METHOD OF TEXTURING SUBSTRATE FOR PERPENDICULAR MAGNETIC RECORDING MEDIA, TEXTURING DEVICE, AND PERPENDICULAR MAGNETIC RECORDING MEDIA

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing advantages and features of the invention will become apparent upon reference to the following detailed description and the accompanying drawings, of which:

FIG. 1 is a conceptual schematic cross-sectional view of a portion of a substrate for perpendicular magnetic recording media, as an example;

FIG. 2 shows in summary the configuration of principal portions of the texturing device of an aspect;

FIG. 3 is a summary side view of the texturing device of FIG. 2;

FIG. 4 is a drawing used to explain operation of the texturing device of FIG. 2;

FIGS. 5A and 5B are graphs which plot the surface roughness of perpendicular magnetic recording media obtained by texturing, when the average fiber diameter of polishing fibers comprised by the polishing tape and the average particle diameter of abrasive particles in the polishing slurry are each varied;

FIGS. 6A and 6B are graphs which plot the tip radius of substrates for perpendicular magnetic recording media obtained by texturing, when the average fiber diameter of polishing fibers in the polishing tape and the average particle diameter of abrasive particles in the polishing slurry are each varied;

FIG. 7 is a graph which plots the number of defects occurring in polishing of the surface of substrates for perpendicular magnetic recording media;

FIG. 8 is a graph which plots the number of scratches occurring in texturing of the surface of substrates for perpendicular magnetic recording media;

FIG. 9 is a graph which plots the test pass rate obtained in glide height tests of perpendicular magnetic recording media fabricated using textured substrates and polished substrates; and,

FIG. 10 is a graph plotting the SNR of perpendicular magnetic recording media fabricated using textured substrates and polished substrates.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Below, aspects of the invention are explained based on the drawings. First, a substrate for perpendicular magnetic recording media, hereafter substrate 10, is subjected to texturing and used in fabricating perpendicular magnetic recording media, as explained. After texturing of substrate 10, a Cr film or other nonmagnetic metal underlayer, Co alloy magnetic film or other magnetic recording film, and amorphous carbon film or other protective layer can be deposited in order by sputtering or another method. Then, by applying a liquid lubricant thereupon, a lubrication layer is formed, to complete fabrication of the perpendicular magnetic recording media.

FIG. 1 is a partial cross-sectional schematic view of the outside in the radial direction, from the center hole, of disk-shaped substrate 10. Substrate 10 is structured by stacking, in order, nonmagnetic base 12, initial reaction layer 14, and soft magnetic underlayer 16.

As nonmagnetic base 12, an aluminum alloy can be used. However, reinforced glass or crystallized glass can also be used to fabricate nonmagnetic base 12; or, polycarbonate, polyolefin, or another plastic resin may be injection-molded to fabricate base 12.

As initial reaction layer 14 provided on nonmagnetic base 12, a Zn film layer, formed by immersing in a zincate solution (a solution comprising zinc oxide and caustic soda aqueous solution), is used. In general, initial reaction layer 14 is subjected to activation treatment by alternating immersion in an acidic tin chloride solution and in acidic palladium chloride solution to cause precipitation of Pd nuclei. Initial reaction layer 14 can also be fabricated from Ni, Ni—P, Cu, Cr, Fe, Pd, or similar by sputtering or by ion plating or another physical adsorption method.

As soft magnetic underlayer 16 deposited onto initial reaction layer 14, a Ni—P layer formed by electroless plating is used. In substrate 10 of this aspect, this Ni—P layer is deposited using an electroless plating method, for reasons of low cost and compatibility with volume production. However, the Ni—P layer can also be fabricated using another well-known film deposition method, such as sputtering, ion plating, or another physical adsorption method, according to the characteristics required. Moreover, soft magnetic underlayer 16 is not limited to a Ni—P layer, but may be fabricated from another material. Soft magnetic underlayer 16 corresponds to the soft magnetic layer in the invention.

Next, texturing device 20 to polish the surface of substrate 10 is explained. FIG. 2 shows in summary texturing device 20 of this aspect, showing the principal portions thereof. FIG. 3 shows in summary a side view of texturing device 20 of FIG. 2. And, FIG. 4 is used to explain operation of the texturing device shown in FIG. 2.

