JP2014010869A - Method for manufacturing glass substrate for hdd - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a glass substrate for HDD which can improve the reliability of an HDD by stabilizing a glass substrate surface layer.SOLUTION: The method for manufacturing a glass substrate for HDD whose recording density is 600 Gbit/inchor more includes a second polish step (S18) for polishing a glass substrate and an aging step (S19) for performing heating treatment of the glass substrate in a gas phase after the second polish step (S18). A product between treatment temperature (unit: °C) and a treatment time (unit: minute) in the aging step (S19) is 1500 or more, and the treatment temperature is less than 40°C super glass transition point temperature.

Description

  The present invention relates to a method for manufacturing a glass substrate for an HDD (Hard Disk Drive).

  Conventionally, an aluminum substrate or a glass substrate is used as an information recording medium (magnetic disk recording medium) used in a computer or the like. A magnetic thin film layer is formed on these substrates, and information is recorded on the magnetic thin film layer by magnetizing the magnetic thin film layer with a magnetic head.

  The storage capacity of HDDs has increased dramatically year by year, and the recording density has also improved year by year. Accordingly, the recording area is further miniaturized, and it is indispensable to reduce the recording area of the medium spent for one bit. In order to improve the read / write function of the magnetic signal in a minute area, the size of the magnetic particle for recording must be reduced in proportion to the reduction in the recording area of the medium, and between the magnetic head and the information recording medium. The distance (flying height) is even smaller.

  As the flying height becomes smaller, there are problems such as read / write errors when accessing data recorded on the medium and head crashes when the magnetic head collides with the medium surface when the information recording medium is used in a hard disk drive. It is likely to occur. In order to suppress these problems, the size of defects on the substrate surface allowed as an information recording medium is also reduced. Therefore, as a glass substrate for information recording media, a glass substrate with higher surface smoothness has been pursued, and in order to suppress foreign matter adhering to the glass substrate surface and undulation of the glass substrate surface, various ingenuity has been applied to the manufacturing method. Has been made.

  On the other hand, in recent years, the storage capacity of HDDs has been further improved. At present, one 2.5-inch recording medium has a recording capacity of 500 GB (single-sided 250 GB) and a surface recording density of 600 Gbit / square inch or more. Things are being developed. In such a high recording density recording medium, even when a very smooth glass substrate was used, it was found that read / write errors during data access may occur, and the cause was analyzed. It turned out not to be an error due to a conventional head crash.

  Regarding the above-mentioned problems, we examined the glass substrate after manufacturing, including the surface condition, but found no defects that could cause read / write errors, and no specific solution was found. It was. However, as a result of further scrutinization, it was found that the signal-to-noise ratio of the magnetic signal varies after the magnetic layer is provided on the manufactured glass substrate, which may cause read / write errors. It was done.

  As a result of further investigation on the cause of the variation in the signal-to-noise ratio of the magnetic signal, the variation in the magnetic signal in the magnetic layer is still caused by the surface state of the glass substrate. found. Generally, a glass substrate for a recording medium is once sealed and packaged after being manufactured and then transported, and then taken out and subjected to a step of coating a magnetic layer. In that case, the surface state of a glass substrate may become non-uniform | heterogenous or few particles may adhere by the difference in the conditions at the time of packing, conveyance, and taking out. Therefore, in order to make the surface state uniform, cleaning is performed using a detergent such as an alkaline detergent that has a relatively high detergency and in some cases has a characteristic of slightly dissolving the surface. The above-mentioned variation in the signal-to-noise ratio of the magnetic signal is caused by the glass surface itself being inspected after manufacturing because the glass surface itself is damaged in the cleaning performed immediately before the coating of the magnetic layer. It became clear that the factor could not be found.

  Efforts to improve the stability of the glass substrate immediately before coating such a magnetic layer have not been studied before, but as a technology to improve the stability by suppressing the elution of components on the surface of the glass substrate, The alkali metal ions present on the surface of the material are replaced with lithium ions, followed by a two-step ion exchange treatment in which the lithium ions are replaced with hydrogen ions. There has been proposed a technique for providing a glass substrate that is suppressed and does not deteriorate in strength even when used and stored for a long time under high temperature and high humidity (for example, see Patent Document 1).

