JPH0330208B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a substrate for recording disks, particularly for magnetic disks, which has a non-porous, non-strained surface layer and has good surface roughness.

[Prior Art and Problems to be Solved] In general, substrates for magnetic recording disks are required to have the following characteristics.

(1) Good surface roughness after polishing 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 non-metallic inclusions present in the material, during machining and polishing processes, these may remain as protrusions on the substrate surface or fall off and create dents, resulting in surface roughness even after sufficient polishing. The thickness is about 200 Å at most, and the surface has protrusions, depressions, and undulations, which is not sufficient as a substrate material for high-density magnetic recording disks.

The quality of the processing of the magnetic disk substrate is directly affected.
Affects magnetic disk runout, acceleration components, media signal errors, 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 1000Kg/cm ² (over 4000Kg/cm ² for ceramics), and it has a high density. As more records are made, the precision of shapes such as scratches, kisses, flatness, and undulations becomes more and more strict, making processing even more difficult. During abrasive processing, the abrasive grains tend to become embedded, resulting in defects. Also, Al
In the case of alloy substrates, sufficient consideration must be given to cleanliness, rust prevention, dirt, etc. in the manufacturing process during the turning process, polishing process, and storage to ensure surface corrosion resistance, weather resistance, and prevention of contamination.

It is also known to form a highly hard film on the surface of Al alloy substrates in order to improve them. For example, a method is used to form an alumite layer on the surface of an Al alloy to increase hardness and improve polishability, but during the alumite formation, trace impurities (Fe, Mn, Si) in the Al alloy are Since it precipitates as a workpiece, that part becomes a cause of dent defects after alumite treatment. Increasing the purity of the base alloy is nearly impossible in terms of the manufacturing process, and
In the case of Al alloys, handling has become a problem in terms of corrosion resistance and cleanliness. In addition, when forming a thin film medium by sputtering or plating on the Al alloy surface, problems arise such as 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, but the Al alloy substrate deforms. It is difficult to perform heat treatment because the shape accuracy deteriorates and surface runout and acceleration increase.

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 contrast to these Al alloy disk substrates, alumina ceramic materials are now widely used in various fields due to their superior heat resistance, wear resistance, weather resistance, insulation properties, and mechanical strength compared to Al alloy materials. However, with the thinner film and higher density of the media in magnetic disk substrates where the surface of the substrate is treated with media, the need for a non-porous substrate surface and a non-distortion substrate has increased. Being forced into sex.

In general, ceramic substrates are manufactured using the single crystal method, molding and sintering methods such as mold molding, rubber pressing, and doctor blade methods.In addition, for higher density, hot pressing (HP), hot isostatic pressing, etc. There is a pressing method (HIP method), but the former single crystallization method has high manufacturing costs and is difficult to manufacture large diameter substrates, and HIP and HP methods are difficult to manufacture with high density substrates. However, since micropores of 5 μm or less are present in the substrate, when used in magnetic disk substrates, problems such as dropouts due to surface microdefects and head crushing occur, which impair reliability.

In general, as a surface polishing method that can be applied to disk substrates, etc., mechanochemical polishing is known as a method for finishing materials such as Si substrates, GGG crystals, ferrite, etc. without degrading their surface properties. When applied to ceramic materials with micropores, the micropores are exposed on the ceramic surface, making it unsatisfactory as a disk substrate with a thin film medium.Also, mechanochemical polishing is applied to alumina-based ceramic materials. Then, since the speed of chemical erosion differs for each material or crystal plane, there is a risk that a crystal step may occur at the same time as the micropores are exposed.

[Problems to be Solved] An object of the present invention is to provide a substrate for a magnetic disk using a ceramic material as a base material, which improves the drawbacks of the conventional method as described above.

[Solution Means and Effects of the Present Invention] The present invention provides a surface roughness of 80 Å or less, preferably 50 Å or less, and The basic feature is a substrate with no pores down to 20 Å or less and a strain-free layer.

