JP2007265505A - Manufacturing method of magnetic disk and evaluating method of magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a magnetic disk capable of suppressing corrosion of a recording and reproducing element of a magnetic head even when the floating height of the magnetic head is specified to ≤10 nm and preventing fly-stiction, head crash, and thermal asperity in a magnetic disk device especially adopting an LUL system, and to provide the evaluating method of the magnetic disk. <P>SOLUTION: An SO<SB>4</SB><SP>2-</SP>ion concentration and a CO<SP>2-</SP>ion concentration extracted by a warm water extraction method after the magnetic disk is left in the atmosphere of an SO<SB>2</SB>gas are controlled by controlling a concentration of nitrogen contained in a carbonic protective layer in a prescribed concentration or more. Thereby corrosion occurrence rate of a recording and reproducing element part of the magnetic head performing recording and reproduction to/from the magnetic disk is reduced to be a prescribed rate or below. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a magnetic disk used in a hard disk drive (HDD) which is a magnetic disk device, and a method for evaluating such a magnetic disk.

  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.

  In such a magnetic disk, a magnetic layer for recording information is formed on a substrate made of glass or the like, and a protective layer for protecting the magnetic layer is formed on the magnetic layer, and a magnetic head flying up is used. A lubricating layer for reducing the interference is formed.

  In recent magnetic disks, as a result of improving the spacing loss between the magnetic disk and the recording / reproducing element of the magnetic head and improving the S / N ratio (Signal Noise Ratio) of the recording signal, the information recording density is 1. It has reached 60 gigabits per square inch, and an ultrahigh recording density exceeding 100 gigabits per square inch is also being realized. 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.

  In such a magnetic disk, in order to realize an information recording density exceeding 60 gigabits per square inch, the magnetic spacing between the magnetic disk and the recording / reproducing element of the magnetic head should be narrowed to 20 nm or less. Is required. Thus, from the viewpoint of realizing sufficiently narrow magnetic spacing, the thickness of the protective layer in the magnetic disk is required to be 3 nm or less. The flying height of the magnetic head is required to be 10 nm or less.

  By the way, in order to increase the information recording capacity of the magnetic disk, it is necessary to reduce the area of a useless area in which no information signal is 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. This is because 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 the LUL system, the flying height of the magnetic head can be further reduced as compared with the magnetic disk for the CSS system, and the S / N ratio of the recording signal can be improved. There is also an advantage that high recording density can be achieved.

  Note that various organic materials are used in the magnetic disk device in which such a magnetic disk is used, and these are vaporized in the magnetic disk device, adsorbed to the magnetic head, and become a contamination source of the magnetic head. There is a fear. Due to such contamination, the magnetic head flying posture may be disturbed, which may result in inability to write / read signals and damage the magnetic disk. In Patent Document 1, as a means for solving such a problem, a gas adsorption film 7 is provided on the non-recording / reproducing surface of a magnetic disk, and the organic gas generated in the magnetic disk apparatus is adsorbed by the gas adsorption film 7. Are listed.

JP 2001-338415 A

  By the way, in the magnetic disk apparatus, along with the introduction of the LUL system as described above, the corrosion failure of the recording / reproducing element portion has frequently occurred in the magnetic head. When a corrosion phenomenon occurs in the recording / reproducing element in the magnetic head, the read signal output decreases, and read errors occur frequently, making it impossible to reproduce at all, or the corroded area increases, causing magnetic fields during flying. There is a risk of damaging the disc.

  As a result of repeated studies on this problem, the present inventor has clarified the cause of frequent occurrence of corrosion failures in a magnetic disk device adopting the LUL method.

  That is, in recent magnetic heads, NPAB sliders (negative pressure sliders) that are easy to control the flying height are employed. When the magnetic head using the NPAB slider is flying, negative pressure is generated on the slider surface. For this reason, the magnetic head gradually collects and concentrates a small amount of organic and inorganic deposits on the recording / reproducing area of the magnetic disk and a highly fluid lubricating layer on the slider surface like a vacuum cleaner. And deposited on the slider surface.

