JP2010086597A - Method for manufacturing glass substrate for magnetic disk, and method for manufacturing magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve low roughness of a main surface and a required end shape in a method for manufacturing a glass substrate for a magnetic disk, and a method for manufacturing the magnetic disk. <P>SOLUTION: In the method for manufacturing the glass substrate for the magnetic disk by grinding the main surface of the glass substrate, when a grinding pad has a thickness of 0.55 to 0.9 mm and a pressing force of 66 to 130 g/cm<SP>2</SP>, a value obtained by subtracting a value of an amount of compression deformation of the pad from a pad modulus value is between 70 and 100. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk used as a recording medium for a computer or the like, and a method for manufacturing a magnetic disk.

  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 the magnetic recording media. However, with the miniaturization, thinning, and high recording density of magnetic disks, glass substrates that are superior in substrate surface flatness and substrate strength compared to aluminum substrates are gradually being replaced.

  In order to effectively use the main surface of the magnetic disk, an LUL (Load UnLoad) method has been used instead of the conventional CSS (Contact Start Stop) method. The CSS system is a system in which a magnetic head is brought into contact with a CSS zone provided on the main surface of the magnetic disk and retracted, and the LUL system is a system in which the magnetic head is retracted to a ramp (inclined portion) provided outside the magnetic disk. It is. The CSS zone cannot only be used as a recording area, but also has to have a certain surface roughness to prevent the magnetic head from being attracted. However, by adopting the LUL method, the entire surface of the magnetic disk can be used as a recording area, and it is not necessary to provide an uneven shape on the surface, and the surface of the magnetic disk can be extremely smoothed.

  Further, 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). However, the GMR head has high sensitivity and high recording density, and if the head and the substrate are separated from each other, information on adjacent recording bits is picked up. Therefore, it is necessary to keep the flying height of the magnetic head low. .

  Under these circumstances, the flying height of the magnetic head is required to be reduced, and the flying height of the magnetic head from the substrate is narrowed to about 8 nm.

  If the flying height of the magnetic head is reduced, a head crash failure or thermal asperity failure may occur. The head crash failure is a failure in which the magnetic head collides with the convex portion of the magnetic disk and is damaged. Thermal asperity failure means that the magnetoresistive element is heated by adiabatic compression or contact of air when the magnetic head passes over a minute convex or concave shape on the magnetic disk surface while flying. This is a failure that causes a read error. Therefore, for a magnetic head equipped with a magnetoresistive element, the magnetic disk surface is required to have extremely high smoothness and flatness, that is, low roughness.

  In particular, recently, as described in Patent Document 1, in order to further improve the recording density, the perpendicular magnetic recording method is becoming the main method. In the case of this perpendicular magnetic recording medium, since the recording density is higher than in the case of the in-plane magnetic recording method, the influence of the roughness of the glass substrate is more likely to appear. For this reason, the glass substrate is required to have even lower roughness.

  In the above situation, a polishing pad is given as a factor that determines the surface roughness of the glass substrate. In order to achieve a lower roughness, it is common to use a soft pad.

JP 2005-44464 A

  By the way, even if the average roughness of the magnetic disk surface is low, a head crash and a head crash may occur when the disk is actually operated as a hard disk. This may occur when the shape of the substrate end of the magnetic disk is a jump shape or a sharp sag shape. When the end portion of the substrate has a jump shape, the head may come into contact with the jump portion and cause a head crash. In addition, when the substrate end has a sharp sagging shape, the flying force of the head is lost at the end, which may cause the head to fall. Therefore, the shape of the substrate end of the magnetic disk is required to be flat or gently sag until the outermost periphery.

  However, it has been found that when a magnetic disk glass substrate is polished using a soft pad, the shape of the end portion of the substrate becomes a sharp sagging shape. Therefore, in the conventional technique, low roughness and flat or gentle sagging shape cannot be established simultaneously. In order to form the end shape into a flat or gentle sagging shape, it is necessary to use a hard pad, and in that case, the required low roughness cannot be obtained.

