JP2806443B2 - Magnetic recording medium and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium and a method for manufacturing the same. More specifically, the present invention relates to a high-density magnetic recording medium having excellent magnetic properties which is inexpensive and easy to manufacture, and a method for manufacturing the same. The magnetic recording medium of the present invention is suitably applied to hard disks, floppy disks, magnetic tapes and the like.

BACKGROUND ART As a conventional magnetic recording medium and a method for manufacturing the same, the following techniques are known.

FIG. 23 is a schematic diagram illustrating a hard disk as an example of a magnetic recording medium. 23, FIG. 23 (a) is a perspective view of the entire magnetic recording medium, and FIG. 23 (b) is a cross-sectional view taken along the line AA 'of FIG. 23 (a).

As a substrate 1, a non-magnetic (Ni-
P) The one provided with the layer 3 is used. On the base 1, a Cr underlayer 4, a ferromagnetic metal layer 5, and a protective layer 6 are laminated.

The nonmagnetic (Ni-P) layer 3 has a diameter of 89 mm (3.5 inches) / a thickness of 1.27 mm (50 mi) by plating or sputtering.
The substrate 1 is formed on the surface of the disk-shaped Al substrate 2 of l). The non-magnetic (Ni-P) layer 3
Are provided with concentric scratches (hereinafter referred to as textures) by mechanical polishing. Generally, the surface roughness of the non-magnetic (Ni-P) layer 3, that is, the average center line roughness Ra measured in the radial direction is 5 nm to 15 nm.
Further, the Cr underlayer 4 and the ferromagnetic metal layer 5 (generally a Co alloy-based magnetic film) are formed by plating, vapor deposition, or sputtering.
The ferromagnetic metal layer 5 is formed on the surface of the
A protective layer 6 made of carbon or the like to protect the surface of
It is provided by a sputtering method. Typical thicknesses of the respective layers are 5 to 15 μm for the non-magnetic (Ni-P) layer 3, 50 to 150 nm for the Cr underlayer, 30 to 100 nm for the ferromagnetic metal layer 5, and 20 to 50 nm for the protective layer 6. .

In order to increase the recording density of the medium, it is necessary to particularly increase the coercive force among the magnetic properties of the medium. Recently, customer needs are shifting from a medium having a coercive force of 1200 Oe to 1600 Oe to a medium having a coercive force of 1800 Oe or more. To cope with this, the following technology is known as a method of increasing the coercive force, which has been conventionally studied in a magnetic recording medium.

Change the composition of the ferromagnetic metal layer.

Refine crystal grains of the ferromagnetic metal layer.

The crystal grains of the ferromagnetic metal layer are magnetically isolated.

 However, the above prior art has the following problems.

The technique (1) is very effective when the ferromagnetic metal layer contains Pt, for example. However, improvements are desired because of the high cost and high media noise. Other materials are easily affected by the film formation atmosphere, and it is difficult to achieve a coercive force of 1800 Oe or more.

The technique (2) is realized by, for example, reducing the thickness of the underlayer. However, if the thickness is reduced too much, the medium noise increases, which is not good.

The technique (3) is realized by utilizing the diffusion of the underlying Cr by, for example, a high-temperature heat treatment after film formation. However, the manufacturing process is complicated because the influence of gas generation in the film formation chamber must be taken into consideration. Is not preferred.

On the other hand, the following technology is known as a method for manufacturing a magnetic recording medium.

Increasing the substrate surface temperature during film formation Adjusting the substrate potential Adjusting the film forming gas pressure However, the above-described conventional technology has the following problems.

In the technique (4), the amount of gas generated from the film forming chamber is increased, and the production becomes unstable, which is not good.

The technique (5) has no effect even when the potential is higher than the conventional one, and abnormal discharge tends to occur frequently, and the film forming process becomes unstable.

The technology of (6) uses a dischargeable area (for example, 1 mtorr to 30 mt).
In orr), no more significant effect can be found.

Here, the current state of the above (1) is summarized in Table 1. When changing the composition of the ferromagnetic metal layer, which is one of the methods for increasing the coercive force, the basic alloy may be, for example, CoNiCr, CoCrTa,
CoCrPt is widely used. Table 1 summarizes the superiority and inferiority of each of these three types of alloys. The number 1 in the table indicates that it is the best among the three alloys.

That is, CoNiCr is excellent in that it is inexpensive as compared with other material systems, but has the drawback that it has an upper limit in coercive force and high medium noise. CoCrTa is superior in that it has lower medium noise and higher normalized coercive force than other material systems. However, since it is easily affected by the film formation atmosphere, it is difficult to construct a mass production process. CoCrPt has a feature that it is easy to produce a high coercive force as compared with other material systems. However, the cost is high due to the use of the precious metal Pt, and the medium noise is also Co
This is a high problem compared to CrTa.

Therefore, the material forming the ferromagnetic metal layer is inexpensive, and 1800
It has been desired to realize a magnetic recording medium having a high coercive force of Oe or more and a low medium noise during recording and reproduction, and a method of manufacturing the same.

An object of the present invention is to provide a magnetic recording medium that realizes a high coercive force using a material that does not contain Pt in a ferromagnetic metal layer, is inexpensive, has low medium noise, and can simplify the manufacturing process. I do.

Another object of the present invention is to provide a method for producing a magnetic recording medium in which a medium having a high coercive force can be formed even when the substrate surface temperature during film formation is low, and the substrate potential and the film formation gas pressure can be the same as before. .

DISCLOSURE OF THE INVENTION In the magnetic recording medium of the present invention, a ferromagnetic metal layer is formed on a surface of a base via a metal underlayer, and in a magnetic recording medium utilizing magnetization reversal, the oxygen concentration of the ferromagnetic metal layer is reduced to 10%.
It is characterized by being set to 0 wtppm or less.

Further, in the magnetic recording medium of the present invention, a ferromagnetic metal layer is formed on a surface of a base via a metal underlayer, and in a magnetic recording medium using magnetization reversal, the oxygen concentration of the metal underlayer is set to 100 wtppm or less. A magnetic recording medium characterized in that:

Furthermore, the magnetic recording medium of the present invention is characterized in that the oxygen concentration of the ferromagnetic metal layer is 100 wtppm or less.

Further, the magnetic recording medium of the present invention is characterized in that a ferromagnetic metal layer is formed on the surface of a substrate, and in a magnetic recording medium utilizing magnetization reversal, the oxygen concentration of the ferromagnetic metal layer is set to 100 wtppm or less. I do.

The method of manufacturing a magnetic recording medium according to the present invention is a method of manufacturing a magnetic recording medium in which a metal underlayer and a ferromagnetic metal layer are sequentially formed on a surface of a substrate by a sputtering method. It is characterized in that the impurity concentration is 10 ppb or less. More preferably, the impurity concentration of the Ar gas is set to 100 ppt or less.

The method of manufacturing a magnetic recording medium according to the present invention, before forming the metal underlayer, using an Ar gas having an impurity concentration of 10 ppb or less, performing a cleaning process on the surface of the base by a high-frequency sputtering method, 0.2 nm It is characterized in that 〜1 nm is removed.

The method for manufacturing a magnetic recording medium of the present invention described above is also effective when the ferromagnetic metal layer is formed directly on the surface of the base.

Further, the substrate is characterized in that a nonmagnetic layer is formed on the surface.

In the method of manufacturing a magnetic recording medium according to the present invention, a negative bias, preferably -100 V to -400 V, is applied to the base during the formation of the metal underlayer and / or the ferromagnetic metal layer, and the ultimate vacuum Is preferably 8 × 10 ⁻⁸ Torr or less. Further, it is preferable that the surface temperature of the substrate is 60 ° C to 150 ° C.

The above-described method for manufacturing a magnetic recording medium of the present invention is also effective when the surface roughness Ra of the substrate is 3 nm or less. Further, the present invention can be applied to the case where the gas used for forming the metal base layer and / or the ferromagnetic metal layer is (Ar + N ₂ ) or (Ar + H ₂ ).

Function In the present invention, in a magnetic recording medium having a ferromagnetic metal layer formed on a surface of a base via a metal underlayer, the oxygen concentration of the ferromagnetic metal layer is set to 100 wtppm or less, so that crystal growth using impurities as nuclei. Since there are few particles to be formed, uniform crystal grains can be obtained, and a magnetic recording medium having a high coercive force in a direction parallel to the film surface can be realized.

Further, according to the present invention, in a magnetic recording medium in which a ferromagnetic metal layer is formed on a surface of a base via a metal underlayer,
By setting the oxygen concentration of the metal underlayer of 100 wtppm or less, good quality crystal growth can be achieved even if the film thickness is small.
As a result, the degree of controlling the orientation plane of the crystal grains forming the ferromagnetic metal layer (that is, the degree of the C-axis of the hcp structure lying in the film plane) is increased, so that the magnetic recording with a high coercive force in the direction parallel to the film plane. A medium can be realized.

Further, according to the present invention, in a magnetic recording medium in which a ferromagnetic metal layer is formed on a surface of a base via a metal underlayer,
Both the ferromagnetic metal layer and the metal underlayer have an oxygen concentration of 100 wtp
pm or less, the nonmagnetic Cr of the metal underlayer passes through the interface between the two layers without being affected by the impurities in the ferromagnetic metal layer and the metal underlayer, and the crystal grains of the ferromagnetic metal layer Easy to spread between. As a result, the magnetic isolation of each crystal grain of the ferromagnetic metal layer is increased, so that a magnetic recording medium having a high coercive force in a direction parallel to the film surface can be realized.

In the magnetic recording medium of the present invention, high coercive force and low medium noise can be simultaneously realized by setting the thickness of the metal underlayer to preferably in the range of 2.5 nm to 100 nm, more preferably in the range of 5 nm to 30 nm.

In the magnetic recording medium of the present invention, a higher coercive force can be realized by setting the thickness of the ferromagnetic metal layer in the range of preferably 2.5 nm to 40 nm, more preferably 5 nm to 20 nm.

