Magnetic recording medium and magnetic storage medium manufacturing method

The present invention relates to a magnetic recording medium capable of high-density magnetic recording and a method for manufacturing a magnetic recording medium.

In recent years, data such as images, videos, and sounds have become multimedia, and the amount of search data per user has increased. Therefore, 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 the magnetic recording medium due to the increase in the recording capacity of the hard disk drive (hereinafter referred to as "HDD"), the size of each recording bit on the magnetic recording medium has become extremely fine, about several tens of nm. It has become to. In order to obtain a reproduction output from such a fine recording bit, it is necessary to secure the saturation magnetization and the film thickness as large as possible for each bit.

However, the miniaturization of the recording bit reduces the amount of magnetization per bit, and causes a problem of loss of magnetization information due to magnetization reversal due to "thermal fluctuation".

In general, this "thermal fluctuation" has a greater effect as the value of Ku · V / kT (where Ku: anisotropic constant, V: minimum magnetization unit volume, k: Boltzmann constant, T: absolute temperature) is smaller. Therefore, empirically, it is said that when Ku V / kT is less than 100, magnetization reversal due to thermal fluctuation occurs.

That is, the magnetic anisotropy energy required to maintain 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. The energy becomes about the thermal fluctuation energy at room temperature, the magnetization fluctuates with time, and the recorded information disappears.

In the magnetic recording medium of the perpendicular magnetic recording system, since the demagnetizing field in the recording bit in the region where the recording density is high becomes strong, it is easily affected by "thermal fluctuation" even when the magnetic particle size is relatively large. On the other hand, in the magnetic recording medium of the perpendicular magnetic recording method, by growing the magnetic particles in the film thickness direction, the minimum magnetization unit volume V can be increased while the particle size on the surface of the medium is small, so that the influence of "thermal fluctuation" is obtained. Can be suppressed. However, if the density of magnetic recording media is further increased in the future, it is expected that the thermal fluctuation resistance will be limited even with the perpendicular magnetic recording method.

As a medium for solving this problem of thermal fluctuation resistance, a magnetic recording medium generally called "patterned medium" is attracting attention (see, for example, Patent Document 1). The patterned media is generally a magnetic recording medium in which a plurality of magnetic material regions serving as recording bit units are independently formed in a non-magnetic material layer. In other words, the patterned media is a medium in which a magnetic thin film that is magnetically continuous is divided into the size of a recording magnetic domain.

In general patterned media, as a non-magnetic layer, for example, SiO₂, Al₂O₃, TiO₂Oxides such as and Si₃N₄, AlN, TiN and other nitrides, TiC and other carbides, and BN and other borides are used, and ferromagnetic regions are selectively formed in these non-magnetic layers.

Since the patterned media 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 per bit is up to about 1000 grains, but as the recording density increases, the number of grains corresponding to 1 bit decreases. Since the recording mark edge is determined by the grain boundaries of the grain, it is necessary to make the grain as small as possible in order to secure the S / N. Therefore, in the conventional continuous film, V has to be reduced, but in the patterned media, the edge of the recording magnetic domain can be defined by the structure, so that the S / N can be expected to be improved without reducing V.

Since the ferromagnetic region, which is a recording bit unit, is independent in the patterned media, it is possible to prevent interference between the respective recording bits, and it is effective in reducing recording loss and noise due to adjacent bits. Further, by patterning, the domain wall movement resistance is increased (the domain wall pinning effect), and it is possible to aim at improving the magnetic characteristics.

On the other hand, in improving the track density, the problem of interference with adjacent tracks has become apparent. In particular, reducing writing bleeding due to the magnetic field fringe effect of the recording head is an important technical issue. Therefore, a discrete track type magnetic recording medium has been proposed in which data is physically separated between recording tracks by a non-magnetic region in which data cannot be written (see, for example, Patent Document 2).

Discrete track type magnetic recording media have high side erase phenomena such as accidentally writing or deleting data to adjacent tracks during recording and side read phenomena such as accidentally reading information from adjacent tracks during playback. Since it is possible to avoid problems peculiar to the magnetic recording medium capable of density recording, the density in the track direction can be significantly increased, and a high-density magnetic recording medium can be provided.

As described above, the patterned media is effective as a high-density magnetic recording medium because it can suppress the magnetization reversal due to "thermal fluctuation". Further, the discrete track medium is effective as a high-density magnetic recording medium because the density in the track direction can be increased.

In the case of manufacturing such a magnetic recording medium, the manufacturing process is significantly increased as compared with the case of manufacturing a conventional continuous film magnetic recording medium, so that an increase in manufacturing cost becomes a problem. For this reason, patterns such as servo signals required for head positioning during recording / playback, such as burst signals, address information signals, and preamble signals, are preliminarily created in the stamper together with the tracks in the recording area, and collectively transferred by the imprint method. By doing so, an increase in manufacturing cost is avoided. Discrete track type magnetic recording media and patterned media produced by imprinting using such a stamper are referred to as "patterned media".

In the production of conventional patterned media, a nanoimprint method is adopted in which a nanometer-sized signal pattern is created in a stamper and transferred in one shot.

