Method for manufacturing perpendicular magnetic recording medium

Abstract

This method for manufacturing a perpendicular magnetic recording medium comprises: a non-magnetic substrate preparation step in which a polishing step for polishing a surface of a non-magnetic substrate having an arithmetic surface roughness (Ra) of 0.2 nm or less using a polishing liquid and a cleaning step for cleaning the surface of the non-magnetic substrate obtained in the polishing step are repeated multiple times to set kurtosis (Rku) of the surface of the non-magnetic substrate to 0.45-0.65 and skewness (Rsk) of the surface of the non-magnetic substrate to 0.3-0.4; and a laminated structure formation step for forming a laminated structure including a soft magnetic layer and a perpendicular magnetic layer on the non-magnetic substrate obtained in the non-magnetic substrate preparation step.

Description

Method for manufacturing a perpendicular magnetic recording medium

[0001] The present disclosure relates to a method for manufacturing a perpendicular magnetic recording medium.

[0002] In recent years, high recording density has been demanded for hard disk drives (HDDs), which are a type of magnetic recording and reproducing device. Therefore, the development of magnetic recording media suitable for high recording density has been progressing.

[0003] Currently, the magnetic recording media mounted in commercially available magnetic recording and reproducing devices are so-called perpendicular magnetic recording media in which the easy axis of magnetization in the magnetic film is mainly oriented vertically. The perpendicular magnetic recording media have a small influence of the demagnetizing field in the boundary region between recording bits when the recording density is increased, and a clear bit boundary is formed, so an increase in noise can be suppressed. In addition, since the perpendicular magnetic recording media have little reduction in the recording bit volume accompanying the increase in recording density, they are also strong against the thermal fluctuation effect. Therefore, a medium structure suitable for perpendicular magnetic recording is being studied.

[0004] Conventionally, texture processing has been performed on the surface of a non-magnetic substrate before forming a magnetic layer or the like on the surface of the non-magnetic substrate in a magnetic recording medium of an in-plane recording system. The texture processing is a process of forming texture stripes (fine irregularities) along the circumferential direction on the surface of the non-magnetic substrate to make the surface of the medium have an appropriate surface roughness and impart circumferential magnetic anisotropy to the magnetic recording medium. It is known that when a magnetic layer is formed on a non-magnetic substrate having fine texture stripes, the electromagnetic conversion characteristics are improved as compared with the case where a magnetic layer is formed on a non-magnetic substrate having no texture stripes. This is because the circumferential crystal orientation of the underlayer and the magnetic layer formed on the surface of the non-magnetic substrate is improved by performing texture processing on the surface of the non-magnetic substrate. Therefore, the circumferential magnetic anisotropy of the magnetic layer can be increased, and magnetic properties such as thermal fluctuation resistance can be improved.

[0005] As a conventional texture processing method, for example, a method of supplying a polishing slurry to the surface of a rotating disk substrate and pressing a running polishing tape against the surface of the disk substrate is disclosed (see Patent Documents 1 and 2, etc.). In the polishing liquid, a dispersion medium in which diamond abrasive grains or the like are dispersed is used.

[0006] Conventional methods for manufacturing perpendicular magnetic recording media include, for example, a method of forming a smooth substrate surface free from abnormal protrusions by performing polishing with diamond particles before forming a magnetic film or the like on the substrate surface (see Patent Document 3, etc.).

[0007] Japanese Patent Publication No. 2004-178777, Japanese Patent Publication No. 2004-259417, Japanese Patent Publication No. 2010-080022

[0008] One aspect of this disclosure aims to provide a method for manufacturing a perpendicular magnetic recording medium that exhibits excellent vertical orientation of magnetic particles and excellent electromagnetic conversion characteristics in a magnetic recording and playback device.

[0009] The means for solving the above-mentioned problems are as follows: <1> A method for manufacturing a perpendicular magnetic recording medium, comprising: a polishing step of polishing the surface of a non-magnetic substrate having an arithmetic surface roughness (Ra) of 0.2 nm or less using a polishing solution; a cleaning step of cleaning the surface of the non-magnetic substrate obtained in the polishing step, repeated multiple times to set the crustosis (Rku) of the surface of the non-magnetic substrate to 0.45 or more and the skewness (Rsk) of the surface of the non-magnetic substrate to 0.3 or more and 0.4 or less; and a laminated structure formation step of forming a laminated structure including a soft magnetic layer and a perpendicular magnetic layer on the non-magnetic substrate obtained in the non-magnetic substrate preparation step. <2> The polishing liquid comprises diamond particles in an amount of 0.001% by mass or more and 0.05% by mass or less relative to the total amount of the polishing liquid, and a polishing accelerator in an amount of 1% by mass or more and 10% by mass or less relative to the total amount of the polishing liquid, the polishing step is performed by fixing the non-magnetic substrate to a spindle, supplying the polishing liquid to the surface of the non-magnetic substrate which is rotated in accordance with the rotation of the spindle, and pressing a polishing tape, which runs in the opposite direction to the rotation of the non-magnetic substrate between a supply roll and a winding roll, onto the surface of the non-magnetic substrate via a pressure roller, the cleaning step is performed by fixing the non-magnetic substrate to a spindle, supplying a cleaning liquid to the surface of the non-magnetic substrate which is rotated in accordance with the rotation of the spindle, and pressing a cleaning tape, which runs between a supply roll and a winding roll, onto the surface of the non-magnetic substrate via a pressure roller, the method for manufacturing a perpendicular magnetic recording medium as described in <1>. <3> The method for manufacturing a perpendicular magnetic recording medium according to <1> or <2>, wherein the time from the completion of the non-magnetic substrate preparation step to the formation of the laminated structure is within 10 hours. <4> The method for manufacturing a perpendicular magnetic recording medium according to <2>, wherein the diamond particles are cluster diamond particles, the primary particle diameter of the cluster diamond particles is 1 nm or more and 50 nm or less, and the secondary particle diameter of the cluster diamond particles is 50 nm or more and 500 nm or less.<5> The polishing accelerator comprises an organic polymer having a sulfonic acid group or a carboxylic acid group, as described in <2> or <4>, as a method for producing a perpendicular magnetic recording medium. <6> The non-magnetic substrate is a glass substrate, as described in any one of <1> to <5>, as a method for producing a perpendicular magnetic recording medium.

