JP2008257756A - Method for manufacturing magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a magnetic recording medium which improves the adhesion ratio of lubricant to a carbon protection layer and does not cause a micro scratch and transfer of the lubricant to a magnetic head. <P>SOLUTION: The method for manufacturing magnetic recording medium 100, having the carbon protection layer 26 and a lubricant layer 28 in this order on a substrate, includes an adding process for adding nitrogen which can bind with a hydroxyl group (OH<SP>-</SP>) on the carbon protection layer 26 by an RF (Radio Frequency) plasma method, and a lubricant layer depositing process for depositing the lubricant layer 28 with perfluoropolyether (PFPE) including a hydroxyl group. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a magnetic recording medium mounted on a perpendicular magnetic recording type HDD (hard disk drive) or the like.

  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 100 GB has been required for a 2.5-inch diameter magnetic disk used for HDDs and the like. In order to meet such a demand, per 1 inch. It is required to realize an information recording density exceeding 150 Gbits.

  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 a magnetic disk of the in-plane magnetic recording method (also called longitudinal magnetic recording method or horizontal magnetic recording method) that has 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, and the so-called thermal fluctuation phenomenon that the recording signal disappears has occurred, which has been an impediment to increasing the recording density of the magnetic disk. In order to solve this obstacle, a perpendicular magnetic recording type magnetic disk has recently been proposed.

  Unlike the case of the in-plane magnetic recording method, the perpendicular magnetic recording method is adjusted so that the easy axis of magnetization of the magnetic recording layer is 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.

  The perpendicular magnetic recording medium is composed of various layers in addition to the magnetic recording layer, and includes, for example, a carbon protective layer for protecting the magnetic recording layer and a lubricating layer laminated thereon.

  In Patent Document 1, in order to prevent the head smear phenomenon (head dirt) that the decomposition product of the lubricant in the lubricant layer adheres to the magnetic head, the head smear phenomenon is prevented by adding nitrogen to the surface layer of the carbon protective layer. Techniques for preventing are disclosed.

  According to Patent Document 1, the carbon protective layer containing nitrogen in the surface layer is formed by a sputtering method in a mixed atmosphere of an inert gas, a nitrogen gas, and a hydrocarbon or hydrogen gas.

Patent Document 2 describes the use of perfluoropolyether (PFPE) as a lubricant for the lubricating layer.
JP-A-9-128732 JP 2006-114182 A

  Currently, it has been reported from the manufacturing process of magnetic recording media that micro scratches, which are invisible to the eye but are so fine that they can be observed by an optical surface analyzer (OSA), are generated on the surface of the medium. This is considered to be caused by a tape burnishing process performed to remove fine dust on the surface of the medium after the perpendicular magnetic recording medium composed of the magnetic recording layer and other various layers has been formed. Yes.

  Carbon overcoat (COC), that is, a carbon protective layer that forms a high-hardness film with a carbon film, can increase the hardness, load unload test, constant flying test, corrosion test, pin-on test, nanoindene The properties as a protective layer, which are measured by various tests such as a station test, are improved.

  However, if the hardness of the carbon protective layer is too high, the number of micro scratches increases.

  Therefore, there is a method of protecting the medium from microscratching by improving the adhesion ratio (hereinafter referred to as “BR”) of the lubricant in the lubricating layer.

  The adhesion rate is expressed by the percentage of lubricant remaining after immersion of a recording medium having a lubricating layer in a solvent capable of decomposing the lubricant for about 30 seconds. If the hydroxyl group present at the end of the lubricating layer (perfluoropolyether) is normally attached to the carbon protective layer, the BR is high, but the hydroxyl group of the perfluoropolyether is not normally attached, and the molecules are in the lubricating layer. If it is merely entangled, it is easily decomposed into a solvent and removed, so that BR becomes low.

  In addition, BR is not improved by simply increasing the thickness of the lubricating layer. If the lubricating layer is made thicker, rather, when the disk-shaped recording medium rotates, migration may occur in which the lubricant moves due to centrifugal force, or the lubricant is transferred (pickup) to the magnetic head and the magnetic head is moved. It gets dirty.

  In view of such problems, the present invention provides a method for manufacturing a magnetic recording medium that improves the adhesion rate of the lubricant to the carbon protective layer and does not cause the transfer of the lubricant to the micro scratch or the magnetic head. Objective.

  In order to solve the above problems, the inventors have intensively studied. It was found that the adhesion rate of the lubricant is improved by bonding. The present invention has been obtained as a result of further research based on this finding.