In the conventional manufacturing process, first, for example, SiO₂, A base layer made of a soft magnetic material and a recording layer made of a ferromagnetic material are sequentially formed on a non-magnetic substrate made of Si or the like. Then, a resist is formed on the recording layer.

Next, on the formed resist, irregularities (grooves) having different patterns such as irregularities (grooves) corresponding to the recording area of the track, irregularities (grooves) corresponding to the burst signal, and preamble signal irregularities (grooves) are formed. Press the stamper to transfer the unevenness. The shape transfer method by pressing using such a stamper is called an imprint process. In the case of shape transfer by the imprint method, a residue remains. When the lower recording layer is etched by dry etching such as RIE (Reactive ion etching) or Ar ion milling with such a residue, the shape is significantly deteriorated.

Since the residue can be removed by oxygen plasma, it is completely removed by, for example, anisotropic etching with oxygen RIE. Then, the lower recording layer is etched by dry etching such as Ar ion milling, and the resist is peeled off after the magnetic material is processed.

<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2001-176049 (Fig. 1)</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 7-85406 (Fig. 1)</text></patcit>

<p> However, such a conventional method for manufacturing a magnetic recording medium has the following problems. When a patterned medium is manufactured by the imprint method using a stamper in which different patterns are mixed, the area ratio of the part with the pattern (convex part of the spanper) and the part without the pattern (concave part of the stamper) (hereinafter, "pattern"). Since the pressure at the time of pressing the resist by the stamper differs depending on the black-and-white ratio "), the pressing depth differs in the resist portion corresponding to the recording area, the preamble area, and the burst area.</p><p> Specifically, in the recording area and the burst part, the pattern black-and-white ratio is generally 1: 3, while the preamble area is 1: 1. The smaller the convex part of the spanper, the easier it is to imprint, so the recording area and burst area can be pressed deeper, but it is difficult to press too deeply in the preamble area with a pattern black-and-white ratio of 1: 1. is there.</p><p> In the case of the magnetic recording medium manufactured by the conventional manufacturing method, when the recording area and the preamble area are compared, the residue of the resist by imprint differs depending on the pattern black-and-white ratio of each, and the pattern black-and-white ratio of the stamper is 1: 3. The residue in the preamble region imprinted in the portion is less than the residue in the recording region imprinted by the portion having a pattern black-and-white ratio of 1: 1.</p><p> Then, in the conventional method for manufacturing a magnetic recording medium by the imprint method, in order to process a magnetic material having a good shape, in order to completely remove the residue of the resist by the imprint, it is optimal in the preamble region having the largest amount of residue. Oxygen plasma etching is performed so that the residue can be removed.</p><p> In such a case, the recording region and the burst region with a small amount of residue are subjected to an excessive etching process, and a side etching phenomenon occurs in which the width of the concave portion is widened more than necessary, resulting in pattern thickening.</p><p> Comparing the flat surface of the magnetic recording medium after removing the imprint residue with the flat surface of the stamper, the pattern of the recording area of the magnetic recording medium is empirically twice as thick as the stamper shape. In other words, even if a small burst mark is formed to support high TPI (Track per inch) recording, a patterned medium manufactured by a conventional manufacturing method can only produce a pattern having twice the size.</p><p> Even if a 50 nm square burst pattern is formed on the stamper by electron beam drawing, the pattern size will increase to 100 nm square by going through the medium processing process from imprinting.</p><p> Furthermore, at a recording density of 300 kTPI, the track pitch is 85 nm and the burst pattern is 30 nm square. Then, considering the above-mentioned pattern fatness, it is necessary to form a 15 nm square pattern by electron beam drawing, and there is a problem that it is difficult to create a patterned medium corresponding to high-density recording.</p><p> When the recording density is high, the above-mentioned thermal fluctuation problem occurs. Therefore, in order to satisfy the condition of Eq. (1), Ku = 2.0x106erg / cc, which is a common CoCrPt alloy as a perpendicular magnetic recording medium, is considered. The minimum magnetization unit volume must be 2000 nm3 or more. Assuming that the film thickness of the recording layer is 10 nm, the magnetic signal disappears due to thermal fluctuation unless the pattern area is 10x10 nm or more. On the other hand, the burst pattern corresponding to the recording density of 600 kTPI is 10 nm below. That is, when a burst pattern corresponding to a recording density of 600 kTPI or more is formed with the structure of the current patterned medium, the magnetization of the pattern disappears due to thermal fluctuation, and positioning by the recording / reproducing head becomes impossible.</p><p> The present invention has been made in view of the above, and an object of the present invention is to provide a magnetic recording medium capable of realizing high-density recording and having excellent thermal fluctuation resistance, and a method for producing such a magnetic recording medium. And.</p>

