Magnetic recording medium inspection method and method for manufacturing magnetic recording medium

Abstract

This magnetic recording medium inspection method is for inspecting a magnetic recording medium having a magnetic layer on a non-magnetic substrate, and is characterized by identifying a defective portion having a non-periodic protruding shape, on the basis of an output signal obtained by scanning a surface of the magnetic recording medium with an inspection head having a heat-sensitive resistance element, the protruding shape having a height of 0.1 nm to 1.5 nm, inclusive, and a width of 1 μm to 15 μm, inclusive.

Description

Method for inspecting magnetic recording media and method for manufacturing magnetic recording media

[0001] This disclosure relates to a method for inspecting magnetic recording media and a method for manufacturing magnetic recording media.

[0002] Magnetic recording and playback devices, such as hard disk drives (HDDs), are widely used as external storage devices for information processing equipment such as computers. In recent years, they have also been used as video recording devices and as high-capacity storage in data centers.

[0003] Magnetic recording media used in HDDs are generally manufactured by sequentially forming an underlayer, magnetic layer, protective layer, and lubricating layer on the surface of a substrate made of aluminum alloy and glass substrate. The manufactured magnetic recording media are evaluated by glide testing, certify testing, and HDIs (Head Disk Interface sensor) testing. Magnetic recording media that have undergone glide testing, certify testing, and HDIs testing are shipped only after it is guaranteed that there are no defects, the amount of defects is below a standard value, or the location of defects has been identified.

[0004] Conventional methods for evaluating magnetic recording media include, for example, a method for evaluating the surface characteristics of a magnetic recording media using signals resulting from the thermal asperity phenomenon caused by contact between a magnetic head having an MR element and protrusions generated on the surface of the magnetic recording media (see Patent Document 1). The thermal asperity phenomenon refers to the phenomenon in which, when an MR element provided on a magnetic head comes into contact with a protrusion on the surface of a magnetic recording media, the heat generated by the contact causes a rapid temperature rise in the reading element, and the electrical resistance value of this reading element changes.

[0005] Other conventional evaluation methods for magnetic recording media include, for example, a method in which the surface of the magnetic recording media is scanned using a thermoresistive element, and signals caused by long-period undulations of wavelength 40 μm or longer on the surface of the magnetic recording media are separated from the signal output from the thermoresistive element, and protrusions on the surface of the magnetic recording media are detected from the separated signal (see Patent Document 2). The signals caused by undulations from the thermoresistive element are output by heat transfer mediated by air between the inspection head and the surface of the magnetic recording media. In other words, it is presumed that the signals caused by undulations from the thermoresistive element are output when the thermoresistive element and the surface of the magnetic recording media are not in contact.

[0006] Japanese Patent Application Publication No. 10-105908 Japanese Patent Application Publication No. 2008-146803

[0007] One aspect of this disclosure aims to provide a reliable method for inspecting magnetic recording media.

[0008] The means for solving the above problems are as follows: <1> A method for inspecting a magnetic recording medium having a magnetic layer on a non-magnetic substrate, wherein a defect portion having a non-periodic convex shape is identified based on an output signal obtained by scanning the surface of the magnetic recording medium with an inspection head having a thermoresistive element, and the convex shape has a height of 0.1 nm or more and a width of 1 μm or more and a width of 1 μm or more and 15 μm or less. <2> The method for inspecting a magnetic recording medium according to <1>, wherein the convex shape is formed in the manufacturing process of the magnetic recording medium. <3> The method for inspecting a magnetic recording medium according to <1> or <2>, wherein a defect portion having the non-periodic convex shape is identified based on the output signal from which signals caused by undulations on the surface of the magnetic recording medium have been removed. <4> The method for inspecting a magnetic recording medium according to any one of <1> to <3>, wherein the thermoresistive element is a magnetoresistive element. <5> A method for manufacturing a magnetic recording medium having a magnetic layer on a non-magnetic substrate, the method for manufacturing the magnetic recording medium comprising: a magnetic recording medium forming step of heating the non-magnetic substrate to form a magnetic layer; and an inspection step of inspecting the magnetic recording medium obtained by the magnetic recording medium forming step using the magnetic recording medium inspection method described in any of <1> to <4>.

[0009] According to one aspect of this disclosure, a method for inspecting a highly reliable magnetic recording medium can be provided.

[0010] It is a schematic cross-sectional view for explaining the mechanism by which the substrate is deformed. It is a graph schematically showing the signal output from the thermal resistance element in the certification inspection and HDIs inspection of the magnetic recording medium. It is a schematic view showing an example of an inspection apparatus for carrying out the inspection method of the magnetic recording medium according to an embodiment of the present disclosure. It is a graph showing an example of an output signal obtained by scanning an inspection head having a thermal resistance element in the inspection method of the magnetic recording medium according to an embodiment of the present disclosure. It is a schematic cross-sectional view showing an example of a magnetic recording medium manufactured by the manufacturing method of the magnetic recording medium according to an embodiment of the present disclosure. It is a schematic perspective view showing an example of a magnetic recording and reproducing apparatus using the magnetic recording medium manufactured by the manufacturing method of the magnetic recording medium according to an embodiment of the present disclosure. It is an example of an AFM observation image of the magnetic recording medium in the example.