JP 2005-187239 A

  As described above, when the HDD recording density is increased to 600 Gbit / in 2 or more, it is not sufficient to increase only the surface smoothness of the glass substrate as in the prior art, and the glass just before the magnetic layer is applied. It is necessary to suppress read / write errors due to variations in the signal-to-noise ratio of the magnetic signal due to the surface state of the substrate.

  According to Patent Document 1, although it is possible to suppress the elution of the skeleton component on the surface of the glass substrate to some extent by a special treatment, a normal polishing step is performed after the above treatment, and the surface state changes as needed. For this reason, the surface state after manufacturing the glass substrate cannot always be controlled. For this reason, the stability of the glass substrate surface is not sufficient, and the elution of slight components occurs by washing with an alkaline detergent or the like applied immediately before applying the magnetic layer, and the signal of the magnetic signal generated thereby. It has been difficult to suppress read / write errors due to variations in the noise ratio.

  The present invention has been made in view of the above problems, and its main purpose is to stabilize the surface layer of the glass substrate and to increase the recording density of the HDD to 600 Gbit / in 2 or more even when the magnetic signal is recorded. An object of the present invention is to provide a method for manufacturing a glass substrate for HDD, which can suppress read / write errors due to variations in signal-to-noise ratio and thereby improve the reliability of the HDD.

  The present inventor has intensively studied in view of the above problems, and found that the magnetic characteristics of the HDD can be improved by sufficiently stabilizing the glass substrate surface layer in the glass substrate production process, and has completed the present invention.

That is, the method for manufacturing a glass substrate for HDD according to the present invention is a method for manufacturing a glass substrate for HDD having a recording density of 600 Gbit / inch ² or more, and includes a step of polishing the glass substrate, a step of polishing, Heat-treating the substrate in the gas phase. The product of the treatment temperature (unit: ° C) and the treatment time (unit: minutes) in the heat treatment step is 1500 or more, and the treatment temperature is higher than 40 ° C and less than the glass transition temperature.

  Preferably in the said manufacturing method, the relative humidity in the gaseous phase in the process of heat-processing is 50% or less. Preferably, the product of the treatment temperature (unit: ° C.) and the treatment time (unit: minutes) in the heat treatment step is 2,000 or more and 100,000 or less.

According to the present invention, the glass substrate surface layer can be stabilized by performing the heat treatment under the above conditions after the polishing step, and a reliable magnetic property is exhibited even in an HDD having a recording density of 600 Gbit / inch ² or more. A highly reliable HDD can be obtained.

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.

  Embodiments and examples of the present invention will be described below. Note that the same or corresponding portions are denoted by the same reference numerals, and the description thereof may not be repeated.

  Note that 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 for the present invention unless otherwise specified.

(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. 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 information recording medium 1 of this embodiment shown in FIG. 2 is an HDD. 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. The recording density of the HDD is 600 Gbit / inch ² or more. 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 for 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, a method of forming by sputtering, a method of electroless The method of forming by 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 a high crystal anisotropy is basically used to adjust 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, tetraalkoxysilane is diluted with an alcohol-based solvent on a Cr layer, and then colloidal silica fine particles are dispersed and applied, followed by baking to form a silicon oxide (SiO ₂ ) layer. It may be formed.

(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 “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 “aging process” of S19, the glass substrate after the polishing process is subjected to heat treatment in a gas phase. The heat treatment is performed by placing the glass substrate in a constant temperature and humidity atmosphere for a predetermined time. There is no particular limitation on the atmosphere in which the heat treatment is performed. For example, the glass substrate can be heat-treated in an arbitrary atmosphere such as the air, an O ₂ atmosphere, an N ₂ atmosphere, or an H ₂ atmosphere.

