JPH0833999B2 - Method for manufacturing titanium magnetic disk substrate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a titanium magnetic disk substrate having good surface properties.

[Prior Art] A magnetic disk used as a recording medium for a computer includes a disk substrate and a magnetic thin film formed thereon. Of these, the magnetic disk substrate is required to have the following characteristics.

(A) The surface quality after precision polishing or precision grinding is good so that the magnetic head can stably run on the disk, or stable magnetic characteristics with few magnetic errors can be obtained. .

(B) There are no protrusions or holes on the substrate surface that would cause defects in the magnetic film formed on the substrate surface.

(C) It has strength and rigidity that can withstand high-speed rotation when manufacturing a substrate.

(D) Being able to withstand heating when forming a magnetic film.

(E) Light weight and non-magnetic.

(F) It has a certain degree of corrosion resistance.

Conventionally, A1−
Aluminum alloys such as Mg alloys are used.

On the other hand, recently, magnetic disks tend to have higher recording densities and smaller sizes. Therefore, the following is required.

(A) A magnetic thin film is being formed by sputtering for the purpose of increasing the recording density, but it must have heat resistance against the temperature rise of the substrate at that time.

(B) The flying height of the magnetic head is reduced in order to minimize the spacing loss and achieve high density, but at this time, the magnetic head can be stably run on the disk so that the magnetic head is stable. Excellent smoothness.

However, A1 which is conventionally used as a substrate material
-Aluminum alloys such as Mg-based alloys have insufficient heat resistance, and further higher performance cannot be expected.

Along with this, various magnetic disk substrates using titanium instead of the conventional aluminum alloy have been proposed.

For example, JP-A-52-105804 discloses a titanium or titanium alloy magnetic disk substrate having an oxide film or a nitride film formed on its surface by oxidation or nitriding.
No. 1 publication, a core plate made of titanium or titanium alloy,
A magnetic disk substrate formed by laminating an insert layer, a layer made of nickel, titanium, a nickel alloy, or a titanium alloy and a layer made of glass or ceramics in this order is disclosed in Japanese Patent Laid-Open No. 59-178625. Disc substrates in which a surface of a medium substrate is covered with a hard valve metal or its nitride and a layer made of an oxide of the valve metal is formed on the surface are disclosed. Further, JP-A-61-199232i discloses a non-magnetic substrate, a non-magnetic hardened layer coated on the non-magnetic substrate, and Si, Ti, Mo, W and Zr coated on the non-magnetic hardened layer.
A magnetic medium comprising a non-magnetic underlayer made of any one of the above, and a magnetic medium layer covered with the non-magnetic underlayer, JP-A-61-199224 discloses a non-magnetic substrate, A non-magnetic hardened layer coated on it, a non-magnetic underlayer made of any one of TiO ₂ , TiC, and TiN coated on this non-magnetic hardened layer, and a magnetic layer coated on this non-magnetic under layer. A magnetic medium with a medium layer is disclosed respectively.

[Problems to be Solved by the Invention] By the way, since the average crystal grain size of titanium is usually as large as about 50 μm, when titanium is used as the magnetic disk substrate, a step due to the crystal during precision polishing or precision grinding is used. Therefore, it is difficult to obtain a good surface quality. In order to avoid this, it is considered that the crystal grain size is made finer by controlling the processing and heat treatment, and the structure in which a film of a substance having fine crystals is formed on the surface of the titanium substrate. . In this case, however, about 10 μm is the limit for making the crystal grain size finer, and even with this grain size, a sufficiently satisfactory surface quality cannot be obtained because of the step due to the crystal orientation. Also, in the case of, there are various problems as shown below.

