JP2007095238A - Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a glass substrate for a magnetic disk by which the magnetic disk wherein expected performance can be obtained, glide height of a magnetic head can be sufficiently narrowed and satisfactory magnetic anisotropy is given to a magnetic layer can be manufactured when the glass substrate for the magnetic disk is manufactured and the magnetic disk is manufactured and to provide the manufacturing method of the magnetic disk by which the magnetic disk having satisfactory characteristics can be manufactured. <P>SOLUTION: In the manufacturing method of the glass substrate for the magnetic disk having a linear texture on the surface thereof, after a principal surface of the glass substrate is washed by using a washing liquid containing an acid to remove a foreign matter on the principal surface, the texture is formed on the principal surface of the glass substrate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk used for a hard disk drive (HDD) that is a magnetic disk device, and a magnetic disk for manufacturing a magnetic disk using the glass substrate for a magnetic disk. It relates to the manufacturing method.

  Today, information recording technology, particularly magnetic recording technology, is required to undergo dramatic technological innovation with the development of the so-called IT industry. Unlike other magnetic recording media such as magnetic tapes and flexible disks, the magnetic disk mounted on a hard disk drive (HDD), which is a magnetic disk device used as a computer storage, is rapidly increasing in information recording density. Has been continued. The information capacity that can be stored in the personal computer device has been dramatically increased, supported by such an increase in the information recording density of the magnetic disk.

  Such a magnetic disk is configured by forming a magnetic layer or the like on a substrate such as a glass substrate or an aluminum alloy disk substrate. In particular, in recent years, with increasing demand for mounting hard disk drives in portable devices (so-called “notebook personal computer devices”, etc.), they have high strength, high rigidity, and high impact resistance. A magnetic disk using a glass substrate has attracted attention.

  In the hard disk drive, an information signal is recorded and reproduced as a magnetization pattern on the magnetic layer by the magnetic head while flying over the magnetic disk rotated at high speed. In a magnetic disk using a glass substrate, since a smooth surface can be obtained, the flying height of the magnetic head can be reduced, and a high information recording density can be realized. That is, by using a glass substrate, a magnetic disk excellent in the low flying height compatibility of the magnetic head can be manufactured.

  On the other hand, in order to increase the information recording capacity of the magnetic disk, it is necessary to reduce the area of a useless area where information signals are not recorded on the magnetic disk. Therefore, instead of the conventionally used CSS method (“Contact Start Stop method”), the LUL method (“load unload”) that can increase the information recording capacity is used as a hard disk drive start / stop method. (Load Unload) method, also known as “ramp load method”) is being introduced.

  In the CSS system, it is necessary to provide a CSS zone on the magnetic disk on which the magnetic head is placed when the magnetic disk is not used (stopped), and information signals cannot be recorded in the CSS zone. The area of the magnetic disk where information signals are recorded is reduced.

  On the other hand, in the LUL method, when the magnetic disk is not in use (stopped), the magnetic head is moved to the outer peripheral side of the magnetic disk and is retracted and supported from the magnetic disk. It is not necessary to provide an area where information signals cannot be recorded such as a zone, and the area of the area where information signals are recorded on the magnetic disk can be secured to the maximum.

  In the LUL method, unlike the CSS method, the magnetic head and the magnetic disk do not come into contact with each other. Therefore, it is not necessary to provide the magnetic disk with an uneven shape for preventing adsorption as in the CSS zone. The main surface can be extremely smoothed. Therefore, in the magnetic disk for LUL system, the flying height of the magnetic head can be further narrowed compared to the magnetic disk for CSS system, and the S / N ratio (Signal Noise Ratio) of the recording signal is improved. There is also an advantage that a high recording density can be achieved.

  As a result of such a non-continuous narrowing of the flying height of the magnetic head accompanying the introduction of the LUL method, the magnetic head can be stably operated even in an extremely narrow flying height of less than 10 nm in recent years. It has come to be required.

  Incidentally, the glass substrate for magnetic disk is manufactured through a plurality of processes such as polishing and cleaning. If there is foreign matter on the surface of the magnetic disk glass substrate, the reliability of the magnetic disk or hard disk drive will be reduced, and in some cases there may be problems such as glide hits and crashes. The surface of the substrate must be smooth and clean.

  Therefore, the manufacturing process of the magnetic disk glass substrate includes a cleaning process and a drying process. As a cleaning process and a drying process in the manufacturing process of the glass substrate for magnetic disks, for example, as described in Patent Document 1, hydrochloric acid is used for the glass substrate in the pre-process or the post-process of the chemical strengthening process. And cleaning techniques are described.

  In manufacturing the magnetic disk, a thin film such as a magnetic layer is formed on the glass substrate for the magnetic disk by a method such as a sputtering film formation to manufacture the magnetic disk.

Japanese Patent Laid-Open No. 10-228643

  Incidentally, in recent magnetic disks, as described above, the spacing loss between the magnetic disk and the magnetic head has been improved and the S / N ratio of the recording signal has been improved, resulting in an information recording density of 1 square inch. It has reached 40 gigabits per unit, and an ultra-high recording density that exceeds 100 gigabits per square inch is also being realized.

  One of the reasons why ultra-high recording density in magnetic disks has become possible is that smoothing of the glass substrate for magnetic disks has been realized. The surface of the glass substrate for magnetic disks is finished to a smooth mirror surface. Therefore, even if the flying height of the magnetic head is 10 nm or less, recording / reproduction can be performed without any problem. In other words, the magnetic disk glass substrate can have a very smooth surface, so that the flying height of the magnetic head can be reduced.

