§119 (e) (1) of the filing date of the Provisional Application No. 60/473,117 filed on May 27, 2003, and the filing date of the Provisional Application No. 60/477,754 filed on June 12,2003, pursuant to 35 U. S. C. §111 (b).

TECHNICAL FIELD The present invention relates to a polishing composition for use in precise polish-finishing of a metal, plastic, glass, or similar material and to a polishing method. More particularly, the invention relates to a polishing composition and a polishing method for a magnetic disk which is installed in a hard disk drive of a computer. Use of the polishing composition of the present invention is very advantageous in that a surface of an aluminum magnetic disk substrate which is plated with, for example, Ni-P can be polished at a high polishing rate, and a high-quality mirror-finished surface is provided without forming surface defects.

BACKGROUND ART The recording density of a magnetic disk has increased by reducing the gap between the magnetic disk and a magnetic head in a hard disk drive (i. e. , flying height). In recent years, in order to cope with trends of a drastic increase in magnetic recording density and a drastic decrease in diameter, there has been continuous demand for a magnetic disk having a high-quality finished surface. In order to meet such demand, a variety of technical developments have been attained.

Recently, as recording density has been

progressively increased from current 40 GB to 60 to 80 GB, rigorous requirements are imposed on polishing agents. Such requirements are diversified and include high polishing rate, reduction in surface roughness, non- surface defects (micro-pits, micro-protrusions, and micro-scratches), reduction in waviness generally and locally, prevention of cut-off at the edge surface, prevention of adhesion of abrasive grains on a disk surface, prevention of staining of a disk surface, and excellent washability.

Regarding the aforementioned polishing composition, there have been conventionally proposed a variety of polishing compositions which attain a high polishing rate and provide a high-quality disk surface.

For example, in order to maintain a high polishing rate, one of the most important characteristics during polishing, and attain a high-quality polished surface which is resistant to polishing-related scratches and surface defects such as scratches, pits, and protrusions, aluminum nitride disclosed in JP-62-25187-A (U. S. Patent No. 4, 705 ; 566) and a variety of inorganic acids and salts thereof have been proposed as a polishing accelerator serving as an additive for a polishing composition.

There have been proposed a variety of etchants based on organic acids such as gluconic acid, lactic acid (both disclosed in JP-02-84485-A (U. S. Patent No. 4,915, 710) ), and organic acids disclosed in subsequent publications, the etchants being effective for reducing surface roughness of a polished surface so as to meet a demand for improvement of surface precision. Furthermore, as the aforementioned polishing compositions effective for attaining, at high efficiency, a high-quality polished surface without surface defects, there have been proposed a polishing composition containing boehmite alumina sol or colloidal alumina disclosed in JP-01-188262-A (U. S.

Patent No. 4,956, 015), and a polishing composition containing boehmite and an organic acid ammonium salt

disclosed in JP 02-158683-A. Furthermore, a chelate compound (U. S. Patent No. 5,366, 542) has been proposed as a polishing accelerator. Boehmite sol and colloidal alumina also have functions of surface modification agents. Prevention of dub-off is a type of surface modification, and JP-2002-167575-A (U. S. Patent No.

6,645, 051) discloses hydroxy polymers such as polyoxyethylene polyoxypropylene alkyl ethers as a dub- off preventing agent.

Meanwhile, use of alumina, titania, ceria, zirconia, and silica of various crystal forms as abrasive grains has been proposed. Among them, a-alumina is predominantly employed as abrasive grains. In JP-2002- 30273-A (U. S. No. 2001-051746-Al), a combination of a- alumina, intermediate alumina, and a dub-off preventing agent is proposed.

However, in the field of rapidly developing computer hardware, there has been continuous and keen demand for a magnetic disk having a higher quality finished surface so as to further increase recording density. Currently, there has never been attained a generally evaluated polishing composition which satisfies all of the aforementioned rigorous requirements in quality (e. g., rate, surface quality, and dub-off).

As mentioned above, in order to increase recording density, the following conditions must be met: excellent smoothness and flatness of a disk, small surface roughness, and absence of pits, protrusions, scratches, waviness, and dub-off generated at the periphery of the disk. In order to attain such high-quality finishing, a more excellent polishing composition is demanded.

In order to meet the demand, an object of the present invention is to provide a polishing composition which provides a high-quality polished surface without surface defects while a high polishing rate is maintained.

SUMMARY OF THE INVENTION The gist of the present invention resides in a polishing composition which can attain the above object and which contains water, abrasive grains, a polishing accelerator, and a polycarboxylic acid salt having a carboxylic group number (n) of 20 to 300 or a derivative thereof (hereinafter also referred to as"a polishing aid"), and further optionally a finely divided crystal powder (hereinafter also referred to as"auxiliary abrasive grains") and a surface modification agent.

Accordingly, the present invention provides the following.

(1) A polishing composition, comprising water, abrasive grains, a polishing accelerator, and a polycarboxylic acid salt having a carboxylic group number (n) of 20 to 300 or a derivative thereof.

(2) The polishing composition as described in (1) above, wherein the abrasive grains have a mean primary crystal size falling within a range of 0.1 to 5 m.

(3) The polishing composition as described in (1) or (2) above 1 or 2, wherein the abrasive grains have a mean secondary particle size falling within a range of 0.3 to 5 m.

(4) The polishing composition as described in any one of (1) to (3) above, which contains the abrasive grains in an amount falling within a range of 1 to 35 mass%.

(5) The polishing composition as described in any one of (1) to (4) above, wherein the abrasive grains are at least one selected from the group consisting of alumina, silica, titania, zirconia, ceria, calcia, magnesia, manganese oxide and iron oxide.

(6) The polishing composition as described in any one of (1) to (4) above, wherein the abrasive grains comprise a-alumina.

(7) The polishing composition as described in any one of (1) to (6) above, wherein the polishing accelerator comprises at least one species selected from among an organic acid, an inorganic acid salt, a combination of an organic acid and an organic acid salt, a combination of an organic acid and an inorganic acid salt, a sol product formed from an aluminum salt, and an organic phosphonic acid chelate compound.

