WO2013099083A1 - Method for manufacturing glass substrate for hdd - Google Patents

Abstract

This method for manufacturing a glass substrate for an HDD is characterized in that: the method has a step wherein a double-sided polishing machine is used; the step has a step of cleaning a polishing agent slurry left on the glass substrate or the like after polishing, and a step of forming a lubricating layer by adding, to the polishing pad, the polishing agent slurry containing colloidal silica; the average primary particle diameter of the colloidal silica is 15-90 nm; and that the surface density of the colloidal silica in the lubricating layer is 10-500 particles/μm². In this manufacturing method, the glass substrate having excellent planarity and less fine warping can be obtained.

Description

Manufacturing method of glass substrate for HDD

The present invention relates to a method for manufacturing a glass substrate for HDD. More specifically, the present invention includes a rinsing process for cleaning the polishing pad and a lubrication layer forming process for providing a lubrication layer on the polishing pad in the mirror polishing process, thereby suppressing micro-waviness of the glass substrate to be obtained and flattening. The present invention relates to a method for manufacturing a glass substrate for HDD, which can increase the degree.

In recent years, with the improvement in performance of disk devices (for example, hard disk drives and HDDs) equipped with information recording media, the quality level required for the media used has increased. A glass substrate for HDD (hereinafter sometimes simply referred to as a glass substrate) is required to have small undulation and high flatness. In the present specification, the micro waviness refers to the height of micro unevenness measured at a constant measurement wavelength using a surface roughness measuring machine. Moreover, flatness means the distance (height difference) of the up-down direction of the highest part and the lowest part of the glass substrate surface. The fine waviness and flatness can be adjusted mainly by precisely polishing both main surfaces of the glass substrate in the mirror polishing process. According to recent research, it is known that micro waviness can be improved by adjusting the opening diameter of a polishing pad used in a mirror polishing process (see Patent Document 1).

By the way, the glass substrate that has undergone the mirror polishing process is sent to the subsequent chemical strengthening process and final cleaning process. In the chemical strengthening step, for example, the glass substrate is immersed in a processing tank that stores the strengthening treatment liquid. In the final cleaning step, for example, the glass substrate is immersed in a storage container in which the cleaning liquid is stored. Since the abrasive slurry remains on the surface of the glass substrate after the mirror polishing process, there is a problem that the glass substrate contaminates the strengthening treatment liquid and the cleaning liquid. Therefore, the glass substrate that has finished the mirror polishing process is washed on the surface plate. At this time, the polishing pad on the surface plate is also cleaned together with the glass substrate.

Here, when mirror polishing is performed using a polishing pad with a small buff amount (surface cutting amount), there is a problem that the flatness of the glass substrate deteriorates at the initial stage of polishing. As a cause of this, when a new unpolished glass substrate is placed on the surface plate that has been cleaned in the mirror polishing step described above, a large frictional force is generated between the glass substrate and the polishing pad, and the buff amount is reduced. When mirror polishing is started using a small polishing pad, smooth horizontal movement of the glass substrate is hindered by the frictional force, and the horizontality of the glass substrate cannot be maintained.

JP 2005-149668 A

The present invention has been made in view of such a conventional problem, and in a method for producing a glass substrate having a mirror polishing step having a cleaning step, a glass substrate having excellent flatness and less microwaviness. It aims at providing the manufacturing method of the glass substrate for obtaining.

A method for producing a glass substrate according to one aspect of the present invention includes a mirror polishing process using a double-side polishing machine having upper and lower surface plates provided with polishing pads, and the mirror polishing process includes polishing the glass substrate after mirror polishing and polishing. A rinsing step for cleaning the abrasive slurry remaining on the pad, a lubricating layer forming step for forming a lubricating layer by moving the glass substrate that has undergone the rinsing step and adding an abrasive slurry containing colloidal silica to the polishing pad, The colloidal silica has an average primary particle diameter of 15 to 90 nm, and the surface density of the colloidal silica in the lubricating layer is 10 to 500 particles / μm ² .

The objects, features and advantages of the present invention will become more apparent from the following detailed description.

Hereinafter, the manufacturing method of the glass substrate of the present embodiment will be described in detail. In this specification, a process of cleaning a glass substrate that has undergone mirror polishing is referred to as a rinsing process in order to distinguish it from cleaning in a final cleaning process subsequent to the mirror polishing process.

