TWI779081B - Magnetic disk substrate and method for producing the same - Google Patents

Abstract

Provided is a magnetic disk substrate that can provide a smoother, defect-free surface as compared to those of the conventional magnetic disk substrates. Specifically, a magnetic disk substrate 10 having a substrate 11 and an electroless NiP plating film 12 formed on the main surface thereof is provided. The substrate 11 has, in each of evaluation sections obtained by dividing the outer peripheral region 10c located between the inner peripheral region 10i and the outermost peripheral region 10p of the main surface at intervals of a predetermined angle in the circumferential direction Dc of the entire circumference of the substrate 11, a root-mean-square roughness Rq of less than or equal to 1.5 Å for a surface shape in the circumferential direction Dc having a space period in the wavelength range of 500 to 1000 mm.

Description

Substrate for magnetic disc and manufacturing method thereof

The present invention relates to a substrate for a magnetic disc and a manufacturing method thereof.

Conventionally, substrates for magnetic disks used in, for example, hard disk drives (HDDs) and their manufacturing methods are well known (refer to the following patent documents 1 to 4).

Patent Document 1 discloses a substrate for a magnetic recording medium in which the surface roughness on the main surface is expressed as 1 Å or less. This substrate has the following general features. Spectrum analysis is carried out on the above-mentioned surface roughness, and it is obtained that the spatial period (L) is the horizontal axis [μm], and the power spectral density (PSD) is the vertical axis [k·Å ² ·μm] (k is a constant) Curve S on the log-log graph. In this curve S, the component in the vertical axis direction of the line segment Z connecting point A with a space period (L) of 10 μm and point B with a space period (L) of 1000 μm is defined as H. The displacement in which the component in the vertical axis direction of the curve S with respect to the line segment Z is the maximum is defined as ΔH. At this time, the value (P) represented by ΔH/H×100 [%] is 15% or less. As a result, a substrate for a magnetic recording medium having excellent surface smoothness can be provided (see the same document, paragraph 0013, etc.).

Patent Document 2 discloses a glass substrate for information recording media in which the arithmetic mean undulation Wa on the surface is less than 0.6 nm, and the root mean square height Rq of the micro undulations in the radial direction is measured at a wavelength of 80 μm to 120 μm. Less than 0.01nm. Thereby, the glass substrate for information recording media which can obtain a low slip collapse value (GA value) can be provided (see the same document, paragraph 0016, etc.).

Patent Document 3 discloses a glass substrate for a magnetic disk having the following characteristics. On the main surface of the glass substrate that is closer to the central portion than the outer peripheral end, two regions of the outer peripheral end and the central portion of the recording/reproducing area are selected. In each of the selected regions, among the surface shapes in each region, the surface shape whose shape wavelength is in the range of 60 to 500 μm is extracted, and the root mean square roughness Rq of the surface shape is determined as the fine waviness Rq. In this case, the difference in the standard deviation of the minute waviness Rq between the two regions is 0.04 nm or less. Furthermore, the ratio of the standard deviation of the minute waviness Rq at the central portion of the recording/reading region to the standard deviation of the minute waviness Rq at the outer peripheral end portion is 1.1 or less. In addition, the average value of the fine waviness Rq on the entire surface of the main surface is 0.4 nm or less. In addition, the Duboff of the outer peripheral end portion of the glass substrate is 30 nm or less. Through this, it is possible to provide a glass substrate for a magnetic disk, which is to achieve a desired slip height (landing height) by determining the micro-differences in the substrate surface in a specific relationship and a specific range (see the same document, Paragraph 0049).

Patent Document 4 discloses a method of manufacturing a disk-shaped glass substrate for a magnetic recording medium having a hole in the center. The method of manufacturing a glass substrate for a magnetic recording medium includes a step of shaping a glass substrate having a plate shape, a step of polishing a main plane of the glass substrate, and a step of cleaning the glass substrate. The above-mentioned polishing step includes: a finishing polishing step of simultaneously polishing both main planes of the glass substrate using a polishing liquid containing abrasive grains with an average particle diameter of 100 nm or less. For the glass substrates polished in the aforementioned finish polishing step, the variation in plate thickness between glass substrates polished in the same batch is 1.5 μm or less. Thereby, the glass substrate for magnetic recording media excellent in the smoothness of a principal plane and an end shape can be manufactured with high productivity (refer to the same document, paragraph 0012, etc.). [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 2013-114730 [Patent Document 2] International Publication No. 2011/033948 Patent Publication [Patent Document 3] Japanese Patent Application Publication No. 2013-225372 [Patent Document 4] Japanese Patent Application Publication No. Patent Publication No. 2011-210286

[Problem to be solved by the invention]

In order to increase the memory capacity per HDD, the number of magnetic disks mounted in one housing is increased, and the magnetic disks are required to be thinner. Moreover, the magnetic disc used in HDD is required to increase the memory capacity of each disc. In order to respond to this request, it is necessary to expand the recording area of the magnetic disk, or to reduce the distance between the magnetic disk and the magnetic head for recording and reading information, that is, the flying height. However, if the thickness of the substrate is reduced, the variation in the circumferential waviness in the radially outer peripheral region of the substrate increases, making it difficult to expand the recording area or reduce the floating height.

The present invention provides a substrate for a magnetic disk and a method of manufacturing the same, which can suppress the deviation of the fluctuation in the circumferential direction in the outer peripheral region of the substrate even when the thickness of the substrate has been reduced, and achieve a thin magnetic disk and memory capacity enhancement. [Means to solve the problem]

The magnetic disk substrate of the present invention has an electroless NiP plating coating film on the main surface of the substrate; it is characterized in that: the aforementioned substrate is tied between the inner peripheral area and the outermost peripheral area of the aforementioned main surface. In each of the evaluation intervals divided by the outer peripheral region around the substrate in the circumferential direction at specific angular intervals, the spatial period of the surface shape in the circumferential direction is a wavelength of 500 [μm] to 1000 [μm] The root mean square roughness Rq in the tape is 1.5 [Å] or less.

In a substrate for a magnetic disk, the influence of smoothness or undulation in the circumferential direction of the substrate tends to be greater in the peripheral area near the outer edge than in the inner peripheral area near the center of the substrate. Moreover, the surface shape in the circumferential direction of the main surface of the substrate for a magnetic disk is the root-mean-square roughness Rq in a wavelength band of a specific spatial period, which may be information that may be given to the magnetic head of the magnetic disk. There is a performance impact when writing or when reading.

Here, the magnetic disk substrate of the present invention focuses on the outer peripheral region where the influence of the smoothness and waviness in the peripheral direction of the substrate is large, and specifies the surface shape in the peripheral direction of the outer peripheral region. Furthermore, the regulation of the surface shape in the circumferential direction of the outer peripheral area is not to specify the average value of the roughness covering the entire circle of the substrate, but to define the outer peripheral area around the substrate in the circumferential direction at a specific angular interval. The root mean square roughness Rq in each evaluation interval divided by the whole circle.

