GB2382818A

GB2382818A - Polishing composition for a magnetic disc substrate and polishing process using the same

Info

Publication number: GB2382818A
Application number: GB0222363A
Authority: GB
Inventors: Tomohide Kamiya; Hiroyasu Sugiyama; Toshiki Owaki
Original assignee: Fujimi Inc
Current assignee: Fujimi Inc
Priority date: 2001-09-27
Filing date: 2002-09-17
Publication date: 2003-06-11
Anticipated expiration: 2022-09-17
Also published as: GB2382818B; MY158135A; MY129705A; GB0222363D0; JP2003170349A

Abstract

A polishing composition for polishing a magnetic disk substrate comprises a first organic acid selected from a specific group including itaconic acid, succinic acid, maleic acid and mixtures thereof; a second organic acid selected from a specific group including glycine, itaconic acid, tartaric acid, maleic acid and mixtures thereof that differs from the first acid; an abrasive material selected form a specific group including aluminium oxide, silicon dioxide, cerium oxide, titanium oxide and mixtures thereof; and water. In one embodiment itaconic acid is an indispensible component of the composition. A polishing process using the polishing composition is also provided.

Description

TITLE OF THE INVENTION POLISHING COMPOSITION FOR A MAGNETIC DISC SUBSTRATE, AND POLISHING PROCESS USING THE SAME BACKGROUND OF THE INVENTION This invention relates to a polishing composition for a magnetic disc substrate.

Magnetic discs used as memory means for computers and home information appliances are made of substrates composed of a blank material and a coating layer provided thereon.

In a blankmaterial manufacturing process, sometimes waviness and unevenness are occurred on its surface. If there are waviness and unevenness on a blank material, these waviness and unevenness will remain on the surface of the substrate. In order to remove these waviness and unevenness which exist on the surface of the substrate andtomake its surface smooth, a substratemust be polished with a polishing composition.

With the recent trend of requiring higher capacity of magnetic discs, the demand for surface qua y of substrates becomes even stricter. As for the surface roughness, at present, a demand for surface roughness Ra, which is measured by probe method surface roughness measurement gauge, that is AFM (manufactured by Digital Instruments Co. , U. S. A), reaches up to 10 angstroms or smaller, even the demand varies with the grade of each magnetic disc.

Therefore, a polishing composition, which may provide smoother surface of the substrate, is required.

Moreover, the low price of magnetic discs is also in demand.

For that reason, cost-down on the process of manufacturing the substrates is required. A polishing composition, which can polish

substrates for a long time stably without clogging polishing pad, has been in demand. Clogging of a polishing pad means that during the substrate polishing process, abrasive materials and chips (shavings) are accumulated on the polishing surface of the pad.

As for the prior art polishing compositions, the polishing compositions disclosed in Japanese laid open patent publication No. 7-216345 (the first prior art) and Japanese laid open patent publication No. 2000-1665 (the second prior art) are known. A polishing composition of the first prior art contains water, an alumina abrasive, and a polishing accelerator that consists of molybdate and organic acid. On the other hand, a polishing composition of the second prior art contains abrasive materials such as aluminum oxide, silicon dioxide, cerium oxide, zirconium oxide, titaniumoxide, titaniumoxide, siliconnitrideandmanganese dioxide, water, and succinic acid or its salt.

However, when previously known polishing compositions are used for polishing a substrate, a polishing pad is clogged during a polishing process, causing a decrease of the stock removal rate, and such defects as pits, micro-protrusion and scratches are occurred on the surface of the substrate. Therefore, to prevent such clogging of polishing pad, the polishing pad had to be washed frequently, and that resulted in high-cost of substrate manufacturing process.

SUMMERY OF THE INVENTION The purpose of the present invention is to provide a polishing composition used for a magnetic disc substrate, which inhibits clogging of a polishing pad during the polishing process, and a polishing method using the same.

To accomplish the above-mentioned purpose, in one aspect of this invention, a polishing composition, which is used when a

magnetic disc substrate is polished, is provided. The polishing composition comprises a first organic acid selected from the group consisting of glycine, glyceric acid, mandelic acid, ascorbic acid, glutamic acid, glyoxylic acid, malic acid, glycolic acid, lactic acid, gluconic acid, succinic acid, tartaric acid, maleic acid, itaconic acid, crotonic acid, nicotinic acid and the mixture thereof, a second organic acid selected from the group consisting of glycine, malic acid, lactic acid, gluconic acid, tartaric acid, maleic acid, itaconic acid, crotonic acid and the mixture thereof and differs from the first organic acid, an abrasive material selected from the group consisting of aluminum oxide, cerium oxide, silicon dioxide, zirconium oxide, titanium oxide, silicon nitride, silicon carbide and the mixture thereof, and water.

In another aspect of this invention, another polishing composition which is used when a magnetic disc substrate is polished, is provided. The polishing composition comprises a first organic acid selected from the group consisting of glycine, glyceric acid, mandelic acid, ascorbic acid, glutamic acid, glyoxylic acid, malic acid, glycolic acid, lactic acid, gluconic acid, succinic acid, tartaric acid, maleic acid, itaconic acid, crotonic acid, nicotinic acid, and the mixture thereof, a second organic acid selected from the group consisting of citric acid, iminodiacetic acid, malonic acid, oxalic acid, alanine, propionic acid, and the mixture thereof, an abrasive material selected from the group consisting of aluminum oxide, cerium oxide, silicon dioxide, zirconium oxide, titanium oxide, silicon nitride, silicon carbide, and Lhe mixture thereof, and water.