In the method for manufacturing a glass substrate of the present embodiment, the glass substrate is, for example, a blanks manufacturing process, a first grinding process, a coring process, an inner / outer grinding process, an inner circumference polishing process, an outer circumference polishing process, a second grinding process, a first It is manufactured through a polishing step (rough polishing step), a second polishing step (mirror polishing step), a chemical strengthening step, and a final cleaning step. The mirror polishing process includes a rinsing process and a lubricating layer forming process. Hereinafter, the mirror polishing process which is a characteristic part of the present embodiment will be described in detail.

<Mirror polishing process>
The mirror polishing process is a polishing process performed on a glass substrate that has been subjected to a rough polishing process described later, and is a process of precisely polishing using a double-side polishing machine. A double-side polishing machine (for example, 16B type manufactured by Hamai Sangyo Co., Ltd.) polishes both main surfaces of a glass substrate while sandwiching them between upper and lower surface plates provided with polishing pads on the surface.

As the polishing pad used in the mirror polishing step, it is preferable to use a soft pad having a lower hardness than the polishing pad used in the rough polishing step described later (for example, NP225 manufactured by Filwel, hardness Asker-C hardness 76). Examples of such a polishing pad include urethane foam and suede polishing pads.

In order to reduce the fine waviness of the glass substrate that has undergone the mirror polishing process, it is preferable to cut the surface of the polishing pad by about 20 to 150 μm before starting the mirror polishing. When the cutting amount exceeds 150 μm, there is a tendency that minute undulation is likely to occur in the obtained glass substrate. On the other hand, when the cutting amount is less than 20 μm, the flatness of the obtained glass substrate may be lowered.

The polishing pad preferably has a holding part (holding means) for holding colloidal silica contained in a lubricating layer described later on the surface layer part. As will be described in detail later, the lubricating layer contains colloidal silica that is abrasive grains. The holding portion is not particularly limited, and examples thereof include a plurality of opening holes formed on the foamed surface.

The depth of the opening hole is not particularly limited, and is generally 10 to 800 μm although it depends on the cutting amount of the polishing pad. Further, the average opening area of the opening holes is not particularly limited, and is approximately 0.0001 to 0.0010 mm ² . Further, the number of opening holes is not particularly limited, and is generally 100 to 800 holes / mm ² .

The colloidal silica held in the holding part continues to contact the glass substrate continuously during the mirror polishing process. Therefore, the polishing accuracy is improved, and the flatness of the obtained glass substrate can be further improved.

As the abrasive, it is possible to use an abrasive slurry in which colloidal silica having an average primary particle size of 15 to 90 nm is dispersed in water as abrasive grains to form a slurry. The mixing ratio of water and colloidal silica is preferably about 1: 9 to 3: 7. If necessary, the pH is preferably adjusted to 1.5 to 6.5 with an adjustment solution containing sulfuric acid. The abrasive slurry is added continuously or as needed on the surface plate during the mirror polishing process. The addition amount of the abrasive slurry is about 200 to 2000 mL / min.

The polishing amount of the glass substrate in the mirror polishing step is preferably about 2 to 5 μm. By setting the polishing amount in such a range, micro defects such as micro undulations generated on the surface of the glass substrate and micro scratches generated in the previous step can be satisfactorily removed. Further, the flatness of both main surfaces of the glass substrate can be reduced to less than 0.5 μm.

The load applied to the glass substrate by the polishing pad in the mirror polishing step is, for example, about 50 to 180 g / cm ² .

In the mirror polishing process of the glass substrate of the present embodiment, the rinsing process is performed after the glass substrate is polished under the above conditions.

(Rinse process)
The rinsing step is a step of cleaning the abrasive slurry remaining on the glass substrate and the polishing pad after mirror polishing.

In the rinsing process, the glass substrate and the polishing pad are cleaned using a rinsing liquid. The cleaning method is not particularly limited. For example, the glass slurry and the polishing pad may be gradually cleaned while replacing the abrasive slurry added at any time during mirror polishing with a rinse liquid. The supply may be stopped and a rinse solution may be added.

The rinse liquid is not particularly limited, and, for example, pure water, deaerated water whose gas dissolved amount is adjusted, and the like can be used.

The addition amount of the rinse liquid is not particularly limited, and is about 0.5 to 20 L / min. When the addition amount of the rinsing liquid is less than 0.5 L / min, the glass substrate cannot be sufficiently cleaned, and the glass substrate may contaminate the tempering treatment liquid or the cleaning liquid in the subsequent chemical strengthening process or the final cleaning process. There is. On the other hand, when the addition amount of the rinsing liquid exceeds 20 L / min, there is a possibility that improvement of the cleaning effect on the glass substrate cannot be expected.

