JP3055795B2 - Manufacturing method of magnetic disk with excellent magnetic properties - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a magnetic disk having excellent magnetic characteristics, and more particularly to an improvement in recording and reproducing characteristics of a magnetic disk called a hard disk.

(Prior Art) In recent years, there has been a demand for a magnetic disk widely used as a file memory in an information processing system to improve the recording density in order to increase its capacity. Therefore, in order to increase the recording density of a magnetic disk medium, it is necessary to reduce the distance between the magnetic disk and the magnetic head and to increase the recording / reproducing characteristics (SN ratio and output) of the magnetic disk. However, these two requirements are completely opposite. In order to reduce the distance between the magnetic disk and the magnetic head, it is effective to reduce the surface roughness of the disk surface. In order to increase the magnetic anisotropy, it is preferable to increase the surface roughness.

By the way, in order to improve the recording / reproducing characteristics of the magnetic disk, it is necessary to increase the coercive force of the medium and to use a medium whose circumferential direction is the axis of easy magnetization, that is, a medium having magnetic anisotropy. Therefore, conventionally, in order to increase the coercive force of the medium, it has been studied to control the components of the magnetic layer and the method of forming the same.For example, if bias sputtering film formation is performed using a CoCrTa-based or CoNiCr-based metal magnetic material, It can be more than 1500 Oe, according to the IEICE Technical Meeting, CPM 88-92 (1
988) P.23.

In order to impart magnetic anisotropy to a magnetic disk, Al
It is effective to provide substantially concentric fine grooves on a non-magnetic substrate such as a plate, and by such concentric fine grooves, the SN ratio at the time of recording / reproduction is improved,
It has been clarified that effects such as an increase in output during recording and reproduction can be obtained (US Pat. No. 4,735,840).
In addition to such recording / reproducing characteristics, the provision of such fine grooves as described above makes it possible to improve the durability of the hard disk against friction with the magnetic head. It has been clarified that it can be improved (Japanese Patent Application Laid-Open No. 61-202324) and is known as a means for improving the recording and reproducing characteristics.

In particular, in the above-mentioned U.S. Patent, in order to obtain crystal magnetic anisotropy, a shadow effect of sputtered particles is induced by fine irregularities of a groove, and a Cr intermediate layer formed thereon is replaced with a (110) crystal of the crystal. It is said that the squareness ratio is improved by making the plane (represented by the Miller index; the same applies hereinafter) parallel to the disk surface, and further causing the crystal orientation of the magnetic film formed thereon. However, in that case, it is clear that the surface roughness needs to be 50 ° or more as measured by a roughness meter, and below that, the orientation of the c-axis of the crystal of the magnetic film is not constant and the squareness ratio is reduced. ing.

In addition, as an industrially available device for providing fine grooves, as shown in the above-mentioned U.S. Patent, a polishing tape or loose abrasive is pressed against the surface while rotating a substrate such as an Al plate. There is an apparatus which forms fine grooves with high reproducibility, thereby forming fine grooves having a depth of, for example, 0.001 to 0.2 μm and a pitch of 100 to 2,000 grooves / mm.

(Problems to be Solved by the Invention) However, when manufacturing a target magnetic disk, as described above, merely providing concentric fine grooves in a substrate such as an Al plate causes a large magnetic anisotropy. It was not obtained, and the size of the magnetic isomer was as small as 1-3 × 10 ⁻³ erg / cc, and the improvement of the squareness ratio could not be greatly expected. The shape (depth, width) of the groove and the density of the groove (the number of grooves per unit length in the radial direction) are disclosed in the above-mentioned JP-A-61-202324. Depth: 0.001-2.
0 μm, density: in the range of 400 to 1600 lines / mm, the recording / reproducing characteristics of the film-forming medium providing the magnetic layer do not change much, and therefore, merely providing the concentric grooves has a greater effect on the recording / reproducing characteristics than not providing it. Although effective, the effect was limited. In particular, when the coercive force is large,
In the case of Oe or more, simply providing a groove will reduce the squareness ratio.
It is not so large as 0.75 to 0.88, which is insufficient. Therefore, further improvement in reproduction output is desired.

As described above, the conventionally proposed method is intended to improve the squareness ratio by using the crystal magnetic anisotropy of the magnetic film, but does not sufficiently achieve the purpose. .