In order to solve the above-mentioned problems, the present invention provides a method for manufacturing a magnetic recording medium comprising a carbon protective layer and a lubricating layer in this order on a substrate. The surface of the carbon protective layer is formed by an RF (Radio Frequency) plasma method. And an addition step of adding nitrogen capable of bonding with a hydroxyl group (OH ⁻ ), and a lubricating layer film forming step of forming the lubricating layer with a perfluoropolyether (PFPE) containing a hydroxyl group.

PFPE has a linear structure, exhibits moderate lubrication performance for magnetic recording media, and has a high adhesion rate to the carbon protective layer by having a hydroxyl group (OH ⁻ ) at the terminal group. . In particular, in the present invention having a step of removing H from the surface layer of the disk protective layer in advance and further adding N, (N ⁺ ) and (OH ⁻ ) have high affinity, so a high adhesion rate of the lubricating layer Can be obtained.

  Moreover, it is good to further perform the rare gas collision process which makes a rare gas collide by applying DC (Direct Current) bias to the surface layer of a carbon protective layer before the above-mentioned addition process.

  By causing the rare gas to collide with the carbon protective layer of the magnetic recording medium that is the target, H is removed from the carbon protective layer having the CH composition, and N is added in the subsequent addition step, thereby increasing the CN composition. This is because the adhesion rate of the lubricating layer is further improved.

  The noble gas mentioned above may be argon, krypton or xenon. This is because any of them can achieve the purpose of removing hydrogen having a small mass from the carbon protective layer by colliding with the carbon protective layer.

  Further, the nitrogen / carbon ratio of the carbon protective layer is preferably 0.04 to 0.12.

  According to the present invention, the content of nitrogen in the surface layer of the carbon protective layer can be increased, and the adhesion rate of the lubricating layer made of a lubricant (PFPE) having an affinity therefor is improved, whereby the carbon protective layer Are preferably protected from microscratches.

  In addition, since the adhesion rate is improved, the transfer of the lubricant to the magnetic head is also prevented.

  Next, an embodiment of a method for manufacturing a magnetic recording medium according to the present invention will be described in detail with reference to the accompanying drawings. In the figure, elements not directly related to the present invention are not shown. Similar elements are denoted by the same reference numerals. Note that dimensions, materials, and other specific numerical values shown in the following embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified.

  FIG. 1 is a diagram for explaining the configuration of a magnetic recording medium according to the present embodiment. A perpendicular magnetic recording medium 100 shown in FIG. 1 includes a disk substrate 10, an adhesion layer 12, a first soft magnetic layer 14a, a spacer layer 14b, a second soft magnetic layer 14c, an orientation control layer 16, a first underlayer 18a, and a second layer. The underlayer 18b, the onset layer 20, the first magnetic recording layer 22a, the second magnetic recording layer 22b, the auxiliary recording layer 24, the carbon protective layer 26, and the lubricating layer 28 are formed. The first soft magnetic layer 14a, the spacer layer 14b, and the second soft magnetic layer 14c together constitute the soft magnetic layer 14. The first base layer 18a and the second base layer 18b together constitute the base layer 18. The first magnetic recording layer 22a and the second magnetic recording layer 22b constitute the magnetic recording layer 22 together.

  First, an amorphous aluminosilicate glass was formed into a disk shape by direct pressing to produce a glass disk. The glass disk was subjected to grinding, polishing, and chemical strengthening in order to obtain a smooth non-magnetic disk base 10 made of a chemically strengthened glass disk.

  On the obtained disk substrate 10, a film is formed in order from the adhesion layer 12 to the auxiliary recording layer 24 by a DC magnetron sputtering method in an Ar atmosphere using a vacuum-deposited film forming apparatus, and a carbon protective layer is formed. No. 26 was formed by CVD. Thereafter, the lubricating layer 28 was formed by dip coating. Note that it is also preferable to use an in-line film forming method in that uniform film formation is possible.

  The feature of this embodiment lies in the structure of the surface layer of the carbon protective layer 26, which will be described later. First, the structure of each layer and the manufacturing method will be described below.

  The adhesion layer 12 was formed using a Ti alloy target so as to be a 10 nm Ti alloy layer. By forming the adhesion layer 12, the adhesion between the disk base 10 and the soft magnetic layer 14 can be improved, so that the soft magnetic layer 14 can be prevented from peeling off. As a material of the adhesion layer 12, for example, a CrTi alloy can be used. From the practical viewpoint, the thickness of the adhesion layer is preferably 1 nm to 50 nm.

  The soft magnetic layer 14 has AFC (Antiferro-magnetic exchange coupling) by interposing a nonmagnetic spacer layer 14b between the first soft magnetic layer 14a and the second soft magnetic layer 14c. It was configured as follows. Thereby, the magnetization direction of the soft magnetic layer 14 can be aligned along the magnetic path (magnetic circuit) with high accuracy, and noise generated from the soft magnetic layer 14 can be reduced. Specifically, the composition of the first soft magnetic layer 14a and the second soft magnetic layer 14c was CoCrFeB, and the composition of the spacer layer 14b was Ru (ruthenium).