<p> In order to solve the above-mentioned problems and achieve the object, the present invention has a concavo-convex shape in which the convex portion is formed of a ferromagnetic material, and each track is physically separated into a data writable recording area. It is characterized in that the convex portion is formed of a ferromagnet and has a concave-convex shape having the ferromagnetic material in the concave portion, and includes a servo region in which position information for positioning the magnetic head at a target position is recorded. It is related to the magnetic recording medium.</p><p> Further, the present invention includes a magnetic portion made of a ferromagnetic material and a separating portion made of a non-magnetic material that separates the magnetic portion, a recording area in which data can be written, and a position for positioning the magnetic head at a target position. It relates to a magnetic recording medium characterized in that information is recorded and a servo region having a ferromagnet in a recess is provided.</p><p> Further, in the present invention, a film forming step of sequentially forming a base layer made of a soft magnetic material and a recording layer made of a ferromagnetic material on a non-magnetic substrate, and a film forming step on the recording layer formed by the film forming step. A resist forming step of forming a resist on the surface, and a concave-convex recording area in which data can be written and position information for positioning the magnetic head at a target position are recorded on the resist formed by the resist forming step. The imprinting step of forming the unevenness on the resist by pressing the stamper having the unevenness formed corresponding to the servo region of the above, and the resist having the unevenness formed by the imprinting step being etched to obtain the recording area. A resist removing step of completely removing the resist from the recesses of the resist and removing the resist so that a residue is present in the recesses of the servo region, and a magnetic material that etches the ferromagnetic material of the recording layer. It is characterized by including a processing process.</p>

<p> According to the present invention, in a discrete magnetic recording medium, since the servo region in which the signal pattern is recorded in advance at the time of manufacturing the medium has a ferromagnet in the recess, it can be used as a signal at the time of recording / playback by the playback recording head. It is possible to realize high-density recording without adversely affecting it, and to provide a magnetic recording medium having excellent resistance to thermal fluctuations.</p><p> Further, according to the present invention, in the so-called patterned media, since the servo region in which the signal pattern is recorded in advance at the time of manufacturing the medium has a ferromagnet in the recess, the signal at the time of recording / reproduction by the reproduction recording head can be used. It is possible to realize high-density recording without adversely affecting it, and to provide a magnetic recording medium having excellent heat fluctuation resistance.</p><p> Further, according to the present invention, stampers having different uneven patterns corresponding to the recording area and the servo area are pressed on the resist formed on the recording layer to form unevenness on the resist, and the unevenness is formed. By etching the resist, the resist is completely removed from the recesses in the recording area, and the resist is removed so that the residue is present in the recesses in the servo area, so that the residue removal conditions are adapted to the servo area. As a result, high-density recording can be realized, and a magnetic recording medium having excellent thermal fluctuation resistance can be manufactured.</p>

The best embodiment of the magnetic recording medium and the magnetic storage medium manufacturing method according to the present invention will be described in detail with reference to the accompanying drawings.

(Embodiment 1) The magnetic recording medium according to the first embodiment is a discrete track type magnetic recording medium. FIGS. 1-1 and 1-2 are structural diagrams showing the structure of the magnetic recording medium according to the first embodiment. FIG. 1-1 is a plan view of the magnetic recording medium according to the first embodiment, and FIG. 1-2 is a cross-sectional view of the magnetic recording medium according to the first embodiment.

As shown in FIG. 1-1, the magnetic recording medium of the present embodiment is referred to when positioning the recording area as the data writing area and the magnetic head to the target sector in the track, and the position information of each sector is referred to. Is composed of a servo area in which is recorded. Then, as shown in FIG. 1-1, data is not writable because it is physically separated from the adjacent track.

The servo area is provided at the beginning of the track, and a preamble area in which a preamble signal which is a signal for synchronizing recording and reproduction by a magnetic head is recorded and a burst signal which is a signal of sector position information are recorded. It is composed of a burst area.

FIG. 1-2 (a) is a cross-sectional view of a recording area, FIG. 1-2 (b) is a cross-sectional view of a preamble area, and FIG. 1-2 (c) is a cross-sectional view of a burst area. As shown in FIG. 1-2, in the magnetic recording medium of the present embodiment, a non-magnetic substrate 103 made of a non-magnetic material, a base layer 102, and a recording layer 101 are laminated. The recording layer 101 is provided with a recess, and as shown in FIG. 1-2 (b), the ferromagnet 104 is present in the recess of the recording layer 101 in the preamble region.

The base layer 102 is made of a soft magnetic material. As the soft magnetic material of the base layer 102, a soft magnetic material containing any element of Fe, Ni, Co in the composition, for example, CoFe, NiFe, CoZrNb, ferrite, silicon iron, carbon iron and the like can be used.

The microstructure of the base layer 102 is preferable in terms of crystallinity and microstructure control as long as it has the same structure as the recording layer 101 made of a ferromagnetic material, but if magnetic characteristics are prioritized, a different structure is intentionally used. You can also do it. For example, it can be an amorphous base layer and a crystalline recording layer, or vice versa.

Further, the base layer may be composed of a plurality of layers having different magnetic characteristics (for example, a multilayer film of a soft magnetic layer / a non-magnetic layer) in which soft magnetic fine particles are present in the non-magnetic matrix, which may be a so-called granular structure. It can also be configured.

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

The base layer 102 may have a holding force such that the magnetic direction (spin direction) is changed by the magnetic field of the monopole head during recording / reproduction to form a closed magnetic loop. Generally, it is preferably several kOe or less, more preferably 1 kOe or less, and even more preferably 50 Oe or less.

