GB2421955A

GB2421955A - Polishing composition for glass substrate

Info

Publication number: GB2421955A
Application number: GB0525057A
Authority: GB
Inventors: Kazuhiko Nishimoto
Original assignee: Kao Corp
Current assignee: Kao Corp
Priority date: 2004-12-13
Filing date: 2005-12-08
Publication date: 2006-07-12
Anticipated expiration: 2025-12-08
Also published as: JP2006167817A; CN1789366A; GB2421955B; GB0525057D0; MY143652A; JP4667848B2; CN101892032A

Abstract

The present invention provides a polishing composition for a glass substrate, containing a silica having an average particle size of primary particles of from 1 to 100 nm, a polymer having a sulfonic acid group, and water; a process for manufacturing a glass substrate with the polishing composition for a glass substrate; and a process for reducing surface stains of a glass substrate with the polishing composition for a glass substrate. The polishing composition for a glass substrate can be suitably used in the manufacture of, for example, glass hard disks, aluminosilicate glass for reinforced glass substrates, and glass ceramic substrate (crystallized glass substrate), and the like. The polymer may be an acrylic acid/sulfonic acid copolymer, and the silica may be a colloidal silica.

Description

POLISHING COMPOSIflON FOR GLASS SUBSTRATE

FIELD OF TEE INVENTION

The present invention relates to a polishing composition for a glass S substrate, a process for manufacturing a glass substrate with the polishing composition for a glass substrate, and a process for reducing surface stains of a glass substrate with the polishing composition for a glass substrate.

BACKGROUND OF THE INVENTION

Conventionally, in the fields of semiconductor devices and magnetic disk recording devices, various polishing compositions have been studied in order to manufacture a subsiraLe having excellent surface qualities inexpensively, In the polishing composition mentioned above, for example, alumina abrasive grains having average particle sizes around 1 un have been well used as an abrasive from the viewpoint of polishing rate and surface smoothness (JP2001-64631 A etc.).

However, in recent years, abrasive grains used in a polishing composition are even more reduced in particle sizes, from the viewpoint of being capable of realizing higher density, obtaining excellent surface qualities and the like. With the development of size reduction in abrasive grains, abrasive grains and polishing debris are more likely to remain on a substrate after polishing, and the substrate is lcss likely to be easily cleaned.

In the step of removing the abrasive grains and polishing debris remaining on the substrate, a scrub-cleaning including the step of rubbing the substrate with a pad made of a polyvinyl alcohol or the like together with a detergent or pure water is generally employed.

However, a substrate made of a brittle material as represented by a glass substrate has a poor impact resistance. Therefore, when the substrate made of the material is subjected to a scrub-cleaning, there is a risk that new damages are generated on the substrate surface, so that there is a possibility that a critical problem in quality such as defects and breakage is likely to be caused.

Therefore, as a cleaning process for a glass substrate, a cleaning process including the step of dissolving away the remaining abrasive grains and polishing debris is generally employed. Specifically, a process includes the steps of dissolving a part of the surface of abrasive grains and polishing debris with an aqueous strongly alkaline solution, such as an aqueous NaOR, simultaneously applying ultrasonication thereto, thereby releasing the abrasive grains and polishing debris from a substrate, subjecting the substrate obtained to ultrasonic immersion and rinsing with pure water, rcmoving water with isopropanol or the like, and steam-drying with isopropanol or the like (JP2003-173518 etc.). In this process, when the alkaline cleaning conditions after polishing are fortified in order to improve the lowered yield caused by substrate stains, for example, a degree of alkalinity is fortified, ultrasonic energy is strengthened (low frequency), the irradiation time period of ultrasonication is extended, or the like, disadvantages such as dent portion defects, dissolution and cracks are likely to be generated on the substrate.

Even more, a silica is used as abrasive grains for a finish-polishing from the viewpoint of high level of smoothening of the substrate surface, and has a similar Composition to a material of a glass substrate to be polished. Therefore, the silica abrasive grains are more likely to remain on the substrate because of the high affinity to the substrate and the finer sizes, whereby a disadvantage that the abrasive grains and polishing debris are less likely to be cleaned off becomes remarkable.

Therefore, a sufficient reduction in substrate stains even under ordinary cleaning conditions with a very few damages on a glass substrate leads to an improvement in yield, which is technologically significant.