  In addition, the fact that a texture imparting magnetic anisotropy to the magnetic layer has been formed on the surface of the glass substrate for a magnetic disk is one reason why the recording density has been increased. The glass substrate for magnetic disk having such a texture formed on the surface can impart excellent magnetic anisotropy to the magnetic layer, so that high recording density can be realized. This texture is formed by sliding the polishing tape against the surface of the magnetic disk glass substrate in a substantially circumferential direction of the magnetic disk glass substrate.

  In recent magnetic disks that can realize such a high information recording density, it is possible to store a practically sufficient amount of information even if the disk area is much smaller than that of a conventional magnetic disk. Have. In addition, the magnetic disk has a feature that information recording speed and reproduction speed (response speed) are extremely fast compared with other information recording media, and information can be written and read at any time. .

  As a result of attention paid to various features of such magnetic disks, in recent years, portable so-called MP3 players, mobile phone devices, digital cameras, and portable information devices (for example, PDA (personal digital assistant)) Alternatively, there is a need for a small hard disk drive that can be mounted on a device that is much smaller than a personal computer device and requires a high response speed, such as a “car navigation system”.

  However, when the flying height of the magnetic head is reduced to increase the recording density as described above, fly stiction failure may occur frequently. The fly stiction failure is a failure in which the magnetic head flying above the magnetic disk modulates the flying posture and the flying height, and is often accompanied by irregular reproduction output fluctuations. In addition, a so-called head crash failure or thermal asperity failure in which the flying magnetic head comes into contact with the magnetic disk may occur.

  Moreover, the following problems have arisen in such a magnetic disk glass substrate. That is, when a magnetic disk glass substrate having a texture formed on the surface is manufactured and the magnetic disk is manufactured, the desired performance may not always be obtained. That is, the glide height of the magnetic head cannot be sufficiently narrowed, or the magnetic anisotropy in the magnetic layer may vary.

  This is because foreign matter adheres to the surface of the glass disk, which is the material of the magnetic disk glass substrate, before the texture forming step, and this foreign matter comes into contact with the polishing tape in the texture forming step. The cause is considered to be a band-shaped scratch on the surface.

  Accordingly, the present invention has been made in view of the above-described circumstances, and a first object of the present invention is to manufacture a magnetic disk glass substrate and obtain a desired performance when manufacturing a magnetic disk. Another object of the present invention is to provide a method of manufacturing a glass substrate for a magnetic disk that can sufficiently narrow the glide height of a magnetic head.

  A second object of the present invention is to provide a method for producing a glass substrate for a magnetic disk, which makes it possible to produce a magnetic disk having a magnetic layer with good magnetic anisotropy.

  Furthermore, a third object of the present invention is to provide a magnetic disk capable of producing a magnetic disk having good characteristics by using the glass substrate for magnetic disk produced by such a method for producing a glass substrate for magnetic disk. It is in providing the manufacturing method of.

  As a result of researches to solve the above problems, the present inventor adheres to the surface of the glass disk as the material of the glass substrate for the magnetic disk before the texture forming process, and contacts the polishing tape in the texture forming process. Thus, a foreign matter (for example, a foreign matter containing iron (Fe), which is a cause of causing a band-like scratch on the surface of the glass substrate for a magnetic disk, may include stainless steel, iron oxide, etc.). This is also known as iron contamination.) The present invention has been completed on the basis of such knowledge, and for the magnetic disk in the texture forming process by performing cleaning that is considered effective for removing iron contamination before the texture forming process. By preventing the surface of the glass substrate from being scratched, a low glide height magnetic disk can be provided.

  That is, the method for manufacturing a glass substrate for a magnetic disk according to the present invention has at least one of the following configurations.

[Configuration 1]
A method for producing a glass substrate for a magnetic disk having a linear texture on the surface, wherein the main surface of the glass substrate is cleaned with a cleaning solution containing an acid, and then a texture is formed on the main surface of the glass substrate. To do.

[Configuration 2]
In the method for manufacturing a glass substrate for a magnetic disk having Configuration 1, the cleaning liquid contains hydrochloric acid as a main component.

[Configuration 3]
In the method for manufacturing a glass substrate for a magnetic disk having the configuration 2, the cleaning liquid has a hydrochloric acid concentration of 0.006 mol% or more and 0.01 mol% or less.

In addition, the ratio (Fe / Si) of iron (Fe) to silicon (Si) in the glass component on the main surface of the glass disk after the cleaning with the cleaning liquid and before the texture forming step is 2 × 10 ⁻⁵ or less. It is preferable that

[Configuration 4]
By pressing the polishing tape against the main surface of the disk-shaped glass substrate and moving the polishing tape and the glass substrate relatively, a substantially regular streak oriented in the circumferential direction of the disk on the main surface of the glass substrate. A method for manufacturing a glass substrate for a magnetic disk including a process for forming a texture having irregularities, wherein the amount of iron element present on the surface of the glass substrate in the region in contact with at least the polishing tape of the glass substrate is determined by total reflection fluorescence X When analyzed based on the line analysis method, the ratio of silicon element contained in the glass (Fe / Si) is 2 × 10 ⁻⁵ or less, and the glass substrate is subjected to a texture forming process. It is characterized by.

[Configuration 5]
In the method for manufacturing a glass substrate for a magnetic disk having the configuration 4, the region in contact with the polishing tape is preliminarily mirror-polished before the formation of the texture.

