate S thus calculated was evaluated in accordance with the evaluation criteria as shown in Table 2. The evaluation results are shown in the column entitled "Polishing Rate" in

Table 1.

Formula Polishing rate (pm/min) -- reduced amount of substrate (a) due to polishing / [area (cm2) of substrate surface to be polished x density (g/cm3) of nickel-phosphor plated layer x polishing time (win)] x 104.

Bach substrate prepared after polishing was observed by an ulLrafine defect visualizing microinspecting apparatus "MicroMax VMX2100" manufactured by VISION PSYTEC CQ. Ltd., and thereby the number of scratches on the surface of the substrate was determined. The average value of the numbers of scratches neasured on both surfaces of each of five samples was evaluated in accordance with the evaluation criteria as shown in rable 2. The evaluation results are shown in the column entitled "Scratches" in Table 1.

Using a non-contact surface roughness measuring device "ChairME'2OOOPlus" manufactured by Chapman Co Ltd., the amount of microwaviness of the substrate prepared after polishing was measured. The rneasurcrrent was carried out will a lOX object lens and a measuring wavelength of from 80 to 400 um. The amount of microwaviness measured was evaluated in accordance with the evaluation criteria as shown in Table 2.

The evalatio.n results are shown in the column entitled "Micro.avir.ess" in Sable 1. :3

['able 1 _ 1'. 5' : IEX 1 SiO2= qallic - -I glycolic I | 39 acid 2 2 ac (NH412HEO4 | 0 1% 0.45% 1 d 0 4% Good Good Good Ex. 2 SiOz garlic 02O | aid (NH) HPO, | Good | Good Good| Ex. 3 aid H O' I glyco ic | (NH<)'H Good Good Good garlic glycolic x. 4 Si3O2* acid HO2 ac.id (NH4)2HLO. l I _ _ j _0.1% __: 1.5t 1% O.4\ Good Good Good Ex. aced NzO2 I qlyco ic (NI14} HPO4|GOOd Good Good Ex. 6 9iO2* a:lA o29% I qlycolic 0 4 | 500d|Good Cood| Ex. 7 311 glycolic Good|Good Gooc| F:x 8 5 gallle H2O, q (NH4) HPO<| Good| Good Good LX. 9 oH2O9 I qlyco ie | (NH4)2HpQ4l Goodl Good Good| x. I n Si8O%2* garlic ol2O2 glyeolie (NH4)2HPO4 _ i C 1t 4.9% 15 0.% Good Good Good Fx. l SiO* l: H20z maleie (NH') HPO'|Good I Good Good gd1 1 i c s u(:ci ni c x. 12 S0%2* ,.e d H20z ae_d l (NH4)2HPO41 ___ _. , C. 1 v. ., , .5 0.4% Good Good Good Ex. 13 Si]= c 0 c, 1. I (NH4) 2HPO4| Very| Go:dl Goo1 Ex. SiO.^ gallie H,O2 3lyolie I HHH2PO l Goodl Good Good x. 1 s i o 0 1 li2O. gl,colLe -c|FAir Gi| x SiG2i:- d rO; aeid I (H2hPC,- - - - - O -, ,;

Table 1 (continued)

[ :hi 1 E 7 SiO2* phosphinic _.aleic _ _ _ x. 1 acta H202 acid (NH4) 21lPO4 Very Good Good x. 1e sicz I acd I [NPi2GPO'I Good| Good Good| sio:* À Àa: P2O2 maleic (NP);HPol Good Good Good| C.Ex. 1 SiO52* gac d _ _. _ _. 0.1% _ Poor L'oor Poor SiOz,, . (NH,) dPOl Poor | Poor Poor| C.x. 3 SiO7i - - | acid l ( h H. ) H P0, 1 Good Good C.Ex. 4 SiO2* _ HzO2 glycolic I _ _ _ _ j 5 O. 9t acd _ Good Eair ?cor C.Ex. sioz' .. I 0 49 Poor Poor Poor C. Ex. f. SiO2*acid 11202 _ _ __ 0.l% O.9\ _ _ Poor Poor Poor C.Ex. 7 SiO2* H202 H3PO4 _ _ O. 95 1 5 _ Gooi Fair ?oor C.F:x. 8 SiO2* ._}202 H3PO4 1 nitric _ * S. 3t _ _ O. 9% lo acid Good P O7 1S colloidal si'ica having an average p rticle die neter Df O.O tni.

