Disc substrate, disc, and method for manufacturing the same

Abstract

The present invention relates to a magnetic disk substrate and a magnetic disk, which have a flatness of 40 μm or less, wherein the mid-frequency Wq (root mean square waviness) is 7 μm or less and the mid-frequency TIR (difference between maximum and minimum) is 10 μm or less.

Description

Technical Field

[0001] This invention relates to a disk substrate with excellent flatness and smoothness, a disk, and a method for manufacturing the same. Background Technology

[0002] Disks used in storage devices such as computers are manufactured using disk substrates (hereinafter referred to as "substrate") that have good plating properties, excellent mechanical properties, and machinability. Disk substrates are made from materials such as aluminum alloy-based substrates and glass-based substrates. For example, JIS 5086 aluminum alloy (containing Mg: 3.5% to 4.5% by mass, Fe: 0.50% by mass or less, Si: 0.40% by mass or less, Mn: 0.20% to 0.70% by mass, Cr: 0.05% to 0.25% by mass, Cu: 0.10% by mass or less, Ti: 0.15% by mass or less, and Zn: 0.25% by mass or less, with the balance being Al and unavoidable impurities) is known as a material for aluminum alloy substrates.

[0003] In the manufacture of a typical hard disk, a ring-shaped disk substrate is first prepared, and a magnetic material is then adhered to the surface of this substrate. For example, a hard disk using an aluminum alloy disk substrate made of the aforementioned JIS 5086 aluminum alloy is manufactured through the following steps.

[0004] First, an aluminum alloy material with a predetermined chemical composition is cast, and the ingot is hot-rolled and then cold-rolled to prepare a rolled material with the required thickness for use as a disk. The rolled material may be annealed during cold rolling or other processes as needed. Next, the rolled material is stamped into a ring shape to prepare a ring-shaped aluminum alloy sheet. Furthermore, to remove strain and other defects generated in the previous manufacturing steps, the ring-shaped aluminum alloy sheets are stacked and annealed under pressure from both sides, thus performing pressure annealing for planarization. This produces a ring-shaped disk blank made of aluminum alloy.

[0005] The aluminum alloy blanks prepared in this way undergo pretreatment processes such as cutting, grinding, degreasing, etching, and zincate treatment (Zn replacement treatment). Next, Ni-P, a hard non-magnetic metal, is chemically plated as a substrate, and the plated surface is polished to manufacture the aluminum alloy substrate for disks.

[0006] Then, magnetic material is sputtered onto the manufactured aluminum alloy substrate for disks to produce a disk made of aluminum alloy. Besides aluminum alloy, materials such as glass can also be used as the disk substrate.

[0007] In recent years, due to the demands of multimedia and other applications, the need for large capacity and high density in disk devices such as hard disk drives (HDDs) has been continuously increasing. Currently, perpendicular magnetic recording (PMR) and shingled magnetic recording (SMR) are used as magnetic recording methods. However, to achieve larger capacities, technologies such as heat-assisted magnetic recording (HAMR) and microwave-assisted magnetic recording (MAMR) have been developed. To further increase capacity through methods other than recording methods, the number of disks in storage devices is trending upwards, thus creating a demand for thinner disks.

[0008] However, the flatness of the disk may deteriorate as its rigidity decreases due to thinning. Consequently, the gap between the disk and other components becomes smaller, and the disk is more prone to colliding with other components when subjected to impacts such as being dropped, thus reducing its shock resistance.

[0009] In addition to the deterioration of disk flatness, there is also the issue of potential degradation in the smoothness of the disk's circumferential surface waviness and height differences. As a result, the read / write head may collide with the disk surface, increasing the likelihood of read / write errors.

[0010] Therefore, in recent years, research has been conducted on improving the shock resistance of disk drives and disk substrates. Since shock resistance may be related to the rigidity of the disk substrate, techniques for improving the rigidity of the disk substrate are also known. For example, Patent Document 1 proposes a method for improving the rigidity of an aluminum alloy substrate by including a large amount of Si, which contributes to increased rigidity.

