JP2017037701A - Method for manufacturing substrate for magnetic disk and polishing pad - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower micro waviness having a wavelength of 50-200 μm in a substrate for a magnetic disk.SOLUTION: A method for manufacturing a substrate for a magnetic disk, includes a polishing treatment of sandwiching a substrate with a pair of polishing pads, supplying a slurry containing abrasive grains between the polishing pad and the substrate, sliding the polishing pad and the substrate relative to each other, and thereby polishing both of main surfaces of the substrate. The polishing pad has a foam resin layer of foamed polyurethane having a plurality of openings thereon. When information of a three-dimensional shape of the surface of the polishing pad is obtained from a picked-up image of the surface of the polishing pad, and an arithmetic average roughness Ra of the surface of the polishing pad is determined from the information of the three-dimensional shape, the Ra is 0.5 μm or less.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for manufacturing a magnetic disk substrate and a polishing pad.

  Conventionally, a glass substrate has been suitably used for a magnetic disk used as one of information recording media. Today, in response to a request for an increase in storage capacity in a hard disk drive device, the density of magnetic recording has been increased. Along with this, the magnetic recording information area is miniaturized by extremely shortening the flying distance from the magnetic recording surface of the magnetic head. In such a glass substrate for a magnetic disk, the demand for reducing the surface irregularities of the substrate, particularly the micro waviness, has been increasing in order to achieve the low flying height of the magnetic head that is essential for a high recording density hard disk drive.

On the other hand, a method of manufacturing a glass substrate for an information recording medium that can accurately control surface micro-waviness and can be used as an information recording medium substrate that supports high-density recording (patent) Reference 1).
The manufacturing method is a method for manufacturing a glass substrate for an information recording medium, which has a polishing step in which a glass substrate for an information recording medium is set between upper and lower surface plates to which a polishing pad of a soft polisher is attached and both main surfaces are polished. is there. This manufacturing method utilizes the phenomenon that the value of the microwaviness of the main surface of the glass substrate for information recording medium after the polishing step depends on the value of the surface roughness of the surface of the polishing pad used in the polishing step. By selecting the surface roughness of the polishing pad surface used in the process, the microwaviness of the main surface of the glass substrate for information recording medium after the polishing process is set to a predetermined value. For example, the surface roughness Rz (maximum height) of the selected polishing pad is 20 μm or less. At this time, the surface roughness Rz of the polishing pad is measured using a stylus type surface roughness meter. Here, the wavelength (period) band of the micro waviness is 2 μm to 4 mm.

JP 2002-92867 A

  Recently, with the miniaturization of magnetic heads, the low flying height, and the high-speed rotation of magnetic disks, the wavelength band of minute undulations to be reduced in the glass substrate for magnetic disks has become smaller. However, when the surface roughness Rz (maximum height) of the polishing pad in the above manufacturing method is in the above numerical range, it is possible to reduce the conventional micro waviness of 2 μm to 4 mm having a wide wavelength band. It was not possible to reduce the fine waviness of the glass substrate having a wavelength of 50 to 200 μm. Regarding the reduction of microwaviness with a wavelength of 2 μm to 4 mm in such a glass substrate, there is a similar problem in the aluminum alloy substrate.

  Therefore, an object of the present invention is to provide a method for manufacturing a magnetic disk substrate and a polishing pad that can reduce microwaviness of a wavelength of 50 to 200 μm.

The inventor of the present application has studied the surface of the polishing pad in detail in order to solve the above conventional problems.
First, the inventor of this application measures the surface roughness Rz of various polishing pads with a stylus type surface roughness meter, and performs polishing by selecting a polishing pad having a very small Rz value from the measured Rz. It was. However, it was not possible to reduce the microwaviness of the glass substrate having a wavelength of 50 μm to 200 μm. That is, the value of the surface roughness Rz measured with a stylus type surface roughness meter did not serve as an index for reducing the microwaviness with a wavelength of 50 μm to 200 μm. For this reason, it was unclear what kind of polishing pad should be used in order to reduce the fine waviness of the glass substrate with a wavelength of 50 μm to 200 μm.
Therefore, the inventor of the present application investigated in detail the surface of various polishing pads using a scanning electron microscope (SEM). As a result, when the surface of the polishing pad was observed with an observable resolution at a wavelength range of 50 μm to 200 μm, which is the target wavelength band of minute waviness, it was found that there was a difference in the surface state of the polishing pad. Specifically, the surface of the polishing pad that cannot reduce micro-waviness with a wavelength of 50 to 200 μm is in a state where the surface of the surface of the polishing pad is roughly broken in the vertical direction around the opening of the foamed pore, that is, the surface is rough. We found that the tip of the surrounding wall was rough, that is, the so-called “crust” shape, and thought that the surface shape of the outermost layer of the polishing pad might affect the micro-waviness with a wavelength of 50 to 200 μm. It was. In addition, the above-mentioned “crushing” state can be said to be a “fluffing” state in which the tip of the wall around the opening is finely torn and the surface is fluffy. It can also be said to be "local fuzziness disorder". In the following description, the concavo-convex state at the tip of the wall around the opening is referred to as a “sagging” state.
Therefore, when we investigated this “sagure”, there were many surface irregularities due to such “sales” (there were many irregularities on the top of the wall around the opening due to “sausage”) or There is a large surface unevenness due to “sagging” (the “sagging” causes the tip of the wall around the opening to be finely split, resulting in a large number of irregularities on the piece), and the surface is uneven. When the surface of the polishing pad is measured with a conventional stylus-type surface roughness meter, including the surface of the polishing pad and the surface of the polishing pad that has no or little “brush”, the measurement results It was found that the obtained surface roughness Rz could not be correlated with the microwaviness having a wavelength of 50 to 200 μm. In a stylus type surface roughness tester, the size of the tip of the needle (stylus) is at least twice the opening diameter (for example, from several tens of μm) so that the tip of the needle does not fall into the opening on the surface of the polishing pad to be measured. Several hundred μm). In addition, since the measurement is performed by pressing the needle against the polishing pad, it is considered that the tip of the needle was measured by crushing the surface roughness of the “crushing”. From this, it was found that the surface state of the outermost layer of the polishing pad used for polishing could not be measured accurately with a stylus type surface roughness meter.
Therefore, in order to measure the surface state of the outermost layer of the polishing pad, the inventor of the present application uses a non-contact type method instead of a contact type method such as a stylus type surface roughness meter. I came up with the present invention.

  The method for manufacturing a magnetic disk substrate and the polishing pad of the present invention have the following aspects.

