JP4199645B2 - Method for manufacturing glass substrate for magnetic disk and method for manufacturing magnetic disk - Google Patents

Description

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

In recent years, the information recording density of magnetic disks has been required to be 60 gigabits or more per square inch. In order to realize such a high recording density, the flying height of the magnetic head that records and reproduces by flying over the magnetic disk needs to be 10 nm or less from the viewpoint of reducing the spacing loss. For this reason, the surface roughness of the magnetic disk substrate needs to be extremely smoothed so that a failure such as a crash can be prevented even if the flying height of the magnetic head is 10 nm. For example, it is necessary to have a mirror surface such that Rmax is 5 nm or less and Ra is 0.5 nm or less.
In order to obtain such a mirror surface, various technical innovations are required in the method for polishing a glass substrate for a magnetic disk, particularly in the mirror polishing method. As one of the methods, there can be mentioned a method of refining abrasive particles (abrasive grains) contained in the abrasive.

However, according to the study of the present inventor, regardless of the currently known Asker C hardness of the polishing cloth, when, for example, cerium oxide (relatively large particle size) is used as the polishing abrasive grain, Insufficient polishing causes a rise in the edge of the main surface (protruding the edge of the main surface beyond the portion of the other main surface), and there is a problem. For example, colloidal silica ( When using a relatively small particle size, the edge of the main surface is scraped off and the edge of the edge of the main surface is “end of the edge” (the edge of the main surface is relatively larger than the parts of the other main surfaces) It was found that this would be a problem. As described above, the problem of the irregular shape of the end portion (protrusion of the end portion and the sag of the end portion) is remarkably improved, and a glass substrate for a magnetic disk sufficiently excellent in the end shape has not yet been obtained (first). Issue).
Further, according to the research of the present inventor, when a polishing cloth having a relatively small Asker C hardness and a relatively soft polishing cloth is used (polishing abrasive grains use cerium oxide), a mirror surface level is known. However, since cerium oxide is used as the abrasive grains as described above, there is a problem that the end of the main surface is raised. It has been found that when a polishing cloth having a relatively large Asker C hardness is used (the polishing abrasive grains are cerium oxide), the bulge at the end can be relatively reduced (not significantly reduced). However, when a hard polishing cloth is used, there is a problem that the mirror surface level is lowered. Therefore, the present inventor tried to use a polishing cloth having a relatively large Asker C hardness and relatively hard, and attempted to reduce the grain size of the abrasive grains (the abrasive grains used colloidal silica). However, in this case, although the decrease in the mirror surface level can be reduced, as described above, since colloidal silica is used as the abrasive grains, the end of the main surface is scraped off, resulting in “end-sag”. It has been found. As described above, the mirror surface of the disk and the irregularity of the end shape (the bulge of the end and the sag of the end) are in a trade-off relationship, and at present, the mirror surface within the above range (Rmax of 5 nm or less, A glass substrate for a magnetic disk having a Ra of 0.5 nm or less) and a sufficiently excellent edge shape has not been obtained yet (first problem 1).
If the disk end shape is disturbed, the flying posture of the magnetic head is disturbed, so that a failure such as a crash is induced near the end.

In recent years, there is a tendency to expand the recording / reproducing area on the surface of the magnetic disk as a hand-raising to improve the information capacity of the magnetic disk. For example, a conventional HDD is a CSS (Contact Start Stop) type HDD, but recently, an LUL (Load Unload) type is being adopted. This is because the LUL magnetic disk does not need to have a CSS area (contact sliding area with the magnetic head), and therefore has an advantage that the recording / reproducing area on the surface of the magnetic disk can be enlarged. Further, in the LUL magnetic disk, since the sliding contact between the magnetic head and the magnetic disk does not occur, it is necessary to provide an uneven shape on the surface of the magnetic disk to prevent the magnetic head from being attracted by the contact. No. Therefore, the LUL magnetic disk has an advantage that the flying height of the magnetic head can be further reduced as compared with the CSS magnetic disk. In other words, it can be said that the system is particularly suitable for the purpose of reducing the spacing loss by mirroring the surface of the magnetic disk substrate.
However, in the LUL type HDD, at the time of activation, the magnetic head enters the disk surface from the outside of the magnetic disk and is activated. At the time of stop, the disk is evacuated from the disk surface and stopped. That is, the magnetic head passes near the end of the disk when starting and stopping. At this time, as described above, when there is a disorder in the shape of the edge on the disk surface (the bulge of the edge or the sag of the edge), the flying posture of the magnetic head is disturbed, and the problem that a crash failure is likely to occur. Occurred. That is, in the LUL type HDD, it is highly necessary to reduce the shape irregularity at the end on the disk surface as compared with the CSS type HDD (second problem).