Texturing device 20 comprises chuck mechanism 22, which detachably holds disk-shaped substrate 10 having a center hole; rotation driving portion 24, linked to chuck mechanism 22, which causes chuck mechanism 22 to rotate together with substrate 10; tape polishing mechanisms 28A and 28B, which respectively hold portions of polishing tape 26 against surfaces of the substrate 10 to be machined; tape polishing mechanism feed devices 30A and 30B, which cause tape polishing mechanisms 28A and 28B to mutually approach or recede along the center axis line of chuck mechanism 22; oscillation device 32, which causes tape polishing mechanisms 28A and 28B to simultaneously move in the radial direction of substrate 10; and polishing slurry providing portions 34A and 34B, which provide polishing slurry (slurry liquid) to the surfaces of substrate 10 to be machined. The rotation support means of this invention comprises chuck mechanism 22 and rotation driving portion 24; the pressing means of this invention comprises tape polishing mechanisms 28A and 28B; and the supply means of this invention comprises polishing slurry providing portions 34A and 34B.

Chuck mechanism 22, positioned on a center axis line common with the hole in substrate 10, holds substrate 10 such that the flat surfaces of substrate 10 intersect the center axis line at substantially right angles. Rotation driving portion 24 is for example a driving motor, which in this aspect is capable of causing rotation of substrate 10 and chuck mechanism 22 in the range of approximately 50 to 500 rpm.

Tape polishing mechanisms 28A and 28B, which are placed in opposition to enclose substrate 10, have the same construction. Hence tape polishing mechanism 28A is here explained, and an explanation of tape polishing mechanism 28B is omitted.

Tape polishing mechanism 28A comprises a feed-out roller 36c, which feeds out polishing tape 26, described below; take-up roller 36b, which takes up polishing tape 26; pressing roller 36a, which presses a portion of the continuously fed polishing tape 26 against the surface of substrate 10 to be machined; and tensioner roller 36d, which applies a tension force to the portion of polishing tape 26 between pressing roller 36a and feed-out roller 36c, and to the portion taken up between pressing roller 36a and take-up roller 36b. Take-up roller 36b is linked to the output shaft of a driving motor, not shown. By this means, when the driving motor is in the operating state, polishing tape 26 fed out from feed-out roller 36c moves in the direction indicated by the arrows in FIG. 2, past pressing roller 36a, to be taken up by take-up roller 36b continuously at a prescribed speed. Hence during texturing, a new portion of the continuously fed polishing tape 26 which is wrapped about the outer surface of pressing roller 36a travels while making constant contact with the surface of substrate 10 to be machined. Further, tape polishing mechanisms 28A and 28B are provided with polishing slurry providing portions 34A and 34B, which provide polishing slurry to the surfaces of substrate 10 to be machined.

Polishing slurry providing portions 34A and 34B are positioned within tape polishing mechanisms 28A and 28B, respectively, such that the tips thereof face the surfaces to be machined of substrate 10. Hence as shown in enlargement in FIG. 4, polishing slurry providing portions 34A and 34B are positioned in mutual opposition enclosing substrate 10. Polishing slurry providing portions 34A and 34B are moveable with respect to tape polishing mechanisms 28A and 28B respectively.

In performing texturing, tape polishing mechanisms 28A and 28B first are moved along the center axis line direction of substrate 10 by tape polishing mechanism feed devices 30A and 30B respectively, from standby positions retracted from the surfaces to be machined of substrate 10 (the positions indicated by broken lines in FIG. 2) to polishing execution positions (the positions indicated by the solid lines in FIG. 2). Next, tape polishing mechanisms 28A and 28B are moved in a radial direction of substrate 10 by oscillation device 32, as shown in FIG. 3. At this time, tape polishing mechanisms 28A and 28B each cause a portion of polishing tape 26 to be pressed against and rub against the surface to be machined of substrate 10 as shown in FIG. 4. Also at this time, polishing slurry is provided to the rubbed portions from polishing slurry providing portions 34A and 34B.

