JP3394855B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to relates to a method of manufacturing a magnetic recording medium material such as a magnetic disk or magnetic tape.

[0002]

2. Description of the Related Art In recent years, the performance of computers such as personal computers has been remarkably improved, and a magnetic disk device (HDD) which is an external storage device of a computer has been downsized, increased in capacity and increased in speed. There is a strong demand for improvement in performance, and in response to this, technical development for increasing the recording density of magnetic recording media is being carried out. Above all, magnetic recording media such as magnetic disks using a magnetic thin film that can essentially achieve high recording density are being actively developed.

Magnetic recording in the magnetic thin film is performed by forming a reversed magnetic domain in a minute region of the magnetic thin film by a magnetic field applied from a magnetic head. In order to perform high density recording, it is necessary to form these magnetic domains small and dense.

When a magnetic domain is formed, a coercive force (Hc) is required to suppress the magnetic domain because a force to re-invert the magnetic domain acts at the same time by the internal magnetic field in the magnetic thin film. In order to form the magnetic domains densely and perform high density recording, it is necessary to reduce the width of the magnetization transition at the boundary of the recorded magnetic domains. This width is B · t / Hc (B: residual magnetic flux density, t: magnetic It is said to be proportional to the thickness of the thin film).
Since both B and t are proportional to the reproduction signal strength and it is not preferable to make them too small, it is necessary to make Hc large.
It is an important guideline for improving the recording density in a magnetic recording medium using a magnetic thin film. This is a report in which a computer simulation of a complicated magnetic recording / reproducing process was performed to examine the medium parameters necessary for achieving high density (Nakamura: Journal of the Japan Society for Applied Magnetics Vol.17, NO.5, p. .768, 1993) and the like.

Each of the reversed magnetic domains formed in the minute regions of the magnetic thin film is further composed of crystal grains of the magnetic substance. The spins of the respective atoms are oriented in the same direction within the crystal grain, but due to the magnetic field from the head, they are reversed at substantially the same time within the crystal grain. Therefore, the crystal grain is the minimum unit of magnetization reversal, and from the viewpoint of improving the recording density, it is ideal that the crystal grain can be made small to form a steep boundary and a small reversal magnetic domain.

By the way, in a magnetic recording medium using a normal magnetic thin film, a force called exchange interaction acts between the crystal grains, and when one crystal grain has a reversal of magnetization, adjacent crystal grains also come into contact. The magnetization will be reversed. As a result, some crystal grains aggregate to form a crystal grain group, and this crystal grain group serves as a unit of magnetization reversal, so that the boundaries of the reversal magnetic domains become rough. For this reason, the inversion magnetic domain cannot be made small, and the boundary of the inversion magnetic domain becomes unclear, so that noise called recording noise or medium noise occurs. For this reason, it has been difficult to perform high-density recording with low noise in an ordinary magnetic recording medium. Further, when a magnetic head having a good sensitivity such as an MR head developed in recent years is used, recording noise is also reproduced well, so that the presence of such noise is a particular problem. Was there.

As described above, in order to improve the recording density without increasing the recording noise in the magnetic recording medium using the magnetic thin film, the coercive force is increased and the width of the magnetic transition corresponding to the boundary of the magnetic domain is decreased. It has been an important technical issue to reduce the exchange coupling interaction between crystal grains so that the boundaries between magnetic domains are clear and free from fluctuations.

In the past, in order to increase the coercive force, attempts have been made to subject the formed magnetic thin film to heat treatment or to add a third element to the constituent element of the magnetic thin film. Further, as a typical solution for reducing the exchange coupling interaction between the crystal grains, an attempt to divide the exchange coupling interaction by adding a third element between the crystal grains has been made. By the way, there is a report example in which it is between crystal grains of about 1 nm.

[0009]

However, in the magnetic recording medium using the magnetic thin film, when the conventional solution such as the heat treatment or the addition of the third element is taken as described above in order to obtain a high coercive force, Under the present circumstances, new problems such as complication of manufacturing process by using various materials, resulting in increase of medium manufacturing cost, and easy deterioration of stability and controllability occur.

