JP6960970B2 - Manufacturing method of fixed abrasive grain grindstone and glass substrate - Google Patents

Description

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

A magnetic disk is one of the information recording media mounted on a magnetic disk device such as a hard disk drive (HDD). A magnetic disk is formed by forming a thin film such as a magnetic layer on a substrate, and an aluminum substrate has been conventionally used as the substrate. However, in recent years, in response to the pursuit of higher recording densities, the proportion of glass substrates capable of narrowing the distance between the magnetic head and the magnetic disk has gradually increased as compared with aluminum substrates. In addition, the surface of the glass substrate is polished with high precision to achieve a high recording density so that the floating height of the magnetic head can be reduced as much as possible. In recent years, the demand for further increasing the recording capacity and lowering the price of HDDs has only increased, and in order to realize this, it is necessary to further improve the quality and reduce the cost of glass substrates for magnetic disks. It's coming.

As described above, high smoothness of the magnetic disk surface is indispensable for low flying height (floating amount) required for high recording density. In order to obtain high smoothness of the magnetic disk surface, a highly smooth substrate surface is required after all, so it is necessary to polish the glass substrate surface with high accuracy. In order to produce such a glass substrate, after adjusting the plate thickness and reducing the flatness (flatness) by grinding (wrapping) processing, further polishing treatment is performed to reduce surface roughness and minute waviness. , Has achieved extremely high smoothness on the main surface.

By the way, conventionally, in a grinding (wrapping) step using free abrasive grains (for example, Patent Document 1 and the like), a grinding method using fixed abrasive grains using a diamond pad has been proposed (for example, Patent Document 2 and Patent Document 3). etc). A diamond pad is an agglomerate of diamond particles or some diamond particles hardened with a binder such as glass, ceramic, metal, or resin, and fixed using a support material such as resin (for example, acrylic resin). The pellets are pasted on a sheet of resin or the like. In addition to this, a resin layer containing diamond may be formed on the sheet, and then a groove may be formed in the resin layer to form a protrusion. The diamond pad referred to here is not necessarily a general name, but in the present specification, it is referred to as a "diamond pad" for convenience.

In the conventional free abrasive grains, abrasive grains with a distorted shape intervene between the surface plate and the glass and exist unevenly. Therefore, when the load on the abrasive grains is not constant and the load is concentrated, the surface plate surface Because of the low elasticity of cast iron, deep cracks occur in the glass, the processed alteration layer is deep, and the processed surface roughness of the glass is also large, so a large amount of removal was required in the mirror polishing process in the subsequent process. It was difficult to reduce the processing cost. On the other hand, in grinding with fixed abrasive grains using a diamond pad, since the abrasive grains are uniformly present on the sheet surface, the abrasive grains are fixed to the sheet using resin in addition to the load not being concentrated. Therefore, even if a load is applied to the abrasive grains, the high elasticity of the resin that fixes the abrasive grains causes the cracks on the machined surface (working alteration layer) to be shallow, making it possible to reduce the machined surface roughness, which is a post-process. The load on the machine (replacement allowance, etc.) is reduced, and the processing cost can be reduced.
After the completion of this grinding (wrapping) process, mirror polishing is performed to obtain a highly accurate flat surface.

Japanese Unexamined Patent Publication No. 2001-6161 Japanese Unexamined Patent Publication No. 2012-99173 Japanese Unexamined Patent Publication No. 2009-99249

As described above, according to the grinding method using fixed abrasive grains using a diamond pad, it is possible to reduce the surface roughness of the machined surface, reduce the load on the subsequent mirror polishing process, and reduce the processing cost of the glass substrate. Although it is possible to reduce the amount, according to the study by the present inventor, it has been found that there are the following problems.
For example, a sheet-shaped glass plate manufactured by a float method or the like is cut into a predetermined shape and directly ground with fixed abrasive grains using a conventional diamond pad as disclosed in Patent Document 2. When processing, since the surface of the glass substrate is a so-called mirror surface, there is a problem that diamond abrasive grains do not easily bite into the surface of the substrate and slip, resulting in a time during which grinding cannot be performed. This significantly reduces productivity.

In Patent Document 3, the surface of the mirror plate glass is roughened by a mechanical or chemical method (for example, free of alumina and the like) before the process of grinding the fixed abrasive grains of the mirror plate glass to the extent that the fixed abrasive grains are polished. Although the technique of wrapping using abrasive grains) is disclosed, the productivity is lowered because another process is added. Moreover, although the wrapping with the free abrasive grains enables stable processing on the mirror surface plate glass, there is a problem that the processing load in the subsequent process increases because the cut (processed alteration layer) is deeply formed.

The present invention has been made to solve such a conventional problem, and an object of the present invention is to reduce the time during which grinding cannot be performed in grinding with fixed abrasive grains, and to perform the grinding without slowing down the processing speed. It is possible to provide a method for manufacturing a glass substrate for a magnetic disk capable of manufacturing a high-quality glass substrate at low cost, and a method for manufacturing a magnetic disk using the glass substrate obtained thereby.

In order to solve the above problems, the present invention has the following configurations.
(Structure 1)
A method for manufacturing a glass substrate for a magnetic disk, which comprises a grinding process for grinding the main surface of the glass substrate using a lubricating liquid and a platen on which fixed abrasive grains containing diamond particles are arranged on the ground surface. The glass substrate is a glass substrate whose main surface is a mirror surface, and the grinding process is a first step of roughening the surface of the glass substrate with a load higher than the load for grinding, and after the first step. The grinding process having the first stage and the second stage for grinding the surface of the glass substrate with a load lower than the load of the first stage is the same device. This is a method for manufacturing a glass substrate for a magnetic disk, which is characterized by using the above method.

(Structure 2)
When the load in the first stage is P1 (g / cm ² ) and the load in the second stage is P2 (g / cm ² ), P1 / P2 = 3.0 or less. The method for manufacturing a glass substrate for a magnetic disk according to the above.
(Structure 3)
The magnetic disk according to configuration 2, wherein t1 <t2 when the time for maintaining the load P1 in the first stage is t1 and the time for maintaining the load P2 in the second stage is t2. Manufacturing method of glass substrate.