In addition, the regulation of the root mean square roughness Rq is limited to the surface shape in the circumferential direction of the evaluation area, and the performance of writing or reading information due to the head of the magnetic disk is affected. Specific wavelength bands of possibility. That is, the root-mean-square roughness Rq of the surface shape of the surface shape in the circumferential direction of each evaluation interval is specified at 1.5[Å ]the following.

As a result, in the substrate for a magnetic disk, in the peripheral region where the influence of the smoothness and waviness in the circumferential direction of the substrate tends to be greater, variation in the waviness in the circumferential direction can be suppressed. Here, the waviness refers to, for example, the surface shape of a wavelength band with a spatial period of 500 [μm] to 1000 [μm], and the variation of the waviness means, for example, the amplitude of the waviness locally becomes larger or smaller. Furthermore, as mentioned above, in the magnetic disc substrate, the surface shape of the wavelength band with a specific spatial period that may affect the performance when writing or reading information by the magnetic head of the magnetic disc is prescribed, Thereby, the thinning and memory capacity of the magnetic disk can be improved.

Regarding the variations in the undulations that occur in the circumferential direction of the substrate, for example, the following reasons are considered. It is difficult for the substrate to slide relative to the polishing pad, and it is difficult for the substrate to rotate relative to the polishing pad. In this way, the substrate is polished in a polishing direction along a specific radial direction of the substrate due to the polishing pad. The circumferential undulation of the substrate becomes smaller in the circumferential direction along the specific polishing direction, or becomes larger in the circumferential direction intersecting the specific polishing direction.

Moreover, the angular range in the circumferential direction of each evaluation interval, that is, the aforementioned specific angular interval when dividing the outer peripheral region of the main surface of the substrate around the substrate in a complete circle in the circumferential direction, can be determined as, for example, 2[°] Above 8[°] and below. In this way, the number of evaluation sections can be prevented from increasing unnecessarily by determining the angular interval at which the outer peripheral area is divided to be 2[°] or more. Furthermore, by setting the angular interval to be 8[°] or less, local waviness in the circumferential direction in the outer peripheral region of the substrate can be suppressed.

In addition, the outer peripheral area of the main surface of the substrate, when the radius of the substrate is determined as R [mm], the distance in the radial direction from the center of the substrate is R-2.5 [mm] or more, and R-0.5 [mm] ] The area below the range is preferable. By determining this range as the outer peripheral area, in the area in which the influence of smoothness or waviness becomes greater in the circumferential direction of the substrate, the deviation of the waviness in the circumferential direction can be suppressed more effectively.

In addition, it is preferable that the average value of the above-mentioned root-mean-square roughness Rq of all the above-mentioned evaluation intervals is 0.9 [Å] or less. As a result, the smoothness in the outer peripheral region of the main surface of the substrate can be further improved, and it is possible to more effectively suppress the variation in the circumferential waviness in the outer peripheral region.

Furthermore, the difference between the above-mentioned average value of the above-mentioned root-mean-square roughness Rq of the above-mentioned main surface of the front and back (surfaces) of the above-mentioned substrate is preferably 0.1 [Å] or less. Through this, the quality of the substrate for the magnetic disk can be improved, and the quality of the magnetic disk can be improved.

Furthermore, it is preferable that the aforementioned substrate is an aluminum substrate. Because the aluminum substrate is cheap and has excellent processability, it can reduce the production cost of the substrate for the magnetic disk and improve the productivity of the substrate for the magnetic disk.

And, the manufacturing method of the substrate for magnetic disk of the present invention has: make the polishing pad rotate and grind the electroless NiP plated coating film of the main surface of substrate; The processing pressure of the irregular sliding of the substrate in a direction different from the direction of rotation of the polishing pad is generated relative to the polishing pad, and the electroless NiP plating coating film is polished, thereby obtaining the aforementioned substrate. In each of the evaluation intervals divided by the outer peripheral region between the inner peripheral region and the outermost peripheral region of the main surface in the circumferential direction around the aforementioned substrate at a specific angular interval, the surface shape in the peripheral direction The root mean square roughness Rq in a wavelength band having a spatial period of 500 [μm] to 1000 [μm] is 1.5 [Å] or less.

According to the manufacturing method of the magnetic disk substrate of the present invention, in the polishing process, the processing pressure is adjusted, and the substrate slides irregularly with respect to the polishing pad in a direction different from the rotation direction of the polishing pad, whereby the appearance of the substrate can be suppressed. Deviation of the circumferential undulation in the surrounding area. Through this, as mentioned above, a substrate for a magnetic disk can be manufactured, which can achieve the thinning of the magnetic disk and the improvement of the memory capacity.

More specifically, in the polishing step, the substrate may be rotated to change the polishing direction of the electroless NiP plating film by the polishing pad, and the electroless NiP plating film may be uniformly polished from multiple directions. membrane. This makes it possible to more effectively suppress variations in the circumferential waviness in the outer peripheral region of the substrate.

The aforementioned grinding process includes: a primary grinding process of performing rough surface finishing on the aforementioned main surface, and a secondary grinding process of performing final finishing on the aforementioned main surface; the aforementioned secondary grinding process includes: A plurality of processing steps; in the aforementioned processing step where the aforementioned processing pressure is the highest, the aforementioned processing pressure is preferably above 7 [kPa] and below 9 [kPa]. In this way, in the secondary polishing process for final finishing, the aforementioned processing pressure is determined to be more than 7 [kPa] and less than 9 [kPa], so that the productivity will not be excessively reduced, and the substrate can be used in the same position as the polishing pad. The polishing pad slides irregularly in different directions of rotation, and the electroless NiP plating film can be polished uniformly from multiple directions. [Invention effect]

According to the present invention, it is possible to provide a substrate for a magnetic disk and a method of manufacturing the same, which can suppress the deviation of the circumferential waviness in the outer peripheral region of the substrate even when the thickness of the substrate has been reduced, and achieve a magnetic disk. The thinning of chips and the improvement of memory capacity.

Hereinafter, an embodiment of the substrate for a magnetic disk and its manufacturing method according to the present invention will be described with reference to the drawings.

[Magnetic Disk Substrate] FIG. 1 is a perspective view showing an example of a hard disk device (HDD) using a magnetic disk substrate 10 according to an embodiment of the present invention. HDD has, for example: a frame body 101; a plurality of magnetic disks 102, which are constituted by the magnetic disk substrate 10 of this embodiment, and are housed inside the frame body 101; and a disk drive unit 103, which is The magnetic disk 102 is rotated.

Moreover, the HDD has, for example: a magnetic head 104 for recording information on the magnetic disk 102 and reading information from the magnetic disk 102; . Furthermore, the HDD includes, for example, a signal processing unit 106 that processes signals related to information recorded on the magnetic disk 102 and signals related to information read from the magnetic disk 102 .

FIG. 2 is a plan view of the magnetic disk substrate 10 constituting the magnetic disk 102 of the HDD shown in FIG. 1 . The magnetic disk substrate 10 of the present embodiment has a substrate 11 and an electroless NiP plating film 12 formed on the main surface of the substrate 11 . The substrate 11 is, for example, a disk-shaped base material having a circular opening 11 a in the center. The substrate 11 is, for example, an aluminum substrate made of aluminum or an aluminum alloy. That is, the magnetic disk substrate 10 of the present embodiment is, for example, an aluminum substrate for a magnetic disk.