On the other hand, the addition of the third element for reducing the exchange coupling interaction between the magnetic crystal grains causes diffusion of the magnetic element and the like, so that the effect of reducing the exchange coupling interaction is small. As a result, several to several tens of dB
Occasionally, a large amount of medium noise was observed.

As described above, according to the conventional coping method,
In a magnetic recording medium using a magnetic thin film, it was difficult to obtain a magnetic recording medium having a high coercive force and a small exchange coupling interaction between magnetic crystal grains.

The present invention has been made to solve the above problems that cannot be solved by the conventional method.
It is an object of the present invention to provide a method for manufacturing a magnetic recording medium which has a large coercive force and a small exchange coupling interaction between magnetic crystal grains and enables high density recording.

[0013]

In the magnetic recording medium of the present invention ,
The manufacturing method is a method for manufacturing a magnetic recording medium in which a magnetic recording layer made of a magnetic thin film is formed on a non-magnetic substrate by a sputtering method , and the energy of the sputtering gas incident on the non-magnetic substrate is 0.001 eV or more 10
eV as to become less, the magnetic thin film is formed
It is characterized in that that.

The magnetic thin film according to the present invention is used as a magnetic recording layer, which is magnetized in a predetermined direction according to information according to a magnetic recording system, and longitudinal recording, oblique recording or perpendicular recording can be performed. Further, the magnetic recording medium of the present invention can be applied to both a system in which the recording / reproducing head is in contact with the magnetic recording medium and a system in which the recording / reproducing head floats. The reproducing principle may be either inductive type or magnetoresistive type.

In the present invention, a material having a large saturation magnetization Is and a large magnetic anisotropy energy is suitable as a material forming the magnetic thin film. From this point of view C
o, Fe, Ni, other ferromagnetic metals, their alloys, or Pt, Sm, Cr, M
Examples thereof include those in which elements such as n and Bi are added alone or in plural. Among these, Co-based alloys having large crystal magnetic anisotropy energy, particularly Co-Pt and Sm
Alloys based on -Co are preferred. In addition, to these metals or alloys, additives for improving magnetic properties,
For example, Nb, V, Ta, Ti, W, Hf, In, S
A compound of i, B or the like or a compound of these elements and at least one element selected from oxygen, nitrogen, carbon and hydrogen may be added.

In the magnetic recording medium according to the present invention , in order to prevent damage when the head contacts the magnetic recording layer,
It is preferable to install a protective film on the magnetic thin film. Although it is generally difficult to accurately determine the physical properties that the protective film should satisfy, the hardness can be adopted as one criterion. In principle, the larger the hardness, the more the magnetic thin film is formed by contact with the head. It is thought that the damage will be reduced. From such a viewpoint, it is preferable that the protective film material used in the magnetic recording medium of the present invention has a high hardness in the bulk state. For example, a compound represented by the general formula MG can be mentioned. Here, M is Si, Al, Zr, Ti, I
At least one element selected from the group consisting of n, Sn and B, and G represents at least one element selected from the group consisting of oxygen, nitrogen and carbon. In particular,
Si-O, Al-O, Zr-O, Ti-O, Si-N,
Al-N, Zr-N, Ti-N, BN, Si-C, T
i-C, B-C, SiAl-ON, Si-ON, AlT
i-OC, In-Sn-O and the like are preferable. Also suitable are carbon allotropes, specifically diamond, amorphous carbon, diamond-like carbon, and the like.
Further, a material having such a crystal structure, for example, graphite (carbon) is also preferable as a material for the protective film, because damage can be prevented by mitigating an impact due to slippage between atoms.

In the present invention, a metal, glass, ceramics, plastic or the like can be used as the substrate for supporting the above magnetic thin film and protective film. A base layer made of a magnetic material or a non-magnetic material may be provided between the base and the magnetic material film.

The magnetic underlayer magnetically interacts with the magnetic domains in the magnetic thin film and the recording / reproducing head through exchange interaction and magnetostatic interaction in order to perform efficient recording / reproducing on the magnetic thin film. Are combined. When installed so as to exchange-couple with a magnetic domain, the magnetic domain can be stabilized by using a magnetic underlayer that is easy to reverse magnetization, or the reproduction output can be increased by using a magnetic underlayer with large magnetization. Have.

