JP5455188B2 - Method for manufacturing perpendicular magnetic recording medium - Google Patents

Description

  The present invention relates to a method for manufacturing a perpendicular magnetic recording medium mounted on a magnetic disk apparatus such as a perpendicular magnetic recording type HDD (hard disk drive).

  Various information recording techniques have been developed with the recent increase in information processing capacity. In particular, the surface recording density of an HDD (hard disk drive) using magnetic recording technology continues to increase at an annual rate of about 100%. Recently, an information recording capacity exceeding 250 Gbytes has been required for a 2.5 inch diameter magnetic disk used for HDDs and the like. In order to meet such a requirement, one square inch is required. It is required to realize an information recording density exceeding 400 Gbits per unit. In order to achieve a high recording density in a magnetic disk used for an HDD or the like, it is necessary to refine the magnetic crystal particles constituting the magnetic recording layer for recording information signals and to reduce the layer thickness. It was. However, in the case of magnetic disks of the in-plane magnetic recording method (also called longitudinal magnetic recording method or horizontal magnetic recording method) that have been commercialized conventionally, as a result of the progress of miniaturization of magnetic crystal grains, superparamagnetic phenomenon The thermal stability of the recording signal is impaired, the recording signal disappears, and a thermal fluctuation phenomenon occurs, which has been an impediment to increasing the recording density of the magnetic disk.

  In order to solve this obstruction factor, in recent years, a magnetic disk for perpendicular magnetic recording has been proposed. In the case of the perpendicular magnetic recording system, unlike the case of the in-plane magnetic recording system, the easy axis of magnetization of the magnetic recording layer is adjusted to be oriented in the direction perpendicular to the substrate surface. The perpendicular magnetic recording method can suppress the thermal fluctuation phenomenon as compared with the in-plane recording method, and is suitable for increasing the recording density. For example, Japanese Patent Laid-Open No. 2002-92865 (Patent Document 1) discloses a technique relating to a perpendicular magnetic recording medium in which a soft magnetic layer, an underlayer, a Co-based perpendicular magnetic recording layer, a protective layer, and the like are formed in this order on a substrate. Is disclosed. In addition, US Pat. No. 6,686,670 (Patent Document 2) discloses a perpendicular magnetic recording medium having a structure in which an artificial lattice film continuous layer (exchange coupling layer) exchange-coupled to a particulate recording layer is attached. ing.

JP 2002-92865 A US Pat. No. 6,468,670

  In a conventional perpendicular magnetic recording medium, an underlayer for appropriately controlling the orientation of the magnetic recording layer is introduced under the magnetic layer. For example, a Ru layer is used as the base layer. Therefore, it is necessary to suitably control the orientation of the Ru underlayer. That is, the c-axis of the Ru layer having a close-packed hexagonal crystal (hcp) structure must be oriented in the direction perpendicular to the film surface. For this purpose, conventionally, the orientation of the Ru layer is controlled by providing another underlayer between the soft magnetic layer on the substrate and the Ru underlayer. The other underlayer is generally called a seed layer. For the conventional seed layer, NiW alloy, CoCr alloy or the like is mainly used. Up to now, it has been known that when the Ru underlayer is formed directly on the soft magnetic layer without providing such a seed layer, the c-axis normal orientation of the Ru underlayer is greatly deteriorated. Yes. Therefore, it has been difficult to control the orientation of the Ru underlayer without using a seed layer.

In view of such a conventional situation, the present invention enables suitable orientation control of the Ru underlayer without providing a seed layer that has been essential in the past, and omits the seed layer, thereby shortening the manufacturing process and cost. It is an object of the present invention to provide a method of manufacturing a perpendicular magnetic recording medium that can realize reduction.

  As a result of intensive studies to solve the above-described conventional problems, the present inventor paid attention to the film formation conditions of the Ru underlayer and applied a predetermined bias when forming the Ru underlayer without the seed layer. It has been found that a Ru underlayer whose orientation is suitably controlled can be obtained directly on the soft magnetic layer, and the present invention has been completed. That is, this invention has the following structures in order to solve the said subject.