SUMMARY OF THE INVENTION

The present invention relates to 111 a polishing composition for a glass substrate, containing a silica having an average particle size of primary particles of from 1 to 100 nm, a polymer having a sulfonic acid group, and water; [21 a process for manUfacturing a glass substrate, including the step of polishing a substrate to be polished with a polishing load of from 3 to 12 kPa and with the polishing composition as defined in the above (1] present between a polishing pad and the substrate; and (3] a process for reducing surface stains of a glass substrate, including the step of polishing a substrate to be polished with a polishing load of from 3 to 12 kPa and with the polishing composition as defined in the above [1] present between a polishing pad and the substrate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a polishing composition for a glass substrate giving a very few substrate stains after cleaning, high polishing rate and excellent surface smoothness, a process for manufacturing a glass substrate with the polishing composition for a glass substrate, and a process for reducing surface stains of a glass substrate with the polishing composition for a glass substrate.

Since the substrate is manufactured with the polishing composition for a glass substrate of the present invention, or by using the process for manufacturing a glass substrate of the present invention, a very few abrasive grains and polishing debris remain after polishing and can be more easily removed, so that the substrate after usual cleaning has a very few substrate stains.

Also, the substrate as described above is manufactured at a high polishing rate and has an excellent surface smoothness, The polishing composition of the present invention, the process for manufacturing a glass substrate or the process for reducing surface stains of a glass substrate of the present invention gives a substrate having an excellent surface smoothness, and the yield can be significantly improved.

These and other advantages of the present invention will be apparent from

the following description.

(1) Polishing Composition for Glass Substrate One of the great features of the polishing composition for a glass substrate of the present invention, as mentioned above, resides in that the polishing composition contains a silica having an average particle size of primary particles of from 1 to 100 urn, a polymer having a sulfonic acid group, and water. With this feature, an effect that a glass substrate having an excellent surface smoothness is obtained with a very few substrate stains after polishing at a high polishing rate is exhibited.

The silica to be used in the present invention includes, for example, colloidal silica, fumed silica, and the like.

The colloidal silica is obtained by a water glass method in which an alkali metal silicate such as sodium silicate used as a raw material is subjected to a condensation reaction in an aqueous solution to allow particles to grow, or an alkoxysilane method in which an alkoxysilane such as tetraethoxysilane used as a raw material is subjected to a condensation reaction in water containing a water-soluble organic solvent such as an alcohol to allow particles to grow.

The fumed silica is obtained by a vapor phase method in which a volatile silicon compound such as silicon tetrachloride used as a raw material is hydrolyzed at a high temperature of 1000 C or higher with an oxygenhydrogen burner to allow particles to grow.

In addition, as the silica, those subjected to surface modification with a functional group, those formed into a composite particle with a surfactant or other particles, and the like can be used.

Among them, the colloidal silica is preferable from the viewpoint of reducing surface roughness and scratches on a substrate surface. These silicas can be used alone or in admixture of two or more kinds.

The silica has an average particle size of prinuuy particles of from 1 to 100 nni. The average particle size is preferably from 1 to 80 nm, more preferably from 3 to 60 nm, and even more preferably from 5 to 40 nm, from the viewpoint of reducing scratches and from the viewpoint of reducing surface roughness (average roughness: Ra).

Here, the method for determining a particle size of primary particles includes a method of determining from an image observed by a transmission electron microscope (TEM), a titration method, a BET method or the like. The average particle size can be calculated as an average of the particle sizes determined in each of the methods.

For example, the photographs of the silica particles observed by a transmission electron microscope "JEM-2000 FX" commercially available from JEOL LTD. at an acceleration voltage of 80 kV and a magnification of 10000 to 50000 are incorporated into a personal computer as image data with a scanner connected thereto. The circular diameter (diameter of a circle having the same area as a projected area of the silica particles) of each silica particle is determined using an image analysis software "W1nROOF' (commercially available from MITANI CORPORATION), and considered as a diameter of the silica particles. After analyzing data for 1000 or more silica particles, the volume of the silica particles are calculated from the diameters of the silica particles based on the analyzed data using a spreadsheet software "EXCEL" (commercially available front Microsoft Corporation). The particle size at 50% counted from a smaller particle size side of the primary particles in a cumulative particle size distribution on the volume basis (1)50) is the average particle size of the primary particles as referred to herein.

In the case where secondary particles of the silica are formed, the aiierage particle size of the secondary particles is preferably from 5 to 150 nm, more preferably from 5 to 100 nm, and even more preferably from 5 to 80 nm, from the viewpoint of reducing scratches and from the viewpoint of reducing the surface roughness (average roughness: Ra).

The method for determining the particle size of secondary particles includes a dynamic light scattering method, an ultrasonic attenuation method, a capillary hydrodynamic fractionation (CHDF) method and the like.

The silica is contained in an amount of preferably from 1 to 50% by weight, more preferably from 2 to 44% by weight, even more preferably from 3 to 30% by weight, and even more preferably from 5 to 25% by weight, of the polishing composition, from the viewpoint of increasing the polishing rate and economically advantageously improving the surface quality.

