JP2001006161A - Manufacture for glass substrate for information- recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shallow a crack depth and reduce a polishing margin by setting a rough polishing pressure to the main surface in a lapping process to be lower in a second half stage than in a first half stage. SOLUTION: Cracks are generated to the main surface of a glass substrate material by polishing in a lapping process. A depth of the crack is (d) and smaller than when the polishing is conducted with a constant polishing pressure. Polishing in a polishing process for removing fine cracks formed in the surface of the glass substrate material is carried out, and then polishing in a final process is carried out. The polishing pressure is set in two stages to be lower in a second half stage than in a first half stage in the lapping process, whereby a sum of margins in the succeeding polishing process and final process can be reduced. The polishing pressure is controlled stepwise, so that the depth of cracks can be shallowed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a glass substrate for an information recording medium for processing the surface of a glass substrate material used as an information recording medium such as an optical disk or a magnetic disk. More specifically, the present invention relates to an improvement in a lapping step of roughly polishing a main surface of a glass substrate material.

[0002]

2. Description of the Related Art In a magnetic disk using a glass substrate material, high-density recording and expansion of a recording area are required to increase a recording capacity. For this reason, it is necessary to make the surface of the glass substrate material to be a recording portion (hereinafter, referred to as a main surface) as smooth as possible, and to secure the area as large as possible.

In general, an optical disk is made by mirror-polishing a glass substrate material, then precision cleaning, and then coating a resist thereon. Further, the resist is irradiated with a laser beam and developed to form pits, and the pits are formed on the glass substrate by nickel plating.

In general, in these glass substrates for information recording media, the processing pressure in the polishing step (lapping step) is a primary processing pressure for preventing cracks due to the polishing processing, and a secondary processing pressure in the actual polishing step (polishing step). The processing is performed separately for the processing pressure and the tertiary processing pressure of the finishing step (final step) for finishing the processing.

Namely, as shown in FIG. 5, the processing pressure in the lapping process in certain P _1, T ₂ from the machining time T ₁
Polishing is carried out until. Thereafter, the processing of the polishing step and a final step is performed at a pressure lower than the pressure P _1.

As the above-mentioned mirror polishing method, for example, Japanese Patent Application Laid-Open No. Hei 10-134424 discloses a first polishing step of applying a first pressure to a holding member for holding a glass master, and a method of applying a lower pressure than the first pressure. A second polishing step of applying a second pressure, and a third polishing step of applying a third pressure lower than the second pressure.
After performing the above polishing step, a method of performing a fourth polishing step so as not to apply pressure to the holding member is disclosed.

[0007]

However, fine cracks are generated on the surface of the glass substrate material by polishing in the lapping step, and the depth D of the cracks is formed deep in the glass substrate material as shown in FIG. It remains in a state where it was left. For this reason, there has been a problem that a large stock removal must be taken in the next polishing step so as to remove such cracks.

On the other hand, in order to make the cracks generated in the lapping step shallow, it is necessary to polish with an abrasive having a fine grain size. In this case, there is a problem that the processing time in the lapping step becomes extremely long. .

The polishing method disclosed in Japanese Patent Application Laid-Open No. Hei 10-134424 is a polishing method intended for a final step performed after a lapping step and a polishing step. Not a problem.

The present invention has been made by focusing on the problems existing in the prior art as described above. The purpose is to reduce the depth of fine cracks generated on the glass substrate material surface in the lapping process without excessively increasing the processing time in the lapping process, and to reduce the polishing allowance in the polishing process and the final process. An object of the present invention is to provide a method for manufacturing a glass substrate for an information recording medium, which can be reduced.

[0011]

In order to achieve the above object, a method of manufacturing a glass substrate for an information recording medium according to the present invention comprises a lapping step of roughly polishing a main surface of a glass substrate material. A polishing step for removing fine cracks formed in the lapping step, and a final step for removing and finishing fine cracks that could not be removed in the polishing step, with respect to the main surface in the lapping step. The rough polishing pressure is set to be lower in the latter period than in the previous period.