Further, in the present invention, in the magnetic recording medium in which the ferromagnetic metal layer is formed on the surface of the base, by reducing the oxygen concentration of the ferromagnetic metal layer to 100 wtppm or less, there are few particles that grow as crystals with impurities as nuclei. In addition, uniform crystal grains can be obtained even in a thin film thickness region of 30 nm or less, and a magnetic recording medium having a high coercive force in a direction perpendicular to the film surface can be realized.

In the magnetic recording medium of the present invention, a higher coercive force can be realized by setting the surface roughness Ra of the substrate to preferably 3 nm or less, more preferably 1 nm or less.

In the magnetic recording medium of the present invention, since the normalized coercive force (expressed as Hc / Hk ^grain ) of the ferromagnetic metal layer is 0.3 or more and less than 0.5, further lower medium noise can be realized.

In the magnetic recording medium of the present invention, an Al alloy, glass, or silicon is preferably used as the material of the substrate because the above surface roughness can be realized at low cost.

In the present invention, a magnetic underlayer and a ferromagnetic metal layer are sequentially formed on a surface of a substrate by a sputtering method to produce a magnetic recording medium, but "sequentially" means that after a metal underlayer is formed,
Until the ferromagnetic metal layer is formed on the surface, it means that the ferromagnetic metal layer is not exposed to an atmosphere having a pressure higher than the gas pressure at the time of film formation. In this sense, the impurity concentration of Ar gas used when sequentially forming the metal underlayer and the ferromagnetic metal layer is 10 ppb or less, preferably 100 ppt or less, thereby lowering the oxygen concentration contained in each of the above layers. And a method of manufacturing a magnetic recording medium that can perform the method.

Therefore, the targets used when forming the metal underlayer and the ferromagnetic metal layer have an oxygen content of 150 ppm or less and 30 ppm or less, respectively. The ultimate vacuum degree is desirably 8 × 10 ⁻⁸ Torr or less.

Further, in the present invention, before forming the metal base layer, the surface of the substrate is subjected to a cleaning treatment by a high frequency sputtering method using an Ar gas having an impurity concentration of 10 ppb or less, and a very thin peeling of 0.2 nm to 1 nm is performed. By performing the processing, a method of manufacturing a magnetic recording medium having the following two functions can be realized.

(1) Since substances that adhere to the surface of the substrate and cannot be removed by storage in a vacuum or heat treatment can be removed, the crystal growth of the Cr film is promoted from the stage where the Cr layer is thin (for example, 5 nm). As a result, even if a ferromagnetic metal layer is formed on a thin Cr layer, a high coercive force in a direction parallel to the film surface can be obtained.

(2) Diffusion of non-magnetic Cr from the Cr layer to the crystal grain boundaries of the ferromagnetic metal layer formed on the Cr layer is facilitated. as a result,
Each crystal grain constituting the ferromagnetic metal layer is less likely to receive a magnetic interaction from an adjacent crystal grain, and a high coercive force in a direction parallel to the film surface is obtained.

The two effects described above, that is, the effect of the cleaning treatment on the impurity concentration of the Ar gas and the surface of the substrate, show the same effect when the ferromagnetic metal layer is formed directly on the surface of the substrate.

The effect of the cleaning process described above is completely opposite to the effect expected from etching by a general sputtering method on a magnetic recording medium, and was first found by the present invention. That is, the cleaning treatment of the surface of the (Ni-P) layer by the general operation method by the high-frequency sputtering method is, as disclosed in, for example, JP-A-64-70925, exclusively for the (Ni-P) layer. The purpose is to remove the surface area and increase the adhesion strength of a thin film formed thereon, and the peeling depth may be as large as 1 nm to 20 nm. Moreover, according to this method, the formed Cr
It is described that the crystal orientation of the underlayer changes and the coercive force of the medium decreases. For this reason, after performing the cleaning process, a complicated and extra oxidation step is required for several tens seconds to several hours, and the productivity is significantly reduced. on the other hand,
As described above, the present invention is capable of mass-producing magnetic recording media having extremely excellent magnetic properties with high productivity by performing a cleaning process of 1 nm or less using Ar gas having a low impurity concentration. It is.

In the present invention, the cleaning rate by the high frequency sputtering method is preferably 0.001 nm / sec to 0.1 nm / sec,
A magnetic recording medium having a high coercive force in this range can be stably obtained.

Further, the coercive force is further improved by applying a negative bias to the base during the formation of the metal underlayer and / or the ferromagnetic metal layer. The bias value at this time is
100V to -400V is preferred.

Further, in the present invention, even when the surface temperature of the substrate when forming the metal underlayer and / or the ferromagnetic metal layer is in the range of 60 ° C. to 150 ° C., conventionally, the temperature cannot be obtained unless the temperature is 250 ° C. or higher. A coercive force can be realized. As a result, the substrate can be manufactured by a lower heating process than before, the amount of gas generated in the film formation chamber can be reduced, and plastics and the like that are weak to high-temperature heating can be used as the base material.

Embodiment Examples Hereinafter, embodiments of the present invention will be described.

(Substrate) As the substrate, for example, aluminum, titanium and alloys thereof, silicon, glass, carbon, ceramic, plastic, resin and composites thereof, and a non-magnetic film of a different material on their surfaces by sputtering, vapor deposition, Examples include those subjected to a surface coating treatment by a plating method or the like. The non-magnetic film provided on the surface of the substrate is not magnetized at high temperature, has conductivity, and is easy to machine, but preferably has an appropriate surface hardness. As a basis that satisfies such conditions, it is particularly preferable to provide a (Ni-P) layer as a nonmagnetic film on the surface of an aluminum alloy.

As the shape of the base, a donut disk shape is used for a disk application. A substrate provided with a magnetic layer or the like described later, that is, a magnetic recording medium, is used while rotating at a speed of, for example, 3600 rpm around the center of the disk during magnetic recording and reproduction. At this time, the magnetic head over the magnetic recording medium
Fly at a height of about 0.1 μm. Therefore, as the substrate, it is necessary to appropriately control the flatness of the surface, the parallelism of the front and back surfaces, the undulation in the circumferential direction of the substrate, and the roughness of the surface.

When the substrate rotates / stops, the surfaces of the magnetic recording medium and the magnetic head come into contact and slide (Contact).
Start Stop, CSS). As a countermeasure, there is a case where a slight concentric scratch (texture) is provided on the surface of the base.

(Metal Underlayer) Examples of the metal underlayer include Cr, Ti, W and alloys thereof. When the alloy is used, for example, V, Nb,
A combination with Ta or the like has been proposed. In particular, Cr is widely used for mass production, and a sputtering method, an evaporation method, or the like is used as a film forming method.

The role of this metal underlayer is such that when a Co-based ferromagnetic metal layer is provided thereon, the axis of easy magnetization of the ferromagnetic metal layer is oriented in the in-plane direction of the substrate, ie, the coercive force in the in-plane direction of the substrate. Is to promote the crystal growth of the ferromagnetic metal layer so that the ratio becomes higher.

When producing a metal underlayer made of Cr by a sputtering method,
The film forming factors for controlling the crystallinity include the surface temperature of the substrate, the gas pressure during film formation, the bias applied to the substrate, and the film thickness to be formed. In particular, since the coercive force of the ferromagnetic metal layer tends to increase in proportion to the Cr film thickness, for example, the Cr film is used in the range of 50 nm to 150 nm.

In order to improve the recording density, it is necessary to reduce the flying height of the magnetic head from the medium surface. On the other hand, when the Cr film thickness is large, the surface roughness of the medium tends to increase. Therefore, it is desired to realize a high coercive force with a small Cr film thickness.

(Ferromagnetic Metal Layer) As the ferromagnetic metal layer, for example, a Co-based alloy containing at least a Co element is used.

When provided on the surface of the substrate via a metal underlayer (that is, in the case of a magnetic film for in-plane recording), for example, CoNiCr, C
oCrTa, CoPtCr, CoPtNi, CoNiCrTa, CoPtCrTa and the like. In particular, CoNiCr is inexpensive and is not easily affected by the film formation atmosphere.CoCrTa has a low medium nozzle. Used. In order to improve the recording density and reduce the manufacturing cost, it is desired to develop a ferromagnetic metal layer which is inexpensive in material cost, has a low medium nozzle, and can realize a high coercive force.

On the other hand, when provided directly on the surface of the substrate without a metal underlayer (ie, in the case of a magnetic film for perpendicular recording), for example, CoCr, CoPt, CoCrTa and the like can be mentioned. In some cases, a soft magnetic metal layer is provided under the ferromagnetic metal layer as a backing layer. In this case, it is desired to establish a material and a manufacturing method capable of maintaining a high coercive force in the direction perpendicular to the film surface even if the thickness of the ferromagnetic metal layer is reduced.

(Magnetic recording medium using magnetization reversal) As a magnetic recording medium using magnetization reversal, a medium (in-plane magnetic recording medium) that forms recording magnetization parallel to the film surface of the ferromagnetic metal layer described above; There are two types, a medium that forms recording magnetization perpendicularly (perpendicular magnetic recording medium).

In either medium, it is necessary to further reduce the recording magnetization in order to improve the recording density. This downsizing reduces the readout signal output from the magnetic head in order to reduce the leakage flux of each recording magnetization. Therefore,
It is desired that the medium noise, which is considered to be influenced by the adjacent recording magnetization, be further reduced.

(Oxygen Concentration of Ferromagnetic Metal Layer) It is known that the oxygen concentration of the ferromagnetic metal layer is, for example, 250 wt ppm or more in the case of a CoNiCr film formed by a conventional sputtering method. It has been desired to investigate the effect of the oxygen concentration of the ferromagnetic metal layer, that is, the effect on the coercive force of the medium and the noise of the medium.

The above-described conventional sputtering method is different from the conventional sputtering method in that the ultimate vacuum degree of the film forming chamber for forming the ferromagnetic metal layer is 1 × 10 ^{−7 to} 5 × 10 ⁻⁷ Torr, and the Ar gas used when forming the ferromagnetic metal layer is Impurity concentration
Refers to film formation under the condition of 1 ppm or more.

