JP2010073289A - Substrate for magnetic disk and magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate suitable for a hard disk which is highly reliable by preventing crash failure even when a magnetic disk is rotated at a high speed and starts and stops by load/unload system, and the magnetic disk using the same. <P>SOLUTION: The substrate for the magnetic disk avoids head crash by controlling a positional relation between apexes of an elevated portion and settling portion of an edge face 13 of an outer periphery of the substrate within a predetermined range and controlling variation of the positional relation between the apexes of the elevated portion and settling portion in the surface of the substrate within the predetermined range. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a magnetic disk substrate used for a magnetic recording medium, and a magnetic disk using the same.

  In recent years, with the advancement of information technology, information recording technology, particularly magnetic recording technology, has made remarkable progress. There is a magnetic disk as a magnetic recording medium mounted on an HDD (Hard Disk Drive) which is one of the magnetic recording media. For magnetic disks, a film such as NiP (nickel phosphorus) is deposited on a metal substrate made of an aluminum-magnesium alloy, or an underlayer, a magnetic layer, a protective layer, and a lubricating layer are sequentially deposited on a substrate such as a glass substrate or a ceramic substrate. It is configured by stacking. Conventionally, aluminum substrates have been widely used as substrates for magnetic disks. However, with the miniaturization, thinning, and high-density recording of magnetic disks, glass substrates that are superior in substrate surface flatness and substrate strength compared to aluminum substrates are gradually being replaced.

  In addition, a highly rigid glass substrate is advantageous in that it is required to improve impact resistance in order to mount a large-capacity magnetic recording medium in a portable device or an automobile. In order to be mounted on a portable device, the size of the substrate tends to be reduced. For this reason, a 2.5-inch substrate, a 1.8-inch substrate, a 1-inch substrate, or a smaller substrate has been demanded from the conventional 3.5-inch substrate. As the substrate becomes smaller, the allowable dimensional error also becomes smaller, and more precise shape processing is required.

  As the magnetic recording technology has been increased in density, the magnetic head has been changed from a thin film head to a magnetoresistive head (MR head) and a large magnetoresistive head (GMR head). The flying height from is narrowed to 10 nm or less. However, when flying the magnetic head over the magnetic disk with such a very small flying height, there is a problem that a fly stiction failure is likely to occur. The fly stiction failure is a failure in which the magnetic head flying and flying over the magnetic disk modulates the flying posture and the flying height, thereby causing irregular reproduction output fluctuations. Further, when this fly stiction failure occurs, a head crash failure may occur in which the flying magnetic head contacts the magnetic disk. Therefore, high flatness and smoothness are required for the glass substrate surface.

  Further, in order to effectively use the surface area of the glass substrate, a load unload method (Load UnLoad) has been adopted instead of the conventional CSS method (Contact Start Stop). The CSS system is a system in which the magnetic head is brought into contact with the substrate surface when the disk is stopped, and it is necessary to provide an area for CSS (area for sliding contact with the magnetic head) on the substrate surface. On the other hand, the load / unload method is a method of retracting the magnetic head to the outside of the glass substrate when the disk is stopped, and has an advantage that the CSS area can also be used as a recording surface. Further, when the magnetic disk device is stopped, even if a strong impact is applied, the magnetic head is retracted, so that damage to the magnetic disk can be minimized. For a portable small hard disk, a combination of a load / unload start-up reproduction system and a magnetic disk using a glass substrate is selected from the viewpoint of securing an information recording capacity and improving impact resistance.

  In the load / unload method, since the magnetic head passes through the end portion of the glass substrate, the shape near the outer peripheral end surface of the glass substrate is particularly problematic. If the shape of the glass substrate is disturbed (protruding or sinking) near the outer edge, the flying position of the magnetic head will be disturbed, making it easier for the magnetic head to come in contact when entering or exiting the glass substrate. May cause a crash failure. Therefore, high flatness is required particularly near the outer peripheral end face of the disk.

