JP2006120222A - Magnetic recording medium and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which enables high density recording and has excellent durability. <P>SOLUTION: The magnetic recording medium comprises: a plurality of recording tracks 6 separately provided on a soft magnetic layer 4 formed on a non-magnetic substrate 2 and consisting of projecting ferromagnetic bodies; a protective film 10 covering the upper surfaces and the side surfaces of the recording tracks the bottom surfaces of recessed parts 8 provided between the recording tracks; and a packing part 12 provided on the protective film of the recessed parts so as to pack the recessed part between the recording tracks and consisting of a material having a composition different from the composition of the material of the protective film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic recording medium and a manufacturing method thereof.

  In recent years, the use of multimedia data such as images, video, and audio has progressed, and the amount of search data per user has increased. For this reason, it is required to increase the capacity and speed of the database. On the other hand, due to the improvement in the surface recording density of a magnetic recording medium accompanying an increase in the recording capacity of an HDD (Hard Disk Drive), each recording bit size on the magnetic recording medium has become extremely fine, about several tens of nm. In order to obtain a reproduction output from such fine recording bits, it is necessary to secure as large saturation magnetization and film thickness as possible for each bit. However, the miniaturization of recording bits reduces the amount of magnetization per bit and causes the problem of disappearance of magnetization information due to magnetization reversal due to “thermal fluctuation”.

  In general, the influence of “thermal fluctuation” increases as the value of Ku · V / (k · T) decreases. Here, Ku is the magnetic anisotropic energy density, V is the minimum magnetization unit volume, k is the Boltzmann constant, and T is the absolute temperature. Empirically, it is said that when Ku · V / (k · T) is less than 100, magnetization reversal due to “thermal fluctuation” occurs. That is, the magnetic anisotropy energy required to keep the magnetization direction of the magnetic particles in one direction is expressed by the product of the magnetic anisotropy energy density Ku and the volume V of the magnetic particles, but Ku · V / ( When k · T) is less than 100, the magnetic anisotropy energy necessary to keep the magnetization direction of the magnetic particles in one direction becomes about the thermal fluctuation energy at room temperature. For this reason, a phenomenon occurs in which magnetization fluctuates with time and recorded information is lost.

  In the longitudinal magnetic recording type magnetic recording medium, since the demagnetizing field in the recording bit in the high recording density region becomes strong, it is easily affected by “thermal fluctuation” from a relatively large magnetic particle diameter. On the other hand, in a perpendicular magnetic recording type magnetic recording medium, by growing magnetic particles in the film thickness direction, the magnetization minimum unit volume V can be increased while the particle diameter of the medium surface is small. Can be suppressed. However, if the magnetic recording medium is further increased in density in the future, even if the perpendicular magnetic recording method is used, the resistance to thermal fluctuation will be limited.

As a medium for solving the problem of resistance to thermal fluctuation, a magnetic recording medium called “patterned medium” has attracted attention (see, for example, Patent Document 1). Patterned media is generally a magnetic recording medium in which a plurality of magnetic regions each serving as a recording bit unit are independently formed in a nonmagnetic layer, but a magnetically continuous magnetic thin film is formed in the size of a recording magnetic domain. It can be said that the medium is divided. In general patterned media, as the non-magnetic material layer, for example, oxides such as SiO ₂ , Al ₂ O ₃ , TiO ₂ , nitrides such as Si 3 N 4, AlN and TiN, carbides such as TiC, and borides such as BN are used. A ferromagnetic region is selectively formed in these nonmagnetic layers (see, for example, Patent Document 2).

  In general, a protective layer is formed on the outermost surface of the patterned medium for protecting the magnetic material and adsorbing the lubricant. For the protective layer, a material satisfying mechanical strength, coverage, and good wettability of the lubricant is preferable, and diamond-like carbon (hereinafter referred to as DLC) is most often used (see, for example, Patent Document 1). The DLC film is formed by a sputtering method using a graphite target. In this method, amorphous carbon in which sp2 bonded carbon and sp3 bonded carbon are mixed is formed. A substance having a large proportion of sp3-bonded carbon is called DLC. Since it is excellent in durability and corrosion resistance and is excellent in surface smoothness because it is amorphous, it is used as a surface protective film for magnetic recording media. DLC film formation by the CVD (Chemical Vapor Deposition) method excites and decomposes the source gas in plasma and generates DLC by chemical reaction. By combining the conditions, DLC richer in sp3 bonded carbon is formed. can do.

  Since the patterned medium is obtained by dividing the magnetic thin film into the size of the recording magnetic domain, the minimum magnetization unit volume V can be increased, and the problem of thermal fluctuation can be avoided. In the conventional continuous magnetic thin film, the number of magnetic particles up to about 1000 grains per bit is used. However, as the recording density increases, the number of grains corresponding to 1 bit decreases. Since the recording mark edge is determined by the grain boundary of the grain, it is necessary to make the grain as small as possible in order to secure the S / N ratio. Therefore, in the conventional continuous film, V must be reduced. However, since the edge of the recording magnetic domain can be defined by the structure in the patterned media, an improvement in the S / N ratio can be expected without reducing V.