Tabl e 2 a1=d o Polishin.: : Good Q.10 or more | _ _ | and Icss than 0. 13 less than 100 less than 0. -l air 0.08 o- more 100 or more _ _ Poor arnd less than 0.10 _ and less than 203 ess than 0.08 _ 200 or more, = _ s is shown in Pable 1, in acI of.-xarn.] es 1 co 'i loot.. ct he polishinq rat:e and rnictowaviness were evalu tod o 1i be good or very good. Particularly, in Example ll, Example 13, Example 1-l, and Example 19 wherein the polishing accelerator contained maleic acid or orthopnosphoric acid, the evaluation of the polishing rate was very good. Further, in each of Examples 1 to 19, and Examples 16 to 19, the evaluation of the scratches was good. In contrast, in each of Comparative Examples 1 to 6, the evaluation of microwaviness was poor.

The present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.

Claims

CLAIMS: 1. A polishing composition characterized by an abrasive, a

microwaviness reducing agent, an oxidizing agent, a polishing accelerator, and water.
2. The polishing composition according to claim l, characterized in that the microwaviness reducing agent is a reductant.
3. The polishing composition according to claim 2, characterized in that the microwaviness reducing agent contains at least one kind selected from phosphoric acid, phosphinic acid, ammonium hypophosphi.te, ammonium sulfite, lo sodium sulfite, hydroquinone, pyrogallol, erysorbic acid, sodium erysorhate acid, L-ascorbic acid, formic acid, sodiarr.

formate, ammonium formats, oxalic acid, ar.mrnonium oxaiate, ammonium iodide, and garlic acid.
4. The polishing composition according to claim 2, characterized in that the microwaviness reducing agent contai.rs at least one kind selected from phosphinic acid, pyrogallol, and garlic acid.
5. The polishing composition according to claim 2, characterized in that the microwaviness reducing agent contains garlic acid.
6. The polishing composition according to any one of claims 1 :30 to 5, characterized in that the content of the rnicrowaviness reducing agent contained in the polishing composition is no less than 0. 01% by mass and no.,:ore than 2% b,' mass.
2. I'he pc:lishinq cor.ipisitior. according to claim i, 3: .haracterizc-id in that the eon' en, of the microwatt ness i / reducing agent contained in the polishing composition is rho less than 0.05% by mass and no more than 1% by mass. -
8. the polishing composition according to any one of claims 1 to 7, characterized in that the polishing accelerator contains at least one kind selected from phosphoric acid, phosphate, and an organic acid, exclusive of formic acid, oxalic acid, and garlic acid.
9. The polishing composition according to any one of claims 1 to 7, characterized in that the polishing accelerator contains phosphate and at least one kind of phosphoric acid and an organic acid, exclusive of formic acid, oxalic acid, and garlic acid. 3
IO. The polishing composition according to claim 8 or 9, characterized in that the phosphoric acid contains at least one kind selected born ort:hophosphoric acid, diphosphoric acid, polyphosphoric acid, and metaphosphoric acid.
11. The polishing composition according to any one of claims 8 to 10, characterized in that the organic acid contains at least one kind selected from citric acid, maleic acid, maleic anhydride, malic acid, glycolic acid, succi.nic acid, itaconic acid, malonic acid, iminodiacetic acid, gluconic acid, lactic acid, mandelic acid, tarl:aic acid, crotonic acid, nlcotinic acid, acetic acid, and adip.ic acid.
12. The pal iS}l_n. composition accocii.ng to any one of claims 0 8 to 12, characterized in that t:rre phosphate contains at least one kind selected from triamrnoniurn phosphate, diarmoniuin hydrogen phosphate, ammonium dihydrocn phosphate, trisodium hosp}-a'e, disQdium hydrocJer, priospi',at:c, sodium dihydroc3en phosphate, triporassium phosphate, dipotassium hydrogen pRcsphate, and potassium dihydroc3en phospha e.
13. The polishing composition according to any one of claims 1 to 12, characterized in that the abrasive contains silicon dioxide.
14. The polishing composition according to any one of claims 1 to 13, characterized in that the oxidizing agent contains hydrogen peroxide.
15. The polishing composition according to any one of claims 1 to 14, characterized in that the polishing composition is used for polishing a substrate for a magnetic disk.
16. The polishing composition according to claim 15, characterized in that the polishing composition is used in final-polishing of a surface of the substrate.
17. A method for polishing a substrate for a magnetic disk, the method characterized by: prepar-iny the polishing composition according to any one of claims 1 to 14; and polishing the surface of the substrate by using the polishing composition.
18. A magnetic disk, characterized in that the magnetic disk is formed from a substrate prepared after polishing by using the polishing composition according to any one of claims 1 to 14. 3G lo
19. A polishing composition substantially as hereinbefore described with reference to

the examples.
20. A method of polishing a substrate for a magnetic disk substantially hereinbefore described Wit]1 reference to the examples.
21. A magnetic disk substantially hereinbefore described with reference to the

examples.