Further, the addition pressure of the rinsing liquid is not particularly limited, and it is added to a glass substrate or polishing pad at a water pressure of 100 to 500 kPa. When the addition pressure of the rinsing liquid is less than 100 kPa, the glass substrate or the polishing pad may not be sufficiently cleaned. On the other hand, when the addition pressure of the rinsing liquid exceeds 500 kPa, the glass substrate and the polishing pad may be damaged.

The temperature of the rinse liquid is not particularly limited, and is about 5 to 50 ° C. When the temperature of the rinse liquid is less than 5 ° C., the glass substrate may not be sufficiently cleaned. On the other hand, when the rinse liquid is washed at a temperature exceeding 50 ° C., the glass substrate may be deformed or the polishing pad may be deteriorated.

The glass substrate that has undergone the rinsing process is sent to the subsequent chemical strengthening process and the final cleaning process. Since the glass substrate is cleaned cleanly by the rinsing process, the strengthening treatment liquid and the cleaning liquid are not extremely contaminated. On the other hand, the surface of the surface plate provided with the polishing pad that has undergone the rinsing process is cleaned cleanly. In the present embodiment, a lubricating layer is formed on such a polishing pad.

(Lubrication layer forming process)
The lubricating layer forming step is a step of adding an abrasive slurry containing colloidal silica to the polishing pad to form a lubricating layer on the surface of the polishing pad. As described above, when a new glass substrate before mirror polishing is placed on a surface plate having a polishing pad with a clean surface and mirror polishing is started, large friction is caused between the glass substrate and the polishing pad. Force is generated. Therefore, the glass substrate cannot smoothly move horizontally in the initial stage of mirror polishing, and the horizontality cannot be maintained. As a result, the levelness of the obtained glass substrate is deteriorated. In the lubricating layer forming step, the frictional force generated when contacting a new glass substrate before mirror polishing is reduced by forming a lubricating layer containing colloidal silica on the surface of a clean polishing pad.

As the abrasive slurry, a slurry in which colloidal silica having an average primary particle diameter of 15 to 90 nm is dispersed in water as abrasive grains can be used. When the average primary particle diameter of the colloidal silica is less than 15 nm, the particle diameter of the colloidal silica held in the lubricating layer described later is too small, so that sufficient lubrication performance tends not to be obtained. On the other hand, when it exceeds 90 nm, since the particle diameter of colloidal silica held in the lubricating layer described later is too large, the fine undulation tends to increase.

The mixing ratio of water and colloidal silica is preferably about 1: 9 to 3: 7. If necessary, it is preferable to adjust the pH to 1.5 to 6 with an adjusting solution containing sulfuric acid.

In addition, the abrasive slurry used in the lubricating layer forming step can be the same as the abrasive slurry used during the mirror polishing step. By using the same abrasive slurry, a new glass substrate can be placed on a surface plate having a polishing pad on which a lubricating layer is formed, and the time required to start mirror polishing can be shortened.

The method of adding the abrasive slurry in the lubricating layer forming step is not particularly limited. As in the case of adding in the mirror polishing step, the abrasive slurry may be added by supplying from the outside through a through-hole disposed on the upper surface plate of the double-side polishing machine. The slurry can be added by a method such as immersing it in a storage container storing the slurry.

The surface density of colloidal silica in the lubricating layer is 10 to 500 / μm ² , and more preferably 100 to 250 / μm ² . When the surface density is less than 10 pieces / μm ² , the flatness of the glass substrate obtained by mirror polishing tends to deteriorate. On the other hand, when the surface density exceeds 500 / μm ² , many defects tend to be formed on the main surface and the end surface of the glass substrate after the mirror polishing. In the present specification, a defect refers to an area or location that cannot be recorded to the extent that it can be accurately reproduced due to scratches or dust existing on the glass substrate, deterioration of the glass substrate, or the like.

The surface density is adjusted to the above range by adjusting the proportion of colloidal silica contained in the abrasive slurry, the average primary particle diameter, the depth, number, and area of the openings formed in the polishing pad surface. Can do.

Next, other steps that can be adopted by the present embodiment will be described. In addition, the manufacturing method of the glass substrate of this Embodiment should just have an above-described mirror polishing process, and it does not specifically limit about other processes. For this reason, the other steps described below are examples, and the design can be changed as appropriate.

