JP4190398B2 - Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk - Google Patents

Description

  The present invention relates to a method for manufacturing a magnetic disk mounted on a magnetic disk device such as an HDD (hard disk drive) and a method for manufacturing a glass substrate for a magnetic disk.

  Today, the information recording technology, particularly the magnetic recording technology, requires rapid technological innovation with the rapid development of the IT industry. In a magnetic disk mounted on an HDD (Hard Disk Drive) or the like, a technique capable of realizing a high recording density of 40 Gbits per square inch or more is required due to a demand for high information capacity.

  In a magnetic disk, as one of the measures for realizing a high recording density, the flying height of the magnetic head is reduced by smoothing the surface roughness of the magnetic disk surface. The surface property of the magnetic disk is largely attributed to the surface property of the magnetic disk substrate. Therefore, efforts are made to reduce the flying height of the magnetic head by smoothing the surface of the magnetic disk substrate.

  However, the CSS type magnetic disk has a problem that if the surface is extremely smoothed, the magnetic head is attracted to the magnetic disk. Therefore, in the CSS type disk, an uneven shape for preventing adsorption is formed on the surface of the substrate. That is, the CSS magnetic disk glass substrate requires a certain degree of unevenness on the surface, and thus the flying height of the magnetic head cannot be reduced to a certain level or less.

  However, when the LUL (load unload) method capable of increasing the information capacity is adopted instead of the conventional CSS method, the HDD start / stop method is attracted to the surface of the magnetic disk substrate. There is no longer a requirement to form uneven shapes for prevention. For this reason, it is possible to reduce the flying height of the magnetic head by one step in the LUL type magnetic disk and the magnetic disk substrate.

  However, when trying to realize a flying height of a magnetic head of 20 nm or less, it has become clear that the realization of a magnetic disk glass substrate is no longer possible by simply smoothing the surface roughness. It was. One of the methods for solving this problem is a technique developed by the present applicant (Patent Document 1). The technique disclosed in this document is based on the idea that a further reduction in the flying height of the magnetic head can be achieved by reducing the fine waviness on the surface of the glass substrate.

Based on this idea, as a result of repeated research and experiments, there is a certain dependency between the surface roughness of the polishing pad used in the polishing process of the glass substrate and the micro waviness of the glass substrate surface after the polishing process. I found something. According to the technology disclosed in the above literature, a magnetic head can be reduced in flying height by selecting a polishing pad having a predetermined surface roughness and performing polishing in accordance with this dependency.
JP 2002-92867 A

  By the way, in recent years, it has been desired to realize a higher recording density, and accordingly, further reduction in the flying height of the magnetic head has become essential. For example, in order to realize an information recording density of 60 Gbits per square inch or more, it is said that the flying height of the magnetic head needs to be 10 nm or less. For this purpose, the size of the micro waviness on the surface of the glass substrate for a magnetic disk must be kept to a size that can realize this.

However, it has been found that the above-described conventional technique cannot always sufficiently respond to such a request. For example, in order to maintain the flying height of the magnetic head stably at 10 nm, at least the glide height of the magnetic disk needs to be 6 nm or less, more safely 5 nm or less. However, with the above-described conventional technology, it has been difficult to realize such a glide height sufficiently satisfactorily.
Further, it has recently been found that in the case of a magnetic disk for a load / unload system, fly stiction failure is likely to occur, and therefore it is necessary to reduce the glide height in particular. Therefore, in particular, in the case of a magnetic disk for the load / unload method, it is desired that the glide height be 5 nm or less. However, with the above-described conventional technology, it has been difficult to realize such a glide height sufficiently satisfactorily. The present invention provides a method for producing a glass substrate for a magnetic disk capable of accurately controlling the microwaviness on the surface of the glass substrate for a magnetic disk so that the flying height of the magnetic head can be stabilized and very low (for example, 10 nm or less), and It is an object of the present invention to provide a method for manufacturing a magnetic disk. Another object of the present invention is to provide a method for manufacturing a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk suitable for the LUL (load unload) system.