According to a second aspect of the present invention, in the method for manufacturing a glass substrate for an information recording medium according to the first aspect, the rough polishing pressure in the lapping step is gradually reduced from the first half to the second half. It is set to be.

According to a third aspect of the present invention, in the method for manufacturing a glass substrate for an information recording medium according to the first or second aspect, the pressure in the latter half of the lapping step is set to be 1 to the pressure in the first half. It is set so as to be in the range from / 2 to 1/4.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

The glass substrate for an information recording medium can be removed by a lapping step of roughly polishing the main surface of the glass substrate material, a polishing step of removing fine cracks formed in the lapping step, and a polishing step. It is manufactured through a final process for removing and finishing cracks that were not present. Then, in the lapping step, the pressure of the rough polishing on the main surface is set to be lower in the latter period than in the former period.

In the lapping step, rough polishing is performed using a polishing material having a relatively coarse particle size at a predetermined polishing pressure for a predetermined processing time. In the subsequent polishing step, polishing is performed at a pressure equal to or lower than the polishing processing pressure in the lapping step. In the final step, the same as the polishing pressure in the polishing step,
Alternatively, polishing is performed at a lower pressure.

Specifically, as shown in FIG. 1, the polishing pressure in the _{first half} of the lapping step is p ₁ and the processing time is from t ₁ to t ₂ , and the polishing pressure in the _{second half} of the lapping step is p ₂ . The polishing is performed under the condition of the processing time from t ₃ to t ₄ . As shown in FIG. 2, cracks occur on the main surface of the glass substrate material by the polishing in the lapping step, and the depth of the cracks becomes d. The depth of the crack d becomes shallower than the depth D of the crack in the case of performing polishing with conventional constant polishing pressure P _1.

Next, in order to remove fine cracks formed on the surface of the glass substrate material in the lapping step,
Polishing in the polishing step is performed. Further, in order to remove and finish cracks on the surface of the glass substrate material that cannot be removed in the polishing step, polishing in the final step is performed.

[0019] The lapping in the step, by polishing pressure p ₂ late compared to polishing pressure p ₁ of the previous period is set to two-stage polishing process pressure so that the low pressure, the subsequent polishing step and final The total allowance in the process can be reduced. As described above, by controlling the pressure of the rough polishing in the lapping step so that the pressure gradually decreases from the first half to the second half, the depth of the formed cracks is reduced to reduce the allowance for removing the cracks. can do.

In order to exert such effects effectively,
It is desirable to set the pressure in the latter half of the lapping step to be in the range of か ら to に 対 し て of the pressure in the first half.

Next, as the glass substrate material, any of aluminosilicate glass, crystallized glass, soda lime glass and the like can be used. Among them, it has good performance such as hardness as a substrate material for information recording media,
From the viewpoint that the generation of fine cracks can be suppressed when the main surface is polished, aluminosilicate glass having the following composition expressed in mol% is preferable.

The silicon oxide _{(SiO 2) 40~72%, (} 2 O 3 Al) 0.5~25% aluminum oxide, lithium oxide (Li ₂ O) 0~22%, sodium oxide (Na ₂ O) 0~ 14%, potassium oxide (K ₂ O) 0 to 10%, R ₂ O 2 to 30%, where R ₂ O = Li ₂ O + Na ₂ O + K ₂ O magnesium oxide (MgO) 0 to 25%, calcium oxide (CaO) 0-25%, strontium oxide (SrO) 0-10%, barium oxide (BaO) 0-10%, RO 0-40% where RO = MgO + CaO + SrO + BaO titanium oxide (TiO ₂ ) 0-10% zirconium oxide (ZrO ₂₎ Glass having such a composition can be manufactured by a float method, has a low melting temperature, and has a chemical strengthening treatment. Of water resistance and weather resistance is good, yet has a coefficient of expansion that can be used in combination with metal products. The float method is a method of manufacturing a plate-like glass by flowing molten glass from one end into a high-temperature bath in which molten tin is contained and the upper space has a reducing atmosphere, and the glass is stretched from the other end. According to this float method, the obtained glass is parallel to each other, has no distortion, has a glossy surface, can be mass-produced, can easily change the plate width, and can easily achieve automation.

