JP5395991B2 - 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.
At present, there is a demand for higher recording density in perpendicular magnetic recording media.

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

In the perpendicular magnetic recording medium used in the perpendicular magnetic recording system, in order to improve the recording density, it is necessary to reduce the magnetization transition region noise of the magnetic recording layer (improve the S / N ratio). For this purpose, it is necessary to improve the grain separation and refinement of the magnetic crystal grains in the magnetic recording layer, the crystal orientation, and the like.

  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. In order to improve crystal orientation and improve characteristics, there is a method of applying a bias when forming a seed layer. However, if a bias is simply applied, the interface with the lower layer (usually a soft magnetic layer) is roughened. This causes a problem that the coercive force Hc decreases. In order to narrow the track width, it is necessary to improve the coercive force of the medium, so a reduction in the coercive force must be avoided.

An object of the present invention is to provide a method of manufacturing a perpendicular magnetic recording medium capable of improving the medium characteristics by improving the orientation and realizing the improvement of the coercive force of the medium.

  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 seed layer, and when the film was formed by applying a bias on the amorphous layer, the interface with the lower layer was roughened. Although the coercive force of the medium is reduced, it has been found that the interface does not become rough even when a film is formed by applying a bias on the crystalline seed layer. It has been found that it is preferable to form a crystalline seed layer by a stepwise film formation process, and the present invention has been completed. That is, this invention has the following structures in order to solve the said subject.

(Configuration 1)
In a perpendicular magnetic recording medium used for information recording in a perpendicular magnetic recording method, the method includes a substrate having at least an amorphous soft magnetic layer, an underlayer, and a magnetic recording layer. First, a crystalline seed layer is formed on the soft magnetic layer or an amorphous seed layer formed on the soft magnetic layer without applying a bias. A method of manufacturing a perpendicular magnetic recording medium, characterized by forming the film by multi-stage film formation while applying a bias.

(Configuration 2)
2. The method for manufacturing a perpendicular magnetic recording medium according to Configuration 1, wherein the crystalline seed layer is made of a material mainly composed of NiW or an alloy thereof.

(Configuration 3)
The crystalline seed layer is formed by two-stage film formation, and a bias is applied in the range of 100V to 500V in the absolute value of the bias voltage during the second-stage film formation. 2. A method for producing a perpendicular magnetic recording medium according to 1.

(Configuration 4)
4. The method for manufacturing a perpendicular magnetic recording medium according to claim 1, wherein a thickness of the crystalline seed layer is in a range of 3 nm to 10 nm.

(Configuration 5)
5. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the multi-stage film formation of the crystalline seed layer is performed in the same chamber of the film forming apparatus by a sputtering method. .

(Configuration 6)
Any one of Structures 1 to 5, wherein the magnetic recording layer includes a crystal layer mainly composed of cobalt (Co) and a granular ferromagnetic layer having a grain boundary portion mainly composed of oxide. 10. A method for producing a perpendicular magnetic recording medium according to item.

(Configuration 7)
The method for manufacturing a perpendicular magnetic recording medium according to any one of Structures 1 to 6, 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 capable of improving the medium characteristics by improving the orientation and realizing the improvement of the coercive force of the medium.

It is a graph which shows the relationship of the coercive force Hc of a medium with respect to the film thickness of the crystalline seed layer in an Example and a comparative example. It is a graph which shows the relationship between Squash and S / N ratio in an Example and a comparative example.

Hereinafter, embodiments of the present invention will be described in detail.
The present invention provides a perpendicular magnetic recording medium used for information recording in the perpendicular magnetic recording system as in Configuration 1, and includes at least an amorphous soft magnetic layer, an underlayer, and a magnetic recording layer on a substrate. First, a crystalline seed layer is biased on the soft magnetic layer or on an amorphous seed layer formed on the soft magnetic layer. It is characterized in that the film is formed by multi-stage film formation in which film formation is performed without applying a voltage, followed by film formation while applying a bias.

As the substrate, a glass substrate is preferably used as described in detail later.
As one embodiment of the layer structure of the perpendicular magnetic recording medium, specifically, for example, an adhesion layer, a soft magnetic layer, a seed layer, an underlayer, a magnetic recording layer (perpendicular magnetic recording layer) from the side close to the substrate. , A protective layer, a lubricating layer, and the like are 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 configured to have AFC (Antiferro-magnetic exchange coupling) by interposing a nonmagnetic spacer layer between the first soft magnetic layer and the second soft magnetic layer. Is preferred. As a result, the magnetization directions of the first soft magnetic layer and the second soft magnetic layer can be aligned antiparallel with high accuracy, and noise generated from the soft magnetic layer can be reduced. Specifically, the composition of the first soft magnetic layer and the second soft magnetic layer is, for example, CoTaZr (cobalt-tantalum-zirconium), CoFeTaZr (cobalt-iron-tantalum-zirconium) or CoFeTaZrAl (cobalt-iron-tantalum- Zirconium-aluminum). The composition of the spacer layer can be, for example, Ru (ruthenium).

  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.