[Configuration 6]
In the method for manufacturing a magnetic disk glass substrate having Configuration 4 or Configuration 5, the region in contact with the polishing tape is cleaned with a processing solution that is soluble in advance against at least iron-containing foreign matter before forming the texture. It is characterized by being.
[Configuration 7]
At least a magnetic layer is formed on the main surface portion of the magnetic disk glass substrate produced by the method for producing a magnetic disk glass substrate having any one of Structures 1 to 6. In the method of manufacturing a magnetic disk,

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention having the configuration 1, since the main surface of the glass substrate is washed with an acid-containing cleaning solution and then a texture is formed on the main surface of the glass substrate, Provided is a glass substrate for a magnetic disk that can effectively remove foreign matters on the surface, prevents generation of scratches on the surface of the glass substrate for magnetic disk in a texture forming process, and can produce a low-glide height magnetic disk. be able to.

  Further, in the method for manufacturing a magnetic disk glass substrate according to the present invention having the configuration 2, since the cleaning liquid contains hydrochloric acid as a main component, foreign matters on the surface of the magnetic disk glass substrate can be effectively removed. it can.

  In the method for manufacturing a magnetic disk glass substrate according to the present invention having Configuration 3, the cleaning liquid has a hydrochloric acid concentration of 0.006 mol% or more and 0.01 mol% or less, whereby the surface of the magnetic disk glass substrate is obtained. It is possible to effectively remove the foreign matter in the surface and to prevent the occurrence of scratches on the surface of the glass substrate for magnetic disks in the texture forming step.

In the glass substrate for a magnetic disk according to the present invention having the configuration 4, in the glass substrate, the amount of the iron element present on the glass substrate surface is determined in the glass substrate at least in the region in contact with the polishing tape of the glass substrate. Since the ratio (Fe / Si) to the silicon element contained in the substrate is 2 × 10 ⁻⁵ or less, it is possible to satisfactorily prevent the occurrence of scratches on the surface of the glass substrate for magnetic disks in the texture forming step.

  In the glass substrate for a magnetic disk according to the present invention having the configuration 5, since the region that comes into contact with the polishing tape is mirror-polished in advance before the formation of the texture, the surface of the glass substrate for the magnetic disk in the texture forming step The occurrence of scratches can be satisfactorily prevented.

  In the glass substrate for a magnetic disk according to the present invention having the configuration 6, the region in contact with the polishing tape is washed with a processing solution that is soluble at least against foreign matters containing iron before the formation of the texture. Further, it is possible to satisfactorily prevent the occurrence of scratches on the surface of the glass substrate for magnetic disk in the texture forming process.

  And in the manufacturing method of the magnetic disk which concerns on this invention which has the structure 7, on the main surface part of the glass substrate for magnetic disks manufactured by the manufacturing method of the glass substrate for magnetic disks which has any one of the structures 1 thru | or the structure 6 Since at least the magnetic layer is formed, a magnetic disk in which occurrence of head crash failure and thermal asperity failure is suppressed can be manufactured.

  That is, according to the present invention, when a glass substrate for a magnetic disk is manufactured and a magnetic disk is manufactured, desired performance can be obtained, and the glide height of the magnetic head can be sufficiently narrowed. It is possible to provide a method of manufacturing a glass substrate for a magnetic disk that enables the manufacture of a magnetic disk having good magnetic anisotropy.

  The present invention also provides a method of manufacturing a magnetic disk, which can manufacture a magnetic disk having good characteristics by using the glass substrate for magnetic disk manufactured by such a method of manufacturing a glass substrate for magnetic disk. Is something that can be done.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  The manufacturing method of the glass substrate for magnetic disks which concerns on this invention is a manufacturing method of the glass substrate for magnetic disks manufactured through a several process so that it may mention later. That is, the magnetic disk glass substrate manufactured by the method for manufacturing a magnetic disk glass substrate is a glass base material obtained by grinding (lapping) the main surface of the plate glass, and the glass base material is cut into glass. A disk is cut out, and the main surface of the glass disk is polished (polished), and further manufactured through a chemical strengthening process, a texture process, a cleaning process, and a drying process.

(1) Manufacture of plate glass First, plate glass used as the material of the glass substrate for magnetic disks is prepared. In the present invention, various types of plate glass can be used as the plate glass used as the material for the magnetic disk glass substrate. The plate-like glass may have a rectangular shape or a disk shape (disk shape). The disk-shaped plate-like glass can be ground using a grinding apparatus used in the manufacture of a conventional magnetic disk glass substrate, and a highly reliable process can be performed at low cost.

  This plate-like glass can be manufactured using a known manufacturing method such as a press method, a float method, or a fusion method, using, for example, molten glass as a material. Of these, plate glass can be produced at low cost by using the pressing method.

  Further, the material of the plate glass used in the present invention is not particularly limited as long as it is glass, but aluminosilicate glass can be preferably mentioned. In particular, aluminosilicate glass containing lithium is preferable. Such an aluminosilicate glass can accurately obtain a compressive stress layer having a preferable compressive stress and a tensile stress layer having a tensile stress by an ion exchange type chemical strengthening treatment, in particular, a low temperature ion exchange type chemical strengthening treatment. Particularly preferred as a material of a chemically strengthened glass substrate for a magnetic disk.

The composition ratio of such aluminosilicate glass, a SiO _2, 58 to 75 wt%, the _Al 2 _{O 3,} 5 to 23 wt%, the Li ₂ O, 3 to 10 wt%, a Na ₂ O, It is preferable to contain 4 to 13% by weight as a main component.

  When such an aluminosilicate glass is subjected to a chemical strengthening treatment, the bending strength is increased and the Knoop hardness is excellent.