  In the patterned media, since the ferromagnetic region which is a recording bit unit is independent, interference between the respective recording bits can be prevented, and it is effective in loss of recording due to adjacent bits and noise reduction. Moreover, the domain wall movement resistance increases by patterning, and it can aim at the improvement of a magnetic characteristic.

  On the other hand, in the improvement of track density, the problem of interference with adjacent tracks has become apparent. In particular, reduction of writing blur due to the magnetic head fringe effect is an important technical issue. Therefore, a discrete track medium that physically separates recording tracks has been proposed (see, for example, Patent Document 3). When a discrete track medium is used, it is possible to reduce a side erase phenomenon during recording, a side lead phenomenon in which information of adjacent tracks is mixed during reproduction, and the like. Since the density in the track direction can be greatly increased, a high-density magnetic recording medium can be provided.

Since patterned media must be physically separated in both the recording track direction and the recording line direction, advanced nanometer processing techniques are required. Since discrete track media separate only the recording track direction, pattern formation is easier than patterned media.
Japanese Patent Laid-Open No. 2001-176049 (FIG. 1) Patent 3286291 (paragraph number (0025)) Japanese Patent Laid-Open No. 7-85406 (FIG. 1)

  As described above, patterned media are effective as high-density magnetic recording media because they can suppress magnetization reversal due to “thermal fluctuation”. A discrete track medium is effective as a high-density magnetic recording medium because the track direction density can be increased.

On the other hand, in order to perform high density recording, it is necessary to reduce the magnetic spacing between the recording / reproducing head and the magnetic recording medium. In the current flying recording / reproducing, there is a magnetic spacing of 27 nm in total, with a protective film 5 nm for the recording medium, a slider protective film 5 nm for the recording / reproducing head, a flying height 13 nm, a margin 4 nm. At a recording density of 200 Gbpsi, it is necessary to reduce the magnetic spacing to 14 nm. However, assuming that the recording medium and the protective film of the slider are the same as before, the flying height must be 0 nm, that is, contact recording must be performed. In contact recording, it is necessary to obtain a sufficient strength against the frictional force and viscous fluid force generated between the head slider and the recording medium surface, and therefore a lubricant formed on the surface of the recording medium is important.

Current lubricants (generally perfluoropolyethers) can move freely without chemically bonding to the part (adsorption layer) that chemically bonds to the carbon formed on the surface of the magnetic recording medium. It consists of a possible part (free layer). The adsorption layer is important for suppressing loss and loss of the lubricant due to contact with the recording / reproducing head, and for preventing spin-off due to centrifugal force during disk rotation. The free layer becomes important for self-healing, which flows into the reduced part and covers that part. In the contact recording, the lubricant on the medium surface is easily depleted, so that there is a problem that the replenishment from the free layer cannot catch up.

  The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a magnetic recording medium capable of high-density recording and excellent in thermal fluctuation resistance, and a manufacturing method thereof.

According to a first aspect of the present invention, there is provided a magnetic recording medium comprising: a plurality of recording tracks made of a convex ferromagnetic material provided separately on a soft magnetic layer formed on a nonmagnetic substrate; The protective film that covers the top and side surfaces and the bottom surface of the recess provided between the recording tracks, and the composition of the protective film provided on the protective film of the recess so as to fill the recesses between the recording tracks are different. And a filling portion made of a material.
Each of the recording tracks may be formed of a ferromagnetic material having a convex cross section in the track width direction.

  Each of the recording tracks is composed of a plurality of ferromagnetic dots, and the protective film is provided on the upper and side surfaces of the ferromagnetic dots and the recesses between the ferromagnetic dots in each recording track. You may comprise so that the said filling part may be provided also on the protective film of the said recessed part between the said ferromagnetic material dots.

The protective film may be formed of carbon as a main component and a material. In this case, the filling portion is preferably formed of any one of SiO ₂ , low temperature sintered SOG, and nitride.

Incidentally, the protective film may be formed of SiO _2. In this case, it is preferable that the filling portion is formed from either low-temperature sintered SOG or nitride.

  Also, the method for manufacturing a magnetic recording medium according to the second aspect of the present invention forms a recording track made of a convex ferromagnetic material provided separately on a soft magnetic layer formed on a nonmagnetic substrate. And a step of exposing the soft magnetic layer between the ferromagnetic materials, a step of forming a protective film covering the upper and side surfaces of the ferromagnetic material and the exposed soft magnetic layer, and on the exposed soft magnetic layer Forming a filling portion made of a material having a composition different from that of the material of the protective film only on the protective film.

  According to the present invention, it is possible to obtain a magnetic recording medium capable of high-density recording and excellent in thermal fluctuation resistance, and a manufacturing method thereof.

Best Mode for Carrying Out the Invention

(First embodiment)
The configuration of the magnetic recording medium according to the first embodiment of the present invention will be described with reference to FIGS. The magnetic recording medium of this embodiment is a discrete track medium, and includes a track area and a servo area. A plan view of the track area and a plan view of the burst of the servo area are shown in FIGS. 2A and 2B, respectively, and a cross-sectional view taken along the cutting line AA shown in FIG. It is shown in 1.

