Patent Application
20080076327
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-256756 | Sep 2006 | JP | national |