  The control layer 16 has a function of protecting the soft magnetic layer 14 and a function of promoting alignment of crystal grain orientations of the underlayer 18.

  The underlayer 18 has a two-layer structure made of Ru. When forming the upper second base layer 18b, the crystal orientation can be improved by making the Ar gas pressure higher than when forming the lower first base layer 18a.

The onset layer 20 is a nonmagnetic granular layer. A nonmagnetic granular layer is formed on the hcp crystal structure of the underlayer 18, and the granular layer of the first magnetic recording layer 22 a is grown thereon to separate the magnetic granular layer from the initial stage (rise). Has an effect. The composition of the onset layer 20 was nonmagnetic CoCr—SiO ₂ .

  The magnetic recording layer 22 includes a thin first magnetic recording layer 22a and a thick second magnetic recording layer 22b.

The first magnetic recording layer 22a is a 2 nm CoCrPt—Cr ₂ O ₃ hcp crystal structure using a hard magnetic target made of CoCrPt containing chromium oxide (Cr ₂ O ₃ ) as an example of a nonmagnetic substance. Formed. The nonmagnetic material segregated around the magnetic material to form grain boundaries, and the magnetic particles (magnetic grains) formed a columnar granular structure. The magnetic grains were epitaxially grown continuously from the granular structure of the onset layer.

The second magnetic recording layer 22b was formed using a CoCrPt—TiO ₂ hcp crystal structure of 10 nm using a hard magnetic target made of CoCrPt containing titanium oxide (TiO ₂ ) as an example of a nonmagnetic substance. Also in the second magnetic recording layer 22b, the magnetic grains formed a granular structure.

  The auxiliary recording layer 24 forms a thin film (continuous layer) exhibiting high perpendicular magnetic anisotropy on the granular magnetic layer to constitute a CGC structure (Coupled Granular Continuous). Thereby, in addition to the high density recording property and low noise property of the granular layer, the high thermal fluctuation resistance of the continuous film can be added. The composition of the auxiliary recording layer 24 was CoCrPtB.

  The carbon protective layer 26 was formed by depositing carbon by a CVD method while maintaining a vacuum. The carbon protective layer 26 is a protective layer for protecting the perpendicular magnetic recording layer from the impact of the magnetic head. In general, carbon deposited by the CVD method has improved film hardness compared to that deposited by the sputtering method, so that the perpendicular magnetic recording layer can be protected more effectively against the impact from the magnetic head.

  In the present embodiment, a rare gas is collided by first applying a DC bias to the surface layer of the carbon protective layer. By applying a DC bias, a rare gas collides against a negatively charged target recording medium. Thus, H is removed from the carbon protective layer 26 having the CH composition.

  The noble gas mentioned above may be argon, krypton or xenon. This is because any of them can achieve the purpose of removing hydrogen having a small mass from the carbon protective layer by colliding with the carbon protective layer.

Next, nitrogen N that can be bonded to a hydroxyl group (OH ⁻ ) is added to the carbon protective layer 26 by an RF plasma method. Thereby, N is suitably added to the surface layer of the carbon protective layer 26, and the composition of CN increases in the carbon protective layer 26.

  The nitrogen / carbon ratio of the carbon protective layer is preferably 0.04 to 0.12. The reason why 0.04 is set as the lower limit is that if the amount of nitrogen on the outermost surface of the carbon can be increased, the adhesion rate (BR) of the lubricant can be improved. However, if the amount of nitrogen increases more than necessary, the carbon strength becomes weak and microscratches tend to enter. Therefore, it is desirable that the upper limit is 0.12, and the nitrogen / carbon ratio is controlled in the range of 0.04 to 0.12.

Following the carbon protective layer 26 having the N content increased in the surface layer as described above, PFPE (perfluoropolyether) containing a hydroxyl group (OH ⁻ ) is formed by dip coating to form the lubricating layer 28. Formed. The film thickness of the lubricating layer 28 is about 1 nm.

PFPE has a linear structure, exhibits moderate lubrication performance for perpendicular magnetic recording media, and has a high adhesion rate to the carbon protective layer by having a hydroxyl group (OH ⁻ ) at the end group. Become. In particular, in the present embodiment having a step of removing H from the surface layer of the disk protective layer in advance and further adding N, (N ⁺ ) and (OH ⁻ ) have high affinity. Rate can be obtained.

  Through the above manufacturing process, a perpendicular magnetic recording medium was obtained. The effectiveness of the present invention will be described below with reference to examples.