That is, the above-mentioned JP-A-52-105804 is an example of this, but in this case, there are crystals of various orientations on the surface of the titanium substrate, and the rate of oxidation or nitridation varies depending on the crystal orientation, so that the orientation is uniform. Oxidation or nitridation is difficult, resulting in a decrease in yield and an increase in manufacturing cost. It has been reported that it is necessary to form a white oxide film with a thickness of 1500 Å or more when forming an oxide film by oxidation on a titanium substrate to a thickness such that a high level surface texture can be obtained after polishing. Yes (Japanese Adhesive Society magazine vol.
21 No. 1, 1985, p. 32). However, when a white oxide film is formed on titanium, the film is easily peeled off (titanium / zirconium vol.32 No.1, 1984 1
Month, p. 19), which leads to lower yields and higher manufacturing costs. In addition, when a nitride film is formed on a titanium substrate by nitriding to a thickness such that a high level surface texture can be obtained after polishing, the surface nitride film is apt to crack (Metal Society of Japan, 1966). , Refer to the photograph on page 28 of Volume 30), which also leads to a decrease in yield and an increase in manufacturing cost.

In the case of the technique disclosed in the above-mentioned Japanese Patent Laid-Open No. 63-142521, since the number of steps is large, the manufacturing cost is high and the manufacturing time is long. Further, when ceramics is used for the outermost layer, a large number of pores are present in the ceramics, so that sufficient surface texture cannot be obtained. Further, in the case of glass, an extremely high level of surface texture of Ra = 0.05 μm can be obtained, but in this case, the head causes sticking with the disk surface, which is not preferable. Further, in the case of the glass surface, N that is an impurity in the glass is increased as the substrate temperature rises when forming the magnetic thin film.
a, Ca, etc. diffuse into the magnetic thin film and adversely affect the magnetic characteristics of the magnetic recording medium.

In addition, the above-mentioned JP-A-59-178625 and JP-A-61-19.
As in the technique disclosed in JP 9232 and JP-A 61-199224, polishing is performed only by overcoating a metal layer, or an oxide, nitride, or carbide layer thereof on a substrate. It cannot be said that the surface quality after the cleaning is sufficient.

As described above, the present situation is that a magnetic disk substrate mainly composed of titanium has not yet been obtained with good characteristics.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a titanium magnetic disk substrate capable of easily manufacturing a titanium magnetic disk substrate having a high level surface texture. And

[Means and Actions for Solving the Problems] As a result of various investigations by the inventors of the present invention for improving the performance of a titanium disk substrate, a certain nonmagnetic transition metal element was formed on a titanium substrate whose surface texture was improved to some extent. It has been found that a titanium magnetic disk substrate having a high degree of surface texture can be manufactured by forming a thin film having a predetermined thickness and polishing these.

That is, on the surface of a titanium substrate having a surface texture represented by Ra of 0.05 μm, a periodic table group IVA, group VA, group VIA,
The above object can be achieved by forming a thin film of a non-magnetic transition metal element belonging to any one of Group VIIA and Group VIIIA to a film thickness of 0.5 μm or more and 10 μm or less and then polishing the surface.

In this case, the thin film of non-magnetic transition metal element can be preferably formed by ion plating, sputtering, vacuum deposition, and CVD. Further, it is preferable to polish the surface with a polishing liquid or a polishing cloth.

Note that titanium as used herein is a concept including both pure titanium and titanium alloy.

 Hereinafter, the present invention will be described in detail.

Since titanium has a high melting point of about 1650 ° C., when titanium is used as the magnetic disk substrate, the heat resistance against the substrate temperature rise when forming the magnetic thin film by sputtering is sufficient. In addition, a titanium substrate is subjected to ion plating, sputtering, vacuum deposition, CVD, or the like by periodic table group IVA, group VA, group VIA, group VIIA, and group VI.
By forming a thin film of a non-magnetic transition metal element of the IIA group elements, the surface can have an extremely fine structure. When the crystal grain size is large, the processing speed changes due to the difference in the crystal orientation of the surface, and a step is formed between the crystals. However, if the surface texture is fine, the difference in the orientation between adjacent crystals is Since it becomes smaller and the step between crystals can be made smaller, a high level surface texture can be obtained. Further, since the thin film of the above-mentioned non-magnetic transition metal element is formed by ion plating, sputtering, vacuum deposition, CVD or the like, it has excellent adhesion. Furthermore,
Periodic Table Group IVA, Group VA, Group VIA, Group VIIA, and Group VI
The non-magnetic transition metal element of the IIA group elements has a melting point of 1
Since the temperature is 200 ° C. or higher, not only the titanium substrate but also the thin film formed of these elements maintain sufficient heat resistance during the sputtering for forming the magnetic thin film.