[0010] According to one aspect of this disclosure, it is possible to provide a method for manufacturing a perpendicular magnetic recording medium that has excellent vertical orientation of magnetic particles and excellent electromagnetic conversion characteristics in a magnetic recording and playback device.

[0011] This is a schematic cross-sectional view showing an example of a perpendicular magnetic recording medium manufactured by the manufacturing method of a perpendicular magnetic recording medium according to an embodiment of this disclosure. This is a schematic side view illustrating an example of an apparatus for performing a polishing process and a cleaning process. This is a schematic plan view of the apparatus of Figure 2A. This is a schematic perspective view showing an example of a magnetic recording and playback apparatus equipped with a perpendicular magnetic recording medium manufactured by the manufacturing method of a perpendicular magnetic recording medium according to an embodiment of this disclosure. This is a graph showing the numerical values ​​and evaluations obtained in the examples and comparative examples.

[0012] Conventional technologies, such as the perpendicular magnetic recording medium described in Patent Document 3, are manufactured using a non-magnetic substrate with a smooth surface. This is because when a magnetic film or the like is deposited on the surface of a non-magnetic substrate that has irregularities and scratches, abnormal protrusions may be formed. Furthermore, the irregularities on the surface of the non-magnetic substrate are reflected in the irregularities on the surface of the perpendicular magnetic recording medium. Therefore, if the surface irregularities are large, it becomes difficult to bring the magnetic head close to the surface of the perpendicular magnetic recording medium, which can worsen the electromagnetic conversion characteristics of the perpendicular magnetic recording medium. Accordingly, substrates used in perpendicular magnetic recording mediums are manufactured through multi-stage lapping and polishing processes, and the surface is polished even immediately before depositing magnetic films or the like to achieve surface smoothness. Polishing processes that enable smoother surfaces than ever before are being attempted for substrates used in perpendicular magnetic recording mediums.

[0013] The Disclosers investigated attempts to improve the electromagnetic conversion characteristics of perpendicular magnetic recording media by reducing the arithmetic mean roughness (Ra), a representative index of substrate surface smoothness, as well as attempts to improve the perpendicular orientation of magnetic particles when a magnetic layer is formed on a substrate surface by optimizing other shape parameters of the substrate surface. As a result, they found that the perpendicular orientation of magnetic particles constituting the magnetic layer can be improved by repeatedly performing polishing and cleaning processes on the substrate so that the kurtosis (Rku) and skewness (Rsk) of the substrate surface fall within a specific numerical range.

[0014] This embodiment of the disclosure (hereinafter simply referred to as "this embodiment") examines the shape of the substrate surface from a viewpoint different from smoothing the substrate surface and optimizes the shape of the substrate surface to provide a method for manufacturing a perpendicular magnetic recording medium that has excellent perpendicular orientation of magnetic particles and excellent electromagnetic conversion characteristics in a magnetic recording and playback device.

[0015] The details of the method for manufacturing a perpendicular magnetic recording medium according to this embodiment are described below.

[0016] (Method for manufacturing a perpendicular magnetic recording medium) The method for manufacturing a perpendicular magnetic recording medium according to this embodiment includes a non-magnetic substrate preparation step, which involves repeatedly polishing the surface of a non-magnetic substrate having an arithmetic surface roughness (Ra) of 0.2 nm or less using a polishing solution, and cleaning the surface of the non-magnetic substrate obtained in the polishing step, to set the crustosis (Rku) of the surface of the non-magnetic substrate to 0.45 or more and the skewness (Rsk) of the surface of the non-magnetic substrate to 0.3 or more and 0.4 or less, and forming a laminated structure on the non-magnetic substrate obtained in the non-magnetic substrate preparation step, and may include other steps as needed.

[0017] In this specification, non-magnetic substrates may be simply referred to as "substrates."

[0018] In this embodiment, arithmetic surface roughness (Ra) is a general parameter for evaluating surface roughness. Specifically, arithmetic surface roughness (Ra) represents the average of the absolute values ​​of the vertical deviations from the surface profile to the mean line. A higher numerical value for arithmetic surface roughness (Ra) indicates a rougher surface.

[0019] In this embodiment, kurtosis (Rku) is a parameter that represents the kurtosis (sharpness of depressions and protrusions) of the surface height distribution. Specifically, kurtosis (Rku) is calculated based on the fourth moment of the surface height. A value of kurtosis (Rku) greater than 3 indicates that the surface height distribution is pointed (many sharp protrusions and deep depressions), while a value of kurtosis (Rku) less than 3 indicates a flat distribution.

[0020] In this embodiment, skewness (Rsk) is a parameter that represents the asymmetry (distortion) of the surface height distribution. Specifically, skewness (Rsk) is calculated based on the third moment of the surface height. A positive value of skewness (Rsk) indicates that there are many protrusions on the surface, a negative value indicates that there are many depressions on the surface, and a value close to 0 indicates that the surface height distribution is symmetrical.

[0021] In this embodiment, there are no particular limitations on the method for measuring arithmetic surface roughness (Ra), crustosis (Rku), and skewness (Rsk), and they can be appropriately selected depending on the purpose. For example, one method is to measure a 1 μm square area on the substrate using an atomic force microscope (AFM).

[0022] Here, the perpendicular magnetic recording medium manufactured by the manufacturing method of the perpendicular magnetic recording medium according to this embodiment, and the polishing and cleaning steps included in the manufacturing method of the perpendicular magnetic recording medium according to this embodiment will be described in detail with reference to the drawings. However, the embodiments shown below are illustrative examples of perpendicular magnetic recording media, polishing and cleaning steps for realizing the technical concept of this disclosure, and are not limited to those described below, and can be modified as appropriate without departing from the gist of this disclosure.

[0023] Furthermore, the dimensions, materials, shapes, numbers, and relative arrangements of the components described in the embodiments are merely illustrative examples and not intended to limit the scope of this disclosure unless otherwise specified. Note that the size and positional relationships of the components shown in each drawing may be exaggerated for clarity. Also, in the following description, the same name and reference numeral indicate the same or identical components, and detailed explanations are omitted as appropriate. To avoid overly complex drawings, schematic diagrams may be used with some elements omitted, or end views showing only the cross-section may be used as cross-sectional views.