That is, the magnetic disk substrate of the present invention has a surface roughness of 80 Å or less and a film thickness of 0.3 μm with a pore-free, strain-free surface on the surface of an alumina-based ceramic material having micropores of 5 μm or less and a relative theoretical density of 96% or more. ~200μm,
The relative difference in thermal expansion coefficient with the ceramic substrate is 20
It is characterized by having a glass coating film of 10 -6 /deg. or less at a glass strain point of 10 ^-6 /deg.

The strain point is the temperature corresponding to the viscosity of glass, approximately 10 ^{to 14.5} poise.

In the present invention, a strain-free surface refers to a surface-treated fluidized bed (Beilby layer) having a thickness of 50 Å or less (measured with an ellipsometer), preferably 20 Å or less. In addition, "non-porous" means that there are no pores larger than 0.2 μm on the surface, preferably no pores larger than 0.1 μm.

The glasses used for the coating film of the present invention include soda lime glass (Na ₂ O-CaO-SiO ₂ system), lead glass (K ₂ O-PbO-SiO ₂ system), and borosilicate glass (Na ₂ O-B ₂ O _{Silicate -} based glasses such as alumina-silicate glass (CaO-MgO-Al ₂ O ₃ -SiO _2- based) are used, but their softening points vary depending on the composition, making it difficult to form thin film media. When the magnetized film
If it is necessary to perform heat treatment at 200° C. or higher, a glass with a high softening point may be used as appropriate, and if the heat treatment temperature is low, any glass may be used. Furthermore, if the difference in the coefficient of thermal expansion between glass and the base material is large, the stress between them will increase, causing problems such as warping and destruction. Therefore, the relative difference in the coefficient of thermal expansion between glass and ceramic base material ^is 1 ⁶ /deg.
The following must be true. Further, since it is better to apply compressive stress to the surface of the glass coating film, it is preferable that the coefficient of thermal expansion of the glass is smaller than that of the base material. The relative difference in thermal expansion coefficients should be as small as possible, and the temperature between the base material and glass should be between 20°C and
Most preferably, the temperature change in the coefficient of thermal expansion at the strain point has the same tendency.

The coating film of the glass alumina substrate of the present invention can be formed by a glazing method, a sputtering method, a vapor deposition method, an ion plating method, a chemical synthesis method using a metal alkoxide solution, or the like. When forming the coating film,
It is more effective to perform this after forming a SiO ₂ film in order to improve the adhesion density and wettability between the substrate and glass.

[Preferred Embodiment] As a result of various studies, the inventors found that the relative theoretical density 96 has micropores of 5 μm or less (preferably 3 μm) on the surface.
In order to maintain insulation with the upper coating on the surface of the alumina ceramic material, the relative difference in thermal expansion coefficient (from 20℃ to strain point) with the above substrate with a thickness of 0.5μm to 220μm is 10 ^-6 /deg. After forming a glass coating film with the following properties, the surface of the thin film is coated with a particle size of 0.1 μm or less and purity.
99% or more of SiO ₂ , MgO, CeO ₂ , Al ₂ O ₃ or
A suspension of at least one Fe ₂ O ₃ fine powder of 0.1 to 20 wt% in pure water is polished at a load of 0.05 to 2 Kg/cm ² to achieve a film thickness of 0.3 μm to 200 μm and a surface roughness. 80 Å or less (preferably 50 Å or less, preferably 20 Å or less)
It has been found that a porosity-free and strain-free surface layer can be obtained, and the characteristics and reliability of the magnetized film formed on the substrate surface can be improved and the reliability guaranteed.

The alumina ceramic material of the present invention is
Al ₂ O ₃ , Al ₂ O ₃ −TiC−TiO ₂ system, Al ₂ O ₃ −TiO ₂ system,
It is an alumina ceramic material mainly composed of Al ₂ O ₃ , such as Al ₂ O ₃ −Fe ₂ O ₃ −TiC system, and is formed by die molding, rubber press, doctor blade method, etc., and is further hot formed. Those obtained by sintering using a hot isostatic pressing method (HP method) or a hot isostatic pressing method (HIP method) are preferable. These alumina-based ceramic materials can contain known grain growth inhibitors such as MgO, NiO, _Cr2O3 , and other sintering aids, and the average alumina grain size is preferably 5 _μm or less. . Incidentally, such alumina-based ceramic base material is available as a commercially available standard product having a density of 96% or more.