Ion plating, sputtering, vacuum deposition,
Alternatively, when a thin film is formed by CVD or the like, the upper limit of the film thickness is at most 10 μm, so that the influence of the substrate surface shape remains on the thin film surface of the non-magnetic transition metal element formed along the substrate surface. . Therefore, if the surface properties of the substrate are poor, it becomes difficult to obtain a high level of surface properties even if the thin film thereon is polished. Therefore, it is necessary that the surface quality of the titanium substrate is Ra ≦ 0.05 μm.

However, the desired surface texture cannot be obtained by only forming the thin film in this way due to the influence of the crystal grains of the substrate. Therefore, in the present invention, the desired surface texture is obtained by polishing the surface of the thin film to eliminate the influence of the substrate. In this case, by polishing with a polishing liquid or a polishing cloth, extremely good surface properties can be obtained.

Further, in order to eliminate the influence of the surface properties of the substrate by polishing, the thickness of the thin film needs to be at least 0.5 μm.

If the thickness of the thin film of nonmagnetic transition metal element exceeds 10 μm, the properties of the film deteriorate, so the upper limit is 10 μm. Therefore, the thickness of the thin film of non-magnetic transition metal is 0.5 μm or more and 10 μm or less.

As described above, according to the present invention, it is possible to manufacture a titanium magnetic disk substrate having an extremely excellent surface property by a simple process having a relatively small number of processes.

[Examples] Examples of the present invention will be described below.

In this example, CP-2 type pure Ti with a thickness of 1.5 mm
From the cold-rolled sheet, an outer diameter of 95 mm, an annular flat plate having an inner diameter of 25 mm is prepared as a blank material, a titanium substrate is prepared by polishing the blank material, and a thin film of a non-magnetic transition metal is formed on it. Then, the surface of the thin film was polished with a polishing liquid or a polishing cloth to prepare a magnetic disc substrate sample. In the production of this sample, the production conditions were variously changed, and the total of Examples 1 to 15 produced under the conditions within the scope of the present invention and Comparative Examples 1 to 13 produced under the conditions outside the scope of the present invention Samples were produced.

The manufacturing conditions and surface properties of each sample at this time are shown in Tables 1 and 2. In Table 1, Examples 1 to 15 and 2
Comparative Examples 1 to 13 are shown in the table.

Next, the manufacturing conditions and surface properties of each sample will be described in detail.

Example 1 The above blank material was sequentially polished with a # 400, # 800, # 1500, and # 4000 numbered grindstone, and then polished with alumina abrasive grains and a buff cloth to obtain a substrate.
The polishing conditions at this time were as shown below. In the case of grinding stones, with any number of grinding stones, water containing 5% rust preventive agent is run at a rate of 1 / min, the pressing pressure against the object to be polished is 80 g / cm ² , the number of rotations of the platen. At 40 rpm to polish both sides. In polishing, 1 g of an alumina particle having an average particle size of 1 μm or less and 1% of a polishing liquid containing 20% hydrogen peroxide solution were used.
/ G / min, pressing pressure against the object to be polished is 80g /
Both sides were polished at cm ² and the number of rotations of the platen of 40 rpm.

When these grindstones are polished and polished, the first
The devices shown in FIGS. (A) and (b) were used. In this device, an internal gear 7 is provided on the inner peripheral portion of a substantially cylindrical main body 10, and
A sun gear 6 fixed to a rotating shaft 9 is provided at the center of the inside of the. Between these internal gear 7 and sun gear 6,
A plurality of sample holders 2 that operate as planetary gears in a state of being meshed with these are set. The sample 1 to be polished is set on the sample holder 2.
Polishing members held on the upper surface plate 4 and the lower surface plate 5 on both sides of the sample holder 2, that is, a grindstone 8 in FIG. 1A, a polishing cloth holding surface plate 11 in FIG. 1B and a polishing cloth on the surface thereof.
12 is provided, and such a polishing member is pressed against the sample 11 with a predetermined pressure. Upper surface plate 4 and upper surface plate 4
The polishing member held by is provided with a polishing liquid supply hole 3 for supplying a polishing liquid. Then, by rotating the rotating shaft 9 by a motor (not shown), the sun gear 6
Both sides of the sample 1 are polished by rotating the sample holder 2 to rotate and revolve the sample holder 2. The surface texture of the substrate after polishing and polishing with such an apparatus is Ra
= 0.03 μm.

