JP5417492B2 - Manufacturing method of substrate for information recording medium - Google Patents

Description

The present invention relates to a method for manufacturing an information recording medium substrate (hard disk substrate). More specifically, the present invention relates to a method for polishing an information recording medium substrate that requires excellent flatness and smoothness using polishing abrasive grains other than CeO ₂ with high efficiency and high quality.

  In recent years, large amounts of data such as moving images and sounds have been handled in personal computers and various electronic devices, and large-capacity information recording apparatuses are required. As a result, the demand for higher recording density has been increasing year by year for information magnetic recording media called so-called hard disks, and it is also necessary to have excellent impact resistance characteristics due to the increasing demand for mobile applications.

In order to cope with this, a hard disk substrate made of a glass-based material used in the next-generation magnetic recording system is required to have a higher level of mechanical strength and surface smoothness.
On the other hand, a part of the hard disk market is being replaced by SSD (solid state drive), which is an information recording device using flash memory, to appeal the unit price per storage capacity, which is an advantage over SSD. Therefore, there is a demand for further reduction in manufacturing costs.
However, since the next generation hard disk substrate has high mechanical strength, the processing efficiency (processing rate) is poor, and if a higher level of surface smoothness is to be realized, the manufacturing cost will increase.
In other words, in the production of next-generation hard disk substrates, a request contrary to the reduction in cost of finishing a material with poor processing efficiency into a material with a higher level of surface smoothness than conventional materials. Must respond to.

JP 9-314458 A

JP-A-11-278865

By the way, polishing abrasive grains made of cerium oxide are currently used for polishing inorganic materials made of glass or crystallized glass in order to obtain high polishing efficiency and high smoothness after polishing. This is because the physical and chemical polishing effect of the cerium oxide abrasive grains is superior to the inorganic material made of glass or crystallized glass.
However, in recent years, the market price of cerium oxide has soared to about 8 times that of the prior art, and the influence on the manufacturing cost has become extremely large.
For this reason, a new polishing process is being sought instead of a polishing process using cerium oxide abrasive grains, but a polishing process that can achieve the same effect as cerium oxide abrasive grains and at a low cost has been developed. It has not been.

Patent Document 1 discloses a polishing method that does not use cerium oxide as loose abrasive grains, but the surface roughness after polishing can only achieve up to 6 mm in Ra.
Patent Document 2 discloses using zirconium oxide (ZrO ₂ ) as abrasive grains. However, it is difficult to achieve extremely high precision surface roughness of the substrate in recent years by polishing using zirconium oxide as abrasive grains. Furthermore, zirconium oxide is approximately twice the market price of conventional cerium oxide, and it is impossible to realize a cost equivalent to the market price of conventional cerium oxide.

An object of the present invention is a material having high mechanical strength required for a next-generation hard disk substrate by a polishing process that can obtain a polishing effect equivalent to that of cerium oxide as an alternative to cerium oxide as free abrasive grains in the polishing liquid. Is to provide a manufacturing method for processing a surface texture with high accuracy at low cost.
Another object of the present invention is to provide a method for manufacturing a substrate for an information recording medium that realizes a manufacturing cost that is equal to or lower than a manufacturing cost using cerium oxide at a conventional market price. That is.

As a result of intensive studies, the present inventors have selected specific abrasive grains and appropriately selected and adjusted the polishing liquid using the abrasive grains and other polishing process conditions according to the workpiece. As a result, the above-mentioned problems have been solved.
Specifically, the present invention provides the following manufacturing method.

(Configuration 8)
A method for producing a substrate for an information recording medium, comprising a polishing step of polishing a plate-like inorganic material containing at least a SiO ₂ component using a polishing liquid and a polishing pad,
The polishing liquid contains at least abrasive grains made of a compound containing Zr and Si,
A method for producing a substrate for an information recording medium, wherein the abrasive concentration in the polishing liquid is in the range of 2 wt% to 40 wt%.
(Configuration 9)
The manufacturing method of the substrate for information recording media of the structure 1 whose average particle diameter d50 of the abrasive grain in the said polishing liquid is 0.2 micrometer-2.0 micrometers.
(Configuration 10)
The inorganic material is in mass% based on the oxide, and the SiO ₂ component is 40 to 82%, the Al ₂ O ₃ component is 2 to 20%, and the R ′ ₂ O component is 0 to 20% (where R ′ is Li, Na, K). 3. The method for producing a substrate for an information recording medium according to Configuration 1 or 2, wherein the substrate comprises 1 or more selected from the group consisting of:
(Configuration 11)
4. The method for manufacturing a substrate for an information recording medium according to any one of configurations 1 to 3, wherein the inorganic material is crystallized glass.
(Configuration 12)
4. The method for manufacturing a substrate for an information recording medium according to any one of configurations 1 to 3, wherein the inorganic material is glass.
(Configuration 13)
6. The method for manufacturing an information recording medium substrate according to any one of configurations 1 to 5, wherein a surface roughness Ra of the substrate after the polishing step is less than 6 mm.
(Configuration 14)
7. The method for manufacturing a substrate for an information recording medium according to Configuration 6, wherein after the polishing step is completed, a polishing step is further performed so that the surface roughness Ra of the substrate after the final polishing step is less than 1.5 mm.

According to the present invention, an inorganic material made of glass or crystallized glass having high mechanical strength required for the next-generation hard disk substrate application even without using cerium oxide or using only a very small amount. Even if it is a material, it can be polished with high polishing efficiency, and a surface property with high smoothness can be obtained at low cost. Therefore, a substrate for an information recording medium such as a glass substrate or a crystallized glass substrate is manufactured at low cost. Can do.
Further, the surface roughness Ra of the substrate obtained by the production method of the present invention can be less than 6 mm after the first polishing step, and in a more preferred embodiment, the surface roughness Ra is 4 mm or less. It is possible to obtain
Furthermore, the surface roughness Ra of the substrate obtained by the production method of the present invention can be less than 1.5 mm after the final polishing step, and in a more preferred embodiment, 1.0 mm. The following surface roughness can be obtained.

