JP2014191851A - Manufacturing method of glass substrate for information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a glass substrate for an information recording medium capable of reducing a change in a signal-to-noise ratio (SNR) of the information recording medium even in the case where "acceptance cleaning" is performed.SOLUTION: A manufacturing method of a glass substrate for an information recording medium used for an information recording medium includes: a step of preparing a glass substrate; a first polishing step of polishing the glass substrate; a step of applying chemical strengthening treatment to the polished glass substrate; a second polishing step of polishing the glass substrate to which the chemical strengthening treatment has been applied; and a step of cleaning the polished glass substrate. In a composition of the glass substrate, a ratio of [LiO+NaO+KO] is 7 mass% to 30 mass%, and the total variation in the composition of [LiO+NaO+KO] on a top layer of the glass substrate to the end of the step of cleaning the glass substrate after the second polishing step is within 50ng/cm.

Description

  The present invention relates to a method for producing a glass substrate for an information recording medium.

  In recent years, in a hard disk drive (HDD) device, the recording density has been increased. As the recording density is increased, the gap between the information recording medium (medium) and the head that reads and writes the recording while floating on the information recording medium is narrowed to about several nanometers.

  A glass substrate for an information recording medium used for an information recording medium (hereinafter sometimes simply referred to as a glass substrate) reduces surface defects of the glass substrate in order to cope with an increase in recording density, I try not to cause a collision.

In the case of a glass substrate used in a hard disk drive device having a recording density of 600 Gbit / inch ² (surface recording density) or more, in order to improve the cleanliness of the surface of the glass substrate, before the formation of the magnetic thin film layer on the glass substrate, After the final cleaning step, a step of cleaning the glass substrate with an alkaline solution and removing a small amount of particles on the glass substrate is newly introduced (see Patent Document 1).

However, it is compatible with the next generation of 630 Gbit / inch ² (surface recording density), and in particular records information on glass substrates with many alkali metals and alkaline earth metal components, and glass substrates that have been subjected to chemical strengthening (surface strengthening). When used as a glass substrate for a medium, there is a problem that the electromagnetic conversion characteristics (SNR) are lowered although there is no problem in smoothness and cleanliness.

  As a result of scrutinizing such a glass substrate, after forming a magnetic thin film layer on the manufactured glass substrate, the signal-to-noise ratio of the magnetic signal varies, which may cause read / write errors. Sex was found. As a result of further investigation on the cause of the variation in the signal-to-noise ratio of the magnetic signal, the following was found.

  A glass substrate used for an information recording medium is once sealed after being manufactured, and is packed in a transport BOX and transported. Next, the glass substrate is unpacked and taken out from the transfer BOX. Then, it is used for the process of apply | coating a magnetic layer to a glass substrate.

  At this time, the surface state of the glass substrate may become non-uniform or fine particles may adhere during packing, transporting, or taking out. In order to make the surface state of the glass substrate uniform, a detergent having a characteristic such as a relatively high detergency such as an alkaline solution and, in some cases, slightly dissolving the surface of the glass substrate is used. Cleaning (hereinafter referred to as “acceptance cleaning”) is performed (see Patent Document 2).

International Publication No. 2008/004470 JP 2006-127624 A

  The above-mentioned variation in the signal-to-noise ratio of the magnetic signal is caused by the alkali cleaning performed immediately before the formation of such a magnetic thin film layer because the stable state of the glass surface is impaired, and the glass substrate itself is inspected after manufacturing. However, it became clear that the cause could not be determined. Furthermore, it was also found that the variation in resistance to alkali cleaning of the glass substrate is also a cause of variation in the signal-to-noise ratio of the magnetic signal.

  Usually, in order to drop metallic deposits, an acidic detergent is used in the step of washing the glass substrate with an acidic detergent and the step of transporting the glass substrate to the next step. However, a glass substrate with a large amount of alkali metal and / or alkaline earth metal, or a glass substrate subjected to chemical strengthening treatment (surface strengthening treatment), the alkali metal is eluted from the surface layer of the glass substrate during the process using acid. It was found that the alkali durability in “acceptance cleaning” varies depending on the elution amount. As a result, signal-to-noise ratio (S / N ratio: SNR) varies between batches.