As a means for solving the above-mentioned problem, the first means is:
A method for producing a glass substrate for a magnetic disk comprising a step of applying a polishing pad having a foamed resin layer to a glass substrate and mirror-polishing both main surfaces of the glass substrate with the polishing pad while supplying a polishing liquid,
When the hardness of the material resin of the foamed resin is A and the opening diameter of the foamed pore on the surface of the polishing pad is B, the ratio of B to A (B / A) and the mirror polishing is performed using this polishing pad. Utilizing the phenomenon that the size of the micro-waviness on the surface of the glass substrate later has a certain correspondence relationship,
This correspondence is obtained on a trial basis in advance.
Based on the obtained correspondence relationship, the ratio of B to A (B / A) corresponding to the desired microwaviness size is determined,
Determine the values of A and B to be this determined ratio (B / A),
A glass substrate for a magnetic disk having a desired surface undulation by mirror polishing with a polishing pad having the determined values A and B. It is a manufacturing method.
The second means is
A method for producing a glass substrate for a magnetic disk comprising a step of applying a polishing pad having a foamed resin layer to a glass substrate and mirror-polishing both main surfaces of the glass substrate with the polishing pad while supplying a polishing liquid,
When the hardness of the material resin of the foamed resin is A and the opening diameter of the foamed pore on the polishing pad surface is B, the ratio of B to A (B / A) is 0.6 μm · cm ² / kg or less. A polishing pad is selected, and mirror polishing is performed using this polishing pad.
However, B is the opening diameter [μm] of the foaming pore on the surface of the polishing pad, A is the hardness of the material resin of the foamed resin, and the resin modulus (100% elongation modulus) hardness [kg / cm 2] Say.
The third means is
A method for producing a glass substrate for a magnetic disk comprising a step of applying a polishing pad having a foamed resin layer to a glass substrate and mirror-polishing both main surfaces of the glass substrate with the polishing pad while supplying a polishing liquid,
A polishing pad in which the hardness A of the material resin of the foamed resin is 120 kg / cm ² or more and the opening diameter B of the foaming pore on the polishing pad surface is 65 μm or less is selected, and mirror polishing is performed using this polishing pad. A method for producing a glass substrate for a magnetic disk.
However, A is the hardness of the resin material of the foamed resin and is the resin modulus (100% elongation modulus) hardness [kg / cm ² ], and B is when the surface of the polishing pad is observed with an electron microscope It means the opening diameter [μm] of the foamed pore of the foamed resin layer obtained.
The fourth means is
The method for producing a glass substrate for a magnetic disk according to any one of the first to third means, wherein the surface roughness of the polishing pad surface is 20 μm or less in Rz.
However, Rz is a ten-point average roughness.
The fifth means is
The method of manufacturing a glass substrate for a magnetic disk according to any one of the first to fourth means, wherein the polishing pad has a hardness (Asker-C hardness) of 62 to 85.
The sixth means is
A magnetic material for a load / unload system, wherein at least a magnetic layer is formed on a glass substrate for a magnetic disk obtained by the method for producing a glass substrate for a magnetic disk according to any one of the first to fifth means. A method for manufacturing a disk.

  The present invention utilizes the phenomenon that the present inventor found for the first time that the ratio (B / A) between the opening diameter B of the foamed pore and the material resin hardness A and the microwaviness of the glass substrate have a certain correspondence relationship. By selecting the ratio (B / A), it is possible to stably manufacture a glass substrate for a magnetic disk in which the size of the microwaviness of the glass substrate is controlled to a desired value. A magnetic disk glass substrate that can stably fly very low (for example, 10 nm or less), or a magnetic disk glass substrate that prevents fly stiction failure and is suitable for the LUL (load unload) system. It can be manufactured stably.

  1 is an explanatory view of a polishing pad, FIG. 1 (a) is a partial sectional view of the polishing pad, FIG. 1 (b) is a partially enlarged plan view of the polishing pad, and FIG. 2 is a double-side polishing apparatus having upper and lower surface plates. FIG. 3 is a cross-sectional view of the main part of FIG. 3, and FIG. 3 shows the hardness of the resin of the foamed resin (layer) constituting the polishing pad in the test examples (corresponding to examples and comparative examples described later), the opening diameter of the foamed pores, and the minuteness of the glass substrate surface FIG. 4 is a table showing waviness, glide height, etc. FIG. 4 shows the ratio (B / A) of the opening diameter B of the foamed pore on the foamed resin surface of the polishing pad and the hardness A of the resin material of the foamed resin, and this polishing pad. It is a graph which shows the correspondence with the magnitude | size of the microwaviness of the glass substrate surface after carrying out mirror polishing using. Hereinafter, a method for manufacturing a magnetic disk glass substrate and a method for manufacturing a magnetic disk according to an embodiment of the present invention will be described with reference to these drawings.

  The method for polishing a glass substrate for a magnetic disk according to the embodiment uses a polishing apparatus 5 (see FIG. 2) having an upper and lower surface plate to which a polishing pad 53a (see FIG. 1) made of foamed resin is attached. Both main surfaces of the glass substrate 4 are mirror-polished. As shown in FIG. 1, the polishing pad 53a (the same applies to the polishing pad 54a) includes a base layer (base layer) 531a formed on a base 530a, and a polishing layer (foamed resin layer) 532a formed thereon. It is a thing. The polishing layer (foamed resin layer) 532a is made of a foamed resin, has a large number of foamed pores 533a inside, and has a large number of foamed pores formed on the surface by cutting the foamed pores 533a along the way. An opening 534a is provided. The opening diameter d of the foam pore opening 534a is the foam pore opening diameter. That is, as shown in FIG. 1, in the polishing pad 53a according to the embodiment, a foamed resin layer 532a is formed on the surface on the polishing surface side of the polishing pad, and the surface of the foamed resin layer 532a, that is, polishing of the polishing pad 53a. The surface side surface is a polishing pad in which foamed pores 533a are opened to form openings 534a. In the mirror polishing step, the polishing pad 53a is pressed against the glass substrate 4 by the pressure applied by the upper surface plate 53, and cooperates with a polishing liquid supplied from a polishing liquid supply unit (not shown) to thereby surface the glass substrate 4 Mirror polished.

