JP2009154232A - Method of manufacturing glass substrate for magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a glass substrate for a magnetic disk, which improves the polishing efficiency by efficiently adjusting a surface state of an abrasive pad. <P>SOLUTION: The method of manufacturing the glass substrate for the magnetic disk includes the following steps. In the polishing step, a polishing liquid containing free abrasive grain is fed between the glass substrate 110 and the polishing pad 200 having a nap layer for polishing a main surface of the glass substrate 110, and the glass substrate 110 and the polishing pad 200 are moved with respect to each other, to thereby polish the glass substrate. In the adjusting step, an adjusting member obtained by fixing polishing abrasive grain to an adjusting surface, is brought into contact with a surface of the polishing pad 200, that has polished the glass substrate 110, and the adjusting member and the polishing pad 200 are moved with respect to each other, to thereby adjust the polishing pad 200. In the method, moving directions of the glass substrate 110 and the adjusting member with respect to the polishing pad 200 are different from each other between the polishing step and the adjusting step. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a glass substrate for a magnetic disk.

  In recent years, with the advancement of information technology, information recording technology, particularly magnetic recording technology, has made remarkable progress. As a substrate for magnetic recording media such as HDD (Hard Disk Drive), which is one of the magnetic recording media, a substrate replacing the aluminum substrate that has been widely used with the miniaturization, thinning, and high-density recording of magnetic disks. A glass substrate excellent in surface flatness and substrate strength has been used.

  As the magnetic recording technology has been increased in density, the magnetic head has been changed from a thin film head to a magnetoresistive head (MR head) and a large magnetoresistive head (GMR head). The flying height from is narrowed to about 6 nm. A magnetic head equipped with such a magnetoresistive element may cause a head crash failure or a thermal asperity failure as an inherent failure. Since these obstacles are caused by minute irregularities on the surface of the magnetic disk, the surface of the magnetic disk is required to have extremely high smoothness and flatness.

  Further, in order to effectively use the surface area of the glass substrate, the LUL method (Load UnLoad) has been adopted instead of the conventional CSS method (Contact Start Stop). In the LUL system, since the magnetic head passes through the end of the glass substrate, the accuracy of the end surface shape (particularly the outer peripheral end surface) of the glass substrate becomes a problem. If there is a shape disorder at the end of the glass substrate (swelling or drooping at the end), the flying position of the magnetic head is disturbed, and the magnetic head enters or exits from the outside of the glass substrate. It may be easy to touch and may cause a crash failure.

  Further, when flying the magnetic head with an extremely narrow flying height of 6 nm or less, there is a problem that fly stiction failure frequently occurs. The fly stiction failure is a failure in which the magnetic head flying and flying over the magnetic disk modulates the flying posture and the flying height, thereby causing irregular reproduction output fluctuations. Further, when this fly stiction failure occurs, a head crash failure may occur in which the flying magnetic head contacts the magnetic disk. For these reasons, the flatness of the substrate surface is particularly important in a glass substrate for a magnetic disk.

  In the polishing process in the manufacturing process of the glass substrate for magnetic disks as described above, polishing is performed using a polishing pad while supplying a polishing liquid (slurry) containing free abrasive grains between the glass substrate and the polishing pad. ing. Also, in order to prevent polishing marks and bias on the glass substrate, a polishing pad is attached to the surface plate, the glass substrate is sandwiched, and the glass substrate and the polishing pad are moved relatively by using a planetary gear mechanism. Polishing.

  The polishing pad used in the polishing process may not be flat when attached to the surface plate of the polishing machine, or the pad surface may become uneven as the polishing process is performed, and the pad surface may not be flat. . When the glass substrate is subjected to a polishing process in a state where the pad surface is not flat, waviness is increased in the polished glass substrate. As described above, this undulation may adversely affect the flying stability of the recording head.

  As a method for improving the unevenness of the pad surface, there is a method of correcting the unevenness of the polishing pad using a correction plate. For example, Patent Document 1 proposes a method of flattening a pad surface by arranging a correction plate on a processing carrier so as to correct the unevenness of the polishing pad surface before or during the polishing step.

Also, as the polishing process is performed, the roughness of the pad surface is lost and the pad surface becomes smooth. As a result, the polishing ability of the pad surface is reduced, and the polishing rate in the polishing process is reduced. Here, the polishing rate is polishing efficiency, and is a value obtained by dividing the machining allowance by time. Such a decrease in the polishing rate can also be improved by correcting the pad surface to an appropriate roughness by the above-described correction method.
JP 2006-159352 A

  However, even if the polishing rate is recovered by the correction method described above, it cannot be fully restored, and the period until the recovered polishing rate decreases again is short, so the pad surface is frequently corrected in a short span. I had to do it. Since the pad surface is corrected by grinding the pad surface with the correction plate, the pad surface is scraped by frequently correcting the pad surface. As a result, the polishing pad becomes thinner and shorter in life.