  That is, the low roughness of the surface of the glass substrate for magnetic disks and the high-quality end shape are basically in a trade-off relationship, and both do not hold at the same time.

  Accordingly, an object of the present invention is to provide a method for manufacturing a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk that can simultaneously satisfy a necessary end shape while realizing low roughness.

As a result of examining the above problems, the present inventor has found that the physical property effective for the surface roughness is the modulus value (kg / cm ² ) of the polishing pad, and the physical property effective for the end shape is the compression of the pad. I found out the amount of deformation. Furthermore, by setting both values within a specific range, the present invention has led to the invention of a polishing pad that can cancel the conventional trade-off relationship and produce a glass substrate for a magnetic disk having low roughness and good edge shape.

The modulus value (kg / cm ² ), which is an effective physical property for the surface roughness, represents the softness and softness of the pad. The smaller the value, the softer the pad.

  The amount of compressive deformation, which is an effective physical property for the end shape, represents how much the pad sinks when a specified value is applied. The smaller the value, the harder the pad.

  In order to obtain a good edge shape with low roughness, it is most effective to use a pad with a low modulus value and a low amount of compressive deformation, but when a resin with a low modulus value is used, compressive deformation The amount is generally higher.

  Therefore, even when a resin having a low modulus value is used, a good end shape with low roughness can be obtained by performing a treatment that can suppress the amount of compressive deformation low. However, since the limit at which the amount of compressive deformation can be suppressed is determined, the reduction value of the modulus value needs to be within a specified range.

  That is, the present invention has any one of the following configurations.

[Configuration 1]
The polishing pad is pressed against both main surfaces of the disk-shaped glass substrate, and the glass substrate and the polishing pad are relatively moved while supplying a polishing liquid containing an abrasive between the glass substrate and the polishing pad. , by polishing the major surface of the glass substrate, in the manufacturing method for manufacturing a magnetic disk glass substrate, the polishing pad has a thickness 0.55Mm～0.9Mm, pressing force at ^66g / cm ^{2 ~130g} / cm 2 In some cases, the value obtained by subtracting the compression deformation value of the pad from the pad modulus value is 70 to 100.

[Configuration 2]
In the method for manufacturing a glass substrate for a magnetic disk having Configuration 1, the polishing pad is characterized in that at least the surface layer is made of a foamed resin.

[Configuration 3]
In the method for manufacturing a glass substrate for a magnetic disk having Configuration 2, the foamed resin that forms at least the surface layer of the polishing pad is a mixed resin of Ester / Ether.

[Configuration 4]
In the method for manufacturing a glass substrate for a magnetic disk having Configuration 1, the abrasive is silica abrasive having a particle size of 30 nm or less.

[Configuration 5]
In the method for manufacturing a glass substrate for a magnetic disk having the configuration 1, polishing using a polishing pad is performed by pressing force 66 g / cm ^{2 to} 130 g / cm ² , polishing machine rotational speed 12 rpm to 26 rpm, abrasive flow rate 300 ml / min to 1500 ml. / Min and the pad polishing time is 8 min to 60 min.

[Configuration 6]
In the manufacturing method of the glass substrate for magnetic disks which has composition 1, it has a prepolishing process which grinds the main surface of a glass substrate using a prepolishing material and a prepolishing pad, before polishing using a polishing pad, The pre-abrasive is cerium abrasive grains.

[Configuration 7]
A method for manufacturing a magnetic disk, wherein at least a magnetic layer is formed on a surface of a glass substrate obtained by the method for manufacturing a glass substrate for a magnetic disk having any one of configurations 1 to 6. It is.

[Configuration 8]
In the method of manufacturing a magnetic disk having Configuration 7, the magnetic disk is a magnetic disk for perpendicular magnetic recording system, the magnetic layer is composed of a plurality of layers, and at least one layer is a soft magnetic layer. To do.