In the above glass composition, SiO 2
₂ is a main component of glass and is an essential component.
When the content is less than 40% by weight, the water resistance after ion exchange for strengthening treatment is deteriorated. When the content is more than 72% by weight, the viscosity of the glass melt becomes too high, and melting and molding become difficult. At the same time, the expansion coefficient becomes too small.

Al ₂ O ₃ is a component necessary for increasing the ion exchange rate and improving the water resistance after ion exchange. When the content is less than 0.5% by weight, such an effect is insufficient, and when the content exceeds 25% by weight, the viscosity of the glass melt becomes too high, making melting and molding difficult, and expanding. Coefficient is too small.

Li ₂ O is an essential component for performing ion exchange and also a component for enhancing solubility.
If the content exceeds 22% by weight, the water resistance after ion exchange deteriorates, the liquidus temperature rises, and molding becomes difficult.

Na ₂ O is a component that enhances solubility. If the content exceeds 14% by weight, the water resistance after ion exchange deteriorates. K ₂ O is a component that enhances solubility, and if its content exceeds 10% by weight, the surface compressive stress after ion exchange decreases.

Further, the above Li ₂ O, Na ₂ O and K ₂
If the total R ₂ O of O is less than 2% by weight, the viscosity of the glass melt becomes too high, making melting and molding difficult, and
If the expansion coefficient is too small and exceeds 30% by weight,
Water resistance after ion exchange deteriorates.

MgO is a component that enhances solubility.
If the amount exceeds 10% by weight, the liquidus temperature rises and molding becomes difficult. CaO is a component that enhances solubility and is an essential component for adjusting the ion exchange rate. If the content exceeds 25% by weight, the liquidus temperature rises and molding becomes difficult. SrO is a component that enhances solubility and is a component that is effective in lowering the liquidus temperature. When the content exceeds 10% by weight, the density of the glass increases and the production cost increases. BaO is a component that enhances solubility and is also a component that is effective in lowering the liquidus temperature. When the content exceeds 10% by weight, the density of the glass increases and the production cost increases.

When the total RO of MgO, CaO, SrO and BaO exceeds 40% by weight, the liquidus temperature rises and molding becomes difficult.

If the content of TiO ₂ exceeds 10% by weight, the quality of the glass substrate deteriorates and the production cost increases. If ZrO ₂ exceeds 10% by weight, the melting temperature or viscosity of the glass base increases, and the production of the glass substrate material tends to be difficult.

In order to maintain the strength required for a substrate for a magnetic disk, the glass is preferably subjected to a chemical strengthening treatment on its surface. In this chemical strengthening treatment, the glass is immersed in a molten salt containing a monovalent metal ion having a larger ionic radius than the monovalent metal ion contained in the composition, and the metal ions in the glass and the metal in the molten salt are mixed. This is performed by ion exchange with ions.

For example, when a glass substrate is immersed in a heated potassium nitrate solution, sodium ions near the surface of the glass substrate are replaced by potassium ions having a larger ion radius. The substrate surface is strengthened. Further, a glass substrate is made of silver nitrate (0.5-3%) and potassium nitrate (97-9%).
9.5%) for 30 minutes to 1 hour. As a result, silver ions quickly penetrate into the glass substrate surface, and the strengthening of the glass substrate surface is promoted. Further, instead of the mixed solution of silver nitrate and potassium nitrate, a mixed solution of potassium nitrate and sodium nitrate can be used.

On the surface of the glass substrate material formed as described above, for example, an underlayer, a magnetic medium layer, a protective layer, and a lubricating layer for improving magnetic properties are sequentially provided to produce a glass substrate for a magnetic disk. Is done. A plurality of intermediate films may be further formed between the glass substrate and the underlayer for the purpose of further improving the magnetic characteristics, improving the adhesive force, and the like.