[0024] Furthermore, the following description uses terms to indicate specific directions or positions as needed (e.g., "up," "down," "side," "top," "bottom," "side," "X," "Y," "Z," and other terms including these terms). However, the use of these terms is solely to facilitate understanding of the invention with reference to the drawings, and the meaning of these terms does not unduly limit the technical scope of this disclosure. For example, if "top" is mentioned, the invention must not always be used in a way that it faces upwards.

[0025] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of a perpendicular magnetic recording medium manufactured by the manufacturing method of the perpendicular magnetic recording medium according to this embodiment.

[0026] The perpendicular magnetic recording medium 10 shown in Figure 1 has a soft magnetic layer 2, an orientation control layer 3, a perpendicular magnetic layer 4, and a protective layer 5 sequentially laminated on a non-magnetic substrate 1 that has undergone the polishing and cleaning steps of the manufacturing method for the perpendicular magnetic recording medium according to this embodiment.

[0027] <Non-magnetic substrate preparation process> The non-magnetic substrate preparation process involves repeating the polishing process and the washing process multiple times to set the crustosis (Rku) of the surface of the non-magnetic substrate to 0.45 or more and 0.65 or less, and the skewness (Rsk) of the surface of the non-magnetic substrate to 0.3 or more and 0.4 or less.

[0028] <<Polishing and Cleaning Processes>> The polishing process is a process of polishing the surface of a non-magnetic substrate having an arithmetic surface roughness (Ra) of 0.2 nm or less using a polishing solution. Preferably, the polishing process is carried out by fixing the non-magnetic substrate to a spindle, supplying a polishing solution to the surface of the non-magnetic substrate which is rotated in conjunction with the rotation of the spindle, and pressing a polishing tape, which runs in the opposite direction to the rotation of the non-magnetic substrate, against the surface of the non-magnetic substrate via a pressure roller between a supply roll and a winding roll.

[0029] The cleaning process is a process of cleaning the surface of the non-magnetic substrate that has been polished in the polishing process. Preferably, the cleaning process is carried out by fixing the non-magnetic substrate to a spindle, supplying a cleaning solution to the surface of the non-magnetic substrate which is rotated as the spindle rotates, and pressing a cleaning tape that runs between a supply roll and a winding roll against the surface of the non-magnetic substrate via a pressure roller.

[0030] [Figures 2A and 2B] Figure 2A is a schematic side view illustrating an example of an apparatus for performing polishing and cleaning processes. Figure 2B is a schematic top view of the apparatus shown in Figure 2A.

[0031] The apparatus shown in Figures 2A and 2B is capable of performing either a polishing process or a cleaning process. In Figure 2B, the left side is the cleaning apparatus for performing the cleaning process, and the right side is the polishing apparatus for performing the polishing process. In this embodiment, the cleaning apparatus for performing the cleaning process and the polishing apparatus for performing the polishing process may be provided independently.

[0032] The apparatus shown in Figures 2A and 2B fixes a non-magnetic substrate 1 to a spindle 101 and supplies polishing liquid S1 to the surface of the non-magnetic substrate 1, which is rotated in conjunction with the rotation of the spindle 101. Furthermore, polishing is performed by pressing a polishing tape 105, which travels in the opposite direction to the rotation of the non-magnetic substrate 1, against the surface of the non-magnetic substrate 1 via a pressure roller 106 between a supply roll 103 and a winding roll 104.

[0033] Although Figures 2A and 2B show an apparatus capable of simultaneously polishing both sides of the non-magnetic substrate 1, the polishing apparatus used to perform the polishing process may also be one that polishes only one side of the non-magnetic substrate 1.

[0034] -Non-magnetic substrate- The non-magnetic substrate 1 has an arithmetic surface roughness (Ra) of 0.2 nm or less, preferably 0.15 nm or less. When the arithmetic surface roughness (Ra) of the non-magnetic substrate 1 is 0.2 nm or less, the smoothness of the surface of the perpendicular magnetic recording medium is increased, and the flying height of the magnetic head during recording and playback of the perpendicular magnetic recording medium is reduced, thereby improving the electromagnetic conversion characteristics.

[0035] There are no particular restrictions on the non-magnetic substrate 1, and it can be appropriately selected according to the purpose, but a glass substrate such as amorphous glass or crystallized glass is preferred.

[0036] Examples of amorphous glass include general-purpose soda-lime glass, aluminoborsilicate glass, and aluminosilicate glass.

[0037] Examples of crystallized glass include lithium-based crystallized glass.

[0038] In addition to a glass substrate, the non-magnetic substrate 1 can also be an aluminum substrate with a hard film such as NiP provided on its surface.

[0039] There are no particular restrictions on the rotational speed of the spindle 101 in the polishing process, and it can be appropriately selected according to the purpose, but 50 rpm (min) －１ ) or more 2,500 rpm (min －１ Preferably less than 200 rpm (min－１ ) or more 800 rpm (min －１ The following are preferable.

[0040] The rotational speed of spindle 101 is 50 rpm (min) －１ ) is preferable because it shortens the processing time for the non-magnetic substrate 1.

[0041] The rotational speed of the spindle 101 is 2,500 rpm (min) －１ If the value is below this limit, problems such as the polishing liquid S1 supplied to the non-magnetic substrate 1 scattering into the surroundings can be eliminated.

[0042] - Polishing liquid S1 - Polishing liquid S1 comprises diamond particles in an amount of 0.001% by mass or more and 0.05% by mass or less relative to the total amount of polishing liquid S1, and a polishing accelerator in an amount of 1% by mass or more and 10% by mass or less relative to the total amount of polishing liquid S1, and may contain other components as needed.

[0043] Polishing solution S1 has similar additive components to polishing solutions used in the manufacturing process of non-magnetic substrates for general magnetic recording media, i.e., the polishing process, but the amounts of additives are significantly different. Typically, polishing solutions used in the polishing process contain about 1% by mass of abrasive particles.