(Structure 4)
The method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 3, wherein the surface roughness of the glass substrate to be charged is 0.05 μm or less in Ra.

(Structure 5)
The method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 4, wherein the processing speed in the grinding process is 3.0 μm / min to 9.0 μm / min.
(Structure 6)
The method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 5, wherein the surface roughness of the glass substrate after the completion of the second step is 0.080 μm to 0.130 μm in Ra.

(Structure 7)
It is a method for manufacturing a magnetic disk, characterized in that at least a magnetic recording layer is formed on the glass substrate for a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk according to any one of the configurations 1 to 6.

According to the present invention, it is possible to improve the decrease in productivity due to the occurrence of time during which grinding cannot be performed in the conventional grinding process using fixed abrasive grains. Further, according to the present invention, it is possible to suppress the surface roughness of the processed surface to a low level without reducing the processing speed, and it is possible to reduce the processing load in the subsequent process. This makes it possible to manufacture a high quality glass substrate at low cost. Further, the glass substrate thus obtained can be used to obtain a highly reliable magnetic disk.

It is a schematic cross-sectional view which shows the structure of the diamond pad used in this invention. It is a schematic diagram for demonstrating the state at the time of grinding. It is a figure which shows an example of the sequence of the applied load in the grinding process of this invention. It is a schematic cross-sectional view which shows the structure of the diamond pad used in this invention.

Hereinafter, embodiments of the present invention will be described in detail.
The present invention includes a grinding process for grinding the main surface of a glass substrate using a lubricating liquid and a platen in which fixed abrasive grains containing diamond particles are arranged on a grinding surface, as shown in the above configuration 1. A method for manufacturing a glass substrate for a disk, wherein the glass substrate is a glass substrate whose main surface is a mirror surface, and the grinding process roughens the surface of the glass substrate with a load higher than the load for grinding. The first step and the second step of grinding the surface of the glass substrate with a load lower than the load of the first step after the first step are provided. The grinding process having the above is a method for manufacturing a glass substrate for a magnetic disk, which is performed by using the same apparatus.

A glass substrate for a magnetic disk is usually manufactured through a rough grinding process (rough wrapping process), a shape processing process, a fine grinding process (fine wrapping process), an end face polishing process, a main surface polishing process, a chemical strengthening process, and the like. ..
In the method for manufacturing a glass substrate for a magnetic disk of the present invention, a glass substrate having a mirror surface as a main surface is obtained by cutting out a sheet-shaped glass manufactured by a float method or a downdraw method into a predetermined size. In addition to this, a glass substrate having a mirror-finished main surface prepared by pressing from molten glass may be used.

Next, the glass substrate is subjected to grinding (wrapping) to improve dimensional accuracy and shape accuracy. In this grinding process, a double-sided lapping device is usually used to grind the main surface of the glass substrate using hard abrasive grains such as diamond. By grinding the main surface of the glass substrate in this way, a predetermined plate thickness and flatness are processed, and a predetermined surface roughness is obtained.

The present invention relates to the improvement of this grinding process. The grinding process in the present invention is a grinding process using fixed abrasive grains containing diamond particles. For example, in a double-sided lapping device, an upper and lower surface plate to which a diamond pad as a grinding tool (fixed abrasive grain grindstone) is attached. The glass substrate held by the carrier is brought into close contact with the glass substrate, and the glass substrate is sandwiched by the upper and lower surface plates at a predetermined pressure while the glass substrate and the upper and lower surface plates are relatively moved. Grind the surface at the same time. At this time, a lubricating liquid (coolant) is supplied to cool the processing working surface and accelerate the processing.

The diamond pad 1 which is a grinding tool (fixed abrasive grain grindstone) used in the present invention is outlined in FIG. 4, but some diamond particles 5 (see FIG. 2) are made of glass, ceramic, metal, or the like. Alternatively, the agglomerates 3 hardened with a binder such as resin are fixed on the sheet using a support material 6 such as resin (for example, acrylic resin or the like). Further, although the outline of another configuration is shown in FIG. 1, some diamond particles 5 (see FIG. 2) are made of a resin (for example, acrylic) in which an agglomerate 3 in which some diamond particles 5 (see FIG. 2) are hardened with a binder such as glass, ceramic, metal, or resin is formed. Pellets 4 fixed using a support material such as (based resin, etc.) are attached to the sheet 2. Of course, the configurations shown in FIGS. 1 and 4 are merely examples, and the present invention is not intended to be limited thereto. For example, a diamond pad may be used in which a resin layer containing the aggregate 3 is formed on the sheet and then a groove is formed in the resin layer to form a protrusion.

It is possible to produce those having different particle diameters (average particle diameters) of the agglomerates 3 and abrasive grain densities in the resin.
In the present embodiment, the case where the diamond-fixed abrasive grains are the agglomerates will be described. Therefore, in the present invention, the term diamond-fixed abrasive grains means the above-mentioned aggregates unless otherwise specified, and the average particle size and the abrasive grain density of the diamond-fixed abrasive grains are used. Means the average particle size of the aggregates and the density of the aggregates in the resin.
However, the present invention is not limited to the case where the diamond-fixed abrasive grains are the above-mentioned aggregates. It is also possible to use a diamond pad in which the diamond fixing abrasive grains are not aggregates but one grain of diamond particles.

As described above, the grinding process in the present invention includes the first step of roughening the surface of the glass substrate with a load higher than the load for grinding, and after the first step, the load of the first step. Also has a second stage of grinding the surface of the glass substrate with a low load, and the grinding process having the first stage and the second stage is performed by using the same device.

In order to directly grind the mirrored glass surface with a diamond pad, it is first necessary to apply a higher load to the glass surface than during normal grinding in order to allow the diamond abrasive grains to bite into the glass substrate surface. A high load increases the depth of cut of the abrasive grains, so that the roughness of the glass surface can be made rough (roughened). The first step is a step in which diamond abrasive grains are made to bite into the mirrored glass surface to roughen the surface.