A titanium film having a thickness of 3 μm was formed on this substrate by ion plating using an ion plating apparatus as shown in FIG. In this apparatus, a titanium substrate 21 is provided in a vacuum container (not shown), an evaporation material 22 is provided so as to face the base 21, and an electron gun 23 is provided below the evaporation material 22. An anode 24 is arranged between the evaporation material 22 and the substrate 21. Then, in a state where an electric field is applied between the substrate 21 and the anode 24, electrons are made to collide with the evaporation material 22 by the electron gun 23, and ions 25 are ejected from the evaporation material 22. The ions 25 are accelerated by the electric field,
A thin film is formed on the lower surface of 21. The thin film forming conditions in this embodiment are as follows: anode voltage is 30V, bias is -500V,
The degree of vacuum was set to 10 ^-5 Torr. In this example, a titanium thin film having a purity of 99.9% by weight was used. The same applies to the following embodiments.

Thereafter, the thin film surface was polished in the same manner as the polishing of the substrate by the apparatus shown in FIG. 1 (b) described above to obtain a magnetic disk substrate sample.

As shown in Table 1, the surface texture Ra was a very good value of 0.002 μm. That is, it was confirmed that the surface texture was remarkably improved by polishing the titanium thin film by ion plating.

Here, Ra is a measurement that removes low-frequency components from the contour curve appearing on the cut surface when the DUT is cut on a plane perpendicular to the measured surface, as shown in FIG. A roughness curve is obtained by the method, a portion having a length L in the surface direction of this curve is extracted, and a roughness curve with the center line of the extraction portion as the x-axis and the vertical magnification direction as the y-axis is y = f (x) When expressed as
The value given by the following equation (1) is expressed in μm.

As a result of observing the surface of the disk substrate sample thus formed with a differential interference microscope, it was confirmed that extremely good surface properties were obtained as shown in FIG. 7 (a).

Example 2 A substrate was prepared in the same manner as in Example 1, and a titanium film was formed on the substrate with a thickness of 3 μm by sputtering using a sputtering apparatus as shown in FIG.
This apparatus has a pair of opposed targets 32a and 32b provided in a vacuum container (not shown), and a base 31 on which a thin film is formed is installed laterally between them. Permanent magnets 34, 35 are provided adjacent to the targets 32a, 32b, respectively, and a magnetic field 38 is formed between the targets by these permanent magnets. Then, by applying a voltage between the targets 2a and 2b, the negative ions 36 and the electrons 37 fly out from the target 2a into the space between the targets, and the electrons 37 collide with the target 32b and knock out the negative ions.
The negative ions knocked out in this way are deposited on the surface of the base 31 that is positively charged. The reference numeral 33 is an anode. In this example, the working gas pressure in the vacuum container during sputtering was set to 10 ⁻⁴ Torr.

After forming the thin film, the surface thereof was polished in the same manner as in Example 1 to prepare a magnetic disk substrate sample.

As shown in Table 1, the surface texture Ra is the same as in Example 1.
It was a very good value of 0.002 μm. That is, it was confirmed that the surface properties are remarkably improved by polishing the titanium thin film after sputtering.

Further, as a result of observing the surface of the disk substrate sample thus formed with a differential interference microscope as in Example 1, it was confirmed that an extremely good surface shape was obtained as shown in FIG. 7 (b). I was able to confirm.