Here, in view of the above circumstances, the present inventors have studied in detail the mechanism of manifestation of magnetic anisotropy that occurs when a magnetic film is formed on a substrate having concentric grooves, and as a result, Magnetic anisotropy with easy axis of magnetization
Utilizing the anisotropy of the strain generated in the magnetic film, it can be enhanced by the reverse magnetostriction effect, thereby obtaining a larger magnetic anisotropy than before, further improving the squareness ratio, and furthermore, the recording / reproducing characteristics Have been found to be able to improve the present invention, and have completed the present invention.

Accordingly, it is an object of the present invention to provide a method of manufacturing a magnetic disk having excellent magnetic characteristics, and a magnetic recording medium (magnetic disk) having an excellent reproduction output voltage value and SN ratio among the recording and reproduction characteristics of the medium. ) To provide a manufacturing method,
In particular, an object is to improve a high coercivity hard disk for high density recording.

(Means for Solving the Problems) The present invention is directed to solving the problems, and is provided as an underlayer on a rigid disk-shaped non-magnetic substrate.
After forming the Ni-P plating layer, the surface of the Ni-P plating layer is physically polished to provide ultra-fine grooves having a pitch of 80 ° and a depth of 40 ° in the radial direction. On the plating layer or on the Ni-P plating layer, a Cr intermediate layer is 200 to 8
Forming a magnetic layer having an in-plane magnetostriction constant of 1.5 to 4 × 10 ^-5 on the intermediate layer after forming the film with a thickness of 00 °; It is.

(Operation) In short, the present invention utilizes the anisotropy of the strain generated in the magnetic film to increase the magnetic anisotropy by the inverse magnetostriction effect, and is based on the following concept.

That is, first, the magnitude (Ku) of the in-plane magnetic anisotropy due to the inverse magnetostriction effect can be expressed by the following equation.

Ku = 3 / 2λE (εθ−εr) where λ: magnetostriction constant E: elastic modulus εθ: circumferential crystal lattice strain εr: radial crystal lattice strain Therefore, to increase crystal magnetic anisotropy by the inverse magnetostriction effect (A) λ> 0 and (εθ−εr)> 0, that is, a method of applying a large tensile strain in the circumferential direction using a magnetic film having a large λ, and (b) a method of applying a large tensile strain in the circumferential direction. εr) <0
That is, a method of giving a large compressive strain in the circumferential direction using a magnetic film having a large | λ | can be considered.
The method (a) was used.

Then, in order to realize such a method (a),
In the present invention, the in-plane magnetostriction constant of the polycrystalline metal thin film providing the magnetic layer of the magnetic disk is set to 1.5 to 4 × 10 ^−5, and if the in-plane magnetostriction constant becomes smaller than this, The effect of inverse magnetostriction is reduced, and the object of the present invention cannot be sufficiently achieved. The in-plane magnetostriction constant of such a polycrystalline metal thin film is determined by the type of magnetic material applied to the magnetic layer.

As described above, in order to realize the method (a) above, in order to increase the value of the magnetostriction constant, it is necessary that the magnetic layer be formed on the intermediate layer mainly composed of Cr as a magnetic material to be employed. When formed, there is, for example, Co ₇₀ Fe ₂₆ Ta ₄ (atomic ratio), and when the intermediate layer is not formed, for example, Co _{70 to 90}
Ni _10-30 , Co _55-85 Ni _10-30 Cr _5-15 , Co _74-94 Cr _5-20
Ta _1-6 , Co _50-90 Pt _5-35 Cr _5-15 (atomic ratio).

In the present invention, the difference between the lattice strain (εr) in the radial direction of the disk and the lattice strain (εθ) in the circumferential direction is negative,
In addition, the absolute value is set to be 0.1 to 0.7%, which makes (εr−εθ) <0 and gives a large compressive strain in the radial direction. When the absolute value of (εr is smaller than 0.1%), the effect of inverse magnetostriction is reduced, and when the absolute value of (εr−εθ) exceeds 0.7%, overwrite characteristics are deteriorated. As a measure to make (εr−εθ) <0 and to increase the absolute value, for example, an underlayer such as a Ni—P plating layer is physically polished, It should be noted that the ultra-fine grooves mentioned here are not grooves that can be measured by a surface roughness meter as conventionally proposed,
It refers to surface irregularities measured using a scanning tunneling microscope. In short, by providing in the radial direction a groove composed of unevenness much smaller than the conventional unevenness,
A radial compressive strain is induced in the magnetic film. And on such a substrate provided with such ultra-fine grooves, or on the substrate
By forming a Co alloy-based magnetic film or the like on the intermediate metal layer such as a Cr film, the absolute value of (εr-εθ) is set to a sufficiently large value, and the reverse magnetostriction effect is obtained. Can be expressed.