<Blanks manufacturing process>
The blanks manufacturing process is a process of melting a glass material and obtaining a glass substrate (blanks) from the molten glass material.

Examples of the glass material include soda lime glass, aluminosilicate glass, borosilicate glass, Li ₂ O—SiO ₂ glass, Li ₂ O—Al ₂ O ₃ —SiO ₂ glass, R′O—Al ₂ O _3. —SiO ₂ glass (R ′ = Mg, Ca, Sr, Ba) or the like can be used. It does not specifically limit as a melting method of a glass raw material, Usually, the method of melting the said glass raw material at high temperature by well-known temperature and time is employable.

The method for obtaining blanks is not particularly limited, and for example, a method of obtaining a disk-shaped glass substrate (blanks) by pouring a molten glass material into a lower mold and press molding with an upper mold can be employed. In addition, blanks are not restricted to press molding, For example, you may cut and produce the sheet glass formed by the down draw method, the float method, etc. with the grinding stone. In this molding process, foreign matter and bubbles are mixed in the vicinity of the surface of the blank, or scratches are generated, resulting in defects.

The size of the blanks is not particularly limited, and for example, blanks having various outer diameters of 2.5 inches, 1.8 inches, 1 inch, 0.8 inches, and the like can be produced. It does not specifically limit about the thickness of a glass substrate, For example, blanks of various thickness, such as 2 mm, 1 mm, 0.8 mm, 0.63 mm, can be produced.

Blanks produced by press molding or cutting can be alternately laminated with heat-stable setters and passed through a high-temperature electric furnace to promote reduction of warpage and crystallization of glass.

<First grinding process>
The first grinding step is a step of preliminarily adjusting the parallelism, flatness and thickness of the glass substrate by grinding both surfaces of the blank.

In the first grinding step, the main surface of the blank is lapped (ground) to obtain a glass base material. The lapping process is performed using alumina-based loose abrasive grains by a double-sided lapping apparatus using a planetary gear mechanism. Specifically, in the lapping process, both main surfaces of the blanks are pressed against the lapping platen from above and below, a grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relatively. Do it. By this lapping process, a glass substrate having a flat main surface is obtained.

<Coring process>
The coring step is a step of opening a circular hole (center hole) in the center of the glass substrate. Specifically, the coring step is a step of forming an annular glass substrate by forming an inner hole at the center of the glass substrate using a cylindrical diamond drill.

<Internal and external grinding process>
The inner / outer grinding step is a step in which the inner peripheral end surface and the outer peripheral end surface of the glass substrate are ground with a drum-shaped grinding wheel using diamond or the like and subjected to a predetermined chamfering process.

<Inner circumference polishing process>
The inner peripheral polishing step is a step of alternately laminating glass substrates and spacers one by one to create a laminate, and polishing the inner peripheral end surface with an inner peripheral end surface polishing machine. The spacer is not particularly limited. For example, a spacer made of polypropylene having a thickness of 0.3 mm, an inner diameter of 21 mm, and an outer diameter of 64 mm can be employed. For example, nylon fibers having a diameter of 0.2 mm can be used for the brush bristles of the polishing machine. The number of rotations of the rotating brush can be set to 10,000 rpm, for example. As the polishing liquid for inner circumference polishing, for example, a polishing liquid containing a hydrofluoric acid solvent can be used, and as the polishing agent, for example, cerium oxide having an average primary particle diameter of 3 μm can be used.

<Outer periphery polishing process>
The outer peripheral polishing step is a step of alternately laminating glass substrates and spacers one by one to create a laminate, and polishing the outer peripheral end surface by an outer peripheral end surface polishing machine. The polishing conditions of the spacer and the polishing machine used are the same as those used in the inner peripheral polishing step.

<Second grinding process>
The second grinding step is a step of grinding both main surfaces of the glass substrate to remove large scratches and improve flatness.

In the second grinding step, both main surfaces of the glass substrate are lapped with a lapping machine (manufactured by HAMAI). The wrapping conditions are not particularly limited. For example, diamond pellets of # 1500 mesh can be used, the load can be 100 g / cm ² , the upper surface plate can be rotated at 30 rpm, and the lower surface plate can be rotated at 10 rpm. As for the surface roughness of the glass substrate obtained through the second grinding step, for example, Rmax is about 3 μm and Ra is about 0.3 μm. The glass substrate that has undergone the second grinding step is substantially free from defects such as large undulations, chippings, and cracks.