  As shown in FIG. 1, the magnetic recording medium of this embodiment is provided with a soft magnetic underlayer 4 on a nonmagnetic substrate 2, and in the track region, a track width made of a ferromagnetic material on the soft magnetic underlayer 4 is provided. A plurality of recording tracks 6 having a convex cross section in the direction are provided. Adjacent recording tracks 6 are separated by a concave portion 8 having a concave cross section in the track width direction. The upper and side surfaces of the recording track 6 and the bottom surface of the recess 8 are covered with a thin protective film 10. The servo area burst is composed of ferromagnetic dots on the soft magnetic underlayer 4. As shown in FIG. 2B, the upper and side surfaces of the burst ferromagnetic dots and the space between the ferromagnetic dots are also covered with a thin protective film 10. In addition to the burst, the servo area includes a preamble and an address portion made of a ferromagnetic material extending in a direction substantially orthogonal to the track direction of the recording track. The body is similarly covered with the protective film 10. In this embodiment, in the track region, the recess 8 is filled with the filling material 12 having a composition different from that of the protective film 10 so that the filling material 12 is exposed on the surface. Similarly, in the servo region, the ferromagnetic material is filled with a filling material 12 having a composition different from that of the protective film 10 so that the filling material 12 is exposed on the surface (see FIG. 2B). .

The protective film 10 on the upper surface of the recording track 6 and the embedding material 12 in the recess 8 are different in wettability with respect to the lubricant. By using a compound that improves the wettability of the lubricant, for example, SiO ₂ , Al ₂ O ₃ , TiC, BC, SiC, or the like, as the filling material 12 for the recesses 8, the lubricant is stored in a portion unrelated to recording / reproduction. I can leave. In Patent Document 1, since a flat protective film is formed on the outermost surface of the patterned medium, the wettability of the lubricant is the same between the recording track and the recess. When a large amount of lubricant is applied for contact recording, the magnetic spacing spreads, so the S / N is lowered and high density recording cannot be performed.

  On the other hand, in the structure of the magnetic recording medium according to the present embodiment, since the minimum lubricant (preferably 1 nm or less) is applied to the upper surface of the recording track 6 related to recording / reproducing, it is not possible to widen the magnetic spacing. Absent. For this reason, high-density recording becomes possible. Further, since a large amount of lubricant can be applied to the recesses 8 not related to recording, it becomes easy to supply the lubricant to the upper surface of the recording track 6 depleted by contact recording, and heat generated by contact recording is absorbed by the lubricant. It becomes possible, and it becomes excellent in thermal fluctuation resistance. Although the height of the protective film 10 on the upper surface of the recording track 6 and the embedding material 12 in the recess 8 may be the same, the height of the embedding material 12 is preferably lower from the viewpoint of magnetic spacing.

  In the present embodiment, carbon is used for the protective film 10. Carbon can be classified into sp2-bonded carbon (graphite) and sp3-bonded carbon (diamond). The sp3-bonded carbon is superior in terms of durability and corrosion resistance, but since it is crystalline, the surface smoothness is inferior to that of graphite. Usually, the carbon film is formed by sputtering using a graphite target. In this method, amorphous carbon in which sp2 bonded carbon and sp3 bonded carbon are mixed is formed. Those having a large proportion of sp3 bonded carbon are called diamond-like carbon (hereinafter referred to as DLC). Since it is excellent in durability and corrosion resistance and is excellent in surface smoothness because it is amorphous, it is used as a surface protective film for magnetic recording media. DLC film formation by the CVD (Chemical Vapor Deposition) method excites and decomposes the source gas in plasma and generates DLC by chemical reaction. By combining the conditions, DLC richer in sp3 bonded carbon is formed. can do.

In this embodiment, a compound that improves the wettability of the lubricant, for example, SiO ₂ , Al ₂ O ₃ , TiC, BC, SiC, or the like is used as the filling material 12, but the protective film 10 is a carbon such as DLC. In the case where it is made of nitride, nitride can be used for the filling material 12. By using a nitride that makes the wettability of the lubricant very good for the embedding material 12 of the recess 8, for example, a nitride such as CN, TiN, Si ₃ N ₄ , or BN, the lubricant that can be stored in the recess 8 The selection range is expanded.

Further, when the protective film 10 is made of carbon such as DLC, SOG (Spin-On-Glass) can be used for the filling material 12. SOG is a coating solution for forming a thin film mainly composed of SiO ₂ by coating to sintering. The main component is made of, for example, RnSi (OH) _4-n and is dissolved in an organic solvent together with an additive. In some cases, CH ₃ or the like is used at the terminal. Usually, it is changed to pure SiO ₂ by sintering at about 600 ° C. Because it is liquid, it is easy to use as an embedding material. However, since it is the OH end or CH ₃ end that increases the wettability of the lubricant, SOG sintered at a low temperature of 500 ° C. or lower is suitable as the embedding material.

In this embodiment, the protective film 10 is made of carbon such as DLC. However, SOG, SiO ₂ , silicon oxynitride (SiON), silicon nitride (SiN (Si ₃ N ₄ etc.)) sintered at high temperature is used. Can be used. When SOG or SiO ₂ sintered at a high temperature is used as the protective film 10, any one of CN, TiN, TaN, BN, and non-sintered SOG can be used as the filling material. When SiON is used as the protective film 10, any one of SiO ₂ , high temperature sintered SOG, CN, TiN, TaN, BN, and non-sintered SOG can be used as the filling material. When SiN is used as the protective film 10, any one of SiN, SiO ₂ , high-temperature sintered SOG, CN, TiN, TaN, BN, and non-sintered SOG can be used as the filling material.