The substrate 10 for a magnetic disk, from the viewpoint of improving the memory capacity of the magnetic disk 102, for example, has an amorphous electroless NiP plating film on the main surface of the front and back (surfaces) of the substrate 11. 12 is better. On the electroless NiP plating coating film 12 on the main surface of the substrate 10 for a magnetic disk, for example, a plurality of magnetic layers and nonmagnetic layers, protective layers, and lubricating films are formed, thereby manufacturing a magnetic disk. Sheet 102.

The size of the magnetic disc substrate 10 , that is, the diameter, is, for example, 2.5 [in], 3.5 [in], 95 [mm], or 97 [mm]. That is, the diameter of the magnetic disc substrate 10 is not less than 63.5 [mm] (2.5 [in]) and not more than 97 [mm], more preferably not less than 95 [mm] and not more than 97 [mm]. Furthermore, the thickness of the substrate 10 for a magnetic disk is not less than 0.6 [mm] and not more than 1.27 [mm], preferably not less than 0.6 [mm] and not more than 0.8 [mm], more preferably not less than 0.6 [mm] and not more than 0.8 [mm]. ]the following. The diameter of the central opening 11 a of the magnetic disk substrate 10 , that is, the inner diameter of the magnetic disk substrate 10 is, for example, not less than 20 [mm] and not more than 25 [mm]. The size of the magnetic disk substrate 10 is not limited to the above-mentioned size. Furthermore, even if the substrate 10 for a magnetic disk is thinner than the above-mentioned thickness, the same effect as that of the substrate 10 for a magnetic disk with the above-mentioned thickness can be obtained, and this is included in the present invention.

Thus, the magnetic disk substrate 10 of this embodiment has the electroless NiP plating film 12 on the main surface of the substrate 11, and is mainly characterized by the following configuration. The substrate 11 is in the respective evaluation intervals divided by dividing the outer peripheral region 10c between the inner peripheral region 10i and the outermost peripheral region 10p of the main surface around the substrate 11 in the circumferential direction Dc at a specific angular interval. Among them, the root mean square roughness Rq in the wavelength band where the spatial period of the surface shape in the circumferential direction Dc is 500 [μm] to 1000 [μm] is 1.5 [Å] or less.

Here, the outer peripheral region 10c of the main surface of the substrate 11 is, for example, when the radius of the substrate 11 is determined as R [mm], the distance in the radial direction from the center C of the substrate 11 is greater than R-a [mm], R-b [mm] range or less. In addition, in the example shown in FIG. 2, a is, for example, 2.5 [mm], and b is, for example, 0.5 [mm]. The outermost peripheral region 10p of the principal surface of the substrate 11 is a region radially outside of the outer peripheral region 10c, and the inner peripheral region 10i is a region radially inward of the outer peripheral region 10c. The root mean square roughness Rq in a specific wavelength band of the surface shape in the circumferential direction Dc in each evaluation interval of the aforementioned outer peripheral region 10c can be obtained, for example, by the following procedure.

FIG. 3 is a graph showing an example of the surface shape of the main surface of the magnetic disk substrate 10 shown in FIG. 2 . In FIG. 3 , the horizontal axis represents the angle θ in the circumferential direction Dc of the magnetic disk substrate 10 , and the vertical axis represents the height h(θ) of the unevenness of the surface shape. First, the surface shape of the substrate 11 in the circumferential direction Dc is measured around the entire circumference of the substrate 11 in the outer peripheral region 10c of the main surface of the substrate 11 . The measurement of the surface shape in the circumferential direction Dc of the principal surface of the substrate 11 can be performed, for example, using an inspection device "Candela" manufactured by KLA-Tencor.

Next, the surface shape in the circumferential direction Dc of the outer peripheral region 10c measured around the entire circumference of the substrate 11 is divided at predetermined angular intervals. In this case, the specific angular interval between the surface shapes of the divided outer peripheral regions 10c may be not less than 2[°] and not more than 8[°]. The divided sections of the surface shape show the surface shape in the circumferential direction Dc of each evaluation section 10z. Next, for example, by "Candela", spectrum analysis of the surface shape in each circumferential direction Dc of the evaluation section 10z is performed.

FIG. 4 is a graph showing the relationship between wavelength and power spectral density (PSD) in each evaluation interval 10z shown in FIG. 3 . The relationship between wavelength [μm] and PSD [Å ² μm] of the surface shape in the circumferential direction Dc of each evaluation section 10z was obtained by performing spectral analysis of the surface shape in the circumferential direction Dc of each evaluation section 10z. From the results of the spectrum analysis, the PSD of the wavelength band whose spatial period is 500 [μm] to 1000 [μm] is extracted, and the root mean square roughness Rq of each evaluation interval 10z is obtained.

FIG. 5 is a graph showing the root mean square roughness Rq in a wavelength band in which the spatial period of the surface shape in the circumferential direction Dc is 500 [μm] to 1000 [μm] in each evaluation interval 10z. The magnetic disk substrate 10 of the present embodiment is in the wavelength band in which the spatial period of the surface shape in the circumferential direction Dc is 500 [μm] to 1000 [μm] in each of the evaluation intervals 10z obtained as described above. The root mean square roughness Rq is 1.5[Å] or less.

In the magnetic disc substrate 10, the influence of smoothness or undulation in the circumferential direction Dc of the substrate 11 tends to be as follows: compared with the inner peripheral region 10i near the center C of the substrate 11, the outer peripheral region near the outer edge 10c will be bigger. Moreover, the surface shape in the circumferential direction Dc of the main surface of the magnetic disc substrate 10 is the root mean square roughness Rq in a wavelength band of a specific spatial period, which may be imposed on the magnetic head 104 of the magnetic disc 102. The performance when writing or reading the corresponding information will be affected.

Here, in the magnetic disk substrate 10 of this embodiment, attention is paid to the difference between the inner peripheral region 10i and the outermost peripheral region 10p of the main surface of the substrate 11, which greatly affects the smoothness or waviness in the circumferential direction Dc of the substrate 11. The outer peripheral area 10c in between, and the surface shape in the circumferential direction Dc in the outer peripheral area 10c is prescribed. Furthermore, the regulation of the surface shape of the peripheral direction Dc of the outer peripheral region 10c is not to specify the average value of the roughness covering the entire circle of the substrate 11, but to specify that the outer peripheral region 10c is spaced at specific angles in the peripheral direction. Dc is the root-mean-square roughness Rq in each of the evaluation intervals 10z divided by one complete circle around the substrate 11 .

In addition, the regulation of the root mean square roughness Rq is limited to the surface shape of the evaluation zone 10z in the circumferential direction Dc, when the information is written or read by the magnetic head 104 with the magnetic disc 102 Specific wavelength bands where performance is likely to be affected. That is, the root-mean-square roughness Rq of the surface shape of the surface shape in the circumferential direction Dc of each evaluation interval 10z is specified at 1.5 [Å] below.