[0011] Hereinafter, embodiments for carrying out the present disclosure will be described. In this specification, "~" indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value unless otherwise specified. Also, when only the unit of the upper limit value is described in the numerical range represented by "~", it means that the lower limit value is also in the same unit.

[0012] The present inventors have discovered that in the conventional HDIs inspection, among the signals output in the state where the thermal resistance element and the magnetic recording medium are non-contact, there are signals different from those caused by the undulations on the surface of the magnetic recording medium. As a result of analyzing this signal, it was found that the signal has a height comparable to that of the undulation, the width is close to the lower limit value of the undulation, has no periodicity like the undulation, and appears superimposed on the signal caused by the undulation.

[0013] When the present inventors investigated the cause of the generation of this signal, they found that it is due to the deformation of the substrate that occurs in the manufacturing process of the magnetic recording medium, particularly in the film forming process. The reasons for the occurrence of substrate deformation are diverse, but the main causes are as follows.

[0014] Inevitable impurities contained near the surface of the substrate react with surrounding substances upon heating of the substrate during film formation, causing volume expansion. It is considered that as the volume of the inevitable impurities expands, the film is pushed up, resulting in deformation of the substrate. Note that inevitable impurities are impurities that unavoidably混入 from raw materials and manufacturing processes. This will be described in detail using Fig. 1.

[0015] Fig. 1 is a schematic cross-sectional view for explaining the mechanism by which the substrate is deformed. Specifically, Fig. 1(a) is a schematic cross-sectional view showing an example of the state of the substrate 14 before the thin film 12 is formed, and Fig. 1(b) is a schematic cross-sectional view showing an example of the state of the substrate 14 after the thin film 12 is formed.

[0016] As shown in Fig. 1(a), assume a case where inevitable impurities 11 are contained near the surface of the substrate 14. Since the surface 10 of the substrate 14 is smoothly polished, the location where the inevitable impurities 11 are contained is also flat without a step with respect to the surroundings. When heating the substrate 14 to form the thin film 12 on the surface 10 of the substrate 14, the inevitable impurities 11 expand in volume according to their own coefficient of thermal expansion, or react with surrounding substances, or expand in volume by crystallizing. Then, since the thin film 12 is pushed up, convex portions 13 may occur on the surface of the thin film 12. Note that the position of the convex portions 13 and the position where the inevitable impurities 11 are contained substantially coincide in a plan view of the substrate 14.

[0017] In the example shown in Fig. 1, the case where the inevitable impurities 11 appear on the surface 10 of the substrate 14 is shown, but the same applies when the inevitable impurities 11 are present inside the substrate 14 and near the surface 10 of the substrate 14.

[0018] It should be noted that the word "混入" in the original text seems to be incorrect or incomplete. I translated it as "混入" for the sake of following the original text, but it might need to be adjusted according to the correct context.The Disclosers have found that, in addition to the presence of unavoidable impurities 11, factors that cause the surface of the substrate 14 to deform after heating and form protrusions 13 on the surface of the magnetic recording medium include aggregation of additive elements, segregation of additive elements, and processing strain. Specific causative materials include aluminum alloy substrates, crystallized glass substrates, amorphous glass substrates, and ceramic substrates. Other causative materials include amorphous NiP-based plating films and other plating films applied to the substrate surface.

[0019] Further investigation by the Disclosers revealed that the protrusions 13 that appear on the surface of the magnetic recording medium have a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm. Magnetic recording media having such protrusions 13 may not be rejected as defective products in the manufacturing process because the protrusions 13 do not come into contact with the thermoresistive element during glide testing, certify testing, and HDIs testing. This can lead to the following problems (1) to (3).

[0020] (1) Unlike the output signal caused by the undulation, the output signal caused by the protrusion lacks periodicity and appears superimposed on the output signal caused by the undulation, thus degrading the electromagnetic conversion characteristics of the magnetic recording medium and making signal processing in the HDD difficult.

[0021] (2) The protrusions may grow significantly even after the product has been manufactured. For example, laser heating in a heat-assisted HDD may cause the protrusions to grow even larger, potentially leading to contact between the magnetic head and the protrusions.

[0022] (3) Since the protrusions are generated during the deposition of magnetic films and the like, strain is introduced into the film, which may cause delamination of the film on magnetic recording media in the future.

[0023] The above problem (1) will be explained in detail using Figure 2.

[0024] Figure 2 is a schematic graph showing the signals output from a thermoresistive element during HDIs inspection of a magnetic recording medium. Specifically, Figure 2(a) is an example of an output signal from a magnetic recording medium with a period of 170 μm. Figure 2(b) is an example of an output signal from a magnetic recording medium with a period of 50 μm. Figure 2(c) is an example of an output signal from a magnetic recording medium with periods of 170 μm and 50 μm. Figure 2(d) is an example of an output signal when a signal 21 from a 10 μm wide protrusion is superimposed on the signal in Figure 2(c). Note that all signals from Figure 2(a) to Figure 2(d) are signals output due to a phenomenon in which the resistance value of the thermoresistive element of the inspection head changes due to temperature changes caused by heat transfer mediated by air between the inspection head (thermoresistive element) and the surface of the magnetic recording medium.

[0025] In the graph shown in Figure 2, the horizontal axis represents time and corresponds to the surface shape of the magnetic recording medium in the circumferential direction. The vertical axis represents signal intensity, and its absolute value corresponds to the magnitude of the surface relief of the magnetic recording medium.