  In view of such problems, the present invention provides a method for manufacturing a glass substrate for a magnetic disk capable of improving the polishing efficiency by effectively correcting the surface state of the polishing pad and thus improving the production efficiency. The purpose is that.

  The inventors of the present invention diligently studied to solve the above problems, and the reason why the polishing efficiency was lowered early in a short period of time was that the holding force for holding the free abrasive grains on the polishing surface of the polishing pad was sufficiently recovered. I thought it was because it was not. And the following causes were considered as a cause which a polishing pad cannot hold | maintain a loose abrasive grain.

  The soft polishing pad is composed of a base layer made of a nonwoven fabric or the like, a nap layer made up of an inner layer containing many independent bubbles and a surface layer in which the bubbles are opened. The bubble has a large bowl shape inside, and the nap hole on the surface layer is a fine opening. In the polishing step, the glass substrate is polished by holding free abrasive grains contained in the polishing liquid in the nap holes. In addition, the nap layer is a soft material having a small elastic force because it has bubbles inside.

  As the polishing is performed, the loose abrasive particles are worn and the polishing ability is lowered. Therefore, it is necessary to replace the loose abrasive particles facing the glass substrate with new ones. However, the loose abrasive grains gradually accumulate in the nap holes, and the free abrasive grains are clogged in the nap holes. In such a state, the nap hole could not be replaced with new free abrasive grains, and it was thought that the polishing efficiency would be reduced.

  One of the reasons why the polishing pad cannot hold loose abrasive grains is that the nap layer structure has fallen in the polishing direction in the polishing process, and even if the correction plate is rubbed in the same direction, It was thought that the free abrasive grains clogged with the material could not be removed.

  As another reason why the polishing pad cannot hold loose abrasive grains, the physical structure of the polishing pad surface layer is weakened in the grinding direction due to grinding using the correction plate. I thought that it was decreasing.

  Therefore, the inventors have further studied to perform a correction process so as to effectively remove clogging of the nap holes and not weaken the physical structure in the polishing direction, and have completed the present invention.

  That is, a typical configuration of the method for manufacturing a glass substrate for a magnetic disk according to the present invention is that a polishing liquid containing free abrasive grains is provided between a glass substrate and a polishing pad having a nap layer for polishing the main surface of the glass substrate. A polishing step of polishing by supplying and relatively moving the glass substrate and the polishing pad, and a correction member having the abrasive grains fixed to the correction surface, contacting the surface of the polishing pad with the polished glass substrate; A correction step of correcting the polishing pad by relatively moving the correction member and the polishing pad, and the movement direction of the glass substrate and the correction member relative to the polishing pad is different between the polishing step and the correction step. Features.

  In order to improve the polishing efficiency, the pad surface needs a holding force of the abrasive grains, and for this purpose, the pad surface needs to have an appropriate roughness. Especially when the polishing pad used for polishing is a soft pad, if the surface is rubbed against the glass substrate in the polishing process, the surface of the polishing pad may be oriented in the polishing direction (such as surface structure falling or clogging). it seems to do. Therefore, the directionality generated on the surface of the polishing pad can be dispersed in different directions by making the movement directions in the polishing process and the correction process different directions.

  Both the moving direction during the polishing step and the correction step include a rotation direction component, and the rotation direction component may be opposite between the polishing step and the correction step.

  The polishing process and the correction process have different purposes, but substantially the same operation is performed using the same apparatus except that the object is a glass substrate or a correction member. In either step, the object (glass substrate or correction member) and the polishing pad are continuously and relatively moved and rubbed, so that the rotational direction component in the relative movement direction. It becomes possible to draw an endless orbit by including. In the polishing process, the structure on the surface of the polishing pad is directional in the rotational direction. Therefore, the directionality generated on the surface of the polishing pad can be corrected by making the rotational direction component in the moving direction of the polishing pad in the correction process reverse.

  Said polishing pad is good to have a nap layer which consists of the inner layer which contained many independent air bubbles, and the surface layer which the air bubbles opened.

  By having the nap layer on the pad surface of the polishing pad, the polishing pad becomes a soft material having a small elastic force. Moreover, by having a nap hole that is an open bubble, free abrasive grains contained in the polishing liquid supplied during the polishing step can be retained, and the polishing efficiency is improved. Further, as described above, the directionality of the surface of the polishing pad is dispersed by changing the moving direction or rotation direction of the carrier, the correction member, the polishing pad, etc. in the direction different from the polishing process and the correction process or in the opposite direction ( It is also possible to remove loose abrasive grains accumulated (clogged) in the nap holes of the nap layer of the polishing pad.

  The glass substrate is engaged with a relatively rotating sun gear and an internal gear and is held by a carrier that moves in a planetary gear and is moved relative to the polishing pad. The gear may be meshed with the internal gear and may be moved relative to the polishing pad by moving the planetary gear.

  During the polishing process, the glass substrate can be moved in various different directions with respect to the polishing pad by holding the glass substrate on the revolving carrier while rotating by planetary gear motion, and can be polished evenly. Therefore, it is possible to reduce the occurrence of polishing marks and bias on the glass substrate. Similarly, during the correction process, the correction member can make a trajectory more complicated than the rotational movement in a certain direction by moving the correction member in a planetary gear. Therefore, the directionality of the polishing pad surface generated during the polishing process can be dispersed in more various directions.

  The relative rotation directions of the sun gear and the internal gear may be opposite in the polishing process and the correction process.

  With the above configuration, the relative movement direction of the polishing pad during the polishing process and during the correction process can be changed. Particularly, since the revolution of the carrier or the correction member becomes a rotation direction component centering on the sun gear, the rotation direction component (revolution direction) can be reversed by rotating in the reverse direction. Therefore, the directionality generated in the polishing process on the polishing pad surface can be efficiently corrected in the correction process.

  Said loose abrasive grain is good in a particle diameter being 80 nm or less. If the particle size of the loose abrasive grains is too large, a predetermined quality (roughness) cannot be obtained when the polishing process is performed. Therefore, the particle size of the free abrasive grains is preferably 80 nm or less. Further, such fine loose abrasive grains are easily clogged in the nap hole, but as described above, according to the present invention, the free abrasive grains accumulated in the nap hole can be efficiently removed.

  The abrasive grains fixed on the correction surface of the correction member may include diamond abrasive grains. Abrasive grains are used to modify the pad surface in a polishing pad modification process. The loose abrasive grains contained in the polishing liquid supplied to the polishing process are abrasive grains having high hardness such as silica abrasive grains. Accordingly, diamond abrasive grains are preferred because the abrasive grains should have a higher polishing ability than the free abrasive grains remaining on the polished polishing pad, that is, have a high hardness.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the manufacturing method of the glass substrate for magnetic discs which can improve polishing efficiency by modifying the surface state of a polishing pad efficiently, and can improve production efficiency by extension. is there.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiment are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  FIG. 1 is an explanatory diagram of a drive mechanism unit of a double-side polishing apparatus. As shown in FIG. 1, the double-side polishing apparatus 100 includes a carrier mounting portion having a sun gear 130 and an internal gear (hereinafter referred to as “internal gear 140”) that are rotationally driven at a predetermined rotation ratio, and the carrier. It has an upper surface plate 150 and a lower surface plate 160 that are driven in reverse rotation with respect to the mounting portion. Polishing pads 200 described later are attached to the surfaces of the upper surface plate 150 and the lower surface plate 160 facing the glass substrate 110, respectively. The carrier 120 is mounted so as to mesh with the sun gear 130 and the internal gear 140.

  FIG. 2 is an overall view of the double-side grinding apparatus. The lower surface plate 160 is fixedly installed in the vertical direction, and the upper surface plate 150 is configured to be movable up and down, and is pressed between the polishing pad 200 and the glass substrate 110 or the pad dresser 300 held by the carrier 120. be able to.

  In the polishing step, polishing is performed while supplying a polishing liquid (slurry) containing loose abrasive grains. The polishing liquid 420 stored in the container 410 is supplied to the upper surface plate 150 by the pump 430 and is collected from the lower surface plate 160 after being subjected to polishing, and is returned to the container 410 for circulation. A filter 440 that collects abrasive grains and polishing debris having a large particle diameter is provided at the outlet of the lower surface plate 160, the outlet from the pipe to the container 410, or the like. In the correction process, coolant (cooling water) is used instead of the polishing liquid 420.

  FIG. 3 is a view showing a carrier for a glass substrate. As shown in FIG. 3A, a plurality of small holes are provided in the carrier 120 having gears on the outer periphery on the lower surface plate 160, and the glass substrate 110 is held in these small holes. . By engaging the carrier 120 with the sun gear 130 and the internal gear 140 and rotating the sun gear 130 in the directions of the arrows, the carriers 120 revolve while rotating as planetary gears in the directions of the arrows. The sun gear 130 and the internal gear 140 need only be relatively rotated, and either one or both may rotate. The internal gear 140 causes the planetary gear movement of the carrier 120 as long as each speed is different from that of the sun gear 130. However, by rotating in the opposite direction to the sun gear 130, the carrier 120 is effectively rotated at a high speed. be able to.

  The upper surface plate 150 rotates with the sun gear 130, and the lower surface plate 160 rotates with the internal gear 140. In the present embodiment, by rotating the sun gear 130 and the internal gear 140 in the opposite directions, the upper surface plate 150 and the lower surface plate 160 rotate in the opposite directions. Even if the sun gear 130 and the internal gear 140 are rotated in the same direction, as long as the carrier 120 moves in a planetary gear, the upper surface plate 150 and the lower surface plate 160 Rotate counterclockwise.

  FIG. 3B is a cross-sectional view of the carrier 120 in FIG. The upper surface plate 150 is movable in the vertical direction with respect to the lower surface plate 160. As shown in FIG. 3B, the upper surface plate 150 and the lower surface plate 160 are each provided with the polishing pad 200 on the polishing surface. The polishing pad 200 is pressed against the main surfaces of the front and back surfaces of the glass substrate 110 with the carrier 120 sandwiched from above and below. Then, while supplying the polishing liquid (slurry) containing free abrasive grains, the planetary gear motion of the carrier 120 and the upper surface plate 150 and the lower surface plate 160 rotate in reverse to each other, whereby the glass substrate 110 and the polishing pad 200 are The main surfaces of the front and back surfaces of the glass substrate 110 are polished relative to each other.

  The double-side polishing apparatus 100 configured as described above uses a plurality of sets each including a set of loose abrasive grains contained in the polishing liquid and a polishing pad 200 that moves relative to the glass substrate 110 while being supplied with the polishing liquid. By this, in the manufacturing process of the glass substrate 110, it can be used for the main surface polishing of the glass substrate 110 which is performed a plurality of times stepwise. In examples described later, as a process of polishing the main surface of the glass substrate 110, two polishing processes of a preliminary polishing (primary polishing) process and a mirror polishing (secondary polishing) process are performed. In these steps, the configuration of the double-side polishing apparatus 100 is substantially the same, but the composition of the free abrasive grains contained in the polishing liquid used and the polishing pad 200 is different. As a general tendency, the grain size of the loose abrasive grains becomes smaller as the later process is performed, and the hardness of the polishing pad 200 becomes softer.

  FIG. 4 is an enlarged cross-sectional view illustrating the configuration of the polishing pad. The polishing pad 200 is made of a synthetic resin foam such as polyurethane or polyester. In particular, polyurethane foam is preferred at present.

  FIG. 4A is an enlarged cross-sectional view illustrating the state of the polishing pad before the polishing process. The polishing pad 200 includes a base layer 210 made of a nonwoven fabric or the like, and a nap layer 220 laminated on the surface of the base layer 210. . The nap layer 220 includes an inner layer 220a in which a large number of independent bubbles 230 are present, and a surface layer 220b in which the bubbles 230 are opened. The bubbles 230 are formed in a bowl shape in the thickness direction of the nap layer 220 (a shape in which the cross-sectional area on the back side increases and the cross-sectional area decreases as it goes to the surface layer side). Called. The hardness of the polishing pad 200 can be adjusted by the amount of bubbles 230 to be mixed. Further, the nap hole 230a holds loose abrasive grains and can effectively polish the main surface of the glass substrate 110.

  FIG. 4B is an enlarged cross-sectional view for explaining the state of the polishing pad after the polishing step. In the polishing pad after the polishing process, the loose abrasive grains 240 contained in the polishing liquid are clogged with the nap holes 230a and the bubbles 230. Further, the nap layer 220 is deformed in the oblique direction by the pressure applied by the upper surface plate 150 and the lower surface plate 160 during the polishing process, and the opening width of the nap hole 230a in the surface layer of the nap layer 220 is narrowed.

  When the polishing pad 200 is in the above-described state, the bubbles 230 are clogged, and the nap layer 220 loses flexibility, making it difficult to perform precise mirror polishing. Further, since the nap hole 230 cannot hold new loose abrasive grains and the opening width of the nap hole 230a is narrowed, directionality occurs on the surface of the polishing pad and the surface becomes smooth. For this reason, a polishing rate falls remarkably, and it will become impossible to perform desired grinding | polishing within a predetermined processing time. Therefore, as described in the prior art, the polishing pad surface is rubbed with a correction member to recover the polishing ability. However, in the prior art, since the restoration is not complete and the period until the recovered polishing rate is lowered again is short, the pad surface must be frequently corrected in a short span.

  Therefore, in this embodiment, the polishing surface of the polishing pad 200 is corrected by the method described below to improve the polishing efficiency.

  FIG. 5 is a view showing a pad dresser which is an example of a correction member. A carrier 310 shown in FIG. 5A has a configuration that can replace the carrier 120 shown in FIG. That is, the fixed abrasive grains 330 that are held by the carrier 310 having a gear on the outer periphery and fixed on the SUS substrate may be attached to the upper and lower sides of the metal core material 320 such as SUS. Alternatively, although not shown, abrasive grains may be directly supported on the surface of the core material. Moreover, although the fixed abrasive grains 330 are illustrated as disk-shaped ones, arc-shaped or rectangular ones can be used.

  The fixed abrasive grains 330 are attached along the outer periphery of the core material 320. The central part of the core material 320 is a circular cavity, and the fixed abrasive grains 330 are not pasted. In the present embodiment, the core material 320 to which the fixed abrasive grains 330 are affixed is used as the pad dresser 300 and is inserted into the hole of the carrier 310. However, the pad dresser 300 and the carrier 310 are integrated. Also good. Since the free abrasive grains 240 supplied during the polishing process are considered to remain on the polishing pad 200 after the polishing process, the fixed abrasive grains 330 should have a higher hardness than the free abrasive grains 240. Examples thereof include diamond abrasive grains.

  The fixed abrasive grains 330 are not provided on the entire surface of the pad dresser 300. This is because if it is provided on the entire surface, the frictional force becomes too large when it comes into contact with the polishing pad 200, and the pad dresser 300 cannot be rotated with respect to the polishing pad 200, and the pad surface of the polishing pad 200 is corrected. This is because the purpose cannot be achieved. In addition, since it is not necessary to cover the entire surface of the pad dresser 300 with the fixed abrasive grains 330, there is an advantage of saving diamond abrasive grains and other material costs.

  Moreover, the thickness of the position where the fixed abrasive grains 330 are provided preferably has a thickness equal to or larger than that of the glass substrate 110 shown in FIG. The reason why the pad dresser 300 has such a thickness is to increase the correction capability of the pad dresser 300. In the case of a double-side polishing machine having an upper surface plate 150 and a lower surface plate 160, the greater the thickness of the object to be processed that is sandwiched between them, the greater the bending strength, so that processing is easier. The same applies when the upper surface plate 150 and the lower surface plate 160 are corrected by the pad dresser 300. The thicker the pad dresser 300, the higher the correction capability. That is, undulation generated by processing a thin workpiece such as the glass substrate 110 can be reduced by processing a thicker target than the workpiece.

  While supplying the coolant (coolant), the correction surface of the pad dresser 300 having such a thickness and the pad surface of the polishing pad 200 provided on the upper surface plate 150 and the lower surface plate 160 are pressed against each other. By making it slide, the smoothness of the grinding surfaces of the upper and lower surface plates 150, 160 can be enhanced.

  FIG. 5B is a diagram showing that the pad dresser 300 can be replaced with the carrier 120. The carrier 120 can be used as a planetary gear when the glass substrate 110 is polished, and the pad dresser 300 shown in FIG. 5A can be used as a planetary gear instead of each carrier 120 when the polishing pad is corrected.

  FIG. 6 is a view showing a state in which a pad dresser is attached to the double-side polishing apparatus. FIG. 6A is a plan view. In this manner, the carrier 120 of the glass substrate 110 to be polished can be replaced with the pad dresser 300.

  FIG. 6B is an XX cross-sectional view of the pad dresser 300 of FIG. When the polishing pad is corrected, the pad dresser 300 replaced with the carrier 120 is sandwiched between the upper surface plate 150 and the lower surface plate 160 on which the polishing pad 200 is provided, as in the case of polishing. Then, the polishing pad 200 provided on the upper surface plate 150 and the lower surface plate 160 and the fixed abrasive grains 330 of the pad dresser 300 are pressed against each other and slid.

  Here, as a characteristic configuration of the present embodiment, the relative movement direction of the polishing pad 200 and the carrier 120 during the polishing process and the relative movement direction of the polishing pad 200 and the pad dresser 300 during the correction process are different directions. Or the relative rotation direction of the sun gear 130 and the internal gear 140 during the polishing process and the relative rotation direction of the sun gear 130 and the internal gear 140 during the correction process are reversed. The pad surface of the polishing pad 200 can be efficiently modified.

  FIG. 7 is a diagram for explaining the movement direction of the drive mechanism member of the double-side polishing apparatus during the polishing process and during the correction process. Here, in the double-side polishing apparatus 100, since the upper surface plate 150 is joined to the sun gear 130, it rotates in the rotation direction of the sun gear 130. Further, since the lower surface plate 160 is joined to the internal gear 140, it rotates in the rotation direction of the internal gear 140. Further, the polishing pad 200 rotates in the rotation direction of the respective surface plates 150 and 160 attached thereto.

  FIG. 7A is a diagram showing the relative movement direction of the polishing pad and the carrier (glass substrate) during the polishing process. During the polishing process, when the sun gear 130 (upper surface plate 150) rotates counterclockwise (counterclockwise), the polishing pad 200 provided on the upper surface plate 150 also rotates in the same direction, and the carrier 120 is sun-heated. While revolving counterclockwise around the gear 130, it rotates clockwise (clockwise). At this time, the internal gear 140 (lower surface plate 160) rotates clockwise, and the polishing pad 200 provided on the lower surface plate 160 also rotates in the same direction. Accordingly, the moving direction of the glass substrate 110 (considering the lower surface plate 160 as a reference) is a superposition of the counterclockwise rotation direction component due to revolution and the radial repetition direction component due to rotation.

  FIG.7 (b) is a figure which shows the relative moving direction of the polishing pad and pad dresser (fixed abrasive grain) at the time of a correction process. At the time of the correction process, the relative movement direction of the polishing pad 200 and the pad dresser 300 is set to be opposite (different) from that at the time of the polishing process. That is, during the correction process, the sun gear 130 (upper surface plate 150) is rotated clockwise. Then, the polishing pad 200 provided on the upper surface plate 150 also rotates in the same direction, and the pad dresser 300 rotates counterclockwise while revolving clockwise around the sun gear 130. At this time, the internal gear 140 (lower surface plate 160) rotates counterclockwise, and the polishing pad 200 provided on the lower surface plate 160 also rotates in the same direction. Accordingly, the moving direction of the glass substrate 110 (considering the lower surface plate 160 as a reference) is a superposition of the clockwise rotational direction component due to revolution and the radial direction component due to rotation.

  With the above configuration, the relative movement direction of the polishing pad 200 and the glass substrate 110 during the polishing process and the relative movement direction of the polishing pad 200 and the fixed abrasive grains 330 during the correction process are different from each other. can do. In particular, if attention is paid to the rotational direction component, the moving direction during the polishing process and during the correction process can be reversed. Accordingly, by dispersing the directionality (such as surface structure collapse or clogging) generated in the nap layer 220 of the polishing pad 200 in the polishing process, the retention force of the free abrasive grains on the pad surface is corrected, and the polishing ability and flexibility are improved. Can be fully recovered. Further, since the physical structure in the polishing direction is not weakened by the correction process, there is no possibility of reducing the holding power of the free abrasive grains.

  Thus, by efficiently correcting the surface state of the polishing pad, it is possible to improve the polishing efficiency and thus improve the production efficiency.

[Example]
Examples of the manufacturing method of the magnetic disk glass substrate to which the present invention is applied will be described below. This glass substrate for magnetic disk and magnetic disk are 0.8 inch type disk (inner diameter 6 mm, outer diameter 21.6 mm, plate thickness 0.381 mm), 1.0 inch type disk (inner diameter 7 mm, outer diameter 27.4 mm, It is manufactured as a magnetic disk having a predetermined shape such as a plate thickness of 0.381 mm) and a 1.8 inch type magnetic disk (inner diameter of 12 mm, outer diameter of 48 mm, plate thickness of 0.508 mm). Further, it may be manufactured as a 2.5 inch type disc or a 3.5 inch type disc.

(1) Shape processing step and lapping step In the method for manufacturing a magnetic disk glass substrate according to this example, first, the surface of the plate-like glass is lapped (ground) to obtain a glass base material. Cut the glass disc. Various plate glasses can be used as the plate glass. This plate-like glass can be manufactured by using a known manufacturing method such as a press method, a float method, a downdraw method, a redraw method, or a fusion method using a molten glass as a material. Of these, plate glass can be produced at low cost by using the pressing method. As the material of the plate glass, amorphous glass or glass ceramics (crystallized glass) can be used. As the material for the plate glass, aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used. In particular, as an amorphous glass, an aluminosilicate glass can be preferably used in that it can be chemically strengthened and a magnetic disk substrate excellent in flatness of the main surface and substrate strength can be supplied.

In this example, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper mold, a lower mold, and a barrel mold to obtain an amorphous plate glass. As the aluminosilicate _glass, SiO 2: 58 to 75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: 3 to 10 _wt%, Na 2 O: 4 to 13 principal component weight% The chemically strengthened glass contained as was used.

  Next, both main surfaces of the plate glass were lapped to form a disk-shaped glass base material. This lapping process was performed using alumina free abrasive grains with a double-sided lapping apparatus using a planetary gear mechanism. Specifically, the lapping platen is pressed from above and below on both sides of the plate glass, a grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relatively to perform lapping. went. By this lapping process, a glass base material having a flat main surface was obtained.

(2) Cutting process (coring, forming, chamfering)
Next, the glass base material was cut using a diamond cutter, and a disk-shaped glass substrate was cut out from the glass base material. Next, using a cylindrical diamond drill, an inner hole was formed in the center of the glass substrate to obtain an annular glass substrate (coring). Then, the inner peripheral end face and the outer peripheral end face were ground with a diamond grindstone and subjected to predetermined chamfering (forming, chamfering).

(3) Second Lapping Step Next, a second lapping process was performed on both main surfaces of the obtained glass substrate in the same manner as in the first lapping step. By performing this second lapping step, it is possible to remove in advance the fine unevenness formed on the main surface in the cutting step and end surface polishing step, which are the previous steps, and shorten the subsequent polishing step on the main surface. Will be able to be completed in time.

(4) End surface grinding | polishing process Next, mirror polishing was performed with the brush grinding | polishing method about the outer peripheral end surface of the glass substrate. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used.

  And the glass substrate which finished the end surface grinding | polishing process was washed with water. By this end face polishing step, the end face of the glass substrate was processed into a mirror state that can prevent the precipitation of sodium and potassium. In particular, the inner peripheral end face was in a good state without a decrease in tolerance and roundness of the inner hole even when a large number of about 200 to 300 sheets were laminated and polished.

(5) Main surface first polishing step As the main surface polishing step, first, a first polishing step was performed. This first polishing step is mainly intended to remove scratches and distortions remaining on the main surface in the lapping step described above. In the first polishing step, the main surface was mirror-polished using a hard resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains were used. The surface roughness of the main surface of the glass substrate after the first polishing step was an arithmetic average roughness Ra = 0.8 nm and a maximum height Rv = 10 nm.

  The glass substrate which finished this 1st grinding | polishing process was immersed in each washing tank of neutral detergent, a pure water, and IPA (isopropyl alcohol) one by one, and was wash | cleaned.

(6) Main surface second polishing step Next, a second polishing step was performed as the main surface polishing step. The second polishing step is the polishing step described above, and aims to finish the main surface in a mirror shape.

  FIG. 8 is a flowchart showing a processing flow of the second polishing step. When grinding the glass substrate, first, a pasting step of pasting the polishing pad 200 on the upper surface plate 150 and the lower surface plate 160 is performed using the above-described double-side polishing apparatus having the planetary gear mechanism (step S400). The polishing pad 200 was a soft foamed resin polisher having an Asker C hardness of 75.

  Next, an initial correction process for grinding the surface of the polishing pad 200 using the pad dresser 300 is performed (step S410). The reason for performing the initial correction is that flatness and smoothness are insufficient on the pad surface simply by attaching to the surface plate.

  Thereafter, a polishing process is performed to polish the main surface of several tens of batches of glass substrates (step S420). As the free abrasive grains, colloidal silica having a particle diameter of 20 nm finer than the cerium oxide abrasive grains used in the first polishing step was used.

  Then, in order to correct the smoothness of the polishing pad 200 lowered in the polishing process, a correction process of the surface plate was performed between the batches of the polishing process using the pad dresser 300 and the coolant (step S430). The correction process was performed for 30 minutes at a processing load of 100 kg and a platen rotation speed of 20 rpm. Here, as described above, the upper surface plate 150, the lower surface plate 160, the sun gear 130, and the internal gear 140 during the correction process were all rotated in the direction opposite to that during the polishing process.

  The glass substrate which finished this 2nd grinding | polishing process was immersed in each washing tank of neutral detergent, a pure water, and IPA (isopropyl alcohol) sequentially, and was wash | cleaned. Note that ultrasonic waves were applied to each cleaning tank.

[Evaluation]
As a comparative example, the upper surface plate 150, the lower surface plate 160, the sun gear 130, and the internal gear 140 at the time of the correction process were all rotated in the same direction as at the time of the polishing process. The processing load, the surface plate rotation speed, and the processing time at this time are the same as in the embodiment. FIG. 9 is a diagram for explaining a comparison between the example and the comparative example. FIG. 9A illustrates a polishing rate according to the example, and FIG. 9B illustrates a polishing rate according to the comparative example. FIG. 9 (c) is a diagram for comparing the fine swells of the example and the comparative example.

  In FIG. 9A showing the embodiment, the polishing rate is rather increased in the first few batches, and the decrease in the polishing rate starts around 5 batches. On the other hand, in FIG. 9B showing the comparative example, the polishing rate is decreasing from the beginning.

  As described above, the polishing rate is increased in the examples because the moving direction is different between the polishing process and the correction process, so that clogging of the nap holes can be effectively removed and the polishing direction is increased. This is probably because the physical structure is not weakened. That is, in the first few batches of the polishing process, it is considered that the polishing rate increases as the nap holes are gradually filled with loose abrasive grains. And, when the filled free abrasive grains start to wear, it is considered that the polishing rate decreases again. On the other hand, in the comparative example, clogging of the nap hole has not been removed and the physical structure in the polishing direction has become weak, and the holding power of the free abrasive grains has been lost from the beginning (not recovered). For this reason, it is considered that the polishing rate is only decreasing.

  FIG. 9C shows the distribution of the root mean square roughness Rq of micro swell (MicroWave) in the example and the comparative example. According to FIG.9 (c), compared with a comparative example, the direction of an Example has many small undulations with small Rq, and it can confirm that it is mirror-polished more effectively.