(2) Grinding process The grinding process is a process aimed at improving the shape accuracy (for example, flatness) and dimensional accuracy (for example, plate thickness accuracy) of the main surface of the sheet glass. In this grinding process, the main surface of the plate glass is ground by pressing a grindstone or a surface plate against the main surface of the plate glass and relatively moving the plate glass and the grindstone or the surface plate. Is done. Such a grinding process can be performed using a double-side grinding apparatus using a planetary gear mechanism.

  Then, the glass base material is cut and a glass disk is cut out. Next, using a cylindrical grindstone, a circular hole with a predetermined diameter is formed in the central portion of the glass disk, and after grinding the outer peripheral end surface to a predetermined diameter, on the outer peripheral end surface and the inner peripheral end surface, Chamfering is performed to form a chamfer along the periphery of the main surface.

(3) Polishing process In the present invention, at least a polishing process is performed on the glass disk cut out from the glass base material to mirror the main surface of the glass disk. The steps after the polishing treatment are preferably performed in a clean room.

  By performing this polishing treatment, cracks on the main surface of the glass disk are removed, and the surface roughness of the main surface is, for example, 10 nm or less in terms of Rmax. If the main surface of the glass disk has such a mirror surface, even if the flying height of the magnetic head is 10 nm in a magnetic disk manufactured using this glass disk, for example, a so-called crash failure And thermal asperity failure can be prevented. Further, if the main surface of the glass disk is such a mirror surface, in the chemical strengthening process described later, the chemical strengthening process can be performed uniformly in the fine region of the glass disk, and delayed fracture due to micro cracks can be performed. Can be prevented.

  This polishing treatment is performed, for example, by pressing a surface plate having a polishing pad (polishing cloth) attached to the main surface of the glass disk and supplying the polishing liquid to the main surface of the glass disk, Is relatively moved, and the main surface of the glass disk is polished. At this time, the polishing liquid may contain polishing abrasive grains. As the abrasive grains, colloidal silica abrasive grains or cerium oxide abrasive grains can be used.

  In the present invention, it is preferable to perform a grinding process before polishing the glass disk. The grinding process at this time can be performed by the same means as the grinding process for the plate-like glass described above. By performing the polishing process after the glass disk is ground, a mirror-finished main surface can be obtained in a shorter time.

  In the present invention, it is preferable to form a chamfered surface of approximately 45 ° along the periphery of the main surface on the end surface of the glass disk, and to mirror-polish this end surface. The end surface of the glass disk has a cut shape between the portions where the chamfered surface is formed. By polishing this end surface to a mirror surface, generation of particles can be suppressed. This is because a so-called thermal asperity failure can be satisfactorily prevented in a magnetic disk manufactured using a disk glass substrate.

(4) Chemical strengthening treatment In the present invention, a chemical strengthening treatment is performed after the glass disk polishing step. By performing the chemical strengthening treatment, a high compressive stress can be generated on the surface of the glass substrate for magnetic disk, and the impact resistance can be improved. In particular, when aluminosilicate glass is used as the material of the glass disk, the chemical strengthening treatment can be suitably performed.

  The chemical strengthening treatment of the glass disk is performed, for example, by bringing the glass disk into contact with a heated chemically strengthened salt, and ions on the surface layer of the glass disk are ion-exchanged with ions of the chemically strengthened salt.

  Here, as the ion exchange method, a low temperature type ion exchange method, a high temperature type ion exchange method, a surface crystallization method, a dealkalization method on the glass surface, etc. are known. It is preferable to use a low-temperature ion exchange method in which ion exchange is performed in a temperature region not exceeding.

  The low-temperature ion exchange method here refers to an increase in the volume of the ion exchange part by substituting alkali ions in the glass with alkali ions having a larger ion radius than the alkali ions in the temperature range below the annealing point of the glass. This refers to a method of generating a compressive stress on the glass surface layer and strengthening the glass surface layer.

  In the present invention, the material of the treatment rod for performing the chemical strengthening treatment is not particularly limited as long as it is excellent in corrosion resistance and has a low dust generation property. Chemically strengthened salt and chemically strengthened molten salt are oxidative and the processing temperature is high, so by selecting materials with excellent corrosion resistance, damage and dust generation are suppressed, resulting in thermal asperity failures and head crashes. It is necessary to suppress. From this point of view, a quartz material is particularly preferable as a material for the treatment rod, but a stainless material, or a martensitic or austenitic stainless material having particularly excellent corrosion resistance can also be used. In addition, although quartz material is excellent in corrosion resistance, since it is expensive, it can select suitably in consideration of profitability.

  The material of the chemically strengthened salt in the present invention is preferably a chemically strengthened salt material containing sodium nitrate and / or potassium nitrate. This is because such a chemically strengthened salt can realize predetermined rigidity and impact resistance as a glass substrate for a magnetic disk when chemically strengthening glass, particularly aluminosilicate glass.

(4) Texture Processing Next, in the present invention, texture processing for forming a texture is performed on the main surface of the glass disk. This texture is a texture that imparts magnetic anisotropy to the magnetic layer when at least the magnetic layer is formed on the magnetic disk glass substrate.

  In performing this texture processing, first, the main surface of the glass disk is cleaned with a cleaning solution containing an acid. The cleaning liquid preferably contains hydrochloric acid as a main component.

  The acid concentration in the cleaning liquid needs to be a concentration at which foreign matter (iron contamination) on the main surface of the glass disk is sufficiently removed, but if the concentration is too high, the surface roughness of the main surface of the glass disk will be low. There is a risk of being damaged by acid. Therefore, the acid concentration in the cleaning liquid is preferably such a concentration that foreign matters are sufficiently removed and the surface roughness of the main surface of the glass disk is not deteriorated. For example, the hydrochloric acid concentration is 0.006. It is preferable that it is mol% or more and 0.01 mol% or less.