[0011] Reference List Patent documents Patent Document 1: WO2016 / 068293 As stated above, the method disclosed in Patent Document 1, which involves containing a large amount of Si in the aluminum alloy, is effective in improving the rigidity of the aluminum alloy substrate. However, when addressing the issue of impact resistance itself, it is necessary to study the improvement in flatness and smoothness caused by the thinning of the disk. Patent Document 1 does not mention the improvement of flatness and smoothness. Therefore, it is desirable to develop a disk with improved flatness and smoothness. Summary of the Invention

[0012] Technical issues The present invention was made in view of the above circumstances, and its object is to provide a disk substrate and a disk exhibiting excellent flatness and smoothness, as well as a method of manufacturing the same.

[0013] Solution to the problem As a result of in-depth research into the relationship between the flatness and smoothness of a disk and the manufacturing steps, the inventors discovered that the preheating step performed before sputtering magnetic materials onto the disk substrate has a significant impact. In particular, the inventors focused on the heating rate and temperature distribution during the preheating step, and found that disk substrates that have undergone predetermined preheating can achieve excellent flatness and smoothness, thus completing this invention.

[0014] The disk substrate according to embodiments of the present invention has a flatness of 40 μm or less, a Wq (root mean square ripple) of 7 μm or less in the middle circumference, and a TIR (height difference) of 10 μm or less in the middle circumference.

[0015] The method for manufacturing a disk substrate according to an embodiment of the present invention includes a preheating step of heating the disk substrate from room temperature to a predetermined temperature, wherein the heating rate in the preheating step is 40°C / s or lower.

[0016] The disk according to an embodiment of the present invention has a flatness of 40 μm or less, a Wq (root mean square ripple) of 7 μm or less in the middle circumference, and a TIR (height difference) of 10 μm or less in the middle circumference.

[0017] The method for manufacturing a disk according to an embodiment of the present invention includes: a preheating step of heating a disk substrate from room temperature to a predetermined temperature; and a sputtering step of adhering a magnetic material to the surface of the preheated disk substrate by sputtering, wherein the heating rate in the preheating step is 40°C / second or lower.

[0018] Beneficial effects of the invention According to the present invention, a disk substrate and a disk exhibiting excellent flatness and smoothness, as well as a method for manufacturing the same, can be provided. Attached Figure Description

[0019] Figure 1 This is a schematic diagram showing the area where the surface temperature of the disk substrate is measured during the preheating step. Detailed Implementation

[0020] The disk substrate, disk, and manufacturing method described in this embodiment will be described in detail below.

[0021] [Disk substrate and disk] The disk substrate described in this embodiment, and the disk manufactured using this disk substrate, exhibit excellent flatness, having a flatness of 40 μm or less. Furthermore, excellent smoothness is also exhibited because the Wq (root mean square waviness) in the central circumference is 7 μm or less, and the TIR (height difference) in the central circumference is 10 μm or less. The disk substrate and disk possessing such flatness and smoothness can be made of, for example, aluminum alloy or glass.

[0022] Flatness The flatness of both the disk substrate and the disk itself is 40 μm or less, preferably 30 μm or less, and more preferably 20 μm or less. When the flatness of both the disk substrate and the disk itself is greater than 40 μm, the gap between the disk and the other component is smaller when the disk is installed into the HDD. When the HDD is subjected to impact such as being dropped, the disk may collide with the other component, reducing its impact resistance.

[0023] Here, "flatness" is represented by the difference between the maximum peak height and the maximum valley depth of the entire surface of the disk substrate and each disk. The maximum peak height is the maximum value within the measurement range (the entire surface of the disk substrate and each disk), and the maximum valley depth is the minimum value within the measurement range (the entire surface of the disk substrate and each disk). Flatness can be measured using a ZyGO non-contact flatness measuring machine according to the method specified in JIS B0182-1993. In JIS B 0182-1993, "flatness" is defined as an index that can be used to evaluate flatness; this is the same as the flatness described above and has the same meaning. Specifically, a fixture for changing the angle of the measuring surface relative to the flatness measuring machine is fixed to a base mounted in the flatness measuring machine. For example, a fixture including three micrometers can be used, and the angle of the fixture relative to the measuring surface can be adjusted in the θ direction (the direction of tilting from the 0° central angle angle θ) and the ψ direction (diameter direction) using the micrometers. Next, the substrate is placed on the fixture, and the angle can be adjusted so that the substrate is parallel to the measuring surface of the flatness measuring machine in order to measure the flatness.