It is the image which observed the surface property of the glass substrate (after 1P) obtained with the manufacturing method of this invention with the viewing angle of 1-10 micrometers ² using the atomic force microscope. It is the image which observed the surface property of the glass substrate (after 1P) obtained with the manufacturing method of this invention with the viewing angle of 1-10 micrometers ² using the atomic force microscope. It is the image which observed the surface property of the glass substrate (after 2P) obtained with the manufacturing method of this invention with the viewing angle of 1-10 micrometers ² using the atomic force microscope. It is the image which observed the surface property of the glass substrate (after 2P) obtained with the manufacturing method of this invention with the viewing angle of 1-10 micrometers ² using the atomic force microscope.

In the present invention, the “information recording medium substrate” means a glass substrate or a crystallized glass substrate for a hard disk.
In the present invention, “inorganic material” means both glass and crystallized glass.
Crystallized glass is also called glass ceramics, and is a material formed by precipitating crystals inside glass by heating the glass, and is distinguished from an amorphous solid. As long as it is made from glass as a starting material, 100% crystallized glass may be used as crystallized glass. Crystallized glass can have physical properties that cannot be obtained with glass due to crystals dispersed inside. For example, crystallized glass imparts properties that cannot be realized with glass, such as mechanical strength such as Young's modulus, fracture toughness, etching characteristics against acidic or alkaline chemicals, thermal properties such as thermal expansion coefficient, etc. Can do.
Similarly, crystallized glass can have different physical properties from ceramics obtained by sintering powder. Since crystallized glass is produced by using glass as a starting material and precipitating crystals inside, it has no voids and can have a dense structure as compared with ceramics.
Although the difference between glass, crystallized glass and ceramics is as described above, it has been experimentally shown that the present invention is effective for both glass and crystallized glass.

An information recording medium substrate made of an inorganic material such as glass or crystallized glass is generally produced by the following method. That is, a glass raw material is melted to form molten glass, and this molten glass is formed into a plate shape. As a method of forming into a plate shape, there are a direct press method in which molten glass is pressed by a mold, a float method in which the molten glass is floated on a molten metal, a known fusion method, a down draw method, a redraw method, and the like. Can be used. In the case of crystallized glass, crystals are precipitated inside by heat-treating the plate glass.
Next, the plate-like inorganic material was pre-processed into a disk shape with a circular hole in the center, and a grinding process for bringing the plate thickness and flatness close to the final shape and a polishing process for obtaining a smooth surface property were performed. Later, it becomes a substrate for a hard disk called a substrate.
If necessary, a step of generating a compressive stress layer on the substrate surface by a chemical strengthening method or the like to increase the strength of the substrate may be included.

The pre-processing process includes a coring process in which a circular hole is formed in the center of a disk-shaped substrate and a chamfering process in which chamfering is performed while the diameters of the outer peripheral portion and the inner peripheral portion are close to desired values.
As a grinding tool used in the coring process and the chamfer process, a metal electrodeposition specification in which diamond particles are bonded with metal or a vitrified electrodeposition specification in which diamond particles are bonded with vitrified can be used. The combination of the roughness of the jig and the finish count is preferably from # 270 to # 1000.

  After pre-processing, a grinding process and a polishing process are performed in this order. Both the grinding process and the polishing process are performed in a plurality of stages, and it is common to reduce the abrasive grains and smooth the surface roughness of the workpiece each time the stages are passed.

  In the grinding process and the polishing process, a predetermined number of sheets are collectively processed for each size of the processing machine and the workpiece (workpiece), and when the processing is completed, the next predetermined number is processed. At this time, one process for processing a predetermined number of materials is called a “batch”.

  The grinding process is performed by holding the plate glass between the upper and lower surface plates and rotating the surface plate and the plate glass while relatively moving while rotating the platen and supplying the polishing liquid (polishing slurry) containing free abrasive grains. Diamond powder is formed into pellets by a grain method or a bond of resin, metal, vitrified, etc., and the surface plate and plate glass are rotated while supplying a grinding liquid (coolant) with a surface plate in which a plurality of pellets are arranged. Conventionally, it is generally performed by a fixed abrasive method performed by relative movement. Further, grinding with a diamond pad may be performed.

  A diamond pad is also called a diamond sheet, and diamond abrasive grains are fixed to a flexible sheet-like resin. The surface of the diamond pad is provided with a groove for supplying coolant to the grinding surface and discharging grinding debris. The grooves are provided in a lattice shape, a spiral shape, a radial shape, a concentric shape, or a combination thereof.

  The grinding step of the present invention may be divided into a plurality of steps, but in at least one grinding step, preferably in the final grinding step, the average diameter of the fixed diamond abrasive grains is 2 μm to 5 μm. It is preferable to grind with a diamond pad. By grinding using the diamond pad as described above, the surface roughness Ra after the grinding process can be reduced without deteriorating the processing rate, and the processing time including the grinding process and the polishing process can be reduced. Can be shortened. A more preferable average diameter of diamond abrasive grains for obtaining the above effect is 2 μm to 4.5 μm. The diamond abrasive grains fixed to the diamond pad are preferably 10 wt% or less. At this time, in the sub-step prior to the final sub-step, the average diameter of the diamond pad abrasive grains is preferably in the range of 6 μm to 10 μm.