  Further, there is a demand not only for high density but also for high speed magnetic disks. Conventionally, a magnetic disk device mounted with a glass substrate uses a relatively low rotational speed such as 4200 rpm. However, in recent years, it has come to be used at a rotational speed of, for example, 7200 rpm or more. In the near future, it is expected to be used at a rotational speed of 10,000 rpm or more. When such high speed rotation is performed, the linear velocity near the outer peripheral end surface of the magnetic disk increases. For example, in a magnetic disk having a rotational speed of 4200 rpm, the linear velocity at a radius of 32.5 mm from the center of the substrate is 14.3 m / second, but at 5400 rpm, the linear velocity is 18.4 m / second, and at 7200 rpm, the linear velocity is 24. 5 m / sec. In this way, the fly stiction failure and the head crash failure are particularly likely to occur in the vicinity of the outer peripheral end surface of the disk where the linear velocity is high. Therefore, also in this respect, high flatness is required particularly near the outer peripheral end face.

On the other hand, as disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-141852), when the main surface of the substrate is polished, the flatness in the vicinity of the outer peripheral end surface is insufficient. That is, the glass substrate is polished by pressing the front and back main surfaces so as to be sandwiched between the polishing pads and relatively moving the glass substrate and the polishing pad while supplying the slurry containing the abrasive. At this time, there is a ridge called ski jump near the outer peripheral edge of the main surface (the vicinity of the outer peripheral edge of the main surface protrudes more than the other main surface), or sedimentation (near the outer peripheral edge of the main surface) May be in a state of being scraped relatively more than other main surface portions).
JP 2005-141852 A

As described above, the vicinity of the outer peripheral end surface of the magnetic disk is the portion where the linear velocity is the largest and therefore the influence of unevenness is great, and the flatness is most required. Also, the flatness is required in the vicinity of the outer peripheral end surface of the magnetic disk for passing the magnetic head in the load / unload system. However, ski jump or roll-off occurs in the vicinity of the outer peripheral end surface, and the flatness tends to be lowered. Therefore, it is necessary to manage ski jumps and roll-offs as much as possible, or to use these reduced glass substrates for magnetic disks. Also, when manufacturing a magnetic disk substrate, this end shape is used as one of the indicators for determining whether the product is good or defective.
However, as a result of producing a magnetic disk using the magnetic disk substrate managed as described above and producing a hard disk, there has been a problem that head crashes frequently occur.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a hard disk that is highly reliable by suppressing the occurrence of a crash failure even when the magnetic disk is rotated at a high speed, and is started and stopped by a load / unload method. An object is to provide a suitable substrate and a magnetic disk using the same.

  In order to achieve the above object, the inventors of the present application have made extensive studies on the above problems, and as a result, even when the above management is strict, the head crash may or may not occur. I tried to observe the shape of the end. Then, in the case where the ridges and sinking parts coexist in the vicinity of the outer peripheral end face of the substrate, the positional relationship between the apex of the protruding portion and the apex of the sinking portion, and the variation in the plane of the substrate in terms of management are managed. It was found to be an important parameter. Then, the positional relationship between the apex of the raised portion and the apex of the sinking portion is managed within a predetermined range, and the variation of the positional relationship within the plane of the substrate is managed within the predetermined range, thereby preventing head crashes. The present inventors have found that a magnetic disk substrate can be provided and have completed the present invention.

  That is, the magnetic disk substrate according to the present invention is an annular substrate, and includes two main surfaces, an end surface, a chamfered surface formed between the main surface and the end surface, and the main surface. Formed on the peripheral edge of the main surface other than the peripheral edge, and a subsidence part formed on the peripheral edge on the main surface and settled on the flat surface. And when viewed from the cross section of the substrate, the first pole of the main surface of one of the substrates is a point where the bulge of the bulge portion is maximum, and the point where the sink of the sink portion is maximum is the second pole. A length from the center of the substrate to the end surface is d, a point on the main surface at a position 0.4d from the center of the substrate, and a point on the main surface at a position 0.6d from the center of the substrate A straight line connecting the first pole and the second pole, and the reference line Is less than 0.003 degrees, variation in the angle on the entire circumference of the main surface is less than 0.003, a line passing through the first pole and parallel to the reference line, and the second pole The distance between the reference line and the line parallel to the reference line is 1 nm or more and 40 nm or less, and the variation in the distance over the entire circumference on the main surface is 20 nm or less.