  The present invention has been made in view of the above situation, and even when “acceptance cleaning” is performed, by suppressing the elution amount of alkali metal from the surface layer of the glass substrate to a predetermined range. A method of manufacturing a glass substrate for an information recording medium that can suppress a change in signal-to-noise ratio (SNR) of the information recording medium even when the information recording medium is manufactured using the glass substrate The purpose is to provide.

In the manufacturing method of the glass substrate for information recording media based on this invention, it is a manufacturing method of the glass substrate for information recording media used for an information recording medium, Comprising: The process of preparing a glass substrate, The said glass substrate is grind | polished. A first polishing step, a step of subjecting the glass substrate subjected to polishing to a chemical strengthening treatment, a second polishing step of polishing the glass substrate subjected to the chemical strengthening treatment, and the polished glass A step of cleaning the substrate, wherein the composition of the glass substrate is such that the ratio of [Li ₂ O + Na ₂ O + K ₂ O] is 7% by mass to 30% by mass, and the glass substrate is disposed after the second polishing step. The total change amount of the composition of [Li ₂ O + Na ₂ O + K ₂ O] on the surface layer of the glass substrate is 50 ng / cm ^{3 or} less until the cleaning step is completed.

In another embodiment, the total change amount of the composition of [Li ₂ O + Na ₂ O + K ₂ O] is within 40 ng / cm ³ .

  In another embodiment, the amount of change in the composition of the surface layer of the glass substrate after the second polishing step until the step of washing the glass substrate is completed is such that Li is 0.1 mass% or more 1 Mass% or less, Na is 0.1 mass% or more and 2.1 mass% or less, and K is 0.05 mass% or more and 0.5 mass% or less.

  In another embodiment, the amount of change in the composition of the surface layer of the glass substrate is such that Na is 0.1% by mass or more and 1.0% by mass or less, and K is 0.05% by mass or more and 0.1% by mass or less. .

  According to the present invention, even when “acceptance cleaning” is performed, the amount of alkali metal eluted from the surface layer of the glass substrate is suppressed to a predetermined range, so that the information recording medium can be used with the glass substrate. Even when manufactured, it is possible to provide a method for manufacturing a glass substrate for an information recording medium that can suppress a small change in the signal-to-noise ratio (SNR) of the information recording medium. To do.

It is a perspective view of the glass substrate for information recording media in an embodiment. It is a perspective view of the information recording medium in an embodiment. It is a flowchart which shows the manufacturing method of the information recording medium in embodiment. For a glass substrate that has been subjected to a “chemical strengthening step” and a glass substrate that has not been subjected to a “chemical strengthening step”, (A) is an elution amount of an alkali component when a “step” that does not contact an acid is employed, (B) is a figure which shows the elution amount of an alkali component at the time of employ | adopting the "process" with many contacts to an acid. It is a figure which shows the evaluation result of the glass substrate for information recording media in Examples 1-3 and Comparative Examples 1-2. It is a figure which shows the evaluation result of the glass substrate for information recording media in Examples AH.

  Embodiments and examples of the present invention will be described below. The same or corresponding parts are denoted by the same reference symbols, and the description thereof may not be repeated. In the embodiments and examples described below, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified. In the following embodiments, each component is not necessarily essential to the present invention unless otherwise specified.

In the present embodiment, “%” indicating a glass composition indicates “mol%” unless otherwise specified. An addition notation of a chemical formula such as “Li ₂ O + Na ₂ O + K ₂ O” indicates the total amount of components represented by such chemical formula. For example, “Li ₂ O + Na ₂ O + K ₂ O” indicates the total amount of Li ₂ O, Na ₂ O, and K ₂ O.

(Configuration of information recording medium 1)
With reference to FIG. 1 and FIG. 2, the structure of the glass substrate 1G for information recording media and the information recording medium 1 is demonstrated. FIG. 1 is a perspective view of a glass substrate 1G for an information recording medium, and FIG. 2 is a perspective view of the information recording medium.

  As shown in FIG. 1, an information recording medium glass substrate 1G used for the information recording medium 1 (hereinafter referred to as “glass substrate 1G”) has an annular disk shape with a hole 11 formed in the center. ing. The glass substrate 1G has an outer peripheral end face 12, an inner peripheral end face 13, a front main surface 14, and a back main surface 15. As the glass substrate 1G, amorphous glass or the like is used. For example, the outer diameter is about 65 mm, the inner diameter is about 20 mm, the thickness is about 0.8 mm, and the surface roughness is about 2.0 mm or less.