A resist is applied to the surface of the glass substrate material, and the resist is irradiated with a laser beam, and further developed to form pits. Next, the glass substrate having the pits formed thereon is plated with nickel to produce a glass substrate for an optical disk.

As described above, according to this embodiment, the following effects are exhibited.

The rough polishing pressure on the main surface in the lapping step is set to be lower in the latter period than in the former period. For this reason, it is possible to reduce the depth of cracks generated on the surface of the glass substrate material in the lapping step and to reduce the polishing allowance in the polishing step and the final step without extremely increasing the processing time in the lapping step. Therefore, the processing time in the polishing step and the final step can be reduced, and the productivity of the glass substrate for an information recording medium can be improved.

As described above, the depth of cracks generated on the surface of the glass substrate material in the lapping step can be reduced, and the stock removal in the polishing step and the final step can be reduced. It is possible to

In addition, the glass substrate material obtained through each of the lapping step, polishing step and final step has good dimensional accuracy and shape accuracy, and its surface is excellent in smoothness. Therefore, such a glass substrate material is suitable as a glass substrate for an information recording medium.

The rough polishing pressure in the lapping step is set so as to gradually decrease from the first half to the second half. For this reason, the pressure of the rough polishing in the lapping step can be easily adjusted.

Further, the pressure in the second half of the lapping step is set to be in a range of か ら to に 対 し て of the pressure in the first half. Therefore, each of the above effects can be more effectively exerted.

[0041]

Next, the embodiment will be described more specifically with reference to examples and comparative examples. Comparative Example 1 A main surface of a disk-shaped glass substrate material having a diameter of 3.0 inches and a thickness of 1.1 mm was polished. The glass substrate material used was made of aluminosilicate glass having the following composition (mol%).

SiO ₂ 66%, Al ₂ O ₃ 10%,
Li ₂ O 7%, Na ₂ O 10%, MgO 3%, C
aO 4%.

In the lapping step, FO # 1000 manufactured by Fujimi Polishing Co., Ltd. was used as an abrasive. And
As shown in FIG. 5, polishing was performed under the conditions that the polishing pressure P ₁ was 90 g / cm ² and the time from the processing time T ₁ to T ₂ was 11 minutes. In this wrapping process, the allowance is 2
It was 52 μm.

Next, polishing in a polishing step was performed to remove fine cracks formed on the surface of the glass substrate material in the lapping step. In this polishing step, polishing was performed under the conditions of a polishing processing pressure of 90 g / cm ² and a processing time of 40 minutes, and the allowance was 40 μm.

Subsequently, polishing was performed in a final step for removing and finishing cracks on the surface of the glass substrate material that could not be removed in the polishing step. In this final step, polishing was performed under the conditions of a polishing pressure of 90 g / cm ² and a processing time of 13 minutes.
μm.

Therefore, the total removal allowance in the polishing step and the final step was 48 μm, and the total processing time was 53 minutes. Example 1 A main surface of a disk-shaped glass substrate material having a diameter of 3.0 inches and a thickness of 0.9 mm was polished. The glass substrate used was made of aluminosilicate glass having the same composition as in Comparative Example 1.

In the lapping step, FO # 1500 manufactured by Fujimi Polishing Co., Ltd. was used as an abrasive. And
As shown in FIG. 1, when the polishing pressure p ₁ is 90 g / cm ² , the time from the processing time t ₁ to t ₂ is 10.5 minutes, and subsequently, when the polishing pressure p ₂ is 40 g / cm ² , the processing time t ₃ to t
Polishing was performed under the condition that the time up to ₄ was 4.5 minutes. In this lapping step, the stock removal is 55 μm when the polishing pressure p ₁ is 90 g / cm ² , and the polishing pressure p ₂ is 40
It was 10 μm at g / cm ² .

Next, polishing in a polishing step was performed to remove fine cracks formed on the surface of the glass substrate material in the lapping step. In this polishing step, when the polishing was performed under the conditions of a polishing pressure of 90 g / cm ² and a processing time of 30 minutes, the allowance was 30 μm.