[0024] <Wq (root mean square ripple) of the middle circumference> The root mean square (RMS) waviness of the intermediate circumference Wq of each disk substrate and disk is 7 μm or less, preferably 5 μm or less, more preferably 4 μm or less, and even more preferably 3 μm or less. Wq represents the root mean square of the disk substrate and each disk at a reference length. The reference length of each disk substrate and disk is the circumferential length of the intermediate circumferential portion of the substrate (radial position: its value is obtained by calculating half the difference between half the outer diameter and half the inner diameter and adding half the inner diameter to the calculated value) in the circumferential direction, and refers to the intermediate circumference of each disk substrate and disk. That is to say, the intermediate circumference Wq (RMS waviness) of each disk substrate and disk corresponds to the root mean square height Rq of each disk substrate and disk at the reference length. Here, the root mean square height (Rq) represents the root mean square of each disk substrate and disk at the reference length, and refers to the standard deviation of the surface roughness.

[0025] When the surface roughness (Wq) of the disk substrate and its respective surface decreases, the effect of stabilizing the smoothness of the disk substrate and its respective surface becomes apparent. When Wq is greater than 7 μm, the read / write head may collide with the disk surface, potentially increasing read / write errors. It should be noted that although a smaller Wq reduces the risk of collision, the lower limit of Wq is preferably 0.5 μm or greater, because if this value is too small when the read / write head is attached to the disk surface, it may be difficult to detach. Here, Wq can be measured according to JISB0601:2013, and using a non-contact flatness measuring machine such as ZyGO.

[0026] <TIR (Height Difference) of the Middle Circumference> The TIR (height difference) of the disk substrate and the disk itself is 10 μm or less, preferably 8 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. TIR represents the height difference between the disk substrate and the disk at a reference length. As described above, the reference length of the disk substrate and the disk itself is the circumferential length of the disk's central circumference (radial position: its value is obtained by calculating half the difference between half the outer diameter and half the inner diameter and adding half the inner diameter to the calculated value) in the circumferential direction of the disk, and refers to the central circumference of the disk substrate and the disk itself. That is to say, the TIR (height difference) of the central circumference of the disk substrate and the disk itself corresponds to the TIR of the disk substrate at the reference length. Here, TIR refers to an index representing the corrugation of the disk substrate and the disk itself, and is the sum of the distances from the least-squares plane of the evaluation surface (substrate surface) to the highest and lowest points.

[0027] When the TIR (Transparent Indentation) on the disk substrate and its respective surface decreases, the effect of stabilizing the smoothness of the disk substrate and its respective surface becomes apparent. When Wq (Transparent Indentation) is greater than 10 μm, the read / write head may collide with the disk surface, potentially increasing read / write errors. It should be noted that although a smaller TIR reduces the risk of collision, the lower limit of TIR is preferably 0.5 μm or greater, because if this value is too small when the read / write head is attached to the disk surface, it may be difficult to detach. Here, TIR can be measured using, for example, a ZyGO non-contact flatness measuring machine.

[0028] <Disk substrate and disk dimensions> The disk substrate and the disk itself preferably have a thickness of 0.50 mm or less, more preferably 0.49 mm or less, and even more preferably 0.42 mm or less. When the thickness of both the disk substrate and the disk is greater than 0.50 mm, the impact resistance of the disk is improved, but the number of disks that can be mounted in an HDD is reduced, which is not suitable for promoting thinner disks. In addition, in order to prevent the disk from deforming or breaking when it is dropped during HDD installation, the lower limit of the thickness of both the disk substrate and the disk is preferably 0.25 mm or greater.