(8) The polishing composition according to (7) above, which contains the organic acid, inorganic acid salt, combination of organic acid and organic acid salt, or combination of organic acid and inorganic acid salt in an amount falling within a range of 0.01 to 10 mass%.

(9) The polishing composition according to (7) or (8) above, which contains the organic acid in an amount of at least 0.003 mass%.

(10) The polishing composition according to (7) above, which contains the sol product formed from an aluminum salt in an amount falling within a range of 0.01 to 5 mass%.

(11) The polishing composition according to (7) above, which contains the organic phosphoric acid chelate compound in an amount falling within a range of 0.01 to 5 mass%.

(12) The polishing composition as described in any one of (1) to (11) above, wherein the polycarboxylic acid salt or derivative thereof is a polyacrylic acid salt, a polymethacrylic acid salt, or a derivative thereof.

(13) The polishing composition as described in any one of (1) to (12) above, which contains the polycarboxylic acid salt or derivative thereof in an amount falling within a range of 0.01 to 5 mass%.

(14) The polishing composition as described in any one of (1) to (13) above, further comprising a finely divided crystal powder having a primary crystal size falling within a range of 0.005 Fm to 0.07 m.

(15) The polishing composition as described in (14)

above, wherein the finely divided crystal powder has a mean secondary particle size falling within a range of 0.05 to 8 m.

(16) The polishing composition as described in (14) or (15) above, which contains the finely divided crystal powder in an amount falling within a range of 0. 1 to 20 mass%.

(17) The polishing composition as described in any one of (14) to (16) above, wherein the finely divided crystal powder is at least one alumina selected from the group consisting of a high-purity alumina formed through an ammonium alum method, an ammonium dawsonite method, an aluminum alkoxide method employing metallic aluminum serving as a starting material, or a spark discharge method; fumed alumina; and/or alumina formed from boehmite/pseudoboehmite/bayerite.

(18) The polishing composition as described in any one of (1) to (17) above, wherein the finely divided crystal powder is the same material as that of the abrasive grains.

(19) The polishing composition as described in any one of (1) to (18) above, which further contains a surface modification agent.

(20) The polishing composition as described in (19) above, wherein the surface modification agent is at least one species selected from among an inorganic acid containing a non-metallic element belonging to Group 5 or 6 of the periodic table, hydroxypropyl cellulose, and a hydroxyalkyl alkyl cellulose.

(21) The polishing composition as described in (19) or (20) above, wherein the surface modification agent comprises at least one species selected from among sulfamic acid, phosphoric acid, nitric acid, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, and ethyl hydroxyethyl cellulose.

(22) The polishing composition according to (20) or

(21) above, which contains the hydroxyalkyl alkyl cellulose in an amount falling within a range of 0.001 to 2 mass%.

(23) The polishing composition as described in any one of (1) to (22) above, which has a pH falling within a range of 2 to 6.

(24) A composition which forms the polishing composition as set forth in any one of (1) to (23) above by dilution.

(25) A method of using the higher-concentration composition as set forth in (24) for the purpose of transportation or storage of the polishing composition.

(26) A method for polishing a substrate, comprising polishing a substrate by means of a polishing composition as set forth in any one of (1) to (23) above.

(27) A method for producing the polishing composition as described in any one of (1) to (23) above, comprising preparing a composition having a concentration higher than that of the polishing composition, and diluting the composition prior to use for polishing.

(28) A method of producing a substrate, the method employing the method as set forth in (26) or (27) above.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic representation employed for explanation of determination of the amount of dub-off. In the figure, the mark S stands for a curve in the vicinity of the periphery of a disk, which is drawn by use of a surfcorder; h stands for a perpendicular line which is in contact with the circumferential end of a disk; A stands for a point on the curve which is 3,000 Fm from perpendicular line h; B stands for a point on the curve which is 2, 000 m from perpendicular line h; C stands for a point on a straight line passing through points A and B, which is 500 ßm from perpendicular line h; k stands for a perpendicular line passing through point C; D

stands for a point at which perpendicular line k and curve S cross; t stands for a length between point C and point D (the amount of dub-off).

MODES OF CARRYING OUT THE INVENTION The abrasive grains employed in the polishing composition of the present invention are alumina, silica, titania, zirconia, ceria, calcia, magnesia, manganese oxide, iron oxide, or a similar compound. Among them, alumina is particularly preferably used.

No particular limitation is imposed on the crystal form (e. g. , a, 0, or y) of the alumina used in the composition. However, a-alumina is preferred as base abrasive grains from the viewpoint of the high polishing rate. In addition, a dense crystal structure including few pores and a smaller primary crystal size are preferred, so long as the powder maintains polishing performance. The mean primary crystal size preferably falls within a range of 0.1 to 5 m, particularly preferably 0.1 to 0.5 ßm where both strength and density are satisfied. The mean secondary particle size falls within a range of 0.3 to 5 m, preferably 0.5 to 3 pm.

The alumina content falls within a range of 1 to 35 mass%, preferably 5 to 30 mass%.

The alumina can be produced by firing at an appropriate firing temperature a finely divided crystal powder aluminum hydroxide (gibbsite or bayerite) having a small mean particle size or firing at an appropriate firing aluminum hydroxide providing a dense crystal structure having few pores after firing (e. g. , boehmite or pseudo-boehmite). Specifically, by virtue of a less crystal water content, a fired product of boehmite-type aluminum hydroxide provides a more dense crystal structure as compared with a fired product of gibbsite- type aluminum hydroxide, thereby enhancing a polishing

rate. From an economical aspect, gibbsite-type a- alumina having a primary crystal size of 0.5 tm or less and a specific surface area (BET value) at least 6 m2/g to about 15 mug is particularly preferred.

The primary crystal size can be determined from an average value obtained through data analysis of a scanning electron microscope (SEM) photograph, and the mean second particle size can be obtained through measurement by means of a laser diffraction scattering particle size analyzer (e. g. , SHIMADZU SALD-2000J), a laser Doppler diffraction particle size analyzer (Microtrac UPA), or a similar apparatus.

The polishing composition of the present invention is characterized by containing a polishing aid. As the polishing aid, a polycarboxylic acid salt having a carboxylic group number per molecule (n) of 20 to 300 or a derivative thereof is used. The polishing aid serves as a mechanical polishing accelerator, thereby enhancing a polishing rate and preventing dub-off.