  According to the present invention, by using a pad in which the value obtained by subtracting the amount of compressive deformation from the modulus value is within the range, the effect of reducing the roughness due to the low modulus value and the good end shape due to the low amount of compressive deformation. Effect can be obtained. That is, according to the present invention, it is possible to produce a glass substrate for a magnetic disk that satisfies both roughness and edge shape quality at the same time.

  That is, the present invention can provide a method for manufacturing a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk that can simultaneously satisfy a necessary end shape while realizing low roughness.

  The best mode for carrying out the present invention will be described below.

In the present invention, as a result of verifying the modulus value (kg / cm ² ) and the optimum value of the amount of compressive deformation with respect to the material forming the polishing pad for polishing the main surface of the glass substrate for magnetic disk, the value of compressive deformation from the modulus value It was found that both the surface roughness and the edge shape of the glass substrate for a magnetic disk can be achieved when the value obtained by subtracting is within a specific range. Outside that range, the quality of either the roughness or the end shape can be satisfied, but the quality cannot be satisfied at the same time.

  The modulus value, which is a physical property effective for the surface roughness, represents the softness and softness of the pad. The smaller the value, the softer the pad.

  The amount of compressive deformation, which is an effective physical property for the end shape, represents how much the pad sinks when a specified value is applied. The smaller the value, the harder the pad.

The polishing pad thickness 0.55Mm～0.9Mm, when the pressing force is ^{66g / cm 2 ~130g / cm 2} , a value obtained by subtracting the deformation amount value of the pad from the pad modulus value at 70 to 100 Preferably there is.

  FIG. 1 is a diagram showing a relationship between a value obtained by subtracting the amount of compressive deformation from a modulus value, roughness, and end shape quality.

As shown in FIG. 1, the range is as follows.
[Modulus value]-[Compression deformation amount] = 70 or less: End shape quality NG
[Modulus value]-[Compression deformation amount] = 70 or more: End shape quality OK
[Modulus value]-[Compression deformation amount] = 100 or less: Roughness quality OK
[Modulus value]-[Compression deformation amount] = 100 or more: Roughness quality NG
[Modulus value]-[Compression deformation amount] = 70-100: Roughness and end shape quality OK

  Thus, when the modulus value−compression deformation amount = 70 to 100, the roughness and the end shape can be satisfied at the same time.

  Further, it is preferable that at least the surface layer of the polishing pad is made of a foamed resin. Further, the foamed resin that forms at least the surface layer of the polishing pad is preferably a mixed resin of Ester / Ether.

  The abrasive is preferably silica abrasive having a particle size of 30 nm or less.

The polishing using the polishing pad is performed under the conditions of a pressing force of 66 g / cm ^{2 to} 130 g / cm ² , a polishing machine rotational speed of 12 rpm to 26 rpm, an abrasive flow rate of 300 ml / min to 1500 ml / min, and a pad polishing time of 8 min to 60 min. Preferably it is done.

  In addition, before performing polishing using the polishing pad, it has a pre-polishing step of polishing the main surface of the glass substrate using the pre-polishing material and the pre-polishing pad, and the pre-polishing material may be cerium abrasive grains. preferable.

  Embodiments of a magnetic disk glass substrate and a magnetic disk manufacturing method 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 first lapping step First, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper die, a lower die, and a barrel die to obtain an amorphous plate glass. The aluminosilicate glass is a glass containing an alkali metal element having a network-like glass skeleton made of SiO and a structure containing aluminum as a modifying ion. In addition to direct pressing, a disk-shaped glass substrate for a magnetic disk may be obtained by cutting a sheet glass formed by a downdraw method or a float method with a grinding wheel. 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% Chemically strengthened glass contained as

  Next, both main surfaces of the plate glass were lapped to form a disk-shaped glass base material. The lapping process is a grinding process in which a lapping platen is pressed against the main surface of the sheet glass and roughed.

(2) Cutting process (coring, forming)
Next, an inner hole was formed in the center using a cylindrical diamond drill (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).

