JPH03160619A - Production of glass substrate for magnetic disk and production of thin film magnetic disk - Google Patents

Abstract

PURPOSE:To obtain good floating property for a head and low cohesion property in radial and circumference directions by subjecting the surface of crystallized glass in which a crystal phase is dispersed in an amorphous glass phase to mirror treatment, dipping the glass in an aqueous solution of hydrofluoric acid to make a rough surface of the glass plate. CONSTITUTION:A disk cut from a glass substrate material (processes 3,4) is subjected to heat treatment to generate crystalization seeds (process 5) in a heat treatment furnace, and the crystallized glass disk (process 6) is mechanically polished to have a mirror surface (process 7). Then the disk is dipped in an aqueous solution of hydrofluoric acid containing at least hydrogen fluoride for chemical etching (process 8). By etching, an amorphous phase which is continuous in the crystallized glass is selectively etched, and the dispersed crystalized phase remains to form projections. Thus, the surface of the substrate is made rough (process 9). The concentration of hydrogen fluoride in the aqueous solution of hydrofluoric acid is 0.05 -2.5 mol/l, and etching is performed to 0.005 - 0.2 mum depth.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a second method for manufacturing a glass substrate used for a so-called thin-film magnetic disk substrate in which a magnetic disk substrate, particularly a magnetic recording medium, is formed by a sputtering method; Concerning the manufacturing method of thin film magnetic disks. [Prior Art] Conventionally, M alloy substrates with a Ni--P chemical plating film formed on the surface have been widely used as substrates for thin-film magnetic disks. Usually, this is called a Ni-P substrate, but this Ni-P substrate, for example,
As described in Section 3, it is widely practiced to form fine grooves in the shape of a concentric circle on the surface. The formation of this micro-machined groove is generally called texturing, and its essence is surface roughening, which is a process in which a flat surface that has been mirror-finished in advance is intentionally roughened. Its main purpose is to prevent adhesion between the magnetic head and disk surface. In other words, by making the surface of the magnetic disk a mirror surface,
If it is smoothed too much, the dynamic pressure of the air flow generated by the rotation of the disk will cause lubricant oil and moisture to collect between the disk surface and the magnetic head surface, which is floating at a small distance, causing the magnetic head to stick to the disk surface. This results in the following. [Problems to be Solved by the Invention] The above conventional technology has a wood-like problem in that when the surface of the Ni-P substrate is textured to reduce the adhesion of the magnetic head, the flying characteristics of the magnetic head deteriorate. Was. Therefore, it has had the disadvantage that the surface roughness of the substrate must be controlled within a very narrow range within which both properties of adhesiveness and head flying properties are reasonably satisfied.

In addition, because conventional texture processing is a unidirectional process in concentric circles, there is a problem in that it is less effective in reducing adhesion when the magnetic head moves in the radial direction, the so-called seek mode operation. ．． Furthermore, this fine groove processing results in the formation of raised protrusions on both sides of the grooves, which hinders the necessary narrow spacing between the disk and the magnetic head.

The purpose of the present invention is to solve these problems with the conventional technology, and the first purpose is to maintain a surface on which the magnetic head can stably fly by the required flying height even in narrow spacing. The second purpose is to develop a method for manufacturing a magnetic disk substrate that does not cause adhesion of the magnetic head and can achieve isotropic low adhesion characteristics in both the radial and circumferential directions. Disc board! Il! of an improved thin-film magnetic disk using the 2-manufacturing method. The goal is to provide each method of construction.