After the glass surface is roughened in the first stage during such processing, a high load is not required for grinding, but rather the original condition is that the load is reduced to make the cutting depth of the abrasive grains shallower. Grinding (main processing) is performed. The second step is the step of performing this main processing. FIG. 2 is a schematic view for explaining a state at the time of grinding, and shows a state in which agglomerates 3 which are diamond-fixed abrasive grains bite into the glass substrate 10 and grind.

By performing the grinding process having the above first stage and the second stage, it is possible to perform the grinding process without slowing down the processing speed. Further, by adjusting the detailed conditions of the grinding process, it is possible to keep the surface roughness of the finished processed surface low.
FIG. 3 is a diagram showing an example of a sequence of applied loads in the grinding process of the present invention.
The horizontal axis of FIG. 3 is time, and the vertical axis is the applied load. The load is gradually increased from the start, and when the load reaches P1 (point A), the load is maintained for a certain period of time (t1). This is the first step above, and the glass surface is roughened.
The load up to point A may be applied in multiple steps. That is, the load may be increased stepwise (stepwise on the sequence diagram).

Then, the load is gradually reduced from the point B, the constant time (t2) is maintained when the normal grinding load P2 is reached (point C), and the grinding process is completed at the point D. This is the second stage described above, which is the stage where the main processing is performed.
The "loads P1 and P2" here refer to values that are maintained for a certain period of time, and do not include loads that are in the process of rising.

The load P1 in the first step is preferably in the range of ^{130 to 200 g / cm 2.} If the load P1 is ^{smaller than 130 g / cm 2} , the roughening is insufficient, so that the time during which the above-mentioned grinding process cannot be performed cannot be sufficiently shortened, and the processing speed may decrease. That is, since the surface roughness after the first stage is not sufficiently large, the fixed abrasive grains may slip even in the second stage, and the grinding rate may decrease. Further, if the load P1 is ^{smaller than 130 g / cm 2} , the adhesion between the glass substrate and the surface plate may be insufficient. In this case, the difference between the load applied by the upper surface plate on the upper surface of the glass substrate and the load applied by the lower surface plate on the lower surface of the glass substrate becomes large, causing a problem that the entire or part of the lower surface of the glass substrate is not ground. In some cases. It is presumed that this is because the coolant tends to accumulate on the lower platen due to the influence of gravity, and a coolant film is formed between the lower platen and the glass substrate. This problem can be solved by firmly sandwiching the glass substrate between the upper and lower surface plates by applying a load higher than 130 g / cm ^2.
On the other hand, if the load P1 is ^{larger than 200 g / cm 2, the} depth of cut by the abrasive grains becomes too deep, many scratches occur, and it becomes necessary to increase the allowance for the main processing and the subsequent polishing process. May become longer. In addition, the glass substrate may be cracked or cracked.

The load P2 in the second stage is preferably in the range of ^{50 to 120 g / cm 2.} By grinding a surface that has been roughened with a load lower than that of the first stage and with a load within the above range, the surface roughness of the machined surface can be suppressed to a low level.
Further, P1 / P2 is preferably 1.20 or more. By doing so, the processing speed can be increased and the roughness can be reduced. More specifically, the surface roughness after grinding can be 0.12 μm or less.
Further, it is preferable that P1 / P2 = 3.0 or less. If P1 / P2 is larger than 3.0, the adhesion between the glass substrate and the surface plate is temporarily insufficient when shifting from the first stage to the second stage, and the entire or part of the lower surface of the glass substrate is present. May not be ground.

Further, it is preferable that the load application speed (inclination k) in the first stage from the start of processing to the point A (load P1) is 0.5 to 15 g / (cm ^{2 · sec).} When the inclination k is ^{smaller than 0.5 g / (cm 2} · sec) (the application speed is slow), the abrasive grains do not slip and bite due to the low load, but rather the abrasive grains are worn out, which is the coarseness in the first stage. It is not preferable because the grinding ability deteriorates, such as insufficient surface formation and a decrease in the processing rate. On the other hand, when the inclination k is ^{larger than 15 g / (cm 2} · sec) (the application speed is fast), a sudden load is applied to the abrasive grains on the glass substrate, so that the abrasive grains are crushed and the grinding ability is lowered. There is a risk of cracking or cracking of the glass substrate. Further, from the viewpoint of the number of times (life) that the grinding pad can be used ^{, it is more preferable that the grinding pad is 4 g / (cm 2} · sec) or more.

Further, the time t1 for roughening with the load P1 in the first step is preferably in the range of, for example, 10 to 600 seconds. If t1 is shorter than 10 seconds, the abrasive grains may not sufficiently bite into the main surface of the glass and the processing speed may be slowed down. On the other hand, if t1 is longer than 600 seconds, deep scratches are likely to occur, and the finished main surface may become rough.

Further, the time from the point B (load P1) to the point C where the load is gradually reduced and reaches the normal grinding load P2 is preferably in the range of, for example, 10 to 90 seconds. If the time between BCs is shorter than 10 seconds, the flatness of the substrate may deteriorate due to sudden load fluctuations. In such a case, the load that the upper surface plate acts on the upper surface of the glass substrate and the load that the lower surface plate acts on the lower surface of the glass substrate are applied by the same mechanism as when ^{the load P1 described above is smaller than 130 g / cm 2.} The difference is expected to increase temporarily. Therefore, it is presumed that a portion having poor flatness remains because the whole or a part of the glass substrate is not properly ground.
On the other hand, if the time between BCs is longer than 90 seconds, the glass is excessively ground during the transition from P1 (first stage) to P2 (second stage), making it difficult to control the plate thickness or deep scratching. May increase the roughness of the main surface of the finished product.

