JP2010231862A - Method for manufacturing magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a magnetic disk having superior magnetic characteristics and reliability characteristics, despite the low floating height of a magnetic head accompanying rapid increase of recording density in recent years and very severe environment resistance required, accompanying the diversified uses. <P>SOLUTION: In the method for manufacturing the magnetic disk having at least a magnetic layer and a protective layer disposed on a substrate, the protective layer is deposited using a plasma CVD method, and a deposition condition of the protective layer is set, in such a way that the hydrogen content in the magnetic layer, as measured with a recoil molecular scattering method, becomes an allowable value, and the protective layer is formed based on the set deposition condition. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a method of manufacturing a magnetic disk mounted on a magnetic disk device such as a hard disk drive (hereinafter abbreviated as HDD).

Various information recording techniques have been developed with the recent increase in information processing capacity. In particular, the surface recording density of HDDs using magnetic recording technology continues to increase at an annual rate of about 100%. Recently, an information recording capacity exceeding 250 Gbytes for a 2.5-inch diameter magnetic disk used for an HDD or the like has been demanded. 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 hindrance factor, in recent years, a magnetic recording medium 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. As such a perpendicular magnetic recording medium, for example, as described in JP-A-2002-74648, a soft magnetic underlayer made of a soft magnetic material and a perpendicular magnetic recording layer made of a hard magnetic material are provided on a substrate. A so-called double-layered perpendicular magnetic recording disk is known.

By the way, in the conventional magnetic disk, in order to ensure the durability and reliability of the magnetic disk, a protective layer and a lubricating layer are provided on the magnetic recording layer formed on the substrate (for example, Patent Document 1). ).

JP 2000-282238 A

As described above, an information recording density of 400 Gbit / inch ² or more has been required in recent HDDs. However, in order to effectively use a limited disk area, an HDD start / stop mechanism has been conventionally used. Instead of the CSS (Contact Start and Stop) method, a LUL (Load Unload) type HDD has been used. In the LUL method, when the HDD is stopped, the magnetic head is retracted to a ramp called a ramp located outside the magnetic disk, and during the start-up operation, after the magnetic disk starts rotating, the magnetic head is moved from the ramp onto the magnetic disk. Slide and fly to record and playback. During the stop operation, the magnetic head is retracted to the ramp outside the magnetic disk, and then the rotation of the magnetic disk is stopped. This series of operations is called LUL operation. The magnetic disk mounted on the LUL type HDD does not need to provide a contact sliding area (CSS area) with the magnetic head as in the CSS type, and the recording / reproducing area can be enlarged, which increases the information capacity. It is because it is preferable.

In order to improve the information recording density under such circumstances, it is necessary to reduce the spacing loss as much as possible by reducing the flying height of the magnetic head. In order to achieve an information recording density of 400 Gbits or more per square inch, the flying height of the magnetic head needs to be at least 5 nm. Unlike the CSS method, the LUL method does not require a concave / convex shape for CSS on the magnetic disk surface, and the magnetic disk surface can be extremely smoothed. Therefore, in the magnetic disk mounted on the LUL type HDD, the flying height of the magnetic head can be further reduced as compared with the CSS type, so that the S / N ratio of the recording signal can be increased, and the magnetic disk apparatus There is also an advantage that the recording capacity can be increased.

Due to a further decrease in the flying height of the magnetic head accompanying the recent introduction of the LUL system, it has been required that the magnetic disk operate stably even at an ultra-low flying height of 5 nm or less. In particular, as described above, in recent years, the magnetic disk has shifted from the in-plane magnetic recording system to the perpendicular magnetic recording system, and there is a strong demand for an increase in the capacity of the magnetic disk and a reduction in flying height associated therewith.

Recently, magnetic disk devices are not only used as storage devices for conventional personal computers, but are also widely used in mobile applications such as mobile phones and car navigation systems. As a result, the environmental resistance required for magnetic disks has become very severe. Therefore, in view of these situations, further improvement in the stability and reliability of the magnetic disk is urgently required than before.