  In the magnetic disk apparatus adopting the CSS method, the deposited material transferred to the magnetic head in this way is cleaned when the magnetic head contacts and slides on the contact sliding area of the magnetic disk. However, in a magnetic disk apparatus adopting the LUL method, such a cleaning is not performed because the magnetic head does not slide on the magnetic disk. For this reason, in the magnetic disk drive adopting the LUL method, the contamination that has been transferred to the magnetic head and concentrated, in particular acidic contamination such as sulfide contamination, chloride contamination, nitride contamination, etc. is generated in the reproducing element section. Cause corrosion. In particular, magnetoresistive effect reproducing elements (MR element, GMR element, TMR element, etc.) with high output are easily corroded by these contaminants.

  Further, the magnetoresistive head has a recording / reproducing separation structure in which a recording element and a reproducing element are separated, unlike a thin film head conventionally used. In a magnetic head having a recording / reproducing separation structure, it is necessary to form a shield made of permalloy or the like such as Fe—Ni between the recording element and the reproducing element. Since such a material such as permalloy is an alloy that is easily corroded, the magnetoresistive head needs to be protected more severely from the corrosion phenomenon than the conventional thin film head.

  Further, in a magnetic disk device adopting the LUL method, cleaning by contact sliding on the magnetic disk is not performed, so that the lubricant forming the lubricating layer of the magnetic disk is easily transferred and deposited on the magnetic head. It has been found that the lubricant transferred and deposited on the magnetic head in this manner greatly disturbs the flying posture of the magnetic head and easily causes fly stiction failure. 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, when this fly stiction failure occurs, 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, and the magnetic disk may be destroyed. is there. Further, it has been found that when a certain amount of transfer material is deposited on the magnetic head, the transfer material may fall on the magnetic disk during the flying of the magnetic head and cause a crash.

  In addition, since the surface of the magnetic disk has been smoothed as a result of adopting the LUL method, a small amount of organic and inorganic deposits present on the surface of the magnetic disk and the movement of a highly fluid lubricant are transferred. It became clear that the transfer of these deposits and lubricants to the magnetic head was promoted. Furthermore, it has been found that a decrease in the flying height of the magnetic head also promotes the transfer of deposits and lubricants to the magnetic head.

  For these reasons, in a magnetic disk apparatus adopting the LUL method, the flying height of the magnetic head can be stabilized without inhibiting the transfer of deposits and lubricant on the magnetic disk to the magnetic head. It was found that it was difficult to make it 10 mm or less.

  The technique described in Patent Document 1 is intended for a magnetic disk having a magnetic layer formed only on one side of the substrate, and can be applied to a magnetic disk having a magnetic layer formed on both sides of the substrate. Can not. In addition, in the magnetic disk apparatus adopting the LUL system as described above, the corrosion failure of the recording / reproducing element portion of the magnetic head cannot be sufficiently prevented.

  Accordingly, the present invention has been proposed in view of the above-described circumstances, and the object thereof is to provide a magnetic disk apparatus that employs the LUL method, even when the flying height of the magnetic head is 10 mm or less. A method of manufacturing a magnetic disk and a method of evaluating such a magnetic disk capable of suppressing corrosion failure of a recording / reproducing element of a magnetic head and preventing fly stiction failure, head crash failure, and thermal asperity failure Is to provide.

The inventor has found that the corrosion phenomenon of the recording / reproducing element of the magnetic head in the magnetic disk apparatus, the concentration of SO ₄ ^2- ion adhering to the surface of the magnetic disk after leaving the magnetic disk in the SO ₂ gas atmosphere, and When the correlation between the CO ² -ion concentration and the nitrogen concentration contained in the protective layer of the magnetic disk was studied, the correlation between these corrosion phenomena and the SO ₄ ² -ion concentration, the CO ² -ion concentration and the nitrogen concentration was investigated. It was found that there was a predetermined correlation.