[0029] Furthermore, the outer diameter of both the disk substrate and the disk is preferably 96 mm or greater, more preferably 97 mm or greater. When the outer diameter of both the disk substrate and the disk is 96 mm or greater, the recording capacity can be further increased.

[0030] <Disk substrate and disk materials> The materials of the disk substrate and the disk itself are not particularly limited; for example, aluminum alloy or glass are preferred. Both the disk substrate and the disk made of such materials can be manufactured using, for example, aluminum alloy substrates or glass substrates.

[0031] <Aluminum alloy substrate for hard disks> The disk substrate can be, for example, an aluminum alloy substrate. The alloy composition of aluminum alloy substrates for disks is described in detail below.

[0032] (The alloy composition of aluminum alloys) To further improve the flutter resistance, impact resistance and coating properties of aluminum alloy substrates, the aluminum alloy used for disk aluminum alloy substrates preferably contains at least one of the following as a first selective element: 0.001% or more and 3.00% or less of Fe (iron) and 0.001% or more and 3.00% or less of Mn (manganese) (hereinafter, mass% is simply referred to as "%").

[0033] In addition, the aluminum alloy may contain one or more of the following as a second optional element, selected from the group consisting of: 0.100% or more and 6.000% or less Mg (magnesium), 0.100% or more and 5.000% or less Ni (nickel), 0.001% or more and 5.000% or less Cr (chromium), 0.001% or more and 5.000% or less Zr (zirconium), 0.001% or more and 5.000% or less Zn (zinc), 0.001% or more and 5.000% or less Cu (copper), and 0.01% or more and 0.40% or less Si (silicon).

[0034] Aluminum alloys may also contain one or more of the following as a third optional element, selected from the group consisting of: Ti (titanium), B (boron) and V (vanadium), in a total content of 0.005% or more and 5.000% or less.

[0035] The balance of the aluminum alloy consists of Al and unavoidable impurities. Examples of unavoidable impurities include Ga (gallium), Sn (tin), Sr (strontium), P (phosphorus), and Na (sodium). As long as each element that is an unavoidable impurity is less than 0.10% and the total amount is less than 0.20%, the properties of the aluminum alloy substrate obtained by this invention will not be impaired.

[0036] <Glass substrate for disks> The disk substrate can be, for example, a glass substrate made of glass material. The following provides a detailed description of the glass materials used in disk substrates.

[0037] (Glass material) As a glass material, glass ceramics (such as amorphous glass and crystallized glass) can be used. From the perspective of formability and processability, amorphous glass is preferred. Examples of glass materials include aluminosilicate glass, soda-lime glass, sodium aluminum silicate glass, aluminum borosilicate glass, and borosilicate glass.

[0038] The preferred glass composition contains 55% or more and 75% or less SiO2 as the main component, 0.3% or more and 25% or less Al2O3, and 0% or more and 20% or less CaO. Furthermore, the preferred glass composition contains one or more of the following: 0.01% or more and 6% or less Li2O, 0.7% or more and 12% or less Na2O, 0% or more and 8% or less K2O, 0% or more and 7% or less MgO, 0% or more and 10% or less ZrO2, and 0% or more and 1% or less TiO2.

[0039] When the SiO2 content is 55% or more and 75% or less, it exhibits an effect of increasing the f (frequency) of the glass substrate. More preferably, the SiO2 content in the glass is 60% or more and 75% or less. Furthermore, when the Al2O3 content is 0.3% or more and 25% or less, it exhibits an effect of increasing the ρ (density) of the glass substrate. More preferably, the Al2O3 content in the glass is 1.0% or more and 25% or less. Further, when the CaO content is 0% or more and 20%, it exhibits an effect of increasing both the f and ρ (density) of the glass substrate. More preferably, the CaO content in the glass is 1% or more and 20% or less.