[Aspect 1]
A method for manufacturing a magnetic disk substrate, comprising:
The substrate is sandwiched between a pair of polishing pads, a slurry containing abrasive grains is supplied between the polishing pad and the substrate, and the polishing pad and the substrate are slid relative to each other. Including a polishing process for polishing the surface,
The polishing pad has a foamed polyurethane foam resin layer having a plurality of openings on the surface,
A picked-up image of the surface of the polishing pad, as long as it is focused while lowering the focus by 5 μm in the height direction from the point of focus on the highest position of the surface of the polishing pad using the image pickup means. By the method of repeating imaging, from the captured image obtained using the rectangular area as the field of view for imaging, information on the three-dimensional shape of the rectangular surface of 1600 × 1200 pixels, with one pixel being a rectangular surface of 0.37 μm × 0.37 μm, Obtained as three-dimensional shape information on the surface of the polishing pad, and when the arithmetic average roughness Ra of the surface of the polishing pad is determined from the three-dimensional shape information, the Ra is 0.5 μm or less. A method of manufacturing a magnetic disk substrate.

[Aspect 2]
The method for producing a magnetic disk substrate according to aspect 1, wherein an average value of the opening diameters of the plurality of openings is 5 to 20 μm.

[Aspect 3]
The method for producing a magnetic disk substrate according to aspect 1 or 2, wherein the foamed resin layer has pores having a depth of 10 μm or more and 600 μm or less.

[Aspect 4]
4. The method for manufacturing a magnetic disk substrate according to any one of aspects 1 to 3, wherein the abrasive grains are colloidal silica having an average particle diameter of 5 nm to 50 nm.

[Aspect 5]
A magnetic disk manufacturing method comprising forming at least a magnetic layer on a main surface of a magnetic disk substrate manufactured by the method for manufacturing a magnetic disk substrate according to any one of aspects 1 to 4.

[Aspect 6]
A polishing pad used in a polishing process for polishing the surface of a substrate,
The polishing pad has a foamed polyurethane foam resin layer having a plurality of openings on the surface,
By focusing on the highest position on the surface of the polishing pad using an imaging unit, the method is repeated until the focus is achieved while lowering the focus by 5 μm in the height direction. From the picked-up image obtained by using the rectangular area as the field of view for picking up, the information of the solid shape of the rectangular surface of 1600 × 1200 pixels is obtained by assuming that one pixel is a rectangular surface of 0.37 μm × 0.37 μm. A polishing pad obtained by obtaining the shape information and calculating the arithmetic average roughness Ra of the surface of the polishing pad from the solid shape information, wherein the Ra is 0.5 μm or less.

[Aspect 7]
The polishing pad according to aspect 6, wherein the 100% tensile modulus of the resin material in the foamed resin layer is 200 kgf / cm ² or less.

[Aspect 8]
The polishing pad according to aspect 6 or 7, wherein an average value of the opening diameters of the plurality of openings is 5 to 20 μm.

[Aspect 9]
The polishing pad according to any one of aspects 6 to 8, wherein the foamed resin layer has pores having a depth of 10 μm or more and 600 μm or less.

[Aspect 10]
The polishing pad according to any one of aspects 6 to 9, which is used in a polishing process in which the surface of the substrate is polished together with a slurry containing colloidal silica as polishing abrasive grains.

  In the method for manufacturing a magnetic disk substrate and the polishing pad described above, the fine waviness of the substrate having a wavelength of 50 μm to 200 μm can be reduced.

(A), (b) is a schematic block diagram of the grinding | polishing apparatus used for the 2nd grinding | polishing in this embodiment. It is a figure explaining grinding | polishing of the grinding | polishing apparatus shown to Fig.1 (a), (b). It is a figure explaining the structure of the polishing pad used by this embodiment. It is a figure explaining the method to measure the three-dimensional shape of the surface of the polishing pad performed in this embodiment.

Hereinafter, the manufacturing method and polishing pad of the glass substrate for magnetic disks of this invention are demonstrated in detail. The magnetic disk substrate of the present invention can be applied to an aluminum alloy substrate in addition to a glass substrate, but in the following description, the magnetic disk glass substrate will be described as this embodiment.
In this embodiment, the glass substrate for a magnetic disk used for the magnetic disk has a disk shape, forms a ring shape with a central portion cut out concentrically, and rotates around the center of the ring as a rotation axis. A magnetic disk is obtained by laminating a magnetic layer or the like on a magnetic disk glass substrate. Therefore, it is important to accurately manage the surface irregularities of the magnetic disk glass substrate. In the method for manufacturing a glass substrate for a magnetic disk according to the present embodiment, the root mean square roughness Rq of minute undulations having a wavelength of 50 to 200 μm on the main surface of the glass substrate can be reduced by polishing the main surface of the glass substrate. Preferably, the root mean square roughness Rq of 0.6 nm or less before polishing can be reduced to 0.06 nm or less. At this time, the polishing pad used for polishing has a foamed resin layer having a plurality of openings on the surface. The arithmetic average roughness Ra described below of the surface of the polishing pad is 0.5 μm or less. The arithmetic average roughness Ra is obtained from information obtained by obtaining three-dimensional shape information on the surface of the polishing pad from a captured image of the surface of the polishing pad. This three-dimensional shape information includes uneven shape information formed at the tip of the wall surrounding the pores of the foamed resin layer.
In addition, the definition of the surface roughness including the root mean square roughness Rq and the arithmetic average roughness Ra of the fine waviness of the wavelength 50 to 200 μm and the fine waviness of the wavelength 2 μm to 4 mm as used in this specification is JIS B 0601. : Conforms to 2001.

An example of a method for producing the magnetic disk glass substrate of the present embodiment will be described below.
First, a glass blank as a material for a plate-like glass substrate for a magnetic disk having a pair of main surfaces is formed. Next, this glass blank is appropriately processed to produce a ring-shaped (annular) glass substrate having a chamfered edge portion with a hole in the central portion. Thereby, a glass substrate is produced | generated. Then, the root mean square roughness Rq of the microwaviness with a wavelength of 50 μm to 200 μm can be reduced by polishing the main surface. For example, the root mean square roughness Rq of minute waviness with a wavelength of 50 μm to 200 μm can be reduced to 0.06 nm or less. The polishing process may be performed in a plurality of processes as necessary. Moreover, you may perform grinding | polishing of a main surface, polishing of an end surface (a chamfer part is included), and chemical strengthening as needed. At this time, the order of each process may be determined as appropriate.
Hereinafter, each process will be described.

(A) Glass blank forming process For forming a glass blank, for example, a float method is used. In the glass blank forming process, first, molten glass is continuously poured into a bath filled with molten metal such as tin to obtain, for example, plate-like glass having the above-described composition. The molten glass flows along the traveling direction in a bathtub that has been subjected to a strict temperature operation, and finally a plate-like glass adjusted to a desired thickness and width is formed. From this plate glass, a plate-shaped glass blank having a predetermined shape (for example, a quadrangular shape in plan view) that is a base of the magnetic disk glass substrate is cut out.
In addition to the float method, for example, a press molding method can be used for forming the plate-shaped glass blank. Furthermore, it can manufacture using well-known manufacturing methods, such as a downdraw method, a redraw method, and a fusion method. A disk-shaped glass blank serving as a base of the magnetic disk glass substrate is cut out by appropriately performing shape processing on the plate-shaped glass produced by these known manufacturing methods.