The recording layer 101 is made of a ferromagnetic material. As the ferromagnetic material of the recording layer 101, a ferromagnetic material generally used in the current magnetic recording medium can be used. That is, those having a large saturation magnetization Is and a large magnetic anisotropy are suitable. From this point of view, 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. Among these, Coalloys having a large magnetocrystalline anisotropy, particularly those based on CoPt, SmCo, and CoCr, and ordered alloys such as FePt and CoPt are more preferably used as ferromagnetic materials for the recording layer. Specifically, Co-Cr, Co-Pt, Co-Cr-Ta, Co-Cr-Pt, Co-Cr-Ta-Pt, Fe₅₀Pt₅₀, Co₅₀Pt₅₀, Fe₅₀Pd₅₀, Co₇₅Pt₂₅Etc. can be used as the ferromagnetic material of the recording layer 101. In addition to these, as ferromagnetic materials for the recording layer 101, Tb-Fe, Tb-Fe-Co, Tb-Co, Gd-Tb-Fe-Co, Gd-Dy-Fe-Co, Nd-Fe- Rare earth-transition metal alloys such as Co, Nd-Tb-Fe-Co, multilayer film of magnetic layer and noble metal layer (artificial lattice: Co / Pt, Co / Pd, etc.), semi-metals such as PtMnSb, Co ferrite, Ba ferrite It can be widely selected from magnetic oxides such as.

For the purpose of controlling the magnetic properties of the recording layer 101, an alloy of the above magnetic material and at least one or more elements selected from the magnetic elements Fe and Ni may be used as the recording layer 101. Good. In addition, additives for improving the magnetic properties of these metals or alloys, such as Cr, Nb, V, Ta, Mo, Ti, W, Hf, Cr, V, In, Zn, Al, Mg, Si, B and 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 recording layer 101, an in-plane magnetic anisotropy component may be present as long as the vertical magnetic anisotropy component is the main component. The thickness of the recording layer 101 is not particularly limited, but considering high-density recording, 100 nm or less is preferable, 50 nm or less is more preferable, and 20 nm or less is further preferable. If it is 0.1 nm or less, it becomes difficult to form a continuous thin film, which is not preferable.

Further, the recording layer 101 is preferably a composite material composed of magnetic particles and a non-magnetic substance existing between them. This is because high-density magnetic recording using magnetic particles as an inversion unit becomes possible. However, when patterning the recording area, the presence of a non-magnetic material is not always necessary, and a continuous amorphous magnetic material such as a rare earth-transition metal alloy may be used.

In the recording layer 101, as shown in FIG. 1-2 (a), there is no ferromagnet in the recess of the groove. If a ferromagnet is present, the noise becomes very large when reading and writing the recorded data by the magnetic head.

On the other hand, a ferromagnet exists in the recess of the servo region. Servo information, which is position information, is physically created as unevenness and forms a servo signal by magnetizing in one direction.Since the signal is not written by the magnetic head, it is used as a noise source. Because it doesn't become.

FIG. 2 is a schematic diagram showing a magnetic state in the recording area and a magnetic state in the servo area (preamble area). FIG. 2 (a) shows the magnetic state in the recording area, and FIG. 2 (b) shows the magnetic state in the servo area (preamble area).

As shown in FIG. 2 (b), the presence of the ferromagnet in the recess increases the effective volume and thus the stability of magnetization. Further, the presence of the ferromagnet in the recess has the effect of increasing the minimum magnetization volume, and the stability of magnetization is dramatically improved. Therefore, in the servo region, it is prevented that the servo information is erased by the stabilization of the magnetism.

In particular, in the magnetic recording medium according to the present embodiment, as shown in FIG. 1-2 (b), a ferromagnet is present in the recess of the preamble region of the servo region. In the manufacturing process of the magnetic recording medium of the present embodiment, when the imprint processing is performed using a stamper in which a plurality of different uneven patterns are mixed corresponding to each of the recording area, the preamble area, and the burst area, the stamper is used. The amount of residue varies depending on the pattern black-and-white ratio. However, the pattern black-and-white ratio of the unevenness of the stamper corresponding to the preamble area is 1: 1, which is the highest ratio as compared with other areas.

However, in the preamble region, the present inventor has created a signal pattern by etching in advance at the time of manufacturing the magnetic recording medium, and does not record with a magnetic head at the time of manufacturing the magnetic recording medium. Therefore, it has been experimentally clarified that even if the shape of the preamble region is deteriorated due to the presence of the resist residue in the recess of the preamble region during the manufacturing process, the preamble signal is not affected.

Therefore, in the magnetic recording medium according to the present embodiment, the presence of the ferromagnetic material in the recess of the preamble region does not affect the preamble signal and has a large pattern black-and-white ratio in the manufacturing process of the magnetic recording medium. In order to remove the resist residue in the recess of the preamble region, it is not necessary to match the etching treatment conditions in the subsequent step with the residue removal in the preamble region, and it is possible to avoid excessive etching treatment and to avoid the recording region and burst. It prevents an extra width (pattern thickening) from being generated in the recess of the area. As a result, a pattern that is almost equal to the burst pattern formed on the stamper can be transferred. Therefore, for example, a small burst pattern can be transferred to the limit of electron beam drawing, which cannot be manufactured by the conventional manufacturing method. It is possible to manufacture a magnetic recording medium compatible with high TPI.

In the present embodiment, the structure is such that the ferromagnet is present only in the recess of the preamble region, but the structure may be such that the ferromagnet is present in the burst region.