As a result, in the magnetic disk substrate 10 , in the peripheral region 10c which tends to have a greater influence on the smoothness or waviness in the circumferential direction Dc of the substrate 11 , variation in the waviness in the circumferential direction Dc can be suppressed. Furthermore, as mentioned above, in the substrate 10 for a magnetic disk, the wavelength band having a specific spatial period that may affect the performance of the magnetic head 104 of the magnetic disk 102 when writing or reading information is prescribed. The surface shape, thereby, can enhance the thinning and memory capacity of the magnetic disc 102 .

Moreover, as mentioned above, when the evaluation interval 10z is obtained, the specific angular interval of dividing the outer peripheral region 10c around the substrate 11 in the circumferential direction Dc is as mentioned above, for example, 2[°] to 8[° ]the following. In this way, the number of evaluation sections 10z can be prevented from increasing unnecessarily by determining the angular interval at which the outer peripheral region 10c is divided to be 2[°] or more. Furthermore, by setting the angular interval to be 8 [°] or more, local undulation in the circumferential direction Dc in the outer peripheral region 10c of the substrate 11 can be suppressed.

And, as mentioned above, when the outer peripheral region 10c of the main surface of the substrate 11 is determined as the radius of the substrate 11 as R [mm], the distance in the radial direction from the center C of the substrate 11 is determined at, for example, R-2.5 [mm] or more and R-0.5[mm] or less. By determining this range as the outer peripheral region 10c, in the region where the influence of smoothness or waviness becomes greater in the circumferential direction Dc of the substrate 11, the deviation of the waviness in the circumferential direction Dc can be more effectively suppressed.

Furthermore, in the magnetic disc substrate 10 of the present embodiment, the average value of the root mean square roughness Rq of all the evaluation intervals 10z is preferably 0.9 [Å] or less. This further improves the smoothness in the outer peripheral region 10 c of the main surface of the substrate 11 , and more effectively suppresses fluctuations in undulation in the circumferential direction Dc in the outer peripheral region 10 c.

Moreover, in the magnetic disc substrate 10 of the present embodiment, the main surface of the front and back (surfaces) of the substrate 11 is preferably the difference between the average values of the above-mentioned root mean square roughness Rq, preferably 0.1 [Å] or less. . Through this, the quality of the magnetic disk substrate 10 can be improved, and the quality of the magnetic disk 102 can be improved.

Moreover, in the magnetic disc substrate 10 of the present embodiment, when the substrate 11 is an aluminum substrate that is inexpensive and has excellent workability, the production cost of the magnetic disc substrate 10 can be reduced, and the magnetic disc substrate 10 can be improved. productivity.

As described above, according to the present embodiment, it is possible to provide the substrate 10 for a magnetic disk that can suppress fluctuations in the circumferential direction Dc in the outer peripheral region 10c of the substrate 11 even when the thickness of the substrate 11 is reduced. The deviation of the magnetic disc 102 can be reduced and the memory capacity can be improved.

[Manufacturing method of magnetic disc substrate] Next, an embodiment of the manufacturing method of the magnetic disc substrate of the present invention will be described. FIG. 6 is a flow chart showing an example of the steps of the manufacturing method S100 of the substrate for a magnetic disk according to the embodiment of the present invention.

The method for manufacturing a substrate for a magnetic disk according to this embodiment includes, for example, an end surface processing step S10, a first heat treatment step S20, a grinding step S30, a second heat treatment step S40, an electroless NiP plating step S50, and a third heat treatment step S60. , a polishing step S70, a cleaning step S80, and a surface inspection step S90. The details will be described later, but the manufacturing method S100 of a substrate for a magnetic disk according to this embodiment is characterized in the polishing step S70. Hereinafter, each process of the manufacturing method S100 of the substrate for a magnetic disk according to the present embodiment will be described in detail.

The end surface processing step S10 is, for example, a process of adjusting the shape of the end surface of the substrate 11 by cutting the unprocessed substrate 11 housed as a material with a lathe or the like. The substrate 11 is, for example, an aluminum substrate made of the above-mentioned aluminum, and is a disc-shaped base material having a circular opening 11 a in the center.

The first heat treatment step S20 is a step of annealing the substrate 11 after the end surface processing step S10 to relax residual stress on the substrate 11 . The grinding step S30 is a step of rough grinding the substrate 11 with, for example, a grinder after the first heat treatment step S20 is completed, and then performing finish grinding to adjust the thickness of the substrate 11 . The second heat treatment step S40 is a step of annealing the substrate 11 after the grinding step S30 to relax the residual stress of the substrate 11 .

The electroless NiP plating step S50 is to impregnate the substrate 11 in the plating solution after pre-treating the substrate 11 that has undergone the second heat treatment step S40, thereby utilizing the reducing power contained in the plating solution to Electrons released by the oxidation of the agent deposit the electroless NiP plating film 12 onto the substrate 11 . Through this process, the electroless NiP plating film 12 was formed on the main surface of the substrate 11, and the substrate 11 having the electroless NiP plating film 12 on the main surface was obtained. The film thickness of the electroless NiP plating film 12 is, for example, 7 [μm] or more and 15 [μm] or less. The third heat treatment step S60 is to anneal the substrate 11 on which the electroless NiP plating film 12 is formed on the main surface, so as to improve the adhesion of the electroless NiP plating film 12 and relax the residual stress of the substrate 11. The process.

FIG. 7 is a perspective view schematically showing an example of the polishing apparatus 200 used in the polishing step S70 shown in FIG. 6 . The polishing step S70 is, for example, a step of polishing the main surfaces of the front and back (surfaces) of the substrate 11 with the polishing apparatus 200 to adjust the surface roughness and waviness of the main surface having the electroless NiP plating film 12 . The polishing device 200 has, for example, an upper plate 210 and a lower plate 220 that rotate in opposite directions. Polishing pads 230 are attached to the lower surface of the upper plate 210 and the upper surface of the lower plate 220 , respectively. As the polishing pad 230 , for example, a porous polishing cloth having an opening diameter within a specific range, such as urethane, can be used.

The lower plate 220 has a sun gear 221 at the center of the upper surface, an internal gear 222 at the periphery of the upper surface, and a plurality of carriers 223 arranged between the sun gear 221 and the internal gear 222 . In the illustrated example, four carriers 223 are placed between the sun gear 221 and the internal gear 222 . The sun gear 221 and the internal gear 222 are respectively driven to rotate at specific rotation ratios.

The carrier 223 is a disc-shaped member having a substrate holding portion 223a for holding the substrate 11 to be polished. The substrate holding portion 223 a is a circular opening formed on the carrier 223 and has an inner diameter corresponding to the shape of the substrate 11 . The substrate holding portion 223 a exposes the main surfaces of the front and back (surfaces) of the substrate 11 in a state where the substrate 11 is held, to the polishing pads 230 of the upper plate 210 and the lower plate 220 . Moreover, the carrier 223 is a gear-shaped member having a plurality of teeth 223t on its outer periphery, and meshes with the sun gear 221 and the internal gear 222. The sun gear 221 and the internal gear 222 rotate at a specific rotation ratio. The planetary motion corresponding to the difference in the number of teeth.