  FIG. 2 is data showing the adhesion rate (BR) of the lubricating layer to the carbon protective layer of this example. In this example, three examples COC1, COC2, and COC3 were prepared. Example COC1 is an example in which N is added to the carbon protective layer by the RF plasma method without performing a collision step with argon, which is a rare gas, on the carbon protective layer formed by the CVD method. Example COC2 is an example in which a step of colliding argon by applying a DC bias was performed before adding N to the carbon protective layer. Example COC3 is an example in which, after adding N to the carbon protective layer, a step of colliding argon by applying a DC bias was performed.

  FIG. 3 is a diagram showing the peak ratio Dh / Gh and the fluorescence intensity ratio B / A in FIG. 2 in the Raman spectrum of the carbon protective layer measured using an Ar ion laser with a wavelength of 514.5 nm.

  When the peak ratio Dh / Gh according to the Raman spectrum is increased, it means that the nitrogen content is high. That is, in principle, the peak ratio Dh / Gh increases or decreases corresponding to N / C in FIG. Comparing the examples COC1 and COC2, the example COC2 in which the DC bias was applied with argon before adding N was N / C = 0.078 and Dh / Gh = 0.7. It is high and it turns out that there is much content of N in a carbon protective layer.

  Therefore, the lubricating layer BR is 76.80 in Example COC2, which is higher than 68.00 in Example COC1, indicating that microscratching can be more effectively prevented.

  In Example COC3 only, N / C = 0.042 is low because the argon collision is performed after the addition of nitrogen, so even C including N added to the surface layer is removed. The result seems to be.

  On the other hand, the background (region S) of the Raman spectrum shown as the fluorescence component is a polymer bond by incorporating hydrogen in the DLC protective layer, and when this fluorescence intensity ratio B / A (≧ 1) increases, Means high hydrogen content.

  Comparing Example COC1 and Example COC2, in Example COC2 in which a DC bias was applied with argon before adding N, the fluorescence intensity ratio B / A = 1.34 was B / A of COC1 = 1.48, indicating that there is little hydrogen.

  On the other hand, when Example COC1 and COC3 are compared, N / C = 0.061 indicates that Example COC1 is higher than COC3 N / C = 0.042 and has a higher nitrogen content. , Dh / Gh is lower in COC1 (0.52 <0.67). That is, Example COC1 has a higher hydrogen content than Example COC3.

  As a result, the lubricating layer BR is higher in COC3 (71.70), and it is shown that a low hydrogen content is important for improving the lubricating layer BR. Although Example COC3 is after the addition of N, it has a low hydrogen content because it performs a step of colliding with argon. And Example COC2 which has only the hydrogen content of this same has improved the lubricating layer BR most by the synergistic effect with the value of N / C being large further.

  As described above, preferred embodiments of the present invention have been described with reference to the accompanying drawings as embodiments and examples of the perpendicular magnetic recording medium. However, the present invention is not limited to such examples and can be widely applied to general magnetic recording media. Needless to say. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  The present invention can be used as a method for manufacturing a magnetic recording medium mounted on a perpendicular magnetic recording type HDD (hard disk drive) or the like.

It is a figure explaining the structure of the perpendicular magnetic recording medium concerning this embodiment. It is data which shows the adhesion rate of the lubricating layer with respect to the carbon protective layer which is a present Example. It is a figure which shows the Raman spectrum of the carbon protective layer in the Example of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Disk base | substrate 12 ... Adhesion layer 14 ... Soft magnetic layer 14a ... First soft magnetic layer 14b ... Spacer layer 14c ... Second soft magnetic layer 16 ... Orientation control layer 18 ... Underlayer 18a ... First underlayer 18b ... Second Underlayer 20 ... onset layer 22 ... magnetic recording layer 22a ... first magnetic recording layer 22b ... second magnetic recording layer 24 ... auxiliary recording layer 26 ... carbon protective layer 28 ... lubricating layer

Claims (4)

In a method for manufacturing a magnetic recording medium comprising a carbon protective layer and a lubricating layer in this order on a substrate,
An addition step of adding nitrogen that can be bonded to a hydroxyl group (OH ⁻ ) to the surface layer of the carbon protective layer by an RF (Radio Frequency) plasma method;
And a lubricating layer forming step of forming the lubricating layer with a perfluoropolyether (PFPE) containing a hydroxyl group.   2. The rare gas collision step of causing a rare gas to collide by applying a DC (Direct Current) bias to a surface layer of the carbon protective layer before the adding step. A method of manufacturing a magnetic recording medium.   The method of manufacturing a magnetic recording medium according to claim 1, wherein the rare gas is argon, krypton, or xenon.   4. The method of manufacturing a magnetic recording medium according to claim 1, wherein the ratio of nitrogen / carbon in the carbon protective layer is 0.04 to 0.12.

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