In addition, there is a possibility that the grinding liquid or glass powder remains on the surface of the glass substrate that has undergone the grinding process. Therefore, in this embodiment, it is preferable to provide a cleaning process. In the cleaning process, various cleaning methods can be employed. For example, the glass substrate may be subjected only to alkali cleaning, may be subjected to acid cleaning after acid cleaning, or may be only subjected to acid cleaning.

<First polishing step (rough polishing step)>
The rough polishing step is a step of polishing both surfaces of the glass substrate so as to efficiently obtain the surface roughness finally required in the subsequent mirror polishing step. It does not specifically limit as a grinding | polishing method employ | adopted at this process, It can grind | polish using a double-side polisher.

As the polishing pad used, it is preferable to use a hard pad, for example, urethane foam is preferable because the shape change of the polishing surface increases when the hardness of the polishing pad decreases due to heat generated by polishing. The polishing liquid preferably uses cerium oxide having an average primary particle size of 0.6 to 2.5 μm as abrasive grains, and the abrasive grains are dispersed in water to form a slurry. The mixing ratio of water and cerium oxide is about 1: 9 to 3: 7. The polishing amount of the glass substrate in the rough polishing step is preferably about 25 to 40 μm. When the polishing amount of the glass substrate is less than 25 μm, there is a tendency that scratches and defects cannot be sufficiently removed. On the other hand, when the polishing amount of the glass substrate exceeds 40 μm, polishing is performed more than necessary, and the production efficiency tends to decrease.

<Second polishing step (mirror polishing step)>
The mirror polishing process has already been described above. The manufacturing method of the glass substrate of this Embodiment has a rinse process in a mirror polishing process, and the glass substrate which finished mirror polishing is wash | cleaned. Therefore, in the subsequent chemical strengthening process and final cleaning process, when the glass substrate is immersed in a strengthening treatment liquid or a cleaning liquid, the glass substrate is unlikely to contaminate these liquids. In addition, since the present embodiment includes the lubricating layer forming step, the lubricating layer is formed on the polishing pad cleaned by the rinsing step. When the glass substrate before mirror polishing is newly placed on the surface plate, a large frictional force is not generated between the polishing pad on which the lubricating layer is formed and the glass substrate. Therefore, in this embodiment, when mirror polishing is started, the horizontal movement of the glass substrate is not hindered, and thus the glass substrate that has undergone this step has excellent flatness.

<Chemical strengthening process>
The chemical strengthening step is a step of immersing the glass substrate in a strengthening treatment solution to improve the impact resistance, vibration resistance, heat resistance, and the like of the glass substrate.

The chemical strengthening method employed in the chemical strengthening step is not particularly limited, but usually, a glass substrate is immersed in a heated strengthening treatment solution, and alkali ions (for example, lithium ions) contained in the glass substrate have a relatively small ion radius. An ion exchange method is employed in which ions are replaced with alkali ions having a larger ion radius (for example, potassium ions and sodium ions). By adopting the chemical strengthening step, a reinforcing layer (ion exchange layer and compressive stress layer) can be formed on the main surface, outer peripheral end surface and inner peripheral end surface of the glass substrate.

In addition, after the chemical strengthening process, a standby process for waiting the glass substrate in the air and a water immersion process are adopted to remove the strengthening treatment liquid adhering to the surface of the glass substrate and to homogenize the surface of the glass substrate. It is preferable. By adopting such a process, the obtained glass substrate has a uniform chemical strengthening layer, a uniform compressive strain, hardly deforms, has good flatness, and is excellent in mechanical strength. The waiting time and the water temperature in the water immersing step are not particularly limited. For example, the water temperature may be waited for 1 to 60 seconds in the air and immersed in water at about 35 to 100 ° C., and is appropriately determined in consideration of manufacturing efficiency.

<Final cleaning process>
The final cleaning step is a step of cleaning and cleaning the glass substrate. It does not specifically limit as a washing | cleaning method, What is necessary is just the washing | cleaning method which can clean the surface of the glass substrate after a mirror polishing process. In the present embodiment, scrub cleaning is employed.

The cleaned glass substrate is subjected to ultrasonic cleaning and drying as necessary. The drying step is a step of drying the surface of the glass substrate after removing the cleaning liquid remaining on the surface of the glass substrate with isopropyl alcohol (IPA) or the like.