Subsequently, polishing in a final step for removing and finishing cracks on the surface of the glass substrate material that could not be removed in the polishing step was performed. In this final step, polishing was performed under the conditions of a polishing pressure of 90 g / cm ² and a processing time of 8 minutes.
m.

Therefore, the total removal allowance in the polishing step and the final step was 35 μm, and the total processing time was 38 minutes. The total machining allowance could be reduced to about 73% compared to Comparative Example 1, and the total processing time could be reduced to about 72% compared to Comparative Example 1.

Further, the surface of the glass substrate material after processing is AF
Examination using M (Atomic Force Microscope) confirmed that the surface was finished to an extremely smooth surface with a surface roughness Ra of 1 nm and no asperity. This shows that the use of the method of the present invention makes it possible to obtain a glass substrate for an information recording medium having a surface smoothness equivalent to that of a conventional glass substrate using a thinner glass substrate material and a shorter polishing time. Example 2 The main surface of a disk-shaped glass substrate material having a diameter of 3.0 inches and a thickness of 0.9 mm was polished. The glass substrate material used was made of aluminosilicate glass having the same composition (mol%) as in Comparative Example 1.

In the lapping step, FO # 1500 manufactured by Fujimi Polishing Co., Ltd. was used as an abrasive. And
As shown in FIG. 1, when the polishing pressure p ₁ is 90 g / cm ² , the time from the processing time t ₁ to t ₂ is 10.5 minutes, and subsequently, when the polishing pressure p ₂ is 40 g / cm ² , the processing time t ₃ to t
Polishing was performed under the condition that the time up to ₄ was 4.5 minutes. In this lapping step, the stock removal is 55 μm when the polishing pressure p ₁ is 90 g / cm ² , and the polishing pressure p ₂ is 40
It was 10 μm at g / cm ² .

Next, in the polishing step, polishing was performed under the conditions of a polishing processing pressure of 90 g / cm ² and a processing time of 30 minutes, and the allowance was 30 μm.

Subsequently, in the final step, polishing was performed under the conditions of a polishing pressure of 90 g / cm ² and a processing time of 8 minutes, and the allowance was 5 μm.

Therefore, the total removal allowance in the polishing step and the final step was 35 μm, and the total processing time was 38 minutes.

The above steps were carried out with the sample number n set to 10, and the processed glass substrate material was visually observed. As a result, no lap mark was found. (Comparative Example 2) The main surface was polished using a glass substrate material made of aluminosilicate glass having the same composition (mol%) as in Example 2 above.

In the lapping step, FO # 1500 manufactured by Fujimi Polishing Co., Ltd. was used as an abrasive. And
As shown in FIG. 5, polishing was performed under the conditions that the polishing pressure P ₁ was 90 g / cm ² and the time from the processing time T ₁ to T ₂ was 11 minutes. In this lapping process, the allowance is 6
It was 0 μm.

Next, in the polishing step, polishing was performed under the conditions of a polishing processing pressure of 90 g / cm ² and a processing time of 40 minutes, and the allowance was 40 μm.

Subsequently, in the final step, polishing was performed under the conditions of a polishing pressure of 90 g / cm ² and a processing time of 13 minutes, and the allowance was 8 μm.

The sample number n was set to 10, and none of the lap marks were visually inspected. However, the total processing time in the polishing step and the final step was 53 minutes, which was longer than 38 minutes in Example 2. Cost. Comparative Example 3 The same glass substrate material as in Comparative Example 2 was used, and polishing was performed in the lapping step under the same conditions as in Comparative Example 2. In this lapping process, the allowance is 60
μm.

Next, in the polishing step, polishing was performed under the conditions of a polishing pressure of 90 g / cm ² and a processing time of 30 minutes, and the allowance was 30 μm.

Subsequently, in the final step, polishing was performed under the conditions of a polishing pressure of 90 g / cm ² and a processing time of 8 minutes, and the allowance was 5 μm.