[Means for Solving the Problems] The first object is as follows: (1) Crystallized glass in which a crystalline phase exists in an amorphous glass phase is used as a substrate for a magnetic disk, and its surface is mirror-machined. After that, the glass substrate is immersed in an aqueous solution of hydrofluoric acid containing at least hydrogen fluoride to leave the crystalline phase on the surface of the glass substrate and selectively and preferentially etch the amorphous phase to a predetermined depth, thereby removing the surface of the glass substrate. The method of manufacturing a glass substrate for magnetic disks, which is made by forming unevenness on the surface of the glass substrate, achieves this precept. Preferably, (2) by setting the concentration of hydrogen fluoride in the hydrofluoric acid aqueous solution to a molar concentration of 0.05 to 2.5 mol/Q, and (3) reducing the concentration of hydrogen fluoride from the surface of the glass substrate. The etching depth is o.
oos~0.2. This is achieved by doing this. In other words, in the present invention, crystallized glass is used as the substrate material,
Mechanical polishing and chemical etching were used to create fine irregularities by taking advantage of the advantages of each. To be more specific about the mechanical polishing method as the first step, it finishes the crystallized glass surface to a very smooth mirror surface. For example, the number should be 1,508 or less, and more preferably 100 or less. In terms of disk performance, the mirror surface is such that the magnetic head can fly with a spacing of around 0.1 μm without colliding with the protrusions on the polishing surface. The second step, chemical etching, involves immersing the mirror-finished substrate in a hydrofluoric acid solution and chemically etching it. During this etching, the glass phase, which is a continuous phase in the crystallized glass, is preferentially and selectively etched by hydrofluoric acid, leaving the crystalline phase in the crystallized glass as an isolated phase in the form of protrusions on the surface. It is in. As a result of this etching, the surface is smoothed and many crystal phases with uniform height are destroyed, and the amorphous phase between each crystal phase is etched by hydrofluoric acid and becomes depressed, so that the surface of the substrate with microscopic irregularities is removed. It can be created. ? Since crystallized glass materials contain alkali metal oxides, alkali metal oxides, Afi20, SiO2, etc., hydrofluoric acid is most suitable for chemically etching these. Furthermore, according to experiments conducted by the present inventors, the concentration of hydrofluoric acid is 0.05 to 2.5 mol/Q (
When high-purity hydrofluoric acid is diluted with water, it is 0.1% by weight.
~5. Owt%) has been found to be suitable for the practice of the present invention.

The concentration of this hydrofluoric acid is 0.05 vgog/Q (0.
This is because if it is less than 1wt%, the etching effect is low and the etching rate is low, making it unsuitable for practical use. On the other hand, if the concentration is as high as 2.5 mo1/Q (5.Owt%) or more, the etching rate will be too high and it will be difficult to control the etching amount, making it impractical. The most preferable range is 0.25 mol/Q (0.5vt%) ~
1.5 mo1/ (1 (31%)). In addition, for example, ammonium fluoride or sodium fluoride may be mixed into the hydrofluoric acid solution to adjust the pH and reduce the etching rate appropriately to make the work easier. is also possible.

Further, the second object is as follows: (4) Continuing from the method for manufacturing a glass substrate for a magnetic disk described in (1), (2) or (3) above. A method for manufacturing a thin-film magnetic disk comprising the steps of sequentially MKIjing a magnetic wtna and a carbon-based protective film on the obtained glass substrate by sputtering, and (5) vacuum baking the substrate prior to the sputtering. This is achieved by the method for manufacturing a magnetic disk described in (4) above, which comprises the steps of applying a lubricant after forming the carbon-based protective film. [Function] The present invention uses a crystallized glass material. The present invention relates to a manufacturing method for forming a magnetic disk substrate and a method for manufacturing a thin film magnetic disk using this substrate. The spacing can form a surface on which the magnetic head can fly. The reason is described below. The crystalline phases in crystallized glass are dispersed within the amorphous phase and each exists in isolation. Therefore, after etching with a hydrofluoric acid solution, the substrate surface has a uniform distribution of protrusions with no directionality in the radial and circumferential directions. This achieves the same adhesive properties for the magnetic head's radial and circumferential operating modes. As explained earlier, in the conventional texturing of Ni-PJ and plates, grooves are carved in the circumferential direction, so the contact of the magnetic head is caused by the bulges (ridges) formed on both sides of the grooves due to the texturing. It has the disadvantage that it becomes close to line contact, the contact area is wide, and the adhesive force is large.Furthermore, the adhesive properties are different in the radial direction and the circumferential direction, and the adhesive force is particularly large in the seek mode in the radial direction. It was. To summarize the effects of the present invention, the first step of mechanical mirror polishing of crystallized glass is closely related to achieving the low spacing flying characteristics of the head, and the subsequent step of hydrofluoric acid polishing works in the second step. This chemical etching affects the low adhesion properties of the magnetic head due to the concave shape. What is important is that the second stage of etching is a unilateral dissolution and removal process from the mirror-finished surface toward the inside of the substrate, which eliminates paris (formed on both sides of the groove), which is a problem that becomes thicker during machining. It is important not to create any excitement. Pars are caused by the action of microscopic abrasive grains and cutting edges digging into the workpiece during machining, and when they occur, they form protrusions that seriously impede the low-spacing flying characteristics of the head. In the chemical etching process, each atom is essentially ionized and removed, so it is a gentle process that does not cause the problems with the conventional techniques mentioned above, and does not leave any processing strain or stress after processing. It is a law. Therefore, this hydrofluoric acid etching process makes it possible to impart adhesive properties to the surface, which has been mechanically polished to a mirror-like finish and achieves the low-spacing flying characteristics of the magnetic head. Become. This effect is the main point of the present invention. [Example] Example 1. The manufacturing process of a crystallized glass substrate for a magnetic disk will be explained according to the diagram in Figure 1. First, the overall structure of this manufacturing process. Through the illustration, glass material adjustment,
It consists of heating melting, glass plate forming, disk processing, crystal nucleation heat treatment, crystal nucleation growth heat treatment, mechanical polishing, and chemical etching using hydrofluoric acid.