As another form of the magnetic recording medium according to the present embodiment, the unevenness of the recording layer is embedded with a non-magnetic material. FIG. 3 is a cross-sectional view showing the structure of a magnetic recording medium in which the unevenness of the recording layer is embedded in a non-magnetic material.

As shown in FIG. 3, this magnetic recording medium has a structure in which a recess of the recording layer 101 is embedded with a non-magnetic material 302 and a protective layer 301 is formed on the recording layer 101 to flatten the surface. .. By flattening the surface in this way, the levitation stability of the magnetic recording / playback head is increased, and lower levitation can be realized. In addition, this makes it possible to achieve high S / N and high resolution, and to support high TPI recording.

Next, a method of manufacturing the magnetic recording medium according to the present embodiment will be described. FIG. 4 is a process diagram showing a manufacturing process of the magnetic recording medium according to the present embodiment, and FIG. 5 is a schematic diagram showing a state of each process of the manufacturing process of the magnetic recording medium. The method for manufacturing a magnetic recording medium according to the present embodiment is a processing method using a nanoimprint method.

First, for example, SiO₂, Si, etc., a base layer 102 made of a soft magnetic material and a recording layer 101 made of a ferromagnetic material are sequentially formed on a non-magnetic substrate 103 (step S401). Next, a resist 502 is formed on the recording layer of the deposited ferromagnetic material (step S402, (a) of FIG. 5). Then, a stamper 501 having irregularities corresponding to a recording area, a preamble signal, a burst signal, or the like is pressed onto the formed resist to transfer the irregularities (step S403, FIG. 5 (b)). When the unevenness is transferred, the amount of residue differs depending on the pattern shape, as shown in FIG. 5 (b). That is, the amount of residue in the recording region and the burst region is smaller than the amount of residue in the preamble region. This is because the stamper's uneven pattern black-and-white ratio corresponding to the preamble area is as high as 1: 1 and the stamper's uneven pattern black-and-white ratio corresponding to the recording area and burst area is as low as 1: 3. This is because the pressure is different.

Next, anisotropic etching is started with oxygen RIE (step S404) to remove the residue of the resist. Since the amount of residue in the recording area and burst area is smaller than the amount of residue in the preamble area, the residue in the recording area and burst area is completely removed before the residue in the preamble area, but the recording area and burst area Anisotropic etching is completed when the residue is completely removed (step S405). As a result, the residue in the preamble region is not completely removed and remains in the recess (see (c) in FIG. 5). Next, dry etching such as Ar ion milling is performed to etch the underlying magnetic layer (step S406). Then, the resist is peeled off after the magnetic material is processed (step S407). As a result, as shown in FIG. 5D, a magnetic recording medium in which the ferromagnet is present in the preamble region and the ferromagnet is not present in the storage region and the burst region is manufactured.

As described above, in the magnetic recording medium according to the present embodiment, in the discrete track type magnetic recording medium, the preamble region in which the signal pattern is recorded in advance at the time of manufacturing the medium has a ferromagnet in the recess, so that the magnetic recording medium can be reproduced. It is possible to realize high-density recording without adversely affecting the signal at the time of recording / reproduction by the recording head, and to provide a magnetic recording medium having excellent resistance to thermal fluctuations.

Further, according to the present invention, stampers having different uneven patterns corresponding to the recording region, the preamble region and the burst region are pressed on the resist formed on the recording layer to form irregularities on the resist. By etching the resist on which the unevenness is formed, the resist is completely removed from the recesses in the recording area, and the resist is removed so that the residue is present in the recesses in the preamble region, the residue removal conditions are patterned black and white. It is not necessary to adapt to the preamble region having a large ratio, and as a result, high-density recording can be realized and a magnetic recording medium having excellent thermal fluctuation resistance can be manufactured.

(Embodiment 2) The magnetic recording medium according to the second embodiment is a magnetic recording medium of a patterned medium. 6 and 6-2 are structural diagrams showing the structure of the magnetic recording medium according to the second embodiment. FIG. 6-1 is a plan view of the magnetic recording medium according to the second embodiment, and FIG. 6-2 is a cross-sectional view of the magnetic recording medium according to the second embodiment.

As shown in FIG. 6-1, the magnetic recording medium of the present embodiment is referred to when the recording area serving as the data writing area and the magnetic head are positioned at the target sector in the track, and the position information of each sector is referred to. Is composed of a servo area in which is recorded. Then, as shown in FIG. 6-1, data is not writable because it is physically separated from the adjacent track.

Further, as shown in Fig. 6-1, the recording area has a structure in which separated ferromagnetic dots 600a are arranged, and the ferromagnetic dots 600a are separated by a non-magnetic material 600b. .. Here, the ferromagnetic dot 600a corresponds to the magnetic part in the present invention. Further, the non-magnetic material 600b corresponds to the separation portion in the present invention.

Further, in the magnetic recording medium of the present embodiment, the servo region is formed as irregularities of the ferromagnetic material.

The servo region is composed of a preamble region and a burst region, as in the magnetic recording medium of the first embodiment.