Furthermore, in order to set the flying height of the magnetic head to 10 nm or less, the magnetic disk has a mirror surface (Rmax 5 nm or less, Ra 0.5 nm or less) within the above-mentioned range and has a sufficiently excellent edge shape. Although it is necessary to obtain a glass substrate, reduction of “microwaviness” on the main surface is also an important factor.
To explain this, in recent years, the flying height of the magnetic head can be lowered even if the surface roughness (Rmax (maximum height), Ra (centerline average roughness)) is reduced by polishing with high accuracy. It became clear that the problem of not being able to occur. The applicant of the present application has determined that the cause is microwaviness existing on the substrate surface, and as a means for reducing this microwaviness, the surface roughness Rz (ten-point average roughness) of the polishing pad surface is determined. An application has already been filed regarding a technology capable of providing a substrate having a low glide height and a low modulation by developing means such as 20 μm or less (Patent Document 1).
However, in order to realize a more advanced requirement to further reduce the flying height of the magnetic head after setting the flying height of the magnetic head to 10 nm or less, it is not sufficient to apply the technology for reducing the fine waviness described above. Further reduction of micro swell is required. According to the inventor's research, it has been found that the “micro-waviness” at the end tends to be larger than the “micro-waviness” on the main surface. That is, when the flying height of the magnetic head is set to 10 nm or less and the flying height of the magnetic head is further reduced, as described above, the “small waviness” at the edge is large. Falls into a state where there is a disturbance in shape. As described above, if the “small waviness” at the end is large, the flying height of the magnetic head is set to 10 nm or less, and it becomes an obstacle to further reducing the flying height of the magnetic head. This is an obstacle to the second problem solving described above.
Therefore, it is desired to develop a technique capable of reducing the “micro-waviness” at the end compared to the “micro-waviness” at the end compared to the “micro-swell” at the end compared to the “small swell” at the end (third problem). ).
JP 2002-92867 A

The present invention has been made in view of the above problems, and a first object thereof is to provide a glass substrate for magnetic disk or a magnetic disk that is sufficiently excellent in mirror surface and end shape.
In addition, we provide a glass substrate or magnetic disk for magnetic disks in which the “micro-waviness” at the end is further reduced compared to the conventional technology, in response to the problem that the “micro-waviness” at the end is larger than the “micro-swell” on the main surface. There is to do.
It is a second object of the present invention to provide a glass substrate for a magnetic disk or a magnetic disk that can stabilize the flying posture even with a magnetic head having a flying height of 10 nm or less.
It is a third object of the present invention to provide a magnetic disk for LUL system or a glass substrate suitable for this magnetic disk.

As a result of intensive research and development in solving the problems of the present invention described above, the present inventor firstly reduced the pore diameter on the base layer side in the foamed resin layer constituting the polishing cloth (Configuration 1). From another point of view, by reducing the compressibility of the polishing cloth (Configuration 2), the end shape irregularities (swelling of the end portion and drooping of the end portion) are conspicuous with respect to the first problem described above. It was first found that a glass substrate for a magnetic disk having a reduced edge shape and a sufficiently excellent edge shape can be obtained.
Further, by reducing the pore diameter on the base layer side in the foamed resin layer constituting the polishing cloth (Configuration 1), in another way, by reducing the compressibility of the polishing cloth (Configuration 2), the above-described first In contrast to the problem 1 ′, the difference between the polishing rate at the end of the main surface and the polishing rate at the other part of the main surface can be reduced, and as a result, the problem of “sagging of the end” can be reduced. I found it. That is, the present invention solves the problem that the mirroring of the disk surface and the disturbance of the end shape (end bulge and end sag) are in a trade-off relationship, and the mirror surface within the above range (Rmax) And 5 nm or less and Ra 0.5 nm or less) and a glass substrate for a magnetic disk that has a sufficiently excellent edge shape.
Secondly, reducing the pore diameter on the base layer side in the foamed resin layer constituting the polishing cloth (Configuration 1), from another viewpoint, reducing the compressibility of the polishing cloth (Configuration 2) is described above. The third problem has been found to be an effective means for reducing the minute waviness at the end of the third problem.
Third, by reducing the surface opening of the polishing cloth, there is an effect of reducing the overall waviness of the entire surface of the substrate, and reducing the surface opening of the polishing cloth means that the end opening has a minute diameter. It has been found fourth (Configuration 3) that it is an effective means for reducing waviness.
Further, in addition to the requirements of Configuration 1 or 2, when a polishing liquid containing colloidal particles is supplied and polished (when the particle size of the polishing particles is reduced), a mirror surface of the main surface newly generated by adopting the requirements of Configuration 1 or 2 The present invention has been completed fifth by finding that the problem of deterioration of the level can be solved and the mirror surface level of the main surface can be suppressed to a level that does not cause a problem even if the flying height of the magnetic head is 10 nm or less.