The polymer having a sulfonic acid group, as used in the present invention, refers to a polymer containing one or more monomers having a suifonic acid group (hereinafter also referred to as "sulfonic acid" or "sulfonic acid group- containing monomer") as a monomer component. The monomer having a sulfonic acid group includes, fox example, isoprenesulfonic acid, (meth)acry1amide-2-methy1propanonic acid, styrenesulfonic acid, methallylsulfonic acid, vinylsulfonic acid, allylsulfonic acid, isoamylenesulfonic acid, and the like. Among them, isoprenesulfonic acid and (mcth) acrylamide-2- methylpropanesulfonic acid are preferable.

These monomers having a sulfonic acid group can be used alone or in admixture of two or more kinds.

The polymer having a sulfonic acid group used in the present invention may be a hoinopolymer of a monomer componcnt having a sulfomc acid group, or a copolyiner further containing a monomer component of another mondmer.

The monomer component of the other monomer is preferably a monomer having a carboxyl group. The monomer having a carboxyl group includes, for example, itaconic acid, (meth)acry]ic acid, maleic acid, and the like. Among them, acrylic acid is preferable, i.e. an acrylic acid/sutfonic acid copolymer is preferable, from the viewpoint of increasing the polishing rate and reducing substrate stains.

In the present invention, although not wanting to be limited by theory, the substrate stains can be suppressed as follows. The carboxyl group in the acrylic acid monomer constituting the above-mentioned acrylic acid/sulfonic acid copolymer adsorbs to the abrasive grains or polishing debris that causes substrate stains, and the sulfonic acid group in the sulfonic acid group-containing monomer disperses the absorbed substances. When the proportion of the sulfonic acid group-containing monomer in the monomers constituting the copolymer is lowered, i.e. when the acrylic acid monomer is contained in a larger proportion, the copolymer itself is more likely to be absorbed to the substrate, so that the polishing rate is likely to be suppressed. Therefore, the proportion of the sulfonic acid-containing monomer of the monomers constituting the copolymer is preferably 3% by mol or more, and more preferably 5% by mol or more; In addition, when the proportion of the sulfonic acid group-containing monomer is higher, i.e. the acrylic acid monomer is contained in a lower proportion, the copolymer is less likely to be absorbed to abrasive grains or polishing debris.

Therefore, the proportion of the sulfonic acid-containing monomer of the monomers constituting the copolymer is preferably 90% by mol or less, more preferably 80% by mol or less, and even more preferably 70% by mol or less. In other words, the proportion is preferably from 3to 90% by mol, more preferably from 5 to 80% by mol, and even more preferably from S to 70% by mol. 1-lere, the acrylic acid group containing a sulfonic acid group is counted as a su1fmic acid group-containing monomer.

The above-mentioned polymer having a sulfonic acid group is preferably water soluble, which may be, for example, in the form of a salt, in order to use the polymer as a constituent of the polishing composition.

I

The counterion for forming a salt is not particularly limited, and one or more members selected from alkali metal ions such as sodium ion and potassium ion, ammonium ion, alkylaminonium ions and the like can be used.

The polymer having a sulfonic acid gioup used in the present invention is obtained by, for example, sulfonating a base polymer containing a diene structure or an aromatic structure according to a known method, for example, a method described in Shin-Jikken Kagaku Koza (Lectures on New Experimental Chemisty) 14 (Yukikagobutsuno Goseito Ifanno (Synthesis and Reaction of Organic Compounds) IU, p.1773, 1978), Edited by Shadanhojin Nippon Kagakukai," or the like.

The poJymer having a suifonic acid group has a weight-average molecular weight of preferably from 1,000 to 10,000, more preferably from 1,000 to 5,000, even more preferably from 1,000 to 4,500, and even more preferably from 1,000 to 4,000, from the viewpoint of giving an effect of dispersing silica and polishing debris, and increasing the polishing rate.

The weight-average molecular weight of the polymer having a sulfonic acid group is determined based on a calculation of the determination results by gel permeation chromatography (OPC) using a calibration curve drawn with sodium polystyrenesulfonate as a standard sample. The GPC conditions are as follows.

(GPC Conditions] Column: G4000PWXL + (J2500PWXL Eluent: 0.2 M Phosphate buffer/acetonitrile = 9/1 (volume ratio) Flow rate: 1.0 mL/min Temperature: 40 C Sample: concentration 5 mgfmL, amount of injection 100 iL The polymer having a sulfonic acid group is contained in an amount of preferably 0.001 % by weight or more, and more preferably 0.01% by weight or S more, of the polishing composition, from the viewpoint of reducing the substrate stains, In addition, the polymer is contained in an amount of preferably 10% by weight or less, more preferably 5% by weight or less, even more preferably 3% by weight or less, even more preferably 1% by weight or less, and even more preferably 0.5% by weight or less, of the polishing composition, from the viewpoint of increasing the polishing rate.