In the magnetic disk substrate according to the present invention, it is preferable that the magnetic disk substrate is made of aluminosilicate glass.
A magnetic disk according to the present invention comprises the above-mentioned magnetic disk substrate and a magnetic recording layer formed on the magnetic disk substrate.

  The magnetic disk substrate according to the present invention manages the positional relationship between the apex of the protuberance and the apex of the subsidence within a predetermined range when the protuberance and the subsidence are in the vicinity of the outer peripheral end surface. By managing variations in the plane of the substrate within a predetermined range, a highly reliable magnetic disk substrate can be provided. That is, in the magnetic disk using the magnetic disk substrate, the positional relationship between the apex of the raised portion near the outer peripheral end face and the apex of the settling portion is within a predetermined range, and the apex of the raised portion and the settling portion Since the variation in the main surface of the substrate in the positional relationship with the apex is managed within a predetermined range, the flatness in the circumferential direction, which is the direction in which the recording head scans, can be improved. Therefore, the flying posture of the magnetic head is not disturbed particularly near the outer peripheral end surface of the magnetic disk, and contact between the magnetic disk and the magnetic head can be suppressed even when the magnetic disk is rotated at a high speed. , Can prevent head crash. Further, even when the magnetic head passes through the load / unload method, there is no possibility that the flying posture of the magnetic head is disturbed particularly in the vicinity of the outer peripheral end surface of the magnetic disk or in contact with the magnetic disk.

  Embodiments of the present invention will be described below with reference to the drawings, examples and the like. In addition, these figures, Examples, etc. and description illustrate the present invention, and do not limit the scope of the present invention. It goes without saying that other embodiments may belong to the category of the present invention as long as they match the gist of the present invention.

  FIG. 1 is a perspective view showing the structure of a magnetic disk substrate according to an embodiment of the present invention. The magnetic disk substrate has an annular shape having a circular hole 11, and has a substantially flat main surface 12, an outer peripheral end surface 13 which is an outer peripheral end, and an inner peripheral end surface 14 which is an inner peripheral end. A chamfered surface 15 is formed between each of the outer peripheral end surface 13 and the inner peripheral end surface 14 and the main surface 12. Let d be the distance from the center of the substrate to the end face.

  Since the main surface 12 is an area for recording and reproducing information on the magnetic disk, it is substantially flat for the recording head to fly. However, when the magnetic disk substrate is manufactured, the peripheral portion of the main surface is a portion that protrudes from the main surface 12 (a raised portion) or sinks at the periphery of the main surface 12. The part (sedimentation part) which becomes is formed. This portion is formed on both the outer peripheral end face 13 side and the inner peripheral end face 14 side of the main surface 12 of the magnetic disk substrate.

  These raised portions and sinking portions in the magnetic disk substrate according to the embodiment of the present invention will be described with reference to FIG. FIG. 2 is an enlarged cross-sectional view in the vicinity of the outer peripheral end surface 13, which is a cross section (substrate cross section) in a plane that passes through the center of the magnetic disk substrate and is perpendicular to the flat portion of the main surface 12. In FIG. 2, a portion protruding from the flat portion of the main surface 12 adjacent to the chamfered surface 15 is a protruding portion 21, and adjacent to the protruding portion 21 to the flat portion of the main surface 12. The portion that has settled down is the sedimentation portion 22. These raised portions 21 and sinking portions 22 are formed on the peripheral edge of the main surface 12 over the entire circumference. In the raised portion 21, the first pole 23, which is the largest raised point, is located at a substantially constant distance from the center of the magnetic disk substrate over the entire circumference of the main surface 12. Similarly, in the settling portion 22, the second pole point 24, which is the point at which settling is greatest, is located at a substantially constant distance from the center of the magnetic disk substrate over the entire circumference of the main surface 12.

