Substrate for magnetic disk

Abstract

The object of this invention is to provide a disk disk substrate that, although particularly thin, effectively suppresses head collisions by effectively suppressing undulations in the outer peripheral region of the disk surface. This invention provides a disk disk substrate in which, using scanning optical interferometry in multiple field-of-view regions located in the outer peripheral region of at least one side, the maximum value of the arithmetic mean height Sa specified in ISO 25178 is less than 0.50 nm in the mid-wavelength region via a Gaussian filter with a cutoff wavelength set to 1.0 mm, and the standard deviation of the aforementioned arithmetic mean height Sa is less than 0.10 nm.

Description

Technical Field

[0001] This invention relates to a substrate for a hard disk. More specifically, it relates to a substrate for a hard disk that, although relatively thin, effectively suppresses head collisions by effectively suppressing undulations present in the outer peripheral region of the disk surface. Background Technology

[0002] In recent years, the rapid popularization of cloud computing has led to a demand for higher capacity hard drives used in data centers. Correspondingly, measures have been taken to increase the number of disk substrates by increasing their diameter and thinning. However, since the dimensions of hard drive casings are already standardized, further increases in diameter are difficult to achieve. Therefore, there is a strong desire for further thinning of disk substrates. However, it is well known that thinner substrates tend to deform due to insufficient rigidity, causing the disk to undulate during high-speed rotation. This undulation is a major cause of collisions between the disk and the read / write head, and therefore, it is preferable to suppress it.

[0003] To date, some research has been conducted on reducing physical errors such as head collisions in hard drives. For example, Patent Document 1 discloses a glass substrate that, through acid treatment, easily achieves high surface cleanliness and smoothness (specifically, the average surface roughness (Ra) is smoothed to less than 0.3 nm).

[0004] [Previous Technical Documents]

[0005] (Patent Documents)

[0006] Patent Document 1: Japanese Patent No. 3959588 Summary of the Invention

[0007] [The problem the invention aims to solve]

[0008] The glass substrate described in Patent Document 1 is a glass substrate whose surface is smoothed by adjusting the two-dimensional surface properties state, i.e., the average surface roughness (Ra), which is measured by lines. If the substrate is thinned in the manner described above, it is prone to deformation due to insufficient rigidity. Therefore, adjusting the two-dimensional surface properties state alone is sometimes insufficient to suppress magnetic head collisions.

[0009] The purpose of this invention is to provide a substrate for a hard disk that, although thin, effectively suppresses head collisions by effectively suppressing undulations in the outer peripheral region of the disk surface.

[0010] [Technical means to solve the problem]

[0011] Through in-depth research, the inventors discovered that if the arithmetic mean height Sa on at least one of the outer peripheral regions of a disk substrate is small, the undulations in the outer peripheral region are suppressed, resulting in less head collisions, thus completing the present invention.

[0012] To achieve the above objectives, the main structure of the present invention is as follows.

[0013] (1) A disk substrate, wherein, in a plurality of field-view regions located on the outer peripheral side region of at least one side, the maximum value of the arithmetic mean height Sa specified in ISO 25178 is less than 0.50 nm when measured in the mid-wavelength side region by a scanning optical interferometry via a Gaussian filter with a cutoff wavelength set to 1.0 mm, and the standard deviation of the aforementioned arithmetic mean height Sa is less than 0.10 nm.

[0014] (2) The disk substrate according to (1) above, wherein the average value of the aforementioned arithmetic mean height Sa is less than 0.40 nm.

[0015] (3) The disk substrate according to (1) or (2) above, wherein the thickness dimension is less than 0.50 mm.

[0016] (4) The disk substrate according to any one of (1) to (3) above, wherein the outer diameter is 95 mm or more.

[0017] (5) A disk in which, in a plurality of field-view regions located on the outer peripheral side of at least one side, the maximum value of the arithmetic mean height Sa specified in ISO 25178 is less than 0.50 nm when measured in the mid-wavelength side region by means of a Gaussian filter with a cutoff wavelength set to 1.0 mm, and the standard deviation of the aforementioned arithmetic mean height Sa is less than 0.10 nm.

[0018] (The effect of the invention)

[0019] According to the present invention, a substrate for a magnetic disk is provided, which, although particularly thin, effectively suppresses head collisions by effectively suppressing undulations present in the outer peripheral region of the disk surface. Attached Figure Description

[0020] Figure 1 This is a top view of a disk substrate according to the present invention, illustrating an example of the outer peripheral region of the upper surface and multiple fields of view for measuring the arithmetic mean height Sa.

[0021] Figure 2 This is a flowchart illustrating an example of the manufacturing process of an aluminum alloy substrate for a disk according to the present invention.

[0022] Figure 3 This is a flowchart illustrating an example of the manufacturing process of a glass substrate for a disk according to the present invention. Detailed Implementation

[0023] The disk substrate according to the present invention will now be described in detail.

[0024] The disk substrate of the present invention is a disk substrate in which, in multiple field-of-view regions located in the outer peripheral region of at least one side, the maximum value of the arithmetic mean height Sa specified in ISO 25178 is less than 0.50 nm when measured in the mid-wavelength region using a scanning optical interferometry via a Gaussian filter with a cutoff wavelength set to 1.0 mm, and in particular the standard deviation of the arithmetic mean height Sa is less than 0.10 nm.

[0025] <Arithmetic Mean Height Sa>

[0026] The "arithmetic mean height Sa" as defined in ISO 25178 refers to the arithmetic mean of the absolute values ​​of the differences in height between points on the substrate surface and the average surface. In other words, it is the three-dimensional arithmetic mean height, used as a general evaluation index for surface roughness. Furthermore, the profile curves of the substrate surface are divided into undulation curves composed of long wavelengths and roughness curves composed of short wavelengths. However, the wavelength at which the profile curve (e.g., undulation curve) of the wavelength region to be detected (extracted) is the "cutoff wavelength," suitable for detecting only the profile curve of the wavelength region to be detected and excluding other profile curves (e.g., roughness curve). For example, if a Gaussian filter is used to remove the uneven components on the shorter wavelength side far from the cutoff wavelength and the larger undulation components on the longer wavelength side, that is, measuring in the mid-wavelength side region centered at the cutoff wavelength of 1.0 mm, then minute undulation components can be specifically evaluated.

[0027] According to the present invention, minute undulations, or so-called wavy surface defects, in the thinned substrate, including the peripheral region of the disk, may be the cause of head collisions. Various countermeasures to prevent hard drive head collisions have been studied in the past, but the impact of wavy surface defects on head collisions has not been investigated until now.