Next, after texturing of the entire surfaces to be machined of substrate 10, the supply of polishing slurry from polishing slurry providing portions 34A and 34B is halted. Then, operation of tape polishing mechanisms 28A and 28B is stopped, and tape polishing mechanisms 28A and 28B are returned to the standby positions, retracted from the surfaces to be machined of substrate 10 by tape polishing mechanism feed devices 30A and 30B. Substrate 10 for which texturing has been completed is removed from chuck mechanism 22, and is transferred to processes to form the magnetic recording layer and other layers.

Below, specific embodiments of texturing of substrates 10 and comparison examples are explained.

In texturing device 20 with the above-described configuration, the fiber diameters of the polishing fibers of polishing tape 26 and the particle diameters of the abrasive particles in the polishing slurry were varied, and polishing, that is, texturing, of substrates 10 was performed. The results are explained below. Here substrates 10 subjected to texturing were polished in advance under prescribed conditions, until the surface shape had reached a prescribed level.

As polishing tape 26, a sheet-shape polishing cloth comprising polishing fibers having nanometer-order diameters was used. More specifically, a polishing tape comprising nylon fibers (nanofibers) the average fiber diameter of which was approximately 200 nm, with diameters in the range 200 nm±40 nm, was used. In addition, polishing tape comprising nylon fibers with fiber diameters in the range 700 nm±50 nm and with an average fiber diameter of approximately 700 nm, as well as polishing tape comprising nylon fibers with fiber diameters in the range 1500 nm±120 nm and with an average fiber diameter of approximately 1500 nm (1.5 μm), were also used, and the results of texturing using these tapes were compared. These polishing fibers substantially consisted of nylon.

Further, as the polishing slurry, slurry in which are dispersed abrasive particles having nanometer-order particle diameters is used. More specifically, as the abrasive particles, diamond particles having an average particle diameter of 50 nm, and more precisely, diamond clusters having an average cluster size of 50 nm, are used; these are dispersed in an alkaline surfactant and prepared in slurry form for use as the polishing slurry. In addition, a polishing slurry in which diamond particles of average particle size 100 nm were dispersed in an alkaline surfactant, and a polishing slurry in which diamond particles of average particle size 150 nm were dispersed in an alkaline surfactant, were also used, and the results of texturing using these were compared.

During testing, substrate 10 was rotated at 300 rpm, polishing tape 26 was fed at 20 mm/min and was pressed against the substrate with a pressure of 10 kgf/cm², and texturing of substrate 10 was performed either continuously or intermittently for 20 seconds. The oscillation amplitude of polishing tape 26 during texturing was 4 mm, and the oscillation cycle rate was 415 cycles/min (6.9 Hz).

In the graph of FIG. 5, the surface roughness (center-line average roughness Ra (units: nm) of substrates 10 obtained by performing texturing is shown, while varying the average fiber diameter of the polishing fibers in the polishing tape 26 and the average particle diameter of abrasive particles in the polishing slurry. FIG. 5A shows the average fiber diameter of polishing fibers along the horizontal axis and the surface roughness of substrate 10 along the vertical axis. In FIG. 5B, the horizontal axis indicates the abrasive particle average diameter, and the vertical axis indicates the surface roughness of substrate 10. The same results as in FIG. 5A are shown, focusing on differences in the average fiber diameter of polishing fibers comprised by polishing tape 26.

In order to reduce the flying height of the magnetic head to an extent compatible with perpendicular magnetic recording, while preventing adhesion of the magnetic head to the perpendicular magnetic recording media, it is preferable that the surface roughness Ra of substrate 10 be 0.15±0.10 nm (0.05 nm to 0.25 nm). Substrates 10 with surface roughness in this range were obtained in all cases in which texturing was performed with the average fiber diameter of polishing fibers comprised by polishing tape 26 equal to 200 nm, and with the average particle diameter of abrasive particles in the polishing slurry at 50 nm, 100 nm, or 150 nm. Substrates 10 having such a surface roughness were also obtained when texturing was performed with the average fiber diameter of polishing fibers comprised by polishing tape 26 at 700 nm, and with the average particle diameter of abrasive particles in the polishing slurry equal to 50 nm. Hence it was made clear that performing texturing using polishing tape 26 comprising polishing fibers having such average fiber diameters, and using a polishing slurry comprising abrasive particles having such average particle diameters, is suitable for polishing of substrate 10.