As the final cleaning step, for example, a step of performing a water rinsing cleaning step on the glass substrate after the scrub cleaning for 2 minutes to remove a residue of the cleaning liquid can be employed. Next, as the final cleaning process, an IPA cleaning process is performed for 2 minutes, and a process of removing water remaining on the surface of the glass substrate by IPA can be employed. Finally, the final cleaning step may employ a step of performing the IPA vapor drying step for 2 minutes and drying while removing the liquid IPA adhering to the surface of the glass substrate with the IPA vapor.

The method for drying the glass substrate is not particularly limited, and a known drying method such as spin drying or air knife drying can be employed. After the glass substrate that has undergone these steps is inspected for scratches, cracks, adhesion of foreign matter, etc. visually or using an optical surface analyzer (for example, “OSA6100” manufactured by KLA-TENCOL), the foreign matter etc. In a clean environment, it is stored in a dedicated storage cassette, vacuum packed, and then shipped.

The present embodiment is not limited to the HDD manufacturing method, and can be used as a manufacturing method of a magneto-optical disk, an optical disk, or the like.

In addition, as necessary, this embodiment is designed to change the grinding process into two processes in order, to omit the rough polishing process, to perform the chemical strengthening process before the mirror polishing process, etc. Is possible.

Furthermore, the present embodiment may perform chemical strengthening treatment on the outer peripheral end face and inner peripheral end face other than the main surface of the glass substrate as a measure for drop strength, or as an edge mitigation process for scratches generated on the glass substrate. The substrate may be subjected to a hydrogen fluoride immersion treatment.

As mentioned above, according to this Embodiment, the manufacturing method of the glass substrate for HDD for obtaining the glass substrate which has the outstanding flatness and few microwaviness can be provided.

The technical features of the glass substrate manufacturing method are summarized below.

The method for producing a glass substrate of the present invention has a mirror polishing process using a double-side polishing machine having upper and lower surface plates provided with a polishing pad, and the mirror polishing process is performed on the glass substrate and the polishing pad after mirror polishing. A rinsing step for cleaning the remaining abrasive slurry, and a lubricating layer forming step for moving the glass substrate that has undergone the rinsing step and adding an abrasive slurry containing colloidal silica to the polishing pad to form a lubricating layer. The average primary particle diameter of the colloidal silica is 15 to 90 nm, and the surface density of the colloidal silica in the lubricating layer is 10 to 500 particles / μm ² .

By washing the glass substrate that has undergone the mirror polishing process in the washing process, the glass substrate is less likely to contaminate the cleaning liquid in the subsequent process. Further, the cleaned polishing pad of the surface plate has a lubrication layer newly containing colloidal silica. Therefore, when the glass substrate before mirror polishing is newly arranged on the surface plate, a large frictional force is unlikely to be generated between the glass substrate and the polishing pad. As a result, when mirror polishing is started, the glass substrate smoothly moves horizontally, and the horizontality of the glass substrate during mirror polishing is maintained. Therefore, a glass substrate having excellent flatness and less microwaviness can be obtained.

It is preferable that the polishing pad has a holding means for holding the lubricating layer on the surface layer portion.

Since the polishing pad has the holding means, the colloidal silica abrasive grains are continuously held on the surface layer portion of the polishing pad during the mirror polishing process, and can come into contact with the glass substrate. As a result, the polishing accuracy is improved, and the flatness of the resulting glass substrate can be further improved.

Hereafter, the manufacturing method of the glass substrate of this invention is explained in full detail by an Example. In addition, the manufacturing method of the glass substrate of this invention is not limited to the Example shown below at all.

<Example 1>
A glass substrate was prepared by the following method.

[Blanks manufacturing process]
As the glass material, an aluminosilicate glass mainly composed of SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li) is used, and the molten glass material is press-molded, and the outer diameter is 67 mm. Disk-shaped blanks were produced. The thickness of the blanks was 1.0 mm.

[First grinding process]
Both main surfaces of the blanks were ground using a double-side grinding machine (Hamai Sangyo Co., Ltd., 16B type). As grinding conditions, alumina powder having a particle size of # 600 was used, the load was 50 g / cm ² , the upper surface plate rotation speed was 30 rpm, and the lower surface plate rotation speed was 20 rpm.

[Coring / Internal / External Grinding Process]
Using a core drill equipped with a cylindrical diamond grindstone, a circular center hole having a diameter of about 19.6 mm was formed in the center of the blank. Using a drum-shaped diamond grindstone, the outer peripheral end surface and the inner peripheral end surface of the blanks were processed to have an inner diameter and an outer diameter of 65 mm in outer diameter and 20 mm in inner diameter.