Based on this correlation, by measuring and managing the SO ₄ ^2- ion concentration and the CO ^{2 -} ion concentration adhering to the surface of the magnetic disk and the nitrogen concentration contained in the protective layer of the magnetic disk, the magnetic It becomes possible to easily predict the corrosion phenomenon of the head, and to manufacture a magnetic disk that does not cause the corrosion phenomenon in the magnetic head.

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

[Configuration 1]
A method of manufacturing a magnetic disk in which at least a magnetic layer, a carbon-based protective layer, and a lubricating layer are formed in this order on a substrate, wherein the concentration of nitrogen contained in the carbon-based protective layer is controlled to a predetermined concentration or more. A recording / reproducing element for a magnetic head that controls the SO ₄ ²⁻ ion concentration and the CO ²⁻ ion concentration extracted by a hot water extraction method after leaving the magnetic disk in an SO ₂ gas atmosphere, and performs recording / reproducing on the magnetic disk. The rate of occurrence of corrosion in the part is set to a predetermined rate or less.

[Configuration 2]
A method for evaluating a magnetic disk in which at least a magnetic layer, a carbon-based protective layer, and a lubricating layer are formed in this order on a substrate, the magnetic disk being left in an SO ₂ gas atmosphere and then extracted by a hot water extraction method The SO ₄ ^2- ion concentration and the CO ^2- ion concentration are measured, and the concentration of nitrogen contained in the carbon-based protective layer is measured. Based on these SO ₄ ^2- ion concentration, CO ^2- ion concentration, and nitrogen concentration Thus, the corrosion occurrence rate in the recording / reproducing element portion of the magnetic head for performing recording / reproducing with respect to the magnetic disk is calculated.

[Configuration 3]
In the method for evaluating a magnetic disk having Configuration 2, the corrosion rate of the recording / reproducing element of the magnetic head is Y (%), the SO ₄ ^2- ion concentration is X ₁ (ng / m ² ), and the CO ² -ion concentration is X ₂ (ng / m ² ), where the concentration of nitrogen contained in the carbon-based protective layer is X ₃ (%), the corrosion in the recording / reproducing element portion of the magnetic head that performs recording / reproducing with respect to this magnetic disk according to the following equation: The occurrence rate is calculated.
Y = 1.19X ₁ + 4.63X ₂ −12.6X ₃ +61.7

In the method of manufacturing a magnetic disk according to the present invention having the configuration 1, the concentration of nitrogen contained in the carbon-based protective layer is controlled to be equal to or higher than a predetermined concentration, so that the magnetic disk is allowed to stand in the SO ₂ gas atmosphere and then heated. Since the SO ₄ ²⁻ ion concentration and the CO ²⁻ ion concentration extracted by the extraction method are controlled, and the corrosion occurrence rate in the recording / reproducing element portion of the magnetic head that performs recording / reproducing with respect to this magnetic disk is set to a predetermined rate or less, Corrosion failure of the read / write element of the magnetic head can be suppressed, and fly stiction failure, head crash failure, and thermal asperity failure can be prevented.

In the method of manufacturing a magnetic disk according to the present invention having the configuration 2, the SO ₄ ^2- ion concentration and the CO ^{2 -} ion concentration extracted by the hot water extraction method are measured after the magnetic disk is left in the SO ₂ gas atmosphere. Further, the recording / reproduction of a magnetic head that measures the concentration of nitrogen contained in the carbon-based protective layer and performs recording / reproduction on the magnetic disk based on the SO ₄ ²⁻ ion concentration, the CO ²⁻ ion concentration, and the nitrogen concentration. Since the corrosion occurrence rate in the element portion is calculated, it is possible to evaluate whether or not this magnetic disk is likely to cause a corrosion failure in the recording / reproducing element of the magnetic head.