(Oxygen Concentration of Metal Underlayer) It is known that the oxygen concentration of the metal underlayer is, for example, 250 wtppm or more in the case of a Cr film formed by a conventional sputtering method. It is desirable to investigate the effect of the oxygen concentration of the metal underlayer, that is, the effect on the crystal growth process depending on the thickness of the metal underlayer, and the effect on the ferromagnetic metal layer formed on the metal underlayer. I was

The meaning of the conventional sputtering method described above is the same as that described in the above section “Oxygen concentration of ferromagnetic metal layer”.

(Normalized coercive force of ferromagnetic metal layer (referred to as Hc / Hk ^grain )) Normalized coercive force of ferromagnetic metal layer is a value obtained by dividing coercive force Hc by anisotropic magnetic field Hk ^grain of crystal grains. And the degree to which the magnetic isolation of the crystal grains increases is referred to as “Magnetizatio
n Reversal Mechanism Evaluated by Rotational Hyste
resis Loss Analysis for the Thin Film Media "Migaku
Takahashi, T.Shimatsu, M.Suekane, M.Miyamura, K.Yamag
uchi and H. Yamasaki: IEEE TRANSACTIONS ON MAGUNETIC
S, VOL. 28, 1992, pp. 3285.

The normalized coercive force of the ferromagnetic metal layer produced by the conventional sputtering method was smaller than 0.3 as long as the ferromagnetic metal layer was a Co-based.According to the Stoner-Wohlfarth theory, crystal grains were completely formed. It is shown that when magnetically isolated, it takes 0.5, which is the upper limit of the normalized coercive force.

Also, J.-G.Zhu and HNBertram: Journal of Appli
According to ed Physics, VOL. 63, 1988, pp. 3248, the fact that the normalized coercive force of the ferromagnetic metal layer is high means that the magnetic interaction of the individual crystal grains constituting the ferromagnetic metal layer is reduced. , A high coercive force can be realized.

Here, the coercive force Hc is a vibration sample type magnetometer (Variab
le Sample Magnetometer, referred to as VSM). The anisotropic magnetic field Hk ^grain of the crystal grain is an applied magnetic field in which the rotational hysteresis loss measured using a high-sensitivity torque magnetometer is completely eliminated. In the case of a magnetic recording medium in which a ferromagnetic metal layer is formed on the surface of a base via a metal underlayer, both the coercive force and the anisotropic magnetic field are values measured in a thin film plane. In the case of a magnetic recording medium on which a ferromagnetic metal layer is formed, the value is measured in a direction perpendicular to the plane of the thin film.

(Aluminum alloy) Examples of the aluminum alloy include an alloy composed of aluminum and magnesium. Currently HD
For (hard disk) applications, those based on aluminum alloys are most used. Since the purpose of use is for magnetic recording, it is preferable that the content of the metal oxide is small.

Further, a nonmagnetic (Ni-P) film is often provided on the surface of the aluminum alloy by a plating method or a sputtering method. The purpose is to improve the corrosion resistance and increase the surface hardness of the substrate. On the surface of this (Ni-P) film,
In order to reduce the frictional force when the magnetic head slides on the medium surface, concentric minor scratches (texture) are provided.

The problems in the case where an aluminum alloy is used as the substrate are to make the substrate thinner and to reduce the surface roughness of the substrate. Currently, the former
The limit is 0.5 mm, and the latter is about 0.5 nm.

(Glass) Examples of the glass include those obtained by strengthening the glass surface by ion doping or the like and those having a structure in which the glass itself is microcrystallized. Both are devised to solve the disadvantage of glass that is “easy to break”.

Since glass has a higher surface hardness than an aluminum alloy, glass is excellent in that it is not necessary to provide a (Ni-P) film or the like. It is also advantageous in terms of thinning of the substrate, smoothness of the substrate surface, high-temperature resistance of the substrate, and the like.

However, in order to produce a magnetic film having a high coercive force, it is better to increase the surface temperature of the substrate during film formation and to form the film while applying a bias to the substrate. May be provided with a non-magnetic layer. In addition, a nonmagnetic layer may be provided to prevent harmful elements from entering the magnetic film from the glass. Alternatively, in order to reduce the frictional force when the magnetic head slides on the surface of the medium, a non-magnetic layer having fine irregularities may be arranged on the surface of the glass.

The problem when glass is used as the substrate is to achieve both the thinning of the substrate and the technology for preventing the substrate from cracking.

(Silicon) As silicon, for example, a silicon wafer having a track record in the semiconductor field and having a disk shape can be used.

Silicon, like glass, is superior to aluminum alloys in that it has a high surface hardness, enables thinning of the substrate, has a high smoothness of the substrate surface, and has good high-temperature resistance characteristics of the substrate. In addition to these, since the crystal orientation and lattice constant of the substrate surface can be selected, it is expected that the controllability of crystal growth of the magnetic film formed thereon is improved. Similarly to the aluminum alloy, the substrate is capable of biasing the substrate to have a conductivity in terms of a more clean can also be achieved in the film forming space for gas release is small, such as H ₂ O from the internal base Is also advantageous.

The problem in the case where silicon is used as the substrate, as in the case of glass, is to achieve both thinning of the substrate and technology for preventing the substrate from cracking.

(Sputtering Method) Examples of the sputtering method include a transfer type in which a thin film is formed while a substrate moves in front of a target, and a stationary type in which a thin film is formed by fixing a substrate in front of a target. The former is advantageous in producing a low-cost medium because of its high mass productivity, and the latter is capable of producing a medium having excellent recording / reproducing characteristics because the incident angle of sputtered particles to a substrate is stable.

(The metal underlayer and the ferromagnetic metal layer are sequentially formed.) The metal underlayer and the ferromagnetic metal layer are sequentially formed as follows. "After the metal underlayer is formed on the surface of the base, the ferromagnetic metal is formed on the surface. Until the layer is formed, it will not be exposed to an atmosphere having a pressure higher than the gas pressure at the time of film formation. " If a ferromagnetic metal layer is formed thereon after exposing the surface of the metal underlayer to the atmosphere, the coercive force of the medium is significantly reduced (for example, no exposure: 1500 Oe → exposed: 50
0 Oe or less) is known.

(Ar gas impurity used for film formation and its concentration) Examples of the Ar gas impurity used for film formation include H
₂ O, O ₂ , CO ₂ , H ₂ , N ₂ , C _x H _{y and the} like. In particular, impurities affecting the amount of oxygen taken into the film include H ₂ O,
O ₂ and CO ₂ are estimated. Therefore, the impurity concentration of the present invention is H ₂ O, O ₂ , CO ₂ contained in Ar gas used for film formation.
Will be expressed as the sum of

(Cleaning process by high frequency sputtering method) As cleaning process by high frequency sputtering method,
For example, there is a method of applying an AC voltage from a RF (radio frequency, 13.56 MHz) power supply to a substrate placed in dischargeable gas pressure air. The feature of this method is that it can be applied even when the substrate is not conductive. In general,
An effect of the cleaning treatment is to improve the adhesion of the thin film to the substrate. However, there are many unclear points about the effect on the film quality of the thin film itself formed on the surface of the substrate after the cleaning process.

(Impurity of Cr Target Used When Forming Metal Underlayer and Its Concentration) Examples of impurities of the Cr target used when forming the metal underlayer include Fe, Si, Al, C, O, N, H and the like. In particular, impurities that affect the amount of oxygen taken into the film are estimated to be O. Therefore, the impurity concentration of the present invention indicates oxygen contained in the Cr target used when forming the metal underlayer.

(Impurity of Target Used When Forming Ferromagnetic Metal Layer and Its Concentration) Examples of impurities of the Co-based target used when forming the ferromagnetic metal layer include Fe, Si, Al, C, O, N and the like. In particular, impurities that affect the amount of oxygen taken into the film are estimated to be O. Therefore, the impurity concentration of the present invention indicates the oxygen contained in the target used when forming the ferromagnetic metal layer.

(Negative bias application to the substrate) Negative bias application to the substrate
When forming a base film or a magnetic film, this refers to applying a DC bias voltage to a substrate. It has been found that applying an appropriate bias voltage increases the coercivity of the medium. It is known that the effect of the above-described bias application is larger when both layers are applied than when only one of the films is manufactured.

(Ultimate vacuum of the film formation chamber for forming the metal underlayer and / or the ferromagnetic metal layer) The ultimate vacuum of the film formation chamber for forming the metal underlayer and / or the ferromagnetic metal layer depends on the material of the ferromagnetic metal layer. In some cases, this is one of the film formation factors that influence the value of the coercive force. In particular, in the case of a Co-based material in which Ta is contained in the ferromagnetic metal layer, the influence is large when the above-mentioned ultimate vacuum is low (for example, 5 × 10 ⁻⁶ Torr or more).

(Surface temperature of substrate when forming metal underlayer and / or ferromagnetic metal layer) The surface temperature of the substrate when forming the metal underlayer and / or ferromagnetic metal layer depends on the material of the ferromagnetic metal layer. Without this, it is one of the film formation factors that influence the value of the coercive force. As long as the substrate is not damaged, a higher coercive force can be realized by forming the film at a high surface temperature. The basic damage means external changes such as warpage, swelling, and cracks, and internal changes such as generation of magnetization and an increase in gas generation.

(Surface Roughness of Base, Ra) The surface roughness of the base includes, for example, an average center line roughness Ra when the surface of the base having a disk shape is measured in a radial direction. As a measuring instrument, RANKTAYLORHO
TALYSTEP manufactured by BSON was used.

When the substrate starts rotating from a stopped state or vice versa, the surfaces of the magnetic recording medium and the magnetic head come into contact with each other and slide (referred to as CSS (Contact Start Stop)). At this time, in order to suppress the adsorption of the magnetic head and the increase in the coefficient of friction,
Ra is preferably larger. On the other hand, when the base reaches the maximum number of rotations, the distance between the magnetic recording medium and the magnetic head,
That is, since it is necessary to secure the flying height of the magnetic head, it is desirable that Ra be small.

Accordingly, the maximum value and the minimum value of the surface roughness and Ra of the base are appropriately determined based on the above-mentioned reason and the required specifications for the magnetic recording medium. For example, when the flying height of the magnetic head is 2 μm
In the case of inch, Ra = 6 nm to 8 nm.