(Second Embodiment)
Next, a method for manufacturing a magnetic recording medium according to the second embodiment of the present invention will be described with reference to FIGS. FIG. 3A to FIG. 4C are cross-sectional views illustrating manufacturing steps of the manufacturing method according to the present embodiment.

First, as shown in FIG. 3A, a soft magnetic underlayer 4 and a magnetic layer 6 are sequentially formed on a nonmagnetic substrate 2 made of, for example, SiO ₂ or Si. A resist 20 is applied thereon, and a stamper 30 on which unevenness corresponding to a recording track, a tracking servo signal, an address information signal, a reproduction clock signal and the like is formed is pressed on the applied resist 20 to transfer the unevenness. Such a shape transfer method using a press using a stamper is called an imprint method.

  The problem with shape transfer by the imprint method is that a residue 21 is formed as shown in FIG. When the lower magnetic layer is etched by dry etching such as RIE (Reactive ion etching) or Ar ion milling in a state where there is such a residue 21, the shape is remarkably deteriorated. Since the residue 21 can be removed by oxygen plasma, anisotropic etching is performed by, for example, RIE using oxygen plasma as shown in FIG. Thereby, a resist pattern 20a from which the residue 21 is completely removed is formed (see FIG. 3C).

  Next, the magnetic layer 6 is patterned by using dry etching such as Ar ion milling using the resist pattern 20a as a mask (see FIG. 3C), and the upper surface and side surfaces are made of a magnetic layer and the bottom surface is soft. A recess 8 in which the magnetic underlayer is exposed is formed (see FIG. 3D). After the patterning of the magnetic layer 6, the resist pattern 20a is peeled off using oxygen plasma treatment or the like (see FIG. 3D).

  Next, a protective film 10 made of, for example, DLC is formed so as to cover the upper surface and side surfaces of the convex portion 6 and the bottom surface of the concave portion 8 by using a sputtering method or a CVD (Chemical Vapor Deposition) method (see FIG. 4A). ). Subsequently, an embedding material 12 having a composition different from that of the protective film 10 and having good wettability with respect to the lubricant is formed on the entire surface by bias sputtering (see FIG. 4B). Thereafter, the embedding material 12 is etched using dry etching such as IBE (Ion Beam Etching), Ar ion milling, or RIE until the protective film 10 formed on the magnetic layer 6 is exposed. 12 is filled (see FIG. 4C). Thereby, the magnetic recording medium of the first embodiment is manufactured.

  As described above, according to the manufacturing method of the present embodiment, the magnetic recording medium of the first embodiment can be manufactured, and a magnetic recording medium capable of high-density recording and excellent in thermal fluctuation can be obtained. be able to.

(Third embodiment)
Next, a method for manufacturing a magnetic recording medium according to the third embodiment of the present invention will be described with reference to FIG. The manufacturing method of this embodiment uses low-temperature sintered SOG as an embedding material, and until the step shown in FIG. 4A of the manufacturing method of the second embodiment, that is, the step of forming a protective film. It carries out similarly to 2nd Embodiment.

  For example, after the protective film 10 made of DLC is formed, SOG 24 is applied on the protective film 10 by spin coating as shown in FIG. Subsequently, heat treatment is performed at a temperature not exceeding 500 ° C. and low temperature sintering is performed to obtain a low temperature sintered SOG 24a (see FIG. 5B). At this time, in order to prevent damage due to oxidation, heat treatment in a forming gas (mixed gas of nitrogen and hydrogen) or hydrogen gas is preferable in a vacuum or a reducing atmosphere.

  Next, by using dry etching such as IBE (Ion Beam Etching), Ar ion milling, or RIE, the low temperature sintered SOG 24a is etched so that the protective film 10 formed on the upper surface of the magnetic layer 6 is exposed (FIG. 5 (c)). As a result, only the concave portion 8 is filled with the SOG 24a sintered at low temperature (see FIG. 5C).

  As described above, according to the manufacturing method of the present embodiment, a magnetic recording medium capable of high-density recording and having excellent thermal fluctuation resistance can be obtained.

  The structure of the magnetic recording medium of the first embodiment and the manufacturing method of the second to third embodiments has a strong cross-sectional shape in the track width direction as shown in FIG. Although the recording track 6 made of a magnetic material and the discrete track medium having the concave portion 8 have been described, the present invention is not limited to this. For example, as shown in FIG. 7, a patterned medium having a structure in which separated ferromagnetic dots 7 are arranged in a recording track 6, a magnetic recording medium having a structure of only a recording track, separated ferromagnetic dots May be a magnetic recording medium having a structure in which are arranged. Moreover, you may manufacture using the pattern which the convex part and recessed part of the resist pattern 20a reversed. The cross section of the discrete track medium cut along the cutting line AA shown in FIG. 6 is as shown in FIG. 1, and the cross section of the patterned medium cut along the cutting line AA shown in FIG. 7 is shown in FIG. It becomes like this.

