Polishing slurry and polishing method using same

Info

Publication number: 20080076327
Type: Application
Filed: Aug 17, 2007
Publication Date: Mar 27, 2008
Applicant:
Inventors: Kazuei Yamaguchi (Tokyo), Yasuyuki Yokota (Tokyo), Sanaki Horimoto (Tokyo)
Application Number: 11/893,830

Abstract

Polishing slurry is caused to be present between a surface of a soft magnetic layer and a polishing tool such as a polishing pad and the surface of the soft magnetic layer and the polishing tool are moved relative to each other. The polishing slurry contains silica particles as abrading particles, compounds containing carboxylic acid and amino polycarboxylic acid and an oxidizing agent as a polishing accelerator, organic and/or inorganic compound of phosphoric acid, nitride and/or nitrite as an anti-corrosion agent and a pH conditioner such that the slurry has pH value between 4 and 11.

Description

Description

This application claims priority on Japanese Patent Application 2006-256756 filed Sep. 22, 2006.

BACKGROUND OF THE INVENTION

This invention relates to polishing slurry for and a method of polishing the surface of a soft magnetic layer formed on the surface of a substrate for a perpendicular magnetic recording hard disk.

Data processing devices for recording and reproducing data such as characters, images and sounds are coming to be incorporated not only into a personal computer but also into an electronic apparatus such as a television, a camera, a portable music player and a portable telephone. Such data processing devices are required to have a higher processing capability (or an increased recording capacity) and an improved accuracy in reproduction, as well as compactness.

Data processing devices record and reproduce such data magnetically by means of a magnetic head on and from a magnetic recording medium. As magnetic recording media of this kind, perpendicular magnetic recording disks are coming to be investigated, as disclosed, for example, in Japanese Patent Publications Tokkai 2004-362746, 5-266455 and 6-103554.

Perpendicular magnetic recording disks are formed by forming a soft magnetic layer for improving the efficiency of recording and reproduction of data signals and a perpendicular magnetic recording layer comprising a perpendicular magnetization film for recording data signals by a conventionally known thin-film technology such as sputtering. In addition to these layers, a non-magnetic layer having functions of improving the crystalline characteristics of the perpendicular magnetic recording layer and controlling the crystalline particle diameters is formed. In order to prevent the generation of noise caused by the displacement of a magnetic wall due to a leaked magnetic field (or spike noise, in particular), the soft magnetic layer may be divided into two layers for inserting a hard magnetic layer in between and pinning the magnetic wall so as to inhibit the movement of the magnetic wall, as disclosed in Japanese Patent Publication Tokkai 5-266455. In order to make the reproduced output waveform uniform within the surface of the perpendicular magnetic recording disk, or for improving the modulation characteristics (or the uniformity of the reproduced output waveform for one cycle of the recording medium at the time of reproduction), furthermore, it has been known to form approximately concentric circular texturing marks in the circumferential direction on the surface of the non-magnetic substrate by carrying out a texturing process, to thereafter form a soft magnetic layer through a hard magnetic layer (also referred to as the bias layer) on the surface of this non-magnetic substrate, and to form a perpendicular magnetic recording layer thereon, as disclosed in Japanese Patent Publication Tokkai 6-103554.

In summary, a perpendicular magnetic recording layer for recording data is formed above a soft magnetic layer (also referred to as a soft magnetic backing layer) which can pass the magnetic fluxes from the magnetic head easily. With such a two-layer structure, the intensity of the generated magnetic field from the magnetic head and the slope of the magnetic field are increased so as to improve the resolution of recordation, and the leaked magnetic fluxes from the medium is also increased such that a high-density recording becomes possible.

As the material for the soft magnetic layer, NiFe alloys and amorphous alloys with Co as the principal component are generally used but a film thickness of 0.1 μm-several μm is necessary in order to obtain a sufficient recording-reproduction characteristics with such a material. From the point of view of mass production, the production cost would be too high if soft magnetic layers with such thickness were to be produced by sputtering. For this reason, soft magnetic layers with Fe, Co, B, etc. being added to NiP such as Ni—Fe—P layers and Ni—Co—P layers and those comprising soft magnetic NiP with concentration of P less than 6% are being used to form films by an electroless plating method in order to reduce the cost of mass production, as disclosed, for example, in Japanese Patent Publications Tokkai 2004-335068, 2005-353177, 2006-21259 and 2006-63438.

Such soft magnetic layers, like soft magnetic NiP layers with concentration of P less than 12% or more, must have the layer surface flattened by polishing. Since NiP layers with P concentration 12% or more have a high acid resistance, a strongly acidic polishing liquid with a high etching power is used but soft magnetic layers as described above are low in acid resistance. If a strongly acidic polishing liquid is used for polishing their surfaces, the layer surface is unevenly dissolved and cannot be made flat and even. Moreover, nickel phosphate is recrystallized due to corrosion and a black film is formed.