(Texture processing) Examples of the texture processing include a method using mechanical polishing, a method using chemical etching, and a method using a physical uneven film. Particularly, in the case of an aluminum alloy substrate which is most widely used as a substrate of a magnetic recording medium, a method by mechanical polishing is adopted. For example, against a (Ni-P) film provided on the surface of an aluminum alloy substrate, a tape having grinding particles adhered to the surface is pressed against a rotating substrate,
There is a method of giving minor scratches concentrically. In this method, the coating particles for grinding may be separated from the tape and used.

(Composite electropolishing process) As the composite electropolishing process, for example, a process of providing an oxidation passivation film using chromium oxide as a product on the inner wall of a vacuum chamber used for forming a magnetic film or the like can be mentioned. . In this case, the material forming the inner wall of the vacuum chamber is preferably, for example, SUS316L. By this treatment, the amount of O ₂ and H ₂ O released from the inner wall of the vacuum chamber can be reduced, so that the amount of oxygen taken into the formed thin film can be further reduced.

In the magnetron sputtering apparatus manufactured by Anelva (model number ILC3013: load lock type stationary facing type) used in the present invention, the inner walls of all vacuum chambers (loading / unloading chamber, film forming chamber, and cleaning chamber) perform the above-described processing. I have.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between the oxygen concentration in a CoNiCr film according to Example 1 and the coercive force of a manufactured medium.

Figure 2 shows a transmission electron microscope (TE) of the surface of a magnetic recording medium.
M) It is a photograph.

Fig. 3 shows a transmission electron microscope (TE) on the surface of a magnetic recording medium.
M) It is a photograph.

FIG. 4 is a graph showing the relationship between the oxygen concentration in the Cr film according to Example 2 and the coercive force of the manufactured medium.

FIG. 5 is a graph illustrating the relationship between the oxygen concentration in the CoNiCr film and the oxygen concentration in the Cr film according to Example 3, and the coercive force of the manufactured medium.

FIG. 6 is a graph showing the relationship between the thickness of the metal underlayer made of Cr according to Example 5 and the coercive force of the manufactured medium.

FIG. 7 is a graph showing the relationship between the thickness of the metal underlayer made of Cr according to Example 5 and the noise Nm of the manufactured medium.

FIG. 8 is a graph showing the relationship between the thickness of the metal underlayer made of CoCrTa according to Example 6 and the coercive force of the manufactured medium.

FIG. 9 is a graph showing the relationship between the oxygen concentration in the CoNiCr film according to Example 7 and the coercive force of the manufactured medium.

FIG. 10 shows the normalized holding force (Hc / Hk ^grain ) according to Example 8.
FIG. 7 is a graph showing a relationship between the noise and the noise (Nm) of a manufactured medium. FIG.

FIG. 11 is a graph showing the relationship between the impurity concentration contained in the Ar gas when forming the ferromagnetic metal layer and the metal underlayer according to Example 9 and the coercive force of the manufactured medium.

FIG. 12 is a graph showing the relationship between the amount of separation of the substrate surface due to the cleaning process according to Example 10 and the coercive force of the manufactured medium.

FIG. 13 is a graph showing an X-ray diffraction result of the medium surface according to Example 10.

FIG. 14 is a graph showing the relationship between the impurity concentration of the target used when forming the metal underlayer according to Example 11 and the coercive force of the manufactured medium.

FIG. 15 is a graph showing the relationship between the impurity concentration of the target used when forming the ferromagnetic metal layer according to Example 12 and the coercive force of the manufactured medium.

FIG. 16 is a graph showing the relationship between the negative bias value applied to the substrate according to Example 13 and the coercive force of the manufactured medium.

FIG. 17 is a graph showing the relationship between the ultimate vacuum of the film formation chamber for forming the metal underlayer and the ferromagnetic metal layer according to Example 14, and the coercive force of the manufactured medium.

FIG. 18 is a graph showing the relationship between the surface temperature of the base when forming the metal underlayer and / or the ferromagnetic metal layer according to Example 15 and the coercive force of the manufactured medium.

FIG. 19 is a graph showing the relationship between the surface temperature of the base when forming the metal underlayer and / or the ferromagnetic metal layer according to Example 15 and the surface roughness Ra of the manufactured medium.

FIG. 20 is a graph showing the relationship between the surface roughness Ra of the base according to Example 16 and the coercive force of the manufactured medium.

Figure 21 is according to Example _{17 (Ar + N 2) N} 2 in the gas
4 is a graph showing a relationship between a gas ratio and a coercive force of a manufactured medium.

Figure 22 is according to Example _{17 (Ar + H 2) H} 2 in the gas
4 is a graph showing a relationship between a gas ratio and a coercive force of a manufactured medium.

 FIG. 23 is a schematic diagram illustrating a magnetic recording medium.

(Description of Signs) 1 Base, 2 Al substrate, 3 Non-magnetic (Ni-P) layer, 4 Cr underlayer, 5 Ferromagnetic metal layer, 6 Protective film.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 In this example, the effect of limiting the concentration of oxygen contained in a ferromagnetic metal layer in a magnetic recording medium in which a ferromagnetic metal layer is formed on the surface of a base via a metal underlayer is shown. In order to confirm this effect, Ar was used to form a ferromagnetic metal layer.
Film formation was performed by changing the concentration of impurities contained in the gas in the range of 10 ppb to 1 ppm. At this time, when forming the metal underlayer, Ar
The concentration of impurities contained in the gas was fixed at 1 ppm.

In this example, the sputtering apparatus used for manufacturing the medium was a magnetron sputtering apparatus manufactured by Anelva (model number: ILC3013: load lock type stationary facing type), and all vacuum chambers (loading / removing chamber (also cleaning chamber), film forming chamber) 1, Deposition chamber 2,
The inner wall of the film forming chamber 3) has been subjected to a composite electrolytic polishing treatment. Table 1 shows film forming conditions when the magnetic recording medium of this example is manufactured.

Hereinafter, a method of manufacturing the magnetic recording medium of this example will be described step by step. The numbers in parentheses below indicate the procedure.

(1) Inner / outer diameter 25mm / 89mm, thickness 1.2
An aluminum alloy substrate having a disk shape of 7 mm was used. On the surface of the aluminum alloy substrate, a (Ni—P) film having a thickness of 10 μm was provided by a plating method. The surface of the (Ni-P) film has concentric minor scratches (texture) by a mechanical method. The surface roughness of the substrate when scanned in the disk radial direction is the average center line roughness. Ra was 5 nm.

(2) The above substrate was subjected to a cleaning process by a mechanical and chemical method and a drying process by hot air or the like before the film formation described later.

(3) The substrate after the drying treatment was set on a substrate holder made of aluminum and placed in a preparation chamber of a sputtering apparatus. After the inside of the charging chamber was evacuated to a final vacuum degree of 1 × 10 ⁻⁷ Torr by a vacuum exhaust device, the substrate was subjected to a heat treatment at 250 ° C. for 5 minutes using an infrared lamp.

(4) The substrate holder was moved from the preparation chamber to the film formation chamber 1 for producing a Cr film. After moving, the substrate was heated and held at 250 ° C. by an infrared lamp. However, the film forming chamber 1 was evacuated to a final vacuum degree of 3 × 10 ⁻⁹ Torr in advance, and the door valve between the charging chamber and the film forming chamber 1 was closed after the movement of the substrate holder. The impurity concentration of the used Cr target was 120 ppm.

(5) Ar gas was introduced into the film forming chamber 1, and the gas pressure in the film forming chamber 1 was set to 2 mTorr. The impurity concentration contained in the used Ar gas was fixed at 1 ppm.

(6) A plasma is generated by applying a voltage of 200 W from a DC power supply to the Cr target. As a result, the Cr target was sputtered, and a 50 nm-thick Cr layer was formed on the surface of the substrate at a position facing the target in parallel.

(7) After forming the Cr layer, the substrate holder was moved from the film formation chamber to the film formation chamber 2 for producing a CoNiCr film. After moving, the substrate was heated and held at 250 ° C. by an infrared lamp. However, the ultimate vacuum degree in the film forming chamber 2 is 3 × 10 ⁻⁹ Torr in advance.
After the movement of the substrate holder, the door valve between the film forming chamber 1 and the film forming chamber 2 was closed. The target composition used was 62.5 at% Co, 30 at% Ni, 7.5 at% C
r, and the impurity concentration of the target was 20 ppm.

(8) Ar gas was introduced into the film forming chamber 2, and the gas pressure in the film forming chamber 2 was set to 2 mTorr. The impurity concentration contained in the used Ar gas was changed in the range of 10 ppb to 1 ppm.

(9) Apply a voltage of 200 W from a DC power supply to the CoNiCr target to generate plasma. As a result, the CoNiCr target was sputtered, and a 40-nm-thick CoNiCr layer was formed on the surface of the Cr-layered substrate at a position facing the target in parallel with the target.

(10) After forming the CoNiCr layer, the substrate holder was moved from the film forming chamber 2 to the film forming chamber 3 for forming a C film. After moving, the substrate was heated and held at 250 ° C. by an infrared lamp. However, the ultimate vacuum degree of the film forming chamber 3 is 3 × 10 ⁻⁹ Torr in advance.
After the substrate holder was moved, the door valve between the film forming chamber 2 and the film forming chamber 3 was closed.

(11) Ar gas was introduced into the film forming chamber 3, and the gas pressure in the film forming chamber 3 was set to 2 mTorr. The impurity concentration contained in the used Ar gas was fixed at 1 ppm.

(12) Generate a plasma by applying a voltage of 400 W from a DC power supply to the C target. As a result, the C target is sputtered and the Co
A C layer having a thickness of 20 nm was formed on the surface of the substrate having the NiCr layer / Cr layer.

(13) After the C layer is formed, it is taken out of the film forming chamber 3 and taken out of the chamber.
The substrate holder was moved. After that, in the removal room
The substrate was taken out after introducing N ₂ gas to atmospheric pressure.
By the above steps (1) to (12), the layer configuration is C / CoNiCr / C
A magnetic recording medium of r / NiP / Al was produced.