And after washing | cleaning by this washing | cleaning liquid and before texturing, ratio (Fe / Si) of iron (Fe) with respect to the silicon (Si) in the glass component in the main surface of a glass disk will be 2 * 10 < ^-5 > or less. It is preferable. The ratio of the amount of iron element to the amount of silicon element on the glass disk surface (Fe / Si) is obtained by using a known total reflection X-ray reflection analyzer (TXRF). It is done.

  In the texture processing, the glass disk is mounted on the tip side of the chucking shaft of the texture processing apparatus in the central hole. The chucking shaft holds the glass disk by inserting the tip side into a circular hole of the glass disk and expanding the diameter. The chucking shaft is rotated around the axis at a predetermined rotational speed and is reciprocated with a predetermined circumference and amplitude in a direction orthogonal to the axis.

  In this texture processing apparatus, a pair of polishing tapes are fed at a predetermined speed. These polishing tapes are fed and operated at an equal speed while being superposed on each other. The glass disk held on the chucking shaft is inserted between a pair of polishing tapes that are operated to feed the portion that becomes the main surface. These polishing tapes are pressed against the main surfaces on both sides of the glass disk by a pressure roller at a predetermined pressure. That is, the glass disk is sandwiched between the main surfaces by a pair of polishing tapes.

  In this state, the chucking shaft is rotated around the axis together with the glass disk, and the chucking shaft is reciprocated with a predetermined circumference and amplitude in a direction orthogonal to the axis. At this time, the reciprocating direction of the chucking shaft is a direction orthogonal to the feeding operation direction of the pair of polishing tapes. At this time, a liquid abrasive is supplied between the glass disk and each polishing tape. At this time, it is preferable to contain abrasive grains in the liquid abrasive. Diamond abrasive grains can be used as the abrasive grains. At this time, the glass disk and each polishing tape are relatively slidably moved.

  Since the speed of the feeding operation of each polishing tape is extremely slow, the relative sliding between the glass disk and each polishing tape is determined by the rotational speed of the glass disk and the period and amplitude of the reciprocating movement. The relative sliding movement of each polishing tape with respect to the glass disk is based on the movement in the circumferential direction (tangential direction) of the glass disk, and is a movement that swings in a sine curve with respect to the circumferential direction. . The texture formed on the main surface of the glass disk in this way is formed so that the cross angle with respect to the circumferential direction (tangential direction) of the glass disk increases from the outer peripheral side to the inner peripheral side of the main surface. . This is because, on the main surface of the glass disk, the tangential speed on the inner peripheral side is slower than that on the outer peripheral side.

(5) Manufacture of magnetic disk In the method of manufacturing a magnetic disk according to the present invention, at least a magnetic layer is formed on the glass substrate for magnetic disk as described above.

  As the magnetic layer formed on the magnetic disk glass substrate, for example, a layer made of a cobalt (Co) -based ferromagnetic material can be used. In particular, it is preferably formed as a magnetic layer made of a cobalt-platinum (Co—Pt) -based ferromagnetic material or a cobalt-chromium (Co—Cr) -based ferromagnetic material that provides a high coercive force. As a method for forming the magnetic layer, a bias sputtering method, a DC magnetron sputtering method, or a bias CVD method can be used.

  It is preferable that an underlayer or the like is appropriately inserted between the glass substrate and the magnetic layer. As the material of these underlayers, an Al—Ru alloy, a Cr alloy, or the like can be used.

  In addition, a protective layer for protecting the magnetic disk from the impact of the magnetic head can be provided on the magnetic layer. As this protective layer, a hard hydrogenated carbon protective layer can be preferably used. A plasma CVD method can be used to form this protective layer.

  Furthermore, by forming a lubricating layer made of a PFPE (perfluoropolyether) compound on this protective layer, interference between the magnetic head and the magnetic disk can be reduced. This lubricating layer can be formed, for example, by coating by a dip method.

  Hereinafter, the present invention will be specifically described by giving examples and comparative examples. In addition, this invention is not limited to the structure of these Examples.

[Example 1]
The glass substrate for a magnetic disk and the magnetic disk in this example described below are prepared by the following steps (1) to (10).
(1) Step for obtaining glass base material (2) Rough grinding step (3) Shape processing step (4) Fine grinding step (5) End face polishing step (6) First polishing step (7) Second polishing step (8) ) Chemical strengthening process (9) Texture processing (10) Magnetic disk manufacturing process (film formation process)

(1) Step of obtaining glass base material First, a disk-shaped glass base material made of amorphous aluminosilicate glass was prepared. This aluminosilicate glass contains lithium. The composition of this aluminosilicate glass is SiO ₂ 63.6% by weight, Al ₂ O ₃ 14.2% by weight, Na ₂ O 10.4% by weight, Li ₂ O 5.4% by weight. %, ZrO ₂ 6.0 wt%, and Sb ₂ O ₃ 0.4 wt%.

The (2) rough grinding step aluminosilicate glass, a SiO _2, 58 to 75 wt%, the _Al 2 _{O 3,} 5 to 23 wt%, a Na ₂ O, 4 to 13 wt%, the Li ₂ O, What is necessary is just to contain 3 to 10% by weight.

  Next, a rough grinding process was performed on the glass disk in order to improve dimensional accuracy and shape accuracy. This rough grinding process was performed using abrasive grains of grain size # 400 using a double-side grinding apparatus.