The number n of samples was 10, and n was 5 as a result of visual inspection of lap marks. From this, it was found that when the polishing pressure in the lapping process was constant, the crack layer formed by the lapping process became thick.

The above embodiment may be modified and embodied as follows.

As shown in FIG. 3, in the lapping step, the rough polishing pressure on the main surface is set to be lower in the latter stage as compared with the polishing pressure p ₁ from the earlier machining time t ₁ to t _2. polishing pressure p ₂ from the processing time t ₃ to t _4, polishing pressure from the processing time t ₅ to t ₆ may be set to be three steps p _3.

With such a configuration, the pressure of the rough polishing in the lapping step can be easily adjusted, and the depth of a fine crack can be controlled to be smaller. Therefore, the stock removal in the polishing step and the final step can be reduced, and the productivity can be further improved.

As shown in FIG. 4, in the lapping step, the pressure of the rough polishing on the main surface is set to be lower in the latter stage as compared with the polishing pressure p ₁ from the earlier machining time t ₁ to t _2. the polishing pressure from the processing time t ₂ to t ₃ may be set to decrease from the p ₁ p ₂ to quadratically continuously.

With such a configuration, the depth of the fine cracks formed in the lapping step can be controlled to be shallower.

The rough polishing in the lapping step may be performed using a hard polisher or a soft polisher.

The technical ideas grasped from the above embodiment will be described below.

The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the pressure of the rough polishing in the lapping step is set to be continuously low from the first half to the second half.

With this configuration, the depth of fine cracks generated on the surface of the glass substrate material in the lapping step can be controlled to be smaller.

The method for producing a glass substrate for an information recording medium according to any one of claims 1 to 3, wherein the glass substrate material is aluminosilicate glass.

With such a configuration, it has good performance such as hardness as a substrate material for an information recording medium, and can suppress generation of fine cracks when its main surface is polished. .

A glass substrate for an information recording medium manufactured by the method for manufacturing a glass substrate for an information recording medium according to any one of claims 1 to 3.

With this configuration, it is possible to provide a glass substrate for an information recording medium that can reduce the depth of fine cracks generated on the surface of the glass substrate material in the lapping step and reduce the stock removal. .

[0077]

As described above, the present invention has the following advantages.

According to the method for manufacturing a glass substrate for an information recording medium according to the first aspect of the present invention, the minute time generated on the surface of the glass substrate material in the lapping step can be obtained without extremely increasing the processing time in the lapping step. The depth of the cracks can be reduced, and the stock removal in the polishing step and the final step can be reduced.

According to the method of manufacturing a glass substrate for an information recording medium according to the second aspect of the present invention, in addition to the effects of the first aspect, the pressure of the rough polishing in the lapping step can be easily adjusted. it can.

According to the method of manufacturing a glass substrate for an information recording medium according to the third aspect of the invention, the effects of the first or second aspect of the invention can be more effectively exerted.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between processing time and polishing pressure in an example.

FIG. 2 is a schematic diagram showing the depth of cracks generated on the surface of a glass substrate.

FIG. 3 is a graph showing the relationship between processing time and polishing pressure in another example.

FIG. 4 is a graph showing the relationship between processing time and polishing pressure in another example.

FIG. 5 is a graph showing the relationship between processing time and polishing pressure in the related art.

FIG. 6 is a schematic diagram showing the depth of a crack generated on the surface of a conventional glass substrate.

Claims (3)

[Claims] 1. A lapping step for roughly polishing a main surface of a glass substrate material, a polishing step for removing fine cracks formed in the lapping step, and a fine crack which cannot be removed in the polishing step. A method of manufacturing a glass substrate for an information recording medium, comprising: setting a rough polishing pressure on a main surface in the lapping step to be lower in a later stage as compared with the earlier stage. 2. The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the pressure of the rough polishing in the lapping step is set so as to gradually decrease from the first half to the second half. 3. The glass substrate for an information recording medium according to claim 1, wherein a pressure in a later stage of the lapping step is set to be in a range of か ら to に 対 し て of a pressure in the earlier stage. Manufacturing method.