[0028] Furthermore, according to the discoveries of the inventors, the wavy surface defects are mainly undulations with a width in the range of a few millimeters. It is more appropriate to remove the minute irregularities on the short-wavelength side and the larger undulations on the long-wavelength side, which are far from the cutoff wavelength of 1.0 mm, during the detection. Therefore, the profile curve of the mid-wavelength side region can be detected simply by using a Gaussian filter with the cutoff wavelength set to 1.0 mm. If Sa is measured in multiple field-of-view regions on the outer peripheral side of at least one side of the substrate in a wavelength region centered at 1.0 mm, wavy surface defects that may cause head collisions can be detected sensitively. If, under such conditions, a scanning optical interferometry method is used for measurement, the maximum value of Sa on the outer peripheral side region of the disk substrate is less than 0.50 nm, and particularly if the standard deviation of Sa is less than 0.10 nm, head collisions can be suppressed.

[0029] (Peripheral region)

[0030] The outer peripheral region of a disk substrate refers to the area enclosed by the outer peripheral edge of the disk substrate and a virtual circle defined by an inner peripheral side a few millimeters away from the outer peripheral edge. Figure 1 This is an example of the outer peripheral region 2 of the upper surface of the disk substrate 1 according to the present invention. The outer peripheral region 2 refers to the area enclosed by the outer peripheral edge 3 of the disk substrate 1 and a virtual inner circle 4 drawn as concentric circles on the center side only a few millimeters away from the outer peripheral edge 3 in a top view of the disk substrate 1. Furthermore, the arithmetic mean height Sa measured in multiple fields of view located in the outer peripheral region 2 is sometimes referred to as "Sa of the outer peripheral region" below.

[0031] The outer peripheral region is considered the area most prone to head collisions during disk use. This is because, as the disk rotates, in addition to centrifugal force, it is also subjected to external forces such as air resistance from the surrounding atmosphere or gases, resulting in vibration or undulation (flutter). The outer peripheral region of the disk is particularly susceptible to deformation due to these external forces. Wavy surface defects in this region can induce flutter, leading to head collisions. Therefore, the outer peripheral region of the disk substrate is crucial for suppressing flutter. The inventors, focusing on the Sa region of the outer peripheral region, have for the first time discovered a method to suppress flutter and reduce the risk of head collisions.

[0032] (Field of view area)

[0033] In the disk substrate 1, the number of measurement locations Sa in the outer peripheral region, i.e., multiple field-of-view areas, is not particularly limited as long as there are two or more areas within the outer peripheral region 2. From the viewpoint of ensuring certainty, it is preferable to have three or more field-of-view areas, for example, four or more. From the viewpoint of facilitating product inspection, it is preferable to have, for example, 16 or fewer areas. More preferably, the maximum value is taken from the arithmetic mean height Sa measured in 6 to 12 areas, for example, 8 areas.

[0034] Multiple field-of-view regions can be configured at any location within the outer peripheral region 2, but based on measuring Sa on the outer peripheral side as comprehensively as possible, they are preferably evenly arranged within the virtual outer circle 5 drawn slightly towards the center of the outer peripheral edge 3 of the disk substrate, interlocking within the field-of-view regions. For example, Figure 1 As shown, if the eight field-of-view regions 6 are respectively arranged at positions of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315° with the corners of the square connected to the inner periphery of the virtual outer circle 5, the Sa of the outer peripheral region 2 can be measured more accurately. Furthermore, the virtual outer circle 5 is preferably a concentric circle that is only about 0.1 to 1 mm from the center relative to the outer peripheral edge 3 of the disk substrate, for example, only about 0.5 mm from the center.

[0035] The size of the field of view 6 is not particularly limited. From a deterministic point of view, it is preferable to perform the measurement in a field of view that is as wide as possible. Considering the convenience of measurement and the characteristics of the measuring device, it is preferable to use a square area of ​​4 to 6 mm, especially a square area of ​​4.5 to 5.0 mm, as the field of view 6. For example, consider... Figure 1 The eight square regions of 4.75 mm each shown are used as the field of view region 6. If the value is measured using scanning optical interferometry, it can more accurately reflect the Sa of the outer peripheral region of the disk substrate 1.

[0036] (Scanning optical interferometry)

[0037] Scanning optical interferometry is a common method for measuring isochronous three-dimensional shapes. In this method, a beam splitter separates the light from the light source into two parts: one part illuminates a reference surface, and the other part illuminates the sample surface. The light reflected from both parts is imaged in a camera. Based on this, the information of the interference fringes obtained by the optical path difference caused by the unevenness of the sample surface is converted into height information, and a three-dimensional shape is generated. Measurement instruments based on scanning optical interferometry are commercially available from various companies, and any of these commercially available instruments can be used in this invention.

[0038] (Sa value)

[0039] As described above, if for a disk substrate, in multiple field-of-view regions located on the outer peripheral side of at least one side, the maximum value of the arithmetic mean height Sa specified in ISO 25178, measured using a scanning optical interferometry via a Gaussian filter with a cutoff wavelength set to 1.0 mm in the mid-wavelength side region, is less than 0.50 nm, then the risk of head collision can be reduced. From the viewpoint of further reducing the risk of head collision, the maximum value of Sa in the outer peripheral side region is preferably less than 0.40 nm, and particularly preferably less than 0.30 nm. Furthermore, since a smaller Sa in the outer peripheral side region is more preferred, its lower limit value does not need to be considered. However, considering the convenience of the manufacturing process, for example, the lower limit value may be set to 0.20 nm or 0.15 nm.

[0040] The arithmetic mean height Sa of each field of view in the outer peripheral region (Sa in the outer peripheral region) is preferably below 0.40 nm, and particularly preferably below 0.30 nm. A smaller average value of Sa is also preferable; however, for manufacturing convenience, the lower limit can be set to 0.20 nm or 0.25 nm, for example. A disk substrate with a maximum value of Sa below 0.50 nm and an average value of Sa below 0.40 nm in the outer peripheral region has an extremely flat surface, further reducing the risk of head collisions.

[0041] Furthermore, a disk substrate with a standard deviation of the arithmetic mean height Sa of each field of view in the outer peripheral region is preferably less than 0.10 nm. In such a disk substrate, Sa is consistently a low value throughout the substrate, resulting in a particularly smooth surface. Therefore, the risk of head collision is further reduced. Moreover, the standard deviation and the aforementioned average value are calculated based on the arithmetic mean height Sa at which the maximum value is obtained.

[0042] For disk drive substrates, it is particularly preferable that the maximum value of the arithmetic mean height Sa, measured in multiple field-of-view regions located on the outer peripheral side of both sides of the substrate, is 0.50 nm or less. If the two surfaces are so flat, it becomes a disk drive substrate that is particularly difficult to cause head collisions. For the same reason, the average value of Sa in multiple field-of-view regions located on the outer peripheral side of both sides of the substrate is preferably 0.40 nm or less, and / or the standard deviation is preferably 0.10 nm or less.