In the magnetic disk substrate according to the embodiment of the present invention, a point on the main surface at a position 0.4d from the center of the substrate and a point on the main surface at a position 0.6d from the center of the substrate Is a reference line 25, the angle α formed by the straight line connecting the first pole point 23 and the second pole point 24 and the reference line 25 is 0.003 degrees or less, and is on the main surface 12. The variation of the angle over the entire circumference is less than 0.003.
The distance between the line passing through the first pole 23 and parallel to the reference line 25 and the line passing through the second pole 24 and parallel to the reference line 25 (indicated by h in FIG. 2) is 1 nm or more and 40 nm or less; The variation of the distance over the entire circumference on the main surface 12 is 20 nm or less.

  By having such a configuration, the magnetic disk substrate according to the present invention has a positional relationship between the apex of the protuberance and the apex of the subsidence even when there are a protuberance and a subsidence near the outer peripheral end face. A magnetic disk substrate capable of preventing head crashes can be provided by managing the variation within the plane of the substrate in relation to the positional relationship within the predetermined range while managing it within a predetermined range.

  As the material for the magnetic disk substrate, aluminosilicate glass, soda lime glass, borosilicate glass, aluminum-magnesium alloy, or the like can be used. In particular, as an amorphous glass, an aluminosilicate glass can be preferably used in that it can be chemically strengthened and can supply a magnetic disk substrate excellent in flatness of the main surface and substrate strength. . Further, as the material of the glass, amorphous glass or glass ceramics (crystallized glass) can be used.

  A magnetic disk is configured by forming at least a magnetic layer on the magnetic disk substrate having the above-described configuration. That is, a magnetic disk is usually manufactured by sequentially laminating a base layer, a magnetic layer, a protective layer, and a lubricating layer on a magnetic disk substrate. The underlayer in the magnetic disk is appropriately selected according to the magnetic layer.

Next, a method for manufacturing a magnetic disk substrate according to an embodiment of the present invention will be described.
In the manufacture of a magnetic disk substrate, (1) a shape processing step and a first lapping step, (2) an end shape step (a coring step for forming a hole, an end (outer end and inner end) Chamfering step for forming a chamfered surface (chamfered surface forming step)), (3) end surface polishing step (outer peripheral end and inner peripheral end), (4) second lapping step, (5) main surface polishing step ( First and second polishing steps). In the case where the magnetic disk substrate is a glass substrate, there is a chemical strengthening step if necessary after the main surface polishing step. Moreover, an edge part grinding | polishing process and a 2nd lapping process may be followed.

  As described above, the magnetic disk substrate is manufactured through various processes. Among the defect shapes formed on the main surface of the substrate, like the magnetic disk substrate according to the present embodiment, a specific defect shape is used. In particular, the final polishing step (second polishing step) is important in order to prevent the generation of.

  As the recording density is improved, the demand for the required shape of the main surface of the substrate is becoming more severe, and most of the factors that determine the shape and size depend on the polishing conditions in the final polishing step. Many of the various polishing conditions in the final polishing step affect the shape of the main surface of the substrate, and in particular, the processing rate (processing speed) and the processing pressure have an effect.

  The final polishing process for polishing the main surface of the glass substrate using a planetary gear type polishing apparatus will be described below. Needless to say, the final polishing step can be performed without using a planetary gear type polishing apparatus. For example, a final polishing step may be performed on the glass substrate using a single wafer polishing apparatus.

  In the final polishing step, the glass substrate is polished by relatively moving the polishing pad and the glass substrate while pressing both main surfaces of the glass substrate with the polishing pad. At this time, the machining allowance per unit time is the processing rate, and the pressure for pressing the glass substrate is the processing pressure.

