JPH044656B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method of manufacturing a substrate for a magnetic disk by precision polishing the surface of a crystallized glass substrate for a magnetic disk. [Technical Background] Generally, the following characteristics are required for a magnetic disk substrate. (1) The surface roughness after polishing must be good to ensure stable flying of the magnetic head and stability of recording characteristics due to the low head flying height of 0.3 μm or less. (2) There are no protrusions or hole-like depressions that can cause defects in the magnetic thin film formed on the substrate surface. (3) Must have sufficient mechanical strength to withstand machining, polishing, or high-speed rotation during use. (4) It must have corrosion resistance, weather resistance, and heat resistance. Conventionally, Al alloys have been used for magnetic disk substrates, but Al alloy substrates suffer from the crystal anisotropy of the material,
Due to material defects and nonmetallic inclusions present in the material, during machining and polishing processes, these may remain as protrusions on the substrate surface, or crystallized portions may fall off in spots and cause depressions. Even after thorough polishing, the surface roughness is only about 200 Å at most, and the surface has protrusions, depressions, and undulations, making it unsatisfactory as a substrate material for high-density magnetic recording disks. Currently, in order to improve the surface condition of substrate materials for sputter disks, a method is being used to form an alumite layer on the surface of an Al alloy to increase hardness and improve polishability.
Since trace impurities (Fe, Mn, Si) in the Al alloy precipitate as intermetallic compounds, these areas become a cause of dent defects after alumite treatment. Increasing the purity of the base alloy is nearly impossible in terms of manufacturing process, and in the case of Al alloys, handling has also become a problem in terms of corrosion resistance and cleanliness. In addition, when forming a thin film magnetic recording medium by sputtering or plating, there are problems with chemical reaction and diffusion between the Al alloy and the magnetic film, and it is also necessary to heat-treat the magnetic film during the process. It is difficult to perform heat treatment because the shape accuracy deteriorates and the surface runout acceleration increases. There is also a method of forming oxides such as SiO ₂ and Al ₂ O ₃ on an Al substrate by sputtering, but
The drawback is that the adhesion to the substrate after spatter formation is weak. In general, the quality of the processing of the magnetic disk substrate is determined by the runout of the magnetic disk, the acceleration component,
It depends on the signal error of the magnetic recording medium, etc. By the way, since Al alloy is a metal material, its Vickers hardness is around 100 (over 600 for ceramics).
The bending strength is also 1000Kg/ ^cm2 (4000Kg/cm2 for ceramics)
Kg/cm ² or more), and as the recording density becomes higher, the shape accuracy such as slugs, scratches, flatness, and waviness becomes stricter, making processing even more difficult. During abrasive processing, abrasive grains tend to become packed together, resulting in defects. In addition, in the case of Al alloy substrates, sufficient consideration must be given to the manufacturing process, such as surface corrosion resistance, weather resistance, prevention of contamination, cleanliness, rust prevention, and dirt during the turning process, polishing process, and storage. . [Objective] The basic object of the present invention is to provide a novel method for manufacturing a magnetic disk substrate that eliminates the above-mentioned drawbacks and problems, and in particular, it is a basic object of the present invention to provide a method for manufacturing a new magnetic disk substrate that eliminates the above-mentioned drawbacks and problems. An object of the present invention is to effectively use dried crystallized glass as a substrate material for magnetic disks. [Summary of the structure of the invention] The present invention provides a magnetic disk substrate which is precision polished to a surface roughness of 80 Å or less in order to improve the characteristics and ensure reliability of the magnetized film formed on the surface of the crystallized glass substrate. Characterized by manufacturing method. That is, the method for manufacturing a magnetic disk substrate of the present invention involves suspending anhydrous alumina fine powder having a surface area per unit volume of 130 m ² /g or less, a substantially spherical shape, and a particle size of 320 Å or less in pure water. The polishing liquid is used as a polishing liquid, and the crystallized glass to be polished and a lapping plate are placed opposite each other in the polishing liquid, and precision polishing is carried out while applying a lapping load of 0.1 to 2 kg/cm ² . [Disclosure of the Invention] In the case of a crystallized glass substrate, the mechanical strength is stronger than that of an Al alloy, and it is relatively easy to control the shape accuracy in abrasive processing. Further, there is no need to pay special attention to corrosion resistance and weather resistance, and the surface can be cleaned by sputter cleaning when forming an insulating thin film by sputtering. Furthermore, when Al alloy is turned, a machining-altered layer remains on the surface, whereas in the case of crystallized glass, due to the mechanochemical polishing finish, the surface is no different from the stress strain in the bulk, and There is no strain transfer to the coated media. Nowadays, crystallized