[0043] The substrate that constitutes such a disk substrate will be described below.

[0044] <Substrate>

[0045] The disk substrate of the present invention can be formed from any known substrate, and its size and material are not particularly limited. However, the effects of the present invention become particularly significant in thinner disk substrates with a thickness of less than 0.5 mm. This is because, in such thin substrates, due to low rigidity, a large surface height Sa in the outer peripheral region can severely affect the reliability of the hard disk. For the same reason, the effects of the present invention become significant in disk substrates with an outer diameter of 95 mm or more. Furthermore, there is no particular limitation on the upper limit of the external dimensions, but considering the size of a typical hard disk drive, it can be set to, for example, 97 mm or less. There is also no particular limitation on the lower limit of the thickness, and considering the rigidity of the disk, it can be set to, for example, about 0.30 mm or more.

[0046] The material of the disk substrate of the present invention can be appropriately selected from previously used materials, such as aluminum alloy and glass. Since disk substrates made of aluminum alloy, glass, etc. are less prone to defects and have good mechanical properties and processability, they are suitable as disk substrates of the present invention.

[0047] <Aluminum alloy substrate>

[0048] Aluminum alloy substrates (sometimes referred to as "aluminum alloy substrates" in this specification) are suitable as substrates for hard disks because they are less prone to defects, have good mechanical properties and machinability, and are low cost. There are no particular limitations on the material of the aluminum alloy substrate; various known materials can be used, with alloys containing elements such as magnesium (Mg), copper (Cu), zinc (Zn), and chromium (Cr) being preferred. These alloys are commonly used materials and therefore have the advantages of low cost, high strength, and low defect rate. Additionally, elements such as iron (Fe), manganese (Mn), and nickel (Ni) that can improve rigidity can also be included. Such high-rigidity substrates are advantageous in suppressing flutter. A5000 series or A8000 series alloys are more preferred, especially A5086. With such alloys, the substrate is less prone to defects and can also be endowed with sufficient mechanical properties.

[0049] If we take specific examples of the composition of the aforementioned aluminum alloys, for example, A5086 contains Mg: 3.5-4.5%, Fe: less than 0.50%, Si: less than 0.40%, Mn: 0.20-0.7%, Cr: 0.05-0.25%, Cu: less than 0.10%, Ti: less than 0.15%, and Zn: less than 0.25%, with the remainder consisting of Al and unavoidable impurities. Furthermore, as examples of other specific compositions of aluminum alloys, we can cite those containing Mg: 1.0-6.5%, Cu: 0-0.070%, Zn: 0-0.60%, Fe: 0-0.50%, Si: 0-0.50%, Cr: 0-0.20%, Mn: 0-0.50%, Zr: 0-0.20%, Be: 0-0.0020%, with the remainder consisting of aluminum and unavoidable impurities. Additionally, for example, each element may contain less than 0.1%, and the total may contain less than 0.3%, other components not mentioned above. Furthermore, in the above composition, "%" refers to "mass %".

[0050] <Glass substrate>

[0051] Glass substrates not only possess characteristics such as low defect resistance, good mechanical properties, and good processability, but also the advantage of being resistant to plastic deformation, making them suitable as substrates for hard disks. There are no particular restrictions on the material of the glass substrate; glass ceramics such as amorphous glass and crystalline glass can be used. However, from the viewpoint of substrate flatness, formability, and processability, amorphous glass is preferred. There are no particular restrictions on the material itself; examples include aluminosilicate glass, soda-lime glass, sodium-aluminate glass, aluminoborosilicate glass, borosilicate glass, and physically tempered and chemically tempered glass treated with air cooling or liquid cooling, etc., and the application is not limited to these. Among these, aluminosilicate glass, especially amorphous aluminosilicate glass, is preferred. Substrates made of this material exhibit excellent flatness and strength, and also offer good long-term reliability.

[0052] As for aluminosilicate glass, for example, aluminosilicate glass with SiO2 as the main component (55-75%) and containing Al2O3 (0.7-25%), Li2O (0.01-6%), Na2O (0.7-12%), K2O (0-8%), MgO (0-7%), CaO (0-10%), ZrO2 (0-10%), and TiO2 (0-1%) can also be used as a substrate in this invention. Furthermore, in the above and following compositions, "%" refers to "mass %".

[0053] In the above glass composition, SiO2 is the main component forming the glass skeleton. If its content is above 55%, it tends to exhibit high chemical durability, while if it is below 75%, it tends to have a lower melting temperature and is easier to form.

[0054] Al₂O₃ is a component that enhances ion exchange capacity and chemical durability. To achieve this effect, it is preferable to set the Al₂O₃ content to 0.7% or higher. Furthermore, if the Al₂O₃ content is below 25%, solubility and resistance to devitrification do not decrease. Therefore, the Al₂O₃ content is preferably between 0.7% and 25%.

[0055] Li₂O is a component that chemically strengthens glass by exchanging Na ions, and it improves melt flowability, formability, and Young's modulus. To achieve this effect, the Li₂O content is preferably 0.01% or higher. Furthermore, if the Li₂O content is below 6%, devitrification resistance and chemical durability do not decrease. Therefore, the Al₂O₃ content is preferably between 0.01% and 6%.

[0056] Na₂O is a component that chemically strengthens glass through ion exchange with potassium (K) and reduces high-temperature viscosity, improves melt flowability and formability, and enhances resistance to devitrification. To achieve these effects, the Na₂O content is preferably 0.7% or higher. Furthermore, if the Na₂O content is below 12%, chemical durability and Knoop hardness are not reduced, making this a preferred option.

[0057] Furthermore, K2O, MgO, CaO, ZrO 2、 TiO2 can be added with any desired ingredients.

[0058] K2O is a component that reduces high-temperature viscosity, improves melt flow, enhances moldability, and improves resistance to devitrification. However, if the K2O content exceeds 8%, there is a tendency for low-temperature viscosity to decrease while thermal expansion and impact resistance to increase. Therefore, the K2O content is preferably 0-8%.

[0059] MgO and CaO are components that reduce high-temperature viscosity, improve solubility and clarity, and enhance formability, while also increasing Young's modulus. CaO, in particular, is an essential component in soda-lime glass. While MgO and CaO reduce high-temperature viscosity, improve solubility and clarity, and enhance formability, they are also expected to increase Young's modulus. However, if the MgO content exceeds 7% and / or the CaO content exceeds 10%, there is a tendency to decrease ion exchange performance and devitrification resistance. Therefore, the MgO content is preferably below 7%, and the CaO content is preferably below 10%.