In yet another aspect of the invention, a polishing composition, which is used when a magnetic disc substrate is polished, isprovided. The polishingcomposition contains itaconic acid as an indispensable element, and comprises an organic acid selected from the group consisting of glycine, glyceric acid, mandelic acid, ascorbic acid,-glutamic acid, glyoxylic acid, malic

acid, glycolic acid, lactic acid, gluconic acid, succinic acid, tartaric acid, maleic acid, crotonic acid, nicotinic acid, citric acid, iminodiacetic acid, malonic acid, oxalic acid, alanine, propionic acid, and the mixture thereof, an abrasive material selected from the group consisting of aluminum oxide, cerium oxide, silicon dioxide, zirconium oxide, titanium oxide, silicon nitride, silicon carbide, and the mixture thereof, and water.

Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment A polishing composition according to a first embodiment of the present invention will be explained as follows.

The polishing composition comprises a first organic acid selected from the group consisting of glycine, glyceric acid, mandelic acid, ascorbic acid, glutamic acid, glyoxylic acid, malic acid, glycolic acid, lactic acid, gluconic acid, succinic acid, tartaric acid, maleic acid, itaconic acid, crotonic acid, nicotinic acid and the mixture thereof, a second organic acid selected from the group consisting of glycine, malic acid, lactic acid, gluconic acid, tartaric acid, maleic acid, itaconic acid, crotonic acid, and the mixture thereof and is different from the first organic acid, an abrasive material selected from the group consisting of aluminum oxide, cerium oxide, silicon dioxide, zirconium oxide, titanium oxide, silicon nitride, silicon carbide, and the mixture thereof, and water.

The first organic acid is a polishing accelerator that promotes mechanical polishing of substrates using an abrasive material, by

etching the surface of the substrates. The preferable first organic acid is malic acid, glycolic acid, succinic acid, or the mixture thereof.

The second organic acid is a polishing accelerator, and also is a precipitation inhibitor that inhibits precipitation of abrasive materials and chips on the surface of the polishing pad by dispersing the abrasive materials and the chips that exist in the polishing composition and prevent them from settling. The preferable second organic acid is glycine, malic acid, lactic acid, gluconic acid, or the mixture thereof, because these acids have high efficacy in dispersing the abrasive materials and the chips.

Each content of the first organic acid and the second organic acid in the polishing composition is preferably 0.01 to 10 weight %, more preferably 0.05 to 5 weight %, the most preferably 0. 1 to 3 weight %. If the content is less than 0-01 weight %, stock removal rate of the polishing composition tends to become lower, and if the content is more than 10 weight %, there is little improvement in the stock removal rate and only the cost will become higher.

The abrasive material mechanically polishes the surface of the substrate. The preferable abrasive material is aluminum oxide or silicon dioxide, because of their low prices and availability.

The particle diameter of the abrasive material is, when the abrasive material is aluminum oxide, cerium oxide, zirconium oxide, titaniumoxide, silicon nitride or silicon carbide, preferablyunder 2 pm, more preferably 0.01 to 1.5 urn, the most preferably 0. 05 to 1.0 pm, if the average particle diameter (D50) measured by Laser Diffraction Particle Diameter Measuring Apparatus LS-230 (manufactured by Coulter Co., Ltd, U. S. A). If the abrasive material is silicon dioxide, the average particle diameter (D50), which is calculated from the relative surface areas measured by BET method, is preferably 0.005 to 0.5 pm, more preferably 0.01 to 0.3 pm, the

most preferably 0.05 to 0.2 pm.

If the particle diameter of the abrasive material is less than 0.01 pm (for aluminum oxide etc. ) or 0. 005 pm (for silicon dioxide), the stock removal rate of the polishing composition becomes lower. Therefore, the amount of the polishing composition consumed is increased, and subsequently the polishing cost tends to become higher. A relatively excessive polishing of the peripheral part of the substrate compared to the central part causes its periphery undesirably rounded. On the other hand, if the particle diameter is over 2 pm (for aluminum oxide etc. ) or 0.5 um (for silicon dioxide), surface roughness of the polished surface of the substrate becomes higher, and also scratches on the polished surface are likely to occur.

To inhibit the occurrence of surface defects on the polished surface of the substrate, moreover to reduce the surface roughness, it is preferable that the abrasive material does not contain large particles whose diameters are 5 pm or more.

The content of the abrasive material in the polishing composition is preferably 0. 1 to 40 weight %, more preferably 1 to 30 weight %, and the most preferably 5 to 25 weight %. If its content is less than 0.1 weight %, the mechanical polishing force of the polishing composition becomes weaker, so the stock removal rate tends to become lower. On the other hand, if its content is over 40 weight %, the viscosity of the polishing composition and its waste fluid becomes larger, and subsequently becomes difficult to handle. Moreover, a clogging of the polishing pad, a decrease of the stock removal rate of the polishing composition, and surface defects of the substrate will likely to occur.

The more detailed explanation on aluminum oxide, silicon dioxide, cerium oxide, zirconium oxide, titanium oxide, silicon nitride and silicon carbide, which are given as examples of the

abrasive material, will be made as follows.

Aluminum oxide includes, for example, a-aluminum oxide, b-aluminum oxide, 8-aluminum oxide, K-aluminum oxide and amorphous aluminum oxide. Preferable aluminum oxide is a-aluminum oxide, because of its highhardness. Themethodformanufacturing aluminum oxide includes, for example, calcined aluminum compound such as aluminumhydroxide, and calcined aluminum compound and subsequently melting it.