In the method for evaluating a magnetic disk according to the present invention having Configuration 3, the corrosion rate of the recording / reproducing element of the magnetic head is Y (%), the SO ₄ ^2- ion concentration is X ₁ (ng / m ² ), CO ^{2. -} ion concentration _{X 2 (ng / m 2)} , when the concentration of nitrogen contained in the carbon-based protective layer was X _{3 (%),} the formula shown these correlations, performs recording and reproduction with respect to the magnetic disk Since the corrosion occurrence rate in the recording / reproducing element portion of the magnetic head is calculated, it is possible to accurately evaluate whether or not this magnetic disk is likely to cause a corrosion failure in the recording / reproducing element of the magnetic head.

  That is, according to the present invention, in the magnetic disk device adopting the LUL method, even when the flying height of the magnetic head is 10 mm or less, the corrosion failure of the recording / reproducing element of the magnetic head can be suppressed. It is possible to provide a method for manufacturing a magnetic disk capable of preventing fly stiction failure, head crash failure, and thermal asperity failure, and a method for evaluating such a magnetic disk.

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

[Outline of magnetic disk and its manufacturing method]
FIG. 1 is a plan view (a) and a cross-sectional view (b) showing the configuration of a magnetic disk manufactured by the method of manufacturing a magnetic disk according to the present invention.

  A magnetic disk manufactured by the method of manufacturing a magnetic disk according to the present invention is a magnetic disk mounted on a hard disk drive, and is made of a nonmagnetic and nonconductive material as shown in FIG. Using a circular disk substrate 1 having a central hole 1a, an underlayer 2, a magnetic layer 3, and a carbon-based protective layer 4 are formed on the surface 1b of the disk substrate 1 as shown in FIG. These layers are stacked in this order to form a film.

  The disk substrate 1 is made of, for example, chemically strengthened glass such as aluminosilicate glass, aluminoborosilicate glass, or soda lime glass. In the case of a 1.0 inch type, the outer diameter is 27 mm and the inner diameter (the diameter of the center hole 1a). Is 7 mm and the thickness is 0.381 mm. The surface 1b of the disk substrate 1 is mirror-polished so that the surface roughness is 0.4 nm or less in Ra and 5 nm or less in Rmax.

  In order to manufacture the magnetic disk 1, first, the first underlayer 2a is formed on the surface 1b of the disk substrate 1 by physical vapor deposition such as DC magnetron sputtering. The first underlayer 2a is, for example, an AlRu alloy thin film having a thickness of 5 nm. Next, the second underlayer 2b is formed on the first underlayer 2a by a DC magnetron sputtering method or the like. The second underlayer 2b is, for example, a CrMoTi alloy thin film having a thickness of 50 nm. The underlayer 2 composed of the first underlayer 2a and the second underlayer 2b is formed in order to improve the crystal structure of the magnetic layer 3.

  Next, the magnetic layer 3 is formed on the underlayer 2 (second underlayer 2b) by physical vapor deposition such as DC magnetron sputtering. The magnetic layer 3 is, for example, a CoCrB alloy thin film having a thickness of 15 nm.

  Next, the carbon-based protective layer 4 is formed on the magnetic layer 3 by plasma CVD. The carbon-based protective layer 4 is made of, for example, amorphous diamond-like carbon having a thickness of 3 nm, and has a function of protecting the magnetic layer 3 by improving wear resistance.

  Next, the lubricating layer 5 is formed on the surface of the protective layer 4 by a dipping method. The lubricating layer 5 is made of, for example, a perfluoropolyether layer having a thickness of 1.2 nm, and has a function of mitigating impact when contacting the magnetic head.

[Evaluation method of magnetic disk]
In the magnetic disk evaluation method according to the present invention, first, the magnetic disk is left in an SO ₂ gas atmosphere. For example, a magnetic disk is placed in a 12.2 L capacity desiccator, 10 ppm of SO ₂ gas is enclosed in the desiccator, and then left in an environment of 40 ° C. and 75% RH for 12 hours.

Through this step, SO ₂ gas is acceleratedly attached to the magnetic disk. By this step, SO ₄ ^2- ion adhering to the magnetic disk becomes substantially the same value as SO ₄ ^2- ion adhering when the magnetic disk is loaded in a normal magnetic disk apparatus and left for 10 days, and the measurement time is reduced. It can be shortened to 1/20.