[0060] ZrO2 is a component that increases Knoop hardness, improves chemical durability, and heat resistance. However, if the ZrO2 content exceeds 10%, it tends to decrease melt permeability and resistance to devitrification. Therefore, the ZrO2 content is preferably between 0% and 10%.

[0061] TiO2 is a component that reduces high-temperature viscosity, improves meltability, stabilizes structure, and enhances durability. However, if the TiO2 content exceeds 1%, it tends to reduce ion exchange performance and resistance to devitrification. Therefore, the preferred TiO2 content is 0-1%.

[0062] In addition to B₂O₃, which reduces viscosity and improves solubility and clarity; SrO and BaO, which reduce high-temperature viscosity, improve solubility and clarity, and enhance formability while increasing Young's modulus; ZnO, which improves ion exchange performance without reducing low-temperature viscosity but reduces high-temperature viscosity; SnO₂, which improves clarity and ion exchange performance; and Fe₂O₃, which functions as a colorant, the glass composition may further contain As₂O₃ and SB₂O₃ as clarifying agents. Furthermore, as trace elements, oxides of lanthanum (La), phosphorus (p), cerium (Ce), antimony (Sb), hafnium (Hf), rubidium (Rb), and yttrium (Y) may also be included. Moreover, B₂O₃ is an essential component in aluminoborosilicate glass or borosilicate glass.

[0063] The glass described above may also contain SiO2: 45-60%, Al2O3: 7-20%, B2O3: 1-8%, P2O5: 0.5-7%, CaO: 0-3%, TiO2: 1-15%, BaO: 0-4%, and other oxides such as MgO: 5-35%.

[0064] <Manufacturing Method of Aluminum Alloy Substrate>

[0065] Figure 2 This is a flowchart illustrating an example of the manufacturing process of an aluminum alloy substrate for a disk according to the present invention. Figure 2In this process, the aluminum alloy composition preparation step (step S101), the aluminum alloy casting step (step S102), the homogenization treatment step (step S103), the hot rolling step (step S104), and the cold rolling step (step S105) are steps to manufacture aluminum alloy materials by melt casting and form them into aluminum alloy sheets. Next, a blank made of aluminum alloy is manufactured by a punching / pressing planarization treatment step (step S106). Furthermore, the manufactured blank is pretreated by a cutting / grinding process (step S107) to produce a ring-shaped aluminum alloy sheet. The substrate is then subjected to a zincate treatment process (step S108) and a chemical Ni-P plating process (step S109) to manufacture an aluminum alloy substrate for disks. The manufactured aluminum alloy substrate for disks (blank substrate) is subjected to a rough polishing process (step S110) and a precision polishing process (step S111), and a disk is formed by a magnetic material attachment process (step S112).

[0066] The following is based on this Figure 2 The process is described in detail, with each step explained in terms of its content.

[0067] First, a molten aluminum alloy material with the above-described composition is prepared by heating / melting using conventional methods (step S101). Next, the prepared molten aluminum alloy material is cast using a semi-continuous casting (DC casting) method or a continuous casting (CC casting) method to produce the aluminum alloy material (step S102). Vertical semi-continuous casting is particularly preferred. The manufacturing conditions for the aluminum alloy material in the DC casting and CC casting methods are described below.

[0068] In the DC casting method, the molten liquid injected through the nozzle is cooled by the bottom block, the walls of the water-cooled mold, and the cooling water sprayed directly onto the outer periphery of the ingot (casting block), and solidifies, and is pulled downward as an aluminum alloy casting block.

[0069] On the other hand, in the CC casting method, molten liquid is supplied between a pair of rollers (or belt casters and block casters) through a casting nozzle, and the heat dissipation from the rollers is used to directly cast thin sheets of aluminum alloy.

[0070] The main difference between DC casting and CC casting lies in the cooling rate during casting. In CC casting, which has a high cooling rate, the second-phase particles are characterized by smaller sizes compared to DC casting.

[0071] The DC-cast aluminum alloy ingots are subjected to homogenization treatment as needed (step S103). During homogenization, it is preferable to perform a heat treatment at 280–620°C for 0.5–30 hours, more preferably at 300–620°C for 1–24 hours. If the heating temperature during homogenization is below 280°C or the heating time is less than 0.5 hours, the homogenization treatment is insufficient, and the deviation in the loss factor of each aluminum alloy sheet may increase. If the heating temperature during homogenization exceeds 620°C, the aluminum alloy ingot may melt. Even if the heating time during homogenization exceeds 30 hours, the effect is saturated, and no more significant improvement can be obtained.

[0072] Next, the aluminum alloy ingot (DC casting) that has undergone homogenization treatment or not, depending on the requirements, is hot-rolled to form a sheet (step S104). During hot rolling, the conditions are not particularly limited, but the starting temperature of hot rolling is preferably set to 250-600°C, and the ending temperature of hot rolling is preferably set to 230-450°C.

[0073] Next, the hot-rolled sheet or the cast sheet cast using the CC casting method is cold-rolled to form an aluminum alloy sheet with a thickness of, for example, about 0.30 to 0.60 mm (step S105). The cold rolling conditions are not limited and can be determined according to the required product sheet strength and sheet thickness (thickness dimension). The rolling rate is preferably set to 10 to 95%.

[0074] Furthermore, annealing is preferably performed before or during cold rolling to ensure cold-rolled processability. The annealing temperature is preferably 250–500°C, and particularly preferably 300–450°C. Annealing under these conditions minimizes deformation even with prolonged use and maintains good flatness. More specific annealing conditions include, for example, intermittent heating at 300–450°C for 0.1–10 hours, and continuous heating at 400–500°C for 0–60 seconds. A holding time of 0 seconds means immediate cooling after reaching the desired holding temperature.

[0075] Then, the aluminum alloy sheet obtained by cold rolling is punched into a ring shape to form a ring-shaped aluminum alloy sheet. The ring-shaped aluminum alloy sheet is preferably formed into a coil by a punching / pressure planarization process (step S106). The punching / pressure planarization process (also known as "pressure annealing") is preferably performed at a temperature above the recrystallization temperature of the aluminum alloy, applying a pressure of 30–60 kg / cm². 2 The process is carried out under pressure. For example, it is carried out in the atmosphere at a temperature of 250–500°C, especially 300–400°C, for 0.5–10 hours, especially for about 1–5 hours, to produce a flattened blank.

[0076] Before subsequent zincate treatment, the blank is first machined / ground (step S107) and then subjected to the required heat treatment. Furthermore, it is preferable to perform a preliminary polishing process to manage the surface of the polishing pad before the polishing process described later, particularly the rough polishing process.