  The magnetic recording medium of the above embodiment is a discrete track medium, and a groove is formed in the track direction, but the bit is a continuous film. Therefore, the resolution in the bit direction is determined by the performance of the recording / reproducing head and the recording layer ferromagnetic material. Therefore, the recording track is separated and isolated also in the bit direction by using a processing method (AASA (Artificially Assisted Self Assembling)) using an array-controlled self-organizing mask. By adopting such a structure, further high density recording can be achieved. A method of manufacturing a magnetic recording medium using this AASA method will be described as a fourth embodiment.

(Fourth embodiment)
A method of manufacturing a magnetic recording medium according to the fourth embodiment of the present invention will be described with reference to FIGS. 9 (a) to 11 (c).

  First, as shown in FIG. 9A, a soft magnetic underlayer 4 is formed on a nonmagnetic substrate 2, and a ferromagnetic layer 6 serving as a magnetic recording layer is formed on the soft magnetic underlayer 4. Thereafter, a resist 20 is applied on the ferromagnetic layer 6. Subsequently, using the stamper 30 in which the grooves are formed, the resist is pressed to transfer the unevenness to the resist 20 (see FIG. 9B). Then, on the resist 20 to which the unevenness is transferred, for example, PS (polystyrene) -PMMA (polymethylmethacrylate) diblock polymer 40 dissolved in an organic solvent is formed by spin coating (see FIG. 9C). ). Note that FIG. 9C is a diagram in which the cross section shown in FIG. 9B is extended in the horizontal direction (left and right on the paper surface) in order to explain the self-organization phenomenon described later.

  Next, as shown in FIG. 10 (a), PS-PMMA diblock copolymer thin film 40 undergoes phase separation due to self-organization by heat treatment at a temperature of about 140 ° C. to 200 ° C. A sea-island structure is obtained. The nano pattern formation method using this self-organization phenomenon is compared with a normal pattern formation method, for example, EB drawing, photolithography, X-ray lithography, near-field optical lithography, interference exposure method, FIB (Focused ion beam), etc. Thus, a nano-pattern with a large area can be formed at a low cost in a short time. Diblock copolymers can use various polymers depending on the desired structure (diameter, pitch, etch rate). PMMA nanometer-sized dots 42 are arranged in a hexagonal lattice pattern by phase separation by self-assembly of PS-PMMA diblock copolymer. In addition, in Fig.10 (a), the code | symbol 44 shows a polystyrene.

Thereafter, only the PMMA dots 42 are selectively removed by oxygen plasma treatment (for example, RIE using oxygen gas) (see FIG. 10B), and the SOG 48 is embedded in the holes 46 from which the PMMA has been removed (FIG. 10C). )reference). Subsequently, the resist layer 20 is patterned by RIE using oxygen gas. At this time, the resist other than the resist covered with SOG 48 is removed, and a resist pattern 20a is formed (see FIG. 10D). The ferromagnetic layer 6 is patterned by RIE using O ₂ gas using the resist mask 20a and SOG 48, and then the resist pattern 56a and SOG 48 are removed. Then, as shown in FIG. 10E, a plurality of patterned ferromagnetic layers 6 are obtained. After that, as described in the second embodiment, the protective film 10 is formed as shown in FIG. 11A, the filling material 12 is formed on the entire surface (see FIG. 11B), and the ferromagnetic layer is formed. The embedding material 12 is etched until the protective film 10 on the upper surface 6 is exposed, and the recesses 8 and 9 between the ferromagnetic layers 6 are filled with the embedding material 12 (see FIG. 11C). In FIG. 11C, the upper surface of the filling material 12 filled in the recesses 9 between the ferromagnetic layers 6 is lower than the upper surface of the protective film 10 on the ferromagnetic layer 6, but is on the same surface. Also good. The recesses 8 between the ferromagnetic layers 6 are the recesses between the recording tracks, and the recesses 9 between the ferromagnetic layers 6 indicate the recesses between the ferromagnetic layers 6 in the same recording track.

  By doing so, the durability is greatly increased, and a nanometer-sized pattern can be formed over a large area at a low cost.

  Note that the stamper 30 used in the process shown in FIG. 9A can use EB drawing, Deep-UV cutting, or the like in addition to normal light exposure.

  Note that the patterned media created by the AASA method has a structure in which magnetic dots are isolated and arranged. One magnetic dot (1 bit 1 cell) may be used for one recording, but one recording may be formed of a large number of magnetic dots (1 bit multicell). When a patterned medium having a magnetic dot particle size of about 10 nm is considered, since there is no practical means for accurately accessing the 10 nm region, one recording is formed by a large number of magnetic dots (1 bit multi-cell). Is preferred. For example, when considering the surface density of 200 Gbpsi, the area of 1 bit is track width 125 nm × recording bit length 25 nm. When the magnetic dot particle diameter is 9 nm, one bit is formed by 42 magnetic dots of 14 magnetic dots (track width) × 3 (track direction) at a surface density of 200 Gbpsi.

By using SiO ₂ or the like instead of the ferromagnetic layer 6, a master for forming the stamper 30 can be obtained. 9A and 9B, after forming the master using the AASA method, the surface of the master is subjected to Ni conductive treatment. In general, a Ni film is formed to a thickness of about 10 nm by sputtering. Thereafter, Ni electroforming is performed to form a stamper having a structure using the AASA method.