The target used was one in which impurities were suppressed as much as possible. The impurities of the Cr formation target are Fe: 88, Si: 34, A
l: 10, C: 60, O: 120, N: 60, H: 1.1 (wtppm). Also,
The target composition for forming the ferromagnetic metal layer is Ni: 29.2at%,
Cr: 7.3 at%, Co: bal, impurities are Fe: 27, Si <10, Al <
10, C: 30, O: 20, N> 10 (wtppm).

In FIG. 1, the magnetic properties of the manufactured medium are indicated by circles. The horizontal axis in FIG. 1 shows the oxygen concentration in the CoNiCr film. The measurement of the oxygen concentration was performed by SIMS. The vertical axis in FIG. 1 represents the coercive force Hc in the circumferential direction of the sample at this time.

Conventionally, the impurity concentration in Ar gas used when forming a ferromagnetic metal layer made of CoNiCr was 1 ppm. Also,
The oxygen concentration in the CoNiCr film of the conventional medium is 260 wtppm.
The coercive force of the conventional medium is shown in FIG.

In this example, as shown in FIG. 1, the coercive force was sharply increased by setting the oxygen concentration in the CoNiCr film to 100 wtppm or less, and a result was obtained that 90 wtppm or less was particularly advantageous. It was separately observed that the value of the saturation magnetization at this time was substantially constant.

2 and 3 are transmission electron microscope (TEM) photographs of the surface of each of the above media. The oxygen concentration in the film of FIG.
FIG. 3 shows the case of 140 wtppm. FIG. 2 shows that the film in the film is uniform and dense, and FIG. 3 is a film having a structure in which the outline of the crystal is unclear.

Therefore, when the oxygen concentration of the ferromagnetic metal layer is set to 100 wtppm or less, the oxygen concentration of the conventional ferromagnetic metal layer made of CoNiCr is reduced.
It was found that the coercive force at 260 wtppm can be increased by 50% or more. That is, it was confirmed that even if Pt was not contained in the magnetic layer, a medium capable of coping with a high recording density could be realized by reducing the oxygen concentration of the ferromagnetic metal layer.

Example 2 In this example, the effect of limiting the concentration of oxygen contained in a metal underlayer in a magnetic recording medium in which a ferromagnetic metal layer is formed on the surface of a base via a metal underlayer is shown. In order to confirm this effect, the film was formed by changing the concentration of impurities contained in the Ar gas when forming the metal underlayer in the range of 10 ppb to 1 ppm. At this time, the impurity concentration contained in the Ar gas when forming the ferromagnetic metal layer was fixed at 1 ppm.

 The other points were the same as in Example 1.

In FIG. 4, the magnetic characteristics of the manufactured medium are indicated by circles. The horizontal axis of FIG. 4 indicates the oxygen concentration in the Cr film. The measurement of the oxygen concentration was performed by SIMS. The vertical axis in FIG. 2 is the coercive force Hc in the circumferential direction of the sample at this time.

Conventionally, the impurity concentration in Ar gas used when forming a metal underlayer made of Cr was 1 ppm. The oxygen concentration in the Cr film of the conventional medium was 260 wtppm, and the coercive force of the conventional medium is shown in FIG.

In this example, as shown in FIG.
It was found that the coercive force was increased by adjusting the content to 0 wtppm or less. It was separately observed that the value of the saturation magnetization at this time was substantially constant.

Therefore, if the oxygen concentration of the metal underlayer is 100 wtppm or less, the oxygen concentration of the conventional metal underlayer made of Cr is 260 wtppm.
It was found that the coercive force possessed in the case of can be increased by 30% or more. That is, it was confirmed that even if Pt was not contained in the magnetic layer, it was possible to realize a medium capable of coping with high recording density by reducing the oxygen concentration of the metal underlayer.

Example 3 In this example, in a magnetic recording medium in which a ferromagnetic metal layer is formed on a surface of a base via a metal underlayer, the oxygen concentration contained in the ferromagnetic metal layer and the oxygen concentration contained in the metal underlayer are included. The effect of limiting both the oxygen concentration and the oxygen concentration will be described. In order to confirm this effect, the film was formed by changing the concentration of impurities contained in the Ar gas when forming the ferromagnetic metal layer in the range of 10 ppb to 1 ppm. At this time, the impurity concentration in the Ar gas when forming the metal underlayer was fixed at 1.5 ppb.

 The other points were the same as in Example 1.

In FIG. 5, the magnetic characteristics of the manufactured medium are indicated by the circles. The horizontal axis in FIG. 5 shows the oxygen concentration in the CoNiCr film. The measurement of the oxygen concentration was performed by SIMS. The vertical axis in FIG. 5 represents the coercive force Hc in the circumferential direction of the sample at this time.

In this example, as shown in FIG. 5, a result was obtained in which the coercive force was further increased by setting the oxygen concentration in the CoNiCr film and the oxygen concentration in the Cr film together to 100 wtppm or less. It was separately observed that the value of the saturation magnetization at this time was substantially constant.

Therefore, it was found that when the oxygen concentration of the ferromagnetic metal layer and the oxygen concentration of the metal underlayer were both set to 100 wtppm or less, the coercive force of the conventional medium could be increased by 100% or more (ie, doubled). Therefore, even if the magnetic layer does not contain Pt, by reducing the oxygen concentration of the ferromagnetic metal layer and the metal underlayer together,
It has been confirmed that a medium which can sufficiently cope with high recording density can be realized.

(Example 4) In this example, instead of Co _62.5 -Ni ₃₀ -Cr _7.5 of Example 3, the following five types of alloys were used as Co-based alloy targets for forming a ferromagnetic metal layer, namely, Co _85.5 -Cr _10.5 −Ta ₄ , Co ₇₅
−Cr ₁₃ −Pt ₁₂ , Co ₇₀ −Ni ₂₀ −Pt ₁₀ , Co _82.5 −Ni ₂₆ −Cr _7.5
−Ta ₄ , Co _75.5 −Cr _10.5 −Ta ₄ −Pt ₁₀ were used. here,
The number after each element indicates the ratio of that element (at
%).

 The other points were the same as in Example 3.

In this example, the oxygen concentration in the Co-based alloy film and the oxygen concentration in the Cr film were both reduced to 100 wtppm or less, despite changing the elements constituting the Co-based alloy and their ratios.
It was confirmed that the coercive force also increased by 50% or more in the Co-based alloy.

Therefore, the coercive force increasing tendency when the oxygen concentration of the ferromagnetic metal layer and the oxygen concentration of the metal underlayer are set to 100 wtppm or less together is judged that the target forming the ferromagnetic metal layer should be a Co-based alloy. Was done. Particularly Co _62.5 -Ni ₃₀ -Cr _7.5 alloy, Co _85.5 -Cr _10.5 -Ta ₄ alloy, Co _82.5 -Ni ₂₆ -Cr _7.5 -
The Ta ₄ alloy is more preferable because the coercive force increases by 100% or more as compared with the conventional medium.

(Example 5) In this example, the effect of limiting the thickness of the metal underlayer in a magnetic recording medium in which a ferromagnetic metal layer is formed on the surface of the base via the metal underlayer will be described. In order to confirm this effect, film formation was performed by changing the thickness of the metal underlayer in the range of 0 to 100 nm. At this time, as the ferromagnetic metal layer, Co _85.5
-Cr _10.5 -Ta ₄ alloy was used, and its film thickness was fixed at 40 nm.

 The other points were the same as in Example 3.

In FIG. 6, the magnetic properties of the manufactured medium are indicated by circles. The horizontal axis in FIG. 6 indicates the thickness of the metal underlayer made of Cr. FIG.
The vertical axis indicates the coercive force Hc in the circumferential direction of the sample at this time.
As a comparative example, the same evaluation was performed for a conventional medium (when both the oxygen concentration in the CoCrTa film and the oxygen concentration in the Cr film were 260 wtppm). The result is indicated by a black circle in FIG.

From FIG. 6, it was found that the coercive force of the medium of this example has a value equal to or more than the maximum value of the conventional medium when the thickness of the Cr metal underlayer is 2.5 nm or more. The thickness of the Cr metal underlayer is 5 nm.
The above is more preferable because a high coercive force of 2000 Oe or more can be realized.

FIG. 7 shows the relationship between the thickness of the metal underlayer made of Cr and the noise N of the manufactured medium. In the figure, a circle indicates a medium of this example, and a circle indicates a conventional medium.

Table 2 shows the above-described medium noise measurement method and measurement conditions. Only the thickness of the Cr layer was variable from 1 nm to 100 nm, and the other conditions were fixed.

From FIG. 7, it was found that the noise of the medium of the present example had a value less than the minimum value of the conventional medium when the thickness of the Cr metal underlayer was 100 nm or less. Further, when the thickness of the Cr metal base layer is 50 nm or less, it is more preferable because medium noise lower by 10% or more can be realized.

Therefore, in this example, the thickness of the metal underlayer made of Cr is 2.
In the range of 5 nm to 100 nm, a medium having a higher coercive force or a lower medium noise than the conventional medium can be obtained. Further, when the thickness of the metal underlayer made of Cr is limited to the range of 5 nm to 50 nm, it is more preferable that the coercive force and the noise of the medium are more excellent than those of the conventional medium.

(Example 6) In this example, the effect of limiting the thickness of the ferromagnetic metal layer in a magnetic recording medium in which a ferromagnetic metal layer is formed on the surface of a base via a metal base layer will be described. In order to confirm this effect, film formation was performed by changing the thickness of the ferromagnetic metal layer in the range of 1 nm to 40 nm. At this time, the thickness of the metal underlayer was 50 nm.
Fixed to.

 The other points were the same as in Example 3.

In FIG. 8, the magnetic characteristics of the manufactured medium are indicated by circles. The horizontal axis of FIG. 8 indicates the thickness of the metal underlayer made of CoCrTa.
The vertical axis in FIG. 8 represents the coercive force Hc in the circumferential direction of the sample at this time. As a comparative example, the same evaluation was performed on a conventional medium (when the oxygen concentration in the CoCrTa film was 260 wtppm).
The result is indicated by a black circle in FIG.