  In order to manufacture the magnetic glass substrate according to the present embodiment, the processing rate is in the range of 0.20 μm / min to 0.45 μm / min, and the processing pressure is in the range of 8.0 Pa to 10.5 Pa. It is preferable that Other polishing conditions are not limited because the influence is relatively small. For example, in the case of a 2.5 inch type disk (φ65 mm), the hardness of the polishing pad is 85 (Asker C hardness), and the particle size of the abrasive is 0. .8 (μm).

  In addition, in order to manufacture the magnetic disk substrate according to the present embodiment, after the substrate is polished with a processing pressure (main processing pressure) intended for polishing in the final polishing step, the processing pressure is lower than the main processing pressure. It is more preferable to polish the substrate with a processing pressure (for example, 1 Pa or less). In particular, it is preferable to polish at this low processing pressure for about half of the polishing time for polishing the substrate at this processing pressure. By doing so, the number of defects can be reduced and the occurrence of abnormal defects (defects of a specific shape) can be prevented.

  In addition, in order to manufacture the magnetic disk substrate according to the present embodiment, the glass substrate for magnetic disk can be obtained by polishing the main surface of the substrate after performing the chemical strengthening process on the glass substrate that can be chemically strengthened. It is preferable to obtain a substrate. After the chemical strengthening treatment (ion exchange treatment), the main surface roughness can be further reduced by polishing the substrate main surface. In particular, the surface roughness of the substrate required in recent perpendicular magnetic recording systems has been significantly reduced as compared with the prior art. In order to satisfy this requirement, it is preferable to perform a main surface polishing treatment after the chemical strengthening treatment to obtain a magnetic disk glass substrate.

  In addition, it is preferable that the surface roughness Ra measured using the AFM (electron microscope) of the magnetic disk substrate according to the present embodiment is 0.15 nm or less.

  Further, in order to manufacture the magnetic disk substrate according to the present embodiment, when performing final polishing using a planetary gear type polishing apparatus, the number of rotations of the carrier and the number of revolutions of revolution within the apparatus are determined. The relationship is also important.

  In the planetary gear system, a plurality of glass substrates are held by a carrier. Then, the held glass substrate is pressed against the upper and lower surfaces of the glass substrate together with the carrier. In this state, the glass substrate is polished as the carrier revolves while rotating. By controlling this state, the surface shape of the substrate can be controlled. Specifically, in order to suitably obtain the magnetic disk substrate (magnetic disk glass substrate) according to the present embodiment, the ratio between the number of rotations and the number of revolutions of the carrier is within the range of 0.15 to 6. It is preferable to set.

  In the magnetic disk substrate obtained through such a process, by controlling the conditions of the second polishing process, the ridges and the sinking parts coexist in the vicinity of the outer peripheral end surface, and further, the apex of the ridges and the sinking are set. The positional relationship with the apex of the part can be managed within a predetermined range. In addition, the variation in the plane of the substrate of the positional relationship between the apex of the raised portion and the apex of the sinking portion can be managed within a predetermined range. As a result, a magnetic disk substrate capable of preventing head crashes when operated as a magnetic disk can be provided.

  Next, examples performed for clarifying the effects of the present invention will be described. Here, a case where a glass substrate is used as the magnetic disk substrate will be described.

(Example)
Embodiments of a magnetic disk substrate and a magnetic disk manufacturing method to which the present invention is applied will be described below. The magnetic disk substrate and the magnetic disk are manufactured as magnetic disks having a predetermined shape such as a 3.5-inch disk (φ89 mm) and a 2.5-inch disk (φ65 mm).

(1) Shape processing step and first lapping step In the method for manufacturing a magnetic disk substrate according to the present embodiment, first, the surface of a plate glass is lapped (ground) to obtain a glass base material, and this glass base material Cut the glass disc. Various plate glasses can be used as the plate glass. This plate-like glass can be manufactured by using a known manufacturing method such as a press method, a float method, a downdraw method, a redraw method, or a fusion method using a molten glass as a material. Of these, plate glass can be produced at low cost by using the pressing method.