Further, the time t2 for performing the grinding process with the load P2 in the second step is preferably 30 seconds or more. Unless a certain amount is processed by the load P2, the groove formed by the load P1 cannot be completely removed, which may remain as a scratch. The upper limit of t2 is appropriately determined in consideration of the finish quality in the grinding process and the like.
It is preferable that t1 <t2 because the roughness of the finished product can be reduced. If t1 ≧ t2, the surface roughness may not be lowered after processing. That is, the present invention is a technique capable of achieving both a high grinding rate and low roughness after processing, but if the processing time of the second stage due to a low load is insufficient, the roughness roughened by the first stage is reduced to the second stage. It may not be possible to keep it low. In addition, scratches may remain. Although these can be eliminated by increasing the cost of the subsequent polishing process, they can contribute to the increase in manufacturing cost.
Further, it is preferable that P1 × t1 (area) <P2 × t2 (area). By doing so, it becomes possible to sufficiently reduce the surface roughness after the grinding process.

Further, in the present invention, the processing speed in the entire grinding process is preferably 2.0 μm / min or more, more preferably 3.0 μm / min or more. Within this range, it is possible to perform grinding without slowing down the processing speed. The processing speed in the entire grinding process is a value obtained by dividing the total grinding thickness by the total processing time (including the first stage and the second stage).

Further, in the present invention, it is preferable that the average particle size of the diamond-fixed abrasive grains is 20 to 40 μm. Further, the individual particle size of the diamond fixed abrasive grains is preferably 10 to 50 μm. If the average particle size or the individual particle size of the diamond abrasive grains is less than the above, the cut into the mirror-shaped glass substrate becomes shallow and the bite into the glass substrate does not proceed. On the other hand, if the average particle size or the individual particle size of the diamond abrasive grains exceeds the above, the roughness of the finished product becomes coarse, so that the replacement load in the subsequent process becomes large.
As described above, the diamond-fixed abrasive grains here mean the agglomerates. The size of the individual diamond particles contained in the aggregate is preferably 1 to 5 μm in average particle size.

In the present invention, the average particle size (D50) is 50% when the cumulative curve is calculated with the total volume of the powder population in the particle size distribution measured by the laser diffraction method as 100%. The particle size of the point (hereinafter referred to as "cumulative average particle size (50% diameter)"). In the present invention, the cumulative average particle size (50% diameter) is specifically a value obtained by measuring using a particle size / particle size distribution measuring device.

As described above, in the present invention, in the grinding process, the same fixed abrasive grain grindstone (diamond pad) is used, and "a load higher than that of normal grinding + a normal load" is continuously performed in one process. Then, in order to increase the productivity, the substrate is replaced and the same process is repeated. At this time, it was found that sludge tends to accumulate on the surface of the fixed abrasive grain grindstone because the main surface of the input substrate is a mirror surface. When processing a glass substrate after wrapping as in the conventional case, since the surface roughness of the input substrate is large, sludge accumulated on the surface of the grindstone by grinding is removed by the new glass substrate surface to be charged one after another. However, the effect cannot be obtained when the mirror-surfaced glass substrate is directly ground as in the present invention.
That is, it was found that it is necessary to precisely control the amount of protrusion of the ground abrasive grains when the same fixed abrasive grain grindstone is used for a large number of treatments in order to improve productivity.

In the grinding process in the present invention, it is preferable to grind the main surface of the glass substrate using a grinding wheel in which the amount of protrusion of the grinding abrasive grains (that is, diamond fixed abrasive grains) is appropriately adjusted.

For example, when a grinding wheel having a low protrusion amount of the grinding wheel is used, sludge accumulates on the surface of the grinding wheel, which hinders the abrasive grains from coming into contact with the glass surface and sufficiently acts on the glass surface. Since there are many abrasive grains that cannot (weakly act on the glass surface), the above-mentioned partial grinding defects occur, and as a result, the occurrence rate of flatness defects after processing increases.

On the other hand, when a grinding wheel in which the amount of protrusion of the grinding wheel is appropriately adjusted is used, it is possible to prevent the grinding wheel from being hindered from coming into contact with the glass surface even if sludge accumulates on the surface of the grinding wheel. Therefore, the grinding abrasive grains act stably on the glass surface, and stable grinding without uneven grinding can be performed.

The amount of protrusion of the grinding abrasive grains of the above-mentioned grinding wheel can be measured as follows.
When the distance from the inner circumference to the outer circumference is 100% with respect to the grinding wheel of the upper and lower surface plates (usually formed in a disk shape) before grinding, 10%, 50%, 90 from the inner circumference. A total of 6 samples (pad pieces) having a size of 2.5 mm × 2.5 mm are cut out from the% position. For each of these 6 samples, for example, 5 arbitrary grinding abrasive grains were selected from the observation images obtained using, for example, a laser microscope, and the height difference between the abrasive grains and the resin portion around the abrasive grains was measured, and all of them were measured. The average value of the height difference of the abrasive grains is defined as the amount of protrusion of the grinding abrasive grains of the grinding wheel.

In order to adjust the amount of protrusion of the grinding abrasive grains, for example, a dressing process can be performed. Specifically, for example, a double-sided grinding device used for grinding is also applied to dressing, and a grindstone controlled to an appropriate thickness variation is applied to the surface of a grinding wheel such as a diamond pad installed on an upper and lower surface plates. The dressing process can be performed in a state where the upper and lower surface plates of the double-sided grinding device are rotated in contact with each other. The material of the grindstone used for the dressing treatment is not particularly limited, but for example, an alumina grindstone is suitable. Further, in this case, the dressing process may be performed stepwise by using a plurality of grindstones having different thickness variations.

In the present invention, the main surface of the glass substrate to be subjected to the grinding process is a mirror surface, and the surface roughness is usually 0.05 μm or less in Ra, more preferably 0.001 to 0.01 μm. In particular, in the present invention, since the surface roughness Ra of the glass substrate to be put into the grinding process can be extremely low as 0.001 to 0.01 μm, the removal allowance in the subsequent process can be minimized, so that the cost is low. It is possible to manufacture a magnetic disk glass substrate.
Further, in the present invention, the surface roughness of the glass substrate after the completion of the first step is generally in the range of 0.100 to 0.150 μm in Ra. By roughening the surface within this range, the subsequent second-stage grinding process is satisfactorily performed.
Further, in the present invention, the surface roughness of the glass substrate after the completion of the second step is finished in the range of 0.080 to 0.130 μm in Ra. Since the roughness of the finished product can be suppressed to a low level in this way, the processing load in the subsequent process can be reduced.