The non-magnetic underlayer is provided for the purpose of controlling the crystal structure of the magnetic thin film and preventing impurities from entering the substrate. For example, by using an underlayer having a lattice spacing close to the lattice spacing of the desired crystal orientation of the magnetic thin film, it is possible to control the crystalline state of the magnetic thin film. Further, for example, if an amorphous underlayer having a surface energy that deteriorates the wettability with the magnetic thin film is used, the crystallinity of the magnetic thin film can be improved. For the purpose of preventing impurities from being mixed in from the substrate, a thin film having a small lattice spacing or a fine structure may be used as the base layer.

The above-mentioned magnetic or non-magnetic underlayer may have the same function. That is, it may be a magnetic underlayer that controls the crystallinity of the magnetic thin film. Further, these underlayers may be surface modification layers of the substrate which are formed by ion plating, doping in atmospheric gas, neutron beam irradiation, or the like. In that case, the thin film deposition process is not necessary and the medium production process is simplified, which is preferable.

Next, a method of manufacturing the magnetic recording medium of the present invention will be described.

The magnetic thin film which is the magnetic recording layer of the magnetic recording medium of the present invention is produced by a sputtering process. In sputtering, a plate-shaped substrate, that is, a substrate is placed in a vacuum chamber so as to face the target,
It is performed by introducing a sputtering gas into the chamber. Usually, Ne, Ar, K is used as the sputtering gas.
An inert gas such as r or Xe is used, but it is also possible to produce a part of the thin film by reacting with a gas. At that time, a reactive gas including oxygen, nitrogen, carbon, hydrogen, etc. is also introduced. .

The sputtering process proceeds as follows. That is, by discharging the sputtering gas while introducing it, the pressure of the sputtering gas in the chamber is maintained at a certain value, and when a voltage is applied between the substrate and the target, discharge occurs. At this time, the atoms forming the sputtering gas are ionized and struck against the target by the electric field, and as a result, the target material jumps out and adheres to the surface of the substrate.

After being hit by the target, the atoms of the sputtering gas are recoiled into the chamber. Ionized atoms neutralize and recoil on the target, and other unionized sputtering gas atoms are repelled by the recoiled atoms, so these neutral atoms that move at high speed also exist in the chamber. . Naturally, in addition to the material atoms of the thin film to be produced, the neutral atoms also fly onto the substrate. When the neutral atom enters the substrate, it gives energy to the substrate based on its velocity and temperature. Since the velocity of neutral atoms greatly changes depending on the number of other atoms that collide with each other before reaching the substrate, this energy can take various values depending on the process conditions.
However, the minimum energy is fixed, which means that the neutral atom is completely decelerated and the velocity becomes zero,
The energy due to the temperature of the neutral atom is kT. Here, k is the Boltzmann constant and T is the absolute temperature of the neutral atom.

It is generally known that when a thin film is produced, the energy applied during the production affects the film quality. For example, when the substrate is heated and thermal energy is applied, the crystal lattice shifts to a more thermally stable state and the crystallinity is improved. The magnetic properties of thin films are also affected by the energy applied during fabrication by a similar mechanism. Therefore, a sputtering apparatus in which the velocity of recoil sputtering gas atoms is variable was manufactured, the energy of recoil atoms was measured, and the relationship between the energy incident on the substrate by the sputtering gas atoms and the magnetic characteristics was investigated. When measuring the energy of recoil atoms, a time-of-flight (TO
F) Measurements were made by a measuring device and evaluated. As a result, the energy of the sputtering gas is 10 eV or less 0.00
Coercive force (Hc) when it is as small as 1 eV or more
It has been found that a magnetic thin film suitable for high density magnetic recording media, in which the exchange interaction between crystal grains is small, can be obtained. The incident energy value is 10 eV or less 0.001
A coercive force that enables high-density recording can be obtained when eV or more,
It is more preferably 1 eV or less, and further preferably 0.1 eV or less, because a larger coercive force is obtained.