(Configuration 1)
A magnetic recording medium for use in perpendicular magnetic recording, comprising: at least a soft magnetic layer, an underlayer, and a magnetic recording layer on a substrate. A method of manufacturing a perpendicular magnetic recording medium, comprising forming a base layer made of ruthenium (Ru) or a compound thereof on a soft magnetic layer while directly applying a bias without passing through another layer.

(Configuration 2)
The underlayer is composed of a plurality of layers, and at least the underlayer made of ruthenium (Ru) or a compound thereof on the soft magnetic layer side is formed while applying a bias. A method of manufacturing a perpendicular magnetic recording medium.

(Configuration 3)
3. The method of manufacturing a perpendicular magnetic recording medium according to Configuration 1 or 2, wherein a bias of −50 V or more is applied to the substrate when forming the base layer made of ruthenium (Ru) or a compound thereof.

(Configuration 4)
The magnetic recording layer includes a ferromagnetic layer having a granular structure having crystal grains mainly composed of cobalt (Co) and a grain boundary portion mainly composed of oxide. 10. A method for producing a perpendicular magnetic recording medium according to item.

(Configuration 5)
5. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein a carbon-based protective layer is formed on the magnetic recording layer.

  According to the present invention, it is possible to provide a method of manufacturing a perpendicular magnetic recording medium that enables suitable orientation control of a Ru underlayer without providing a seed layer that has been conventionally required. Further, it is possible to provide a perpendicular magnetic recording medium that can shorten the manufacturing process and reduce the cost by omitting the seed layer.

It is a figure which shows the layer structure of the Example of the perpendicular magnetic recording medium based on this invention. It is a figure which shows the measurement result of the crystal orientation degree of Ru base layer with respect to a bias applied voltage.

Hereinafter, embodiments of the present invention will be described in detail.
The present invention provides a magnetic recording medium used for perpendicular magnetic recording as in Configuration 1, wherein the perpendicular magnetic recording medium comprises at least a soft magnetic layer, an underlayer, and a magnetic recording layer on a substrate. After forming the soft magnetic layer, a base layer made of ruthenium (Ru) or a compound thereof is formed on the soft magnetic layer while directly applying a bias without passing through another layer. Is.

As the substrate, a glass substrate is preferably used as described in detail later.
As one embodiment of the layer configuration of the perpendicular magnetic recording medium, specifically, for example, an adhesion layer, a soft magnetic layer, an underlayer, a magnetic recording layer (perpendicular magnetic recording layer), and a protective layer from the side close to the substrate In addition, a lubricating layer or the like is laminated.

  It is preferable to provide a soft magnetic layer on the substrate for suitably adjusting the magnetic circuit of the perpendicular magnetic recording layer. The soft magnetic layer is not particularly limited as long as it is made of a magnetic material having a soft magnetic property and a large saturation magnetic flux density. For example, the coercive force (Hc) is 0.01 to 80 oersted, preferably 0.01 to 50 oersted. Preferably it is a characteristic. The saturation magnetic flux density (Bs) preferably has a magnetic characteristic of 500 emu / cc to 1920 emu / cc. Examples of soft magnetic layers and materials include Fe-based and Co-based alloys. For example, Fe-based soft magnetic materials such as FeTaC-based alloys, FeTaN-based alloys, FeNi-based alloys, FeCoB-based alloys and FeCo-based alloys, Co-based soft magnetic materials such as CoTaZr-based alloys and CoNbZr-based alloys, or FeCo-based alloy soft magnetic materials Materials and the like can be used.

  The soft magnetic layer may have a multilayer structure in order to suppress the formation of a domain wall. For example, there is a structure in which a thin film layer (spacer) made of a nonmagnetic material such as Ru is provided between two soft magnetic layers and the magnetization is pinned using antiferromagnetic coupling.