[0044] There are no particular restrictions on the diamond particles, and they can be appropriately selected depending on the purpose. However, cluster diamond particles are preferred from the viewpoint of making it easier to set the kurtosis (Rku) of the nonmagnetic substrate surface to 0.45 or more and the skewness (Rsk) of the nonmagnetic substrate surface to 0.3 or more and 0.4 or less.

[0045] There are no particular restrictions on the particle size of the diamond particles, and they can be appropriately selected according to the purpose. However, from the viewpoint of making it easier to set the kurtosis (Rku) of the surface of the non-magnetic substrate to 0.45 or more and the skewness (Rsk) of the surface of the non-magnetic substrate to 0.3 or more and 0.4 or less, it is preferable that the primary particle size is 1 nm or more and 50 nm or less, and the secondary particle size is 50 nm or more and 500 nm or less.

[0046] There are no particular restrictions on the method for measuring the particle size of diamond particles, and it can be appropriately selected depending on the purpose. For example, it can be measured using a light scattering particle size distribution analyzer (HORIBA, NANO PARTICLE ANALYZER, SZ-100).

[0047] There are no particular restrictions on the polishing accelerator, and it can be appropriately selected according to the purpose. However, from the viewpoint of making it easier to set the crustosis (Rku) of the surface of the non-magnetic substrate to 0.45 or more and the skewness (Rsk) of the surface of the non-magnetic substrate to 0.3 or more and 0.4 or less, it is preferable to include an organic polymer having a sulfonic acid group or a carboxylic acid group, and it is more preferable to include an organic polymer containing sodium sulfonate or sodium carboxylate.

[0048] As the organic polymer containing sodium sulfonate or sodium carboxylate, a synthesized product may be used as appropriate, or a commercially available product may be used. Examples of commercially available products include, by product name, Tex Cool 2318 (manufactured by Yokkaichi Gosei Co., Ltd.), GEROPON SC / 213 (manufactured by Rhodia), GEROPON T / 36 (manufactured by Rhodia), GEROPON TA / 10 (manufactured by Rhodia), GEROPON TA / 72 (manufactured by Rhodia), New Calgen WG-5 (manufactured by Takemoto Oil & Fat Co., Ltd.), Agrizol G-200 (manufactured by Kao Corporation), Demol EP Powder (manufactured by Kao Corporation), Demol RNL (manufactured by Kao Corporation), Isoban 600-SF35 (manufactured by Kuraray Co., Ltd.), Polystar OM (manufactured by Nippon Oil & Fat Co., Ltd.), Sokalan CP9 (manufactured by BASF Japan Co., Ltd.), Sokalan Examples include PA-15 (manufactured by BASF Japan Co., Ltd.), Toxanon GR-31A (manufactured by Sanyo Chemical Industries, Ltd.), Solpol 7248 (manufactured by Toho Chemical Industry Co., Ltd.), Sharol AN-103P (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Aron T-40 (manufactured by Toagosei Chemical Industry Co., Ltd.), Panakayaku CP (manufactured by Nippon Kayaku Co., Ltd.), and Disrol H12C (manufactured by Nippon Emulsifier Co., Ltd.). Among these, Tex Cool 2318 (manufactured by Yokkaichi Gosei Co., Ltd.) is preferred.

[0049] Other components included in the polishing solution S1 are not particularly limited and can be appropriately selected depending on the purpose. Examples include water and dispersion media such as alcohol.

[0050] The polishing liquid S1 is preferably a dispersion in which diamond particles are dispersed in a dispersion medium containing a polishing accelerator.

[0051] The polishing liquid S1 is supplied from the nozzle 102. There are no particular restrictions on the flow rate of the polishing liquid S1 supplied from the nozzle 102, and it can be appropriately selected according to the purpose. However, from the viewpoint of being able to supply a sufficient amount of diamond particles necessary for processing and suppressing slippage of the polishing tape, thereby enabling a more stable polishing process of the non-magnetic substrate surface, a flow rate of 10 mL / min or more and 100 mL / min or less is preferred.

[0052] The polishing liquid S1 may be supplied continuously or discontinuously to the surface of the non-magnetic substrate 1.

[0053] In the polishing process, it is sufficient that the polishing liquid S1 is supplied between the non-magnetic substrate 1 and the polishing tape 105 before polishing is performed with the polishing tape 105. For example, the polishing liquid S1 may be supplied to the surface of the polishing tape 105 that is in contact with the non-magnetic substrate 1.

[0054] - Abrasive Tape 105 - There are no particular restrictions on the abrasive tape 105, and it can be appropriately selected according to the purpose. Examples include nonwoven fabric tape, woven fabric tape, and foamed polyurethane tape. Among these, nonwoven fabric tape is preferred from the viewpoint of suppressing the occurrence of scratches, etc., and making it easier to set the kurtosis (Rku) of the surface of the nonmagnetic substrate to 0.45 or more and 0.65 or less, and the skewness (Rsk) of the surface of the nonmagnetic substrate to 0.3 or more and 0.4 or less.

[0055] The abrasive tape 105 may be a compounded one as appropriate, or a commercially available product may be used. Examples of commercially available nonwoven tapes include TX014F and KSN06LPU (both manufactured by Toray Industries, Inc.), and ZN7503 (manufactured by Kuraray Co., Ltd.). Examples of commercially available woven tapes include Tracy (manufactured by Toray Industries, Inc.).

[0056] When using a nonwoven fabric tape as the abrasive tape 105, there are no particular restrictions on the fiber diameter of the nonwoven fabric tape, and it can be appropriately selected according to the purpose. However, from the viewpoint of making it easier to set the kurtosis (Rku) of the surface of the nonmagnetic substrate to 0.45 or more and the skewness (Rsk) of the surface of the nonmagnetic substrate to 0.3 or more and 0.4 or less, it is preferable to set it to 0.04 denier or less.

[0057] There are no particular restrictions on the running speed of the abrasive tape 105, and it can be appropriately selected according to the purpose, but a speed of 5 mm / min or more and 150 mm / min or less is preferred, and a speed of 10 mm / min or more and 100 mm / min or less is more preferred.