  As shown in FIG. 2, the polishing pad 53 a is attached to the upper surface plate 53 of the polishing apparatus 5 having an upper surface plate 53 and a lower surface plate 54. A similar polishing pad 54 a is also attached to the lower surface plate 54. The magnetic disk glass substrate 4 to be polished is set in the object holding hole 2 of the polishing carrier 1 and is disposed between the upper surface plate 53 and the lower surface plate 54. Although not shown, the polishing apparatus 5 rotates in the reverse direction with the polishing carrier 1 sandwiched between the upper surface plate 53 and the lower surface plate 54, and the polishing carrier 1 also moves in a planetary motion by the polishing pads 53a and 54a. It has a mechanism for polishing the magnetic disk glass substrate 4. That is, a double-side polishing apparatus using a planetary gear mechanism.

  In general, a glass substrate for a magnetic disk is formed by directly pressing a molten glass into a disk shape having a diameter of 66 mmφ and a thickness of about 1.2 mm, and then (1) a rough lapping step, (2) a shape adding step, ( 3) End polishing step, (4) Fine lapping step, (5) First polishing step, (6) Second polishing step (mirror polishing step), (7) Cleaning step, (8) Chemical strengthening step, (9) It is obtained through steps such as washing. The magnetic disk can be obtained by performing a magnetic disk manufacturing process (10) after the process (9). Here, (6) the second polishing step is a step of mirror-polishing both main surfaces of the magnetic disk glass substrate by attaching a polishing pad having a foamed resin layer formed on the upper and lower surface plates of the polishing apparatus 5 to the surface. It is. The method for polishing a glass substrate for magnetic disk according to this embodiment is applied to the polishing method in the above (6) second polishing step.

  In the method for manufacturing a glass substrate for magnetic disk according to the embodiment, first, a plurality of glass substrates for magnetic disk and magnetic disks are manufactured by performing the above-described steps (1) to (10) as a test. . In that case, the material resin hardness A of the foamed resin layer 532a of the polishing pad used in the second polishing step (6) and the opening diameter B of the foamed pores are changed variously for each glass substrate production, and the ratio (B / Make A) different. Specifically, a resin having various hardness A is selected as a material resin to be a material of the foamed resin (layer), the foamed resin is produced to produce a foamed resin, and a polishing pad formed with the foamed resin as a layer is used. Mirror polishing of the glass substrate is performed. And after manufacture of a glass substrate, the magnitude | size of the microwaviness of each board | substrate is measured and the relationship between both is calculated | required. And when actually producing the product, if the size of the micro waviness required for the product is determined, the material resin hardness and the opening diameter of the foaming pore are determined based on the above obtained correspondence, and this resin hardness A desired foamed resin is produced by foaming the material resin, and a product is manufactured by performing the above (6) second polishing step using a polishing pad formed with this foamed resin as a layer. Thereby, the glass substrate product for magnetic disks which has the desired micro wave | undulation can be obtained stably and reliably. Note that the opening diameter of the foamed pore can be adjusted as desired by scraping (dressing) the surface of the foamed resin layer before mirror polishing.

  Here, the opening diameter d (= B) of the foam pore opening 534a of the foam pore 533a on the surface of the polishing pad 53a can be specifically determined by observing the surface of the polishing pad with an electron microscope or the like. it can. The unit is, for example, [μm]. As the opening diameter value of the foamed pore, an average opening diameter (average opening diameter) is used. Moreover, in the above-mentioned embodiment, the thickness of a preferable polishing layer (foamed resin layer) is 200 to 600 μm, more preferably 300 to 550 μm.

  Further, the “micro wave” is defined by a measurement by a multifunctional surface analyzer (MicroXAM) manufactured by Phase Shift Technology. Unlike a conventional stylus type surface roughness meter, a predetermined area on a glass substrate surface of a magnetic disk is scanned using light (wavelength: 552.8 nm) obtained by passing white light through a coherent filter, and the magnetic disk It is obtained by synthesizing the reflected light from the glass substrate surface and the reflected light from the reference surface, and calculating minute undulations from the interference fringes generated at the synthesis point.

  FIG. 5 is an explanatory view of the measurement principle of the multifunctional surface analysis apparatus. As shown in FIG. 5, according to the principle of the interferometer, the light wave is divided into two and then synthesized. The interference fringes appear due to the optical path difference between the optical path of A → B and the optical path of C → D. The light used for the measurement can be changed without departing from the principle of the measurement.

  The measurement of micro waviness of the multifunctional surface analyzer is within a range of 50 μm 2 to 4 mm 2 in an arbitrary area in the recording / reproducing area on the main surface of the glass substrate, preferably a central part or an area separated by a predetermined distance from the end part. A rectangular area is appropriately selected from the above. For example, the microwaviness of test examples (examples and comparative examples) described later is a measurement value when a rectangular area of 500 μm × 600 μm is selected. Moreover, 2 μm to 4 mm was selected as the wavelength of the undulation (distance between the mountain and the mountain or the valley and the valley). The micro swell is obtained by the following formula.