  The inch size of the glass substrate 1G is not particularly limited, and various glass substrates 1G of 0.8 inch, 1.0 inch, 1.8 inch, 2.5 inch, and 3.5 inch are manufactured as disks for information recording media. May be.

  The thickness of the glass substrate 1G is preferably 0.30 mm to 2.2 mm because it is effective against cracking of the glass substrate 1G due to drop impact. The thickness of the glass substrate 1 </ b> G here means an average value of values measured at some arbitrary points to be pointed on the substrate.

The size of the glass substrate 1 is, for example, 0.8 inch, 1.0 inch, 1.8 inch, 2.5 inch, or 3.5 inch. The thickness of the glass substrate is, for example, 0.30 mm to 2.2 mm from the viewpoint of preventing breakage. In the present embodiment, the glass substrate has an outer diameter of about 64 mm, an inner diameter of about 20 mm, and a thickness of about 0.8 mm. The thickness of the glass substrate is a value calculated by averaging the values measured at a plurality of arbitrary points to be pointed on the glass substrate. From the viewpoint of increasing the hardness of the glass substrate, the Vickers hardness of the glass substrate 1 is preferably 610 kg / mm ² or more.

The glass substrate may have any composition as long as the glass transition temperature (Tg) is glass of 650 ° C. or higher, but the ratio of Li ₂ O + Na ₂ O + K ₂ O is 7% by mass to 30% by mass. If the composition contains a lot of alkali components, the SNR change due to elution of the alkali components becomes larger, so that the effects in this embodiment may be remarkably obtained.

In the present embodiment, the ratio of SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ is 50 mass (wt)% to 85 mass (wt)%, and the ratio of MgO + CaO + K ₂ O is 2 mass (wt)% to 20 The mass (wt)% is preferred.

  Furthermore, in the chemical strengthening step (S70) described later, it is more preferable to use a glass having the following composition from the viewpoint that the aluminosilicate glass easily forms a stress layer by ion exchange.

Preferred glass substrate compositions include, for example, SiO ₂ of 50 mass (wt)% to 70 mass (wt)%, Al ₂ O ₃ of 0 mass (wt)% to 20 mass (wt)%, B ₂ O. ₃ is 0 mass (wt)% to 5 mass (wt)%, P ₂ O ₅ is 0.1 mass (wt)% to 3 mass (wt)%, Na ₂ O is 2 mass (wt)% ~ 6 mass (wt)%, MgO is 6 mass (wt)% to 12 mass (wt)%, CaO is 0.1 mass (wt)% to 3 mass (wt)%, ZnO is 3 mass ( wt)% to 8 mass (wt)%, TiO ₂ is 3 mass (wt)% to 8 mass (wt)%, Li ₂ O is 0 mass (wt)% to 4 mass (wt)%, Na ₂ O is 2 mass (wt)% to 6 mass (wt)%, and K ₂ O is 0 mass (wt)% to 3 mass (wt)%.

  As shown in FIG. 2, in the information recording medium 1, a magnetic thin film layer 23 is formed on the front main surface 14 of the glass substrate 1G. In the figure, the magnetic thin film layer 23 is formed only on the front main surface 14, but it is also possible to provide the magnetic thin film layer 23 on the back main surface 15.

  As a method of forming the magnetic thin film layer 23, a conventionally known method can be used. For example, a method of spin-coating a thermosetting resin in which magnetic particles are dispersed on the glass substrate 1G, a method of forming by sputtering. The method of forming by electroless plating is mentioned.

  The film thickness by spin coating is about 0.3 to 1.2 μm, the film thickness by sputtering is about 0.04 to 0.08 μm, and the film thickness by electroless plating is 0.05 to 0.1 μm. From the viewpoint of thinning and high density, film formation by sputtering and electroless plating is preferable.