The line α1 in FIG. 5A crosses the horizontal axis at an average fiber diameter of 100 nm, and the line α2 crosses the horizontal axis at an average fiber diameter of 400 nm. Focusing on line α2 and on line β1 which crosses the vertical axis at a surface roughness Ra of 0.25 nm, by performing texturing of substrate 10 with the average fiber diameter of polishing fibers comprised by polishing tape 26 at 400 nm and the average particle diameter of abrasive particles in the polishing slurry at 150 nm, it is inferred that the surface roughness Ra of substrate 10 can be made equal to or less than the 0.25 nm set as the value currently enabling use in perpendicular magnetic recording media. And, focusing on the line α1 and on the line β2 which crosses the vertical axis at a surface roughness Ra of 0.05 nm, by performing texturing of substrate 10 with the average fiber diameter of polishing fibers comprised by polishing tape 26 at 100 nm and the average particle diameter of abrasive particles in the polishing slurry at 50 nm, it is inferred that the surface roughness Ra of substrate 10 can be made the low value of approximately 0.05 nm. Hence, when the average particle diameter of abrasive particles in the polishing slurry is from 50 nm to 150 nm, if the average fiber diameter of polishing fibers comprised by polishing tape 26 is made 100 nm or greater but 400 nm or less and texturing of substrate 10 is performed, a substrate with surface roughness Ra of 0.15±0.10 nm can be obtained.

Further, in FIG. 5A, focusing on line α3 which crosses the horizontal axis at an average fiber diameter of 800 nm and on line β1, by performing texturing of substrate 10 with the average fiber diameter of polishing fibers comprised by polishing tape 26 at 800 nm and with the average particle diameter of abrasive particles in the polishing slurry at 100 nm, it is inferred that there are cases in which the surface roughness Ra of substrate 10 can be made 0.25 nm or less. Hence when the average particle diameter of abrasive particles in the polishing slurry is made from 50 nm to 100 nm, by texturing substrate 10 with the average fiber diameter of polishing fibers comprised by polishing tape 26 at 100 nm or higher but 800 nm or lower, it is thought that substrate 10 with a surface roughness Ra of 0.15±0.10 nm can effectively be obtained.

Further, focusing on line α4 which crosses the horizontal axis at the average fiber diameter of 1400 nm and on line β1 in FIG. 5A, by performing texturing of substrate 10 with the average fiber diameter of polishing fibers comprised by polishing tape 26 at 1400 nm and with the average particle diameter of abrasive particles in the polishing slurry at 50 nm, it is inferred that the surface roughness Ra of substrate 10 can be made 0.25 nm or less. Hence when the average particle diameter of abrasive particles in the polishing slurry is made 50 nm, by texturing substrate 10 with the average fiber diameter of polishing fibers comprised by polishing tape 26 at 100 nm or higher but 1400 nm or lower, it is thought that substrate 10 with a surface roughness Ra of 0.15±0.10 nm can be obtained.

Next, the graph of FIG. 6 shows tip radii (Rcp) (units: nm) of the surfaces of substrates 10 when texturing is performed while varying the average fiber diameter of polishing fibers of polishing tape 26 and the average particle diameter of abrasive particles in the polishing slurry. In FIG. 6A, the horizontal axis indicates the average fiber diameter of polishing fibers, and the vertical axis indicates the tip radius of substrate 10; results are displayed which focus on differences in the average particle diameters of abrasive particles in the polishing slurry. In FIG. 6B, the average particle diameter of abrasive particles is indicated by the horizontal axis and the tip diameter of substrate 10 is taken along the vertical axis. The same results as in FIG. 6A are shown, focusing on differences in average fiber diameters of polishing fibers in the polishing tape 26.