  In the above embodiment, a soft magnetic underlayer, a ferromagnetic layer, carbon, and a self-assembled diblock copolymer are used. These materials will be described below.

(Soft magnetic underlayer)
As the soft magnetic layer, a soft magnetic material containing any element of Fe, Ni, Co, for example, CoFe, NiFe, CoZrNb, ferrite, silicon iron, carbon iron, etc. can be used.

  If the soft magnetic layer has a fine structure similar to that of the ferromagnetic layer, it is preferable in terms of crystallinity and fine structure control. However, when the magnetic properties are prioritized, another structure may be used. For example, an amorphous soft magnetic layer and a crystalline ferromagnetic layer, or vice versa are conceivable. The soft magnetic layer may have a so-called granular structure in which soft magnetic fine particles are present in a non-magnetic matrix, or a plurality of layers having different magnetic characteristics (for example, a multilayer film of soft magnetic layers / non-magnetic layers). ).

  The direction of the magnetic anisotropy of the soft magnetic layer other than during recording / reproduction may be perpendicular to the film surface, in the in-plane circumferential direction, in the in-plane radial direction, or a combination thereof.

  The soft magnetic layer only needs to have a coercive force enough to form a closed magnetic loop by changing the magnetic direction (spin direction) by the magnetic field of the single-pole head during recording and reproduction. Generally, it is preferably several kOe or less, more preferably 1 kOe or less, and even more preferably 50 Oe or less.

(Ferromagnetic layer)
As the ferromagnetic layer, a ferromagnetic material generally used in current magnetic recording media can be used. That is, a material having a large saturation magnetization Is and a large magnetic anisotropy is suitable. From this viewpoint, for example, at least one selected from the group consisting of Co, Pt, Sm, Fe, Ni, Cr, Mn, Bi, and Al and alloys of these metals can be used. Of these, Co alloys having a large magnetocrystalline anisotropy, particularly those based on CoPt, SmCo, and CoCr, and ordered alloys such as FePt and CoPt are more preferable. Specifically, Co—Cr, Co—Pt, Co—Cr—Ta, Co—Cr—Pt, Co—Cr—Ta—Pt, Fe ₅₀ Pt ₅₀ , Co ₅₀ Pt ₅₀ , Fe ₅₀ Pd ₅₀ , Co ₇₅ Pt ₂₅ or the like. Besides these, Tb-Fe, Tb-Fe-Co, Tb-Co, Gd-Tb-Fe-Co, Gd-Dy-Fe-Co, Nd-Fe-Co, Nd-Tb-Fe- Wide range from rare earth-transition metal alloys such as Co, multilayer films of magnetic and noble metal layers (artificial lattices: Co / Pt, Co / Pd, etc.), semimetals such as PtMnSb, magnetic oxides such as Co ferrite, Ba ferrite, etc. You can choose.

  For the purpose of controlling the magnetic properties of the ferromagnetic layer, an alloy obtained by alloying the above magnetic material with at least one element selected from the magnetic elements Fe and Ni may be used as the ferromagnetic layer. Good. In addition to these metals or alloys, additives for improving magnetic properties, such as Cr, Nb, V, Ta, Mo, Ti, W, Hf, Cr, V, In, Zn, Al, Mg, Si, B or the like, or a compound of these elements and at least one element selected from oxygen, nitrogen, carbon, and hydrogen may be added.

  Regarding the magnetic anisotropy of the ferromagnetic layer, an in-plane magnetic anisotropy component may be present as long as the perpendicular magnetic anisotropy component is the main component. The thickness of the ferromagnetic layer is not particularly limited, but is preferably 100 nm or less, more preferably 50 nm or less, and still more preferably 20 nm or less in consideration of high-density recording. In addition, since it will become difficult to comprise a continuous thin film when it becomes 0.1 nm or less, it is not preferable.

  Further, the ferromagnetic layer is preferably a composite material composed of magnetic particles and a nonmagnetic substance existing therebetween. This is because high-density magnetic recording using magnetic particles as a reversal unit is possible. However, in the case of patterning the recording area, the presence of a nonmagnetic material is not always necessary, and a continuous amorphous magnetic material such as a rare earth-transition metal alloy may be used.