Silicon dioxide includes, for example, colloidal silica, fumed silica and precipitated silica. Preferable silica is colloidal silica, because it has high hydrophilic property, so that it hardly causes the surface defects on the substrate. The method for manufacturing the colloidal silica includes, for example, allowing for the growth of ultra-fine particles of colloidal silica, which were obtained by an ion-exchange of sodium silicate.

Colloidal silica can keep its colloidal state even if its density becomes high, by adding acid or base, or by using ion-exchange treatment, to adjust its pH. Colloidal silica on the market includes, for example, monodisperse silica, associated silica formed by bonding some particles, and high purity silica in which the content of metal impurities is lowered.

Ceriumoxide includes, for example, ceriumoxide (III), cerium oxide (IV), hexagonal cerium oxide, isometric cerium oxide and face-centered cerium oxide. Zirconium oxide includes, monoclinic system zirconium oxide, tetragonal zirconium oxide, amorphous zirconium oxide and fumed zirconia. Titanium oxide includes, for example, titanium monoxide, dititaniumtrioxide, titanium dioxide and fumed titania.

Silicon nitride includes, for example, a-silicon nitride and P-silicon nitride. In addition, generally it is said that a-silicon nitride can easily be shattered, so its fine particles are easily

obtained. On the other hand, P-silicon nitride has high hardness.

The method for manufacturing silicon nitride includes, for example, is to reduce silicon oxide by carbon powder and nitrogen gas, to heat metal silica directly in the presence of nitrogen gas, and to allow for the reaction of silicon tetrachloride and ammonia (imide decomposition method).

Silicon carbide includes, for example, ex-silicon carbide and -silicon carbide. In addition, green-colored and black-colored silicon carbide generally used as abrasive materials are of-silicon carbide. The method for manufacturing silicon carbide includes, for example, to reduce silicon oxide by carbon, and to allow for the direct reaction of metal silicon with carbon.

The abrasive material may be the mixture of the abrasive materials of a different form, a method of manufacturing, and a character.

Water is a solvent for the organic acid, and a dispersion medi. um for the abrasive material. Preferably the water does not contain impurities as much as possible. For example, water obtained by filtering ion-exchange water, or distilled water is preferable.

The pH of the polishing composition is preferably 2 to 7.

If pH is less than 2, a machine such as a polishing apparatus, which is used when polishing the substrate, is easily eroded. On the other hand, if pH is over 7, the stock removal rate of the polishing composition tends to become lower, together with the surface roughness of the substrate becomes higher, and scratches on the polished surface of the substrate tend to occur. Therefore, it is preferable to keep pH of the polishing composition within the above-mentioned range, by adding acid or base to the polishing composition.

Celluloses such as cellulose, carboxymethyl cellulose and

hydroxyethyl cellulose, water soluble alcohols such as ethanol, propanol and ethylene glycol, surface active agents such as sodium alkylarylsulfonate, and formalin condensed naphthalenesulfonic acid, organic polyanion substances such as lignin surfonate salt and polyacryl acid salt, water soluble polymers (emulsifying agent) such as polyvinyl alcohol, chelating agents such as dimethylglyoxime, dithizone, oxine, acetylacetone, glycinc, ethylenediamine tetra-acetic acid and nitrilotriacetic acid, sterilizers such as sodium alginate and potassium hydrogen carbonate, inorganic salts such as aluminum sulfate, nickel sulfate, aluminum nitrate, nickel nitrate, iron nitrate and ammonium molybdat, higher fatty amines, sulfonate, and water base modified oils that contain anticorrosive agents can be added to the polishing composition.

The polishing composition is prepared by mixing the first organic acid, the second organic acid, the abrasive material and water, together with other elements when needed. The polishing composition is mixed by means of, for example, stirring with a wing stirrer, ultrasonic dispersion, or shear stirring with a homomixer.

Amethod or manufacturingamemory hard disc such as a magnetic disc, and a method for polishing the substrate using the polishing composition will be explained as follows. A memory hard disc is manufactured from the substrate. The substrates include Ni-P disc, Ni-Fe disc, boron carbide disc and carbon disc. Preferable substrate is Ni-P disc, which has an electroless plating layer made of nickel-phosphorus alloy on the blank material made of aluminum or aluminum alloy, because of its cheap price and availability.

The substrate is first polished using polishing composition.

The polishing method and the polishing condition follow the conventional method. The polishing machine used in polishing the substrate includes, for example, one-side polishing machine and double-sides polishing machine. The polishing pad includes suede,

unwoven cloth, woven cloth and gigging pads.

Recently, as higher capacity of a memory hard disc than ever has been required, smoothness of the substrate surface is required more than ever. Therefore, polishing of a substrate is often done in two, three or more stages. In the first stage of the polishing waviness and surface defects such as huge scratches or unevenness on the substrate are removed. In the second and further stages of the polishing, the roughness of the polished surface of the substrate is adjusted to the required surface roughness, and the surface defects, which are generated during the first stage of polishing or which could not be removed by the first polishing, are removed.

The polishing composition can be used both in the first stage, and the second and further stage of polishing. Suitable polishing composition for the first stage of polishing is, because of its

high stock removal rate, the polishing composition contained abrasive material that have relatively large diameter. Suitable polishing composition for the second and further stage of polishing is, the polishing composition contained abrasive material that have relatively small diameter, because they keep good balance between the mechanical polishing with the abrasive material and etching with the organic acid.

Next, grooves or textures are formed on the substrate concentrically along the rotational direction of the memory hard disc, by using the texture forming composition that contains abrasive material such as diamondmicro powder, process accelerating agents and water. The memory hard disc is manufactured by forming magnetic layer and protection layer on the surface of the substrate on which the textures have already been formed.