[Inner grinding / outer grinding]
100 blanks were stacked, and in this state, the outer peripheral end surface and the inner peripheral end surface of the blanks were polished using an end surface polishing machine (TKV-1 manufactured by Hadano Machinery Co., Ltd.). Nylon fiber having a diameter of 0.2 mm was used as the brush hair of the polishing machine. As the polishing liquid, a slurry containing cerium oxide having an average primary particle diameter of 3 μm as abrasive grains (polishing liquid component) was used.

[Second grinding process]
Both surfaces of the blanks were ground again using a double-side grinding machine (Hamai Sangyo Co., Ltd., 16B type). As grinding conditions, diamond pellets of # 1700 mesh were used, the load was 100 g / cm ² , the upper platen was rotated at 30 rpm, and the lower platen was rotated at 20 rpm.

[Rough polishing process]
Both surfaces of the blanks were roughly polished using a double-side polishing machine (Hamai Sangyo Co., Ltd., 16B type). A foamed urethane pad was used as the polishing pad, and a cerium oxide abrasive having an average primary particle diameter of 1 μm was used as the abrasive. The load was 100 g / cm ² .

[Mirror polishing process]
(Rinse process)
First, a glass substrate that had been mirror-polished before this example was washed with pure water together with a surface plate having a polishing pad. The washing conditions were a washing time of 5 minutes, a water temperature of 20 ° C., 5 L / min, and a water pressure of about 250 kPa. As the polishing pad, a soft suede pad (NP225 manufactured by Filwel, hardness Asker-C hardness 76) was used. The surface of the polishing pad was cut by 50 μm from the initial state where buffing was not performed by surface buffing.

(Lubrication layer forming process)
Next, the glass substrate was moved, a polishing slurry was added to the polishing pad, and a lubricating layer was formed on the polishing pad. The added polishing slurry was a slurry obtained by dispersing colloidal silica having an average primary particle size of 20 nm as abrasive grains (polishing component) in water. The mixing ratio of water and abrasive grains in the polishing slurry was adjusted between 99: 1 and 80:20 so that the surface density of the colloidal silica in the lubricating layer of the polishing pad was a predetermined value. Further, the pH was adjusted to 4.5 with an adjusting solution containing sulfuric acid.

The surface density of the colloidal silica in the lubricating layer of the obtained polishing pad was 120 / μm ² . The surface density was calculated by drying the polishing pad with the lubricating layer formed and measuring the number of colloidal silica particles on the surface with a scanning electron microscope (SEM). About the aggregated colloidal silica, the number was estimated from the area, and it was set as the number of particles of colloidal silica.

Using the polishing pad on which the lubricating layer was formed, both main surfaces of the glass substrate were polished more precisely by using a double-side polishing machine (Type 16B, manufactured by Hamai Sangyo Co., Ltd.). As the abrasive slurry, colloidal silica having an average primary particle diameter of 20 nm was dispersed in water as abrasive grains (polishing liquid component) to form a slurry, and the mixing ratio of water and abrasive grains was 80:20 did. Furthermore, pH was adjusted with the adjustment liquid containing a sulfuric acid. The load was 120 g / cm ² . In this step, 100 batches of glass substrates were processed into 5 batches.

[Chemical strengthening process]
Subsequently, the obtained glass substrate was chemically strengthened. As the chemical strengthening treatment liquid, an aqueous solution of a mixed molten salt of potassium nitrate (KNO ₃ ) and sodium nitrate (NaNO ₃ ) was used. The mixing ratio was 1: 1 by mass ratio. The temperature of the chemical strengthening treatment liquid was 380 ° C., and the immersion time was 25 minutes.

[Final cleaning process]
The glass substrate was scrubbed. As a cleaning liquid, a liquid obtained by diluting KOH and NaOH mixed at a mass ratio of 1: 1 with ultrapure water (DI water) and adding a nonionic surfactant to enhance the cleaning performance is obtained. Using. The cleaning liquid was supplied by spraying. After scrub cleaning, in order to remove the cleaning liquid remaining on the surface of the glass substrate, a water rinse cleaning process is performed in an ultrasonic bath for 2 minutes, an IPA cleaning process is performed in an ultrasonic bath for 2 minutes, and finally the glass substrate is cleaned with IPA vapor. The surface of was dried.

<Example 2>
A glass substrate was produced in the same manner as in Example 1 except that the surface density of the colloidal silica in the lubricating layer forming step was 200 pieces / μm ² .