[0026] Periodic output signals, as shown in Figures 2(a) to 2(c), become easier to filter and remove by identifying their period. Furthermore, periodic output signals often possess specific frequency components, and by designing appropriate bandstop and bandpass filters, noise components can be effectively removed. Additionally, signal processing techniques such as Fourier transforms can be used to separate and remove periodic output components in the frequency domain.

[0027] As shown in Figure 2(d), the non-periodic output signal 21 often lacks specific frequency components, making it difficult to remove. Therefore, signals containing the irregularly appearing output signal 21, as shown in Figure 2(d), make signal processing in the HDD difficult.

[0028] Furthermore, the non-periodic output signal 21 is superimposed on the signal caused by undulation, as shown in Figures 2(a) to 2(c), which can increase the signal intensity and degrade the electromagnetic conversion characteristics of the magnetic recording medium.

[0029] The magnetic recording medium inspection method according to the embodiment of this disclosure (hereinafter sometimes simply referred to as "this embodiment") has been proposed in view of the above circumstances and provides a highly reliable magnetic recording medium inspection method.

[0030] The following describes in detail the inspection method and manufacturing method of the magnetic recording medium according to this embodiment.

[0031] (Method for inspecting magnetic recording media) The method for inspecting magnetic recording media according to this embodiment is a method for inspecting a magnetic recording media having a magnetic layer on a non-magnetic substrate, wherein a defect portion having a non-periodic convex shape is identified based on an output signal obtained by scanning the surface of the magnetic recording media with an inspection head having a thermosensitive resistance element, and the convex shape has a height of 0.1 nm or more and 1.5 nm or less, and a width of 1 μm or more and 15 μm or less. The method for inspecting magnetic recording media according to this embodiment may include other steps as necessary.

[0032] According to the magnetic recording medium inspection method of this embodiment, it is possible to inspect the shape of the surface of the magnetic recording medium at high speed and identify defective portions having a non-periodic convex shape. Magnetic recording mediums in which defective portions are detected are either removed from the production line, the amount of defective portions in the magnetic recording medium is identified, or the location of the defective portions in the magnetic recording medium is identified. In other words, according to the magnetic recording medium inspection method of this embodiment, it is guaranteed that there are no defective portions in the magnetic recording medium, or that the amount of defective portions in the magnetic recording medium is below a standard value, or the location of the defective portions in the magnetic recording medium is identified, making it possible to ship highly reliable and high-quality products.

[0033] In this disclosure, the specific reference values ​​for the amount of non-periodic convex shapes present are preferably 1,000, more preferably 500, even more preferably 100, and particularly preferably 0 per face of the non-magnetic substrate.

[0034] By applying a magnetic recording medium that has passed the inspection method for magnetic recording media according to this embodiment to a magnetic recording and playback device, the generation of noise signals can be suppressed, the electromagnetic conversion characteristics of the magnetic recording medium can be improved, and signal processing in the magnetic recording and playback device can be facilitated.

[0035] According to the magnetic recording medium inspection method of this embodiment, it is possible to eliminate magnetic recording media having potentially growing defective portions in a commercially available magnetic recording and playback device, or to identify the location of such defective portions. Therefore, the risk of film peeling of the magnetic recording medium can be reduced, and the location of such risk can be identified, thereby providing a highly reliable magnetic recording and playback device.

[0036] <Inspection Target> In the inspection method for magnetic recording media according to this embodiment, the inspection target is a magnetic recording media having a magnetic layer on a non-magnetic substrate. There are no restrictions on the type and number of each layer stacked, and they can be appropriately selected according to the purpose.

[0037] <Defective portion> The defective portion has a non-periodic convex shape. The convex shape has a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm.

[0038] As mentioned above, it is preferable that the convex shape is formed during the manufacturing process of the magnetic recording medium.

[0039] The height of the convex shape is 0.1 nm or more and 1.5 nm or less, preferably 0.5 nm or more and 1.0 nm or less. In this specification, "height of the convex shape" refers to the maximum height of the convex shape when viewed from the cross-sectional direction with respect to the surface of the magnetic recording medium.

[0040] The width of the convex shape is 1 μm or more and 15 μm or less, preferably 5 μm or more and 13 μm or less. In this specification, "width of the convex shape" refers to the maximum length of the convex shape when viewed from the cross-sectional direction in the planar direction of the magnetic recording medium.

[0041] The height and width of the convex shape are defined by the following measurement method: (1) In AFM measurement, the measurement is taken over a quadrilateral region (preferably 50 μm) that includes the entire convex shape and a flat region of at least 10 μm around it. (2) A cross-sectional profile of the convex shape is taken, passing through the position of the apex of the convex shape. (3) A flat region of at least 10 μm around the convex shape of the obtained cross-sectional profile is taken as the baseline (preferably 15 μm). (4) Using the baseline obtained in (3) as a reference, the length from the cross-sectional profile to the apex of the convex shape is taken as the "height of the convex shape". (5) Using the baseline obtained in (3) as a reference, the length of the bottom surface of the convex shape is taken as the "width of the convex shape".