The steps above will be explained in detail below. In this example, LiO. -SiO2-P
,O, system was used. Lid. Ingredients are 10.4vt%. S
in. Boru is 77.9wt%, p,o, Arubu is 2.7w
The raw materials were weighed so as to be equal to t% and mixed in the usual manner. After heating and melting this mixture at 1,400°C, a thickness of 2.0
- It was shaped into a glass plate. From this glass plate. Outer diameter 13
A disk having dimensions of 0 mwφ and an inner diameter of 40a*φ was cut out by machining.

Next, this glass disk was placed in a heat treatment furnace at a temperature of 10°C/m.
After heating to 550°C at a heating rate of in, hold for 1 minute,
Thereafter, the temperature was raised to 600° C. at a temperature increase rate of 10° C./win, held for 1 minute, and then cooled at a cooling rate of 5° C./win.

The above heat treatment at 550°C is a crystal nucleation heat treatment to generate crystal nuclei in the glass, and the 600°C heat treatment is a crystal nucleation lengthening heat treatment to grow the nodule nucleus and make it into a predetermined size. .

Since the size and density of the crystal nuclei can be controlled by these heat treatment conditions, these heat treatment conditions and even the glass material can be changed as appropriate depending on the characteristics of the magnetic disk. Next, the disk, which had been heat-treated to become crystallized glass, was mechanically mirror-polished using a polishing machine.

In the polishing machine, a glass disk was set between two upper and lower surface plates via a spacer, and the surface plates were pressurized and rotated while supplying machining fluid containing alumina powder or SiC powder. ．． At this time, the glass gate plate was moved by planetary gears using spacers in order to equalize the amount of processing and give it a mirror-like smoothness.

After polishing, the disk surface was cleaned by brushing with pure water and dried. The surface roughness of the polished surface of the glass disk obtained in this way was measured by Talystep's contact type surface roughness meter.
IIax There were 100 people. This roughness varies depending on processing conditions, and a mirror surface of about 508 can be achieved, but for the purposes of the present invention, it is desirable to achieve a roughness of 150 or less. This is the value necessary to allow the magnetic head to fly stably with a narrow spacing of about 0.10μ without colliding with any protrusions. Next, the disk was chemically etched by immersing it in an aqueous solution containing 2.5 wt% of high-purity hydrofluoric acid using a rack jig made of polytetrafluoroethylene. The etching solution was kept at 20° C., stirred and passed through continuously, and the etching time was 20 seconds.

Note that the preferred liquid temperature is 30°C or lower, 15 to 25°C.
℃ is more desirable. The etching time can be set according to the desired etching depth. This etching selectively etches the amorphous phase, which is the continuous phase in crystallized glass, and leaves the dispersed crystalline phase remaining as protrusions, forming irregularities on the substrate surface. Therefore, the etching time. When the concentration of hydrofluoric acid is increased, the unevenness becomes larger and R■
It is natural that ax increases. The size of the unevenness necessary and sufficient to reduce adhesion, that is, the setting of the value of Rmax, is determined by the performance of the magnetic disk device and the characteristics of the magnetic head, and is not determined uniquely, but depends on the numerical range. has a certain degree of freedom. However, if there is insufficient etching, the effect of reducing head adhesion will be small, and if there is too much etching, the surface roughness will become too large.
Needless to say, the low spacing and flying characteristics of the head will be impaired, making it unusable. What is important in this chemical etching process is that the suitable concentration range for the hydrofluoric acid etching solution is 0.1 to 5. There is a certain Owt%, and if it is less or more than this, as mentioned earlier, it becomes difficult to control the etching amount and speed, making it impractical. Is it possible to obtain the desired glass substrate through the above steps? was completed.