[0058] By setting the running speed of the polishing tape 105 to 5 mm / min or more and 150 mm / min or less, problems such as scratches occurring, diamond particles in the polishing liquid S1 becoming embedded in the surface of the non-magnetic substrate 1, or diamond particles in the polishing liquid S1 becoming embedded in the surface of the non-magnetic substrate 1 can be eliminated.

[0059] The abrasive tape 105 can be moved and simultaneously oscillated radially on the non-magnetic substrate 1. There are no particular restrictions on the oscillation speed of the abrasive tape 105, and it can be appropriately selected according to the purpose, but it is preferably 0.1 times / second or more and 20 times / second or less, and more preferably 0.5 times / second or more and 10 times / second or less.

[0060] When the oscillation speed of the abrasive tape 105 is between 0.1 times / second and 20 times / second, a sufficient amount of polishing can be obtained, and the occurrence of scratches and the like can be suppressed, so that a non-magnetic substrate 1 with a uniform polished state can be obtained.

[0061] There are no particular restrictions on the pressing pressure of the pressure roller 106 against the abrasive tape 105, and it can be appropriately selected according to the purpose. However, from the viewpoint of making it easier to set the kurtosis (Rku) of the surface of the non-magnetic substrate to 0.45 or more and the skewness (Rsk) of the surface of the non-magnetic substrate to 0.3 or more and 0.4 or less, a pressure of 1.0 N or more and 20 N or less is preferred, and a pressure of 5 N or more and 15 N or less is more preferred.

[0062] After polishing, a cleaning process is performed. This cleaning process removes any residue from the polishing process from the surface of the non-magnetic substrate 1.

[0063] The apparatus shown in Figures 2A and 2B fixes a non-magnetic substrate 1 to a spindle 101 and supplies a cleaning liquid S2 to the surface of the non-magnetic substrate 1, which is rotated in conjunction with the rotation of the spindle 101. Furthermore, a cleaning tape 205, which runs between a supply roll 203 and a winding roll 204, is pressed against the surface of the non-magnetic substrate 1 via a pressure roller 206 to perform the cleaning process.

[0064] Although Figures 2A and 2B show an apparatus capable of simultaneously cleaning both sides of the non-magnetic substrate 1, the cleaning apparatus used to perform the cleaning process may also be one capable of cleaning only one side of the non-magnetic substrate 1.

[0065] -Cleaning Solution S2- The cleaning solution S2 is not particularly limited as long as it can clean the non-magnetic substrate 1, and can be appropriately selected according to the purpose. Examples include water and alcohol. Furthermore, the cleaning solution S2 may contain a surfactant from the viewpoint of enhancing its cleaning ability.

[0066] - Cleaning Tape 205 - There are no particular restrictions on the cleaning tape 205, and it can be appropriately selected according to the purpose. Examples include flocked tape, nonwoven tape, foamed polyurethane tape, nonwoven tape and woven tape.

[0067] The cleaning tape 205 may be a suitably synthesized tape or a commercially available product. Examples of commercially available nonwoven tapes include TX014F and KSN06LPU (both manufactured by Toray Industries, Inc.) and ZN7503 (manufactured by Kuraray Co., Ltd.). Examples of commercially available woven tapes include Tracy (manufactured by Toray Industries, Inc.).

[0068] There are no particular restrictions on the running speed of the cleaning tape 205, and it can be appropriately selected according to the purpose, but a speed of 5 mm / min or more and 150 mm / min or less is preferred, and a speed of 10 mm / min or more and 100 mm / min or less is more preferred.

[0069] The cleaning tape 205 can be moved and simultaneously oscillated radially on the non-magnetic substrate 1. There are no particular restrictions on the oscillation speed of the cleaning tape 205, and it can be appropriately selected according to the purpose, but it is preferably 0.1 times / second or more and 20 times / second or less, and more preferably 0.5 times / second or more and 10 times / second or less.

[0070] There are no particular restrictions on the pressure applied by the pressing roller 206 to the cleaning tape 205, and it can be appropriately selected according to the purpose, but it is preferably 1.0 N to 20 N, and more preferably 5 N to 15 N.

[0071] Unlike the manufacturing process for non-magnetic substrates for magnetic recording media, the non-magnetic substrate preparation step is preferably performed immediately before the deposition of a magnetic film or the like on the surface of the non-magnetic substrate 1. In particular, the time from the completion of the non-magnetic substrate preparation step to the formation of the laminated structure is preferably within 10 hours.

[0072] <Laminated Structure Formation Process> The laminated structure formation process is a process of forming a laminated structure including a soft magnetic layer and a perpendicular magnetic layer on a non-magnetic substrate obtained in the non-magnetic substrate preparation process. The laminated structure formation process preferably includes a soft magnetic layer formation process, an orientation control layer formation process, and a perpendicular magnetic layer formation process, and may also include a protective layer formation process as needed.

[0073] <<Soft Magnetic Layer Formation Process>> The soft magnetic layer formation process is a process of forming a soft magnetic layer 2 on a non-magnetic substrate 1. Specifically, it is a process of forming a soft magnetic layer 2 on the non-magnetic substrate 1 obtained in the non-magnetic substrate preparation process using a sputtering target by DC (Direct Current) or RF (Radio Frequency) magnetron sputtering method. The non-magnetic substrate 1 has a surface crustosis (Rku) of 0.45 or more and a surface skewness (Rsk) of 0.3 or more and 0.4 or less.

[0074] The soft magnetic layer formation process involves, for example, maintaining a vacuum of 10 in the chamber used for forming the soft magnetic layer. －４ Pa or more 10 －７This can be performed by evacuating the system until the pressure drops below Pa, then placing the non-magnetic substrate 1 inside the chamber, introducing sputtering gas, and causing a discharge.

[0075] There are no particular restrictions on the sputtering gas; it can be appropriately selected depending on the purpose. For example, Ar gas can be used.

[0076] In the soft magnetic layer formation process, it is preferable to use a sputtering target made of a soft magnetic material, from the viewpoint of easily forming the soft magnetic layer 2.