In this example, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper mold, a lower mold, and a barrel mold to obtain an amorphous plate glass. As the aluminosilicate _{glass, SiO} 2: 58 wt% to 75 _wt%, Al _{2 O} 3: 5 wt% to 23 wt%, _Li 2 O: 3% to 10% by weight, _Na 2 O: 4 by weight Glass containing from 13 to 13% by weight as a main component was used.

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

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

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

(4) End surface polishing step Next, the outer peripheral end surface and the inner peripheral end surface of the glass substrate were mirror-polished by a brush polishing method. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used. And the glass substrate which finished the end surface grinding | polishing process was washed with water. By this end face polishing step, the end face of the glass substrate was processed into a mirror state that can prevent the precipitation of sodium and potassium.

(5) Main surface polishing step (first polishing step)
As a main surface polishing step, first, a first polishing step was performed. This first polishing step is mainly intended to remove scratches and distortions remaining on the main surface in the lapping step described above. In the first polishing step, the main surface was polished using a hard resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains were used.

(6) Chemical strengthening process Next, the glass substrate which finished the above-mentioned lapping process and polishing process was chemically strengthened. For chemical strengthening, a chemical strengthening solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and the chemically strengthened solution is heated to 400 ° C., and the cleaned glass substrate is preheated to 300 ° C. And was immersed in the chemical strengthening solution for about 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, it was performed in a state of being housed in a holder so that a plurality of glass substrates were held at the end surfaces.

  Thus, by immersing in the chemical strengthening solution, the lithium ions and sodium ions in the surface layer of the glass substrate are replaced with sodium ions and potassium ions in the chemical strengthening solution, respectively, and the glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 μm.

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

(7) Main surface polishing process (final polishing process)
Next, a second polishing step was performed as a final polishing step. The purpose of this second polishing step is to finish the main surface into a mirror surface. In the second polishing step, mirror polishing of the main surface was performed using a soft foamed resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains (average particle diameter 0.8 μm) finer than the cerium oxide abrasive grains used in the first polishing step were used. The glass substrate which finished this 2nd grinding | polishing process was immersed in each washing | cleaning tank of neutral detergent, a pure water, and IPA sequentially, and was wash | cleaned. Note that ultrasonic waves were applied to each cleaning tank.

  As described above, by applying the first lapping step, the cutting step, the second lapping step, the end surface polishing step, the first polishing step, the chemical strengthening step, and the second polishing step, a flat and smooth, high rigidity A magnetic disk substrate was obtained.

(8) Magnetic disk manufacturing process On both surfaces of the glass substrate obtained through the above-described processes, an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoTaZr-based alloy, an underlayer made of Ru, and a granular structure on the surface of the glass substrate. A perpendicular magnetic recording disk is manufactured by sequentially forming a nonmagnetic underlayer having a magnetic layer, a perpendicular magnetic recording layer having a granular structure made of a CoCrPt alloy, a protective layer made of hydrocarbon, and a lubricating layer made of perfluoropolyether. did. More specifically, using an in-line type sputtering apparatus, a CrTi adhesion layer, a CoTaZr / Ru / CoTaZr soft magnetic layer, a Ru intermediate layer, a CoCrSiO ₂ nonmagnetic granular underlayer, CoCrPt on a glass substrate. A granular magnetic layer of -SiO ₂ / TiO ₂ and a hydrogenated carbon protective film were sequentially formed, and a perfluoropolyether lubricating layer was formed by a dip method to obtain a magnetic disk.

(9) Magnetic Disk Device Manufacturing Process A magnetic disk device was manufactured by incorporating the magnetic disk into the device. Since the configuration of the magnetic disk device is well known, detailed description thereof is omitted here.