The present invention has the following configuration.
(Configuration 1) A method for producing a glass substrate for a magnetic disk that uses a polishing cloth having a base layer and a foamed resin layer, and moves the glass disk and the polishing cloth relatively to perform polishing.
A method for producing a glass substrate for a magnetic disk, comprising selecting a polishing cloth provided with a foamed resin layer having a pore diameter of 200 μm or less on the base layer side, and polishing a glass disk by supplying a polishing liquid containing colloidal particles. .
(Configuration 2) A method of manufacturing a glass substrate for a magnetic disk, in which polishing is performed by using a polishing cloth and relatively moving the glass disk and the polishing cloth,
A magnetic disk comprising: measuring a compressibility of the polishing cloth; selecting a polishing cloth having a compressibility of 1.0% or less; and supplying a polishing liquid containing colloidal particles to polish a glass disk. Method for manufacturing glass substrate.
(Configuration 3) A method of manufacturing a glass substrate for a magnetic disk according to Configuration 1,
A method for producing a glass substrate for a magnetic disk, comprising polishing a glass disk by selecting a polishing cloth provided with a foamed resin layer having a pore diameter of 50 μm or less opened on a polished surface.
Colloidal particles contained in (Configuration 4) The polishing liquid has an average particle diameter _{(D 50),} the manufacture of glass substrate according to any one of configurations 1 to 3, characterized in that the 10nm~120nm Method.
(Constitution 5) The method for producing a glass substrate for a magnetic disk according to any one of constitutions 1 to 4, wherein the colloidal particles contained in the polishing liquid are colloidal silica abrasive grains.
(Configuration 6) A method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 5,
A method for producing a glass substrate for a magnetic disk, comprising polishing by pressing a polishing cloth from a base layer side of the polishing cloth.
(Structure 7) A method of manufacturing a magnetic disk, comprising forming a magnetic layer on the glass substrate for a magnetic disk according to any one of structures 1 to 6.
(Configuration 8) A magnetic disk glass substrate having a surface roughness Rmax of 5 nm or less and Ra of 0.5 nm or less when the main surface of the disk is measured with an atomic force microscope,
A point on the main surface of 0.34 mm from the outer peripheral edge of the disk toward the disk center is A, and B is a point on the main surface of 3.54 mm from the outer edge of the disk toward the disk center. A glass substrate for a magnetic disk, wherein a divergence distance from the virtual line to the main surface is 50 nm or less when a virtual line connecting points B is used as a reference.
(Configuration 9) A glass substrate for a magnetic disk having a surface roughness of 5 nm or less in Rmax and 0.5 nm or less in Ra when the disk main surface is measured with an atomic force microscope,
Of the surface shapes in a rectangular area of 3.8 square mm centered on a point on the main surface of 2.5 mm from the outer peripheral edge of the disk toward the center of the disk, the surface shape having a shape wavelength of 16 μm to 1.9 mm band Is extracted, and the surface roughness of the root mean square roughness Rq (RMS) is defined as a microwaviness Rq, the microwaviness Rq is 1.42 nm or less.
(Structure 10) A magnetic disk for load / unload system, wherein at least a magnetic layer is formed on the glass substrate for magnetic disk according to Structure 8 or Structure 9.

ADVANTAGE OF THE INVENTION According to this invention, the glass substrate for magnetic discs or magnetic discs which were fully excellent in the mirror surface and edge part shape can be provided. In addition, the glass substrate for magnetic disk or the magnetic disk can be provided in which the “micro-waviness” at the end portion is smaller than the conventional one in response to the problem that the “micro-waviness” at the end portion becomes larger than the “micro-waviness” on the main surface. .
Furthermore, it is possible to provide a glass substrate for a magnetic disk or a magnetic disk that can stabilize the flying posture even with a magnetic head having a flying height of 10 nm or less.
In addition, a magnetic disk for LUL system or a glass substrate suitable for this magnetic disk can be provided.

The present invention will be described in detail below.
The invention which concerns on the structure 1 of this invention is related with the manufacturing method of the glass substrate for magnetic discs which grind | polishes using an abrasive cloth provided with a base layer and a foamed resin layer, moving a glass disk and an abrasive cloth relatively.
Here, urethane is widely used as the foamed resin layer. Examples of the polishing cloth having a base layer and a foamed resin layer include a suede type and a urethane foam type. As shown in FIG. 6, a suede-type polishing cloth (polishing pad) is coated (laminated) with polyurethane on the base layer (base layer), a foam layer is grown in the polyurethane, the surface portion is removed, and the foam layer is opened. Part (opening of polishing surface, opening of surface). The pores that are traces of foaming are called pores, the portion of the polyurethane layer where pores are present is called a nap layer, and the thin layer near the base layer (usually the portion where pores are not present) is called a microlayer. The foamed urethane type polishing pad is obtained by slicing a foamed urethane block, and is bonded to the base layer to form a polishing cloth having a base layer and a foamed resin layer. The base layer in the suede type polishing cloth is a woven or non-woven cloth made of natural fibers, recycled fibers or synthetic fibers, or a rubbery substance such as styrene butadiene rubber or nitrile butadiene rubber, or a resin such as polyurethane elastomer. Although the base material obtained by filling is generally used, in the invention according to Configuration 1, by adopting a resin film (for example, a PET resin film) as the base layer, the pore diameter on the base layer side of the foamed resin layer is reduced. A resin film is preferably used as the base layer because it is considered that a synergistic effect with the function and effect obtained by reducing the diameter to a predetermined value is exhibited. When using a resin film as a base layer, from the viewpoint of the synergistic effect, the thickness of the resin film is preferably 400 nm or less, and particularly preferably 300 nm or less. Although it is not necessary to specifically limit the lower limit, it can be practically 50 nm or more.