Examples of the polycarboxylic acid salt or derivative thereof serving as the polishing aid include a polyacrylic acid salt, a polymethacrylic acid salt, and derivative salts thereof. Examples of preferred alkali components for forming a polycarboxylic acid salt include ammonia and alkali metals such as sodium and potassium.

Examples of derivative salts include salts of a copolymer or an ester polymer of (meth) acrylic acid-another carboxylic acid, (meth) acrylic acid-sulfonic acid, (meth) acrylic acid-maleic acid or a similar derivative.

Examples of the derivatives mentioned in the specification include copolymers and ester polymers of acrylic acid-carboxylic acid, acrylic acid-sulfonic acid, or acrylic acid-maleic acid.

Notably, the carboxylic group number (n) is preferably 20 to 300, more preferably 60 to 120. When the carboxylic group number (n) is too small, the effects

of enhancing the polishing rate and preventing the dub- off cannot be obtained, whereas when the number (n) is excessively large, the viscosity of the polishing composition slurry increases, thereby disturbing the removal thereof, impairing performance such as increasing the dub-off.

The polishing aid promotes polishing performance of abrasive grains contained in a slurry-like polishing composition. That is, the polishing aid enhances a thread-forming property of the slurry and disperses abrasive grains in the slurry, so as to prevent coarsening of abrasive grains due to aggregation. The polishing aid regulates behavior of abrasive grains which are in direct contact with the polishing surface of a substrate, thereby promoting mechanical polishing action.

As a result, the polishing performance of abrasive grains is remarkably enhanced. In addition, the polishing aid has been confirmed not to adversely affect the quality of the polished surface. Thus, a surface of an aluminum magnetic disk substrate which is plated with, for example, Ni-P can be polished at a remarkably increased polishing rate, and a high-quality polished surface; i. e. , a surface having no surface defects and having high surface precision and reduced dub-off and waviness, can be obtained.

The polishing aid is added in an amount falling within a range of 0.01 to 5 mass%, preferably 0.1 to 3 mass%, more preferably 0.3 to 2 mass%, from the viewpoint of enhancement of the polishing rate. A too small amount and an excessive amount fail to attain the effect of the polishing aid.

In a preferred embodiment of the invention, the polishing composition may employ a finely divided crystal powder serving as auxiliary abrasive grains. The finely divided crystal powder may be formed from a material identical to or different from that of the aforementioned abrasive grains. However, the same material is more

preferred, with alumina being particularly preferred.

When alumina is employed as the finely divided crystal powder, no particular limitation is imposed on the crystal form (e.g., α, #, #). However, the alumina species which is readily crushed to form particles of a primary crystal size level is preferred for the purpose of regulating the surface roughness and surface quality in combination with the aforementioned base abrasive grains. The primary crystal size preferably falls within a range of 0.005 Fm to 0.07 µm, particularly preferably 0.01 to 0.05 Am. The crystal form is preferably a, 0, K, 6, and y, with 0, 6, and y being more particularly preferred. The specific surface area (BET value) is preferably 20 to 250 m2/g, particularly preferably 60 to 100 m2/g. The mean secondary particle size falls within a range of 0.05 to 8 µm, preferably 0.5 to 5 µm. The alumina content falls within a range of 0.1 to 20 mass%, preferably 0.5 to 10 mass%.

The primary crystal size D is determined from particle density p and specific surface area S determined by use of a BET specific surface area meter (e. g., SHIMADZU FlowSorb II), in accordance with the following equation (D [pm] = 6/(p [g/cm3] x S [m2/g])).

The mean secondary particle size can be determined through measurement by means of the aforementioned laser diffraction scattering particle size analyzer (e. g.; SHIMADZU SALD-2000J), a laser doppler diffraction particle size analyzer (Microtrac UPA), or a similar apparatus.

Combination of the finely divided crystal powder and the aforementioned abrasive grains may enhance the polishing rate. In addition, through addition of finely divided crystal powder, a high quality polished surface having a small surface roughness and few surface defects may be attained.

Examples of particularly preferred finely divided alumina crystal powders include high-purity alumina products such as UA series (product of Showa Denko K. K., obtained through ammonium alum method), Baikalox CE series, TM series (product of Taimei Chemicals Co., Ltd. , obtained through the ammonium dawsonite method), AKP series (product of Sumitomo Chemical Co. , Ltd. , obtained through the aluminum alkoxide method starting from aluminum), alumina of R, RA, RG, RK grades (product of Iwatani Kagaku, obtained through the spark discharge method); fumed alumina products such as UFA series (product of Showa Denko K. K. ) and products of Nippon Aerosil Co. , Ltd.; and derived alumina products obtained through firing boehmite-type or bayerite-type aluminum hydroxide such as products of Sasol, products of Alcoa Kasei Ltd., and versal alumina (product of UOP).

The auxiliary abrasive grains included in a slurry- like polishing composition promote polishing performance of abrasive grains. That is, by adding auxiliary abrasive grains having a fine particle size to abrasive grains, the auxiliary abrasive grains act directly on the polishing surface, thereby remarkably enhancing the polishing action. In addition, the quality of the polished surface is not adversely affected.

A conceivable action of the auxiliary abrasive grains is considered as follows. Generally, abrasive grains act on a polishing surface by means of mechanical energy provided through agitation of the abrasive grains upon polishing a substrate. Therefore, a limitation is imposed on the reduction of the diameter of the abrasive grains to a minute level. Thus, abrasive grains themselves must be relatively large in size with respect to the roughness of the polishing surface.

In contrast to abrasive grains, auxiliary abrasive grains have a remarkably small particle size. Therefore, the auxiliary abrasive grains themselves have a low kinetic energy, resulting in a small action force of

polishing. However, by virtue of their small particle radius, the auxiliary abrasive grains are considered to provide an edgy polishing action to the polishing surface.

In other words, the conceivable action may be as follows. When the finely divided crystal abrasive powder serving as auxiliary abrasive grains intervene between the polishing surface and abrasive grains, the finely divided crystal abrasive grains interact with abrasive grains. For example, the kinetic energy of abrasive grains is transferred to the finely divided crystal abrasive grains via collision with abrasive grains or pressing by abrasive grains. As a result, auxiliary abrasive grains exert mechanical energy directly to the polishing surface, thereby providing a sharp polishing action.