[0077] Next, the surface of the blank is degreased and etched, and then subjected to zincate treatment (Zn replacement treatment) (step S108). Degreasing can be performed using commercially available AD-68F (manufactured by Uemura Kogyo Co., Ltd.) degreasing solution, at a concentration of 200–800 mL / L, a temperature of 40–70°C, and a treatment time of 3–10 min. Etching can be performed using commercially available AD-107F (manufactured by Uemura Kogyo Co., Ltd.) etching solution, at a concentration of 20–100 mL / L, a temperature of 50–75°C, and a treatment time of 0.5–5 min. During zincate treatment, a zincate film is formed on the surface of the blank. Zincate treatment can be performed using commercially available zincate treatment solutions, preferably at a concentration of 100–500 mL / L, a temperature of 10–35°C, and a treatment time of 0.1–5 min. Zincate treatment can be performed at least once, or more than twice. By performing zincate treatment multiple times, fine Zn particles can be precipitated to form a uniform zincate film.

[0078] When performing more than one zincate treatment, a Zn stripping treatment can also be performed between treatments. The Zn stripping treatment uses an HNO3 solution, preferably at a concentration of 10–60%, a temperature of 15–40°C, and a treatment time of 10–120 seconds (hence, it is also called "nitric acid stripping treatment"). Furthermore, subsequent zincate treatments are preferably performed under the same conditions as the initial zincate treatment.

[0079] Furthermore, the zincate-treated blank surface is subjected to, for example, electroless Ni-P plating (step S109) as a substrate for magnetic attachment. The electroless Ni-P plating process uses a commercially available plating solution, such as NIMUDEN (registered trademark) HDX manufactured by Uemura Industries, Ltd., preferably under the following conditions: Ni concentration: 3–10 g / L, temperature: 80–95°C, and processing time: 30–180 minutes.

[0080] The plated surface after electroless Ni-P plating is polished (steps S110-S111) to form a disk substrate. A magnetic material is then attached to this substrate (step S112), and layers are stacked as needed, thereby enabling the manufacture of disks such as hard disks. The attachment of the magnetic material can be performed, for example, by sputtering.

[0081] Furthermore, the Sa value in the outer peripheral region can be measured on the disk substrate before the magnet is attached, but it can also be measured after the magnet is attached, as described later. This is because the magnet is thin enough not to affect the Sa value in the outer peripheral region.

[0082] <Method for Manufacturing Glass Substrates>

[0083] Figure 3 This is a flowchart illustrating an example of the manufacturing process of a glass substrate for a disk according to the present invention. First, a glass plate of a predetermined thickness is prepared (steps S201-S202). Next, the prepared glass plate is cored and the inner and outer peripheral end faces are polished to form / process a ring-shaped glass substrate (steps S203-S204). Next, a polishing process using diamond particles or the like is performed on the formed glass substrate as needed (step S205). Next, or after step S204, a rough polishing process is performed, in which the glass substrates are clamped together from top to bottom using a polishing pad, and multiple glass substrates are polished simultaneously, for example, using cerium oxide abrasive grains (step S206). After performing a chemical strengthening treatment as needed (step S207), a precision polishing process is performed, for example, using colloidal silica abrasive grains (step S208). Next, a disk is manufactured by attaching a magnetic material (step S209).

[0084] The following is based on this Figure 3 The process outlines the steps and provides a detailed explanation of each step.

[0085] First, a molten liquid of glass material having the above-described composition is prepared by heating / melting according to conventional methods (step S201). Next, the prepared molten liquid of glass material is formed into a glass sheet using known manufacturing methods such as float glass, downdraw glass, direct pressing glass, redrawing glass, and bleaching glass (step S202). Among these methods, the redrawing glass method, which involves heating and softening a base glass sheet manufactured using the float glass method and stretching it to the desired thickness, is preferred because it allows for easier production of glass sheets with smaller thickness deviations.

[0086] Next, the glass plate obtained in step S202 is used to form a ring-shaped glass substrate through a core-forming process (step S203). The inner and outer circumferential end faces can also be polished using cutting / grinding (step S204). The formed glass substrate (glass blank) forms a ring-shaped plate with two main surfaces and a central hole.

[0087] The obtained glass blank can also be subjected to annealing. Annealing can be performed, for example, by holding the glass blank at a temperature near the strain point for about 15 minutes or more and then slowly cooling it for about 3 to 12 hours. Although the annealing temperature depends on the glass material, it is preferably 250 to 750°C, and particularly preferably 500 to 700°C. By performing annealing under such conditions, deformation is less likely to occur during long-term use, and good flatness can be maintained. As more specific annealing conditions, for example, if intermittent heating is used, it can be carried out at 500 to 650°C for 0.1 to 10 hours, and if continuous heating is used, it can be carried out at 500 to 750°C for 0 to 60 seconds. Here, a holding time of 0 seconds means cooling immediately after reaching the desired holding temperature. The glass substrate of the present invention can also be manufactured, for example, by forming a commercially available glass plate with the composition described above into a ring shape and then annealing it.

[0088] Next, in step S205, a grinding process is arbitrarily performed on the formed annular plate to adjust the plate thickness. Furthermore, depending on the plate thickness of the glass substrate obtained in the processes up to step S204, the grinding process S205 can be omitted, and the process can proceed to the polishing process described below. For example, since glass plates manufactured using the heavy drawing method generally have small thickness deviations, the grinding process S205 may not be performed. When manufacturing glass plates using the float glass or direct pressing method, the grinding process S205 is preferably performed. The grinding process can be performed, for example, using an intermittent double-sided polishing machine that uses diamond particles.

[0089] The surface of the glass substrate (blank substrate) obtained as described above is polished (steps S206 to S208) to form a disk substrate. A magnetic material is attached to the substrate (step S209), and the substrates are stacked as needed, thereby enabling the manufacture of disks such as hard disks.

[0090] In the above polishing process, it is preferable to perform a chemical strengthening treatment (step S207) on the glass substrate between coarse polishing (step S206) and fine polishing (step S208). Through chemical strengthening, lithium ions and sodium ions on the surface of the glass substrate are replaced by sodium ions and potassium ions with relatively larger ionic radii in the chemical strengthening solution, respectively. As a result, a compressive stress layer is formed on the surface, and the glass substrate is strengthened. The chemical strengthening method is not particularly limited; for example, it can be performed by immersing the glass substrate in a chemical strengthening solution heated to 300–400°C for about 3–4 hours. The chemical strengthening solution is also not particularly limited; for example, a mixture of potassium nitrate (60 wt%) and sodium sulfate (40 wt%) can be used. Furthermore, it is preferable to clean the glass substrate before chemical strengthening and preheat it to about 200–300°C. Additionally, it is preferable to clean the glass substrate after chemical strengthening. For example, after cleaning with an acid such as sulfuric acid, it can be further cleaned with pure water.

