JPS6361412A - Substrate for magnetic disk - Google Patents

Abstract

PURPOSE:To improve the characteristics of a deposited magnetic film to be formed on the surface of a substrate and the reliability thereof by specifying the surface roughness and nonporousness of the substrate. CONSTITUTION:The substrate has a glass coating film having <=80Angstrom surface roughness, 0.3-200mum film thickness on the nonporous and distortionless surface and <=10<-6>/deg relative difference in coefft. of thermal expansion from the ceramic substrate at 20 deg.C - glass distortion point on the surface of an alumina ceramic material having fine pores of <=5mum and >=96% relative theoretical density. The temp. corresponding to about 10<14.5> poise viscosity of glass is determined as the distortion point.

Description

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

[Prior Art and Problems to be Solved] Generally, substrates for magnetic recording disks are required to have first-order characteristics.

(+) 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 dents that may cause defects in the magnetic thin film formed on the surface of the substrate.

(3) Must have sufficient mechanical strength to withstand machining, polishing, or high speed/rotation during use.

(4) It should have corrosion resistance, weather resistance, and heat resistance.

Conventionally, alloys have been used for magnetic disk substrates, but alloy substrates have problems in machining and polishing processes due to material crystal anisotropy, material defects, and nonmetallic inclusions present in the material. , these may remain as protrusions on the surface of the substrate, or may fall off and cause dents. It is not sufficient as a substrate material for high-density magnetic recording disks.

The quality of the processing of the magnetic disk board is the same.

Affects magnetic disk runout, acceleration components, media signal errors, etc.

By the way, AJ gold alloy is a metal material.

Vickers hardness is around 100 (600 for ceramics)
2), and the bending strength is also 1000kg/cj (
In the case of ceramics, the weight is 4000 kg/c♂ or more), and as the recording density becomes higher, scratches, scratches, and flatness occur.

Shape considerations such as waviness are becoming more stringent, making processing even more difficult. During abrasive processing, the abrasive grains tend to become embedded, resulting in defects. Also, AI! 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 prevent corrosion resistance, weather resistance, and contamination of the surface.

It is also known to form a highly hard film on the surface of an alloy substrate in order to improve the alloy substrate. - For example, aluminium on the surface of AJ alloy!・A method is used to form a layer to increase hardness and improve polishing workability, but during alumite formation, trace impurities (Fe, Mn, Si) in the alloy precipitate as intermetallic workpieces. Therefore, after alumite treatment, that part becomes a cause of dent defects. Increasing the purity of the base alloy is nearly impossible in terms of the manufacturing process, and in the case of A1 alloy, there are also problems in its handling in terms of corrosion resistance and 2Sf purity. A again! When forming a thin film medium by sputtering or plating on the alloy surface, problems arise such as chemical reaction and diffusion between the A72 alloy and the magnetic film, and it is also necessary to heat-treat the magnetic film during the process.
The alloy substrate is a deformed product.

It is difficult to perform heat treatment because the shape accuracy deteriorates and surface runout and acceleration increase.

Note that there is also a method of forming oxides such as SiO, A I!203, etc. on the A (substrate) by sputtering;
(The drawback is that the adhesion to the substrate after sputtering is weak.

In contrast to these LE alloy disk substrates, alumina ceramic materials are currently being used in various fields due to their superior heat resistance, wear resistance, weather resistance, insulation properties, and mechanical strength compared to A℃ alloy materials. Although it has come to be used in a wide range of applications, magnetic disk substrates whose surfaces are treated with media have become thinner and more dense, making the substrate surfaces non-porous and creating distortion-free substrates. It is forced by necessity.

Generally, the manufacturing method for ceramic substrates is the single crystal method,
There are methods of sintering after molding using mold molding, rubber press, doctor blade method, etc., and hot press method (HP) and hot isostatic pressing method (HIP method) for higher density. With the single crystallization method, manufacturing costs are high and it is difficult to manufacture large diameter substrates, and with the HIP method and the HF' method.

Even in high-density substrates, there are micropores of 5 μm or less in the substrate, so when used for magnetic disk substrates, there are problems such as dropouts due to surface micro defects and head crashes that impair reliability. there were.

In general, as a surface polishing method that can be applied to disk substrates, etc., mechanochemical polishing is known as a method for finishing St 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 substrate for a disk with a thin film medium. When applied, since the rate of chemical erosion is different for each material or crystal plane, there is a risk that crystal steps may occur at the same time as micropores are exposed.