The reason why a large coercive force is obtained when the value of the incident energy is such small is presumed to be as follows. When the sputtering gas atoms with large energy are incident on the substrate, the growth of the magnetic thin film on the substrate is hindered, a crystal in which each atom that constitutes the alloy is uniformly contained is formed, and the film quality is also porous. As a result, the magnetic anisotropy energy decreases and the coercive force decreases. Furthermore, since the boundaries between magnetic crystal grains become unclear,
Exchange coupling interaction is increased. On the other hand, 10 eV
Energy smaller than that does not hinder the crystal growth of the magnetic thin film, but causes crystal growth in a state close to thermal equilibrium, and for example, film growth in which Cr precipitates between CoPt crystal grains is likely to occur. . As a result, the magnetic anisotropy energy increases, the coercive force increases, and the exchange coupling interaction decreases.

As described above, the lower limit of the magnitude of incident energy is represented by the temperature of the sputtering gas.
The boiling point of He, which is the inert gas with the lowest boiling point, is 4.1K
Considering that the energy is 3.5 × 10 ^-4 eV, the energy of the gas incident on the substrate must be 0.001 eV or more in order to perform stable sputtering without using a special cooling mechanism. Becomes

In order to improve the sputter rate by increasing the exhaust capacity of the pump used for exhausting the inside of the chamber,
It is preferable to use an element heavier than He as the sputtering gas, and generally Ar is often used. In order to perform sputtering efficiently using this Ar, the energy of the gas incident on the substrate is more preferably 7.5 × 10 ⁻³ eV or more, considering the boiling point of Ar. In the case of sputtering a Co alloy, it is more preferable to use Xe, which is heavier than Ar, in order to reduce the energy of recoil particles. Therefore, considering the boiling point of Xe, the energy of the gas incident on the substrate is more preferably 0.015 eV or more.

The present invention was made on the basis of the above findings, and in the production of the magnetic recording medium of the present invention, the energy required for forming a magnetic recording layer made of a magnetic thin film on a non-magnetic substrate by a sputtering method. Is 0.001 eV or more
It is characterized in that a sputtering gas of 10 eV or less, more preferably 0.0075 eV or more and 1 eV or less is incident on the non-magnetic substrate to form the magnetic thin film.

In the method of manufacturing a magnetic recording medium of the present invention, the energy of the sputtering gas is 0.001 eV or more.
As a means for controlling to a small value of 10 eV or less, it is preferable that the sputtering gas is cooled to room temperature or less. The reason is as follows. As previously mentioned,
The lowest level of the energy of the sputtering gas that is incident on the substrate during the production of the thin film, which is said to affect the magnetic properties of the magnetic thin film, is the gas temperature. Therefore,
By lowering the temperature of the sputtering gas, it becomes easier to reduce the energy incident on the substrate, and a larger H
This is because it becomes easy to obtain c.

In the present invention, as a method of cooling the sputtering gas more simply in terms of equipment when cooling the sputtering gas, there is a method of cooling the gas outside the chamber and introducing the cooled gas into the chamber. can give. To cool the gas outside the chamber and introduce it into the chamber, there are methods such as installing a cooler in a part of the gas introducing pipe or passing the gas introducing pipe through liquid nitrogen or liquid helium. To be

The same effect as the effect of lowering the temperature of the introduced sputtering gas can be obtained by cooling the entire vacuum chamber of the sputtering apparatus. That is, most of the sputtering gas atoms that recoiled at the target or obtained kinetic energy by collision between sputtering gases also collide with the wall surface of the chamber. At that time, the kinetic energy of the sputtering gas atoms becomes smaller due to the cooling from the wall surface. It also has the effect of cooling the sputtering atoms in the chamber by cooling from the chamber. As a method of cooling the entire chamber, a cooled cold body is installed in the chamber,
Alternatively, a method of cooling the side wall surface of the chamber may be used. To cool the side wall surface, there are methods such as directly connecting the side wall surface to a cooler and circulating liquid nitrogen or the like around the sputtering chamber.