In order for the auxiliary abrasive grains to satisfactorily support abrasive grains, a limitation is preferably imposed on the amount of auxiliary abrasive grains intervening between the polishing surface and abrasive grains. When the auxiliary abrasive grains are present in an excessively large amount, the auxiliary abrasive grains absorb and disperse the energy of abrasive grains, causing a retardation of polishing.

Therefore, the auxiliary abrasive grains must be dispersed without causing an aggregation. In addition, an aggregation of abrasive grains with the auxiliary abrasive grains must be prevented. In order to cause dispersal of the auxiliary abrasive grains, a polishing aid is used to support polishing action of the auxiliary abrasive grains.

Among micro-ridges and micro-troughs present in the polishing surface, the micro-ridges receive the brunt of polishing action of the auxiliary abrasive grains, while the auxiliary abrasive grains are buried in the micro- troughs to cover the polishing surface. Thus, excessive polishing of the micro-troughs is prevented.

According to the polishing composition of the present invention, a surface of an aluminum magnetic disk substrate which is plated with, for example, Ni-P can be polished at a remarkably increased polishing rate, and a high-quality polished surface; i. e., a surface having no surface defects and having high surface precision and reduced dub-off and waviness, can be obtained.

The polishing accelerator (chemical polishing accelerator) employed in the polishing composition of the present invention may be an organic acid or an inorganic acid salt.

The organic acid may be at least one species selected from the group consisting of malonic acid, succinic acid, adipic acid, lactic acid, malic acid, citric acid, glycine, aspartic acid, tartaric acid, gluconic acid, heptogluconic acid, iminodiacetic acid, and fumaric acid. The inorganic acid salt may be at least one species selected from the group consisting of sodium sulfate, magnesium sulfate, nickel sulfate, aluminum sulfate, ammonium sulfate, nickel nitrate, aluminum nitrate, ammonium nitrate, ferric nitrate, aluminum chloride, and nickel sulfamate. The organic acid content or the inorganic acid salt content preferably fall. s within a range of. 0.01 to 10 mass%.

When the content is too small, the effect of the polishing accelerator is less, whereas the content is excessively large, pits and protrusions may be generated, in which case the quality of the polished surface may be deteriorated. An excessively large content may also adversely affect the quality of the polishing liquid, for example, an aggregation of alumina particles.

The aforementioned polishing accelerator may be a combination of an organic acid and an organic acid salt, a combination of an organic acid and an inorganic acid salt, or a combination of an organic acid, an organic acid salt and an inorganic acid salt.

As mentioned above, the organic acid may be at least

one species selected from the group consisting of malonic acid, succinic acid, adipic acid, lactic acid, malic acid, citric acid, glycine, aspartic acid, tartaric acid, gluconic acid, heptogluconic acid, iminodiacetic acid, and fumaric acid. The organic acid salt may be at least one species selected from the group consisting a potassium salt, a sodium salt, or an ammonium salt of the aforementioned organic acids. Also as mentioned above, the inorganic acid salt may be at least one species selected from the group consisting of sodium sulfate, magnesium sulfate, nickel sulfate, aluminum sulfate, ammonium sulfate, nickel nitrate, aluminum nitrate, ammonium nitrate, ferric nitrate, aluminum chloride, and nickel sulfamate. In any of combinations of an organic acid with an organic acid salt and/or an inorganic acid salt, the total amount thereof preferably falls within a range of 0.01 to 10 mass% based on the entire polishing composition. Among these components, the organic acid is more preferably incorporated in an amount at least 0.003 mass%. In the case of where a combination type polishing accelerator is used, when the polishing aid content is less than 0.01 mass%, the effect of the polishing accelerator is poor, whereas when the content is in excess of 10 mass%, the quality of a polishing solution may be adversely affected, for example, an excessive increase in viscosity of the solution or aggregation of alumina particles, and'the quality of the polished surface may be deteriorated through generation of pits and protrusions, which are disadvantageous. Notably, when an organic acid and an organic acid salt are used in combination, a combination of the same acid species attains more excellent polishing characteristics.

The aforementioned polishing accelerator may be a sol product derived from an aluminum salt described in JP-2002-20732 (WO02/02712). Specifically, the sol product is produced through a high shear agitation and mixing of an aqueous solution containing any one aluminum

salt hydrate or anhydrate selected from among inorganic acid aluminum salts such as aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum phosphate, and aluminum borate; and organic acid aluminum salts such as aluminum acetate, aluminum lactate, and aluminum stearate, with one species selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonia, organic amine compounds such as an alkyl amine (e. g., monomethylamine) and an alkanolamine (e. g., triethanolamine), aminocarboxylic acids such as glycine, amine chelate compounds such as iminodiacetic acid, aminocarboxylic acid chelate compounds such as ethylenediaminetetraacetic acid, aminophosphonic acid chelate compounds such as diethylenetriaminepentamethylenephosphonic acid and aminotrismethylenephosphonic acid. The sol product is formed in a chain mechanism by mixing an aluminum salt with a substance (e. g. , ammonia or amine) which readily releases a hydroxyl group upon reaction with water, a compound having a terminal hydroxyl group, or a compound having a hydroxyl group such as sodium hydroxide or potassium hydroxide.

The amount of the sol product derived from an aluminum salt falls preferably within a range of 0.01 to 5 mass% based on the entire polishing composition. When the amount is too small, the effect of the sol product is poor, whereas when the amount is excessively large, gelation may occur and surface defects such as pits and protrusions may be generated. More preferably, the amount falls within a range of 0.05 to 2 mass%.

The aforementioned polishing accelerator may be a organic phosphonic acid chelate compound described in Japanese Patent application Laid-Open (kokai) NO. 2001- 131535. Specifically, the chelate compound is at least one species selected from the group consisting of diethylenetriaminepentamethylenephosphonic acid, phosphonobutanetricarboxilic acid (hereinafter

abbreviated as PBTC), phosphonohydroxyacetic acid, hydroxyethyldimethylphosphonic acid, aminotrismethylenephosphonic acid (NTMP), hydroxyethanediphosphonic acid (HEDP), ethylenediaminetetramethylenephosphonic acid, hexamethylenediaminetetramethylenephosphonic acid, and salts thereof.