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

rSolving Means and Effects of the Present Invention] The present invention provides surface roughness of 80 Å or less, preferably 50 Å or less, and further 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 two pore-free and strain-free surfaces with a surface roughness of 80 Å or less and a film thickness of 0.3 μm on the surface of an alumina ceramic material having a relative theoretical density of 9696 or more and having micropores of 5 μm or less. It is characterized by having a glass coating film with a relative difference in coefficient of thermal expansion of ~200 μm and the ceramic substrate of 1 O −6 /deg at a temperature of 20° C. to glass strain point.

The strain point refers to the temperature corresponding to the viscosity of glass of approximately 1014.5 poise.

In the present invention, a strain-free surface is defined as a surface-treated fluidized bed (Beilbyl surface).
ayer) thickness 50 Å or less (ΔIIJ with ellipsometer)
20 Å or less, preferably 20 Å or less. Furthermore, "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 0-CaO-8in2 type) and lead glass (KOP b OS t O2 type).

Borosilicate glass (N a OB 203S i02
system), alumina silicate glass (CaO-MgO-AJ!
Silicate glasses such as O-3iO A glass having a high softening point may be used as appropriate, and any glass may be used if the heat treatment temperature is low. Furthermore, if the difference in thermal expansion coefficient between the glass and the base material is large, the stress between them will increase.

Because problems such as warping and destruction occur, the relative difference in thermal expansion coefficient between glass and ceramic base material is I x 10-6/deg.
, requires that: 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. It is most preferable that the t-direction difference in the coefficient of thermal expansion is as small as possible, and that the temperature changes in the coefficient of thermal expansion from 20° C. to the strain point of the base material and the glass have the same tendency.

The coating film of the glass of the present invention on an alumina-based substrate can be formed by a glazing method, a sputtering method, a vapor deposition method, an ion blasting method, a chemical synthesis method using a metal alkoxide solution, or the like. When forming a coating film.

It is more effective to perform this after forming the S L O2 film in order to improve the adhesive density and wettability between the substrate and the glass.

[Preferred Embodiment] As a result of various studies, the inventor found that
In order to maintain insulation from the upper wave film on the surface of an alumina ceramic material having a relative theoretical density of 96% or more and having micropores on the surface of 0.5 μm to 220 μm thick, (20℃~strain point) relative difference is 10-6/
After forming a glass coating film having a particle size of 0.1 μm or less and a purity of 99% or more, the surface of the thin film was coated with S t O2 having a particle size of 0.1 μm or less and a purity of 99% or more.

A suspension of at least one of MgO, CeO, A, e O, or Fe 20 a fine powder suspended in 0.1 to 20 vt% pure water is 0.05 to 2 kg/ca? By polishing with a load of
It has been found that a pore-free and strain-free surface layer can be obtained, and that the properties and reliability of the magnetic film formed on the substrate surface can be improved and the reliability guaranteed.

As the alumina ceramic material of the present invention, A j!
O, A 1 0 T iCT t O2 system.

A j! OT I O2 series, Aff1203-
It is an alumina-based ceramic material mainly composed of 203 in A, such as Fe20-TiC system, and is formed by die molding, rubber press, doctor blade method, etc., and is also formed by hot forming method (HP method), hot static method, etc. Preferably, it is obtained by sintering using a hydraulic press method (HIP method). These alumina ceramic materials include MgO, N i O, Cr
It may contain a known grain growth inhibitor such as No. 203 and other sintering aids, and preferably has an average alumina grain size of 5 μm or less. Incidentally, such alumina ceramic base material is commercially available as a general product standard with a density of 9696 or higher.

If the micropores on the surface of the alumina ceramic substrate of the present invention are 5 μm or more, air bubbles will occur or remain when forming a coating film in the micropores, impairing the accuracy during film formation, so the micropores should be 5 μm or less. , preferably 3 μm
It is necessary to do the following. 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 if the glazing method is used as the coating method, the coating thickness should be kept constant at less than 0 μm. However, it is difficult to achieve the required surface roughness and porosity by mechanochemical polishing (MCP method) of the coating surface.

It is not possible to make the film strain-free, and if the thickness exceeds 220 μm, there is a risk of large distortion occurring in the base material due to stress caused by the difference in expansion coefficient with the base material, so the film thickness at the time of film formation is 10 μm to 22
It is necessary to set it to 0 μm. In addition, when sputtering is used as a coating method, it is difficult to maintain a constant coating thickness when the coating thickness is less than 0.5 μm, and the required surface roughness is achieved by mechanochemical polishing19 (MCP method) of the coating surface. It is impossible to make it hard, pore-free, and distortion-free, and 220
If the thickness exceeds μm, there is a risk that large distortions will occur in the base material due to stress caused by the difference in expansion coefficient with the substrate. From the point of view, preferably 15 μm to 25 μn1
It is. What is the thickness of the coating film after polishing?