Next, this magnetic disk is immersed in pure water at 80 ° C. to perform hot water extraction. This is a process for measuring the concentration of SO ₄ ^2- ion and CO ^{2 -} ion adhering to the magnetic disk exposed to SO ₂ gas. The CO ²⁻ ions are considered to be caused by atoms diffusing from the magnetic layer 3.

The hot water extraction refers to, for example, extracting five magnetic disks and 50 ml of pure water in a polypropylene bag and immersing them in water heated to 80 ° C. for 60 minutes. After hot water extraction, ions extracted into pure water are analyzed by ion chromatography, and the concentrations of SO ₄ ^2- ion and CO ^2- ion are measured.

  On the other hand, the concentration of nitrogen contained in the carbon-based protective film 4 of this magnetic disk is measured by X-ray photoelectron spectroscopy.

In the present invention, the magnetic disk uses the SO ₄ ²⁻ ion concentration, the CO ²⁻ ion concentration, and the nitrogen concentration to corrode the recording / reproducing element of the magnetic head that performs recording / reproducing with respect to the magnetic disk. It is evaluated whether or not the magnetic disk is likely to cause a magnetic disk. Therefore, in the present invention, the correlation between the concentration of SO ₄ ²⁻ ions, the concentration of CO ²⁻ ions and the concentration of nitrogen and the corrosion rate of the recording / reproducing element of the magnetic head is obtained in advance. By applying SO ₄ ²⁻ ion concentration, CO ²⁻ ion concentration and nitrogen concentration to this correlation, the corrosion rate of the recording / reproducing element of the magnetic head is calculated to evaluate the magnetic head.

In order to obtain this correlation, the load / unload endurance test (LUL test) was performed for the magnetic disk left (exposed) in the SO ₂ gas atmosphere as described above in an environment of 70 ° and 80% RH. )I do. That is, the magnetic disk is mounted on the hard disk drive, and the load / unload operation is continuously repeated. After completion of the load / unload durability test, the recording / reproducing element portion of the magnetic head is observed with a scanning electron microscope to observe the presence or absence of corrosion.

By comparing the corrosion rate of the recording / reproducing element of the magnetic head in the result of such a load / unload durability test with the above-mentioned SO ₄ ^2- ion concentration, CO ^2- ion concentration, and nitrogen concentration, these SO 4 ₄ Correlation between ^2- ion concentration, CO ^2- ion concentration and nitrogen concentration and the corrosion rate of the read / write element of the magnetic head is obtained.

The correlation thus obtained is that the corrosion occurrence rate of the recording / reproducing element of the magnetic head is Y (%), the SO ₄ ^2- ion concentration is X ₁ (ng / m ² ), and the CO ^2- ion concentration is X ₂ (ng / m ² ), when the concentration of nitrogen contained in the carbon-based protective layer was X ₃ (%), as shown in the examples described later, it was represented by the following formula.

Y = 1.19X ₁ + 4.63X ₂ −12.6X ₃ +61.7
In the present invention, since the outgas control is enhanced in the magnetic disk device, even when the corrosion of the magnetic head is hardly observed by a normal load / unload durability test, the magnetic disk is left in the SO ₂ gas atmosphere. Since the sulfur-based gas is adhered to the magnetic disk in a short time and by adjusting the amount of adhesion, a quick evaluation can be performed.

After the correlation between the SO ₄ ²⁻ ion concentration, the CO ²⁻ ion concentration and the nitrogen concentration and the corrosion rate of the recording / reproducing element of the magnetic head is obtained, the SO ₄ ²⁻ ion concentration, Since only the CO ²⁻ ion concentration and the nitrogen concentration are obtained, the corrosion rate of the recording / reproducing element can be calculated. Therefore, the magnetic disk can be evaluated without performing a load / unload durability test.