  The magnetic material used for the magnetic thin film layer 23 is not particularly limited, and a conventionally known material can be used. However, in order to obtain a high coercive force, Co having high crystal anisotropy is basically used for the purpose of adjusting the residual magnetic flux density. Co-based alloys to which Ni and Cr are added are suitable. In recent years, FePt-based materials have been used as magnetic layer materials suitable for heat-assisted recording.

  In order to improve the sliding of the magnetic head, the surface of the magnetic thin film layer 23 may be thinly coated with a lubricant. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

  If necessary, an underlayer and a protective layer may be provided. The underlayer in the information recording medium 1 is selected according to the magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni.

  The underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

  Examples of the protective layer for preventing wear and corrosion of the magnetic thin film layer 23 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. The protective layer can be formed continuously with an in-line sputtering apparatus, such as an underlayer and a magnetic film. The protective layer may be a single layer, or may have a multilayer structure composed of the same or different layers.

  Another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, colloidal silica fine particles are dispersed and coated on a Cr layer diluted with an alcohol-based solvent, and then fired to form a silicon oxide (SiO2) layer. May be.

(Manufacturing process of glass substrate 1G)
Next, a method for manufacturing the glass substrate 1G and the information recording medium 1 according to the present embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing a method for manufacturing the glass substrate 1G and the information recording medium 1.

  First, in the “glass melting step” of step 10 (hereinafter abbreviated as “S10”, the same applies to step 11 and subsequent steps), the glass material constituting the glass substrate is melted.

  In the “press molding step” of S11, a glass substrate was produced by pressing the molten glass material using an upper mold and a lower mold. The glass composition used was a general aluminosilicate glass. The method for producing the glass substrate is not limited to molding, and may be cut out from plate glass, which is a known technique, and the glass composition is not limited thereto.

  In the “first lapping step” of S12, both main surfaces of the glass substrate were lapped. This first lapping step was performed using a double-sided lapping device using a planetary gear mechanism. Specifically, the lapping platen was pressed on both surfaces of the glass substrate from above and below, the grinding liquid was supplied onto the main surface of the glass substrate, and these were moved relatively to perform lapping. By this lapping process, a glass substrate having a substantially flat main surface was obtained.

  In the “coring step” of S13, a cylindrical diamond drill was used to form a hole in the center of the glass substrate to produce an annular glass substrate. The inner peripheral end surface and the outer peripheral end surface of the glass substrate were ground with a diamond grindstone, and a predetermined chamfering process was performed.

  In the “second lapping step” of S14, lapping was performed on both main surfaces of the glass substrate in the same manner as in the first lapping step (S12). By performing the second lapping step, the fine uneven shape formed on the main surface in the coring and end face processing in the previous step can be removed in advance. As a result, the polishing time of the main surface in the subsequent process can be shortened.

  In the “peripheral polishing step” of S15, the outer peripheral end face of the glass substrate was subjected to mirror polishing by brush polishing. At this time, as the abrasive grains, a slurry containing general cerium oxide abrasive grains was used. In the present embodiment, S10 to S15 are steps for preparing a glass substrate.

  In the “first polishing step” of S16, main surface polishing was performed. The first polishing step is mainly intended to correct scratches and warpage remaining on the main surface in the first and second lapping steps (S12, S14) described above. In the first polishing step, the main surface was polished by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, general cerium oxide abrasive grains were used.

  In the “chemical strengthening step” of S17, a surface reinforcing layer was formed on the main surface of the glass substrate 1G. Specifically, chemical strengthening was performed by immersing the glass substrate 1G in a mixed solution of potassium nitrate (70%) and sodium nitrate (30%) heated to 300 ° C. for about 30 minutes. As a result, the lithium ion and sodium ion on the inner peripheral end surface and outer peripheral end surface of the glass substrate are respectively replaced with sodium ions and potassium ions in the chemical strengthening solution, and a compressive stress layer is formed, thereby forming the main surface of the glass substrate and The end face was strengthened.

  In the “second polishing step” of S18, a main surface polishing step was performed. This second polishing step aims to eliminate the fine defects on the main surface that have been generated and remain in the above-described steps and finish it in a mirror shape, to eliminate warpage and finish it to a desired flatness. In the second polishing step, polishing was performed by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, colloidal silica having an average particle diameter of about 20 nm was used to obtain a smooth surface.