For this reason, alkaline polishing liquids with pH8 or high were used or the size of the abrading particles in the polishing slurry was specified for the surface polishing of a soft magnetic layer, as disclosed in Japanese Patent Publications Tokkai 2004-259378, 2004-342294, 2005-149603, 2005-216465 and 2005-302137.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide polishing slurry capable of polishing the surface of a soft magnetic layer formed on the surface of a substrate for a perpendicular magnetic recording hard disk without corroding it excessively and at a high polishing rate at a high level of accuracy, as well as a polishing method using such polishing slurry.

Polishing slurry of this invention is characterized as comprising abrading particles, a polishing accelerator, an anti-corrosion agent, a pH conditioner and water.

Silica particles are contained as the abrading particles. They are colloidal silica with an average particle diameter of 20 nm or more and 100 nm or less.

A compound containing carboxylic acid, a compound containing amino polycarboxylic acid and an oxidizing agent are contained as the polishing accelerator. At least one of the compound containing carboxylic acid and the compound containing amino polycarboxylic acid is ammonium salt. The oxidizing agent is hydrogen peroxide water.

The anti-corrosion agent includes one or more compounds selected from the group consisting of organic and inorganic compounds of phosphoric acid, nitrides and nitrites.

The pH conditioner is added such that the polishing slurry is conditioned to be between pH4 and pH11.

If the pH value of the polishing slurry is less than 7, the anti-corrosion agent comprises an organic or inorganic compound of phosphoric acid and the pH conditioner comprises hydroxylic acids.

If the pH value of the polishing slurry is more than 7, the anti-corrosion agent comprises a nitride and the pH conditioner comprises an amine.

With respect to the total weight of the polishing slurry of this invention, silica particles are contained at a rate of 1 weight % or more and 30 weight % or less, the compound containing carboxylic acid and the compound containing amino polycarboxylic acid of the polishing accelerator are together contained at a rate of 0.01 weight % or more and 20 weight % or less, the oxidizing agent of the polishing accelerator is contained at a rate of 0.1 weight % or more and 20 weight % or less, and the anti-corrosion agent is contained at a rate of 0.001 weight % or more and 5 weight % or less.

A method of this invention for polishing the surface of a soft magnetic layer formed on the surface of a substrate for a perpendicular magnetic recording hard disk is characterized as comprising the steps of causing polishing slurry of this invention as described above to be present between the surface of the soft magnetic layer and a polishing tool which preferably comprises a polishing pad, and causing the surface of the soft magnetic layer and the polishing tool to move relative to each other;

According to this invention, the surface of a soft magnetic layer formed on the surface of a substrate for a perpendicular magnetic recording hard disk can be made flat and even (such that the average surface roughness (Ra) is 0.2 nm or less and the surface waviness is 0.1 nm or less) at a high polishing rate and with a high level of accuracy, without excessively corroding the surface of the soft magnetic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B respectively show a lower lapping plate and an upper lapping plate of a polishing machine that may be used for the method of this invention.

DETAILED DESCRIPTION OF THE INVENTION

Polishing slurry of this invention is for polishing the surface of a soft magnetic layer formed on the surface of a substrate for a perpendicular magnetic recording hard disk, comprising abrading particles, a polishing accelerator, an anti-corrosion agent, an pH conditioner and water.

As the abrading particles, silica particles are included, and their average diameter is in the range of 5 nm or more and 300 nm or less. As silica particles, colloidal silica obtainable by hydrolysis such as metallic alkoxides and sodium silicate or fumed silica obtainable by the spray-dry method, etc. may be used. It is preferable to use colloidal silica with average diameter in the range of 20 nm or more and 100 nm or less.

Examples of polishing accelerator include compounds containing carboxylic acid, compounds containing amino polycarboxylic acid and oxidizing agents.

Examples of compound containing carboxylic acid include compounds of carboxylic acid and polyvalent carboxylic acid such as oxalic acid, lactic acid, malic acid, citric acid, malonic acid, tartaric acid, succinic acid, fumaric acid, maleic acid, formic acid, acetic acid, butyric acid, valerianic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid and oxocarboxylic acid. A preferred example of compound containing carboxylic acid is ammonium oxalate.