Example 3 A substrate was prepared in the same manner as in Example 1, and a titanium film was formed on the substrate with a thickness of 3 μm by vacuum evaporation using a vacuum evaporation apparatus as shown in FIG. In this apparatus, a base 41 is installed in a vacuum container (not shown), an evaporation material 42 is provided so as to face the base 41, and an electron gun 43 is further provided below the evaporation material 42. Then, the vapor 44 is evaporated from the surface of the evaporation material 42 by the electron gun 43, and this vapor is deposited on the surface of the base 41. In this example, the degree of vacuum in the vacuum container was 10 ⁻⁶ Torr.

After forming the thin film, the surface thereof was polished in the same manner as in Example 1 to prepare a magnetic disk substrate sample.

As shown in Table 1, the surface texture Ra was a very good value of 0.003 μm. That is, it was confirmed that the surface properties were remarkably improved by polishing the titanium thin film by vacuum deposition and then polishing.

Example 4 A substrate was prepared in the same manner as in Example 1, and a titanium film was formed on the substrate to a thickness of 3 μm by CVD using a CVD apparatus as shown in FIG. This equipment is chamber 53
A substrate 51 is installed inside, and a gas supply unit 52 is provided above the substrate 51. A gas supply system 55 is connected to the gas supply unit 55, and a reaction gas such as a metal compound salt vapor and a carrier gas are introduced into the chamber 53 from the gas supply system 55 via the gas supply unit 52. An exhaust system 54 is connected to the chamber 53. Then, the metal generated by the reaction of the reaction gas is deposited on the base 51 while a predetermined voltage is applied to the base 51. The film forming conditions at this time were that titanium tetrachloride was used as the metal compound salt, argon gas was used as the carrier gas, the working gas pressure was 4 × 10 ² Torr, and the applied voltage to the substrate 51 was 1000V.

After forming the thin film, the surface thereof was polished in the same manner as in Example 1 to prepare a magnetic disk substrate sample.

As shown in Table 1, the surface texture Ra was a very good value of 0.003 μm. That is, it was confirmed that the surface properties were significantly improved by polishing the titanium thin film by CVD and then polishing.

Example 5 A blank material equivalent to the blank material used in Example 1 was sequentially polished under the same polishing conditions with a numbered grinding stone of # 400, # 800, # 1500, and # 4000 to obtain a substrate without polishing. did. The surface texture Ra of this substrate was 0.05 μm. A titanium thin film having a thickness of 3 μm was formed on the surface of this substrate by ion plating in the same manner as in Example 1, and the surface was polished in the same manner as in Example 1 to prepare a magnetic disk substrate sample.

As shown in Table 1, the surface texture Ra was a very good value of 0.003 μm. That is, it was confirmed that even if the surface of the substrate was not polished, if the surface texture Ra was 0.05 μm, the surface texture was remarkably improved by forming the titanium thin film by ion plating and then polishing the surface.

Example 6 A substrate equivalent to that of Example 5 was prepared, and a titanium thin film of 3 μm was formed on the surface of the substrate by sputtering in the same manner as in Example 2.
And the surface thereof was polished in the same manner as in Example 1 to prepare a magnetic disk substrate sample.

As shown in Table 1, the surface texture Ra was a very good value of 0.002 μm. That is, it was confirmed that even if the surface of the substrate was not polished, if the surface texture Ra was 0.05 μm, the surface texture was remarkably improved by forming the titanium thin film by sputtering and then polishing the surface.

Example 7 A substrate equivalent to that of Example 5 was prepared, a titanium thin film was formed on the surface of the substrate by vacuum vapor deposition to a thickness of 3 μm as in Example 3, and the surface was polished in the same manner as in Example 1. A magnetic disk substrate sample was prepared.

As shown in Table 1, the surface texture Ra was a very good value of 0.004 μm. That is, it was confirmed that even if the surface of the substrate was not polished, if the surface texture Ra was 0.05 μm, the surface texture was remarkably improved by forming the titanium thin film by vacuum deposition and then polishing the surface.

Example 8 A magnetic disk substrate sample was prepared under the same conditions as in Example 1 except that the thickness of the titanium thin film formed by ion plating was 0.5 μm. As shown in Table 1, the surface texture Ra was 0.004 μm, which was an extremely good value, and it was confirmed that the surface texture was improved by polishing.