[0040] It should be noted that the glass may further contain: B2O3 (an essential component in aluminoborosilicate or borosilicate glass), which reduces viscosity and improves solubility and clarity; SrO or BaO, which reduces viscosity at high temperatures, improves solubility, clarity, and formability, and also increases Young's modulus; ZnO, which improves ion exchange performance and reduces viscosity at high temperatures without reducing viscosity at low temperatures; SnO2, which improves clarity and ion exchange performance; Fe2O3 as a colorant; and As2O3 or Sb2O3 as a clarifying agent. In addition, oxides of elements such as La, P, Ce, Sb, Hf, Rb, and Y may be included as trace elements. The content of these components may be 15% or less.

[0041] <Methods for Manufacturing Disk Substrates and Disks> To ensure that the disk substrate described in this embodiment meets the aforementioned standards for flatness, Wq, and TIR, it is necessary to optimize the heating conditions during the preheating step prior to the sputtering step in the process of manufacturing disks using this disk substrate. A detailed explanation will follow.

[0042] The following provides a detailed description of each step and process condition of the method for manufacturing the disk substrate and disk as described in this embodiment. First, the manufacturing methods for the aluminum alloy substrate and glass substrate will be described up to the sputtering step. For the aluminum alloy substrate, in the aluminum alloy composition adjustment step to the cold rolling step, an aluminum alloy material is obtained by melting and casting a predetermined aluminum alloy, and an aluminum alloy sheet is prepared using this material. Next, the aluminum alloy sheet is pressurized and planarized to manufacture an aluminum alloy disk blank. Further, the manufactured disk blank undergoes pretreatment processes such as cutting and grinding, zincate treatment, and Ni-P plating, followed by surface polishing and heat treatment to manufacture an aluminum alloy substrate for disks.

[0043] Next, an example of a method for manufacturing a glass substrate will be described. First, a glass sheet is manufactured as raw material. Next, the manufactured glass sheet is cored to form a doughnut-shaped glass substrate. Further, chamfered surfaces are formed on the inner and outer peripheral end faces of the formed glass substrate, and the chamfered inner and outer peripheral end faces of the glass substrate are polished, followed by surface polishing. This polishing step includes rough polishing and fine polishing, through which a glass substrate for disks is manufactured.

[0044] A preheating step is performed on the disk substrate (an aluminum alloy disk substrate or a glass disk substrate manufactured as described above), and heating is carried out under predetermined heating conditions. This yields a disk substrate exhibiting excellent flatness and smoothness. The preheating step is described in detail below.

[0045] Before attaching the magnet to the surface of a disk substrate such as aluminum alloy or glass, it is necessary to raise the temperature of the substrate; the step used to do this is called the preheating step. Since a large number of substrates need to be processed in a short time, the substrate is rapidly heated to a predetermined temperature using infrared radiation or similar methods. In the prior art, the flatness and smoothness of the disk obtained in the preheating step do not deteriorate due to the large thickness of the substrate; however, it has been found that flatness and smoothness deteriorate as the disk becomes thinner. This is believed to be because a high heating rate in the preheating step generates thermal stress due to temperature distribution on the substrate surface, and the reduced rigidity due to the thinner disk can cause deformation. When the heating rate from room temperature to the predetermined temperature is less than or equal to 40°C / s, the deterioration of flatness and smoothness in the preheating step can be suppressed, thereby obtaining a disk substrate exhibiting excellent flatness and smoothness. It should be noted that the heating rate is preferably 30°C / s or less, more preferably 20°C / s or less. Here, the room temperature is 20°C ± 15°C, and the predetermined temperature is in the range of 150°C or higher and 750°C or lower, preferably in the range of 200°C or higher and 300°C or lower.

[0046] Furthermore, since disk productivity decreases when the heating rate is low, it is preferable to heat multiple substrates simultaneously rather than just one substrate during the preheating step. The number of substrates is preferably two or more, more preferably three or more.