  In the above steps, (7) by adjusting the conditions of the main surface polishing step (final polishing step), three types (Example 1, Example 2 and Comparative Example 1) of magnetic disk substrates are manufactured, Were used to manufacture magnetic disks and magnetic disk devices.

(A) Surface shape measurement About each magnetic disk board | substrate, the shape of the outer peripheral end surface vicinity of a main surface was measured using the stylus-type measuring device (SV3000 by Mitutoyo). Specifically, the position of the first pole that is the highest position among the raised portions on a predetermined radius and the position of the second pole that is the lowest position among the sinking portions were measured. The vertical distance between the first pole and the second pole from the positions of the first and second poles (that is, a line passing through the first pole and parallel to the reference line of the board and a reference line of the board passing through the second pole (Distance to a line parallel to) was calculated as the height (indicated by h in FIG. 2). The reference line is a point on the main surface at a position 0.4d from the center of the substrate and a position 0.6d from the center of the substrate, where d is the length from the center of the substrate to the end surface. A straight line connecting points on the main surface was used. Similarly, from the position of the first pole and the second pole, an angle α formed by a straight line connecting the first pole and the second pole and the reference line was calculated.
The same measurement was performed at a total of 12 locations while rotating the radius direction by 30 degrees, and each variation (the average value of each measurement value and the absolute value of the difference between each measurement value) was measured. Further, as the variation in the pole position, the variation in the radial position of the first pole point and the second pole point was similarly calculated.

表１からわかるとおり、実施例１においては、高さｈの平均値は４０ｎｍで、その基板表面内でのばらつきは２０ｎｍ以下であった。また、角度αの平均値は、０．００３度で、その基板表面内でのばらつきは、０．００３未満であった。実施例２においては、高さｈの平均値は２０ｎｍで、その基板表面内でのばらつきは１０ｎｍ以下であった。また、角度αの平均値は、０．００１度で、その基板表面内でのばらつきは、０．００１未満であった。比較例１においては、高さｈの平均値は５０ｎｍで、その基板表面内でのばらつきは３０ｎｍ以下であった。また、角度αの平均値は、０．００５度で、その基板表面内でのばらつきは、０．００５未満であった。 The results are shown in Table 1 below.

As can be seen from Table 1, in Example 1, the average value of the height h was 40 nm, and the variation within the substrate surface was 20 nm or less. The average value of the angle α was 0.003 degrees, and the variation in the substrate surface was less than 0.003. In Example 2, the average value of the height h was 20 nm, and the variation within the substrate surface was 10 nm or less. The average value of the angle α was 0.001 degrees, and the variation in the substrate surface was less than 0.001. In Comparative Example 1, the average value of the height h was 50 nm, and the variation within the substrate surface was 30 nm or less. The average value of the angle α was 0.005 degrees, and the variation within the substrate surface was less than 0.005.

  Moreover, in Example 1 and Example 2, the variation in the radial position of the first pole point and the second pole point is 0.4 mm and 0.1 mm, respectively, both over the entire circumference on the main surface of the substrate. It was confirmed that it is located substantially equidistant from the center.

(B) Comparison of load / unload test As described above, after manufacturing magnetic disks each having a magnetic layer formed on a magnetic disk substrate according to Example 1, Example 2, and Comparative Example 1, a magnetic disk device was manufactured. Then, a load / unload test was conducted. Note that this test is performed in a state of using a magnetic disk. Specifically, the test was performed in the case where the flying height of the recording head was set to 8 nm and the number of rotations of the disk was 5400 rpm and 7200 rpm.

  As a result, in the case of the magnetic disks according to Example 1 and Example 2, no crash occurred even when the load / unload was repeated 1 million times at a rotational speed of 5400 rpm. For the magnetic disk of Comparative Example 1, a crash occurred in a load / unload test of 1 million times.

  Further, when a load / unload test was performed at a rotational speed of 7200 rpm, in the case of the magnetic disks according to Example 1 and Example 2, no crash occurred even when the load / unload was repeated 1 million times. In the case of the magnetic disk of No. 1, a crash occurred when loading and unloading was repeated 600,000 times.