ここで、Ｒａ'は、中心線から測定曲線までの偏差の絶対値の平均の差、ｘｉは、測定ポイントにおける測定ポイント値（測定ポイントにおいてある基準線から測定曲線までの高さ）、ｘは、上記測定ポイント値の平均値ｎは、測定ポイント数とする。なお、この微小うねりＲａ'は、日本工業規格ＪＩＳＢ０６０１に掲げる表面粗さＲａの算出計算式を、本発明で定義される微小うねりの概念に拡張した算出方法である。

Here, Ra ′ is an average difference of absolute values of deviation from the center line to the measurement curve, xi is a measurement point value at the measurement point (height from a reference line to the measurement curve at the measurement point), and x is The average value n of the measurement point values is the number of measurement points. The minute undulation Ra ′ is a calculation method in which the calculation formula of the surface roughness Ra listed in Japanese Industrial Standard JISB0601 is expanded to the concept of minute undulation defined in the present invention.

  Note that, as a method for calculating the minute undulation, the maximum height wa of the minute undulation can also be used. The maximum height wa of the micro waviness is a value of a difference between the highest point and the lowest point of the measurement curve at all measurement points in the measurement area. However, the surface of the magnetic disk glass substrate may contain abnormal protrusions such as particles that are not directly related to the surface state of the magnetic disk glass substrate itself. In some cases, the measurement is performed in a form including a point of an abnormal protrusion, and if the maximum height wa is used, a large error may occur.

  As a method for excluding the measurement values of abnormal protrusions, a histogram (measurement value and its correspondence) is shown with the measurement value on the horizontal axis and the number of measurement results obtained on the vertical axis for all measurement points. Distribution graph showing the relationship with the number, which is usually a normal distribution curve), the measurement value corresponding to each measurement value is gradually increased from the minimum value in the distribution curve. When the number is accumulated, a method of setting the measured value when the accumulated number reaches 95% of the total number as the maximum value of the effective measured value can be used. The maximum value by this method can be expressed as “95% PV value”, the “95% PV value” can be expressed as the maximum height wa, and the maximum height wa can be expressed as a minute undulation. (For details, refer to JP 2000-348330 A).

  In the present embodiment, the above-described Ra ′ and 95% PV value can be adopted as the microwaviness on the surface of the magnetic disk glass substrate, but it is easy to use Ra ′ practically. In order to ensure that the glide height is 6 nm or less, particularly 5 nm or less when a magnetic disk is used, Ra ′ is preferably 0.35 nm or less. This point is found from the table of test examples (Examples and Comparative Examples) shown in FIG. Further, the foamed resin polishing pad used in the present invention is not particularly limited. The polishing pad made of foamed resin is roughly classified into an independent foaming system and a continuous foaming system depending on the foaming structure. In the closed foaming system, the polishing slurry does not penetrate into the polishing cloth from the foamed form, and there is only a contact interface between the workpiece and the polishing cloth, so generally the flow rate of the slurry is reduced under the same processing pressure. It is supposed to be possible. As an independent foaming system, there are a bubble mixed type and a bubble-free type.

  In the continuous foaming system, a nonwoven fabric is generally used as a base layer (base layer), and various resins impregnated in the transition entangled body act as a binder between fibers, and the resin phase itself has a continuous foaming structure. The continuous foaming system differs from the closed foaming system in that the slurry penetrates into the polishing cloth. As the independent foaming system, there are a suede type and a polishing cloth (coagulated polymer type, coagulated / light type) having a non-woven fabric as a base layer (base layer).

  Among them, a suede type is used as a polishing pad for precision polishing of a glass substrate for a magnetic disk. The suede type polishing cloth is filled with, for example, a woven or non-woven cloth made of natural fiber, recycled fiber or synthetic fiber, or a rubbery substance such as styrene butadiene rubber or nitrile butadiene rubber, or a resin such as polyurethane elastomer. A polyurethane elastomer solution is applied to the obtained base layer (base layer), this is treated with a coagulation liquid, and wet coagulation is performed to form a porous silver surface layer. After washing with water and drying, the surface of the silver surface layer is sandpaper. A suede-type polishing cloth having spindle-shaped pores having a uniform surface hole shape and a uniform cross-sectional hole shape perpendicular to the substrate surface is manufactured. Polyurethane is suitable as the material resin for the foamed resin layer. However, according to the present invention, it has been found that it is particularly preferable to select polyester-based polyurethane.