In other words, the polymer is contained in an amount of preferably from 0.001 to 10% by weight, more preferably from 0.01 to 5% by weight, even more preferably from 0.01 to 3% by weight, even more preferably from 0.01 to 1% by weight, and even more preferably from 0.01 to 0.5% by weight, of the polishing composition, from the viewpoint of reducing the substrate stains and increasing the polishing rate.

Also, as to the relationship of the formulation amounts of the silica and the polymer in the present invention, a concentration ratio of the silica to the polymer in the polishing composition, i.e. the concentration of the silica (% by weight)/concentration of the polymer (% by weight), is preferably from 10 to 5000, more preferably from 2010 3000, even more preferably from 30 to 2000, and even more preferably from 50 to 1000, from the viewpoint of increasing the polishing rate and reducing substrate stains.

As the water used in the present invention, ion-exchanged water, distilled water, ultrapure water or the like can be favorably used. The water is contained in an amount of preferably from 40 to 99% by weight, more preferably from 50 to 98% by weight, even more preferably from 50 to 97 96 by weight, and even more preferably from 50 to 95% by weight, from the viewpoint of maintaining fluidity of the polishing composition and increasing the polishing rate.

The material for a glass substrate that is subject for polishing in the present invention includes, for example, quartz glass, soda-lime glass, aluminosilicate glass, borosilicate glass, aluminoborosilicate glass, nonalkaline glass, crystallized glass and the like.

Since the pblishing composition of the present invention used in the step of polishing a glass substrate can realize an economically advantageous polishing rate, give excellent surface smoothness to a substrate after polishing, and remarkably reduce substrate stains after cleaning, a highquality glass substrate having excellent surface properties can be manufactured.

The substrate stains are important properties in the advancement of higher density especially in a hard disk substrate.

The substrate stains are caused by the abrasive grains in the polishing composition and polishing debris, remaining on the substrate surface. The substrate stains can be usually observed with an optical microscope or an atomic force microscope, and can be quantitatively evaluated by the number detected as projection portion defects in the defect detection apparatus used in the quality inspection.

Although not wanting to be limited by theory, the mechanism for reducing substrate stains is not elucidated, but is presumably as follows. As mentioned above, a steric effect caused by adsorption of the polymer having a sulfonic acid group contained in the polishing composition on the surface of abrasive grains and polishing debris leads to suppression of the deposition or remaining on the substrate after polishing and alter cleaning.

The polishing composition of the present invention can be prepared by mixing each of the components by a known method. The polishing composition is usually prepared as a concentrate and diluted upon use in many cases, from the viewpoint of economic advantages.

The polishing composition of the present invention may contain an optional component such as an inorganic acid, an organic phosphonic acid, a carboxylic acid, an aminocarboxylic acid, or a salt thereof.

Also, the counterion (cation) of the above-mentioned salt includes alkali metal ions such as sodium ion and potassium ion, ammonium ion, alkylammonium ions, and the like. Among them, the alkali metal ions are preferable.

Also, other optional components include thickeners, dispersing agents, basic substances, surfactanis, chelating agents, defoaming agents, antibacterial agents, anticorrosive agents and the like.

These optional components are contained in an amount of preferably 5% by weight or less, more preferably 4% by weight or less, and even more preferably 3% by weight or less, of the polishing compos,tion, from the viewpoint of increasing the polishing rate.

Here, the concentration of each of the components may be any of the concentration during the preparation and the concentration upon use.

(2) Process for Manufacturing Glass Substrate The process for manufacturing a glass substrate of the present invention includes the step of polishing a substrate to be polished with a polishing load of from 3 to 12 kPa and with the polishing composition as defined above present between a polishing pad and the substrate.

The polishing load is3 k.Pa or more, preferably 4 kPa or more, more preferably 5 kra or more, and even more preferably 6 kPa or more, from the viewpoint of increasing the polishing rate, thereby polishing the substrate economically advantageously. Also, the polishing load is 12 kPa or less, preferably 11 kPa or less, more preferably 10 kPa or less, and even more preferably 9 kPa or less, from the viewpoint of improving the surface quality and relaxing the stress remaining on the substrate surface. Therefore, the polishing load is from 3 to 12 kPa, preferably from 4 to 11 kPa, more preferably from 5 to kra, and even more preferably from 6 to 9 kPa, from the viewpoint of increasing the polishing rate and improving the surface quality.