[0042] Defects with a non-periodic convex shape are identified based on an output signal obtained by scanning the surface of a magnetic recording medium with an inspection head having a thermoresistive element in a non-contact manner. This signal is output due to a phenomenon in which the resistance value of the thermoresistive element of the inspection head changes due to temperature changes caused by heat transfer mediated by air between the thermoresistive element and the convex defect.

[0043] Here, the inspection apparatus used in the magnetic recording medium inspection method according to this embodiment will be described in detail with reference to the drawings. The embodiments shown below are illustrative of inspection apparatus 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.

[0044] 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.

[0045] 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.

[0046] <Inspection Apparatus> Figure 3 is a schematic diagram showing an example of an inspection apparatus for carrying out the inspection method for magnetic recording media according to this embodiment. The inspection apparatus 41 shown in Figure 3 comprises a rotation mechanism 43 for rotating the magnetic recording media 42, an inspection head 50 positioned opposite the measurement area of ​​the magnetic recording media 42, and an inspection head drive mechanism 60 for driving the inspection head 50 via a suspension 70.

[0047] The inspection head 50 includes a magnetic writing unit 51 that magnetizes the measurement area without contact, a magnetic reading unit 52 that reads the leakage magnetic field of the measurement area without contact, and an HDI sensor unit.

[0048] The HDI sensor unit functions as a thermoresistive element whose physical properties, such as resistance, change as the temperature rises, and can output a signal resulting from the phenomenon of the resistance value of the thermoresistive element changing.

[0049] Examples of thermoresistive elements include MR elements that utilize the magnetoresistance (MR) effect, GMR elements that utilize the giant magnetoresistance (GMR) effect, and TMR elements that utilize the tunnel magnetoresistance (TuMR) effect. In this specification, MR elements, GMR elements, and TMR elements may be referred to as "magnetoresistive elements."

[0050] The inspection device 41 may also have a laser heating mechanism 40 that heats the measurement area non-contact when the magnetic recording medium 42 is used in a heat-assisted manner.

[0051] The inspection head 50 can adjust the height of the thermoresistive element relative to the surface of the magnetic recording medium 42 by changing the rotation speed (movement speed) of the magnetic recording medium 42. Furthermore, the inspection head 50 can also adjust the height of the thermoresistive element relative to the surface of the magnetic recording medium 42 by causing expansion or contraction of the area around the thermoresistive element due to the heat generated by a heater located near the thermoresistive element.

[0052] The inspection device 41 may be used in conjunction with the certify inspection and HDIs inspection in the manufacturing process of the magnetic recording medium 42, or it may be provided separately from the certify inspection and HDIs inspection.

[0053] Figure 4 is a graph showing an example of an output signal obtained by scanning an inspection head having a thermoresistive element in the inspection method for a magnetic recording medium according to this embodiment. Specifically, Figure 4(a) is an example of a signal in which three convex signals 21 with a width of 10 μm are superimposed on a signal 53 having undulations with a period of 170 μm and undulations with a period of 50 μm. Figure 4(b) is an example of a signal obtained by filtering out the signal 53 having undulations with a period of 170 μm and undulations with a period of 50 μm from the signal in Figure 4(a).

[0054] Both signals shown in Figure 4(a) and Figure 4(b) are signals output due to a phenomenon in which the resistance value of the thermoresistive element of the inspection head changes due to temperature changes caused by heat transfer between the thermoresistive element and the surface of the magnetic recording medium via air.

[0055] In the graphs shown in Figures 4(a) and 4(b), the horizontal axis represents time and corresponds to the surface shape of the magnetic recording medium in the circumferential direction. The vertical axis represents signal intensity, and its absolute value corresponds to the magnitude of the surface relief.

[0056] In other words, the height of the convex shape is indicated by the signal intensity on the vertical axis in Figure 4, and the higher the convex shape, the larger the negative potential. The width of the convex shape is indicated by time on the horizontal axis in Figure 4, and the larger the width of the convex shape, the larger the time interval. The width of the convex shape is calculated from the relative speed of the inspection head on the surface of the magnetic recording medium.

[0057] As shown in Figure 4(a), the undulation signal 53 on the surface of the magnetic recording medium has periodicity, while the convex signal 21 does not. Therefore, it is easy to identify the convex signal 21 from the signals in Figure 4(a).

[0058] Here, of the three convex-shaped signals 21 in Figure 4(a), the leftmost signal 21 has a higher signal strength than signal 53 and is easy to identify, but the rightmost signal 21 is difficult to identify because it is buried in the signal strength of signal 53. Therefore, in order to facilitate the identification of all convex shapes, it is preferable to remove signals caused by undulations on the surface of the magnetic recording medium from the output signal from the thermoresistive element.

[0059] Most of the undulations that appear on the surface of magnetic recording media are caused by undulations on the surface of the non-magnetic substrate used in the magnetic recording media. In other words, undulations on the surface of the non-magnetic substrate are affected by the thin film surface formed on it, and as a result appear on the surface of the magnetic recording media.

[0060] Since the undulations on the surface of non-magnetic substrates used in magnetic recording media often have wavelength components of 10 μm to 1 mm, it is preferable to remove periodic signals of 10 μm to 1 mm from the output signal from the thermoresistive element.