From FIG. 8, it was found that when the thickness of the ferromagnetic metal layer was in the range of 2.5 nm to 40 nm, a medium having a higher coercive force than the conventional medium could be obtained. When the thickness of the ferromagnetic metal layer is limited to the range of 5 nm to 20 nm, the coercive force can be 2500 Oe or more. Conventionally, when the thickness of the ferromagnetic metal layer was reduced to 20 nm or less, a large decrease in coercive force was observed.According to the present invention, a good coercive force was obtained even at 20 nm or less, and the degree of freedom in media design was further expanded It became possible.

Example 7 In this example, the effect of limiting the concentration of oxygen contained in a ferromagnetic metal layer in a magnetic recording medium having a ferromagnetic metal layer formed on the surface of a base will be described. In order to confirm this effect, film formation was performed by changing the concentration of impurities contained in Ar gas when forming the ferromagnetic metal layer in the range of 10 ppb to 1 ppm.

The sputtering apparatus used for producing the medium in this example is a magnetron sputtering apparatus made by Anelva (model number ILC3
013: load lock type stationary facing type). Table 3 shows film forming conditions when the magnetic recording medium of this example is manufactured.

Hereinafter, a method of manufacturing the magnetic recording medium of this example will be described step by step. The numbers in parentheses below indicate the procedure.

(1) Inner / outer diameter 25mm / 89mm, thickness 1.2
An aluminum alloy substrate having a disk shape of 7 mm was used. On the surface of the aluminum alloy substrate, a (Ni—P) film having a thickness of 10 μm was provided by a plating method. The surface of the (Ni-P) film has concentric minor scratches (texture) by a mechanical method. The surface roughness of the substrate when scanned in the disk radial direction is the average center line roughness. Ra was 5 nm.

(2) The above substrate was subjected to a cleaning process by a mechanical and chemical method and a drying process by hot air or the like before the film formation described later.

(3) The substrate after the drying treatment was set on a substrate holder made of aluminum and placed in a preparation chamber of a sputtering apparatus. After the interior of the preparation chamber was evacuated to a final vacuum degree of 3 × 10 ⁻⁹ Torr by a vacuum exhaust device, the substrate was subjected to a heat treatment at 230 ° C. for 5 minutes using an infrared lamp.

(4) The substrate holder was moved from the preparation chamber to the film formation chamber 1 for producing a CoCr film. After the transfer, the substrate was heated and maintained at 230 ° C. by an infrared lamp. However, the film forming chamber 1 was evacuated to a final vacuum degree of 3 × 10 ⁻⁹ Torr in advance, and the door valve between the charging chamber and the film forming chamber 1 was closed after the movement of the substrate holder. The impurity concentration of the used CoCr target was 20 ppm.

(5) Ar gas was introduced into the film forming chamber 1, and the gas pressure in the film forming chamber 1 was set to 2 mTorr. The impurity concentration contained in the used Ar gas was changed in the range of 10 ppb to 1 ppm.

(6) A plasma is generated by applying a voltage of 200 W from a DC power supply to the CoCr target. As a result, the CoCr target was sputtered, and a 100-nm-thick CoCr layer was formed on the surface of the base at a position facing the target in parallel.

(7) After forming the CoCr layer, the substrate holder was moved from the film forming chamber 1 to the take-out chamber. Thereafter, the substrate was taken out after introducing N ₂ gas into the take-out chamber to make it atmospheric pressure. By the above steps (1) to (6), the layer structure becomes CoCr / N
A magnetic recording medium of iP / Al was manufactured.

The target used was one in which impurities were suppressed as much as possible. The target composition used was 85 at% Co, 15 at% Cr, and the impurity concentration of the target was 20 ppm. Impurities are Fe: 27, Si <10, Al <10, C: 30, O: 20, N <10 (wtppm)
Met.

In FIG. 9, the magnetic characteristics of the manufactured medium are indicated by circles. The horizontal axis in FIG. 9 indicates the oxygen concentration in the CoNiCr film. The measurement of the oxygen concentration was performed by SIMS. The vertical axis in FIG. 9 indicates the coercive force Hc in the circumferential direction of the sample at this time.

Conventionally, the impurity concentration in Ar gas used when forming a ferromagnetic metal layer made of CoCr was 1 ppm. Further, the oxygen concentration in the CoCr film of the conventional medium was 260 wtppm, and the coercive force of the conventional medium is shown in FIG.

In this example, as shown in FIG. 9, the oxygen concentration in the CoCr film was
It was found that the coercivity in the direction perpendicular to the film surface was greatly increased by setting the content to 100 wtppm or less. It was separately observed that the value of the saturation magnetization at this time was substantially constant.

Therefore, when the oxygen concentration of the ferromagnetic metal layer is set to 100 wtppm or less, the oxygen concentration of the conventional ferromagnetic metal layer made of CoCr becomes 26 wtppm.
It was found that the coercive force at 0 wtppm could be increased by 20% or more. That is, it was confirmed that a medium capable of coping with high recording density can be realized by reducing the oxygen concentration of the ferromagnetic metal layer.

Further, in this example, the case where the ferromagnetic metal layer is CoCr in the magnetic recording medium in which the ferromagnetic metal layer is formed on the surface of the base has been described, but the case where the ferromagnetic metal layer is CoCrTa or CoPt is also described above. The same tendency was confirmed.

Further, a soft magnetic film such as NiFe, CoZr is formed on the surface of the substrate.
Even when the ferromagnetic metal layer is provided via Nb or the like, the same effect as described above was obtained.

In the above embodiments, the Ni-P / Al substrate was used as the base, but when a nonmagnetic layer was provided on the surface of the base, for example,
It was confirmed that the method was effective even when using a glass substrate on which Ti, C, etc. were formed.

Example 8 In this example, the effect of limiting the normalized coercive force (denoted as Hc / Hk ^grain ) in a magnetic recording medium in which a ferromagnetic metal layer is formed on the surface of a base via a metal underlayer. It shows about. To confirm this effect, the impurity concentration in the Ar gas when forming the ferromagnetic metal layer and the metal underlayer was 10 ppb.
The film was formed by changing both layers together to 1 ppm. At this time, the material of the metal underlayer was Cr, and the film thickness was fixed at 50 nm. The materials of the ferromagnetic metal layer were six types of Co-based alloys, and the film thickness was fixed at 40 nm. The six types of Co-based alloys are Co _62.5 −Ni ₃₀ −Cr _7.5 , Co _85.5 −Cr _10.5 −Ta ₄ ,
Co ₇₅ −Cr ₁₃ −Pt ₁₂ , Co ₇₀ −Ni ₂₀ −Pt ₁₀ , Co _82.5 −Ni ₂₆ −Cr
_7.5 −Ta ₄ , Co _75.5 −Cr _10.5 −Ta ₄ −Pt ₁₀ . here,
The number after each element indicates the ratio of that element (at
%).

 The other points were the same as in Example 3.

In FIG. 10, the magnetic characteristics of the manufactured medium are indicated by circles. Figure
The horizontal axis of 10 is the normalized coercive force (Hc / Hk ^grain ).
The vertical axis indicates the noise N of the manufactured medium. The measurement method and measurement conditions of the medium noise were the same as in Example 5. As a comparative example, the same evaluation was performed on a conventional medium (when the oxygen concentration in the ferromagnetic metal layer was 260 wtppm). The result is indicated by the mark ● in FIG.

Table 4 shows the normalized coercive force values of the Co-based alloy shown in FIG.

From FIG. 10, it was found that the standardized coercive force of the conventional medium was smaller than 0.3 and the medium of the present example had a high value of 0.3 or more, regardless of the material of the ferromagnetic metal layer. Further, the medium noise of the present example was all smaller than that of the conventional medium. By the way, the upper limit of the normalized coercive force is theoretically shown to be 0.5 when crystal grains are completely isolated, but in a system having a somewhat random portion such as a thin film, it is 0.5. Has a smaller value.

Therefore, the normalized coercive force (Hc / Hk ^grain
It was confirmed that by limiting the range to 0.3 or more and less than 0.5, a low-noise medium capable of coping with high recording density can be realized.

In the above embodiments, the Ni-P / Al substrate was used as the base, but in addition, Al, glass, Si, Ti, C, ceramic, plastic, resin, and those formed with a metal film or an insulating film thereon. Can be used.

Example 9 In this example, in a method of manufacturing a magnetic recording medium in which a metal base layer and a ferromagnetic metal layer were sequentially formed on a surface of a base by sputtering, the impurity concentration of Ar gas used for film formation was reduced. , 10 ppb and below, and 100 ppt and below. In order to confirm this effect, the concentration of impurities contained in the Ar gas when forming the ferromagnetic metal layer and the metal underlayer was changed to
The film formation was performed while changing the range together in the range of 10 ppm to 10 ppm.

 The other points were the same as in Example 3.

In FIG. 11, the magnetic characteristics of the manufactured medium are indicated by circles. Figure
The abscissa axis of 11 is for forming the ferromagnetic metal layer and the metal underlayer.
The impurity concentration contained in the Ar gas is shown, and the vertical axis in FIG. 11 is the coercive force Hc in the circumferential direction of the sample at this time. Further, as a comparative example, the results of the conventional medium are indicated by a black circle. However, the concentration of impurities contained in the Ar gas used at the time of manufacturing the conventional medium is 1 ppm or more.

From FIG. 11, it was found that when the concentration of impurities contained in the Ar gas was 10 ppb or less, a medium having a coercive force 30% or more higher than that of the related art was obtained. Further, it is more preferable to set the impurity concentration contained in the Ar gas to 100 ppt or less, since a coercive force higher by 50% or more than that of the conventional art can be realized.

Further, it has been separately confirmed that the above-mentioned effect is effective even when a Co-based alloy layer is provided directly on the surface of the base without using a metal base layer.

(Example 10) In this example, the effect of performing a cleaning process on the surface of the base before forming the metal base layer will be described.
The cleaning method used to confirm this effect,
The procedure is as follows.