Examples of compound containing amino polycarboxylic acid include compounds such as ethylene diamine-4-acetic acid, diethylene triamine-5-acetic acid, hydroxy ethylene diamine-2-acetic acid, triethylene tetramine-6-acetic acid, hydroxy ethylimino-2-acetic acid, dihydroxy ethylglycine and 1,3-propane diamine-4-acetic acid. Being capable of exhibiting similar effects as these compounds, amino polyphosphonic acid may be also included. A preferred example of compound containing amino polycarboxylic acid is diethylene triamine-5-acetic acid-2-ammonium.

Between compounds containing carboxylic acid and compounds containing amino polycarboxylic acid, a compound of either category is an ammonium salt.

Examples of oxidizing agent contained in a polishing accelerator include hydrogen peroxide water, ozone water, sodium hypochlorite, potassium hypochlorite and calcium hypochlorite. A preferred example of oxidizing agent is hydrogen peroxide water.

Examples of anti-corrosion agent include compounds having one or more selected from organic compounds of phosphoric acid, inorganic compounds of phosphoric acid, nitrides and nitrites.

Examples of organic and inorganic salts of phosphoric acid include compounds of phosphoric acid, polyphosphoric acid, pyrophosphoric acid, metaphosphoric acid and phosphonic acid. Examples of nitride include triazoles such as benzotriazole, triazole, imitazole and tolyltrizole and imidazoles. Examples of nitrite include nitrites such as sodium nitrite, potassium nitrite, calcium nitrite, ethyl nitrite, isoamyl nitrite, isobutyl nitrite and isopropyl nitrite, and nitrite esters.

When the acidity-alkalinity of the polishing slurry of this invention is adjusted to pH7 or over, inorganic phosphoric acids are preferable as the anti-corrosion agent. When the acidity-alkalinity of the polishing slurry of this invention is adjusted to less than pH7, nitrides are preferable as the anti-corrosion agent.

Examples of pH conditioner include salts of phosphoric acid and boric acid such as phosphoric acid-2-hydrogen-ammonium, phosphoric acid-hydrogen-2-ammonium and ammonium tetraborate tetrahydrate.

When the acidity-alkalinity of the polishing slurry of this invention is adjusted to pH7 or over, alkaline pH conditioners are preferred such as ammonia water, ammonium carbonate, and amines such as ethylamine, methylamine, triethyl amine and tetramethyl amine. Salts of phosphoric acid are included as preferred example of pH conditioner.

When the acidity-alkalinity of the polishing slurry of this invention is adjusted to less than pH7, acidic pH conditioners are preferred, inclusive of hydroxylic acids such as lactic acid, citric acid, malic acid, tartaric acid and glyceric acid.

A method of this invention for polishing the surface of a soft magnetic layer formed on the surface of a substrate for a perpendicular magnetic recording hard disk includes the steps of causing polishing slurry of this invention as described above to be present between the surface of the soft magnetic layer of the substrate and a polishing tool and moving the surface of the soft magnetic layer and the polishing tool relative to each other. Preferable examples of the polishing tool include polishing pads.

As a preferable example, a double-surface polishing machine as shown in FIGS. 1A and 1B may be used to polish the surfaces of soft magnetic layers formed on the surfaces of a substrate 15 for a perpendicular magnetic recording hard disk to make them flat and even. As shown, the polishing of the both surfaces of the substrate 15 is carried out by placing the substrate 15 at the opening 14 of a solar gear 17 of a lower lapping plate 12 having a polishing pad 10 pasted on its surface and a planet gear 13 engaging with an internal gear 16, pressing it from above with an upper lapping plate 11 having another polishing pad 10′ on its surface, and causing the solar gear 17 to rotate in the direction of arrow W by means of an external driver motor while supplying polishing slurry of this invention through openings 18 in the upper lapping plate 11 into the space between the upper and lower lapping plates 11 and 12 such that the planet gear 13 rotates in the direction of arrow X and around the solar gear in the direction of arrow Y.

Prior art sheets of suede, woven or unwoven cloth, flocked cloth or foamed material may be cut into the form of a pad may be used as the polishing pads 10 and 10′. Polishing pads of a suede type are preferably used.

Polishing Test 1

Samples of polishing slurry Test Examples (1-1)-(1-12) and Comparison Examples (1-1)-(1-5) (all acidic with pH value less than 7 except for Comparison Example (1-5)) were used to polish both surfaces of substrates for a perpendicular magnetic recording hard disk having soft magnetic layers formed on the surfaces and the results were compared in terms of polishing rate, average surface roughness (Ra), surface waviness, numbers of corrosion, scratches and particles after the polishing.

The substrates that were polished were aluminum substrates with diameter 95 mm having non-magnetic Ni—P films (with P concentration of 12% or more) formed on both surfaces by the electroless plating method and Ni—Co—P layers (soft magnetic layers) with thickness about 3.0 μm formed thereon. The average surface roughness (Ra) (average surface roughness of their soft magnetic layers) of these substrates before the polishing was 0.50 nm-0.10 nm, and their surface waviness (Wa) was 0.10 nm-0.15 nm.