In the method for producing a perpendicular magnetic recording medium of the present invention, an amorphous seed layer is formed on the soft magnetic layer, and a crystalline seed layer is formed on the amorphous seed layer. Film. The crystalline seed layer is formed by multi-stage film formation in which a film is first applied without applying a bias and subsequently formed while applying a bias.

As the amorphous seed layer, for example, a material mainly composed of CrTa or an alloy thereof is preferably used. The thickness of the amorphous seed layer is not particularly limited, but is preferably in the range of about 1 to 10 nm, for example.

As the crystalline seed layer, in the present invention, for example, a material mainly composed of NiW or an alloy thereof is preferably used. The NiW alloy contains at least one element selected from, for example, Al, Cr, Si and the like in NiW.

When the crystalline seed layer is formed by, for example, two-stage film formation, the first stage is formed without applying a bias voltage, and the absolute value of the bias voltage is 100V to It is preferable to form a film while applying a bias in the range of 500V. If the absolute value of the bias voltage is lower than 100 V, the orientation may not be sufficiently improved.

If a film is formed by applying a bias on the amorphous layer, the interface with the lower layer is roughened and the coercive force of the medium is reduced. However, as in the present invention, no bias is applied by multi-stage film formation. Even if a film is formed by applying a bias continuously on the crystalline seed layer formed on the surface, the interface is not roughened, and the effect of improving the orientation by applying the bias and improving the S / N ratio is suitably exhibited. A reduction in coercive force can also be prevented.

  The film thickness of the crystalline seed layer is not particularly limited, but is desirably a minimum film thickness necessary for improving crystal orientation and the like, for example, a total range of about 3 nm to 10 nm. Is appropriate. In order to better demonstrate the effect of the present invention, the film thickness to be formed without applying a bias is in the range of about 2 nm to 5 nm, and the film thickness to be formed with a bias applied is as follows: A range of about 1 nm to 5 nm is preferable.

Further, the multi-stage film formation of the crystalline seed layer can be continuously performed in the same chamber of the film forming apparatus by, for example, a sputtering method.
In the present invention, a crystalline seed layer may be formed directly on the soft magnetic layer without using an amorphous seed layer.

  The underlayer is used for suitably controlling the crystal orientation of the perpendicular magnetic recording layer (orienting the crystal orientation in a direction perpendicular to the substrate surface), crystal grain size, and grain boundary segregation. For example, Ru or an alloy 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.

  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. When the soft magnetic layer is amorphous, it is preferable that the substrate is made of amorphous glass. 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.

Further, the perpendicular magnetic recording layer includes crystal grains mainly composed of cobalt (Co) and grain boundary portions mainly composed of oxide or Si, Ti, Cr, Co or Si, Ti, Cr, Co oxide. It is preferable to include a ferromagnetic layer having a granular structure having
Specifically, as the Co-based magnetic material constituting the ferromagnetic layer, a hard magnetic target made of CoCrPt (cobalt-chromium-platinum) containing silicon oxide, titanium oxide (TiO ₂ ), etc., which are non-magnetic substances. A material that molds the hcp crystal structure is desirable. Moreover, it is preferable that the film thickness of this ferromagnetic layer is 20 nm or less, for example.

Further, by providing the auxiliary recording layer above the perpendicular magnetic recording layer via the exchange coupling control layer, high heat resistance can be added in addition to the high density recording property and low noise property of the magnetic recording layer. The composition of the auxiliary recording layer can be, for example, CoCrPtB

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 65 mm. 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 2.18 nm and Ra of 0.18 nm. Rmax and Ra conform to Japanese Industrial Standard (JIS).

Next, an adhesion layer, a soft magnetic layer, and a non-magnetic layer are sequentially formed on the obtained glass substrate by a DC magnetron sputtering method using a film forming apparatus that has been evacuated (degree of ultimate vacuum: 10 ⁻⁵ Pa or less). A crystalline seed layer, a crystalline seed layer, an underlayer, and a magnetic recording layer were formed.

First, a 10 nm CrTi layer was formed as an adhesion layer.
Next, as a soft magnetic layer, a laminated film of two soft magnetic material layers that are antiferromagnetic exchange coupled with a nonmagnetic layer interposed therebetween was formed. That is, first, a 24 nm amorphous FeCoTaZr layer is formed as the first soft magnetic material layer, then a 0.55 nm Ru layer is formed as the nonmagnetic layer, and then the second soft magnetic material layer is formed. As the layer, the same amorphous FeCoTaZr layer as the first soft magnetic material layer was formed to a thickness of 24 nm.

Next, a 2 nm CrTa layer was formed as an amorphous seed layer on the soft magnetic layer. A 4 to 7 nm NiW layer was formed as a crystalline seed layer on the amorphous seed layer. This crystalline seed layer is composed of a two-stage film formation process. In the first stage, 3 nm is formed without applying a bias, and in the second stage, 1 to 4 nm is formed with a bias of −500 V applied. Filmed.

Next, two Ru layers were formed as an underlayer. The upper layer (second layer) was made of oxide-containing RuTiO2. The film thicknesses of the first and second Ru layers were 10 nm and 8 nm, respectively. Note that the gas pressure of the sputtering gas at the time of forming the first layer was made smaller than the gas pressure of the sputtering gas at the time of forming the second layer.