glass has come to be used for a wide range of applications in various fields due to its superior heat resistance, abrasion resistance, weather resistance, insulation properties, and mechanical strength compared to Al alloy substrates. In magnetic disk substrates whose surfaces are subjected to thin film media processing, as the density of media increases, there is an increasing need for smooth substrate surfaces and distortion-free substrates. When using crystallized glass as a magnetic disk substrate, there are problems such as dropouts due to surface micro defects and head crushing, which impair reliability. There were some difficulties. Conventionally, as a precision polishing method for crystallized glass, a fused amorphous glass polishing method, which is applied to photomasks, lenses, etc., has been adopted. This polishing method uses cerium oxide or red iron abrasive grains and can finish the surface of lenses, etc. to a roughness of 50 Å or less. However, even when applied to crystallized glass, since the material is substantially crystallized, fine protrusions and depressions are generated on the polished surface, resulting in a problem that only a surface roughness of about 250 Å can be obtained. For this purpose, the present inventors developed a method for high-precision surface polishing of crystallized glass and filed a patent application (Japanese Patent Application No. 155176-155178). That is, these relate to a polishing method for precisely polishing the surface of a crystallized glass substrate for a thin film magnetic head to a surface roughness of 50 Å or less. The present invention further seeks to apply the method to the manufacture of substrates for magnetic disks. The crystallized glass to be polished is glass whose material is substantially (for example, 20% or more) crystallized and has high strength.
It is preferable to use one that has high hardness and is thermally and electrically stable. There are many crystallized glasses that meet these conditions. Precipitated crystals include β-eucryptite (Li ₂ O・Al ₂ O ₃・2SiO ₂ ), β-spodiumene (Li ₂ O・Al ₂ O ₃・4SiO ₂ ), quartz (SiO ₂ ), and metasilicic acid. The most common are those using lithium (Li ₂ O.SiO ₂ ), lithium disilicate (Li ₂ O.2SiO ₂ ), or a mixture thereof. Other cordierite (2MgO・2Al ₂ O ₃・5SiO ₂ ), gahnite (ZnO・
Al ₂ O ₃ ), fluorine phlogopite, and alkali silicates (Na ₂ O, Al ₂ O ₃ , 2SiO _2, etc.). Although it is common to use a nucleating agent for crystallization, there are some methods that do not use a nucleating agent. As a nucleating agent, photosensitive metals (Au, Ag, Cu
), noble metals (Pt, Pd, etc.), titanium oxide, zirconium oxide, fluorides (CaF _2, etc.), transition metal compounds (oxides of Cr, V, Fe, Co, Ni, Th, Mo, etc.), phosphoric acid compounds, arsenic compounds (P ₂ O ₅ , As ₂ O ₃
etc.), Sb oxide, Sn oxide, etc. The thermal expansion coefficient of crystallized glass is approximately 0 to 130×
10 ^-7 /°C, but it has the advantage that it can be selected from a wide range in consideration of matching with the magnetic medium used. For example, a soft magnetic thin film such as sendust or permalloy has a high thermal expansion coefficient, a ceramic magnetic medium has a correspondingly small one, or a low expansion coefficient to suppress disk track position shift due to temperature changes. It is possible to make a selection such as selecting one of the following. A preferable example of crystallized glass is SiO ₂ −
Li ₂ O (or even −Al ₂ O ₃ ) based (and Ce,
(containing Ag, etc.), Na ₂ O-based products, etc. The crystal grain size is preferably fine and crystallized to a range that can be made non-porous by ultra-precision polishing. A crystal grain size of 80 Å or less (even 50 Å or less) is preferable. For use as a disk, the higher the strength, the better, and a bending strength of about 1000 Kg/cm ² or more is preferred. The anhydrous alumina fine powder suspended in pure water is approximately spherical with a particle size of 320 Å or less, and is obtained by a dry manufacturing method, but the surface area per unit volume is
If it exceeds 130 m ² /g, the grain shape becomes irregular, the cutting and scratching action on the polished surface is strong during lapping, the resulting surface roughness deteriorates, and micro protrusions and depressions are likely to occur on the polished surface. Therefore, the surface area per unit volume should be 130 m ² /g or less. Since the anhydrous alumina fine powder used in this invention is obtained by a dry manufacturing method, it has a large active area of 100% compared to hydrated alumina produced by a wet manufacturing method, so it is highly reactive and has a chemical effect that improves processing efficiency. The purity is 99.9% or higher, which means less contamination of the surface by fine powder and stable polishing. The aqueous solution exhibits silanol groups at pH 4 to 5, and a chemical effect can be obtained. Furthermore, since the powder shape is substantially spherical, there is little cutting or scratching effect on the polished surface, which is effective in improving the polished surface quality.
SiO ₂ , the main component of crystallized glass, is negatively charged, and the fine powder itself is positively charged, so SiO ₂
and anhydrous alumina powder suspension due to electric field effect,
The number of abrasive grains for processing increases, and the processing efficiency increases and the agglomeration effect reduces the processing unit to several tens of Å.
Therefore, the crystallized glass surface should be 80 Å, preferably 50 Å