The invention according to Configuration 1 of the present invention is characterized in that a polishing cloth including a foamed resin layer having a pore diameter of 200 μm or less on the base layer side is selected, and a glass disk is polished by supplying a polishing liquid containing colloidal particles. And Thus, when the pore diameter is reduced to 200 μm or less, the following effects are obtained.
First, in contrast to the first problem described above, the end shape disorder (swelling of the end portion and end sag) is significantly reduced, and the end shape is sufficiently excellent (the end shape is almost the same). A glass substrate for a magnetic disk (which can be said to be flat) is obtained.
Second, the difference between the polishing rate of the end portion of the main surface and the polishing rate of the other portion of the main surface can be reduced with respect to the first 'problem described above. Secondly, the problem can be reduced. That is, according to the present invention (Configuration 1), the problem that the mirror surface of the disk surface is mirror-finished and the end shape is distorted (the bulge of the end portion or the sag of the end portion) is in a trade-off relationship. It is possible to achieve for the first time a magnetic disk glass substrate having a mirror surface (Rmax of 5 nm or less, Ra of 0.5 nm or less) and having a sufficiently excellent end shape.
Third, it is an effective means for reducing the minute waviness of the end portion with respect to the third problem described above.
Note that the difference in pore diameter is a structural difference, and it is considered that an action that cannot be captured at a compression rate, which will be described later, or a synergistic action may be exhibited in a state where the polishing cloth at the time of actual polishing is compressed. It is done.
In the foamed resin layer, there are pores formed during foaming from the base layer side to about half to about one third of the thickness of the foamed resin layer, and the pores formed by reducing the diameter in the direction in which air escapes from the surface The shape continues to the opening. In the present invention, the pore diameter on the base layer side means the diameter of pores in the region from the base layer side to about half to about ３ of the thickness of the foamed resin layer (preferably, the longitudinal section of the foamed resin layer was seen. The diameter (size) of the cross section of the hole. For example, as shown in the examples to be described later, if the maximum pore diameter on the base layer side is managed, a polishing cloth that is reduced in diameter compared with the conventional one and exhibits the effects of the present invention can be selected. The maximum pore diameter on the base layer side may be managed by the maximum diameter among the pore diameters on the base layer side, and is managed by the average value of the maximum diameters of the pore diameters on the base layer side. Also good. In addition to managing the maximum pore diameter on the base layer side in this way, an arbitrary reference line (a line parallel to the base layer) is drawn from the base layer side to a portion from about half to about one third of the thickness of the foamed resin layer. The management can also be performed by the average diameter of the pore diameters in the reference line. In this case, it is preferable to draw a reference line at a site where the average pore diameter is maximum. The pore diameter on the base layer side can be managed by the pore diameter at a reference line (line parallel to the base layer) at a site of 100 μm to 300 μm in the thickness direction of the foamed resin layer from the base layer side. Further, for example, it is possible to perform management based on an average value of a plurality of pore diameters arbitrarily selected (preferably a representative one) among a large number of pore diameters on the base layer side. As described above, according to the present invention, the pore diameter is controlled so that the pore diameter is reduced compared with the conventional relatively large pores generated at the time of foaming, and the polishing cloth that exhibits the effects of the present invention can be selected. Just do.
In order to more effectively express the effect of the present invention, it is preferable to make the dispersion (dispersion) of the pore diameter on the base layer side uniform. When variation (dispersion) in the pore diameter on the base layer side is uniform, it is easy to manage the maximum pore diameter on the base layer side.
In order to more effectively express the effects of the present invention, the pore diameter on the base layer side is more preferably 150 μm or less.
A scanning electron microscope is suitable as a specific means for observing the pore diameter on the base layer side.
As a specific material for the foamed resin, polyurethane is currently preferred.
The thickness of the foamed resin layer is selected within a range of 650 μm or less, and more preferably 450 μm or less. Although it is not necessary to specifically limit the lower limit, it can be practically 50 nm or more.

The invention which concerns on the structure 2 of this invention is related with the manufacturing method of the glass substrate for magnetic discs which grind | polishes using an abrasive cloth and moving a glass disk and an abrasive cloth relatively.
Here, the polishing cloth is not particularly limited as long as it has a predetermined compression rate. This is because the difference in compressibility is a difference in function as the entire polishing cloth (for example, the base layer and the foamed resin layer). This is because it is considered that the polishing cloth at the time of polishing may be exhibited in a compressed state. However, even if the compression rate is the same, if a polishing cloth including a foamed resin layer having a pore diameter reduced to a predetermined value as shown in the above-described configuration 1 is used, the pore on the base layer side of the foamed resin layer is used. Since it is considered that a synergistic effect between the effect obtained by reducing the diameter to a predetermined value and the effect obtained by setting the compression rate to a predetermined value may be exhibited, the configuration 1 described above is shown. It is preferable to use an abrasive cloth provided with a base layer and a foamed resin layer. In addition, as the base layer in the polishing cloth provided with the base layer and the foamed resin layer shown in the above configuration 1, a woven or nonwoven fabric made of natural fibers, recycled fibers or synthetic fibers, or styrene butadiene rubber, nitrile butadiene rubber, etc. A base material obtained by filling a resin such as a rubbery substance or a polyurethane elastomer is generally used, but in the invention according to Configuration 2, by adopting a resin film (for example, a PET resin film) as a base layer, Since it is thought that a synergistic effect is exhibited, it is preferable to use a resin film as a base layer.

In the invention according to Configuration 2 of the present invention, the compressibility of the polishing cloth is measured, a polishing cloth having a compression ratio of 1.0% or less is selected, and a polishing liquid containing colloidal particles is supplied to provide a glass disk. It is characterized by polishing. Thus, reducing the compressibility of the polishing pad has the following effects.
First, in contrast to the first problem described above, the end shape disorder (swelling of the end portion and end sag) is significantly reduced, and the end shape is sufficiently excellent (the end shape is almost the same). A glass substrate for a magnetic disk (which can be said to be flat) is obtained.
Second, the difference between the polishing rate of the end portion of the main surface and the polishing rate of the other portion of the main surface can be reduced with respect to the first 'problem described above. Secondly, the problem can be reduced. In other words, the present invention (Configuration 2) solves the problem that the mirror surface of the disk and the disturbance of the end shape (the rising of the end and the sag of the end) are in a trade-off relationship. It is possible for the first time to obtain a glass substrate for a magnetic disk that has a mirror surface and has a sufficiently excellent end shape.
Third, it is an effective means for reducing the minute waviness of the end portion with respect to the third problem described above.
In order to more effectively express the effects of the present invention, the compression ratio is preferably less than 1.0%, more preferably 0.8% or less, and even more preferably 0.5% or less. It is.
The compression rate defined in Japanese Industrial Standard L1096 was used as the compression rate.
In order to lower the compressibility of the polishing cloth, it is effective to mainly reduce the pore diameter on the base layer side in the foamed resin layer. In addition, means for thinning the foamed resin layer and the base layer and means for changing the material of the base layer are also effective. Therefore, it is effective to employ a combination of these means. When these means are employed, the rate of change in the compression ratio is large, but the rate of change (relative difference) is very small although the Asker C hardness slightly increases. Therefore, it can be said that the compression ratio is a parameter that can make the difference according to the presence / absence of these means and the adoption level more obvious than the Asker C hardness. This is because the compression rate is measured after a certain time has passed in a state where a load in a range including an average load (for example, 80 g / cm ² ) applied to the polishing cloth at the time of polishing is applied. This is probably because the hardness of the polishing cloth and its polishing action are better and faithfully reflected than the Asker C hardness. In the present invention, focusing on this, the hardness of the abrasive cloth is generally controlled by the Asker C hardness, whereas the compressibility of the abrasive cloth is measured and the characteristics of the abrasive cloth are determined as the compressibility. It is something to be managed with.
The thickness of the foamed resin layer is selected within a range of 650 μm or less, and more preferably 450 μm or less.