Next, a magnetic recording layer was formed on the underlayer. First, a 1.7 nm CoCrPtCr2O3 film was formed as the first recording layer, and an 8.5 nm CoCrPt-SiO2-TiO2-CoO film was subsequently formed as the second recording layer. Next, a 0.3 nm Ru layer was formed as a nonmagnetic layer, and a 6.8 nm CoCrPtB layer was formed as an auxiliary recording layer thereon.

Next, a carbon-based protective layer made of hydrogenated diamond-like carbon was formed on the magnetic recording layer by a CVD method. 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 was obtained.

(Comparative Example 1)
A perpendicular magnetic recording medium of Comparative Example 1 was fabricated in the same manner as in Example 1, except that the crystalline seed layer in Example 1 was formed as a single layer without applying a bias.

(Comparative Example 2)
A perpendicular magnetic recording medium of Comparative Example 2 was fabricated in the same manner as in Example 1, except that a single layer was formed by applying a bias of −500 V when the crystalline seed layer in Example 1 was formed. did.

(Evaluation)
The following evaluations were performed using the perpendicular magnetic recording media of the above examples and comparative examples.
That is, the coercive force (Hc) was measured by evaluating the magnetostatic characteristics by the Kerr effect for each of the perpendicular magnetic recording media of Example 1 and Comparative Examples 1 and 2. The recording / reproduction characteristics were evaluated by measuring the relationship between Squash and the S / N ratio (signal / noise ratio) using an R / W analyzer and a magnetic head for perpendicular magnetic recording. Squash is a value that serves as an evaluation index of the signal decrease rate due to the influence of adjacent tracks.Specifically, the frequency is 5% at both sides of the written signal, at a position of about 80% of the track width. A signal shifted by a certain degree is written, and then the output of the first written signal is measured and calculated at the rate of change.

  FIG. 1 is a graph of the coercivity Hc of a medium with respect to the film thickness of a crystalline seed layer. According to the result of FIG. 1, the medium of Example 1 in which the crystalline seed layer was formed by the two-stage film formation with no bias applied in the first stage and the bias applied in the second stage had the highest coercive force. It can be seen that it has Hc. This is presumably because the first stage without bias application suppressed the roughness of the interface with the lower layer, and the second stage film formation with bias applied was suitably performed without loss.

  FIG. 2 shows the result of measuring the relationship between Squash and the S / N ratio (signal / noise ratio). Here, Squash indicates that the larger the value is on the right side of the graph, the smaller the signal decrease due to the influence from the adjacent track. In addition, as the S / N ratio is larger and the value is higher in the graph, the noise is less. Note that the points plotted in FIG. 2 are when the film thickness of the crystalline seed layer is 5 nm and 7 nm.

  According to the result of FIG. 2, it can be confirmed that the medium of Example 1 and Comparative Example 2 with bias application has a large and excellent S / N ratio compared to the medium of Comparative Example 1 without bias application. This is considered to be due to an improvement in orientation by bias application. Moreover, regarding Squash, it can be confirmed that the medium of Example 1 has a larger value than the medium of Comparative Example 1 and Comparative Example 2 and is a good result. This is considered to be due to the high coercive force Hc of the medium of Example 1. However, if the reason is further investigated, it is considered that it is due to the suppression of the roughening of the interface by the two-stage film formation and the improvement of the orientation.

As described above, as in the embodiment of the present invention, the crystalline seed layer is formed without applying a bias first, and then formed with applying a bias. In Example 1, it is formed by two-stage film formation). It is possible to obtain a perpendicular magnetic recording medium that can improve the medium characteristics by improving the orientation and can also improve the coercive force of the medium.

Claims (7)

A perpendicular magnetic recording medium used for information recording in a perpendicular magnetic recording system,
In a method for manufacturing a perpendicular magnetic recording medium comprising at least an amorphous soft magnetic layer, an underlayer and a magnetic recording layer on a substrate,
A crystalline seed layer is first formed without applying a bias on the soft magnetic layer or on an amorphous seed layer formed on the soft magnetic layer, and subsequently a bias is applied. A method of manufacturing a perpendicular magnetic recording medium, characterized in that the film is formed by multi-stage film formation in which film formation is performed while applying a magnetic field.   2. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the crystalline seed layer is made of a material mainly composed of NiW or an alloy thereof.   The crystalline seed layer is formed by two-stage film formation, and a bias is applied in the range of 100 V to 500 V in the absolute value of the bias voltage during the second-stage film formation. 3. A method for producing a perpendicular magnetic recording medium according to 2.   4. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein a film thickness of the crystalline seed layer is in a range of 3 nm to 10 nm.   5. The perpendicular magnetic recording medium manufacturing according to claim 1, wherein the multi-stage film formation of the crystalline seed layer is performed in a same chamber of a film forming apparatus by a sputtering method. Method.   6. 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. A method of manufacturing a perpendicular magnetic recording medium according to one item. The method for manufacturing a perpendicular magnetic recording medium according to claim 1, wherein a carbon-based protective layer is formed on the magnetic recording layer.

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