  In the “cleaning step” of S19, final cleaning of the main surface and end surface of the glass substrate is performed. Thereby, the deposits remaining on the glass substrate are removed.

  In the “inspection step” of S20, the amount of change in the composition of the surface layer of the glass substrate was inspected. After that, in the “magnetic thin film deposition step” of S21, both main surfaces of the glass substrate that passed the above-described inspection were subjected to an adhesion layer composed of a Cr alloy, a soft magnetic layer composed of a CoFeZr alloy, and an orientation control composed of Ru. An information recording medium of a perpendicular magnetic recording system was manufactured by sequentially forming a base layer, a perpendicular magnetic recording layer made of a CoCrPt alloy, a C-based protective layer, and an F-based lubricating layer. This configuration is an example of a configuration of a perpendicular magnetic recording system, and a magnetic layer or the like may be configured as an in-plane information recording medium. Thereafter, by performing a “post heat treatment step”, the information recording medium is completed.

  The manufacturing method of the glass substrate in this Embodiment is comprised as mentioned above. The glass substrate 1G shown in FIG. 1 is obtained by using this glass substrate manufacturing method. Thereafter, the information recording medium 1 shown in FIG. 2 is obtained using the glass substrate 1G thus obtained.

  Here, with reference to FIG. 4, (A) does not contact an acid with respect to the glass substrate which performed the above-mentioned "chemical strengthening process" of S17, and the glass substrate which has not performed the "chemical strengthening process". The elution amount of the alkali component when the “process” is adopted is shown, and (B) shows the elution amount of the alkali component when the “process” where the contact with the acid is large is adopted. Here, the “process” means a dipping process in water and a cleaning process between transports.

  In the case of (A), which employs a “process” that does not come into contact with acid, the elution amount of the alkali component of the glass substrate subjected to the “chemical strengthening step” is compared with the elution amount of the glass substrate not subjected to the “chemical strengthening step”. And there are few. However, in the case of (B), which employs a “process” that has a lot of contact with acid, the elution amount of the alkali component of the glass substrate subjected to the “chemical strengthening process” is the elution amount of the glass substrate not subjected to the “chemical strengthening process”. It is larger than the amount.

  If the elution amount of the alkali component is large during the manufacturing process of the glass substrate, the alkali cleaning resistance in the receiving cleaning is lowered and SNR variation is generated. Therefore, it is important to adopt a “process” that suppresses the elution amount of the alkali component during the manufacturing process of the glass substrate.

(Example)
Various conditions of the cleaning step (S18) after the second polishing step (S18) are set, and the surface layer of the glass substrate during the second polishing step (S18) until the step of cleaning the glass substrate is completed. The amount of change in composition was adjusted.

In the following examples, as a material of the glass substrate, by mass%, Li ₂ O = 4.0%, Na ₂ O = 11.0%, K ₂ O = 1.0%, MgO = 1.0%, CaO = 2.0%, SiO ₂ = 65.5%, Al ₂ O ₃ = 15.5% glass material was used.

  The glass substrates were manufactured up to the second polishing step (S18), with 100 batches as one batch. Then, it processed with the 50 mL solution of the conditions shown in the following Examples 1-comparative example 2. Then, 10 sheets were extracted, and the elution amounts of Li, Na, and K in the solution were evaluated using ICP-MS (inductively coupled plasma mass spectrometer, SPQ9700 manufactured by SII Nano Technology).

  Further, 10 pieces were extracted from the remaining, and the amount of Si elution when treated with pH 11 NaOH at 40 ° C. for 30 minutes was measured with ICP-AES (inductively coupled plasma emission spectrometer, SPS3520UV manufactured by SII Nano Technology). , “Average value” and “3σ”.

A magnetic thin film layer was formed on the remaining 80 glass substrates, and SNR evaluation was performed. (Of the processed 100 sheets, 10 were processed with single wafers, and the remaining 90 were manufactured in a normal manufacturing process.)
In Examples 1 and 2 shown below, FIG. 5 shows the elution amount (ng / cm ³ ), Li elution amount (ppb), and SNR change (db) of Li + Na + K. In FIG. 5, the value in () of the Si elution amount indicates a value of 3σ. The smaller the value, the smaller the variation.