FIGS. 1A and 1B show the double-surface polishing machine (product name: 9BF, produced by Hamai Sangyo Kabushiki Kaisha) that was used for the polishing. Polishing pads of the suede-type were pasted onto the upper and lower lapping plates, and both surfaces of ten substrates were polished simultaneously. The conditions of the polishing were as shown in Table 1.

TABLE 1 Polishing pressure 90 gf/cm² Rotational speed Upper lapping plate 40 rpm of lapping plates Lower lapping plate 40 rpm Supply rate of polishing slurry 200 ml/minute Polishing time 10 minutes

The polishing rate, defined as the polished quantity per unit time in units of mg/minute), is obtained by dividing the difference in weight of the substrate before and after the polishing by the polishing time. The weight of the substrate was measured by using a commercially available measuring instrument (product name: HF-20 produced by A&M Corporation).

The average surface roughness (Ra) was measured in units of nm by using an atomic force microscope AFM (product name: Nanoscope Dimension 3100 Series produced by Digital Instruments Corporation) over a measurement field of vision of 10 μm×10 μm.

The surface waviness (Wa) was measured in units of nm by using a non-contact three-dimensional surface profiler (product name: NewView 5000 produced by ZYGO CORPORATION) (object lens=10 times; intermediate lens=0.8; and cutoff filter=0.05 mm-0.5 mm).

The numbers of corrosion, scratches and particles per surface were each counted from each of the surfaces of the substrate after the polishing by using a disk surface observation device (Product Name: MicroMaX VMX-2100, produced by Vision Sitec, Ltd.) and averaging the counted numbers.

The composition of each of the samples of polishing slurry Test Examples (1-1)-(1-12) is shown in Tables 2 and 3 (in units of weight %). Test Example (1-1) is a preferred example in the range of pH4-pH5. Test Example (1-2) is different therefrom only in that salt of phosphoric acid is not added. Test Example (1-3) is a preferred example in the range of pH5-pH6. Test Example (1-4) is a preferred example in the range of less than and about equal to pH7. Test Example (1-5) is different from Test Example (1-4) only in that the average diameter of the silica particles is 80 nm. Test Example (1-6) has nitrous acid added as anti-corrosion agent. Test Example (1-7) has a nitrite (benzotriazole) added as anti-corrosion agent. Test Example (1-8) has a reduced amount (concentration) of amino polycarboxylic acid. Test Example (1-9) has an increased concentration (quantity) of oxidizing agent (hydrogen peroxide water). Test Example (1-10) has an increased concentration (quantity) of compound of carboxylic acid (ammonium oxalate). Test Example (1-11) uses potassium oxalate as compound of carboxylic acid. Test Example (1-12) uses ammonium formate as compound of carboxylic acid.

The composition of each of the samples of polishing slurry Comparison Examples (1-1)-(1-5) is shown in Table 4 (in units of weight %). Comparison Example (1-1) is conditioned to pH3.5. Comparison Example (1-2) does not include any anti-corrosion agent and is conditioned to pH4.5. Comparison Example (1-3) is conditioned to less than pH3. Comparison Example (1-4) is conditioned to pH4.6. Comparison Example (1-5) is conditioned to be alkaline at pH9.3.

TABLE 2 Test Examples 1-1 1-2 1-3 1-4 1-5 1-6 Silica particles 40 nm 5.0 5.0 5.0 5.0 — 5.0 80 nm — — — — 5.0 — Compound of Ammonium oxalate 0.25 0.25 0.25 0.25 0.25 0.25 carboxylic acid Potassium oxalate — — — — — — Ammonium formate — — — — — — Compound of amino DTPA 2 ammonium 5.0 5.0 5.0 5.0 5.0 5.0 polycarboxylic acid Oxidizing agent Hydrogen peroxide 2.5 2.5 2.5 2.5 2.5 2.5 water Anti-corrosion agent Inorganic salt of 0.5 0.5 0.5 0.5 0.5 — phosphoric acid Nitrite — — — — — 0.5 Benzotriazole — — — — — — pH conditioner Ammonia water — — — 0.1 0.1 0.1 Lactic acid 0.2 0.2 — — — — Salt of phosphoric acid 0.2 — 0.2 0.2 0.2 0.2 Water Pure water 86.35 86.55 86.55 86.45 86.45 86.45 pH 4.6 4.5 5.5 6.7 6.0 4.3 DTPA: Diethylene triamine-5-acetic acid