The amount of the organic phosphonic acid chelate compound preferably falls within a range of 0.01 to 5 mass% based on the entire polishing composition. When the amount is too small, the effect of polishing rate enhancement is less, whereas when the amount is excessively large, surface defects such as pits and protrusions may be generated. More preferably, the amount falls within a range of 0.05 to 2 mass%.

The polishing composition may further contain as a surface modification agent an inorganic acid containing a non-metallic element belonging to Group 5 or 6 in the periodic table. Examples of the inorganic acid containing a non-metallic element belonging to Group 5 or 6 in the periodic table include sulfamic acid, phosphoric acid, and nitric acid. Through addition of such an inorganic acid in an appropriate amount, generation of pits and protrusion is prevented, thereby enhance surface quality. The amount of the inorganic acid preferably falls within a range of 0.01 to 5 mass% based on the entire polishing composition. Both a too small amount and an excessive amount result in poor effect of the inorganic acid. An excessive amount may reduce polishing rate. More preferably, the amount falls within a range of 0.05 to 2 mass%.

As a surface modification agent (dub-off preventing agent), a hydroxyalkyl alkyl cellulose (hereinafter abbreviated as HRRC) disclosed in Pamphlet of WO 01/23485 may be used. Specifically, the hydroxyalkyl alkyl cellulose is at least one species selected from the group consisting of hydroxypropyl cellulose (HPC),

hydroxypropyl methyl cellulose (HPMC), hydroxyethyl methyl cellulose, and ethyl hydroxyethyl cellulose. The amount of the HRRC preferably falls within a range of 0.001 to 2 mass% based on the entire polishing composition. When the amount is too small, the effect of reducing the dub-off is poor, whereas when the amount is excessively large, the polishing rate may decrease. More preferably, the amount falls within a range of 0. 01 to 1 mass%.

In addition to the aforementioned additives, the polishing composition may further contains, in accordance with needs, alumina sol, a surfactant, a detergent, an anticorrosive agent, an antiseptic agent, a pH-regulator, other cellulose species, or a surface modification agent.

Notably, the aforementioned concentrations of components constituting the polishing composition of the present invention are suitable concentrations for polishing a substrate. Thus, in an alternative way, the polishing composition of the present invention is prepared at component concentrations higher than the aforementioned concentrations, and upon use, diluted so as the concentrations to fall within the aforementioned ranges. The polishing composition having a higher concentration may be preferably used for the purpose of transportation and storage.

In order to for the aforementioned characteristics to be obtained quite easily, the polishing composition preferably has a pH falling within a range of 2 to 6.

EXAMPLES The present invention will next be described in detail by way of examples, which should not be construed as limiting the invention thereto. Any modification to the examples performed without deviating the spirit of the invention described above and below falls within the technical scope of the present invention.

Each polishing composition was prepared in the

following manner, and the composition was evaluated in terms of polishing performance.

Polishing Composition I: <Preparation of polishing compositions> Aluminum hydroxide was heated at about 1, 200°C in a firing furnace under atmospheric conditions, to thereby form a-alumina. Separately, a carefully selected commercial alumina serving as a starting material was pulverized and classified in a wet manner, to thereby form an alumina base material sample having a mean secondary particle size of 0.7 m. In addition, a finely divided alumina crystal powder was prepared by calcining at an appropriate temperature high-purity alumina or aluminum hydroxide prepared through a specific method. A sol product derived from an aluminum salt was prepared by mixing the aluminum salt with a specific compound such as aqueous ammonia. In accordance with the compositional proportions shown in Tables 1 and 2, polishing composition samples were prepared by sequentially weighing, adding, and mixing the following components: water, alumina, a finely divided alumina crystal powder, a polishing accelerator such as an organic acid or an organic acid salt, a sol product derived from an aluminum salt, a chelating agent, an inorganic acid containing a Group 5 element or Group 6 element, a cellulose-based surface modification agent dissolved in water, and a polishing aid. These samples were subjected to a polishing test.

Polishing conditions, polishing characteristics, and the evaluation method are as follows.

(Polishing Conditions) An electroless-NiP-plated aluminum disk (size: 3.5 inch) was employed as a workpiece to be polished. A polishing test and evaluation of the disk were carried out under the following conditions.

Polishing test conditions

Polishing test machine; 9B double-sided polishing machine (product of System Seiko K. K.) Polishing pad; H9900S Number of revolutions of surface plate; upper surface plate 28 rpm, lower surface plate 45 rpm, Sun gear 8 rpm - Feed rate of slurry; 100 mL/min Polishing time; 5 minutes operation pressure; 80 g/cm2 (Evaluation of disk) Polishing rate; Calculated by difference in the weight before and after polishing the disk Quality of polished surface; Surface defects (pits, protrusions, and scratches) on the side and backside of each disk were observed crosswise under a microscope (product of Nikon, differential interference type, x100). Rating"good"was assigned when no defects were observed ("A" : the total number of defects is 0,"B" : the total number of defects is 1 to 5), and rating"bad (C)"was assigned when the total number of defects was six or more for both sides of five disks.

'Surface roughness: Tencor P-12 'Amount of dub-off: Determined by use of a surfcorder (model: SE-30D, product of Kosaka Kenkyujo). With reference to Fig. 1, determination of the amount of the dub-off will be described. Curve S is drawn by use of a surfcorder in the vicinity of the periphery of a polished hard disk surface, and perpendicular line h is provided at the outermost portion of the curve S. A point on the curve which is 3,000 Wm from perpendicular line h toward the center of the disk is represented by A, and a point on the curve which is 2,000 pm from perpendicular line h toward the center of the disk is represented by B. C represents a point on a straight line passing

through points A and B, and is 500 µm from perpendicular line h. Perpendicular line k passing through point C is provided. D represents a point at which perpendicular line k and curve S cross.

Length t between point C and point D was employed as the amount of dub-off.