  The judgment criteria are “AAA” for +0.15 db, “AA” for 0 or more and less than 0.15 db, “A” for less than 0 and −0.1 db or less, and “A” for 0 to −0.1 db or less. “B” and −0.11 to 0.20 db were evaluated as “C”, −0.21 to 0.30 db as “D”, and −0.31 db and “E” as “E”.

Example 1
Between each process, in a conveyance process (immersion), after being immersed in a solution of pH 8 for 1 minute, the process proceeds to the next process, and the cleaning process (S19) after the second polishing process (S18) is performed using an alkaline detergent. I did it. In Example 1, the elution amount of Li + Na + K was 33 ng / cm ³ , the Si elution amount was 80 ppb (the value of 3σ was “6”), and the SNR change was 0 db. The determination was “B”.

(Example 2)
Between each process, in the conveyance process (immersion), after being immersed in pure water of pH 7 for 1 minute, the process proceeds to the next process, and the cleaning process (S19) after the second polishing process (S18) is performed using an alkaline detergent. It was done. In Example 2, the elution amount of Li + Na + K was 35 ng / cm ³ , the Si elution amount was 100 ppb (the value of 3σ was “9”), and the SNR change was −0.01 db. The determination was “B”.

(Example 3)
Between each process, in a conveyance process (immersion), after being kept in pure water of pH 7 for 5 minutes, the process proceeds to the next process, and the cleaning process (S19) of the second polishing process (S18) is performed using an alkaline detergent. I did it. In Example 3, the elution amount of Li + Na + K was 48 ng / cm ³ , the Si elution amount was 105 ppb (the value of 3σ was “10”), and the SNR change was −0.03 db. The determination was “C”.

(Comparative Example 1)
Between each process, in a conveyance process (immersion), after being kept in a solution of pH 3 for 5 minutes, the process proceeds to the next process, and the cleaning process (S19) of the second polishing process (S18) is performed using an alkaline detergent. It was. In Comparative Example 1, the elution amount of Li + Na + K was 55 ng / cm ³ , the Si elution amount was 200 ppb (the value of 3σ was “55”), and the SNR change was −0.4 db. The determination was “D”.

(Comparative Example 2)
Between each process, in a conveyance process (immersion), after being kept in a solution of pH 5 for 5 minutes, the process proceeds to the next process, and the cleaning process (S19) of the second polishing process (S18) is performed using an alkaline detergent. It was. In Comparative Example 1, the elution amount of Li + Na + K was 60 ng / cm ³ , the Si elution amount was 180 ppb (the value of 3σ was “40”), and the SNR change was −0.32 db. The determination was “D”.

(Examples A to H)
Various conditions of the cleaning step (S18) after the second polishing step (S18) were set to adjust the amount of change in alkali metal. The glass substrates were manufactured up to the second polishing step (S18), with 100 batches as one batch. The treatment was carried out with 50 mL of the solution so as to be the same conditions as the steps shown in Example 1 and Comparative Example 2.

  Thereafter, 10 samples were extracted, and the elution amount of Li, Na, K was evaluated using ICP-MS (inductively coupled plasma mass spectrometer, SPQ9700 manufactured by SII Nano Technology), and the elution amount of Li + Na + K was Confirmed to be the same.

  Ten sheets are extracted from the remaining 90 sheets, and XPS (Scanning X-ray Photoelectron Spectrometer, Quantera SXM manufactured by ULVAC-PHI) is used to perform elemental analysis of the extreme surface, compared to the original composition of Li, Na. , K change was evaluated.

  Furthermore, 10 sheets were extracted from the remaining 80 sheets, and the elution amount of Si when treated with pH 11 and NaOH for 30 minutes at 40 ° C. was measured with ICP-AES (inductively coupled plasma emission spectrometer, SPS3520UV manufactured by SII Nano Technology). Measured and evaluated by average value and 3σ.