Incidentally, the protective layer of a magnetic disk is generally often formed by a plasma CVD method. However, in the film formation process by the plasma CVD method, it is expected that hydrogen is generated by the decomposition of the source gas, and this hydrogen is taken into the protective layer and the magnetic layer of the magnetic disk. In the protective layer, an appropriate amount of hydrogen is desirable because the film quality of the protective layer can be improved. However, if the hydrogen content exceeds that, it is considered that the reliability characteristics of the magnetic disk are affected. Further, it is considered that when hydrogen penetrates and is taken into the magnetic layer, the magnetic properties are affected. Conventionally, however, there is no means for analyzing the hydrogen content in the depth direction, and what is the specific amount of hydrogen incorporated in the protective layer and magnetic layer of the magnetic disk, which is the magnetic property of the magnetic disk. The current situation is that everyone has no idea how much the reliability characteristics are affected. Conventionally, an analysis method by Rutherford backscattering is known, but this method cannot detect hydrogen contained in the film.

The present invention has been made in view of such a conventional situation. The object of the present invention is to reduce the flying height of a magnetic head with the recent rapid increase in recording density and diversify the applications. It is an object of the present invention to provide a method of manufacturing a magnetic disk having good magnetic characteristics and reliability characteristics under the extremely severe environmental resistance accompanying the above.

As a result of intensive studies, the present inventor has found that the above-described problems can be solved by the following invention, and completed the present invention.
That is, the present invention has the following configuration.
(Configuration 1)
A method of manufacturing a magnetic disk in which at least a magnetic layer and a protective layer are provided on a substrate, wherein the hydrogen content in the magnetic layer measured using a recoil molecular scattering method is an allowable value of 7 atomic% or less. The method for manufacturing a magnetic disk is characterized in that the film forming conditions for the protective layer are set as described above, and the protective layer is formed according to the set film forming conditions.

(Configuration 2)
For a magnetic disk whose film formation conditions for the protective layer are known in advance, the hydrogen content in the magnetic layer is measured using a recoil molecular scattering method, and an allowable value for the hydrogen content in the magnetic layer is set. 2. The method of manufacturing a magnetic disk according to claim 1, wherein a film forming condition of the protective layer is set so as to satisfy the set allowable value.

(Configuration 3)
The method for manufacturing a magnetic disk according to claim 1, wherein the protective layer is a carbon-based protective layer formed by a plasma CVD method.

(Configuration 4)
4. The method of manufacturing a magnetic disk according to claim 2, wherein the protective layer deposition conditions are set by controlling the substrate heating temperature before deposition and / or the gas flow rate.

(Configuration 5)
The magnetic layer includes at least a perpendicular magnetic recording layer and an auxiliary recording layer provided thereon, and the film forming conditions of the protective layer are set so that the hydrogen content in the auxiliary recording layer becomes an allowable value. The method of manufacturing a magnetic disk according to claim 1, wherein the magnetic disk is manufactured as follows.

(Configuration 6)
6. The method of manufacturing a magnetic disk according to claim 1, wherein the start / stop mechanism is a magnetic disk mounted on a load / unload type magnetic disk device.

According to the present invention, the hydrogen content in the magnetic layer can be monitored, and the film formation conditions of the protective layer can be optimized so that this becomes an allowable value, so that the hydrogen content can be suitably controlled. Magnetic disks with good magnetic characteristics and reliability characteristics under the low flying height of magnetic heads due to the rapid increase in recording density and extremely severe environmental resistance due to diversification of applications. Obtainable.

Hereinafter, the present invention will be described in detail by embodiments.
First, an outline of the magnetic disk will be described.

  For example, as a layer structure of a perpendicular magnetic recording disk effective for increasing the recording density, 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. Layer), a protective layer, a lubricating layer, and the like.

Examples of the glass for a substrate include aluminosilicate glass, aluminoborosilicate glass, soda time glass, and aluminosilicate glass is preferred. 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 1 nm or less in terms of Rmax and 0.3 nm or less in terms of Ra.