[0061] Figure 4(b) shows a signal in which three convex-shaped signals 21 with a width of 10 μm are superimposed on a stable amplitude signal 54. In the signal in Figure 4(b), it is even easier to identify all of the convex-shaped signals 21. This is because signals caused by swells repeat at a constant period, and by identifying that period, filtering and other removal techniques become easier to apply. Also, signals caused by swells often have specific frequency components, and can be effectively removed by designing appropriate bandstop filters and bandpass filters. Furthermore, it is also effective to use signal processing techniques such as Fourier transforms to separate periodic noise components in the frequency domain and effectively remove signals caused by swells.

[0062] In the inspection method for the magnetic recording medium according to this embodiment, it is preferable to identify a defect portion having a non-periodic convex shape based on the output signal from which signals caused by undulations on the surface of the magnetic recording medium have been removed, as described above.

[0063] (Method for manufacturing a magnetic recording medium) The method for manufacturing a magnetic recording medium according to this embodiment is a method for manufacturing a magnetic recording medium having a magnetic layer on a non-magnetic substrate, and includes a magnetic recording medium formation step and an inspection step, and may include other steps as necessary.

[0064] The magnetic recording medium manufactured by the manufacturing method of the magnetic recording medium according to this embodiment is not particularly limited and can be appropriately selected according to the purpose. Examples include conventional magnetic recording media, magnetic recording media used in a heat-assisted method, and magnetic recording media used in a microwave-assisted method.

[0065] In the method for manufacturing a magnetic recording medium according to this embodiment, a magnetic recording medium used in the heat-assisted method will be described in detail below with reference to Figure 5.

[0066] Figure 5 is a schematic cross-sectional view showing an example of a magnetic recording medium manufactured by the manufacturing method of the magnetic recording medium according to this embodiment. In the magnetic recording medium shown in Figure 5, a soft magnetic layer 2, an underlayer 3, a perpendicular magnetic layer 4, and a protective layer 5 are sequentially laminated on both main surfaces of a non-magnetic substrate 1. Although Figure 5 shows the layers laminated on both sides of the non-magnetic substrate 1, the magnetic recording medium may also have the layers laminated on only one side of the non-magnetic substrate 1.

[0067] The shape of the magnetic recording medium is not particularly limited as long as it can be applied to a magnetic recording and playback device, and can be appropriately selected according to the purpose. For example, a disc shape with a central hole can be used.

[0068] <Magnetic recording medium formation process> The magnetic recording medium formation process is a process of heating a non-magnetic substrate 1 to form a magnetic layer. The magnetic recording medium formation process may include a soft magnetic layer formation process, a base layer formation process, a perpendicular magnetic layer formation process, a protective layer formation process, a liquid lubricant layer formation process, and a varnish process.

[0069] As the heating process in the magnetic recording medium forming process, there are no particular restrictions, and the heating processes used in known film forming methods can be appropriately adopted. For example, heating processes performed before and after the process of forming a thin film by sputtering method (sputtering process) and the process of heating a laminate of a thin film including a non-magnetic substrate can be mentioned. These heating processes aim at improving and enhancing the crystal structure of the thin film, repairing defects, relaxing stress, promoting diffusion processes, promoting chemical reactions, improving the adhesion of the thin film, promoting surface diffusion, promoting interface reactions, and forming specific phases.

[0070] <<Soft magnetic layer forming process>> The soft magnetic layer forming process is a process of forming a soft magnetic layer 2 on a non-magnetic substrate 1.

[0071] - Non-magnetic substrate 1 - As the non-magnetic substrate 1, there are no particular restrictions, and it can be appropriately selected according to the purpose. For example, metal substrates and non-metal substrates can be mentioned.

[0072] - - Non-metal substrate - - As the non-metal substrate, for example, those formed of non-metal materials such as glass can be mentioned.

[0073] As the glass substrate, for example, SiO ２ - Al ２ O ３ - R ２ O-based chemically strengthened glass, SiO ２ - Al ２ O ３ - Li ２ O-based glass ceramics and SiO ２ - Al ２ O ３ - MgO - TiO ２ - based glass ceramics and the like can be mentioned. Here, R represents at least one or more selected from alkali metal elements.

[0074] Among these glass substrates, SiO ２ - Al ２ O ３ - MgO - CaO - Li ２ O - Na ２ O - ZrO ２ - Y ２ O ３ - TiO ２-As ２ O ３ Chemically strengthened glass, SiO ２ - Al ２ O ３ -Li ２ O-Na ２ O-ZrO ２ -As ２ O ３ Chemically strengthened glass, SiO ２ - Al ２ O ３ -MgO-ZnO-Li ２ O-P ２ O ５ -ZrO ２ -K ２ O-Sb ２ O ３ Glass ceramics, SiO ２ - Al ２ O ３ -MgO-CaO-BaO-TiO ２ -P ２ O ５ -As ２ O ３ Glass ceramics and SiO ２ - Al ２ O ３ -MgO-CaO-SrO-BaO-TiO ２ -ZrO ２ -Bi ２ O ３ -Sb ２ O ３ Glass-ceramic materials are preferred.

[0075] --Metal Substrate-- Examples of metal substrates include those made of metallic materials such as aluminum alloys. An aluminum alloy substrate may contain, for example, additive elements including Mg and Cr, with the remainder being Al, and may also contain unavoidable impurities.