It is thought that precision polishing can be performed to the following (even to the order of 20 Å or less). Furthermore, if the particle size of the anhydrous alumina fine powder exceeds 320 Å, it is not preferable because it will form scratches on the surface to be polished and deteriorate the surface roughness. As for the polishing conditions, if the lap load is less than 0.1 kg/cm ² , the required surface roughness cannot be obtained and the machining efficiency is low; if it exceeds 2.0 kg/cm ² , it is preferable in terms of machining efficiency, but the lap load is This is not preferable because it increases the cost as the scale of the device increases and the polishing accuracy deteriorates. In addition, soft metals such as Sn, Pb, solder alloys, cloth, etc. are most suitable for the lap board.
The lapping machine and the material to be polished are preferably polished in relative rotation. "Pure water" as used herein refers to water that does not contain organic dirt and dust (usually having a size of 3000 Å or more), and may be ion-exchanged water, distilled water, or the like. [Preferred embodiments] Examples will be described below. The crystallized glass to be polished has approximately
Photoceram (trade name, manufactured by Corning Inc.) with 30% crystallization was used, and the sample was 90 mm in diameter.
It was 2 mm thick and had a surface roughness of 300 Å. The polishing liquid has a surface area of 90 m ² /g to 120 m 2 /g per unit volume.
A PH4 suspension in which 1 wt % of amorphous anhydrous alumina fine powder having a particle diameter of 300 Å and m ² /g was dispersed in pure water was used. The processing machine uses a double-sided polisher, and the polisher uses a 600mmφ Sn disk, and the polished surface of the photoceram is brought into contact with the surface of the polisher.The rotation speed is 60rpm, and the lap loads are 0.5Kg/cm ² and 2Kg/cm, respectively. ²
Polishing was carried out for 30 minutes under the processing conditions of a load loading of 100 cm, while rotating the two relative to each other, and continuously dropping the polishing liquid at a rate of 100 c.c./h during the polishing process. In addition, for comparison, a case of a polishing liquid using CeO ₂ as the abrasive grains (Comparative Example C), a case of a polishing liquid using a hydrated alumina fine powder (Comparative Example D), and an anhydrous alumina fine powder same as the present invention are also shown. Polishing was carried out under various processing conditions using a polishing liquid using a polishing solution using a lap load other than the conditions of the present invention (Comparative Example E). The polishing conditions at this time and the surface roughness of the material to be polished were measured, and are shown in Table 1 together with the surface roughness measurement results obtained by the method of the present invention. The surface roughness of the polished surface was measured using a surface step measuring device (Talystep device, stylus, 0.5 μm, stylus force 7 mg).
The state of protrusions and recesses on the surface was measured using a Nomarski differential interference microscope. As is clear from Table 1, in the case of Comparative Example C using the conventional glass polishing method, a surface roughness of only 300 Å was obtained for crystallized glass, and when using hydrated alumina fine powder, The grain shape is irregular and not spherical, the surface area is large, the cutting and scratching action is large, and the surface roughness is deteriorated.Furthermore, even if the polishing liquid of the present invention is used, the lap load is outside the conditions. If there is, a surface roughness of only 200 Å can be obtained,
In either case, it is unsuitable for precision polishing of crystallized glass, whereas in the case of the method of the present invention, there are no protrusions or depressions on the surface of crystallized glass, and an excellent surface roughness of 20 Å is obtained. I can see that it was done. Incidentally, the surface roughness of each polished surface of Invention A and Comparative Example C was measured and graphed on two scales shown in FIG. 1 and FIG. 2. It is clear that the surface to be polished according to the present invention shown in FIG. 1 provides a much more precisely flat surface than the surface to be polished according to the conventional method shown in FIG.

[Table] In addition, in the present invention, the surface roughness of the magnetic disk substrate using crystallized glass is 80 Å or less, there are no surface defects, and the straightness in the radial direction is
0.5 μm, flatness 1.5 μm, no edge sag, and the shape accuracy of the magnetic disk is superior to that of a substrate made of aluminum alloy turned. That is, it can be seen that the present invention is extremely effective in improving the reliability, electromagnetic conversion characteristics, and yield of magnetic disks by using crystallized glass for the magnetic disk substrate and by using the precision polishing method for crystallized glass.

[Brief explanation of drawings]

FIGS. 1 and 2 are graphs showing the measurement results of the surface roughness of the surfaces to be polished of an example of the present invention and a comparative example, respectively, on different scales a and b.

Claims (1)

[Claims] 1. A polishing solution prepared by suspending anhydrous alumina fine powder with a surface area of 130 m ² /g or less, a substantially spherical shape, and a particle size of 320 Å or less in pure water is used as a polishing solution. A magnetic disk characterized by forming a surface layer with a surface roughness of 80 Å or less and no strain, which is formed by precision polishing a polished crystallized glass and a lap surface plate facing each other while applying a lap load of 0.1 to ² kg/cm 2. method for manufacturing substrates for