FIG. 6-2 (a) is a cross-sectional view of the preamble region, and FIG. 6-2 (b) is a cross-sectional view of the burst region. As shown in FIG. 6-2, in the magnetic recording medium of the present embodiment, a non-magnetic substrate 603 made of a non-magnetic material, a base layer 602, and a recording layer 601 are laminated. Then, as shown in FIG. 6-2 (a), the recording layer 601 is provided with a recess, and the ferromagnet 604 is present in the recess of the recording layer 601 in the preamble region.

In the magnetic recording medium of the present embodiment, a groove is formed in the track direction of the recording area, but the bit is a continuous film. Therefore, the resolution in the bit direction is determined by the performance of the recording / playback head and the recording layer ferromagnet. Therefore, the AASA method is used to separate and isolate the recording area in the bit direction as well, and such a structure realizes higher density recording.

Next, a method of manufacturing the magnetic recording medium according to the present embodiment will be described. FIG. 7 is a process diagram showing the manufacturing process of the recording area of the magnetic recording medium according to the present embodiment, and FIG. 8 is a schematic diagram showing the state of each step of the manufacturing process of the recording area of the magnetic recording medium. .. The method for manufacturing the recording area of the magnetic recording medium according to the present embodiment is a processing method using the AASA (Artificially Assisted Self-Assembling) method.

The AASA method utilizes the self-assembly phenomenon of diblock copolymers to form nanometer-sized fine patterns (see "IEEE Trans. Magn., Vol38, pp1949, 2002 (Fig. 4)"). The self-organizing phenomenon is a method that can inexpensively produce a fine pattern in a large area, but it is impossible to artificially control the uniform direction (domain) of the fine pattern produced by self-organization. Therefore, in the AASA method, a guide groove is formed in advance, and self-organization is performed only in the guide groove to artificially create a region in which self-organization is uniform.

Since a patterned medium such as the magnetic recording medium of the present embodiment needs to be physically separated in both the track direction and the recording line direction of the recording area, advanced nanometer processing technology is required. On the other hand, the discrete track type magnetic recording medium separates only the recording track direction, so that pattern formation can be easily performed as compared with the patterned media.

First, for example, SiO₂, Si, etc., a base layer 602 made of a soft magnetic material and a recording layer 601 made of a ferromagnetic material are sequentially formed on a non-magnetic substrate 603 (process S701). Next, a resist 802 is formed on the recording layer of the deposited ferromagnetic material (step S702, (a) of FIG. 8).

Next, the stamper 801 on which the unevenness is formed is pressed against the resist formed on the recording layer 601 of the ferromagnetic material to transfer the unevenness (nanoimprint) to form a batch groove (step S703, FIG. 8). (b)).

Next, the self-assembled material 803 is filled in the formed guide groove and annealed to form a nanopattern by self-assembly (step S704, FIGS. 8 (c) and 8 (d)). Then, nanoholes are formed by oxygen RIE (step S705, (e) of FIG. 8), and SOG (Spin on glass) 805 is filled (step S706, (f) of FIG. 8).

Next, oxygen RIE is performed (step S707, (g) in FIG. 8) to obtain a high aspect ratio mask, then the ferromagnet is etched by ion milling (step S708), and the resist is completely removed by ashing (step S707). Step S709, (h) in FIG. As a result, the magnetic recording medium according to the present embodiment is manufactured.

Here, the stamper 801 can use EB drawing, Deep-UV cutting, and the like in addition to normal light exposure. Further, by omitting the steps S704 to S705 ((c) (d) (e) in FIG. 8) 5, it is possible to manufacture a discrete track type magnetic recording medium.

The magnetic recording medium manufactured by using 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 configured to be formed by a large number of magnetic dots (1 bit multi-cell). In the case of patterned media with a magnetic dot particle size of about 10 nm, it is preferable to form one recording with a large number of magnetic dots (1 bit multi-cell) because there is no practical means to access the 10 nm region accurately. .. For example, considering the surface density of 200 Gbpsi, the area of 1 bit is a track width of 125 nm x a recording bit length of 25 nm. When the magnetic dot particle size is 9 nm, 1 bit is formed by 42 magnetic dots with 14 magnetic dots (track width) × 3 (track direction) at an area density of 200 Gbpsi.

SiO instead of ferromagnet₂By using the above, it can be used as a master for stamper formation. In the steps shown in FIGS. 7 and 8, after forming the AASA master, the surface of the master is subjected to Ni conductivity treatment. Generally, Ni is formed into a film of about 10 nm by a sputtering method. After that, Ni electroforming can be performed to form a stamper having an AASA structure.

Here, a diblock copolymer is used as the self-assembling material 803 to be filled in the guide groove transferred onto the resist in step S704. A block copolymer is a copolymer (copolymer) composed of a linear polymer having a plurality of single polymers as partial constituents (blocks). For example, polymer chains A and B have a structure such as-(AA ... AA)-(BB ... BB)-.

The block copolymer has a phase-separated structure in which polymer A is agglomerated and polymer B is agglomerated by applying heat treatment. For example, there are "lamellar" structures in which A and B phases appear alternately and regularly, "cylinder" structures in which one phase is rod-shaped, and "sea island" structures in which one phase is spherically distributed.