Example 2. In Example 1, the glass material is Li, 0-
Although SiO, -P20, and other materials were used, mechanical polishing and chemical etching were also performed on other glass materials with the compositions shown below. As with Example 1, good results were obtained with these as substrates for magnetic disks. Li20-SiO. system, Li,O-At,O,-SiO■ system, Li,O-MgO-At,O,-SiO■ system, MgO-
AI, 03-SiO, system, Na. O-AI, O, -SiO, system, BaO-AI, O, -Sto, system Example 3. As shown in the diagram in FIG. 2, a magnetic recording film was formed on the surface of the glass substrate obtained in Example 1 by sputtering, and a protective film of carbon or the like was further formed.
A lubricant is applied on top of it, and the thin film magnetic disk is completed. Hereinafter, detailed explanation will be given according to this process diagram. After setting the glass substrate obtained in Example 1 in a substrate holder of a sputtering device and vacuum baking at 300°C,
A chromium base film, a Co-Ni magnetic film, and a carbon protective film were successively formed. After taking it out from the sputtering device, a lubricant was applied to the surface to complete a magnetic disk.

In this way↑! 》Characteristics of the magnetic disks were evaluated using standard evaluation methods. As a result, the minimum flying height of the magnetic head is O. The adhesive strength of the magnetic head is 80% lower than that of conventional coated disks.
~90%, which is about 1/2 that of a textured Ni-P substrate, and has achieved characteristics that can simultaneously satisfy both head adhesion and low flying characteristics. In addition, CSS characteristics (Contact Start St
When the magnetic head (op) was evaluated, no head crash occurred even after so and ooo times, and no stains on the magnetic head slider surface were observed. [Effects of the Invention] According to the present invention, by taking advantage of the characteristics of glass, which is a hard material and has good polishability, a magnetic head can be levitated with a small spacing, and at the same time, the crystal phase in crystallized glass can be formed into microprotrusions. This can greatly reduce the adhesion between the magnetic head and the disk. In other words, the present invention can simultaneously achieve the head flying characteristics and adhesion characteristics, which were in a trade-off relationship with conventional Ni-P substrates. Therefore, by using this substrate, it is possible to form magnetic disks with extremely excellent characteristics. There is a certain effect that can be achieved.

In addition, because the cross-sectional shape of the substrate surface is isotropic in any direction due to the material and the processing method of the present invention, the adhesion properties for the radial and circumferential movements of the magnetic head are also the same. - It is possible to solve the problem of increased adhesive force in the opposite radial direction, which was a problem with P substrates. This has the effect of reducing the burden on the swinging mechanism of the magnetic head and simplifying it. The present invention can be said to replace the portion of conventional Ni-P substrate texture processing with chemical etching processing, so it is economical in that processing costs can be greatly reduced and the price of processing equipment can also be reduced. In addition, chemical etching has the advantage of being able to process a large number of disks simultaneously in a rack, so it is also excellent in productivity and mass production.

The crystallized glass substrate is a single material substrate, and the conventional Ni
-Compared to the fact that the P substrate is a composite material substrate of Al alloy and Ni-P plating film, the process disadvantage, number of equipment, material cost,
Since all processing costs can be reduced to about 172, it goes without saying that this is an essentially inexpensive substrate with excellent characteristics.

[Brief explanation of the drawing]

Claims (1)

[Claims] 1. Using crystallized glass in which a crystalline phase is dispersed in an amorphous glass phase as a substrate for a magnetic disk, after mirror-machining the surface, hydrogen fluoride containing at least hydrogen fluoride is used. A glass for a magnetic disk, which is formed by immersing the glass substrate in an aqueous acid solution to leave the crystalline phase on the surface of the glass substrate and selectively and preferentially etching the amorphous phase to a predetermined depth to form irregularities on the surface of the glass substrate. Substrate manufacturing method. 2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the concentration of hydrogen fluoride in the aqueous hydrofluoric acid solution is set to a molar concentration of 0.05 to 2.5 mol/l. 3. The etching depth from the surface of the glass substrate is 0.0.
3. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the glass substrate has a thickness of 0.05 to 0.2 μm. 4. A thin film magnetic material comprising the step of sequentially laminating a magnetic thin film and a carbon-based protective film on the obtained glass substrate by sputtering, following the method for producing a glass substrate for a magnetic disk according to claim 1, 2 or 3. Disc manufacturing method. 5. The method of manufacturing a magnetic disk according to claim 4, further comprising the steps of vacuum baking the substrate prior to the sputtering, and applying a lubricant after forming the carbon-based protective film.