JP2010040077A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which can be manufactured by the same number of steps as that of conventional one and has excellent corrosion resistance. <P>SOLUTION: In the magnetic recording medium, an uneven pattern is formed wherein magnetic recording layers for recording information and groove parts having no recording function are alternately arranged on a disk substrate. Each of projecting shapes has ≥100° tapered angle. A protective layer is formed on the surfaces of the magnetic recording layers of the magnetic recording medium on which the uneven pattern is formed. Aperture parts of the groove parts (recessed parts) are blocked by the protective layer and cavities are formed at the inside of the recessed parts. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium for discrete track media (DTM) and bit patterned media (BPM) in which recording layers are formed in a continuous and uneven pattern.

  In a magnetic recording medium, a protective layer is usually formed on the magnetic recording layer in order to protect the magnetic recording layer from contact with the magnetic head, damage from sliding, and corrosion. In a conventional magnetic recording medium, a soft magnetic layer, a magnetic layer, and the like are laminated on a flat substrate, and a protective layer is formed thereon.

Examples of the material for the protective layer include a diamond-like carbon (DLC) film, a nitride film, an oxide film including SiO ₂ , and a metal film. As a method for forming the protective layer, a sputtering method, a plasma CVD method, a thermal CVD method, or the like is used.

  When the DLC film formed by the sputtering method and the DLC film formed by the CVD method are compared, the DLC film formed by the CVD method is denser and harder. This is presumably because the DLC film formed by the CVD method is formed from hydrocarbon radicals, so that it is easy to take a three-dimensional rigid tetrahedral structure via hydrogen. In addition, it is considered that the film-forming property to the trench structure (structure having a groove) is better than the sputtering method.

  On the other hand, as next-generation media, discrete track media (DTM) in which adjacent magnetic recording layers are separated in order to improve areal recording density, and uneven patterns are formed on the magnetic recording layer, and bit patterned media (BPM) having dot shapes Development is underway.

  For example, Patent Document 1 describes a magnetic recording medium for a discrete track medium (DTM) in which a concavo-convex pattern is formed on a magnetic recording layer and a bit patterned medium (BPM) having a dot shape. This magnetic recording medium has a silicon protective layer on the top of the patterned magnetic recording layer, and carbon so as to cover the top and side surfaces of the silicon protective layer on the top of the convex portion, the side surface of the magnetic recording layer, and the bottom portion of the concave portion. A system protective layer is provided.

  Further, for example, in Patent Document 2, as a magnetic recording medium for discrete track media, a concave portion of a concavo-convex pattern is filled with a nonmagnetic material, and the surface of the magnetic recording layer that forms grains, and A magnetic recording medium is described in which the surface of the magnetic material is planarized.

JP 2006-12216 A JP 2006-92632 A

  When a protective layer is formed on the surface of a structure having an uneven shape such as DTM as in Patent Document 1, if the angle (taper angle) between the convex side wall and the concave base exceeds 45 °, that is, the taper angle In the range of 45 ° or more and 90 ° or less, the method of attaching the protective layer differs between the side wall of the concavo-convex shape, the upper side (top) of the convex portion, and the bottom side (bottom) of the concave portion. The protective layer is unlikely to form a film on the side walls or the corners of the recesses, and the thickness of the protective layer at that portion becomes thin, and pinholes are likely to occur. Due to a decrease in the coverage of the protective layer, metal elution from the magnetic recording layer and a decrease in corrosion resistance occur. There is also a method to change the sample inclination angle when forming the protective layer to make it easier to attach a film to the side wall of the convex part or the bottom of the concave part. In this case, however, the film thickness of the convex top is reduced and the flatness is lowered. There is a problem that the wear resistance and characteristics of the steel deteriorate.

  In addition, the method of forming a protective layer after filling the recesses with a nonmagnetic material and flattening the surface of the magnetic recording layer as in Patent Document 2 is the most effective in preventing metal elution from the magnetic recording layer. High reliability. However, there is a problem in that mass productivity is reduced due to an increase in the number of steps such as a filling step and subsequent curing and cleaning.

  In view of such a situation, without filling the concave portion with a nonmagnetic material, the rear portion of the concave portion and the surface of the magnetic recording layer are covered with a protective layer and flattened, so that metal elution from the magnetic recording layer can be reliably performed. An object of the present invention is to provide a magnetic recording medium that can be prevented and that does not reduce mass productivity as in Patent Document 2.