  The underlayer is used to suitably control the crystal orientation of the perpendicular magnetic recording layer (the crystal orientation is oriented in the direction perpendicular to the substrate surface), the crystal grain size, and the grain boundary segregation. For example, Ru or a compound thereof is preferably used as the material for the underlayer. In the case of Ru, the effect of controlling the crystal axis (c axis) of the CoPt-based perpendicular magnetic recording layer having the hcp crystal structure to be oriented in the perpendicular direction is high and suitable.

  In the present invention, for example, the underlayer made of Ru or a compound thereof is formed by sputtering on the soft magnetic layer while directly applying a bias without using another layer such as a conventional seed layer. By forming a film of Ru or the like while applying a bias, the surface roughness of the soft magnetic layer is improved, and Ru (0002) can be favorably grown in the direction perpendicular to the surface. That is, by applying a predetermined bias at the time of forming an underlayer such as Ru, it is possible to obtain an underlayer such as Ru whose orientation is suitably controlled directly on the soft magnetic layer without a seed layer. The Ru compound forming the underlayer is preferably an Ru alloy, such as Ru—Co or Ru—Cr.

  In the present invention, the bias voltage applied to the substrate during the formation of the underlying layer of Ru or the like is preferably −50 V or more, more preferably −300 V to −500 V. If the bias voltage is lower than −50 V, the orientation control of the Ru underlayer may not be sufficiently achieved. On the other hand, even if the bias voltage is higher than −500 V, there is no significant change in the orientation controllability of the Ru underlayer, and there is a risk of film deterioration.

  In addition, the underlayer can have a plurality of layers. In this case, it is possible to combine different materials as well as combinations of the same materials, but in the present invention, it is preferable to combine the same Ru materials.

  When the underlayer is composed of a plurality of layers, it is preferable to form the underlayer made of Ru or the like on at least the lowermost soft magnetic layer side while applying a bias. The preferable bias voltage range is the same as that of the base layer made of a single layer of Ru or the like. It should be noted that it is not essential to apply a bias at the time of film formation for the base layer other than the bottom base layer formed directly on the soft magnetic layer.

  In the present invention, the film thickness of the underlayer made of Ru or a compound thereof is preferably the minimum film thickness necessary for controlling the crystal orientation of the magnetic recording layer, but for example, 20 nm to A thickness of about 40 nm is preferable. In the case where the underlayer is composed of a plurality of layers, each layer may have a slight difference, but it is preferable that the thicknesses are substantially the same.

  It is also preferable to form an adhesion layer (adhesion layer) between the substrate and the soft magnetic layer. By forming the adhesion layer, the adhesion between the substrate and the soft magnetic layer can be improved, so that the soft magnetic layer can be prevented from peeling off. As a material for the adhesion layer, for example, a Ti-containing material can be used.

  Examples of the substrate glass include aluminosilicate glass, aluminoborosilicate glass, soda time glass, and the like. Among these, aluminosilicate glass is preferable. Amorphous glass and crystallized glass can also be used. Use of chemically strengthened glass is preferable because of its high rigidity. In the present invention, the surface roughness of the main surface of the substrate is preferably 10 nm or less in terms of Rmax and 0.3 nm or less in terms of Ra.

In addition, the magnetic recording layer preferably includes a ferromagnetic layer having a granular structure having crystal grains mainly composed of cobalt (Co) and a grain boundary portion mainly composed of oxide.
As the Co-based magnetic material constituting the ferromagnetic layer, a CoPt-based or CoPtCr-based magnetic material is particularly preferable. CoPt-based or CoPtCr-based magnetic materials have high coercive force Hc, and the magnetization reversal generation magnetic field Hn can be set to a small value of less than zero, so that resistance to thermal fluctuation can be improved and a high S / N ratio can be obtained. Therefore, it is preferable. By incorporating elements such as silicon (Si) and Ti and oxides thereof into CoPt or CoPtCr magnetic materials, Si, Ti and oxides thereof can be segregated at the grain boundary portions of the magnetic crystal grains. In addition, the exchange interaction between the magnetic crystal grains can be reduced to reduce the medium noise and improve the S / N ratio at a high recording density. The film thickness of this ferromagnetic layer is preferably 20 nm or less, for example.