In the present invention, as in the configuration 3, it is preferable to polish a glass disk by selecting a polishing cloth having a foamed resin layer having a pore diameter of 50 μm or less opened on the polishing surface. Thus, if the surface opening of the polishing cloth is made small, there is an effect of reducing the micro waviness on the entire surface of the substrate, and it is an effective means for reducing the micro waviness of the end portion.
To explain this, for example, when polishing is performed using cerium oxide using a polishing cloth having a relatively large surface opening, the bulge of the end portion occurs, and as shown in FIG. It was found that the effect of reducing the minute waviness at the end was not sufficient.
On the other hand, the surface opening of the polishing cloth is reduced in diameter (for example, the polishing cloth shown in the comparative example described later is used. In this case, the Asker C hardness of the polishing cloth is slightly increased, but the conventional category and polishing particles are not changed. 7), as shown by A → B in FIG. 7, it was found that the micro-waviness of the entire surface of the substrate can be reduced as a whole, and therefore the micro-waviness of the end portion can be reduced. However, from another perspective, FIG. 7 cannot be said to be sufficient in reducing the micro-waviness of the end portion by reducing the diameter of the surface opening of the polishing cloth, as compared with other locations. On the other hand, by combining the requirement for reducing the diameter of the surface opening of the polishing cloth and the requirement of the above-described configuration 1 or 2, as shown in B → C of FIG. I found it effective. In other words, such a combined configuration remarkably solves the problem that the disk surface is mirror-finished and the end shape is distorted (the bulge of the end and the sag of the end) are in a trade-off relationship. It is possible to obtain a glass substrate for a magnetic disk having an inner mirror surface (Rmax of 5 nm or less, Ra of 0.5 nm or less) and having a remarkably excellent end shape.
In order to more effectively express the effects of the present invention, the pore diameter opened to the polished surface is preferably 20 μm or less.
In order to more effectively express the effects of the present invention, it is preferable to make the variation (dispersion) in the pore diameters opened in the polishing surface uniform.
A scanning electron microscope is suitable as a specific means for observing the pore diameter opening in the polished surface.

In the present invention, it is preferable to polish by supplying a polishing liquid containing colloidal particles as in the above-described configurations 1 and 2. As described above, when polishing is performed by supplying a polishing liquid containing colloidal particles (when the particle size of the polishing particles is reduced), a problem arises that the mirror surface level of the main surface newly generated by adopting the requirements of the above configuration 1 or 2 deteriorates. The mirror surface level of the main surface can be suppressed to a level that does not cause a problem even if the flying height of the magnetic head is 10 nm or less.
Specifically, the colloidal particles are preferably colloidal silica particles (colloidal silica abrasive grains) (Configuration 5), and the polishing liquid containing colloidal particles is preferably a microsilica slurry. When the average particle diameter (D ₅₀ ) of the colloidal silica is 10 nm to 120 nm, the effect of the present invention becomes remarkable (Configuration 4), more preferably 90 nm or less, and more preferably 80 nm or less. preferable. The polishing liquid is preferably alkaline, and specifically, the pH is preferably 8-12.
Colloidal silica is a colloid of SiO ₂ or its hydrate that does not have a certain structure. It is obtained by dialysis after the action of dilute hydrochloric acid on silicate, and it is a sol that does not easily precipitate at room temperature. When it is left for a long time, water is evaporated, or an electrolyte is added, it becomes a hydrous silicon dioxide gel .

The present invention is applicable to a method for manufacturing a glass substrate for a magnetic disk that uses an abrasive cloth and moves the glass disk and the abrasive cloth relative to each other, and preferably, from the base layer side of the abrasive cloth. It is preferably applied to a method for producing a glass substrate for a magnetic disk that is polished by applying a polishing cloth (Structure 6). To more effectively express the effect of the present invention preferably ranges pressure with the polishing cloth from the base layer side of the polishing cloth is ^{50g / cm 3 ~150g / cm 3} . In the present invention, it is preferable to use an abrasive cloth provided with a base layer and a foamed resin layer.