[0076] In aluminum alloy substrates, Mg has the function of improving mechanical strength. There are no particular restrictions on the Mg content, and it can be appropriately selected depending on the purpose, but it is preferable that it be 2% by mass or more and 7% by mass or less of the total weight of the aluminum alloy substrate.

[0077] In aluminum alloy substrates, Cr has the function of improving strength at high temperatures and improving extrusion processing. There are no particular restrictions on the Cr content, and it can be appropriately selected depending on the purpose, but it is preferable that it be 0.02% by mass or more and 0.3% by mass or less of the total amount of the aluminum alloy substrate.

[0078] In addition to Mg and Cr as additive elements, the aluminum alloy substrate may also contain one or more elements selected from the group consisting of Si, Zn, Mn, Ti, Cr, V, Zr, Mo, and Co.

[0079] Unavoidable impurities include, for example, B and P.

[0080] NiP-based alloy layers may be formed on the surfaces of metal and non-metallic substrates. The NiP-based alloy layers can be formed, for example, by plating and sputtering.

[0081] Among these non-magnetic substrates, heat-resistant glass substrates with a softening temperature of 500°C or higher and aluminum alloy substrates with heat-resistant plating such as NiMoP are preferred, and heat-resistant glass substrates with a softening temperature of 600°C or higher are more preferred.

[0082] There are no particular restrictions on the method for forming the soft magnetic layer 2, and it can be appropriately selected according to the purpose. For example, general film deposition methods such as sputtering can be used.

[0083] There are no particular restrictions on the sputtering method, and it can be appropriately selected depending on the purpose. Examples include DC (Direct Current) sputtering, DC magnetron sputtering, and RF (Radio Frequency) sputtering.

[0084] When using the sputtering method as the method for forming the soft magnetic layer 2, it is preferable to use a target containing the material for forming the soft magnetic layer.

[0085] Examples of targets containing materials that form a soft magnetic layer include soft magnetic alloys such as FeCo-based alloys, CoZrNb-based alloys, and CoTaZr-based alloys.

[0086] <<Substrate Formation Process>> The substrate formation process is the process of forming a substrate 3 on the soft magnetic layer 2. The substrate formation process may include a first substrate formation process in which a first substrate is formed on the soft magnetic layer 2, a second substrate formation process in which a second substrate is formed on the first substrate, and a third substrate formation process in which a third substrate is formed on the second substrate.

[0087] There are no particular restrictions on the method for forming the underlayer 3, and it can be appropriately selected according to the purpose. For example, general film deposition methods such as sputtering can be used.

[0088] When using the sputtering method as the method for forming the base layer 3, it is preferable to use a target that contains the material for forming the base layer.

[0089] In the first subsoil formation process, there are no particular restrictions on the material used to form the first subsoil, and it can be appropriately selected according to the purpose. For example, a Cr alloy in which a bcc alloy mainly composed of Cr is (100) oriented can be used.

[0090] In the second sublayer formation process, there are no particular restrictions on the material used to form the second sublayer, and it can be appropriately selected according to the purpose. For example, a W alloy in which a bcc alloy mainly composed of W is (100) oriented can be used.

[0091] In the third subsoil formation process, there are no particular restrictions on the material used to form the third subsoil, and it can be appropriately selected according to the purpose. Examples include NaCl-type compounds. Examples of NaCl-type compounds include MgO.

[0092] It is preferable to include a heating step before and after each of the first, second, and third subsoil formation steps. The heating temperature at this time is preferably 150°C or higher, and more preferably 200°C or higher.

[0093] <<Perpendicular Magnetic Layer Formation Process>> The perpendicular magnetic layer formation process is a process of forming a perpendicular magnetic layer 4 on the base layer 3.

[0094] There are no particular restrictions on the method for forming the perpendicular magnetic layer 4, and it can be appropriately selected according to the purpose. For example, general film deposition methods such as sputtering can be used.

[0095] When using the sputtering method as the method for forming the perpendicular magnetic layer 4, it is preferable to use a target that contains the material for forming the perpendicular magnetic layer.

[0096] There are no particular limitations on the target material that forms the perpendicular magnetic layer 4, and it can be appropriately selected according to the purpose, for example, L1 ０ Examples include targets containing alloys with a specific structure.

[0097] L1 ０ Examples of alloys with a structure include alloys containing Fe or Co and Pt, etc. L1 ０ Specific examples of alloys with a structure include FePt-based alloys and CoPt-based alloys.

[0098] In the perpendicular magnetic layer formation process, it is preferable to include a heating step in which the non-magnetic substrate 1, soft magnetic layer 2, underlayer 3, and perpendicular magnetic layer 4 are heated in a laminated state, from the viewpoint of improving the crystal orientation of the perpendicular magnetic layer 4. As the heating means at this time, known methods such as halogen lamps, lasers, LEDs, high-frequency waves, and electromagnetic waves such as microwaves can be used.

[0099] L1 ０ If the FePt alloy has a structure, it is preferable to heat it to a high temperature of 400°C or higher to regularize it.

[0100] <<Protective Layer Formation Process>> The protective layer formation process is the process of forming a protective layer 5 on the perpendicular magnetic layer 4.