[0047] As described above, when temperature distribution exists on the substrate surface during the heating process, the flatness of the substrate deteriorates. However, in the preheating step, the maximum temperature difference between the surface temperature T1 of one region and the surface temperature T2 of another region (these two regions are in a linearly symmetrical position relative to an axis passing through the center of the substrate and parallel to the substrate surface) is 20°C or greater, thus causing the substrate shape to change concentrically. Since the circumferential surface smoothness has a significant impact on the movement of the read / write head during HDD operation, the substrate shape is preferably concentric. Because the substrate shape is concentric, the circumferential waviness and height difference are improved. Therefore, as described above, by providing a predetermined temperature difference between the surface temperature T1 of one region and the surface temperature T2 of another region (these two regions are in a linearly symmetrical position on the substrate surface), the smoothness of the disk substrate surface can be further improved. The temperature difference between the surface temperature T1 of one region and the surface temperature T2 of another region (these two regions are in a linearly symmetrical position on the substrate surface) is more preferably 25°C or higher, and more preferably 30°C or higher. Furthermore, from the perspective of suppressing flatness degradation, the upper limit of the temperature difference is preferably 100°C or lower. It should be noted that as long as one region and another region are in a linearly symmetrical position, have the same size and shape, and are at the same distance from the center of the substrate, the size, shape, and distance from the center of the substrate of each region are not particularly limited. Furthermore, as a method to obtain the desired temperature difference, adjusting the position of the heat source, etc., is exemplified.

[0048] The magnetic material is adhered to the surface of a preheated disk substrate by sputtering. The disk is manufactured through this sputtering step, and a magnetic material layer is formed on the surface of the disk substrate by sputtering.

[0049] The magnetic layer can be a single layer or formed from multiple layers with different compositions. After sputtering, if necessary, a protective layer made of carbon-based material can be formed on the magnetic layer by CVD, or a lubricating oil can be coated on the protective layer to form a lubricating layer.

[0050] The preheating and sputtering steps described above impart excellent flatness and smoothness to the obtained disk, with particularly significant effects when the desired disk thickness is small, such as when fabricating disks with a thickness of 0.49 mm or less and an outer diameter of 96 mm or greater. Furthermore, since such effects are applicable to disks using heat-assisted magnetic recording (HAMR) as a next-generation recording method, the disk substrate and disk described in this embodiment are effectively used as a disk substrate and a disk substrate for HAMR, respectively.

[0051] Based on the above embodiments, the present invention relates to the following [1] to

[16] . [1] A disk substrate having a flatness of 40 μm or less, a Wq (root mean square corrugation) of 7 μm or less in the middle circumference, and a TIR (height difference) of 10 μm or less in the middle circumference. [2] The disk substrate described above [1] has a thickness of 0.50 mm or less. [3] The disk substrate described above [2] has a thickness of 0.49 mm or less. [4] The disk substrate according to any one of [1] to [3] above has an outer diameter of 96 mm or greater. [5] The disk substrate according to any one of [1] to [4] above is a disk substrate for use in a heat-assisted magnetic recording method. [6] A method for manufacturing a disk substrate, which is the method for manufacturing a disk substrate as described in any one of [1] to [5] above, the method comprising: The preheating step involves heating the substrate for the disk from room temperature to a predetermined temperature, wherein... The heating rate during the preheating step is 40°C / second or lower. [7] According to the manufacturing method described above [6], multiple substrates are heated simultaneously in the preheating step. [8] According to the manufacturing method described in [6] or [7] above, in the preheating step, the maximum temperature difference between the surface temperature T1 of one region and the surface temperature T2 of another region is 20°C or greater, and the two regions are in a linearly symmetrical position relative to an axis passing through the center of the substrate and parallel to the surface of the substrate. [9] A disk having a flatness of 40 μm or less, a Wq (root mean square ripple) of 7 μm or less in the middle circumference, and a TIR (height difference) of 10 μm or less in the middle circumference.

[10] The disk described above [9] has a thickness of 0.50 mm or less.

[11] The disk described above

[10] has a thickness of 0.49 mm or less.

[12] The disk according to any one of [9] to

[11] above has an outer diameter of 96 mm or greater.

[13] The disk according to any one of [9] to

[12] above is a disk substrate for a heat-assisted magnetic recording method.