(3) End surface polishing process Next, the end surface of the glass substrate was mirror-polished by a brush polishing method. By this end surface polishing step, the end surface of the glass substrate was processed into a mirror surface state capable of preventing generation of particles and the like.

(4) 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 process, it is possible to remove in advance the fine irregularities formed on the main surface in the previous cutting process and end face polishing process, and shorten the subsequent polishing process on the main surface. Will be able to be completed in time.

  In the second lapping step, # 1000 is selected as the grain size of the abrasive grains, the flatness of the main surface is 3 μm, the surface roughness Rmax is about 2 μm, and the arithmetic average roughness Ra is about 0.2 μm (Rmax and Ra are According to Japanese Industrial Standard (JIS) B0601). Rmax and Ra were measured with an atomic force microscope (AFM) (Digital Instruments Nanoscope). The flatness is measured by a flatness measuring device, and is the distance (height difference) between the highest part and the lowest part of the substrate surface in the vertical direction (direction perpendicular to the surface).

(5) First polishing step of the main surface (pre-polishing step)
As a main surface polishing step, first, a first polishing step was performed. The primary purpose of this first polishing step is to polish the main surface in advance prior to the second polishing step (mirror polishing step), which is the next step, and to remove scratches and distortions remaining on the main surface in the lapping step described above. To do.

  In the first polishing step, 100 to 200 glass substrates were polished at once by a double-side polishing apparatus capable of polishing. This double-side polishing apparatus performs polishing by sandwiching a large number of glass substrates with an upper surface plate and a lower surface plate through a polishing cloth and relatively moving them by a planetary gear mechanism. A hard resin polisher was used as the polishing cloth in the first polishing step. As the abrasive, cerium oxide abrasive grains were used, and those having a maximum particle size of 3.5 μm, an average value of 1.1 μm, and a D50 value of 1.1 μm were mixed in water.

  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) Second polishing step for main surface Next, a second polishing step was performed as a polishing step for the main surface. The purpose of this second polishing step is to finish the main surface into a mirror surface. In this second polishing step, a double-side polishing apparatus similar to the first polishing step is used, and a soft foamed resin polisher, specifically, polyurethane foam, is used as a polishing cloth having a value within the above-described range. Mirror polishing was performed.

That is, when the polishing pad has a thickness of 0.55 mm to 0.9 mm and a pressing force of 66 g / cm ^{2 to} 130 g / cm ² , a value obtained by subtracting the pad deformation value from the pad modulus value is 70 to 70. 100.

  As an abrasive, colloidal silica abrasive grains having a particle diameter of 30 nm were prepared, and a polishing liquid was prepared by adding water, sulfuric acid as a total dissociating inorganic acid, and tartaric acid as an organic acid as a chemical solution having a buffering action. The content of silica in the polishing liquid is preferably 5 to 40% by weight. In this example, it was 10% by weight. The balance in the polishing liquid is ultrapure water.

The polishing conditions, the pressing force ^{66g / cm 2 ~130g / cm 2} , the polishing machine rotating speed 12Rpm～26rpm, abrasive flow rate 300ml / min~1500ml / min, and a pad polishing time 8Min～60min.

(7) Cleaning step after mirror polishing The glass substrate after the second polishing step was immersed in an aqueous NaOH solution having a concentration of 3 to 5 wt% to perform alkali cleaning. The cleaning was performed by applying ultrasonic waves. Furthermore, it wash | cleaned by immersing in each washing tank of neutral detergent, a pure water, a pure water, IPA, and IPA (steam drying) sequentially. Note that ultrasonic waves were applied to each cleaning tank.

(8) Chemical strengthening process Next, the glass substrate which finished the above-mentioned lapping process, the 1st grinding | polishing process, and the 2nd grinding | polishing process was chemically strengthened. For chemical strengthening, a chemical strengthening solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and the chemically strengthened solution is heated to 375 ° C., and the cleaned glass substrate is preheated to 300 ° C. And was immersed in the chemical strengthening solution for about 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, it was performed in a state of being housed in a holder so that a plurality of glass substrates were held at the end surfaces.