If the micropores on the surface of the alumina ceramic substrate of the present invention are 5 μm or more, air bubbles will be generated or remain when forming the coating film in the micropores, impairing the accuracy during film formation.
The thickness should preferably be 3 μm or less. In addition, the thickness of the glass coating film on the alumina ceramic substrate in the present invention is selected depending on each application, but when a glazing method is used as the coating method, the coating thickness should be kept constant if the film thickness is less than 10 μm. is difficult,
And mechanochemical polishing method (MCP method) of the coating surface
Therefore, it is not possible to achieve the required surface roughness, porosity, and distortion, and if the thickness exceeds 220 μm, there is a risk that large distortions may occur in the base material due to stress caused by the difference in expansion coefficient with the base material. Film thickness at the time of formation is 10 μm ~
It needs to be 220μm. Furthermore, when sputtering is used as a coating method, it is difficult to maintain a constant coating thickness if the coating thickness is less than 0.5 μm, and the required surface roughness and It is not possible to make the film non-porous and distortion-free, and if the thickness exceeds 220 μm, there is a risk of large distortion occurring within the base material due to stress caused by the difference in expansion coefficient with the substrate, so the film thickness at the time of film formation is
The thickness needs to be 0.5 μm to 220 μm, and preferably 15 μm to 25 μm from the viewpoint of film formation speed. The thickness of the coating film after polishing is 3 to 3 when using the glazing method, considering the same reason and polishing accuracy.
200μm, 0.3-200μm when using sputtering method,
Preferably it is 10 to 20 μm.

Furthermore, as a condition for the MCP method in the present invention, if the particle size of SiO ₂ , MgO, CeO ₂ or Al ₂ O ₃ fine powder suspended in pure water exceeds 0.1 μm, eaves will occur on the surface of the coating film to be polished. This is not preferable because it deteriorates the surface roughness. Also, the content of the fine powder in pure water is
If it is less than 0.1wt%, the polishing effect will be small, and if it exceeds 20wt%, the heat of hydration due to each fine powder will easily be generated or gelatinized, and the activity will increase and the surface condition will deteriorate, so 0.1 to 20wt%. shall be. This pure water is water that does not contain metal ions, inorganic substances, or pollutants, especially organic pollutants or suspended matter, and may be ion-exchanged water, distilled water, or the like.

As a lap board, Sn solder alloy, soft metal such as Pb, or hard cloth is most suitable. If the lap load is less than 0.05Kg/ ^cm2 , the required surface roughness cannot be obtained and the machining efficiency is low, and if it exceeds 2Kg/ ^cm2 , the polishing accuracy, which is preferable in terms of machining efficiency, will deteriorate, so it is not preferable. .

In addition, when the substrate of the present invention is used for a double-sided recording magnetic disk, a glass coating film is formed on both sides of the alumina ceramic substrate, and both sides are coated simultaneously.
The internal stress in the thin film on both sides is reduced by MCP.
As a result, a substrate with excellent flatness, surface roughness, no pores, and no distortion can be obtained.

In the case of the glass coating film-formed alumina-based ceramic substrate of the present invention, the mechanical strength is stronger than that of Al alloy, and the control of shape accuracy during abrasive processing is relatively easy. 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 an insulating thin film is further formed by sputtering.

Furthermore, when turning an Al alloy, a process-affected layer remains on the surface, whereas in the case of the alumina-based ceramic substrate of the present invention, the stress strain between the surface and the bulk is reduced by mechanochemical polishing. There is no difference and no strain transfer to the media that is coated onto the substrate.

That is, since the coating film of the substrate according to the present invention is made of glass, the crystalline state is an amorphous uniform structure. Furthermore, the polishing method of the present invention makes it possible to prevent surface processing distortion from occurring.