An example of a polishing apparatus that is preferably used in a method for manufacturing a glass substrate for a magnetic disk that performs polishing by using a polishing cloth and relatively moving the glass disk and the polishing cloth will be described.
FIG. 9 is a cross-sectional view of the main part of a double-side polishing apparatus having upper and lower surface plates, and FIG. 10 is an explanatory view of a drive mechanism section of the polishing apparatus. This device is a planetary gear type double-side polishing device in which a glass disk, which is narrowly pressed on an upper and lower surface plate via a polishing cloth (polishing pad), revolves while rotating on a standard surface to be polished on both sides. 9 and 10, the polishing apparatus 5 includes a polishing carrier mounting portion having an internal gear 51 and a sun gear 52 that are driven to rotate at a predetermined rotation ratio, and a reverse rotation drive with the polishing carrier mounting portion interposed therebetween. The upper surface plate 53 and the lower surface plate 54 are provided. When a plurality of polishing carriers 1 are set in the polishing carrier mounting portion, the gears of the polishing carrier 1 are engaged with the internal gear 51 and the sun gear 52. When the glass disk 4 as the object to be polished is set in the object to be polished holding hole of each polishing carrier 1 and polishing is started, the polishing carrier 1 performs planetary motion due to the difference in rotational speed between the internal gear 51 and the sun gear 52. Do. At the same time, the upper surface plate 53 and the lower surface plate 54 rotate reversely to each other, and the front and back surfaces of the magnetic disk glass substrate 4 are polished by the polishing pads 53a and 54a provided on them.

  The glass type, size, etc. of the glass substrate for magnetic disk of the present invention 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 in terms 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 substrate 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 is preferable because it has higher mechanical strength than amorphous glass, and is excellent in flatness and has a high smoothness due to advantages such as grinding with diamond pellets in the manufacturing process.

By forming at least the magnetic layer on the main surface of the glass substrate for magnetic disk described above, a magnetic disk compatible with high-density recording can be obtained (Configuration 7).
Here, the material of the magnetic layer formed on the glass substrate is not particularly limited. Examples of the magnetic layer include magnetic films such as CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, and CoCrPtTaB containing Co as a main component. The magnetic layer may have a multilayer structure in which the magnetic film is divided by a nonmagnetic film (for example, Cr, CrMo, CrV, CrMnC, etc.) to reduce noise. If necessary, a seed layer or an underlayer may be provided between the glass substrate and the magnetic layer, and a protective layer or 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.

Next, the present invention will be described in more detail with reference to examples of the present invention.
Example 1 includes (1) rough lapping step, (2) shape adding step, (3) end surface polishing step, (4) fine lapping step, (5) first polishing step, (6) second polishing step, ( 7) cleaning process, (8) chemical strengthening process, (9) cleaning process, (10) evaluation process, and (11) magnetic disk manufacturing process. Hereinafter, each process will be described in detail.

(1) Coarse lapping process First, the molten glass was directly pressed using an upper mold, a lower mold, and a trunk mold to obtain a glass substrate made of a disc-shaped aluminosilicate glass having a diameter of 66 mmφ and a thickness of 1.2 mm. . In this case, in addition to the direct press, a disk-shaped glass substrate may be obtained by cutting out from 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 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, the load L is set to about 100 kg, and the inner rotation gear and the outer rotation gear are rotated, so that both surfaces of the glass substrate housed in the carrier have surface accuracy of 0 to 0. Finished to about 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, and the outer peripheral end surface is ground to a diameter of 65 mmφ, followed by predetermined chamfering on the outer peripheral end surface and the inner peripheral surface. Was given. The surface roughness of the glass substrate end face (inner circumference, outer circumference) at this time was about 4 μm in Rmax.

(3) End face polishing step Next, the surface roughness of the end face (inner circumference, outer circumference) of the glass substrate was polished to about 1 μm by Rmax and about 0.3 μm by Ra while rotating the glass substrate by brush polishing. The surface of the glass substrate after the end face polishing step was washed with water.

(4) Fine lapping step Next, the grain size of the abrasive grains was changed to # 1000, and the glass substrate surface was lapped, so that the flatness was 3 μm, the surface roughness Rmax was about 2 μm, and Ra was about 0.2 μm. Rmax and Ra were measured with an atomic force microscope (AFM), and flatness was measured with a flatness measuring device. The vertical direction between the highest part and the lowest part of the substrate surface (perpendicular to the surface). Direction) (the difference in height). The glass substrate after the fine wrapping step was washed by sequentially immersing it in each washing tank of neutral detergent and water.

(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 the polisher, and the polishing was performed under the following conditions.
Polishing liquid: cerium oxide (average particle size 1.3 μm) free abrasive grains in which water is added to abrasive grains Load (applied pressure): 80 to 100 g / cm ²
Polishing time: 30-50 minutes Removal amount: 35-45 μm

  The glass substrate that had been subjected to the polishing step was sequentially immersed in each washing bath of neutral detergent, pure water, pure water, IPA, and IPA (steam drying) and washed. An ultrasonic wave was 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 substrate, and the like.