The preferred feeding rate of the polishing composition cannot be generally determined because the feeding rate would differ depending upon the area of the polishing pad contacting the substrate to be polished and the total area of the substrate introduced, and further upon the kinds of the polishing composition. The feeding rate is preferably from 0.06 to 5 mLfmin, more preferably from 0.08 to 4 mI/mm, and even more preferably from 0.1 to 3 mL'min per unit area (1 cm2) of the substrate to be polished, from the viewpoint of increasing the polishing rate and polishing the substrate economically advantageously.

In a case where the substrate to be polished is, for example, a glass hard disk substrate, the substrate is manufactured through the steps of subjecting a glass substrate obtained by a die press of a molten glass, or a method of cutting out the substrate from a sheet glass to a rough grinding step, optionally a crystalliiing step, a shaping step, an edgefinishing step, a precision-grinding step, a polishing step, a cleaning step, optionally chemical reinforcement step, and a magnetic disk manufacturing step.

For example, alumina abrasive grains of #400 or so are used in the rough grinding step, a cylindrical grinding stone is used in the shaping step, a brush is used in the shoulder mirror-finishing step, and alumina abrasive grains of #1000 orso are used in the precision-grinding step.

The polishing step can be divided into a first polishing step and a second polishing step, and further a final (finish) polishing step may be carried out, for example, for the purpose of improving the surface quality in many cases.

Cerium oxide is preferably used in the first polishing step, and the silica is preferably used in the final (finish) polishing step. It is preferable that the polishing composition of the present invention is used in the second polishing step or the final (finish) polishing step.

After the polishing step, in order to dissolve away the silica abrasive grains and polishing debris remaining on a glass substrate surface, the substrate is subjected to a strongly alkali ultrasonication cleaning with an aqueous NaOR, and subsequently subjected to dip cleaning with ultrapure water, isopropanol or the like, and steam-drying with isopropanol or the like.

Thereafter, a seed layer, an undercoat layer, an intermediate layer, a magnetic layer, a protective layer, and a lubricating layer are each formed into a film, to give a magnetic disk.

In the course of the manufacturing steps, a crystallization step in which a crystal core is formed by a heat treatment to form a crystalline phase may be carried out in the case of a crystallized glass substrate, and a chemical reinforcement step in which a substrate is subjected to a dip treatment in a heated chemically reinforced salt such as potassium nitrate and sodium nitrate may be carried out to substitute the ions in the surface layer therewith in the case of a reinforced glass substrate.

As to the glass hard disk substrate, smoothness that docs not generate any read-write errors in the magnetic head is requireci. In other words, the substrate surface is desired to be excellent from the viewpoint of planarization (roughness, waviness and the like) and defects (projection portions such as abrasive grains, and dens portions such as scratches and pits). Among the steps for manufacturing a substrate, the polishing step plays a role for giving such excellent properties, and especially the second polishing step or the final (finish) polishing step is important.

(3) Polishing Process The polishing machine for a glass substrate using the polishing composition of the present invention is not particularly limited, and a polishing machine comprising a jig (carrier, made of aramide or the like) for holding an object to be polished and a polishing pad can be used. Among them, a dotble- sided polishing machine that is usable in the polishing step is suitably used.

As to the polishing pad, a polishing pad made of an organic polymer- based foamed article, a non-foamed article, or a nonwoven fabric can be used.

For example, a sueded rigid pad made of urethane is suitably used in the first polishing step, and a sueded soft pad made of urethane is suitably used in the second polishing Step and the final polishing step.

Specific examples of the polishing process using the polishing machine include the polishing process including the steps of putting an object to be polished held with a carrier between polishing platens to which a polishing pad is attached, feeding the polishing composition of the present invention between the polishing pad and the object to be polished, and moving the polishing platens and/or the object to be polished, while appLying a given pressure, thereby polishing the object to be polished while contacting with the polishing composition of the present invention. The preferred polishing toad in the polishing process may be the sante as the polishing load in the process for manufactuiing a glass substrate mentioned above.

The above-mentioned polishing process is preferably employed in a second or subsequent polishing step, and more preferably in a final (finish) polishing step.

As the process for feeding a polishing composition, a process including the step of feeding a polishing composition in the state that the constituents of the polishing composition are sufficiently mixed in advance, between a polishing pad and an object to be polished with a pump or the like; a process including the step of feeding a polishing composition prepared by mixing the constituents in the feed lines and the like immediately before polishing; a process including the step of separately feeding a silica slurry and an aqueous solution prepared by dissolving a polymer having a sulfonic add group to a polishing machine; and the like can be used. The preferred feeding rate for the polishing composition may be the same as the feeding rate in the process for manufacturing a glass substrate mentioned above.