By using such a magnetic disk substrate, a highly reliable high-density magnetic disk recording medium can be manufactured. Further, as the starting alumina ceramic base material, one having a relative theoretical density of 96% or more can be used, which is advantageous for mass production.

[Example] The present invention will be explained below with reference to Examples.

Example 1 A substrate with a purity of 200 mm in diameter and 2 mm in thickness with micropores of 5 μm or less on the HIP-treated surface
99.95% and relative theoretical density 97%, coefficient of thermal expansion (20
°C to glass strain point) 77×10 ^-7 /deg., average grain size
After precision polishing the substrate to a surface roughness of 200 Å or less using a 4 μm Al ₂ O ₃ ceramic material, the thermal expansion coefficient (20% to strain point) was applied to the substrate.
74×10 ^-7 /deg., softening point 720℃, strain point 510℃, powder particle size 200 mesh through, SiO ₂ 72wt%,
_Na2O13wt %, _K2O6wt %, ZnO4wt%,
After making a paste of glass with a composition of 3wt% Al ₂ O ₃ and 2wt% TiO ₂ and applying it to a film thickness of about 100μm,
The temperature was maintained at 1000°C for 5 minutes to form a coating film in air. The temperature increase rate at this time is 500℃/Hr,
The cooling temperature is 500℃/Hr until the glass strain point.
The glass was held at the glass strain point for 1 hour, the strain was removed, and then slowly cooled. At this time, the surface accuracy was 5 μm, and almost no bubbles were observed.

Next, the surface of the formed coating film is pre-processed using GC abrasive grains with a grain size of 2000 mesh through and CeO ₂ abrasive grains with a grain size of 6000 mesh through.
A suspension of SiO ₂ fine powder with a particle size of 0.01 μm in 5 wt% pure water was subjected to MCP using an Sn disc as a lapping disc at a lapping load of 0.5 kg/cm ² to give a surface roughness of 40 Å. At that time, the machining allowance was 3 μm and the flatness was 1 μm.

FIG. 1A shows the surface condition of the glass coating film after MCP according to the present invention, and FIG. 1B shows the surface condition of the substrate before coating.

The surface condition in FIG. 1 is the result of measurement using a thin film step measuring device (Talystep) with a stylus diameter of 0.1 μmR.

It is clear from FIG. 1 that the fine pores on the surface of the ceramic substrate were made non-porous in the surface layer by the MCP of the glass coating film according to the present invention, and the surface roughness was finished to 40 Å.

As a method to judge the adhesion between the film and the substrate, we used a hardness tester to increase the loading weight from 50g to 1000g, and the criterion was whether the glass coating film would peel off. He showed his strength. The thickness of the surface-treated fluidized bed was measured with an ellipsometer and was less than 20 Å.

Example 2 Substrate with micropores of 3 μm or less on the HIP-treated surface Dimensions: diameter 100 mm x thickness 2 mm, purity
99.95%, relative theoretical density 99%, coefficient of thermal expansion (20℃
~Glass strain point) 78×10 ^-7 /deg., Al ₂ O ₃ 65wt%
Al ₂ O ₃ −TiC ceramic material (average grain size 4 μm)
After precision polishing the surface roughness of the substrate to 200 Å or less using
Using SiO ₂ with a purity of 99.9% mm, after forming a sputter film of about 0.1 μm, the coefficient of thermal expansion (20℃ ~ strain point) is 77.
×10 ^-7 /deg., softening point 470℃, strain point 380℃
PbO60wt%, ZnO19wt%, _{B2O3 12wt} %,
Glass having a composition of 9 wt% SiO ₂ was crushed to a mesh throughput of 200, made into a paste, coated to a thickness of 30 μm, and coated by holding the glass at 800° C. for 10 minutes in the atmosphere. At this time, the temperature increase rate is 500℃/Hr
After holding at 400°C for 1 hour, the temperature was raised to 800°C at the same temperature increase rate of 500°C/Hr and held for 10 minutes.
The cooling rate was 500° C./Hr until the strain point was reached, and after being held at the strain point for 1 hour, it was gradually cooled. The formed coating film was coated with 2wt% of CeO ₂ fine powder with a particle size of 0.05μm.
When the surface roughness is finished to 40Å by MCP using a hard cloth as a lapping plate in a suspension suspended in pure water and a lapping load of 1 kg/cm ^2, the machining allowance is
It was 20μm.