Two-phase volume fractions are important for the formation of microphase-separated structures in block copolymers. Any polymer can be selected as the polymer A and the polymer B, but from the viewpoint of lithography, it is preferable to select a polymer having a large difference in dry etching rate. Aromatic polymers with relatively good etching resistance (eg polystyrene, polyvinylnaphthalene, poly-α-methylstyrene, polyvinylpyridine, etc.) and acrylic polymers with fast dry etching rates (eg, PMMA, polytbutylmethacrylate, etc.), etc. The combination is preferred. In the case of diblock copolymers in which PS (polystyrene) and PMMA are bonded, it is possible to selectively remove only PMMA by taking advantage of the large difference in dry etching resistance. Although the diblock copolymer of PS and polyvinylpyridine is well phase-separated into a sea-island structure, it is difficult to use the phase-separated structure as an etching mask because there is almost no difference in dry etching resistance. The size of the phase-separated structure (dot diameter, pitch) can be controlled by the molecular weights 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. When the molecular weight is reduced, the structure also becomes smaller. For example, by setting the molecular weight of PS to 43000 and the molecular weight of PMMA to 10000, the diameter of PMMA dots can be set to 10 nm and the pitch can be set to 29 nm.

The method for manufacturing the servo region of the magnetic recording medium according to the present embodiment is the same as the manufacturing method for the first embodiment.

As described above, in the magnetic recording medium according to the present embodiment, the signal pattern is recorded in advance at the time of manufacturing the medium in the patterned media in which the recording region is a ferromagnetic material and the magnetic part of the ferromagnetic material is separated by a non-magnetic material. Since the preamble region has a ferromagnet in the recess, high-density recording can be realized without adversely affecting the signal during recording and reproduction by the reproduction recording head, and magnetic recording with excellent thermal fluctuation resistance is possible. A medium can be provided.

(Example 1) By electron beam exposure, a disk-shaped stamper having 100 sectors of the uneven pattern shown in FIG. 1 was formed. Then, a discrete magnetic recording medium was manufactured by the steps described in FIGS. 4 and 5.

That is, CoZrNb, which is a soft magnetic material, was formed on a glass substrate with a film thickness of 200 nm to form a base layer. Then, a 20 nm film of a CoCrPt alloy, which is a ferromagnetic material, was formed into a recording layer by using a sputtering vapor deposition method. Then, a resist was formed on the recording layer with a film thickness of 100 nm.

Next, a pattern was formed by imprinting using a stamper in which the unevenness corresponding to the servo area and the unevenness corresponding to the recording area were mixed, and the residue due to imprinting was removed by oxygen RIE. At that time, the residue removal condition was set to 30 seconds for the oxygen RIE time according to the burst signal portion. After etching the magnetic layer with Ar ion milling, the resist was peeled off to form a carbon protective film at 5 nm. That is, a patterned media having a cross-sectional shape as shown in FIG. 1 was manufactured.

Lubrication was applied, and evaluation was performed using a levitation type recording / playback head at a levitation amount of 12 nm and 4200 rpm. By band erase, all 5 μm in the track direction was DC degaussed and the servo pattern was magnetized in one direction. After that, when the reproduced waveform was detected by an oscilloscope, a reproduced signal corresponding to the burst pattern as shown in (b) of FIG. 9 was obtained. This signal is differentiated and displayed. The signal of the burst C part was zero. I was able to apply the tracking servo in this state.

(Comparative Example 1) A discrete track type magnetic recording medium was manufactured by a general conventional manufacturing method. At that time, the oxygen RIE time was set to 45 seconds according to the preamble signal portion as the condition for removing the residue by imprinting. When the evaluation was performed by the levitation type recording / playback head, a playback signal corresponding to the burst pattern as shown in (c) of FIG. 9 was obtained. Even if the recording / playback head was moved in various ways for detection, the signal in the burst C portion did not become zero. Tracking servo cannot be applied in this state. This indicates that in the conventional discrete track type magnetic recording medium, the burst mark becomes thick and the signal in the burst C portion cannot be set to zero, and high TPI recording cannot be realized. all right.

(Example 2) By the same manufacturing method as in Example 1, a discrete track type magnetic recording medium in which a ferromagnet is present in a recess in a preamble region and no ferromagnet is present in a recess in a recording region and a burst region is manufactured. did. Then, an evaluation was performed using a levitation type recording / playback head at a levitation amount of 12 nm and 4200 rpm.

By band erase, all 5 μm in the track direction was DC degaussed and the servo pattern was magnetized in one direction. After that, as a result of measuring the amplitude intensity of the reproduced waveform of the preamble signal with an oscilloscope, the intensity of 1.6 mV was measured. Three months later, the amplitude intensity of the reproduced waveform of the preamble signal was measured without DC degaussing, and as a result, the intensity of 1.6 mV was measured. When the temperature was raised to 100 ° C and the same measurement was attempted, there was no deterioration in signal strength.

(Comparative Example 2) A discrete track type magnetic recording medium was manufactured by a general conventional manufacturing method. Shape evaluation by cross-sectional TEM confirmed that there was no magnetic material in the recesses in all areas.