(B) Shape processing treatment Next, in the shape processing treatment, a disk-shaped glass substrate having circular through holes is formed by forming a circular hole using a known processing method after the glass blank forming treatment. Thereafter, further chamfering may be performed. Further, the main surface may be ground for the purpose of adjusting the plate thickness or reducing the flatness.

(C) First polishing treatment Next, a first polishing treatment is performed on the main surface of the glass substrate. The first polishing treatment aims at mirror polishing of the main surface. Specifically, the main surfaces on both sides of the glass substrate are polished while holding the glass substrate in a holding hole provided in a holding member (carrier) attached to the double-side polishing apparatus. The machining allowance by the first polishing is, for example, about several μm to 100 μm. The first polishing treatment is intended to remove, for example, scratches and distortions remaining on the main surface, or to adjust minute surface irregularities. Note that the first polishing process may be divided into a plurality of polishing processes in order to further reduce the surface unevenness or to perform more precise adjustment.

  In the first polishing process, the glass substrate is polished while applying polishing slurry using a known double-side polishing apparatus having an upper surface plate, a lower surface plate, an internal gear, a carrier, and a sun gear and having a planetary gear mechanism. In the first polishing treatment, a polishing slurry containing polishing abrasive grains (free abrasive grains) is used. As the free abrasive grains used in the first polishing, for example, abrasive grains of cerium oxide, zirconia, colloidal silica, etc. (particle size: diameter of about 0.3 to 3 μm) are used. In the double-side polishing apparatus, the glass substrate is held between a pair of upper and lower surface plates. An annular flat polishing pad (for example, a resin polisher) is attached to the upper surface of the lower surface plate and the bottom surface of the upper surface plate. Then, by moving either the upper surface plate or the lower surface plate, or both, the glass substrate and each surface plate are relatively moved, thereby polishing both main surfaces of the glass substrate.

(D) Chemical strengthening treatment The glass substrate can be appropriately chemically strengthened. As the chemical strengthening liquid, for example, a molten liquid obtained by heating potassium nitrate or sodium nitrate or a mixture thereof to 300 ° C. to 500 ° C. can be used. And a glass substrate is immersed in a chemical strengthening liquid for 1 hour-10 hours, for example.
By immersing the glass substrate in the chemical strengthening solution, lithium ions and sodium ions in the glass composition on the surface layer of the glass substrate are replaced with sodium ions and potassium ions having relatively large ionic radii in the chemical strengthening solution, respectively. As a result, a compressive stress layer is formed on the surface layer portion, and the glass substrate is strengthened.
The timing of performing the chemical strengthening treatment can be determined as appropriate. However, if the polishing treatment is performed after the chemical strengthening treatment, the foreign matter fixed to the surface of the glass substrate by the chemical strengthening treatment can be removed together with the smoothing of the surface. This is particularly preferable because it can be performed. The chemical strengthening treatment is not necessarily performed.

(E) Second Polishing (Final Polishing) Process Next, a second polishing process is performed on the glass substrate after the chemical strengthening process. The second polishing treatment aims at mirror polishing of the main surface. Also in the second polishing, a double-side polishing apparatus having the same configuration as the double-side polishing apparatus used for the first polishing is used. The machining allowance by the second polishing is, for example, about 0.5 μm to 10 μm.
In the second polishing process, polishing is performed using a slurry containing loose abrasive grains. Colloidal silica is preferably used as the free abrasive. The average particle diameter of the colloidal silica is preferably 5 nm or more and 50 nm or less, from the viewpoint of reducing the root mean square roughness Rq of minute undulations having a wavelength of 50 to 200 μm on the main surface of the glass substrate G. If the average particle size is larger than 50 nm, there is a possibility that the fine waviness with a wavelength of 50 to 200 μm cannot be sufficiently reduced. Moreover, there exists a possibility that surface roughness cannot fully be reduced. On the other hand, if the average particle size is less than 5 nm, the polishing rate may be extremely lowered and productivity may be lowered.
In the present embodiment, the average particle diameter is 50% when the cumulative curve is obtained with the total volume of the powder population in the particle size distribution measured by the light scattering method as 100%. This refers to the particle size of the dots (also called cumulative average particle size (50% diameter) or D50).
FIGS. 1A and 1B are schematic configuration diagrams of a polishing apparatus 10 used for the second polishing. A similar apparatus can be used for the first polishing.

As shown in FIGS. 1A and 1B, the polishing apparatus 10 includes a lower surface plate 12, an upper surface plate 14, an internal gear 16, a carrier 18, a polishing pad 20, a sun gear 22, An internal gear 24 and a container 26 are provided.
The polishing apparatus 10 sandwiches the internal gear 16 between the lower surface plate 12 and the upper surface plate 14 from the vertical direction. A plurality of carriers 18 are held in the internal gear 16 during polishing. In FIG. 2B, five carriers 18 are shown. A polishing pad 20 is planarly bonded to the lower surface plate 12 and the upper surface plate 14. The lower surface plate 12 and the upper surface plate 14 are configured to rotate (rotate) around the rotation axis center of the lower surface plate 12 and the upper surface plate 14.

  As shown in FIG. 2, the lower main surface of the glass substrate G abuts on the polishing pad 20 on the lower surface plate 12, and the upper main surface of the glass substrate G contacts the polishing pad 20 on the upper surface plate 14. The carrier 18 is disposed so as to contact. By polishing in such a state, the main surfaces on both sides of the glass substrate G processed into an annular shape can be polished.

  As shown in FIG. 1B, an annular glass substrate G is held in a circular hole provided in each carrier 18. On the other hand, the glass substrate G is held on a carrier 18 having a gear 19 on the outer periphery on the lower surface plate 12. The carrier 18 meshes with a sun gear 22 and an internal gear 24 provided on the lower surface plate 12. By rotating the sun gear 22 in the direction of the arrow shown in FIG. 1B, each carrier 208 revolves while rotating as a planetary gear in the direction of the arrow. As a result, the glass substrate G is polished using the polishing pad 20. At the time of polishing, the glass substrate G is pressed and polished, for example, at 0.002 to 0.02 MPa. The slurry used for polishing is supplied to the upper surface plate 14 as shown in FIG. 1A, flows to the lower surface plate 12, and is collected in an external container.