With the polishing apparatus 200 having such a configuration, firstly, a plurality of substrates 11 are transported by a loader grip portion (not shown) in polishing the substrates 11 , and placed on the substrate holding portion 223 a of the carrier 223 . Next, the upper plate 210 and the lower plate 220 are approached to pinch the substrate 11 between the polishing pad 230 on the lower surface of the upper plate 210 and the polishing pad 230 on the upper surface of the lower plate 220 . Then, the slurry for grinding is supplied between the polishing pad 230 on the lower surface of the upper plate 210 and the polishing pad 230 on the upper surface of the lower plate 220, and the upper plate 210 and the lower plate 220 are rotated in the opposite direction while the The sun gear 221 and the inner gear 222 rotate to make the carrier 223 do planetary motion.

In this manner, in the polishing step S70 , the polishing pad 230 is rotated to polish the electroless NiP plating film 12 on the main surface of the substrate 11 . The manufacturing method S100 of the substrate for magnetic discs of the present embodiment is that in the polishing step S70, the processing pressure is such that the substrate 11 generates irregular sliding in a direction different from the rotation direction of the polishing pad 230 with respect to the polishing pad 230. , the electroless NiP plating coating film 12 is polished. In this way, in the polishing step S70 , the substrate 11 can be prevented from being polished in a specific direction by performing polishing with a processing pressure as low as that the substrate 11 slides against the polishing pad 230 .

Thereby, as described above, the substrate 10 for a magnetic disk can be manufactured in which the fluctuation of the fluctuation in the circumferential direction Dc in the outer peripheral region 10c of the substrate 11 is suppressed. More specifically, the magnetic disk substrate 10 manufactured by the manufacturing method of this embodiment has the following characteristics. The substrate 11 is in the respective evaluation intervals divided by dividing the outer peripheral region 10c between the inner peripheral region 10i and the outermost peripheral region 10p of the main surface around the substrate 11 in the circumferential direction Dc at a specific angular interval. In 10z, the root mean square roughness Rq in the wavelength band where the spatial period of the surface shape in the circumferential direction Dc is 500 [μm] to 1000 [μm] is 1.5 [Å] or less.

In the grinding process S70, for example, by using the aforementioned grinding device 200, the substrate 11 and the carrier 223 are rotated together to change the grinding direction of the electroless NiP plated coating film 12 caused by the grinding pad 230, which can be changed from multiple directions. The electroless NiP plating film 12 is uniformly polished. As a result, it is possible to more effectively suppress variation in the undulation in the circumferential direction Dc in the outer peripheral region 10 c of the substrate 11 .

FIG. 8 is a flowchart showing an example of steps included in the polishing step S70 shown in FIG. 6 . The polishing step S70 includes, for example: a primary polishing step S71 of performing rough finishing on the main surface of the substrate 11 having the electroless NiP plating film 12; and a secondary polishing step S72 of The final finishing of its main face is carried out. Furthermore, the primary grinding process S71 and the secondary grinding process S72 can be performed using the aforementioned grinding device 200 .

In primary grinding process S71, for example, can use: from 20 [nm] to about 400 [nm] SiO ₂ abrasive grains and pH from about 1.2 to 1.6 slurry, and the opening diameter is from 20 [μm] ] to a polishing pad 230 of about 60 [μm]. In the secondary grinding process S72, for example, it is possible to use: a slurry containing _SiO2 abrasive grains with a particle diameter of about 10 [nm] to 30 [nm] and a pH of about 1.2 to 1.8, and an opening diameter of 20 [μm] ] The following abrasive pad 230.

One grinding step S71 may have a plurality of processing steps with different processing pressures, for example. More specifically, the primary polishing step S71 may include, for example, five stages of processing steps from the first processing step to the fifth processing step.

In the first processing step of the primary polishing process S71, for example, in order to prevent damage to the polishing pad 230, the slurry is infiltrated into the polishing pad 230, so even among the processing steps, the processing pressure is relatively low, and the processing pressure is relatively short. time for processing. The second processing step of the primary grinding process S71 is to increase the processing pressure to the highest processing pressure in each processing step in the next third processing step, so the processing pressure is increased to a little higher than that of the first processing step. point, and other conditions are the same conditions as the first processing step for processing.

In the third processing step of the primary polishing step S71 , the substrate 11 is polished at the highest processing pressure in each processing step in order to control the difference between the processing margin of the main surface of the substrate 11 and the front and back (surfaces). In the third processing step, the processing pressure for polishing the substrate 11 is, for example, about 10 kPa to about 14 kPa. The processing time of the third processing step is, for example, about 10 to 20 times longer than the processing time of the first processing step and the second processing step. In this third processing step, for example, the rotation speed of the upper plate 210 and the rotation speed of the lower plate 220 are increased compared to the first processing step and the second processing step.

The grinding in the fourth processing step of the primary grinding step S71 is to improve the surface quality of the electroless NiP plating coating film on the main surface of the substrate 11 subjected to the high pressure processing in the third processing step, such as scratches or undulations. etc. Therefore, processing is performed at a processing pressure slightly lower than that in the third processing step. The processing time of the fourth processing step is, for example, equivalent to or approximately 1.5 times the processing time of the first processing step and the second processing step. In this fourth processing step, the rotation speed of the upper plate 210 and the rotation speed of the lower plate 220 are determined to be equal to those of the third processing step, for example.

The fifth processing step of the primary polishing step S71 is, for example, a cleaning step of supplying pure water for washing instead of the polishing slurry to wash off the abrasive adhering to the substrate 11 that has been subjected to the fourth processing step. The processing pressure of the substrate 11 in this fifth processing step is the lowest among the respective processing steps. The processing time of the fifth processing step takes, for example, about half of the processing time of the first processing step and the second processing step. In this fifth processing step, the rotation speed of the upper plate 210 and the rotation speed of the lower plate 220 are determined to be equal to, for example, the first processing step and the second processing step.

The processing conditions of each processing step in the above primary polishing step S71 are shown in Table 1 below.

In Table 1, processing time T ₁₁ -T ₁₅ , upper plate rotation speed Vu ₁₁ -Vu ₁₅ , lower plate rotation speed Vd ₁₁ -Vd ₁₅ , processing pressure P ₁₁ -P ₁₅ , The sun gear rotational speeds Vs ₁₁ to Vs ₁₅ have the following relationships respectively.

Processing time: T ₁₅ < T ₁₁ = T ₁₂ ≦ T ₁₄ < T ₁₃ Upper plate rotation speed: Vu ₁₁ = Vu ₁₂ = Vu ₁₅ < Vu ₁₃ = Vu ₁₄ Lower plate rotation speed: Vd ₁₁ = Vd ₁₂ = Vd ₁₅ < Vd ₁₃ =Vd ₁₄ Processing pressure: P ₁₅ <P ₁₁ <P ₁₂ <P ₁₄ <P ₁₃ Sun gear rotation speed: Vs ₁₁ =Vs ₁₂ =Vs ₁₃ =Vs ₁₄ =Vs ₁₅

Furthermore, the processing pressure P ₁₃ in the third processing step satisfies, for example, 10 [kPa]≦P ₁₃ ≦14 [kPa] as described above. Furthermore, the processing time can be as long as possible. After the primary polishing step S71 is completed, the secondary polishing step S72 is performed as shown in FIG. 8 .