In order to effectively reduce substrate stains, the substrate to be polished is polished by using the polishing composition of the present invention, or a polishing composition is prepared by mixing each of the components so as to make up components for the polishing composition of the present invention. By polishing the substrate to be polished as mentioned above, surface defects of the substrate to be polished, especially the substrate stains, can be remarkably reduced, and a substrate having a low surface roughness and excellent surface quality can be manufactured. Even more, the present invention is suitable for the manufacture of a glass hard disk substrate.

Therefore, the present invention also relates to a process for reducing surface stains of a glass substrate includes the step of polishing a substrate to be polished with a polishing load of from 3 to 12 kPa and with the polishing composition as defined above pzesent between a polishing pad and the substrate. The materials of the object to be polished include, for example, quartz

glass, soda-lime glass, aluniinosilicate glass, borosilicate glass, aluminoborosilicate glass, non-alkaline glass, crystallized glass and the like.

Among them, the aluminosffic glass for a reinforced glass substrate or a glass ceramic substrate (crystallized glass substrate) is suitable for polishing.

The aluminosillcate glass is preferable from the viewpoint that the aluminosilicate glass has excellent chemical durability, so that the generation of damages (dent portion defects) during the alkaline cleaning which is carried out for the purpose of removing particles remaining on the substrate after polishing can be reduced, thereby giving an even higher surface quality.

The polishing composition of the present invention is especially effective in the second or subsequent step, and the polishing composition can be applied in the same manner to a polishing step other than above, for example, a first polishing step or a lapping step.

The shape for the substrate is not particularly limited. For example, those having shapes containing planar portions such as discs, plates, slabs and prisms, or shapes containing curved portions such as lenses can bc also used. Among them, those having the disc-shaped objects to be polished are even more preferable in polishing.

As to the surface roughness, which is a measure of the surface smoothness, the method for evaluation is not limited. The surface roughness is evaluated as a determinable roughness in a short wavelength, for example, a wavelength of 10 p.m or less in an atomic force microscope (AFM'), and can be expressed as an average roughness Us (AFM-Ra). The polishing composition of the present invention is suitable for the polishing step for a glass substrate, even more preferably for a polishing step for reducing the surface roughness (A.FM-Ra) of the substrate after polishing to 0.2 nm or less.

In the steps for manufacturing a substrate, it is preferable that the polishing composition of the present invention is used in the second polishing step or the subsequent step, and it is more preferable that the polishing composition is used in the final polishing step, from the viewpoint of remarkably reducing substrate stains and the surface roughness, thereby obtaining excellent surface smoothness. The final polishing step refers at least to the last polishing step of the polishing steps when the polishing is carried out in plural steps.

During the polishing, in order to avoid admixture of the polishing composItion used in the previous steps or admixture of polishing debris, the polishing steps can be each carried out in separate polishing machines. When each of separate polishing machines is used, it is preferable that the substrate is cleaned for every polishing step. Here, the polishing machine is not particularly limited.

The substrate manufactured in the manner as described above has remarkably reduced substrate stains and excellent surface smoothness.

Specifically, the substrate has a surface roughness (AFM-Ra) after poiishing of, for example, 0.2 nm or less, preferably 0.19 nm or less, and more preferably 0.18 rim or less.

The surface properties of the substrate before subjecting to the polishing step using the polishing composition of the present invention are not particularly limited. For example, the substrate having surface properties such as an AFM- Ra oft nm or less is suitably used.

The substrate manufactured by using the polishing composition of the present invention, or the process for manufacturing a substrate of the present invention in the manner, as described above has excellent surface smoothness, and one that has a surface roughness (AFM-Ra) of, for example, 0.2 urn or less, preferably 0.19 nm or less, and more preferably 0.18 rim or less can be obtained.

In addition, the manufactured substrate has very few substrate stains.

Therefore, when the substrate is, for example, a memory hard disk substrate, the substrate can meet the requirement of a recording density of 100 G bits/inch2, even more 1250 bits/inch2.

EXAMPLES

The following examples further describe and demonstrate embodiments of the present invention. The examples are given solely for the purposes of ifiustration and are not to be construed as limitations of the present invention. 2.5

[Substrate to be Polishedi A glass substrate made of aluminosilicate for hard disks, having a thickness of 0.635 mm, an outer diameter of 65 mm and an inner diameter of mm, previously subjected to first and second polishing steps with a polishing $ composition containing a ceria abrasive so as to give a surface roughness MM- Ra of 0.3 urn was used as the substrate to be polished for the evaluation of polishing.

Example 1

A polishing composition containing a colloidal silica slurry (commercially available from Du Pont K.K., average paiticle size of primary particles: 30 nm, concentration of silica particles: 40% by weight, the balance being water) in an amount of 95% by weight based on net silica particles, an acrylic acid/acrylamide-2-methylpropanesulfonic acid copolymer (molar ratio of monomers: 8/1, weight-average molecular weight: 2000, solid content: 40% by weight, a product neutralized with sodium) in an amount of 0.04% by weight based on net copolymer, and the balance ion-exchanged water was prepared.