  In order to achieve the above-described object, the magnetic recording medium of the present invention is a magnetic recording in which a concavo-convex pattern in which magnetic recording layers for recording information and grooves having no recording function are alternately arranged on a disk substrate is formed. In the medium, the convex portion has a taper angle of 100 ° or more, a protective layer is formed on the surface of the magnetic recording medium of the magnetic recording medium on which the concavo-convex pattern is formed, and the opening of the groove (concave portion) is blocked by the protective layer. And a cavity is formed inside the recess.

  According to the present invention, a magnetic recording medium excellent in corrosion resistance can be manufactured with the same number of steps as in the prior art.

FIG. 1 is a sectional view showing an example of the basic configuration of the magnetic recording medium of the present invention.
The magnetic recording medium shown in FIG. 1 has a magnetic recording layer 3 formed on a soft magnetic layer 2 provided on a disk substrate 1. The magnetic recording layer 3 has an uneven pattern formed on the surface.

  In the magnetic recording layer 3, the width of the top of the convex portion is larger than the width of the portion of the magnetic recording layer in contact with the soft magnetic layer, and the taper angle of the convex shape is 100 ° or more. From the viewpoint of physical stability of the convex portion, the taper angle is preferably 135 ° or less.

In the magnetic recording medium of the present invention, the protective layer 4 is formed on the surface of the magnetic recording layer 3 of the magnetic recording medium on which the concavo-convex pattern is formed. This protective layer is preferably made of an oxide such as a DLC film or SiO ₂ film, or a nitride such as a SiN film, and these films can be formed by a plasma CVD method.

Even if the line width and groove width (both of the bottom portions) of the concavo-convex pattern are the widths that are normally employed in the magnetic recording medium, the convex portion has a taper angle of 100 ° or more, so that the top portion of the convex portion is adjacent. When the distance between the convex portions is reduced and a protective layer is formed on the surface of the structure, the film concentrates on the side wall of the entrance, and the entrance is closed before the inside of the concave portion is completely filled with the protective layer. Therefore, there is a feature that a nearly flat surface can be obtained without filling the recess. If the taper angle of the convex shape is less than 100 °, the distance between adjacent convex portions at the top of the convex portion becomes wide, and it is difficult to close the entrance before the concave portion is completely filled with the protective layer. In order to reduce the distance between adjacent convex portions at the top of the convex portion, stable patterning can be achieved by reducing the line width and groove width (both of the bottom portions) of the concave / convex pattern, which are usually employed in magnetic recording media. And the frequency of occurrence of defective products such as adjacent magnetic recording media is increased.
By the way, in order to fill the entire recess with a protective film and flatten the surface, it is necessary to repeat film formation and flattening (polishing or etching), which has the disadvantage that the number of steps increases and the tact time becomes long. . As in the present invention, the method of covering with a protective film while leaving a cavity in the recess has the advantages of fewer steps and shorter tact time.

  Fabrication of a taper angle of 100 ° or more can be performed by using a combination of resists having different etching rates or by appropriately adjusting the inclination of the sample during processing.

  The materials constituting the substrate 1, the soft magnetic layer 2, and the magnetic recording layer 3 used in the present invention are usually any materials that constitute the substrate, soft magnetic layer, and magnetic recording layer used in the magnetic recording medium. There is no particular limitation. The resist used for patterning the magnetic recording layer is not particularly limited as long as the etching rate can be appropriately selected. The material for forming the protective layer may be any material that is usually used for protecting the magnetic recording layer, such as a film containing carbon as a main component, an oxide film, and a nitride film.

The present invention will be further described below with reference to examples.
<Examples 1 and 2 and Comparative Examples 1 to 3>
Using the nanoimprint method, a discrete track medium in which a predetermined uneven pattern was formed on the magnetic recording layer was produced. The concavo-convex pattern shape had a line width of 30 nm, a groove width (bottom) of 30 nm, and a groove depth of 10 nm. The taper angles were 45 ° (Comparative Example 1), 60 ° (Comparative Example 2), 90 ° (Comparative Example 3), 100 ° (Example 2), and 110 ° (Example 1).

  A 3.5 nm DLC film was formed by plasma CVD on the magnetic recording layer on which the concavo-convex pattern was formed. The obtained magnetic recording medium was subjected to a metal elution test and evaluated for corrosion resistance. The result is shown in FIG. In Comparative Example 1 having a taper angle of 45 °, when the thickness of the magnetic recording layer is 10 nm, for example, the bottom portion of the magnetic recording layer is 10 nm and the both sides are 20 nm, and the gap between the tops of adjacent magnetic recording layers is increased. There is a problem that the structure cannot be made too compact.