  Further, in the case where the first-stage polishing process (rough polishing process) that has been conventionally performed is omitted, it is possible to perform grinding with a diamond pad having an average diameter of diamond abrasive grains of 0.1 μm or more and less than 2 μm in the final process of the grinding process. preferable. Conventionally, the polishing process after the grinding process is divided into two or more stages, and processing is performed while changing the type of abrasive grains and the average grain size for each stage. At this time, if the rough polishing process can be omitted, the manufacturing process can be shortened, and the cost can be greatly reduced. In the present invention, it is necessary in the rough polishing process while maintaining the processing speed required in the grinding process by grinding with a diamond pad having an average diameter of diamond abrasive grains of 0.1 μm or more and less than 2 μm in the final process of the grinding process. Since smooth surface smoothness can be obtained, the rough polishing step can be omitted. For example, it is possible to obtain the surface properties necessary for an information recording medium substrate even in only one polishing step. More preferably, the average diameter of the diamond abrasive grains is 0.2 μm or more and 1.8 μm or less. This effect is particularly remarkable when a substrate made of crystallized glass is processed. It is considered that one of the factors is that the grindability of the crystallized glass with a diamond pad is less likely to cause scratches. In this case, although not essential, it is preferable to perform grinding with a diamond pad having an average diameter of diamond abrasive grains of 2 μm to 10 μm in the step before the final step in the grinding step in order to improve the efficiency of the entire processing.

Therefore, as the diamond pad used in the grinding process, a diamond diamond having an average diameter of 0.1 μm to 5 μm can be used.
The average diameter of the diamond abrasive grains fixed to the diamond pad may be a volume-based d50 value measured by a laser diffraction confusion method. Usually, it is grasped by the particle size distribution of diamond abrasive grains managed in the manufacturing stage, but it is also possible to measure only diamond abrasive grains by dissolving the diamond pad with a chemical solution.

  As in the grinding process, the polishing process holds the plate glass between the upper and lower surface plates, affixes the polishing pad to the surface plate, and rotates the surface plate and plate glass while supplying the polishing liquid containing free abrasive grains. The relative movement is performed.

  Moreover, the board | substrate used as the object of this invention can acquire the effect which improves a mechanical strength more by providing a compressive-stress layer in the board | substrate surface irrespective of glass and crystallized glass.

  As a method for forming the compressive stress layer, for example, there is a chemical strengthening method by causing an exchange reaction between an alkali metal component present on the surface layer of the substrate before the formation of the compressive stress layer and an alkali metal component having a larger ionic radius. Further, there are a heat strengthening method in which a glass substrate is heated and then rapidly cooled, and an ion implantation method in which ions are implanted into the surface layer of the glass substrate.

As the chemical strengthening method, for example, a salt containing potassium or sodium, for example, a molten salt of potassium nitrate (KNO ₃ ), sodium nitrate (NaNO ₃ ) or a complex salt thereof is heated to 300 to 600 ° C., and a substrate is placed on the molten salt. Soak for 0.1-12 hours. By this step, the lithium component present in the vicinity of the substrate surface (Li ⁺ ion) is replaced with sodium component (Na ⁺ ion) or potassium component ^{(K +} ion), or sodium present on the substrate surface components (Na ⁺ Ions) are exchanged for potassium (K ⁺ ions) components. As a result, compressive stress is generated in the substrate surface layer.
Although the exchange of the alkali metal component has been described above, an exchange process of the alkaline earth metal component can also be performed.

  The formation of the compressive stress layer on the substrate surface by the chemical strengthening method may be performed after polishing the substrate surface. However, after the substrate is lifted from the molten salt, the molten salt may crystallize and adhere to the surface of the substrate and may not be completely removed even after washing. Therefore, it is preferable to perform the polishing step at least once after the step of forming the compressive stress layer by the chemical strengthening method. This is because it becomes easy to remove the salt crystals adhering to the substrate surface by the polishing step after the chemical strengthening step.

Polishing that can be used to hold a plate-like inorganic material that is glass or crystallized glass, which is a workpiece or a crystallized glass, through a polishing pad between the upper and lower surface plates, and to move the polishing pad and the workpiece relative to each other for polishing. The apparatus will be described.
Examples of the polishing apparatus include a known planetary gear type double-side polishing apparatus.
The planetary gear type double-side polishing machine has a lower surface plate, a sun gear with external teeth, an internal gear with internal teeth, and an upper surface plate, each of which can rotate to the machine base with the same rotation axis. It is supported. The upper surface plate can be further moved up and down, and it is possible to pressurize the workpiece (workpiece).
Also, during polishing, polishing pads are attached to the upper and lower surface plates, respectively.
The workpiece is accommodated in a holding hole of a circular carrier having external teeth, and is held between an upper surface plate and a lower surface plate to which a polishing pad is attached.
When the outer teeth of the carrier mesh with the sun gear and the internal gear, the carrier rotates while revolving, and when the upper and lower surface plates rotate, the workpiece and the polishing pad move relative to each other and the workpiece is polished. In addition, well-known accessory devices such as a polishing liquid supply device can be used.

As the polishing liquid, one obtained by dispersing fine abrasive grains in the liquid is used. In the present invention, abrasive grains made of a compound containing at least Zr and Si must be used as the abrasive grains. By using abrasive grains made of a compound containing Zr and Si, the polishing rate (polishing efficiency) can be increased, the surface roughness after polishing can be made particularly smooth, and scratches generated on the surface can be obtained. Can be reduced to the limit.
Examples of the compound containing Zr and Si include zircon (ZrSiO ₄ ) and ZrSi ₂ , and other compounds in which other elements are dissolved in these compounds may be used. Zircon has a market price approximately half that of conventional cerium oxide, and by using it as abrasive grains, it becomes possible to further reduce the cost compared to the production cost before the market price of cerium oxide soars.
In addition to abrasive grains made of a compound containing Zr and Si, other abrasive grains can be mixed in the polishing liquid. Therefore, the content of abrasive grains composed of a compound containing Zr and Si is preferably 70 wt% or more, more preferably 80 wt% or more, and more preferably 90 wt% or more, based on the total abrasive weight in the polishing liquid. Most preferably. As other abrasive grains, spinel (RAl ₂ O ₄ , where R is one or more selected from Zn, Mg, and Fe) or silicon oxide (SiO ₂ ) is preferably exemplified. The other abrasive grains are preferably mixed within a range that does not impair the effect of the abrasive grains made of a compound containing Zr and Si, and most preferably only zircon (ZrSiO ₄ ) is used.