TABLE 3 Test Examples 1-7 1-8 1-9 1-10 1-11 1-12 Silica particles 40 nm 5.0 5.0 5.0 5.0 5.0 5.0 80 nm — — — — — — Compound of Ammonium oxalate 0.25 0.25 0.25 0.50 — — carboxylic acid Potassium oxalate — — — — 0.25 — Ammonium formate — — — — — 0.25 Compound of amino DTPA 2 ammonium 5.0 2.5 5.0 5.0 5.0 5.0 polycarboxylic acid Oxidizing agent Hydrogen peroxide 2.5 2.5 5.0 2.5 2.5 2.5 water Anti-corrosion agent Inorganic salt of — 0.5 0.5 0.5 0.5 0.5 phosphoric acid Nitrite — — — — — — Benzotriazole 0.1 — — — — — pH conditioner Ammonia water — — — — — — Lactic acid 0.2 — — — — — Salt of phosphoric acid 0.2 0.2 0.2 0.2 0.2 0.2 Water Pure water 86.75 89.05 84.04 86.30 86.55 86.55 pH 4.1 5.8 5.5 6.0 5.6 5.0 DTPA: Diethylene triamine-5-acetic acid

TABLE 4 Comparison Examples 1-1 1-2 1-3 1-4 1-5 Silica particles 40 nm 5.0 5.0 5.0 5.0 5.0 Compound of Ammonium oxalate 0.25 0.25 0.25 — — carboxylic acid Potassium oxalate — — — 0.25 0.25 Compound of amino DTPA 2 ammonium 5.0 5.0 5.0 — — polycarboxylic acid DTPA 5 sodium — — — 5.0 5.0 Oxidizing agent Hydrogen peroxide water 2.5 2.5 2.5 2.5 2.5 Anti-corrosion agent Inorganic salt of phosphoric acid 0.5 — 0.5 0.5 — pH conditioner Lactic acid 0.3 0.1 1.0 0.5 — Salt of phosphoric acid 0.2 0.2 0.2 0.2 — Water Pure water 86.25 86.95 85.55 86.05 87.25 pH 3.5 4.5 2.9 4.6 9.3 DTPA: Diethylene triamine-5-acetic acid

Test results with Test Examples (1-1)-(1-12) and Comparison Examples (1-1)-(1-5) are summarized in Tables 5 and 6. Regarding the numbers of corrosion, scratches and particles, A indicates less than 10, B indicates 10 or more and less than 20, C indicates 20 or more and less than 40, and D indicates 40 or more.

TABLE 5 Test Examples 1-1 1-2 1-3 1-4 1-5 1-6 Polishing rate (mg/minute) 6.8 6.2 6.0 4.3 6.4 4.9 Average surface 0.14 0.14 0.11 0.10 0.19 0.15 roughness (Ra) (nm) Surface waviness (Wa) (nm) 0.07 0.08 0.06 0.06 0.09 0.07 Corrosion (number/surface) B B A A B B Scratches (number/surface) B B B B B B Particles (number/surface) B B B B B B Test Examples 1-7 1-8 1-9 1-10 1-11 1-12 Polishing rate (mg/minute) 5.0 5.5 5.9 5.4 5.0 4.4 Average surface 0.13 0.12 0.13 0.11 0.16 0.18 roughness (Ra) (nm) Surface waviness (Wa) (nm) 0.07 0.07 0.06 0.07 0.08 0.09 Corrosion (number/surface) B B A A B B Scratches (number/surface) B B B B B B Particles (number/surface) B B B B B B

TABLE 6 Comparison Examples 1-1 1-2 1-3 1-4 1-5 Polishing rate (mg/minute) 7.0 7.2 7.7 4.0 2.0 Average surface 0.25 0.24 0.25 0.20 0.11 roughness (Ra) (nm) Surface waviness (Wa) (nm) 0.12 0.11 0.10 0.08 0.09 Corrosion (number/surface) D D D C B Scratches (number/surface) C C C B B Particles (number/surface) B B B B B

Tables 5 and 6 show that a high level of accuracy in polishing is accomplished with each of the Test Examples embodying this invention with average surface roughness of 0.2 nm or less and surface waviness of 0.1 nm or less and that equivalent or better results are obtained regarding corrosion, scratches and particles compared to any of Comparison Examples.

Although equivalent results are obtained with Comparison Example (1-5), this slurry is alkaline and its polishing rate is lower (less than ½).

Polishing Test 1 was for the polishing of a Ni—Co—P layer (soft magnetic layer) and the results depend on the material of the soft magnetic layer. In the case of a Ni—Co—P layer, however, it can be understood from the results of Comparison Examples (1-1) and (1-3) that corrosions occur even if an anti-corrosion agent is added if the polishing slurry has pH4 or less in the case of a Ni—Co—P layer.