Considering the same reason and polishing accuracy, the thickness is 3 to 200 .mu.m when the glazing method is used.7 The thickness is 0.3 to 200 .mu.m when the subac method is used, preferably 10 to 20 .mu.m.

2. SiO, MgO, CeO2 or A, Q suspended in pure water as a condition of the MCP method in the present invention. If the particle size of the 03 fine powder exceeds 0.1 μm, eaves will occur on the surface of the coated film to be polished, which will deteriorate the surface roughness.

Further, the total content of the fine powder in pure water is 0. If it is less than lvt%, the polishing effect is small, and if it exceeds 20wt%, the heat of hydration due to each fine powder is likely to be generated or gelation is likely to occur, and
0.1 to 20 because the activity increases and the surface condition deteriorates.
Let it be νt%. This pure water is water that does not contain metal ions, inorganic substances, or pollutants, especially machine pollutants or suspended matter, and may be ion-exchanged water, distilled water, or the like.

As the lapping machine, Sn solder alloy, soft metal such as Pb, hard cloth, etc. are most suitable.

If the lap load is less than 0.05 kg/c♂, the required surface roughness cannot be obtained, and the machining efficiency is low;
If it exceeds cJ, it is preferable from the point of view of processing efficiency, but it is not preferable because the polishing accuracy deteriorates.

In addition, when the substrate of the present invention is used in a double-sided recording magnetic disk, by forming a glass coating film on both sides of the alumina-based ceramic substrate and applying MCP at one time, the internal stress in the thin film on both sides is canceled out. A substrate with excellent flatness, a surface of 11/i'', no pores, and no distortion can be obtained.

In the case of the alumina-based ceramic substrate on which the glass coating film is formed according to the present invention, the mechanical strength is stronger than that of the Af-gold 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 even if one surface is contaminated, the surface can be cleaned by sputter cleaning when an insulating thin film is further formed by sputtering.

In addition, when turning A (alloy), a process-affected layer remains on the surface, whereas in the case of the alumina ceramic substrate of the present invention, the stress strain between the surface and bulk is reduced by mechanochemical polishing. No difference occurs and no strain transfer to the media coated on the substrate occurs.

Namely, since the coating film of the substrate according to the present invention is made of glass, the crystalline state is amorphous and has a 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 Hatake density magnetic disk recording medium can be manufactured. In addition, as the starting alumina ceramic base material,
A material having a relative theoretical density of 96% or more can be used, which is advantageous in terms of mass production.

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

Example 1 Fine M of 5 μm or less on the HIP-treated surface of the substrate
Hole *J method diameter 200mm x/! 〆sa 2 mt
nO) Purity 99.95% and relative theoretical density 97%, thermal expansion coefficient (20°C to glass strain point) 77X 10-7/
deg,, using A 203 ceramic material with an average crystal grain size of 4 μm, the substrate was precision polished to a surface roughness of 200 Å or less by a precision lapping method, and then the thermal expansion coefficient (
20℃~strain point) 74X LN7/dcg, softening point 720℃, strain point 510℃, powder particle size 200 mesh through, SiO272wt%, NaO13wt%,
K20 8wt%, ZnO4vt%, Ajj O
3vt9.6. Glass having a composition of 22 wt % Ti0 was made into a paste and applied to a film thickness of about 100 μm, and then held at 1000° C. for 5 minutes to form a coating film in air. The temperature increase rate at this time is 500℃/Ilr
The cooling temperature was 500° C./11r up to the glass strain point, and the glass was held at the glass strain point for 1 hour, and then slowly cooled after removing the strain. At this time, the surface accuracy was 5 μm, and almost no bubbles were observed.

Next, apply GCC abrasive powder with a particle size of 2000 mesh through C to a particle size of 6000 mesh through C.
e Perform pre-processing using an O2 abrasive, then 2 grain sizes o,
A lapped M
The material was finished to a surface roughness of 40 using MCPL at O, 5 kg/cd, and the machining allowance at that time was 3 μm and the flatness was 1 μm.

FIG. 1(A) shows the surface condition of the glass coating film after MCP in the present invention, and FIG. 1(B) 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 by the MCP of the glass coating film according to the present invention, resulting in a surface roughness of 40.

As a method to judge the adhesion between the film and the substrate, we used a hardness meter to increase the amount of balls hit from 50g to 1000g, and the criterion was whether the glass coating film peeled off.
There was no peeling up to 1,000 g, and strong adhesion was exhibited.