[0101] There are no particular restrictions on the method for forming the protective layer 5, and general film deposition methods can be used. Examples include the RF-CVD (Radio Frequency-Chemical Vapor Deposition) method, which decomposes a hydrocarbon source gas with a high-frequency plasma to form a film; the IBD (Ion Beam Deposition) method, which ionizes the source gas with electrons emitted from a filament to form a film; and the FCVA (Filtered Cathodic Vacuum Arc) method, which uses a solid carbon target to form a film without using a source gas.

[0102] It is preferable to include a heating step before the protective layer formation step. The heating temperature at this step is preferably 150°C or higher, and more preferably 200°C or higher.

[0103] <<Liquid Lubricant Layer Formation Process>> The liquid lubricant layer formation process is a process of forming a liquid lubricant layer on the protective layer 5.

[0104] The liquid lubricant layer can be formed by applying a fluorine-based lubricant such as a perfluoropolyether using methods such as the dip method and the spin coating method.

[0105] <<Burning Process>> The burning process is a process of burning the surface of the laminate with an abrasive material. Specifically, it is a process of pressing a tape containing an abrasive material (abrasive tape) against the surface of the laminate and rubbing it.

[0106] <Inspection Process> The inspection process involves inspecting the magnetic recording medium obtained by the magnetic recording medium formation process using the magnetic recording medium inspection method. Note that the magnetic recording medium inspection method is the same as described above (Magnetic Recording Medium Inspection Method), so redundant descriptions are omitted.

[0107] The inspection process may include glide testing, certify testing, and HDIs testing, in addition to the magnetic recording medium inspection method according to this embodiment.

[0108] <<Glide Inspection>> Glide inspection is an inspection to check for the presence of protrusions on the surface of a magnetic recording medium. When recording and playing back a magnetic recording medium using a magnetic head, if there are protrusions on the surface of the magnetic recording medium that are taller than the levitation amount (the distance between the medium and the magnetic head), the magnetic head may collide with the protrusion, causing damage to the magnetic head or defects in the magnetic recording medium. Therefore, magnetic recording mediums that are detected to have tall protrusions on their surface through glide inspection are removed from the manufacturing process as defective products.

[0109] Magnetic recording media that pass the glide test undergo a certify test and an HDIs test.

[0110] <<Certify Test>> The Certify test is an inspection to verify the defects and quality of the electromagnetic conversion characteristics of a magnetic recording medium. In the Certify test, a predetermined signal is recorded on the magnetic recording medium using a magnetic head, similar to the recording and playback in a normal HDD, and then the signal is reproduced. The electromagnetic conversion characteristics are then evaluated from the obtained reproduced signal.

[0111] <<HDIs Testing>> HDIs testing is a test that checks for the presence or absence of convex and concave defects in magnetic recording media. By checking what kinds of convex and concave defects exist on the surface of the magnetic recording media, HDIs testing evaluates the data read / write performance and the reliability of the magnetic recording media.

[0112] The magnetic recording medium inspection method according to this embodiment is preferably performed in conjunction with HDIs inspection.

[0113] The inspection method for magnetic recording media according to this embodiment does not necessarily require inspection of the entire area of ​​the magnetic recording media. A common practice in magnetic recording media inspection methods is to evaluate an area that includes 3% or more, more preferably 5% or more, of the inner, middle, and outer circumferences of the magnetic recording media, thereby providing a sufficient understanding of its overall characteristics. The accuracy increases as the proportion of the area evaluated increases.

[0114] For a 2.5-inch diameter magnetic recording medium, the positions of the inner circumference, middle circumference, and outer circumference at the radial position are approximately 15 mm for the inner circumference, approximately 24 mm for the middle circumference, and approximately 33 mm for the outer circumference.

[0115] For a 3.5-inch diameter magnetic recording medium, the positions of the inner circumference, middle circumference, and outer circumference at the radial position are approximately 20 mm for the inner circumference, approximately 31.5 mm for the middle circumference, and approximately 43 mm for the outer circumference.

[0116] Figure 6 is a schematic perspective view showing an example of a magnetic recording and playback device using a magnetic recording medium manufactured by the manufacturing method of the magnetic recording medium according to this embodiment. The magnetic recording and playback device shown in Figure 6 comprises a magnetic recording medium 30, a rotational drive unit (a medium drive unit that drives the magnetic recording medium in the recording direction) 31 that rotates the magnetic recording medium 30, a magnetic head 32 that performs recording and playback operations on the magnetic recording medium 30, a head drive unit (a head moving means that moves the magnetic head relative to the magnetic recording medium) 33 that moves the magnetic head 32 in the radial direction of the magnetic recording medium 30, and a recording and playback signal processing system (a recording and playback signal processing means) 34 for inputting signals to the magnetic head 32 and playing back output signals from the magnetic head 32.

[0117] In the magnetic recording and playback device shown in Figure 6, further improvements in reliability can be achieved by using the magnetic recording medium 30 that has been judged to pass the inspection method for magnetic recording media according to this embodiment.

[0118] The embodiment will be described in more detail below with reference to examples, but the embodiment is not limited to the following examples.

[0119] (Manufacturing of magnetic recording media) A magnetic recording media with an outer diameter of 3.5 inches, used in a heat-assisted method, was manufactured using the method described below.

[0120] A heat-resistant glass substrate was used as the non-magnetic substrate.