Example 9 A magnetic disk substrate sample was prepared under the same conditions as in Example 1 except that the thickness of the titanium thin film formed by ion plating was 9 μm. As shown in Table 1, the surface texture Ra was 0.004 μm, which was an extremely good value, and it was confirmed that the surface texture was improved by polishing.

Example 10 The thickness of the titanium thin film formed by sputtering is
A magnetic disk substrate sample was prepared under the same conditions as in Example 2 except that the thickness was 0.5 μm. As shown in Table 1, the surface texture Ra is 0.004 μm, which is an extremely good value.
It was confirmed that the surface properties were improved by polishing.

Example 11 A magnetic disk substrate sample was prepared under the same conditions as in Example 1 except that the thin film formed by ion plating was a vanadium thin film. As shown in Table 1, the surface texture Ra was 0.004 μm, which was an extremely good value, and it was confirmed that the surface texture was improved by polishing. The vanadium used had a purity of 99.9% by weight.

Example 12 A magnetic disk substrate sample was prepared under the same conditions as in Example 1 except that the thin film formed by ion plating was a chromium thin film. As shown in Table 1, the surface texture Ra is 0.003 μm, which is an extremely good value.
It was confirmed that the surface properties were improved by polishing. The chromium used had a purity of 99.9% by weight.

Example 13 A magnetic disk substrate sample was prepared under the same conditions as in Example 1 except that the thin film formed by ion plating was a manganese thin film. As shown in Table 1, the surface texture Ra is 0.004 μm, which is an extremely good value.
It was confirmed that the surface properties were improved by polishing. The manganese used had a purity of 99.9% by weight.

Example 14 A magnetic disk substrate sample was prepared under the same conditions as in Example 1 except that the thin film formed by ion plating was a ruthenium thin film. As shown in Table 1, the surface texture Ra was 0.003 μm, which was a very good value, and it was confirmed that the surface texture was improved by polishing. The ruthenium used had a purity of 99.9% by weight.

Example 15 A magnetic disk substrate sample was prepared under the same conditions as in Example 1 except that the thin film formed by ion plating was a palladium thin film. As shown in Table 1, the surface texture Ra was 0.003 μm, which was a very good value, and it was confirmed that the surface texture was improved by polishing. The palladium used had a purity of 99.9% by weight.

Comparative Example 1 A blank material similar to that of Example 1 was polished and polished under the same conditions as the titanium substrate of Example 1 to obtain a magnetic disk substrate sample. That is, this sample is obtained by removing the titanium thin film from the sample of Example 1. The surface texture Ra of this sample was 0.03 μm as shown in Table 2. In order to use it as a magnetic disk substrate, the surface texture Ra must be 0.02 μm or less,
In Comparative Example 1, it was confirmed that this condition was not satisfied.

Further, as a result of observing the surface of the disk substrate sample thus formed with a differential interference microscope, as shown in FIG. 8 (a), a step between crystals can be clearly confirmed, and as shown in FIG. It was confirmed that the surface properties were clearly worse than those of the samples of Examples 1 and 2.

Comparative Example 2 The blank material used in Example 1 was subjected to # 40 under the same polishing conditions.
Polishing was sequentially carried out with a numbered grindstone of 0, # 800 and # 1500, and this was used as a base. The surface texture Ra of this substrate is 0.08μ
It was m. A titanium thin film having a thickness of 3 μm was formed on the surface of this substrate by ion plating in the same manner as in Example 1, and the surface was polished in the same manner as in Example 1,
A magnetic disk substrate sample was prepared.

As shown in Table 2, the surface texture Ra was 0.07 μm. In order to use it as a magnetic disk substrate, it is necessary that the surface texture Ra be 0.02 μm or less, so that this comparative example 2 does not satisfy this condition. That is, it was confirmed that when the surface texture Ra of the substrate exceeds 0.05 μm, excellent surface texture cannot be obtained.