The type of loose abrasive used in the second polishing, the particle size, the variation in particle size, the hardness of the resin used for the polishing pad 20, the opening diameter of the pores on the surface of the polishing pad 20 as will be described later, etc. From time to time. In the present embodiment, at least in the final polishing process, the arithmetic average of the surface of the polishing pad 20 is such that the root mean square roughness Rq of the fine waviness of the polished glass substrate with a wavelength of 50 to 200 μm is 0.06 nm or less. It is preferable to adjust the roughness Ra.
In addition, in order to further reduce the surface unevenness of the glass substrate G or perform more precise adjustment, each polishing process may be further divided into a plurality of polishing processes. At that time, in each polishing treatment, it is preferable to appropriately adjust the type, particle size, variation in particle size, hardness of resin used for the polishing pad, pore diameter of the pores on the polishing pad surface, and the like.
After the second polishing, the glass substrate G is washed to produce a magnetic disk glass substrate.

(Polishing pad)
Next, the polishing pad 20 used for the second polishing will be described in detail below.
The polishing pad 20 is made of a foamed resin having a plurality of openings on the surface, for example, made of foamed polyurethane. The diameter of the opening on the surface of the polishing pad 20 is preferably 5 μm or more and 20 μm or less. When the aperture diameter is smaller than 5 μm, it becomes difficult to store the slurry in a foam material having a structure having a large number of small pores in the form of droplets, or to supply the stored slurry appropriately, and the polishing rate is increased. Reduced and cannot be polished. On the other hand, when the diameter of the opening is larger than 20 μm, the surface roughness of the polishing pad 20 becomes large, and the fine waviness of the wavelength of 50 to 200 μm cannot be reduced.
The arithmetic average roughness Ra of the surface of the polishing pad 20 is 0.5 μm or less. Specifically, the arithmetic average roughness Ra is obtained from information obtained by obtaining information about the three-dimensional shape of the surface of the polishing pad 20 from a captured image of the surface of the polishing pad 20. The optical measurement using the captured image will be described later. The lower limit of the arithmetic average roughness Ra of the surface of the polishing pad 20 is not particularly limited, but is, for example, 0.1 μm. If Ra is less than 0.1 μm, the polishing rate may decrease and productivity may deteriorate.
Through the polishing using the polishing pad 20, the root mean square roughness Rq of the microwaviness having a wavelength of 50 μm to 200 μm on the main surface of the glass substrate G can be reduced. Preferably, the root mean square roughness Rq can be reduced to 0.06 nm or less. In this case, it is preferable that the root mean square roughness Rq of the microwaviness with a wavelength of 50 to 200 μm in the glass substrate G before the second polishing treatment is 0.6 nm or less. If the Rq of the glass substrate G before the second polishing treatment is larger than 0.6 nm, the machining allowance increases because Rq is polished to 0.06 nm or less, and the productivity may deteriorate. In addition, a drop (roll-off) may increase in the shape of the outermost peripheral portion on the main surface.
Moreover, it is preferable to perform the grinding | polishing process using this polishing pad with respect to the main surface by which the chemical strengthening process was carried out. Since the compressive stress layer is formed on the main surface of the glass substrate after the chemical strengthening process, when the polishing process is performed, the release of the compressive stress is locally disturbed by the “paddle” of the polishing pad, resulting in minute waviness. In some cases, the roughness cannot be reduced sufficiently. In the present polishing pad, the “wrinkle” is suppressed so that the arithmetic average roughness Ra of the surface of the polishing pad is 0.5 μm or less, so that the fine waviness and roughness can be reduced well.
The arithmetic average roughness Ra of the surface roughness of the glass substrate G after the second polishing is 0.2 nm or less, preferably 0.15 nm or less. Here, the arithmetic average roughness Ra of the surface roughness is a value when measured with a resolution of 256 × 256 pixels in a measurement area of 1 μm × 1 μm using an AFM (atomic force microscope).
As will be described later, there is a correlation between the arithmetic average roughness Ra of the surface roughness of the polishing pad and the root mean square roughness Rq of the microwaviness having a wavelength of 50 μm to 200 μm on the main surface of the glass substrate after the polishing treatment. . For this reason, a plurality of types of polishing pads having different arithmetic average roughness Ra of the surface roughness are prepared in advance, and in order to achieve a desired microwaviness on the main surface of the substrate, Is appropriately selected. In this case, the relationship between the root mean square roughness Rq of the microwaviness having a wavelength of 50 μm or more and 200 μm or less on the main surface of the substrate after the polishing treatment and the arithmetic average roughness Ra of the polishing pad surface used for the polishing treatment is previously determined. A polishing pad having an arithmetic average roughness Ra of the polishing pad surface that achieves a desired microwaviness on the main surface of the substrate is selected using the above relationship, and the selected polishing pad is used for the polishing process. preferable.

  Since the polishing pad 20 is made of foamed resin (foamed resin layer), it has a pore opening on the surface. For this reason, the slurry containing loose abrasive grains can be made to enter the cavity inside the polishing pad 20 from the opening, and polishing can be performed efficiently. However, if the polishing process is performed many times, the polishing rate may decrease and the polishing efficiency may deteriorate. In such a case, the polishing rate can be recovered by dressing the polishing pad 20. On the other hand, the surface of the polishing pad 20, that is, the front end of the wall surrounding the pores (pores) of the foamed resin layer is forcibly scraped by the dressing process. . When the shape of the surface of the polishing pad 20 that cannot reduce micro-waviness with a wavelength of 50 to 200 μm is observed with a scanning electron microscope, the tips of the resin portions around the openings of a large number of foaming pores are in a “squirting” state. I understood. And it turned out that the tip part of the "sagging" state is thin and film-like. The rigidity of the tip in such a “crushing” state is extremely low, and it is easy to bend with a slight force. It is considered that this “sackle” state is formed by tearing the surface layer of the polishing pad by diamond abrasive grains during the dressing process. A surface state in which the surface is in such a “sagging” state and has an uneven surface cannot be measured with a stylus type surface roughness meter. In the stylus type surface roughness meter, the size of the tip of the needle (stylus) is at least twice the opening diameter (for example, several tens of μm) so that the tip of the needle does not fall into the opening on the surface of the polishing pad 20 to be measured. To several hundred μm). In addition, the measurement is performed by pressing the needle against the polishing pad. For this reason, the tip of the needle is measured while holding the “squirt” state. Therefore, it is not possible to measure surface irregularities including a “crushing” state from the measurement results obtained with a stylus type surface roughness meter. Therefore, the present embodiment uses optical measurement using a captured image. By reducing the arithmetic average roughness Ra of the surface of the polishing pad 20 obtained by this optical measurement, it is possible to reduce micro-waviness with a wavelength of 50 to 200 μm on the main surface of the glass substrate G. Preferably, the root mean square roughness Rq of minute waviness with a wavelength of 50 to 200 μm on the main surface of the glass substrate G can be reduced to 0.06 nm or less. In this case, it is preferable that the root mean square roughness Rq of the microwaviness with a wavelength of 50 to 200 μm on the main surface of the glass substrate G before polishing is 0.6 nm or less.