The secondary grinding process S72 is the same as the primary grinding process S71, for example, may have a plurality of processing steps with different processing pressures. More specifically, the secondary polishing step S72 may include, for example, six processing steps from the first processing step to the sixth processing step.

The secondary grinding step S72 is a step of finalizing the main surface of the substrate 11 . The purpose of each processing step from the first processing step to the fifth processing step in the secondary polishing step S72 is the same as the purpose of each processing step in the primary polishing step S71. However, in the secondary polishing step S72, as described above, the main surface of the substrate 11 is electrolessly electrolyzed using a slurry containing finer abrasive grains and a polishing pad 230 with finer opening diameters than those in the primary polishing step S71. Polishing of the NiP plating film 12 .

Furthermore, the secondary polishing step S72 further includes a sixth processing step after the fifth processing step of washing off the abrasive adhering to the substrate 11 subjected to the fourth processing step. The 6th processing step of the secondary grinding process S72 is the same as the 5th processing step, for example, instead of the grinding slurry, pure water for cleaning is supplied, and the substrate 11 attached to the 5th processing step is attached to the substrate 11. Cleaning process for washing off abrasives.

The processing time of the first processing step of the secondary grinding step S72 can be determined, for example, from half to twice the processing time of the first processing step of the primary grinding step S71. Moreover, the processing time of the second processing step of the secondary grinding step S72 can be determined to be about twice the processing time of the first processing step of the primary grinding step S71, for example. Furthermore, the processing time of the third processing step of the secondary grinding step S72 can be determined to be, for example, equal to about 1.5 times the processing time of the third processing step of the primary grinding step S71. Moreover, the processing time of the fourth processing step of the secondary grinding step S72 can be determined from about 0.75 times to 5 times of the processing time of the second processing step of the secondary grinding step S72. Furthermore, the processing time of the fifth processing step and the sixth processing step of the secondary grinding step S72 can be determined to be equal to the processing time of the fifth processing step of the primary grinding step S71.

The rotation speed of the upper plate 210 in the first processing step of the secondary grinding step S72 can be determined to be, for example, about 0.4 times the rotation speed of the upper plate 210 in the first processing step of the primary grinding step S71. The rotation speed of the upper plate 210 in the second processing step of the secondary grinding step S72 can be determined to be about twice the rotation speed of the upper plate 210 in the first processing step of the secondary grinding step S72, for example. The rotation speed of the upper plate 210 in the third processing step of the secondary grinding step S72 can be determined to be, for example, about three times the rotation speed of the upper plate 210 in the first processing step of the secondary grinding step S72. The rotation speed of the upper plate 210 in the fourth processing step of the secondary grinding step S72 can be determined to be equal to the rotation speed of the upper flat plate 210 in the second processing step of the secondary grinding step S72, for example. The rotation speed of the upper plate 210 in the fifth and sixth processing steps of the secondary grinding step S72 can be determined to be equal to the rotation speed of the upper plate 210 in the first processing step of the secondary grinding step S72, for example.

The rotation speed of the lower plate 220 in the first processing step of the secondary grinding step S72 can be determined to be, for example, about 0.6 times the rotation speed of the lower plate 220 in the first processing step of the primary grinding step S71. The rotation speed of the lower plate 220 in the second processing step of the secondary grinding step S72 can be determined to be about twice the rotation speed of the lower plate 220 in the first processing step of the secondary grinding step S72, for example. The rotation speed of the lower plate 220 in the third processing step of the secondary grinding step S72 can be determined to be, for example, about 1.25 times the rotation speed of the lower plate 220 in the third processing step of the primary grinding step S71. The rotation speed of the lower plate 220 in the fourth processing step of the secondary grinding step S72 can be determined to be equal to the rotation speed of the lower plate 220 in the second processing step of the secondary grinding step S72, for example. The rotation speed of the lower plate 220 in the fifth and sixth processing steps of the secondary grinding step S72 can be determined to be equal to the rotation speed of the lower plate 220 in the first processing step of the secondary grinding step S72, for example.

The processing pressure of the first processing step and the second processing step of the secondary grinding step S72 can be determined to be equal to the processing pressure of the first processing step and the second processing step of the primary grinding step S71, for example. The processing pressure of the third processing step of the secondary grinding step S72 can be determined to be lower than the processing pressure of the third processing step of the primary grinding step S71, for example. More specifically, the processing pressure in the third processing step of the secondary grinding step S72 can be determined to be, for example, 7 [kPa] or more and 9 [kPa] or less. The processing pressure of the fourth processing step of the secondary grinding step S72 can be determined to be slightly lower than the processing pressure of the third processing step of the secondary grinding step S72, for example. The processing pressure of the fifth processing step of the secondary grinding step S72 can be determined to be, for example, about twice the processing pressure of the fifth processing step of the primary grinding step S71. The processing pressure of the sixth processing step of the secondary grinding step S72 can be determined to be equal to the processing pressure of the fifth processing step of the primary grinding step S71, for example.

The rotational speed of the sun gear 221 from the first processing step to the fourth processing step of the secondary grinding step S72 can be determined, for example, as the rotation speed of the sun gear 221 from the first processing step to the fifth processing step of the primary grinding step S71. about 1.5 times the rotation speed. The rotation speed of the sun gear 221 in the fifth processing step and the sixth processing step of the secondary grinding step S72 can be determined as the rotation speed of the sun gear 221 from the first processing step to the fourth processing step of the secondary grinding step S72. Less than 0.3 times the speed.

The processing conditions of each processing step in the above secondary polishing step S72 are shown in Table 2 below.

In Table 2, the processing time T ₂₁ to T ₂₆ , the rotation speed of the upper plate Vu ₂₁ to Vu ₂₆ , the rotation speed of the lower plate Vd ₂₁ to Vd ₂₆ , and the processing pressure P ₂₁ to P ₂₆ in each processing step of the secondary grinding process S72 , and the rotation speeds Vs ₂₁ to Vs ₂₆ of the sun gear 221 respectively hold the following relationships.