Here the “tip radius” is used to quantitatively compare the shapes of the tips of protrusions in the surfaces of substrates 10 formed by texturing, and indicates the sharpness (roundness) of the tips of protruding portions. More specifically, the tip radius indicates the radius of the circle when the tip outline of a protruding portion on the surface of substrate 10 is approximated by a circle. From the graph of FIG. 6 it is seen that the narrower the average fiber diameter of polishing fibers comprised by polishing tape 26, or the smaller the average particle diameter of abrasive particles comprised by the polishing slurry, the larger the tip radii of the protruding portions on the surface of substrate 10 which is obtained.

In general, the tip radius is correlated with the ratio of magnetization values (OR-Mrt) in the circumferential direction and in the radial direction of substrate 10; the larger the tip radius, the lower the magnetic susceptibility ratio. The ratio of magnetization values indicates the extent to which magnets on the magnetic recording media are aligned in the circumferential direction. In the case of longitudinal magnetic recording media, signals are written so as to cause minute magnets to be arranged in the longitudinal direction (that is, the circumferential direction), and so it is preferable that magnets be aligned neatly in the circumferential direction. However, in the case of perpendicular magnetic recording, signals are written with minute magnets arranged in the perpendicular direction, and so if magnets are aligned in the circumferential direction, they become a source of noise, and the electromagnetic transducing characteristic is degraded. Hence it is desirable that tip radii on the surface of substrate 10 for perpendicular magnetic recording be large, and that the ratio of magnetization values be low. Here, the above results are taken into consideration, according to which the narrower the average fiber diameter of polishing fibers in polishing tape 26, and the smaller the average particle diameter of abrasive particles in the polishing slurry, the larger is the tip radius of substrate 10 obtained. As a result, it is clear that texturing using polishing tape 26 with polishing fibers the average fiber diameter of which is approximately 200 nm, and using polishing slurry comprising abrasive particles having an average particle diameter of 50 nm to 150 nm, is appropriate for polishing the surface of substrate 10 for use in perpendicular magnetic recording media.

Next, results are compared for substrates which have been textured after the above-described polishing (textured substrates) and for substrates subjected only to polishing (polished substrates). Here, the average particle diameter of abrasive particles in the polishing slurry used in texturing was 100 nm.

FIG. 7 shows the number of defects arising from polishing of the substrate surface (hereafter “number of substrate defects”) (units: number/surface). Even when texturing is performed using polishing tape comprising nanofibers with average fiber diameters of 200 nm and 700 nm, and when texturing is performed using polishing tape comprising nanofibers with an average fiber diameter of 1500 nm (1.5 μm), it is seen that by performing texturing the number of substrate defects is greatly reduced.

On the other hand, from the graph showing the number of scratches arising from texturing on the substrate surface (hereafter “texturing scratches”) (units: number/surface) in FIG. 8, it is seen that when a polishing tape was used having microfibers with an average fiber diameter of 1500 nm (1.5 μm), there were numerous texturing scratches, and clear texture marks were formed on the substrate. On the other hand, when texturing was performed using polishing tape 26 with nanometer-order fibers, and in particular 200 nm nanofibers, only approximately the same scratching as on substrates subjected to polishing alone without texturing was observed, and it became clear that only very slight texture marks were formed. That is, by performing texturing using polishing tape 26 comprising polishing fibers with an average fiber diameter of approximately 200 nm, not only can defects arising from polishing be eliminated, but also the formation of scratches arising from texturing can be suppressed.

Using both textured substrates which had been textured using a polishing slurry comprising abrasive particles of average particle diameter 100 nm, as well as polished substrates which had been subjected to polishing only, perpendicular magnetic recording media were fabricated by depositing thereupon a nonmagnetic metal underlayer, magnetic recording layer, and protective layer in order, and then forming a lubricating layer on top, as described above. Then, the perpendicular magnetic recording media was subjected to glide height tests, and test pass rates (GHT) were determined (as percentages).

Results are shown in FIG. 9. Glide height tests are tests in which a head for inspection is caused to fly above the surface of perpendicular magnetic recording media, seeking on the perpendicular magnetic recording media is performed, and inspections for the occurrence of anomalous protrusions at the surface are performed A Hitachi DECO tester RQ7800 was used in measurements. In the case of perpendicular magnetic recording media which employed polished substrates, there were numerous occurrences of anomalous protrusions arising from polishing, collisions with the head, and crashes due to head flying instability, so that the pass rate was poor. On the other hand, in the case of perpendicular magnetic recording media which employed textured substrates, excellent pass rates were obtained. This indicates that by subjecting substrates 10 to texturing, anomalous protrusions due to polishing can be eliminated, and the minute protrusions and depressions formed in the circumferential direction by texturing enable stable head flight.