[14] A method for manufacturing a disk, which is a method for manufacturing a disk as described in any one of [9] to

[13] above, the method comprising: The preheating step involves heating the substrate for the disk from room temperature to a predetermined temperature; and The sputtering step involves attaching a magnetic material to the surface of a preheated disk substrate via sputtering. The heating rate during the preheating step is 40°C / second or lower.

[15] According to the manufacturing method described above

[14] , multiple substrates are heated simultaneously in the preheating step.

[16] According to the manufacturing method described above

[14] or

[15] , in the preheating step, the maximum temperature difference between the surface temperature T1 of one region and the surface temperature T2 of another region is 20°C or greater, and the two regions are in a linearly symmetrical position relative to an axis passing through the center of the substrate and parallel to the surface of the substrate.

[0068] Although the disk substrate, disk and manufacturing method thereof according to the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications and changes can be made based on the technical concept of the present invention.

[0069] Example The invention will be described in more detail below with reference to examples, but the invention is not limited thereto.

[0070] In the following examples and comparative examples, multiple aluminum alloy substrates and glass substrates were manufactured as disk substrates, and their properties were evaluated.

[0071] A. Manufacturing of aluminum alloy substrate for hard disks The aluminum alloy substrate manufactured by conventional methods and then polished contains Mg: 4.0%, Fe: 0.02%, Si: 0.02%, Cr: 0.05%, Cu: 0.02%, and Zn: 0.3%, with the balance being Al and unavoidable impurities. The outer diameter of the aluminum alloy substrate is 97 mm, the inner diameter of the circular holes is 25 mm, and the thickness is shown in Table 1.

[0072] B. Manufacturing of glass substrates for hard disks The glass substrate, manufactured by conventional methods and with a polished surface, is made of aluminosilicate glass. The outer diameter of the glass substrate is 97 mm, the inner diameter of the circular hole is 25 mm, and the thickness is shown in Table 1.

[0073] C. Evaluation of disk substrate characteristics Each substrate was preheated using the following method, and then the flatness, Wq in the middle circumference, and TIR in the middle circumference of the obtained substrate were measured and evaluated.

[0074] First, each substrate was preheated under the conditions shown in Table 1. An infrared heating lamp, a bulb-type radiant heating source, was used as the heat source, emitting light through an electrically heated filament. After the substrate reached its maximum temperature, it was held for at least one minute, and then cooled by turning off the heater. The substrate was fixed at three points on its outer periphery during heating using conventional methods. Furthermore, as... Figure 1 As shown, an infrared radiation thermometer was used to measure the surface temperatures of two regions, R1 and R2, which are linearly symmetrical with respect to an axis A passing through the center C of the substrate and parallel to the substrate surface. The temperature measurement interval was set to 1 second. The temperature difference between regions R1 and R2 at the same measurement time was used as the temperature difference calculation, and the maximum value of the measured temperature difference was defined as the temperature difference between the surface temperatures T1 and T2 of regions R1 and R2. The difference between the temperature at a certain moment and the temperature one second earlier was calculated, and the heating rate was calculated using (T2-T1) / (t2-t1). This used the surface temperature (T1) and a certain time (t1) during which the temperature difference change per second was greater than or equal to 3℃ when the temperature was less than or equal to 50℃; and the surface temperature (T2) and a certain time (t2) during which the temperature difference change per second was less than 3℃ one second earlier when the temperature was greater than 50℃.

[0075] The flatness, Wq (weight of material) in the center circumference, and TIR (transformation intensity) in the center circumference of the preheated substrate were measured. It should be noted that the meanings of flatness, Wq, and TIR are as described above. Flatness, Wq, and TIR were measured using a ZyGO non-contact flatness measuring machine.

[0076] Table 1 shows the evaluation results of properties such as flatness, Wq, and TIR for each substrate.

[0077] [Table 1]

[0078] As shown in Table 1, in Examples 1 to 5, disk substrates exhibiting excellent flatness and smoothness were obtained due to the flatness being 40 μm or less, the intermediate circumference Wq being 7 μm or less, and the intermediate circumference TIR being 10 μm or less.