When cerium oxide abrasive grains are not included or included together with the above-mentioned abrasive grains, the amount is very small. The amount is 20% or less, more preferably 10% or less, based on the total abrasive weight in the polishing liquid. % Or less is most preferable.
Although there is zirconium oxide (ZrO ₂ ) as a compound containing Zr, when zirconium oxide is used, many scratches are generated on the surface of the substrate, and it is difficult to achieve the extremely high precision surface roughness of the substrate in recent years. Therefore, zirconium oxide is limited to 7% or less with respect to the total abrasive weight in the polishing liquid, more preferably 3% or less, and most preferably not used as abrasive grains.
Aluminum oxide (Al ₂ O ₃ ), manganese oxide (MnO, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , Mn ₂ O _7, etc.), aluminum hydroxide, and boehmite (AlOOH) are smooth surfaces. Is not obtained or the processing rate is low, the content is limited to 7% or less with respect to the total abrasive weight in the polishing liquid, more preferably 3% or less, and most preferably not used.
The abrasive grains are preferably used in a polishing process other than the final polishing process, and most preferably used in the first-stage polishing process.

  In the final polishing step, it is preferable to use colloidal silica.

In general, the first stage polishing is performed with abrasive grains having a large grain size, and the second stage polishing is performed as a final polishing process with abrasive grains having a smaller grain size. In this manufacturing method, not only the two-stage polishing process but also an appropriate abrasive grain may be selected, and the polishing process may be only one stage, or three or more stages.
Of the multiple stages of polishing processes, other processes are particularly limited as long as at least one polishing process using a polishing liquid containing at least abrasive grains made of a compound containing Zr and Si is included. Not.

When the concentration of the abrasive grains in the polishing liquid is 2 wt% or more, the processing rate becomes higher and the polishing process proceeds. Therefore, the concentration is preferably 2 wt% or more, more preferably 10 wt% or more, and most preferably 15 wt% or more. Moreover, since the fluidity | liquidity of polishing liquid becomes it high that it is 40 wt% or less and the cost of polishing liquid becomes lower, 40 wt% or less is preferable, 29 wt% or less is more preferable, and 27 wt% or less is the most preferable.
It is preferable to manage the concentration of the abrasive grains in the polishing liquid stored in the tank so as to be in the above range. The concentration of the polishing liquid can be determined from the specific gravity of the abrasive grains and the solvent by measuring the weight of a predetermined amount of slurry.

The pH of the polishing liquid can be appropriately adjusted according to the composition and type of the material to be polished. A known pH adjuster can be used to adjust the pH.
For example, in the case of crystallized glass having a spinel crystal as the main crystal, if the polishing liquid has a pH of 5.0 or more, the surface roughness of the substrate is further reduced and a smoother surface is obtained. The above is preferable, 7.0 or more is more preferable, 8.5 or more is further preferable, and 9.0 or more is most preferable. Further, if it is 12.0 or less, the chemical polishing action during the polishing process acts moderately, the surface of the glass substrate is more roughened, and a smoother surface is obtained. .5 or less is more preferable, and 11.0 or less is most preferable.

  Since the dispersion state of the abrasive grains in the polishing liquid changes according to the pH of the polishing liquid, the dispersion state can be adjusted with a known dispersion adjusting agent.

When the average particle diameter d50 of the abrasive grains is 0.2 μm or more, a sufficient mechanical polishing action during the polishing process can be obtained, and a high processing rate can be obtained. Is preferable, and 0.4 μm or more is most preferable.
In addition, when the average particle size d50 of the abrasive grains is 3.0 μm or less, the generation of micro scratches on the glass substrate surface is further reduced, and a smoother surface is obtained, so 3.0 μm or less is preferable, and 2.8 μm or less. Is more preferable, and 2.6 μm or less is most preferable.

  The temperature of the polishing liquid may be adjusted by a temperature control means such as a cooling / heating chiller unit or a cooling chiller surface plate.

It is preferable to use a so-called hard pad made of foamed hard resin or a so-called suede type soft pad as the polishing pad because a high processing rate can be obtained. A suede-type polishing pad refers to a base layer and a nap layer having a large number of bubbles and exhibiting a suede-like appearance. The nap layer is a surface layer located on the object side. As the material of the base material layer, a polyester resin, a polyolefin resin, a polyamide resin, a polyurethane resin, or the like can be used. For example, polyethylene ethylene terephthalate is preferable. As the shape of the base material layer, a film or a non-woven fabric made of the above materials can be used.
As the material of the nap layer, polyurethane resin, polyester resin, polyether, polycarbonate or the like can be used, and those obtained by adding different materials to these resins may be used.
An example of the hard pad is an abrasive-containing urethane pad. In the present invention, at least one surface layer or nap layer of the polishing pad is one or more fine particles selected from boehmite, aluminum oxide, manganese oxide, zinc oxide, spinel compounds, carbon black, silicon oxide, silicon carbide, silicon nitride, and zirconium oxide. May be included in a dispersed manner. Thereby, a polishing rate can be improved more and the surface property after grinding | polishing can be made more favorable. A soft pad in which carbon black is added to the resin of the nap layer is preferable in that scratches after polishing can be effectively reduced with respect to the target material of the present invention.

  The hardness (Asker C) of the polishing pad and the opening diameter range of the polishing pad may be appropriately selected according to the material to be polished. Further, when a suede type polishing pad is used, the nap length may be appropriately selected according to the material to be polished.

  The flatness of the hard pad is preferably in the range of −25 μm to +25 μm in the X and Y directions when measured with a 5-point span gauge. It becomes easy to obtain a flat glass substrate by setting it as this range. More preferably, it is in the range of −15 μm to +15 μm.

Processing pressure of the polishing step is preferably ^{50g / cm 2 ~160g / cm 2} , 90g / cm 2 ~150g / cm 2 is more preferable. The rotation speed is preferably 10 to 50 rpm. The rotation ratio is 10 to 40 rpm for the lower surface plate, 5 to 30 rpm for the upper surface plate, and may not be revolved, but 1 to 15 rpm is preferable when revolving.