As a result of measuring the amplitude intensity of the reproduced waveform of the preamble signal with an oscilloscope in the same manner as in Example 2, the intensity of 1.6 mV was measured. Three months later, as a result of measuring the amplitude intensity of the reproduced waveform of the preamble signal without performing DC degaussing, the signal intensity deteriorated to 1.4 mV. When the temperature was raised to 100 ° C and the same measurement was attempted, the signal strength deteriorated to 1.0 mV. From this result, it was found that the stability of magnetization is lowered because the ferromagnet is not present in the recess.

(Example 3) A discrete track type magnetic recording medium in which a ferromagnet is present in the recesses in the preamble region and no ferromagnet is present in the recesses in the recording region and the burst region is manufactured by the same manufacturing method as in Example 1. did. SiO by bias sputtering before forming a carbon protective film on the recording layer₂Was formed into a 200 nm film and etched back by milling. Then, a carbon protective film was formed to form a 5 nm film, and a discrete track type magnetic recording medium having the cross-sectional structure shown in FIG. 3 was manufactured.

When the levitation variation of the levitation head was measured by the laser Doppler method, the measurement result was Fh = 1.0 to 2.0 nm. This value is about the same as that of the continuous film before etching. By band erase, all 5 μm in the track direction was DC degaussed and the servo pattern was magnetized in one direction. After that, as a result of measuring the amplitude intensity of the reproduced waveform of the preamble signal with an oscilloscope, the intensity of 3.0 mV was measured. From this result, it was found that the signal strength was significantly improved by stabilizing the floating of the head.

(Comparative Example 3) A discrete track type magnetic recording medium in which a ferromagnet is present in the recesses in the preamble region and no ferromagnet is present in the recesses in the recording region and the burst region is manufactured by the same manufacturing method as in Example 1. did.

When the levitation variation of the levitation head was measured by the laser Doppler method, the measurement result was Fh = 10 nm. As a result of measuring the amplitude intensity of the reproduced waveform of the preamble signal with an oscilloscope, the intensity of 1.6 mV was measured. In a magnetic recording medium having a structure in which the recesses of the recording layer are not embedded with a non-magnetic material and are not flattened by a protective film, the signal strength may decrease and the S / N ratio may decrease due to levitation variation due to the levitation head. found.

(Example 4) A structure in which 12 rows of dots having a diameter of 15 nm and a pitch of 30 nm were arranged in a recording area by the AASA method was manufactured on a Si substrate. After that, a servo pattern was formed by EB exposure, and a stamper was made by Ni electroforming. Then, the patterned media was manufactured by the steps described in FIGS. 4 and 5. In the shape evaluation by the cross-sectional TEM, it was confirmed that the ferromagnet was present in the recess in the preamble region and that the ferromagnet was not present in the recess in the recording region (ferromagnet dot) and the burst region. That is, the patterned media shown in Fig. 6-1 and Fig. 6-2 were manufactured.

Lubrication was applied, and evaluation was performed using a levitation type recording / playback head at a levitation amount of 12 nm and 4200 rpm. By band erase, all 5 μm in the track direction was DC degaussed and the servo pattern was magnetized in one direction. After that, when the reproduced waveform was detected by an oscilloscope, a reproduced signal corresponding to the burst pattern as shown in (b) of FIG. 9 was obtained. Since the signal of the burst C part is 0, the tracking servo could be applied.

Further, since the recording area is divided into dots having a diameter of 15 nm and a pitch of 30 nm, the signal S / N ratio is improved by about twice as compared with the discrete track type magnetic recording medium of Example 1.

As described above, the magnetic recording medium and the method for manufacturing the magnetic recording medium according to the present invention are useful for the magnetic recording medium used for the hard disk and the method for manufacturing the magnetic recording medium.

<figref num="1-1">It is a top view of the magnetic recording medium which concerns on Embodiment 1. FIG.</figref><figref num="1-2">It is sectional drawing of the magnetic recording medium which concerns on Embodiment 1. FIG.</figref><figref num="2">It is a schematic diagram which shows the magnetic state in a recording area and the magnetic state in a servo area (preamble area).</figref><figref num="3">It is sectional drawing which shows the structure of the magnetic recording medium in which the unevenness of a recording layer is embedded with a non-magnetic material.</figref><figref num="4">It is a process drawing which shows the manufacturing process of the magnetic recording medium which concerns on this Embodiment.</figref><figref num="5">It is a schematic diagram which shows the state of each process of the manufacturing process of a magnetic recording medium.</figref><figref num="6-1">It is a top view of the magnetic recording medium which concerns on Embodiment 2. FIG.</figref><figref num="6-2">It is sectional drawing of the magnetic recording medium which concerns on Embodiment 2. FIG.</figref><figref num="7">It is a process drawing which shows the manufacturing process of the recording area of the magnetic recording medium which concerns on this Embodiment.</figref><figref num="8">It is a schematic diagram which shows the state of each process of the manufacturing process of the recording area of a magnetic recording medium.</figref><figref num="9">It is explanatory drawing which shows the measurement result of the preamble signal by an Example.</figref>

Code description

101,601 Recording layer 102,602 Base layer 103,603 Non-magnetic substrate 104,604 Ferromagnetic material 301 Protective layer 302 Non-magnetic material 501,801 Stamper 502,802 Resist 600a Ferromagnetic material dot 600b Non-magnetic material 801 Stamper 803 Self-assembling material 805 SOG