By the way, the magnetic disk according to the present invention, particularly a hard disk, generally has an underlayer such as a Ni-P plating layer on a rigid disk-shaped nonmagnetic substrate, and overlies or underlies the underlayer. On top of this, a non-magnetic metal intermediate layer made of an alloy containing Cr as a main component, a metal thin-film magnetic layer on this, and further a protective film and a lubricating film are provided thereon, but such The non-magnetic substrate used in manufacturing a suitable magnetic disk is appropriately selected from known ones such as Al or its alloy, glass, ceramics, and engineering plastic. The thickness of such a substrate is generally about 0.5 mm to 1.9 mm, and is used in a donut-shaped disk shape. Above all, the material of the substrate is generally an Al alloy among the above materials, and a predetermined base layer, for example, a Ni-P plating layer is formed on such a substrate by an electroless plating method.

Then, the substrate provided with such an underlayer is subjected to an appropriate polishing operation in the same manner as in the prior art, so that the surface roughness of the magnetic disk is determined from the flying height of the magnetic head. In general, it is effective to reduce the surface roughness in order to avoid collision with the protrusions on the substrate when the head floats, while to avoid the suction that occurs when the head comes in contact with the substrate, it is necessary to reduce the surface roughness. It is necessary to increase, and therefore, the surface roughness: Ra value is the magnitude of the motor drive torque value of the disk drive,
Also, it is selected so as to be appropriate from the head flying height.

Then, on the base layer of the substrate subjected to the normal polishing operation, (εr−εθ) <0 is set on the irregularities,
In addition, in order to increase the absolute value, ultrafine grooves are formed in the radial direction by physical polishing. As described above, the ultrafine grooves are not grooves (irregularities) that can be measured by a conventional surface roughness meter, but are much smaller. It is measured using a scanning tunneling microscope (eg, using a nanoscope, 1.5 × 10 ⁵ horizontal / vertical).
10 ⁶ times), the conventional pitch of groove as usual: 0.2
It has a pitch much less than 500 μm,
Further, even if it has a depth (height), it is a groove of about 10 to 50 °, and the presence of such an ultra-fine groove in the radial direction has an effect of inducing compressive strain on the surface of the magnetic layer.

In addition, as described above, since the ultra-fine grooves can be distinguished from the conventional grooves, even if the conventional grooves measured using the surface roughness meter are provided in the circumferential direction, Even if the grooves are provided not in the circumferential direction but in the radial direction, or even if they are provided isotropically, if the fine grooves as described above are provided in the Can be sufficiently exerted.

In addition, a magnetic film of Co alloy or the like is formed on a substrate provided with such an ultra-fine groove or a Cr-based film or the like containing Cr as a main component is formed as an intermediate layer on the substrate. (Magnetic layer) is formed. The crystal orientation of the Cr-based film as the intermediate metal layer is such that the (110) plane is parallel to the disk surface in the conventional example, whereas the (100) plane is parallel to the disk surface in the present invention. To be. For this purpose, the heating temperature at the time of sputter deposition of a Cr-based film or a magnetic film is conventionally 150 to 250 ° C., but it is increased to 250 to 300 ° C., and the ultimate vacuum degree of the sputtering chamber is 5 ×. 10 ^-6 Torr
On the other hand, in the present invention, 1 × 10 ⁻⁶ Torr or less,
Preferably, the pressure is 2 × 10 ⁻⁷ Torr or less. The Ar gas pressure at the time of sputtering is preferably 2 to 10 mm Torr when forming any of the Cr-based film and the magnetic film. The Ar gas pressure during sputtering (sputter atmosphere pressure) is 20 to 40.
At mm Torr, although the c-axis of the magnetic film such as a cobalt alloy is in the disk surface, the direction is random.

In the present invention, the smaller the thickness of the intermediate metal layer such as a Cr-based film formed by the sputtering method, the smaller (εr
Although it has been recognized that the absolute value of −εθ) increases and the squareness ratio improves, however, if the film thickness is too thin, the coercive force decreases, which is not preferable. In the present invention, in order that the absolute value of (εr−εθ) is sufficiently large and the reverse magnetostriction effect is advantageously exhibited, the thickness of the Cr-based film or the like is 150
Å ～ 2000Å

After that, after such a magnetic film (magnetic layer) is sputtered, a carbon protective film and a lubricating film are further formed thereon sequentially in the same manner as in the prior art. Is done.