It is preferable to provide a soft magnetic layer on the substrate for suitably adjusting the magnetic circuit of the perpendicular magnetic recording layer. Such a 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).
The film thickness of the soft magnetic layer varies depending on the structure and the structure and characteristics of the magnetic head, but is preferably 15 nm to 100 nm as a whole. The thickness of the upper and lower layers may be slightly different for the purpose of optimizing recording / reproduction, but it is desirable that the thicknesses be approximately the same.

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

The seed layer is used to control the orientation and crystallinity of the underlayer. When all the layers are continuously formed, it may not be particularly necessary. However, the crystal growth property may be deteriorated depending on the compatibility of the soft magnetic layer and the underlayer. It is possible to prevent the deterioration of crystal growth. It is desirable that the seed layer has a minimum thickness necessary for controlling the crystal growth of the underlayer. If it is too thick, it may cause a decrease in signal writing capability.

The underlayer is used to suitably control 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. The material of the underlayer is preferably a simple substance or an alloy having a face-centered cubic (fcc) structure or a hexagonal close-packed (hcp) structure, and examples thereof include Ru, Pd, Pt, Titp, and alloys containing them. There is no limitation. In the present invention, Ru or an alloy thereof is particularly preferably used. 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.

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 titanium oxide (TiO ₂ ) which is a nonmagnetic substance is used. 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, it is preferable to provide an auxiliary recording layer above the perpendicular magnetic recording layer so that the high recording resistance of the auxiliary recording layer 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. In the carbon-based protective layer according to the present invention, for example, a composition gradient layer in which nitrogen is contained on the lubricating layer side of the protective layer and hydrogen is contained on the magnetic layer side is preferable. Further, the thickness of the protective layer is preferably about 3 to 7 nm. If it is less than 3 nm, the performance as a protective layer may be deteriorated. Moreover, when exceeding 7 nm, it is unpreferable from a viewpoint of thin film formation.

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.

The present invention provides a method for manufacturing a magnetic disk having at least a magnetic layer and a protective layer provided on a substrate as in Configuration 1, wherein the magnetic layer is measured using a recoil molecular scattering method. The method for manufacturing a magnetic disk is characterized in that a film forming condition of the protective layer is set so that a hydrogen content becomes an allowable value, and the protective layer is formed according to the set film forming condition.

As a result of intensive studies, the inventor has found that the amount of hydrogen contained in the film in the depth direction of the magnetic disk can be suitably analyzed by using a recoil molecular scattering method having a high depth resolution. I found it. The measurement principle of the recoil molecular scattering method is known in the physics and chemistry literature.

The following are mentioned as preferable embodiment in this invention.
(1) The hydrogen content in the magnetic layer is measured using a recoil molecular scattering method with respect to one or a plurality of magnetic disks for which the film forming conditions of the protective layer are known in advance. In the present invention, the measurement condition in the recoil molecular scattering method when measuring the hydrogen content in the magnetic layer is incident from 30 degrees at 480 keV using incident ions N2. The incident current is about 0.2 nA.

(2) An allowable value of the hydrogen content in the magnetic layer is set. According to the study of the present inventor, it is desirable that the allowable value of the hydrogen content in the magnetic layer is 7 atomic% or less in order not to deteriorate the good magnetic properties.
(3) The film forming conditions for the protective layer are set so that the set allowable value is obtained.
(4) The protective layer is formed according to the set film formation conditions.

When the carbon-based protective layer is formed in the present invention, it is particularly preferable to use an amorphous carbon protective layer formed by a plasma CVD method. By forming the film by plasma CVD, the surface of the protective layer becomes uniform and densely formed.

  According to the inventor's study, when a protective layer is formed by plasma CVD, the amount of hydrogen generated by decomposition of the source gas is adjusted by appropriately controlling the substrate heating temperature and the gas flow rate during film formation, for example. As a result, the amount of hydrogen taken into the protective layer and the magnetic layer can be controlled.

Therefore, taking into account the known deposition conditions of the protective layer, the hydrogen content in the magnetic layer of the magnetic disk, and the allowable value of the hydrogen content in the set magnetic layer, the set allowable value Optimized film formation conditions for the protective layer such as the substrate heating temperature during film formation and the gas flow rate can be set.