[Method of manufacturing magnetic disk]
In the present invention, in the magnetic disk manufacturing process, the recording / reproducing element portion of the magnetic head that performs recording / reproducing on the magnetic disk by controlling the concentration of nitrogen contained in the carbon-based protective layer to a predetermined concentration or less. The corrosion occurrence rate in can be reduced to a predetermined rate or less.

That is, from the correlation between the SO ₄ ²⁻ ion concentration, the CO ²⁻ ion concentration and the nitrogen concentration obtained as described above, and the corrosion rate of the recording / reproducing element of the magnetic head, it is included in the carbon-based protective layer. By controlling the concentration of nitrogen, the SO ₄ ^2- ion concentration and the CO ^{2 -} ion concentration extracted by the hot water extraction method after the magnetic disk is left in the SO ₂ gas atmosphere can be controlled below a predetermined concentration. The corrosion rate of the recording / reproducing element can be lowered.

That is, from the above equation showing the correlation, the concentration X ₃ of nitrogen contained in the carbon-based protective layer is 4.91%, the SO ₄ ^2- ion concentration X ₁ is 0 ng / m ² , and the CO ^2- ion concentration X _{If 2} is 0 ng / m ² , the corrosion rate Y of the recording / reproducing element is 0%.

Further, even when the SO ₄ ^2- ion concentration X ₁ due to adhesion and the CO ^2- ion concentration X ₂ due to elution are not 0 ng / m ² , the concentration X ₃ of nitrogen contained in the carbon-based protective layer is increased. Further, the corrosion rate Y of the recording / reproducing element can be reduced. This, the higher the concentration X ₃ of nitrogen contained in the carbon-based protective layer, hardly occur adhesion of SO ₄ ^2-ions, also dissolution of CO ^2-ions by becoming high coverage of the carbon-based protective layer It seems to be because there is less.

Therefore, it is preferable that the concentration X ₃ of nitrogen contained in the carbon-based protective layer and 4.91% or more.

  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.

The magnetic disk in this example described below was prepared by the following steps (1) to (8).
(1) Rough grinding step (2) Shape processing step (3) Fine grinding step (4) End surface polishing step (5) First polishing step (6) Second polishing step (7) Chemical strengthening step

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%.

(1) Rough grinding process Using a sheet glass of 0.6 mm thickness formed from a molten aluminosilicate glass as a glass base material, from this sheet glass, a diameter of 28.7 mm and a thickness of 0.6 mm A disk-shaped glass disk was obtained.

As a method for forming the sheet glass, a downdraw method or a float method is generally used. However, in addition to this, a disk-shaped glass base material may be obtained by direct pressing. The aluminosilicate glass which is a material of the sheet glass, a SiO ₂ 58 to 75 wt%, _Al 2 _{O 3} from 5 to 23 wt%, a Na ₂ O 4 to 13 wt%, Li ₂ O 3 to 10 Any material may be used as long as it contains 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.

(2) Shape processing step Next, while using a cylindrical grindstone, a circular hole having a diameter of 6.1 mm was formed in the central portion of the glass disk, and the outer peripheral end face was ground to a diameter of 27.43 mm. Thereafter, chamfering of approximately 45 ° was performed along the peripheral edge of the main surface at the outer peripheral end surface and the inner peripheral end surface. The surface roughness of the end face of the glass disk at this time was about 4 μm in Rmax.

(3) Fine grinding step Next, the grain size of the abrasive grains is changed to # 1000, and the main surface of the glass disk is ground, so that 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.

(4) End face polishing step Next, the end face of the glass disk is polished by brush polishing conventionally used while rotating the glass disk, 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. When the diameter of the glass disk was measured after the end face polishing process, it was 27.4 mm.

(5) First Polishing Step Next, a first polishing step was performed using a double-side polishing apparatus in order to remove scratches and distortion 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 examples. 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.

(6) 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 changed to 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.

  And the glass disk which finished this 2nd grinding | polishing process is immersed in each washing | cleaning tank of neutral detergent, pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying) one by one. , Ultrasonically cleaned and dried.