The method of controlling the energy of the sputtering gas by cooling as described above is based on Hc such as mechanical properties and adhesion of the thin film.
It is effective when the conditions are set for the purpose of improving various characteristics other than the above and they cannot be changed so much.

Further, in the method of manufacturing a magnetic recording medium of the present invention, it is desirable to install a shield plate between the substrate and the target in the vacuum chamber for differential evacuation. By adjusting the position of the shield plate, the sputtering gas flow rate and the exhaust speed control valve for differential exhaust,
The atomic concentration of the sputtering gas near the substrate can be changed. By changing the concentration of the sputtering gas in the vicinity of the substrate, it is possible to change the velocity or energy of the sputtering gas atoms that jump into the substrate.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to Examples.

Examples 1 to 7 Magnetic recording media having the sectional structure shown in FIG. 1 were produced.
As shown in FIG. 1, a magnetic thin film 12 and a nonmagnetic protective layer 13 are provided on a glass substrate 11. In preparation, a magnetic thin film was prepared by using a sputtering apparatus whose outline is shown in FIG. As shown in FIG.
Inside the vacuum chamber 20, a shield plate 23 is installed between a target 21 and a substrate 22 that are provided so as to face each other. The shield plate 23 can be moved in the direction of the arrow shown in the figure. The sputtering gas 24 is introduced into the chamber 20 through the sputtering gas inlet 25. A vacuum pump 26 is provided inside the chamber 20.
Exhausted by. Exhaust condition is exhaust speed control valve 27
Regulated by The substrate 22 has a TOF analyzer 2
8 was attached, and the energy of the sputtering gas 24 incident on the substrate 22 was measured. A CoPtCr alloy is used as the target 21, and a sputtering gas 24
Xe is used as the target, sputtering is performed by applying a DC voltage of 300 V to the target, and CoPtC having a thickness of 25 nm is used.
An r magnetic thin film was prepared.

By selecting an appropriate gas flow rate and exhaust speed, it was possible to change the position of the shield plate and change the incident energy of the Xe gas in seven ways within the range of 0.05 eV to 10 eV. Then, sputtering was performed with each energy to manufacture a magnetic recording medium. A protective film made of C and having a thickness of 15 nm was provided on the magnetic thin film.

Comparative Examples 1 to 2 A magnetic recording medium was produced in the same manner as in the example except that the sputtering was performed while changing the incident energy of Xe gas in two ways within the range of 10 eV or more.

Then, in evaluating the magnetic recording media obtained in the above-mentioned Examples and Comparative Examples, coercive force was measured and ΔM was calculated. The ΔM method is a method for evaluating the strength of exchange coupling interaction between crystal grains of a magnetic thin film, and is the difference in the rising of the magnetization from the residual magnetization state in the case of unidirectional magnetization and the case of AC demagnetization. And shows that the larger ΔM is, the larger the exchange coupling interaction (normalized by 1) is.

FIG. 3 shows the incident energy of the sputtering gas at the time of manufacture, the coercive force in the in-plane direction, and the measurement results of ΔM evaluation in the magnetic recording media of the above-mentioned Examples and Comparative Examples. In FIG. 3, ◯ indicates coercive force in the in-plane direction, and Δ indicates ΔM. The numbers 1 to 7 attached to the ◯ mark and the Δ mark represent the numbers of the examples, and the ratios 1 and 2 represent the comparative examples 1 and 2. As is clear from FIG. 3, when the energy of the sputtering gas incident on the substrate becomes smaller than 10 eV, the coercive force of the magnetic recording medium to be manufactured exceeds 2 kOe and is 0.1 eV.
In the following, it can be seen that it increases to 3 kOe or more. Also, Δ
The value of M becomes smaller as the energy becomes smaller, and it also sharply decreases below 10 eV and becomes 0.4 or less.

It has been reported so far that in order to carry out high-density magnetic recording of about 10 Gb / in ^2, about ² kOe or more, 2.5 kOe or more, or about 4.5 KOe is required (M. Futamoto et.al. .: IEEE Trans.Magn., M
AG-27, p.5280, 1991), (ESMurdock: IEEE Trans Magn.
vol.28, NO.5, p3078, 1992) etc. Therefore, it will be understood that the present invention provides a magnetic recording medium having a coercive force high enough to perform high density magnetic recording.