Comparative Example 3 A titanium substrate was prepared in the same manner as in Comparative Example 2, and a titanium thin film having a thickness of 3 μm was formed on the surface of this substrate by sputtering in the same manner as in Example 2, and the surface was polished in the same manner as in Example 2. Then, a magnetic disk substrate sample was prepared.

As shown in Table 2, the surface texture Ra was 0.06 μm. In order to use it as a magnetic disk substrate, it is necessary that the surface texture Ra be 0.02 μm or less, so it was confirmed that this comparative example 3 did not satisfy this condition.

Comparative Example 4 A titanium substrate was prepared in the same manner as in Comparative Example 2, and a titanium thin film was formed on the surface of this substrate by vacuum vapor deposition to a thickness of 3 μm in the same manner as in Example 3, and the surface was formed in the same manner as in Example 3. Polishing was performed to prepare a magnetic disk substrate sample.

As shown in Table 2, the surface texture Ra was 0.06 μm. In order to use it as a magnetic disk substrate, it is necessary that the surface texture Ra be 0.02 μm or less, so that it was confirmed in Comparative Example 4 that this condition was not satisfied.

Comparative Example 5 A titanium substrate was prepared in the same manner as in Comparative Example 2, and a titanium thin film of 3 μm was formed on the surface of this substrate by CVD as in Example 4.
A magnetic disk substrate sample was prepared by forming the magnetic disk substrate with a thickness of m and polishing the surface in the same manner as in Example 4.

As shown in Table 2, the surface texture Ra was 0.06 μm. The surface texture Ra must be 0.02 μm or less for use as a magnetic disk substrate. In this Comparative Example 5, it was confirmed that this condition was not satisfied.

Comparative Example 6 A titanium substrate was prepared in the same manner as in Example 1, and a titanium thin film having a thickness of 3 μm was formed on the surface of the substrate by ion plating in the same manner as in Example 1 to prepare a magnetic disk substrate sample without polishing. And

As shown in Table 2, the surface texture Ra was 0.04 μm. The surface texture Ra must be 0.02 μm or less for use as a magnetic disk substrate. This comparative example 6 does not satisfy this condition. That is, it was confirmed that even if a thin film was formed, excellent surface properties could not be obtained unless the surface was polished thereafter.

Also, as a result of observing the surface of the disk substrate sample thus formed with a differential interference microscope, as shown in FIG. 8 (b), a step between crystals can be clearly confirmed, and as shown in FIG. It was confirmed that the surface properties were clearly worse than those of the samples of Examples 1 and 2.

Comparative Example 7 A magnetic disk substrate sample was prepared under the same conditions as in Example 1 except that the titanium thin film formed by ion plating had a thickness of 0.2 μm. As shown in Table 2, the surface texture Ra was 0.06 μm. The surface texture Ra is 0.02μm for use as a magnetic disk substrate.
Because it needs to be: This comparative example 7 does not satisfy this condition. That is, it was confirmed that when the thickness of the thin film was too thin, excellent surface properties could not be obtained.

Comparative Example 8 A magnetic disk substrate sample was prepared under the same conditions as in Example 1 except that the thickness of the titanium thin film formed by ion plating was 15 μm. As shown in Table 2, the surface texture Ra was 0.08 μm. The surface texture Ra must be 0.02 μm or less for use as a magnetic disk substrate. This comparative example 8 does not satisfy this condition. That is, it was confirmed that when the thickness of the thin film was too thin, excellent surface properties could not be obtained.

Comparative Example 9 A magnetic disk substrate sample was prepared under the same conditions as in Comparative Example 7 except that the thin film was formed of vanadium. As shown in Table 2, the surface texture Ra was 0.07 μm. In order to use it as a magnetic disk substrate, the surface texture Ra is 0.02.
Because it needs to be less than μm. In Comparative Example 9, it was confirmed that this condition was not satisfied.

Comparative Example 10 A magnetic disk substrate sample was prepared under the same conditions as in Comparative Example 7 except that the thin film was formed of chromium. As shown in Table 2, the surface texture Ra was 0.07 μm. The surface texture Ra is 0.02μm for use as a magnetic disk substrate.
Because it needs to be: It was confirmed in Comparative Example 10 that this condition was not satisfied.