[0077] There are no particular restrictions on the soft magnetic material, and it can be appropriately selected according to the purpose. Examples include CoFe alloys, FeCo alloys, FeNi alloys, FeAl alloys, FeCr alloys, FeTa alloys, FeMg alloys, FeZr alloys, FeC alloys, FeN alloys, FeSi alloys, FeP alloys, FeNb alloys, FeHf alloys, and FeB alloys.

[0078] Examples of CoFe alloys include CoFeTaZr and CoFeZrNb.

[0079] Examples of FeCo-based alloys include FeCo and FeCoV.

[0080] Examples of FeNi-based alloys include FeNi, FeNiMo, FeNiCr, and FeNiSi.

[0081] Examples of FeAl-based alloys include FeAl, FeAlSi, FeAlSiCr, FeAlSiTiRu, and FeAlO.

[0082] Examples of FeCr-based alloys include FeCr, FeCrTi, and FeCrCu.

[0083] Examples of FeTa-based alloys include FeTa, FeTaC, and FeTaN.

[0084] Examples of FeMg-based alloys include FeMgO.

[0085] Examples of FeZr-based alloys include FeZrN.

[0086] In addition to the above, other soft magnetic materials include FeAlO, FeMgO, FeTaN, and FeZrN, which contain 60 at% or more of Fe.

[0087] Among these soft magnetic materials, CoZr, CoZrNb, CoZrTa, CoZrCr, and CoZrMo alloys are preferred, as they contain 80 at% or more of Co, at least one of Zr, Nb, Ta, Cr, and Mo, and have an amorphous structure.

[0088] There are no particular restrictions on the average thickness of the soft magnetic layer 2, and it can be appropriately selected according to the purpose, but it is preferably 15 nm to 100 nm. The average thickness of the soft magnetic layer 2 can be adjusted by changing the discharge time and the power supplied.

[0089] <<Orientation Control Layer Formation Process>> The orientation control layer formation process is a process of forming an orientation control layer 3 on the soft magnetic layer 2. Specifically, it is a process of forming an orientation control layer 3 on the soft magnetic layer 2 obtained in the soft magnetic layer formation process using a sputtering target by DC or RF magnetron sputtering.

[0090] There are no particular restrictions on the sputtering target used in the orientation-controlled layer formation process, and it can be appropriately selected according to the purpose. Examples include Ru-based alloys, Ni-based alloys, and Co-based alloys.

[0091] There are no particular restrictions on the average film thickness of the orientation control layer 3, and it can be appropriately selected according to the purpose, but it is preferably 5 nm to 40 nm, and more preferably 8 nm to 30 nm. The average film thickness of the orientation control layer 3 can be adjusted by changing the discharge time and the power supplied.

[0092] <<Perpendicular Magnetic Layer Formation Process>> The perpendicular magnetic layer formation process is a process of forming a perpendicular magnetic layer 4 on the orientation control layer 3. Specifically, it is a process of forming a perpendicular magnetic layer 4 on the orientation control layer 3 obtained in the orientation control layer formation process using a sputtering target by DC or RF magnetron sputtering.

[0093] The perpendicular magnetic layer 4 may be either a magnetic layer having a granular structure containing an oxide or a magnetic layer not containing an oxide, or may have a structure combining these.

[0094] There are no particular restrictions on the sputtering target for forming the magnetic layer having a granular structure containing an oxide, and it can be appropriately selected according to the purpose. For example, (Co １４ Cr １８ Pt) ９０ -(SiO ２ ) １０ [Metal composition consisting of 14 at% Cr content, 18 at% Pt content, and the balance Co is 90 mol%, and oxide composition consisting of SiO ２ is 10 mol%], (Co １０ Cr １６ Pt) <00者00017>-(SiO ２ ) ８ [Metal composition consisting of 10 at% Cr content, 16 at% Pt content, and the balance Co is 92 mol%, and oxide composition consisting of SiO ２ is 8 mol%], (Co ８ Cr １４ Pt ４ Nb) ９４ -(Cr ２ O ３ ) ６ [Metal composition consisting of 8 at% Cr content, 14 at% Pt content, 4 at% Nb content, and the balance Co is 94 mol%, and oxide composition consisting of Cr ２ O ３ is 6 mol%], (CoCrPt)-(Ta ２ O ５ ), (CoCrPt)-(Cr [[ID=5者000032>O ３ )-(TiO ２ ), (CoCrPt)-(Cr ２ O ３ )-(SiO ２ ), (CoCrPt)-(Cr ２ O ３ )-(SiO ２ )-(TiO ２ ), (CoCrPtMo)-(TiO), (CoCrPtW)-(TiO ２ ), (CoCrPtB)-(Al２ O ３ ), (CoCrPtTaNd)-(MgO), (CoCrPtBCu)-(Y ２ O ３ ) and (CoCrPtRu)-(SiO ２ ) are some examples.

[0095] The oxide content in a sputtering target for forming a magnetic layer having a granular structure containing oxides is not particularly limited and can be appropriately selected depending on the purpose, but it is preferably 3 mol% to 18 mol%, and more preferably 6 mol% to 13 mol%, relative to the total amount of Co, Cr, and Pt.

[0096] There are no particular restrictions on the sputtering target used to form an oxide-free magnetic layer, and it can be appropriately selected according to the purpose. Examples include CoCrPt-based, CoCrPtB-based, CoCrPtTa-based, CoCrPtTaB-based, CoCrPtBNd-based, CoCrPtTaNd-based, CoCrPtNb-based, CoCrPtBW, CoCrPtMo, CoCrPtCuRu, and CoCrPtRe.

[0097] As for CoCrPt systems, for example, Co １４～２４ Cr ８～２２ Examples include Pt [Cr content 14-24 at%, Pt content 8-22 at%, remainder Co].

[0098] As for the CoCrPtB system, Co １０～２４ Cr ８～２２ Pt １～１６ Examples include B [Cr content 10-24 at%, Pt content 8-22 at%, B content 1-16 at%, remainder Co].

[0099] As for CoCrPtTa systems, Co １０～２４ Cr １～５ Examples include Ta [Cr content 10-24 at%, Ta content 1-5 at%, remainder Co].