  Thus, by immersing in a chemical strengthening solution, the lithium ion and sodium ion of the surface layer of a glass substrate are each substituted by the sodium ion and potassium ion in a chemical strengthening solution, and a glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 μm to 200 μm.

  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.

(9) Inspection step of glass substrate for magnetic disk The glass substrate for magnetic disk manufactured as described above was inspected. The surface of the glass substrate was a clean mirror surface. There were no foreign objects on the surface that could hinder the flying of the magnetic head or cause thermal asperity failure. That is, a flat and smooth high-rigidity glass substrate for a magnetic disk was obtained.

  Using the magnetic disk glass substrate manufactured as described above, a perpendicular magnetic recording type magnetic disk was manufactured.

(10) 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.

(11) Magnetic disk inspection process The magnetic disk manufactured as described above was inspected. When a head crash test was carried out by flying over a magnetic disk using an inspection head having a flying height of 10 nm, the magnetic head did not come into contact with a foreign object or the like, and no crash failure occurred.

  Next, with respect to the magnetic disk formed of the glass substrate of the example, the flying height is 8 nm, the reproducing element portion is a magnetoresistive element, the recording element portion is a single magnetic pole element, and recording is performed by the perpendicular recording method. When a reproduction test was performed, it was confirmed that information was recorded and reproduced normally. The thermal asperity signal was not detected in the reproduction signal. Recording and reproduction could be performed at 100 gigabits per square inch.

  Next, a glide height test was performed on the magnetic disk made of the glass substrate of the example. In this test, when the flying height of the inspection head is gradually lowered, the flying height is checked to determine the contact between the testing head and the magnetic disk. As a result, in the magnetic disk of this example, no contact occurred even when the flying height was 4 nm from the inner edge portion to the outer edge portion of the magnetic disk. At the outer edge portion of the magnetic disk, the glide height was 3.7 nm.

  As mentioned above, although the suitable Example of this invention was described, it cannot be overemphasized that this invention is not limited to the example which concerns. 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.

It is a figure showing the relationship between the value of a modulus value-compression deformation amount, roughness, and end shape quality.

Claims (8)

While pressing a polishing pad against both main surfaces of a disk-shaped glass substrate and supplying a polishing liquid containing an abrasive between the glass substrate and the polishing pad, the glass substrate and the polishing pad are relatively In the manufacturing method of moving and polishing the main surface of the glass substrate to manufacture a glass substrate for a magnetic disk,
The polishing pad has a thickness of 0.55Mm～0.9Mm, when the pressing force is ^{66g / cm 2 ~130g / cm 2} , a value obtained by subtracting the deformation amount value of the pad from the pad modulus value of 70 to 100 A method for producing a glass substrate for a magnetic disk, wherein: The method for producing a glass substrate for a magnetic disk according to claim 1, wherein at least a surface layer of the polishing pad is made of a foamed resin. The method for producing a glass substrate for a magnetic disk according to claim 2, wherein the foamed resin forming at least a surface layer of the polishing pad is a mixed resin of Ester / Ether. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the abrasive is silica abrasive grains having a particle size of 30 nm or less. Polishing using the polishing pad is performed pressing force ^{66g / cm 2 ~130g / cm 2} , the polishing machine rotating speed 12Rpm～26rpm, abrasive flow rate 300ml / min~1500ml / min, under conditions of pad polishing time 8min~60min The method for producing a glass substrate for a magnetic disk according to claim 1. Before polishing using the polishing pad, a pre-polishing step of polishing the main surface of the glass substrate using a pre-polishing material and a pre-polishing pad;
The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the pre-abrasive material is cerium abrasive grains. A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on a surface of a glass substrate obtained by the method for manufacturing a glass substrate for a magnetic disk according to any one of claims 1 to 6. The magnetic disk is a magnetic disk for perpendicular magnetic recording system,
The method of manufacturing a magnetic disk according to claim 7, wherein the magnetic layer includes a plurality of layers, and at least one layer is a soft magnetic layer.

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