Magnetic thin film layers were formed on the remaining 70 glass substrates, and SNR evaluation was performed. (Of the processed 100 sheets, 10 were processed with single wafers, and the remaining 90 were manufactured in a normal manufacturing process.)
In Examples A to H shown below, FIG. 6 shows the elution amount of Li + Na + K (ng / cm ³ ), the change amount of Li (mass%), the change amount of Na (mass%), and the change amount of K (mass%). ), Si elution amount (ppb), and SNR change (db). In FIG. 5, the value in () of the Si elution amount indicates a value of 3σ. The smaller the value, the smaller the variation. The judgment criteria are “AAA” when the SNR change is +0.15 db, “AA” when 0 or more and less than 0.15 db, “A” when less than 0 and less than −0.1 db, 0 to −0 .1 db or less was evaluated as “B”, −0.11 to 0.20 db as “C”, −0.21 to 0.30 db as “D”, and −0.31 db as “E”.

(Example A)
Between each process, in the transport process (immersion), the process proceeds directly to the next process within 1 minute (so that the surface of the glass substrate does not dry) without being immersed in the solution, and after the second polishing process (S18). The washing step (S19) was performed using an alkaline detergent. In Example A, the elution amount of Li + Na + K was 38 ng / cm ³ , the change amount of Li was 0.15 mass%, the change amount of Na was 0.10 mass%, and the change amount of K was 0.06 mass %, Si elution amount was 60 ppb (3σ value was “5”), and SNR change was 0.16 db. The determination was “AAA”.

(Example B)
Between each process, after being immersed in a pH 8 solution for 30 seconds in the transport process (immersion), the process proceeds to the next process, and the cleaning process (S19) after the second polishing process (S18) is performed using an alkaline detergent. I did it. In Example B, the elution amount of Li + Na + K was 38 ng / cm ³ , the change amount of Li was 0.30% by mass, the change amount of Na was 1.10% by mass, and the change amount of K was 0.08% by mass. %, The elution amount of Si was 80 ppb (the value of 3σ was “10”), and the SNR change was 0.04 db. The determination was “AA”.

(Example C)
Between each process, after being immersed in pH 7 pure water for 30 seconds in the transport process (immersion), the process proceeds to the next process, and the cleaning process (S19) after the second polishing process (S18) is performed using an alkaline detergent. It was done. In Example C, the elution amount of Li + Na + K is 38 ng / cm ³ , the change amount of Li is 0.25% by mass, the change amount of Na is 0.90% by mass, and the change amount of K is 0.13% by mass. %, Si elution amount was 85 ppb (the value of 3σ was “8”), and the SNR change was 0.05 db. The determination was “AA”.

(Example D)
Between each process, after being immersed in pure water of pH 7 for 1 minute in the transport process (immersion), the process proceeds to the next process, and the cleaning process (S19) after the second polishing process (S18) is performed using an alkaline detergent. It was done. In Example D, the elution amount of Li + Na + K was 38 ng / cm ³ , the change amount of Li was 0.30% by mass, the change amount of Na was 2.13% by mass, and the change amount of K was 0.40% by mass. %, The elution amount of Si was 100 ppb (the value of 3σ was “10”), and the SNR change was −0.02 db. The determination was “A”.

(Example E)
Between each process, after being immersed in a pH 8 solution for 1 minute in the transport process (immersion), the process proceeds to the next process, and the cleaning process (S19) after the second polishing process (S18) is performed using an alkaline detergent. I did it. In Example E, the elution amount of Li + Na + K was 38 ng / cm ³ , the change amount of Li was 0.33 mass%, the change amount of Na was 0.33 mass%, and the change amount of K was 0.54 mass %, Si elution amount was 90 ppb (the value of 3σ was “10”), and the SNR change was −0.06 db. The determination was “A”.

(Example F)
Between each process, after being immersed in a pH 7.5 solution for 1 minute in the transport process (immersion), the process proceeds to the next process, and the cleaning process (S19) after the second polishing process (S18) is performed with an alkaline detergent. Performed. In Example F, the elution amount of Li + Na + K is 38 ng / cm ³ , the change amount of Li is 1.03% by mass, the change amount of Na is 0.38% by mass, and the change amount of K is 0.17 mass%. %, The elution amount of Si was 100 ppb (the value of 3σ was “7”), and the SNR change was −0.07 db. The determination was “A”.

(Example G)
Between each process, after being allowed to stay in the pH 8 solution for 5 minutes in the transport process (immersion), the process proceeds to the next process, and the cleaning process (S19) after the second polishing process (S18) is performed using an alkaline detergent. I did it. In Example G, the elution amount of Li + Na + K is 38 ng / cm ³ , the change amount of Li is 0.90% by mass, the change amount of Na is 2.13% by mass, and the change amount of K is 0.52% by mass. %, The elution amount of Si was 105 ppb (the value of 3σ was “10”), and the SNR change was −0.15 db. The determination was “B”.