As a pretreatment for the metal dissolution test, the sample was subjected to a standing test at 80 ° C. and 90% RH for 100 hours. In the metal elution test, in order to prevent metal elution from other than the protective layer surface, the periphery of a 20 mm × 20 mm square sample was sealed with silicon resin, and the sample was immersed in a 1 wt% Na ₂ SO ₄ solution at 20 ° C. for 30 minutes. After measuring the immersion potential, the amount of metal eluted was examined by analyzing the solution. The amount of metal eluted in Reference Example 1 was taken as 1.

<Reference Example 1>
A 3.5 nm DLC film was formed by a plasma CVD method on a continuous magnetic recording layer having no uneven pattern processing. The obtained magnetic recording medium was subjected to a metal elution test and evaluated for corrosion resistance.

  From FIG. 2, when the protective layer was formed along the concavo-convex pattern, the metal elution amount was the same as that of the continuous film (Reference Example 1) up to a taper angle of 45 ° as in Comparative Example 1. When the taper angle is increased, the metal elution amount increases as in Comparative Example 2 (taper angle 60 °), and is highest at a taper angle of 90 ° (Comparative Example 3). This is presumably because when the taper angle increases, the film hardly adheres to the sidewall, and the metal is eluted from the place where the pinhole is generated. However, the elution amount decreased conversely at 100 ° or more (Examples 1 and 2). This is because when the taper angle exceeds 90 ° and becomes a reverse taper, the film is likely to be deposited in the groove opening before being deposited inside the groove, and the opening is blocked while leaving a void inside.

  From this result, it can be seen that a DTM having high corrosion resistance can be obtained by setting the taper angle of the concavo-convex pattern to 100 ° or more.

<Example 3>
Using the nanoimprint method, a discrete track medium in which a predetermined uneven pattern was formed on the magnetic recording layer was produced. The concavo-convex pattern shape had a line width of 60 nm, a groove width (bottom) of 30 nm, and a groove depth of 10 nm. The taper angle was 100 °.

  A DLC film having a thickness of 3.0 nm was formed on the magnetic recording layer on which the concavo-convex pattern was formed by a plasma CVD apparatus. The obtained magnetic recording medium was subjected to the same metal elution test as in Example 1 to evaluate the corrosion resistance. The result is shown in FIG. In FIG. 3, the metal elution amount was set to 1 in Comparative Example 4.

<Comparative Example 4>
Using the nanoimprint method, a discrete track medium in which a predetermined uneven pattern was formed on the magnetic recording layer was produced. The concavo-convex pattern shape had a line width of 60 nm, a groove width (bottom) of 40 nm, and a groove depth of 10 nm. The taper angle was 80 °.

The surface of the sample by sputtering filled with SiO ₂ in the groove, and was a SiO ₂ film as an SiO ₂ film is also formed on the surface of the protrusion. Thereafter, the sample was etched while being tilted, and the SiO ₂ film formed on the surface of the convex portion was removed. After planarizing the surface, a 3.0 nm DLC film was formed by a plasma CVD apparatus. The obtained magnetic recording medium was subjected to the same metal elution test as in Example 1 to evaluate the corrosion resistance. The results are shown in FIG. 3 together with the results of Example 3.

From FIG. 3, assuming that the metal elution amount of Comparative Example 2 in which the groove portion is filled with SiO ₂ is 1.0, the metal elution amount of Example 2 in which the protective layer is formed along the uneven pattern is substantially equal to 1.15. It was a result. This indicates that there is no problem in reliability if the opening can be completely sealed even if a gap is left inside the groove.

  According to the present invention, a magnetic recording medium excellent in corrosion resistance can be provided with the same number of steps as in the prior art.

It is a figure which shows the basic composition of the discrete track media (DTM) of this invention. It is a figure which shows the relationship between the taper angle of a convex part shape, and a metal elution amount. It is a graph showing by comparison the metal elution amount of Examples Comparative Examples and the present invention with embedded SiO ₂ in the groove.

Explanation of symbols

1 Substrate 2 Soft magnetic layer 3 Magnetic recording layer 4 Protective layer

Claims (2)

  In the magnetic recording medium on which a concavo-convex pattern formed by alternately arranging magnetic recording layers for recording information on the disk substrate and grooves having no recording function, the taper angle of the convex shape is 100 ° or more, A protective layer is formed on the surface of the magnetic recording medium of the magnetic recording medium on which the concavo-convex pattern is formed, the opening of the groove (recess) is sealed with the protective layer, and a cavity is formed inside the recess. Magnetic recording medium.   2. The magnetic recording medium according to claim 1, wherein the protective layer is made of a film mainly composed of carbon, an oxide film, and a nitride film.

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