In addition, the modulus (tensile stress) of the resin material in the foamed resin layer used for the polishing pad 20 is 200 kgf / cm ² or less. Rq is preferable in that it efficiently reduces to 0.06 nm or less. Here, the modulus is 100% modulus. Note that if the modulus to 100 kgf / cm ² or less can prevent the fine scratches on the glass substrate G is generated, it is more preferable to below 100 kgf / cm ^2. On the other hand, when it is less than 50 kgf / cm ² , there is a possibility that productivity is lowered due to a decrease in the polishing rate. In addition, when the modulus is made smaller than 50 kgf / cm ^{2, in} the region near the outer peripheral end surface of the glass main surface of the glass substrate, the glass main surface gently inclines in a curved shape toward the outer peripheral end surface, and the degree of smoothness is disturbed. There is. Such disturbance of smoothness in the area near the outer peripheral edge of the glass main surface is due to the recording of magnetic information to the vicinity of the outer peripheral edge of the glass main surface by forming a magnetic layer on the entire surface of the glass main surface in order to increase the storage capacity. And is not preferable in that reading is performed accurately. Therefore, the lower limit of the modulus is not particularly limited, but is, for example, 50 kgf / cm ² . The tensile modulus of the resin material is measured by a tensile tester (Tensilon tester).
The arithmetic average roughness Ra ′ of the surface roughness of the polishing pad 20 before the dressing process is preferably 0.8 μm or less. The arithmetic average roughness Ra ′ is measured by using a stylus type surface roughness measuring machine using a stylus having a tip radius of curvature of several tens to several hundreds μm. By setting Ra ′ before the dressing process to 0.8 μm or less, the arithmetic average roughness Ra measured using the imaging camera on the surface of the polishing pad is easily set to 0.5 μm or less even after the dressing process. be able to. This is because the smaller the roughness of the polishing pad surface, the more stable the dressing process. That is, the dressing process does not cause unevenness on the entire surface of the polishing pad.

When the polishing pad 20 is unused (not used for polishing in the past) and is a new product, the polishing pad 20 is made of an independently foamed resin and therefore has no opening on the surface. For this reason, before starting the use of polishing, dressing is performed and the surface is shaved along the dotted line X shown in FIG. 3, so that a plurality of openings are formed on the surface, for example, a diameter of 5 to 20 μm and a depth of 10 to 600 μm. Make holes with openings appear. That is, in polishing, it is preferable to use a polishing pad having an opening diameter (diameter) of 5 μm or more and 20 μm or less. When the opening diameter is less than 5 μm, the polishing rate is lowered and productivity may be lowered. On the other hand, if the aperture diameter is larger than 20 μm, the micro swell in the wavelength band of 50 to 200 μm may not be reduced. Further, it is preferable to use a polishing pad having pores having a depth of 10 μm or more and 600 μm or less. When the depth is less than 10 μm, the polishing rate becomes low and the productivity may decrease. On the other hand, if the depth is larger than 600 μm, the thickness of the nap layer in which pores are continuously formed increases, so that the amount of compressive deformation of the polishing pad 20 increases, and locally high pressure is applied to the outermost peripheral portion of the substrate. It becomes easy to apply, and the roll-off amount may become large. The diameter of the opening and the depth of the pores (pores) can be measured by observing the surface or cross section of the polishing pad with an SEM.
The three-dimensional shape information on the surface of the polishing pad 20 of the present embodiment is preferably information on the surface state used for polishing.
The above is the description of the polishing pad 20.

(Surface measurement of polishing pad)
FIG. 4 is a diagram for explaining a method for measuring the three-dimensional shape of the surface of the polishing pad 20 performed in the present embodiment.

  As described above, the polishing pad used in the conventional polishing has a polishing pad surface roughness Rz measured using a stylus type surface roughness meter in order to reduce minute waviness of the glass substrate having a wavelength of 2 μm to 4 mm. Was 20 μm or less. In this case, the arithmetic average roughness Ra ′ is about 3.0 μm or less. However, in the stylus type surface roughness tester, when the surface as described above is in the “throwing” state, Is not measured. For this reason, in this embodiment, instead of the stylus type surface roughness meter, the arithmetic average roughness Ra obtained by optical measurement using a photographed image is measured.

Specifically, the imaging camera 40 is used to photograph the surface at a magnification of 500 times with a rectangular area of 600 μm × 450 μm as a field of view for imaging and a pixel as a rectangular surface of 0.37 μm × 0.37 μm. At this time, imaging is started when the focal point is focused on the highest position on the surface of the polishing pad 20, the position of the photographing camera 40 is moved by 5 μm in the height direction, and the focal point is set to any pixel in the captured image. Repeat shooting until it matches. Then, the imaging is ended when the focus is not achieved on any pixel.
As the imaging camera 40, for example, a CCD camera can be used. This may be used in combination with an optical microscope, or an apparatus in which they are integrated.

  Each of the captured images obtained by imaging at intervals of 5 μm in this way is sent to the image processing device 42 and image processing is performed. In the image processing device 42, information on the three-dimensional shape of the surface of the polishing pad 20 is obtained for each pixel. The information on the three-dimensional shape includes information on the concavo-convex shape formed at the tip of the wall surrounding the pores of the foamed resin layer, that is, the “crushing” state. Specifically, the image processing device 42 calculates information on the position in the height direction of each pixel from the obtained image data of the captured images at 5 μm intervals. The method for calculating the position information in the height direction of each pixel from the image data is not particularly limited, and a known method can be used. As an example, information on the position in the height direction is calculated by obtaining information on the position in the height direction (focus position) when each pixel is focused from the image data of the captured images at intervals of 5 μm. In this case, since the in-focus position is obtained every 5 μm, the position information in the height direction around the pixels obtained at intervals of 5 μm is preferably interpolated to calculate the position information finely as a position less than 5 μm. be able to.

  The image processing device 42 is configured by a computer, and the image processing operates by calling and executing software stored in the memory of the computer. The software may be commercially available software or original software as long as the above processing can be appropriately executed.

  The information on the three-dimensional shape of the surface of the three-dimensional polishing pad 20 obtained by such image processing is different from the measurement using a conventional stylus type surface roughness meter, depending on the state of the surface of the foamed resin. Surface irregularities can be reproduced. The image processing device 42 calculates the arithmetic average roughness Ra using the information on the three-dimensional shape of the surface of the three-dimensional polishing pad 20.

  The root mean square roughness Rq of the microwaviness with a wavelength of 50 to 200 μm of the glass substrate for magnetic disk to be produced is determined for a radius region of 14 mm to 31.5 mm on the main surface of the glass substrate using a surface shape measuring instrument. . Specifically, the surface shape is measured by setting the measurement pitch in the radial direction to 0.01 mm and the measurement region in one circumference in the circumferential direction to be 1024. As the surface shape measuring device, a laser Doppler vibrometer (LDV) can be used. This measuring apparatus can measure a wide wavelength band from surface roughness to waviness. Micro waviness of a wavelength of 50 μm to 200 μm is obtained using data filtered using a bandpass filter corresponding to a wavelength of 50 μm to 200 μm.