Results of Comparison Examples (1-1) and (1-2) indicate that corrosions occur unless an anti-corrosion agent is added if the polishing slurry has pH4 or over and is weakly acid with pH7 or lower. In other words, in the case of a Ni—Co—P layer, it is necessary that acidity of the polishing slurry be over pH4 and pH7 or below and an anti-corrosion agent be added.

From the results of Comparison Examples (1-4) and (1-5), as compared to the results of Comparison Examples (1-1)-(1-3), it is understood that the polishing rate drops significantly if ammonium salt is not contained as polishing accelerator. It is to be noted that every example according to this invention contains ammonium salt.

Polishing Test 2

Samples of polishing slurry Test Examples (2-1)-(2-11) and Comparison Examples (2-1)-(2-6) (all alkaline with pH value 8 or more) were used to polish both surfaces of substrates for a perpendicular magnetic recording hard disk having soft magnetic layers formed on the surfaces and the results were compared in terms of polishing rate, average surface roughness (Ra), surface waviness, numbers of corrosion, scratches and particles after the polishing.

The substrates that were polished were similar to those used in Polishing Test 1 with diameter 95 mm having non-magnetic Ni—P films (with P concentration 12% or more) formed on both surfaces by the electroless plating method and Ni—Co—P layers (soft magnetic layers) with thickness about 3.0 μm formed thereon. The average surface roughness (Ra) (average surface roughness of their soft magnetic layers) of these substrates before the polishing was 0.50 nm-0.10 nm, and their surface waviness (Wa) was 0.10 nm-0.15 nm.

A double-surface polishing machine (product name: 9BF, produced by Hamai Sangyo Kabushiki Kaisha), as used in Polishing Test 1 and described above, was used for the polishing. Polishing pads of the suede-type were pasted onto the upper and lower lapping plates, and both surfaces of ten substrates were polished simultaneously. The conditions of the polishing were as shown in Table 1 described above.

The polishing rate, the average surface roughness (Ra) and the surface waviness (Wa) were measured as described above.

The numbers of corrosion, scratches and particles per surface were each counted also as described above and the counted numbers were averaged.

The composition of each of the samples of polishing slurry Test Examples (2-1)-(2-11) is shown in Tables 7 and 8. Test Example (2-1) is a preferred example with alkalinity in the neighborhood of pH9. Test Example (2-2) is different therefrom only in that anti-corrosive agent is not added. Test Example (2-3) is different from Test Example (2-1) in that inorganic salt of phosphoric acid is added as anti-corrosion agent. Test Example (2-4) has ammonium carbonate added as pH conditioner. Test Example (2-5) has tetramethyl ammonium hydroxide added as pH conditioner. Test Example (2-6) has salt of boric acid added as pH conditioner. Test Example (2-7) is an example not using any pH conditioner. Test Example (2-8) has phthalic acid added as polishing accelerator. Test Example (2-9) has tartaric acid added as polishing accelerator. Test Example (2-10) has boric acid added as polishing accelerator. Test Example (2-11) has malonic acid added as polishing accelerator.

TABLE 7 Test Examples 2-1 2-2 2-3 2-4 2-5 2-6 Silica particles 40 nm 5.0 5.0 5.0 5.0 5.0 5.0 Compound of Ammonium oxalate 0.25 0.25 0.25 0.25 0.25 0.25 carboxylic acid Phthalic acid — — — — — — Tartaric acid — — — — — — Boric acid — — — — — — Malonic acid — — — — — — Compound of amino DTPA 2 ammonium 5.0 5.0 5.0 5.0 5.0 5.0 polycarboxylic acid Oxidizing agent Hydrogen peroxide 2.5 2.5 2.5 2.5 2.5 2.5 water Anti-corrosion agent Inorganic salt of — — 0.5 — — — phosphoric acid Benzotriazole 0.1 — — 0.1 0.1 0.1 pH conditioner Ammonia water 0.5 0.5 0.4 — — 0.5 Ammonium carbonate — — — 0.5 — — Tetramethyl — — — — 0.5 — ammonium hydroxide Phosphoric acid 0.2 0.2 0.2 0.2 0.2 — Boric acid (pH — — — — — 0.2 conditioner) Water Pure water 86.45 86.55 86.15 86.45 86.45 86.95 pH 8.8 8.8 8.8 8.2 8.3 8.4 DTPA: Diethylene triamine-5-acetic acid