As described above, in the grinding process of the present invention, it is possible to improve the decrease in productivity due to the occurrence of time during which the grinding process cannot be performed in the conventional grinding process using fixed abrasive grains, and the first step is Since the grinding process having the second stage can be continuously performed using the same device, it is possible to increase the productivity. Further, according to the grinding process of the present invention, it is possible to suppress the surface roughness of the processed surface to a low level without reducing the processing speed, and it is possible to reduce the processing load in the subsequent process.

In the present invention, the glass (glass type) constituting the glass substrate is preferably amorphous aluminosilicate glass. Such a glass substrate can be finished into a smooth mirror surface by mirror polishing the surface, and the strength after processing is good. As such an aluminosilicate glass, for example, _{a glass containing SiO 2} as a main component and Al ₂ O _{3 in an amount} of 20% by weight or less is preferable. Further, it is more preferable to use a glass containing _{SiO 2} as a main component and Al ₂ O _{3 in an amount of 15% by weight or less.} Specifically, SiO ₂ is 62% by weight or more and 75% by weight or less, Al ₂ O ₃ is 5% by weight or more and 15% by weight or less, Li ₂ O is 4% by weight or more and 10% by weight or less, and Na ₂ O is 4% by weight. % Or more and 12% by weight or less, ZrO ₂ is 5.5% by weight or more and 15% by weight or less as a main component, and _{the weight ratio of Na 2} O / ZrO ₂ is 0.5 or more and 2.0 or less, Al ₂ O. _{Aluminosilicate glass containing no phosphor oxide having a weight ratio of 3} / ZrO ₂ of 0.4 or more and 2.5 or less can be used.
In addition, as this aluminosilicate glass, it is expressed in% by weight,
SiO ₂ 58 to 66%, Al ₂ O ₃ 13 to 19%, Li ₂ O 3 to 4.5%, Na ₂ O 6 to 13%, K ₂ O 0 to 5%, R ₂ O 10 to 18%, (However, R ₂ O = Li ₂ O + Na ₂ O + K ₂ O)
MgO 0 to 3.5%, CaO 1 to 7%, SrO 0 to 2%, BaO 0 to 2%, RO 2 to 10% (however, RO = MgO + CaO + SrO + BaO)
TiO _{20 to} 2%, CeO _{20 to} 2%, Fe ₂ O _{30 to} 2%, MnO 0 to 1% (however, TiO ₂ + CeO ₂ + Fe ₂ O ₃ + MnO = 0.01 to 3%) Chemically strengthened glass containing the composition can be used.

As the heat-resistant glass, for example, SiO ₂ is 50 to 75%, Al ₂ O ₃ is 0 to 5%, BaO is 0 to 2%, and Li ₂ O is 0 to 3% in mol% display. ZnO is 0 to 5%, Na ₂ O and K ₂ O are 3 to 15% in total, MgO, CaO, SrO and BaO are 14 to 35% in total, ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ Contains O ₃ , Yb ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂ in total of 2-9%, and the molar ratio [(MgO + CaO) / (MgO + CaO + SrO + BaO)] is in the range of 0.85-1. Glass having a molar ratio [Al ₂ O ₃ / (MgO + CaO)] in the range of 0 to 0.30 can be preferably used.
Further, a total of 6 to 15 mol of alkali metal oxides selected from the group consisting of 56 to 75 mol% of _{SiO 2} , 1 to 9 mol% of _{Al 2} O _{3 and Li 2} O, Na ₂ O and K _{2 O.} %, MgO, CaO and SrO selected from the group consisting of 10 to 30 mol% of alkaline earth metal oxides in total, ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Nb _The glass may contain a total of more than 0% and 10 mol% or less of oxides selected from the group consisting of 2 O ₅ and Ta ₂ O _5.
In the present invention, _{the content of Al 2} O ₃ in the glass composition is preferably 15% by weight or less. Furthermore, it is still preferable that the content of _{Al 2} O _{3 is 5 mol% or less.}

Conventionally, the grinding process is generally performed through two stages of a rough grinding process (first grinding process) and a fine grinding process (second grinding process), but the grinding process according to the present invention. By applying the treatment, it is possible to carry out in one step.

After the completion of this grinding process, a mirror polishing process is performed to obtain a highly accurate flat surface. In the present invention, in the grinding process, by applying the fixed abrasive grain method according to the present invention to the conventional free abrasive grain method, it is possible to reduce the processed surface roughness. The amount of waste removed is small, the processing load is reduced, and the processing cost can be reduced.

As a mirror polishing method for a glass substrate, it is preferable to use a polisher polishing pad such as polyurethane while supplying a slurry (polishing liquid) containing a polishing material of a metal oxide such as cerium oxide or colloidal silica. be. A glass substrate having high smoothness is obtained, for example, by polishing with a cerium oxide-based polishing material (first polishing process) and then by finish polishing (mirror surface polishing) using colloidal silica abrasive grains (second polishing process). It is possible.

In the present invention, the surface of the glass substrate after the mirror polishing process is preferably a mirror surface having an arithmetic average surface roughness Ra of 0.2 nm or less, more preferably 0.13 nm or less. In the present invention, the terms Ra and Rmax mean the roughness calculated in accordance with Japanese Industrial Standards (JIS) B0601.
Further, in the present invention, the surface roughness (for example, maximum roughness Rmax, arithmetic average roughness Ra) is the surface roughness of the surface shape obtained when a square area of 5 μm × 5 μm is measured with an atomic force microscope (AFM). It is practically preferable to use this. In addition, you may measure using a stylus type surface roughness meter.