[0079] Conversely, in Comparative Example 1, stable flatness was not achieved due to the flatness being 81 μm or larger, and the overall flatness being poor. Furthermore, the smoothness was also poor due to the middle circumference Wq being 18 μm or smaller.

[0080] D. Evaluation of disk characteristics Each substrate was preheated using the same method as described in C above. Then, the disk obtained by sputtering a 5 nm magnetic film was measured and evaluated for its flatness, Wq in the middle circumference, and TIR in the middle circumference.

[0081] Table 2 shows the evaluation results of characteristics such as flatness, Wq, and TIR for each disk.

[0082] [Table 2]

[0083] As shown in Table 2, in Examples 6 to 8, disks exhibiting excellent flatness and smoothness were obtained due to a flatness of 40 μm or less, a central circumference Wq of 7 μm or less, and a central circumference TIR of 10 μm or less.

[0084] Conversely, in Comparative Example 2, stable flatness was not achieved due to the flatness being 81 μm or larger, and the overall flatness being poor. Furthermore, the smoothness was also poor due to the central circumference Wq being 18 μm or smaller.

[0085] [Industrial Applicability] According to the present invention, a disk substrate exhibiting excellent flatness and smoothness, a disk, and a method thereof can be provided.

Claims

1. A disk substrate having a flatness of 40 μm or less, a Wq (root mean square corrugation) of 7 μm or less in the middle circumference, and a TIR (height difference) of 10 μm or less in the middle circumference.

2. The disk substrate according to claim 1, wherein the thickness is 0.50 mm or less.

3. The disk substrate according to claim 2, wherein the thickness is 0.49 mm or less.

4. The disk substrate according to claim 1 or 2, wherein its outer diameter is 96 mm or greater.

5. The disk substrate according to claim 1 or 2, wherein it is a disk substrate for a heat-assisted magnetic recording method.

6. A method for manufacturing a disk substrate, comprising the method for manufacturing a disk substrate according to claim 1 or 2, the method comprising: The preheating step involves heating the substrate for the disk from room temperature to a predetermined temperature, wherein... The heating rate in the preheating step is 40°C / second or lower.

7. The manufacturing method according to claim 6, wherein, Multiple substrates are heated simultaneously during the preheating step.

8. The manufacturing method according to claim 6, wherein, In the preheating step, the maximum temperature difference between the surface temperature T1 of one region and the surface temperature T2 of another region is 20°C or greater, and the one region and the other region are linearly symmetrical about each other with respect to an axis passing through the center of the substrate and parallel to the surface of the substrate.

9. A disk having a flatness of 40 μm or less, a Wq (root mean square ripple) of 7 μm or less in the intermediate circumference, and a TIR (height difference) of 10 μm or less in the intermediate circumference.

10. The disk according to claim 9, wherein the thickness is 0.50 mm or less.

11. The disk according to claim 10, wherein the thickness is 0.49 mm or less.

12. The disk according to claim 9 or 10, wherein the outer diameter is 96 mm or greater.

13. The disk according to claim 9 or 10, wherein it is a disk substrate for a heat-assisted magnetic recording method.

14. A method for manufacturing a disk, comprising the method for manufacturing a disk according to claim 9 or 10, the method comprising: The preheating step involves heating the substrate for the disk from room temperature to a predetermined temperature; as well as The sputtering step involves attaching a magnetic material to the surface of a preheated disk substrate via sputtering. The heating rate in the preheating step is 40°C / second or lower.

15. The manufacturing method according to claim 14, wherein, Multiple substrates are heated simultaneously during the preheating step.

16. The manufacturing method according to claim 14, wherein, In the preheating step, the maximum temperature difference between the surface temperature T1 of one region and the surface temperature T2 of another region is 20°C or greater, and the one region and the other region are linearly symmetrical about each other with respect to an axis passing through the center of the substrate and parallel to the surface of the substrate.

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