[0091] Polishing process

[0092] Generally, regardless of the substrate material, disk substrates require planarization polishing before the magnetic material is attached. This polishing process is preferably performed in multiple stages after adjusting the diameter of the polishing abrasive grains. Generally, a dual-sided simultaneous polishing machine is preferred for both rough and fine polishing; however, the disk substrate of this invention can also be polished using a commercially available intermittent dual-sided simultaneous polishing machine. Furthermore, it is preferable to first perform a dummy polishing management polishing pad on the surface before rough polishing.

[0093] (Double-sided polishing machine)

[0094] A double-sided simultaneous polishing machine typically comprises a cast iron upper and lower platform, a carrier holding multiple substrates between the upper and lower platforms, and polishing pads mounted on the substrate contact surfaces of the upper and lower platforms. During polishing, multiple substrates are typically held between the upper and lower platforms by the carrier, and the upper and lower platforms clamp each substrate with a fixed processing pressure. This causes each substrate to be clamped together from above by the polishing pads. Next, polishing fluid is supplied between the polishing pads and each substrate at a predetermined rate, while the upper and lower platforms rotate in opposite directions. At this time, the carrier also rotates via a sun gear, thus causing the substrates to undergo planetary motion. As a result, the substrates slide on the surface of the polishing pads, and both surfaces are polished simultaneously.

[0095] There are no particular restrictions on the type and structural details of the double-sided polishing machine; any commercially available device can be used. However, the thickness of the carrier holding the substrate in the double-sided polishing machine is preferably only 0.05 to 0.15 mm smaller than the thickness of the substrate, and particularly only 0.07 to 0.12 mm smaller. With such a carrier, it is possible to more reliably manufacture disks where the maximum Sa value in the outer peripheral region is below 0.50 nm, and particularly the average Sa value is below 0.4 nm. Areas with large Sa values ​​mainly occur in the coarse polishing process; therefore, especially in the coarse polishing process, the thickness of the carrier in the polishing machine is preferably only 0.05 to 0.15 mm smaller than the thickness of the substrate.

[0096] (Rough polishing)

[0097] There are no particular limitations on the method of rough polishing, and it can be performed under any conditions corresponding to the material of the substrate. For example, rough polishing of aluminum alloy plates can be performed using a polishing slurry containing alumina with a particle size of 0.1 to 1.0 μm and a polishing pad made of hard or soft polyurethane. Similarly, rough polishing of glass substrates can be performed using a polishing slurry containing cerium oxide with a particle size of 0.1 to 1.0 μm and a polishing pad made of hard polyurethane, etc. However, the conditions for rough polishing are not limited to these, and desired conditions can be selected from known polishing conditions. For example, abrasive grains of desired particle size such as silica, zirconium oxide, SiC, or diamond can be used instead of the aforementioned alumina or cerium oxide. Furthermore, "hard" refers to a material with a hardness (asker C) of 85 or higher as measured by the method specified in the Japan Rubber Industry Association standard specification (according to specification: SRIS0101), and "soft" refers to a material with a hardness of 60 to 80.

[0098] The specific rough polishing conditions are also influenced by the material of the substrate used and the processes up to rough polishing (e.g., steps S101-S109 in the manufacturing of aluminum alloy substrates, and steps S201-S205 in the manufacturing of glass substrates), making it difficult to determine uniquely. Furthermore, they are not limited to specific conditions. For example, the rough polishing conditions for aluminum alloy substrates could be set as follows: polishing time 2-5 minutes, polishing platform speed 10-35 rpm, sun gear speed 5-15 rpm, polishing slurry supply rate 1000-5000 mL / min, and processing pressure 20-250 g / cm³. 2 Preferably, it is 20–150 g / cm³ 2 More preferably 60–120 g / cm³ 2 Set the polishing amount to 2.5–3.5 μm.

[0099] There are no particular limitations on the conditions for rough polishing of glass substrates. For example, when using a hard polishing pad with a hardness of 86 to 88, it is preferable to set the polishing platform speed to 10 to 35 rpm, the sun gear speed to 5 to 15 rpm, the polishing slurry supply rate to 1000 to 5000 mL / min, and the processing pressure to 20 to 250 g / cm³. 2 Preferably, it is 20–150 g / cm³ 2 More preferably 60–120 g / cm³ 2 Set the polishing time to 2-10 minutes.

[0100] (Implicit polishing)

[0101] During the polishing process, it is preferable to perform a dummy polishing process to manage the surface of the polishing pad before the rough polishing as described above. Generally, the dummy polishing process uses a dummy substrate, and like the rough polishing process, it is preferably performed under the same conditions. There are no particular limitations on the dummy substrate used; for example, an aluminum alloy substrate can be used for dummy polishing before the rough polishing of the glass substrate. However, it is preferable to use a blank substrate of the same type as the product's blank substrate, especially a blank substrate manufactured under the same conditions as the product's blank substrate. In the dummy polishing process of the present invention, for example, it is also possible to polish until the arithmetic mean fluctuation Wa measured in the long wavelength side region with the cutoff wavelength set to 0.4 to 5.0 mm is less than 2.5 nm, thereby managing the surface of the polishing pad.

[0102] According to the present invention, the Sa value of the peripheral region is related to the arithmetic mean fluctuation Wa. By using a polishing pad managed based on Wa, it is possible to manufacture a disk substrate with a maximum Sa value of less than 0.50 nm in the peripheral region. The arithmetic mean fluctuation Wa in the dummy polishing process can be measured using conventional methods, such as using Optiflat (trade name) manufactured by Phase Shift Technology Co., Ltd., to measure the entire single side of the main surface of the dummy substrate.

[0103] By performing this dummy polishing, the surface of the polishing pad used in the rough polishing process described above can be adjusted to a suitable state. Furthermore, dummy polishing is an optional process; it can be omitted if the polishing pad surface has already been adjusted / managed. For example, dummy polishing can be performed before the rough polishing batch begins, and the rough polishing of the product blank substrate can be repeated multiple times using the adjusted polishing pad.

[0104] (Precision polishing)

[0105] There are no particular limitations on the methods for precision polishing, and various known methods can be used. For example, precision polishing of aluminum alloy substrates can be performed using a polishing slurry containing colloidal silica with a particle size of approximately 0.01 to 0.10 μm and a soft polishing pad. Similarly, precision polishing of glass substrates can be performed using a polishing slurry containing colloidal silica with a particle size of approximately 0.01 to 0.10 μm, particularly 10 to 50 nm, and a softer polishing pad made of materials such as polyurethane foam. Of course, the conditions for precision polishing are not limited to these. Abrasive grains such as cerium oxide, zirconium oxide, SiC, and diamond with desired particle sizes can also be used. Furthermore, through this treatment, the main surface of the substrate is mirror-polished to produce a substrate for disk drives. After polishing, the substrate is preferably cleaned using a neutral detergent, pure water, or IPA.