The order of mixing each component was such that a given amount of an aqueous solution of the above copolymer diluted five-folds with ionexchanged water was added to and mixed with the colloidal silica slurry while stirring, and finally the balance of ion-exchanged water was gradually added to and mixed with the slurry.

Example 2

A polishing composition containing a colloidal silica slurry (commercially available from Du Pont K.K., average particle size of primary particles: 30 nm, concentration of silica particles: 40% by weight, and the balance being water) in an amount of 9.3% by weight based on net silica particles, the copolymer used in Example 1 in an amount of 0.10% by weight, and the balance ion-exchanged water was prepared in the same manner as in Example 1.

ELample3 A polishing composition containing a colloidal silica slurry (commercially available from Du Pont K.K, average particle size of primary particles: 20 nm, concentration of silica particles: 40% by weight, and the balance being water) in an amount of 9.3% by weight based on net silica particles, the copolymer used in Example 1 in an amount of 0.04% by weight, and the balance ion-exchanged water was prepared in th&saine manner as in Example 1.

Eflmple4 A polishing composition containing a colloidal silica slurry (commercially available from CATALYSTS & CHEMICeuj.,s INDUSTRIES CO., LID. , average particle size of primary particles: 80 nm, concentration of silica partieJes: 40% by weight, and the balance being water) in an amount of 9.5% by weight based on net silica particles, the copolymer used in Example 1 in an amount of 0.04% by weight, and the balance ion- exchanged water was prepared in the same manner as in Example 1.

Examples

A polishing composition containing the colloidal silica slurry used in Example 3 in an amount of 9.5% by weight based on net silica particles, an acrylic acid/acrylamide_2methylpropanesuIfQnic acid copolymer (molar ratio of monomers: 96/4, weight-average molecular weight: 4000, solid content: 36% by weight, a product neutralized with sodium) in an amount of 0.04% by weight based on net copolymer, and the balance ion-exchanged water was prepared in the same manner as in Example 1.

xanulc6 A polishing composition containing the colloidal silica slurry used in Example 3 in an amount of 9.5% by weight based on net silica particles, an acrylic acid/acrylamide2methylpfopanesulfothc acid copolymer (molar ratio of monOmers: 96/4, weight-average molecular weight: 6000, solid content: 43% by weight, a product neutral zed with sodium) in an amount of 0.10% by weight based on net copolymer, and the balance ion-exchanged water was prepared in the same manner as in Example 1.

omoarative Example 1

A polishing composition containing a colloidal silica slurry (commercially available from CATALYSTS & CHEMICALS lNDUSTpj CO., LTh., average particle size of primary particles: 150 nm, concentration of silica particles: 16% by weight, and the balance being water) in an amount of 8.4% by weight based on net silica particles, and the balance ion-exchanged water was prepared in the Same manner as in Example 1.

paratjve Example 2

A polishing composition containing a colloidal silica slurry (commercially available from flu Pont K.K., average particle size of primary particles: 20 inn, concentration of silica particles: 40% by weight, and the balance being water) in an amount of 9.7% by weight based on net silica particles, and the balance ion- exchanged water was prepared in the same manner as in Example 1.

Comparative Example 3 A polishing composition containing a colloidal silica slurry (commercially available from CATALYSTS & CHEMICALS INDUSTRIES CO., LTD., average particle size of primary particles: 150 nm, concentration of silica particles: 16% by weight, and the balance being water) in an amount of 8.3% by weight based on net silica particles, the copolymer used in Example 1 in an amount of 0.04% by weight, and the balance ion-exchanged water was prepared in the same manner as in Example 1.

The substrate to be polished was polished with each of the polishing compositions obtained in Examples 1 to 6 and Comparative Examples 1 to 3, and the stains on substrate, the polishing rate and the surface roughness (AFM-Ra) were determined and evaluated according to the following methods.

[Polishing Conditions] Polishing testing machine: commercially available from Musashino Denshi K..K., MA-300 single-sided polishing machine, platen diameter: 300 mm Polishing pad: Finish polishing pad made of an urethane Rotational speed of platen: 90 rlmin Rotational speed of carrier: 90 r/min, forced driving type Feeding rate for polishing Composition: 50 gfmin (about 1.5 mL/minJcm2) Polishing time period: 15 miii Polishing load; 5.9 kPa (constant load with a plummet) Rinsing Conditions: load: 3.9 kPa, time: 5 mm, feeding rate for ion-exchangeci water: about I 11mm) Drcssing conditions: A brush dressing was carried out for 03 minutes every cycle of polishing, while feeding ion-exchanged water.