Processing time: T ₂₅ =T ₂₆ ≦T ₂₁ ≦T ₂₂ ≦T ₂₄ <T ₂₃ Upper plate rotation speed: Vu ₂₁ =Vu ₂₅ =Vu ₂₆ <Vu ₂₂ =Vu ₂₄ <Vu ₂₃ Lower plate rotation speed: Vd ₂₁ = Vd ₂₅ =Vd ₂₆ <Vd ₂₂ =Vd ₂₄ <Vd ₂₃ Processing pressure: P ₂₆ <P ₂₁ =P ₂₅ <P ₂₂ <P ₂₄ <P ₂₃ Sun gear rotation speed: Vs ₂₅ =Vs ₂₆ <Vs ₂₁ =Vs ₂₂ =Vs ₂₃ =Vs ₂₄

FIG. 9 is a graph showing one example of the relationship between machining times T ₂₁ to T ₂₆ and machining pressures P ₂₁ to P ₂₆ in each machining step of the secondary polishing step S72 . Furthermore, the processing pressure P ₂₃ in the third processing step of the secondary grinding step S72 satisfies, for example, 7 [kPa]≦P ₂₃ ≦9 [kPa] as described above. The processing pressure P ₂₃ is lower than P ₁₃ which is the highest processing pressure in the primary grinding step S71. In addition, conventionally, the highest processing pressure in the final finish of the polishing step is equal to the highest processing pressure in the primary polishing step S71. That is, in the manufacturing method S100 of the magnetic disc substrate of this embodiment, the highest processing pressure in the secondary polishing step S72 is determined to be higher than the highest processing pressure in the primary polishing step S71 or the conventional polishing pressure. The processing pressure of the final finish of the process is even lower.

As a result, in the third processing step of the secondary polishing step S72 , the substrate 11 irregularly slides relative to the polishing pad 230 in a direction different from the rotation direction of the polishing pad 230 . In this way, in the polishing step S70 , the substrate 11 can be prevented from being polished in a specific direction by performing polishing with such a low processing pressure that the substrate 11 slides against the polishing pad 230 . Therefore, as described above, it is possible to manufacture the substrate 10 for a magnetic disk in which variation in fluctuation in the circumferential direction Dc in the outer peripheral region 10c of the substrate 11 is suppressed. Furthermore, the processing time T ₂₁ to T ₂₆ in each processing step can be as long as possible. After the secondary polishing step S72 is completed, as shown in FIG. 6 , a cleaning step S80 is performed.

In the cleaning step S80, after the polishing step S70 is completed, for example, the substrate 11 is taken out from the polishing device 200, dipped in a cleaning solution, and after precision cleaning by ultrasonic waves, it is cleaned by pure water. A process of drying the substrate 11 . The surface inspection step S90 is a step of inspecting the substrate 11 after the cleaning step S80 by an inspection machine for defects such as protrusions and pitting. According to the manufacturing method S100 of the magnetic disk substrate of this embodiment, the magnetic disk substrate 10 can be manufactured through the above steps.

As described above, in the manufacturing method S100 of the substrate for a magnetic disk of the present embodiment, in the polishing step S70, the substrate 11 generates irregular sliding in a direction different from the rotation direction of the polishing pad 230 with respect to the polishing pad 230. The electroless NiP plating coating film 12 is polished under the processing pressure. Through this, it is possible to provide a manufacturing method S100 of a substrate for a magnetic disk, which can suppress the deviation of the undulation in the circumferential direction Dc in the outer peripheral region 10c of the substrate 11 even when the thickness of the substrate 11 has been reduced, The thinning of the magnetic disc 102 and the improvement of memory capacity are achieved.

As mentioned above, the embodiment of the present invention has been described in detail using the drawings. However, the specific configuration is not limited to this embodiment, and any design changes within the range not departing from the gist of the present invention are included in the present invention. included.

[Examples] The magnetic disk substrates of Examples 1 to 5 were manufactured according to the method of manufacturing the magnetic disk substrates described in the foregoing embodiments. Also, in Examples 1 to 3, an aluminum substrate with a thickness of 0.610 [mm] and an outer diameter of about 97 [mm] was used, and in Examples 4 and 5, an aluminum substrate with a thickness of 0.610 [mm] and an outer diameter of about 97 [mm] was used. An aluminum substrate with a diameter of about 95 [mm].

And when the manufacture of the substrate for magnetic disc of each embodiment, in the polishing process, with the low working pressure that produces the irregular sliding of the direction different from the direction of rotation of the polishing pad with respect to the polishing pad, lapping Electroless NiP plating coating film. More specifically, a grinding process including a primary grinding process and a secondary grinding process is implemented, and the processing pressure of the third processing step of the secondary grinding process is determined to be 7 [kPa] to 9 [kPa] to manufacture a magnetic disk Chip substrate.

Afterwards, it was measured that the front and back (surfaces) of the manufactured magnetic disk substrates from Examples 1 to 5 had electroless NiP plating coating films by using an inspection device "Candela" manufactured by KLA-Tencor Corporation. The surface shape in the circumferential direction of the outer peripheral area of the main surface. Here, in the magnetic disk substrates of Examples 1 to 3, the outer peripheral region is determined to be within a range of 94.5 [mm] to 96.5 [mm] from the center of the substrate. Furthermore, in the magnetic disk substrates of Examples 4 and 5, the outer peripheral region is determined to be within a range of 92.5 [mm] to 94.5 [mm] from the center of the substrate.

Next, use the inspection device "Candela" to divide the contour of the surface shape in the circumferential direction of the outer peripheral region at an angular interval of 5.8[°] around the entire circuit of the substrate. Next, using the inspection device "Candela", spectral analysis was performed on the contour of the surface shape in the circumferential direction of each of the divided evaluation intervals in the outer peripheral area, and the wavelength [μm] and power spectral density of each evaluation interval were obtained. (PSD)[Å ² μm]. Next, from the results of the spectrum analysis, the PSD of the wavelength band having a spatial period of 500 [μm] to 1000 [μm] is extracted, and the root mean square roughness Rq of each evaluation interval is obtained.

Table 3 below shows the processing pressure in the third processing step in the secondary polishing step for the magnetic disk substrates of Examples 1 to 5. Furthermore, in Table 3, the root mean square roughness in each evaluation interval is shown in each main surface of the surface (top) and the back (bottom) of the magnetic disk substrates from Example 1 to Example 5. The maximum value of Rq (Rq_max), the average value of the root mean square roughness Rq (Rq_ave) of the entire evaluation interval, and the average value of the root mean square roughness Rq (Rq_ave) of the main surface of the front and back (surface) Difference (ΔRq_ave).

As shown in Table 3, in the substrates for magnetic discs from Example 1 to Example 5, in each evaluation interval, the spatial period of the surface shape in the circumferential direction is not less than 500 [μm] and not more than 1000 [μm]. The root mean square roughness Rq in the wavelength band is 1.5 [Å] or less. Furthermore, the average value (Rq_ave) of the root mean square roughness Rq of all the evaluation intervals is 0.9 [Å] or less. Furthermore, the difference (ΔRq_ave) between the main surfaces of the front and back (surfaces) of the substrate, which is the average value of the root mean square roughness Rq, is 0.1 [Å] or less.

These substrates for magnetic disks from Example 1 to Example 5 can suppress the deviation of the fluctuation in the circumferential direction in the outer peripheral region of the substrate, and can reduce the thickness of the magnetic disk and improve the memory capacity. , received good reviews.