[0106] The specific conditions for precision polishing are influenced by the material of the substrate and the processes up to rough polishing, making them difficult to determine definitively. Furthermore, they are not limited to specific conditions. For example, in the precision polishing of aluminum alloy substrates, the polishing time can be set to 2–5 minutes, the polishing platform speed to 10–35 rpm, the sun gear speed to 5–15 rpm, the polishing slurry supply rate to 1000–5000 mL / min, and the processing pressure to, for example, 10–200 g / cm³. 2 Preferably 20–120 g / cm³ 2 The preferred value is 50–100 g / cm³. 2 Set the polishing amount to 1.0–1.5 μm.

[0107] There are no particular limitations on the conditions for precision polishing of glass substrates. For example, a soft polishing pad with a hardness of 75-77 is used, the preferred polishing platform speed is set to 10-35 rpm, the sun gear speed is set to 5-15 rpm, the polishing slurry supply rate is set to 1000-5000 mL / min, and the processing pressure is set to, for example, 10-200 g / cm³. 2 The preferred value is 20–120 g / cm³. 2 The preferred value is 50–100 g / cm³. 2 Set the polishing time to 2-12 minutes.

[0108] <Disk Baseboard>

[0109] Using the method described above, the disk substrate of the present invention can be manufactured. The disk substrate of the present invention exhibits reduced wavy surface defects, significantly improving the reliability of the hard disk.

[0110] <Disk>

[0111] The Sa value in the outer peripheral region can also be measured after the magnetic material is attached, as described above. Even if the maximum value, average value, standard deviation, etc. of Sa specified for the disk substrate of the above embodiment are reflected in the disk with the attached magnetic material, the problem of suppressing head collisions that this invention aims to solve can be solved. This invention also includes a disk in which, in multiple field-of-view regions located in the outer peripheral region of at least one side, the maximum value of the arithmetic mean height Sa specified in ISO 25178 is less than 0.50 nm when measured in the mid-wavelength side region using a scanning optical interferometry via a Gaussian filter with a cutoff wavelength set to 1.0 mm.

[0112] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and includes all aspects contained in the concept of the present invention and the scope of the patent claims, and various changes can be made within the scope of the present invention.

[0113] For example, even for any type of disk with a magnetic layer, a protective film layer, or a lubricating film layer (such as a magnetic layer) on the substrate, as long as the maximum value of the arithmetic mean height Sa is less than 0.50 mm, the wavy surface caused by flutter will be reduced, thus achieving the objective of this application.

[0114] Example

[0115] The present invention will be further described in detail below based on embodiments, but the present invention is not limited thereto.

[0116] [Example 1]

[0117] After dissolving A5086 alloy (aluminum alloy A) using conventional methods, DC casting was performed to produce a slab with a length of 7600 mm, a width of 1310 mm, and a thickness of 500 mm. The slab was then trimmed 10 mm from both sides, homogenized at 540°C for 6 hours, and hot-rolled at 540°C to a thickness of 3.0 mm. This hot-rolled slab was then cold-rolled to a thickness of 0.48 mm. The cold-rolled slab was then punched with holes of φ24 mm inner diameter × φ98 mm outer diameter using a punch press at 30 kg / cm². 2 The surface is planarized by pressurized annealing at 320°C for 3 hours. Further, the inner and outer circumferences are machined to form an inner diameter of φ25mm × an outer diameter of φ97mm. Simultaneously, the inner and outer circumferential end faces are chamfered.

[0118] The substrate was surface-ground using a 4000 series SiC grinding stone to achieve a thickness of 0.46 mm. At this point, the carrier thickness was 0.40 mm. The substrate was then subjected to degreasing, acid etching, and finally zincate treatment.

[0119] Degreasing treatment is performed, for example, using AD-68F degreasing solution manufactured by Uemura Industries, Ltd., at a concentration of 500 mL / L, a temperature of 45°C, and a treatment time of 3 minutes. Acid etching treatment is performed, for example, using AD-107F etching solution manufactured by Uemura Industries, Ltd., at a concentration of 50 mL / L, a temperature of 60°C, and a treatment time of 2 minutes. Zincate treatment is performed by two zincate treatments with an intermediate nitric acid stripping treatment. Specifically, the sequence is: first zincate treatment, pure water rinsing, nitric acid stripping treatment, pure water rinsing, and second zincate treatment. The first zincate treatment is performed, for example, using AD-301F-3X zincate treatment solution manufactured by Uemura Industries, Ltd., at a concentration of 200 mL / L, a temperature of 20°C, and a treatment time of 1 minute. The nitric acid stripping treatment is performed at a nitric acid concentration of 30% by volume, a temperature of 25°C, and a treatment time of 1 minute. The second zincate treatment is performed under the same conditions as the first zincate treatment.

[0120] Next, a chemical Ni-P plating treatment was performed. The chemical Ni-P plating treatment was carried out using Nimden (registered trademark) HDX chemical plating solution manufactured by Uemura Kogyo Co., Ltd., under the conditions of Ni concentration: 6 g / L, temperature: 88°C, and treatment time: 130 minutes, forming a chemical Ni-P film with a thickness of 13 μm on both sides.

[0121] Both sides (front and back) of the substrate after electroless Ni-P plating were subjected to rough polishing. The rough polishing was performed using a hard polyurethane polishing pad with a hardness of 87 and alumina abrasive grains with a diameter of 0.4 μm, via double-sided polishing. The substrate thickness for the rough polishing process was 0.40 mm. Furthermore, in the rough polishing process, the polishing platform speed was set to 30 rpm, the sun gear speed to 10 rpm, the polishing slurry supply rate to 3500 cc / min, and the processing pressure to 100 g / cm³. 2 .

[0122] Furthermore, prior to the aforementioned coarse polishing process, a dummy polishing was performed. The dummy polishing used another substrate, prepared using the same electroless Ni-P plating method as described above, as the dummy substrate. Multiple dummy polishing operations were performed under the same conditions as the coarse polishing. As a result, on the sixth pass, the Optiflat Wa (arithmetic mean variability measured in the long-wavelength side region with a cutoff wavelength of 0.4–5.0 mm: long-wavelength variability) of the dummy substrate was less than 2.5 nm (2.19 nm). Therefore, the dummy polishing was terminated at this point. Furthermore, the arithmetic mean variability Wa of the dummy substrate was measured on the entire single side of the coarsely polished dummy substrate using Optiflat (trade name) manufactured by Phase Shift Technology.

[0123] After cleaning the roughly polished substrate with pure water, precision polishing is performed to produce a disk substrate with a thickness of 0.48 mm. Precision polishing uses a soft polyurethane polishing pad with a hardness of 76 and colloidal silica abrasive grains with a particle size of 0.08 μm. The polishing time is set to 5 minutes, and the processing pressure is set to 50–100 g / cm². 2 In addition, it is carried out under the same conditions as rough polishing.