[Evaluation of Substrate (Stains, Surface Roughness)] Cleaning Process: The substrate to be polished was taken out after the termination of polishing and rinsing, and cleaned under running water of ion- exchanged water. Next, the substrate was subjected to ultrasonic cleaning (100 kHz, 3 miii), while being immemed in ion-exchanged water. The substrate was further cleaned under running water of ion-exchanged water, and dried by a spin- dry method, The evaluation method: Stains on the substrate were observed with an optical microscope and an atomic force microscope (AFM).

For the surface roughness, AFMRa was determined using an atomic force microscope (AFM).

[Determination Method with A.FM] Determination Apparatus: TM-M5E Commercially available from Veeco Mode: non-contact Scan rate: 1.0Hz Scan area: 10 un x 10 j.tm Evaluation method: Stains on the substrate were observed at two scanning points near the midpoints of the inner circumference and the outer circumference on any center lines. Here, based on the total number of projections with a height of 1 mu or more in the above scan area (the sum in the two scanning points), the case of the total number of 1 or less was evaluated as "extremely few stains on substrate," the case of the total number of 2 to 4 was evaluated as "few stains on substrate," and the case of the total number of 5 or more was evaluated as "heavy stains on substrate." As for the surface roughness, the average of the numerical values in the two scanning points was determined in the same manner, and the average value was used as AFM-Ra.

(Method of Calculating Polishing Rate The weight difference (g) in the substrate before and after polishing was divided by the density of the substrate (2.46 g/cm3), the surface area of the substrate (30.04 cm2) and the polishing timc (minute), to give a polished amount per unit time, and the polishing rate (mi/minute) was calculated.

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Table 1

I Silica Polymer Having Sulfonic Arid Group I R Ratio of Monomer 1 Polishing Surface \ I Average Roughness I N Particle Sie Molecular Substrate - Weight Group ______ (urn) (% by wL) - (% by mole) (% by wL) (imfjnln) (urn) Ex. 1 30 95 2000 11 0.04 1. 0.013 0.189 Lx. 2 30 93 2000 11 0.10 1, 0.014 0.188 93 2000 11 0.94 2 0.009 0.177 Ex.4 80 9.5 2000 11 0.04 1 0.009_- 0.209 Lx. 5 20 9.5 4000 4 0.04 - 2 0.009 0.178 EL 6 20 9.5 6000 4 0.10 2 - 0.009 0. 180 ______ - 150 8.4 - - 000 2 0.007 0.217 9.7 - 0.00 3 0.009 0.187 (:1:. iso 8.3 2000 11 0.04 1 0.007 0.207 1) I: Extremely Few Stains on Substrate 2: Pew Stains on Substrate It can be seen from the results in Table 1 that tht Polishing COrnpositio obtainj in Exampies 1 to 6 have reducj staj, on subsuate high POlishing rates and lowered surface roughe5 as compared to those in Comparaj

Examples I to 3.

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The Polishing composjtj0 for a glass substrate of the present invention can be suitably used in the manufacture of, for example, glass hard disks, alumiflosuicate glass for reinforced glass substrates and glass ceramic substrate (crystal1f glass substrate), and the like, I0 The present invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regnd4j as a dep from the spirit and Scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included withj the scope of the following claims.

Claims

I. A polishing composition for a glass substrate, comprising a silica having an average particle size of primary particles of from 1 to 100 nm, a polymer having sulfonic acid groups, and water.
2. The polishing composition according to claim 1, wherein the polymer has a weight-average molecular weight of from 1,000 to 5,000.
3. The polishing composition according to claim I or 2, wherein the polymer is an acrylic acidlsulfonjc acid copolymer.
4. The polishing composition according to claim 3, wherein the sulfonic acid groupcontaining monomer component comprises from 3 to 90% by mole of the monomers constituting the acrylic acid/sulfonic acid copolymer.
5. The polishing composition according to any preceding claim, wherein the weight ratio of silica:polymer is from 1:10 to 1:5000.
6. The polishing composition according to any preceding claim, wherein the silica is a colloidal silica.
7. A process for manufacturing a glass substrate, comprising the step of polishing the substrate at a polishing load of from 3 to 12 kPa with a polishing composition as defined in any preceding claim present between a polishing pad and the substrate.
8. The process according to claim 7, wherein the substrate to be polished is a glass hard disk substrate.
9. A process for reducing surface stains on a glass substrate, comprising the step of polishing the substrate at a polishing load of from 3 to 12 kPa with a polisbftg composjfio as defined in polishing pad and the substra any ing claim present between a