In the present invention, it is preferable to perform a chemical strengthening treatment after the first polishing process and before the second polishing process. As a method of chemical strengthening treatment, for example, a low-temperature ion exchange method in which ion exchange is performed in a temperature range not exceeding the temperature of the glass transition point is preferable. The chemical strengthening treatment is to bring the molten chemically strengthened salt into contact with the glass substrate, so that the alkali metal element having a relatively large atomic radius in the chemically strengthened salt and the relatively small atomic radius in the glass substrate are formed. This is a process in which an alkali metal element is ion-exchanged, the alkali metal element having a large ion radius is infiltrated into the surface layer of the glass substrate, and a compressive stress is generated on the surface of the glass substrate. Since the chemically strengthened glass substrate has excellent impact resistance, it is particularly preferable to mount it on, for example, an HDD for mobile use. As the chemically fortified salt, an alkali metal nitrate such as potassium nitrate or sodium nitrate can be preferably used.

The present invention also provides a method for manufacturing a magnetic disk using the above glass substrate for a magnetic disk. In the present invention, the magnetic disk is manufactured by forming at least a magnetic layer on the glass substrate for the magnetic disk according to the present invention. As the material of the magnetic layer, a CoCrPt-based or CoPt-based ferromagnetic alloy, which is a hexagonal system having a large anisotropic magnetic field, can be used. As a method for forming the magnetic layer, it is preferable to use a sputtering method, for example, a method of forming a magnetic layer on a glass substrate by a DC magnetron sputtering method. Further, by inserting a base layer between the glass substrate and the magnetic layer, the orientation direction of the magnetic grains of the magnetic layer and the size of the magnetic grains can be controlled. For example, by using a cubic base layer such as a Cr-based alloy, the direction in which the magnetic layer can be easily magnetized can be oriented along the magnetic disk surface. In this case, an in-plane magnetic recording type magnetic disk is manufactured. Further, for example, by using a hexagonal base layer containing Ru and Ti, for example, the easy magnetization direction of the magnetic layer can be oriented along the normal of the magnetic disk surface. In this case, a perpendicular magnetic recording type magnetic disk is manufactured. The base layer can be formed by a sputtering method like the magnetic layer.

Further, the protective layer and the lubricating layer may be formed in this order on the magnetic layer. As the protective layer, an amorphous carbon hydride-based protective layer is suitable. For example, a protective layer can be formed by a plasma CVD method. Further, as the lubricating layer, a lubricant having a functional group at the end of the main chain of the perfluoropolyether compound can be used. In particular, it is preferable that the main component is a perfluoropolyether compound having a hydroxyl group at the end as a polar functional group. The lubricating layer can be applied and formed by the dip method.
By using the glass substrate obtained by the present invention, a highly reliable magnetic disk can be obtained.

Hereinafter, embodiments of the present invention will be specifically described with reference to examples. The present invention is not limited to the following examples.
(Example 1)
The following (1) substrate preparation process, (2) shape processing process, (3) end face polishing process, (4) main surface polishing process, (5) main surface polishing process (first polishing process), (6) chemistry The glass substrate for the magnetic disk of this example was manufactured through a strengthening step and (7) a main surface polishing step (second polishing step).

(1) Substrate preparation step A large plate glass made of aluminosilicate glass having a thickness of 1 mm manufactured by the float method was prepared and cut into small pieces using a diamond cutter. Next, using a diamond cutter, it was processed into a disk shape having a circular hole having an outer diameter of 65 mm and an inner diameter of 20 mm in the center. For this aluminosilicate glass, it is expressed in% by weight.
SiO ₂ 58 to 66%, Al ₂ O ₃ 13 to 19%, Li ₂ O 3 to 4.5%, Na ₂ O 6 to 13%, K ₂ O 0 to 5%, R ₂ O 10 to 18%, (However, R ₂ O = Li ₂ O + Na ₂ O + K ₂ O)
MgO 0 to 3.5%, CaO 1 to 7%, SrO 0 to 2%, BaO 0 to 2%, RO 2 to 10% (however, RO = MgO + CaO + SrO + BaO)
TiO _{20 to} 2%, CeO _{20 to} 2%, Fe ₂ O _{30 to} 2%, MnO 0 to 1% (however, TiO ₂ + CeO ₂ + Fe ₂ O ₃ + MnO = 0.01 to 3%) A chemically strengthened glass containing the composition was used.

(2) Shape Machining Step Next, a predetermined chamfering process was performed on the outer peripheral end face and the inner peripheral end face. In general, a 2.5-inch HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.

(3) End Face Polishing Step Next, the surface of the end face (inner circumference, outer circumference) of the glass substrate was polished while rotating the glass substrate by a known brush polishing method.

(4) Main surface grinding process This main surface grinding process was performed by using a double-sided lapping device and setting a glass substrate held by a carrier between the upper and lower surface plates to which a diamond pad was attached. As the diamond pad, a fixed-abrasive grindstone was used in which agglomerates in which a plurality of diamond particles were vitrified and bonded with glass were fixed with a resin to form fixed abrasive grains. Here, the average particle size of the aggregate was about 25 μm, and the average particle size (D50) of the individual diamond particles in the aggregate was 2.5 μm. In addition, it was carried out while using a lubricating liquid. The main surface of the glass substrate before the grinding process was a mirror surface. Moreover, when the roughness of the main surface was measured with a stylus type roughness meter, it was 5 nm in Ra.

Specifically, the rotation speed of the surface plate was appropriately selected in the range of 10 to 100 rpm, and the load on the glass substrate was applied according to the sequence shown in FIG. In this embodiment, the load (P1) of the first stage (roughening) is set to 150 g / cm ² , and the load (P2) of the second stage (main processing) is ^{set to 100 g / cm 2} , respectively. By rotating the sun gear and internal gear of the above, both sides of the glass substrate housed in the carrier were processed.
The slope k in FIG. 3 was 10 g / (cm ² · sec), t1 was 60 seconds, the time between BCs was 15 seconds, and t2 was 200 seconds longer than t1.
The glass substrate that had been subjected to the above grinding process was sequentially immersed in each cleaning tank (ultrasonic application) of a neutral detergent and water to perform ultrasonic cleaning.