  Specifically, first, using alumina abrasive grains of particle size # 400, setting the load to about 100 kg, and rotating the sun gear and the internal gear, both surfaces of the glass disk housed in the carrier are improved in surface accuracy. It was ground to 0 to 1 μm and surface roughness (Rmax) of about 6 μm.

(3) Shape processing step Next, a cylindrical grindstone is used to form a circular hole in the central portion of the glass disk, and the chamfer of approximately 45 ° along the peripheral edge of the main surface at the outer peripheral end surface and the inner peripheral end surface. Processed. The surface roughness of the end face of the glass disk at this time was about 4 μm in Rmax.

(4) Fine grinding step Next, by changing the grain size of the abrasive grains to # 1000 and grinding the main surface of the glass disk, the surface roughness of the main surface is about 2 μm for Rmax and about 0.2 μm for Ra. did.

  By performing this fine grinding step, it is possible to remove the fine uneven shape formed on the main surface in the rough grinding step and the shape processing step which are the previous steps.

  The glass disk after such a fine grinding process was immersed in each washing tank of neutral detergent and water to which ultrasonic waves were applied in order to perform ultrasonic cleaning.

(5) End face polishing process Next, the end face of the glass disk is polished while rotating the glass disk by brush polishing conventionally used, and the surface of the end face (inner peripheral end face and outer peripheral end face) of this glass disk is polished. The roughness was polished to about 1 μm for Rmax and about 0.3 μm for Ra.

  And the main surface of the glass disk which finished the end surface grinding | polishing process was water-washed.

  In this end face polishing process, the glass disk is overlapped to polish the end face. At this time, in order to avoid scratches or the like on the main surface of the glass disk, before the first polishing process described later. Alternatively, it is preferably performed before and after the second polishing step.

  By this end face polishing process, the end face of the glass disk was processed into a mirror surface state capable of preventing generation of particles and the like.

(6) First Polishing Step Next, a first polishing step was performed using a double-side polishing apparatus in order to remove scratches and distortions remaining in the fine grinding step described above.

  In the screen polishing apparatus, a glass disk held by a carrier is brought into close contact between the upper and lower surface plates to which the polishing pad is attached, and the carrier is engaged with the sun gear and the internal gear, and the glass disk is moved to the upper and lower surface plates. To pinch. Then, by rotating the sun gear while supplying the polishing liquid between the polishing pad and the polishing surface (main surface) of the glass disk, the glass disk revolves around the internal gear while rotating on the surface plate. Thus, both main surfaces are polished simultaneously.

The same apparatus is used as a double-side polishing apparatus used in the following polishing steps. Specifically, the first polishing step was performed using a hard polisher (hard urethane foam) as the polisher. The polishing conditions were a polishing liquid composed of cerium oxide (average particle size 1.3 μm) and RO water, a load of 100 g / cm ² and a polishing time of 15 minutes. And the glass disk which finished this 1st grinding | polishing process is immersed in each washing | cleaning tank of a neutral detergent, a pure water (1), a pure water (2), IPA (isopropyl alcohol), and IPA (steam drying) one by one. , Ultrasonically cleaned and dried.

(7) Second polishing step Next, using a double-side polishing device similar to the double-side polishing device used in the first polishing step, the polisher is replaced with a soft polisher (suede pad), and as a mirror polishing step of the main surface, A second polishing step was performed.

  In the second polishing step, the surface roughness Ra of the main surface is reduced to, for example, about 0.5 to 0.3 nm or less while maintaining the flat main surface obtained by the first polishing step. It is for the purpose.

The polishing conditions were a polishing liquid composed of colloidal silica (average particle size 80 nm) and RO water, a load of 100 g / cm ² and a polishing time of 5 minutes.

  Then, the glass disk after the second polishing step is immersed in each of the acid, pure water (1), neutral detergent, pure water (2), and IPA (isopropyl alcohol) cleaning tanks in order, and subjected to ultrasonic cleaning. And then dried with IPA vapor.

(8) Chemical strengthening process Next, the chemical strengthening process was performed with respect to the glass disk which finished washing | cleaning. The chemical strengthening treatment was performed using a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed, and the lithium content eluted from the strengthened glass disk was measured using an ICP emission analyzer.

  This chemical strengthening solution was heated to 340 ° C. to 380 ° C., and the glass disk that had been washed and dried was immersed for about 2 hours to 4 hours to perform chemical strengthening treatment. In this immersion, in order to chemically strengthen the entire surface of the glass disk, it was carried out in a state of being accommodated in a holder so that a plurality of glass disks were held on the outer peripheral end surface.

  The glass disk that had been subjected to the chemical strengthening treatment was immersed in a water bath at 20 ° C. to be rapidly cooled and maintained for about 10 minutes.

  And the glass disk which finished quenching was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned. Further, the magnetic disk glass substrate after the sulfuric acid cleaning is immersed in each of the cleaning tanks of pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying), and then ultrasonically cleaned. And dried.

  Next, a visual inspection was performed on the main surface and end surface of the glass disk that had been cleaned, and further a detailed inspection using light reflection, scattering, and transmission was performed. As a result, no defects such as protrusions or scratches due to deposits were found on the main surface and end surface of the glass disk.

  Further, the surface roughness of the main surface of the glass disk that has undergone the above-described steps was measured by an atomic force microscope (AFM). As a result, the Rmax was 2.5 nm, the Ra was 0.30 nm, It was confirmed that The numerical value of the surface roughness is calculated according to Japanese Industrial Standard (JIS) B0601 for the surface shape measured by AFM (Atomic Force Microscope).