In the manufacturing method of the glass substrate for magnetic disks of this embodiment, the polishing pad 20 used for the second polishing polishes the glass substrate G after the dressing process. One polishing pad 20 is used for a plurality of second polishing processes. One time of the second polishing process is a process of reducing the Rq of the microwaviness with a wavelength of 50 to 200 μm on the main surface of the glass substrate G to 0.06 nm or less.
The polishing rate of the polishing pad 20 decreases as the number of second polishing processes for the glass substrate G increases. For this reason, when the polishing rate falls below the allowable range, the polishing pad 20 is dressed. This dressing process is preferably performed under different conditions from the initial dressing process that is initially performed on a new polishing pad 20 having no openings formed on the surface. This dressing process is referred to as a second or subsequent dressing process when it is described separately from the first dressing process. When the first dressing process and the second and subsequent dressing processes are collectively referred to without distinction, they are simply called dressing processes. In the second and subsequent dressing processes, since “sagging” is more likely to occur on the surface of the polishing pad than in the first dressing, it is preferably performed under different conditions. This is presumably because a large number of openings are already generated even before the dressing process.
When the arithmetic average roughness Ra of the surface of the polishing pad after the dressing process exceeds 0.5 μm, even if the surface of the polishing pad 20 becomes familiar with the loose abrasive grains, the surface of the glass substrate G has a minute undulation of 50 μm to 200 μm. Rq cannot be reduced to 0.06 nm or less. On the other hand, when the arithmetic average roughness Ra of the surface of the polishing pad after dressing by the method using the imaging camera is 0.5 μm or less, the Rq of 50 to 200 μm minute undulation of the glass substrate G is set to 0.06 nm or less. Can be reduced.

  The dressing process referred to in this specification uses the polishing apparatus 10 shown in FIGS. 1A, 1B, and 2, and instead of the glass substrate G, a polishing material with, for example, diamond abrasive grains attached to both surfaces of the substrate is applied. Use the attached dresser. For example, water may be supplied instead of the polishing liquid. Abrasive grains used for the dresser from the viewpoint of suppressing the surface “sagging” of the polishing pad 20 by the first dressing process, and further suppressing the surface “sagling” of the polishing pad 20 by the second and subsequent dressing processes. It is preferable to appropriately adjust the average particle size, the particle size dispersion, the resin material for fixing the abrasive grains, the load on the surface plate during dressing, the number of revolutions, the rotation / revolution of the planetary gear, and other conditions.

  The diamond abrasive grains used for the dressing process preferably have a particle diameter of 10 to 30 μm. The smaller the particle size, the more effective the suppression of the “paddle” on the surface of the polishing pad. However, when the particle size is smaller than 10 μm, the removal rate of the polishing pad is reduced, and the dressing process takes time and the productivity is lowered. There is a case. On the other hand, if the particle size is larger than 30 μm, the surface unevenness due to “thrust” becomes large, or the number of surface unevenness due to “thrust” increases, and Ra on the surface of the polishing pad may not be sufficiently reduced.

  Moreover, it is preferable to make the load by the surface plate at the time of dressing processing smaller than at the time of polishing processing. Specifically, the pressure applied to the polishing pad is preferably 0.001 to 0.005 MPa. If the load at the time of dressing is smaller than that at the time of polishing, it is effective to suppress the increase of “sapling” on the surface of the polishing pad, but if the pressure applied to the polishing pad is less than 0.001 MPa, the polishing pad is removed. The rate may decrease and the dressing process takes time, and productivity may decrease. On the other hand, when the pressure applied to the polishing pad is greater than 0.005 MPa, the surface unevenness due to “thrust” increases, or the number of surface unevenness due to “thrust” increases, and Ra on the surface of the polishing pad may not be sufficiently reduced. .

The relative speed between the dresser and the polishing surface plate (polishing pad) is preferably 1.5 to 3 times that during the polishing process. The higher the relative speed, the more effective the suppression of the “paddle” on the surface of the polishing pad, but if the relative speed during dressing is higher than 3 times that during polishing, the supply of water to the surface of the polishing pad cannot catch up. In some cases, uniform dressing cannot be performed. On the other hand, if the relative speed during the dressing process is less than 1.5 times, the diamond abrasive grains may bite into the surface of the polishing pad and “crushing” may not be suppressed.
Further, by adjusting the relative load with the polishing pad and reducing the load during the dressing process, the dressing process can be performed while preventing the occurrence of “squirrel” even better.

Moreover, when raising the upper surface plate immediately after performing the dressing process, it is preferable to raise the upper surface plate while maintaining the movement (rotation) of at least one of the rotating upper surface plate and the carrier (dresser). By doing so, it is possible to prevent the surface of the polishing pad from being “turned up” due to the slight shaking generated on the upper surface plate when the upper surface plate is raised after the dressing process. Therefore, when raising the upper surface plate, raising the upper surface plate and at least one of the carrier (dresser) while moving (rotating) the arithmetic average roughness Ra of the polishing pad 20 to 0.5 μm or less. This is preferable.
When dressing, the above-mentioned various conditions may be adjusted as appropriate and further combined.

  Further, when dressing the polishing pad 20, the arithmetic average roughness Ra of the surface of the polishing pad 20 before the dressing process and the arithmetic average roughness Ra of the surface of the polishing pad 20 before the dressing process are set to 0.5 μm or less. Measurement of the arithmetic average roughness Ra of the surface of the polishing pad before dressing is obtained in advance with the correspondence relationship with dressing conditions (dressing processing time, surface plate load, rotational speed, etc.) Using the result information and the correspondence, the dress process conditions are determined and the dress process is performed. Thereby, disorder of the surface shape of the polishing pad 20 due to “sagure” can be suppressed.