  The “material resin hardness” is the resin hardness of a resin that is a material of foamed resin (for example, foamed polyurethane, etc.). According to the present inventors, it has been found that it is preferable to use a resin modulus (100% elongation modulus) hardness as the resin hardness. Resin modulus (100% elongation modulus) hardness is defined as the stress per unit cross-sectional area of the resin material when the resin material is elongated 100%. Specifically, it can be measured using a measuring device such as an autograph. For example, a sample of a resin material film (about 0.5 cm × 4 cm) is prepared, and a mark line is drawn at an appropriate interval in the center of the film. Next, the sample film is stretched by a tensile force, and the strength when the interval between the mark lines is stretched by 100% is recorded. The value obtained by dividing the strength, that is, the tensile stress by the cross-sectional area of the sample film, is the resin modulus (100% elongation modulus) hardness. The unit is, for example, [kg / cm 2].

Further, Asker C hardness can be used as the hardness of the polishing pad itself after the foamed resin layer is formed. The ASKER C hardness is defined in the Japan Rubber Association Standard (SRIS0101) and can be specified by a durometer (spring type hardness meter) or the like. A polishing pad suitable for the present invention is preferably selected from polishing pads having an Asker C hardness of 62 to 85.

  Next, as a test, the above-described steps (1) to (10) are carried out to manufacture a plurality of glass substrates for magnetic disks and magnetic disks. ) Material hardness (A) and foam pore opening diameter d (B) of the foamed resin layer 532a of the polishing pad 53a used in the second polishing step are made different, and after manufacturing, the size of the micro waviness of each substrate is measured. An example in which the relationship between these is obtained will be described below.

(1) Coarse lapping process First, a glass substrate for a magnetic disk comprising a disc-shaped aluminosilicate glass having a diameter of 66 mmφ and a thickness of 1.2 mm is obtained by directly pressing molten glass using an upper mold, a lower mold, and a body mold. Got. In this case, in addition to the direct press, a disk-shaped glass substrate for a magnetic disk may be obtained by cutting a sheet glass formed by a downdraw method or a float method with a grinding wheel. As the aluminosilicate _glass, SiO 2: 58 to 75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: 3 to 10 _wt%, Na 2 O: 4 to 13 principal component weight% Chemically strengthened glass contained as

  Next, a lapping process was performed on the magnetic disk glass substrate. This lapping process aims to improve the size system and the shape system. The lapping process was performed using a double-sided lapping apparatus, and the abrasive grain size was # 400. Specifically, by using alumina abrasive grains having a particle size of # 400, setting the load L to about 100 kg, and rotating the inner rotation gear and the outer rotation gear, both surfaces of the glass substrate for the magnetic disk stored in the carrier are faced. Finished to an accuracy of 0 to 1 μm and a surface roughness Rmax of about 6 μm.

(2) Shape processing step Next, a cylindrical grindstone is used to make a hole in the central portion of the glass substrate for a magnetic disk, and the outer peripheral end surface is ground to a diameter of 65 mm. Chamfered. At this time, the surface roughness of the end surface (inner circumference, outer circumference) of the glass substrate for magnetic disk was about 4 μm in Rmax.

(3) End surface polishing step Next, the surface roughness of the end surface (inner and outer periphery) of the magnetic disk glass substrate is set to about 1 μm for Rmax and about 0.3 μm for Ra while rotating the glass substrate for magnetic disk by brush polishing. Polished. The surface of the glass substrate for magnetic disks after the end face polishing step was washed with water.

(4) Fine lapping step Next, by changing the grain size of the abrasive grains to # 1000 and lapping the glass substrate surface for magnetic disk, the flatness is 3 μm, the surface roughness Rmax is about 2 μm, and Ra is about 0.2 μm. did. Rmax and Ra are measured with an atomic force microscope (AFM), and flatness is measured with a flatness measuring device. The vertical direction between the highest part and the lowest part of the glass substrate surface for magnetic disks ( Distance in the direction perpendicular to the surface (height difference). The magnetic disk glass substrate after the fine lapping process was washed by immersing it in neutral detergent and water wash tanks.

(5) First Polishing Step Next, a polishing step was performed. This polishing process is intended to remove scratches and distortions remaining in the lapping process described above, and was performed using a double-side polishing apparatus. Specifically, a hard polisher was used as a polishing pad and the following polishing conditions were used.
Polishing liquid: Cerium oxide (average particle size 1.3 μm) + water load (pressure applied): 80 to 100 g / cm ²
Polishing time: 30-50 minutes Removal amount: 35-45 μm

  The magnetic disk glass substrate that had undergone the above polishing process was washed by sequentially immersing it in each washing tank of neutral detergent, pure water, pure water, IPA, and IPA (steam drying). In addition, ultrasonic waves were applied to each cleaning tank. Further, this cleaning step can be omitted when the polishing liquid used in the next second polishing step is the same. The hard polisher used in the first polishing step is not particularly limited, and can be appropriately selected depending on the target surface roughness, the end shape of the glass substrate for magnetic disk, and the like.