  Further, the surface roughness of the inner peripheral end face of the circular hole of this glass disk is as follows: Rmax at the chamfered surface is 0.4 μm, Ra is 0.04 μm, Rmax is 0.4 μm at the portion other than the chamfered surface, and Ra is 0.05 μm. Met. The surface roughness Ra at the outer peripheral end face was 0.04 μm at the chamfered surface and 0.07 μm at portions other than the chamfered surface. As described above, it was confirmed that the inner peripheral end face was finished in a mirror shape like the outer peripheral end face.

  Further, no foreign matter or particles causing thermal asperity were found on the surface of the glass disk, and no foreign matter or cracks were found on the inner peripheral end face of the circular hole.

(9) Texture processing Prior to texture processing, first, the main surface of the glass disk was cleaned with a cleaning solution containing acid. A cleaning liquid containing hydrochloric acid as a main component was used.

The concentration of hydrochloric acid in this cleaning solution was 0.006 mol%. And after washing | cleaning by this washing | cleaning liquid and before texturing, ratio (Fe / Si) of the quantity of the iron element with respect to the quantity of the silicon element in the surface of a glass disk was about 2 * 10 < ^-5 >.

  FIG. 1 shows the amount of foreign matter (iron contamination) on the surface of the glass disk before texture processing in this example and other examples and comparative examples described later.

  Next, texture processing was performed. This texturing is performed by “mechanical texturing” in which a glass disk and an abrasive tape sandwiching both main surfaces of the glass disk are relatively slidably moved in a predetermined state using a texturing apparatus. I went to the end face. Relative sliding between the glass disk and each polishing tape was performed as a movement that swings in a sine curve with respect to the circumferential direction, based on movement in the circumferential direction (tangential direction) of the glass disk. . At this time, a liquid abrasive containing diamond abrasive grains as abrasive grains was supplied between the glass disk and each abrasive tape.

  After the texturing, the glass disk was scrubbed to obtain a magnetic disk glass substrate.

  In addition, the surface roughness of the main surface of the glass substrate for magnetic discs in this example, other examples described later, and each comparative example is shown in FIG.

(10) Magnetic disk manufacturing process (film formation process)
Next, the magnetic disk according to the present invention was manufactured through the following steps.

  On both main surfaces of the glass substrate for a magnetic disk obtained by the above-described process, using a stationary facing DC magnetron sputtering apparatus, an Al—Ru alloy seed layer, a Cr—W alloy underlayer, Co—Cr—Pt A magnetic layer of Ta alloy and a hydrogenated carbon protective layer were sequentially formed. The seed layer has an effect of refining the magnetic grains of the magnetic layer, and the underlayer has an effect of orienting the easy axis of magnetization of the magnetic layer in the in-plane direction.

  This magnetic disk is a non-magnetic substrate for a magnetic disk, a magnetic layer formed on the magnetic disk glass substrate, a protective layer formed on the magnetic layer, and formed on the protective layer. And at least a lubricated layer.

  A nonmagnetic metal layer (nonmagnetic underlayer) including a seed layer and an underlayer is formed between the magnetic disk glass substrate and the magnetic layer. In this magnetic disk, the layers other than the magnetic layer are all made of a nonmagnetic material. In this example, the magnetic layer, the protective layer, the protective layer, and the lubricating layer were formed in contact with each other.

  That is, first, an Al—Ru (aluminum-ruthenium) alloy (Al: 50 at%, Ru: 50 at%) is used as a sputtering target, and is made of a 30 nm thick Al—Ru alloy on a magnetic disk glass substrate. A seed layer was formed by sputtering. Next, using a Cr—W (chromium-tungsten) alloy (Cr: 80 at%, W: 20 at%) as a sputtering target, an underlayer made of a 20 nm thick Cr—W alloy is formed on the seed layer 5. A film was formed by sputtering. Next, as a sputtering target, using a sputtering target made of a Co—Cr—Pt—Ta (cobalt-chromium-platinum-tantalum) alloy (Cr: 20 at%, Pt: 12 at%, Ta: 5 at%, balance Co), A magnetic layer made of a Co—Cr—Pt—Ta alloy having a film thickness of 15 nm was formed on the underlayer by bias sputtering.

  Next, a protective layer made of hydrogenated carbon was formed on the magnetic layer by a bias CVD method, and a lubricating layer made of PFPE (perfluoropolyether) was formed by a dip method. The protective layer functions to protect the magnetic layer from the impact of the magnetic head. In this way, a magnetic disk was obtained.

[Example 2]
In Example 2, the concentration of hydrochloric acid used as a cleaning liquid in the cleaning of the main surface of the glass disk prior to texturing was set to 0.01 M%. And after washing | cleaning by this washing | cleaning liquid and before texture processing, ratio (Fe / Si) of the quantity of the iron element with respect to the quantity of the silicon element in the surface of a glass disk was about 1.6 * 10 < ^-5 >.

  Otherwise, a glass substrate for magnetic disk was prepared in the same manner as in Example 1 described above. A magnetic disk was prepared using this magnetic disk glass substrate.

Example 3
In Example 3, the concentration of hydrochloric acid used as a cleaning liquid in the cleaning of the main surface of the glass disk prior to texturing was set to 0.002 M%. And after washing | cleaning by this washing | cleaning liquid and before texturing, ratio (Fe / Si) of the quantity of the iron element with respect to the quantity of the silicon element in the surface of a glass disk was about 1.7 * 10 < ^-5 >.

  Otherwise, a glass substrate for magnetic disk was prepared in the same manner as in Example 1 described above. A magnetic disk was prepared using this magnetic disk glass substrate.