In addition, for the second and subsequent dressing processes, the dressing process can be performed in which the cleaning liquid is sprayed and sprayed onto the polishing pad 20 without using the polishing apparatus 10. Specifically, a vertically long nozzle having a discharge port whose center is expanded forward is moved to the entire surface of the polishing pad to produce cleaning liquid mist with a particle size of 1 μm to 300 μm. The mist is made to collide with the polishing pad 20 at a speed of 10 m / second or more and 500 m / second or less. At this time, by appropriately adjusting various conditions, it is possible to satisfactorily remove the abrasive grains accumulated in the foamed pores without causing a new “thrust” state on the surface of the polishing pad. This dressing method is preferably applied to the polishing pad after being used in the polishing process. By doing so, it is possible to suppress the progress of the “paddle” state on the surface of the polishing pad by performing the dressing process with the diamond dresser a plurality of times, and it is obtained by the polishing process after the second and subsequent dressing processes. It is possible to prevent the deterioration of the micro swell of the glass substrate.
In the second and subsequent dressing processes, it is preferable to use both the above-described dressing process using abrasive grains such as diamond abrasive grains and the dressing process in which the cleaning liquid is sprayed and sprayed onto the polishing pad 20. Since such a dressing process can be performed softer than a dressing process that uses abrasive grains such as diamond abrasive grains, it is possible to prevent the “paddle” state of the polishing pad 20 after the dressing process from progressing. can do.
As described above, the polishing pad 20 used for the second polishing of the present embodiment is the one after the first and second dressing processes, and the three-dimensional surface of the polishing pad 20 is obtained from the captured image of the surface of the polishing pad 20. When the shape information is obtained, the arithmetic average roughness Ra of the surface of the polishing pad 20 obtained from this information is 0.5 μm or less.
Although this embodiment has been described using a glass substrate, as described above, it can be applied to an aluminum alloy substrate in addition to the glass substrate. Since the glass substrate has higher rigidity (hardness) than the aluminum alloy substrate, when using the glass substrate, it is preferable to increase the modulus of the polishing pad 20 to improve the polishing rate in order to increase productivity. On the other hand, because the high modulus of the polishing pad 20 tends to increase the rigidity of the tip of the surface irregularities of the “sapling” as compared with the case of the aluminum alloy substrate, the micro-waviness is likely to deteriorate compared to the aluminum alloy substrate. Small scratches are likely to occur. For this reason, it is preferable to apply the polishing treatment of the present invention to a glass substrate.

[Example]
In order to investigate the effect of the optical measurement method (this embodiment method) using the photographed image of the polishing pad of the present embodiment and the effect of the polishing pad in the second polishing, the second polishing is performed by changing the polishing pad variously. It was. The glass substrate G used was a 2.5-inch glass substrate for a magnetic disk. The surface unevenness of the glass substrate G before polishing was measured using an optical surface shape measuring machine. The root mean square roughness Rq of the microwaviness with a wavelength of 50 to 200 μm on the main surface was 0.1 to 1.0 nm.
As shown in FIG. 3, the polishing pad is made of a polyurethane resin having a foam structure having a large number of droplet-shaped pores in the surface layer portion, and the polishing apparatus 10 shown in FIGS. 1 (a) and 1 (b) is used. Previously dressed. In the dressing process, a diamond abrasive dresser was used, and the above processing conditions were appropriately adjusted. For this reason, each of the polishing pads has a plurality of openings formed on the surface by dressing. By using foam with a structure having many droplet-shaped vacancies, it is possible to reduce the opening of the portion in contact with the glass substrate, and the surface roughness of the polished glass substrate and the fine waviness of a wavelength of 50 to 200 μm Can be reduced. In addition, more abrasive can be stored inside the foam than the foamed structure with a spherical shape and shape whose diameter does not change in the depth direction, so the abrasive rate can be stably supplied and the polishing rate can be kept high for a long time. be able to. Here, a polishing pad having an average opening diameter (diameter) of 15 μm was used.

In the polishing of the glass substrate G, the polishing apparatus 10 shown in FIGS. 1A and 1B is used to apply a pressure of 0.01 MPa to the glass substrate G, so that colloidal silica polishing abrasive grains having an average particle size of 30 nm are applied. The slurry contained was polished while being supplied to the glass substrate G. The machining allowance was 5 μm.
On the other hand, in Examples 1 to 4, the surface of the polishing pad was used to obtain the arithmetic average roughness Ra ′ (conventional method) using a stylus type surface roughness meter, and in Examples 5 to 8, the optical measurement of this embodiment was performed. The arithmetic average roughness Ra (embodiment method) was obtained using the photographed image obtained by the above.
Furthermore, the surface irregularities of the polished glass substrate G were measured using the above-described optical surface shape measuring instrument to determine the root mean square roughness Rq of micro-waviness with a wavelength of 50 to 200 μm.

Tables 1 and 2 below show the arithmetic average roughness Ra and Ra ′ of the surface of the polishing pad immediately before polishing when polishing using various polishing pads, and when the second polishing process is performed using this polishing pad. The root mean square roughness Rq, Rq ′ of the microwaviness of the glass substrate is shown. In Examples 1 to 4, the root mean square roughness Rq ′ of fine waviness with a wavelength of 2 μm to 4 mm and the root mean square roughness Rq of micro waviness with a wavelength of 50 μm to 200 μm were obtained. In Examples 5 to 8, the root mean square roughness Rq of the microwaviness with a wavelength of 50 μm to 200 μm was obtained. In addition, the root mean square roughness of the microwaviness with a wavelength of 50 μm to 200 μm is represented as Rq, and the root mean square roughness of the microwaviness with a wavelength of 2 μm to 4 mm is represented as Rq ′. In addition, the arithmetic average roughness of the polishing pad surface according to the conventional method is represented as Ra ′, and the arithmetic average roughness of the polishing pad surface according to the present embodiment method is represented as Ra.
The root mean square roughness Rq ′ of minute waviness with a wavelength of 2 μm to 4 mm was measured using a known multifunctional surface analysis apparatus described in JP-A-2002-92867. In this apparatus, the light is divided and reflected on both the test surface and the reference surface, and the root mean square roughness Rq ′ of the microwaviness of the wavelength of 2 μm to 4 mm is calculated from the interference fringes when the light is recombined. obtain. As the measurement region, a rectangular region (about 250,000 pixels) of about 500 μm × about 600 μm in the vicinity of the middle periphery of the glass substrate was selected.

From Table 1, although the surface roughness of the polishing pad according to the conventional method is correlated with the root mean square roughness Rq ′ of the fine waviness of the wavelength 2 μm to 4 mm of the glass substrate surface, the square of the fine waviness of the wavelength 50 μm to 200 μm. It can be seen that there is no correlation with the average square root roughness Rq. For this reason, even if the surface roughness of the polishing pad according to the conventional method is reduced, it is not possible to reduce the microwaviness with a wavelength of 50 to 200 μm.
On the other hand, it can be seen from Table 2 that the arithmetic average roughness Ra of the surface of the polishing pad according to the present embodiment has a correlation with the root mean square roughness Rq of the microwaviness of the wavelength 50 μm to 200 μm of the glass substrate surface. And, when the arithmetic average roughness Ra of the surface of the polishing pad is 0.5 μm or less, the root mean square roughness Rq of the microwaviness of the wavelength of 50 μm to 200 μm is the arithmetic average roughness Ra is 0.75 μm. On the other hand, it turned out that it falls greatly. In particular, it can be seen that by setting the arithmetic average roughness Ra of the surface of the polishing pad to 0.5 μm or less, the root mean square roughness Rq of minute undulations with a wavelength of 50 μm to 200 μm can be extremely reduced to 0.06 nm or less. It was.
On the glass main surface of the glass substrate for a magnetic disk obtained in Examples 5 to 8, an adhesion layer, an underlayer, a magnetic recording layer, a protective layer, and a lubricating layer are sequentially formed on the main surface of the glass substrate by sputtering and vapor deposition. The magnetic disk was manufactured using the method. The manufactured magnetic disk was incorporated into an HDD (hard disk drive device) together with a magnetic head (DFH head) equipped with a DFH (Dynamic Flying Height) mechanism, and a flying durability test was performed. A magnetic head having a femto slider was used, the flying height of the slider surface was set to 9 nm, and the back-off amount of the magnetic head element part (the gap between the magnetic head element part and the magnetic disk surface) was set to 1 nm. The HDD was placed in a constant temperature bath at 80 ° C. and a humidity of 80% and randomly seeked for 30 days. After the evaluation, the magnetic head was taken out, and the dirt on the slider surface was evaluated with an optical microscope. As a result, no contamination was observed when the magnetic disks of Examples 5 to 7 were used. However, when the magnetic disk of Example 8 was used, there was a rubbing trace in the direction corresponding to the magnetic disk rotation direction around the element portion. Was observed.
From the above results, it was confirmed that by setting the minute undulation Rq to 0.06 nm or less, the flying characteristics are good even when the element portion is extremely close to the magnetic disk using the DFH head.