(7) Chemical strengthening process Next, the chemical strengthening process was performed with respect to the glass disk which finished the 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. In addition, the glass disk that has been washed with sulfuric acid is immersed in a cleaning bath of pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying) sequentially, ultrasonically cleaned, and dried. I let you.

  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).

  In addition, the glass disk that has undergone the above-described steps has an inner diameter of 7 mm, an outer diameter of 27.4 mm, and a plate thickness of 0.381 mm, which is a predetermined size of a glass substrate used for a “1.0 inch type” magnetic disk. I confirmed that there was.

  Further, the surface roughness of the inner peripheral end surface of the circular hole of the glass substrate is as follows: Rmax at the chamfered surface is 0.4 μm, Ra is 0.04 μm, Rmax is 0.4 μm at other portions 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 substrate, and no foreign matter or cracks were found on the inner peripheral end face of the circular hole.

(8) Film-forming process On the both main surfaces of the glass substrate obtained by the above-mentioned process, the first underlayer of the Al—Ru alloy and the second of the Cr—W alloy are used by using a stationary opposed DC magnetron sputtering apparatus. An underlayer, a Co—Cr—Pt—Ta alloy magnetic layer, and a carbon-based protective layer were sequentially formed. The first underlayer has the effect of reducing the magnetic grains of the magnetic layer, and the second underlayer has the effect of orienting the easy axis of magnetization of the magnetic layer in the in-plane direction.

  Using a Al—Ru (aluminum-ruthenium) alloy (Al: 50 at%, Ru: 50 at%) as a sputtering target, a first underlayer made of an Al—Ru alloy with a thickness of 30 nm is sputtered on a glass substrate. Was formed. Next, using a Cr—W (chromium-tungsten) alloy (Cr: 80 at%, W: 20 at%) as a sputtering target, the first underlayer 5 is made of a 20 nm thick Cr—W alloy. An underlayer 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 carbon-based protective layer (hydrogenated carbon protective layer) 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 carbon-based protective layer has an effect of protecting the magnetic layer from the impact of the magnetic head. In this way, a magnetic disk was obtained. About this carbon-type protective layer, the thing from which the nitrogen concentration contained differs was created.

[Evaluation of magnetic disk]
As described above, magnetic disks having different nitrogen concentrations contained in the carbon-based protective film were prepared, and each was exposed to SO ₂ gas, followed by hot water extraction to obtain SO ₄ ^2- ion and CO ^2- ion. The concentration of was measured. For each magnetic disk, the concentration of nitrogen contained in the carbon-based protective film was measured.

For exposure to SO ₂ gas, each magnetic disk was placed in a 12.2 L capacity desiccator, 10 ppm of SO ₂ gas was sealed in the desiccator, and then left in an environment of 40 ° C. and 75% RH for 12 hours. Hot water extraction was carried out by placing each magnetic disk in a polypropylene bag with 50 ml of pure water every 5 sheets and immersing it in water heated to 80 ° C. for 60 minutes. The concentration of SO ₄ ²⁻ ions and CO ²⁻ ions was measured by analyzing ions extracted into pure water after hot water extraction by ion chromatography. The concentration of nitrogen contained in the carbon-based protective film was measured by X-ray photoelectron spectroscopy.

Each magnetic disk after exposure to SO ₂ gas was subjected to a load / unload durability test (LUL test) of 400,000 times, and the corrosion state of the recording / reproducing element portion of the magnetic head after the completion was measured using a scanning electron microscope ( Observation by SEM) gave the data shown in [Table 1] below.

In Table 1, Y is the corrosion rate (%) of the recording / reproducing element of the magnetic head, X ₁ is the measured SO ₄ ²⁻ ion concentration (ng / m ² ), and X ₂ is measured. CO ²⁻ ion concentration (ng / m ² ) and X ₃ are the concentration (%) of nitrogen contained in the measured carbon-based protective layer.