[Comparative example] The steps other than the polishing process were the same as the method for producing the magnetic disc substrates from the aforementioned Example 1 to Example 5, and the magnetic disc substrates from Comparative Example 1 to Comparative Example 5 were produced. Also, in Comparative Example 1 to Comparative Example 5, an aluminum substrate having a thickness of 0.610 [mm] and an outer diameter of about 95 [mm] was used. And, during the manufacture of the substrate for magnetic disc of each comparative example, in the polishing process, the irregular sliding of the direction different from the direction of rotation of the polishing pad does not occur with the substrate relative to the polishing pad. Processing pressure, polishing electroless NiP plating film. More specifically, a grinding process including a primary grinding process and a secondary grinding process is performed, and the processing pressure in the third processing step of the secondary grinding process is determined to be 10 [kPa] or more to manufacture a substrate for a magnetic disc.

Next, the same measurement as in Example 1 to Example 5 was performed on the substrates for magnetic disks from Comparative Example 1 to Comparative Example 5 using the inspection device "Candela". The results are shown in Table 4 below.

As shown in Table 4, in the magnetic disk substrates from Comparative Example 1 to Comparative Example 5, in each evaluation interval, the spatial period of the surface shape in the circumferential direction is a wavelength of 500 [μm] to 1000 [μm] The maximum value (Rq_max) of the root-mean-square roughness Rq in the band was 1.5 [Å] or more except for the surface (top) of Comparative Example 2 and Comparative Example 5. And, at the back of Comparative Example 1 and Comparative Example 2, the front and back (face) of Comparative Example 3, and the back of Comparative Example 5, the average value (Rq_ave) of the root mean square roughness Rq of all evaluation intervals exceeds 0.9[Å]. Furthermore, in Comparative Example 1, Comparative Example 2, and Comparative Example 5, the difference (ΔRq_ave) between the main surfaces of the front and back (faces) of the substrate, the mean value of the root mean square roughness Rq, exceeded 0.1 [Å ].

In addition, in Comparative Example 2 and Comparative Example 3, the value of ΔH/H×100[%] specified in Patent Document 1 is 7% to 9%.

These substrates for magnetic discs from Comparative Example 1 to Comparative Example 5 have deviations in the circumferential direction fluctuations in the outer peripheral region of the substrate. From the viewpoint of thinning of the magnetic disc and improvement of memory capacity, Can't get a good rating.

10‧‧‧Substrate for magnetic disc 10c‧‧‧outer peripheral area 10i‧‧‧inner peripheral area 10p‧‧‧outer peripheral area 10z‧‧‧evaluation interval 11‧‧‧substrate 12‧‧‧electrolytic NiP Plating coating 230‧‧‧polishing pad C‧‧‧center Dc‧‧‧circumferential direction S70‧‧‧grinding process S71‧‧‧primary grinding process S72‧‧‧secondary grinding process S100‧‧‧magnetic disc Method for manufacturing substrates

[ Fig. 1 ] is a perspective view showing an HDD using a magnetic disk substrate according to an embodiment of the present invention. [FIG. 2] is a plan view of a substrate for a magnetic disk constituting the HDD shown in FIG. 1. [FIG. 3] is a graph showing one example of the surface shape of the main surface of the magnetic disk substrate shown in FIG. 2. [Fig. 4] is a graph showing the relationship between the wavelength and PSD of the surface shape in each evaluation section shown in Fig. 3. [Fig. 5] is a graph showing the root mean square roughness Rq for each evaluation interval. [FIG. 6] It is a flow chart showing the manufacturing process using the magnetic disk substrate which concerns on one embodiment of this invention. [FIG. 7] is a perspective view schematically showing an example of a polishing apparatus used in the polishing step shown in FIG. 6. [FIG. 8] is a flow chart showing an example of the steps included in the polishing step shown in FIG. 6. [FIG. 9] is a graph showing an example of the processing time and processing pressure in the secondary grinding process shown in FIG. 8.

10‧‧‧Magnetic disc substrate

10c‧‧‧outer surrounding area

10i‧‧‧inner surrounding area

10p‧‧‧Outermost surrounding area

11‧‧‧substrate

11a‧‧‧opening

12‧‧‧Electroless NiP coating film

C‧‧‧Center

Dc‧‧‧circumferential direction

Claims (7)

A substrate for a magnetic disc, which has an electroless NiP plating coating film on the main surface of the substrate; it is characterized in that when the radius of the substrate is determined as R [mm], the radius calculated from the center of the substrate is The area of the aforementioned main surface whose distance in the direction is more than R-2.5 [mm] and less than R-0.5 [mm] is regarded as the outer peripheral area; In each of the evaluation intervals divided by the aforementioned outer peripheral area between the areas with an angular interval of 2 [°] to 8 [°] in the circumferential direction around the aforementioned substrate, the space of the surface shape in the aforementioned circumferential direction The root-mean-square roughness Rq in the wavelength band whose period is 500 [μm] to 1000 [μm] is 1.5 [Å] or less. The magnetic disc substrate according to claim 1, wherein the average value of the root mean square roughness Rq in all the evaluation intervals is 0.9 [Å] or less. The magnetic disk substrate according to claim 2, wherein the difference between the above-mentioned average value of the above-mentioned root-mean-square roughness Rq of the front and back (surfaces) of the above-mentioned main surface of the above-mentioned substrate is 0.1 [Å] or less. The magnetic disc substrate according to any one of claim 1 to claim 3, Wherein, the aforementioned substrate is an aluminum substrate. A method for manufacturing a substrate for a magnetic disc, comprising: a polishing step of rotating a polishing pad to grind an electroless NiP plated coating film on the main surface of the substrate; it is characterized in that: the radius of the substrate is determined as R [mm ], the area of the aforementioned main surface whose distance in the radial direction from the center of the aforementioned substrate is more than R-2.5 [mm] and less than R-0.5 [mm] is taken as the outer peripheral area; in the aforementioned grinding step, The aforementioned electroless NiP plated coating film is polished with a processing pressure as low as that irregular sliding of the aforementioned substrate with respect to the aforementioned polishing pad, whereby the aforementioned substrate is obtained by connecting the inner peripheral region of the aforementioned main surface with the In each of the evaluation intervals divided by the aforementioned outer peripheral area between the outermost peripheral areas at an angular interval of 2 [°] to 8 [°] in the circumferential direction around the aforementioned substrate, the The root mean square roughness Rq in the wavelength band where the spatial period of the surface shape is 500 [μm] to 1000 [μm] is 1.5 [Å] or less. The method of manufacturing a substrate for a magnetic disc according to claim 5, wherein, in the polishing step, the substrate is rotated to change the polishing direction of the electroless NiP plated film by the polishing pad, from multiple directions The aforementioned electroless NiP plating film was uniformly polished. The method for manufacturing a substrate for a magnetic disc according to claim 5 or claim 6, wherein the grinding process includes: a primary grinding process of performing a rough surface finish on the aforementioned main surface, and performing a final finish on the aforementioned main surface The secondary grinding process; the aforementioned secondary grinding process has: a plurality of processing steps different from the aforementioned processing pressure; in the aforementioned processing step where the aforementioned processing pressure is the highest, the aforementioned processing pressure is above 7 [kPa], 9 [kPa] ]the following.

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