FIG. 2A shows the surface condition of the glass coating film after MCP of this example, and FIG. 2B shows the surface condition of the coating base material. Note that the same thin film step measuring device as in Example 1 was used to measure the surface condition.

It is clear from FIG. 2 that the fine pores on the surface of the ceramic substrate were made non-porous in the surface layer by the MCP of the glass coating film according to the present invention, and the surface roughness was finished to 40 Å.

The thickness of the surface treatment fluidized bed (Beilby layer) was less than 20 Å.

Example 3 Dimensions: diameter 200 mm x thickness 2 mm, relative theoretical density 97%, coefficient of thermal expansion (20-510°C) 78 x HIP-treated surface with micropores of 5 μm or less as a base material
_The ^surface _roughness of _{the substrate} was
After precision polishing to 200Å or less using the precision lap method,
A high-frequency sputtering device was used on the base material to form a target plate with a coefficient of thermal expansion of 74×10 ^-7 /deg. (20 to 510
°C), SiO ₂ 72wt% with dimensions 350mm diameter x 6mm thickness,
_Na2O12wt %, _K2O6wt %, ZnO4wt%,
Sputtering was performed using a glass having a composition of 3 wt% Al ₂ O ₃ and 3 wt% TiO ₂ after evacuation to reach an Ar pressure of 1×10 ⁻⁵ mbar. To clean the substrate surface, approximately 500 Å of the surface layer was removed by reverse sputter cleaning before forward sputtering.

The input power of the normal sputter is 3kW. A negative bias (-100V) was applied to the substrate side. Due to the bias effect, step coverage of the ceramic bore is achieved, and glass is also adhered to the bore. The surface roughness of the sputtered film was approximately 500 Å. In the conventional oxide sputtering method, the sputtering speed was slow and it took time to form a film, but by setting the distance between the electrodes to 40 mm and increasing the input power, the sputtering rate was 500 Å/min, and it took 400 minutes to form a 20 μm film. It took.

Next, the surface of the formed sputtered film was
A lapping load of 0.5 Kg/cm ² was applied using an Sn disc as a lapping disc in a suspension of 5wt% SiO ₂ fine powder suspended in pure water.
MCP was performed to obtain a surface roughness of 40 Å.The machining allowance at that time was 3 μm and the flatness was 1 μm.

The surface condition of the sputtered film after MCP and the surface condition of the substrate before sputtering obtained in this example are as follows:
These are shown in FIGS. 3A and 3B, respectively. Note that the same thin film step measuring device as in Example 1 was used to measure the surface condition.

As described above, the present invention is effective in preventing a decrease in product yield due to substrate defects, as well as ensuring characteristics and improving reliability of a magnetized film formed on a non-porous substrate surface.

[Brief explanation of drawings]

A and B in FIGS. 1, 2, and 3 are graphs showing the measurement results of the surface conditions of Examples 1, 2, and 3 of the present invention, respectively. In each case, A indicates the surface of the glass coating film after polishing, and B indicates the surface of the alumina base material before coating.

Claims (1)

[Claims] 1. Relative theoretical density of 96% with micropores of 5 μm or less
On the surface of the above alumina ceramic material, the surface roughness is 80 Å or less, and the film thickness of the non-porous and unstrained surface is 0.3 μm.
~200μm, relative difference in thermal expansion coefficient with the substrate is 1
A substrate for a recording disk, characterized in that it has a glass coating film having a glass coating film of x10 ^-6 /deg. or less. 2. The recording disk substrate according to claim 1, wherein the glass coating film on the substrate surface constitutes a surface on which a magnetic film is directly formed.