TABLE 8 Test Examples 2-7 2-8 2-9 2-10 2-11 Silica particles 40 nm 5.0 5.0 5.0 5.0 5.0 Compound of carboxylic acid Ammonium oxalate 0.25 — — — — Phthalic acid — 0.25 — — — Tartaric acid — — 0.25 — — Boric acid — — — 0.25 — Malonic acid — — — — 0.25 Compound of amino DTPA 2 ammonium 5.0 5.0 5.0 5.0 5.0 polycarboxylic acid Oxidizing agent Hydrogen peroxide 2.5 2.5 2.5 2.5 2.5 water Anti-corrosion agent Inorganic salt of — — — — — phosphoric acid Benzotriazole 0.1 0.1 0.1 0.1 0.1 pH conditioner Ammonia water 0.2 1.6 1.2 1.1 1.7 Ammonium carbonate — — — — — Tetramethyl — — — — — ammonium hydroxide Phosphoric acid — 0.2 0.2 0.2 0.2 Boric acid (pH — — — — — conditioner) Water Pure water 86.95 85.15 85.50 85.60 85.00 pH 7.1 8.8 8.8 8.8 8.8 DTPA: Diethylene triamine-5-acetic acid

The composition of each of the samples of polishing slurry Comparison Examples (2-1)-(2-6) is shown is Table 9 (in units of weight %). Comparison Example (2-1) is conditioned to above pH11. Comparison Example (2-2) has EDTA-4-Na added as polishing accelerator. Comparison Example (2-3) has HEDP-4-Na added as polishing accelerator. Comparison Example (2-4) has DTPA-5-Na added as polishing accelerator. Comparison Example (2-5) has caustic soda added as pH conditioner. Comparison Example (2-6) has no pH conditioner added but alkylene glycol and glycerol added.

TABLE 9 Comparison Examples 2-1 2-2 2-3 2-4 2-5 2-6 Silica particles 40 nm 5.0 5.0 5.0 5.0 5.0 5.0 Compound of Ammonium oxalate 0.25 0.25 0.25 0.25 0.25 0.25 carboxylic acid Carboxylic acid — — — — — 1.2 derivative Compound of amino DTPA-2-ammonium 5.0 — — — 5.0 — polycarboxylic acid EDTA-4-Na — 5.0 — — — 7.0 HEDP-4-Na — — 5.0 — — — DTPA-5-Na — — — 5.0 — — Oxidizing agent Hydrogen peroxide 2.5 2.5 2.5 2.5 2.5 — water Anti-corrosion agent Benzotriazole 0.1 0.1 0.1 0.1 0.1 — pH conditioner Ammonia water 10.0 — — — — — Caustic soda — — — — 0.05 — Salt of phosphoric acid — 0.2 0.2 0.2 — — Others Alkylene glycol — — — — — 0.24 glycerol — — — — — 0.1 Water Pure water 77.15 86.95 86.95 86.95 87.10 92.51 pH 11.1 9.0 9.0 8.4 11.0 9.0 DTPA: Diethylene triamine-5-acetic acid Carboxylic acid derivative: Polycarboxylate polymer type surfactant (product name: DEMOL-EP produced by Kao Kabushiki Kaisha) Alkylene glycol: diethylene glycol mono-n-butylether EDTA: Ethylene diamine-4-acetic acid HEDP: Hydroxy ethylene diphosphonic acid (compound of amino polyphosphonic acid) having effects similar to amino polycarboxylic acids.

Test results with Test Examples (2-1)-(2-11) and Comparison Examples (2-1)-(2-6) are summarized in Tables 10 and 11. Regarding the numbers of corrosion, scratches and particles, A indicates less than 10, B indicates 10 or more and less than 20, C indicates 20 or more and less than 40, and D indicates 40 or more, as in Tables 4 and 5.

TABLE 10 Test Examples 2-1 2-2 2-3 2-4 2-5 2-6 Polishing rate (mg/minute) 3.5 3.1 2.4 3.9 3.8 2.8 Average surface 0.11 0.11 0.11 0.12 0.10 0.12 roughness (Ra) (nm) Surface waviness (Wa) (nm) 0.06 0.06 0.06 0.07 0.06 0.06 Corrosion (number/surface) A B A A A A Scratches (number/surface) B B B B B B Particles (number/surface) B B B B B B Test Examples 2-7 2-8 2-9 2-10 2-11 Polishing rate (mg/minute) 3.4 3.0 2.8 2.7 2.7 Average surface roughness (Ra) (nm) 0.11 0.10 0.10 0.12 0.10 Surface waviness (Wa) (nm) 0.06 0.07 0.06 0.08 0.06 Corrosion (number/surface) A A A A A Scratches (number/surface) B B B B B Particles (number/surface) B B B B B

TABLE 11 Comparison Examples 2-1 2-2 2-3 2-4 2-5 2-6 Polishing rate (mg/minute) 6.4 2.4 1.8 2.5 2.6 1.6 Average surface 0.28 0.11 0.11 0.10 0.11 0.10 roughness (Ra) (nm) Surface waviness (Wa) (nm) 0.12 0.06 0.07 0.06 0.06 0.06 Corrosion (number/surface) D A A A A A Scratches (number/surface) C B B B B A Particles (number/surface) B B B B B A

Tables 10 and 11 show that a high level of accuracy in polishing is accomplished with each of the Test Examples embodying this invention with average surface roughness of 0.2 nm or less and surface waviness of 0.1 nm or less and that equivalent or better results are obtained regarding corrosion, scratches and particles compared to any of Comparison Examples.