  By applying heat treatment to the glass substrate after the polishing step, the bonding state of the glass surface layer is stabilized. This is because the glass surface layer immediately after polishing is in an unstable state due to increased dangling bonds of Si, but dangling bonds on the glass surface layer are reduced by heat treatment in a constant temperature and humidity atmosphere. This is considered to be because the surface-bound state is stabilized. By stabilizing the bonding state of the glass surface layer, the signal-to-noise ratio characteristics are improved in the HDD formed through the subsequent steps. When heat treatment is performed in the liquid phase, the stability of the surface may be impaired depending on conditions. Therefore, in the present invention, heat treatment is performed in the gas phase.

  The heat treatment is performed on the glass substrate after the polishing process. This is because the surface of the glass substrate is activated in the polishing step, and the effect is lost even if the surface layer of the glass substrate is stabilized by heat treatment first. Similarly, the heat treatment is performed on the glass substrate after the chemical strengthening (ion exchange) treatment. This is because the glass surface layer after chemical strengthening is activated, and the effect is canceled even if the surface layer is first stabilized by heat treatment.

  The heat treatment is performed so that the product of the treatment temperature (unit: ° C.) and the treatment time (unit: minutes) is 1500 or more. If the product of the processing temperature and the processing time is less than 1500, the effect of stabilizing the surface layer of the glass substrate cannot be sufficiently obtained. A more preferable range is a range in which the product of the processing temperature (unit: ° C.) and the processing time (unit: minutes) is 2000 or more and 100,000 or less.

  The heat treatment is performed at a temperature lower than the glass transition temperature Tg. When the processing temperature is set to Tg or higher, the atomic structure in the glass starts to move as a whole, which may cause deformation of the glass substrate. The heat treatment is performed at a temperature higher than 40 ° C. When the processing temperature is 40 ° C. or lower, the temperature is low, and thus the effect of stabilizing the glass substrate surface layer cannot be sufficiently obtained.

  The heat treatment is preferably performed in an atmosphere having a relative humidity of 50% or less. By making the relative humidity 50% or less, the effect of stabilizing the surface layer of the glass substrate can be obtained more remarkably.

  Next, in the “final cleaning step” of S20, final cleaning of the main surface and the end surface of the glass substrate is performed. Thereby, the deposits remaining on the glass substrate are removed.

  In the “magnetic thin film layer forming step” of S21, after cleaning the glass substrate obtained through the above-described steps, an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoFeZr alloy, Ru on both main surfaces of the glass substrate, An information recording medium of a perpendicular magnetic recording system was manufactured by sequentially forming an orientation control underlayer made of, 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, the “post heat treatment step” of S22 is performed to complete the information recording medium.

  As described above, in the present embodiment, in the aging step (step 19), the glass substrate after the polishing treatment is placed in a constant temperature and humidity atmosphere for a predetermined time, and the glass substrate is subjected to heat treatment (aging treatment). Thereby, the surface layer of a glass substrate can be stabilized. If a magnetic film is formed on a heat-treated glass substrate to produce an HDD as an information recording medium, a highly reliable HDD showing good signal-to-noise ratio characteristics can be obtained even when used for a long period of time. it can.

Hereinafter, each Example and comparative example of the manufacturing method of the glass substrate for HDD are demonstrated. According to the flowchart shown in FIG. 3, information recording media of Examples and Comparative Examples were manufactured. In the examples and comparative examples, the SiO ₂ of 65 mol%, and 5 mol% of _Al 2 _{O 3,} and 5 mol% of Na ₂ O, and 3 mol% of _{K 2} O, and 6 mol% of MgO,: 14 mol% of CaO And verification using a glass composition containing ₂ mol% of ZrO ₂ . The glass transition temperature Tg of the glass composition is 601 ° C. In addition, the glass composition of this invention is not limited to the said composition, It can apply with all the compositions which can be used for the glass substrate for HDD.

  The glass substrate after the polishing step was placed in an environmental tester (SH-221 manufactured by Espec Corp.), the glass substrate was exposed to a constant temperature and humidity state, and the glass substrate was subjected to heat treatment. The glass substrate after the heat treatment was immersed in 50 ml of NaOH solution in a Teflon (registered trademark) container for 30 minutes. The pH of NaOH was 11.