  Since the second and subsequent polishing steps are finish polishing, it is necessary to process to a certain degree of surface roughness immediately before the second polishing in order to use abrasive grains having a low polishing power such as colloidal silica. is there. In order to obtain the next generation hard disk substrate and to reduce the processing cost, it is preferable that the surface roughness of the substrate is set to Ra1Å or more and less than 6Å after at least the first polishing step. In view of this, in order to obtain the above-described surface roughness after the first stage processing, the surface roughness before grinding and the first stage polishing process is set to Ra 0.05 to 0.40 μm after the first stage processing. It is preferable to set the processing time of 5 to 120 minutes. If it is less than 120 minutes, it will not become desired surface roughness, but if it exceeds 120 minutes, it will become easy to deteriorate flatness, and processing cost will also deteriorate. More preferably, it is 5 minutes to 60 minutes, and most preferably 5 minutes to 45 minutes.

  The above-described conditions can obtain a particularly remarkable effect in the first stage polishing.

  It is preferable to clean the substrate after each polishing step or chemical strengthening step. Cleaning is performed using RO water, acid, alkali, IPA, etc., using an ultrasonic cleaning device or the like.

The material to be processed targeted by the present invention is an inorganic material made of glass or crystallized glass containing at least a SiO ₂ component. This material is a material with high mechanical hardness that meets the requirements of next-generation hard disk substrates.
When the inorganic material is crystallized glass, the main crystal phase is a spinel crystal (RAl ₂ O ₄ : R is one or more selected from Zn, Mg, Fe), R ₂ TiO ₄ , lithium disilicate, enstatite ( Crystallized glass containing one or more kinds of crystals selected from MgSiO ₃ ), β-quartz, α-cristobalite, and solid solutions thereof can be used.
When the inorganic material is glass, aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, or the like can be used.
More preferably, the material to be processed which is the object of the present invention is a mass% based on oxides, 40 to 82% of SiO ₂ component, _{2 to} 20% of Al ₂ O ₃ component, and 0 to 20% of R ′ ₂ O component. (Where R ′ is one or more selected from Li, Na, and K) and is an inorganic material made of glass or crystallized glass.
More preferably, it is 40% to 82% of SiO ₂ component, _{2 to} 20% of Al ₂ O ₃ component, and 0 to 20% of R ′ ₂ O component (provided that R ′ is Li, Na, K) in terms of mass% based on oxide. one or more selected _from), P 2 _{O 5} component 0 to 7% ZrO ₂ component _0% B 2 _{O 3} component 0-15%, BaO component 0-15%, SrO component 0-15%, It is a glass or crystallized glass inorganic material containing 0 to 35% of ZnO component, 0 to 35% of MgO component and 0 to 35% of FeO component.
Other components can also be included as appropriate.

Among them, in particular, by mass% based on oxide, SiO ₂ component 40-60%, Al ₂ O ₃ component 7-20%, RO component 1-35% (where R is selected from Zn, Mg, Fe) 1 or more types), TiO ₂ component 1 to 15%, R ′ ₂ O component 2 to 15% (where R ′ is one or more selected from Li, Na and K), P ₂ O ₅ component 0 to 7% , B ₂ O ₃ component 0% or more and less than 8%, CaO component 0-15%, SrO component 0-5%, BaO component 0-5%, ZrO ₂ component 0-10%, SnO ₂ + CeO ₂ : 0.01 Glass containing ~ 1.0% of each component is heat-treated and selected from RAl ₂ O ₄ , R ₂ TiO ₄ (where R is one or more selected from Zn, Mg, Fe) as the main crystal phase. Crystallized glass containing one or more crystalline phases has particularly high mechanical strength. Therefore, the significance of using the production method of the present invention is significant.

Also, in terms of% by mass on the oxide basis, SiO ₂ components 40 to 82%, _Al 2 _{O 3} component 2 to 20%, R _'2 O component 0-20% (provided that, R' is selected from Li, Na, K 1 or _more), P 2 _{O 5} component 0-7% which, ZrO ₂ component _0~10%, B 2 _{O 3} component 0 to 15%, BaO components 0 to 15%, SrO component 0 to 15%, ZnO component The effect of the production method of the present invention can also be obtained for glass containing 0 to 35%, MgO component 0 to 35%, and FeO component 0 to 35%.

In recent years, in consideration of the environment, it is preferable to use a CeO ₂ component or a SnO ₂ component without using an As ₂ O ₃ component or an Sb ₂ O ₃ component as a fining agent when melting glass. However, may be used _As 2 _{O 3} component and the _Sb 2 _{O 3} component as a refining agent.

  The shape of the material to be processed applied to the present invention can be a plate formed by the direct press method, the float method, the fusion method, the down draw method, the redraw method, etc., and is used for a hard disk substrate. Is more preferably a disk shape or a disk shape having a circular hole in the center.

[Process for preparing plate-like glass-based material]
Batch materials of oxides and carbonates were mixed so as to have the composition shown in Table 1 in terms of mass% based on oxides, and were melted at a temperature of about 1250 to 1450 ° C. using a quartz crucible.
In the melting step, the raw material batch is sufficiently melted so that no undissolved residue is generated, and then the temperature is raised to a temperature of about 1,350 to 1,500 ° C. and then lowered to a temperature of 1,450 to 1,250 ° C. The foam generated inside the glass was defoamed and clarified.
Thereafter, a predetermined amount of molten glass is flowed out while maintaining the temperature, and a direct press method is used with a molding die in which the temperature of the upper die is set to 300 ± 100 ° C. and the temperature of the lower die is set to Tg ± 50 ° C. of the glass. The disk was formed into a disk shape having a diameter of about 67 mm and a thickness of 0.95 mm.
Next, the disk-shaped ceramic setter and the obtained glass disk were alternately stacked, held at a nucleation temperature of 670 ° C. for 3 hours, and then held at a crystal growth temperature of 750 ° C. for 5 hours to precipitate crystals.