[0124] [Comparative Example 1]

[0125] In the rough grinding, a double-sided polishing machine with a carrier thickness of 0.3 mm is used. Otherwise, the same operation as in Example 1 is performed to produce a substrate for a disk.

[0126] [Example 2]

[0127] A glass material composed of SiO2: 65% by mass, Al2O3: 18% by mass, Li2O: 4% by mass, Na2O: 1% by mass, K2O: 0.2% by mass, CaO: 4% by mass, and ZrO2: 0.8% by mass is heated / melted at 1600–1700°C to prepare the glass material (step S201). Next, the prepared glass material is drawn into an aluminosilicate glass plate of 100 mm in diameter and 10 m in length using a redrawing method (step S202). Then, glass plates with a thickness close to 0.6 mm are selected for core forming and end-face polishing of the inner and outer circumferences (cutting of the inner and outer diameters of the glass disk, dimensional adjustment, chamfering, and grinding of the chamfered area) to form a ring-shaped glass substrate with an outer diameter of 97 mm and an inner diameter of 25 mm for the circular hole (steps S203–S204).

[0128] Next, the formed glass substrate is placed on a double-sided polishing machine for rough polishing and precision polishing to produce a disk substrate with a thickness of 0.48 mm. The substrate thickness in the rough polishing process is 0.40 mm. Furthermore, since the blank substrate is produced using the heavy-drawing method in this embodiment, the thickness deviation is negligible; therefore, the S205 polishing process is omitted. Additionally, since the polishing pad is also properly maintained, sham polishing is not performed. The rough polishing process uses a hard polyurethane polishing pad with a hardness of 87 and a polishing slurry in which cerium oxide polishing abrasive grains with an average particle size of 0.19 μm are added to pure water to form free abrasive grains. The polishing platform rotation speed is set to 25 rpm, the polishing slurry supply rate is set to 1500 cc / min, and the processing pressure is set to 120 g / cm³. 2 The same procedure as in Example 1 was followed.

[0129] Precision polishing uses a soft polyurethane polishing pad with a hardness of 76 and a polishing slurry made of colloidal silica with an average particle size of 0.08 μm and pure water to form free abrasive particles. The polishing time is set to 8.5 minutes, and the processing pressure is set to 50–120 g / cm. 2 The procedure was performed in the same manner as in Example 1. The thickness of the obtained substrate was 0.48 mm, both as measured and actual.

[0130] [Comparative Example 2]

[0131] The rough polished carrier was set to 0.3 mm, and the same procedures as in Example 2 were performed to fabricate the disk substrate. The measurement results of Sa in the outer peripheral region are shown in Table 1.

[0132] The Sa region of the outer peripheral area was measured for each substrate used in the fabrication of the disk. The measurement method is described below.

[0133] (Sa in the peripheral region)

[0134] The Sa region of the outer periphery was measured using a device with a 2.5x objective lens mounted on a VS1800 manufactured by Hitachi High Technology Scientific Co., Ltd. For example... Figure 1 As shown, in eight 4.75 mm square fields of view that are evenly located in the outer peripheral region and connected to the inner side of the virtual outer circle 5 which is only 1 mm away from the center side of the outer peripheral edge 3 of the disk, the arithmetic mean height Sa of the mid-wavelength side region with a cutoff wavelength of 1.0 mm (Gaussian filter) is measured according to ISO25178, and the maximum value and average value are calculated.

[0135] Based on the measurement results, each disk substrate was evaluated according to the following criteria. The results are shown in Table 1.

[0136] “〇”: The maximum value of Sa in the outer peripheral region is below 0.50 nm.

[0137] "×": Cases where the maximum value of Sa in the outer peripheral region exceeds 0.50 nm.

[0138] Furthermore, disk substrates marked with "0" in the above standard are deemed to have no problems in the hard disk drive manufacturing process tests. On the other hand, disk substrates marked with "×" are deemed to have problems in the same tests. Therefore, in Table 1 below, these markings of "0" and "×" describe indicators of hard disk (HD) performance.

[0139] [Table 1]

[0140]

[0141] *Unit: nm #Substrate material (aluminum: aluminum alloy)

[0142] According to the present invention, the disk substrates of Examples 1 and 2, in which the maximum value of the arithmetic mean height Sa over the eight viewing areas of the outer peripheral region is less than 0.50 nm, did not cause problems in the hard disk drive manufacturing process. On the other hand, the disk substrates of Comparative Examples 1 and 2, in which the maximum value exceeds 0.50 nm, had problems in the hard disk drive manufacturing process. According to the present invention, a disk substrate is provided that, although thinner, suppresses undulations (wavy surface defects) in the outer peripheral region of the disk, thus minimizing problems in hard disk drives.

[0143] Figure Labels

[0144] 1: Disk baseboard

[0145] 2: Peripheral region

[0146] 3: Outer perimeter

[0147] 4: Virtual Inner Circle

[0148] 5: Virtual outer circle

[0149] 6: Field of view area

Claims

1. A disk substrate, wherein, using scanning optical interferometry, in eight field-view regions located on the outer peripheral side of at least one side, the maximum value of the arithmetic mean height Sa as specified in ISO 25178 is less than 0.50 nm when measured in the mid-wavelength side region via a Gaussian filter with a cutoff wavelength set to 1.0 mm, and... The standard deviation of the aforementioned arithmetic mean height Sa is below 0.10 nm. The aforementioned eight field-of-view regions are arranged at 45° intervals, in a manner that connects to the inner side of a concentric circle 0.1 to 1 mm from the center side of the outer peripheral edge of the aforementioned substrate.

2. The substrate for a disk drive according to claim 1, wherein, The average value of the aforementioned arithmetic mean height Sa is below 0.40 nm.

3. The substrate for a disk drive according to claim 1 or 2, wherein, The thickness dimension is less than 0.50 mm.

4. The substrate for a disk drive according to claim 1 or 2, wherein, The outer diameter is 95 mm or more.

5. A disk, wherein, using scanning optical interferometry, in eight field-of-view regions located on the outer peripheral side of at least one side, the maximum value of the arithmetic mean height Sa specified in ISO 25178 is less than 0.50 nm when measured in the mid-wavelength side region via a Gaussian filter with a cutoff wavelength set to 1.0 mm, and... The standard deviation of the aforementioned arithmetic mean height Sa is below 0.10 nm. The aforementioned eight field-of-view regions are arranged at 45° intervals, in a manner that connects to the inner side of a concentric circle 0.1 to 1 mm from the center side of the outer peripheral edge of the aforementioned substrate.

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