(Self-organization: diblock copolymer)
The block copolymer is a copolymer (copolymer) composed of a linear polymer having a plurality of single polymers as partial constituent components (blocks). For example, polymer chains A and B have a structure of-(AA ·· AA)-(BB ·· BB)-. The block copolymer has a phase-separated structure in which the polymer A and the polymer B are aggregated by applying heat treatment. For example, there is a “lamella” structure in which A phase and B phase appear alternately and regularly, a “cylinder” structure in which one phase is rod-shaped, and a “sea-island” structure in which one phase is distributed spherically. In order to form a microphase separation structure with a block copolymer, the volume fraction of two phases is important. Although any polymer can be selected as the polymer A and the polymer B, it is preferable to select a polymer having a large difference in dry etching rate from the viewpoint of lithography. A combination of an aromatic polymer (for example, polystyrene, polyvinyl naphthalene, poly α-methyl styrene, polyvinyl pyridine, etc.) having relatively high etching resistance and an acrylic polymer (for example, PMMA, poly-tbutyl methacrylate, etc.) having a fast dry etching rate. good. In the case of a diblock copolymer in which PS (polystyrene) and PMMA are bonded, it is possible to selectively remove only PMMA by utilizing a large difference in dry etching resistance. The diblock copolymer of PS and polyvinylpyridine phase separates into a clean sea-island structure, but since there is almost no difference in dry etching resistance, it is difficult to use the phase separated structure as an etching mask. The size of the phase separation structure (dot diameter, pitch) can be controlled by the molecular weight of polymer A and polymer B. For example, in the case of PS-PMMA diblock copolymer, the diameter of PMMA dots can be 40 nm and the pitch can be 80 nm by setting the molecular weight of PS to 172000 and the molecular weight of PMMA to 41500. Reducing the molecular weight also reduces the structure. For example, by setting the molecular weight of PS to 43,000 and the molecular weight of PMMA to 10,000, the diameter of PMMA dots can be 10 nm and the pitch can be 29 nm.

  Examples of the present invention will be described below.

Example 1
A disc-shaped stamper having 100 sectors as shown in FIG. 6 was formed by electron beam exposure. Thereafter, a discrete medium was manufactured by the steps shown in FIGS. 3 (a) to 4 (c). That is, a soft magnetic underlayer 4 made of CoZrNb and having a thickness of 200 nm was formed on the glass substrate 2. Subsequently, Ru was deposited to 20 nm for the purpose of orientation control, and a CoCrPt—SiO ₂ alloy was deposited to a thickness of 20 nm as the ferromagnetic layer 6 by sputtering.

Thereafter, a resist 20 was formed with a film thickness of 100 nm. Subsequently, a pattern was formed by imprinting using a stamper 30 in which servo information and recording tracks were mixed, and the imprinting residue was removed by oxygen RIE. At that time, the residue removal condition was an oxygen RIE time of 30 seconds. Then, after etching the 20 nm-thick ferromagnetic layer 6 by Ar ion milling, the resist was peeled off to form a carbon protective film 10 having a thickness of 5 nm. Thereafter, SiO ₂ was deposited as a filling material 12 by 150 nm by bias sputtering.

When the cross-sectional shape was observed with an SEM (scanning electron microscope), there were almost no surface irregularities. Subsequently, etching back was performed with IBE for 15 minutes to expose the protective film 10 formed on the ferromagnetic layer 6. The carbon that is the protective film 10 is a DLC that has a large proportion of sp3-bonded carbon and is excellent in mechanical strength. Therefore, the IBE rate is slower than that of SiO ₂ that is the embedding material 12. Therefore, as shown in FIG. 1, the height of the protective film 10 on the top of the recording track 6 is higher than that of the filling material 12. In this way, a discrete track medium having a cross-sectional shape as shown in FIG. 1 was produced.

  When a lubricant was applied and a durability test was conducted with a contact type recording / reproducing head, the reproduced waveform could be clearly observed even after one week.

  Subsequently, the lubricant film thickness variation in the disk radial direction was evaluated by OSA (Optical Surface Analyzer). The film thickness variation immediately after sliding the recording / reproducing head for 10 minutes was 2 mm. The film thickness variation after standing for 3 hours was 0.3 mm or less. The self-healing of the lubricant was found to work.

(Comparative Example 1)
Discrete track media were produced by a general method. That is, a pattern is formed by an imprint method using a stamper in which servo information and recording tracks are mixed, the imprint residue is removed by oxygen RIE, the magnetic layer 20 nm is etched by Ar ion milling, and then SiO ₂ is bias-sputtered. 150 nm was deposited by the method. Etch back by IBE for 15 minutes, and after exposing the upper part of the ferromagnetic material, a carbon protective film was formed to 5 nm.

  When a lubricant was applied and a durability test was performed with a contact-type recording / reproducing head, a good reproduction waveform was obtained for the first two days, but the signal intensity gradually decreased, and S / N after one week. The ratio decreased to about half.

  It was found that the discrete media of the conventional method with a uniform protective film on the surface of the recording medium has less free layer of lubricant and cannot cope with lubricant depletion due to sliding of the contact-type recording / reproducing head. .

(Example 2)
A discrete track medium was prepared using the same method as in Example 1 except that the embedding material was TiN.

  When a lubricant was applied and a durability test was conducted with a contact type recording / reproducing head, the reproduced waveform could be clearly observed even after one week.

Subsequently, the lubricant film thickness variation in the disk radial direction was evaluated by OSA. The film thickness variation immediately after sliding the recording / reproducing head for 10 minutes was 0.5 mm. The film thickness variation after standing for 3 hours was 0.3 mm or less. Compared to the sample embedded with SiO ₂ shown in Example 1, it was found that the film thickness variation was small. It has been found that the use of nitride as an embedding agent further improves the self-healing property of the lubricant.