When the information of the three-dimensional shape of the surface of the polishing pad is obtained by the above-described embodiment method for the captured image of the surface of the polishing pad, the arithmetic average roughness Ra of the surface of the polishing pad obtained from this information is 0.5 μm. It is important that:
Thus, the effect of this embodiment system and the effect of setting the arithmetic average roughness Ra of the surface of the polishing pad to 0.5 μm or less could be confirmed.

  Next, a polishing pad having a different modulus (100% modulus) was prepared by variously changing the resin of the polishing pad, and the second polishing was performed. In any polishing pad, the arithmetic average roughness Ra of the polishing pad according to the present embodiment was 0.5 μm or less. After performing the second polishing process for 1000 sheets each, the glass substrate was washed, the number of fine scratches existing on the main surface was counted using an optical surface analyzer, and the level was determined in 10 stages. The smaller the level, the smaller the fine scratches and the better. Regarding the level, specifically, the number of micro scratches is counted for a glass substrate which is a predetermined reference, and when the count number at this time is set to 100%, the level of the micro scratch is defined as level 10, The level when the fine scratch count in Examples 9 to 14 below is 0 to 10% of the reference number of fine scratches on the glass substrate is defined as level 1, and the level when it is 11 to 20% is level 2. The level in the case of 21-30% was determined as level 3, and similarly, the level 9 (81-90%) was determined. Table 3 below shows the results.

In all of Examples 9 to 14, the root mean square roughness Rq of the microwaviness of the wavelength 50 μm to 200 μm of the glass substrate G after the second polishing was 0.06 nm or less, but there was a difference in the generation level of microscratches. It was seen. In Examples 9 to 14, since the conditions were such that scratches remaining on the main surface due to the first polishing and the previous processing were removed, the polishing pad suddenly applied the surface of the glass substrate in the second polishing. Probably caused by hurting. If the level is greater than 5, it means that the production stability of the second polishing may be poor. Therefore, it is preferable to set the modulus to 200 kgf / cm ² or less because production stability is improved. Further, it is more preferable that the modulus is 130 kgf / cm ² or less. It is even more preferable that the modulus be 70 kgf / cm ² or less. On the other hand, when the modulus was set to 50 kgf / cm ² or less, the abrasion of the polishing pad was accelerated and the production efficiency was lowered.

  As described above, the method for manufacturing a magnetic disk substrate and the polishing pad of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiments and examples, and various improvements and modifications can be made without departing from the spirit of the present invention. Of course, changes may be made.

DESCRIPTION OF SYMBOLS 10 Polishing apparatus 12 Lower surface plate 14 Upper surface plate 16 Internal gear 18 Carrier 20 Polishing pad 22 Sun gear 24 Internal gear 26 Container 28 Coolant 30 Pump 32 Filter

Claims (10)

A method for manufacturing a magnetic disk substrate, comprising:
The substrate is sandwiched between a pair of polishing pads, a slurry containing abrasive grains is supplied between the polishing pad and the substrate, and the polishing pad and the substrate are slid relative to each other. Including a polishing process for polishing the surface,
The polishing pad has a foamed polyurethane foam resin layer having a plurality of openings on the surface,
A picked-up image of the surface of the polishing pad, as long as it is focused while lowering the focus by 5 μm in the height direction from the point of focus on the highest position of the surface of the polishing pad using the image pickup means. By the method of repeating imaging, from the captured image obtained using the rectangular area as the field of view for imaging, information on the three-dimensional shape of the rectangular surface of 1600 × 1200 pixels, with one pixel being a rectangular surface of 0.37 μm × 0.37 μm, Obtained as three-dimensional shape information on the surface of the polishing pad, and when the arithmetic average roughness Ra of the surface of the polishing pad is determined from the three-dimensional shape information, the Ra is 0.5 μm or less. A method of manufacturing a magnetic disk substrate.   The method for manufacturing a magnetic disk substrate according to claim 1, wherein an average value of the opening diameters of the plurality of openings is 5 to 20 μm.   The method for manufacturing a magnetic disk substrate according to claim 1, wherein the foamed resin layer has pores having a depth of 10 μm or more and 600 μm or less.   The method for producing a magnetic disk substrate according to claim 1, wherein the abrasive grains are colloidal silica having an average particle diameter of 5 nm to 50 nm.   A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on a main surface of the magnetic disk substrate manufactured by the method for manufacturing a magnetic disk substrate according to claim 1. A polishing pad used in a polishing process for polishing the surface of a substrate,
The polishing pad has a foamed polyurethane foam resin layer having a plurality of openings on the surface,
By focusing on the highest position on the surface of the polishing pad using an imaging unit, the method is repeated until the focus is achieved while lowering the focus by 5 μm in the height direction. From the picked-up image obtained by using the rectangular area as the field of view for picking up, the information of the solid shape of the rectangular surface of 1600 × 1200 pixels is obtained by assuming that one pixel is a rectangular surface of 0.37 μm × 0.37 μm. A polishing pad obtained by obtaining the shape information and calculating the arithmetic average roughness Ra of the surface of the polishing pad from the solid shape information, wherein the Ra is 0.5 μm or less. The polishing pad according to claim 6, wherein a 100% tensile modulus of the resin material in the foamed resin layer is 200 kgf / cm ² or less.   The polishing pad according to claim 6 or 7, wherein an average value of the opening diameters of the plurality of openings is 5 to 20 µm.   The polishing pad according to any one of claims 6 to 8, wherein the foamed resin layer has pores having a depth of 10 µm or more and 600 µm or less. The polishing pad of any one of Claims 6-9 used for the grinding | polishing process which grind | polishes the surface of the said board | substrate with the slurry which contains colloidal silica as an abrasive grain.

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