In order to achieve higher capacity, some memory hard discs aremade of substrates on which light textures with shallower grooves

than those of the conventional texture are formed, or made of non-texture substrates on which no textures are formed. The polishing composition can be used in manufacturing substrates on which normal textures will be formed, substrates on which light textures will be formed and substrates on which no textures will be formed.

The polishing composition according to the first embodiment has following advantages.

The polishing composition inhibits the clogging of the polishing pad during the polishing process, so the decrease of the stock removal rate and the surface defects on the substrate can be suppressed. Further, the first organic acid and the second organic acid inhibit adhesion of the abrasive material and chips to the substrate, and also inhibit scratches on the substrate by the abrasive material and the chips, by acting on the surface of the abrasive material and of the chips. Therefore, the polishing composition can reduce the surface defects on the substrate, caused by the adhesion of the abrasive material and the chips on the substrate, and caused by scratches by the abrasive material and the chips.

A second embodiment Next, a polishing composition according to a second embodiment of the invention will be explained, mainly about the differences from the polishing composition according to the first embodiment.

The polishing composition according to the second embodiment contains a first organic acid selected from the group consisting of glycine, glyceric acid, mandelic acid, ascorbic acid, qlutamic acid, glyoxylic acid, malic acid, glycolic acid, lactic acid, gluconic acid, succinic acid, tartaric acid, maleic acid, itaconic acid, crotonicacid, nicotinicacidandthemixture thereof, asecond organic acid selected from the group consisting of citric acid,

iminodiacetic acid malonic acid, oxalic acid, alanine, propionic acid and the mixture thereof and is different from the first organic acid, an abrasive material selected from the group consisting of aluminum oxide, cerium oxide, silicon dioxide, zirconium oxide, titanium oxide, silicon nitride, silicon carbide and the mixture thereof, and water.

The first organic acid is a polishing accelerator. The preferable first organic acid is malic acid, glycolic acid succinic acid and the mixture thereof.

The content of the first organic acid in the polishing composition is preferably 0. 01 to 10 weight %, more preferably 0. 05 to 5 weight %, the most preferably 0. 1 to 3 weight %. If this content is less than 0. 01 weight %, the stock removal rate of the polishing composition tends to be lowered, and if the content is over 10 weight %, little improvement in the stock removal rate can be seen, therefore the cost will be higher.

The second organic acid is a polishing accelerator and also an inhibitor of precipitation The preferable second organic acid is citric acid, iminodiacetic acid or the mixture thereof, because they have high proficiency in dispersing the abrasive material and the chips. More preferable second organic acid is citric acid.

The content of the second organic acid is preferably 0.01 to 5 weight %, more preferably 0.05 to 3 weight %, and the most preferably 0. 1 to 1 weight %. If this content is less than 0.01 weight %, clogging of the polishing pad will easily be occurred, and if the content is over 5 weight %, little improvement j n inhibiting the clogging of the polishing pad, therefore the cost will be higher.

A third embodiment An polishing composition according to a third embodiment contains itaconic acid as the essential component, and comprises

an organic acid selected from the group consisting of glycine, glyceric acid, mandelic acid, ascorbic acid, glutamic acid, glyoxylic acid, malic acid, glycolic acid, lactic acid, gluconic acid, succinic acid, tartaric acid, maleic acid, crotonic acid, nicotinic acid, citric acid, iminodiacetic acid, malonic acid, oxalic acid, alanine, propionic acid and the mixture thereof, an abrasive material selected from the group consisting of aluminum oxide, cerium oxide, silicon dioxide, zirconium oxide, titanium

oxide, silicon nitride, silicon carbide and the mixture thereof, and water.

Itaconic acid shown in the following formula (1) is a polishing accelerator and inhibitor of the precipitation. When itaconic acid is solved in water, hydrogen ions are dissociated from the carboxyl groups of the itaconic acid, and itaconic acid subsequently changes itaconic acid ion that has two carboxyl groups ionized (COO-). Itaconic acid ion prevents cohesion of the abrasive material and the chips by directly acting on the abrasive material and the chips, or by acting as a chelate, to inhibit the clogging of the polishing pad.

Formula 1

The content of the itaconic acid is preferably 0. 01 to 5 weight %, more preferably 0. 05 to 3 weight %, the most preferably 0. 1 to 1 weight %. If the content is less than 0. 01 weight %, it sometimes cannot inhibit the clogging of the polishing pad. On the other hand, if the content is over 5 weight %, little improvement can be seen in the inhibition of the clogging of the polishing pad, therefore only the cost will rise.

The organic acid is a polishing accelerator. It is preferable

that the polishing composition contains at least citric acid, and more preferable that the polishing composition contains both citric acid and succinic acid.

When the citric acid shown in the following formula (2) is dissolved in water, it changes citric acid ion that has three ionized carboxyl groups. The citric acid ion prevents cohesion of the abrasive material and the chips by acting on itaconic acid ion mutually, to inhibit the clogging of the polishing pad.

Formula 2

The succinic acid shown in the following formula (3) has a higher etching ability compared to the other organic acids When the polishing composition contains at least both citric acid and succinic acid, the stock removal rate of the polishing composition will be greatly improved, because the citric acid and the itaconic acid enhance the etching force.

Formula 3

The content of the organic acid is preferably 0. 01 to 10 weight %, more preferably 0. 05 to 5 weight %, the most preferably 0. 1 to 3 weight %. If this content is less than 0. 01 weight %, sometimes the stock removal rate is not improved. On the other hand, if the content is over 10 weight %, there is little improvement in the stock removal rate, therefore the cost will rise.

