JPH09204657A - Polishing composition and method for polishing magnetic disc substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To practice a polishing operation continually without causing the clogging of a polishing pad, etc., by a method wherein gelling-proof agent by which the level of a surface defect is minimized is contained in polishing composition. SOLUTION: Polishing composition with which a magnetic disc substrate is polished to have a mirror plane is composed of water, colloidal particles, aluminum nitrate and gelling-proof agent. Colloidal silica particles are used as the colloidal particles and their average particle diameter is, preferably, 5-120nm and the weight content of the colloidal silica is 1-40%. One or more of mixture of posphonic acid, phenanthroline and acetylacetoaluminum salt is used as the gelling-proof agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention makes it possible to polish a magnetic disk substrate used in a storage device such as a computer, especially an NiP-plated aluminum disk substrate to a high mirror surface, and to manufacture a high density magnetic disk substrate. And a method for polishing a magnetic disk substrate.

[0002]

2. Description of the Related Art Conventionally, for polishing a magnetic disk substrate, particularly an aluminum disk substrate, a method of using a polishing slurry prepared by adding various polishing accelerators to alumina fine particles is generally adopted. Along with the improvement of the storage density of the magnetic disk, the alumina fine particles and the polishing accelerator have been improved, and the polishing surface accuracy has also been improved. However, the polishing surface roughness achieved by this method is about 10Å in Ra. Recently,
There is a demand for a substrate capable of supporting a high density magnetic disk of 1 gigabyte or more with a 3.5 inch magnetic disk. In order to achieve this requirement, the average surface roughness Ra of the polished surface is 10 Å or less, preferably 7 Å or less, and the surface defects such as minute polishing marks and micropits which have not been a problem in the past are minimized. Need to In order to meet such requirements, the above-mentioned required conditions cannot be satisfied by the conventional method of polishing with the above-mentioned polishing slurry based on alumina fine particles.

[0003] Recently published Japanese Patent Application Laid-Open No. 7-240025 proposes a polishing method using a slurry in which a chemical corrosive agent is added to colloidal silica. When the magnetic disk substrate is polished based on this method, the surface roughness R
a satisfies the above requirement.

[0004]

However, when the inventors of the present invention tried the method of the above-mentioned Japanese Patent Laid-Open No. 7-240025, when the rinse (cleaning) was performed after polishing, the polishing liquid remaining in the polishing machine was removed. It was found that gelation occurred rapidly as the pH went into the neutral range. The occurrence of such gelation causes clogging of the polishing pad, and as a result, it becomes difficult to continue the polishing operation, which is not a practical method. The polishing method for the high-density magnetic disk substrate is currently in the above-mentioned situation, and no method that can be industrially adopted has been found. Therefore, there is a demand for development of a polishing method that satisfies the requirements for the polished surface roughness required for a high-density magnetic disk substrate.

[0005]

In view of such circumstances, the present inventors have found that gelation in the method disclosed in Japanese Patent Laid-Open No. 7-240025 makes continuous polishing operation difficult. The present inventors have found that the surface roughness such as micro pits and micro pits, which is industrially applicable and has a polishing surface roughness Ra of 10 Å or less, which is required for a high-density magnetic disk substrate, has been studied. The polishing composition and polishing method capable of minimizing the number of defects were investigated.
The inventors of the present invention have made diligent efforts to achieve the above-mentioned object, and as a result, studied, a polishing slurry composed of water, colloidal particles and aluminum nitrate was treated with phosphonic acid, phenanthroline,
The present inventors have found a polishing composition containing an anti-gelling agent which is one or a mixture of two or more acetylacetone aluminum salts.

[0006]

The colloidal particles used in the present invention are
Usually, negatively charged amorphous silica particles are dispersed in water to form a colloidal form (colloidal silica). Further, colloidal particles of alumina hydrate and ceria hydrate are referred to as colloidal particles. You may use it. The colloidal silica preferably has an average particle size of 5 to 120 nm. This is because if the average particle size is less than 5 nm, the processing rate is remarkably low, and particles larger than 120 nm tend to be difficult to industrially and stably manufacture. In addition, the particle size distribution is such that the peak part of the distribution curve is broad and wide, or the peak part of the distribution curve has two peaks of fine particles and coarse particles, rather than the peak parts of the distribution curve are sharp and the particle diameters are uniform. Has a higher processing rate. The amount of colloidal silica added to the polishing slurry is 1
-40% by weight is desirable. This is because if the addition amount is less than 1% by weight, the polishing rate is remarkably low, and if it exceeds 40% by weight, not only the polishing rate is not improved but also gelation tends to occur.

Aluminum nitrate (Al used in the present invention
_{(NO 3) 3 · 9H 2} O) , there is the action of the polishing accelerator, the addition amount is desirably 0.1 to 20 wt%, the most preferred amount is 1 to 20% by weight. The amount added is 0.
This is because if it is less than 1% by weight, its function is not sufficiently fulfilled, and if it exceeds 20% by weight, gelation tends to occur more easily.