The crystallized glass obtained had a spinel compound (RAl ₂ O ₄ , where R is one or more selected from Zn, Mg, and Fe), and the crystallinity was 6% by mass or less. The average crystal grain size of the crystal phase is 6 nm or less, the Young's modulus is 91 to 98 GPa, the specific gravity is 2.56 to 2.72, the Vickers hardness Hv is 660 to 730, and the average linear expansion coefficient is 50 × 10 ^−7. / ° C. to 58 × 10 ⁻⁷ / ° C., and fracture toughness was 1.3 to 1.9.

Similarly, oxide and carbonate batch raw materials were mixed so as to have the composition shown in Table 2 in mass% based on the oxide, and this was melted at a temperature of about 1250 to 1450 ° C. using a quartz crucible.
In the melting step, the raw material batch is sufficiently melted so that no undissolved residue is generated, and then the temperature is raised to a temperature of about 1,350 to 1,500 ° C. and then lowered to a temperature of 1,450 to 1,250 ° C. The foam generated inside the glass was defoamed and clarified.
Thereafter, a predetermined amount of molten glass is flowed out while maintaining the temperature, and a direct press method is used with a molding die in which the temperature of the upper die is set to 300 ± 100 ° C. and the temperature of the lower die is set to Tg ± 50 ° C. of the glass. The disk was formed into a disk shape having a diameter of about 67 mm and a thickness of 0.95 mm.
Next, the disk-shaped ceramic setter and the obtained glass disk were alternately stacked and heat-treated under the conditions shown in Table 2 to precipitate crystals.

The crystallized phase of the obtained crystallized glass is that the material 5 is a β quartz solid solution, the material 6 is lithium disilicate, the material 7 is enstatite, and the crystallinity is 70% by mass, 45% by mass, 45%, respectively. It was mass%. The average crystal grain sizes of the crystal phases are 30 nm, 100 nm, and 40 nm, respectively, Young's modulus is 90 GPa, 98 GPa, and 150 GPa, specific gravity is 2.54, 2.47, and 2.95, and Vickers hardness Hv is 570 and 740. 850, the average linear expansion coefficient was 2 × 10 ⁻⁷ / ° C., 85 × 10 ⁻⁷ / ° C., and 75 × 10 ⁻⁷ / ° C.

The average linear expansion coefficient is a value measured by changing the temperature range from 25 ° C. to 100 ° C. according to JOGIS (Japan Optical Glass Industry Association Standard) 16-2003 “Measurement Method of Average Linear Expansion Coefficient of Optical Glass Near Room Temperature”. is there.
Specific gravity was measured using Archimedes method, and Young's modulus was measured using ultrasonic method.
The Vickers hardness was obtained by dividing a load (N) when a pyramid-shaped depression was made on a test surface by using a diamond square cone indenter having a facing angle of 136 ° by a surface area (mm ² ) calculated from the length of the depression. Indicated by value. Using a micro hardness tester MVK-E manufactured by Akashi Seisakusho Co., Ltd., the test load was 4.90 (N) and the holding time was 15 (seconds).
The crystallinity was determined from the amount (mass%) of crystals calculated from the diffraction intensity obtained from powder XRD using the Rietveld method. Regarding the Rietveld method, the “Crystal Analysis Handbook” Editorial Committee edited by the Crystallographic Society of Japan, “Crystal Analysis Handbook”, Kyoritsu Publishing Co., Ltd., September 1999, p. The method described in 492-499 was used.
The average crystal grain size of the crystal phase is obtained by acquiring an image of an arbitrary part at a magnification of 100,000 to 500,000 with a TEM (transmission electron microscope), and the crystals appearing in the obtained image are two parallel straight lines. The average value of the longest distance when sandwiched. The n number at this time was 100.
For the fracture toughness (K _1C ), the value obtained by the SEPB method (JIS R1607) was used.

  Next, glass (amorphous glass) was produced. The composition of the glass is as shown in Table 3 and Table 4 in terms of mass% based on oxide, and is manufactured in the same manner as Materials 1-7 except that it is not subjected to heat treatment for crystallization, and formed into a disk shape. did.

[Pre-processing process]
Next, a hole of Φ18.7 mm was drilled in the central portion of these disk-shaped materials with a core drill, and then the inner and outer peripheral end faces of the workpiece were ground with a core tool, and chamfered shape processing was performed.
As the grinding tool, a metal electrodeposition specification in which diamond particles are bonded by metal, or a vitrified electrodeposition specification in which diamond particles are bonded by vitrification may be used.
The combination of the roughness of the jig and the finish count is preferably from # 270 to # 1000.

[Grinding process]
1) First step: A 12B-16B double-sided processing machine manufactured by Hamai Sangyo Co., Ltd. or Speed Fam Co., Ltd., was used for grinding using a # 1000 diamond sheet.
In some cases, the first-stage grinding may be omitted, and the grinding process may be only a grinding process using a diamond sheet.
2) Second stage sub-process (final sub-process or only grinding process)
Grinding was performed using a 12B-16B double-sided processing machine manufactured by Hamai Sangyo Co., Ltd. or Speed Fam Co., Ltd., and a diamond sheet having diamond particles dispersed in a sheet-like resin.

[Inner and outer periphery polishing process]
After the grinding step, the inner and outer peripheral end surfaces were polished smoothly. The diameter of the disk after processing is 65.0 mm.