  Thereafter, a magnetic film was formed on the glass substrate, and the number of reading errors when operating at 15000 rpm was evaluated. Evaluation is carried out with 100 glass substrates for each of the examples and comparative examples. When the number of errors is 2 or less, it is evaluated as “excellent”, and when the number of errors is 3 or more and 4 or less, “good”. Evaluation was made as “Yes” if the number of errors was 5 or more and 7 or less, and “No” was evaluated if the number of errors was 8 or more. Table 1 shows the processing conditions of the glass substrates and the evaluation results of the HDD operation evaluation test of each example and comparative example.

In Examples 1-7 and Comparative Examples 1-2, the glass substrate after polishing was subjected to heat treatment in the air under the conditions shown in Table 1, respectively. In Comparative Example 3, the polished glass substrate was immersed in a LiNO ₃ solution at 130 ° C. for 1 hour, and then immersed in an adipic acid aqueous solution at 130 ° C. for 1 hour.

  As a result of analyzing the location where the error occurred after the HDD operation evaluation test, there was no convex defect considered to be a head crash, and all errors were caused by a magnetic material.

  As shown in Table 1, the HDDs produced using the glass substrates of Examples 1 to 7 were evaluated as “excellent”, “good” or “possible” as a result of the operation evaluation test, and passed.

  Comparing Example 4 and Example 5, the evaluation result of Example 5 having a relative humidity of 45% was better than the evaluation result of Example 4 having a relative humidity of 55%. From this result, it was shown that the magnetic properties of the HDD can be improved by performing a heat treatment on the glass substrate with a relative humidity of 50% or less.

  In comparison with Example 1 and Examples 2 to 4, the evaluation result of Example 1 in which the product of the processing temperature and the processing time is 2000 or more is an example in which the product of the processing temperature and the processing time is less than 2000. It was better than the evaluation results of 2-4. On the other hand, comparing the example 6 and the example 7, the evaluation result of the example 6 in which the product of the processing temperature and the processing time is 100,000 or less is an example in which the product of the processing temperature and the processing time exceeds 100,000. It was better than the evaluation result of 7. From these results, it was shown that the magnetic characteristics of the HDD can be further improved by setting the product of the treatment temperature and the treatment time in the heat treatment to 2000 or more and 100,000 or less.

  In the comparative example 1, since it heat-processed in the temperature range exceeding 601 degreeC which is Tg of a glass substrate, a deformation | transformation generate | occur | produced in the glass substrate. Therefore, the HDD operation evaluation test was impossible.

  In Comparative Example 2, the HDD operation evaluation test was evaluated as “impossible” and failed. This is probably because the effect of stabilizing the surface layer of the glass substrate was not sufficiently obtained because the processing temperature was low.

  In Comparative Example 3, the result was evaluated as “impossible” in the HDD operation evaluation test, which was unacceptable. In the HDD of Comparative Example 3, an error due to the magnetic material was detected. However, when component analysis was performed on the detected portion, it was confirmed that all Li was contained. That is, in Comparative Example 3, since the Li ion concentration on the surface layer of the glass substrate is increased, Li contained in the glass substrate is eluted, which affects the magnetic characteristics of the magnetic film, and it is considered that an error has occurred.

  Although the embodiments 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, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 Information recording medium, 1G glass substrate, 14 front main surface, 15 back main surface, 23 magnetic thin film layer.

Claims (3)

In the manufacturing method of the glass substrate for HDD whose recording density is 600 Gbit / inch ² or more,
Polishing the glass substrate;
A step of heat-treating the glass substrate in a gas phase after the polishing step;
A product of a processing temperature (unit: ° C.) and a processing time (unit: min) in the heat treatment step is 1500 or more, and the processing temperature is higher than 40 ° C. and lower than a glass transition temperature. Production method.   The manufacturing method of the glass substrate for HDD of Claim 1 whose relative humidity in the said gaseous phase in the process to heat-process is 50% or less.   The manufacturing method of the glass substrate for HDD of Claim 1 or Claim 2 whose product of the processing temperature (unit: degreeC) and the processing time (unit: minute) in the process of said heat processing is 2000-100000.

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