As described above, the gelling agent used in the present invention is one kind or a mixture of two or more kinds of phosphonic acid, phenanthroline and acetylacetone aluminum salt. More specifically, the phosphonic acid is 1-hydroxyethylidene-1,1-diphosphonic acid _{(C 2 H 6 O 7 P} 2) or amino trimethylene phosphonic acid _{(C 2 H 12 O 9 P} 3 N), as the phenanthroline 1,10-phenanthroline monohydrate Japanese products (C ₁₂ H ₈
N ₂ · H ₂ O) as an aluminum acetylacetone aluminum salt, an aluminum complex salt of acetylacetone (Al [C
H (COCH ₃ ) ₃ ]) can be exemplified. Further, the content is preferably 0.1 to 10% by weight,
Since the optimum addition amount depends on the concentration (addition amount) of the colloidal silica, the particle diameter, the pH, and the type of the gelation inhibitor, it is necessary to adjust the addition amount according to each composition in practice. When the amount of the gelling agent added is too small, for example, less than 0.1% by weight, the gelation preventing effect is not exhibited, and when it is too large, for example, more than 10% by weight, gelation occurs by itself. Therefore, it is necessary to be careful when adjusting the addition amount.

In the polishing composition of the present invention comprising each of the above components, --Si is formed on the surface of the colloidal silica particles.
OH groups and -OH ^- ion present, the electric double layer is formed by alkali ions, although stabilized by repulsive forces between the particles, the polishing accelerating effect is imparted upon the addition of the aluminum nitrate as a polishing accelerator On the other hand, aluminum ions interfere with the surface charge, resulting in imbalance and gelation due to contact between particles. However, if the phosphonic acid, phenanthroline, and acetylacetone aluminum salt are added before the addition of aluminum nitrate, the buffering of aluminum ions can be prevented, and as a result, gelation can be prevented.

The polishing composition of the present invention contains a surfactant, a dispersant, a preservative, a stabilizer, and an acid or alkali agent for pH adjustment, in addition to the above components. Is also good. However, it is necessary to pay close attention to the kind and amount of addition so as not to cause gelation.

[0011]

EXAMPLE Nominal 3.5 ″ (φ95 mm) NiP-plated disks having the composition shown in Table 1 were prepared according to Example 7 and Comparative Example 2.
Polishing was performed under the polishing conditions shown below using one of the polishing compositions, and the polishing performance was measured. Table 3 shows the method of measuring the polishing performance. (Polishing conditions) Polishing machine: 4-way double-sided polishing machine (Plate diameter φ
640 mm) Polishing pad; Suede type (manufactured by Polytex DG Rodel Co., Ltd.) Lower platen rotation speed; 60 rpm Slurry supply amount; 30 ml / min Polishing time; 5 minutes Processing pressure; 50 g / cm ² Although the types and amounts of the particles and the antigelling agent were described, 5% by weight of aluminum nitrate was added to all the polishing compositions, and the balance was water. The slurry properties were also measured according to the measurement method shown in Table 3.
Further, the thickness of the polished substrate is 10
A 0 nm Cr layer, a 40 nm thick Co ₈₆ Cr ₁₂ Ta ₂ magnetic layer and a 25 nm thick carbon protective film were formed, and finally a lubricant was applied to a thickness of 2 nm to form magnetic disks. The magnetic characteristics of these magnetic disks were also measured according to the measuring method shown in Table 3. All results (polishing performance, slurry properties, magnetic properties) are shown in Table 2.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

[Table 3]

As is clear from Table 2, the polishing composition using alumina of Comparative Example 1 is not suitable for polishing a high-density magnetic disk substrate because the polishing rate is high but the surface roughness is large. It was a thing. In the polishing composition of Comparative Example 2 in which the gelling inhibitor was not added to the colloidal silica, the phenomenon of gelation was confirmed. In contrast, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotrimethylenephosphonic acid, 1,10-phenanthroline monohydrate, and polishing with the polishing composition of Examples 1 to 7 to which acetylacetone aluminum salt was added As a result, gelation did not occur due to the effect of adding the gelation inhibitor. Further, the addition of the gelation inhibitor did not show any deterioration in polishing rate, polishing surface accuracy (surface roughness, polishing marks), and performance as a magnetic disk (surface defect, glide test, certifier test).

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be implemented in any manner as long as the configuration described in the claims is not changed.

[0017]

As described above, the polishing composition and the polishing method of the present invention have a polishing surface roughness Ra of 10 Å or less required for a high-density magnetic disk substrate and have surface defects such as minute polishing marks and micropits. It is possible to obtain a polishing surface with a minimal level, and it is possible to continuously perform the polishing operation without causing clogging of the polishing pad. Therefore, the present invention is suitable for manufacturing a magnetic disk substrate used for a storage device such as a computer, particularly a high-density magnetic disk substrate.

Claims (8)

[Claims] 1. A polishing composition for mirror-polishing a magnetic disk substrate, which comprises water, colloidal particles, aluminum nitrate and an anti-gelling agent. 2. The polishing composition according to claim 1, wherein the colloidal particles are colloidal silica. 3. The polishing composition according to claim 2, wherein the particle size of colloidal silica is 5 to 120 nm in average diameter. 4. The weight ratio of colloidal silica is 1 to 40.
%, And the polishing composition according to claim 2 or 3. 5. The weight ratio of aluminum nitrate is 0.1 to 0.1.
It is 20%, The polishing composition as described in any one of Claims 1-4. 6. The anti-gelling agent is one or a mixture of two or more of phosphonic acid, phenanthroline, and acetylacetoaluminum salt.
The polishing composition according to any one of 1. 7. The weight ratio of the gelling inhibitor is 0.1-10.
%, And the polishing composition according to any one of claims 1 to 6. 8. A method for polishing a magnetic disk substrate, which comprises polishing with the polishing composition according to claim 1 in a method for mirror-polishing a magnetic disk substrate.