[First polishing step (1P)]
1) First step (1P)
For the purpose of setting the surface roughness Ra to less than 5.0 to 6.0 mm, use a 16B double-sided processing machine and a polishing pad manufactured by Hamai Sangyo Co., Ltd. While holding the crystallized glass plate subjected to the grinding step and the inner and outer peripheral polishing step together with the resin carrier between the upper and lower surface plates (between the polishing pads), the polishing slurry containing free abrasive grains is recycled and supplied 1 The polishing process at the stage was continuously performed for 3 to 5 batches, and the polishing efficiency (processing rate) was measured while changing the conditions.
Polishing pad is hard foamed urethane (hardness (Asker C) 90 or 100: HPC90D2 manufactured by Hamai Sangyo Co., Ltd.), soft pad containing carbon black in the nap layer (Hardness (Asker C) 81: manufactured by FILWEL, Hardness (Asker C)) 86: manufactured by Hamai Sangyo).
Prior to use, the polishing pad was dressed with # 400, # 600, and # 800 dressers.
In the polishing slurry, zircon having an average particle diameter (d50) of 0.2 to 2.0 μm was dispersed in water as free abrasive grains, and various dilution concentrations were used. An aqueous NaOH solution was added as necessary to adjust the pH of the polishing slurry.
In the polishing slurry tank, 38 liters of the polishing slurry was stored at the start of the first batch, and polishing was performed by changing the concentration of the polishing slurry to 30 wt% and various pH values. A 100 μm filter was provided in the circulating supply path of the polishing slurry.
From the start of machining, both the rotation speed and the machining pressure are increased stepwise, maintained at the maximum rotation speed and the maximum machining pressure for a certain period of time, and then both the rotation speed and the machining pressure are lowered.
The number of processed sheets per batch is 110 disks. The measurement was conducted by arbitrarily removing two sheets from the inner and outer circumferences. After the end of one batch, a new disk after the completion of the grinding process was prepared, and the next batch was processed. Prior to the start of one example or comparative example, processing was performed by replacing with an unused polishing slurry.

The results of comparative examples are shown in Table 5, Table 6, and Table 7, and the results of Examples are shown in Tables 8 to 13. In the table, when the work was performed before the processing of the batch, the work was described in the column of the pre-processing work. A means polishing pad dressing, and B means adjustment of the pH of the polishing slurry (addition of NaOH aqueous solution or the like). In addition, the main processing time in the table is the processing time at the maximum processing pressure. The evaluation of the substrate quality is “◎” when the Dub-Off value is 70 Å or less and less than the substrate surface roughness Ra6 Å, and when the substrate edge shape Dub-Off value is 100 Å or less and less than the substrate surface roughness Ra6 「 “◯”, those having a substrate edge shape Dub-Off value of 180 Å or less and a substrate surface roughness Ra of 10 Å or less were designated as “Δ”, and those not satisfying these conditions were designated as “X”.
The Dub-Off value is an index for the sagging shape at the edge of the substrate, and is preferably close to zero. The Dub-Off value in the present invention is perpendicular to the main surface of the substrate, and the outer diameter that appears in a cross section passing through the center of the substrate is directed from the vertical line that contacts the outer periphery of the substrate when the substrate is held horizontally to the center. Two points, a point on the substrate surface at a distance of 0.575 mm horizontally and a point on the substrate surface at a distance of 0.475 mm horizontally from the vertical line in contact with the outer peripheral edge of the substrate toward the center, The maximum distance between the straight line connecting the two points and the substrate outer diameter line between the two points.

  Comparative Examples 1-5 are examples using conventional free abrasive grains of cerium oxide.

In Comparative Example 15, the weight ratio of the abrasive grains is CeO ₂ : ZrO ₂ = 1: 9.

Example 3 is a reference example of the present invention.
In Examples 1 to 5, both the surface quality and the processing rate were good.

Examples 6 and 9 are reference examples of the present invention.
In Example 6, ZrSiO in a weight ratio _{4: CeO} 2 = 9: 1.
In Example 7, ZrSiO in a weight ratio _{4: SiO} 2 = 9: 1.
In Examples 1 to 5, both the surface quality and the processing rate were good.

  In Examples 11 to 15, both the surface quality and the processing rate were good.

In Example 20, ZrSiO in a weight ratio _{4: SiO} 2 = 9: 1.
In Examples 16 to 20, both the surface quality and the processing rate were good.

In Example 21, ZrSiO in a weight ratio _{4: SiO} 2 = 9: 1.
In Examples 21 to 25, both the surface quality and the processing rate were good.

Examples 29 and 30 are reference examples of the present invention.
In Example 29, ZrSiO in a weight ratio _{4: CeO} 2 = 8: 2.
In Example 30, ZrSiO in a weight ratio _{4: SiO} 2 = 7: 3.
In Examples 26 to 30, both the surface quality and the processing rate were good.

[Second stage polishing process (2P)]
Using the 16B double-sided processing machine manufactured by Hamai Sangyo Co., Ltd., the 16B double-sided processing machine manufactured by Speed Fam Co., Ltd., and a suede polishing pad, the substrate after cleaning is supplied in two stages under the following conditions while supplying polishing slurry containing loose abrasive grains. The eyes were polished so that the surface roughness Ra was 1.0 mm or less.
Abrasive grains: colloidal silica (average particle diameter d50 = 0.02 μm)
Polishing slurry pH: 1.0 to 7.7
Polishing slurry concentration: 10-30 wt%
Maximum processing pressure: 110 g / cm ²
Maximum rotation speed: 25rpm
Processing time: Table 14 shows the surface roughness after processing for 30 minutes and the plate edge shape Dub-Off value.

  From the above, it can be seen that the polishing method of the present invention is a polishing method having the same substrate quality and processing rate as compared with the polishing method using cerium oxide as loose abrasive grains.

[Chemical strengthening process]
In order to improve the mechanical strength of the substrate, chemical strengthening treatment was performed. The chemical strengthening process can be appropriately performed after the grinding process, after the first polishing process, or after the final polishing process.