(1) The substrate made of the aluminum alloy substrate used in Example 3 was placed in a cleaning processing chamber, and the processing chamber was evacuated to 6 × 10 ⁻⁷ Torr.

(2) The substrate was heated for 5 minutes using an infrared lamp so that the surface temperature of the substrate was 230 ° C.

(3) The impurity concentration is 10
Ar gas of ppb was introduced, and the gas pressure was set to 1 mTorr.

(4) A cleaning process was performed by applying a voltage from an RF power source to the substrate. The condition is power density 2.5W / c
m ² , the cleaning speed was 0.013 nm / sec, and the peeling amount was changed from 0 to 2.4 nm by changing the cleaning time.

(5) Then, as a metal underlayer on the surface of the base,
A Cr film, a CoNiCr film as a ferromagnetic metal layer, and a C film as a protective layer were formed. The film forming conditions were the same as in Example 3.

FIG. 12 shows the relationship between the amount of peeling of the substrate surface due to the cleaning treatment and the coercive force of the manufactured medium. The horizontal axis indicates the cleaning time for the (Ni-P) layer surface, where 130 seconds corresponds to a 2.4 nm peeling amount. The vertical axis indicates the coercive force of the medium at this time, Hc (cir) indicates the coercive force in the circumferential direction of the disk-shaped substrate, and Hc (rad) indicates the value of the coercive force in the radial direction. Indicated. Further, as a comparative example, the coercive force of the medium when the cleaning treatment was performed with Ar gas having an impurity concentration of 20 ppb was also indicated by a black circle and a white circle.

As shown in FIG. 12, the coercive force in the circumferential or radial direction increases when the amount of separation of the substrate surface due to the cleaning treatment is 0.2 nm to 1.0 nm, and the coercive force ratio Hc (cir) / Hc (rad) also increases. Can be changed. 0.3n especially for increasing coercive force
m-0.6 nm has been found to be advantageous.

FIG. 13 shows an X-ray diffraction result of each medium surface at this time.
The crystal structure of the Cr underlayer and the
If the crystal structure of the Co alloy layer changes and the amount of peeling is too large,
This shows that the diffraction peaks of (200) and CoNiCr (110) disappear.

Therefore, it has been found that cleaning the surface of the base by an appropriate amount before the formation of the metal base layer is effective for realizing a high coercive force. This effect is due to other Co-based alloys such as Co _85.5 -Cr _10.5 -Ta ₄ , Co ₇₅
−Cr ₁₃ −Pt ₁₂ , Co ₇₀ −Ni ₂₀ −Pt ₁₀ , Co _82.5 −Ni ₂₆ −Cr _7.5
−Ta ₄ , Co _75.5 −Cr _10.5 −Ta ₄ −Pt ₁₀ Here, the numbers described after each element represent the ratio of the element in (at%). Also, the above effects
It was separately confirmed that the method was effective even when a Co-based alloy layer was provided directly on the surface of the base without using a metal base layer.

(Example 11) In this example, the effect of limiting the impurity concentration of the target used when forming the metal base layer to 150 ppm or less will be described. In order to confirm this effect, the impurity concentration in the target when forming the metal underlayer made of Cr was increased by 50%.
The film was formed in a range of ppm to 300 ppm. At this time, the CoNiCr target used to form the ferromagnetic metal layer had an impurity concentration of 20 ppm. The impurity concentration of Ar gas used for forming the metal underlayer and the ferromagnetic metal layer was 1.5 ppb.

 Other points were the same as in Example 19.

FIG. 14 shows the relationship between the impurity concentration of the target used for forming the metal underlayer and the coercive force of the manufactured medium. The vertical axis indicates the value of the coercive force in the circumferential direction of the disk-shaped substrate.

As shown in FIG. 14, it was found that when the impurity concentration of the target used when forming the metal underlayer was 150 ppm or less, the coercive force of the medium sharply increased.

(Example 12) In this example, an effect of limiting the impurity concentration of a target used in forming a ferromagnetic metal layer to 30 ppm or less will be described. In order to confirm this effect, Co _85.5 -Cr _10.5 -Ta ₄ was used as a target when forming a ferromagnetic metal layer, and the impurity concentration contained in this target was 5 ppm to 20 ppm.
Film formation was performed while changing the range of 0 ppm. At this time, the impurity concentration of the Cr target used to form the metal underlayer is:
It was 120 ppm. The impurity concentration of Ar gas used for forming the metal underlayer and the ferromagnetic metal layer was 1.5 ppb.

 Other points were the same as in Example 19.

FIG. 15 shows the relationship between the impurity concentration of the target used for forming the ferromagnetic metal layer and the coercive force of the manufactured medium. The vertical axis indicates the value of the coercive force in the circumferential direction of the disk-shaped substrate.

As shown in FIG. 15, it was found that when the impurity concentration of the target used in forming the ferromagnetic metal layer was set to 30 ppm or less, the coercive force of the medium rapidly increased.

(Example 13) In this example, the effect of applying a negative bias to the base during the formation of the metal underlayer and / or the ferromagnetic metal layer will be described. In order to confirm this effect, the film was formed by changing the value of the applied bias in the range of 0 to -500 V. In addition, three kinds of combinations of layers produced by applying a bias (only the metal underlayer, only the ferromagnetic metal layer, and both the metal underlayer and the ferromagnetic metal layer) were implemented. At this time, the impurity concentration of the Cr target used to form the metal underlayer is
120 ppm of Co used for forming the ferromagnetic metal layer.
The impurity concentration of the NiCr target was 20 ppm. Also,
Ar used to form the metal underlayer and the ferromagnetic metal layer
The impurity concentration of the gas was 1.5 ppb.

 Other points were the same as in Example 19.

FIG. 16 shows the relationship between the negative bias value applied to the substrate and the coercive force of the manufactured medium. On the vertical axis, the value of the coercive force in the circumferential direction of the disk-shaped substrate is indicated by a circle. As a comparative example, the same evaluation was performed on a conventional medium (when both the oxygen concentration in the CoNiCr film and the oxygen concentration in the Cr film were 260 wtppm). The result is indicated by a black circle in FIG.

As shown in FIG. 16, even when a bias is applied only when each single layer is formed, the coercive force of the medium increases, but it is more preferable that the coercive force can be further increased by applying a bias to both layers. In addition, the value of the applied bias is -100V to -400V.
Is limited to the range of
It was found that a coercive force higher than 10% can be realized.

(Example 14) In this example, the effect of reducing the ultimate vacuum degree of a film formation chamber for forming a metal base layer and / or a ferromagnetic metal layer to 8 × 10 ⁻⁸ Torr or less will be described. In order to confirm this effect, the film was formed by changing the value of the ultimate vacuum of the film forming chamber for forming the metal underlayer and the ferromagnetic metal layer in the range of 3 × 10 ⁻⁹ Torr to 5 × 10 ⁻⁷ Torr. Was done. At this time, it was used to form a metal underlayer.
The impurity concentration of the Cr target was 120 ppm, and the impurity concentration of the CoNiCr target used for forming the ferromagnetic metal layer was 20 ppm. The impurity concentration of the Ar gas used for forming the metal underlayer and the ferromagnetic metal layer is 1.5 p.
pb.

 Other points were the same as in Example 19.

FIG. 17 shows the relationship between the ultimate degree of vacuum in the film formation chamber for forming the metal base layer and the ferromagnetic metal layer and the coercive force of the manufactured medium. The vertical axis indicates the value of the coercive force in the circumferential direction of the disk-shaped substrate.

As shown in FIG. 17, the ultimate vacuum degree is set to 8 × 10 ⁻⁸ Torr.
Under the following, the coercive force increased rapidly. Also, 5 × 10
^-8 Torr or less is more preferable because a high holding power of 2000 Oe or more can be obtained.

Also, when the ultimate vacuum degree of the film formation chamber for forming the metal base layer or the ferromagnetic metal layer was set to 8 × 10 ⁻⁸ Torr or less, an increase in the coercive force was separately confirmed.

(Example 15) In this example, the effect of setting the surface temperature of the substrate to 60 ° C to 150 ° C when forming the metal base layer and / or the ferromagnetic metal layer will be described. In order to confirm this effect, a film was formed by changing the surface temperature of the substrate when forming the metal underlayer and the ferromagnetic metal layer in the range of 25 ° C to 250 ° C. At this time,
The impurity concentration of the Cr target used to form the metal underlayer was 120 ppm, and the impurity concentration of the CoNiCr target used to form the ferromagnetic metal layer was 20 ppm. The impurity concentration of Ar gas used for forming the metal underlayer and the ferromagnetic metal layer was 1.5 ppb. As a substrate, textured N having a surface roughness Ra of 0.7 nm was used.
An iP / Al substrate was used.

 Other points were the same as in Example 19.

FIG. 18 shows the relationship between the surface temperature of the substrate when forming the metal base layer and / or the ferromagnetic metal layer and the coercive force of the manufactured medium. On the vertical axis, the value of the coercive force in the circumferential direction of the disk-shaped substrate is indicated by a circle. Also, as a conventional example, the coercive force when the impurity concentration of the Ar gas used for forming the metal base layer and the ferromagnetic metal layer was set to 20 ppb is indicated by a black mark.

FIG. 19 shows the surface temperature of the substrate when forming the metal underlayer and / or the ferromagnetic metal layer, and the surface roughness Ra of the produced medium.
The relationship was shown.

As shown in FIG. 18, when the above-mentioned surface temperature was set to 60 ° C. or higher, a higher coercive force than the conventional medium was obtained. On the other hand, as shown in FIG. 19, above 150 ° C., the surface roughness Ra of the medium increased. For such media, the flying height of the magnetic head is
When a magnetic head flying test was performed at 15 nm, a phenomenon in which the magnetic head collided with the surface of the medium, that is, a head crash frequently occurred. Also, no head crash occurred when the surface temperature of the base was 60 ° C. to 150 ° C. when forming the metal underlayer or the ferromagnetic metal layer.

Therefore, in order to simultaneously achieve a higher coercive force than before and a low magnetic head flying height of 15 nm or less, the surface temperature of the base when forming the metal underlayer and / or the ferromagnetic metal layer must be 60 ° C. to 150 ° C. It was found that it was necessary to set the temperature to ° C.