Example 4
In Example 4, in the cleaning of the main surface of the glass disk prior to the texturing, the concentration of hydrochloric acid used as the cleaning liquid was 0.02 M%. And after washing | cleaning by this washing | cleaning liquid and before texturing, ratio (Fe / Si) of the quantity of the iron element with respect to the quantity of the silicon element in the surface of a glass disc was about 3 * 10 < ^-5 >.

  Otherwise, a glass substrate for magnetic disk was prepared in the same manner as in Example 1 described above. A magnetic disk was prepared using this magnetic disk glass substrate.

[Comparative Example 1]
In Comparative Example 1, the main surface of the glass disk was not cleaned prior to texturing. Prior to texturing, the ratio of the amount of iron to the amount of silicon on the surface of the glass disk (Fe / Si) was about 7 × 10 ⁻⁵ .

  In addition, when the glass surface was observed using the scanning electron microscope (SEM: Scanning Electron Microscope), many iron contaminations remained.

  Otherwise, a glass substrate for magnetic disk was prepared in the same manner as in Example 1 described above. A magnetic disk was prepared using this magnetic disk glass substrate.

[Comparative Example 2]
In Comparative Example 2, a potassium hydroxide (KOH) solution was used as a cleaning solution in cleaning the main surface of the glass disk prior to texturing. After cleaning with this cleaning solution and before texturing, the ratio of the amount of iron element to the amount of silicon element (Fe / Si) on the surface of the glass disk was about 4 × 10 ⁻⁵ .

  In addition, when the glass surface was observed using the scanning electron microscope (SEM: Scanning Electron Microscope), many iron contaminations remained.

  Otherwise, a glass substrate for magnetic disk was prepared in the same manner as in Example 1 described above. A magnetic disk was prepared using this magnetic disk glass substrate.

[Contrast of Examples and Comparative Examples]
Glide inspection was performed on a magnetic disk manufactured using the glass substrate for magnetic disk of each of the above-described Examples and Comparative Examples with a glide head having a flying height of 6 nm. The results are shown in [Table 1] below. This glide inspection is to determine whether or not the magnetic head maintains a stable flying state by detecting a foreign object or the like that collides with the magnetic head.

  The non-defective rate of the glide test is desired to be 90% or more, but the magnetic disks in Examples 1 to 4 all have a satisfactory pass rate of 90% or more in the glide inspection. However, in Example 3 and Example 4, the ratio of the amount of iron element to the amount of silicon element on the glass substrate surface is significantly reduced as compared with Comparative Example 2 without cleaning, but as shown in FIG. In addition, since the specification ranges Rmax 3 nm to 10 nm and Ra 0.4 nm to 1.7 nm required here are out of the range, the surface roughness is somewhat deteriorated, and this seems to affect the yield rate of the glide test. .

  On the other hand, the magnetic disk in each comparative example has a low pass rate of 65% in the glide inspection. In Comparative Example 1 and Comparative Example 2, the ratio of the amount of iron element to the amount of silicon element on the main surface of the glass disk is larger than that of the glass disk in each example, which seems to affect the non-defective rate of the glide test. .

  In the magnetic disks of Example 1 and Example 2, good results with a magnetic anisotropy of 1.5 or more were obtained.

  In addition, a load / unload durability test was performed on the magnetic disks obtained in Examples 1 to 4. That is, the obtained magnetic disk was mounted on a hard disk drive, and the load / unload operation was repeated continuously. As a result, it was confirmed that the load / unload durability was sufficient for a load / unload operation of 600,000 times or more and the durability was sufficient.

It is a graph which shows ratio of the quantity of the iron element with respect to the quantity of the silicon element in the surface of the glass disk of each Example which concerns on this invention, and each comparative example. It is a graph which shows the surface roughness of the main surface of the glass substrate for magnetic discs of each Example which concerns on this invention, and each comparative example.

Claims (7)

A method for producing a glass substrate for a magnetic disk having a linear texture on the surface,
After the main surface of the glass substrate is cleaned with a cleaning solution containing an acid, a texture is formed on the main surface of the glass substrate. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the cleaning liquid contains hydrochloric acid as a main component. The method for producing a glass substrate for a magnetic disk according to claim 2, wherein the cleaning liquid has a hydrochloric acid concentration of 0.006 mol% or more and 0.01 mol% or less. By pressing a polishing tape against the main surface of the disk-shaped glass substrate and relatively moving the polishing tape and the glass substrate, a substantially regular line oriented in the circumferential direction of the disk on the main surface of the glass substrate. A method for producing a glass substrate for a magnetic disk including a process for forming a texture having a concavo-convex shape,
When the amount of iron element present on the surface of the glass substrate is analyzed based on the total reflection X-ray fluorescence analysis method in at least the region of the glass substrate that contacts the polishing tape, the silicon element contained in the glass and The ratio (Fe / Si) of 2 × 10 ⁻⁵ or less,
A process for forming the texture is performed on the glass substrate. A method of manufacturing a glass substrate for magnetic disks. The method for producing a glass substrate for a magnetic disk according to claim 4, wherein the region in contact with the polishing tape is mirror-polished in advance before forming the texture. The region in contact with the polishing tape is cleaned in advance with a processing solution that is soluble in at least iron-containing foreign matter before the formation of the texture. The manufacturing method of the glass substrate for magnetic disks of description. A magnetic disk comprising at least a magnetic layer formed on a main surface portion of a glass substrate for magnetic disk manufactured by the method for manufacturing a glass substrate for magnetic disk according to claim 1. Manufacturing method.