<Example 3>
A glass substrate was produced in the same manner as in Example 1 except that the surface density of the colloidal silica in the lubricating layer forming step was 400 / μm ² .

<Example 4>
A glass substrate was produced in the same manner as in Example 1 except that the average primary particle diameter of colloidal silica in the lubricating layer forming step was 80 nm and the surface density was 200 particles / μm ² .

<Example 5>
A glass substrate was produced in the same manner as in Example 1 except that the surface density of the colloidal silica in the lubricating layer forming step was 12 / μm ² .

<Example 6>
A glass substrate was produced in the same manner as in Example 1 except that the surface density of the colloidal silica in the lubricating layer forming step was 80 / μm ² .

<Comparative Example 1>
A glass substrate was produced in the same manner as in Example 1 except that the lubricating layer forming step was not adopted.

<Comparative example 2>
A glass substrate was produced in the same manner as in Example 1 except that the surface density of the colloidal silica in the lubricating layer forming step was 8 pieces / μm ² .

<Comparative Example 3>
A glass substrate was produced in the same manner as in Example 1 except that the surface density of the colloidal silica in the lubricating layer forming step was 800 pieces / μm ² .

<Comparative Example 4>
A glass substrate was produced in the same manner as in Example 1 except that the average primary particle diameter of colloidal silica in the lubricating layer forming step was 10 nm.

<Comparative Example 5>
A glass substrate was produced in the same manner as in Example 1 except that the average primary particle diameter of colloidal silica in the lubricating layer forming step was 100 nm and the surface density was 200 particles / μm ² .

The glass substrates obtained in Examples 1 to 6 and Comparative Examples 1 to 5 were subjected to flatness measurement, microwaviness measurement, and deposit inspection. The test method is shown below, and the results are shown in Table 1.

[Flatness measurement]
It measured using the surface shape measuring apparatus (The phase shift technology company make, Optiflat).
(Evaluation criteria)
A: The flatness was less than 0.3 μm.
A: The flatness was 0.3 μm or more and less than 0.6 μm.
X: The flatness was 0.6 μm or more.

[Small waviness measurement]
It measured using the optical measuring device (The Zygo company make, Newview5000). The measurement was performed at a surface point of 29 mm in the radial direction from the center of the glass substrate, and the arithmetic average roughness for the waviness component having a wavelength of 50 to 300 μm was evaluated.
(Evaluation criteria)
A: The arithmetic average roughness was less than 1.0 mm.
X: The arithmetic average roughness was 1.0 mm or more.

[Adhesion inspection]
Deposits on the surface of the glass substrate were measured with a laser surface inspection apparatus (OSA6100, manufactured by KLA-TENCOR).
(Evaluation criteria)
○: The number of defects was 29 or less.
X: The number of defects was 30 or more.

As shown in Table 1, in the glass substrate production methods of Examples 1 to 6, glass substrates having excellent flatness, small undulations, and few deposits were obtained. In Comparative Example 1, friction acted on the substrate in the initial stage of processing, and the flatness was 0.6 μm or more. In Comparative Example 2, since the surface density of the colloidal silica held in the lubricating layer was small, the effect as the lubricating layer was not obtained, the friction acted on the substrate in the initial stage of processing, and the flatness was 0.6 μm or more. It was. In Comparative Example 3, since the surface density of the colloidal silica held in the lubricating layer was too large, the amount of deposits increased. In Comparative Example 4, since the average primary particle diameter of the colloidal silica held in the lubricating layer was small, sufficient lubrication performance was not exhibited, friction acted on the substrate at the initial stage of processing, and the flatness was 0.6 μm or more. It was. In Comparative Example 5, since the average primary particle diameter of the colloidal silica held in the lubricating layer was too large, the value of the microwaviness was high.

Claims (2)

Having a mirror polishing process using a double-side polishing machine having upper and lower surface plates with polishing pads;
The mirror polishing process includes
A rinsing step of cleaning the abrasive slurry remaining on the glass substrate and the polishing pad after mirror polishing;
A lubricating layer forming step of moving the glass substrate that has undergone the rinsing step and adding an abrasive slurry containing colloidal silica to the polishing pad to form a lubricating layer;
The colloidal silica has an average primary particle size of 15 to 90 nm,
The method for producing a glass substrate for HDD, wherein the surface density of the colloidal silica in the lubricating layer is 10 to 500 pieces / μm ² . The manufacturing method of the glass substrate for HDD of Claim 1 with which the said polishing pad has a holding means to hold | maintain a lubricating layer in the surface layer part.