(6) Second polishing process (mirror polishing process)
Next, using the double-side polishing apparatus using the planetary gear mechanism described above, the second polishing step was carried out by changing the polishing pad. The foamed resin used was a polyester-based polyurethane having a material resin hardness of 130 kg / cm ² in terms of resin modulus (100% elongation modulus) hardness. The opening diameter (average diameter) of the foamed pores opened on the surface of the polishing pad when observed with an electron microscope is 40 μm. [Aperture diameter of the pores on the surface of the polishing pad / resin modulus (100% elongation modulus) hardness observed with an electron microscope] is 0.31 μm · cm ² / kg. As the polishing pad, a polishing pad having a surface roughness Rz (Rz is a ten-point average roughness) in the range of 1 μm to 10 μm was selected. The polishing pad had an Asker C hardness of 75.

As the polishing liquid, cerium oxide (average particle size 0.5 μm) was selected as polishing abrasive grains (abrasive), and a slurry (free abrasive grains) mixed with ultrapure water was used.
Other polishing conditions are:
Load (applied pressure): 50 to 150 g / cm ²
Polishing time: 10-15 minutes Removal amount: 3-5 μm.

(7) Cleaning step The magnetic disk glass substrate after the second polishing step was immersed in sulfuric acid for cleaning. In addition, ultrasonic waves were applied to each cleaning tank. Furthermore, it wash | cleaned by immersing in each washing tank of neutral detergent, a pure water, a pure water, IPA, and IPA (steam drying) one by one.

(8) Chemical strengthening process Next, the glass substrate for magnetic disks which finished the said lapping, polishing, and washing | cleaning process was chemically strengthened. For chemical strengthening, a chemically strengthened salt prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared. This chemically strengthened salt is heated to 375 ° C and preheated to 300 ° C for a washed magnetic disk. The glass substrate was immersed for about 3 hours. In this immersion, the plurality of magnetic disk glass substrates were housed in a holder so as to be held at the end surfaces so that the entire surface of the magnetic disk glass substrate was chemically strengthened.

  As described above, by immersing in the chemically strengthened salt, the lithium ion and sodium ion on the surface layer of the magnetic disk glass substrate are replaced with the sodium ion and potassium ion in the chemically strengthened salt, respectively, and the magnetic disk glass substrate is strengthened. The The thickness of the compressive stress layer formed on the surface layer of the glass substrate for magnetic disks was about 100 to 200 μm. The glass substrate for magnetic disk that had been subjected to the above chemical strengthening was immersed in a 20 ° C. water bath for rapid cooling and maintained for about 10 minutes.

(9) Washing Step The glass substrate for magnetic disk after the rapid cooling was immersed in sulfuric acid and washed while applying ultrasonic waves. The surface roughness of the surface of the magnetic disk glass substrate thus obtained was measured by AFM. As a result, it was in a mirror state, and the values were Rmax = 3.42 nm and Ra = 0.35 nm. Moreover, the average roughness Ra ′ of the fine waviness was 0.33 nm, and good results were obtained.

(10) Magnetic disk manufacturing process A NiAl seed layer, a CrV underlayer, a CoPtCrB magnetic layer, and a hydrogenated carbon protective layer are formed on a glass substrate for a magnetic disk obtained through the above-described processes using a sputtering apparatus. Then, a perfluoropolyether lubricating layer was formed by a dip method to produce a magnetic disk.

The obtained magnetic disk was subjected to a glide height and load / unload durability test (600,000 continuous load / unload) using an AE sensor, and the glide height was 4.8 nm. In the load / unload durability test, there was no fly stiction failure or head crash failure.
The results of this test example are listed as Example 1 in the table of FIG.

Next, as another test example, the polishing pad used in the second polishing step was selected as shown in the table shown in FIG. 3 (Examples 2 to 5). Note that items not listed in FIG. 3 are the same as those in the first embodiment. Adjustment of the opening diameter of the foaming pore was carried out by performing both adjustment by the foaming form and adjustment by the surface dress of the foamed resin layer.

In the load / unload endurance test (600,000 continuous load / unload) performed in Examples 2 to 5, as in Example 1, no fly stiction failure or head crash failure occurred.

As shown in FIG. 3, in the test examples of Examples 1 to 4, it can be seen that a glide height of 5.0 nm or less can be realized. Moreover, in the test example of Examples 1-5, it turns out that glide height 6.0nm or less is realizable.

Next, as another test example, the polishing pad used in the second polishing step was selected as shown in the table shown in FIG. 3 (Comparative Examples 1 to 4). In addition, Comparative Examples 1-4 here means the comparative example about the invention regarding the 2nd means or 3rd means of this invention, Comprising: About the 1st means, it is a test example. The foamed resins of Comparative Examples 1 to 4 are polycarbonate polyurethane.

  The results in the above test examples (Examples and Comparative Examples) are as shown in the table in FIG. In Comparative Examples 1 to 4, the microwaviness Ra ′ cannot be made 0.35 nm or less and the glide height becomes 7 nm or more, so that the flying height of the magnetic head cannot be made 10 nm or less.

In Comparative Examples 1 to 4, a fly stiction failure occurred in the load / unload durability test. For this reason, the load / unload could only endure about 200,000 times. Therefore, according to the present invention, it can be seen that the fly stiction failure which is a particular problem in the load / unload type magnetic disk can be suitably prevented.