(Example H)
Between each process, after being kept in pure water of pH 7 for 5 minutes in the transport process (immersion), the process proceeds to the next process, and the cleaning process (S19) after the second polishing process (S18) is performed using an alkaline detergent. It was done. In Example H, the elution amount of Li + Na + K was 38 ng / cm ³ , the change amount of Li was 1.02 mass%, the change amount of Na was 2.22 mass%, and the change amount of K was 0.60 mass %, The elution amount of Si was 110 ppb (the value of 3σ was “8”), and the SNR change was −0.17 db. The determination was “B”.

According to the above Examples 1 to 3, Examples A to H, and Comparative Examples 1 and 2, the glass substrate was composed of a glass material having a relatively large proportion of Li ₂ O + Na ₂ O + K ₂ O. Even in this case, the total change amount of the composition of [Li ₂ O + Na ₂ O + K ₂ O] on the surface layer of the glass substrate until the step of cleaning the glass substrate after the second polishing step is completed is 50 ng. Even when the information recording medium is manufactured using the glass substrate by performing cleaning under the conditions within / cm ³ (Examples 1 to 3, Examples A to H), the SNR of the information recording medium It is possible to reduce the change of.
)
If the total change amount of the composition of [Li ₂ O + Na ₂ O + K ₂ O] is within 40 ng / cm ³ (Examples 1, 2, and Examples A to H), the change in SNR of the information recording medium is further reduced. It becomes possible to do.

  The amount of change in the composition of the surface layer of the glass substrate during the period after the second polishing step until the step of cleaning the glass substrate is completed, Li is 0.1 mass% or more and 1 mass% or less, and Na is 0.1 mass % To 2.1% by mass and K is 0.05% to 0.5% by mass (Examples A to C), the change in SNR of the information recording medium (+0.04 to +0.16) can be reduced.

  More preferably, the amount of change in the composition of the surface layer of the glass substrate is such that Na is 0.1% by mass or more and 1.0% by mass or less, and K is 0.05% by mass or more and 0.1% by mass or less (Example) B) The SNR change (+0.04) of the information recording medium can be further reduced.

  Although the embodiments and examples of the present invention have been described above, the embodiments and examples disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Information recording medium, 1G Glass substrate for information recording media, 11 hole, 12 outer peripheral end surface, 13 inner peripheral end surface, 14 front main surface, 15 back main surface, 23 magnetic thin film layer.

Claims (4)

A method for producing a glass substrate for an information recording medium used for an information recording medium,
Preparing a glass substrate;
A first polishing step for polishing the glass substrate;
Applying chemical strengthening treatment to the polished glass substrate;
A second polishing step of polishing the glass substrate subjected to the chemical strengthening treatment;
Cleaning the polished glass substrate;
With
The composition of the glass substrate is such that the ratio of [Li ₂ O + Na ₂ O + K ₂ O] is 7% by mass to 30% by mass,
The total change amount of the composition of [Li ₂ O + Na ₂ O + K ₂ O] on the surface layer of the glass substrate after the second polishing step until the step of cleaning the glass substrate is completed is 50 ng / cm ^3. The manufacturing method of the glass substrate for information recording media which is within. The total amount of change in composition of _{[Li 2 O + Na 2 O} + K 2 O] is within 40 ng / cm ^3, a method of manufacturing a glass substrate for information recording medium according to claim 1.   The amount of change in the composition of the surface layer of the glass substrate during the period after the second polishing step until the step of cleaning the glass substrate is completed, Li is 0.1 mass% or more and 1 mass% or less, and Na is The manufacturing method of the glass substrate for information recording media of Claim 1 or 2 which is 0.1 mass% or more and 2.1 mass% or less and K is 0.05 mass% or more and 0.5 mass% or less.   The amount of change in the composition of the surface layer of the glass substrate is such that Na is 0.1 mass% or more and 1.0 mass% or less, and K is 0.05 mass% or more and 0.1 mass% or less. The manufacturing method of the glass substrate for information recording media of.

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