(6) Second polishing process (mirror polishing process)
Next, the double polishing apparatus used in the first polishing process was used, and the second polishing process was performed by changing the hard polisher to the soft polisher as the polisher. Here, as the polishing cloth (soft polisher), four types having the characteristics shown in Table 1 are prepared, and the four types of polishing cloth (polishing pad) are sequentially replaced, and mirror polishing is performed using each polishing cloth. A process (final polishing) was performed.
Scanning electron micrographs (SEM photographs) of longitudinal sections of four types of polishing cloths having various characteristics shown in Table 1 are shown in FIGS. 1 (1) is a comparative example of Table 1, FIG. 1 (2) is Example 1-1 of Table 1, FIG. 1 (3) is Example 1-2 of Table 1, and FIG. Corresponds to Examples 1-3 in Table 1, respectively.
In Table 1, the layer thickness of the base layer, the layer thickness of the foamed resin layer, and the pore diameter on the base layer side were determined by analyzing the longitudinal section of the polishing pad with a scanning electron microscope (SEM). In the column of the pore diameter on the base layer side of the foamed resin layer in Table 1, “maximum diameter” indicates the value of the maximum diameter among the pore diameters on the base layer side in each figure of FIG. 1 represents the average value of the maximum diameters of the pores on the base layer side that are numerous in each figure of FIG. 1, and the “minimum diameter” is the maximum of the pore diameters on the base layer side in the figures of FIG. The value of the small diameter is shown.
The hardness (Asker-C) was determined by an evaluation method defined in the Japan Rubber Association Standard (SRISO101). The compression rate was based on the evaluation method defined in Japanese Industrial Standard JIS L1096.
The polishing conditions in final polishing are as follows: polishing liquid: colloidal silica (average particle diameter 80 nm) free abrasive grains obtained by adding water, load (pressure applied): 80 to 100 g / cm ² , polishing time: 10 to 30 minutes, Removal amount: 0.1 to 5 μm.
Note that the surface roughness Rz (ten-point average roughness) of the polishing cloth (see Patent Document 1) is a small surface roughness measuring instrument (Surf Test SJ-401: manufactured by Mitutoyo Corporation) which is a stylus type surface roughness meter. ) Was 8.0 μm.
Moreover, when the pore diameter opened to the grinding | polishing surface of a foamed resin layer was measured with the scanning electron microscope (SEM), it was 20 micrometers.

(7) Washing step The glass substrate after the second polishing step was washed by immersing it sequentially in alkali (NaOH) and sulfuric acid. An ultrasonic wave was 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 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, and this chemically strengthened salt is heated to 375 ° C. and a cleaned glass substrate preheated to 300 ° C. is prepared. It was immersed for about 3 hours. During this immersion, the plurality of glass substrates were housed in a holder so that the entire surface of the glass substrate was chemically strengthened so that the glass substrates were held at the end surfaces.

  Thus, by immersing in the chemically strengthened salt, the lithium ions and sodium ions on the surface of the glass substrate are replaced with sodium ions and potassium ions in the chemically strengthened salt, 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 to 200 μm. The glass substrate after the chemical strengthening was immersed in a 20 ° C. water bath and rapidly cooled, and maintained for about 10 minutes.

(9) Washing Step The glass substrate after the rapid cooling was immersed in sulfuric acid heated to about 40 ° C. and washed while applying ultrasonic waves.
As described above, a 2.5-inch glass substrate having an inner diameter (inner diameter) of 20 mm and an outer diameter (outer diameter) of 65 mm (measured from the central portion, an inner peripheral end of 10 mm and an outer peripheral end of 32.5 mm) was obtained.

(10) Evaluation process Table 2 and Figs. 1 to 3 show various measurement results of the glass substrate surface thus obtained.
In addition, the measurement conditions in Table 2 are as shown in the following (1) to (3).
(1) “Surface roughness Ra” was calculated in accordance with the arithmetic average roughness Ra of Japanese Industrial Standard JISB0601, using the surface shape measurement result by atomic force microscope (AFM) for the surface of the 5 square μm rectangular region. .
For each sample, the surface roughness (measurement position = radius 23 mm) of the middle circumference was measured by the above method, and for each sample, the mirror surface within the predetermined range to be obtained by the present invention (Rmax: 5 nm) Hereinafter, it was confirmed that Ra was 0.5 nm or less). Specifically, when the surface roughness (measurement position = radius 23 mm) of the main surface of the sample of Example 1-1 was measured by the above method, it was 2.3 nm for Rmax, 0.24 nm for Ra, The same was true for the samples.
(2) “Micro wave swell Rq” is a surface by optical interferometry using a multi-function surface analyzer (MicroXAM) manufactured by Face Shift Technology, Inc., and using a light of 550 nm wavelength on a surface of 3.8 square mm rectangular area. Using the shape measurement results, a surface shape having a shape wavelength of 16 μm to 1,9 mm band was extracted and calculated as the root mean square roughness Rq (RMS) of this surface shape. (See FIG. 8 for the measurement concept of the minute undulation Rq at the end).
(3) “End shape” is a surface shape measurement result obtained by the stylus method for a certain measurement section, and a virtual line connecting both ends of this measurement section is used as a reference, from the virtual line to the surface. The position where the distance was the largest was identified, and the distance from the virtual line to the surface at this position was calculated as the end shape. The value of “end shape” in Table 2 is an absolute value, and indicates the size of “end droop” as shown in FIG.

FIG. 2 shows the relationship between the four types of polishing cloth, the pore diameter on the base layer side, and the compression rate. As shown in FIG. 2, it can be seen that there is a correlation between the pore diameter on the base layer side and the compression ratio. FIG. 3 shows the relationship between the four types of polishing cloth and the minute waviness at the end. Further, FIG. 4 shows the relationship between the four types of polishing cloth and the end shape.
As shown in the examples in Table 2 and FIGS. 3 and 4, depending on the degree of diameter reduction of the pore diameter on the base layer side of the foamed resin layer and the degree of elastic modulus of the polishing cloth, the end shape is disturbed. Reduction (FIG. 3), reduction of minute waviness at the end (FIG. 4), and also the surface roughness of the central portion within a predetermined range to be obtained by the present invention (Rmax 5 nm or less, Ra 0.5 nm or less) is obtained. On the other hand, as shown in the comparative example of Table 2 and FIGS. 3 and 4, polishing in which the degree of pore diameter reduction on the base layer side of the foamed resin layer and the degree of elastic modulus of the polishing cloth are insufficient. When a cloth is used, a mirror surface within a predetermined range can be obtained, and the end shape disturbance and the minute waviness at the end are all insufficient. From the above, according to the present invention, the problem that the mirror surface of the disk is mirror-finished and the end shape is disturbed (the bulge of the end and the sag of the end) are in a trade-off relationship, and the predetermined range is reached. It can be seen that a glass substrate for a magnetic disk having an inner mirror surface (Rmax of 5 nm or less, Ra of 0.5 nm or less) and having an edge shape sufficient or remarkably excellent can be obtained.