In addition, since it is possible to manufacture a medium at a low temperature where a high coercive force cannot be obtained conventionally, it is possible to use a substrate, for example, a ceramic, a plastic, a resin, and the like that could not be used because a gas is generated from the substrate by heating. became.

In the above embodiments, the Ni-P / Al substrate was used as the base, but when a nonmagnetic layer was provided on the surface of the base, for example,
It was confirmed that the method was effective even when using a glass substrate on which Ti, C, etc. were formed.

(Example 16) In this example, the effect of setting the surface roughness Ra of the base to 3 nm or less or 1 nm or less will be described. To see this effect,
The film was formed by changing the value of the surface roughness in the range of 0.5 nm to 7 nm. At this time, the Cr used to form the metal underlayer was used.
The impurity concentration of the target was 120 ppm, and the impurity concentration of the CoNiCr target used for forming the ferromagnetic metal layer was 20 ppm. The impurity concentration of Ar gas used for forming the metal underlayer and the ferromagnetic metal layer is 1.5 ppb.
Met.

 Other points were the same as in Example 19.

FIG. 20 shows the relationship between the surface roughness Ra of the substrate and the coercive force of the manufactured medium. On the vertical axis, the value of the coercive force in the circumferential direction of the disk-shaped substrate is indicated by a circle. Also, as a conventional example, the coercive force when the impurity concentration of the Ar gas used for forming the metal base layer and the ferromagnetic metal layer was set to 20 ppb is indicated by a black mark.

As shown in FIG. 20, by setting the surface roughness Ra of the base to 3 nm or less, a high coercive force of 30% or more was obtained. Also,
Ra of 1 nm or less is more preferable because the coercive force further increases. On the other hand, in the conventional medium, the coercive force decreased rapidly as Ra became smaller.

Therefore, in this example, since a small Ra value for realizing a low flying height of the magnetic head and a high coercive force can be achieved at the same time, a medium suitable for high recording density can be obtained.

(Example 17) In this example, the effect of using a gas used for forming the metal underlayer and / or the ferromagnetic metal layer instead of Ar, (Ar + N ₂ ) or (Ar + H ₂ ) will be described. At this time, the impurity concentration of the Cr target used for forming the metal underlayer was 120 ppm, and the impurity concentration used for forming the ferromagnetic metal layer was 120 ppm.
The impurity concentration of the CoNiCr target was 20 ppm. The impurity concentration of Ar gas used for forming the metal underlayer and the ferromagnetic metal layer was 1.5 ppb.

 Other points were the same as in Example 19.

FIG. 21 shows the ratio of N ₂ gas in (Ar + N ₂ ) gas,
The relationship between the coercive force of the manufactured medium and the coercive force was indicated by a circle. Fig. 22
The relationship between the ratio of the N ₂ gas in the (Ar + H ₂ ) gas and the coercive force of the produced medium is indicated by a circle. As a comparative example, the same evaluation was performed on a conventional medium (when both the oxygen concentration in the CoNiCr film and the oxygen concentration in the Cr film were 260 wtppm). The results are indicated by the black circles in FIGS. 21 and 22.

As shown in FIG. 21, when the ratio of the N ₂ gas in the (Ar + N ₂ ) gas was 0.05 or less, a higher coercive force was obtained than when only the Ar gas was used. As shown in FIG. 22, (Ar
Even when the ratio of H ₂ gas in the + H ₂ ) gas was set to 0.03 or less, a higher coercive force was obtained than when only the Ar gas was used.

Therefore, by using at least one of N ₂ gas and H ₂ gas mixed with Ar gas as the gas used for forming the metal base layer and / or the ferromagnetic metal layer, high recording density can be achieved. A corresponding high coercivity medium can be realized.

INDUSTRIAL APPLICABILITY The magnetic recording medium of the present invention can realize a high coercive force and low medium noise, and can provide a magnetic recording medium that can cope with high recording density.

According to the method of manufacturing a magnetic recording medium of the present invention, the magnetic isolation of the crystal grains in the ferromagnetic metal film is improved, and the coercive force can be increased. Also, since the medium noise is reduced, the recording / reproducing characteristics can be improved. Further, since the ferromagnetic metal film can be manufactured by an inexpensive material that does not contain Pt by an operation with high mass productivity, it is possible to drastically reduce the cost of a magnetic recording medium corresponding to high recording density.

Claims (34)

(57) [Claims] A ferromagnetic metal layer is formed on a surface of a base via a metal underlayer, and in a magnetic recording medium utilizing magnetization reversal, the oxygen concentration of the ferromagnetic metal layer is set to 100 wtppm or less. Magnetic recording medium. 2. A magnetic recording medium utilizing a magnetization reversal, wherein a ferromagnetic metal layer is formed on a surface of a base via a metal underlayer, and the oxygen concentration of the metal underlayer is 100 wtppm or less. Magnetic recording medium. 3. The magnetic recording medium according to claim 2, wherein the oxygen concentration of the ferromagnetic metal layer is 100 wtppm or less. 4. The magnetic recording medium according to claim 1, wherein the ferromagnetic metal layer is a Co-based alloy. 5. The method according to claim 1, wherein the Co-based alloy is CoNiCr, CoCrTa, CoPtCr, C
5. The magnetic recording medium according to claim 4, wherein the magnetic recording medium is one of oPtNi, CoNiCrTa, and CoCrPtTa. 6. The magnetic recording medium according to claim 1, wherein said metal underlayer is Cr. 7. The magnetic recording medium according to claim 1, wherein said metal underlayer has a thickness of 2.5 nm to 100 nm. 8. The magnetic recording medium according to claim 1, wherein said metal underlayer has a thickness of 5 nm to 30 nm. 9. The magnetic recording medium according to claim 1, wherein said ferromagnetic metal layer has a thickness of 2.5 nm to 40 nm. 10. The ferromagnetic metal layer has a thickness of 5 nm to 20 nm.
The magnetic recording medium according to claim 1, wherein: 11. A magnetic recording medium in which a ferromagnetic metal layer is formed on the surface of a substrate, and wherein the ferromagnetic metal layer has an oxygen concentration of 100 wt ppm or less in a magnetic recording medium utilizing magnetization reversal. 12. The magnetic recording medium according to claim 11, wherein said ferromagnetic metal layer is a Co-based alloy. 13. The method according to claim 12, wherein the Co-based alloy is one of CoCr, CoCrTa, and CoPt.
13. The magnetic recording medium according to 12. 14. The magnetic recording medium according to claim 1, wherein a nonmagnetic layer is formed on a surface of the base. 15. A normalized coercive force (Hc / Hc) of said ferromagnetic metal layer.
The magnetic recording medium according to any one of claims 1 to 14, wherein (k ^grain ) is 0.3 or more and less than 0.5. 16. The magnetic recording medium according to claim 1, wherein the base is made of an Al alloy. 17. The magnetic recording medium according to claim 1, wherein the substrate is glass. 18. The magnetic recording medium according to claim 1, wherein said base is made of silicon. 19. A method for manufacturing a magnetic recording medium, comprising forming a metal underlayer and a ferromagnetic metal layer on a surface of a substrate in order by a sputtering method, wherein the impurity concentration of Ar gas used for film formation is 10 ppb or less. A method for manufacturing a magnetic recording medium, comprising: 20. The method according to claim 19, wherein the impurity concentration of the Ar gas is 100 ppt or less. 21. Before the formation of the metal underlayer, the surface of the substrate is subjected to a cleaning treatment by a high frequency sputtering method using an Ar gas having an impurity concentration of 10 ppb or less, so that the surface of the substrate is 21. The method for manufacturing a magnetic recording medium according to claim 19, wherein the magnetic recording medium is removed by 1 nm. 22. The metal underlayer is made of Cr, and the target used for forming the metal underlayer has an impurity concentration of
22. The method for producing a magnetic recording medium according to claim 19, wherein the amount is 150 ppm or less. 23. A method for manufacturing a magnetic recording medium comprising a ferromagnetic metal layer formed on a surface of a substrate by sputtering, wherein the impurity concentration of Ar gas used for film formation is 10 ppb or less. A method for manufacturing a magnetic recording medium. 24. The method according to claim 23, wherein the impurity concentration of the Ar gas is 100 ppt or less. 25. The method according to claim 23, wherein before forming the ferromagnetic metal layer, the surface of the substrate is subjected to a cleaning process by a high frequency sputtering method to remove the surface of the substrate by 0.2 nm to 1 nm. 25. The method for manufacturing a magnetic recording medium according to 24. 26. The method of manufacturing a magnetic recording medium according to claim 19, wherein the target used for forming the ferromagnetic metal layer has an impurity concentration of 30 ppm or less. Method. 27. A magnetic recording medium according to claim 19, wherein a negative bias is applied to said base when said metal underlayer and / or ferromagnetic metal layer is formed. Manufacturing method. 28. The method according to claim 27, wherein the negative bias is between -100 V and -400 V. 29. An apparatus according to claim 19, wherein the ultimate degree of vacuum of the film forming chamber for forming the metal underlayer and / or the ferromagnetic metal layer is 8 × 10 ⁻⁸ Torr or less. 2. The method for manufacturing a magnetic recording medium according to claim 1. 30. A surface temperature of the base when forming the metal base layer and / or the ferromagnetic metal layer is 60 ° C. to 150 ° C.
30. The method of manufacturing a magnetic recording medium according to claim 19, wherein: 31. The method for manufacturing a magnetic recording medium according to claim 19, wherein the base has a non-magnetic layer formed on a surface thereof. 32. The method for manufacturing a magnetic recording medium according to claim 19, wherein the surface roughness Ra of the base is 3 nm or less. 33. The method for manufacturing a magnetic recording medium according to claim 19, wherein the surface roughness Ra of the substrate is 1 nm or less. 34. The gas used for forming the metal underlayer and / or the ferromagnetic metal layer is Ar gas, N ₂ gas, H ₂ gas, or the like.
The method for manufacturing a magnetic recording medium according to any one of claims 19 to 33, wherein at least one of the gases is used as a mixture.