The polishing composition according to the third embodiment is particularly effective in inhibiting the clogging of the polishing pad during the polishing process, because it contains itaconic acid as an indispensable component, resulting in longer life of the polishing pad.

The embodiments can be modified as follows : It is possible that the polishing composition is prepared as an undiluted solution of a relatively high concentration, and then it is diluted with water when used in polishing. In this case, treatment efficiency when stored and transported will be improved.

Next, examples and comparative examples will be explained.

Examples 1 to 33 and comparative examples 1 to 15 In each of examples 1 to 33, the polishing composition is prepared by mixing aluminum oxide, ion-exchanged water and organic acid shown in Table 1. In each of comparative examples 1 to 15, the polishing composition is prepared by mixing aluminum oxide, ion-exchanged water, organic acid and the compound shown in Table 2. In each polishing composition, the average particle diameter of aluminum oxide is 0.8 pm, and the content of the aluminum oxide is 20 weight %.

(1) Preliminary polishing One side surface of the substrate ( 5" Ni-P disc) is preliminary polished for 5 minutes, using the polishing composition diluted four times by ion-exchange water. Before and after the polishing, the weight of the substrate is measured, and the stock removal rate (Ro) was calculatedfrom the weight difference, specific gravity of the nickel-phosphorous plating, area of the substrate and the polishing time. From the stock removal rate (Ro), the time required for reducing the thickness of the substrate by 1 pm through

polishing was calculated. In addition, other conditions of the preliminary polishing process were as follows.

The machine: single-side polishing machine (the standard plate diameter #300 mm, manufactured by Udagawa Tekko Co.) The polishing pad: BELLATR1X NOO48 (manufactured by Kanebo, Ltd. ) Pressure: 90 g/cm2 Revolution: 100 rpm Slurry Feed Rate: 4 cm3/min 300 batches of the substrates (p3. 5" Ni-P dìsc) were continuouslypolishedusingthepolishingcompositiondilutedfour times by ion-exchange water. The polishing time of each batch is the processing time required in the preliminary polishing of the item (1). Other polishing condition is the same as the preliminary polishing mentioned in the item (1). After the continuous polishing, estimation of the following items (2) to (5) was done.

The results are shown in Tables 1 and 2.

(2) Decrease rate of the stock removal rate At the 300th substrate batch, stock removal rate (Roo) was calculated from the rate of the decreased weight of the substrate, specific gravity of nickel-phosphorous plating, area of the substrate and polishing time. Decrease rate of the stock removal rate was calculated by following formula.

Decrease rate of the stock removal rate - (1-R3oo/Ro) 100 The evaluation was done in four steps. If the decrease rate is less than 10 %, it is represented by, if 10 % or over and under 20 %, it is represented by 0, if 20 % or over and under 30 %, it is represented by A, and if 30 % or over, it is represented by X.

(3) Dispersing property 100 cm3 of the fluid of the polishing composition discharged between 280 to 300 batches was collected in colometric tube, the inner radius of which is 2.5 cm. The waste fluid collected in the colometrie tube was then shaken and dispersed uniformly, and allowed to stand still. After two hours passed, the bulk height of the precipitate in the waste fluid was measured. If the ratio of the precipitate height to the waste fluid height was 60 % or more, it was evaluated dz if the ratio was 50 % or more and less than 60 %, it was evaluated 0, if the ratio was 40 % or more and less than 50 %, it was evaluated A, and if the ratio was under 40 %, it was evaluated X.

(4) Clogging condition of the polishing pad After completing continuous polishing process, the surface of the polishing pad was examined visually. If no clogging of the polishing surface was found, it was evaluated (D, if the clogging was found partly on the whole surface of the polishing pad, but it present no problem, it was evaluated 0, if the clogging was found on the whole surface of the polishing pad, it was evaluated

x, (5) The surface defects After completing washing and drying of the 300th batch substrate, it was observed whether a pit having the diameter of 10 urn or more was made at which the portions of 5 mm away from outer and inner peripheries of the polished surface using a Differential Interference Microscope : OPTIPHOT 66 (manufactured by Nikon Co., 10-fold ocular lens, 5-fold objective lens). If no pit occurrence was observed, it was evaluated &commat;, if the pit occurrence was observed, but the level of which presents no problem, it was evaluated 0 , if the pit occurrence was observed, it was evaluated X.