Tables 1 and 2 show polishing test scores of the samples of the Examples of the present invention, and Table 3 shows polishing test scores of the samples of the Comparative Examples.

Table 1 (1/4) Ex. Alumina Polishing accelerator Type Primary Amount Organic acid Organic acid salt / Al sulfate Chelating crystal size Inorganic acid salt sol agent mass% Type mass% Type mass% mass% mass% µm Citric Ammonium NTMP 1 A-1 0.2 7.0 0.5 0.5 0.5 acid citrate 0.5 Citric Ammonium PBTC 2 A-1 0.2 7.0 0.5 0.5 0.5 acid citrate 0.5 Citric Ammonium HEDP 3 A-1 0.2 7.0 0.5 0.5 0.5 acid citrate 0.5 Citric Ammonium 4 A-1 0.2 7.0 0.5 0.5 0.5 - acid citrate Citric Ammonium HEDP 5 A-1 0.2 7.0 0.5 0.5 - acid citrate 0.5 Citric Ammonium PBTC 6 A-2 0.2 7.0 0.5 0.5 0.5 acid citrate 0.5 Citric Ammonium 7 A-3 3.0 7.0 0.5 0.5 0.5 - acid citrate Table 1 (2/4) Ex. Surface modification Polishing aid Evaluation of polishing agent Inorganic acid HRRC Polycarboxylic Polishing Surface Surface Dub- acid salt rate defect roughness off mass% mass% mass% Rank Å nm µm/min Phosphoric acid HPMC PCN 1 0.96 A 9.3 80 0.1 0.05 0.5 HPC PCN1 2 - 0.98 A 9.3 80 0.05 0.5 Nitric acid HPMC PAN 3 0.94 A 9.2 80 0.2 0.05 0.5 Sulfamic acid PAN1 4 - 0.95 A 9.3 100 0.2 0.5 Sulfamic acid HPMC PANE 5 0.96 A 9.4 80 0.2 0.05 0.5 Phosphoric acid HPMC PAA 6 1.04 A 9.6 80 0.1 0.05 0.5 Phosphoric acid HPMC PAN 7 0.89 A 9.5 80 0.1 0.05 0.5 Table 1 (3/4) Ex. Alumina Polishing accelerator Type Primary Amount Organic acid Organic acid salt / Al Chelating crystal size Inorganic acid salt sulfate agent sol mass% Type mass% Type mass% mass% mass% µm Citric Ammonium PBTC 8 A-1 0.2 7.0 0.5 0.5 0.5 acid citrate 0.5 Citric Ammonium NTMP 9 A-1 0.2 7.0 0.5 0.5 0.5 acid citrate 0.5 Citric Ammonium NTMP 10 A-1 0.2 7.0 0.5 0.5 0.5 acid citate 0.5 Citric Ammonium NTMP 11 A-1 0.2 7.0 0.5 0.5 0.5 acid citrate 0.5 Citric ammonium 12 A-1 0.2 7.0 0.5 0.5 - - acid citrate Malic Sodium NTMP 13 A-1 0.2 7.0 0.5 0.5 0.5 acid malate 0.5 Citric Ammonium NTMP 14 A-1 0.2 7.0 0.5 0.5 0.5 acid citrate 0.5 Table 1 (4/4) Ex. Surface modification Polishing aid Evaluation of polishing agent Inorganic acid HRRC Polycarboxylic Polishing Surface Surface Dub- acid salt rate defect roughness off mass% mass% mass% Rank Å nm µm/min PAN 8 - - 0.90 B 9.4 100 0.1 HPMC PAN 9 - 0.99 B 9.2 80 0.05 1.0 Phosphoric acid HPMC PAN 10 1.01 A 9.4 80 0.1 0.05 4.0 Phosphoric acid PAA 11 - 1.03 A 9.3 110 0.1 0.5 Phosphoric acid HEMC PAN 12 0.99 A 9.2 80 0.1 0.05 0.5 Phosphoric acid HPMC PAN 13 0.90 A 9.4 80 0.1 0.05 0.5 PAN 14 - - 1.04 B 9.3 110 0.5

In Tables 1 and 2, A-1 and A-3 represent gibbsite- derived a-alumina, and A-2 represents boehmite-derived a-alumina. With regard to polishing aids, PCN represents sodium polycarboxylate (number of carboxyl groups n = about 100). PCN1 represents sodium polycarboxylate (number of carboxyl groups n = about 60).

PAN represents sodium polyacrylate (carboxyl group n = about 100). PAN1 represents sodium polyacrylate (number of carboxyl groups n = about 60). PANE represents sodium polyacrylate ester (number of carboxyl groups n = about 100). PAA represents ammonium polyacrylate (number of carboxyl groups n = about 100).

Table 2 (1/2) Comp. Alumina Polishing accelerator Ex. Type Primary Amount Organic acid Organic acid salt / Al sulfate Chelating crystal size Inorganic acid salt sol agent mass% Type mass% Type mass% mass% mass% µm Citric Al sulfate NTMP 1 A-1 0.2 7.0 0.5 Ammonium citrate 0.5 acid 0.5 0.5 Citric Al sulfate NTMP 2 A-1 0.2 7.0 0.5 Ammonium ditrate 0.5 acid 0.5 0.5 Citric Al sulfate NTMP 3 A-1 0.2 7.0 0.5 Ammonium citrate 0.5 acid 0.5 0.5 Boehmite 4 A-1 0.2 7.0 - - Ammonium acetate 1.0 - 3.0 Citric Al sulfate PBTC 5 A-2 0.2 7.0 0.5 Ammonium citrate 0.5 acid 0.5 0.5 Citric al sulfate 6 A-3 3.0 7.0 0.5 Ammonium citrate 0.5 0.5 acid 0.5 Citric Al sulfate HEDP 7 A-1 0.2 7.0 0.5 ammonium citrate 0.5 acid 0.5 0.5 Citric Al sulfate 8 A-1 0.2 7.0 0.5 ammonium citrate 0.5 - acid 0.5 Malic NTMP 9 A-1 0.2 7.0 0.5 Sodium Malate 0.5 0.5 acid 0.5 Citric NTMP 10 A-1 0.2 7.0 0.5 Ammonium citrate 0.5 0.5 acid 0.5 Table 2 (2/2) Comp. Surface modification Polishing aid Evaluation of polishing Ex. agent Inorganic acid HRRC Polycarboxylic Polishing Surface Surface Dub- acid salt rate defect roughness off mass% mass% mass% Rank Å nm µm/min Phosphoric acid HPMC PAN2 1 0.74 B 9.9 120 0.1 0.05 0.5 Phosphoric acid 2 0.05 - 0.74 B 9.8 120 0.1 Phosphoric acid PAN3 3 0.05 0.73 B 9.9 120 0.1 0.5 4 - - - 0.74 C 9.7 200 Phosphoric acid HPMC 5 - 0.84 C 9.8 110 0.1 0.05 Phosphoric acid 6 0.05 - 0.66 B 9.9 110 0.1 sulfamic acid HPMC 7 - 0.78 B 9.7 120 0.2 0.05 Sulfamic acid 8 - - 0.67 B 10.0 170 0.2 Phosphoric acid HPMC 9 - 0.65 B 10.3 120 0.1 0.05 10 - - - 0.79 C 10.0 190