  Further, it is preferable to provide an auxiliary recording layer having a function of optimizing recording / reproducing characteristics adjacent to the perpendicular magnetic recording layer or via an exchange coupling control layer. For the ferromagnetic layer made of a Co-based magnetic material, the auxiliary recording layer is specifically made of a cobalt (Co) -containing alloy and may be composed of a plurality of layers. For example, it is preferably made of a CoCrPt alloy or the like.

It is preferable that an exchange coupling control layer is provided between the perpendicular magnetic recording layer and the auxiliary recording layer. By providing the exchange coupling control layer, the strength of exchange coupling between the perpendicular magnetic recording layer and the auxiliary recording layer can be suitably controlled to optimize the recording / reproducing characteristics. For example, Ru is preferably used as the exchange coupling control layer.

As a method for forming the perpendicular magnetic recording layer including the ferromagnetic layer, it is preferable to form the film by sputtering. In particular, the DC magnetron sputtering method is preferable because uniform film formation is possible.

Moreover, it is preferable to provide a protective layer on the perpendicular magnetic recording layer. By providing the protective layer, the surface of the magnetic disk can be protected from the magnetic head flying over the magnetic recording medium. As a material for the protective layer, for example, a carbon-based protective layer is suitable. Further, the thickness of the protective layer is preferably about 3 to 7 nm.

  It is also preferable to further provide a lubricating layer on the protective layer. By providing the lubricating layer, wear between the magnetic head and the magnetic disk can be suppressed, and the durability of the magnetic disk can be improved. As a material for the lubricating layer, for example, a PFPE (perfluoropolyether) compound is preferable. The lubricating layer can be formed by, for example, a dip coating method.

Hereinafter, the embodiment of the present invention will be described more specifically with reference to examples and comparative examples.
Example 1
Amorphous aluminosilicate glass was molded into a disk shape with a direct press to create a glass disk. The glass disk was ground, polished, and chemically strengthened in order to obtain a smooth nonmagnetic glass substrate made of the chemically strengthened glass disk. The disc diameter is 65mm. When the surface roughness of the main surface of this glass substrate was measured by AFM (Atomic Force Microscope), it was a smooth surface shape with Rmax of 4.8 nm and Ra of 0.42 nm. Rmax and Ra conform to Japanese Industrial Standard (JIS).

Next, an adhesion layer and a first soft magnetic layer are sequentially formed on the obtained glass substrate by a DC magnetron sputtering method using a vacuum-deposited film forming apparatus (degree of vacuum 10 ⁻⁵ Pa or less). The nonmagnetic spacer layer, the second soft magnetic layer, the first underlayer, the second underlayer, the onset layer, the first magnetic layer, the second magnetic layer, the exchange coupling layer, and the continuous layer were formed. .

First, a 10 nm CrTi layer was formed as an adhesion layer.
Next, as the first soft magnetic layer, FeCoTaZr was deposited to 25 nm, as the nonmagnetic spacer layer, the Ru layer was 0.7 nm, and as the second soft magnetic layer, FeCoTaZr was deposited to 25 nm.

Next, two Ru layers (each 12 nm) were formed as a base layer. During the formation of the first underlayer, which was formed immediately above the second soft magnetic layer, the film was formed while applying a bias of −500 V to the substrate. For the second underlayer thereabove, no bias was applied during film formation.
On the second underlayer, a CoCr film was formed at 2 nm or less as an onset layer.

Furthermore, as a perpendicular magnetic recording layer, CoCrPtCr2O3 is 2 nm (first magnetic layer), CoCrPt-SiO2-TiO2 is 8 nm (second magnetic layer), and an exchange coupling (control) layer is Ru of 0.3 nm continuously. As a layer (auxiliary recording layer), a CoCrPtB film having a thickness of 7 nm was formed.