As described above, in the perpendicular magnetic recording medium, the magnetic layer preferably has at least a perpendicular magnetic recording layer and an auxiliary recording layer provided thereon. In this case, the auxiliary recording layer through which hydrogen can permeate is provided. It is preferable to set the film forming conditions of the protective layer so that the hydrogen content in the inside becomes an allowable value.

The magnetic disk obtained by the present invention is particularly suitable as a magnetic disk mounted in a LUL type magnetic disk device. Due to the further decrease in the flying height of the magnetic head accompanying the introduction of the LUL method, it has been demanded that the magnetic disk operates stably even at an ultra-low flying height of 5 nm or less, for example. The magnetic disk of the present invention having good magnetic characteristics and reliability is suitable.

Hereinafter, the present invention will be described more specifically with reference to examples.
(Manufacture of magnetic disk)
As described below, an adhesion layer, a soft magnetic layer, a seed layer, an underlayer, a magnetic recording layer, a carbon-based protective layer, and a lubricating layer were sequentially formed on the substrate to produce a magnetic disk.

A 2.5-inch glass disk (outer diameter 65 mm, inner diameter 20 mm, disk thickness 0.635 mm) made of chemically strengthened aluminosilicate glass was prepared and used as a disk substrate. The main surface of the disk substrate 1 is mirror-polished so that Rmax is 2.13 nm and Ra is 0.20 nm.
On this disk substrate, an adhesion layer, a soft magnetic layer, a seed layer, an underlayer, and a magnetic recording layer were sequentially formed in an Ar gas atmosphere by a DC magnetron sputtering method.

The numerical values in the description of each material below indicate the composition.
First, a 10 nm Cr-50Ti layer was formed as an adhesion layer.
Next, as the soft magnetic layer, a laminated film of two soft magnetic layers that are antiferromagnetic exchange coupled with a nonmagnetic layer interposed therebetween was formed. That is, a 25 nm (50Fe-50Co) -3Ta4Zr layer is first formed as the first soft magnetic layer, then a 0.7 nm Ru layer is formed as the nonmagnetic layer, and the second layer is further formed. As the soft magnetic layer, the same (50Fe-50Co) -3Ta4Zr layer as the first soft magnetic layer was formed to a thickness of 25 nm.

Next, a 5 nm NiW layer was formed as a seed layer on the soft magnetic layer.

Next, two Ru layers were formed as an underlayer. That is, Ru was formed to a thickness of 12 nm at an Ar gas pressure of 0.7 Pa as the base first layer, and Ru was formed to a thickness of 12 nm at an Ar gas pressure of 4.5 Pa as the base second layer.

Next, a magnetic recording layer was formed on the underlayer. First, 90 nm (Co-10Cr-16Pt) -5SiO2-5TiO2 of 10 nm was formed as a perpendicular magnetic recording layer. Next, a 0.3 nm Ru layer was formed as an exchange coupling control layer, and a 7 nm Co-15Cr-15Pt-5B film was formed thereon as an auxiliary recording layer of the magnetic recording layer.

Next, a carbon-based protective layer made of hydrogenated diamond-like carbon was formed on the magnetic recording layer by plasma CVD. The substrate heating temperature and gas flow rate during film formation were set to predetermined values. The film thickness of the carbon-based protective layer was 5 nm.
And it took out from the vacuum apparatus, and the lubricating layer which consists of PFPE (perfluoropolyether) was formed by the dip coating method after this. The thickness of the lubricating layer was 1 nm.
Through the above manufacturing process, the perpendicular magnetic recording disk A was obtained.

For the magnetic disk A obtained as described above, the amount of hydrogen contained in the protective layer and the magnetic recording layer was analyzed using a recoil molecular scattering method. The measurement conditions by the recoil molecular scattering method were incident from 30 degrees at 480 keV using incident ions N2. The incident current was about 0.2 nA.

As a result of analysis, it was found that hydrogen penetrated to the auxiliary recording layer of the magnetic recording layer in the depth direction. The hydrogen content in this auxiliary recording layer was 9 atomic%. According to the study of the present inventor, in order not to deteriorate the good magnetic characteristics, the allowable value of the hydrogen content in the auxiliary recording layer is considered to be 7 atomic% or less. It was found that the hydrogen content in the auxiliary recording layer in A exceeded the allowable value.