In this grinding process, 50 sheets were processed per process (1 batch). The surface roughness of the processed glass substrate was measured using a stylus type surface roughness meter. Tables 1 and 2 show the measurement results of the surface roughness (Ra) and the processing speed in the entire grinding process. The processing speed in the entire grinding process is a value obtained by dividing the total grinding thickness by the total processing time (including the first stage and the second stage). In addition, scratches were evaluated by counting the number of glass substrates in which scratches were generated on the main surface using a condensing lamp in a dark room.

(5) Main surface polishing process (first polishing process)
Next, the first polishing step for removing scratches and strains remaining in the above-mentioned grinding process was performed using a double-sided polishing device. In a double-sided polishing device, a glass substrate held by a carrier is brought into close contact between the upper and lower polishing surface plates to which a polishing pad is attached, and this carrier is meshed with a sun gear (sun gear) and an internal gear (internal gear). , The glass substrate is sandwiched by the upper and lower surface plates. After that, by supplying a polishing liquid between the polishing pad and the polishing surface of the glass substrate and rotating the glass substrate, the glass substrate revolves while rotating on the surface plate to simultaneously polish both sides. Specifically, a hard polisher (hard urethane foam) was used as the polisher, and the first polishing step was carried out. As the polishing liquid, a cerium oxide dispersed in water as an abrasive was used.

(6) Chemical strengthening step Next, the glass substrate after the above cleaning was chemically strengthened. The chemical strengthening treatment was carried out by preparing a chemical strengthening solution obtained by mixing and melting potassium nitrate and sodium nitrate, and immersing a glass substrate in the chemically strengthening solution.

(7) Main surface polishing process (second polishing process)
Then, using the same double-sided polishing apparatus used in the first polishing step, the polisher was replaced with a soft polisher (suede) polishing pad, and the second polishing step was carried out. This second polishing step is a mirror polishing process for further reducing the surface roughness to finish a smooth mirror surface while maintaining the flat surface obtained in the first polishing step described above. As the polishing liquid, a colloidal silica dispersed in water was used. The glass substrate after the second polishing step was appropriately washed and dried.

Further, when the surface roughness of the main surface of the glass substrate obtained through the above steps was measured by an atomic force microscope (AFM), it had an ultra-smooth surface with Rmax = 1.53 nm and Ra = 0.13 nm. A glass substrate was obtained. Moreover, when the surface of the glass substrate was analyzed by an atomic force microscope (AFM) and an electron microscope, it was mirror-like and no surface defects such as protrusions and scratches were observed.
The outer diameter of the obtained glass substrate was 65 mm, the inner diameter was 20 mm, and the plate thickness was 0.635 mm.
In this way, the glass substrate for the magnetic disk of this example was obtained.

(Example 2)
In the grinding process of Example 1, the grinding process was performed in the same manner as in Example 1 except that the load (P1) of the first stage (roughening) ^{was set to 130 g / cm 2.} Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 1 shows the measurement results of scratches on the ground surface and the processing speed of the entire grinding process for the glass substrate after the grinding process.

(Example 3)
In the grinding process of Example 1, the grinding process was performed in the same manner as in Example 1 except that the load (P1) of the first stage (roughening) ^{was set to 200 g / cm 2.} Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 1 shows the measurement results of scratches on the ground surface and the processing speed of the entire grinding process for the glass substrate after the grinding process.

(Example 4)
In the grinding process of Example 1, the grinding process was performed in the same manner as in Example 1 except that the load (P2) of the second stage (main processing) ^{was set to 50 g / cm 2.} Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 2 shows the surface roughness (Ra) measured in the same manner as in Example 1 and the measurement results of the processing speed in the entire grinding process for the glass substrate after the grinding process.

(Example 5)
In the grinding process of Example 1, the grinding process was performed in the same manner as in Example 1 except that the load (P2) of the second stage (main processing) ^{was set to 70 g / cm 2.} Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 2 shows the surface roughness (Ra) measured in the same manner as in Example 1 and the measurement results of the processing speed in the entire grinding process for the glass substrate after the grinding process.

(Example 6)
In the grinding process of Example 1, the grinding process was performed in the same manner as in Example 1 except that the load (P2) of the second stage (main processing) ^{was set to 120 g / cm 2.} Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 2 shows the surface roughness (Ra) measured in the same manner as in Example 1 and the measurement results of the processing speed in the entire grinding process for the glass substrate after the grinding process.

(Example 7)
In the grinding process of Example 1, the grinding process was performed in the same manner as in Example 1 except that the load (P1) of the first stage (roughening) ^{was set to 120 g / cm 2.} Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 1 shows the measurement results of scratches on the ground surface and the processing speed of the entire grinding process for the glass substrate after the grinding process.

(Example 8)
In the grinding process of Example 1, the grinding process was performed in the same manner as in Example 1 except that the load (P1) of the first stage (roughening) ^{was set to 210 g / cm 2.} Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 1 shows the measurement results of scratches on the ground surface and the processing speed of the entire grinding process for the glass substrate after the grinding process.

(Example 9)
In the grinding process of Example 1, the grinding process was performed in the same manner as in Example 1 except that the load (P2) of the second stage (main processing) ^{was set to 40 g / cm 2.} Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 2 shows the surface roughness (Ra) measured in the same manner as in Example 1 and the measurement results of the processing speed in the entire grinding process for the glass substrate after the grinding process.

(Example 10)
In the grinding process of Example 1, the grinding process was performed in the same manner as in Example 1 except that the load (P2) of the second stage (main processing) ^{was set to 130 g / cm 2.} Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 2 shows the surface roughness (Ra) measured in the same manner as in Example 1 and the measurement results of the processing speed in the entire grinding process for the glass substrate after the grinding process.

(Comparison example)
In the grinding process of Example 1, the load ^{was set to 100 g / cm 2} and the grinding process (main process) was performed from the beginning. Then, a glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for the grinding process.
Table 1 shows the measurement results of scratches on the ground surface and the processing speed of the entire grinding process for the glass substrate after the grinding process.