Although equivalent results are obtained with Comparison Example (2-6), this slurry sample does not contain any pH conditioner and its polishing rate is lower (less than ½) than by any of the other Comparison Examples.

Polishing Test 2 was for the polishing of a Ni—Co—P layer (soft magnetic layer) and the results depend on the material of the soft magnetic layer. In the case of a Ni—Co—P layer, however, it can be understood from the results of Comparison Examples (2-1) and (2-5) that corrosion takes place even if an anti-corrosion agent is added if the polishing slurry exceeds pH 11. In other words, in the case of a Ni—Co—P layer, it is understood that the pH value should be 11 or less.

Results of Test Examples (2-1)-(2-11) containing ammonium salts of DTPA as amino polycarboxylic acid compound and Comparison Examples (2-2)-(2-4) containing sodium salts of EDTA, HEDP and DTPA indicate that samples containing ammonium salts as amino polycarboxylic acid compound of polishing accelerator has equivalent or higher polishing rates compared to those containing sodium salts. From Comparison Examples (2-1) and (2-5), furthermore, it can be learned that the polishing rate increases if ammonia water (amine) is added as pH conditioner than if caustic soda is added.

Claims

1. Polishing slurry for polishing the surface of a soft magnetic layer formed on the surface of a substrate for a perpendicular magnetic recording hard disk, said polishing slurry comprising:

abrading particles;

a polishing accelerator;

an anti-corrosion agent;

a pH conditioner; and

water;

wherein said abrading particles include silica particles;

wherein said polishing accelerator includes a compound containing carboxylic acid, a compound containing amino polycarboxylic acid and an oxidizing agent;

wherein said anti-corrosion agent includes one or more compounds selected from the group consisting of organic and inorganic compounds of phosphoric acid, nitrides and nitrites; and

wherein said polishing slurry is conditioned to be between pH4 and pH 11 by said pH conditioner.

2. The polishing slurry of claim 1 wherein at least either of said compound containing carboxylic acid and said compound containing amino polycarboxylic acid is ammonium salt.

3. The polishing slurry of claim 1 wherein said oxidizing agent is hydrogen peroxide water.

4. The polishing slurry of claim 1 wherein the pH value of said polishing slurry is less than 7 and said anti-corrosion agent comprises an organic or inorganic compound of phosphoric acid.

5. The polishing slurry of claim 1 wherein the pH value of said polishing slurry is more than 7 and said anti-corrosion agent comprises a nitride.

6. The polishing slurry of claim 1 wherein the pH value of said polishing slurry is less than 7 and said pH conditioner comprises hydroxylic acids.

7. The polishing slurry of claim 1 wherein the pH value of said polishing slurry is more than 7 and said pH conditioner comprises an amine.

8. The polishing slurry of claim 1 wherein said silica particles comprise colloidal silica with an average particle diameter of 5 nm or more and 300 nm or less.

9. The polishing slurry of claim 1 wherein said silica particles comprise colloidal silica with an average particle diameter of 20 nm or more and 100 nm or less.

10. The polishing slurry of claim 1 wherein said silica particles are contained at a rate of 1 weight % or more and 30 weight % or less of the total weight of said polishing slurry;

wherein said compound containing carboxylic acid and said compound containing amino polycarboxylic acid are together contained at a rate of 0.01 weight % or more and 20 weight % or less of the total weight of said polishing slurry;

wherein said oxidizing agent is contained at a rate of 0.1 weight % or more and 20 weight % or less of the total weight of said polishing slurry; and

wherein said anti-corrosion agent is contained at a rate of 0.001 weight % or more and 5 weight % or less of the total weight of said polishing slurry.

11. A method of polishing the surface of a soft magnetic layer formed on the surface of a substrate for a perpendicular magnetic recording hard disk; said method comprising the steps of:

causing polishing slurry to be present between said surface of said soft magnetic layer and a polishing tool; and

causing said surface of said soft magnetic layer and said polishing tool to move relative to each other;

wherein said polishing slurry comprises: