JP5345425B2 - Manufacturing method of glass substrate and manufacturing method of magnetic recording medium - Google Patents

Description

  The present invention relates to a glass substrate manufacturing method, a glass substrate manufactured by a glass substrate manufacturing method, and a magnetic recording medium.

  In recent years, with the advancement of information technology, information recording technology, particularly magnetic recording technology, has made remarkable progress.

  An aluminum substrate has been widely used as a substrate for a magnetic recording medium such as an HDD (Hard Disk Drive) which is one of such magnetic recording techniques.

  However, with the downsizing, thinning, and high-density recording of magnetic disks, in recent years, there has been an increasing demand for glass substrates that have superior substrate surface flatness and substrate strength compared to aluminum substrates.

  Conventionally, for example, as shown in paragraph [0004] of Patent Document 1, a glass substrate is chamfered by forming glass into a disk shape, and end faces and main surfaces are polished, and then impact resistance and vibration resistance are obtained. It has been manufactured by applying a chemical strengthening treatment for improving (Patent Document 1).

  In the chemical strengthening step for performing the chemical strengthening treatment, for example, as described in [0014] of Patent Document 1, the glass substrate to be treated is immersed in the chemical strengthening solution, and the glass substrate and the chemical strengthening solution are ion-exchanged. Is done by letting

  On the other hand, since chemical strengthening is also a process of replacing ions contained in glass with ions having a larger ion radius, the size and shape of the glass substrate change when chemical strengthening is performed.

  For this reason, there is a growing demand for higher recording density of magnetic disks, and as a result, stricter dimensional accuracy is required for glass substrates. As shown in [0012] of Patent Document 1, chemical strengthening is required. In some cases, the main surface of the glass substrate may be polished after the above.

Japanese Unexamined Patent Publication No. 2000-076652

  Here, in the manufacturing method in which polishing is performed after chemical strengthening, the chemically strengthened layer is scraped by polishing, and therefore the chemical strengthened layer in the manufactured glass substrate is likely to be thinner than in the manufacturing method in which chemical strengthening is performed after polishing.

  When the chemically strengthened layer becomes thin, unevenness in the thickness of the chemically strengthened layers on the two main surfaces tends to be prominent when the polishing amounts of the two main surfaces differ in the polishing step.

  Therefore, the glass substrate is warped due to non-uniformity of the thickness of the chemically strengthened layers on the two main surfaces, which may lead to deterioration of dimensional accuracy. It is necessary to manufacture more carefully.

  Here, the change in flatness of the glass may inevitably change depending on factors such as replacement of the polishing pad used for polishing.

  However, Patent Document 1 does not consider such an unavoidable change in flatness, and when the change in flatness occurs, the flatness cannot be quickly suppressed.

  The present invention has been made in view of the above problems, and its purpose is to quickly suppress the change in flatness when the flatness of the glass substrate changes even when polishing is performed after chemical strengthening. An object of the present invention is to provide a method for manufacturing a glass substrate.

  In order to solve the above problems, the present invention has the following configuration.

(Configuration 1) Step (a) of performing chemical strengthening by immersing a glass base material in a chemical strengthening solution that is a solution containing ions and replacing ions on the surface of the glass base material with ions of the chemical strengthening solution. And a step (b) of polishing the main surface of the glass substrate subjected to the chemical strengthening, wherein the flatness of the main surface of the glass substrate polished last time is a constant value. A method for producing a glass substrate, comprising: a step of performing polishing by changing polishing conditions when polishing the glass substrate after the next time when it is detected that the glass substrate is exceeded.

(Configuration 2) Before the step (a), the change in polishing conditions is measured to measure the change in flatness of the main surface of the glass substrate when the main surface of the glass substrate is polished. A step (c) of obtaining in advance data on the amount of change in flatness of the glass, wherein the step (b) detects that the flatness of the main surface of the glass substrate polished last time exceeds a certain value. In addition, based on the data, when polishing the glass substrate after the next time, the polishing condition is selected such that the flatness of the main surface of the glass substrate is close to 0, and the polishing condition is changed. A method for producing a glass substrate according to Configuration 1, which is a step of polishing.

(Configuration 3) The step (b) is a step of wet-polishing the glass substrate in batch units using a polishing pad, and the flatness of the main surface of the glass substrate of the batch polished last time is constant. Polishing so that the flatness of the main surface of the glass substrate is close to 0 when the glass substrate after the next batch is polished based on the data when it is detected that the value has been exceeded. The method for producing a glass substrate according to Configuration 2, wherein the polishing is performed by selecting conditions and changing the polishing conditions.

(Configuration 4) The glass substrate manufacturing method according to Configuration 3, wherein the polishing conditions include at least one of the number of rotations of the polishing pad, the pressure during polishing, and the flow rate of a polishing liquid used for polishing. Method.

(Structure 5) A glass substrate manufactured by the method for manufacturing a glass substrate according to any one of Structures 1 to 4.

(Structure 6) A magnetic recording medium comprising the glass substrate according to Structure 5 and an underlayer, a magnetic layer, a protective layer, and a lubricating layer provided on the glass substrate.

  According to the present invention, there is provided a method for manufacturing a glass substrate capable of quickly suppressing a change in flatness when the flatness of the glass substrate changes even when polishing is performed after chemical strengthening. Can do.

1A is a plan view of the glass substrate 1, FIG. 1B is a cross-sectional view taken along the line AA of FIG. 1A, and FIG. 1C is a cross-sectional view showing the magnetic recording medium 100. It is a figure which shows the outline of the manufacturing method of the glass substrate. 3 is a flowchart illustrating an outline of a method for manufacturing the glass substrate 1. 2 is a cross-sectional view showing a grinding device 21. FIG. It is a perspective view which shows the chemical strengthening apparatus 51. FIG. 2 is a block diagram showing a configuration of a polishing system 61. FIG. It is sectional drawing which shows the grinding | polishing apparatus 21a. It is a figure which shows the relationship between polishing conditions and the flatness of the glass base material 1a. It is a flowchart which shows the detail of step 107 of FIG. It is a figure which shows the flatness of the glass base material 1a for every batch.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  First, with reference to FIG. 1, the structure of the glass substrate 1 manufactured using the manufacturing method of the glass substrate 1 concerning this embodiment is demonstrated easily.

  As shown in FIG. 1A, the glass substrate 1 has a main body 3 having a disc shape, and an inner hole 5 is formed at the center of the main body 3.

  As shown in FIG. 1B, the main body 3 has substantially smooth main surfaces 7a and 7b.

  The main surfaces 7a and 7b are surfaces on which a layer for recording / reproducing information is formed. For example, as shown in FIG. 1C, one or both of the main surfaces 7a and 7b are provided with an underlayer 18a and magnetic layers. By providing the layer 18b, the protective layer 18c, and the lubricating layer 18d, the glass substrate 1 becomes the magnetic recording medium 100 (at least the magnetic layer 18b is necessary as a recording layer).

  The main body 3 has an inner peripheral end surface 11 and an outer peripheral end surface 9 which are orthogonal to the main surfaces 7a and 7b.

  The inner peripheral end face 11 and the outer peripheral end face 9 are chamfered, and an inner peripheral chamfered face 13 and an outer peripheral chamfered face 15 are provided, respectively.

  Furthermore, the chemical strengthening layer 17 is formed on the surface of the main body 3.

  Although details of the chemical strengthening layer 17 will be described later, for example, a part of the glass ions used as the raw material of the glass substrate 1 is replaced with ions having a larger ion radius to form a compressive stress layer.

  Next, with reference to FIGS. 2-10, the manufacturing method of the glass substrate 1 concerning this embodiment is demonstrated.

  In the following description, the glass in the manufacturing process is referred to as “glass substrate 1a”, and the finished product is referred to as “glass substrate 1”.

  First, an outline of the manufacturing method will be briefly described with reference to FIG.

  First, glass as a raw material is processed to produce a disk-shaped glass substrate 1a as shown in FIG.

  Next, the glass substrate 1a is chemically strengthened to form a compressive stress layer on the surface.

  Next, the main surfaces 7a and 7b of the glass substrate 1a subjected to chemical strengthening are polished to be substantially smooth.

  Here, as is apparent from FIG. 2, the present embodiment is a manufacturing method in which the main surfaces 7a and 7b are polished after chemically strengthening the glass substrate 1a, and polishing is performed after chemical strengthening.

  Next, a specific manufacturing method will be described with reference to FIGS.

  First, as shown in FIG. 3, glass as a raw material is formed into a disk shape to produce a glass substrate 1a (step 101).

  Examples of the glass used as a raw material include soda lime glass, aluminosilicate glass, borosilicate glass, and crystallized glass produced by a float method, a downdraw method, a redraw method, or a press method.

  In the following embodiments, glass manufactured by a press method will be described as an example.

  Next, as shown in FIG. 3, the main surfaces 7a and 7b are ground (first lapping) in order to adjust the plate thickness of the glass substrate 1a (step 102).

  Here, an example of the structure of the grinding apparatus 21 used for grinding and an example of the grinding method will be briefly described with reference to FIG.

  As shown in FIG. 4, the grinding device 21 meshes with the sun gear 23, the internal gear 25 arranged concentrically on the outer side thereof, the sun gear 23 and the internal gear 25, and the sun gear 23 and the internal gear A carrier 27 that revolves and rotates according to the rotation of the gear 25, an upper surface plate 29 and a lower surface plate 31 that can sandwich the glass substrate 1 a held by the carrier 27, and an upper surface plate 29 and a lower surface plate 31. A polishing liquid supply unit (not shown) for supplying a polishing liquid therebetween is provided.

  At the time of grinding, the grinding device 21 sandwiches the glass substrate 1a held by the carrier 27 between the upper surface plate 29 and the lower surface plate 31, and between the upper surface plate 29 and the lower surface plate 31 and the glass substrate 1a. While supplying the polishing liquid, the carrier 27 revolves and rotates according to the rotation of the sun gear 23 and the internal gear 25, whereby the upper and lower surfaces (main surfaces 7a, 7b) of the glass substrate 1a are ground.

  As the polishing liquid, for example, a slurry obtained by dispersing abrasive grains such as alumina in water is used.

  Next, as shown in FIG. 3, the inner hole 5 (see FIG. 1) is formed in the center of the glass substrate 1a (step 103).

  The inner hole 5 is formed using, for example, a core drill.

  When sheet glass is used, steps 101 to 103 are not performed. Instead, a process of cutting the glass from the sheet shape into a disk shape using a cutter and further cutting the inner hole 5 (cutting process) is performed.

  Next, as shown in FIG. 3, the inner peripheral end face 11 and the outer peripheral end face 9 are chamfered to remove cracks on the end face of the glass substrate 1a (step 104). The chamfering is performed using, for example, a grindstone to which diamond abrasive grains are attached.

  In addition, you may add the process of grinding (2nd lapping) main surface 7a, 7b after chamfering. Thereby, the unevenness | corrugation produced by formation and chamfering of the inner hole 5 can be ground, and the burden at the time of grinding | polishing can be reduced.

  Next, as shown in FIG. 3, the inner peripheral end face 11 and the outer peripheral end face 9 of the glass substrate 1a are polished, that is, end face polishing is performed (step 105).

  The end surface polishing is performed using, for example, a rotating brush.

  Next, as shown in FIG. 3, the glass substrate 1a is chemically strengthened to form the chemically strengthened layer 17 (step 106).

  Here, an example of the structure of the chemical strengthening apparatus 51 used for chemical strengthening and an example of the chemical strengthening method will be briefly described with reference to FIG.

  As shown in FIG. 5, the chemical strengthening apparatus 51 includes a holder 53 that holds the glass substrate 1 a and a treatment tank 57 that is filled with a chemical strengthening solution 59.

  The holder 53 is provided with a holding portion 55 for holding the glass substrate 1a.

  As is clear from FIG. 5, the chemical strengthening apparatus 51 has a structure in which the glass substrate 1a is chemically strengthened in batch units for every several tens to 100 sheets, but the present invention is a process in batch units. It is not limited to.

  When chemically strengthening the glass substrate 1 a using the chemical strengthening device 51, first, the glass substrate 1 a is accommodated in the holder 53 by hooking the glass substrate 1 a on the holding portion 55, and the holder 53 and the inside of the treatment tank 57 are contained. The glass substrate 1a is immersed in the chemical strengthening liquid 59.

  The composition of the chemical strengthening liquid 59 is, for example, a mixture of potassium nitrate, sodium nitrate, or the like alone or in combination.

  The temperature of the chemical strengthening liquid 59 is preferably about 50 to 150 ° C. lower than the strain point of the material of the glass substrate 1a, and more preferably the temperature of the chemical strengthening liquid 59 itself is about 350 to 400 ° C.

  When the glass substrate 1a is immersed in the chemical strengthening solution 59, ions contained in the chemical strengthening solution 59 and ions contained in the glass substrate 1a are ion-exchanged.

  Specifically, for example, lithium ions and sodium ions contained in the glass substrate 1a are exchanged with sodium ions and potassium ions contained in the chemical strengthening solution 59, respectively.

  At this time, when ion exchange occurs with ions having a larger ion radius than the ions contained in the glass substrate 1a, the chemically strengthened layer 17 becomes a compressive stress layer, and the strength of the surface of the glass substrate 1a increases.

  Next, after chemical strengthening is completed, the glass substrate 1a is washed to remove the surface chemical strengthening solution, and then, as shown in FIG. 3, the flatness and surface roughness of the main surfaces 7a and 7b of the glass substrate 1a. In order to adjust the thickness (substantially smooth), the main surfaces 7a and 7b are polished (step 107).

  Here, the configuration of the polishing system 61 used in step 107 will be described with reference to FIGS.

  As shown in FIG. 6, the polishing system 61 includes a polishing device 21a for polishing the glass substrate 1a and a flatness measuring device 63 (basic for measuring the flatness (of the main surfaces 7a and 7b) of the polished glass substrate 1a. In this case, the stand-alone type is independent of the polishing apparatus, and the integrated type with the polishing apparatus is preferable. A determination unit 66 for setting polishing conditions to be described later is connected to the polishing device 21a and the flatness measuring device 63. The determination unit 66 is a CPU (Central Processing Unit) or the like.

  The determination unit 66 is connected to a data storage unit 69 in which data 71 indicating a relationship between polishing conditions described later and flatness (of the main surfaces 7a and 7b) is stored. The data storage unit 69 is a semiconductor memory / hard disk device or the like, which is an external storage device.

  Here, an example of the structure of the polishing apparatus 21a used for polishing and an example of the polishing method will be briefly described with reference to FIG.

  The structure of the polishing device 21a is the same as that of the grinding device 21, but a polishing pad 33 is attached to the upper surface plate 29 and the lower surface plate 31, as shown in FIG.

  During the polishing process, the polishing apparatus 21a sandwiches the glass substrate 1a held by the carrier 27 between the upper surface plate 29 and the lower surface plate 31, and supplies the polishing liquid between the polishing pad 33 and the glass substrate 1a. However, when the carrier 27 revolves and rotates according to the rotation of the sun gear 23 and the internal gear 25, the upper and lower surfaces (main surfaces 7a and 7b) of the glass substrate 1a are polished (wet polishing).

  The polishing pad 33 is preferably a polishing pad of a soft polisher. The polishing pad 33 preferably has an Asker C hardness of 60 to 80. The contact surface of the polishing pad 33 with the glass substrate 1a is preferably made of a foamed resin having foamed pores, particularly foamed polyurethane. When polishing is performed in this manner, the main surfaces 7a and 7b of the glass substrate 1a can be polished into a smooth mirror surface.

  As the polishing liquid, for example, a slurry obtained by dispersing abrasive grains such as cerium oxide or lanthanum oxide in water is used.

  Next, data 71 indicating the relationship between polishing conditions and flatness will be described with reference to FIG.

  FIG. 8 shows an example of data 71 indicating the relationship between the polishing conditions and the flatness (of the main surfaces 7a and 7b). The polishing conditions are expressed by alphabets A to E.

  The polishing conditions are, for example, the rotational speed of the sun gear 23 and the internal gear 25 (the rotational speed of the polishing pad 33), the pressure during polishing, the supply amount of the polishing liquid, and the like.

  The vertical line in FIG. 8 for each condition indicates the flatness range that can be controlled by each condition, and + α and −α on the vertical axis are the upper and lower limits of the flatness tolerance.

  For example, when the flatness of the main surfaces 7a and 7b of the polished glass substrate 1a in a certain batch is β in FIG. 8, it exceeds the upper limit value α of the flatness allowable value, so that the glass substrate after the next batch When polishing 1a, polishing must be performed while changing the polishing conditions so that the flatness falls within the allowable value ± α.

  Here, in FIG. 8, the flatness β is within the range of flatness controllable under the polishing condition B. Therefore, when polishing the glass substrate 1 a after the next batch, the polishing condition B is set to 0. By changing so that it may approach, the flatness of the glass substrate 1a of the next batch can be accommodated in tolerance.

  The data 71 indicating the relationship between the polishing conditions and the flatness is obtained in advance before Step 107. Specifically, the main surfaces 7a and 7b of the glass substrate 1a are changed by changing the polishing conditions. Is obtained by measuring the change in flatness of the glass substrate 1a.

  Next, a specific procedure of step 107 will be described with reference to FIGS.

  First, as shown in FIG. 9, the polishing apparatus 21a (see FIG. 7) polishes the glass substrate 1a (step 201).

  Since the specific polishing method has already been described in the description of the polishing apparatus 21a, it is omitted here.

  Next, as shown in FIG. 9, the flatness measuring device 63 measures the flatness (of the main surfaces 7a and 7b) of the polished glass substrate 1a, and the measured flatness values are shown in FIG. 66 (step 202).

  Next, as shown in FIG. 9, the determination unit 66 determines whether or not the flatness is within the allowable value range. If it is within the range, the process proceeds to step 204, and if it is out of the range, the process proceeds to step 205. (Step 203).

  Note that when the flatness is out of the allowable range, for example, the batch immediately after the polishing pad 33 of the polishing apparatus 21a is replaced (the first batch in FIG. 10) is polished.

  Further, there may be mentioned a case where a batch (n-th batch in FIG. 10) immediately after the dressing process (a process of removing clogging by polishing the surface of the polishing pad 33) is polished on the polishing pad 33.

  When the flatness is within the allowable range, it is not necessary to change the polishing conditions. Therefore, the determination unit 66 does not change the polishing conditions (step 204), and the polishing apparatus 21a uses the glass substrate of the batch after the next batch. Polish 1a under the same conditions as the previous batch.

  When the flatness is out of the allowable range, that is, when it is detected that the flatness exceeds a certain value, the determination unit 66 refers to the data storage unit 69 and shows the relationship between the polishing condition and the flatness. 71, a polishing condition in which the measured flatness is within a controllable flatness range is selected (step 205), and the polishing apparatus 21a is instructed to change the condition (step 206).

  For example, in FIG. 10, the flatness β of the batch (first batch) immediately after the polishing pad 33 is replaced is outside the range of ± α, which is an allowable flatness, but as shown in FIG. Since β is within the controllable range of the polishing condition B, the determination unit 66 selects the polishing condition B as the polishing condition for the next batch (second batch) and thereafter so that the flatness approaches 0. The polishing apparatus 21a is instructed to change to

  For example, when there are a plurality of selectable polishing conditions (conditions B and D in FIG. 8), such as the flatness γ of the n-th batch in FIG. It is desirable to select a condition that allows the degree to approach 0 (condition D in FIG. 8).

  In this way, when the flatness of the glass substrate 1a of a certain batch is out of the allowable range, by polishing with changing the polishing conditions, as shown in FIG. The flatness of the glass substrate 1a can be within the allowable range.

  That is, it is possible to quickly suppress a change in flatness.

  The above is the specific procedure of step 107.

  The polishing may be performed in two stages.

  Specifically, for example, as abrasive grains contained in the polishing liquid, two types of abrasive grains having different particle diameters are used, and first polishing is performed using abrasive grains having a relatively large particle diameter, and then the grains Second polishing is performed using abrasive grains having a relatively small diameter.

  When the polishing is completed, as shown in FIG. 3, the glass substrate 1a is washed to remove abrasives and impurities adhering to the surface during manufacture (step 108).

  Specific examples include physical cleaning such as scrub cleaning and ultrasonic cleaning, and chemical cleaning using a fluoride, organic acid, hydrogen peroxide, surfactant, and the like.

  Finally, as shown in FIG. 3, product inspection (for example, inspection of the surface roughness of the main surfaces 7a and 7b and the amount of particles) is performed (step 109).

  Specifically, defect inspection is performed using, for example, ODT (Optical Defect Tester) or OSA (Optical Surface Analyzer).

  The glass substrate 1 is completed by the above process.

  Thus, according to the manufacturing method of the glass substrate 1 concerning this embodiment, after performing the chemical strengthening to the glass base material 1a, main surface 7a, 7b is grind | polished, and in a grinding | polishing process, before When the flatness is out of the allowable range in the batch, the polishing conditions are selected such that the flatness approaches 0, and the polishing is performed for the next batch (next time) and thereafter by changing this.

  Therefore, even when polishing is performed after chemical strengthening, it is possible to quickly suppress the change in flatness when the flatness of the glass substrate 1 changes greatly.

  In the above-described embodiment, the case where the present invention is applied to the manufacturing method for manufacturing the glass substrate 1 for a magnetic recording medium has been described. However, the present invention is not limited to this, and it is necessary to perform polishing after chemical strengthening. It can be applied to all glass manufacturing methods.

  In the above-described embodiment, the determination unit 66 determines whether or not the flatness is within the allowable range and selects the polishing condition. However, an operator may perform the determination.

  In the above-described embodiment, a semiconductor memory / hard disk device or the like made of an external storage device is exemplified as the data storage unit 69. However, the data storage unit 69 can hold the data 71 or the operator can visually recognize the data 71. If there is, it will not be specifically limited.

DESCRIPTION OF SYMBOLS 1 ......... Glass substrate 1a ............ Glass base material 3 ......... Main body 5 ............ Inner hole 7a ............ Main surface 17 ............ Chemical strengthening layer 18b ......... Magnetic layer 21... Grinding device 21 a... Polishing device 51... Chemical strengthening device 59... Chemical strengthening solution 66. …data

Claims (5)

(A) performing chemical strengthening by immersing the glass base material in a chemical strengthening solution that is a solution containing ions and replacing the ions on the surface of the glass base material with ions of the chemical strengthening solution;
Polishing both main surfaces of the glass substrate subjected to the chemical strengthening (b);
Prior to the step (b), for each of a plurality of polishing conditions in the step (b), the polishing condition was changed and the main surface of the glass substrate was polished to change the polishing conditions. Measure the change in flatness of the glass substrate due to the non-uniform thickness of the chemically strengthened layer on the two main surfaces of the glass substrate, and obtain data on the range of flatness size that can be controlled by the polishing conditions. Having a step (c) obtained in advance;
The step (b)
When it is detected that the flatness of the main surface of the glass substrate polished last time exceeds a certain allowable value,
Based on the data, when polishing the glass substrate from the next time on, the polishing conditions that can control the flatness of the main surface of the glass substrate within an allowable value are selected, and the glass substrate from the next time on is selected. A method of manufacturing a glass substrate, wherein the polishing is performed while changing the selected polishing conditions so that the flatness of the film falls within the allowable value. The step (b) is a step of wet-polishing the glass substrate in batch units using a polishing pad,
And when it is detected that the flatness of the main surface of the glass substrate of the batch polished last time exceeds a certain allowable value,
Based on the data, when polishing the glass substrate after the next batch, select the polishing conditions that can control the flatness of the main surface of the glass substrate within an allowable value, the glass after the next 2. The method of manufacturing a glass substrate according to claim 1, wherein the polishing is performed by changing the selected polishing conditions so that the flatness of the substrate falls within the allowable value.   The method for producing a glass substrate according to claim 2, wherein the polishing conditions include at least one of the number of rotations of the polishing pad, the pressure during polishing, and the flow rate of a polishing liquid used for polishing. The step (b)
When there are a plurality of polishing conditions that can control the flatness of the main surface of the glass base material within the allowable value after the next time, the polishing conditions that can make the magnitude of the flatness closer to 0 are selected. The manufacturing method of the glass substrate of Claim 1.   A magnetic recording medium comprising: at least an underlayer, a magnetic layer, a protective layer, and a lubricating layer on a glass substrate produced by the method for producing a glass substrate according to claim 1. Production method.

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