(Example 31)
About the board | substrate of the material 3, it wash | cleaned by RO water after completion | finish of a grinding process, and performed the chemical strengthening process on the following conditions.
Strengthening salt: Potassium nitrate (KNO ₃ : Purity 99.5%)
Temperature: 530 ° C
Time: 60 minutes After lifting the substrate from the molten salt for chemical strengthening, the substrate was immersed in 70 ° C. RO water for 10 minutes, and then washed with an aqueous KOH solution at pH 10 for 5 minutes.
Thereafter, the first and second polishing steps were performed under the conditions of Example 1.
This substrate was not subjected to the chemical strengthening treatment step, and it was confirmed that the ring bending strength was improved 3 to 6 times compared to the substrate prepared under the same conditions except for this.
The ring bending strength is a bending strength measured by a concentric bending method in which the strength of the disk-shaped sample is measured with a circular support ring and a load ring.

(Example 32)
About the board | substrate manufactured on the same conditions as Example 1, the washing | cleaning by KOH was performed after completion | finish of the 1st polishing process, and the chemical strengthening process was performed on the following conditions.
Strengthening salt: Potassium nitrate (KNO ₃ : Purity 99.5%)
Temperature: 500 ° C
Time: 30 minutes After lifting the substrate from the molten salt for chemical strengthening, it was immersed in 70 ° C. RO water for 10 minutes, and then washed with KOH at pH 10 for 5 minutes.
Thereafter, the second stage polishing was performed under the conditions of Example 1.
This substrate was not subjected to the chemical strengthening treatment step, and it was confirmed that the ring bending strength was improved by 1.5 to 4 times compared to the substrate prepared under the same conditions except for this.

(Example 33)
The substrate was prepared in the same conditions as in Example 1, after the final polishing step is completed, washed by H ₂ SO _4, was chemically strengthening treatment under the following conditions.
Strengthening salt: Potassium nitrate (KNO ₃ : Purity 99.5%)
Temperature: 450 ° C
Time: 15 minutes After lifting the substrate from the molten salt for chemical strengthening, the substrate was immersed in 70 ° C. RO water for 10 minutes, and then washed with H ₂ SO ₄ having a pH of ₂ .
This substrate was not subjected to the chemical strengthening treatment step, and it was confirmed that the ring bending strength was improved by 1.5 to 3 times compared to the substrate prepared under the same conditions except for this.

(Example 34)
About the board | substrate of the material 11, after completion | finish of a grinding process, it wash | cleaned by RO water and performed the chemical strengthening process on the following conditions.
Strengthening salt: Potassium nitrate (KNO ₃ : Purity 99.5%)
Temperature: 430 ° C
Time: 40 minutes After the substrate was lifted from the molten salt for chemical strengthening, it was immersed in 70 ° C. RO water for 10 minutes, and then washed with a KOH aqueous solution at pH 10 for 5 minutes.
Thereafter, the first and second stages of polishing were performed under the conditions of Example 18.
This substrate was not subjected to the chemical strengthening treatment step, and it was confirmed that the ring bending strength was improved 3 to 6 times compared to the substrate prepared under the same conditions except for this.

(Example 35)
The substrate was prepared in the same conditions as in Example 15, after the final polishing step is completed, washed by H ₂ SO _4, was chemically strengthening treatment under the following conditions.
Strengthening salt: Mixed salt of potassium nitrate and sodium nitrate (KNO ₃ : NaNO ₃ = 1: 3, purity 99.5%)
Temperature: 400 ° C
Time: 15 minutes After lifting the substrate from the molten salt for chemical strengthening, the substrate was immersed in 70 ° C. RO water for 10 minutes, and then washed with H ₂ SO ₄ having a pH of ₂ .
This substrate was not subjected to the chemical strengthening treatment step, and it was confirmed that the ring bending strength was improved by 1.5 to 3 times compared to the substrate prepared under the same conditions except for this.

When a continuous batch test was performed without changing and adding the slurry under the conditions of Example 1, no decrease in the polishing rate was observed until the seventh batch of polishing.
On the other hand, when a continuous batch test was performed in the same manner as in Comparative Example 11 without replacing and adding the slurry, it was confirmed that the polishing rate was lowered in the third batch.
In addition, when a continuous batch test was performed in the same manner as in Comparative Example 12 without exchanging and adding the slurry, it was confirmed that the polishing rate was lowered in the third batch.

Claims (8)

A method for producing a substrate for an information recording medium comprising a polishing step of polishing a plate-like inorganic material made of glass or crystallized glass containing at least a SiO ₂ component using a polishing liquid and a polishing pad,
The polishing liquid contains at least a compound containing Zr and Si as abrasive grains,
The abrasive concentration in the polishing liquid at the start of polishing is in the range of 15 wt% to 40 wt%,
Relative to the total weight of abrasive grains in the polishing liquid, the Ri abrasive der content 80 wt% or more of a compound containing Zr and Si, when containing cerium oxide as abrasive grains, the content of cerium oxide the method of the information recording medium substrate to the abrasive grains, wherein less der Rukoto 20 wt% relative to the total weight in the polishing liquid.   The method for producing a substrate for an information recording medium according to claim 1, wherein an average particle diameter d50 of the abrasive grains in the polishing liquid is 0.2 μm to 2.0 μm. The inorganic material is in mass% based on the oxide, and the SiO ₂ component is 40 to 82%, the Al ₂ O ₃ component is 2 to 20%, and the R ′ ₂ O component is 0 to 20% (where R ′ is Li, Na, K). The method for producing a substrate for an information recording medium according to claim 1, wherein at least one selected from the group consisting of:   The method for manufacturing a substrate for an information recording medium according to claim 1, wherein the inorganic material is crystallized glass.   The method for manufacturing a substrate for an information recording medium according to claim 1, wherein the inorganic material is glass.   6. The method for manufacturing a substrate for an information recording medium according to claim 1, wherein the surface roughness Ra of the substrate after the polishing step is less than 6 mm.   The method for manufacturing a substrate for an information recording medium according to claim 6, wherein after the polishing step is finished, a polishing step is further performed so that the surface roughness Ra of the substrate after the final polishing step is less than 1.5 mm.   The method for manufacturing a substrate for an information recording medium according to claim 1, wherein another polishing step using colloidal silica is performed after the polishing step.