Therefore, the film formation conditions for the carbon-based protective layer by the plasma CVD method were reviewed, and new film formation conditions for the protective layer were set by controlling the substrate heating temperature and the gas flow rate during film formation. A magnetic disk B was produced in the same manner as the magnetic disk A, except that the carbon-based protective layer was formed by plasma CVD under the newly set film forming conditions.

For the obtained magnetic disk B, the amount of hydrogen contained in the protective layer and the magnetic recording layer was analyzed using the same recoil molecular scattering method as described above. The amount was confirmed to be within the above tolerance.

Next, the magnetic disk B and the magnetic disk A (reference example) were evaluated by the following test methods.
(1) First, the magnetostatic characteristics were evaluated by measuring the coercive force (Hc) using a Kerr effect measuring device. As a result, the coercive force Hc of the magnetic disk B was 4200 Oe, and the coercive force Hc of the magnetic disk A was 3500 Oe. there were. It can be seen that the magnetic disk B has better magnetostatic characteristics than the magnetic disk A.

(2) Next, in order to evaluate the LUL (load / unload) durability of the magnetic disk, a LUL durability test was performed.
A LUL type HDD (5400 rpm rotating type) was prepared, and a magnetic head having a flying height of 5 nm and a magnetic disk B were mounted. The slider of the magnetic head is an NPAB (negative pressure) slider, and the reproducing element is equipped with a magnetoresistive element (GMR element). The shield part is an FeNi permalloy alloy. The LUL type HDD was made to repeat the continuous LUL operation, and the number of LULs that the magnetic disk was durable before the failure occurred was measured.

As a result, the magnetic disk B endured 600,000 times of LUL operation without failure under an ultra-low flying height of 5 nm. It is said that the use of about 10 years is necessary for the number of LULs to exceed 400,000 times under normal HDD usage environment, and it is said that it is preferable to endure 600,000 times or more at present. It can be said that the magnetic disk B has extremely high reliability.
Similarly, the magnetic disk A was subjected to the LUL durability test. As a result, it failed at 250,000 times under an ultra-low flying height of 5 nm.

As described above, according to the present invention, the hydrogen content in the magnetic layer can be monitored and suitably controlled so as to be an allowable value, and as a result, with the recent rapid increase in recording density. It was confirmed that a magnetic disk having good magnetic characteristics and reliability characteristics can be obtained under the low flying height of the magnetic head and under extremely severe environmental resistance accompanying diversification of applications.

Claims (6)

A method of manufacturing a magnetic disk having at least a magnetic layer and a protective layer provided on a substrate,
The film-forming condition of the protective layer is set so that the hydrogen content in the magnetic layer measured using a recoil molecular scattering method is an allowable value of 7 atomic% or less, and the protection is performed according to the set film-forming condition. A method of manufacturing a magnetic disk, comprising forming a layer.   For a magnetic disk whose film formation conditions for the protective layer are known in advance, the hydrogen content in the magnetic layer is measured using a recoil molecular scattering method, and an allowable value for the hydrogen content in the magnetic layer is set. 2. The method of manufacturing a magnetic disk according to claim 1, wherein a film forming condition of the protective layer is set so as to satisfy the set allowable value.   The method for manufacturing a magnetic disk according to claim 1, wherein the protective layer is a carbon-based protective layer formed by a plasma CVD method.   4. The method of manufacturing a magnetic disk according to claim 2, wherein the protective layer deposition conditions are set by controlling the substrate heating temperature before deposition and / or the gas flow rate.   The magnetic layer includes at least a perpendicular magnetic recording layer and an auxiliary recording layer provided thereon, and the film forming conditions of the protective layer are set so that the hydrogen content in the auxiliary recording layer becomes an allowable value. The method of manufacturing a magnetic disk according to claim 1, wherein the magnetic disk is manufactured as follows. 6. The method of manufacturing a magnetic disk according to claim 1, wherein the start / stop mechanism is a magnetic disk mounted on a load / unload type magnetic disk device.