Here, assuming that the coefficients of X ₁ , X ₂ , and X ₃ are M ₁ , M ₂ , and M ₃ , the corrosion rate Y can be expressed as follows.

Y = M ₁ X ₁ + M ₂ X ₂ + M ₃ X ₃ + B
Based on this equation, regression analysis was performed using the method of least squares. As a result, the following equation was obtained.

Y = 1.19X ₁ + 4.63X ₂ −12.6X ₃ +61.7
The correlation coefficient was R = 0.95, indicating that there was a correlation.

Thus, by actually measuring the SO ₄ ²⁻ ion concentration, the CO ²⁻ ion concentration and the nitrogen concentration contained in the carbon-based protective film after exposure to SO ₂ gas, a load / unload endurance test is not actually performed. In both cases, since these correlations are required, it was confirmed that the corrosion rate of the recording / reproducing element portion of the magnetic head can be predicted.

  Further, it was confirmed that the magnetic disk of Examples 1 to 7 in which the concentration of nitrogen contained in the carbon-based protective film was 4.91% or more had a low corrosion rate at the recording / reproducing element portion of the magnetic head.

[Comparative example]
The magnetic disk of Comparative Examples 1 to 7 was prepared in the same manner as the magnetic disk of the example except that the nitrogen concentration contained in the carbon-based protective film was less than 4.91%. These magnetic disks were exposed to SO ₂ gas and then extracted with warm water, and the concentrations of SO ₄ ^2- ion and CO ^2- ion were measured in the same manner as in the Examples. For each magnetic disk, the concentration of nitrogen contained in the carbon-based protective film was measured. The measurement results are shown in [Table 1].

  As shown in Table 1, in the magnetic disks of Comparative Examples 1 to 7 in which the nitrogen concentration contained in the carbon-based protective film was less than 4.91%, the corrosion rate of the recording / reproducing element portion of the magnetic head was high. It was confirmed to be high.

FIG. 1 is a plan view (a) and a cross-sectional view (b) showing the configuration of a magnetic disk manufactured by the method of manufacturing a magnetic disk according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Disc substrate 1a Center hole 2 Underlayer 3 Magnetic layer 4 Carbon-based protective layer 5 Lubrication layer

Claims (3)

A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer, a carbon-based protective layer and a lubricating layer in this order on a substrate,
By controlling the concentration of nitrogen contained in the carbon-based protective layer to a predetermined concentration or more, the concentration of SO ₄ ^2- ion and CO ² extracted by the hot water extraction method after the magnetic disk is left in the SO ₂ gas atmosphere. ^A method of manufacturing a magnetic disk, characterized in that the corrosion rate in a recording / reproducing element portion of a magnetic head that controls the ion concentration and performs recording / reproducing on the magnetic disk is not more than a predetermined rate. A method for evaluating a magnetic disk in which at least a magnetic layer, a carbon-based protective layer, and a lubricating layer are formed in this order on a substrate,
After the magnetic disk is left in the SO ₂ gas atmosphere, the SO ₄ ^2- ion concentration and the CO ^{2 -} ion concentration extracted by the hot water extraction method are measured, and the concentration of nitrogen contained in the carbon-based protective layer is determined. Measure and calculate the corrosion occurrence rate in the recording / reproducing element portion of the magnetic head that performs recording / reproducing on this magnetic disk based on the SO ₄ ²⁻ ion concentration, CO ²⁻ ion concentration and nitrogen concentration. Magnetic disk evaluation method. Corrosion occurrence rate of the recording / reproducing element of the magnetic head is Y (%), SO ₄ ^2- ion concentration is X ₁ (ng / m ² ), CO ^2- ion concentration is X ₂ (ng / m ² ), carbon-based protection When the concentration of nitrogen contained in the layer is X ₃ (%),
Y = 1.19X ₁ + 4.63X ₂ −12.6X ₃ +61.7
The magnetic disk evaluation method according to claim 2, wherein a corrosion occurrence rate in a recording / reproducing element portion of a magnetic head that performs recording / reproducing on the magnetic disk is calculated by:

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