  Next, a carbon-based protective layer made of hydrogenated diamond-like carbon was formed on the perpendicular magnetic recording layer by plasma CVD using ethylene gas. The film thickness of the carbon-based protective layer was 5 nm. Thereafter, a lubricating layer made of PFPE (perfluoropolyether) was formed by a dip coating method. The thickness of the lubricating layer was 1 nm.

Through the above manufacturing process, the perpendicular magnetic recording medium of Example 1 having the layer configuration shown in FIG. 1 was obtained.

(Example 2)
A perpendicular magnetic recording medium of Example 2 was fabricated in exactly the same manner as in Example 1 except that the applied bias at the time of forming the first underlayer in Example 1 was −300 V.

(Example 3)
A perpendicular magnetic recording medium of Example 3 was manufactured in the same manner as in Example 1 except that the applied bias at the time of forming the first underlayer in Example 1 was set to −100V.

(Comparative example)
A perpendicular magnetic recording medium of this comparative example was fabricated in exactly the same manner as in Example 1, except that the first underlayer in Example 1 was formed without applying a bias.

The following evaluations were performed using the perpendicular magnetic recording media of the above examples and comparative examples.
[Evaluation of crystal orientation]
The Ru crystal orientation degree of the first underlayer in each perpendicular magnetic recording medium was measured by an X-ray diffractometer, and the result is shown in FIG.

  From the results shown in FIG. 2, in the perpendicular magnetic recording medium of the comparative example in which the first Ru underlayer was directly formed on the soft magnetic layer without applying a bias, the index of orientation dispersion in the perpendicular direction of the Ru crystal grains It can be seen that the Δθ50 value (unit is “degree”) is large, the crystal orientation is insufficient, and the orientation is not controlled appropriately. In contrast, the perpendicular magnetic recording medium of Example 1 in which the first Ru underlayer was directly formed on the soft magnetic layer while applying a bias of -500 V, and the first Ru underlayer was applied with a bias of -300 V. In each of the perpendicular magnetic recording media of Example 2 formed directly on the soft magnetic layer while being applied, the Δθ50 value was greatly reduced as compared with the comparative example, and a Ru underlayer having a suitably controlled orientation was obtained. You can see that In addition, in the perpendicular magnetic recording medium of Example 3 in which the first Ru underlayer was directly formed on the soft magnetic layer while applying a bias of −100 V, the reduction in Δθ50 value was small compared to Examples 1 and 2. .

According to the present invention, a seed layer made of Ru or an alloy thereof is formed on a soft magnetic layer while applying a bias directly, whereby a seed layer that has been conventionally essential for the crystal orientation of the Ru underlayer is formed. Even if it is not provided, it is possible to obtain a perpendicular magnetic recording medium in which the Ru underlayer is suitably controlled in orientation. In addition, by omitting the seed layer, the manufacturing process can be shortened and the cost can be reduced.

Claims (4)

A magnetic recording medium used for perpendicular magnetic recording,
In a method for manufacturing a perpendicular magnetic recording medium comprising at least a soft magnetic layer, an underlayer, and a magnetic recording layer on a substrate,
After forming the soft magnetic layer, a plurality of underlayers are formed directly on the soft magnetic layer without any other layers, and at least the ruthenium (at the soft magnetic layer side) A method for producing a perpendicular magnetic recording medium, comprising forming a base layer made of Ru) or a compound thereof while applying a bias . 2. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein a bias of −50 V or more is applied to the substrate during the formation of the base layer made of ruthenium (Ru) or a compound thereof. The magnetic recording layer is comprised of cobalt and crystal grains mainly composed of (Co), according to claim 1 or 2, characterized in that it comprises a ferromagnetic layer of a granular structure having grain boundary mainly composed of oxide A method of manufacturing a perpendicular magnetic recording medium. A method of manufacturing a perpendicular magnetic recording medium according to any one of claims 1 to 3, characterized in that to form a carbon-based protective layer on the magnetic recording layer.

Images