Table 1

Organic acid Organic acid Kind/Kind/pH a* b* c* d* Rate of addition (wtX) Rate of addition (wt%) Ex.1 Malic acid 1 Glycine 0.5 3.6 # # # # Ex.2 Glycolic acid 1 Malic acid 0.5 2.8 # # # # Ex.3 Succinic acid 1 Glycine 0.5 3.8 # # # # Ex. 4 Succinic acid 1 Malic acid 0.5 3.0 0 0 0 0 Ex. 5 Succinicacid 1 Lactic acid 0.5 3.3 0 0 0 0 Ex. 6 Succinic acid 1 Gluconie acid 0.5 3.4 0 0 0 0 Ex.7 Maleic acid 1 Glyoine 0.5 3.9 # # # # Ex.8 Itaconic acid 1 Malic acid 0.5 2.7 # # # # Ex. 9 Crotonic acid 1 Lactic acid 0.5 2.9 0 0 0 0 Ex.10 Nicotinic acid 1 Gluconie acid 0.5 3. 3 0 0 0 0 Ex. 11 Malio aoid 1 Citric acid 0.2 2.6 0 0 0 0 Ex. 12 Malic acid 1 Citric acid 0.5 2.5 # # # # Ex. 13 Malio arid 0. 5 Citric acid 1 2, 3 &commat; Ex. 14 Malic acid 1 Citric acid 1 2. 2 # # # # Ex.15 Glycolic acid 1 Citric acid 0.2 2.7 0 0 0 0 Ex. 16 Glycolic acid 1 Citric acid 0.5 2. 6 # # # # Ex.17 Glycolic acid 0.5 Citric acid 1 2.3 # # # # Ex.18 Glycolic acid 1 Citric acid 1 2. 2 # # # # Ex. 19 Succinic acid 1 Citric acid 0. 2 2. 9 0 0 0 0 Ex. 20 Succinic acid 1 Citric acid 0.5 2. 7 &commat; &commat; ( &commat; Ex21 Succinic acid 0.5 Citric acid 1 2.2 # # # 3 Ex. 22 Succinic acid 1 Citric acid 1 2. 5 # # # # Ex. 23 Maleic acid 1 Citric acid 0.5 2. 2 # # # # Ex.24 Itaconic acid 1 Gitric acid 0.5 2.3 # # # # Ex. 25 Crotonic acid 1 Citric acid 0.5 2. 6 &commat; &commat; &commat; &commat; EX. 26 Nicotinic acid 1 Citric acid 0.5 2. 9 # # # Ex. 27 Malic acid 1 Iminodiacetic acid 0.5 3.0 0 0 0 0 Ex. 28 Glycolic acid 1 Iminodiacetic acid 0. 5 3. 1 0 0 0 0 Ex. 29 Succinic aoid 1 lminodiacetic acid 0. 5 3. 3 0 0 0 0 Ex. 30 Maleic acid 1 Iminodiacetic acid 0.5 2.7 0 0 0 0 Ex. 31 Itaconic acid 1 Iminodiacetic acid 0.5 2.8 0 0 0 0 Ex. 32 Orotonic acid 1 Iminodiacetic acid 0.5 3.2 0 0 0 0 Ex. 33 Nicotinic acid 1 Iminodiacetic acid 0.5 3. 5 0 0 0 0 a* = decrease rate of the stock removal rate b* = dispersing property c* == clogging condition of the polishing pad d*= surface defects

Table zu

Organic acid compound Kind/ Kind/ pH a* b* c* d* Rate of addition (wt%) Rate of addition (wt%) C. Ex. 1 Lactic acid 1 Colloidal alumina 0.5 2. 9 x 000 C. Ex. 2 Gluconic acid 1 Colloidal alumina 0.5 3. 1 x 0 00 C. Ex-3 Succinio acid 1 Colloidal alumina 0.5 3.5 x x x 0 C. Ex. 4 Succinic acid 1 Ammonium molybdate 0. 5 3. 4 x x # # C. Ex. 5 Malic acid 1-2. 9 0 0 0 x C. Ex. 6 Glycolic acid 1--3. 0 x x x x C. Ex. 7 Succinic acid 1 - - 3. 5 x x x 0 C. Ex-8 8 Maleic acid 1 - - 2. 3 A A 0 x C. Ex. 9 Itaconic acid 1 2. 6 A A 0 X C. Ex.10 Crotonic acid 1 - - 3. 3 A A 0 x C. Ex. 11 Citric acid 1 - - 2.3 x # # # C. Ex. 12 Oyootfoacid 1 Glyceric acid 0.5 2. 8 x x x x C. Ex. 13 Succinic acid 1 Mandelic acid 0. 5 3.2 x X x 0 C. Ex. 14 Succinic acid 1 Ascorbic acid 0.5 3. 4 x x X 0 C. Ex. 15 Nicotinic acid 1 Succinic acid 0. 5 3. 5 x x x 0 at-decrease rate of the stock removal rate b* = dispersing property c* = clogging conditions of the polishing pad d* = surface defects As shown in Table 1, excellent evaluations were made for all of the followings: the decrease rate of the stock removal rate, dispersing property, clogging condition of the polishing pad and the surface defects, in the examples of 1 to 33. On the other hand, as shown in Table 2, the decrease rate of the stock removal rate became 30 % or more, because they did not contain the organic acid which acts as precipitation inhibiting agent, in the comparative examples 3 and 4. In the comparative examples 5 to 11, low evaluation was made for the decrease rate of the stock removal rate, dispersing property, clogging condition of the polishing pad and the surface defects, because the organic acid was contained solely. In the comparative examples 12 to 15, low evaluation was made for the decrease rate of the stock removal rate, dispersing property and

clogging of the polishingpad, because the combination of the organic acids contained in each comparative examples'polishing composition was different from the combination of the organic acids contained

in the polishing composition of each embodiment.

As for the polishing composition of the comparative examples 1,2 and 11, no clogging of the polishing pad was observed, but much of polishing composition and the waste fluid were left on the polishing pad even after the polishing process. The reason for the low evaluation made for the decrease rate of the stock removal rate regardless of the excellent evaluation for the dispersing property and the clogging of the polishing pad, it is considered that not enough power was transmitted to the substrate from the polishing pad, because of the floating state of the substrate by the remaining polishing composition and waste fluid on the polishing pad.

Examples 34 to 50 and comparative examples 16 to 30 In the examples 34 to 50, the polishing composition was prepared by mixing aluminum oxide, ion-exchange water and the organic acid shown in Table 3. In the comparative examples 16 to 30, the polishing composition was prepared by mixing aluminum oxide, ion-exchange water, the organic acid and the compound shown in Table 4. For any of these polishing compositions, the average particle diameter of aluminum oxide contained is 0.8 pm and the content of aluminum oxide is 20 weight %.