In Table 3, similar to Table 1, A-1 and A-3 represent gibbsite-derived a-alumina. A-2 represents boehmite-derived a-alumina. Regarding polishing aids, PAN2 represents sodium polyacrylate (number of carboxyl groups n = about 500), and PAN3 represents sodium polyacrylate (number of carboxyl groups n = about 10).

The above Table 1 shows test results of Examples 1 to 14, wherein polishing compositions falling within the scope of the present invention. As is clear from Table 1, all these samples provide polished surfaces of excellent surface morphology in terms of surface defects, surface roughness, dub-off, etc. , and provide a remarkably enhanced polishing rate. In contrast, as shown in Table 2, all the samples of Comparative Examples 1 to 10 containing no such polishing aid described in the attached claims exhibit poor polishing rate and inferior surface morphology.

Polishing Composition II: <Preparation of polishing compositions Aluminum hydroxide was heated at about 1, 200°C in a firing furnace under atmospheric conditions, to thereby form a-alumina. Separately, a carefully selected commercial alumina serving as a starting material was pulverized and classified in a wet manner, to thereby form an alumina base material sample having a mean secondary particle size of 0.7 m. In addition, a finely divided alumina crystal powder was prepared by calcining at an appropriate temperature high-purity alumina or aluminum hydroxide prepared through a specific method. A sol product derived from an aluminum salt was prepared by mixing the aluminum salt with a specific compound such as aqueous ammonia. In accordance with the compositional proportions shown in Tables 1 to 3, polishing composition samples were prepared by sequentially weighing, adding, and mixing the following components: water, alumina, a finely divided alumina crystal powder, a polishing

accelerator such as an organic acid or an organic acid salt, a sol product derived from an aluminum salt, a chelating agent, an inorganic acid containing an element of Group 5 or 6 in the periodic table, a cellulose-based surface modification agent dissolved in water, and a polishing aid. These samples were subjected to a polishing test.

Polishing conditions, polishing characteristics, and the evaluation method are the same as those for Polishing Composition I.

Tables 3 and 4 show polishing test scores of the samples of the Examples 21 to 35 of the present invention, and Table 2 shows polishing test scores of the samples of the Comparative Examples 11 to 16.

Table 3 (1/2) Ex. Alumina /Finely divided Polishing accelerator alumina crystals Type Primary Amount Organic acid Organic acid salt / Al sulfate Chelating crystal size Inorganic acid salt sol agent mass% Type mass% Type mass% mass% mass% µm A-1 / 6.0 / Citric NTMP 21 0.2 / 0.01 0.5 Ammonium citrate 0.5 0.5 UAγ 1.0 acid 0.5 A-1 / 6.0 / Citric NTMP 22 0.2 / 0.01 0.5 Ammonium citrate 0.5 0.5 UAγ 1.0 acid 0.5 A-1 / 6.0 / Citric NTMP 23 0.2 / 0.01 0.5 Ammonium citrate 0.5 0.5 UAγ acid 0.5 A-1 / 6.0 / Citric NTMP 24 0.2 / 0.01 0.5 Ammonium citrate 0.5 0.5 UAγ 1.0 acid 0.5 A-1 / 6.0 / Citric NTMP 25 0.2 / 0.01 0.5 Ammonium citrate 0.5 0.5 UAγ 1.0 acid 0.5 A-1 / 6.0 / Citric NTMP 26 0.2 / 0.01 0.5 Ammonium citrate 0.5 0.5 UAγ 1.0 acid 0.5 A-2 / 6.0 / Citric NTMP 27 0.2 / 0.03 0.5 Ammonium citrate 0.5 0.5 UAγ 1.0 acid 0.5 A-1 / 6.0 / Citric NTMP 28 0.2 / 0.07 0.5 Ammonium citrate 0.5 0.5 UAα 1.0 acid 0.5 Table 3 (2/2) Ex Surface modification Surfactant Evaluation of polishing agent Inorganic acid HRRC Polycarboxylic Polishing surface Surface Dub- acid salt rate defect roughness off mass% mass% mass% Rank Å nm µm/min Phosphoric acid HPMC PCN 21 1.12 A 9.0 80 0.1 0.05 0.5 Phosphoric acid HPMC PCN1 22 1.04 A 9.1 70 0.1 0.05 0.5 Phosphoric acid HPMC PAN 23 1.04 A 9.0 70 0.1 0.05 0.5 Phosphoric acid HPMC PAN1 24 1.02 A 9.3 70 0.1 0.05 0.5 Phosphoric acid HPMC PANE 25 1.10 A 9.1 70 0.1 0.05 0.5 Phosphoric acid HPMC PAA 26 1.08 A 9.0 70 0.1 0.05 0.5 Phosphoric acid HPMC PCN 27 1.14 A 9.5 70 0.1 0.05 0.5 Phosphoric acid HPMC PCN 28 0.99 A 9.1 80 0.1 0.05 0.5 Table 4 (1/2) Ex. Alumina /Finely divided Polishing accelerator alumina crystals Type Primary Amount Organic acid Organic acid salt / Al sulfate Chelating crystal size Inorganic acid salt sol agent mass% Type mass% Type mass% mass% mass% µm A-1 / 6.0 / Citric NTMP 29 0.2 / 0.03 0.5 Ammonium citrate 0.5 0.5 CRγ 1.0 acid 0.5 A-1 / 6.0 / Citric NTMP 30 0.2 / 0.03 0.5 Ammonium citrate 0.5 0.5 UFAγ 1.0 acid 0.5 A-1 / 6.0 / Citric NTMP 31 0.2 / 0.03 0.5 Ammonium citrate 0.5 0.5 AKPγ 1.0 acid 0.5 A-1 / 6.0 / Citric NTMP 32 0.2 / 0.05 0.5 Ammonium citrate 0.5 0.5 RGγ 1.0 acid 0.5 A-1 / 6.0 / Citric NTMP 33 0.2 / 0.05 0.5 Ammonium citrate 0.5 0.5 A-2γ 1.0 acid 0.5 A-1 / 6.0 / Citric NTMP 34 0.2 / 0.07 0.5 Ammonium citrate 0.5 0.5 A-1# 1.0 acid 0.5 A-1 / 6.0 / Citric NTMP 35 0.2 / 0.01 0.5 Ammonium citrate 0.5 0.5 UAγ 1.0 acid 0.5 Table 4 (2/2) Ex. Surface modification Surfactant Evaluation of polishing agent Inorganic acid HRRC Polycarboxylic Polishing Surface Surface Dub- acid salt rate defect roughness off mass% mass% mass% Rank Å nm µm/min Phosphoric acid HPMC PCN 29 1.00 A 9.2 70 0.1 0.05 0.5 Phosphoric acid HPMC PCN 30 1.12 A 9.0 80 0.1 0.05 0.5 Phosphoric acid HPMC PCN 31 1.11 A 9.0 70 0.1 0.05 0.5 Phosphoric acid HPMC PCN 32 1.11 A 9.0 70 0.1 0.05 0.5 Phosphoric acid HPMC PCN 33 1.11 A 9.0 80 0.1 0.05 0.5 Phosphoric acid HPMC PCN 34 1.08 A 9.1 70 0.1 0.05 0.5 PCN 35 - - 1.11 B 9.0 120 0.5