(Example 3)
A discrete track medium in which up to a protective film made of carbon was formed in the same manner as in Example 1 was prepared. Thereafter, SOG was spin-coated by 4000 rpm spin coating and annealed at 450 ° C. for 1 hour in a forming gas atmosphere. When the cross-sectional shape was observed with an SEM, there were almost no surface irregularities. When the embedding agent is deposited by the bias sputtering method, a film thickness of about 150 nm is necessary in order to completely bury the surface unevenness, but in the case of SOG, the unevenness is sufficiently embedded even with a film thickness of about 80 nm. did it. Subsequently, the film was etched back with IBE for 8 minutes to expose the protective film formed on the ferromagnetic material. Since the IBE rate of SOG as the embedding agent was faster, a discrete track medium in which the protective film above the recording track was higher than the embedding agent as shown in FIG. 1 was completed.

  When a lubricant was applied and a durability test was conducted with a contact type recording / reproducing head, the reproduced waveform could be clearly observed even after one week.

  Subsequently, the lubricant film thickness variation in the disk radial direction was evaluated by OSA. The film thickness variation immediately after sliding the recording / reproducing head for 10 minutes was 0.5 mm. The film thickness variation after standing for 3 hours was 0.3 mm or less. It was found that there was a self-healing property equivalent to the sample embedded with the nitride shown in Example 2. In addition, since the film thickness of the embedding agent is as small as about 80 nm, the IBE etch back time may be short, so that the mass productivity is excellent.

(Comparative Example 2)
A discrete track medium using SOG as an embedding agent was prepared in the same manner as in Example 3 except that annealing was performed at 600 ° C. for 1 hour in a forming gas atmosphere.

  When a lubricant was applied and a durability test was conducted with a contact type recording / reproducing head, the reproduced waveform could be clearly observed even after one week.

Subsequently, the lubricant film thickness variation in the disk radial direction was evaluated by OSA. The film thickness variation immediately after sliding the recording / reproducing head for 10 minutes was 2 mm. The film thickness variation after standing for 3 hours was 0.3 mm or less. The self-healing of the lubricant was found to work. However, since SOG was sintered at a high temperature, SOG changed to SiO ₂ , and it was found that the self-repairing property of the lubricant is inferior to that of nitride or low-temperature sintered SOG.

  As described above, according to each embodiment of the present invention, a patterned medium compatible with high-density recording and a manufacturing method thereof can be provided.

1 is a cross-sectional view showing a configuration of a magnetic recording medium according to a first embodiment of the present invention. 1 is a plan view showing a configuration of a magnetic recording medium according to a first embodiment of the present invention. Sectional drawing which shows the manufacturing process of the manufacturing method of the magnetic-recording medium by 2nd Embodiment of this invention. Sectional drawing which shows the manufacturing process of the manufacturing method of the magnetic-recording medium by 2nd Embodiment of this invention. Sectional drawing which shows the manufacturing process of the manufacturing method of the magnetic-recording medium by 3rd Embodiment of this invention. 1 is a plan view showing a configuration of a discrete track medium according to an embodiment of the present invention. The top view which shows the structure of the patterned media by one Embodiment of this invention. Sectional drawing cut | disconnected by the cutting line AA shown in FIG. Sectional drawing which shows the manufacturing process of the manufacturing method of the magnetic-recording medium by 4th Embodiment of this invention. Sectional drawing which shows the manufacturing process of the manufacturing method of the magnetic-recording medium by 4th Embodiment of this invention. Sectional drawing which shows the manufacturing process of the manufacturing method of the magnetic-recording medium by 4th Embodiment of this invention.

Explanation of symbols

2 Nonmagnetic substrate 4 Soft magnetic underlayer 6 Ferromagnetic layer (recording track)
8 Recess 10 Protective film 12 Embed

Claims (8)

A plurality of recording tracks made of a convex ferromagnetic material provided separately on a soft magnetic layer formed on a nonmagnetic substrate;
A protective film covering the upper and side surfaces of the recording track and the bottom surface of the recess provided between the recording tracks;
A filling portion made of a material having a composition different from that of the protective film provided on the protective film of the concave portion so as to fill the concave portion between the recording tracks;
A magnetic recording medium comprising:   2. The magnetic recording medium according to claim 1, wherein each of the recording tracks is made of a ferromagnetic material having a convex cross section in the track width direction.   Each of the recording tracks is composed of a plurality of ferromagnetic dots, and the upper surface and side surfaces of the ferromagnetic dots and the concave portions between the ferromagnetic dots in each recording track are provided with the protective film and the strong film. The magnetic recording medium according to claim 1, wherein the filling portion is also provided on a protective film of the concave portion between the magnetic dots.   The magnetic recording medium according to claim 1, wherein the protective film is formed of carbon as a main component and a material. The magnetic recording medium according to claim 4, wherein the filling portion is formed of any one of SiO ₂ , low-temperature sintered SOG, and nitride. The magnetic recording medium according to claim 1, wherein the protective film is made of SiO ₂ .   The magnetic recording medium according to claim 6, wherein the filling portion is made of either low temperature sintered SOG or nitride. Forming a recording track made of a convex ferromagnetic material provided separately on a soft magnetic layer formed on a nonmagnetic substrate and exposing the soft magnetic layer between the ferromagnetic materials;
Forming a protective film covering the upper and side surfaces of the ferromagnetic material and the exposed soft magnetic layer;
Forming a filling portion made of a material having a composition different from that of the material of the protective film only on the protective film on the exposed soft magnetic layer;
A method of manufacturing a magnetic recording medium, comprising:

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