Example 8 A magnetic thin film was prepared by performing sputtering in the same manner as in Examples 1 to 7 except that Ar was used as the sputtering gas and the temperature of the gas incident on the substrate was the same as room temperature. did. As a result of analysis by TOF measurement, the incident energy of the sputtering gas was 1 eV.

Example 9 A magnetic thin film was prepared by performing sputtering in the same manner as in Example 8 except that the temperature of the sputtering gas was 100K. As a result, the energy of the sputtering gas incident on the substrate was 0.12 eV.

Example 10 Example 8 was repeated except that the temperature of the sputtering gas was 30K.
Sputtering was performed in the same manner as the above to prepare a magnetic thin film. As a result, the energy of the sputtering gas incident on the substrate was 0.08 eV.

Note that FIG. 4 shows the relationship between the temperature of the introduced gas and the energy of the sputtering gas incident on the substrate in Examples 8 to 10. The numbers attached to the circles in the figure represent the numbers of the examples. As is clear from FIG. 4, the incident energy becomes smaller as the temperature of the introduced sputtering gas is lowered from room temperature. In combination with the results shown in FIG. 3, cooling the introduced sputtering gas to a temperature lower than room temperature can increase the coercive force of the magnetic thin film to be produced and reduce the exchange interaction between the magnetic crystal grains. confirmed.

From the viewpoint of obtaining a large coercive force, the lower the gas temperature is, the more preferable it is. However, the lower the temperature is, the more complicated the apparatus for cooling the gas becomes. Therefore, if the gas cooling temperature is around 100K, it can be said that 100K is more practical and preferable as the temperature of the gas to be cooled, since it can be realized by a relatively simple apparatus using liquid nitrogen.

[0047]

As described in detail above, according to the present invention,
Since a magnetic thin film having a large coercive force and a small exchange coupling interaction between crystal grains can be easily produced, a magnetic recording medium capable of high density recording can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view of an example of a magnetic recording medium according to the present invention.

FIG. 2 is a schematic view showing an example of a sputtering apparatus for producing a magnetic thin film of a magnetic recording medium according to the present invention.

FIG. 3 is a diagram showing the relationship between the energy of the sputtering gas incident on the substrate during the production of the magnetic recording medium according to the present invention, the in-plane coercive force of the produced magnetic recording medium, and the value of ΔM. .

FIG. 4 is a diagram showing the relationship between the temperature of the introduced sputtering gas and the energy of the sputtering gas incident on the substrate.

[Explanation of symbols]

11 ... substrate 12 ... Magnetic thin film 13 ………… Non-magnetic protective layer 20 ... Vacuum chamber 21 ......... Target 22 ………… Substrate 23 ... Shield plate 24 ......... Sputtering gas 25 ……… Sputtering gas inlet 26 ... Vacuum pump 27 ... Exhaust speed control valve 28 ... TOF analyzer

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-4-147434 (JP, A) JP-A-2-220224 (JP, A) JP-A-5-205263 (JP, A) JP-A-63- 26825 (JP, A) JP 56-112471 (JP, A) JP 56-69371 (JP, A) JP 2-126550 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B 5/851 C23C 14/34

Claims (3)

(57) [Claims] 1. A method of manufacturing a magnetic recording medium comprising a magnetic recording layer made of a magnetic thin film formed on a non-magnetic substrate by a sputtering method , wherein the energy of a sputtering gas incident on the non-magnetic substrate is 0.001 eV or more. 1
0eV as to become less, the magnetic thin film is of form
A method of manufacturing a magnetic recording medium , comprising: Wherein said magnetic thin film The method for producing a magnetic recording medium to that請 Motomeko 1 wherein characterized in that it consists of an alloy containing at least Co. Wherein the sputtering gas, the production of magnetic recording media 請 Motomeko 1 or 2, wherein you, characterized in that it is introduced into the sputtering chamber was cooled to below room temperature
Way .