From the above examples, according to the method of the present invention, a magnetic disk glass substrate having a surface roughness Rmax of 5 nm or less and Ra of 0.5 nm or less when the disk main surface was measured with an atomic force microscope was used. A point on the main surface of 0.34 mm from the outer periphery of the disk toward the center of the disk is A, and B is a point on the main surface of 3.54 mm from the outer periphery of the disk toward the center of the disk. A glass substrate for a magnetic disk having a divergence distance from the virtual line to the main surface of 50 nm or less when a virtual line connecting the point and the point B is used as a reference can be obtained. The divergence distance from the imaginary line to the main surface is preferably 40 nm or less, more preferably 35 nm or less.
In addition, from the above examples, according to the method of the present invention, a glass substrate for a magnetic disk having a surface roughness Rmax of 5 nm or less and Ra of 0.5 nm or less when the disk main surface is measured with an atomic force microscope, Among the surface shapes in a rectangular area of 3.8 square mm centered on a point on the main surface of 2.5 mm from the outer peripheral edge of the disk toward the center of the disk, the surface having a shape wavelength of 16 μm to 1.9 mm When the shape is extracted and the root mean square roughness Rq (RMS) of the surface shape is defined as the fine waviness Rq, the glass substrate for a magnetic disk having the fine waviness Rq of 1.42 nm or less can be obtained. The minute undulation Rq is preferably 0.9 nm or less, more preferably 0.7 nm or less.
In addition, since it is difficult to satisfy both the divergence distance from the imaginary line to the main surface and the minute undulation Rq at the same time, it is preferable in the present invention to satisfy both of them simultaneously.

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

The glide height characteristic (nm) of the obtained magnetic disk was examined by a touchdown height evaluation method. The results are shown in Table 3 and FIG. As shown in Table 3 and FIG. 5, the glide height characteristic (nm) at the end portion is improved according to the degree of reduction in the pore diameter on the base layer side of the foamed resin layer and the degree of compressibility of the polishing cloth. It can be seen that
These magnetic disks were subjected to a load / unload durability test (whether or not they could endure a continuous load / unload operation of 600,000 times) using a magnetic head having a flying height of 10 nm. As a result, in the magnetic disk of the example, no significant failure occurred in the load / unload method such as the fly stiction failure, and it was able to endure 600,000 times without any problem. The magnetic disk of the comparative example failed at 200,000 times because a fly stiction failure occurred near the outer periphery of the disk. Therefore, according to the present invention, fly stiction failure can be prevented, and it is particularly suitable as a glass substrate for a load / unload type magnetic disk and a magnetic disk.

It is a figure which shows the scanning electron micrograph (SEM photograph) of the longitudinal cross-section of four types of each polishing cloth. It is a figure which shows the relationship between four types of polishing cloth, the pore diameter of a base layer side, and a compression rate. It is a figure which shows the relationship between four types of polishing cloth and the microwaviness of an edge part. It is a figure which shows the relationship between four types of polishing cloth and an edge shape. It is a figure which shows the result of having investigated the glide height characteristic (nm) of four types of each polishing cloth. It is a schematic diagram for demonstrating a suede type polishing cloth (polishing pad). It is a schematic diagram for demonstrating the reduction effect of micro waviness. It is a schematic diagram for demonstrating the measurement concept of an end shape, and "end droop". It is principal part sectional drawing of the grinding | polishing apparatus which has an upper and lower surface plate. It is explanatory drawing of the drive mechanism part of a grinding | polishing apparatus.

Explanation of symbols

4 Glass disk 53a Polishing cloth 54a Polishing cloth

Claims (7)

Using a polishing cloth comprising a base layer and a foamed resin layer, a method for producing a glass substrate for a magnetic disk that performs polishing by relatively moving the glass disk and the polishing cloth,
A method for producing a glass substrate for a magnetic disk, comprising selecting a polishing cloth provided with a foamed resin layer having a pore diameter of 200 μm or less on the base layer side, and polishing a glass disk by supplying a polishing liquid containing colloidal particles. . It is a manufacturing method of the glass substrate for magnetic discs of Claim 1, Comprising:
A magnetic disk comprising: measuring a compressibility of the polishing cloth; selecting a polishing cloth having a compressibility of 1.0% or less; and supplying a polishing liquid containing colloidal particles to polish a glass disk. Method for manufacturing glass substrate. It is a manufacturing method of the glass substrate for magnetic discs of Claim 1, Comprising:
A method for producing a glass substrate for a magnetic disk, comprising polishing a glass disk by selecting a polishing cloth provided with a foamed resin layer having a pore diameter of 50 μm or less opened on a polished surface. Colloidal particles contained in the polishing liquid, the average particle diameter _{(D 50),} 10Nm～120nm
The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 3, wherein: The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the colloidal particles contained in the polishing liquid are colloidal silica abrasive grains. It is a manufacturing method of the glass substrate for magnetic discs in any one of Claims 1-5,
A method for producing a glass substrate for a magnetic disk, comprising polishing by pressing a polishing cloth from a base layer side of the polishing cloth. A method for producing a magnetic disk, comprising forming a magnetic layer on the glass substrate for a magnetic disk according to claim 1.

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