[0100] As for the CoCrPtTaB system, Co １０～２４ Cr ８～２２ Pt １～５ Ta １～１０Examples include B [Cr content 10-24 at%, Pt content 8-22 at%, Ta content 1-5 at%, B content 1-10 at%, remainder Co].

[0101] Among the sputtering targets used to form magnetic layers that do not contain these oxides, CoCrPt-based and CoCrPtB-based targets are preferred.

[0102] <<Protective Layer Formation Process>> The protective layer formation process is the process of forming a protective layer 5 on the perpendicular magnetic layer 4. The protective layer 5 can be formed, for example, by known sputtering methods, plasma CVD methods, and combinations thereof.

[0103] The material for the protective layer 5 is not particularly limited as long as it has a protective function, and can be appropriately selected according to the purpose. For example, a material mainly composed of carbon can be used.

[0104] A lubricating layer may be formed on the protective layer 5 as needed. This lubricating layer can be formed by applying a perfluoropolyether fluorine-based lubricant using methods such as the dip method and the spin-coat method.

[0105] There are no particular restrictions on the method for measuring the average thickness of each layer, such as the soft magnetic layer, orientation control layer, perpendicular magnetic layer, and protective layer, and a suitable method can be selected according to the purpose. For example, it can be measured by methods using X-ray fluorescence analysis (XRF) or by observing the cross-section of each layer with a scanning electron microscope (SEM) and measuring its length.

[0106] [Figure 3] Figure 3 is a schematic perspective view showing an example of a magnetic recording and playback apparatus equipped with a perpendicular magnetic recording medium manufactured by the method for manufacturing a perpendicular magnetic recording medium according to this embodiment.

[0107] The magnetic recording and playback device 20 comprises a perpendicular magnetic recording medium 10, a media drive unit 11 for rotating the perpendicular magnetic recording medium 10, a magnetic head 12 for recording and playback of information on the perpendicular magnetic recording medium 10, a head drive unit 13 for moving the magnetic head 12 relative to the perpendicular magnetic recording medium 10, and a recording and playback signal processing system 14.

[0108] The recording and playback signal processing system 14 can process data input from an external source and send a recording signal to the magnetic head 12, and process the playback signal from the magnetic head 12 and send the data to the outside.

[0109] The magnetic head 12 can utilize an MR (magnetoresistance) element that employs the anisotropic magnetoresistance effect (AMR) and a GMR element that employs the giant magnetoresistance effect (GMR) as regeneration elements, making it suitable for high recording density heads.

[0110] The embodiments will be described in more detail below with reference to examples, but the embodiments are not limited to these examples.

[0111] <Polishing Process> A non-magnetic substrate was fixed to a spindle, and polishing fluid was supplied to the surface of the non-magnetic substrate as it rotated with the rotation of the spindle. Polishing was performed by pressing a polishing tape (polyester woven cloth) that ran in the opposite direction to the rotation of the non-magnetic substrate between a supply roll and a winding roll onto the surface of the non-magnetic substrate via a pressure roller.

[0112] For the non-magnetic substrate, a glass substrate (3.5 inches in size) manufactured by HOYA Corporation was used.

[0113] The polishing solution used contained the following materials and was dropped onto the surface of a non-magnetic substrate at a dropping rate of 50 ml / min for 2 seconds: • Cluster diamond (primary particle size: 25 nm, secondary particle size: 150 nm) 0.01% by mass • Total polishing solution (Tex Cool 2318, manufactured by Yokkaichi Gosei Co., Ltd.) 4% by mass • Remainder of pure water

[0114] The conditions in the polishing process are as follows: • Polishing tape travel speed: 75 mm / min • Rotation speed of the non-magnetic substrate: 600 rpm (min) －１ ) • Oscillation speed of non-magnetic substrate: 5.0 times / second • Pressing force of polishing tape: 8.0 N • Polishing time: 10 seconds

[0115] <Cleaning Process> Next, the non-magnetic substrate was fixed to the spindle, and water was supplied to the surface of the non-magnetic substrate as it rotated with the rotation of the spindle. The cleaning was performed by pressing a cleaning tape (polyester woven fabric) that ran between the supply roll and the winding roll against the surface of the non-magnetic substrate via a pressure roller.

[0116] The various conditions in the cleaning process are as follows: • Cleaning tape running speed: 75 mm / min • Non-magnetic substrate rotation speed: 200 rpm (min) －１ ) • Oscillation speed of non-magnetic substrate: 3.0 times / second • Pressing force of cleaning tape: 5.0 N • Cleaning time: 5 seconds

[0117] A total of 12 samples were prepared by repeating the polishing and washing processes described above 0 to 12 times. Before each polishing step, an atomic force microscope (AFM) was used to observe a 1 μm square area on the non-magnetic substrate, and the arithmetic surface roughness (Ra), crustosis (Rku), and skewness (Rsk) were measured. The results are shown in Tables 1 and 2.

[0118] Each sample is placed in the deposition chamber of a DC magnetron sputtering system (Anelva C-3010), achieving a vacuum of 1 × 10⁻¹⁰. －５ After evacuating the deposition chamber until the temperature reached Pa, a soft magnetic layer with an average thickness of 100 nm was formed on a non-magnetic substrate using a target. At this time, the substrate temperature was kept below 100°C, and the target was treated with Co- ４ Zr- ７ Nb [Zr content: 4 at%, Nb content: 7 at%, balance Co] was used.

[0119] After depositing a Ru layer on a soft magnetic layer with an average thickness of 8 nm, further Co- ４ Zr- ７ A soft magnetic layer of Nb was deposited with an average thickness of 100 nm to form a soft magnetic underlayer.

[0120] Next, Ni on top of the soft magnetic underlayer ６ Using a W [W content 6 at%, remainder Ni] target and a Ru target, films were sequentially deposited with average film thicknesses of 10 nm and 20 nm, respectively, to form an orientation-controlled layer.

[0121] Further, on the orientation control layer, (Co １３ Cr １６ Pt) ９０ -(SiO ２ ) ４ -(Cr ２ O ３ ) ３ -(TiO ２ ) ３ [An alloy composition with a Cr content of 13 at%, a Pt content of 16 at%, and the balance Co of 90 mol%, an oxide composed of SiO ２ of 4 mol%, an oxide composed of Cr ２ O ３ of 3 mol%, and an oxide composed of TiO ２ of 3 mol%] was formed as the first magnetic layer with an average film thickness of 60 nm.