From the results in Tables 1 and 2 above, the following can be seen.
1. 1. In the comparative example in which the first step is not provided, the load is set to the load of the grinding process (main processing), and the grinding process (main processing) is performed from the beginning, the time during which the grinding process cannot be performed becomes longer and the processing speed increases. It will drop.
2. On the other hand, according to the embodiment of the present invention, it is possible to reduce the time during which grinding cannot be performed in the conventional grinding process using fixed abrasive grains, and to perform the grinding process without reducing the processing speed. Furthermore, it is possible to keep the surface roughness of the machined surface low by adjusting the grinding conditions. In particular, the load P1 in the first stage, a range of 130~200g / cm ^2, the load P2 in the second stage, by the range of 50 to 120 / cm ^2, better results are obtained.
If the load P1 in the first stage ^{is smaller than 130 g / cm 2} (Example 7), the time during which grinding cannot be performed cannot be sufficiently shortened, and the processing speed is lowered. On the other hand, when the load P1 is ^{larger than 200 g / cm 2} (Example 8), the depth of cut by the abrasive grains becomes too deep, scratches occur, and it becomes necessary to increase the allowance for the main processing and the subsequent polishing process. Therefore, the entire processing time becomes long. ^{That is, P1 is preferably 130 g / cm 2} or more from the viewpoint of processing speed, and preferably 200 g / cm ² or less from the viewpoint of scratch.
Further, the value of P1 / P2 is preferably 1.20 or more or 3 or less from the above results.

Further, as another example (comparative example), the glass substrate was treated and evaluated in the same manner as in Example 1 with ^{P1 being 100 (g / cm 2} ) and P2 being 130 (g / cm ^2). It was found that the manufacturing cost could not be reduced because Ra became 0.132 μm and it became necessary to increase the allowance for the subsequent polishing process.

In addition, using each of the conditions of the examples in Table 2, continuous processing of 50 batches was performed continuously so as to always use a new glass substrate, and a total of 2500 processed glass substrates were investigated. Only under the conditions of Example 9, one substrate was found in which a part of the main surface was not ground. Such unground substrates can be found using the same methods as for scratch inspection.
Further, from the conditions of Example 4, only P1 was changed to 160 (g / cm ² ) and 140 (g / cm ² ), and the same continuous processing was performed (these are Examples 11 and 12, respectively. When P1 / P2 was set to 3.2 and 2.8) and 140 (g / cm ² ), the above unground substrate was not found, but it was set to 160 (g / cm ² ). In the case, one was found.
That is, from the results of Examples 4, 9, 11 and 12, it was found that when P1 / P2 is larger than 3, there is a possibility that an unground substrate may be generated during continuous machining.

Further, the amount of protrusion of the grinding abrasive grains (aggregates) in the diamond pad used in Example 1 was changed between 0.3 μm and 8 μm.
Except for this point, the grinding process was continuously performed in the same manner as in Example 1, and the surface observation results of the obtained 2500 glass substrates are shown in Table 3 below.

From the results in Table 3 above, on the surface of the diamond pad used for the grinding process, the amount of protrusion of the grinding abrasive grains is particularly preferably in the range of 0.5 μm to 7 μm.

(Manufacturing of magnetic disks)
The glass substrate for a magnetic disk obtained in Example 1 was subjected to the following film forming step to obtain a magnetic disk for perpendicular magnetic recording.
That is, on the glass substrate, an adhesion layer made of a Ti-based alloy thin film, a soft magnetic layer made of a CoTaZr alloy thin film, a base layer made of a Ru thin film, a perpendicular magnetic recording layer made of a CoCrPt alloy, a carbon protective layer, and a lubricating layer are sequentially formed. A film was formed. The protective layer is for preventing the magnetic recording layer from being deteriorated by contact with the magnetic head, is made of carbon hydride, and has abrasion resistance. Further, as the lubricating layer, a liquid lubricant of alcohol-modified perfluoropolyether was formed by a dip method.
The obtained magnetic disk was incorporated into an HDD equipped with a DFH head, and a load / unload durability test was conducted for one month while operating the DFH function in a high temperature and high humidity environment of 80 ° C. and 80% RH. There were no particular obstacles, and good results were obtained.

1 Diamond pad 2 Sheet 3 Aggregate 4 Pellets 5 Diamond particles 6 Support material 10 Glass substrate

Claims (6)

The glass substrate held by the carrier is brought into close contact between the upper and lower surface plates, and the glass substrate and the upper and lower surface plates are relatively moved while being sandwiched by the upper and lower surface plates at a predetermined pressure. A fixed abrasive grain grindstone that is attached to the upper and lower surface plates when both main surfaces of a glass substrate are simultaneously ground.
The fixed abrasive grain grindstone is used for grinding a glass substrate whose main surface is a mirror surface.
The grinding process has a first step of roughening the surface of the glass substrate and a second step of grinding the glass substrate, which is carried out after the first step.
The fixed abrasive grain grindstone is used through the first step and the second step.
The fixed abrasive grain grindstone includes fixed abrasive grains containing diamond particles.
The amount of protrusion of the fixed abrasive grains is 0.5 μm to 7 μm.
A method for manufacturing a glass substrate, which comprises a process of grinding the main surface of the glass substrate using the fixed abrasive grain grindstone. The method for producing a glass substrate according to claim 1, wherein the fixed abrasive grains are aggregates in which some diamond particles are hardened with a binder of glass, ceramic, metal, or resin. The method for producing a glass substrate according to claim 1 or 2 , wherein the fixed abrasive grains have an average particle size of 20 to 40 μm. The method for producing a glass substrate according to any one of claims 1 to 3 , wherein the average particle size of the diamond particles is 1 to 5 μm. The method for manufacturing a glass substrate according to any one of claims 1 to 4, wherein the glass substrate is a glass substrate used for manufacturing a glass substrate for a magnetic disk. A method for producing a glass substrate, which comprises, after the process of grinding the main surface of the glass substrate according to any one of claims 1 to 5, a process of further polishing the main surface of the glass substrate.

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