(C) Modulation Test A modulation test was performed on the magnetic disks obtained in Example 1, Example 2, and Comparative Example 1. Specifically, the modulation was measured in a region where the distance from the center of the glass substrate at 2.5 inches (outer diameter 65 mmφ) was 29.9 mm (R1) to the point (R2) at 31.5 mm.

Specific measurement was performed according to the following procedures (1) to (3).
(1) A magnetic disk is set in an electromagnetic conversion characteristic measuring machine (Gusik Technical Enterprise), a magnetic head (DFH (dynamic flying height) head) is loaded on the magnetic disk, and then an MF pattern (high frequency used in a hard disk). Half the frequency).
(2) Input the readout signal to the oscilloscope.
(3) Then, the modulation for each sector at an arbitrary radial position within the above range is obtained.

  As a result of the above measurement, when Example 1 and Example 2 were compared with Comparative Example 1, Example 1 and Example 2 had better modulation values than Comparative Example 1.

  From the above results, as in the magnetic disk substrates according to Examples 1 and 2, the height h (distance between the apex of the raised portion and the apex of the sinking portion in the direction perpendicular to the reference line of the substrate) is 40 nm or less. The variation within the substrate surface is 20 nm or less, and the angle α (the angle formed by the straight line connecting the apex of the raised portion and the apex of the sinking portion and the reference line of the substrate) is 0.003 degrees. If the variation in the substrate surface is less than 0.003, a good result is obtained in the load and load test and the modulation test, and a highly reliable magnetic disk with little fly stiction failure or head crash failure is obtained. The obtained magnetic disk substrate can be obtained.

  In addition, this invention is not limited to the said embodiment, It can implement by changing suitably. For example, in the above embodiment, the case where the magnetic disk substrate is a glass substrate has been described. However, the present invention can also be applied to the case where the magnetic disk substrate is an aluminum alloy substrate or the like.

  In addition, the material, size, processing procedure, and the like in the above-described embodiment are merely examples, and various modifications can be made within the range where the effects of the present invention are exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

The figure which shows the external appearance of the board | substrate for magnetic discs in embodiment of this invention. The figure which shows the outer peripheral end surface vicinity of the board | substrate for magnetic discs in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Circular hole 12 Main surface 13 Outer peripheral end surface 14 Inner peripheral end surface 15 Chamfered surface 21 Raised portion 22 Settling portion 23 First pole 24 Second pole

Claims (3)

An annular substrate having two main surfaces, an end surface, a chamfered surface formed between the main surface and the end surface, and a peripheral edge on the main surface, the other than the peripheral edge A raised portion that is raised with respect to a flat surface on the main surface, and a settling portion that is formed at a peripheral edge on the main surface and sinks with respect to the flat surface,
When viewed from the cross section of the substrate, the point on the one main surface of the substrate where the bulge of the bulging portion is the maximum is the first pole, the point where the sinking of the sinking portion is the maximum is the second pole, A straight line connecting a point on the main surface at a position 0.4d from the center of the substrate and a point on the main surface at a position 0.6d from the center of the substrate, where d is a length from the center to the end surface. As a reference line,
The angle formed by the straight line connecting the first pole and the second pole and the reference line is 0.003 degrees or less, and the variation in the angle over the entire circumference on the main surface is less than 0.003. And
The distance between the line passing through the first pole and parallel to the reference line and the line passing through the second pole and parallel to the reference line is not less than 1 nm and not more than 40 nm, and the distance on the entire circumference on the main surface is The variation is 20 nm or less for a magnetic disk substrate.   The magnetic disk substrate according to claim 1, wherein the magnetic disk substrate is made of aluminosilicate glass.   A magnetic disk comprising the magnetic disk substrate according to claim 1 and a magnetic recording layer formed on the magnetic disk substrate.

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