Comparative Example 11 A magnetic disk substrate sample was prepared under the same conditions as in Comparative Example 7 except that the thin film was formed of manganese. As shown in Table 2, the surface texture Ra was 0.06 μm. The surface texture Ra is 0.02μ for use as a magnetic disk substrate.
Because it is necessary to be m or less. It was confirmed that this Comparative Example 11 did not satisfy this condition.

Comparative Example 12 A magnetic disk substrate sample was prepared under the same conditions as in Comparative Example 7 except that the thin film was formed of ruthenium. As shown in Table 2, the surface texture Ra was 0.08 μm. In order to use it as a magnetic disk substrate, the surface texture Ra is 0.02.
Because it needs to be less than μm. It was confirmed that this Comparative Example 12 did not satisfy this condition.

Comparative Example 13 A magnetic disk substrate sample was prepared under the same conditions as in Comparative Example 7 except that the thin film was formed of palladium. As shown in Table 2, the surface texture Ra was 0.09 μm. In order to use it as a magnetic disk substrate, the surface texture Ra is 0.02.
Because it needs to be less than μm. It was confirmed that this Comparative Example 13 did not satisfy this condition.

From the above examples, it was confirmed that a magnetic disk substrate having excellent surface properties can be obtained as long as the conditions specified in the present invention are satisfied.

The present invention is not limited to the above embodiment. For example, the thin film is formed of one kind of element, but as long as the other conditions are within the range specified in the present invention, the thin film may be a thin film containing two or more kinds of elements or may be a multi-layer film. Further, the polishing conditions are merely examples, and the polishing conditions are not limited to these.

[Effect of the Invention] According to the present invention, a titanium magnetic disk substrate having excellent surface properties can be obtained in a simple process. Therefore, the present invention is extremely practical.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a polishing apparatus used in an embodiment of the present invention, FIG. 2 is a schematic diagram of an ion plating apparatus for forming a thin film on a titanium substrate, and FIG. 3 is a method for obtaining Ra. FIG. 4 is a schematic diagram of a sputtering apparatus for forming a thin film on a titanium substrate, FIG. 5 is a schematic view of a vacuum deposition apparatus for forming a thin film on a titanium substrate, FIG. FIG. 6 is a schematic view of a CVD apparatus for forming a thin film on a titanium substrate, and FIGS. 7 and 8 are photographs showing the metallographic structure of the substrate sample surface. 1; sample, 2; holder, 3; hole, 4,5; surface plate, 6; sun gear, 7; internal gear, 8: grindstone, 9; shaft, 10; body, 11; polishing cloth holding surface plate, 12 Polishing cloth, 21,31,41,51; substrate, 22,42; evaporation material, 2
3,43; electron gun, 24,33; anode, 32a, 32b; target, 3
4; 35; permanent magnet, 38; magnetic field, 52; gas supply part, 53; chamber, 54; exhaust system, 55; gas supply system.

Front Page Continuation (72) Inventor Ken Ono Marunouchi 1-2-2 Nihon Steel Pipe Co., Ltd., Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Hiroshi Kibe 1-2-1 Marunouchi Chiyoda-ku, Tokyo Nippon Steel Pipe Incorporated (72) Inventor Masahiko Naoe 2-10-40 Ookayama, Meguro-ku, Tokyo 3 of CD (56) Reference JP-A-62-157326 (JP, A)

Claims (2)

[Claims] 1. A group IVA, VA, VIA of the periodic table on the surface of a titanium substrate having a surface texture represented by Ra of 0.05 μm or less.
A disk substrate made of titanium, characterized in that a thin film of a nonmagnetic transition metal element belonging to any one of Group III, Group VIIA, and Group VIIIA is formed to a thickness of 0.5 μm or more and 10 μm or less, and then the surface is polished. Manufacturing method. 2. The method for manufacturing a titanium disk substrate according to claim 1, wherein the thin film is formed by ion plating, sputtering, vacuum deposition, or CVD.