(6) The preliminary polishing One side surface of the substrate (3. 5t'Ni-P disc) was preliminarily polished for 5 minutes, using each polishing composition diluted four times with ion-exchange water. Then, the stock removal rate (Ro) was calculated using the same manner in the preliminary polishing process described in the item (1), and subsequently processing time was obtained from the stock removal rate (Ro). ln addition, other conditions of the preliminary polishing process were as follows.

The machine: single-side polishing machine (the standard

plate diameter 300 mm, manufactured by Udagawa Tekko Co.) The polishing pad : BELLATRIX N0048 (manufactured by Kanebo Co.)' Pressure : 150 g/cm2 Revolution: 100 rpm Slurry Feed Rate: 3 cm/min The substrates ( (p3. 5'' Ni-Pdisc) were continuously polished for 300 batches, using the polishing composition diluted four-times with ion-exchange water. The polishing time for each batch was the processing time obtained by the preliminary polishing process mentioned in the item (6). Other polishing conditions were the same as that of the preliminary polishing process After the continuous polishing process, evaluations for the following points (7) to (10) were made. The results are shown in Tables 3 and 4.

(7) Decrease rate of the stock removal rate Decrease rate of the stock removal rate was obtained for each polishing composition using the same manner as the item (2), and evaluated in four grades.

(8) Dispersing property The dispersing property was evaluated for each polishing composition using the same manner as the item (3).

(9) Clogging conditions of the polishing pad The clogging conditions of the polishing pads were evaluated for each polishing composition using Lhe same manner as item (4).

(10) Surface defects The surface defects were evaluated for each polishing composition using the same manner as item (5).

Table 3

Organic acid Organic acid Organic acid Kind/ Kind/ Kind/ Rate of addition Rate of addition Rate of addition pH a* b* c* d* (wt%) (wt%) (wt%) Ex.34 Succinic acid 1 Malic acid 0.5 - - 3.0 # # # x Ex. 35 Malic acid 1 Citric acid 0. 5 - - 25 0 0 0 0 Ex. 36 Itaconic acid 1 Malic acid 0. 5 - - 2. 7 0 0 0 0 Ex. 37 Glycolic acid 1 Citric acid 0. 5--2. 6 0 # 0 0 Ex. 38 Succinic acid I Citric acid 0. 5 2-7 0 # 0 0 Ex. 39 Malaic acid 1 Citric acid 0.5 - - 2. 2 0 &commat; 0 0 Ex. 40 Itaconic acid 1 Citric acid 0. 5--2. 3 0 &commat; 0 0 Ex. 41 Crotonic acid 1 Citric acid 0. 5 2. 6 0 &commat; 0 0 Ex. 42 Nicotinic acid 1 Citric acid 0. 5 - - 2.9 0 &commat; 0 0 Ex.43 Itaconic acid 1 Iminodiacetic 0.5 - - 2.8 0 0 0 0 acid Ex. 44 Succinic acid 1 Itaconic acid 0.5 Malic acid 0.5 2. 7 0 0 0 0 Ex. 45 Malic acid 1 Itaconic acid 0.5 Citric acid 0. 5 2-5 &commat; &commat; &commat; &commat; Ex. 46 Glycolic acid 1 Itaconic acid 0.5 Citric acid 0.5 2.5 # # # # Ex. 47 Succinic acid 1 Itaconic acid 0.5 Citric acid 0.5 2. 7 # # # # Ex. 48 Maleic acid 1 Itaconic acid 0.5 Citric acid 0. 5 2. 3 # # # # Ex. 49 Crotonic acid 1 Itaconic acid 0. 5 Citric acid 0.5 2. 8 # # # # Ex. 50 Nicotinic acid 1 Itaconic acid 0.5 Citric acid 0.5 2.8 # # # # a* = decrease rate of the stock removal rate b'= dispensing property c* = clogging conditions of the polishing pad d* = surface defects

Table 4

Organic acid Compound Kind/Kind/pH a*b* c* d* Rate of addition (wt%) Rate of addition (wt%) C. Ex. 16 Lactic acid 1 Colloidal alumina 0. 5 2. 9 x 0 x x C. Ex. 17 Gluconic acid 1 Colloidal alumina 0.5 3.1 x 0 x x C. Ex. 18 Succinic acid 1 Colloidal alumina 0.5 3. 5 x x x x O. Ex. 19 Succinic acid 1 Ammonium molybdate 0.5 3. 4 x x X x C. Ex. 20 Malic acid 1--2. 9 A A 0 x C. Ex. 21 Glycolic acid 1 3. 0 x x x x c Succinic acid 1 3. 5 x x x x C. Ex. 23 Maleic acid 1 2. 3 x A x x C. Ex. 24 Itaconic acid 1 - - 2.6 x # # x C. Ex. 25 Crotonic acid 1 - - 3.3 x # x x O. Ex. 26 Citric acid 1--2. 3 x 0 0 x C. Ex. 27 Glycolic acid 1 Glyceric acid 0.5 2.8 x x x x C. Ex-28 Succinic acid 1 Mandelio acid 0.5 32 x x x x C. Ex. 29 Succinic acid 1 Ascorbic acid 0. 5 3.4 x x x x C. Ex.30 Nicotinic acid 1 Succinic acid 0. 5 3.5 x x x x s1'= decrease rate of the stock removal rate b* = dispersing property c* = clogging conditions of the polishing pad d'= surface defects As shown in Table 3, excellent evaluations were obtained for the dispersion properties and the clogging conditions of the polishing pads in the example 34. As for the examples 35 to 50, excellent evaluations were obtained for each of the decrease rate of the stock removal rate, the dispersion properties, the clogging conditions of the polishing pads, and the surface defects. In addition, in the example 47, the stock removal rate (Ro) was larger compared to other examples.