  FIG. 4 is a graph showing the correspondence between the ratio (B / A) of the opening diameter B of the foamed pore and the material resin hardness A of the foamed resin layer in the table of FIG. 3 and the size of the microwaviness on the surface of the glass substrate. is there. As shown in FIG. 4, it can be seen that there is a causal relationship between B / A and the size of the microwaviness.

  From the above, in order to achieve the object of the present invention, it is necessary to simultaneously manage the opening diameter B of the foamed pore and the hardness A of the material resin of the foamed resin layer. By selecting the ratio (B / A) of B to the material resin hardness A, the size of the microwaviness of the glass substrate can be set to a desired value by utilizing the causal relationship between B / A and the microwaviness of the glass substrate surface. It can be seen that it can be a value. Therefore, when the size of the microwaviness required for the product is determined when the product is actually produced, the ratio of the opening diameter B of the foamed pore to the material resin hardness A (B / A) is selected, and the product is manufactured by performing the above-mentioned (6) second polishing step using the selected polishing pad. Thereby, the glass substrate product for magnetic disks which has the desired micro wave | undulation can be obtained stably and reliably.

Further, if the polishing pad is 0.6 μm · cm ² / kg or less as the B / A, the microwaviness Ra ′ can be 0.35 nm or less, and the glide height can be 6 nm or less. For example, when a lower glide height is required, such as for a load / unload system, the B / A is preferably 0.5 μm · cm ² / kg or less. This is because the glide height can be 5 nm or less in this case. The lower limit of B / A is not particularly defined, but it is necessary that the value be practically greater than 0. In addition, if the hardness of the foam resin material resin is 120 kg / cm ² or more and at the same time the polishing pad has an opening diameter of the foam pores of 65 μm or less, the micro waviness Ra ′ is 0.35 nm or less. In addition, the glide height can be 6 nm or less. For example, when a lower glide height is required, such as for a load / unload system, the hardness of the foam resin material resin is 130 kg / cm ² or more, and at the same time, the opening diameter of the foam pores on the surface of the polishing pad is A polishing pad of 60 μm or less is preferable. This is because the glide height can be 5 nm or less in this case.

In order to float the magnetic head more safely, it is preferable to use a polishing pad having a foam pore opening diameter of 40 μm or less on the surface of the polishing pad. In this case, it is because the glide height can be surely made less than 5 nm (for example, Example 1). The hardness of the material resin of the foamed resin is preferably as high as possible, but an upper limit of 200 kg / cm ² or less can be given from a practical viewpoint. The opening diameter of the foamed pore is preferably as small as possible, but practically needs to be a value exceeding 0.

  The glass type, size, etc. of the magnetic disk glass substrate according to the present embodiment are not particularly limited. Examples of the glass type include aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, and crystallized glass. In terms of smoothness, amorphous glass is generally better than crystallized glass, and chemically tempered glass such as aluminosilicate glass is particularly preferred from the viewpoint of mechanical strength, impact resistance, vibration resistance, and the like.

The aluminosilicate _glass, SiO 2: containing 4-13% by weight as the main component: 58 to 75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: 3 to 10 _wt%, Na 2 O Chemical tempered glass is preferred. In recent years, since a glass substrate for a magnetic disk having high smoothness has been demanded, a crystallized glass substrate having a crystal grain size of 100 nm or less has been developed. Crystallized glass has a higher mechanical strength than amorphous glass, and is excellent in flatness due to advantages such as grinding with diamond pellets in the manufacturing process, and a glass substrate for magnetic disks with high smoothness can be obtained. Therefore, it is preferable.

Further, as the polishing liquid, cerium oxide free abrasive grains can be suitably used. As an average particle diameter of the polishing abrasive grains contained in the polishing liquid, it is preferable to select polishing abrasive grains of 0.04 μm to 0.8 μm. The pressure applied to the glass substrate during mirror polishing is preferably 50 to 150 g / cm ₂ , and the surface roughness Rz of the polishing pad is preferably 20 μm or less, particularly preferably 10 μm or less. If it exceeds 20 μm, it may be difficult to reduce the glide height. From the viewpoint of obtaining a glass substrate for magnetic disk or a magnetic disk particularly suitable for load / unload applications with a glide height of 5 nm or less, Rz is preferably 10 μm or less.
The surface roughness of the main surface of the glass substrate for a magnetic disk to be obtained in the present invention is preferably a mirror surface having an Rmax of 6 nm or less and an Ra of 0.6 nm or less. If the surface roughness is exceeded, it is difficult to make the glide height 6 nm or less. Particularly preferably, Rmax is 5 nm or less, and Ra is 0.5 nm or less.
The material of the magnetic layer formed on the magnetic disk glass substrate is not particularly limited. Examples of the magnetic layer include a magnetic film containing Co as a main component. If necessary, a seed layer and an underlayer may be provided between the magnetic disk glass substrate and the magnetic layer, and a protective layer and a lubricating layer may be provided on the magnetic layer.