The magnetic disk of the present invention has a large in-plane magnetic anisotropy,
Therefore, the recording / reproducing characteristics of the magnetic disk are improved, but this is caused not only by the improvement of the in-plane magnetic anisotropy as described above, but also by the improvement of the coercive force which hinders the movement of the domain wall in the circumferential direction. That is, this coercive force has a value of 0.85 to 1.0 times the circumferential coercive force, which was conventionally considered to have a correlation with the SN ratio, and S
Correlate with N ratio. It is presumed that the formation of the ultrafine grooves also contributes to the improvement of the coercive force that hinders the movement of the domain wall in the circumferential direction.

(Examples) Hereinafter, some examples of the present invention will be shown to clarify the present invention more specifically.

First, diameter: 130mm, thickness: 1.92mm Al-Mg alloy (JIS-
A5024 alloy) substrate, and a thickness of 18 μm
The Ni-P underlayer was formed by a known electroless plating method. Thereafter, texture polishing was performed using a texturing apparatus (manufactured by Strassbau, USA) using the alumina free abrasive grains as an abrasive, so that the surface of the Ni-P plating base layer was made uneven. The texture-polished underlayer surface has a surface roughness (Ra) of 40 ° in a radial direction measured by a surface roughness meter using a 2.5 μm square stylus, and a surface roughness in a circumferential direction (Ra). Ra) was 40Å.

Next, ultrafine irregularities were formed in the radial direction on the textured disk substrate in the following manner. That is, using a commercially available final tape polishing machine (manufactured by Exclusive Design Company, USA), the polishing tape was pressed while vibrating in the radial direction while rotating the substrate, and ultrafine irregularities in the radial direction were formed on the substrate surface. . As the polishing tape, a polyester resin tape was used.
The processing was performed for 5 minutes at a time / minute and a contact pressure of 2 kg / cm ² .
During processing, a lubricating oil for cooling was applied to prevent seizure.

In the disk substrate thus obtained, the surface roughness is, despite having been subjected to the above-mentioned ultra-fine unevenness processing,
Ra was 40 ° in both the radial and circumferential directions, unchanged from before the processing step. However, in the case where the ultra-fine unevenness processing step is performed (Invention Example 1) and the case where such a step is omitted (Comparative Example 1), the substrates after the sputter deposition are respectively formed using a scanning tunneling microscope. As a result of the observation, in the case of Invention Example 1, the pitch: 80 °
As a result, it was recognized that irregularities having a height of about 30 mm were generated in the radial direction.

Then, a metal intermediate layer, a magnetic layer, and a carbon protective layer were sequentially formed on the disk substrate thus obtained, which had been subjected to the ultrafine unevenness processing, by sputtering. That is, the metal intermediate layer, the magnetic layer, and the carbon protective film have the ultimate vacuum degree of 1 × 10 ⁻⁷ when the disk substrate is placed in a vacuum chamber, and the circular target and the substrate are stationary and opposed to each other coaxially.
After increasing the degree of vacuum to Torr, the substrate temperature was raised to 290 ° C., and the film was formed by continuous sputtering.
The metal intermediate layer was a Cr film, and its thickness was 300 °. The magnetic layer is composed of 70 atomic% of Co, 26 atomic% of Fe,
A Co-based alloy having a composition of at. At this time, -300 V was applied as a substrate bias. Further, the thickness of the carbon protective film was 400 °. The Ar gas pressure during film formation was 5 mmTorr, and the DC power was 3 kW.

The magnetic disk thus obtained was referred to as Inventive Example 1, while the magnetic disk which was not subjected to the ultra-fine unevenness processing and was otherwise obtained in the same manner as Comparative Example 1 was used for performance comparison later.

In addition, a case where the thickness of the Cr film as the metal intermediate layer was set to 800 ° was Invention Example 2, and the heating temperature during sputtering was set to
Inventive Example 3 of the magnetic disk in which the temperature was 295 ° C. and the thickness of the Cr film was 200 °.

Further, a magnetic layer was formed in the same manner as in Invention Example 1 except that a metal intermediate layer was not formed and a Co-based alloy having a composition of 88 atomic% of Co, 9 atomic% of Cr, and 3 atomic% of Ta was used as a magnetic layer. The disc was designated as Invention Example 4.