The thickness of the surface-treated fluidized bed was measured with an ellipsometer and was 20 Å or less.

Example 2 Dimensions having micropores of 3 μm or less on the HIP-treated surface as a substrate: diameter 100+n+n x thickness 2 ++n+
, purity 99, purity 99, 95 °C ~ glass strain point) 78xlO /deg. ,
AI! 20385vt% A R 2 O a T
After precision polishing the surface roughness of the substrate to 200 Å or less using a C-based ceramic material (average crystal grain size 4 μm), a high frequency sputtering device was used on the substrate to form a target plate with dimensions of diameter 350+n+n x thickness 6IIffl. Using S t O 2 with a purity of 99.9%, approximately 0.1μ
After forming a sputtered film of about m, the coefficient of thermal expansion (20°C to strain point) is 77x to-7/deg. , softening point 470℃,
Pb060wt%, Zn019vt% at strain point 380℃,
B O 12wt%, S L 02 9vt
After crushing glass with a composition of % to 200 mesh through.

Make it into a paste and apply it to a film thickness of 30μm and leave it in the air for 8 hours.
The coating was carried out by holding at 00°C for 10 minutes. At this time, the temperature was raised at a rate of 500°C/Hr, and the temperature was maintained at 400°C for 1 hour, and then the temperature was raised to 800°C at the same rate of 500°C/Hr, and held for 10 minutes. The cooling rate was 500° C./)Ir until the strain point was reached, and the sample was held at the strain point for 1 hour and then slowly cooled. The formed coating film has a particle size of 0.05 μm.
A hard cloth was used as a lapping machine in a suspension of C e O 2 fine powder suspended in 2vt% pure water, and the surface roughness was finished to 40 by MCP at a lapping load of 1 kg/c4. The machining allowance was 20 μm.

FIG. 2(A) shows the surface condition of the glass coating film after MCP of this example, and FIG. 2(B) shows the surface condition of the coating substrate. 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 by the MCP of the glass coating film according to the present invention, and a surface roughness of 40 was achieved.

Surface treatment fluidized bed (Bellby 1ayer) thickness is 2
It was 0 Å or less.

Example 3 Base material having micropores of 5 μm or less on the HIP-treated surface Dimensions: diameter 200 mm x thickness 2 + n + n, relative theoretical density 9 ko 10 /deg. , A A203 [15 wt% A
(Using a 203-TiC ceramic material (alumina average crystal grain size 4 μm, TiC average crystal grain size 2 μm), the surface roughness of the substrate was precision polished to 200 Å or less by a precision lapping method, and then Using a high frequency sputtering device, the target plate has a thermal expansion coefficient of 74 x IO''''7/dc.
g, (20-510℃) 2 dimensions diameter 350mm xr
S i O2 72 wt%, N a 2 with a v length of 6 mm
0 12wt 96゜K2O6wt%, Z n O
4vt%, -A j! 20 a3 vt%.

Sputtering was performed using glass having a composition of 23 wt% TiO after evacuation to reach an Ar pressure of 1 x 10-5 mbar. To clean the substrate surface, approximately 500 surface layers were removed by reverse sputter cleaning before forward sputtering.

The input power for normal sputtering was 3 kW. A negative bias (-100V) was applied to the substrate side. The bias effect provides step coverage of the ceramic bore,
Glass is also attached to the bore. Note that the surface roughness of the sputtered film surface was about 500. In the conventional oxide sputtering method, the sputtering speed was slow and it took a long 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 sputtering/m1n, which was 2.
0. It took 400 minutes to form czm.

Next, the surface of the sputtered film was coated with S of grain size 0.01 μm.
In a suspension of iO2 fine powder suspended in 5wt% pure water, an Sn disc was used as a lapping machine and the lapping load was 0.5 kg/c-
MCP was carried out to give a surface roughness of 40. At that time, the machining allowance 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. 3(A) and 3(B), respectively. For the surface condition, the same thin film step II measuring device as in Example 1 was used.

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

[Brief explanation of the drawing]

1, 2, 2 and 3 (A) and (B). 3 is a graph showing the measurement results of the surface conditions of Examples 1, 2, and 3 of the present invention, respectively. In each case, (A) shows the surface of the glass coating film after polishing, and (B) shows the surface of the alumina base material before coating.

Claims (1)

[Claims] 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, a surface roughness of 80 Å or less and a film thickness of 0.3 μm to 200 μm on a non-porous and unstrained surface.
, the relative difference in thermal expansion coefficient with the substrate is 10^-^6/d
eg. A recording disk substrate characterized by having a glass coating film as follows.