The seed layer has a role of controlling the crystal grain size of the underlayer and magnetic layer formed thereon, and examples thereof include materials such as NiAl, CrNi, and CrTi. The underlayer is provided for the purpose of improving magnetic properties, and is made of, for example, a non-magnetic material made of at least one material selected from nonmagnetic metals such as Cr, Mo, V, Ta, Ti, W, B, Al, and Ni. An example is a magnetic film. The underlayer may be a single layer or a plurality of layers. The protective layer is provided for mechanical durability, corrosion resistance, and the like, and examples thereof include Cr, Cr alloy, carbon, hydrogenated carbon, carbon nitride, zirconia, and SiO ₂ . The lubricating layer is provided to prevent adsorption with the magnetic head and reduce the friction coefficient, and a perfluoropolyether lubricant or the like is generally used.

  The present invention provides a magnetic disk glass substrate manufacturing method and a magnetic disk capable of accurately controlling the microwaviness on the surface of the magnetic disk glass substrate so that the flying height of the magnetic head can be stabilized and very low (for example, 10 nm or less). Or a glass substrate for a magnetic disk suitable for the LUL (load / unload) method.

It is explanatory drawing of a polishing pad. It is principal part sectional drawing of the grinding | polishing apparatus which has an upper and lower surface plate. It is the figure which showed the resin hardness of the polishing pad in the test example (Examples 1-5, Comparative Examples 1-4), the opening diameter of a foaming pore, the microwaviness of the glass substrate surface, etc. as a table | surface. The ratio (B / A) of the opening diameter B of the foam pore on the foamed resin surface of the polishing pad and the material resin hardness A of the foamed resin and the size of the microwaviness on the surface of the glass substrate after mirror polishing using this polishing pad It is a graph which shows a correspondence. It is explanatory drawing of the measurement principle of a multifunctional surface analyzer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polishing carrier 4 Magnetic disk glass substrate 5 Polishing apparatus 53 Upper surface plate 53a Polishing pad 54 Lower surface plate 530a Base body 531a Base layer (base layer)
532a Polishing layer (foamed resin layer)
533a Foamed pore 534a Foamed pore opening

Claims (6)

A method for producing a glass substrate for a magnetic disk comprising a step of applying a polishing pad having a foamed resin layer to a glass substrate and mirror-polishing both main surfaces of the glass substrate with the polishing pad while supplying a polishing liquid,
When the hardness of the material resin of the foamed resin is A and the opening diameter of the foamed pore on the surface of the polishing pad is B, the ratio of B to A (B / A) and the mirror polishing is performed using this polishing pad. Utilizing the phenomenon that the size of the micro-waviness on the surface of the glass substrate later has a certain correspondence relationship,
This correspondence is obtained on a trial basis in advance.
Based on the obtained correspondence relationship, the ratio of B to A (B / A) corresponding to the desired microwaviness size is determined,
Determine the values of A and B to be this determined ratio (B / A),
A glass substrate for a magnetic disk having a desired surface undulation by mirror polishing with a polishing pad having the determined values A and B. Production method. A method for producing a glass substrate for a magnetic disk comprising a step of applying a polishing pad having a foamed resin layer to a glass substrate and mirror-polishing both main surfaces of the glass substrate with the polishing pad while supplying a polishing liquid,
When the hardness of the material resin of the foamed resin is A and the opening diameter of the foamed pore on the polishing pad surface is B, the ratio of B to A (B / A) is 0.6 μm · cm ² / kg or less. A method for producing a glass substrate for a magnetic disk, comprising: selecting a polishing pad to be mirror-polished using the polishing pad.
However, B is the opening diameter [μm] of the foaming pore on the surface of the polishing pad, A is the hardness of the material resin of the foamed resin, and the resin modulus (100% elongation modulus) hardness [kg / cm 2] Say. A method for producing a glass substrate for a magnetic disk comprising a step of applying a polishing pad having a foamed resin layer to a glass substrate and mirror-polishing both main surfaces of the glass substrate with the polishing pad while supplying a polishing liquid,
A polishing pad in which the hardness A of the material resin of the foamed resin is 120 kg / cm ² or more and the opening diameter B of the foaming pore on the polishing pad surface is 65 μm or less is selected, and mirror polishing is performed using this polishing pad. A method for producing a glass substrate for a magnetic disk. However, A is the hardness of the resin material of the foamed resin and is the resin modulus (100% elongation modulus) hardness [kg / cm ² ], and B is when the surface of the polishing pad is observed with an electron microscope It means the opening diameter [μm] of the foamed pore of the foamed resin layer obtained. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the surface roughness of the polishing pad surface is 20 μm or less in terms of Rz.
However, Rz is a ten-point average roughness.   The method for manufacturing a glass substrate for a magnetic disk according to any one of claims 1 to 4, wherein the polishing pad has a hardness (Asker-C hardness) of 62 to 85.   A magnetic disk for a load / unload system, wherein at least a magnetic layer is formed on the glass substrate for a magnetic disk obtained by the method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 5. Manufacturing method.

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