[0122] On the first magnetic layer, a first non-magnetic layer composed of (Co ２０ Cr) ８８ -(TiO ２ ) １２ was formed with an average film thickness of 10 nm. On the first non-magnetic layer, a second magnetic layer composed of (Co ９．５ Cr １６ Pt ７ Ru) ９２ -(SiO ２ ) ５ -(Cr ２ O ３ ) ３ was formed with an average film thickness of 30 nm. Further, a second non-magnetic layer composed of Ru was formed on the second magnetic layer with an average film thickness of 10 nm.

[0123] On the second non-magnetic layer, using a target composed of Co １６ Cr １６ Pt<x ８ B [Cr content 16 at%, Pt content 16 at%, B content 8 at%, balance Co], a perpendicular magnetic layer was formed with an average film thickness of 10 nm at a sputtering pressure of 3 Pa.

[0124] Next, a carbon film was formed as a protective layer with an average film thickness of 5 nm by CVD method. Next, a lubricating layer composed of perfluoropolyether was formed by dipping method to obtain each perpendicular magnetic recording medium.

[0125] [Evaluation of Magnetic Regeneration Characteristics (ADC)] The recording density (ADC) of each perpendicular magnetic recording medium was evaluated. The results are shown in Tables 1 and 2. The recording density (ADC) was measured using a GUZIK RWA1632 read / write analyzer and a S1701MP spin stand. The head used was one with a single-pole magnetic pole for writing and a GMR element for the regeneration section. The recording density (ADC) was evaluated by comparing the amplitude of the recording signal to each perpendicular magnetic recording medium with the output signal of the signal recorded on each perpendicular magnetic recording medium. The higher the ADC value, the higher the number of recording bits per square inch in the perpendicular magnetic recording medium, indicating a higher recording density.

[0126]

[0127]

[0128] The results shown in Tables 1 and 2 are illustrated in the graph in Figure 4. As shown in Figure 4, in Example 1, where the polishing and cleaning processes were repeated four times; Example 2, where they were repeated five times; and Example 3, where they were repeated six times, the kurtosis (Rku) of the surface of the non-magnetic substrate was between 0.45 and 0.65, and the skewness (Rsk) of the surface of the non-magnetic substrate was between 0.3 and 0.4. Therefore, it was found that the ADC of the perpendicular magnetic recording medium was the best.

[0129] As described above, embodiments of this disclosure have been explained, but these embodiments are provided as examples only and do not limit this disclosure. The embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, or modifications are possible without departing from the spirit of the invention. The embodiments and their variations are included in the scope or spirit of the invention and are included in the scope of the invention and its equivalents as described in the claims.

[0130] This application claims priority based on Japanese Patent Application No. 2024-227976, filed with the Japan Patent Office on December 24, 2024, and incorporates all the contents of the said application.

[0131] 1...Non-magnetic substrate 2...Soft magnetic layer 3...Orientation control layer 4...Perpendicular magnetic layer 5...Protective layer 10...Perpendicular magnetic recording medium 11...Media drive unit 12...Magnetic head 13...Head drive unit 14...Recording / playback signal processing system 20...Magnetic recording / playback device 101...Spindle 102...Nozzle 103...Supply roll 104...Winding roll 105...Abrasive tape 106...Pressing roller S1...Abrasive liquid 202...Nozzle 203...Supply roll 204...Winding roll 205...Cleaning tape 206...Pressing roller S2...Cleaning liquid

Claims

1. A method for manufacturing a perpendicular magnetic recording medium, comprising: a polishing step of polishing the surface of a non-magnetic substrate having an arithmetic surface roughness (Ra) of 0.2 nm or less using a polishing solution; a cleaning step of washing the surface of the non-magnetic substrate obtained in the polishing step, and repeating these steps multiple times to set the kurtosis (Rku) of the surface of the non-magnetic substrate to 0.45 or more and the skewness (Rsk) of the surface of the non-magnetic substrate to 0.3 or more and 0.4 or less; and a laminated structure formation step of forming a laminated structure including a soft magnetic layer and a perpendicular magnetic layer on the non-magnetic substrate obtained in the non-magnetic substrate preparation step.

2. The manufacturing method for a perpendicular magnetic recording medium according to claim 1, wherein the polishing liquid comprises diamond particles in an amount of 0.001% by mass or more and 0.05% by mass or less relative to the total amount of the polishing liquid, and a polishing accelerator in an amount of 1% by mass or more and 10% by mass or less relative to the total amount of the polishing liquid, the polishing step is performed by fixing the non-magnetic substrate to a spindle, supplying the polishing liquid to the surface of the non-magnetic substrate which is rotated in conjunction with the rotation of the spindle, and pressing a polishing tape, which runs in the opposite direction to the rotation of the non-magnetic substrate between a supply roll and a winding roll, onto the surface of the non-magnetic substrate via a pressure roller, the cleaning step is performed by fixing the non-magnetic substrate to a spindle, supplying a cleaning liquid to the surface of the non-magnetic substrate which is rotated in conjunction with the rotation of the spindle, and pressing a cleaning tape, which runs between a supply roll and a winding roll, onto the surface of the non-magnetic substrate via a pressure roller.

3. The method for manufacturing a perpendicular magnetic recording medium according to claim 1 or 2, wherein the time from the completion of the non-magnetic substrate preparation step to the formation of the laminated structure is within 10 hours.

4. The method for manufacturing a perpendicular magnetic recording medium according to claim 2, wherein the diamond particles are cluster diamond particles, the primary particle diameter of the cluster diamond particles is 1 nm or more and 50 nm or less, and the secondary particle diameter of the cluster diamond particles is 50 nm or more and 500 nm or less.

5. The method for producing a perpendicular magnetic recording medium according to claim 2, wherein the polishing accelerator comprises an organic polymer having a sulfonic acid group or a carboxylic acid group.

6. The method for manufacturing a perpendicular magnetic recording medium according to any one of claims 1 to 5, wherein the non-magnetic substrate is a glass substrate.

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