(7) Chemical strengthening process Next, the glass substrate was chemically strengthened. For chemical strengthening, first prepare a powdered chemical strengthening salt mixed with potassium nitrate (60%) and sodium nitrate (40%) as a solid chemical strengthening salt, put it into a salt charging container, and heat it with an electromagnetic wave generator. Melted.

  Thus, lithium ions and sodium ions in the glass substrate were replaced with sodium ions and potassium ions in the chemical strengthening solution, respectively, and the glass substrate was strengthened.

  The glass substrate that had been subjected to the chemical strengthening treatment was immersed in a 20 ° C. water bath and rapidly cooled, and maintained for about 10 minutes. And the glass substrate which finished quenching was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned. Further, the glass substrate after the sulfuric acid cleaning was cleaned by immersing in a cleaning bath of pure water and IPA (isopropyl alcohol) sequentially.

  As described above, a flat and smooth, high-rigidity glass substrate for a magnetic disk is obtained by performing a lapping process, a cutting process, a grinding process, an end face polishing process, first and second polishing processes, and a chemical strengthening process. Obtained.

(8) Magnetic disk manufacturing process On both surfaces of the glass substrate obtained through the above-described processes, an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoTaZr-based alloy, an underlayer made of Ru, and a CoCrPt group on the surface of the glass substrate A perpendicular magnetic recording disk was manufactured by sequentially forming a perpendicular magnetic recording layer made of an alloy, a protective layer made of hydrogenated carbon, and a lubricating layer made of perfluoropolyether. Although this configuration is an example of a configuration of a perpendicular magnetic disk, a magnetic layer or the like may be configured as an in-plane magnetic disk.

  As mentioned above, although the suitable Example of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this embodiment. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  The present invention can be used in a method for manufacturing a magnetic disk glass substrate.

It is explanatory drawing of the drive mechanism part of a double-side polish apparatus. 1 is an overall view of a double-side grinding apparatus. It is a figure which shows the carrier for glass substrates. It is an expanded sectional view explaining the composition of a polishing pad. It is a figure which shows the pad dresser which is an example of a correction member. It is a figure which shows the state which mounted | wore the double-side polish apparatus with the pad dresser. It is a figure explaining the moving direction at the time of the grinding | polishing process and correction process of the drive mechanism member of a double-side polish apparatus. It is a flowchart which shows the flow of a process of a 2nd grinding | polishing process. It is a figure explaining the comparison of an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Double-side polish apparatus, 110 ... Glass substrate, 120 ... Carrier, 130 ... Sun gear, 140 ... Internal gear, 150 ... Upper surface plate, 160 ... Lower surface plate, 200 ... Polishing pad, 210 ... Base layer, 220 ... Nap layer 220a ... inner layer, 220b ... surface layer, 230 ... bubbles, 230a ... nap hole, 240 ... free abrasive grains, 300 ... pad dresser, 310 ... carrier, 320 ... core material, 330 ... fixed abrasive grains, 410 ... container, 420 ... Polishing liquid, 430 ... pump, 440 ... filter

Claims (7)

By supplying a polishing liquid containing free abrasive grains between a glass substrate and a polishing pad having a nap layer for polishing the main surface of the glass substrate, and relatively moving the glass substrate and the polishing pad A polishing step for polishing;
The polishing pad is corrected by moving the correction member and the polishing pad relative to each other by bringing a correction member having polishing grains fixed on the correction surface into contact with the surface of the polishing pad on which the glass substrate has been polished. A correction process to
A method for manufacturing a glass substrate for a magnetic disk, wherein the moving direction of the glass substrate and the correction member relative to the polishing pad is different between the polishing step and the correction step.   The moving direction during the polishing step and during the correction step includes a rotational direction component, and the rotational direction component is opposite between the polishing step and the correction step. Manufacturing method of glass substrate for magnetic disk.   3. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the polishing pad has a nap layer composed of an inner layer containing a large number of independent bubbles and a surface layer in which the bubbles are opened. The glass substrate is moved relative to the polishing pad by being held by a carrier that meshes with a relatively rotating sun gear and an internal gear and performs planetary gear motion,
4. The correction member according to claim 1, wherein the correction member meshes with a relatively rotating sun gear and an internal gear and is moved relative to the polishing pad by moving as a planetary gear. 5. The manufacturing method of the glass substrate for magnetic disks of description.   5. The magnetism according to claim 1, wherein a relative rotation direction of the sun gear and the internal gear is opposite in the polishing process and the correction process. 6. A method for producing a glass substrate for a disk.   The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 5, wherein the loose abrasive has a particle diameter of 80 nm or less.   The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the abrasive grains fixed on the correction surface of the correction member include diamond abrasive grains.

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