[0121] Using the sputtering method, a Cr-50at%Ti alloy layer with an average thickness of 100 nm and a Co-27at%Fe-5at%Zr-5at%B alloy layer with an average thickness of 30 nm were sequentially formed. Next, after heating the non-magnetic substrate to 200°C, a Cr layer with an average thickness of 10 nm and an MgO layer with an average thickness of 5 nm were sequentially formed using the sputtering method. Next, after heating the non-magnetic substrate to 400°C, a (Fe-49at%Pt)-40 volume% hexagonal boron nitride layer (magnetic layer) with an average thickness of 13 nm was sequentially formed using the sputtering method. Finally, the non-magnetic substrate was heated to 200°C to form a carbon film with an average thickness of 3 nm as a protective layer.

[0122] (Evaluation of magnetic recording media by glide testing) The obtained magnetic recording media were subjected to glide testing using a glide tester equipped with a piezoelectric element head, with the glide height of the head (the distance between the head and the surface of the magnetic recording media assuming no surface defects) set to 10 nm, in order to exclude magnetic recording media with large protrusions on the surface.

[0123] (Evaluation of magnetic recording media by HDIs inspection) <First HDIs inspection> 100 magnetic recording media that passed the glide inspection were prepared, and each magnetic recording media was subjected to HDIs inspection using an inspection head equipped with a thermoresistive element. Specifically, the glide height (height from the surface of the magnetic recording media to the thermoresistive element) was set to 1.5 nm, and a recording media was considered to have passed if the signal output from the thermoresistive element of the inspection head was 500 mV or more in absolute value and there were no defects. The track pitch during inspection was set to 20 μm, and the magnetic recording media was evaluated from the inner circumference to the outer circumference. This corresponds to evaluating 5% of the entire area of ​​the magnetic recording media. 96 magnetic recording media passed the inspection.

[0124] <Second HDIs Inspection> Next, a second HDIs inspection was performed on the 96 magnetic recording media that had passed, under modified conditions. Specifically, the glide height was not changed, and a bandpass filter from 800 kHz to 10 MHz was used to remove signals caused by undulation from the output signal from the thermoresistive element of the inspection head, and to extract only signals corresponding to non-periodic convex shapes (height of 0.1 nm to 1.5 nm and width of 1 μm to 15 μm). Among the extracted signals, those without defects of 400 mV or more in absolute value were deemed to pass. 91 magnetic recording media passed the inspection.

[0125] When the defective areas of the magnetic recording media that failed the second HDIs inspection were observed using an AFM (Atomic Force Microscope), a non-periodic convex shape (with a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm) was observed on the surface of the magnetic recording media. An example of the observed image is shown in Figure 7. The convex part in Figure 7 had a height of 0.68 nm and a width of 13.52 μm. It was determined that all of the convex shapes of the magnetic recording media that failed the second HDIs inspection were caused by bulging of the substrate during film deposition.

[0126] The signal-to-noise ratio (SNR) of magnetic recording media that passed the second HDIs test and those that failed the second HDIs test were compared. SNR was measured using a spin stand tester with a magnetic head equipped with a laser spot heating mechanism. The current supplied to the laser diode was adjusted so that the recording track width (MWW), defined as the half-width of the reproduced signal waveform, was 70 nm, and the SNR was checked. It was confirmed that the SNR of the passing products improved by an average of 0.3%.

[0127] <Third HDIs Test> A third HDIs test was performed on magnetic recording media that had passed the second HDIs test, with modified conditions. Specifically, the track pitch was set to 1 μm, and the magnetic recording media was evaluated from the inner circumference to the outer circumference. This is equivalent to evaluating the entire area of ​​the magnetic recording media, and all magnetic recording media passed the test.

[0128] 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.

[0129] This application claims priority based on Japanese Patent Application No. 2024-227899, filed with the Japan Patent Office on December 24, 2024, and incorporates all the contents of the said application.

[0130] 1...Non-magnetic substrate 2...Soft magnetic layer 3...Underlayment 4...Perpendicular magnetic layer 5...Protective layer 30...Magnetic recording medium 31...Media drive unit 32...Magnetic head 33...Head drive unit 34...Recording / playback signal processing system

Claims

1. A method for inspecting a magnetic recording medium having a magnetic layer on a non-magnetic substrate, comprising: identifying a defect portion having a non-periodic convex shape based on an output signal obtained by scanning the surface of the magnetic recording medium with an inspection head having a thermoresistive element, wherein the convex shape has a height of 0.1 nm or more and a width of 1 μm or more and a width of 1 μm or more and 15 μm or less.

2. The method for inspecting a magnetic recording medium according to claim 1, wherein the convex shape is formed in the manufacturing process of the magnetic recording medium.

3. A method for inspecting a magnetic recording medium according to claim 1 or 2, wherein a non-periodic defect portion having a convex shape is identified based on the output signal from which signals caused by undulations on the surface of the magnetic recording medium have been removed.

4. The method for inspecting a magnetic recording medium according to any one of claims 1 to 3, wherein the thermoresistive element is a magnetoresistive element.

5. A method for manufacturing a magnetic recording medium having a magnetic layer on a non-magnetic substrate, the method for manufacturing the magnetic recording medium comprising: a magnetic recording medium forming step of heating the non-magnetic substrate to form a magnetic layer; and an inspection step of inspecting the magnetic recording medium obtained by the magnetic recording medium forming step using the magnetic recording medium inspection method described in any one of claims 1 to 4.

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