On the other hand, as shown in Table 4, the decrease rate of the stock removal rate became 30 % or more for the comparative examples 16 to 19, because the organic acid which acts as the precipitation inhibiting agent was not contained. In the comparative examples 20 to 26, the organic acidwas solely contained, so low evaluation values were obtained for the decrease rate of the stock removal rate, the dispersion properties, the clogging

of the polishing pads, and the surface defects. In the comparative examples 27 to 30, low evaluation values were obtained for the decrease rate of the stock removal rate, the dispersion properties, the clogging of the polishing pad, and the surface defects, because the combinations of the organic acid contained in the polishing composition of each comparative examples were different from the combinations of the organic acids contained in the polishing composition of each embodiment.

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

Claims

CLAIMS:

1. A polishing composition for polishing a substrate for a magnetic disc, characterized in that the composition includes, a first organic acid selected from the group consisting of glycine, glyceric acid, mandelic acid, ascorbic acid, glutamic acid, glyoxylic acid, malic acid, glycolic acid, lactic acid, gluconic acid, succinic acid, tartaric acid, maleic acid, itaconic acid, crotonic acid, nicotinic acid and the mixture thereof, a second organic acid selected from the group consisting of glycine, malic acid, lactic acid, gluconic acid, tartaric acid, maleic acid, itaconic acid, crotonic acid and the mixture thereof, and differs from the first organic acid, an abrasive material selected from the group consisting of aluminum oxide, silicon dioxide, cerium oxide, zirconium oxide, titanium oxide, silicon nitride, silicon carbide, and the mixture thereof, and water.

2. The polishing composition of claim 1, characterized in that said second organic acid is selected from the group consisting of glycine, malic acid, lactic acid, gluconic acid, and the mixture thereof.

3. The polishing composition of claim 1 or 2,-characterized in that said first organic acid is selected from the group consisting of malic acid, glycolic acid, succinic acid, and the mixture thereof.

4. The polishing composition according to any one of claims 1 to 3, characterized in that the weight of each said first organic acid and said second organic acid is 0.01 to 10 weight % of the total weight of said polishing composition.

5. A polishing composition for polishing a substrate for a magnetic disc, characterized in that the composition includes,

a first organic acid selected from the group consisting of glycine, glyceric acid, mandelic acid, ascorbic acid, glutamic acid, glyoxylic acid, malic acid, glycolic acid, lactic acid, gluconic acid, succinic acid, tartaric acid, maleic acid, itaconic acid, crotonic acid, nicotinic acid, and the mixture thereof, a second organic acid selected from the group consisting of citric acid, iminodiaceticacid, malonicacid, oxalic acid, alanine, propionic acid, and the mixture thereof, an abrasive material selected from the group consisting of aluminum oxide, silicon dioxide, cerium oxide, zirconium oxide, titanium oxide, silicon nitride, silicon carbide, and the mixture thereof, and water.

6. The polishing composition of claim 5, characterized in that said second organic acid is selected from the group consisting of citric acid, iminodiacetic acid, and the mixture thereof.

7. The polishing composition of claim 6, characterized in that said second organic acid is citric acid.

8. The polishing composition according to any one of claims 5 to 7, characterized in that said first organic acid is selected from the group consisting of malic acid, glycolic acid, succinic acid, and the mixture thereof.

9. The polishing composition according to any one of claims 5 to 8, characterized in that the weight of said first organic acid is 0.01 to 10 weight % of the total weight of said polishing composition and the weight of said second organic acid is 0.01 to 5 weight % of the total weight of said polishing composition.

10. A polishing composition for polishing a substrate for a magnetic disc, characterized in that the composition includes itaconic acid as an indispensable component,

an organic acid selected from the group consisting of glycine, glyceric acid, mandelic acid, ascorbic acid, glutamic acid, glyoxylic acid, malic acid, glycolic acid, lactic acid, gluconic acid, succinic acid, tartaric acid, maleic acid, crotonic acid, nicotinic acid, citric acid, iminodiacetic acid, malonic acid, oxalic acid, alanine, propionic acid, and the mixture thereof, an abrasive material selected from the group consisting of aluminum oxide, silicon dioxide, cerium oxide, zirconium oxide, titanium oxide, silicon nitride, silicon carbide, and the mixture thereof, and water.

11. The polishing composition of claim 10, characterized in that the composition contains at least citric acid as the organic acid.

12. The polishing composition of claim 11, characterized in that the composition further contains succinic acid as the organic acid.

13. The polishing composition according to any one of claims 10 to 12, characterized in that the weight of the itaconic acid is 0.01 to 5 weight % of total weight of said polishing composition.

14. The polishing composition according to any one of claims 10 to 13, characterized in that the weight of said organic acid is 0. 01 to 10 weight % of the total weight of said polishing composition,

15. The polishing composition according to any one of claims 1 to 14, characterized in that said abrasive material is on8 of aluminum oxide and silicon dioxide.

16. The polishing composition according to any one of claims 1 to 15, characterized in that the weight of said abrasive material is 0. 1 to 40 weight % of total weight of said polishing composition.

17. The polishing composition according to any one of claims 1

to 16, characterized in that pH of said polishing composition is 2 to 7.

18. A polishing process for polishing a substrate of a magnetic disc, the process characterized by using said polishing composition according to any one of claims I to 17.

19. A polishing composition substantially as hereinbefore described with reference to the accompanying examples.

20. A polishing process substantially as hereinbefore described with reference to the accompanying examples.

<