On the other hand, in the same process as above, the thickness of the Cr film was 3000
The magnetic disk described as Comparative Example 2 was used. Compare magnetic disks with magnetic layers with a small absolute value of the magnetostriction constant obtained by sputtering using a Co-based alloy with a composition of 77 atomic% of Co, 20 atomic% of Cr, and 3 atomic% of Ta. Example 3 was used.

Further, for the disk substrate on which the Ni-P plating base layer is formed, without using the texture device as described above,
Using a tape polishing device (US: Exclusive Design Company), polishing the tape at a polishing tape count of # 4000, contact pressure: 0.8 kg / cm ² , no vibration in the radial direction, work rotation speed: 140 times / min. Implemented, after forming a circumferential groove in such a disk substrate, ultimate vacuum degree: 1 × 10 ^-5
Torr, heating temperature: 200 ℃, Cr film (metal intermediate layer), and
Co: 70 atom%, Fe: 15 atom%, Cr: 11 atom%, Ta: 4 atom%
A magnetic layer composed of a Co-based alloy having the following composition was formed. Comparative Example 4 was used when the Cr film thickness was 1500 比較, and Comparative Example 5 was used when the Cr film thickness was 500 Å.

With respect to the magnetic disks of Invention Examples 1 to 4 and Comparative Examples 1 to 5 thus obtained, the difference in lattice strain (εr−εθ) between the radial direction and the circumferential direction was measured. The recording and reproducing characteristics and magnetic characteristics of each magnetic disk (the magnetostriction constant of the magnetic film, the coercive force in the circumferential direction,
The results are shown in Table 1 below together with the coercive force that hinders domain wall movement in the circumferential direction.

The lattice distortion of the magnetic film (layer) of the magnetic disk is determined by X-ray diffraction by the Schulz method, and the lattice spacing of the (1011) plane of Co is set in two directions (α ′ = 40 °, radial direction and circumferential direction). β =
0 °, 90 °), and (εr−
εθ) was determined.

Where, dr: radial direction, lattice spacing measured at α ′ = 40 ° dθ = circumferential direction, lattice spacing measured at α ′ = 40 ° As apparent from Table 1 below, Examples 1 to 4 relate to Invention Examples 1 to 4. Magnetic disks have recording and playback characteristics (output, resolution, SN ratio,
It is recognized that both the overwriting and the magnetic properties (square ratio) are superior to the magnetic disks of Comparative Examples 1 to 5.

(Effects of the Invention) As is clear from the above description, according to the present invention, it is possible to provide a magnetic disk having excellent magnetic characteristics, furthermore, recording and reproducing characteristics, among which, the reproducing output voltage value and the SN ratio are excellent. This can greatly contribute to realizing high-density recording on a magnetic disk.

Continuation of the front page (72) Inventor Fuminori Higami 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries Co., Ltd. (72) Inventor Nobuyuki Muto 3-1-1-12 Minato-ku, Nagoya-shi, Aichi Kouhei Hirooka, Examiner, Technical Research Laboratory, Sumitomo Light Metal Industries, Ltd. (56) Reference: JP-A-1-283803 (JP, A) JP-A-62-146434 (JP, A) JP-A-3-224121 (JP, A) JP-A-4-13219 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/66 G11B 5/82 G11B 5 / 84

Claims (2)

(57) [Claims] An Ni-P plating layer is formed as a base layer on a rigid disk-shaped non-magnetic substrate, and the surface of the Ni-P plating layer is physically polished to a pitch of 80 ° and a depth of Provided an ultra-fine groove of 40 ° in the radial direction, and then the Ni-P
A method for manufacturing a magnetic disk having excellent magnetic properties, comprising forming a magnetic layer having an in-plane magnetostriction constant of 1.5 to 4 × 10 ⁻⁵ on a plating layer. 2. A Ni-P plating layer is formed as a base layer on a rigid disk-shaped non-magnetic substrate, and the surface of the Ni-P plating layer is physically polished to a pitch of 80 ° and a depth of Provided an ultra-fine groove of 40 ° in the radial direction, and then the Ni-P
A Cr intermediate layer having a thickness of 200 to 800 mm is formed on the plating layer, and then, an in-plane magnetostriction constant of 1.5 to 4 × 1 is formed on the intermediate layer.
0 ^-5 preparation of a magnetic disk having excellent magnetic properties, characterized in that the deposition of the magnetic layer.