Next, the SNR (Signal-to-Noise Ratio) (units: dB), which is the ratio of the signal output to noise for perpendicular magnetic recording media, was investigated for the above-described perpendicular magnetic recording media, fabricated using textured substrates and using polished substrates.

Results appear in FIG. 10. A higher SNR was obtained from perpendicular magnetic recording media using a substrate obtained by performing texturing using polishing tape comprising nanofibers with an average fiber diameter of 200 nm than from perpendicular magnetic recording media using substrates obtained by texturing using polishing tape comprising fibers with an average fiber diameter of 1500 nm or 700 nm. This SNR was substantially the same as the SNR of perpendicular magnetic recording media obtained using a polished substrate, and is a satisfactory value for perpendicular magnetic recording media. From the above it is clear that when texturing substrates for use in perpendicular magnetic recording media, by using polishing tape 26 comprising nanofibers with an average fiber diameter of approximately 200 nm, perpendicular magnetic recording media can be obtained in which head flying stability is secured through minute protrusions and depressions in the circumferential direction, and moreover satisfactory electromagnetic transducing characteristics are obtained.

From the above it is seen that texturing is extremely effective for polishing of substrates 10, and that by performing texturing, a substrate having a more uniform and flat surface shape, suitable for perpendicular magnetic recording media, can be obtained. In particular, it has become clear that, in the above-described texturing device 20, it is extremely effective to perform texturing of the surface of substrate 10 using polishing tape 26, pressed against and running over the surface of substrate 10, the average fiber diameter of the polishing fibers in which is substantially 200 nm, and with an average particle diameter of the abrasive particles dispersed in the polishing slurry supplied from polishing slurry providing portions 34A and 34B equal to 50 nm or greater but 150 nm or less.

In the above, the invention has been explained based on aspects; but the invention is not limited to these aspects. Substrate 10 which is to be textured by a texturing device for perpendicular magnetic recording media substrates of this invention may have any other configuration if the substrate is to be used in perpendicular magnetic recording media, and further polishing may also be performed in advance. Also, texturing devices 20 are not limited to the above-described configuration, but may adopt various other forms. And, the polishing fibers and similar of polishing sheets may be formed from other materials, and the abrasive particles of the polishing slurry may be of other material, such as for example single-crystal diamond or polycrystalline diamond. The polishing fibers of the polishing sheet may be fabricated using the technology disclosed in Japanese Patent Laid-open No. 2005-325494, or by another method.

In the above aspects, the invention was explained with a certain degree of specificity. However, it should be understood that various modifications and improvements can be made without deviating from the spirit or scope of the invention as disclosed in the claims. That is, the invention comprises the scope of the attached claims and inventions equivalent thereto, as well as various modifications and alterations thereto.

Thus, a method of texturing substrate for perpendicular magnetic recording media, texturing device, and perpendicular magnetic recording media has been described according to the present invention. Many modifications and variations may be made to the techniques and structures described and illustrated herein without departing from the spirit and scope of the invention. Accordingly, it should be understood that the methods and apparatus described herein are illustrative only and are not limiting upon the scope of the invention.

FIG. 5
Average Fiber Diameter (Nm)
Average Particle Diameter (Nm)
FIG. 6
Average Fiber Diameter (Nm)
Average Particle Diameter (Nm)
FIG. 7
Number of Substrate Defects (Number/Surface)
Polished Substrate
Textured Substrate
FIG. 8
Texture Scratches (Number/Surface)
Polished Substrate
Textured Substrate
FIG. 9
Polished Substrate
Textured Substrate
FIG. 10
Polished Substrate

Textured Substrate

METHOD OF TEXTURING SUBSTRATE FOR PERPENDICULAR MAGNETIC RECORDING MEDIA, TEXTURING DEVICE, AND PERPENDICULAR MAGNETIC RECORDING MEDIA

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