In Tables 3 and 4, A-1 represents gibbsite-derived a-alumina, and A-2 represents boehmite-derived a- alumina. UAy and Usa represent y-alumina and a-alumina, respectively, produced through the ammonium alum method (products of Showa Denko K. K.). CRy represents y- alumina produced through the same method (product of Baikowski). UFA represents fumed y-alumina (product of Showa Denko K. K.). AKPy represents y-alumina produced through the aluminum alkoxide method (product of Sumitomo Chemical Co. , Ltd.). RGy represents y-alumina produced through the spark discharge method (Iwatani Kagaku). A- 2y represents y-alumina produced by firing boehmite, and A-l6y represents Oy-alumina produced by firing gibbsite.

With regard to polishing aids, PCN represents sodium polycarboxylate (number of carboxyl groups n = about 100). PCN1 represents sodium polycarboxylate (number of carboxyl groups n = about 60). PAN represents sodium polyacrylate (number of carboxyl groups n = about 100).

PAN1 represents sodium polyacrylate (number of carboxyl groups n = about 60). PANE represents sodium polyacrylate ester (number of carboxyl groups n = about 100). PAA represents ammonium polyacrylate (number of carboxyl groups n = about 100).

Table 5 (1/2) Comp. Alumina / Coarse alumina Polishing accelerator Ex. crystals Type Primary Amount Organic acid Organic acid slat / Al sulfate Chelating crystal size Inorganic acid salt sol agent mass% Organic mass% Type mass% mass% mass% µm acid Citric Ammonium NTMP 11 A-1 0.2 7.0 0.5 0.5 0.5 acid citrate 0.5 Citric ammonium NTMP 12 A-1 0.2 7.0 0.5 0.5 0.5 acid citrate 0.5 Citric Ammonium NTMP 13 A-2 0.2 7.0 0.5 0.5 0.5 acid citrate 0.5 Citric Ammonium NTMP 14 A-3 3.0 7.0 0.5 0.5 0.5 acid acetate 0.5 A-1 / 6.0 / Citric Ammonium NTMP 15 0.2 / 3.0 0.5 0.5 0.5 A-3 1.0 acid citrate 0.5 Citric Ammonium NTMP 16 A-1 0.2 7.0 0.5 0.5 0.5 acid citrate 0.5 Table 5 (2/2) Comp. Surface modification Surfactant Evaluation of polishing Ex. agent Inorganic acid HRRC Polycarboxylic Polishing Surface Surface Dub- acid salt rate defect roughness off mass% mass% mass% Rank Å nm µm/min Phosphoric HPMC 11 acid - 0.75 B 9.9 110 0.05 0.1 Phosphoric HPMC PAN2 12 acid 0.67 B 9.9 120 0.05 0.5 0.1 Phosphoric HPMC 13 acid - 0.85 B 9.8 110 0.05 0.1 Phosphoric HPMC 14 acid - 0.67 B 9.9 110 0.05 0.1 Phosphoric HPMC 15 acid - 0.63 C 12.3 110 0.05 0.1 16 - - - 0.78 C 10.0 190

In Table 5, similar to Table 1, A-1 and A-3 represent gibbsite-derived a-alumina. A-2 represents boehmite-derived a-alumina. Regarding polishing aids, PAN2 represents sodium polyacrylate (number of carboxyl groups n = about 500).

The above Tables 3 and 4 show the test results of Examples 21 to 35, wherein polishing compositions falling within the scope of the present invention. As is clear from the Tables, all these samples provide polished surfaces of excellent surface morphology in terms of surface defects, surface roughness, dub-off, etc. , and provide a remarkably enhanced polishing rate. In contrast, as shown in Table 3, all the samples of Comparative Examples 11 to 16 containing no finely divided crystal powder and a polishing aid exhibit poor polishing rate and inferior surface morphology.

INDUSTRIAL APPLICABILITY The polishing composition of the present invention, having the aforementioned constitution, attains high polishing rate and provides high-quality mirror-finished surface without forming surface defects. Thus, the composition is remarkably useful.